A biomechanical analysis of the soft tissue and osseous constraints of the hip joint.

PURPOSE: The goal of this study was to determine the role of soft tissue and osseous constraints in hip biomechanics using a unique robotic testing apparatus. METHODS: Four fresh-frozen human cadaveric hemi-pelvises without degenerative changes or dysplasia were stripped of all soft tissue except the ligamentous capsule and the intra-articular structures. All hips were tested using a robotic manipulator/universal force-moment sensor testing system to measure and compare end-range of motion (ROM) and kinematic translations in "capsule vented" (a small hole in the capsule) and "capsule separated" (capsular ligaments separated from each other) states. Then, the "capsule vented" state was compared to the condition in which the capsule and labrum were removed to calculate bone and soft tissue forces with 40 N of load applied in six different directions along three axes. RESULTS: There were no significant differences in end-ROM or kinematic translations between the "capsule vented" and "capsule separated" states. Bone forces significantly increased with loads applied in the anterior, posterior and superior directions. Soft tissue forces increased significantly with loads applied in the medial, lateral and inferior directions. CONCLUSION: The individual hip capsular ligaments act independently of each other to resist end-ROM. Both osseous and soft tissue constraints are important to hip biomechanics depending upon the direction of applied force. The clinical relevance is that surgical management for hip disorders should preserve the soft tissue constraints in the hip when possible to maintain normal hip biomechanics.

Modes of failure of knotted and knotless suture anchors in an arthroscopic bankart repair model with the capsulolabral tissues intact.

The purpose of this study was to assess failure modes of knotless and knotted anchors in a Bankart repair model with the capsulolabral soft tissues intact. Previous reports used a model stripped of soft tissues. In 8 matched pairs of cadaver shoulders, a Bankart lesion was repaired arthroscopically using either 2 Bio-SutureTak anchors (Arthrex, Naples, Florida) or 2 Bioknotless anchors (Mitek, Westwood, Massachusetts). The shoulders were mounted with the repaired capsulolabral tissues attached to a custom sinusoidal clamp, and were tested in cyclic loading (20-80 N, 100 cycles, 0.5 mm/s) and then load to failure (1.25 mm/s). Cut-through at the suture-tissue interface (23/32 anchors) was more common than pullout at the anchor-bone interface (9/32) as a mode of failure (P = .02). Failure at the suture-tissue interface occurred in 10/16 knotted and 13/16 knotless anchors. Mean (SD) ultimate load of knotted vs knotless anchors was 125.3 (67.4) N and 96.9 (95.1) N, respectively. Mean (SD) stiffness of knotted vs knotless anchors was 20.9 (6.4) N/mm and 19.8 (8.6)N/mm, respectively. We concluded that both knotted and knotless anchors fail most often at the suture-tissue interface. The tested model with the capsulolabral tissues intact is distinct from previous models, which tested the anchor-bone interface only.

Biomechanical evaluation of 2 arthroscopic biceps tenodeses: double-anchor versus percutaneous intra-articular transtendon (PITT) techniques.

BACKGROUND: Recently, there is increasing interest in different arthroscopic biceps tenodesis techniques. However, little data have been published about the biomechanical properties of soft tissue tenodesis. PURPOSE: This study was undertaken to evaluate the biomechanical properties of 2 different arthroscopic biceps tenodeses: the percutaneous intra-articular transtendon (PITT) technique and the suture-anchor technique. STUDY DESIGN: Controlled laboratory study. METHODS: Fifteen fresh-frozen cadaveric specimens were randomly allocated to the 2 different biceps tenodesis techniques. The humerus with biceps tenodesis was mounted on a materials testing machine to perform a load to failure test. The structural properties including ultimate load (N) and stiffness (N/mm) were derived from the load-displacement curve. The mode of failure was also recorded. Ultimate load and stiffness were compared with the parametric Student t test. RESULTS: Both repairs showed typical load-displacement curves followed by a constant increase in load and displacement until failure occurred. Suture-anchor and PITT techniques had ultimate loads of 175.4 +/- 40.4 N and 142.7 +/- 30.9 N (P = .10) and stiffness of 15.9 +/- 8.4 N/mm and 13.3 +/- 3 N/mm (P = .36), respectively, with no significant differences between them. All of the surgical constructs failed in the tendon site by pulling out with the sutures through the substance of the tendon. CONCLUSION: The suture-anchor and PITT techniques exhibited satisfactory initial strength with no statistical difference between the 2 groups. These findings, along with the consistent pullout of the suture through the tendon during failure, suggest that the most important factor for initial strength is not the attachment site but the quality of the biceps tendon. CLINICAL RELEVANCE: The quality of the tendon should be taken into account when deciding the surgical technique and the rehabilitation program. The PITT technique has the benefit of avoiding hardware complications and cost.

Interference screw versus suture anchor fixation for subpectoral tenodesis of the proximal biceps tendon: a cadaveric study.

PURPOSE: The purpose of this study was to compare the biomechanical properties of 2 fixation methods for subpectoral proximal biceps tenodesis. METHODS: In 9 matched pairs of cadaveric shoulders, an open subpectoral tenodesis was performed 1 cm proximal to the inferior border of the pectoralis major tendon by use of either an 8 x 12-mm Bio-Tenodesis screw (Arthrex, Naples, FL) with No. 2 FiberWire sutures (Arthrex) or a 5.5-mm Bio-Corkscrew double-loaded suture anchor (Arthrex) with No. 2 FiberWire sutures. The specimens were dissected and mounted in a material testing machine. Cyclic loading (20 to 60 N, 100 cycles, 0.5 mm/s, 5-N preload) was performed, followed by an unloaded 30-minute rest, a 5-N preload, and a load-to-failure protocol (1.25 mm/s) with a 100-lb load cell. Ultimate load (in Newtons), stiffness (in Newtons per millimeter), and modes of failure were recorded. Data were analyzed by use of paired t tests and Wilcoxon signed rank tests. RESULTS: Proximal biceps tenodeses with Bio-Tenodesis screws had a significantly higher mean load to failure (169.6 +/- 50.5 N; range, 99.6 to 244.7 N) than those with Bio-Corkscrew suture anchors (68.5 +/- 33.0 N; range, 24.2 to 119.4 N) (P = .002). Bio-Tenodesis screws also had a significantly higher stiffness (34.1 +/- 9.0 N/mm; range, 20.6 to 48.9 N/mm) than Bio-Corkscrews (19.3 +/- 10.5; range, 5.9 to 32.9 N/mm) (P = .038). CONCLUSIONS: In this cadaveric study the Bio-Tenodesis screw showed a statistically significantly higher load to failure and significantly higher stiffness than the Bio-Corkscrew anchor when used for tenodesis of the proximal biceps tendon in a subpectoral location. CLINICAL RELEVANCE: Biomechanical comparison of these 2 fixation techniques provides information on stiffness and load to failure of alternate fixation methods.

Computer-assisted evaluation of kinematics of the two bundles of the anterior cruciate ligament.

The aim of this cadaveric study was to describe the kinematics of the anterior cruciate ligament (ACL)-intact, posterolateral (PL) bundle-deficient and ACL-deficient knee by applying a protocol for computer-assisted evaluation of knee kinematics. The hypothesis that the PL bundle functions mainly at low knee flexion angles was tested. An optical tracking system was used to acquire knee joint motion on 10 knees during clinical evaluations by tracking markers rigidly attached to the bones. The protocol included acquisition of anterior-posterior (AP) translations and internal-external (IE) rotations, and evaluation of three clinical knee laxity tests (anterior drawer, manual and instrumented Lachman). The data demonstrated no significant contribution to AP translation and IE laxity from the PL bundle over the entire range of motion. The clinical knee laxity tests showed no significant differences between the ACL-intact and PL bundle-deficient states. The hypothesis could not be proven. Current clinical knee laxity measurements may not be suited for detecting subtle changes such as PL bundle deficiency in the ACL anatomy. The computation of knee laxity might be a step towards a more precise kinematic test of knee stability not only in the native and torn ACL state of the knee but also in the reconstructed knee.

Computer evaluation of kinematics of anterior cruciate ligament reconstructions.

Current clinical and instrumented outcome measurements of knee instability lack accuracy, especially when multiplanar instability is considered. The aim of our cadaveric study was to describe the kinematics in the intact, double bundle, and anteromedial bundle reconstructed anterior cruciate ligament knee by applying a protocol for computer-assisted evaluation of knee kinematics. An optical navigation system was used to acquire knee motion (n = 5) during clinical evaluations by tracking markers rigidly attached to the bones. The protocol included acquisition of anteroposterior translations and internal-external rotations and evaluation of three clinical knee laxity tests (anterior drawer, manual, and instrumented Lachman). Our anteroposterior translation data showed the double-bundle technique and anteromedial bundle technique could restore anteroposterior stability comparable to the intact state. For internal-external laxity, the double-bundle technique demonstrated overcorrection at 15 degrees, 60 degrees, 75 degrees, and 90 degrees. The anterior drawer and manual Lachman knee laxity tests showed improved stability for the double-bundle compared to the anteromedial bundle technique. This pilot study suggests the computation of knee laxity with a high precision method might be a step toward a more precise kinematic test of knee stability for evaluating different reconstruction methods.

Development of a simple device for measurement of rotational knee laxity.

The goal of this study was to develop a new device for the measurement of rotational knee laxity and to measure intra-observer and inter-observer reliability in a cadaveric study. An array of established tools was utilized to design the device with a basis that consists of an Aircast Foam Walkertrade mark boot. A load cell was attached to the boot with a handle bar for application of moments about the knee. An electromagnetic tracking system was used to record the motion of the tibia with respect to the femur. The total arc of motion ranged from 23 degrees at full extension to 46 degrees at 90 degrees of knee flexion. The intra-tester ICCs ranged from 0.94 to 0.99. The ICC for inter-tester reliability ranged from 0.95 to 0.99. In summary, the new device for measurement of rotational knee laxity is simple, reliable, and can be used in a non-invasive fashion in the office or surgical suite document clinical outcome in terms of rotational knee laxity.

Biomechanical rationale for development of anatomical reconstructions of coracoclavicular ligaments after complete acromioclavicular joint dislocations.

BACKGROUND: Surgical treatments of complete acromioclavicular joint dislocations replace or reconstruct the coracoclavicular ligaments with a single structure and do not account for the anatomical variance of each ligament in the design. PURPOSE: To evaluate the cyclic behavior and structural properties of an anatomic tendon reconstruction of the coracoclavicular ligament complex after a simulated acromioclavicular joint dislocation. STUDY DESIGN: Controlled laboratory study. METHODS: Cyclic loading followed by a load-to-failure protocol (simulated dislocation) of the normal coracoclavicular ligament complex was performed and repeated after an anatomic reconstruction on the same specimen (n = 9). The anatomical reconstruction consisted of a semitendinosus tendon that replicated the direction and orientation of both the trapezoid and conoid ligaments. RESULTS: The coracoclavicular ligament and anatomical reconstruction complexes had clinically insignificant (<3 mm) permanent elongation after cyclic loading. The stiffness and ultimate load of the coracoclavicular ligament complex (60.8 +/- 12.2 N/mm and 560 +/- 206 N) were significantly greater than for the anatomical reconstruction complex (23.4 +/- 5.2 N/mm and 406 +/- 60 N), respectively (P < .05). Further analysis of the complexes revealed a 40% decrease in the bending stiffness of the clavicle after the simulated dislocation and failure of the normal coracoclavicular ligament complex (P < .05), which contributed to the diminished properties of the anatomic reconstruction. CONCLUSIONS: The low level of permanent elongation after cyclic loading suggests that the anatomic reconstruction complex could withstand early rehabilitation; however, the decrease in the structural properties and stiffness of the clavicle should be considered in optimizing the anatomic reconstruction technique. CLINICAL RELEVANCE: Despite the differences compared to the normal coracoclavicular ligament complex, the anatomical reconstruction complex more closely approximates the stiffness of the coracoclavicular ligament complex than current surgical constructs, and the incorporation of biological tissue could improve the overall structural properties with healing.

Biomechanical function of surgical procedures for acromioclavicular joint dislocations.

PURPOSE: Surgical procedures for treatment of acromioclavicular (AC) joint dislocation replace the coracoclavicular (CC) ligaments to minimize motion, allow scarring, and increase the subsequent stability of the joint. The purpose of this study was to evaluate the biomechanical function of the surgically repaired or reconstructed (CC Sling, Rockwood Screw [DePuy Orthopaedics, Warsaw, IN], and Coracoacromial [CA] Ligament Transfer Construct) AC joint after AC joint dislocation. TYPE OF STUDY: A cadaver study using a convenience sample. METHODS: Twelve cadaveric shoulders were tested using a robotic/UFS testing system. Three external loading conditions (anterior, posterior, or superior load of 70 N) were applied to intact and surgically repaired or reconstructed AC joint. The resulting kinematics of the AC joint and in situ forces in the CC ligaments or surgical constructs was determined. RESULTS: For the CC Sling, anterior and posterior translation significantly increased by 110% and 330% in response to an anterior and posterior load, respectively. However, the posterior translation for the Rockwood Screw significantly decreased by 60%. Anterior, posterior, and superior translation for the CA Ligament Transfer Construct significantly increased by 110%, 360%, and 100%, respectively. The coupled translations also significantly increased for the CC Sling and CA Ligament Transfer Construct in response to all loading conditions. In contrast, the coupled translations for the Rockwood Screw tended to decrease. Furthermore, the in situ forces increased significantly for all 3 surgical constructs compared with the intact CC Ligaments in response to an anterior and posterior load. CONCLUSIONS: At time zero, increases in the primary and coupled motion for the CC Sling and CA Ligament Transfer Construct could comprise the initial healing period prescribed for AC joint dislocation. Our findings also suggest that the Rockwood Screw provides a highly rigid fixation and may explain the complications frequently seen in clinical practice. CLINICAL RELEVANCE: Current surgical procedures do not have the appropriate stiffness to restore the stability of the intact joint before healing. Therefore, our results may lead to the design and development of new repairs, reconstructions, and rehabilitation protocols for AC joint dislocation.

Viscoelastic behavior and structural properties of the coracoclavicular ligaments.

During contact sports such as football, hockey or rugby, the coracoclavicular ligaments are commonly ruptured. Currently, the limited biomechanical data on the properties and function of these ligaments have led to debate on the "gold standard" treatment for these injuries. Therefore, the objective of this study was to characterize the geometry, viscoelastic behavior and structural properties of the coracoclavicular ligaments (n=11). The trapezoid and conoid were found to have similar length (9.6+/-4.4 vs. 11.2+/-4.1 mm) and cross-sectional area (103+/-43 vs. 69+/-51 mm2), respectively (P>0.05). Static and cyclic stress relaxation tests were then performed, followed by uniaxial tensile testing with the insertions of each ligament aligned to ensure a uniform distribution of load across the fibers. No significant differences were observed for the trapezoid and conoid during the static (36+/-8% vs. 31+/-7%) and cyclic (23+/-12% vs. 16+/-6%) stress relaxation tests, respectively (P>0.05). Similarly, no statistically significant differences were found between the trapezoid and conoid for linear stiffness (83+/-40 vs. 70+/-23 N mm(-1)), ultimate load (312+/-133 vs. 266+/- 108 N), energy absorbed at failure (820+/-576 vs. 752+/- 410 N mm), percent elongation (74+/-47% vs. 62+/-22%) and elongation at failure (5.8+/-2.2 vs. 6.1+/-1.6 mm), respectively (P>0.05). A comparison of our data to previous studies suggests that the complex fiber orientation of these ligaments has a significant role in determining the maximum load that can be transferred between the clavicle and scapula by each bone-ligament-bone complex. Our findings also further confirm the functional role of the coracoclavicular ligaments in supporting the upper extremity, and provide data for reconstruction and rehabilitation protocols as well as computational models.

Joint compression alters the kinematics and loading patterns of the intact and capsule-transected AC joint.

High compressive loads are transmitted through the shoulder across the acromioclavicular (AC) joint to the axial skeleton during activities of daily living and can lead to early joint degeneration or instability. The objective of this study was to quantify the effect of joint compression on the biomechanics of the intact and capsule-transected AC joint during application of three loading conditions. A robotic/universal force-moment sensor testing system was utilized to apply an anterior, posterior or superior load of 70 N in combination with 10 or 70 N of joint compression to fresh-frozen cadaveric shoulders (n=12). The application of joint compression to the intact AC joint decreased the posterior translation in response to a posterior load (-6.6+/-2.5 vs -3.7+/-1.0 mm, p<0.05). Joint compression also decreased the in situ force in the superior AC capsule by 10 N while increasing the joint contact force by 20 N for all loading conditions (p<0.05). The application of joint compression to the capsule-transected AC joint significantly decreased the amount of posterior and superior translation during posterior (-12.7+/-6.1 vs -5.5+/-3.2 mm, p<0.05) and superior (5.3+/-2.9 vs 4.2+/-2.3 mm, p<0.05) loading, respectively, while significantly increasing the coupled translations (anterior-posterior, superior-inferior or proximal-distal) in all loading conditions (p<0.05). The joint contact force also significantly increased by 20 N for all loading conditions (p<0.05). This quantitative data suggests: (1) common surgical techniques such as distal clavicle resection, which initially reduce painful joint contact, may cause unusually high loads to be supported by the soft tissue structures at the AC joint; and (2) compressive loads transmitted across a capsule-transected AC joint could be concentrated over a smaller area due to the increased coupled motion and joint contact force.