Elongation Patterns of the Posterior Cruciate Ligament after Total Knee Arthroplasty

This study aimed to understand the ability of fixed-bearing posterior cruciate ligament (PCL)-retaining implants to maintain functionality of the PCL in vivo. To achieve this, elongation of the PCL was examined in six subjects with good clinical and functional outcomes using 3D kinematics reconstructed from video-fluoroscopy, together with multibody modelling of the knee. Here, length-change patterns of the ligament bundles were tracked throughout complete cycles of level walking and stair descent. Throughout both activities, elongation of the anterolateral bundle exhibited a flexion-dependent pattern with more stretching during swing than stance phase (e.g., at 40° flexion, anterolateral bundle experienced 3.9% strain during stance and 9.1% during swing phase of stair descent). The posteromedial bundle remained shorter than its reference length (defined at heel strike of the level gait cycle) during both activities. Compared with loading patterns of the healthy ligament, postoperative elongation patterns indicate a slackening of the ligament at early flexion followed by peak ligament lengths at considerably smaller flexion angles. The reported data provide a novel insight into in vivo PCL function during activities of daily living that has not been captured previously. The findings support previous investigations reporting difficulties in achieving a balanced tension in the retained PCL.

Long-term Results of Isolated Anterolateral Bundle Reconstructions of the Posterior Cruciate Ligament

Background Little is known about the parameters that influence the long-term results of isolated arthroscopically assisted reconstructions of the anterolateral bundle of the posterior cruciate ligament (PCL). Hypothesis Chondrosis, time interval from injury to surgery, and graft choice significantly influence the long-term results of single-bundle PCL reconstructions. Study Design Case series; Level of evidence, 4. Methods Between 1995 and 2001, 22 male and 3 female patients with a mean age of 30.8 years (range, 17-52) underwent an anterolateral bundle reconstruction of the PCL for functional instability and pain. Nine were treated with a bone–patellar tendon– bone autograft (BPTB), 15 with a semitendinosus gracilis (STG) autograft, and 1 with an Achilles tendon allograft. Twenty-two patients were clinically and radiographically reviewed at a mean follow-up of 9.1 years (range, 6.5-12.6). Three patients were interviewed by telephone. Thirteen patients had chondrosis at time of surgery. The mean time from injury to surgery was 1.5 years. Results The mean final International Knee Documentation Committee (IKDC), Lysholm, and functional visual analog scale (VAS) scores (65, 75, and 8, respectively) were fair to good and were significantly better than preoperatively (38, 50, and 4, respectively) (P <. 001). The final Tegner (5.7) score was significantly lower than the preinjury score (7.2) (P <. 001). The mean anteroposterior laxity measured by KT-1000 arthrometer and Telos stress radiographs was significantly increased on the operated side (mean side-to-side difference of 2.1 mm and 4.7 mm, respectively). The functional scores were not significantly different between the BPTB and STG reconstructions. Patients without chondrosis at time of surgery and patients operated within the first year from injury had significantly better functional results at final follow-up (P <. 05). Conclusion Arthroscopically assisted reconstructions of the anterolateral bundle of the PCL in patients with symptomatic isolated grade II to IV PCL-deficient knees lead to significantly improved functional results at long term if there is no cartilage damage at time of surgery. Nonoperative treatment should not be extended more than 1 year from injury. Graft choice did not significantly influence the functional outcome at long term.

Function of Posterior Cruciate Ligament Bundles during in Vivo Knee Flexion

Background The biomechanical functions of the anterolateral and posteromedial bundles of the posterior cruciate ligament over the range of flexion of the knee joint remain unclear. Hypothesis The posterior cruciate ligament bundles have minimal length at low flexion angles and maximal length at high flexion angles. Study Design Descriptive laboratory study. Methods Seven knees from normal, healthy subjects were scanned with magnetic resonance, and 3-dimensional models of the femur, tibia, and posterior cruciate ligament attachment sites were created. The lines connecting the centroids of the corresponding bundle attachment sites on the femur and tibia represented the anterolateral and posteromedial bundles of the posterior cruciate ligament. Each knee was imaged during weightbearing flexion (from 0° to maximal flexion) using a dual-orthogonal fluoroscopic system. The length, elevation, deviation, and twist of the posterior cruciate ligament bundles were measured as a function of flexion. Results The lengths of the anterolateral and posteromedial bundles increased with flexion from 0° to 120° and decreased beyond 120° of flexion. The posteromedial bundle had a lower elevation angle than the anterolateral bundle beyond 60° of flexion. The anterolateral bundle had a larger deviation angle than the posteromedial bundle beyond 75° of flexion. The femoral attachment of the posterior cruciate ligament twisted externally with increasing flexion and reached a maximum of 86.4° ± 14.7° at 135° of flexion (P < .05). Conclusion These data suggest that there is no reciprocal function of the bundles with flexion, which is contrary to previous findings. The orientation of the anterolateral and posteromedial bundles suggests that at high flexion, the anterolateral bundle might play an important role in constraining the mediolateral translation, whereas the posteromedial bundle might play an important role in constraining the anteroposterior translation of the tibia. Clinical Relevance These data provide a better understanding of the biomechanical function of the posterior cruciate ligament bundles and may help to improve the design of the 2-bundle reconstruction techniques of the ruptured posterior cruciate ligament.

Codominance of the Individual Posterior Cruciate Ligament Bundles: An Analysis of Bundle Lengths and Orientation

Background: It is unclear how each bundle of the posterior cruciate ligament contributes to posterior knee stability. Hypothesis: Changes in bundle orientation and length occur such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. Study Design: Controlled laboratory study. Methods: Six fresh-frozen cadaveric knees were studied in a joint-testing rig with individual quadriceps and hamstring muscle loading. Kinematic data for the tibia and femur were obtained at knee flexion angles from 0° to 120°. The joint was then disarticulated, and the insertions of the two bundles on the tibia and femur were digitized. Results: Length of the anterolateral bundle increased with increasing knee flexion angle from 10° to 120°. Length of the posteromedial bundle decreased with increasing knee flexion angle from 0° to 45° and increased slightly from 60° to 120°. Length of the anteromedial bundle was significantly less than that of the posteromedial at 0°, 10°, and 20° of knee flexion. The anterolateral bundle was significantly more horizontal at flexion angles of 0°, 10°, 20°, 30°, and 45° (P < 0.05). The posteromedial bundle was more horizontal at 120°. Conclusions: Changes in orientation take place such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. Clinical Relevance: Double-bundle reconstructions achieve more physiologic knee function.

Determination of the In Situ Forces in the Human Posterior Cruciate Ligament Using Robotic Technology

We examined the in situ forces in the posterior cruciate ligament as well as the force distribution between its anterolateral and posteromedial bundles. Using a robotic manipulator in conjunction with a universal force-moment sensor system, we applied posterior tibial loads from 22 to 110 N to the joint at 0° to 90° of knee flexion. The magnitude of the in situ force in the posterior cruciate ligament and its bundles was significantly affected by knee flexion angle and posterior tibial loading. In situ forces in the posterior cruciate ligament ranged from 6.1 6.0 N under a 22-N posterior tibial load at 0° of knee flexion to 112.3 28.5 N under a 110-N load at 90°. The force in the posteromedial bundle reached a maximum of 67.9 31.5 N at 90° of knee flexion, and the force in the anterolateral bundle reached a maximum of 47.8 23.0 N at 60° of knee flexion under a 110-N load. No significant differences existed between the in situ forces in the two bundles at any knee flexion angle. This study provides insight into the knee flexion angle at which each bundle of the posterior cruciate ligament experiences the highest in situ forces under posterior tibial loading. This information can help guide us in more accurate graft placement, fixation, and tensioning, and serve as an assessment of graft performance.