"Can You Feel It": An Early Experience with Simulated Vibration to Recreate Glenoid Reaming.

When developing educational simulators, meaningful haptic feedback is important. To our knowledge, no shoulder arthroplasty surgical simulator exists. This study focuses on simulating vibration haptics of glenoid reaming for shoulder arthroplasty using a novel glenoid reaming simulator. Methods: We validated a novel custom simulator constructed using a vibration transducer transmitting simulated reaming vibrations to a powered nonwearing reamer tip through a 3D-printed glenoid. Validation and system fidelity were evaluated by 9 fellowship-trained shoulder surgeon experts performing a series of simulated reamings. We then completed the validation process through a questionnaire focused on experts' experience with the simulator. Results: Experts correctly identified 52% ± 8% of surface profiles and 69% ± 21% of cartilage layers. Experts identified the vibration interface between simulated cartilage and subchondral bone (77% ± 23% of the time), indicating high fidelity for the system. An interclass correlation coefficient for experts' reaming to the subchondral plate was 0.682 (confidence interval 0.262-0.908). On a general questionnaire, the perceived utility of the simulator as a teaching tool was highly ranked (4/5), and experts scored "ease of instrument manipulation" (4.19/5) and "realism of the simulator" (4.11/5) the highest. The mean global evaluation score was 6.8/10 (range 5-10). Conclusions: We examined a simulated glenoid reamer and feasibility of haptic vibrational feedback for training. Experts validated simulated vibration feedback for glenoid simulation reaming, and the results suggested that this may be a useful additional training adjuvant. Level of Evidence: Level II, prospective study.

Comparison of clinical-CT segmentation techniques for measuring subchondral bone cyst volume in glenohumeral osteoarthritis.

PURPOSE: This study aimed to assess the accuracy and reproducibility of four common segmentation techniques measuring subchondral bone cyst volume in clinical-CT scans of glenohumeral OA patients. METHODS: Ten humeral head osteotomies collected from cystic OA patients, having undergone total shoulder arthroplasty, were scanned within a micro-CT scanner, and corresponding preoperative clinical-CT scans were gathered. Cyst volumes were measured manually in micro-CT and served as a reference standard (n = 13). Respective cyst volumes were measured on the clinical-CT scans by two independent graders using four segmentation techniques: Qualitative, Edge Detection, Region Growing, and Thresholding. Cyst volume measured in micro-CT was compared to the different clinical-CT techniques using linear regression and Bland-Altman analysis. Reproducibility of each technique was assessed using intraclass correlation coefficient (ICC). RESULTS: Each technique outputted lower volumes on average than the reference standard (-0.24 to -3.99 mm3). All linear regression slopes and intercepts were not significantly different than 1 and 0, respectively (p < 0.05). Cyst volumes measured using Qualitative and Edge Detection techniques had the highest overall agreement with reference micro-CT volumes (mean discrepancy: 0.24, 0.92 mm3). These techniques showed good to excellent reproducibility between graders. CONCLUSIONS: Qualitative and Edge Detection techniques were found to accurately and reproducibly measure subchondral cyst volume in clinical-CT. These findings provide evidence that clinical-CT may accurately gauge glenohumeral cystic presence, which may be useful for disease monitoring and preoperative planning. LEVEL OF EVIDENCE: Retrospective cohort Level 3 study.

Interfascicular Anatomy of the Motor Branch of the Ulnar Nerve: A Cadaveric Study.

PURPOSE: The motor branch of the ulnar nerve contains fascicles that innervate the intrinsic musculature of the hand. This cadaveric study aimed to describe the organization and consistency of the internal topography of the motor branch of the ulnar nerve. METHODS: Five fresh-frozen cadaveric specimens with an average age of 74 years (range, 65-88 years) were dissected. The ulnar nerve was exposed and transfixed to the underlying tissues to maintain its orientation throughout the dissection. The dorsal cutaneous branch (DCB) and the volar sensory branch were identified and reflected to expose the motor branch. The fascicles to the first dorsal interosseus (FDI), flexor pollicis brevis, and abductor digiti minimi (ADM) were identified. Internal neurolysis was performed distal to proximal to identify the interfascicular arrangement of these fascicles within the motor branch. The organization of these fascicles was noted, and the branch points of the DCB, FDI, and ADM were measured relative to the pisiform using a handheld electronic caliper. RESULTS: The internal topography of the motor branch was consistent among all specimens. Proximal to the pisiform, the arrangement from radial to ulnar was as follows: volar sensory branch, flexor pollicis brevis, FDI/intrinsic muscles, ADM, and DCB. The position of these branches remained consistent as the deep motor branch curved radially within the palm and traveled to the terminal musculature. The locations of the average branch points of the FDI, ADM, and DCB with respect to the pisiform were as follows: FDI, 4.6 cm distal (range, 4.1-4.9 cm), 4.5 cm radial (range, 4.1-4.9 cm); ADM, 0.65 cm distal (range, 0.3-1.1 cm), 0.7 cm radial (range, 0.3-1.1 cm), DCB, 7.7 cm proximal (range, 4.2-10.1 cm), and 0.4 cm ulnar (range, 0.3-0.8 cm). CONCLUSIONS: The internal topography of the ulnar nerve motor branch was consistent among the specimens studied. The topography of the motor branches was maintained as the motor branch turns radially within the palm. CLINICAL RELEVANCE: This study provides further understanding of the internal topography of the ulnar nerve motor branch at the wrist level.

The Effect of Flexor Digitorum Profundus Repair Position Relative to Camper Chiasm on Tendon Biomechanics.

PURPOSE: The purpose of this study was to investigate the impact of repairing a zone II flexor digitorum profundus (FDP) laceration anatomically versus extra-anatomically on tendon loads and work of flexion (WOF). METHODS: Twenty digits from 5 cadaveric specimens were tested using an in vitro active finger motion simulator under 2 FDP tendon repair conditions: anatomic and extra-anatomic. Tensile loads in FDP and flexor digitorum superficialis (FDS), WOF, and total active finger range of motion (ROM) were measured using in-line load cells and electromagnetic tracking, respectively. RESULTS: The anatomic repairs had no effect on tendon loads or WOF for either FDP or FDS. The extra-anatomic repairs increased FDP loads by 32% and decreased FDS loads by 9% compared with those in the intact condition. This pattern was similar for WOF following extra-anatomic repairs, which increased FDP WOF by 31% and decreased FDS WOF by 18%. Comparing the 2 repairs, FDP loads and WOF were 25% and 22% greater, respectively, with extra-anatomic repairs compared with anatomic repairs, with no significant change in FDS. Total active ROM was not affected by either repair. CONCLUSIONS: In this in vitro cadaveric model, extra-anatomic repairs of FDP increased tendon loads and WOF compared with anatomic repairs. CLINICAL RELEVANCE: On the basis of this study, reconstitution of the anatomic relationship of FDP and FDS at the Camper chiasm during the repair of zone II flexor tendon lacerations is recommended.

Effect of a Flexor Digitorum Superficialis Hemitenodesis on Reducing Volar Plate Strains for Swan Neck Deformities.

BACKGROUND: Flexor digitorum superficialis (FDS) hemitenodesis is a common procedure to treat swan neck deformity (SND). We hypothesize that this surgical technique is a biomechanically effective way to reduce strain in the volar plate at the proximal interphalangeal joint (PIPJ). METHODS: Fifteen digits from 5 cadaveric specimens were tested using a novel in vitro active finger motion simulator under 4 finger conditions: intact, SND, FDS hemitenodesis, and FDS hemitenodesis with distal interphalangeal (DIP) joint fusion. Tensile loads in FDS and flexor digitorum profundus (FDP) and joint ranges of motion were measured by electromagnetic tracking. In addition, strain gauges were inserted under the volar plate to measure strain during PIPJ hyperextension. Results were analyzed using 1-way repeated-measures analysis of variance tests. RESULTS: The SND condition increased volar plate strain by 176% ± 25% (P < .001) compared with the intact condition. The FDS hemitenodesis repair relieved more than 50% of the SND strain, restoring it to within no statistical difference from intact. The DIP fusion further reduced strain with no further statistical significance. At full flexion, FDS and FDP tendon loads diverged as a function of the test condition (P < .001). With the FDS hemitenodesis, the FDP load increased by 2.1 ± 1.5 N from the SND condition (P < .001), whereas the FDS load decreased by 1.3 ± 1.3 N (P = .012). CONCLUSION: The FDS hemitenodesis repair restored strains to within 3.0 milli-strain of the intact condition with no significant difference. Application of DIP fusion did not further protect the PIPJ from increased hyperextension and further exacerbated the imbalance of flexor tendon loads.

Strength Comparison of Fibrin Glue and Suture Constructs in Upper Extremity Peripheral Nerve Coaptations: An In Vitro Study.

PURPOSE: To compare in vitro failure loads of nerve coaptations using fibrin glue alone, a suture alone, and a combination of fibrin glue and a suture. METHODS: The median, radial, and ulnar nerves of 15 fresh-frozen cadaveric upper extremity specimens (45 nerves in total) were dissected in vitro and transected 5 cm proximal to the wrist crease to simulate an injury requiring coaptation. Three coaptation techniques were used: fibrin glue alone, a suture alone, and a suture augmented with fibrin glue. The load to failure of each repair was measured using a linear servo-actuator with an in-line force sensor. The results were analyzed using 2-way repeated measures analysis of variance tests and pairwise comparisons with Bonferroni correction. RESULTS: Both the nerve coaptation technique and the specific nerve that was repaired had a significant effect on failure load. Suture-glue repair had the highest load to failure, 11.2 ± 2.9 N, and significantly increased the load to failure by 2.9 ± 1.7 N compared with glue repair alone. There was no significant difference between suture-glue repair and suture repair alone or between glue repair alone and suture repair alone. CONCLUSIONS: In this in vitro cadaveric model, nerve injury coaptation using both a suture and fibrin glue resulted in the strongest repair. The addition of fibrin glue may provide some benefit when used to augment suture repair, but when used in isolation, it is inferior to combined suture-and-glue constructs. CLINICAL RELEVANCE: Combined suture-and-glue nerve coaptations might be useful in the early postoperative period in increasing nerve repair strength and potentially reducing rupture rates.

The Evaluation of a Flexor Digitorum Profundus-to-Volar Plate Zone I Repair Versus Button Repair: An In vitro Biomechanics Study.

PURPOSE: The purpose of the study was to evaluate joint kinematics and tendon work of flexion (WOF) following a flexor digitorum profundus (FDP)-to-volar plate (VP) repair technique relative to a pullout button for zone I flexor tendon injuries. METHODS: Fourteen digits were tested using an in vitro active finger motion simulator under 3 repaired conditions following a simulated zone I avulsion: button, FDP-VP, and "no slack" FDP-VP (corrected for additional VP length). Outcome metrics included active joint range of motion (ROM), fingertip strength, FDP and flexor digitorum superficialis tensile loads, and WOF. RESULTS: The button and FDP-VP techniques restored WOF to the intact condition for FDP and flexor digitorum superficialis. All repairs restored distal interphalangeal joint ROM and kinematics to the intact condition. Similarly, all repairs restored WOF; however, the "no slack" FDP-VP significantly increased WOF by 10% to 12% over the simple FDP-VP repair. The button technique had similar fingertip strength to the intact condition, whereas the FDP-VP repairs significantly reduced peak fingertip strength from intact, albeit only 1-2 N compared with the button repair. CONCLUSION: In this in vitro cadaveric model, the button and FDP-VP techniques restored WOF and ROM to within intact levels, with no difference between these repairs in all measured outcome metrics. CLINICAL RELEVANCE: Based on its initial strength and its equal biomechanical performance compared with the button repair, the FDP-VP technique may be a viable option for treating FDP avulsions.

Does the osteoarthritic shoulder have altered rotator cuff vectors with increasing glenoid deformity? An in silico analysis.

BACKGROUND: A transverse force couple (TFC) functional imbalance has been demonstrated in osteoarthritic shoulders by recent 3-dimensional (3D) muscle volumetric studies. Altered rotator cuff vectors may be an additional factor contributing to a muscle imbalance and the propagation of glenoid deformity. METHODS: Computed tomography images of 33 Walch type A and 60 Walch type B shoulders were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (ISP-Tm) and scapula were manually segmented. The volume masks and scapular landmarks were imported into MATLAB to create a coordinate system, enabling calculation of muscle force vectors. The direction of each muscle force vector was described in the transverse and vertical plane, calculated with respect to the glenoid. Each muscle vector was then resolved into compression and shear force across the glenoid face. The relationship between muscle force vectors, glenoid retroversion or inclination, compression/shear forces on the glenoid, and Walch type was determined using linear regression. RESULTS: In the transverse plane with all rotator cuff muscles combined, increasing retroversion was significantly associated with increasing posterior drag (P < .001). Type B glenoids had significantly more posterior drag than type A (P < .001). In the vertical plane for each individual muscle group and in combination, superior drag increases as superior inclination increases (P < .001). Analysis of individual muscle groups showed that the anterior thrust of ISP-Tm and supraspinatus switched to a posterior drag at 8° and 10° of retroversion respectively. The compression force on the glenoid face by ISP-Tm and supraspinatus did not change with increasing retroversion for type A shoulders (P = .592 and P = .715, respectively), but they did for type B shoulders (P < .001 for both). The glenoid shear force ratio in the transverse plane for the ISP-Tm and supraspinatus moved from anterior to posterior shear with increasing glenoid retroversion, crossing zero at 8° and 10° of retroversion, whereas the subscapularis exerted a posterior shear force for every retroversion angle. CONCLUSION: Increased glenoid retroversion is associated with increased posterior shear and decreased compression forces on the glenoid face, explaining some of the pathognomonic bone morphometrics that characterize the osteoarthritic shoulder. Although the subscapularis always maintains a posterior thrust, the ISP-Tm and supraspinatus together showed an inflection at 8° and 10° of retroversion, changing from an anterior thrust to a posterior drag. This finding highlights the importance that in anatomic TSA the rotator cuff functional balance might be better restored by correcting glenoid retroversion to less than 8°.

Experimental DVC validation of heterogeneous micro finite element models applied to subchondral trabecular bone of the humeral head.

Subchondral trabecular bone (STB) undergoes adaptive changes during osteoarthritic (OA) disease progression. These changes alter both the mineralization patterns and structure of bone and may contribute to variations in the mechanical properties. Similarly, when images are downsampled - as is often performed in micro finite element model (microFEM) generation - the morphological and mineralization patterns may further alter the mechanical properties due to partial volume effects. MicroFEMs accounting for material heterogeneity can account for these tissue variations, but no studies have validated these with robust full-field testing methods. As such, this study compared homogeneous and heterogeneous microFEMs to experimentally loaded trabecular bone cores from the humeral head combined with digital volume correlation (DVC). These microFEMs were used to compare apparent mechanical properties between normal and OA STB. Morphological and mineralization patterns between groups were also compared. There were no significant differences in tissue or bone mineral density between groups. The only significant differences in morphometric parameters were in trabecular thickness between groups. There were no significant differences in linear regression parameters between normal and OA STB apparent mechanical properties estimated using heterogeneous microFEMs with an element-wise bilinear elastic-plastic constitutive model. Clinical significance: Validated heterogeneous microFEMs applied to STB of the humeral head have the potential to significantly improve our understanding of mechanical variations in the bone that occur during OA progression.

Development of an In Vitro Swan Neck Deformity Biomechanical Model.

BACKGROUND: Injury to the finger's extensor mechanism is a common cause of swan neck deformity (SND). Progression of extensor and flexor tendon imbalance negatively affects laxity of the volar plate, resulting in the inhibition of proper finger motion. The complexity of finger anatomy, however, makes understanding the pathomechanics of these deformities challenging. Therefore, development of an SND model is imperative to understand its influence on finger biomechanics and to provide an in vitro model to evaluate the various treatment options. METHODS: The index, middle, and ring fingers from 8 cadaveric specimens were used in an in vitro active motion simulator to replicate finger flexion/extension. An SND model was developed through sectioning of the terminal extensor tendon at the distal insertion (creating a mallet finger) and transverse retinacular ligament (TRL). A strain gauge inserted under the volar plate measured laxity of the plate, and electromagnetic trackers recorded proximal interphalangeal joint (PIPJ) angles. RESULTS: Strain in the volar plate increased progressively with creation of the mallet and SND conditions (P = .015). Although not statistically significant, the mallet finger condition accounted for 26% of the increase, whereas sectioning of the TRL accounted for 74% (P = .031). As predicted, PIPJ hyperextension was not detectable by joint angle measurement; however, the PIPJ angle had a strong positive correlation with volar plate strain (R2 = 1.0, P < .001). CONCLUSION: Volar plate strain measurement, in an in vitro model, can detect an induced SND. Moreover, as a surrogate for PIPJ hyperextension, volar plate strain may be useful to evaluate the time-zero effectiveness of various surgical interventions.

Biomechanical Impact of a Zygoma Complex Fracture Using Human Cadaver.

ABSTRACT: Zygomaticomaxillary complex fractures are common in midface trauma, with treatment often involving repair using titanium mini plates. However, the need for plate fixation along the zygomaticomaxillary suture on the infraorbital rim remains controversial. This study utilized a previously reported bite force simulator to investigate craniofacial strain patterns following zygomaticomaxillary complex fracture repairs with and without plating of the infraorbital rim. Osteotomies were made to 6 fresh-frozen cadaveric heads to simulate 2 types of zygomatic complex fractures: a dipod fracture with osteotomies at the zygomaticofrontal and zygomaticomaxillary sutures, and a tripod fracture with an additional osteotomies at the zygomaticotemporal suture. Repairs with and without the use of a titanium mini plate across the infraorbital rim were compared in both dipod and tripod fractures. Physiologically proportional masticatory loads were applied using the bite force simulator by actuating intrinsic muscle lines of action. The outcome metric was facial bone strains measured using uniaxial strain gauges. Mixed-effects linear models did not find a significant main effect on the overall strain pattern with the use of an infraorbital rim plate in both dipod (P = 0.198) and tripod (P = 0.117) fracture repairs. However, statistically significant differences were found locally at the zygomatic buttress (P = 0.019) and the zygomatic arch (P = 0.027) on the fractured side in dipod fractures. This is the first known study that successfully utilized a mechanical simulator to reproduce physiological intrinsic masticatory loads in a fracture fixation study. This new technology opens avenues for future biomechanical investigations on maxillofacial fracture repairs and other surgical treatments.

Does the Walch type B shoulder have a transverse force couple imbalance? A volumetric analysis of segmented rotator cuff muscles in osteoarthritic shoulders.

BACKGROUND: The etiology of the Walch type B shoulder remains unclear. We hypothesized that a scapulohumeral muscle imbalance, due to a disturbed transverse force couple (TFC) between the anterior and posterior rotator cuff muscles, may have a role in the pathogenesis of the type B morphology. The purpose of this study was to determine whether there is a TFC imbalance in the Walch type B shoulder using an imaging-based 3-dimensional (3D) volumetric and fatty infiltration assessment of segmented rotator cuff muscles. METHODS: Computed tomography images of 33 Walch type A and 60 Walch type B shoulders with the complete scapula and humerus including the distal humeral epicondyles were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (Infra-Tm) were manually segmented and analyzed. Additionally, anthropometric parameters including glenoid version, glenoid inclination, posterior humeral head subluxation, and humeral torsion were measured. The 3D muscle analysis was then compared with the anthropometric parameters using the Wilcoxon rank sum and Kruskal-Wallis tests. RESULTS: There were no significant differences (P > .200) in muscle volume ratios between the Infra-Tm and the subscapularis in Walch type A (0.93) and type B (0.96) shoulders. The fatty infiltration percentage ratio, however, was significantly greater in type B shoulders (0.94 vs. 0.75, P < .001). The Infra-Tm to subscapularis fatty infiltration percentage ratio was significantly larger in patients with >75% humeral head subluxation than in those with 60%-75% head subluxation (0.97 vs. 0.74, P < .001) and significantly larger in patients with >25° of retroversion than in those with <15° of retroversion (1.10 vs. 0.75, P = .004). The supraspinatus fatty infiltration percentage was significantly lower in Walch type B shoulders than type A shoulders (P = .004). Walch type A shoulders had mean humeral retrotorsion of 22° ± 10° whereas Walch type B shoulders had humeral retrotorsion of only 14° ± 9° relative to the epicondylar axis (P < .001). CONCLUSION: The TFC is in balance in the Walch type B shoulder in terms of 3D volumetric rotator cuff muscle analysis; however, the posterior rotator cuff does demonstrate increased fatty infiltration. Posterior humeral head subluxation and glenoid retroversion, which are pathognomonic of the Walch type B shoulder, may lead to a disturbance in the length-tension relationship of the posterior rotator cuff, causing fatty infiltration.

Use of Thermoplastic Rings Following Venting of Flexor Tendon Pulleys: A Biomechanical Analysis.

PURPOSE: Normal digital flexion relies on flexor tendon pulleys to convert linear muscular force to angular digital motion. However, there is a growing trend to vent them partially during flexor tendon repair. The objective of this study was to examine the effects of a thermoplastic ring, acting as an external pulley, on flexor tendon biomechanics and finger range of motion (ROM) after pulley venting. METHODS: We tested 15 cadaveric digits using an in vitro active finger motion simulator. We measured loads induced by flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) as well as joint ROM with sequential sectioning of the A2, A3, and A4 pulleys compared with an intact pulley condition. At each stage, external thermoplastic pulley rings were applied snugly over the proximal and middle phalanges to recreate A2 and A4 function, respectively. RESULTS: After complete venting of the A2, A3, and A4 pulleys, proximal interphalangeal joint ROM significantly decreased by 13.4° ± 2.7° and distal interphalangeal joint ROM decreased by 15.8° ± 2.1°. Application of external rings over the proximal and middle phalanx resulted in a residual ROM decrease of 8.3° ± 1.9° at the proximal interphalangeal joint and 7.9° ± 2.1° at the distal interphalangeal joint, nearly restoring ROM. Similarly, complete pulley venting resulted in reduced FDS load by 37% and FDP load by 50% compared with intact pulleys. After application of external rings, loads were restored almost to normal, with a 9% reduction for FDS load and 9% reduction for FDP load compared with intact pulleys. CONCLUSIONS: The application of thermoplastic rings acting as external pulleys is an effective, noninvasive, and reproducible approach to restore flexor tendon biomechanics and digit ROM after pulley venting. CLINICAL RELEVANCE: Thermoplastic rings may be a useful therapeutic adjunct in restoring joint ROM and flexor tendon loads after surgical venting of the pulleys.

The Application of Digital Volume Correlation (DVC) to Evaluate Strain Predictions Generated by Finite Element Models of the Osteoarthritic Humeral Head.

Continuum-level finite element models (FEMs) of the humerus offer the ability to evaluate joint replacement designs preclinically; however, experimental validation of these models is critical to ensure accuracy. The objective of the current study was to quantify experimental full-field strain magnitudes within osteoarthritic (OA) humeral heads by combining mechanical loading with volumetric microCT imaging and digital volume correlation (DVC). The experimental data was used to evaluate the accuracy of corresponding FEMs. Six OA humeral head osteotomies were harvested from patients being treated with total shoulder arthroplasty and mechanical testing was performed within a microCT scanner. MicroCT images (33.5 µm isotropic voxels) were obtained in a pre- and post-loaded state and BoneDVC was used to quantify full-field experimental strains (≈ 1 mm nodal spacing, accuracy = 351 µstrain, precision = 518 µstrain). Continuum-level FEMs with two types of boundary conditions (BCs) were simulated: DVC-driven and force-driven. Accuracy of the FEMs was found to be sensitive to the BC simulated with better agreement found with the use of DVC-driven BCs (slope = 0.83, r2 = 0.80) compared to force-driven BCs (slope = 0.22, r2 = 0.12). This study quantified mechanical strain distributions within OA trabecular bone and demonstrated the importance of BCs to ensure the accuracy of predictions generated by corresponding FEMs.

Revision shoulder arthroplasty: a systematic review and comparison of North American vs. European outcomes and complications.

BACKGROUND: Joint registries provide invaluable data on primary arthroplasties with revision as the endpoint; however, the revision outcomes are often excluded. Therefore, a PROSPERO registered review (CRD42015032531) of all revision studies in North America and Europe was conducted to evaluate demographics, etiologies and indications, implant manufacturer, and complications by geographic region. METHODS: The MEDLINE, EMBASE, and CENTRAL databases were searched for revision arthroplasty clinical studies with a minimum mean 24-month follow-up. There were no language exclusions. Articles published in German, French, and Italian were reviewed by research personnel proficient in each language. RESULTS: The mean age at revision was 66 ± 5 years (male = 759, female = 1123). The male-female ratio in North American and Europeans studies was 43:57 and 34:66, respectively. The most common etiology for primary surgery in both regions was osteoarthritis or glenoid arthrosis (38%). The most common revision indication overall was rotator cuff tear, deficiency, or arthropathy (26%). The most common implant type used in revisions was a reverse shoulder arthroplasty (54%). The complication rate for all revisions was 17%. There were a total of 465 complications, and of those, 74% lead to a reoperation. CONCLUSION: Generally, shoulder arthroplasties are designed to last 10-15 years; however, revisions are being performed at a mean 3.9 years from the primary procedure, based on the published studies included in this systematic review. Additionally, of the complications, a large number (74%) went on to a reoperation. Further insight into the reasons for early revisions and standardized reporting metrics and data collection on revisions is needed.

Morphological and Apparent-Level Stiffness Variations Between Normal and Osteoarthritic Bone in the Humeral Head.

Osteoarthritis (OA) is characterized by morphological changes that alter bone structure and mechanical properties. This study compared bone morphometric parameters and apparent modulus between humeral heads excised from end-stage OA patients undergoing total shoulder arthroplasty (n = 28) and non-pathologic normal cadavers (n = 28). Morphometric parameters were determined in central cores, with regional variations compared in four medial to lateral regions. Linear regression compared apparent modulus, morphometric parameters, and age. Micro finite element models estimated trabecular apparent modulus and derived density-modulus relationships. Significant differences were found for bone volume fraction (p < 0.001) and trabecular thickness (p < 0.001) in the most medial regions. No significant differences occurred between morphometric parameters and apparent modulus or age, except in slope between groups for apparent modulus versus trabecular number (p = 0.021), and in intercept for trabecular thickness versus age (p = 0.040). Significant differences occurred in both slope and intercept between density-modulus regression fits for each group (p ≤ 0.001). The normal group showed high correlations in the power-fit (r2 = 0.87), with a lower correlation (r2 = 0.61) and a more linear relationship, in the OA group. This study suggests that alterations in structure and apparent modulus persist mainly in subchondral regions of end-stage OA bone. As such, if pathologic regions are removed during joint replacement, computational models that utilize modeling parameters from non-pathologic normal bone may be applied to end-stage OA bone. An improved understanding of humeral trabecular bone variations has potential to improve the surgical management of end-stage OA patients. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:503-509, 2020.

Bite Force Simulator: A Novel Technique to Simulate Craniofacial Strain In Vitro.

Existing in vitro simulators rely on external manipulation of the skull to replicate masticatory forces; however, external manipulations do not accurately represent internal loads as in physiological muscle forces.The purpose of the project is to develop an in vitro simulator that internally replicates the forces of mastication. The simulator has 3-dimensional-printed piston mounts that are reverse-engineered using a computed tomography scan of the specimen. The mounts are attached to the skull at muscle attachment sites using adhesive. The pneumatic pistons are sutured to muscle tendons; when the pistons are activated, they pull on the tendons which proportionally replicate muscle loads. The force output of the pistons can be individually modified by a custom software. Strain gauges are attached to craniofacial bones to measure deformation under replicated muscle loads. A 6 degrees-of freedom force sensor is placed intraorally to measure the generated bite force.The methodology was validated on 6 fresh-frozen cadaveric heads. Change in strain measurements was observed with change in simulated muscle loads. The simulator can validate computer simulation models and provide an experimental platform for craniofacial and dental implants. It sets the framework for a new, more physiologically consistent way of studying craniofacial stresses.

Correction to: Material Mapping of QCT-Derived Scapular Models: A Comparison with Micro-CT Loaded Specimens Using Digital Volume Correlation.

The article Material Mapping of QCT-Derived Scapular Models: A Comparison with Micro-CT Loaded Specimens Using Digital Volume Correlation, written by Knowles et al, was originally published electronically on the publisher's internet portal (currently SpringerLink) on 11 July 2019 without open access. With the author(s)' decision to opt for Open Choice the copyright of the article changed on [August 30] to © The Author(s) 2019 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

Analysis of the process parameters affecting the bone burring process: An in-vitro porcine study.

BACKGROUND: A stable bone burring process, which avoids thermal osteonecrosis and minimizes harmful vibrations, is important for certain orthopedic surgical procedures, and especially relevant to robot-operated bone burring systems. METHODS: An experimental characterization of the effects of several bone burring process parameters was performed. Burring parameters were evaluated by resultant bone temperature, tool vibration, and burring force. RESULTS: An optimal combination of bone burring parameters produced minimums in both bone temperature (<40°C) and tool vibration (<4 g-rms). A cylindrical burr, oriented normal to the specimen, resulted in significantly higher temperatures (50.8 ± 6.8°C) compared with a spherical burr (33.5 ± 4.3°C) (P = .008). Regardless of the parameters tested, burring forces were less than 10 N. CONCLUSIONS: The recommended configuration, which minimized both bone temperature and vibrations experimentally, was a 6-mm spherical burr at 15 000 rpm with a 2 mm/s feed rate.

Material Mapping of QCT-Derived Scapular Models: A Comparison with Micro-CT Loaded Specimens Using Digital Volume Correlation.

Subject- and site-specific modeling techniques greatly improve finite element models (FEMs) derived from clinical-resolution CT data. A variety of density-modulus relationships are used in scapula FEMs, but the sensitivity to selection of relationships has yet to be experimentally evaluated. The objectives of this study were to compare quantitative-CT (QCT) derived FEMs mapped with different density-modulus relationships and material mapping strategies to experimentally loaded cadaveric scapular specimens. Six specimens were loaded within a micro-CT (33.5 µm isotropic voxels) using a custom-hexapod loading device. Digital volume correlation (DVC) was used to estimate full-field displacements by registering images in pre- and post-loaded states. Experimental loads were measured using a 6-DOF load cell. QCT-FEMs replicated the experimental setup using DVC-driven boundary conditions (BCs) and were mapped with one of fifteen density-modulus relationships using elemental or nodal material mapping strategies. Models were compared based on predicted QCT-FEM nodal reaction forces compared to experimental load cell measurements and linear regression of the full-field nodal displacements compared to the DVC full-field displacements. Comparing full-field displacements, linear regression showed slopes ranging from 0.86 to 1.06, r-squared values of 0.82-1.00, and max errors of 0.039 mm for all three Cartesian directions. Nearly identical linear regression results occurred for both elemental and nodal material mapping strategies. Comparing QCT-FEM to experimental reaction forces, errors ranged from - 46 to 965% for all specimens, with specimen-specific errors as low as 3%. This study utilized volumetric imaging combined with mechanical loading to derive full-field experimental measurements to evaluate various density-modulus relationships required for QCT-FEMs applied to whole-bone scapular loading. The results suggest that elemental and nodal material mapping strategies are both able to simultaneously replicate experimental full-field displacements and reactions forces dependent on the density-modulus relationship used.