Failure by fatigue is one mechanism by which ligaments can rupture, with the accumulation of damage gradually degrading the ligament strength. Baseball pitchers who perform repeated high-level ...throwing continuously subject the medial ligament complex of the elbow to extreme levels of loading, which can lead to fatigue and eventual rupture. This study sought to investigate this behavior and quantify the fatigue properties of the anterior bundle of the medial collateral ligament (AMCL) with respect to valgus elbow torque. Eleven pairs of cadaveric elbow specimens were used for this study. One side of each pair was tested in vertical elongation at four flexion angles and then tested to failure at 90° of flexion. The contralateral specimens were tested in valgus fatigue at 90° of flexion using a specialized apparatus with application of known moments based on the elongation failure load. The average tensile failure load for the AMCL was 595.3 ± 201.9 N. During cycling, the average increase in the maximum valgus rotation angle was 4.77° ± 2.82°. The average maximum stretch of the AMCL middle band increased from 1.066 ± 0.017 to 1.076 ± 0.018 near the time of fatigue failure. The average cycles to failure for specimens tested at 90% and 80% of the estimated failure torque were 3211 ± 4721.33 and 25063 ± 30487.58, respectively. The nonlinear non-dimensional fatigue life and damage accretion results work in conjunction to predict the fatigue properties for a valgus elbow motion of arbitrary torque magnitude at 90° of elbow flexion.
Repair of severed nerves without autograft or allograft has included suture, suture with glue alone, suture with conduit and suture with glue augmentation to conduit, where use of conduit is ...considered for separation of the nerve ends from 5 mm to 3 cm. Repairs must not only serve acutely to provide apposition of nerve ends but must enable the healing of the nerve. Using biological conduit can place suture at the ends of the conduit while fibrin glue alone eliminates suture but with limited strength. The combination of conduit and glue offers the growth guidance of conduit with sufficient strength from the glue to maintain the nerve within the conduit. The role of fibrin glue in the integrity of the repair remains an open question, however. We sought to determine the factors in the strength of a glue-conduit-nerve construct and include consideration of standard suture repair. Fresh-frozen cadaveric digital nerves were repaired with suture alone, with glue alone or with suture and glue together and then loaded to failure. Previously tested specimens with conduit, suture and glue were considered for comparison. The suture alone (2.02 N) and suture with glue (2.24 N) were not statistically different from each other but were statistically stronger than glue alone (0.15 N). When compared to the earlier results of the strength of conduit with glue (0.65 N), these simple results show that the glue and conduit act together. The increased area over which the glue adheres to the nerve and conduit creates a composite structure stronger than either alone.
A study was undertaken to determine how well contacting fracture fragments of composite bone replicated the behavior of fracture fragments in real bone. Ten composite and ten real humeral diaphyses ...were transected and reconstructed with limited-contact dynamic-compression plates. Two screws were placed on each side of the transection site and a calibrated electronic sensor sheet was placed between the imitated fracture fragments. After insertion of the distal screws, pressure measurements were made during insertion of the first proximal screw in compression mode, during insertion of the second screw in compression mode after loosening the first screw, and finally after retightening the first screw. The process was repeated after bending the plate. The contact area, the net compression force and the average compressive stress were computed and statistically compared. The composite bone and cadaveric bone differed in contact area and compressive stress but not in net compressive force. Plate bending did not produce a significant difference between composite and cadaveric bone. The results indicate that composite bone does not reproduce all the local fracture fragment conditions so that hardware testing in composite bone should proceed carefully. A gap between fracture fragments as is often used in comminuted fracture tests may remain as the most appropriate situation for fracture hardware testing.
Anterior cruciate ligament (ACL) graft failure rate has been reported to be greater than 5% at 5 years. Our study evaluated ACL excursion with anatomic and nonanatomic femoral and tibial tunnels to ...determine optimal flexion angle to tension the ACL to minimize excursion. Ten cadaveric knee specimens were used. The ACL was sectioned and the femoral and tibial attachments were marked. A 1/16-inch drill created a tunnel in the center of the ACL footprint on the tibia and femur and additional tunnels were made 5 mm from this. A suture was passed through each tunnel combination and attached to a string potentiometer. The knee was ranged from full extension to 120 degrees of flexion for 10 cycles while mounted in a custom fixture. The change in length (excursion) of the suture during movement was recorded for each combination of femoral and tibial tunnels. Anatomic reconstruction of the ACL with tunnel placement in the center of the femoral and tibial footprint did not result in an isometric graft, with excursion of the ACL during knee motion of 7.46 mm (standard deviation SD: 2.7mm), greatest at 2.84 degrees of flexion (SD: 4.22). The tunnel combination that resulted in the least excursion was a femoral footprint 5 mm anterior to the femoral and 5 mm posterior to the tibial footprint (4. 2mm, SD: 1.37 mm). The tunnel combination that resulted in the most excursion utilized femoral footprint 5 mm proximal to the femoral and 5 mm posterior to the tibial footprint (9.81 mm, SD: 2.68 mm). Anatomic ACL reconstruction results in significant excursion of the ACL throughout motion. If not tensioned properly, the ACL can stretch during range of motion, potentially leading to rerupture. To prevent stretching of the graft, the current biomechanical study recommends tensioning an anatomic ACL reconstruction at its point of maximal excursion, or between 0 and 5 degrees of flexion. The level of evidence is IV.
Injuries to the elbow medial ulnar collateral ligament (mUCL) pose a diagnostic challenge, with the moving valgus stress test (MVST) currently accepted as the gold-standard clinical test. This study ...sought to biomechanically evaluate the change in length of the ulnar collateral ligament (UCL) during flexion-extension using a null hypothesis that the mUCL will not experience a greater change in length with movement than with static loading.
Seven fresh-frozen human cadaveric elbows were tested with static and dynamic valgus stress. We measured (1) ligament length with a multi-camera optical system, (2) elbow flexion with an incremental encoder, and (3) valgus deviation with an electronic inclinometer. With a force applied to the wrist to simulate a clinical stress examination, the elbow was flexed and extended in a physiological elbow simulator to mimic the flexion and extension of the MVST.
The simulated MVST produced more elongation of the UCL compared with static stress testing (P < .001). Ninety degrees of flexion produced the highest mean change, and the anterior and posterior bands demonstrated different length change characteristics. Comparison of dynamic flexion and extension showed a statistically significant difference in change in length: The mUCL reached the greatest change during extension, with the greatest changes during extension near 90° of flexion.
The MVST produces significantly more elongation of the mUCL than either a static test or a moving test in flexion. This study provides biomechanical evidence of the validity of the MVST as a superior examination technique for injuries to the UCL.
Floating shoulder injuries cause instability and deformity due to disruptions of the scapula, clavicle, and superior shoulder suspensory complex ligaments (SSSC). Resulting deformity of the ...glenopolar angle (GPA) has not previously been established, nor has the impact on stability and deformity when surgical fixation is performed. This study sought to quantify stability and deformity for multiple injury patterns and the improvement to these parameters provided by clavicle and coracoclavicular (CC) ligament fixation.
Fourteen cadaveric specimen upper extremities were used, which included the entire upper extremity, scapula, clavicle, and cranial-most ribs. After being mounted upright, a scapular neck fracture was created, followed by either a midshaft clavicle fracture or sectioning of the acromioclavicular and coracoacromial ligaments. Subsequent sectioning of the other structure(s) followed by the CC ligaments was then performed. In all specimens, the clavicle was then plated, followed by a CC ligament repair. At each step, a radiograph in the AP plane of the scapula was taken to measure GPA and displacement of the glenoid fragment using radiopaque markers placed in the scapula. These radiographs were taken both unloaded and with a 100-N applied medializing force.
When evaluating deformity related to sectioning, the GPA was reduced when the CC ligaments were sectioned compared to an isolated scapula fracture (P = .022) and compared to a combined scapula and clavicle fracture (P = .037). For stability, displacement with a 100-N force was significantly increased when the CC ligaments were sectioned compared to an isolated scapula fracture (P = .027). In cases of an ipsilateral scapula neck and clavicle fracture with intact ligaments, fixation of the clavicle alone provided a statistically significant improvement in the GPA (P = .002); but not in reduction of displacement (P = .061). In cases of an ipsilateral scapula neck and clavicle fracture with concomitant disruption of the coracoacromial, acromioclavicular, and CC ligaments, the GPA was improved by clavicle fixation (P < .001) and increasingly so by subsequent CC ligament repair (P < .001). Displacement was also improved in these 2 states (P < .001, P = .008, respectively).
This biomechanical study confirmed the importance of the acromioclavicular, coracoacromial, and CC ligaments in conferring stability in SSSC injuries. Disruption of the CC ligaments created significant deformity of the GPA and instability with a medializing force. Clinical treatment should consider the integrity of these ligaments and their repair in conjunction with clavicle fixation, knowing that this combination should restore a biomechanical state equivalent to an isolated scapula fracture.
Background:
Many techniques are used for digital nerve repair, most commonly coaptation by sutures. Nerve repairs must be strong while offering an environment for nerve regeneration. Sutures can ...damage the nerve and thereby limit growth and regeneration. Sutures can rip and cause sudden catastrophic failure. Fibrin glue and conduit-wraps allow a good environment for growth, but neither provides much strength. A benefit to conduit repair would arise if the repair maintained integrity after the peak load so that the path for regrowth stayed in place. The goal for this study was to determine whether conduit with glue provides continued strength after a maximum load is reached.
Methods:
Digital cadaveric nerves were harvested and repaired with 2 epineurial sutures, conduit, and fibrin glue in all combinations. Tests to failure were performed, gap displacement between nerve ends recorded, and the postpeak load energy to dissociation of the nerve and conduit was calculated.
Results:
Conduit with glue and 2 sutures at the end had the greatest energy and displacement after the peak load but was not significantly different than conduit with glue and 1 suture. Conduit with glue alone obtained statistically the same displacement as conduit with glue and 2 sutures. Conduit, with or without glue, and 2 sutures was statistically the same as suture only repair for peak load.
Conclusion:
Conduit/wrap maintains a load capacity and a path for nerve regeneration after the peak. Suture at the ends of conduit, not at the coaptation site, reduces damage at the point of injury.
The radial tuberosity contributes to the biceps supination moment arm and the elbow flexion moment. The purpose of our study was to compare the impact of a cortical bone trough versus an anatomic ...repair on measurements of the forearm supination moment arm and elbow flexion force efficiency. Our hypothesis was that a trough repair would decrease the tuberosity height, the native biceps supination moment arm, and elbow flexion force efficiency compared with an anatomic repair.
The isometric supination moment arm and elbow flexion force efficiency were measured in ten matched pairs of cadaveric upper limbs. After testing, the geometry of the proximal aspect of the radius was reconstructed with use of stereophotogrammetry. All of the repair sites were three-dimensionally reconstructed to quantify the disturbance of the trough on native anatomy. The tuberosity distance was defined as the distance between the central axis of the radius and the centroid of the respective repair site.
Specimens with a trough repair had a 27% lower supination moment arm at 60° of supination (p = 0.036). There were no differences found for pronation or neutral forearm positioning (p > 0.235). Flexion force efficiency was not significantly different between the trough and anatomic repair groups. The average tuberosity distance was 11.0 ± 2.1 mm for the anatomic repairs and 8.3 ± 1.4 mm for the trough repairs (p = 0.003). The percentage of distance lost due to the trough was 25%. Furthermore, the supination moment arm in the supinated position was significantly correlated with the tuberosity distance.
The trough technique resulted in a significant decrease (p = 0.036) in the moment arm of a 60° supinated forearm and a significant reduction (p = 0.003) in radial tuberosity height. The loss of the supination moment arm was correlated with the decrease in tuberosity height, providing evidence that the radial protuberance acts as a mechanical cam.
The anterior protuberance of the radial tuberosity functions as a supination cam; therefore, consideration should be given to preserve its topographical anatomy during a distal biceps repair.
Purpose This study sought to compare the strength of quadrupled hamstring tendon (QHT) grafts of 6 to 9.5 mm in clinical diameter with that of 10-mm bone–patellar tendon–bone (BPTB) grafts. Methods ...Twenty cadaveric semitendinosus and gracilis tendons were combined into QHT grafts. These were sized using a standard graft-sizing device and an area micrometer, yielding grafts ranging from 6 to 9.5 mm in diameter. The grafts were tested to failure. Five 10-mm BPTB grafts were also sized and tested. Results Clinical sizing did predict the strength of the graft but not profoundly. As a material alone, without consideration of fixation in bone tunnels, QHT grafts were stronger than BPTB grafts. Graft strength decreased with size, but a linear relation between strength and diameter ( r2 = 0.715, P < .001) was found to be as good as the expected quadratic fit ( r2 = 0.709). Compared with BPTB grafts, even the smallest QHT grafts (diameter <6.5 mm) were still significantly stronger than 10-mm BPTB grafts ( P = .004). The elastic moduli of the QHT and BPTB grafts were 761 ± 187 MPa and 615 ± 403 MPa, respectively; elongations at failure were 12.0% ± 2.0% and 7.5% ± 1.6%, respectively; and failure stresses were 105 ± 18 MPa and 50 ± 14 MPa, respectively. Conclusions This work shows that a clinical size of QHT grafts of 6 mm in diameter is not a concern regarding the strength itself. For a possible lower-end prediction of acceptable size, assuming that a gracilis-semitendinosus graft would have only the stress of the weakest measured QHT graft of 88 MPa, a graft of 5.5 mm in diameter would suffice, having more strength in newtons than the average patellar tendon. Clinical Relevance Clinically sized QHT grafts have a higher failure strength than 10-mm patellar tendon grafts. Therefore the strength of the graft cannot account for the higher clinical failure rates of smaller hamstring grafts in active patients in clinical studies.
To quantify the biomechanical properties of the hip capsule with human dermal allograft reconstruction to determine whether a dermal patch restored capsular resistance to distraction.
Nine cadaveric ...hip specimens were dissected until capsule and bony structures remained and were then mounted in a testing fixture in neutral flexion and abduction. Four states of the hip capsule were sequentially tested under axial distraction of 5 mm measured with video analysis and with resultant force measurement: (1) intact hip capsule, (2) interportal capsulotomy, (3) capsulectomy to the zona orbicularis, and (4) capsular reconstruction with human dermal allograft using acetabular anchors and capsule-to-patch sutures.
Capsulectomy was different from intact (P = .036), capsulotomy differed from capsulectomy (P = .012), and the repair was statistically significantly different from capsulectomy (P = .042); intact and reconstructed cases were not statistically significantly different. The force required for 5 mm of distraction decreased after interportal capsulotomy by an average of 9% compared with the intact state and further decreased after capsulectomy by 30% compared with the intact state. After capsular reconstruction using dermal allograft, force requirements increased by an average of 36% from the capsulectomy state, only 5% below the intact state.
Human dermal allograft tissue graft provides restoration of distractive strength for use during hip capsule reconstruction with acetabular anchor fixation and distal soft-tissue fixation after capsulectomy in a cadaveric model.
Capsular repair or reconstruction with a dermal patch offers time-zero restoration of function; intact and reconstructed cases showed no difference, and reconstruction restored a capsulectomy to a biomechanical equivalent of the intact case when distraction was applied.
