Xiang-Hua Deng

Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint

The purpose of this study was to determine the contri butions of specific capsuloligamentous structures to restraining superior-inferior translation of the glenohu meral joint. Eleven cadaveric shoulders were tested using a four degrees-of-freedom test apparatus. The humerus was free to translate in three planes and free to flex and extend when a superior and inferior force of 50 N was applied. Testing was performed in three positions of abduction (0°, 45°, and 90°) and three positions of rotation (neutral, maximum internal, and external). Shoulders were tested intact, vented, and after division of specific capsuloligamentous structures. The primary restraint to inferior translation of the ad ducted shoulder was the superior glenohumeral liga ment. The coracohumeral ligament appeared to have no significant suspensory role. With progressive abduc tion, the anterior and posterior portions of the gleno humeral ligament become the main static stabilizers resisting inferior translation: the anterior portion was the primary capsular restraint at 45° of abduction, while the posterior portion was the primary restraint at 90° of abduction, neutral rotation. Our results indicate that clinical assessment of glenohumeral translation in the superior-inferior plane should be performed in multiple positions of abduction and rotation.

Use of Recombinant Human Bone Morphogenetic Protein-2 to Enhance Tendon Healing in a Bone Tunnel

This study examines the hypothesis that recombinant human bone morphogenetic protein-2 can enhance bone ingrowth into a tendon graft placed into a bone tunnel. We transplanted the long digital extensor tendon into a drill hole in the proximal tibia in 65 adult mongrel dogs. We applied two different doses of the bone morphogenetic protein to the tendon-bone interface in one limb using an absorbable type I collagen sponge carrier and only the collagen sponge to the contralateral (control) limb. The healed tendon-bone attachment was evaluated at serial times between 3 days and 8 weeks using radiography, histologic examination, and biomechanical testing. At all time points, histologic and radiographic examination demonstrated more extensive bone formation around the tendon with closer apposition of new bone to the tendon in the protein-treated limb than in the paired control limb. Biomechanical testing demonstrated higher tendon pull-out strength in the protein-treated side at all time points, with a statistically significant difference between the low-dose-treated side and the control side at 2 weeks. The histologic and biomechanical data suggested superior healing at the lower protein dose. This study demonstrated that bone morphogenetic protein can accelerate the healing process when a tendon graft is transplanted into a bone tunnel.

Biomechanical evaluation of a simulated Bankart lesion.

The purpose of this study was to determine the effect of sectioning of the anterior part of the inferior glenohumeral ligament (a simulated Bankart lesion) on load-induced multidirectional glenohumeral motion. Nine fresh, intact cadaveric shoulders were tested on a special apparatus that constrained three rotations but allowed simultaneous measurement of anterior-posterior, superior-inferior, and medial-lateral translation. Coupled anterior-posterior and superior-posterior translations were recorded while anterior, posterior, superior, and inferior forces of fifty newtons were applied sequentially. Testing was done in three positions of humeral elevation in the scapular plane, in three positions of humeral rotation, and with an externally applied joint-compression load of twenty-two newtons. A liquid-metal strain-gauge was placed on the posterior band of the inferior glenohumeral ligament to assess concomitant posterior capsular strain during the various test conditions. All shoulders were tested intact and again after the inferior glenohumeral ligament and the labrum had been detached from the glenoid from just superior to the anterior band of the inferior glenohumeral ligament to a point just posterior to the infraglenoid tubercle. The simulated Bankart lesion resulted in selected increases in anterior translation at all positions of elevation, in posterior translation at 90 degrees of elevation, and in inferior translation at all positions of elevation. However, these increases were very small; the maximum mean increase in translation seen over-all was only 3.4 millimeters, which occurred during inferior translation at 45 degrees of elevation.(ABSTRACT TRUNCATED AT 250 WORDS)

The Role of the Cruciate and Posterolateral Ligaments in Stability of the Knee A Biomechanical Study

The role of the posterolateral and cruciate ligaments in restraining knee motion was studied in 11 human ca daveric knees. The posterolateral ligaments sectioned included the lateral collateral and arcuate ligaments, the popliteofibular ligament, and the popliteal tendon at tachment to the tibia. Combined sectioning of the an terior cruciate and posterolateral ligaments resulted in maximal increases in primary anterior and posterior translations at 30° of knee flexion. Primary varus, pri mary internal, and coupled external rotation also in creased and were maximal at 30° of knee flexion. Com bined sectioning of the posterior cruciate and posterolateral ligaments resulted in increased primary posterior translation, primary varus and external rota tion, and coupled external rotation at all angles of knee flexion. Examination of the knee at 30° and 90° of knee flexion can discriminate between combined posterior cruciate ligament and posterolateral injury and isolated posterolateral injury. The standard external rotation test performed at 30° of knee flexion may not be routinely reliable for detecting combined anterior cruciate and posterolateral ligament injury. However, measurements of primary anterior-posterior translation, primary varus rotation, and coupled external rotation may be used to detect combined anterior cruciate and posterolateral ligament injury.

Biomechanical evaluation of the medial collateral ligament of the elbow

Anatomical dissection and biomechanical testing were used to study twenty-eight cadaveric elbows in order to determine the role of the medial collateral ligament under valgus loading. The medial collateral ligament was composed of anterior, posterior, and occasionally transverse bundles. The anterior bundle was, in turn, composed of anterior and posterior bands that tightened in reciprocal fashion as the elbow was flexed and extended. Sequential cutting of the ligament was performed while rotation caused by valgus torque was measured. The anterior band of the anterior bundle was the primary restraint to valgus rotation at 30, 60, and 90 degrees of flexion and was a co-primary restraint at 120 degrees of flexion. The posterior band of the anterior bundle was a co-primary restraint at 120 degrees of flexion and a secondary restraint at 30 and 90 degrees of flexion. The posterior bundle was a secondary restraint at 30 degrees only. The reciprocal anterior and posterior bands have distinct biomechanical roles and theoretically may be injured separately. The anterior band was more vulnerable to valgus overload when the elbow was extended, whereas the posterior band was more vulnerable when the elbow was flexed. The posterior bundle was not vulnerable to valgus overload unless the anterior bundle was completely disrupted. The intact elbows rotated a mean of 3.6 degrees between the neutral position and the two-newton-meter valgus torque position. Cutting of the entire anterior bundle caused an additional 3.2 degrees of rotation at 90 degrees of flexion, where the effect was greatest. CLINICAL RELEVANCE: Physical findings in a patient who has an injury of the anterior bundle may be subtle, and an examination should be performed with the elbow in 90 degrees of flexion for greatest sensitivity. As the anterior bundle is the major restraint to valgus rotation, reconstructive procedures should focus on anatomical reproduction of that structure. Parallel limbs of tendon graft placed from the inferior aspect of the medial epicondyle to the area of the sublimis tubercle will simulate the reciprocal bands of the anterior bundle. Temporary immobilization with the elbow in flexion may relax the critically important anterior band of the reconstruction during healing.

The strength of the central third patellar. tendon graft A biomechanical study

Thirty-seven bone-patellar tendon-bone composite grafts from the knees of 21 human cadavers were tested to failure. Average donor age was 28 years. The composites were divided into 4 groups: 3 groups with 10 grafts (5 pairs) and 1 group with 7 grafts from 6 donors. In Group 1 we tested 10- versus 15-mm wide grafts that were used without twisting; Group II, 10- mm wide grafts without twisting versus 10-mm wide grafts that were twisted 90°; Group III, 10-mm wide grafts twisted 90° versus 10-mm wide grafts twisted 180°; and Group IV, 10- versus 7-mm wide grafts that were not twisted. The tests were performed using a newly described potting technique and clamp system and a servohydraulic testing machine with an elongation rate of 5 cm/sec. The results of this study suggest that the central third of the patellar tendon is stronger than previously re ported. The mean ultimate load of a 15-mm bone- patellar tendon-bone composite was 4389 N (±708); of the 10-mm wide composites, 2977 N (±516); and of the 7-mm composites, 2238 N (±316). Twisting the graft 90° increased the strength (P < 0.05). Further twisting to 180° had no significant effect compared with twisting 90°. This study supports the practice of using smaller (10 mm) bone-patellar tendon-bone grafts to avoid the potential complications of patellar fracture and graft impingement in the notch.

The Popliteofibular Ligament Rediscovery of a Key Element in Posterolateral Stability

We have recently become aware of a strong direct attachment of the popliteal tendon to the fibula. To investigate the importance of this attachment, we ex amined 20 cadaveric knees. The popliteofibular liga ment was identified in all 20 knees. The cross-sectional area of the popliteofibular ligament was 6.9 ± 2.1 mm 2, compared with 7.2 ± 2.7 mm2 for the lateral collateral ligament. Biomechanical testing of these structures, simulating a purely varus stress on the knee, revealed that the lateral collateral ligament always failed first, followed by the popliteofibular ligament, and then the muscle belly of the popliteus. The mean maximal force to failure of the popliteofibular ligament approached 425 N (range, 204 to 778), compared with 750 N (range, 317 to 1203) for the lateral collateral ligament. Our results indicate that the popliteofibular ligament contributes to posterolateral stability.

Effect of lesions of the superior portion of the glenoid labrum on glenohumeral translation.

Lesions of the superior portion of the glenoid labrum were created in seven cadaveric shoulders. The shoulders were mounted on a special apparatus attached to a servocontrolled hydraulic materials-testing device. Sequential fifty-newton anterior, posterior, superior, and inferior forces and a twenty-two-newton joint compressive load were applied to the shoulders. In addition, a fifty-five-newton force was applied to the tendon of the long head of the biceps brachii. The shoulders were tested in seven positions of glenohumeral elevation and rotation. An isolated lesion of the anterosuperior portion of the labrum, which did not involve the supraglenoid insertion of the biceps brachii, had no significant effect on anteroposterior or superoinferior glenohumeral translation, either with or without application of the fifty-five-newton force to the biceps brachii tendon. In contrast, a complete lesion of the superior portion of the labrum that destabilized the insertion of the biceps resulted in significant increases in anteroposterior and superoinferior glenohumeral translations. At 45 degrees of glenohumeral elevation, the complete lesion led to a 6.0-millimeter increase in anterior translation when the arm was in neutral rotation and to a 6.3-millimeter increase when the arm was in internal rotation; inferior translation also increased, by 1.9 to 2.5 millimeters. The increases in translation persisted despite application of a fifty-five-newton force to the long head of the biceps.

Thermal modification of collagen

Shoulder capsular shrinkage has recently been proposed as a therapeutic modality in a select group of patients with instability. Basic science research studying the mechanism of collagen shrinkage and the effect of shrinkage on the tissues mechanical properties is essential to define the ideal process by which to achieve optimal tissue shrinkage. Tissue shrinkage is a function of both time and temperature. This relationship was studied, and a model was derived to describe the relationship mathematically. Tissue shrinkage rate was extremely sensitive to temperature changes. The purpose of this study, was to shrink collagenous tissue thermally and then to measure the mechanical property changes as a function of tissue shrinkage. Uniaxial tensile testing of normal and heat-shrunken bovine tendon was carried out, and a model was developed to express the relationship between shrinkage and mechanical properties. We found that the mechanical properties decreased with increasing shrinkage, and that the maximal allowable shrinkage before significant material property changes occurred was between 15% to 20%. Ultrastructural analysis with transmission electron microscopy showed denaturation of the collagen fibrillar structure and provided direct support for the observed material changes.

Bone Marrow–Derived Mesenchymal Stem Cells Transduced With Scleraxis Improve Rotator Cuff Healing in a Rat Model

Background: Rotator cuffs heal through a scar tissue interface after repair that makes them prone to failure. Scleraxis (Scx) is a basic helix-loop-helix transcription factor that is thought to direct tendon development during embryogenesis. The purpose of this study was to determine if the application of mesenchymal stem cells (MSCs) transduced with adenoviral-mediated scleraxis (Ad-Scx) could improve regeneration of the tendon-bone insertion site in a rat rotator cuff repair model. Hypothesis: Bone marrow–derived cells transduced with Scx would improve the structure of the healing tendon-bone interface and result in increased tendon attachment strength. Study Design: Controlled laboratory study. Methods: Sixty Lewis rats underwent unilateral detachment and repair of the supraspinatus tendon. Thirty animals received MSCs in a fibrin glue carrier, and 30 received Ad-Scx-transduced MSCs. Animals were sacrificed at 2 weeks and 4 weeks and evaluated for the presence of fibrocartilage and collagen fiber organization at the insertion. Biomechanical testing was performed to determine the structural and material properties of the repaired tissue. Statistical analysis was performed with a Wilcoxon rank sum test with significance set at P = .05. Results: There were no differences between the Scx and MSC groups in terms of histologic appearance at 2 weeks. However, the Scx group had higher ultimate stress-to-failure (2.6 ± 0.9 vs 1.7 ± 0.3 MPa; P = .03) and stiffness (8.4 ± 2.9 vs 5.0 ± 1.9 N/mm; P = .01) compared with the MSC group. At 4 weeks, the Scx group had more fibrocartilage (728.7 ± 50.4 vs 342.6 ± 217.0 mm2; P = .04), higher ultimate load to failure (26.7 ± 4.6 vs 20.8 ± 4.4 N; P = .01), higher ultimate stress to failure (4.7 ± 1.3 vs 3.5 ± 1.0 MPa; P < .04), and higher stiffness values (15.3 ± 3.4 vs 9.3 ± 2.2 N/mm; P < .001) as compared with the MSC group. Conclusion: Mesenchymal stem cells genetically modified with Scx can augment rotator cuff healing at early time points. Clinical Relevance: Biologic augmentation of acutely injured rotator cuffs with Scx-transduced MSCs may improve rotator cuff tendon healing and reduce the incidence of re-tears. However, further studies are needed to determine if this remains safe and effective in larger models.