Steven R. Jackson

Effects of Applied Quadriceps and Hamstrings Muscle Loads on Forces in the Anterior and Posterior Cruciate Ligaments

Background Muscle contraction can subject healing knee ligament grafts to high loads. Purpose To directly measure the effects of quadriceps and hamstrings muscle loads on forces in the anterior cruciate ligaments and posterior cruciate ligaments. Study Design Controlled laboratory study. Methods Thirteen cadaveric knee specimens had load cells installed to record resultant forces in both anterior and posterior cruciate ligaments under 5 loading conditions. Cruciate force measurements were repeated with a 100-N load applied to the quadriceps tendon and again with a combined 50-N biceps load and 50-N semimembranosus-semitendinosus load. Results Applied quadriceps loads resulted in mean changes in anterior cruciate ligament and posterior cruciate ligament forces that were less than 20 N for all loading conditions. Hamstrings load significantly increased mean posterior cruciate ligament force between 30° and 105° of flexion with 100 N of applied posterior tibial force. Conclusions At the muscle force levels used in this study, the hamstrings were more effective than the quadriceps in altering cruciate force levels, especially near 90° of flexion, where they have an excellent mechanical advantage for controlling anterior-posterior tibial translation. Clinical Relevance Isolated hamstrings activity generally had little or no effect on anterior cruciate ligament forces but significantly increased forces in the posterior cruciate ligament beyond approximately 30° of flexion.

Anterior-Posterior and Rotatory Stability of Single and Double-Bundle Anterior Cruciate Ligament Reconstructions

BACKGROUND Some surgeons presently reconstruct both the anteromedial and posterolateral bundles of the anterior cruciate ligament. The purposes of this study were to measure the abilities of single-bundle and anatomic double-bundle reconstructions to restore anteroposterior laxities and rotational kinematics to intact knee levels and to compare graft forces in reconstructed knees with forces in the native anterior cruciate ligament for the same loading conditions. METHODS Native anterior cruciate ligament force and tibial rotations were recorded during passive knee extension tests with and without applied tibial loads. The anteromedial and posterolateral bundles were reconstructed with patellar tendon tissue sized to fit tightly within 7-mm femoral tunnels. Testing was repeated with the anteromedial graft alone (single bundle), tensioned to restore anteroposterior laxity at 30 degrees of flexion, and with double-bundle grafts. For double-bundle reconstructions, the anteromedial graft was first tensioned as above and then the posterolateral graft was tensioned with use of one of four protocols: posterolateral tension = anteromedial tension at 10 degrees (DB1), posterolateral tension = anteromedial tension at 30 degrees (DB2), posterolateral tension = (anteromedial tension + 30 N) at 10 degrees (DB3), and posterolateral tension = (anteromedial tension + 30 N) at 30 degrees (DB4). RESULTS The posterolateral graft underwent a greater length change than the anteromedial graft between 0 degrees and 90 degrees . This difference in elongation patterns produced high forces in the posterolateral graft at 0 degrees when both grafts were tensioned and fixed at 30 degrees . The mean laxities for single-bundle reconstructions were within 1.1 mm of those of the intact knee between 0 degrees and 90 degrees ; the mean graft force at 0 degrees was 76 N. The mean laxities for DB4 reconstructions were from 0.9 to 2.8 mm less than those of the intact knee, and the mean graft force at 0 degrees was 264 N. Coupled internal tibial rotations from valgus moment were normal with the single-bundle graft. Internal rotations from tibial torque were approximately 2 degrees to 4 degrees greater than normal with a single-bundle graft. DB3 and DB4 reconstructions overcorrected the coupled tibial rotations from valgus moment and restored tibial rotations from internal torque to normal from 0 degrees to 45 degrees . The graft forces from tibial torque and valgus moment were normal with the single-bundle graft. The mean double-bundle graft forces at 0 degrees were 57 N to 143 N and 34 N to 171 N greater than normal for internal torque and valgus moment, respectively. CONCLUSIONS The single-bundle reconstruction produced graft forces, knee laxities, and coupled tibial rotations that were closest to normal. Adding a posterolateral graft to an anteromedial graft tended to reduce laxities and tibial rotations, but the reductions were accompanied by markedly higher forces in the posterolateral graft near 0 degrees that occasionally caused it to fail during tests with internal torque or anterior tibial force.

Biomechanical Studies of Double-Bundle Posterior Cruciate Ligament Reconstructions

BACKGROUND Double-bundle reconstruction of the posterior cruciate ligament has been advocated to better replicate the anatomy of the native ligament and restore normal knee biomechanics. The goal of this study was to measure knee laxities and graft forces following single and double-bundle reconstructions and to compare these values with those for the intact knee in a cadaver model. METHODS Forces in the posterior cruciate ligament were measured as the knee was passively extended from 120 degrees to 0 degrees with applied tibial loading. Anterior-posterior laxities were measured as well. An anterolateral tunnel was located at the anterolateral margin of the native ligament footprint, and a posteromedial tunnel was placed at one of two locations within the footprint; one location resulted in a wide bridge separating the tunnels and the other, a narrow bridge. Testing was repeated with a single anterolateral graft tensioned to match, within +/-1 mm, the laxity in the intact knee at 90 degrees of flexion. Double-bundle reconstructions were tested with the addition of a posteromedial graft tensioned at 30 degrees of flexion. Two levels of posteromedial graft tension (10 and 30 N) were studied in both the narrow and the wide-bridge posteromedial tunnels. RESULTS Mean laxities with a single anterolateral graft were 1.1 to 2.0 mm greater than normal between 0 degrees and 30 degrees of flexion. With the posteromedial graft tensioned to 10 N in the wide-bridge tunnel, the mean laxity of the double grafts was not significantly different from that in the intact knee at any flexion angle. With the posteromedial graft tensioned to 10 N in the narrow-bridge tunnel, the mean laxity at 0 degrees was 0.9 mm greater than that in the intact knee. With the posteromedial graft tensioned to 30 N, the mean laxity at 10 degrees was 1.7 mm less than the intact-knee value in the wide-bridge tunnel and 1.3 mm less than the intact-knee value in the narrow bridge-tunnel. Increasing posteromedial graft tension from 10 to 30 N decreased the mean laxities by 0.5 to 1.1 mm between 0 degrees and 30 degrees . Mean graft forces following a single anterolateral reconstruction were not significantly different from the native posterior cruciate ligament forces under any mode of loading except valgus moment. With the wide-bridge tunnel, the mean forces with the posteromedial graft tensioned to 10 N were somewhat higher than the native posterior cruciate ligament forces at full extension; when the graft was tensioned to 30 N, the mean forces were substantially higher. CONCLUSIONS A single anterolateral graft best reproduced the normal posterior cruciate ligament force profiles, but laxities were greater than normal between 0 degrees and 30 degrees of knee flexion. The addition of a second, posteromedial graft reduced laxity in this flexion range but did so at the expense of higher-than-normal forces in the posteromedial graft.

Simulated pivot-shift testing with single and double-bundle anterior cruciate ligament reconstructions.

BACKGROUND One of the principal rationales for performing a double-bundle reconstruction of the anterior cruciate ligament is the suggestion that it may be superior to a single-bundle reconstruction in restoring a normal pivot-shift sign. The purpose of this study was to measure the abilities of single-bundle and anatomic double-bundle reconstructions to restore normal knee kinematics and graft forces during a simulated pivot-shift test. METHODS Graft force and knee kinematics were recorded during a simulated pivot-shift event with and without the anterior cruciate ligament and after graft reconstructions. With a single bundle, the graft was tensioned to restore anterior-posterior laxity at 30 degrees of flexion. With double-bundle reconstructions, the anteromedial graft was first tensioned as above and then the posterolateral graft tension was set with use of one of four protocols: posterolateral tension = anteromedial tension at 10 degrees of flexion (DB1); posterolateral tension = anteromedial tension at 30 degrees (DB2); posterolateral tension = (anteromedial tension + 30 N) at 10 degrees (DB3); and posterolateral tension = (anteromedial tension + 30 N) at 30 degrees (DB4). RESULTS A single-bundle reconstruction restored all displacements and rotations during the pivot shift to the intact knee levels. The mean tibial rotations and lateral plateau displacements during the pivot shift with DB2, DB3, and DB4 reconstructions were less than those in the intact knee and also less than those in a single-bundle reconstruction. Before the pivot shift, the mean graft forces with all reconstructions were greater than that of the intact knee; the mean graft forces with the DB3 and DB4 reconstructions were also greater than that of a single-bundle reconstruction. After the pivot shift, the mean graft forces for all reconstructions were less than the levels before the pivot shift with single-bundle forces lower than intact knee levels and DB4 forces higher than intact knee levels. CONCLUSIONS Reduction or elimination of the pivot-shift sign is an important goal for anterior cruciate ligament reconstruction. In our model, the results show that a single-bundle reconstruction was sufficient to restore intact knee kinematics during a simulated pivot-shift event. The higher graft forces with some double-bundle graft-tensioning protocols reduced the coupled rotations and displacements from an applied valgus moment to less than the intact levels. This overcorrection should theoretically make the knee less likely to pivot but could have unknown clinical consequences.

How Well Do Anatomical Reconstructions of the Posterolateral Corner Restore Varus Stability to the Posterior Cruciate Ligament–Reconstructed Knee?

Background With grade 3 posterolateral injuries of the knee, reconstructions of the lateral collateral ligament, popliteus tendon, and popliteofibular ligament are commonly performed in conjunction with a posterior cruciate ligament reconstruction to restore knee stability. Hypothesis A lateral collateral ligament reconstruction, alone or with a popliteus tendon or popliteofibular ligament reconstruction, will produce normal varus rotation patterns and restore posterior cruciate ligament graft forces to normal levels in response to an applied varus moment. Study Design Controlled laboratory study. Methods Forces in the native posterior cruciate ligament were recorded for 15 intact knees during passive extension from 120° to 0° with an applied 5 N·m varus moment. The posterior cruciate ligament was removed and reconstructed with a single bundle inlay graft tensioned to restore intact knee laxity at 90°. Posterior cruciate ligament graft force, varus rotation, and tibial rotation were recorded before and after a grade 3 posterolateral corner injury. Testing was repeated with lateral collateral ligament, lateral collateral ligament plus popliteus tendon, and lateral collateral ligament plus popliteofibular ligament graft reconstructions; all grafts were tensioned to 30 N at 30° with the tibia locked in neutral rotation. Results All 3 posterolateral graft combinations rotated the tibia into slight valgus as the knee was taken through a passive range of motion. During the varus test, popliteus tendon and popliteofibular ligament reconstructions internally rotated the tibia from 1.5° (0° flexion) to approximately 12° (45° flexion). With an applied varus moment, mean varus rotations with a lateral collateral ligament graft were significantly less than those with the intact lateral collateral ligament beyond 0° flexion; mean decreases ranged from 0.8° (at 5° flexion) to 5.6° (at 120° flexion). Addition of a popliteus tendon or popliteofibular ligament graft further reduced varus rotation (compared with a lateral collateral ligament graft) beyond 25° of flexion; both grafts had equal effects. A lateral collateral ligament reconstruction alone restored posterior cruciate ligament graft forces to normal levels between 0° and 100° of flexion; lateral collateral ligament plus popliteus tendon and lateral collateral ligament plus popliteofibular ligament reconstructions reduced posterior cruciate ligament graft forces to below-normal levels—beyond 95° and 85° of flexion, respectively. Conclusions With a grade 3 posterolateral corner injury, popliteus tendon or popliteofibular ligament reconstructions are commonly performed to limit external tibial rotation; we found that they also limited varus rotation. With the graft tensioning protocols used in this study, all posterolateral graft combinations tested overconstrained varus rotation. Further studies with posterolateral reconstructions are required to better restore normal kinematics and provide more optimum load sharing between the PCL graft and posterolateral grafts. Clinical Relevance A lower level of posterolateral graft tension, perhaps applied at a different flexion angle, may be indicated to better restore normal varus stability. The clinical implications of overconstraining varus rotation are unknown.

Effects of Posterolateral Reconstructions on External Tibial Rotation and Forces in a Posterior Cruciate Ligament Graft

BACKGROUND In patients with a Grade-3 injury, reconstructions of the lateral collateral ligament, popliteus tendon, and popliteofibular ligament are commonly performed in conjunction with a reconstruction of the posterior cruciate ligament. The objectives of this study were (1) to compare the abilities of three types of posterolateral graft reconstruction to restrain external tibial rotation and alter forces in a posterior cruciate graft and (2) to compare tibial rotations and posterior cruciate graft forces associated with two levels of initial posterolateral graft tension. METHODS Forces in the posterior cruciate ligament were recorded as the knee was extended from 120 degrees to 0 degrees and a 5-N-m external tibial torque was applied. The posterior cruciate ligament was reconstructed, and external tibial rotation and the forces in the posterior cruciate graft were recorded. These measurements were again recorded after sectioning of the posterolateral structures and after reconstruction of the lateral collateral ligament, alone as well as in combination with reconstruction of the popliteus tendon and in combination with reconstruction of the popliteofibular ligament. RESULTS With the lateral collateral ligament intact, removal of the popliteus tendon from its femoral origin significantly increased external tibial rotation. Applying tension to a popliteus or popliteofibular graft internally rotated the tibia, with no significant difference between the rotations caused by the tensioning of the two grafts. Tibial rotation was significantly greater when graft tensioning had been performed with the tibia free to rotate than it was when the tensioning had been done with the tibia locked in neutral rotation. With an applied external tibial torque, a reconstruction of the lateral collateral ligament alone was not sufficient to reduce posterior cruciate graft forces to normal. The addition of a popliteus or popliteofibular reconstruction to the lateral collateral ligament reconstruction significantly reduced posterior cruciate graft forces to normal (or below normal) levels. The external rotations associated with these two combined reconstructions were equivalent and significantly less than that in the intact knee. Increasing tension in either the popliteus or the popliteofibular graft from 10 to 30 N significantly decreased external rotation. CONCLUSIONS The posterolateral grafts acted to resist applied external torque, thereby off-loading the posterior cruciate graft. Popliteus and popliteofibular grafts were more favorably aligned than a lateral collateral ligament graft to resist external rotation, and they had similar effects.

Where Should the Femoral Tunnel of a Posterior Cruciate Ligament Reconstruction Be Placed to Best Restore Anteroposterior Laxity and Ligament Forces

Background Objective results of posterior cruciate ligament reconstruction are often less than satisfactory, with many patients exhibiting excessive posterior laxity. Hypothesis Changes in the position of the femoral tunnel within the posterior cruciate ligaments femoral footprint will significantly affect anteroposterior laxities and graft forces. Study Design Controlled laboratory study. Methods The posterior cruciate ligaments femoral origin was mechanically isolated in 13 fresh-frozen knee specimens, and the bone cap containing the ligaments insertion was attached to a load cell that recorded resultant force during tibial loading tests. Anteroposterior laxity (at ± 200 N applied force) was also measured. Cast acrylic replicas of the bone cap were fabricated, with tunnels placed in anterolateral, central, and posteromedial regions of the footprint. A graft reconstruction was tested in each tunnel. Results Mean laxities with the anterolateral tunnel were + 0.9 mm to + 1.7 mm greater than normal between 0 ° and 45 ° of flexion. Mean laxities with the posteromedial tunnel were –2.4 mm to –3.7 mm less than normal between 10 ° and 45 ° of flexion. Mean laxities with the central tunnel were not significantly different from intact knee values, except at 0 ° (0.9 mm greater). Mean graft forces with the anterolateral tunnel were normal for most modes of loading, whereas there were significant increases in graft forces with the posteromedial and central tunnels. Conclusion The anterolateral tunnel reproduced normal posterior cruciate ligament force profiles but produced a knee that was more lax than normal between 0 ° and 45 ° of flexion. The central tunnel best matched intact knee laxities, but graft forces were higher than posterior cruciate ligament forces between 0 ° and 45 ° of flexion. The posteromedial tunnel overconstrained anteroposterior laxity approximately 2 to 4 mm between 0 ° and 45 ° of flexion and generated higher graft forces in the same flexion range. Clinical Relevance This study suggests that a posteromedial tunnel should not be used for single-bundle posterior cruciate ligament reconstruction.

Contributions of the Posterolateral Bundle of the Anterior Cruciate Ligament to Anterior-Posterior Knee Laxity and Ligament Forces

PURPOSE The purpose of this study was to measure changes in anterior-posterior (AP) laxity and graft forces after cutting the posterolateral (PL) bundle of the anterior cruciate ligament (ACL). METHODS Twelve fresh-frozen cadaveric knees underwent AP laxity testing at +/- 100 N of applied tibial force. Resultant forces in the ACL were recorded during passive extension from 120 degrees to 0 degrees with no tibial force, 100 N of anterior tibial force, 100 N of quadriceps force, and 5 Nm of internal tibial torque. The femoral origin of the PL bundle was identified, the ligament fibers were dissected from bone, and tests were repeated. RESULTS Cutting the PL bundle significantly increased mean laxity by +1.3 mm (at 0 degrees ), +1.1 mm (at 10 degrees ), and +0.5 mm (at 30 degrees ). For the passive knee extension tests, cutting the PL bundle significantly decreased mean ACL force at 0 degrees for all loading modes; the mean decreases were 31 N (with no tibial force), 50 N (with 100 N of anterior force), 33 N (with 100 N of quadriceps force), and 40 N (with 5 Nm of internal torque). CONCLUSIONS The decreases in ACL force at 0 degrees from cutting the PL bundle are consistent with the commonly accepted view that the PL bundle tightens with knee extension. Cutting the taut PL bundle did significantly increase AP laxity between 0 degrees and 30 degrees , but the increases were relatively small. Therefore we conclude that the PL bundle plays a relatively minor role in controlling anterior tibial translation. CLINICAL RELEVANCE In view of our findings, the need to reconstruct the PL bundle for better restoration of a normal AP laxity profile is questioned.

Relationship between the pivot shift and Lachman tests: a cadaver study.

BACKGROUND While the Lachman and pivot shift tests have been used clinically for decades to assess the anterior cruciate ligament, the relationship between the two has undergone limited experimental study. The goal of this study was to evaluate biomechanical relationships between the Lachman and pivot shift tests in anterior cruciate ligament-deficient and reconstructed knees. METHODS Knee kinematics during simulated pivot-shift testing and anteroposterior knee laxities were measured in seventeen knees in the intact condition, in the anterior cruciate ligament-deficient condition, and after anterior cruciate ligament reconstruction. Pivot shift magnitude was plotted against laxity for all knees with the grafts unfixed (the cruciate ligament-deficient condition). The grafts were then tensioned to match the laxities of the intact knees, and the change in pivot shift magnitude was plotted versus the change in laxity for all knees. In a separate series of tests for individual specimens, pivot shift magnitude was plotted versus laxity for each knee by incrementally loosening the anterior cruciate ligament graft. RESULTS Linear correlations between pivot shift magnitude and absolute laxity for anterior cruciate ligament-deficient knees were weak. When the unfixed grafts were tensioned to match anteroposterior laxities of the intact knees, changes in pivot shift were better correlated with corresponding changes in anteroposterior laxity (r(2) = 0.53 for tibial rotation and 0.73 for lateral tibial plateau displacement). When graft fixation was progressively loosened for each reconstructed knee, pivot shift magnitude increased linearly from the laxity of the intact knee up to an end point of the linear range, at which point the slope decreased abruptly. Between this end point and the anterior cruciate ligament-deficient condition, further increases in pivot shift were relatively small. CONCLUSIONS Our findings suggest that the magnitude of laxity of an injured knee, when considered alone, may not accurately predict the magnitude of the pivot shift, but the difference in laxity between the injured knee and the normal knee (the injured-normal difference) could be a good clinical predictor of the injured-normal difference in the pivot shift. We demonstrated that an insufficiently tensioned anterior cruciate ligament graft could substantially reduce anterior laxity, while leaving the pivot shift evaluation virtually unchanged.

Single- Versus Double-Bundle Posterior Cruciate Ligament Reconstruction Effects of Femoral Tunnel Separation

Background: Double-bundle posterior cruciate ligament reconstructions are performed to more closely replicate the anatomy of the native posterior cruciate ligament and to better restore normal knee biomechanics and kinematics than a single graft. The femoral tunnel for the anterolateral graft is normally located near the anterior margin of the posterior cruciate ligament footprint. However, there is considerable variability with regard to placement of the posteromedial tunnel within the footprint margins. Hypothesis: A double-bundle posterior cruciate ligament reconstruction will better replicate normal knee biomechanics and kinematics than a single anterolateral graft, and the separation distance between femoral tunnels will significantly affect the recorded measurements. Study Design: Controlled laboratory study. Methods: The posterior cruciate ligament’s femoral origin was mechanically isolated using a cylindrical coring cutter, and a cap of bone containing the ligament fibers was attached to a load cell that recorded resultant force in the posterior cruciate ligament as the knee was loaded. Cast acrylic replicas of the femoral bone cap, with 9-mm and 6-mm holes for the anterolateral and posteromedial grafts, respectively, were attached to the load cell. Graft isometries, anterior-posterior laxities, graft forces, and tibial rotations were measured for an anterolateral graft alone, and for anterolateral and posteromedial grafts with narrow (0-mm) and wide (3-mm) bridges between tunnels. Results: Mean laxities with an anterolateral graft alone were within 1.2 mm of normal, between 0° and 90°; means with double-bundle grafts were 1.7 mm to 2.4 mm less than normal, between 10° and 45°. Relative length change of the anterolateral graft between 0° and 90° was within +1.3 mm, while the posteromedial graft, placed in either tunnel, tightened approximately 6 mm with knee extension from 90° to 0°. At 0°, mean forces with a single anterolateral graft were not significantly different from posterior cruciate ligament forces for any loading mode tested; mean forces with double-bundle grafts were 74 N to 154 N higher than posterior cruciate ligament forces at 0°. During passive knee extension, the double-bundle reconstruction externally rotated the tibia (relative to intact) between 0° and 50°. There were no significant differences in mean knee laxities, graft forces, or tibial rotations between narrow and wide tunnel separations. Conclusion: In contrast to the anterolateral graft, which experienced minimal length changes, the posteromedial graft tightened 3.1 mm to 4.3 mm from 30° to 0°. When the posteromedial graft was tensioned and fixed at 30°, it developed relatively high graft forces as the knee was extended to 0°; this tended to reduce knee laxity and increase graft forces. With double-bundle grafts, tunnel separation distance was not an important variable with respect to the biomechanical and kinematic measurements recorded in this study. Clinical Relevance: The need for a posteromedial graft during posterior cruciate ligament reconstruction is questioned, especially in view of the relatively high graft forces at full extension that could cause it to permanently elongate with time. If a double-bundle reconstruction is performed, there is no biomechanical advantage in making the bone bridge between tunnels less than 3 mm.