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Background: Antibiotic bone cement is commonly used in staged revision arthroplasty as well as the treatment of open fractures. Multiple factors affect antibiotic elution from bone cement. This study was performed to investigate the effect of two variables, the quantity of liquid monomer and the timing of antibiotic addition, on the ultimate elution of antibiotic from bone cement.Methods: Vancomycin-loaded Simplex P and SmartSet MV bone cement was prepared with three different methods: a common surgical technique, a mixing technique that doubled the amount of liquid monomer, and a novel technique that delayed antibiotic addition until after thirty seconds of polymerization. Cylinders of a standardized size were created from each preparation. The elution profiles of five cylinders from each preparation were measured over six weeks with use of high-performance liquid chromatography. Cylinders were tested in compression to quantify strength.Results: Delayed antibiotic addition resulted in significantly greater cumulative elution over six weeks (p < 0.0001), with minimal reduction in strength, compared with the other groups. Doubling the liquid monomer significantly reduced cumulative elution over six weeks compared with either of the other techniques (p < 0.0001). Vancomycin elution from Simplex P was 52%greater and vancomycin elution from SmartSet MV was 25% greater in the delayed-antibiotic-addition groups than it was in the corresponding standard surgical technique groups. The majority of the antibiotic was released over the first week in all groups. : High-dose-antibiotic bone cement prepared with delayed antibiotic addition increased vancomycin elution compared with the standard surgical preparation. Incorporating additional liquid monomer decreased vancomycin elution from high-dose-antibiotic cement. We recommend preparing high-dose-antibiotic bone cement with the delayed-antibiotic addition technique and not incorporating additional liquid monomer.Clinical Relevance: Both the relative volume of liquid monomer and the timing of antibiotic addition have substantial effects on the elution of antibiotic from bone cement. [ABSTRACT FROM AUTHOR]

Infection is a leading cause of total joint arthroplasty failure. Current preventative measures incorporate antibiotics into the poly (methyl methacrylate) (PMMA) bone cement that anchors the implant into the natural bone. With bacterial resistance to antibiotics on the rise, the development of alternative antibacterial materials is crucial to mitigate infection. Borate bioactive glass, 13-93-B3, has been studied previously for use in orthopedic applications due to its ability to be incorporated into bone cements and other scaffolds, convert into hydroxyapatite (HA)-like layer, and enhance the osseointegration and antibacterial properties of the material. The purpose of this study is to better understand how glass composition and change in surrounding pH effects the composite's antibacterial characteristics by comparing the incorporation of 30% wt/wt 13-93-B3 glass and pH neutral borophosphate bioactive glass into PMMA bone cement. We also aim to elucidate how HA-like layer formation on the cement's surface may affect bacterial adhesion. These studies showed that 13-93-B3 incorporated cements had significant reduction of bacterial growth surrounding the composite beyond 24 h of exposure when compared to a neutral borate bioactive glass incorporated cement ( p < 0.01) and cement only ( p < 0.0001). Additionally, through soaking cement composites in simulated body fluid and then exposing them to a bioluminescent strand of staphylococcus aureus, we found that the presence of a HA-like layer on the 13-93-B3 or pH neutral glass incorporated cement disks resulted in an increase in bacterial attachment on the composite cement's surface, where p < 0.001, and p < 0.05 respectively. Overall, our studies demonstrated that borate bioactive glass incorporated PMMA bone cement has innate antimicrobial properties that make it a promising material to prevent infection in total joint arthroplasties., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Hageman, Blatt, Kuenne, Brow and McIff.)

The basilar thumb joint is the joint second most commonly affected by osteoarthritis (OA) in the hand. Evaluation of dorsal subluxation of the thumb during a functional task such as key pinch could help assess OA risk. The objectives of this study were to determine the best imaging angle for measuring thumb dorsal subluxation during key pinch and to compare subluxation to corresponding OA grades on the Eaton-Glickel, Outerbridge, and International Cartilage Repair Society scales. Eleven cadaveric forearm specimens were rigged to simulate key pinch. A mobile c-arm captured anteroposterior (AP) view images of the hand and was rotated in 5 deg increments toward the ulnar aspect of the arm up to 60 deg. Dorsal subluxation was measured on each image and compared to determine which angle captured maximum subluxation. The resulting best imaging angle was used for comparisons between dorsal subluxation of the thumb and OA grades for the basilar thumb joint. The max subluxation was in the AP view for most specimens. There was a significant correlation between subluxation and the Eaton-Glickel grade (p = 0.003, R2 = 0.779), but not with either Outerbridge grades (p = 0.8018) or International Cartilage Repair Society grades (p = 0.7001). Our results indicate that dorsal thumb subluxation during key pinch should be measured in the AP view of the forearm/hand. Dorsal thumb subluxation during key pinch had a significant correlation with the Eaton-Glickel radiographic measure of OA but not with more accurate visual classifications of OA., (Copyright © 2021 by ASME.)

Aims: Poly(methyl methacrylate) (PMMA)-based bone cements are the industry standard in orthopaedics. PMMA cement has inherent disadvantages, which has led to the development and evaluation of a novel silorane-based biomaterial (SBB) for use as an orthopaedic cement. In this study we test both elution and mechanical properties of both PMMA and SBB, with and without antibiotic loading., Methods: For each cement (PMMA or SBB), three formulations were prepared (rifampin-added, vancomycin-added, and control) and made into pellets (6 mm × 12 mm) for testing. Antibiotic elution into phosphate-buffered saline was measured over 14 days. Compressive strength and modulus of all cement pellets were tested over 14 days., Results: The SBB cement was able to deliver rifampin over 14 days, while PMMA was unable to do so. SBB released more vancomycin overall than did PMMA. The mechanical properties of PMMA were significantly reduced upon rifampin incorporation, while there was no effect to the SBB cement. Vancomycin incorporation had no effect on the strength of either cement., Conclusion: SBB was found to be superior in terms of rifampin and vancomycin elution. Additionally, the incorporation of these antibiotics into SBB did not reduce the strength of the resultant SBB cement composite whereas rifampin substantially attenuates the strength of PMMA. Thus, SBB emerges as a potential weight-bearing alternative to PMMA for the local delivery of antibiotics. Cite this article: Bone Joint Res  2021;10(4):277-284.

Bone cement is used extensively in orthopedics to anchor prostheses to bone and fill voids. Incorporating bioactive glass into poly(methyl methacrylate) (PMMA)-based bone cement could potentially improve its effectiveness for these tasks. This study characterizes the mechanical and degradation properties of composites containing PMMA-based bone cement and particles of borate bioactive glass designated as 13-93B3. Glass particles of size 5, 33, and 100 μm were mixed with PMMA bone cement to create composites containing 20, 30, and 40 wt % glass. Composites and a bone cement control were soaked in phosphate-buffered saline. Compressive strength, Young's modulus, weight loss, water uptake, solution pH, and ionic concentrations were measured over 21 days. The compressive strengths of composites decreased over 21 days. Average Young's moduli of the composites remained below 3 GPa. Weight loss and water uptake of specimens did not exceed 2 and 6%, respectively. Boron concentrations and pH of all solutions increased over time, with higher glass weight fractions leading to higher pH values. Results demonstrated that the composite can sustain glass degradation and ionic release without compromising short-term mechanical strength., (© 2020 Wiley Periodicals, Inc.)

Study Design: Biomechanical evaluation of woven polyester tethers., Objectives: To quantify changes in tether elongation, stiffness, and failure characteristics after cyclic loading. Ligamentous augmentation is gaining interest as a technique to prevent proximal junctional kyphosis (PJK) in adult spinal fusions. There are a lack of data regarding the effects of cyclic loading on polyester tether mechanical properties. Tether stretch may lead to loss of stabilization and increased risk of tether failure. Biomechanical data are needed to determine the effects of cyclic loading on tether integrity., Methods: Testing was done in two materials: (1) a synthetic cortical bone composite to determine baseline mechanical properties, and (2) nine cadaveric L1 spinous processes. 5 mm woven polyester tethers were looped through 2.5 mm holes drilled in each material. First, five tethers were tested directly to failure in the synthetic bone to establish baseline failure properties. Next, tethers were tested at one of the three cyclic load ranges [5%, 25%, and 50% (n = 5 each) of baseline failure] for 1000 cycles and then loaded to failure. Cadaveric tests were done at the 25% range and compared to synthetic bone tests at the same range. Cadaveric failure tests were classified as either tether failure or spinous process bone failure., Results: Greater cyclic loading range had a significant effect on tether loop elongation, increased stiffness, and decreased ultimate tensile force. Among the cadaveric failure tests, 56% resulted in tether failure and the remaining 44% resulted in bone failure., Conclusions: Polyester tethers stretch significantly when loaded to physiological ranges. Anticipation of tether stretch may be an important consideration for a tethering strategy to prevent PJK. Improved understanding of tether material properties can provide guidance for the evaluation of clinical outcomes associated with techniques to reduce the risk of PJK caused by ligamentous laxity., Level of Evidence: Biomechanical study.

Laxity of the anterior oblique ligament (AOL) and/or the dorsoradial ligament (DRL) are believed to contribute to the progression of osteoarthritis in the trapeziometacarpal joint through increased dorsal subluxation. Stress radiographs during functional tasks, such as key pinch, can be used to evaluate such joint instability. Cadaveric experiments can explore joint contact pressures as well as subluxation under varying conditions, to gain knowledge about joint mechanics. The disturbance of supporting tissues, such as the joint capsule, during experiments may affect the recorded stability of the joint. To evaluate potential effects of opening the joint capsule and severing the AOL, eleven cadaveric specimens were rigged to simulate key pinch. An anteroposterior (AP) radiograph of the hand was recorded for each specimen while intact, after partially opening the joint capsule and after sectioning the AOL. First metacarpal subluxation levels were compared between the intact joint, partially open joint capsule, and sectioned AOL. Neither opening the joint capsule nor cutting the AOL had a statistically significant effect on metacarpal subluxation. The results indicate that partially opening the joint capsule has a negligible effect on joint mechanics and support recent studies that postulate that the AOL plays a less substantial role in preventing subluxation., (Copyright © 2020 by ASME.)

Borate bioactive glass 13-93B3 converts into an osteoconductive hydroxyapatite-like material in a liquid medium. In this study, 13-93B3 was incorporated into a commercial PMMA (poly(methyl methacrylate)) bone cement, and the conversion of the glass into a precipitate in solution was investigated with scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared (spectroscopy)-attenuated total reflection, and micro-Raman spectroscopy. Glass particles of 5, 33, and 100 μm diameter were each mixed with the PMMA cement to create 20, 30, and 40% glass-loaded composites. Precipitate formation was found to be a calcium-deficient apatite partially substituted with magnesium ions that resembles native bone material and would ideally encourage bone growth better than stoichiometric hydroxyapatite. Composites of bone cement and 13-93B3 show promise as a means of encouraging bone attachment to the surface of the bone cement., (© 2019 Wiley Periodicals, Inc.)

Introduction: Forefoot strike has been advocated for many runners because of the relatively lower impact and push-off forces compared to a heel strike. The purpose of this study was to explore the ability of mature (> 30 years old), experienced runners to transition from a heel foot strike to a forefoot strike when first introduced to barefoot running on a treadmill. We hypothesized: 1) mature runners who heel strike while wearing traditional training shoes would persist in heel striking immediately following a switch to barefoot, 2) mean shoe heel-to-toe drop would be significantly greater in runners who persist in heel striking when running barefoot compared to those who transition to a forefoot strike pattern, and 3) there would be a significant decrease in heel striking in the barefoot condition as running speeds increased., Methods: This was a controlled crossover laboratory study. Thirty-three experienced runners (average 23.4 miles per week) with an average age of 45.6 years were recruited for this study. The participants first ran in their standard running shoes and subsequently barefoot. A motion capture system was utilized to detect and analyze any transition from heel strike to forefoot strike made by study participants., Results: Of the 26 participants who were classified as heel strike runners in their running shoes, 50% (13/26, p = 0.001) transitioned to forefoot strike when changing from running in shoes to running barefoot., Conclusions: The injuries associated with transition from standard running shoes to barefoot running or minimalist shoes may be influenced by the persistence of heel striking in mature runners. Older experienced runners may have limited ability to transition from heel to forefoot striking when first introduced to barefoot running. Mature runners should be cautious when beginning a minimalist shoe or barefoot running regimen., (© 2019 The University of Kansas Medical Center.)

Introduction: The objective of this study was to evaluate the effect of ultrasound frequency and treatment duration on antibiotic-impregnated polymethylmethacrylate (PMMA) antibiotic elution rates and mechanical strength., Methods: Two batches of PMMA were prepared: one with five grams of vancomycin powder and one without. Each batch was divided into two frequency groups: kHz and MHz. Each frequency group was divided into two duration groups: two minutes and ten minutes. Elution samples were measured daily using flow injection analysis. After one week of elution, ultrasound treatments were done daily until each group's average concentration fell below those of non-ultrasound control groups. After elution testing, compression testing determined mechanical properties. Paired t-tests were used to compare daily elution amounts to baseline values. Univariate ANOVAs were used to test for effects of both frequency and treatment duration on antibiotic elution amounts and on mechanical properties., Results: All ultrasound treatments resulted in significant increases in antibiotic elution. Frequency and duration had significant effects of increasing antibiotic elution (p < 0.001). The kHz group produced significantly greater antibiotic elution than the MHz group (p < 0.001). The 10-minute duration produced significantly greater antibiotic elution than the two-minute duration (both p < 0.001). Frequency and duration did not have significant effects on yield stress (p = 0.841 and p = 0.179, respectively). Frequency had a significant effect (p = 0.024) on modulus, but duration did not (p = 0.136)., Conclusions: Ultrasound frequency and treatment duration significantly affect antibiotic elution from PMMA which may be helpful for treatment of periprosthetic joint infections during revision arthroplasty.

Objectives: The objective of this study was to characterize the effect of rifampin incorporation into poly(methyl methacrylate) (PMMA) bone cement. While incompatibilities between the two materials have been previously noted, we sought to identify and quantify the cause of rifampin's effects, including alterations in curing properties, mechanical strength, and residual monomer content., Methods: Four cement groups were prepared using commercial PMMA bone cement: a control; one with 1 g of rifampin; and one each with equimolar amounts of ascorbic acid or hydroquinone relative to the amount of rifampin added. The handling properties, setting time, exothermic output, and monomer loss were measured throughout curing. The mechanical strength of each group was tested over 14 days. A radical scavenging assay was used to assess the scavenging abilities of rifampin and its individual moieties., Results: Compared with control, the rifampin-incorporated cement had a prolonged setting time and a reduction in exothermic output during polymerization. The rifampin cement showed significantly reduced strength and was below the orthopaedic weight-bearing threshold of 70 MPa. Based on the radical scavenging assay and strength tests, the hydroquinone structure within rifampin was identified as the polymerization inhibitor., Conclusion: The incorporation of rifampin into PMMA bone cement interferes with the cement's radical polymerization. This interference is due to the hydroquinone moiety within rifampin. This combination alters the cement's handling and curing properties, and lowers the strength below the threshold for weight-bearing applications. Additionally, the incomplete polymerization leads to increased toxic monomer output, which discourages its use even in non-weight-bearing applications. Cite this article : G. A. Funk, E. M. Menuey, K. A. Cole, T. P. Schuman, K. V. Kilway, T. E. McIff. Radical scavenging of poly(methyl methacrylate) bone cement by rifampin and clinically relevant properties of the rifampin-loaded cement. Bone Joint Res 2019;8:81-89. DOI: 10.1302/2046-3758.82.BJR-2018-0170.R2.

Study Design: Biomechanical study., Objectives: Compare effects of four spinous process (SP) tether looping methods on segmental flexion range of motion (ROM), intervertebral disc (IVD) pressures, and peak tether forces., Summary of Background Data: SP tethering has been gaining interest as a prophylactic technique to prevent PJK caused by ligamentous laxity in ASD corrective surgery. Several SP tether looping methods have been proposed; however, there is no consensus on appropriate technique. No study has investigated the effect of the tether looping method on segmental biomechanics., Methods: Nine T1-T4 cadaveric motion segments were tested to 5 Nm of flexion-extension. The uppermost instrumented vertebra (UIV) was located at T3 using standard pedicle screws and fusion rods. A crosslink (CL) was placed inferior to the pedicle screws. A 5-mm polyester tether was looped under the CL at UIV and through holes drilled at the base of UIV + 1 and UIV + 2 SPs. Biomechanical measurements included flexion ROM, IVD pressure, and peak tether forces at UIV/UIV + 1 and UIV + 1/UIV + 2. An untethered test was used for baseline values. Tethered tests included one single-level (SL) method and three double-level (DL) methods: common (CM), chained (CH), and figure-8 (F8)., Results: SL yielded significant reductions in flexion ROM at UIV/UIV + 1 (p = .001) and in IVD pressure at UIV/UIV + 1 (p = .007). Choice of DL method had a significant effect on flexion ROM at UIV/UIV + 1 (p = .004) but not at UIV + 1/UIV + 2 (p = .14). Choice of DL method also had a significant effect on IVD pressure at UIV/UIV + 1 (p < .001) but not at UIV + 1/UIV + 2 (p = .311). CM produced the greatest reductions in flexion ROM and IVD pressure, with the lowest peak tether forces among the DL methods., Conclusion: Tether looping method significantly alters segmental biomechanics. Tethering with the CM method to UIV + 2 allows for reductions in loads acting on the UIV + 1 SP and posterior ligaments., Level of Evidence: Level V, biomechanical study., (Copyright © 2018 Scoliosis Research Society. Published by Elsevier Inc. All rights reserved.)

Study Design: Biomechanical evaluation of cadaver functional spinal units (FSUs)., Objectives: Demonstrate the effect of increasing spinous process (SP) tether pretension on FSU flexion range of motion (ROM), intervertebral disc (IVD) pressure, and SP force. Quantify SP tether pull-out forces and relate them to SP forces generated at maximum flexion., Summary of Background Data: There has been recent interest in the use of SP tethering for prophylactic treatment of proximal junctional kyphosis (PJK). There is currently no consensus on standard tethering technique and no biomechanical data on the effect of tether pretension., Methods: Nine T11-T12 FSUs were tested to 5 Nm of flexion-extension bending. A strain gauge was applied at the base of the T11 SP to measure force. Two custom pressure sensors were inserted into the anterior and posterior thirds of the IVD. Motion kinematics were measured by a motion capture system. An untethered test was done to describe baseline behavior. A 5-mm polyester tether was looped through holes drilled at the base of each SP and pretensioned to five different pretensions ranging from 0 to 88 N. Following ROM testing, specimens were dissected into individual vertebra and then SP pull-out testing was done at each level., Results: Increasing pretension significantly reduced flexion ROM, reduced IVD pressures, and increased SP force. All pretensions, including the minimum, significantly reduced flexion ROM. SP pull-out forces were significantly greater than SP forces generated at maximum flexion., Conclusions: Tether pretension significantly affects segmental FSU biomechanics. Pretension should be considered an integral factor in the overall success of a tethering strategy. Efforts should be made to control and record pretension intraoperatively., Level of Evidence: Level V, biomechanical study., (Copyright © 2018 Scoliosis Research Society. Published by Elsevier Inc. All rights reserved.)

Introduction: Local delivery of antibiotics using bone cement as the delivery vehicle is an established method of managing implant-associated orthopedic infections. Various fillers have been added to cement to increase antibiotic elution, but they often do so at the expense of strength. This study evaluated the effect of adding a borate bioactive glass, previously shown to promote bone formation, on vancomycin elution from PMMA bone cement. Methods: Five cement composites were made: three loaded with borate bioactive glass along with 0, 1, and 5 grams of vancomycin and two without any glass but with 1 and 5 grams vancomycin to serve as controls. The specimens were soaked in PBS. Eluate of vancomycin was collected every 24 hours and analyzed by HPLC. Orthopedic-relevant mechanical properties of each composite were tested over time. Results: The addition of borate bioactive glass provided an increase in vancomycin release at Day 1 and an increase in sustained vancomycin release throughout the treatment period. An 87.6% and 21.1% increase in cumulative vancomycin release was seen for both 1g and 5g loading groups, respectively. Compressive strength of all composites remained above the weight-bearing threshold of 70 MPa throughout the duration of the study with the glass-containing composites showing comparable strength to their respective controls. Conclusion: The incorporation of borate bioactive glass into commercial PMMA bone cement can significantly increase the elution of vancomycin. The mechanical strength of the cement-glass composites remained above 70 MPa even after soaking for 8 weeks, suggesting their suitability for orthopedic weight-bearing applications., Competing Interests: Competing Interests: The authors have declared that no competing interest exists.

Background: Scapholunate ligament injury is a commonly occurring carpal ligament injury. Pathology associated with scapholunate ligament injury depends on several factors such as the time after injury, type of injury (instability) and the development of osteoarthritis. The aim of this study was to investigate and compare contact mechanics in the lunocapitate and scaphocapitate joints in the normal, injured (scapholunate dissociation) and repaired (postoperative) wrist., Methods: Four human subjects with scapholunate ligament dissociation participated in this study. MR images of normal (contralateral), injured and postoperative wrists were obtained during relaxed condition and during active light grasp. Relaxed MR images were used to construct model geometry (bones with cartilage) for the capitate, lunate and scaphoid. Kinematic transformations were obtained by using image registration between the unloaded and functionally loaded image sets. Joint surface contact mechanics were then calculated., Findings: All contact measures (contact force, pressure, mean pressure and area) tended to increase with injury in both articulations. A significantly higher contact area was found in the injured scaphocapitate joint compared to normal. A significant increase in peak pressure was observed in the postoperative state compared to normal., Interpretation: Injury to the scapholunate ligament increased contact measures, suggesting a risk for onset of osteoarthritis in both the scaphocapitate and lunocapitate joints. Surgical repair appeared to restore most measures of contact mechanics to near normal values, more so for the lunocapitate joint when compared to scaphocapitate joint. The elevated postoperative peak pressures indicate the difficulty to fully restore joint mechanics., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Study Design: A retrospective historical cohort design., Objective: To determine what effect the addition of intrawound vancomycin powder to the prophylactic regimen of posterior instrumented spinal arthrodesis procedures has had on acute surgical site infections (SSIs)., Summary of Background Data: SSIs are known complications in instrumented spinal arthrodesis procedures, and are predominately caused by Staphylococcus aureus. Recent reports have suggested that placing vancomycin powder into the surgical wound before closure prevents SSIs in spinal surgery. Risk factors for SSIs in the setting of intrawound vancomycin powder use have not been previously reported on., Materials and Methods: SSI rates after 342 posterior instrumented spinal arthrodeses (October 2008-September 2011) in which intrawound vancomycin powder was used in addition to the standard antimicrobial prophylaxis (Vanco cohort) were compared with 341 posterior instrumented spinal arthrodeses (April 2005-October 2008) in which no vancomycin powder was added (non-Vanco cohort). Both 2 sample t test and χ test (Fisher where appropriate) were used for group comparisons. A subanalysis of the Vanco cohort was undertaken to identify risk factors for SSIs despite intrawound vancomycin use., Results: There was a significant reduction in the number of acute staphylococcal SSIs in the Vanco cohort (1.1%) compared with the non-Vanco cohort (3.8%; P=0.029). Deep staphylococcal infections decreased to 0 compared with 7 in the non-Vanco cohort (2.1%; P=0.008). Deep methicillin-resistant S. aureus infections decreased to 0 compared with 5 in the non-Vanco cohort (1.5%; P=0.031). A subanalysis of the Vanco cohort identified that being discharged to an inpatient rehabilitation or skilled nursing facility was associated with developing a SSI., Conclusions: Intrawound vancomycin powder use has decreased the rate of acute staphylococcal SSIs in our posterior instrumented spine arthrodesis surgeries. Patients who are discharged to skilled nursing or rehabilitation facilities are at an increased risk for developing SSIs despite intrawound vancomycin use.

The distribution, location, and spatial arrangement of mechanoreceptors are important for neural signal conciseness and accuracy in proprioceptive information required to maintain functional joint stability. The glenohumeral joint capsule and labrum are mechanoreceptor-containing tissues for which the distribution of mechanoreceptors has not been determined despite the importance of these tissues in stabilizing the shoulder. More recently, it has been shown that damage to articular mechanoreceptors can result in proprioceptive deficits that may lead to recurrent instability. Awareness of mechanoreceptor distribution in the glenohumeral joint capsule and labrum may allow preservation of the mechanoreceptors during surgical treatment for shoulder instability, and in turn retain the joint's proprioceptive integrity. For this reason, we sought to develop a neuroanatomical map of the mechanoreceptors within the capsule and labrum. We postulated that the mechanoreceptors in these tissues are distributed in a unique pattern, with mechanoreceptor-scarce regions that may be more appropriate for surgical dissection. We determined the neuroanatomical distribution of mechanoreceptors and their associated fascicles in the capsule and labrum from eight human cadaver shoulder pairs using our improved gold chloride staining technique and light microscopy. A distribution pattern was consistently observed in the capsule and labrum from which we derived a neuroanatomical map. Both tissues demonstrated mechanoreceptor-dense and -scarce regions that may be considered during surgical treatment for instability. Capsular fascicles were located in the subsynovial layer, whereas labral fascicles were concentrated in the peri-core zone. The capsular fascicles presented as a lattice network and with a plexiform appearance. Fascicles within the labrum resembled a cable structure with the fascicles running in parallel. Our findings contribute to the neuroanatomical knowledge of the two glenohumeral joint stabilizers, namely, capsule and labrum, primarily involved in the onset of shoulder instability and recurrent instability. Neuroanatomical knowledge of articular mechanoreceptors is important for (i) developing a topographical map that reflects correspondence between the joint and surrounding musculature, (ii) understanding proprioceptive deficits that are only partially restored post surgical and post rehabilitative treatment, and (iii) gaining further knowledge about articular mechanoreceptors., (© 2014 Anatomical Society.)

Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. This may be partially achieved by monitoring changes in joint mechanics that are a direct consequence of injury. Techniques such as image-based finite element modeling can provide in vivo joint mechanics data but can also be laborious and computationally expensive. Alternate modeling techniques that can provide similar results in a computationally efficient manner are an attractive prospect. It is likely possible to estimate risk of OA due to injury from surface contact mechanics data alone. The objective of this study was to compare joint contact mechanics from image-based surface contact modeling (SCM) and finite element modeling (FEM) in normal, injured (scapholunate ligament tear), and surgically repaired radiocarpal joints. Since FEM is accepted as the gold standard to evaluate joint contact stresses, our assumption was that results obtained using this method would accurately represent the true value. Magnetic resonance images (MRI) of the normal, injured, and postoperative wrists of three subjects were acquired when relaxed and during functional grasp. Surface and volumetric models of the radiolunate and radioscaphoid articulations were constructed from the relaxed images for SCM and FEM analyses, respectively. Kinematic boundary conditions were acquired from image registration between the relaxed and grasp images. For the SCM technique, a linear contact relationship was used to estimate contact outcomes based on interactions of the rigid articular surfaces in contact. For FEM, a pressure-overclosure relationship was used to estimate outcomes based on deformable body contact interactions. The SCM technique was able to evaluate variations in contact outcomes arising from scapholunate ligament injury and also the effects of surgical repair, with similar accuracy to the FEM gold standard. At least 80% of contact forces, peak contact pressures, mean contact pressures and contact areas from SCM were within 10 N, 0.5 MPa, 0.2 MPa, and 15 mm2, respectively, of the results from FEM, regardless of the state of the wrist. Depending on the application, the MRI-based SCM technique has the potential to provide clinically relevant subject-specific results in a computationally efficient manner compared to FEM.

This study was undertaken to assess magnetic resonance imaging (MRI)-based radiocarpal surface contact models of functional loading in a clinical MRI scanner for future in vivo studies, by comparison with experimental measures from three cadaver forearm specimens. Experimental data were acquired using a Tekscan sensor during simulated light grasp. Magnetic resonance (MR) images were used to obtain model geometry and kinematics (image registration). Peak contact pressures (PPs) and average contact pressures (APs), contact forces and contact areas were determined in the radiolunate and radioscaphoid joints. Contact area was also measured directly from MR images acquired with load and compared with model data. Based on the validation criteria (within 25% of experimental data), out of the six articulations (three specimens with two articulations each), two met the criterion for AP (0%, 14%); one for peak pressure (20%); one for contact force (5%); four for contact area with respect to experiment (8%, 13%, 19% and 23%), and three contact areas met the criterion with respect to direct measurements (14%, 21% and 21%). Absolute differences between model and experimental PPs were reasonably low (within 2.5 MPa). Overall, the results indicate that MRI-based models generated from 3T clinical MR scanner appear sufficient to obtain clinically relevant data.

We investigated the effects of scapholunate ligament injury on in vivo radiocarpal joint mechanics using image-based surface contact modeling. Magnetic resonance images of 10 injured and contralateral normal wrists were acquired at high resolution (hand relaxed) and during functional grasp. Three-dimensional surface models of the radioscaphoid and radiolunate articulations were constructed from the relaxed images, and image registration between the relaxed and grasp images provided kinematics. The displacement driven models were implemented in contact modeling software. Contact parameters were determined from interpenetration of interacting bodies and a linear contact rule. Peak and mean contact pressures, contact forces and contact areas were compared between the normal and injured wrists. Also measured were effective (direct) contact areas and intercentroid distances from the grasp images. Means of the model contact areas were within 10 mm(2) of the direct contact areas for both articulations. With injury, all contact parameters significantly increased in the radioscaphoid articulation, while only peak contact pressure and contact force significantly increased in the radiolunate articulation. Intercentroid distances also increased significantly with injury. This study provides novel in vivo contact mechanics data from scapholunate ligament injury and confirms detrimental alterations as a result of injury., (Copyright © 2013 Orthopaedic Research Society.)

Disruption of the scapholunate ligament can cause a loss of normal scapholunate mechanics and eventually lead to osteoarthritis. Surgical reconstruction attempts to restore scapholunate relationship show improvement in functional outcomes, but postoperative effectiveness in restoring normal radiocarpal mechanics still remains a question. The objective of this study was to investigate the benefits of surgical repair by observing changes in contact mechanics on the cartilage surface before and after surgical treatment. Six patients with unilateral scapholunate dissociation were enrolled in the study, and displacement driven magnetic resonance image-based surface contact modeling was used to investigate normal, injured and postoperative radiocarpal mechanics. Model geometry was acquired from images of wrists taken in a relaxed position. Kinematics were acquired from image registration between the relaxed images, and images taken during functional loading. Results showed a trend for increase in radiocarpal contact parameters with injury. Peak and mean contact pressures significantly decreased after surgery in the radiolunate articulation and there were no significant differences between normal and postoperative wrists. Results indicated that surgical repair improves contact mechanics after injury and that contact mechanics can be surgically restored to be similar to normal. This study provides novel contact mechanics data on the effects of surgical repair after scapholunate ligament injury. With further work, it may be possible to more effectively differentiate between treatments and degenerative changes based on in vivo contact mechanics data., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The objective of this study was to validate the MRI-based joint contact modeling methodology in the radiocarpal joints by comparison of model results with invasive specimen-specific radiocarpal contact measurements from four cadaver experiments. We used a single validation criterion for multiple outcome measures to characterize the utility and overall validity of the modeling approach. For each experiment, a Pressurex film and a Tekscan sensor were sequentially placed into the radiocarpal joints during simulated grasp. Computer models were constructed based on MRI visualization of the cadaver specimens without load. Images were also acquired during the loaded configuration used with the direct experimental measurements. Geometric surface models of the radius, scaphoid and lunate (including cartilage) were constructed from the images acquired without the load. The carpal bone motions from the unloaded state to the loaded state were determined using a series of 3D image registrations. Cartilage thickness was assumed uniform at 1.0 mm with an effective compressive modulus of 4 MPa. Validation was based on experimental versus model contact area, contact force, average contact pressure and peak contact pressure for the radioscaphoid and radiolunate articulations. Contact area was also measured directly from images acquired under load and compared to the experimental and model data. Qualitatively, there was good correspondence between the MRI-based model data and experimental data, with consistent relative size, shape and location of radioscaphoid and radiolunate contact regions. Quantitative data from the model generally compared well with the experimental data for all specimens. Contact area from the MRI-based model was very similar to the contact area measured directly from the images. For all outcome measures except average and peak pressures, at least two specimen models met the validation criteria with respect to experimental measurements for both articulations. Only the model for one specimen met the validation criteria for average and peak pressure of both articulations; however the experimental measures for peak pressure also exhibited high variability. MRI-based modeling can reliably be used for evaluating the contact area and contact force with similar confidence as in currently available experimental techniques. Average contact pressure, and peak contact pressure were more variable from all measurement techniques, and these measures from MRI-based modeling should be used with some caution.

Background: Fat embolization (FE) is an often overlooked and poorly understood complication of skeletal trauma and some orthopedic procedures. Fat embolism can lead to major pulmonary damage associated with fat embolism syndrome (FES)., Methods: A model of FE in unanesthetized rats, using intravenous injection of the neutral fat triolein, was used to study the potential therapeutic effect on lung histopathology of altering the production of, or response to, endogenous angiotensin (Ang) II. Either captopril, an Ang I converting enzyme inhibitor, or losartan, an Ang II type 1 receptor blocker, was injected 1 hour after FE by triolein injection. After euthanasia at 48 hours, histopathologic evaluation was used to compare the drug-treated animals with control animals that received only triolein., Results: Histology of the lungs of rats treated only with triolein revealed severe, diffuse pathology. Alveolar septa showed severe, diffuse inflammation. Bronchial lumina showed severe mucosal epithelial loss. The media of the pulmonary small arteries and arterioles was thicker, and the lumen patency was reduced 60% to 70%. Trichrome staining confirmed the abundant presence of collagen in the media and adventitia, as well as collagen infiltrating the bronchial musculature. Both captopril and losartan treatments reduced the inflammatory, vasoconstrictor, and profibrotic effects present at 48 hours (p<0.001). With treatment, the vascular lumen remained patent, and the fat droplets were reduced in size and number. There was a reduction in the number of infiltrating leukocytes, macrophages, myofibroblasts, and eosinophils, along with a significant decrease in hemorrhage and collagen deposition (p<0.001). Pathologic changes in bronchial epithelium were also diminished., Conclusions: The results suggest that the use of drugs that act on the renin-Ang system might provide an effective and targeted therapy for fat embolism syndrome.

We evaluated the ultimate compression strength (UCS), porosity, and fracture surface roughness of 2 commercially available single-antibiotic bone cements vacuum-mixed with additional amounts of vancomycin (2, 4, 6, and 8 g). At least 8 g could be added to Palacos R + 0.5 g gentamicin (UCS = 75.04 +/- 6.64 MPa) and no more than 6 g to Simplex P + 1 g tobramycin (UCS = 78.93 +/- 4.98 MPa) to maintain a UCS above the International Organization for Standardization minimum standard (70 MPa). Increasing vancomycin concentration correlated with a decrease in porosity but showed a trend towards greater fracture surface roughness., (Copyright 2010 Elsevier Inc. All rights reserved.)

Background: The use of thoracic pedicle screws in spinal deformity, trauma, and tumor reconstruction is becoming more common. Unsuccessful screw placement may require salvage techniques utilizing transverse process hooks. The effect of different starting point placement techniques on the strength of the transverse process has not previously been reported. The purpose of this paper is to determine the biomechanical properties of the thoracic transverse process following various pedicle screw starting point placement techniques., Methods: Forty-seven fresh-frozen human cadaveric thoracic vertebrae from T2 to T9 were disarticulated and matched by bone mineral density (BMD) and transverse process (TP) cross-sectional area. Specimens were randomized to one of four groups: A, control, and three others based on thoracic pedicle screw placement technique; B, straightforward; C, funnel; and D, in-out-in. Initial cortical bone removal for pedicle screw placement was made using a burr at the location on the transverse process or transverse process-laminar junction as published in the original description of each technique. The transverse process was tested measuring load-to-failure simulating a hook in compression mode. Analysis of covariance and Pearson correlation coefficients were used to examine the data., Results: Technique was a significant predictor of load-to-failure (P = 0.0007). The least squares mean (LS mean) load-to-failure of group A (control) was 377 N, group B (straightforward) 355 N, group C (funnel) 229 N, and group D (in-out-in) 301 N. Significant differences were noted between groups A and C, A and D, B and C, and C and D. BMD (0.925 g/cm2 [range, 0.624-1.301 g/cm2]) was also a significant predictor of load-to-failure, for all specimens grouped together (P < 0.0001) and for each technique (P <0.05). Level and side tested were not found to significantly correlate with load-to-failure., Conclusions: The residual coronal plane compressive strength of the thoracic transverse process is dependent upon the screw starting point placement technique. The funnel technique significantly weakens transverse processes as compared to the straightforward technique, which does not significantly weaken the transverse process. It is also dependent upon bone mineral density, and low failure loads even in some control specimens suggest limited usefulness of the transverse process for axial compression loading in the osteoporotic thoracic spine.

Background: Internal fixation of the os calcis is often complicated by prolonged soft tissue management and posterior facet disruption. An ideal calcaneal construct would include minimal hardware prominence, sturdy posterior facet fixation and nominal soft tissue disruption. The purpose of this study was to develop such a construct and provide a biomechanical analysis comparing our technique to a standard internal fixation technique., Methods and Materials: Twenty fresh-frozen cadaver calcanei were used to create a reproducible Sanders type-IIB calcaneal fracture pattern. One calcaneus of each pair was randomly selected to be fixed using our compressive headless screw technique. The contralateral matched calcaneus was fixed with a nonlocking calcaneal plate in a traditional fashion. Each calcaneus was cyclically loaded at a frequency of 1 Hz for 4000 cycles using an increasing force from 250 N to 1000 N. An Optotrak motion capturing system was used to detect relative motion of the three fracture fragments at eight different points along the fracture lines. Horizontal separation and vertical displacement at the fracture lines was recorded, as well as relative rotation at the primary fracture line., Results: When the data were averaged, there was more horizontal displacement at the primary fracture line of the plate and screw construct compared to the headless screw construct. The headless screw construct also had less vertical displacement at the primary fracture line at every load. On average those fractures fixed with the headless screw technique had less rotation than those fixed with the side plate technique., Conclusion: A new headless screw technique for calcaneus fracture fixation was shown to provide stability as good as, or better than, a standard side plating technique under the axial loading conditions of our model. Although further testing is needed, the stability of the proposed technique is similar to that typically provided by intramedullary fixation., Clinical Relevance: This fixation technique provides a biomechanically stable construct with the potential for a minimally invasive approach and improved post-operative soft tissue healing.

The pathophysiology of Fat Embolism Syndrome (FES) is poorly understood and subject to some controversy. Evaluation of the evolution of histological changes in the lungs of patients with FES is impractical. The current theories of FES were established through acute clinical observations and acute animal experiments, but sequential changes in the histology of lungs over a prolonged period have not been made. The progressive effects of fat embolization of the lungs were examined in a rat model over a period of 11 days. Triolein, a major bone marrow fat, was administered to conscious Sprague-Dawley rats via the caudal vein. Rats were euthanized at 24, 48, 96 h, and 11 days, but some died within a few hours. Histomorphometric evaluations of lung tissue were made, including stains for fat, collagen, and smooth muscle actin. Arterial and arteriolar patency decreased progressively up to 96 h, but returned toward normal after 11 days. A striking finding was the very early presence of inflammation and fibrosis after only several hours, persisting up to 11 days. The results of this study provide evidence of both very early and prolonged changes due to fat embolization., ((c) 2009 Orthopaedic Research Society.)

Study Design: This in vitro human cadaveric study tested the loss of thoracic motion segment flexion stiffness after sequential posterior upper instrumented vertebra anchor placement techniques and posterior column destabilization., Objective: This study was designed to determine the possible destabilizing effects of upper thoracic instrumentation anchor site preparation., Summary of Background Data: Proximal junctional kyphosis after instrumentation and arthrodesis for scoliosis and related spine deformities has recently been reported to range from 10% to 46%. The effect of posterior skeletal dissection associated with upper instrumented vertebra anchor placement on adjacent motion segment flexion stiffness has not been previously studied. METHODS.: Twenty-three intact thoracic motion segments were obtained from 6 human cadavers. Biomechanical testing was performed with each motion segment flexed to approximately 3.2 degrees at a rate of 0.1 Hz, with corresponding torques recorded. Data were collected after a series of 6 posterior procedures. Differences with P value <0.01 were considered significant and those with P value <0.05 marginally significant., Results: Supratransverse process hook, supralaminar hook, pedicle screw placement, or pedicle screw removal done, bilaterally, produced similar, small (range, 2.09%-6.03%), nonsignificant reductions in motion segment flexion stiffness. But when totaled, these 4 procedures resulted in a significant 16.31% loss of flexion stiffness. The fifth procedure of supraspinous and interspinous process ligament transection added a marginally significant 6.59% incremental loss of flexion stiffness. Supralaminar hook site preparation combined with supraspinous and interspinous process ligament transection resulted in a marginally significant 12.62% incremental loss of flexion stiffness. Transection of the remaining posterior structures (facet joints and all other posterior soft tissue structures) produced a significant additional flexion stiffness loss of 44.72%. The anterior column alone provided only 32.39% of the total motion segment flexion stiffness. Transection of all posterior stabilizing structures, similar to a Smith-Peterson/chevron/Ponte resection, decreased motion segment flexion stiffness significantly, 67.61%., Conclusion: Posterior thoracic skeletal structures involved in upper instrumented vertebra exposure andanchor placement were found to contribute to adjacent segment flexion stiffness. Although stiffness loss was small after individual procedures, the effects were additive for routinely used combinations.

This study evaluated the resistance to gapping and the mode of failure for 2 knotless suture anchor systems used for rotator cuff repair compared with the performance of a conventional titanium anchor system. Eight matched pairs of fresh-frozen humeri were dissected free of all soft tissues and scanned to measure bone mineral density (BMD). The suture anchor systems tested were the TwinFix 5.0 Titanium (Smith & Nephew, Andover, MA), Bioknotless RC (DePuy Mitek, Norwood, MA), and Magnum (Opus Medical, San Juan Capistrano, CA), and each was inserted into each humerus. Cyclic, tensile loading was applied through the suture loop for 5000 cycles, or until failure, by using a servohydraulic testing machine. Gapping distances, defined as increasing elongation of the bone/anchor/suture system, were continuously measured. Total cycles to failure and mechanism of failure were documented. Mean initial (first cycle) and final (last cycle) gapping distances were 3.81 mm and 5.36 mm for the TwinFix 5.0, 4.02 mm and 5.34 mm for the Bioknotless RC, and 3.56 mm and 4.98 mm for the Magnum anchors. No significant difference was detected among mean gap openings (P > .05). However, the Bioknotless RC had more early failures (5) than the other 2 implants (1 each), approaching significance (P = .07). Trials of the Bioknotless RC that did not fail early were found to have significantly less gap opening than the other 2 systems for both initial (1.89 mm vs 3.82 mm for the TwinFix 5.0 and 3.56 mm for the Magnum) and final (2.00 mm vs 4.68 mm for the TwinFix 5.0 and 4.24 mm for the Magnum) gap opening. BMD was a significant predictor of initial (P = .029) and final (P = .008) gap opening, whereas the site of anchor insertion was a significant predictor of final displacement. The Opus Magnum was comparable with a conventional suture anchor, but the Mitek Bioknotless RC showed a trend toward early failure. Biomechanical analysis of knotless suture anchor systems can demonstrate trends among implants in an experimental setting. Knowledge of these trends could influence implant selection.

Background: Static facial suspension (SFS) continues to play a role for rehabilitation in patients with facial paralysis. We perform SFS almost exclusively with a suture technique in our practice. Monofilament polypropylene suture (Prolene) is commonly used for SFS, but we have witnessed occasional failure and some stretching with this material. The purpose of this study was to establish and compare the biomechanical properties of 3 suture types-polypropylene, polybutilate-coated braided polyester (PBCP) (Ethibond Excel), and braided polyester impregnated with polytetrafluoroethylene (PIP) (Tevdek)-to assess their suitability for SFS., Methods: Six samples of 0, 2-0, and 3-0 polypropylene, PBCP, and PIP were tested. The mean load to failure was calculated for each suture type. Stiffness and elongation at specific loads were calculated to compare stretch between materials., Results: The load to failure of PBCP and PIP was significantly greater than that for polypropylene for all suture sizes. In addition, PBCP and PIP had significantly less elongation than did polypropylene at clinically relevant loads., Conclusions: Both PBCP and PIP had superior load-bearing properties and decreased stretch when compared with polypropylene. These properties suggest that, for SFS with suture, use of PBCP or PIP may reduce the incidence of breakage and elongation, improving outcomes.

Purpose: Locking plates are thought to have many advantages such as a decreased incidence of loss of reduction secondary to screw toggling and improved bone healing due to an increased periosteal blood supply. We hypothesized that locking plates will also provide increased stiffness and increased load to failure when they are applied dorsally to stabilize dorsally comminuted distal radius fractures. This study compared the stiffness and strength of dorsally applied locking and standard (nonlocking) T-plates applied to a dorsally comminuted distal radius fracture model., Methods: Sixteen pairs of embalmed cadaveric human radii were potted, and a standard wedge osteotomy was performed simulating a dorsally comminuted distal radius fracture. The radii were randomized into 2 groups, so that 8 pairs received a 3.5-mm dorsal locking T-plate over the osteotomy on the right radius and 8 pairs received the same on the left radius. A dorsal 3.5-mm standard T-plate was placed over the osteotomy on the contralateral radius in each group. An axial load was used to test the strength and stiffness of each construct. Paired t tests were then used to compare the strength and stiffness of the locking plate with those of the standard plate., Results: A significant difference was found in both the stiffness and the strength between the locking and standard nonlocking plates. The locking T-plate was 33% stiffer than the standard T-plate. The locking T-plate had a 91% increase in the load to failure. Failure for both locking and standard T-plates occurred via volar cortex bone fracture., Conclusions: Locking T-plates increased both the stiffness and strength of dorsally comminuted distal radius fractures compared with standard nonlocking T-plates by a statistically significant margin.

When performing the Scandinavian Total Ankle Replacement (STAR), the positioning of the talar component and the selection of mobile-bearing thickness are critical. A biomechanical experiment was undertaken to establish the effects of these variables on the range of movement (ROM) of the ankle. Six cadaver ankles containing a specially-modified STAR prosthesis were subjected to ROM determination, under weight-bearing conditions, while monitoring the strain in the peri-ankle ligaments. Each specimen was tested with the talar component positions in neutral, as well as 3 and 6 mm of anterior and posterior displacement. The sequence was repeated with an anatomical bearing thickness, as well as at 2 mm reduced and increased thicknesses. The movement limits were defined as 10% strain in any ligament, bearing lift-off from the talar component or limitations of the hardware. Both anterior talar component displacement and bearing thickness reduction caused a decrease in plantar flexion, which was associated with bearing lift-off. With increased bearing thickness, posterior displacement of the talar component decreased plantar flexion, whereas anterior displacement decreased dorsiflexion.

In the Agility total ankle replacement system, motion is constrained by the implant's articulating surfaces and the peri-ankle ligaments. The effects of plausibly occurring implant malpositioning on peri-ankle ligament functional extension during walking were explored in this study. The intent was to determine whether certain ligaments could serve as guides to assist in proper component positioning at implantation. Using a cadaver preparation with simulated physiologic motion and loading, we monitored change of ligament length of the anterior talofibular, posterior talofibular, calcaneofibular, and tibiocalcaneal ligaments resulting from controlled malpositioning of the tibial component relative to a neutral position. During a simulated walking cycle, effects of mediolateral and anterior/posterior translation, internal and external rotation, inversion and eversion, and elevation of the component were evaluated. In all cases, tibial component displacement from the neutral position caused atypical length change in one or more of the peri-ankle ligaments. In particular, anterior/posterior displacement significantly changed the lengthening behavior of all four tested ligaments. The anterior talofibular ligament was sensitive to transverse plane displacements, whereas the tibiocalcaneal ligament was sensitive to coronal plane displacements. For the Agility prosthesis, these two ligaments seem to be sensitive guides for tibial component positioning at implantation.

The surgical treatment of painful, end-stage ankle arthritis includes ankle arthrodesis and total ankle replacement. In the past decade, total ankle replacement has become a viable alternative to ankle arthrodesis. Modern implant designs either involve a syndesmosis fusion and resurfacing of the medial and lateral recesses of the ankle joint or the use of a 3-component, mobile bearing implant. In limited clinical series, the early results of both these prosthetic design approaches are encouraging. In selected patients, ankle arthroplasty is an effective approach to relieving pain and improving function. The purposes of this paper are to review the clinical results from total ankle replacement and ankle arthrodesis; discuss indications, contraindications, design features, postoperative rehabilitation, and initial results for the major current total ankle designs; and present concepts for future total ankle development. In particular, this article explores the advantages and concerns with 2 prevalent but different design approaches. It also discusses future directions for total ankle replacement.