The Frank Stinchfield Award: Assembly and Dissociation Forces Differ Between Commonly Used Dual Mobility Implants: A Biomechanical Study.

BACKGROUND: Intraprosthetic dissociation (IPD) is a complication unique to dual mobility (DM) implants where the outer polyethylene head dissociates from the inner femoral head. Increasing reports of IPD at the time of closed reduction of large head DM dislocations prompted this biomechanical study evaluating the assembly and dissociation forces of DM heads. METHODS: We tested 17 polyethylene DM heads from 5 vendors. Of the heads, 12 were highly cross-linked polyethylene (4 vendors) and 5 were infused with vitamin E (2 vendors). Heads were between 46 and 47 mm in diameter, accepting a 28 mm-inner ceramic head. Implants were assembled and disassembled using a servohydraulic machine that recorded the forces and torques applied during testing. Dissociation was tested via both axial pull-out and lever-out techniques, where lever-out simulated stem-on-acetabular component impingement. RESULTS: The initial maximum assembly force was significantly different between all vendors (P < .01) and decreased for all implants with subsequent assembly. Vendor 4-E (Link with vitamin E) heads required the highest assembly force (1,831.9 ± 81.95 N), followed by Vendor 3 (Smith & Nephew), Vendor 5 (DePuy Synthes), Vendor 1-E (Zimmer Biomet with vitamin E), Vendor 2 (Stryker), and Vendor 1 (Zimmer Biomet Arcom). Vendor 4-E implants showed the greatest dissociation resistance in both pull-out (2,059.89 N, n = 1) and lever-out (38.95 ± 2.79 Nm) tests. Vendor 1-E implants with vitamin E required higher assembly force, dissociation force, and energy than Vendor 1 heads without vitamin E. CONCLUSIONS: There were notable differences in DM assembly and dissociation forces between implants. Diminishing force was required for assembly with each additional trial across vendors. Vendor 4-E DM heads required the highest assembly and dissociation forces. Vitamin E appeared to increase the assembly and dissociation forces. Based on these results, DM polyethylene heads should not be reimplanted after dissociation, and there may be a role for establishing a minimum dissociation energy standard to minimize IPD risk.

Optimal Distal Tendon Insertion Point for Elbow Flexion in Free-Functioning Gracilis Muscle Transfer for Panbrachial Plexus Injuries: A Cadaveric Study.

PURPOSE: Following pan-brachial plexus injuries, restoration of elbow flexion is widely accepted as the reconstructive priority. A gracilis free functioning muscle transfer (FFMT) can be used to restore elbow flexion alone with insertion into the biceps brachii (BIC) or brachioradialis (BRD) tendons or restore combined elbow and finger flexion with a more distal insertion into the flexor digitorum profundus (FDP) tendons. Using cadaveric experiments, we determined the peak instantaneous moment arm for each insertion option. METHODS: Six simulated gracilis transfer surgeries were performed using both arms of three fresh-frozen full body cadaveric specimens (age: 79 + 10 years. 2 female). The gracilis muscles from both legs were harvested and transferred to the contralateral upper extremity. The elbow was manually moved through three flexion-extension cycles while the instantaneous moment arm was calculated from measurements of gracilis excursion and elbow joint angle for the three distal insertion sites. RESULTS: Peak instantaneous moment arm for all three insertions occurred at an elbow angle between 83° to 92° with a magnitude ranging from 33 mm to 54 mm. The more distal (FDP/BRD) insertions produced a significantly greater (∼1.5 times) peak elbow flexion instantaneous moment arm compared to the BIC insertion. CONCLUSIONS: Based on the instantaneous moment arm, the gracilis FFMT distal insertion locations could result in greater reconstructed elbow flexion strength. In addition, direct measurement of the shape and magnitude of the moment arm curve for differing insertion sites allows high resolution surgical planning and model testing. CLINICAL RELEVANCE: This study presents the first direct experimental quantification of the gracilis FFMT instantaneous moment arm. The experimental evidence supports the use of FDP/BRD insertion locations by providing a quantitative explanation for the increased elbow flexion torque observed clinically in patients with a gracilis FFMT and distal FDP insertion.

Prospective Study Assessing Impact of Ethylene Oxide Sterilization on Endoscopic Ultrasound Image Quality.

BACKGROUND & AIMS: Duodenoscope-associated transmission of infections has raised questions about efficacy of endoscope reprocessing using high-level disinfection (HLD). Although ethylene oxide (ETO) gas sterilization is effective in eradicating microbes, the impact of ETO on endoscopic ultrasound (EUS) imaging equipment remains unknown. In this study, we aimed to compare the changes in EUS image quality associated with HLD vs HLD followed by ETO sterilization. METHODS: Four new EUS instruments were assigned to 2 groups: Group 1 (HLD) and Group 2 (HLD + ETO). The echoendoscopes were assessed at baseline, monthly for 6 months, and once every 3 to 4 months thereafter, for a total of 12 time points. At each time point, review of EUS video and still image quality was performed by an expert panel of reviewers along with phantom-based objective testing. Linear mixed effects models were used to assess whether the modality of reprocessing impacted image and video quality. RESULTS: For clinical testing, mixed linear models showed minimal quantitative differences in linear analog score (P = .04; estimated change, 3.12; scale, 0-100) and overall image quality value (P = .007; estimated change, -0.12; scale, 1-5) favoring ETO but not for rank value (P = .06). On phantom testing, maximum depth of penetration was lower for ETO endoscopes (P < .001; change in depth, 0.49 cm). CONCLUSIONS: In this prospective study, expert review and phantom-based testing demonstrated minimal differences in image quality between echoendoscopes reprocessed using HLD vs ETO + HLD over 2 years of clinical use. Further studies are warranted to assess the long-term clinical impact of these findings. In the interim, these results support use of ETO sterilization of EUS instruments if deemed clinically necessary.

Does proximal versus distal injury location of the medial ulnar collateral ligament of the elbow differentially impact elbow stability? An ultrasound-guided and robot-assisted biomechanical study.

BACKGROUND: The location (proximal vs. distal) of elbow medial ulnar collateral ligament (MUCL) tears impacts clinical outcomes of nonoperative treatment. The purposes of our study were to (1) determine whether selective releases of the MUCL could be performed under ultrasound (US) guidance without disrupting overlying soft tissues, (2) assess the difference in medial elbow stability for proximal and distal releases of the MUCL using stress US and a robotic testing device, and (3) elucidate the flexion angle that resulted in the greatest amount of medial elbow laxity after MUCL injury. METHODS: Sixteen paired, fresh-frozen elbow specimens were used. Valgus laxity was evaluated with both US and robotic-assisted measurements before and after selective MUCL releases. A percutaneous US-guided technique was used to perform proximal MUCL releases in 8 elbows and to perform distal MUCL releases in their matched pairs. The robot was used to determine the elbow flexion angle at which the maximum valgus displacement occurred for both proximally and distally released specimens. Open dissection was then performed to assess the accuracy of the percutaneous releases. RESULTS: Percutaneous US-guided releases were successfully performed in 15 of 16 specimens. The proximal release resulted in greater valgus angle displacement (11° ± 2°) than the distal release (8° ± 2°) between flexion angles of 30° and 70° (P < .0001 at 30°, P < .0001 at 40°, P = .001 at 50°, P = .005 at 60°, and P = .020 at 70°). Valgus displacement between release locations did not reach the level of statistical significance between 80° and 120° (P = .051 at 80°, P = .131 at 90°, P = .245 at 100°, P = .400 at 110°, and P = .532 at 120°). When we compared the values for the mean increase in US delta gap (stressed - supported state) from before to after MUCL release, the proximally released elbows had larger increases than the distally released elbows (5.0 mm proximal vs. 3.7 mm distal, P = .032). After MUCL release, maximum mean valgus displacement occurred at 49° of flexion. CONCLUSIONS: US-guided selective releases of the MUCL can be performed reliably without violating the overlying musculature. Valgus instability is not of greater magnitude for distal releases when compared with proximal releases. This findings suggests there must be alternative factors to explain the difference in clinical prognosis between distal and proximal tears. The observed flexion angle for maximum valgus laxity could have important implications for elbow positioning during US or fluoroscopic stress examination, as well as surgical repair or reconstruction of the MUCL.

The Biomechanical Consequences of Trapeziectomy and Partial Trapezoidectomy in the Treatment of Thumb Carpometacarpal and Scaphotrapeziotrapezoid Arthritis.

PURPOSE: To determine, using a biomechanical cadaveric model, whether, in the treatment of thumb carpometacarpal and scaphotrapeziotrapezoid arthritis, partial trapezoid resection following trapeziectomy causes carpal, specifically lunocapitate and scapholunate, instability. METHODS: Eight fresh-frozen mid-forearm cadaver specimens with type I lunates and devoid of basilar thumb arthritis were used in the study. Specimens were mounted onto a wrist simulator applying cyclical wrist flexion/extension and radial/ulnar deviation motions. Carpal kinematics, specifically lunocapitate and scapholunate joint relationships, were measured at 4 different conditions: (1) a native intact state, (2) after trapeziectomy, (3) after 2-mm partial trapezoid resection, and (4) after 4-mm partial trapezoid resection. RESULTS: During both flexion/extension and radial/ulnar deviation of the wrist, the lunocapitate and scapholunate joint relationship did not show any notable change following any of trapeziectomy, 2-mm, or 4-mm trapezoid resection compared with the intact state. Changes to the lunocapitate and scapholunate angles were clinically insignificant-a maximum of 6° and 4° change, respectively. CONCLUSIONS: This biomechanical cadaveric study shows that performing a trapeziectomy followed by up to 4 mm of proximal trapezoid resection has a negligible effect upon carpal, specifically lunocapitate and scapholunate, stability. Further research is needed to elucidate the long-term clinical consequences of limited trapezoid resection in vivo. CLINICAL RELEVANCE: There may be no clinically relevant effects of resection of up to 4 mm of trapezoid in the surgical management of combined basilar thumb and scaphotrapeziotrapezoid arthritis.

Contribution of the Ligamentum Teres to Hip Stability in the Presence of an Intact Capsule: A Cadaveric Study.

PURPOSE: To determine the contribution of the ligamentum teres (LT) to hip stability in the presence of an intact capsule with special attention to the change in range of motion and femoral head translation. METHODS: Seven fresh-frozen cadaveric pelvises were used. Following visual inspection of the LT at different hip positions, internal rotation angles were measured at 10° of extension and at 0° of flexion, while external rotation was measured at 60°, 90°, and 110° of flexion with different hip abduction angles using electromagnetic motion tracking sensor. Femoral head translations were measured simultaneously. The tests were repeated after resection of the LT. The capsule was left intact for all test conditions. The results were compared between intact and LT resected conditions when torque of 2 and 4 Nm was applied. RESULTS: Compared with the intact hip, the LT resected hip showed no significant difference when 2 Nm torque was applied in all scenarios. With 4 Nm torque application, significant increase in external rotation was found at 60° and at 90° of flexion (1.7° ± 0.8° and 2.1° ± 1.0°, respectively). Significant difference was also noted at 60°, 90°, and 110° of flexion when the hip was in the adducted position while at 90° in the abducted hip. However, LT resection did not show significant change in internal rotation. There was no significant difference in the translation distance of the femoral head in the intact hip compared with the LT resected hip (0.77-1.11 mm vs 0.79-1.29 mm). CONCLUSIONS: Our results indicate that within the physiologic range of motion, LT can minimally limit external rotation when the hip is in the flexed position but does not contribute to translation stability. CLINICAL RELEVANCE: In the hip with intact capsule, LT deficiency can result in a slight increase in range of motion, but its contribution to stability is questionable.

Experience Influences the Agreement and Reliability of Tibial Component Positioning in Total Knee Arthroplasty.

BACKGROUND: Poor rotation of the tibial component is associated with unfavorable total knee arthroplasty outcomes. Some surgeons utilize the tibial tubercle (TT method), while others utilize the femoral cam (Box method) as a rotational landmark during total knee arthroplasty. Our purpose is to determine the reproducibility of 2 methods for establishing intra-operative tibial component rotation, while also comparing the effect of level of training. METHODS: Twelve surgeons positioned and sized a symmetric tibial component on 7 cadaver knees. Surgeons were allowed to utilize their preferred method for establishing tibial component rotation. Seven surgeons selected the TT method, 4 utilized the Box method, and 1 used both methods depending on the specimen. Repeat measurements were completed by each surgeon after a rest period. The differences between tibial tray positions were assessed using computer-assisted optoelectronic measurements. Intra-class correlation coefficients were calculated to determine inter-observer agreement (IOA) and intra-rater reliability (IRR). RESULTS: Overall, both the Box method and the TT method demonstrated high IRR for tibial component rotation. Experienced surgeons were more consistent at establishing component rotation regardless of technique. Trainees were more consistent when utilizing the Box method (IRR 0.96, IOA 0.94) than the TT method (IRR 0.71, IOA 0.72). CONCLUSION: Surgeon experience influences the agreement and reliability of tibial component position. For less experienced surgeons, the Box method was more effective than the TT method for consistently reproducing tibial component rotation.

Role of the lateral collateral ligament in posteromedial rotatory instability of the elbow.

BACKGROUND: Posteromedial rotatory instability (PMRI) of the elbow consists of an anteromedial coronoid fracture with lateral collateral ligament (LCL) and posterior bundle of the medial collateral ligament (PMCL) tears. We hypothesized that the LCL tear is required for elbow subluxation/joint incongruity and that an elbow affected by an anteromedial subtype 2 coronoid fracture and a PMCL tear exhibits contact pressures different from both an intact elbow and an elbow affected by PMRI. MATERIALS AND METHODS: Six cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads and to passively flex the elbow from 0° to 90° and measure joint contact pressures. After testing of the intact specimen (INTACT-elbow), an anteromedial subtype 2 coronoid fracture with a PMCL tear (COR+PMCL-elbow) and a PMRI injury (PMRI-elbow), after adding an LCL tear, were tested. The highest values of mean contact pressure were used for the comparison among the 3 groups. RESULTS: Neither subluxation nor joint incongruity was observed in the COR+PMCL-elbow. The addition of an LCL detachment consistently caused subluxation and joint incongruity. Mean contact pressures were higher in the COR+PMCL-elbow compared with the INTACT-elbow (P < .03) but lower than in the PMRI-elbow (P < .001). CONCLUSIONS: The LCL lesion in PMRI is necessary for elbow subluxation and causes marked elevations in contact pressures. Even without subluxation, the COR+PMCL-elbow showed higher contact pressures compared with the INTACT-elbow. Treatment of PMRI should be directed toward prevention of joint incongruity, whether by surgical or nonsurgical means, to prevent high articular contact pressures.

Coronoid reconstruction using osteochondral grafts: a biomechanical study.

HYPOTHESIS: The purposes of this study were to test the hypothesis that coronoid deficiency in the setting of posteromedial rotatory instability (PMRI) must be reconstructed to restore articular contact pressures to normal and to compare 3 different osteochondral grafts for this purpose. METHODS: After creation of a anteromedial fracture, six cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads and to passively flex the elbow. Mean articular surface contact pressure data were collected and processed using TekScan sensors and software. After testing of the intact specimen (intact condition), a PMRI injury was created (PMRI condition). Testing was repeated after reconstruction of the lateral collateral ligament (LCL) (LCL-only condition), followed by reconstruction of the coronoid with 3 different osteochondral graft techniques (reconstructed conditions). RESULTS: Contact pressure was consistently significantly higher in the PMRI elbow compared with the intact, LCL-only, and reconstructed conditions (P < .006). The LCL-only elbow contact pressure was significantly higher than that of the intact and reconstructed conditions from 5° to 55° of flexion (P = .018). The contact pressure of the intact elbow was never significantly different from that of the reconstructed elbow, except at 5° of flexion (P ≤ .008). No significant difference was detected between each of the reconstructed techniques (P ≥ .15). However, the annular surface of the radial head was the only graft that yielded contact pressures not significantly different from normal at any flexion angle. CONCLUSION: Isolated reconstruction of the LCL did not restore native articular surface contact pressure, and reconstruction of the coronoid using osteochondral graft was necessary. There was no difference in contact pressures among the 3 coronoid reconstruction techniques.

Comparison of Passive Stiffness Changes in the Supraspinatus Muscle After Double-Row and Knotless Transosseous-Equivalent Rotator Cuff Repair Techniques: A Cadaveric Study.

PURPOSE: To investigate the alteration of passive stiffness in the supraspinatus muscle after double-row (DR) and knotless transosseous-equivalent (KL-TOE) repair techniques, using shear wave elastography (SWE) in cadavers with rotator cuff tears. We also aimed to compare altered muscular stiffness after these repairs to that obtained from shoulders with intact rotator cuff tendon. METHODS: Twelve fresh-frozen cadaveric shoulders with rotator cuff tear (tear size: small [6], medium-large [6]) were used. Passive stiffness of 4 anatomic regions in the supraspinatus muscle was measured based on an established SWE method. Each specimen underwent DR and KL-TOE footprint repairs at 30° glenohumeral abduction. SWE values, obtained at 0°, 10°, 20°, 30°, 60°, and 90° abduction, were assessed in 3 different conditions: preoperative (torn) and postoperative conditions with the 2 techniques. The increased ratio of SWE values after repair was compared among the 4 regions to assess stiffness distribution. In addition, SWE values were obtained on 12 shoulders with intact rotator cuff tendons as control. RESULTS: In shoulders with medium-large-sized tears, supraspinatus muscles showed an increased passive stiffness after rotator cuff repairs, and this was significantly observed at adducted positions. KL-TOE repair showed uniform stiffness changes among the 4 regions of the supraspinatus muscle (mean, 189% to 218% increase after repair), whereas DR repair caused a significantly heterogeneous stiffness distribution within the muscle (mean, 187% to 319% after repair, P = .002). Although a repair-induced increase in muscle stiffness was observed also in small-sized tears, there were no significant differences in repaired stiffness changes between DR and KL-TOE (mean, 127% to 138% and 127% to 130% after repairs, respectively). Shoulders with intact rotator cuff tendon showed uniform SWE values among the 4 regions of the supraspinatus muscle (mean, 38.2 to 43.0 kPa). CONCLUSIONS: Passive stiffness of the supraspinatus muscle increases after rotator cuff repairs for medium-large-sized tears. KL-TOE technique for the medium-large-sized tear provided a more uniform stiffness distribution across the repaired supraspinatus muscles compared with the DR technique. CLINICAL RELEVANCE: Based on this insight, investigating rotator cuff muscle stiffness changes, further studies using SWE may determine the optimal repair technique for various sizes of rotator cuff tears.

Mini Tightrope Fixation Versus Ligament Reconstruction - Tendon Interposition for Maintenance of Post-trapeziectomy Space Height: A Biomechanical Study.

PURPOSE: To test the biomechanical stability of ligament reconstruction and tendon interposition (LRTI) compared with Mini TightRope fixation for thumb metacarpal subsidence after trapeziectomy. METHODS: Fifteen fresh human cadaveric hands underwent trapeziectomy and were divided into 3 treatment groups: LRTI using a biotenodesis screw and single versus dual Mini TightRope fixation. The thumb and index fingers were removed distal to the metacarpal; the distal ends of the metacarpals and proximal radius were potted in urethane resin and mounted onto a servohydraulic testing machine. A cyclic axial load was applied to stress the trapezial cavity. We recorded displacement of the first metacarpal via the position of the actuator head and computed the size of the trapezial space as the difference of the initial size and first metacarpal displacement. Each specimen underwent cyclical loading until the first metacarpal had collapsed completely onto the scaphoid (failure of the repair) or until 6 hours of testing had been completed. The number of cycles to failure, change in the size of the trapezium cavity, and relative change in size of the trapezium cavity were determined. RESULTS: The trapezial space had completely closed before 6 hours of testing were completed in all biotenodesis screw-augmented LRTI specimens and remained present in all single and dual Mini TightRope specimens. Absolute (and normalized) changes in the size of the trapezial cavity in the single and dual Mini TightRope specimens were 11 ± 2 and 10 ± 2 mm, respectively. CONCLUSIONS: Dual Mini TightRope fixation provided superior load bearing and maintenance of trapezial space height compared with single Mini TightRope or LRTI biotenodesis screw procedures. CLINICAL RELEVANCE: This study demonstrates that patients who undergo suture suspension arthroplasty may be able to move earlier because of the immediate stability the construct affords.

The effect of the remplissage procedure on shoulder range of motion: a cadaveric study.

PURPOSE: The purpose of this in vitro biomechanical study was to assess the effects of the remplissage procedure for small- and large-sized Hill-Sachs lesions (HSLs) on shoulder range of motion (ROM) with a special interest in the apprehension position. METHODS: HSLs of 50% and 100% of the glenoid width were simulated in 7 cadaveric shoulders as small and large lesions, respectively, and the postoperative condition was reproduced by placing suture anchors on the articular surface and tying down the infraspinatus at the medial edge of the would-be lesion site. ROMs were measured in abduction, internal rotation, and external rotation with the humerus in the adducted and abducted position. In addition, the ROM was measured in the anterior apprehension position, in which 2 torques of external rotation and extension were applied simultaneously, and external rotation and horizontal extension ROMs were measured with the humerus in different abduction angles (20°, 40°, and 60°). RESULTS: For standard ROMs, the procedure for the 50% HSL maintained complete ROMs, whereas the procedure for the 100% HSL significantly decreased external rotation ROM with the humerus in both the adducted and abducted positions, as well as abduction ROM. In the apprehension position, remplissage for the 50% HSL decreased extension ROM with the humerus abducted to 40° and 60°. Remplissage for the 100% HSL significantly decreased both external and extension ROMs regardless of the humeral abduction angle. CONCLUSIONS: In the cadaveric model with an intact humeral head and the simulated postoperative condition, the remplissage procedure for a large HSL caused significant restrictions in ROM of abduction in the scapular plane and external rotation with the humerus in both adduction and abduction. It also caused significant restrictions in both external rotation and extension ROMs in the apprehension position. CLINICAL RELEVANCE: The indication for the remplissage procedure for the larger HSL should be considered carefully, especially for the competitive throwing athlete who needs exceptional external rotation ROM for optimal overhead throwing performance.

Tensile properties of a morphologically split supraspinatus tendon.

The supraspinatus tendon consists morphologically of two sub-regions, anterior and posterior. The anterior sub-region is thick and tubular while the posterior is thin and strap-like. The purpose of this study was to compare the structural and mechanical properties of the anterior and posterior sub-regions of the supraspinatus tendon. The supraspinatus tendons from seven human cadaveric shoulders were morphologically divided into the anterior and posterior sub-regions. Length, width, and thickness were measured. A servo-hydraulic testing machine (MTS Systems Corporation, Minneapolis, MN) was used for tensile testing. The maximal load at failure, modulus of elasticity and ultimate tendon stress were calculated. Repeated measures were used for statistical comparisons. The mean anterior tendon cross-sectional area was 47.3 mm(2) and the posterior was 32.1 mm(2) . Failure occurred most often at the insertion site: anterior (5/7) and posterior (6/7). All parameters of the anterior sub-region were significantly greater than those of the posterior sub-region. The moduli of elasticity at the insertion site were 592.4 MPa in the anterior sub-region and 217.7 MPa in the posterior (P = 0.01). The ultimate failure loads were 779.2 N in the anterior sub-region and 335.6 N in the posterior (P = 0.003). The ultimate stresses were 22.1 MPa in the anterior sub-region and 11.6 MPa in the posterior (P = 0.008). We recognized that the anterior and posterior sub-regions of the SSP tendon have significantly different mechanical properties. In a future study, we need to evaluate how best to repair an SSP tendon considering these region-specific properties.

Proximal Scaphoid Reconstruction Techniques Comparison of Three Techniques for Proximal Scaphoid Recontruction.

Introduction The costo-osteochondral autograft, vascularized medial femoral trochlear osteochondral autograft, and proximal hamate autograft have been used for the reconstruction of unsalvageable proximal pole scaphoid nonunions. Our hypothesis is that there is no difference in carpal kinematics after the proximal pole of the scaphoid is reconstructed with these three graft options. Methods Wireless sensors were mounted to the carpus that was loaded through cyclical motion. Each specimen was tested under a series of the three reconstructed conditions and their kinematics compared. Results No significant differences were found in scapholunate and lunocapitate joint motion during wrist flexion-extension and wrist radioulnar deviation between the three reconstructed conditions ( p > 0.05). Discussion and Conclusion There are minimal differences in carpal kinematics when comparing reconstruction of the proximal pole of the scaphoid with the costoosteochondral, medial femoral trochlear, and proximal hamate grafts.

Biomechanical Stability of Diaphyseal Ulnar Shaft Fractures and Ulnar Shortening Osteotomies After Fixation.

BACKGROUND: To determine the amount of micromotion during forearm rotation after diaphyseal ulnar shaft fracture or osteotomy. METHODS: This was a biomechanical study using 7 paired-matched cadavers. The upper extremity was mounted in a custom rig and the forearm brought through full pronation and supination. A Hall effect sensor was placed at the fracture ends to measure micromotion for all tested conditions. There were 4 conditions tested: (1) intact ulnar shaft with plate to act as a control; (2) transverse fracture/osteotomy without stabilization; (3) fracture/osteotomy with cortical apposition stabilized with plate fixation; and (4) 50% comminuted fracture stabilized with plate. RESULTS: There was a significantly greater amount of fracture site motion in the fracture/osteotomy model without stabilization compared with all other tested conditions (P < .001, .0001, .0003, respectively). The fracture/osteotomy site with cortical apposition and the comminuted fracture models showed no statistically significant differences in the amount of micromotion compared with each another (P = .952) or compared with the intact ulnar shaft (P = .997, .889, respectively). CONCLUSIONS: There was no significant difference in the amount of motion between an intact ulnar shaft, an ulnar shaft fracture with cortical apposition stabilized with a plate, and a plated comminuted fracture. These findings may help surgeons decide on their type of postoperative immobilization in the setting of isolated ulnar shaft fractures or ulnar shaft osteotomies stabilized with plate fixation.

Shear wave elastography demonstrates different material properties between the medial collateral ligament and anterolateral ligament.

BACKGROUND: Anterolateral ligament and medial collateral ligament injuries could happen concomitantly with anterior cruciate ligament ruptures. The anterolateral ligament is injured more often than the medial collateral ligament during concomitant anterior cruciate ligament ruptures although it offers less restraint to knee movement. Comparing the material properties of the medial collateral ligament and anterolateral ligament helps improve our understanding of their structure-function relationship and injury risk before the onset of injury. METHODS: Eight cadaveric lower extremity specimens were prepared and mechanically tested to failure in a laboratory setting using a hydraulic platform. Measurements of surface strains of superficial surface of each medial collateral ligament and anterolateral ligament specimen were found using three-dimensional digital image correlation. Ligament stiffness was found using ultrasound shear-wave elastography. t-tests were used to assess for significant differences in strain, stress, Young's modulus, and stiffness in the two ligaments. FINDINGS: The medial collateral ligament exhibited greater ultimate failure strain along its longitudinal axis (p = 0.03) and Young's modulus (p < 0.0018) than the anterolateral ligament. Conversely, the anterolateral ligament exhibited greater ultimate failure stress than the medial collateral ligament (p < 0.0001). Medial collateral ligament failure occurred mostly in the proximal aspect of the ligament, while most anterolateral ligament failure occurred in the distal or midsubstance aspect (P = 0.04). INTERPRETATION: Despite both being ligamentous structures, the medial collateral ligament and anterolateral ligament exhibited separate material properties during ultimate failure testing. The weaker material properties of the anterolateral ligament likely contribute to higher rates of concomitant injury with anterior cruciate ligament ruptures.

Viability of shear wave elastography to predict mechanical/ultimate failure in the anterolateral and medial collateral ligaments of the knee.

The purpose of this study was (1) to determine the utility of shear wave elastography as a predictor for the mechanical failure of superficial knee ligaments and (2) to determine the viability of shear wave elastography to assess injury risk potential. Our hypothesis was that shear wave elastography measurements of the anterolateral ligament and medial collateral ligament would directly correlate with the material properties and the mechanical failure of the ligament, serving as a prognostic measurement for injury risk. 8 cadaveric specimens were acquired, and tissue stiffness for the anterolateral ligament and medial collateral ligament were evaluated with shear wave elastography. The anterolateral ligament and medial collateral ligament were dissected and isolated for unilateral mechanical failure testing. Ultimate failure testing was performed at 100 % strain per second after 50 cycles of 3 % strain viscoelastic conditioning. Each specimen was assessed for load, displacement, and surface strain throughout failure testing. Rate of force, rate of strain development, and Young's modulus were calculated from these variables. Shear wave elastography stiffness for the anterolateral ligament correlated with mean longitudinal anterolateral ligament strain at failure (R2 = 0.853; P<0.05). Medial collateral ligament shear wave elastography calculated modulus was significantly greater than the anterolateral ligament shear wave elastography calculated modulus. Shear wave elastography currently offers limited reliability in the prediction of mechanical performance of superficial knee ligaments. The utility of shear wave elastography assessment for injury risk potential remains undetermined.

Effect of mechanical fatigue on commercial bioprosthetic TAVR valve mechanical and microstructural properties.

Valvular structural deterioration is of particular concern for transcatheter aortic valve replacements due to their suspected shorter longevity and increasing use in younger patient populations. In this work we investigated the mechanical and microstructural changes in commercial TAVR valves composed of both glutaraldehyde fixed bovine and porcine pericardium (GLBP and GLPP) following accelerated wear testing (AWT) as outlined in ISO 5840 standards. This provided greater physiological relevance to the loading compared to previous studies and by utilizing digital image correlation we were able to obtain strain contours for each leaflet pre and post fatigue and identify sites of fatigue damage. The areas of greatest change in mechanical strain for each leaflet were then further probed using biaxial tensile testing, confocal microscopy, and electron microscopy. It was observed that overall strain decreased in the GLPP valves following AWT of 200 million cycles while the GLBP valve showed an increase in overall strain. Biaxial tensile testing showed a statistically significant reduction in stress for GLPP while no significant changes were seen for GLBP. Both confocal and electron microscopy showed a disruption to the gross collagen organization and fibrillar structure, including fragmentation, for GLPP but only the former for GLBP. However, further test data is required to confirm these findings and to provide a better understanding of this fatigue pathway is required such that it can be incorporated into both valve design and selection processes to improve overall longevity for both GLPP and GLBP devices.

Moment arms of the anatomical subregions of the rotator cuff muscles during shoulder rotation.

BACKGROUND: Rotator cuff muscles are responsible for humeral rotation. Moment arms of different regions of these muscles during humeral rotation were analyzed in neutral and abducted positions. METHODS: In eight cadaveric shoulders, subregions of the rotator cuff muscles were identified and their excursion during humeral rotation was measured in neutral and abducted positions from an internal rotation of 30° to an external rotation of 45°, with 15° increments, using a 3-D digitizing system. Statistical tests were used to assess differences between subregions within a single muscle. FINDINGS: The posterior-deep subregion of the supraspinatus muscle had greater moment arms compared to the anterior-superficial and anterior-middle subregions in both positions (p < 0.001). The middle and inferior subregions of the infraspinatus muscle and the teres minor muscle showed differences in moment arms compared to the superior region in an abducted position (p < 0.042). The superior subregion of the subscapularis muscle showed differences in moment arms compared to the middle and inferior subregions in an abducted position (p < 0.001). INTERPRETATION: The posterior-deep subregion of the supraspinatus muscle behaved similar to the infraspinatus muscle, as an external rotator. The anterior-superficial and anterior-middle subregions of the supraspinatus muscle showed a biphasic behavior during rotation at a neutral position, but acted as pure external rotators during rotation at an abducted position. Inferior subregions of the infraspinatus and subscapularis muscles showed the largest moment arms compared to superior subregions. These findings support distinct functional roles of the rotator cuff muscle subregions.

Does Proximal Hamate Graft for Proximal Scaphoid Reconstruction Restore Native Wrist Kinematics?

BACKGROUND: The objective of this study was to determine whether reconstruction of the proximal pole of the scaphoid with a proximal hamate graft restores native carpal kinematics. METHODS: A cadaveric study was designed assessing wrist kinematic after proximal hamate graft for proximal pole of the scaphoid nonunion. Wireless sensors were mounted to the carpus using a custom pin and suture anchor system to 8 cadavers. A wrist simulator was used to move the wrist through a cyclical motion about the flexion/extension and radial/ulnar deviation axes. Each specimen was tested under a series of 3 conditions: (1) a native state, "Intact"; (2) fractured scaphoid proximal pole, "Fracture"; and (3) post-reconstruction of the proximal pole of the scaphoid using a proximal hamate graft, "Graft." RESULTS: The fracture condition resulted in a statistically significant change in scapholunate kinematics across the entire arc of motion relative to the intact condition. Reconstruction with proximal hamate grafts restored scapholunate kinematics close to the intact state in both flexion/extension and radial/ulnar deviation axes. The lunocapitate flexion during wrist flexion was significantly different after the hamate graft reconstruction. CONCLUSIONS: Proximal hamate to scaphoid transfer resulted in restoration of near normal carpal kinematics to the intact state.