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Background An extended trochanteric osteotomy (ETO) safely addresses femoral component removal during challenging revision total hip arthroplasty. However, no prior study has evaluated whether a difference in axial stability exists between ETO closure performed before (reconstitution) or after (scaffolding) canal preparation and stem impaction. We hypothesized that given the absence of clinical reports of outcome differences despite the wide use of both practices, no significant difference in the initial axial stability would exist between the 2 fixation techniques. Methods ETOs were performed and repaired using the reconstitution technique for the 6 right-sided femora and the scaffolding technique for the six left-sided femora. The 195-mm long, 3.5°-tapered splined titanium monobloc stems were impacted into 6 matched pairs of human fresh cadaveric femora. Three beaded cables were placed in a standardized fashion on each specimen, 1 for prophylaxis against osteotomy propagation during reaming/impaction and 2 to close the ETO. Stepwise axial loading was performed to 2600 N or until failure, which was defined as subsidence >5 mm or femoral/cable fracture. Results All specimens successfully resisted axial testing, with no stem in either ETO repair group subsiding >2 mm. The mean subsidence for the reconstitution group was 0.9 ± 0.4 mm, compared to 1.2 ± 0.5 mm for the scaffolding group (P = .2). Conclusion In this cadaveric model with satisfactory proximal bone stock, no difference existed between the reconstitution and scaffolding ETO repair techniques, and both provide sufficient immediate axial stability in a simulated revision total hip arthroplasty setting under physiologic loads.

Titanium tapered stems (TTS) achieve fixation in the femoral diaphysis and are commonly used in revision total hip arthroplasty. The initial stability of a TTS is critical, but the minimum contact length needed and impact of implant-specific taper angles on axial stability are unknown. This biomechanical study was performed to better guide operative decision-making by addressing these clinical questions.Two TTS with varying conical taper angles (2° spline taper vs 3.5° spline taper) were implanted in 9 right and left matched fresh human femora. The proximal femur was removed, and the remaining femoral diaphysis was prepared to allow for either a 2 cm (n = 6), 3 cm (n = 6), or 4 cm (n = 6) cortical contact length with each implanted stem. Stepwise axial load was then applied to a maximum of 2600N or until the femur fractured. Failure was defined as either subsidence5 mm or femur fracture.All 6 femora with 2 cm of stem-cortical contact length failed axial testing, a significantly higher failure rate (P.02) than the 4 out of 6 femora and all 6 femora that passed testing at 3 cm and 4 cm, respectively, which were not statistically different from each other (P = .12). Taper angle did not influence success rates, as each matched pair either succeeded or failed at the tested contact length.4 cm of cortical contact length with a TTS demonstrates reliable initial axial stability, while 2 cm is insufficient regardless of taper angle. For 3 cm of cortical contact, successful initial fixation can be achieved in most cases with both taper angle designs.

Purpose To investigate alterations in technique for medial patellofemoral ligament (MPFL) reconstruction in the setting of patella alta and describe the effect of these alterations on MPFL anatomometry. Methods Ten cadaveric knees were used. Four candidate femoral attachment sites of MPFL were tested. The attachment sites were Schottle’s point (SP), 5 mm distal to SP, 5 mm proximal to SP, and 10 mm proximal to SP. A suture anchor was placed at the upper 40% of the medial border of the patella with the emanating suture used to simulate the reconstructed ligament. MPFL maximum length change was calculated through a range of motion between 0° and 110°. Recordings at all 4 candidate femoral attachments sites were repeated after a flat tibial tubercle osteotomy and transfer to achieve alta as measured by the Caton–Deschamps Index (CDI) of 1.3, 1.4, and 1.5. Results The 10 specimens had an average CDI of 0.99, range 0.87 to 1.16. In the native tibial tubercle condition, SP was more isometric through 20° to 70° range of motion, or anatomometric, than any other candidate femoral attachment location. With patella alta with a CDI of 1.3 and 1.4, attachment site 5 mm proximal to SP exhibited more anatomometry than SP. With patella alta with a CDI of 1.5, attachment site 10 mm proximal to SP exhibited more anatomometry than SP. Conclusions Increased patella alta significantly alters MPFL anatomometry. With increasing degrees of patella alta, more proximal candidate femoral attachment sites demonstrate decreased change in length compared with SP. None of the varied femoral attachments produced anatomometry over the entirety of the flexion range from 20° to 70°, suggesting that in cases of significant patella alta, proximalization the femoral attachment site of MPFL reconstruction may be necessary to achieve an anatomometric MPFL reconstruction. Clinical Relevance A standardized, isolated MPFL reconstruction may be prone to failure in the setting of patella alta, given the anisometry demonstrated. Alternative femoral attachment sites for MPFL reconstruction should be considered in these patients.

Background: The distribution of contact forces across the dysplastic patellofemoral joint has not been adequately quantified because models cannot easily mimic the dysplasia of both the trochlea and the patella. Thus, the mechanical consequences of surgical treatments to correct dysplasia cannot be established. Purpose/Hypothesis: The objective of this study was to quantify the contact mechanics and kinematics of normal, mild, and severely dysplastic patellofemoral joints using synthetic mimics of the articulating surfaces on cadavers. We tested the hypothesis that severely dysplastic joints would result in significantly increased patellofemoral contact forces and abnormal kinematics. Study Design: Controlled laboratory study. Method: Patellofemoral dysplasia was simulated in 9 cadaveric knees by replacing the native patellar and trochlear surfaces with synthetic patellar and trochlear implants. For each knee, 3 synthetic surface geometries (normal, showing no signs of dysplasia; mild, exemplifying Dejour type A; and severe, exemplifying Dejour type B) were randomized for implantation and testing. Patellar kinematics and the sum of forces acting on the medial and lateral patellar facets were computed for each knee and for each condition at 10° increments from 0° to 70° of flexion. Results: A pronounced lateral shift in the weighted center of contact of the lateral facet occurred for severely dysplastic knees from 20° to 70° of flexion. Compared with normal geometries, lateral patellar facet forces exhibited a significant increase only with mild dysplasia from 50° to 70° of flexion and with severe dysplasia at 70° of flexion. No measurable differences in medial patellar facet mechanics or joint kinematics occurred. Conclusion: Our hypothesis was rejected: Severely dysplastic joints did not result in significantly increased patellofemoral contact forces and abnormal kinematics in our cadaveric simulation. Rather, severe dysplasia resulted in a pronounced lateral shift in contact forces across the lateral patellar facet, while changes in kinematics and the magnitude of contact forces were not significant. Clinical Relevance: Including dysplasia of both the patella and trochlea is required to fully capture the mechanics of this complex joint. The pronounced lateralization of contact force in severely dysplastic patellofemoral joints should be considered to avoid cartilage overload with surgical manipulation.

Isolated injuries of the scapholunate interosseous ligament (SLIL) are insufficient to produce dorsal intercalated segment instability. There is no consensus about which additional ligamentous stabilizers are critical determinants of dorsal intercalated segment instability. The aim of this study was to evaluate the role of the long radiolunate (LRL), scaphotrapeziotrapezoid (STT), and dorsal intercarpal (DIC) ligaments in preventing dorsal intercalated segment instability.Thirty fresh-frozen forearms were randomized to 5 ligament section sequences to study the SLIL, LRL, STT, and DIC ligaments. The DIC-lunate insertion (DIC) and scaphoid insertion (DIC) were studied separately; the DIC insertions on the trapezium and triquetrum were left intact. Loaded posteroanterior and lateral fluoroscopic images were obtained at baseline and repeated after each ligament was sectioned. After each sequence, the wrists were loaded cyclically (71 N). The radiolunate angle was measured with load. Dorsal intercalated segment instability was defined as an increase of15° in the radiolunate angle compared with baseline.Division of the SLIL did not increase the radiolunate angle. Section of the SLIL+LRL or SLIL+DIC significantly increased the radiolunate angle but did not produce dorsal intercalated segment instability. Section of the SLIL+STT or SLIL+DIC+DIC produced dorsal intercalated segment instability.In order to produce dorsal intercalated segment instability, complete scapholunate injuries require the disruption of at least 1 critical ligament stabilizer of the scaphoid or lunate (the STT or DIC+DIC).When treating SLIL tears with dorsal intercalated segment instability, techniques to evaluate the volar and dorsal critical stabilizers of the proximal carpal row should be considered.

The purposes of this study were (1) to evaluate the percentage of gluteus medius and minimus tendon footprint restoration that can be achieved with fixation using single-row repair versus double-row repair and (2) to evaluate the yield load of a repair of the gluteus medius and minimus tendon using single-row versus double-row repair techniques.Twelve human fresh-frozen cadaveric hip specimens (6 matched pairs, 4 female, mean age 47.5 ± 14.5 years) were tested. Specimens were excluded if they had any prior hip surgery or injury, if any abnormality of the tendon was noted on dissection, or if they had a body mass index20 or35 or a T-score2.0 on dual-energy x-ray absorptiometry scanning. Matched pairs were randomized to receive either double-row repair with 2 standard suture anchors and 2 knotless anchor devices or a single-row repair with suture anchors only. The percentage of the footprint area covered after repair was determined using a computer-assisted digitization algorithm. With a mechanical testing system, each repaired specimen was tested for mechanical strength first with cyclic loading and then load to failure testing.Footprint coverage of the lateral facet was significantly greater for double-row repair (mean 76.6%) compared with single-row repair (mean 50.3%) (P = .03). There was no significant difference between single- and double-row repair for posterior-superior or anterior facet coverage. Mechanical testing showed a higher mean yield load for double-row anchor repair (197.6 ± 61.7 N vs 163.5 ± 35.4 N for single-row repair), but this did not reach statistical significance (P = .15). The predominant mode of failure was suture pullout through the musculotendinous unit (9/12 specimens: 5 double-row and 4 single-row).For hip abductor tears, double-row suture repair yields improved footprint coverage compared with single-row repair. Although it did not reach statistical significance, there was a higher mean yield load in the double-row group.Double-row suture fixation technique for hip abductor tears maximizes strength and footprint coverage of the repair.

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.

Purpose To compare the kinematic effects of the dorsal fiber-splitting approach for scapholunate ligament repair to a dorsal “window” approach that spares all ligaments. Methods We randomized 24 fresh-frozen paired cadaveric forearms to either the dorsal fiber-splitting capsulotomy approach (FSC) or the dorsal window approach (window) following scapholunate interosseous ligament (SLIL) division. Loaded fluoroscopic radiographs were obtained after each of the 4 testing conditions following cyclic loading (200 cycles; 71 N): (1) intact SLIL, (2) SLIL-division, (3) surgical approach , and (4) closure. FSC specimens were randomly allocated to 2 subgroups for closure with either a suture anchor (n = 6) or a simple running suture closure (n = 6). Radiographic parameter measurements included the scapholunate gap, radiolunate angle, scapholunate angle, and dorsal scaphoid translation. Results Following the FSC, there were significant alterations in all radiographic parameters when compared with the intact and SLIL-division conditions. The window approach did not result in significant changes in any radiographic parameter. When compared to the window approach, all radiographic parameters of the FSC approach were significantly altered. Following closure with suture anchors in the FSC group, radiographic parameters improved, whereas with standard closure they failed to do so. Despite anchor closure, dorsal scaphoid translation, radiolunate angle, and scapholunate angle all remained elevated compared with scapholunate-divided wrists. Conclusions The FSC produced significant changes in carpal posture under load, including scapholunate diastasis, dorsal intercalated segment instability, and dorsal scaphoid translation in SLIL-deficient wrists. The window approach preserved the critical dorsal ligament stabilizers and did not produce changes in carpal posture. Clinical relevance The FSC may create iatrogenic changes in carpal posture that cannot be fully corrected with standard or anchor closure. The window approach does not alter carpal posture and should be considered when performing surgical procedures on the scaphoid or lunate.

Annular repair devices offer a solution to recurrent disc herniations by closing an annular defect and lowering the risk of reherniation. Given the significant risk of neurologic injury from device failure it is imperative that a reliable preclinical model exists to demonstrate a high load to failure for the disc repair devices.To establish a preclinical model for disc herniation and demonstrate how changes in species, intervertebral disc height and Pfirrmann classification impacts failure load on an injured disc. We hypothesized that: (1) The force required for disc herniation would be variable across disc morphologies and species, and (2) for human discs the force to herniation would inversely correlate with the degree of disc degeneration.Animal and human cadaveric biomechanical model of disc herniation.We tested calf lumbar spines, bovine tail segments and human lumbar spines. We first divided individual lumbar or tail segments to include the vertebral bodies and disc. We then hydrated the specimens by placing them in a saline bath overnight. A magnetic resonance images were acquired from human specimens and a Pfirrmann classification was made. A stab incision measuring 25% of the diameter of the disc was then done to each specimen along the posterior intervertebral disc space. Each specimen was placed in custom test fixtures on a servo-hydraulic test frame (MTS, Eden Prarie, MN) such that the superior body was attached to a 10,000 lb load cell and the inferior body was supported on the piston. A compressive ramping load was placed on the specimen in load control at 4 MPa/sec stopping at 75% of the disc height. Load was recorded throughout the test and failure load calculated. Once the test was completed each specimen was sliced through the center of the disc and photos were taken of the cut surface.Fifteen each of calf, human, and bovine tail segments were tested. The failure load varied significantly between specimens (p.001) with human specimens having the highest average failure load (8154±2049 N). Disc height was higher for lumbar/bovine tail segments as compared to calf specimens (p.001) with bovine tails having the highest disc height (7.1±1.7 mm). Similarly, human lumbar discs had a cross sectional area that was greater than both bovine tail/calf lumbar spines (p.001). There was no correlation between disc height and failure load within each individual species (p.05). Cross sectional area and failure load did not correlate with failure load for human lumbar spine and bovine tails (p.05) but did correlate with calf spine (r=0.53, p=.04). There was a statistically significant inverse correlation between disc height and Pfirrmann classification for human lumbar spines (r=-0.84, p.001). There was also a statistically significant inverse relationship between Pfirrmann classification and failure load (r=-0.58, p=.02).We have established a model for disc herniation and have shown how results of this model vary between species, disc morphology, and Pfirrmann classification. Both hypotheses were accepted: The force required for disc herniation was variable across species, and the force to herniation for human spines was inversely correlated with the degree of disc degeneration. We recommend that models using human intervertebral discs should include data on Pfirrmann classification, while biomechanical models using calf spines should report cross sectional area. Failure loads do not vary based on dimensions for bovine tails.Our analysis of models for disc herniation will allow for quicker, reliable comparisons of failure forces required to induce a disc herniation. Future work with these models may facilitate rapid testing of devices to repair a torn/ruptured annulus.

Purpose To investigate whether the location of distal radius osteotomy/shortening relative to the radial insertion of the distal interosseous membrane (DIOM) is correlated with distal radioulnar joint (DRUJ) instability. We hypothesized that distal radius osteotomy and shortening proximal to the DIOM insertion would result in increased DRUJ instability because of induced laxity in the DIOM. Methods Osteotomies of the distal radius were performed proximal and distal to the DIOM insertion in 14 fresh-frozen cadaveric specimens. Using a volar plate, 5 conditions were tested: anatomical radius alignment; 2- and 4-mm shortening at the proximal osteotomy site; and 2- and 4-mm shortening at the distal osteotomy site. Basilar ulnar styloid osteotomy was performed to simulate triangular fibrocartilage complex (TFCC) detachment—specimens were tested with the ulnar styloid detached and the ulnar styloid fixed (to restore normal anatomy). The DRUJ stability was quantified using dorsal-volar displacement of the radius in response to 20 N of force using a force-displacement probe in neutral, pronation, and supination. Posttesting specimen dissections assessed DIOM and distal oblique bundle (DOB) anatomy. The DRUJ stability in each experimental condition was compared with a multifactor repeated measures analysis of variance with the specimen treated as the repeated factor. Results There were no significant differences in dorsal-volar translation of the radius (ie, DRUJ stability) between radial osteotomy/shortening proximal and distal to the DIOM insertion, regardless of forearm rotational position or magnitude of shortening. Five (36%) of the 14 specimens had a DOB present. There was a significant increase in DRUJ instability in the setting of TFCC detachment (via basilar ulnar styloid osteotomy). Conclusions No difference in DRUJ stability was observed between distal radius osteotomy/shortening proximal and distal to the DIOM radial insertion, regardless of forearm rotation, magnitude of shortening, and/or TFCC detachment. Clinical relevance Distal radius osteotomy and shortening did not affect DRUJ stability regardless of location relative to the DIOM insertion.

Purpose To evaluate the biomechanical properties of 3 scapholunate repair techniques. Methods In 51 cadavers, the scapholunate ligament was exposed through a dorsal approach, incised at its scaphoid insertion, and repaired using 1 of 3 techniques: 2 single-loaded suture anchors, 2 double-loaded suture anchors, or 2 transosseous sutures. Twenty-four repaired specimens underwent load to failure (LTF) testing using tensile distraction on a servo-hydraulic machine. Twenty-seven specimens underwent cyclical testing to measure gap formation at the scapholunate joint. Results The mode of failure was suture pullout through the substance of the ligament in 22 specimens, failure at the bone suture interface in 1, and anchor pullout in 1. Double-loaded anchor repairs demonstrated a significantly higher mean ultimate LTF compared with single-loaded anchor (91 N vs 35 N) and transosseous (91 N vs 60 N) repairs. Transosseous repairs demonstrated a higher mean ultimate LTF compared with single-loaded suture repairs (60 N vs 35 N). After 300 cycles, the average gap for the transosseous repair group was double that for the single- and double-loaded repairs, although not statistically significant. Conclusions Primary scapholunate ligament repairs using double-loaded suture anchors demonstrated significantly higher strength compared with single-loaded anchors and transosseous repairs. On cyclic loading, transosseous repairs demonstrated the greatest gap formation with no measurable difference between single- and double-loaded repairs. Clinical relevance In a cadaveric model for primary repairs, double-loaded suture anchors demonstrated the highest LTF and offer a similar but unproven performance in vivo .

To assess the impact elevated tibial tubercle-trochlear groove (TT-TG) distance and patella height, as measured by the Caton-Deschamps Index (CDI), have on the isometry of a reconstructed medial patellofemoral ligament (MPFL).Nine fresh-frozen cadaveric knees were placed on a custom testing fixture, with a fixed femur and a mobile tibia. A suture fixed to the MPFL origin on the patella and free to move at the Schöttle point on the femur represented a reconstructed MPFL. A local coordinate system was established, and retroreflective markers attached to the suture quantified MPFL length changes by use of a 3-dimensional motion capture system. The tubercle was transferred to create TT-TG distances of 20 mm and 25 mm and CDIs of 1.2 and 1.4 (patella alta). Recordings of the MPFL suture length change as the knee was brought through a range of motion were made using all combinations of tubercle anatomy in a randomized order for each specimen. A generalized estimating equation modeling technique was used to analyze and control for the clustered nature of the data.Knees with native tibial tubercle anatomy showed MPFL isometry through 20° to 70° range of motion. Tibial tubercle lateralization (increased TT-TG distance) significantly altered MPFL isometry with a TT-TG distance of 20 mm (P.0001). Patella alta significantly altered MPFL isometry with a CDI of 1.2 (P = .0182). The interaction of tibial tubercle lateralization combined with patella alta significantly increased the amount of anisometry seen in the reconstructed MPFL (P.001).Increased tibial tubercle lateralization and patella alta produce anisometry in an MPFL reconstruction using currently recommended landmarks, leading to potentially increased graft tension and potential failure.Tibial tubercle transfer should be considered when performing an MPFL reconstruction for recurrent patellofemoral instability in the setting of significant patella alta and an elevated TT-TG distance-especially when both are present-because an isolated MPFL reconstruction will be prone to failure given the anisometry shown in this study.

Controversy exists regarding the optimal treatment of isolated fractures of the capitellum that are not amenable to open reduction and internal fixation. Excision of the capitellum could result in instability of the elbow, though only limited the clinical or laboratory evidence exists to support this outcome. The aim of our study was to determine if capitellum excision leads to significant instability by measuring the relative change in varus–valgus displacement of the elbow. The varus–valgus displacement was recorded in 11 cadaveric elbows before and after isolated excision of the capitellum. Specimens were testing in varus-loaded and valgus-loaded positions with and without a 1 kg weight on the forearm. The varus–valgus displacement at the elbow was measured using a 3D motion capture system. Capitellum excision did not significantly change varus–valgus displacements in either the adducted, varus, or valgus position of the elbow (p = 0.80, p = 0.28, p = 0.51). Furthermore, the addition of the 1 kg external functional load to the forearm did not produce a significant change in the varus and valgus loaded positions (p = 0.16, p = 0.36). Our results demonstrate that excision of the capitellum in the setting of intact ligamentous structures does not result in significant instability in either the adducted varus loaded or valgus loaded positions of the elbow. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:346–350, 2014.

STUDY DESIGN: Biomechanical testing of human cadaveric spines. OBJECTIVE: To determine the effect of anterior and posterior anatomic structures on the rotational stability of the thoracic spine. SUMMARY OF BACKGROUND DATA: Historically, large and/or stiff spinal deformities were treated with anterior release to facilitate correction. However, anterior release increases risks and requires a 2-part procedure. Recently, large or rigid deformities have been treated with a single posterior procedure using pedicle screws and spinal osteotomies. No study has yet evaluated the effect of anterior release or posterior osteotomy on thoracic spinal column rotation. METHODS: Thoracolumbar spines were obtained from cadavers and segmented into upper, middle, and lower specimens. Specimens were cyclically loaded with a ±5 N·m moment in axial rotation for 10 cycles. Specimens were tested intact and then retested after sectioning or removal of each structure to simulate those removed during anterior release and posterior osteotomy. The total increases in axial rotation after posterior and anterior resections were calculated using a 3-dimensional motion capture camera system. For each ligament resection, the absolute and percent change in degrees of rotation was calculated from comparison with the intact specimen. The median data points were compared to account for outliers. RESULTS: Resection of anterior structures was more efficacious than resection of posterior structures. An 8.8% to 71.9% increase in the amount of axial rotation was achieved by a posterior release, whereas resection of anterior structures led to a 141% to 288% increase in rotation. The differences between the anterior and posterior resections at all levels tested (T2-T3, T6-T7, and T10-T11) were significant (P < 0.05). CONCLUSION: Anterior release generated significantly more thoracic rotation than posterior osteotomy in biomechanical testing of human cadaver spines. LEVEL OF EVIDENCE: N/A.

Purpose This study biomechanically evaluated a technically easy variation of anatomical reconstruction of the thumb metacarpophalangeal (MCP) joint ulnar (UCL) and radial (RCL) collateral ligaments. Based on previous work describing the anatomical origin and insertion of these ligaments, we hypothesized that, using these attachment points, joint stability would be restored without significant loss of MCP flexion. Methods The collateral ligaments were isolated in 30 cadaveric thumbs (15 UCLs and 15 RCLs). A cyclical load was applied to the MCP joint to assess flexion, radial/ulnar deviation in neutral, and radial/ulnar deviation in 30° of flexion. The collateral ligaments were detached from the bone while their origin and insertion points were marked. Using these sites, anatomical ligament reconstruction was performed with a palmaris longus tendon graft and interference screw fixation. Cyclical testing was repeated on the reconstructed ligaments. Results No significant difference was found between intact and reconstructed UCLs when tested for radial deviation in neutral, radial deviation in 30° of flexion, or total MCP flexion. No significant difference was found between intact and reconstructed RCLs when tested for ulnar deviation in neutral, ulnar deviation in 30° of flexion, or total MCP flexion. Conclusions Our anatomical reconstruction is simple and restores UCL and RCL anatomy as compared with current techniques in the literature by placing the origin and insertion at their anatomical points with use of an interference screw. Using these anatomical origins and insertions, we were able to restore the MCP flexion and stability seen in an intact ligament. Clinical relevance Our anatomical reconstruction offers a technically easy option for reconstruction of thumb MCP collateral ligament injuries, restoring joint stability without sacrificing flexion.

Objectives: Medial patellofemoral ligament (MPFL) reconstruction is a common procedure to treat recurrent patellofemoral instability. However, the effects of an elevated tibial tubercle-trochlear groove (TT-TG) distance and patella alta, as measured by the Caton-Deschamps (C/D) ratio, on MPFL isometry remain unclear. We hypothesized that increased lateralization and proximalization of the tibial tubercle (TT) will have increasingly adverse effects on the isometry of the MPFL. Methods: Ten fresh-frozen cadaveric knees were placed on a custom testing fixture, with a fixed femur and tibia mobile through 120 degrees of flexion. The quadriceps tendon was loaded with 10.8 N in an anatomic direction using a weighted pulley system. A 0.2 N patellar lateral displacement load was used to simulate an intact lateral retinaculum to avoid over-medializing the patella. A tunnel was drilled under fluoroscopic guidance from Schottle’s point on the medial distal femur through the lateral cortex. A suture anchor was placed at the upper 66% of the medial border of the patella and the sutures were shuttled through to the lateral side and attached to a pulley with a 1 N weight. Retroreflective markers were attached to the femur, tibia, patella, and suture. MPFL length change, as measured by suture marker motion, was assessed using a 3D motion capture system through a range of motion between 0 deg and 110 deg with the native TT anatomy. Recordings were repeated after a flat TT osteotomy and transfer to a TT-TG of 20 mm and 25 mm and a C/D ratio of 1.2 and 1.4, including all combinations. Generalized estimating equation (GEE) modeling technique was used to analyze and control for the clustered nature of the data. SAS version 9.3 (SAS Inc., Cary, NC) was used for all data analyses. Results: Analysis was performed on 9 specimens secondary to significant deviations in the baseline normative data. Intact knees showed MPFL isometry through 20-70 degrees range of motion. Tibial tubercle lateralization significantly altered MPFL isometry with a threshold TT-TG of 25 mm (p=0.045) (Figure 1). Patella alta significantly altered MPFL isometry with a threshold C/D of 1.4 (p=0.025) (Figure 2). The effect of TT lateralization combined with patella alta compounded the anisometry, lowering the threshold for patella alta to a C/D of 1.2 when combined with a TT-TG of 25 mm (PConclusion: Increased TT lateralization and proximalization significantly alter MPFL isometry. Tibial tubercle transfer should be considered when performing an MPFL reconstruction for recurrent patellofemoral instability in the setting of significant patella alta, elevated TT-TG and especially when both are present as an isolated MPFL reconstruction may be prone to failure given the anisometry demonstrated.

Background context Dynamic stabilization is an alternative to fusion intended to eliminate or at least minimize the potential for adjacent level degeneration. Different design approaches are used in pedicle screw-based systems that should have very different effects on the loading of the posterior column and intervertebral disc. If the implant system distributes these loads more evenly, loads in the pedicle screws will be reduced, and screw loosening will be prevented. Purpose The purpose of this study was to determine how two different design approaches to dynamic stabilization systems, Dynesys System and the Total Posterior Spine (TOPS) System, affect the load carried by the pedicle screws. Study design/setting A controlled laboratory study in which the magnitude of the moments on pedicle screws during flexion–extension and lateral bending were measured after implantation of two posterior dynamic stabilization devices into cadaveric spines. Methods Five lumbar spines were tested in flexion–extension and lateral bending. Specimens were tested sequentially: first intact, then with the Dynesys system implanted, and finally with the TOPS system implanted. Range of motion (ROM) for each construct was measured with a 210N and 630N compressive load. The pedicle screws were instrumented with strain gages, which were calibrated so that the moments on the screws could be determined from the strain measurements. Results Compared with intact values, ROM decreased in flexion–extension and lateral bending when the Dynesys System was implanted. With implantation of the TOPS System, ROM returned to values that were not significantly different from the intact values. The moments in the screws with the Dynesys System were significantly higher than with the TOPS System with increases of as much as 56% in flexion–extension and 86% in lateral bending. Conclusions The design of the posterior stabilization device influences the amount of load seen by the pedicle screws and therefore the load sharing between spinal implant and bone.

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.

Purpose Shift of the distal fragment of a distal radius fracture (DRF) in the coronal plane (coronal shift) may compromise the contributions of the distal oblique bundle (DOB) of the interosseous membrane to distal radioulnar joint (DRUJ) stability. The purpose of the study was to test our hypothesis that coronal shift of the distal fragment would increase dorsal-volar DRUJ displacement in response to applied load. Methods A distal radius osteotomy was performed proximal to the sigmoid notch base and the ulnar styloid was cut (to simulate triangular fibrocartilage complex detachment) in 10 cadaveric specimens. A volarly placed plate was used to shift the distal radius fragment radially in 2-mm increments. A mechanical testing apparatus applied a 20 N load to the distal fragment perpendicular to the volar cortex with the forearm in neutral, 60° pronation, and 60° supination. Dorsal-volar displacement of the radius relative to the fixed ulna was measured in the control state (DRF and ulnar styloid anatomically fixed) and in 3 positions (anatomical reduction, 2-mm coronal shift, 4-mm coronal shift) with ulnar styloid displacement. The specimens were dissected post hoc to evaluate for a distinct DOB (thickness, > 0.5 mm). Dorsal-volar DRUJ displacement was compared among testing and control states using analysis of variance. Results In specimens with a distinct DOB, 2-mm coronal shift significantly increased dorsal-volar DRUJ displacement. However, there was no difference in DRUJ displacement between 4-mm coronal shift and control state. Coronal shift did not affect dorsal-volar DRUJ displacement in specimens without a distinct DOB. Conclusions In the setting of an ulnar styloid fracture, a 2-mm (but not a 4-mm) coronal shift of the DRF is associated with increased dorsal-volar DRUJ displacement in specimens with a distinct DOB, but not in specimens without a distinct DOB. Clinical relevance Awareness of the importance of coronal shift may aid in prevention of DRUJ instability associated with DRF, especially in patients with a DOB.

Purpose To describe the origin and insertion of the ulnar (UCL) and radial collateral ligaments (RCL) of the thumb metacarpophalangeal (MCP) joint. Methods We dissected 18 UCLs and 18 RCLs from fresh-frozen human cadaveric thumbs. We removed all soft tissue overlying the MCP joint, isolating the proper collateral ligaments. We detached the collateral ligaments from the bone while marking their origin and insertion points and measured these attachment sites in relation to bony landmarks by digital photo analysis. Results The center of the UCL origin at the metacarpal was 4.2 mm from the dorsal surface and 5.3 mm from the articular surface. The dorsal aspect of the metacarpal origin site was 2.1 mm from the dorsal edge of the metacarpal. The center of the phalangeal insertion was 2.8 mm from the volar surface and 3.4 mm from the articular surface. The volar aspect of the phalangeal insertion site was 0.7 mm from the volar edge of the phalanx. The center of the RCL origin at the metacarpal was 3.5 mm from the dorsal surface and 3.3 mm from the articular surface. The dorsal aspect of the metacarpal origin site was 1.5 mm from the dorsal edge of the metacarpal. The center of the phalangeal insertion was 2.8 mm from the volar surface and 2.6 mm from the articular surface. The volar aspect of the phalangeal insertion site was 0.5 mm from the volar edge of the phalanx. Conclusions Our study accurately defined the origin and insertion sites of the UCL and RCL of the thumb MCP joint. Clinical relevance An accurate definition of the anatomical origin and insertion points of the thumb MCP UCL and RCL may allow for more successful surgical repair and reconstruction.

Background Safely permitting early range of motion after a destabilizing injury to the elbow is believed to optimize return of function. However, the range-of-motion exercises must be balanced against the risk of re-dislocation or subluxation. The goal of this study was to describe the position of the upper limb that permitted the greatest motion while minimizing the risk of re-dislocation or subluxation. Methods Seven cadaveric elbows were affixed with a 3-dimensional motion capture system. Ulnohumeral distraction was recorded at flexion angles from 10° to 90° for intact, approach only (sham procedure), and LCL-sectioned. Ulnohumeral separation was recorded in 3 distinct positions of the upper limb that are frequently used in a clinical setting: 1) trunk seated upright with arm at the side; 2) trunk seated upright with elbow in hinged-brace; and 3) trunk supine with shoulder flexed and internally rotated – “gravity-assisted overhead motion” protocol. Results A significant ulnohumeral distraction difference was found between the supine and the upright protocols. Upon direct comparison, 104% more displacement occurred across the ulnohumeral joint in the upright LCL-sectioned condition compared to the supine LCL-sectioned condition ( P = .001). The greatest ulnohumeral distraction occurred in the seated upright range of motion with a hinged elbow brace (range, 2.5-5.6 mm). Conclusion The overhead motion protocol is a safe protocol for unstable elbows. The supine position results in the least amount of ulnohumeral distraction across flexion angles from 10° to 90°. The upright protocols, especially with the hinged elbow brace, exhibited ulnohumeral distraction that may result in dislocation.

Dorsal instability of the metatarsophalangeal joint (MTPJ) of the lesser toes is an important cause of forefoot pain. Both conservative and surgical treatment options have been proposed. However, the role of each static stabilizing structure has not been elucidated. We hypothesized that isolated sectioning of the plantar plate (PP) would result in greater dorsal translation compared to isolated sectioning of the medial collateral ligaments (MCL) or lateral (LCL) collateral ligaments, or the extensor hood (EH), and that combined injury to two or more structures would result in greater dorsal translation compared to isolated PP injury. Fifty-four cadaveric lesser toe specimens were randomized into groups for individual and combined sectioning of the PP, EH, and LCL and MCL. A 30 N axial load was applied to each specimen in the plantar–dorsal direction and dorsal translation of the phalanx was measured for each condition. ANOVA was used to compare groups. A 19% change in MTP translation was found from intact after sectioning the PP. No significant difference in translation was seen after individual sectioning of the EH, MCL, or LCL. A significant increase in translation occurred from intact with the following sectioning combinations: MCL + LCL, 37%; EH + MCL + LCL, 45%; and PP + MCL + LCL, 63%. Thus, the PP is the main restraint for dorsal MTPJ translation. MCL and LCL have important partial contribution to MTPJ stability. Injury to the PP, individually, or combined injuries to the PP, EH, MCL, or LCL, appear to cause significant instability that may warrant more aggressive treatment. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1995–1998, 2012

Avoidance of patellar eversion during total knee arthroplasty may help to prevent injury to the patellar tendon. The purpose of this study was to compare the load-to-failure of the everted versus the noneverted patella in a cadaveric model. Fourteen cadaver knees (seven pairs) were loaded to failure with the patella everted in one knee and not everted in the other. Mean load-at-ultimate failure in the patella-everted group was 1,111 ± 572 N, and in the patella-noneverted group was 1,621 ± 683 N (p = 0.01). Additionally, loads-at-initial-partial failure were lower (p = 0.04) in the patella-everted compared to the patella-noneverted group, 573 ± 302 N versus 1,115 ± 358 N, respectively. A partial failure of the patellar tendon occurred in 100% of the everted specimens, whereas only 57% of the noneverted specimens had partial failure. These findings suggest patella eversion may lead to failure of the patellar insertion at lower loads than when the patella is not everted.

Background: In difficult ankle arthrodesis situations, intramedullary (IM) arthrodesis nails and external fixation are often considered in lieu of standard fusion techniques. The purpose of this study was to compare the amount of micromotion measured across an ankle fusion site stabilized with either an IM nail or with the Ilizarov external fixator. Materials and Methods: The relative bone mineral density of 8 pairs of human cadaveric lower legs was measured by DEXA scanning. One specimen from each pair was randomly assigned to be stabilized with a new generation IM nail and the other with an Ilizarov external fixator. Specimens were tested in compression, rotation, and dorsiflexion. Optical motion capture was used to measure the direct motion occurring at the fusion site. Results: No significant difference was found between the axial displacements ( p = 0.94), torsional displacement ( p = 0.07), or the dorsiflexion angular displacement ( p = 0.28) for the IM rod group and the external fixation group. A weak correlation was found between BMD and displacement. Conclusion: Both the new generation IM nail and the Ilizarov external fixator imparted excellent stability to the fusion site despite a wide range of bone mineral densities. Medialization of the talus, the ability to compress the nail, and the addition of a posterior-to-anterior locking screw were thought to improve the performance of the nail. Clinical Relevance: Both IM nail and Ilizarov external fixation provided excellent fusion site stability. The decision of which implant to use for complex arthrodesis should be dictated by the clinical needs.