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.

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.

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°.

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.

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.

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.

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.

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.

The Walch type B humerus: glenoid retroversion is associated with torsional differences in the humerus.

BACKGROUND: The Walch type B glenoid has the hallmark features of retroversion, joint subluxation, and bony erosion. Although the type B glenoid has been well described, the morphology of the corresponding type B humerus is poorly understood. As such, the aim of this imaging-based anthropometric study was to investigate humeral torsion in Walch type B shoulders. METHODS: Three-dimensional models of the full-length humerus were generated from computed tomography data for the Walch type B group (n = 59) and for a control group of normal nonarthritic shoulders (n = 59). An anatomic humeral head-neck plane was created and used to determine humeral torsion relative to the epicondylar axis. Measurements were repeated, and intraclass correlation coefficients were calculated. RESULTS: The type B humeri had significantly (P < .001) less retrotorsion (14° ± 9°) than the control group (36° ± 12°) relative to the epicondylar axis. Male and female individuals within the control group showed statistically significant differences in humeral torsion (P = .043), which were not found in the type B group. Inter-rater reliability showed excellent agreement for humeral torsion (intraclass correlation coefficient, 0.962). A subgroup analysis between Walch type B2 and B3 shoulders showed no significant differences in any of the humeral or glenoid parameters. CONCLUSION: The Walch type B humerus has significantly less retrotorsion than non-osteoarthritic shoulders. At present, it is unknown whether the altered humeral retrotorsion is a cause or effect of the type B glenoid. In addition, it is unknown whether surgeons should be reconstructing type B2 humeral component version to pathologic torsion or to nonpathologic population means to optimize arthroplasty survivorship.

Characterization of the Walch B3 glenoid in primary osteoarthritis.

BACKGROUND: The type B3 glenoid is an addition to the Walch classification. A potential etiologic theory is that it is a progression of the B2. It is characterized by uniconcavity, absent paleoglenoid, medialization, retroversion, and subluxation. The purpose of this study was to describe the morphology of B3 glenoids. METHODS: Fifty-two patients with B3 glenoids underwent 3-dimensional analysis of computed tomography data. Glenoid measurements (retroversion, inclination, medialization) and humeral head subluxation according to the scapular and glenoid planes were determined. The measured variables were compared between male and female patients. RESULTS: The mean B3 retroversion, inclination, and medialization were 24° ± 7°, 8° ± 6° superior, and 14 ± 4 mm, respectively. The mean posterior subluxation was 80% ± 8% and 54% ± 6% according to the scapular and glenoid planes, respectively. There were no differences in B3 characteristics between sexes (P > .05). A significant correlation existed between glenoid retroversion and humeral head subluxation relative to the scapular plane, with every 1° increase in retroversion translating to a 1% increase in subluxation (P < .001). In contrast, when referencing the glenoid plane, the humeral head remained concentric to the erosion. CONCLUSIONS: The B3 is uniconcave and retroverted. As glenoid retroversion increases, posterior humeral head subluxation significantly increases as referenced to the scapular plane; however, when referenced to the glenoid plane, the head remains concentric to the erosion. This appearance of "concentricity" is acquired secondary to the wear pattern, creating a uniconcave glenoid. Therefore, surgeons should be aware that the visualized concentricity is a product of the erosion pattern and thus may conceal a greater amount of subluxation potential.

In-Vitro Quantification of Medial Collateral Ligament Tension in the Elbow.

The anterior bundle of the medial collateral ligament (AMCL) of the elbow is commonly injured in patients with elbow dislocations and in throwing athletes. This in-vitro study quantified tension in the native AMCL throughout elbow flexion for different arm positions. We conducted passive and simulated active elbow flexion in seven fresh-frozen cadaveric upper extremities using an established motion simulator. Motions were performed in the valgus and vertical positions from 20-120° while measuring AMCL tension using a custom transducer. Average AMCL tension was higher in the valgus compared to vertical position for both active (p = 0.03) and passive (p = 0.01) motion. Peak AMCL tension was higher in the valgus position for active (p = 0.02) and passive (p = 0.01) motion. There was no significant difference in AMCL tension between active and passive motion in the valgus (p = 0.15) or vertical (p = 0.39) positions. In the valgus position, tension increased with elbow flexion from 20-70° for both active (p = 0.04) and passive (p = 0.02) motion, but not from 70-120°. This in-vitro study demonstrated that AMCL tension increases with elbow flexion, and is greater in the valgus position relative to the vertical position. This information has important implications to the desired target strength of repair and reconstruction techniques.

Premorbid retroversion is significantly greater in type B2 glenoids.

BACKGROUND: Posterior glenoid erosion is thought to be initiated by humeral head subluxation. However, it is unknown whether subluxation is entirely caused by soft-tissue instability and unbalanced muscle activity or whether osseous morphology is a contributing factor. We hypothesized that patients with posterior erosion may exhibit premorbid glenoid morphology that is inherently retroverted and inferiorly inclined compared with age-matched normal glenoids. METHODS: This study examined 80 scapulae, evenly distributed between 2 groups: osteoarthritic with type B2 glenoids and age-matched normal glenoids. From 3-dimensional computed tomography reconstructions, version and inclination were measured from the anterior paleoglenoid region of the B2 glenoids, which is representative of the premorbid glenoid, and compared with measurements obtained from similar regions in the normal cohort. RESULTS: The anterior paleoglenoid region of B2 glenoids was significantly (P < .001) more retroverted (-14° ± 6°) compared with similar regions in nonarthritic normal glenoids (-5° ± 5°). There were no significant differences (P = .166) in the glenoid inclination angle between type B2 glenoids (0° ± 6°) and nonarthritic normal glenoids (2° ± 5°). Negative values represent retroverted and inferiorly inclined glenoids. DISCUSSION: Understanding premorbid glenoid morphologic variations may provide insight into the pathoanatomy of humeral head subluxation, osteoarthritis, and posterior glenoid erosion. The results of this study indicate that patients with type B2 osteoarthritic glenoids have significantly greater premorbid glenoid retroversion compared with nonarthritic normal glenoids, suggesting that this premorbid morphologic variation may be one contributing factor to posterior erosion.

A comparison of normal and osteoarthritic humeral head size and morphology.

BACKGROUND: The purpose of this study was to evaluate and to compare the size and morphologic patterns among normal and osteoarthritic (OA) humeral heads. METHODS: This comparative anatomic imaging study evaluated 150 humeral heads that were separated into 3 cohorts: normal, OA with symmetric glenoid erosion, and OA with asymmetric (type B2) glenoid erosion. Three-dimensional models were created of the humeral head from computed tomography data, and point coordinates were extracted for evaluation. Parameters measured were diameter (sphere fit and circle fit), chord distance (superoinferior and anteroposterior), and humeral head height. RESULTS: The sphere-fit diameter of the humeral head for the entire OA cohort (100 patients; mean diameter, 59 ± 9 mm) was significantly greater (P < .001) than that of the normal cohort (50 patients; mean diameter, 49 ± 5 mm). Similarly, the humeral head circle-fit diameters in the superoinferior and anteroposterior planes were significantly greater (P < .001) in the combined OA cohorts (59 ± 9 mm and 56 ± 10 mm, respectively) compared with the normal cohort (51 ± 5 mm and 47 ± 5 mm, respectively). However, there were no significant differences (P ≥ .099) between the symmetric and asymmetric OA cohorts in sphere-fit or circle-fit diameters. The mean values of humeral head heights were not significantly different (P = .382) between cohorts, 19 ± 2 mm, 18 ± 2 mm, and 18 ± 2 mm for the normal, symmetric, and asymmetric cohorts, respectively. DISCUSSION: Although OA humeral head morphology varies significantly from normal, it does not vary as a function of the Walch classification between symmetric and asymmetric glenoids. Understanding of the morphologic variability of the pathologic humeral head may provide insight into the pathoanatomy of osteoarthritis and the development of various erosion patterns.

Hemiarthroplasty of the elbow: the effect of implant size on joint congruency.

BACKGROUND: Distal humeral hemiarthroplasty is a treatment option for elbow joint disease that predominantly affects the distal humerus, including distal humerus fractures, nonunions, and avascular necrosis. The effect of hemiarthroplasty implants on joint contact has not been reported. The purpose of this in vitro study was to quantify the effects of hemiarthroplasty and implant size on ulnohumeral joint congruency. METHODS: Five fresh frozen cadaveric upper extremities were mounted to a custom elbow testing system. Active and passive motion were performed in dependent, horizontal, varus, and valgus positions. A registration and interbone distance algorithm was used to quantify ulnohumeral joint congruency throughout elbow flexion. RESULTS: The optimally sized hemiarthroplasty implant demonstrated the greatest joint congruency with the ulna, followed by the oversized implant, then the undersized implant. Joint congruency was greater during active vs. passive flexion, indicating that the elbow joint is more reduced in active flexion than in passive flexion. CONCLUSION: This study demonstrates that undersized distal humeral hemiarthroplasty implants have the lowest joint congruency compared with an optimally sized or oversized implant.

Development of a Computational Elbow Model with Experimental Validation of Kinematics and Muscle Forces.

A computational elbow joint model was developed with a main goal of providing complimentary data to experimental results. The computational model was developed and validated using an experimental elbow joint phantom consisting of a linked total joint replacement. An established in-vitro motion simulator was used to actively flex/extend the experimental elbow in multiple orientations. Muscle forces predicted by the computational model were similar to the experimental model in 4 out of the 5 orientations with errors less than 7.5 N. Valgus angle kinematics were in agreement with differences less than 2.3°. In addition, changes in radial head length, a clinically relevant condition following elbow reconstruction, were simulated in both models and compared. Both lengthening and shortening of the radial head prosthesis altered muscle forces by less than 3.5 N in both models, and valgus angles agreed within 1°. The computational model proved valuable in cross validation with the experimental model, elucidating important limitations in the in-vitro motion simulator's controller. With continued development, the computational model can be a complimentary tool to experimental studies by providing additional noninvasive outcome measurements.

Load transfer at the distal ulna following simulated distal radius fracture malalignment.

PURPOSE: To measure the effects of distal radius malalignment on loading at the distal ulna. METHODS: Using an adjustable mechanism to simulate angulated and translated malalignments, clinically relevant distal radius deformities were simulated in a cadaveric model. A custom-built load cell was inserted just proximal to the native ulna head to measure the resultant force and torque in the distal ulna. Loads were measured before and after transecting the triangular fibrocartilage complex (TFCC). RESULTS: There was an increase in distal ulna load and torque with increasing dorsal translation and angulation. Combined conditions of angulation and translation increased force and torque in the distal ulna to a greater extent than with either condition in isolation. Transecting the TFCC resulted in a reduction in distal ulna load and torque. CONCLUSIONS: A progressive increase in load at the distal ulna was observed with increasing severity of malalignment, which may be an important contributor to residual ulnar wrist pain and dysfunction. However, no clear-cut threshold of malalignment of a dorsally angulated and translated distal radius fracture was identified. These observations suggest that radius deformities cause articular incongruity, which increases TFCC tension and distal radioulnar joint load. Cutting of the TFCC decreased distal ulna loading, likely by releasing the articular constraining effect of the TFCC on the distal radioulnar joint, allowing the radius to rotate more freely with respect to the ulna. CLINICAL RELEVANCE: Anatomical reduction of a distal radius fracture minimizes the forces in the distal ulna and may reduce residual ulnar wrist pain and dysfunction.

Effect of Volarly Angulated Distal Radius Fractures on Forearm Rotation and Distal Radioulnar Joint Kinematics.

PURPOSE: To examine the effect of volar angulation deformities of the distal radius with and without triangular fibrocartilage complex (TFCC) rupture on forearm range of motion and the kinematics of the ulnar head at the distal radioulnar joint (DRUJ) during simulated active forearm rotation. METHODS: Volar angulation deformities of the distal radius with 10° and 20° angulation from the native orientation were created in 8 cadaveric specimens using an adjustable apparatus. Active supination and pronation were performed using a forearm motion simulator. Pronation and supination range of motion was quantified with each deformity. In addition, changes in the dorsovolar position of the ulnar head relative to the radius were calculated after simulating each distal radial deformity. Testing was performed with the TFCC intact and sectioned. RESULTS: Volar angulation deformities of 20° decreased the supination range with preservation of pronation. There was no effect of TFCC status on the range of forearm rotation. With the TFCC intact, volar angulation deformities translated the ulna slightly dorsally in pronation and volarly in supination. After sectioning the TFCC, volar angulation deformities of 10° and 20° translated the ulna dorsally throughout forearm rotation. CONCLUSIONS: Volar angulation deformities reduce supination range and alter the DRUJ kinematics. The increased tension in the intact TFCC caused by volar angulation deformities likely prevented the expected dorsovolar displacement at the DRUJ and restricted supination. Dividing the TFCC released the constraining effect on the DRUJ and allowed the ulna to translate dorsally. However, supination remained limited, presumably because of impediment from the dorsally subluxated ulna. CLINICAL RELEVANCE: This study demonstrated the importance of correcting volar angulation deformities of the distal radius to less than 20° in order to maintain normal range of forearm rotation and to less than 10° to maintain normal DRUJ kinematics when the TFCC is ruptured.

Augmented glenoid component designs for type B2 erosions: a computational comparison by volume of bone removal and quality of remaining bone.

BACKGROUND: The purpose of this computational modeling study was to compare the volume of glenoid bone removal required to implant 3 augmented component designs for management of B2 erosions. In addition, we assessed bone quality of the supporting bone directly beneath the implants by measuring bone density and porosity. METHODS: Three augmented component designs­full-wedge, posterior-wedge, and posterior-step­were studied by virtual implantation in a cohort of 16 patients with B2 glenoids. B2 retroversion was corrected to 0° and 10°. The outcome variables were the volume of glenoid bone removal required for implantation and the density and porosity of the bone immediately beneath the implant. RESULTS: Implant design had a significant effect on the volume of bone removal (P < .001). When correcting to 0°, the posterior-wedge implant removed less bone than the posterior-step (P < .001) and the full-wedge (P = .004). At 10° retroversion, the posterior-wedge removed less bone (P = .029) than the posterior-step but was no different than the full-wedge (P = .143). The residual glenoid bone density with the posterior-wedge was significantly greater than with the posterior-step (P = .048), with no other significant differences (P > .05). Residual glenoid bone porosity was not significantly different between implants (P > .262). CONCLUSIONS: Augmented components can provide a bone-preserving option for B2 glenoid management. Substantial variations in the volume of bone removal and the quality of the remaining glenoid bone were found between 3 different designs of augmented implants. Simulations with the posterior-wedge implant resulted in substantially less glenoid bone removal, with the remaining supporting bone being of better quality.