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Component alignment in total knee arthroplasty is a determining factor for implant longevity. Mechanical alignment, which provides balanced load transfer, is the most common alignment strategy. However, a retrospective review found that varus alignment, which could lead to unbalanced loading, can happen in up to 18% of tibial baseplates. This may be particularly burdensome for cementless tibial baseplates, which require low bone-implant micromotion and avoidance of bone overload to obtain bone ingrowth. Our aim was to assess the effect of varus alignment on the bone-implant interaction of cementless baseplates. We virtually implanted 11 patients with knee OA with a modern cementless tibial baseplate in mechanical alignment and in 2° of tibial varus alignment. We performed finite element simulations throughout gait, with loading conditions derived from literature. Throughout the stance phase, varus alignment had greater micromotion and percentage of bone volume at risk of failure than mechanical alignment. At mid-stance, when the most critical conditions occurred, the average increase in peak micromotion and amount of bone at risk of failure due to varus alignment were 79% and 59%, respectively. Varus alignment also resulted in the decrease of the surface area with micromotion compatible with bone ingrowth. However, for both alignments, this surface area was larger than the average area of ingrowth reported for well-fixed implants retrieved post-mortem. Our findings suggest that small varus deviations from mechanical alignment can adversely impact the biomechanics of the bone-implant interaction for cementless tibial baseplates during gait; however, the clinical implications of such changes remain unclear.

The tibial component in total knee arthroplasty (TKA) is often chosen to maximize coverage of the tibial cut, which can result in excessive internal rotation of the component. Optimal rotational alignment may require a smaller baseplate with suboptimal coverage that could threaten fixation. We asked: "does undersizing the tibial component of a cementless TKA to gain external rotation increase the risk of bone failure?"We developed computational finite element (FE) analysis models from the computed tomography (CT) scans of 12 patients scheduled for primary TKA. The models were implanted with a cementless tibial baseplate that maximized coverage and one or two sizes smaller and externally rotated by 5°. We calculated the risk of bone collapse under loads representative of stair ascent.Undersizing the implant increased the area at risk of collapse for eight patients. However, the area at risk of collapse for the undersized implant (range, 5.2%-16.4%) was no different (P = .24) to the optimally sized implant (range, 4.5%-17.9%). The bone at risk of collapse was concentrated along the posterior edge of the implant. The area at risk of collapse was not proportional to implant size, and for four subjects undersizing the implant actually decreased the area at risk of collapse.While implants should maximize coverage of the tibial cut and seek support on dense bone, undersizing the tibial component to gain external rotation had minimal impact on the load transfer to the underlying bone. This FE analysis model of a cementless tibial baseplate may require further validation and additional studies to investigate the long-term biomechanical effects of undersizing the tibial baseplate. In conclusion, while surgeons should strive to use the appropriate tibial baseplate for each patient, our model identified only minor biomechanical consequences of undersizing the implant for the immediate postoperative bone-implant interaction and implant subsidence.

BACKGROUND: Surgical treatment options for addressing recurrent dislocation after total hip arthroplasty (THA) vary. Identifying impingement mechanisms in an unstable THA may be beneficial in determining appropriate treatment. QUESTIONS/PURPOSES: We sought to assess the effectiveness of developing pre-operative plans for treating hip instability after THA. We used advanced imaging and three-dimensional modeling techniques to perform impingement analyses in patients with unstable THA. METHODS: We evaluated a series of eight patients who would require revision THA to treat recurrent dislocation. Using a pre-operative algorithmic approach, we built patient-specific models and evaluated hip range of motion with computed tomographic scanning and biplanar radiography. This information was used to determine a surgical treatment plan that was then executed intra-operatively. Patients were followed for 2 years to determine whether they experienced another hip dislocation following treatment. RESULTS: Pre-operative kinematic modeling showed four of the eight patients had limited hip range of motion during flexion and internal rotation; a prominent anterior inferior iliac spine (AIIS) was found to limit hip range of motion in some of these cases. In the other four patients, range of motion was acceptable, suggesting soft-tissue causes of dislocation. No patients in this series experienced dislocation after undergoing revision THA. CONCLUSION: Advanced modeling techniques may be useful for identifying the impingement mechanisms responsible for instability after THA. Once variables contributing to limited hip range of motion are identified, surgeons can develop treatment plans to improve patient outcomes. Resecting a hypertrophic AIIS may improve hip range of motion and may be an important consideration for hip surgeons when revising unstable THAs. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11420-019-09704-z) contains supplementary material, which is available to authorized users.

Aims Custom flange acetabular components (CFACs) are a patient-specific option for addressing large acetabular defects at revision total hip arthroplasty (THA), but patient and implant characteristics that affect survivorship remain unknown. This study aimed to identify patient and design factors related to survivorship. Patients and Methods A retrospective review of 91 patients who underwent revision THA using 96 CFACs was undertaken, comparing features between radiologically failed and successful cases. Patient characteristics (demographic, clinical, and radiological) and implant features (design characteristics and intraoperative features) were collected. There were 74 women and 22 men; their mean age was 62 years (31 to 85). The mean follow-up was 24.9 months (sd 27.6; 0 to 116). Two sets of statistical analyses were performed: 1) univariate analyses (Pearson’s chi-squared and independent-samples Student’s t-tests) for each feature; and 2) bivariable logistic regressions using features identified from a random forest analysis. Results Radiological failure and revision rates were 23% and 12.5%, respectively. Revisions were undertaken at a mean of 25.1 months (sd 26.4) postoperatively. Patients with radiological failure were younger at the time of the initial procedure, were less likely to have a diagnosis of primary osteoarthritis (OA), were more likely to have had ischial screws in previous surgery, had fewer ischial screw holes in their CFAC design, and had more proximal ischial fixation. Random forest analysis identified the age of the patient and the number of locking and non-locking screws used for inclusion in subsequent bivariable logistic regression, but only age (odds ratio 0.93 per year) was found to be significant. Conclusion We identified both patient and design features predictive of CFAC survivorship. We found a higher rate of failure in younger patients, those whose primary diagnosis was not OA, and those with more proximal ischial fixation or fewer ischial fixation options. Cite this article: Bone Joint J 2019;101-B(6 Supple B):68–76.

BACKGROUND: Acetabular component position alone has not been predictive of stability after total hip arthroplasty (THA). Combined anteversion of the acetabulum and femur has the potential of being more predictive of stability. Unfortunately, femoral component position is difficult to measure on plain radiographs. Computed tomography (CT) is the gold standard for measuring implant position post-operatively, but CT exposes patients to a substantial amount of radiation. QUESTIONS/PURPOSES: We sought to determine whether biplanar low-dose radiography can be used to accurately measure both acetabular and femoral implant position after THA. METHODS: Twenty patients underwent standing low-dose biplanar spine-to-ankle radiographs and supine CT scans 6 weeks after THA. Measurements of acetabular inclination, acetabular anteversion, and femoral anteversion were performed by two blinded observers and compared. RESULTS: The average absolute differences between biplanar radiographs and CT scans were 2° ± 2° for acetabular inclination, 3° ± 2° for acetabular anteversion, and 4° ± 4° for femoral anteversion between EOS measurements and CT measurements. Interobserver agreement was good for acetabular inclination, acetabular anteversion, and femoral anteversion (Cronbach’s α = 0.90) using biplanar low-dose imaging. CONCLUSION: Biplanar radiography is a reliable low-radiation alternative for measuring acetabular inclination, acetabular anteversion, femoral version, and thus combined anteversion compared to CT. Femoral anteversion had the most variability but is still clinically relevant. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11420-018-09659-7) contains supplementary material, which is available to authorized users.

Finite element (FE) models are frequently used to assess mechanical interactions between orthopedic implants and surrounding bone. However, FE studies are often limited by the small number of bones that are modeled; the use of normal bones that do not reflect the altered bone density distributions that result from osteoarthritis (OA); and the application of simplified load cases usually based on peak forces and without consideration of tibiofemoral kinematics. To overcome these limitations, we undertook an integrated approach to determine the most critical scenario for the interaction between an uncemented tibial component and surrounding proximal tibial bone. A cementless component, based on a modern design, was virtually implanted using computed-tomography scans from 13 patients with knee OA. FE simulations were performed across a demanding activity, stair ascent, by combining in vivo experimental forces from the literature with tibiofemoral kinematics measured from patients who had received the same design of knee component. The worst conditions for the bone-implant interaction, in terms of micromotion and percentage of interfacial bone mass at risk of failure, did not arise from the maximum applied loads. We also found large variability among bones and tibiofemoral kinematics sets. Our results suggest that future FE studies should not focus solely on peak loads as this approach does not consistently correlate to worst-case scenarios. Moreover, multiple load cases and multiple bones should be considered to best reflect variations in tibiofemoral kinematics, anatomy, and tissue properties. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:350-357, 2019.

BACKGROUND: Satisfactory management of bone defects is important to achieve an adequate reconstruction in revision TKA. Metaphyseal cones to address such defects in the proximal tibia are increasingly being used; however, the biomechanical superiority of cones over traditional techniques like fully cementing the implant into the defect has not yet been demonstrated. Moreover, although long stems are often used to bypass the defects, the biomechanical efficacy of long stems compared with short, cemented stems when combined with metaphyseal cones remains unclear. QUESTIONS/PURPOSES: We developed and validated finite-element models of nine cadaveric specimens to determine: (1) whether using cones for addressing moderate metaphyseal tibial defects in revision TKA reduces the risk of implant-cement debonding compared with cementing the implant alone, and (2) when using metaphyseal cones, whether long, uncemented stems (or diaphyseal-engaging stems) reduce the risk of implant-cement debonding and the cone-bone micromotions compared with short, cemented stems. METHODS: We divided nine cadaveric specimens (six male, three female, aged 57 to 73 years, BMI 24 to 47 kg/m(2)) with standardized tibial metaphyseal defects into three study groups: no cone with short (50-mm) cemented stem, in which the defect was filled with cement; cone with short (50-mm) cemented stem, in which a metaphyseal cone was implanted before cementing the implant; and cone with long, diaphyseal-engaging stem, which received a metaphyseal cone and the largest 150-mm stem that could fit the diaphyseal canal. The specimens were implanted and mechanically tested. Then, we developed and validated finite-element models to investigate the interaction between the implant and the bone during the demanding activity of stair ascent. We quantified the risk of implant debonding from the cement mantle by comparing the axial and shear stress at the cement-implant interface against an experimentally derived interface failure index criterion that has been previously used to quantify the risk of cement debonding. We considered the risk of debonding to be minimal when the failure index was below 10% of the strength of the interface (or failure index < 0.1). We also quantified the micromotion between the cone and the bone, as a guide to the likelihood of fixation by bone ingrowth. To this end, we assumed bone ingrowth for micromotion values below the most restrictive reported threshold for bone ingrowth, 20 µm. RESULTS: When using a short, 50-mm cemented stem and cement alone to fill the defect, 77% to 86% of the cement-implant interface had minimal risk of debonding (failure index < 0.1). When using a short, 50-mm cemented stem with a cone, 87% to 93% of the cement-implant interface had minimal debonding risk. When combining a cone with a long (150-mm) uncemented stem, 92% to 94% of the cement-implant interface had minimal debonding risk. The differences in cone-bone micromotion between short, cemented stems and long, uncemented stems were minimal and, for both configurations, most cones had micromotions below the most restrictive 20-µm threshold for ingrowth. However, the maximum micromotion between the cone and the bone was in general smaller when using a long, uncemented stem (13-23 µm) than when using a short, cemented stem (11-31 µm). CONCLUSION: Although the risk of debonding was low in all cases, metaphyseal cones help reduce the biomechanical burden on the implant-cement interface of short-stemmed implants in high-demand activities such as stair ascent. When using cones in revision TKA, long, diaphyseal-engaging stems did not provide a clear biomechanical advantage over short stems. Future studies should explore additional loading conditions, quantify the interspecimen variability, consider more critical defects, and evaluate the behavior of the reconstructive techniques under repetitive loads. CLINICAL RELEVANCE: Cones and stems are routinely used to address tibial defects in revision TKA. Despite our finding that metaphyseal cones may help reduce the risk of implant-cement debonding and allow using shorter stems with comparable biomechanical behavior to longer stems, either cones or cement alone can provide comparable results in contained metaphyseal defects. However, longer term clinical studies are needed to compare these techniques over time.

Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces. Therefore, a computational model of the tibiofemoral joint was used to determine how non-conforming, fixed bearing medial UKA affects tibiofemoral kinematics, and tension in the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) during passive knee flexion. Fixed bearing medial UKA could not maintain the medial pivoting that occurred in the intact knee from 0° to 30° of passive flexion. Abnormal anterior-posterior (AP) translations of the femoral condyles relative to the tibia delayed coupled internal tibial rotation, which occurred in the intact knee from 0° to 30° of flexion, but occurred from 30° to 90° of flexion following UKA. Increasing or decreasing tibial insert thickness following medial UKA also failed to restore the medial pivoting behavior of the intact knee despite modulating MCL and ACL forces. Reduced AP constraint in non-conforming medial UKA relative to the intact knee leads to abnormal condylar translations regardless of insert thickness even with intact cruciate and collateral ligaments. This finding suggests that the conformity of the medial compartment as driven by the medial meniscus and articular morphology plays an important role in controlling AP condylar translations in the intact tibiofemoral joint during passive flexion. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1868-1875, 2018.

Background The bone morphologies of intact knees were measured and compared between Chinese and Caucasian populations. However, to assess if distinct designs of implants are necessary for the Chinese population owing to different morphologies and sizes, the knee measurements after osteotomy performed in total knee arthroplasty were evaluated. Methods Thirty-seven Caucasian and 50 Chinese patients' knees were examined using computed tomography scans. Mimics were applied to reconstruct 3-dimensional bone models. Dimensions of the 3-dimensional knee models and simulated bone resections during total knee arthroplasty were measured using Geomagic Studio and Pro/ENGINEER. The morphologic measurements of the native and resected femur and tibia included the anteroposterior (AP) depth, mediolateral (ML) width, notch width, knee physical valgus angle, tibial slope angle, and the ML-to-AP ratio of the femur, tibia, and resected femur. Statistical analysis was performed using the independent samples t test and the Pearson correlation coefficient in SPSS for Windows. Values of P < .05 were considered significant. Results No measurements were significantly different between the Chinese and Caucasian knees. However, the Chinese female showed significant differences compared with the Chinese male on distal femoral measurements both presimulated and postsimulated osteotomy such as a smaller mean ML-to-AP ratio in presimulated (1.3 ± 0.1) and postsimulated (1.3 ± 0.1) osteotomy. Conclusion The necessity of designing a full set of total knee components specifically for the Chinese population is still undetermined. However, we suggest designing femoral components specific for the Chinese females because of different postosteotomy distal femoral ML-to-AP ratio between the Chinese males and the Chinese females.

Introduction Acetabular reconstruction in the setting of severe bone loss or pelvic discontinuity remains a challenging problem. Multiple methods of treatment have been described including antiprotrusio cages (APCs). The objective of this study is to combine biomechanical analysis of retrieved APCs with radiographic and clinical data to determine which factors influence or predict APC failure. Methods 41 APCs were identified. Sequential radiographs were examined for cage and polyethylene cup abduction angles, change in centre of rotation, screw placement, progression of cage failure, and failure mechanism. Cages were manually examined for gross macroscopic findings, breakage, and the location of breakage. High-resolution microscopy was used for further analysis. Results 24 cages were included in the analysis. Mean age of patients was 64.5 years (range 43-85 years); average length of implantation was 42.5 months (range 3-108 months). Average cage abduction angles were 56°; abduction for the cemented polyethylene cup was 44°. 14 of 24 cages were broken; 10 were intact. Of the broken cages, 10/14 broke through a screw hole in the ischial flange or just superior to the ischial flange. In the intact group, 6/10 failed due to pullout of the ischial screws. Discussion All cages had superior and lateralised centres of rotation. The majority of cages failed due to breakage or pullout at the ischial flange. Pelvic discontinuity was a large risk factor for a broken cage. Future design and technique modifications may result in superior outcomes in these complex acetabular reconstructions.

Finite element (FE) models are frequently used to assess mechanical interactions between orthopedic implants and surrounding bone. However, FE studies are often limited by the small number of bones that are modeled; the use of normal bones that do not reflect the altered bone density distributions that result from osteoarthritis (OA); and the application of simplified load cases usually based on peak forces and without consideration of tibiofemoral kinematics. To overcome these limitations, we undertook an integrated approach to determine the most critical scenario for the interaction between an uncemented tibial component and surrounding proximal tibial bone. A cementless component, based on a modern design, was virtually implanted using computed-tomography scans from 13 patients with knee OA. FE simulations were performed across a demanding activity, stair ascent, by combining in vivo experimental forces from the literature with tibiofemoral kinematics measured from patients who had received the same design of knee component. The worst conditions for the bone-implant interaction, in terms of micromotion and percentage of interfacial bone mass at risk of failure, did not arise from the maximum applied loads. We also found large variability among bones and tibiofemoral kinematics sets. Our results suggest that future FE studies should not focus solely on peak loads as this approach does not consistently correlate to worst-case scenarios. Moreover, multiple load cases and multiple bones should be considered to best reflect variations in tibiofemoral kinematics, anatomy, and tissue properties. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:350-357, 2019.

Background Central and perpendicular (PERP) screw orientations have each been described for scaphoid fracture fixation. It is unclear, however, which orientation produces greater compression. Questions/Purposes This study compares compression in scaphoid waist fractures with screw fixation in both PERP and pole-to-pole (PTP) configurations. PERP orientation was hypothesized to produce greater compression than PTP orientation. Methods Ten preoperative computed tomography scans of scaphoid waist fractures were classified by fracture type and orientation in the coronal and sagittal planes. Three-dimensional models of each scaphoid and fracture plane were created. Simulated Acutrak 2 (Acumed, Hillsboro, OR) screws were placed into the models in both PERP and PTP orientations. Engagement length and screw angle relative to the fracture were measured. Compression strength was calculated from the shear area, average density, and angle acuity. Results The PTP angle between screw and fracture ranged from 36 to 84 degrees. By definition, the PERP screw-to-fracture angle was 90 degrees. Perpendicularity of the PTP screw to the fracture was positively correlated to compression strength. PERP screws had greater compression than PTP screws when the PTP screw-to-fracture angle was 80 degrees, approximating the PERP screw. Conclusion Increasing screw perpendicularity resulted in higher compression when the screw-to-fracture angle of the PTP screw was Clinical Relevance These results provide guidelines for optimal screw placement in scaphoid waist fractures.

Background Larsen syndrome is a rare genetic disorder caused by congenital weakness of the connective tissues. It can present with a variety of musculoskeletal and cardiovascular abnormalities. The current report describes two siblings with Larsen Syndrome who presented with severe bilateral hip arthritis and underwent one stage bilateral total hip arthroplasty (THA). The aim was to report on the clinical features of Larsen Syndrome and their implications for total hip replacement surgery. Methods Two siblings, a 32 year-old female and a 30 year-old male, presented with severe bilateral hip arthritis and a history of Larsen Syndrome. Both patients underwent a detailed, multidisciplinary preoperative medical work up and radiological imaging including computer tomography. All four hips were operated using a cementless primary press-fit cup (Pinnacle, DePuy, Warsaw, IN) and a cementless modular stem system (S-ROM, DePuy, Warsaw, IN) utilizing a posterior approach. Prophylactic cerclages wires were placed proximal to the lesser trochanter before stem preparation and bone grafting of bone cysts in the greater trochanter was performed in all four hips. Results After 2 years both patients reported significant improvements of function, pain and quality of life. The Oxford hip score improved from preoperative 21 (range 12-24) points up to 39 (range 38-41) points at 2-year follow up. Radiographic follow-up showed good graft incorporation and no signs of implant loosening. Conclusion The current case report suggests that one stage bilateral THA is a feasible treatment option for young adults with Larsen syndrome and secondary arthritis of the hip.

Radiostereometric analysis (RSA) is the most accurate technique to measure implant migration. However, it requires special equipment, technical expertise and analysis software and has not gained wide acceptance. The current paper analyzes a novel method to measure implant migration utilizing widely available computer tomography (CT). Three uncemented total hip replacements were performed in three human cadavers and six tantalum beads were inserted into the femoral bone similar to RSA. Six different 28 mm heads (−3, 0, 2.5, 5.0, 7.5 and 10 mm) were added to simulate five reproducible translations (maximum total point migration) of the center of the head. Implant migration was measured in a 3-D analysis software (Geomagic Studio 7). Repeat manual reconstructions of the center of the head were performed by two investigators to determine repeatability and accuracy. The accuracy of measurements between the centers of two head sizes was 0.11 mm with a CI 95 % of 0.22 mm. The intra-observer repeatability was 0.13 mm (CI 95 % 0.25 mm). The interrater-reliability was 0.943. CT based measurement of head displacement in a cadaver model were highly accurate and reproducible.

Scaphoid fractures are one of the most common fractures treated by hand surgeons. The complex anatomy and size of the scaphoid bone can make the reduction and fixation of these fractures technically challenging. Careful preoperative planning is required to ensure stable fixation is achieved. We report on the use of 3-dimensional printing to improve preoperative planning for a series of complex scaphoid fractures.

The current study compared the impact of low radiation CT protocols on the accuracy, repeatability, and inter- and intra-observer variability of implant migration studies in total hip arthroplasty. Two total hip replacements were performed in two human cadavers and six tantalum beads were inserted into the femur similar to radiostereometric analysis. Six different 28 mm heads (-3 mm, 0 mm, 2.5 mm, 5.0 mm, 7.5 mm, and 10 mm) were added to simulate five reproducible translations (maximum total point migration) of the center of the head. Three CT scans with varying levels of radiation were performed for each head position. The effective dose (mSv) was 3.8 mSv for Protocol A (standard protocol), 0.7 mSv for Protocol B and 1.6 mSv for Protocol C. Implant migration was measured in a 3-D analysis software (Geomagic Studio 7). The accuracy was 0.16 mm for CT Protocol A, 0.13 mm for Protocol B and 0.14 mm for Protocol C; The repeatability was 0.22 mm for CT Protocol A, 0.18 mm for Protocol B and 0.20 mm for Protocol C; ICC for inter observer reliability was 0.89, intra observer reliability was 0.95. The difference in accuracy between standard protocol A and the two low radiation protocols (B, C) was less than 0.05 mm. The accuracy, inter- and intra-observer reliability of all three CT protocols is comparable to radiostereometric analysis. Reducing the CT radiation exposure to numbers similar to an AP Pelvis radiograph (0.7 mSv protocol B) does not affect the accuracy of implant migration measurements.

Background Headless screw fixation of scaphoid fractures and nonunions yields predictably excellent outcomes with a relatively low complication profile. However, intramedullary implants affect the load to failure and stress distribution within bone and may be implicated in subsequent fracture. Case Description We describe a posttraumatic fracture pattern of the scaphoid proximal pole originating at the previous headless screw insertion site in three young male patients with healed scaphoid nonunions. Each fracture was remarkably similar in shape and size, comprised the volar proximal pole, and was contiguous with the screw entry point. Treatment was challenging but successful in all cases. Literature Review Previous reports have posited that stress-raisers secondary to screw orientation may be implicated in subsequent peri-implant fracture of the femoral neck. Repeat scaphoid fracture after screw fixation has also been reported. However, the shape and locality of secondary fracture have not been described, nor has the potential role of screw fixation in the production of distinct fracture patterns. Clinical Relevance Hand surgeons must be aware of this difficult complication that may follow antegrade headless screw fixation of scaphoid fracture nonunion, and of available treatment strategies.

Background The Optetrak® PS (Exactech, Inc., Gainesville, FL) has been a well-functioning posterior stabilized knee replacement since its introduction in 1995. In 2009, the Optetrak Logic® incorporated modifications to the anterior face of the tibial post and the corresponding anterior articulating surface of the femoral component to reduce edge loading on the polyethylene post. In this study, we provide the rationale for the design change and compare the damage on retrieved tibial components of both designs to demonstrate the effectiveness of the design modifications in decreasing post damage. Methods We integrated retrieval findings of tibial post damage with finite element analysis to redesign the anterior tibial post-femoral box articulation. We then used subsequent retrieval analysis on a 3:1 matched sample of 60 PS and 20 Logic® inserts to examine the impact of the design change on polyethylene damage. Results Polyethylene stresses were markedly reduced when rounded contact geometries were incorporated. The comparison of the new and old designs using retrieval analysis demonstrated that the redesign led to reduction in surface damage and deformation on the tibial post. Conclusions This study shows the use of a design cycle by which a problem is identified through retrieval analysis, analytical tools are used to suggest design solutions, and then retrieval analysis is applied again on the new design to confirm improved performance. Clinical relevance Anterior post damage has been markedly reduced through the introduction of design changes to the post-box geometry.

In an effort to minimize graft impingement among various ACL deficient states, we sought to quantitatively determine requirements for bone resection during notchplasty with respect to both volumetric amount and location.A validated method was used to evaluate Magnetic Resonance Imaging scans. We measured the ATT of the medial and lateral compartments in the following four states: intact ACL (27 patients), acute ACL disruption;2 months post-injury (76 patients), chronic ACL disruption; 12 months post-injury (42 patients) and failed ACL reconstruction (75 patients). Subsequently, 11 cadaveric knees underwent Computed Tomography (CT) scanning. Specialized software allowed virtual anterior translation of the tibia according to the average ATT measured on MRI. Impingement volume was analyzed by performing virtual ACLRs onto the various associated CT scans. Location was analyzed by overlaying an on-screen protractor. The center of the notch was defined as 0°.Average impingement volume changed significantly in the various groups compared to the intact ACL group (acute 577 ± 200 mm(3), chronic 615 ± 199 mm(3), failed ACLR 678 ± 210 mm(3), p=0.0001). The location of the required notchplasty of the distal femoral wall border did not change significantly. The proximal femoral border moved significantly towards the center of the notch (acute 8.6° ± 4.8°, chronic 7.8° ± 4.2° (p=0.013), failed ACLR 5.1° ± 5.9° (p=0.002)).Our data suggests that attention should be paid peri-operatively to the required volume and location of notchplasty among the various ACL deficient states to minimize graft impingement.

Component malposition is one of the major reasons for early failure of unicompartmental knee arthroplasty (UKA). It was investigated how reproducibly patient-specific instrumentation (PSI) achieved preoperatively planned placement of the tibial component in UKA specifically assessing coronal alignment, slope and flexion of the components and axial rotation. Based on computer tomography models of ten cadaver legs, PSI jigs were generated to guide cuts perpendicular to the tibial axis in the coronal and sagittal planes and in neutral axial rotation. Deviation ≥3° from the designed orientation in a postoperative CT was defined as outside the range of acceptable alignment. Mean coronal alignment was 0.4 ± 3.2° varus with two outliers. Mean slope was 2.8 ± 3.9° with six components in excessive flexion. It was noted that the implants were put in a mean of 1.7 ± 8.0° of external rotation with seven outliers PSI helped achieve the planned coronal orientation of the component. The guides were less accurate in setting optimal tray rotation and slope.

Newer arthroplasty designs claim to provide superior range of motion (ROM) and greater stability than their predecessors. However, there is no way to compare ROM of implant systems in an equivalent anatomical environment in a clinical setting. This study used computer-aided design to compare ROM after hip resurfacing, 28 mm THA, 36 mm THA, and anatomic dual mobility (ADM) THA in 3D models of 5 cadaver pelvises. ROM to impingement was then tested in 10 different motions and a one-way ANOVA was used to compare results. The hip resurfacing resulted in restricted ROM compared to the other 3 models in all motions except adduction. The ADM, 36 mm, and 28 mm THA resulted in similar ROM. Dual mobility constructs provide comparable ROM in patients where large head THA is not appropriate.

Acetabular osteophytes are common findings during total hip arthroplasty (THA).This study was designed to determine the extent to which osteophytes may limit range of motion (ROM) and in which locations impingement is likely to occur if osteophytes are not removed during surgery.Computer-aided design was used to compare ROM of a modern hip implant in four cadaver models with and without 10-mm acetabular rim osteophytes added. A clock face, with 12 o'clock at the superior pole of the right acetabulum, was used to map impingement.The osteophyte model limited ROM in flexion (101° v. 113°, p = 0.03), 90° of flexion with internal rotation (16.7° v. 31.6°, p = 0.01), and external rotation (30.4° v. 49.5°, p = 0.01). Impingement occurred between 7 and 8 o'clock in external rotation and 1 and 2 o'clock in the other two motions.Osteophytes in these positions have the greatest impact on ROM and should be removed during THA.

Manual techniques of reproducing a preoperative plan for primary bone tumor resection using rudimentary devices and imprecise localization techniques can result in compromised margins or unnecessary removal of unaffected tissue. We examined whether a novel technique using computer-generated custom jigs more accurately reproduces a preoperative resection plan than a standard manual technique. Using CT images and advanced imaging, reverse engineering, and computer-assisted design software, custom jigs were designed to precisely conform to a specific location on the surface of partially skeletonized cadaveric femurs. The jigs were used to perform a hemimetaphyseal resection. We performed CT scans on six matched pairs of cadaveric femurs. Based on a primary bone sarcoma model, a joint-sparing, hemimetaphyseal wide resection was precisely outlined on each femur. For each pair, the resection was performed using the standard manual technique on one specimen and the custom jig-assisted technique on the other. Superimposition of preoperative and postresection images enabled quantitative analysis of resection accuracy. The mean maximum deviation from the preoperative plan was 9.0 mm for the manual group and 2.0 mm for the custom-jig group. The percentages of times the maximum deviation was greater than 3 mm and greater than 4 mm was 100% and 72% for the manual group and 5.6% and 0.0% for the custom-jig group, respectively. Our findings suggest that custom-jig technology substantially improves the accuracy of primary bone tumor resection, enabling a surgeon to reproduce a given preoperative plan reliably and consistently.

Background Ideal internal fixation of the scaphoid relies on adequate bone stock for screw purchase; so, knowledge of regional bone density of the scaphoid is crucial. Questions/Purpose The purpose of this study was to evaluate regional variations in scaphoid bone density. Materials and Methods Three-dimensional CT models of fractured scaphoids were created and sectioned into proximal/distal segments and then into quadrants (volar/dorsal/radial/ulnar). Concentric shells in the proximal and distal pole were constructed in 2-mm increments moving from exterior to interior. Bone density was measured in Hounsfield units (HU). Results Bone density of the distal scaphoid (453.2 ± 70.8 HU) was less than the proximal scaphoid (619.8 ± 124.2 HU). There was no difference in bone density between the four quadrants in either pole. In both the poles, the first subchondral shell was the densest. In both the proximal and distal poles, bone density decreased significantly in all three deeper shells. Conclusion The proximal scaphoid had a greater density than the distal scaphoid. Within the poles, there was no difference in bone density between the quadrants. The subchondral 2-mm shell had the greatest density. Bone density dropped off significantly between the first and second shell in both the proximal and distal scaphoids. Clinical Relevance In scaphoid fracture ORIF, optimal screw placement engages the subchondral 2-mm shell, especially in the distal pole, which has an overall lower bone density, and the second shell has only two-third the density of the first shell.

Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces. Therefore, a computational model of the tibiofemoral joint was used to determine how non-conforming, fixed bearing medial UKA affects tibiofemoral kinematics, and tension in the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) during passive knee flexion. Fixed bearing medial UKA could not maintain the medial pivoting that occurred in the intact knee from 0° to 30° of passive flexion. Abnormal anterior-posterior (AP) translations of the femoral condyles relative to the tibia delayed coupled internal tibial rotation, which occurred in the intact knee from 0° to 30° of flexion, but occurred from 30° to 90° of flexion following UKA. Increasing or decreasing tibial insert thickness following medial UKA also failed to restore the medial pivoting behavior of the intact knee despite modulating MCL and ACL forces. Reduced AP constraint in non-conforming medial UKA relative to the intact knee leads to abnormal condylar translations regardless of insert thickness even with intact cruciate and collateral ligaments. This finding suggests that the conformity of the medial compartment as driven by the medial meniscus and articular morphology plays an important role in controlling AP condylar translations in the intact tibiofemoral joint during passive flexion. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1868-1875, 2018.

Background: Impingement of anterior cruciate ligament (ACL) grafts against the femoral notch and the posterior cruciate ligament (PCL) is thought to be influenced primarily by tunnel position and graft orientation. Recent data have implied that the native ACL is ribbon-shaped. Purpose: To evaluate the 3-dimensional shape and cross-sectional area of the native ACL versus the ACL graft and to compare the degree of impingement against the femoral notch and PCL. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Bilateral knee magnetic resonance images were analyzed for 27 patients with unilateral bone–patellar tendon–bone (BPTB) ACL reconstruction performed via transtibial or anteromedial portal femoral tunneling techniques. Three-dimensional models of the ACL, PCL, femur, and tibia were digitally rendered. The cross-sectional area and dimensions of the native ACL and the reconstructed graft were determined at 3 equally spaced locations and compared via Wilcoxon-Mann-Whitney and Kruskal-Wallis tests. In addition, impingement of the ACL on the PCL and femoral notch was graded in 3 groups. Chi-square or Fisher exact tests were used to compare the proportional differences of impingement of the native and reconstructed ACL on the PCL and femoral notch, respectively. All analyses were performed using 2-sided hypothesis testing, with statistical significance at P < .05. Results: Cross-sectional areas at all 3 points on the ACL graft were significantly greater than those of the native ACL ( P < .001). The long- to short-axis ratio for the native ACL was significantly greater at each location compared with the corresponding locations along the ACL graft ( P < .001), implying that the native ACL is “flatter” than is an ACL graft. There were 19 operated knees (70%) with contact or impingement between the ACL graft and the femoral notch compared with zero knees with a native ACL ( P < .001). In addition, 22 operated knees (81%) showed contact or impingement between the ACL graft and the PCL, compared with 7 knees (26%) with a native ACL ( P < .001). No significant differences in impingement frequency were noted between the transtibial and anteromedial tunneling techniques for ACL graft specimens ( P > .05). Conclusion: Native ACLs have a smaller cross-sectional area, are “flatter,” and experience less incidence of impingement compared with anatomically placed BPTB ACL grafts.

OBJECTIVE. The purpose of this study was to describe the normal and abnormal MRI appearances of polyethylene tibial inserts. Subjects who underwent MRI before revision total knee arthroplasty were identified. The polyethylene tibial insert's shape was categorized on MRI, and the presence of abnormalities was noted. CONCLUSION. The shape of the polyethylene tibial insert varied with the design. Polyethylene tibial insert abnormalities seen on MRI included displacement and fracture. MRI distinguishes various designs of polyethylene tibial inserts and can show associated abnormalities.

Purpose The purpose of this study was to evaluate the utility of computer-assisted 3-dimensional modeling in diagnosing and treating symptomatic hip impingement. Methods Eight patients with symptomatic, focal cam and/or pincer impingement lesions underwent high-resolution computed tomography scans and computer-assisted, 3-dimensional modeling of the involved hip. Cam location, alpha angle, neck-shaft angle, femoral version, and acetabular version at the 12-o'clock through 3-o'clock positions were measured. The model was subsequently dynamized to define the preoperative range of motion and location of impingement with hip flexion, internal rotation, and internal rotation at 90° of hip flexion. Virtual cam and pincer osteoplasty was performed to establish normal head-neck offset and head sphericity and to eliminate focal rim impingement lesions. Range of motion and location of impingement were reassessed after resection in the defined area of impingement. Results The cam lesion was located between the 12-o'clock and 4-o'clock positions in all cases. The mean alpha angle was 66.4° (range, 53° to 80°). Mean femoral version was 14.6° (range, 5° to 23°). Mean preoperative hip flexion was 109.7° (range, 87.5° to 125.5°), and mean internal rotation at 90° of hip flexion was 16.2° (range, 1.7° to 25.5°). The location of impingement was unique in each case and not predictable based on radiographic measures alone. Virtual osteoplasty in the defined regions of impingement resulted in significant improvements in both hip flexion and internal rotation ( P Conclusions Computed tomography–based computer modeling can localize regions of anticipated mechanical impingement in symptomatic patients with hip pain. Computer-assisted navigation may be a valuable surgical tool to more accurately and reliably eliminate offending impingement lesions. Level of Evidence Level IV, diagnostic study.

Using 3-dimensional high-resolution magnetic resonance imaging (MRI), we sought to compare femoral and tibial tunnel position and resultant graft obliquity with single-bundle anterior cruciate ligament (ACL) reconstruction using transtibial (TT) or anteromedial (AM) portal femoral tunnel reaming techniques.Thirty patients were prospectively enrolled after primary, autogenous bone-patellar tendon-bone ACL reconstruction by 2 groups of high-volume, fellowship-trained sports medicine surgeons. With the TT technique, an external starting point was used to maximize graft obliquity and femoral footprint capture. By use of high-resolution MRI and imaging analysis software, bilateral 3-dimensional knee models were created, mirrored, and superimposed. Differences between centroids for each femoral and tibial insertion, as well as corresponding ACL/graft obliquity, were evaluated with paired t tests and 2-sided Mann-Whitney nonparametric tests, with P.05 defined as significant.No significant differences were observed between groups in position of reconstructed femoral footprints. However, on the tibial side, AM centroids averaged 0.8 ± 1.9 mm anterior to native ACL centroids, whereas the TT group centered 5.23 ± 2.4 mm posterior to native ACL centroids (P.001). Sagittal obliquity was closely restored with the AM technique (mean, 52.2° v. 53.5° for native ACL) but was significantly more vertical (mean, 66.9°) (P = .0001) for the TT group.In this clinical series, AM portal femoral tunnel reaming more accurately restored native ACL anatomy than the TT technique. Although both techniques can capture the native femoral footprint with similar accuracy, the TT technique requires significantly greater posterior placement of the tibial tunnel, resulting in decreased sagittal graft obliquity. When a tibial tunnel is drilled without the need to accommodate subsequent femoral tunnel reaming, more accurate tibial tunnel position and resultant sagittal graft obliquity are achieved.Level III, retrospective comparative study.

Background Femoroacetabular impingement (FAI) is now recognized as the most common cause of early osteoarthritis in the nondysplastic hip. While the surgical treatment of FAI has demonstrated favorable clinical outcomes, the ability of an osteoplasty to reliably improve hip kinematics and range of motion remains unknown. Purpose This study used computer-assisted 3-dimensional (3D) analysis to assess differences in hip range of motion before and after the arthroscopic surgical treatment of symptomatic FAI. Study Design Case series; Level of evidence, 4. Methods Ten patients with symptomatic, focal cam and/or pincer impingement lesions underwent high-resolution computed tomography scans and computer-assisted 3D modeling of the involved hip before and after corrective arthroscopic surgery by the senior author. Cam location, alpha angle, neck-shaft angle, femoral version, and acetabular version at 12-o'clock through 3-o'clock positions were measured. The model was subsequently dynamized to define the preoperative and postoperative range of motion and location of impingement with hip flexion, internal rotation, and internal rotation at 90° of hip flexion. Statistical analysis of preoperative and postoperative hip flexion and internal rotation at 90° of hip flexion was performed using paired t tests with P < .05 defined as significant. Results The cam lesion was located between 12 o'clock and 5 o'clock in all cases. Mean preoperative alpha angle was 59.8° (range, 36°-76°). Mean femoral version was 12.5° (range, −15° to 32°). Mean preoperative hip flexion was 107.40° ± 11.6°, and mean internal rotation at 90° of hip flexion was 19.10° ± 13.0°. The location of impingement was unique in each case and not predictable based on simple radiographic measures (ie, alpha angle) alone. Corrective femoral and rim osteoplasty resulted in significant improvements in both hip flexion (3.8°; P = .002) and internal rotation (9.3°; P = .0002). Mean postoperative alpha angle was 36.4° (range, 22°-46°). Conclusion Focal cam and/or rim osteoplasty can reliably improve hip kinematics and range of motion in patients with symptomatic FAI, particularly the limitation of internal rotation in a flexed position. Computed tomography–based computer modeling can localize regions of anticipated mechanical impingement in symptomatic patients. A complete osteoplasty in these defined regions, through an arthroscopic or open approach, predictably improves range of motion and may help to eliminate the recurrent mechanical collision and secondary chondral injury associated with FAI.

Unicondylar knee arthroplasty (UKA) is considered an alternative to total knee arthroplasty for patients who have arthritis limited to one compartment of the knee. This study examined surface damage of 3 contemporary UKA designs that were retrieved at revision surgery. Two of the UKA designs were fixed bearing and one was mobile bearing. Demographic information was collected, as well as information about the implants used at revision surgery. Articular surface damage was greater in the fixed-bearing designs as compared to the mobile bearing, although the mobile-bearing implants had significantly shorter length of implantation. Backside damage was also graded for the mobile bearing and when combined with articular wear resulted in overall damage scores higher than both fixed-bearing designs. The fixed-bearing designs showed delamination and surface deformation, whereas the mobile bearing had no evidence of these damage modes. However, mobile-bearing components showed other types of wear, and significant wear damage was present on the bearing surfaces of the mobile-bearing implants despite a short time of implantation. At the time of conversion to a total knee arthroplasty, more than 50% of cases required the use of stems, augments, or constrained inserts for the tibial reconstruction. In conclusion, wear modes differed among UKA prosthesis designs. Revision of a UKA to a total knee arthroplasty remains complex with the tibial preparation more complicated than in the primary setting.

Polyethylene tibial post wear in posterior-stabilized knee designs is a major problem. The Insall-Burstein II (IB PS II) reportedly has severe anterior wear of the post in retrieved implants. We hypothesized the more anterior placement in the IB PS II would be reflected in greater wear at the anterior face than the IB PS I. We examined 234 retrieved inserts using subjective scales to grade post damage and wear. Of the IB PS II inserts, 38% demonstrated severe wear compared with only 25% of IB PS I inserts. The most prevalent damage location for the IB PS II was the anterior face, whereas the IB PS I sustained wear mainly on the medial face. While the IB PS post was not designed to constrain posterior femoral displacement, our observations confirm contact in hyperextension or other paradoxic anterior tibial translation is common and design-dependent. Minimizing wear and damage through proper post placement and changes in implant design to anticipate contact on the anterior post should be considered for future posterior stabilized knee replacements. These changes cannot occur in isolation, however, because changes in post placement and design also depend on their relation to the shape and location of the tibial bearing surfaces.

The impact of design changes intended to improve wear of knee replacements can be assessed from analysis of retrieved implants. We hypothesized changes in bearing surface conformity from the Insall-Burstein II knee to a successor, the Optetrak, intended to improve contact stresses would be apparent in wear patterns observed on retrieved tibial inserts. From 151 Insall-Burstein II and 54 Optetrak retrieved components, 35 pairs (Insall-Burstein II and Optetrak) were matched on length of implantation, body mass index, and age. Digital images of the bearing surfaces were used to identify and measure wear modes, which were then converted to a percentage of the total possible contact area. Burnishing was the most prevalent mode for both designs followed by scratching and then pitting. The percentage of involved area was greater for the Optetrak for 23 pairs. Interestingly, for the nine matched pairs with length of implantation longer than 2 years, six of the Insall-Burstein II inserts had considerably greater scratching and pitting and five exhibited abrasion and creep absent from Optetrak implants. Bearing surface design is a major factor that can affect kinematics and contact patterns. Our observations confirm the considerable impact of small changes in conformity and suggest models predicting contact stresses adequately reflect in vivo performance.

Low-back pain is a common, disabling medical condition, and one of the major causes is disc degeneration. Total disc replacements are intended to treat back pain by restoring disc height and re-establishing functional motion and stability at the index level. The objective of this study was to determine the effect on range of motion (ROM) and stiffness after implantation of the ProDisc®-L device in comparison to the intact state. Twelve L5–S1 lumbar spine segments were tested in flexion/extension, lateral bending, and axial rotation with axial compressive loads of 600 N and 1,200 N. Specimens were tested in the intact state and after implantation with the ProDisc®-L device. ROM was not significantly different in the implanted spines when compared to their intact state in flexion/extension and axial rotation but increased in lateral bending. Increased compressive load did not affect ROM in flexion/extension or axial rotation but did result in decreased ROM in lateral bending and increased stiffness in both intact and implanted spine segments. The ProDisc®-L successfully restored or maintained normal spine segment motion.

The effect of fixed spinal deformities on a functional pelvis from standing to sitting is not fully understood. We aimed to assess the change in preoperative sagittal pelvic tilt angle (SPTA) from standing to sitting in patients undergoing total hip arthroplasty, comparing flexible and fixed spinal deformities.Between July 2011 and October 2011, 68 consecutive unilateral total hip arthroplasties were implanted in 68 patients with a mean age of 71 ± 6 years. Fixed spinal deformity was defined as10° of the change in SPTA from standing to sitting. Preoperative radiographic evaluation included standing (weight-bearing) anteroposterior and lateral pelvic and lumbosacral radiographs and a sitting lateral pelvic radiograph.The mean standing and sitting SPTA was 3.7° of anterior tilt and 17.7° of posterior tilt, respectively (change of 21.4 ± 12.5°). Seventy-five percent had flexible pelvises, all of which had a posterior tilt from standing to sitting. One patient in the fixed pelvis (1.4%) had a loss of posterior tilt from standing to sitting. The mean change of SPTA from standing to sitting in the fixed and flexible pelvis groups was 5.9 ± 3.5° to 26.7 ± 9.6° of posterior tilt, which was statistically significant (P.05).There was a significant change in sagittal pelvic tilt from standing to sitting, especially in patients with a flexible spine, in which the functional anteversion increases with sitting. The patients with a fixed pelvis had significantly less SPTA in standing (less anteversion) with less posterior sagittal tilt in sitting, which should be incorporated in cup positioning.

A multibody model of the knee was developed and the predicted ligament forces and kinematics during passive flexion corroborated subject-specific measurements obtained from a human cadaveric knee that was tested using a robotic manipulator. The model incorporated a novel strategy to estimate the slack length of ligament fibers based on experimentally measured ligament forces at full extension and included multifiber representations for the cruciates. The model captured experimentally measured ligament forces (≤5.7 N root mean square (RMS) difference), coupled internal rotation (≤1.6 deg RMS difference), and coupled anterior translation (≤0.4 mm RMS difference) through 130 deg of passive flexion. This integrated framework of model and experiment improves our understanding of how passive structures, such as ligaments and articular geometries, interact to generate knee kinematics and ligament forces.

Dislocation following hip arthroplasty remains problematic. While the etiology of dislocation may be multifactorial, implant system design may play a role. Using a computer aided design program, virtual range of motion of several commonly implanted designs was performed with prosthetic interference representing impingement used as an endpoint. Implants with small diameter head size (22mm) and a larger trunion geometry (type II taper) demonstrated impingement in flexion at less than 90°, suggesting an increased risk for dislocation. To investigate this clinically, we performed a review of a consecutive series of 254 primary hip arthroplasties performed by a single surgeon using an implant with a type II taper (Biomet™, Warsaw, IN). At a minimum 2 year followup, 12 patients with 12 hips (4.8%) had at least one episode of dislocation. Stratified by head size, the dislocation rates were 3.6% for 28 mm, 4.8% for 26 mm, and 18.8% for 22mm bearings. These findings support the notion that computer aided design modeling of implant systems is useful in evaluating range of motion and this technique could be employed during the design of any new implant system. Level of Evidence: Therapeutic study, level IV (case series). See Guidelines for Authors for a complete description of levels of evidence.

Although spine fusion is a versatile and effective technique in the treatment of spinal disorders, increased stresses on adjacent unfused levels lead to symptomatic adjacent level degeneration in many patients. The goal of nonfusion devices in spine surgery is to ablate or unload painful structures while preserving segmental motion. The intended performance of nonfusion devices such as disc replacement, nucleus pulposus replacement, and posterior stabilization devices can be understood from the biomechanics of the functional spinal unit in health and disease and the interplay between the motion segment and the device. Implant design issues can also markedly affect performance.

Function and kinematics following unicondylar knee arthroplasty (UKA) have been reported to be close to the native knee. Gait, stair climbing and activities of daily living expose the knee joint to a combination of varus and valgus moments. Replacement of the medial compartment via UKA is likely to change the physiologic knee stability and its ability to respond to varus and valgus moments. It was hypothesized that UKA implantation would stiffen the knee and decrease range of motion in the frontal plane. Six fresh frozen cadaver knees were prepared and mounted in a six-degrees-of-freedom robot. An axial load of 200 N was applied with the knee in 15°, 45° and 90° of flexion. Varus and valgus moments were added, respectively, before and after implantation of medial UKA. Tests were than redone with a thicker polyethylene inlay to simulate overstuffing of the medial compartment. Range of motion in the frontal plane and the tibial response to moments were recorded via the industrial robot. The range of motion in the frontal plane was decreased with both, balanced and overstuffed UKA and shifted towards valgus. When exposed to valgus moments, knees following UKA were stiffer in comparison with the native knee. The effect was even more pronounced with medial overstuffing. In UKA, the compressive anatomy is replaced by much stiffer components. This lack of medial compression and relative overstuffing leads to a tighter medial collateral ligament. This drives the trend towards a stiffer joint as documented by a decrease in frontal plane range of motion. Overstuffing should strictly be avoided when performing UKA.

An infraacetabular screw path facilitates the closure of a periacetabular fixation frame to increase the plate fixation strength in acetabular fractures up to 50%. Knowledge of the variance in corridor sizes and axes has substantial surgical relevance for safe screw placement.(1) What proportion of healthy pelvis specimens have an infraacetabular corridor that is 5 mm or larger in diameter? (2) Does a universal corridor axis and specific screw entry point exist? (3) Are there sex-specific differences in the infraacetabular corridor size or axis and are these correlated with anthropometric parameters like age, body weight and height, or the acetabular diameter?A template pelvis with a mean shape from 523 segmented pelvis specimens was generated using a CT-based advanced image analyzing system. Each individual pelvis was registered to the template using a free-form registration algorithm. Feasible surface regions for the entry and exit points of the infraacetabular corridor were marked on the template and automatically mapped to the individual samples to perform a measurement of the maximum sizes and axes of the infraacetabular corridor on each specimen. A minimum corridor diameter of at least 5 mm was defined as a cutoff for placing a 3.5-mm cortical screw in clinical settings.In 484 of 523 pelves (93%), an infraacetabular corridor with a diameter of at least 5 mm was found. Using the mean axis angulations (54.8° [95% confidence interval {CI}, 0.6] from anterocranial to posterocaudal in relation to the anterior pelvic plane and 1.5° [95% CI, 0.4] from anteromedial to posterolateral in relation to the sagittal midline plane), a sufficient osseous corridor was present in 64% of pelves. Allowing adjustment of the three-dimensional axis by another 5° included an additional 25% of pelves. All corridor parameters were different between females and males (corridor diameter, 6.9 [95% CI, 0.2] versus 7.7 [95% CI, 0.2] mm; p0.001; corridor length, 96.2 [95% CI, 0.7] versus 106.4 [95% CI, 0.6] mm; p0.001; anterior pelvic plane angle, 54.0° [95% CI, 0.9] versus 55.3° [95% CI, 0.8]; p0.01; sagittal midline plane angle, 4.3° [95% CI, 0.6] versus -0.3° [95% CI, 0.5]; p0.001).This study provided reference values for placement of a 3.5-mm cortical screw in the infraacetabular osseous corridor in 90% of female and 94% of male pelves. Based on the sex-related differences in corridor axes, the mean screw trajectory is approximately parallel to the sagittal midline plane in males but has to be tilted from medial to lateral in females. Considering the narrow corridor diameters, we suggest an individual preoperative CT scan analysis for fine adjustments in each patient.

Objective. A new design concept has been developed to reduce the propensity for dislocation in total hip patients. The ability of this design to increase the stability of the hip joint is studied. Design. The new design involves a convex-curved acetabular lip, extending from the hemispherical articulating surface to the outer edge of the cup. The femoral component has a matching, reverse curve. Background. Dislocation is a continuing problem in total hip arthroplasty, a complication experienced by 2–11% of patients with primary surgeries, and much higher percentage of patients in revision series. Confounding factors and sources of variability in the clinical domain make it difficult to identify specific parameter influences. Methods. A three-dimensional nonlinear finite element model has been developed for the purpose of studying the dislocation event. We report the first use of this finite element model to analyze the potential for improving hip stability by a new total hip component design concept. Results. The results show that this new design achieves 28% more resisting moment build-up during dislocation, and has a higher range of motion from impingement to onset of subluxation. The new curved lip design also develops 50% less polyethylene von Mises stress in the impingement zone. Conclusions. This design has excellent potential for increasing the inherent stability of the total hip joint. Relevance Recurrent dislocation is the second leading cause of total hip failure next to late loosening. This study shows the potential of a new total hip design to increase the stability of the artificial hip joint.

Background The literature available on the results after noncemented total elbow arthroplasty (TEA) in inflammatory arthritis is limited. Methods Ten patients (7 women, 3 men; 14 elbows total) who underwent custom, noncemented TEA from 1988 to 1995 were retrospectively reviewed. The average age was 28 years (range, 17-45 years). Four patients (4 elbows) had rheumatoid arthritis, and 6 patients (10 elbows) had juvenile rheumatoid arthritis. The mean follow-up was 18 years. All patients underwent a custom, noncemented, semiconstrained TEA with a plasma spray surface designed from preoperative computed tomography scan to achieve metaphyseal fit. The primary outcome was the Mayo Elbow Performance Score, and secondary outcomes were flexion and rotation arc of motion. Intraoperative and postoperative complications and revisions performed were also recorded. Radiographs taken at final follow-up were evaluated for evidence of loosening. Results The Mayo Elbow Performance Score improved from a mean of 35 preoperatively to a mean of 91 postoperatively. Flexion arc of motion improved from 50° preoperatively to 111° postoperatively, and rotation arc improved from 75° preoperatively to 145° postoperatively. Four patients underwent bushing revision at 8, 8, 22, and 22 years (29%), respectively, and there was 1 deep infection (7%). One patient had an intraoperative fracture in the humerus that did not require further treatment. On final radiographic follow-up at a mean of 18 years, all the components were fully ingrown, and there was no evidence of loosening or loss of fixation. Conclusion In the younger population with inflammatory arthritis, noncemented TEA has reliable outcomes clinically and radiographically at long-term follow-up.

Posterior stabilized total knee arthroplasty requires an intercondylar notch to accommodate the cam housing that articulates with the tibial post to create femoral rollback required for deep flexion. The volume of bone resected for the intercondylar notch varies with implant design, and newer designs may accommodate high flexion with less bone resection.This study aims to analyze the bone volume and density resected from the intercondylar notch for three posterior stabilized implants from a single company: a Posterior Stabilized (PS) system, a Hi-Flex system (HF), and a rounded new box-reamer (RB) system and to further assess whether the newer RB with a cylindrical cutting tool would preserve more native bone.Using a computer model, the PS, HF, and RB femoral components were digitally implanted into CT scans of 19 cadaver femurs. Nine cadavers were fit with a size 4 implant, six with size 3, and four with a size 2. The volume of intercondylar bone resected digitally for femoral preparation was measured. Bone density was measured by CT scans in Hounsfield units (HU). A paired t test was used to compare the mean volume of bone resected for each implant.For the size 4 femurs, the newer RB design removed 8% less intercondylar bone than the PS design (7,832 ± 501 vs. 8,547 ± 377 mm(3), p 0.001) and 28% less bone than the HF design (7,832 ± 501 vs. 10,897 ± 444 mm(3), p 0.001). The average HU for size 4 femurs for RB design was 427 ± 72 (PS = 399 ± 69, p 0.001; HF = 379 ± 66, p 0.001). For the size 3 femurs, the RB design removed 12% less intercondylar bone than the PS (6,664 ± 786 vs. 7,516 ± 648 mm(3), p 0.001) and 27% less bone than the HF (6,664 ± 786 vs. 9,078 ± 713 mm(3), p 0.001). HU for size 3 femurs for the RB design was 452 ± 70 (PS = 422 ± 53, p 0.1; HF = 410 ± 59, p 0.01). For the size 2 femurs, the RB design removed 5% less intercondylar bone than the PS (5,730 ± 552 vs. 6,009 ± 472 mm(3), p 0.01) and 22% less bone than the HF (5,730 ± 552 vs. 7,380 ± 532 mm(3), p 0.001). HU for size 2 femurs for the RB design was 430 ± 48 (PS = 408 ± 55, p 0.01; HF = 385 ± 56, p 0.01).The newer RB design removes less bone from the intercondylar notch than the classic PS and HF designs in all sizes tested. The bone-conserving cuts incorporated into this newer implant design appear to preserve native bone without compromising design objectives.

Periprosthetic supracondylar fractures in the setting of an ipsilateral total knee and hip replacement are a rare but serious orthopedic challenge.In this unique situation, we consider insertion of a custom coupling device with a distal femoral replacement as an appropriate surgical solution that allows for stability and preserves hip and knee functionality, while not relying on the poor healing potential of the remaining intercalary femoral bone.We report the outcomes of two patients who underwent this custom coupling procedure.These custom devices resulted in successful outcomes with restoration of ambulatory function and range of motion at greater than 14 months follow-up.We found that this technique provides sufficient stability and preserves functionality in a difficult-to-treat patient population. The results indicate that this technique may be considered as an alternative to more invasive procedures including total femoral replacement and complete femoral allograft constructs.

Large head total hip arthroplasty (THA) is known to increase range of motion to impingement and decrease risk of dislocation, however, this is dependent on accurate component positioning and patient anatomy. In this study, a computer-aided design model was used to determine the effects of component positioning on range of motion to impingement with increasing head size. Three-dimensional models were made of 7 cadaver CT scans and virtual THA was performed with a conventional implant system. Theoretical range of motion to impingement was tested before and after the components were implanted in flexion, extension, internal/external rotation, abduction, adduction, and flexed internal/external rotation. Range of motion increased non-linearly in every motion except for external rotation and adduction with increasing head size, with gains in ROM limited by osseous impingement. Use of large head THA leads to increased ROM to impingement, but with larger head sizes, benefits are limited by bony anatomy.

Introduction Patients may experience a loss of internal rotation (IR) and external rotation (ER) after reverse total shoulder arthroplasty (RTSA). We hypothesized that alterations in the glenosphere position will affect the amount of impingement-free IR and ER. Materials and methods Computed tomography (CT) scans of the scapula and humerus were obtained from 7 cadaveric specimens, and 3-dimensional reconstructions were created. RTSA models were virtually implanted into each specimen. The glenosphere position was determined in relation to the neutral position in 7 settings: medialization (5 mm), lateralization (10 mm), superior translation (6 mm), inferior translation (6 mm), superior tilt (20°), and inferior tilt (15° and 30°). The humerus in each virtual model was allowed to freely rotate at a fixed scaption angle (0°, 20°, 40°, and 60°) until encountering bone-to-bone or bone-to-implant impingement (180° of limitation). Measurements were recorded for each scaption angulation. Results At 0° scaption, only inferior translation, lateralization, and inferior tilt (30°) allowed any impingement-free motion in IR and ER. At the midranges of scaption (20° and 40°), increased lateralization and inferior translation resulted in improved rotation. Supraphysiologic motion (>90° rotation) was seen consistently at 60° of scaption in IR. Superior translation (6 mm) resulted in no rotation at 0° and 20° of scaption for IR and ER. Conclusions Glenosphere position significantly affected humeral IR and ER after RTSA. Superior translation resulted in significant restrictions on IR and ER. Optimal glenosphere positioning was achieved with inferior translation, inferior tilt, and lateralization in all degrees of scaption.

Background Reverse total shoulder arthroplasty offers pain relief and functional improvement for patients with rotator cuff–deficient shoulders. The purpose of this study was to determine the optimal amount of humeral retroversion for this prosthesis. Materials and methods Six cadaveric shoulders underwent computed tomography (CT) imaging and were then dissected of soft tissues, except for their tendinous attachments. A reverse total shoulder arthroplasty was implanted in 0°, 20°, 30°, and 40° of retroversion, and the shoulders were mounted on a simulator to determine the muscle forces required to achieve 30° and 60° of scaption. CT images were converted into 3-dimensional models, and the amount of internal and external rotation was determined with computer modeling at various scaption angles. Results No differences were found in the forces required for 30° or 60° of scaption for any muscle, at any retroversion. With increasing retroversion, more impingement-free external rotation was obtained, with a concomitant decrease in the amount of internal rotation. Above 60°, the humerus was allowed to rotate around the glenosphere unencumbered. Conclusions Increasing retroversion did not affect the muscle force requirements for scaption across the shoulder. Placing the humeral component in 0° to 20° of retroversion allows maximum internal rotation with the arm at the side, a movement that is required for daily activities. This limits external rotation with the arm at the side, but has no effect on external rotation with the arm elevated.

It has been 60 years since the first knee implant surgery was performed yet questions concerning which material and implant design is most effective for specific populations still remain unanswered. There is a need for a faster, cost effective solution to test implants for their efficacy under physiological conditions. The primary objective of this project is to establish a workable design space for developing meniscal implants. This paper describes the process of building a 3-D model from multiple volumetric MRI data using commercially available segmentation and model building software. The model, when simulated under a variety of physiological conditions using a finite element formulation developed for 3-D contact of biphasic tissues, will be verified against experimental data in whole in-vitro knee tests.

Preoperative 3-dimensional modeling methods are commonly used in orthopedic surgery but there have been limited reports of their use for planning upper extremity surgery. In this report, we describe a case of a malunited olecranon fracture and its management using custom preoperative computed tomographic templating and mechanical modeling. One year after surgery, the patient demonstrated nearly full painless restoration of function and motion.