Richard E. Debski

Biomechanical Analysis of an Anatomic Anterior Cruciate Ligament Reconstruction

Background: The focus of most anterior cruciate ligament reconstructions has been on replacing the anteromedial bundle and not the posterolateral bundle. Hypothesis: Anatomic two-bundle reconstruction restores knee kinematics more closely to normal than does single-bundle reconstruction. Study Design: Controlled laboratory study. Methods: Ten cadaveric knees were subjected to external loading conditions: 1) a 134-N anterior tibial load and 2) a combined rotatory load of 5-N·m internal tibial torque and 10-N·m valgus torque. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for 1) intact, 2) anterior cruciate ligament deficient, 3) single-bundle reconstructed, and 4) anatomically reconstructed knees. Results: Anterior tibial translation for the anatomic reconstruction was significantly closer to that of the intact knee than was the single-bundle reconstruction. The in situ force normalized to the intact anterior cruciate ligament for the anatomic reconstruction was 97% ± 9%, whereas the single-bundle reconstruction was only 89% ± 13%. With a combined rotatory load, the normalized in situ force for the single-bundle and anatomic reconstructions at 30° of flexion was 66% ± 40% and 91% ± 35%, respectively. Conclusions: Anatomic reconstruction may produce a better biomechanical outcome, especially during rotatory loads. Clinical Relevance: Results may lead to the use of a two-bundle technique.

Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads

The anterior cruciate ligament (ACL) can be anatomically divided into anteromedial (AM) and posterolateral (PL) bundles. Current ACL reconstruction techniques focus primarily on reproducing the AM bundle, but are insufficient in response to rotatory loads. The objective of this study was to determine the distribution of in situ force between the two bundles when the knee is subjected to anterior tibial and rotatory loads. Ten cadaveric knees (50 ± 10 years) were tested using a robotic/universal forcemoment sensor (UFS) testing system. Two external loading conditions were applied: a 134 N anterior tibial load at full knee extension and 15°, 30°, 60°, and 90° of flexion and a combined rotatory load of 10 N m valgus and 5 N m internal tibial torque at 15° and 30° of flexion. The resulting 6 degrees of freedom kinematics of the knee and the in situ forces in the ACL and its two bundles were determined. Under an anterior tibial load, the in situ force in the PL bundle was the highest at full extension (67 ± 30 N) and decreased with increasing flexion. The in situ force in the AM bundle was lower than in the PL bundle at full extension, but increased with increasing flexion, reaching a maximum (90 ± 17 N) at 60° of flexion and then decreasing at 90°. Under a combined rotatory load, the in situ force of the PL bundle was higher at 15° (21 ± 11 N) and lower at 30° of flexion (14 ± 6 N). The in situ force in the AM bundle was similar at 15° and 30° of knee flexion (30 ± 15 vs. 35 ± 16 N, respectively). Comparing these two external loading conditions demonstrated the importance of the PL bundle, especially when the knee is near full extension. These findings provide a better understanding of the function of the two bundles of the ACL and could serve as a basis for future considerations of surgical reconstruction in the replacement of the ACL.

Knee stability and graft function after anterior cruciate ligament reconstruction: a comparison of a lateral and an anatomical femoral tunnel placement.

Background Locations of femoral tunnels for anterior cruciate ligament replacement grafts remain a subject of debate. Hypothesis A lateral femoral tunnel placed at the insertion of the posterolateral bundle of the anterior cruciate ligament can restore knee function comparably to anatomical femoral tunnel placement. Study Design Controlled laboratory study. Methods Ten cadaveric knees were subjected to the following external loading conditions: (1) a 134-N anterior tibial load and (2) combined rotatory loads of 10-N.m valgus and 5-N.m internal tibial torques. Data on resulting knee kinematics and in situ force of the intact anterior cruciate ligament and anterior cruciate ligament graft were collected using a robotic/universal force-moment sensor testing system for (1) intact, (2) anterior cruciate ligament-deficient, (3) anatomical double-bundle reconstructed, and (4) laterally placed single-bundle reconstructed knees. Results In response to anterior tibial load, anterior tibial translation and in situ force in the graft were not significantly different between the 2 reconstructions except at high knee flexion. For example, at 90° of knee flexion, anterior tibial translation was 6.1 ± 2.3 mm for anatomical double-bundle reconstruction and 7.6 ± 2.6 mm for laterally placed single-bundle reconstruction (P < .05). In response to rotatory loads, there were no significant differences between the 2 reconstruction procedures (4.8 ± 2.4 mm vs 4.8 ± 3.0 mm in anterior tibial translation at 15° of knee flexion, P > .05). Conclusion Lateral tunnel placement can restore rotatory and anterior knee stability similarly to an anatomical reconstruction when the knee is near extension. However, the same is not true when the knee is at high flexion angles. Clinical Relevance To reproduce the complex function of the anterior cruciate ligament, reproducing both bundles of the anterior cruciate ligament may be necessary.

Varying Femoral Tunnels Between the Anatomical Footprint and Isometric Positions Effect on Kinematics of the Anterior Cruciate Ligament–Reconstructed Knee

Background Knee kinematics and in situ forces resulting from anterior cruciate ligament reconstructions with 2 femoral tunnel positions were evaluated. Hypothesis A graft placed inside the anatomical footprint of the anterior cruciate ligament will restore knee function better than a graft placed at a position for best graft isometry. Study Design Controlled laboratory study. Methods Ten cadaveric knees were tested in response to a 134-N anterior load and a combined 10-N·m valgus and 5-N·m internal rotation load. A robotic universal force-moment sensor testing system was used to apply loads, and resulting kinematics were recorded. An active surgical robot system was used for positioning tunnels in 2 locations in the femoral notch: inside the anatomical footprint of the anterior cruciate ligament and a position for best graft isometry. The same quadrupled hamstring tendon graft was used for both tunnel positions. The 2 loading conditions were applied. Results At 30° of knee flexion, anterior tibial translation in response to the anterior load for the intact knee was 9.8 ± 3.1 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 13.8 ± 4.6 mm; position 2: 16.6 ± 3.7 mm; P <. 05). There was a significant difference between the 2 tunnel positions. At the same flexion angle, the anterior tibial translation in response to the combined load for the intact knee was 7.7 ± 4.0 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 10.4 ± 5.5 mm; position 2: 12.0 ± 5.2 mm; P <. 05), with a significant difference between the tunnel positions. Conclusion Neither femoral tunnel position restores normal kinematics of the intact knee. A femoral tunnel position inside the anatomical footprint of the anterior cruciate ligament results in knee kinematics closer to the intact knee than does a tunnel position located for best graft isometry. Clinical Relevance Anatomical femoral tunnel position is important in reproducing function of the anterior cruciate ligament.

Biomechanics of Knee Ligaments

Significant advances have been made during the past 25 years in characterizing the properties of ligaments as a tissue and as an individual component in the bone-ligament-bone complex. The contribution of ligaments to joint function have also been well characterized. We have presented many studies that sought to characterize the tensile and viscoelastic properties of ligaments. As a result of these investigations, some of the most important experimental and biologic factors affecting the measurements of these properties have been identified and elucidated. The identification of the tensile properties of normal ligaments can serve as the basis for evaluating their success in healing and repair after injury. Furthermore, characterization of normal ligament function is crucial for diagnosing joint injuries as well as for evaluating reconstruction strategies and developing rehabilitation protocols. The recent introduction of robotic technology to the study of joint kinematics has resulted in significant advances in the understanding of the relative importance of ligaments to joint function. With the more accurate simulation of joint kinematics that include multiple degrees of freedom motion, data on the in situ forces in ligaments can be used to improve the treatment of ligament repair and reconstruction. More complex external loading conditions that mimic sports activities and rehabilitation protocols can also be introduced in the future. Furthermore, this technology can be extended to study other frequently injured joints, such as the shoulder.

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.

Effect of Capsular Injury on Acromioclavicular Joint Mechanics

Background: Traumatic disruption of the acromioclavicular joint capsule is associated with pain and instability after the injury and may lead to degenerative joint disease. The objective of this study was to quantify the effect of transection of the acromioclavicular joint capsule on the kinematics and the in situ forces in the coracoclavicular ligaments in response to external loading conditions. Methods: Eleven fresh-frozen human cadaveric shoulders were tested with use of a robotic/universal force-moment sensor testing system. The shoulders were subjected to three loading conditions (an anterior, posterior, and superior load of 70 N) in their intact state and after transection of the acromioclavicular joint capsule. Results: Transection of the capsule resulted in a significant (p < 0.05) increase in anterior translation (6.4 mm) and posterior translation (3.6 mm) but not in superior translation (1.6 mm). The effect of capsule transection on the forces in the coracoclavicular ligaments was also significant (p < 0.05) in response to anterior and posterior loading but not in response to superior loading. However, differences were found between the forces in the trapezoid and conoid ligaments. Under an anterior load, the mean in situ force (and standard deviation) in the trapezoid increased from 14 ± 14 N to 25 ± 19 N, while the mean force in the conoid increased from 15 ± 14 N to 49 ± 23 N, or 227%. In contrast, in response to a posterior load, the mean in situ force in the trapezoid increased from 23 ± 15 N to 38 ± 23 N, or 66% (p < 0.05), while the mean force in the conoid increased only 9%. Conclusions and Clinical Relevance: The large differences in the change of force in the conoid and trapezoid ligaments suggest that these ligaments should not be considered as one structure when surgical treatment is considered. Furthermore, transection of the capsule resulted in a shift of load to the coracoclavicular ligaments, which may render the intact coracoclavicular ligaments more likely to fail with anterior or posterior loading. The results of the present study also suggest that the intact coracoclavicular ligaments cannot compensate for the loss of capsular function during anterior-posterior loading as occurs in type-II acromioclavicular joint injuries.

Functional Evaluation of the Ligaments at the Acromioclavicular Joint during Anteroposterior and Superoinferior Translation

We examined the anatomy and measured the in situ force in ligaments at the acromioclavicular joint using a universal force-moment sensor. The in situ force in the coracoacromial, conoid, trapezoid, superior acromio clavicular capsular, and inferior acromioclavicular cap sular ligaments of 10 fresh-frozen cadaveric shoulders was determined for a load of 70 N applied to the clavicle in anteroposterior and superoinferior direc tions. The lengths of the conoid and trapezoid liga ments were found to be 15.1 ± 4.1 and 11.5 ± 2.2 mm, respectively; the widths of the conoid and trapezoid ligaments were 10.7 ± 1.5 and 11.0 ± 2.8 mm, respec tively. The in situ force of the trapezoid (42.9 ± 15.4 N) was significantly greater than that for the other liga ments during posterior displacement. Otherwise, no statistically significant differences could be found be tween any of the in situ forces in each ligament during all other motions examined. During anterior displace ment, the inferior acromioclavicular capsular ligament appeared to be the major restraint. The trapezoid lig ament was the primary restraint during posterior dis placement and provided 55.8% ± 20.0% of the resist ing force. Our results suggest that the coracoclavicular and other acromioclavicular joint capsular ligaments should be considered for reconstruction to restore normal joint function, especially in the anterior, poste rior, and superior directions.

A quantitative analysis of valgus torque on the ACL: A human cadaveric study

The loads needed to elicit a positive pivot shift test in a knee with an anterior cruciate ligament (ACL) rupture have not been quantified. The coupled anteriol tibial translation (ATT), coupled internal tibial rotation (ITR), and the in situ force in the ACL in response to a valgus torque, an inherent component of the pivot shift test, were measured in 10 human cadaveric knee specimens. Using a robotic/universal force–moment sensor testing system, valgus torques ranging from 0.0 to 10.0 N m were applied in nine increments on the intact and ACL‐deficient knee in flexion ranging from 0° to 90°. At 15° of knee flexion, the coupled ATT and ITR were significantly increased in the ACL‐deficient knee when compared to the intact knee. Coupled ATT increased a maximum of 291% (6.7 mm, p < 0.05), while coupled ITR increased a maximum of 85% (5.1°, p < 0.05). At 30°, the increases in coupled ATT and ITR were significant at valgus loads of 3.3 N m and greater with a maximum increase in coupled ATT of 137% (6.3 mm, p < 0.05) and a maximum increase in coupled ITR of 38% (3.6°, p < 0.05). At 45°, coupled ATT increased significantly (maximum of 69%, 4.4 mm, p < 0.05), but only at torques ⩾ 6.7 N m. The in situ force in the ACL was less than 20 N for all flexion angles when a torque between 3.3 and 5.0 N m was applied. Low valgus torque elicited tibial subluxation in the ACL‐deficient knee with low in situ ACL forces, similar to a positive pivot shift test. Thus, application of a valgus torque may be suitable to evaluate ACL‐deficient and ACL‐reconstructed knees, since subluxation can be achieved with minimal harm to the ACL graft. This work is important in understanding one load component needed for the pivot shift examination; further studies quantifying other load components are essential for better comprehension of the in vivo pivot shift examination.

Hill-Sachs Defects and Repair Using Osteoarticular Allograft Transplantation Biomechanical Analysis Using a Joint Compression Model

Background Humeral head defects have been associated with failed anterior shoulder instability repairs. Quantitative data are required to determine (1) the critical defect size for consideration of surgical repair and (2) the ability of proposed repair techniques to restore normal joint function. Hypotheses Increasing defect size will decrease stability and anterior translation before dislocation. Stability will decrease in shoulder positions where the defect is oriented in line with the anterior glenoid. Osteoarticular repair will restore joint stability to intact shoulder level. Study design Controlled laboratory study. Methods A robotic/universal force-moment sensor testing system was used to apply joint compression (22 N) and an anterior load (40 N) to cadaveric shoulders (n = 9) with all soft tissues removed (intact) at joint orientations with 60° of glenohumeral abduction and 0° and 60° of external rotation. Four posterolateral osteoarticular defects were created (12.5%, 25.0%, 37.5%, and 50.0% defect) followed by an osteoarticular allograft transplantation (repair). The loading protocol was repeated in each shoulder state for both joint orientations. The anterior translation and stability ratio (anterior load/compressive load) were recorded before dislocation. Results All shoulders dislocated at 60° of external rotation with all sizes of defects. At 0° of external rotation, shoulders with the 12.5% to 37.5% defects did not dislocate, and only 2 shoulders with the 50.0% defect dislocated. At 60° of external rotation, the 25.0% defect and 37.5% defect had significantly less anterior translation before dislocation, as compared with the intact (P < .05), both of which became similar to the intact after repair (P > .05). The stability ratio at 60° of external rotation significantly decreased in the 25.0% and 37.5% defects, as compared with the intact (P < .05), representing a 25% and 40% decrease in stability ratio. The stability ratio became similar to intact after repair (P > .05). Conclusion The size and orientation of the defect has important contributions to glenohumeral joint function. Increasing defect size required less anterior translation before dislocation and decreased the stability ratio, thereby increasing the risk of recurrent instability. Clinical Relevance Defects as small as 12.5% of the humeral head have biomechanical consequences that may affect joint stability. In addition, shoulders with large osteoarticular defects (37.5% or 50.0%) may benefit from osteoarticular allograft transplantation to restore shoulder stability.