Background: Most patients with isolated posterior cruciate ligament (PCL) injuries have minimal symptoms, and nonoperative treatment is recommended. However, over time, these patients can develop significant degenerative changes in their knees. Historically, PCL laxity is graded by nonweightbearing anteroposterior measuring techniques that do not reproduce the true, dynamic weightbearing conditions in the injured knee. The purpose of this study was to determine the patholaxity in patients with isolated PCL deficiency during functional weightbearing activities (running, walking, and stair ascent).
Hypothesis: Patients with unilateral, isolated PCL deficiency will demonstrate dynamic anteroposterior and rotational instability in their affected knees during functional activities of level running and stair ascent compared with their unaffected, contralateral knees.
Study Design: Controlled laboratory study.
Methods: Nine asymptomatic patients with isolated grade II PCL injury underwent Dynamic Stereo X-Ray (DSX) of both knees during level running and stair ascent. Three-dimensional reconstructions of the patients’ bilateral distal femurs and proximal tibias were created from high-resolution computed tomography (CT) scans. Three-dimensional joint kinematics were determined using a model-based tracking approach to align the radiographic images with CT-derived bone models. The resulting tibiofemoral rotations and translations for the PCL-deficient and PCL-intact knees were then compared.
Results: During level running, the tibia of the PCL-deficient knee was approximately 2 mm posteriorly subluxated and had an anterior velocity relative to the femur approximately 40 mm/s greater than the contralateral, uninjured knee; however, this was only during the swing phase. No significant differences were found during the stance phase of running. During stair ascent, the tibia of the PCL-deficient knee was approximately 4 mm posteriorly subluxated compared with the intact limb during the terminal swing phase and early stance phase. Between foot strike and the time of peak ground-reaction force (GRF), the tibia of the PCL-deficient knee translated anteriorly relative to the femur with velocities 3 to 4 times greater than in the intact limb. Level walking was also evaluated in 3 patients, but no differences were seen, and it was not tested in the remaining 6 patients.
Conclusion: Changes in knee kinematics due to isolated PCL injuries were highly activity dependent. During running, small differences were identified only during the swing phase when the knee was unloaded. However, during stair ascent, significant differences extended from the late swing into early stance phase. During the swing phase of stair ascent, the tibia in the PCL-deficient joint subluxated posteriorly. Then, as load was transferred to the ascending limb, the tibia reduced anteriorly with high velocity relative to the femur. The resulting shear motion may expose the loaded joint to abnormal and potentially damaging forces.
Clinical Relevance: During functional activities, patients with isolated PCL injuries experience significant knee instability that cannot be identified by standard nonweightbearing static laxity measurements. The finding that different activities create different degrees of instability may have important implications for rehabilitation and activity limitations for PCL-deficient individuals.
Background: Posterolateral corner (PLC) injuries are difficult to diagnose and cause significant morbidity. The ideal method for the dial test and its accuracy remain unclear.
Purpose: This study compares the accuracy of measuring tibial external rotation at the skeletal level to measuring the patella-tubercle angle (PTA) and the thigh-foot angle (TFA) in the supine position to assess the most accurate method to measure rotation during the dial test.
Study Design: Controlled laboratory study.
Methods: Measurements were compared simultaneously using rotational goniometers at a cutaneous splint over the tibia, at a foot splint, and directly from the tibial skeleton. Six lower limbs were used. The femur was held rigidly and the knee tested at 90° and 30° of flexion. External rotation torque up to 8 N·m was applied through the foot splint, and the rotations were measured by 2 testers.
Results: Measurements at the tibial splint and directly on the tibia showed significant correlation at both knee flexion angles. The mean tibial external rotation was 24° at 90° of flexion and 26° at 30° of flexion (P < .05). The soft tissue effect caused the tibial splint to overestimate rotations by a mean of 6° and 9° at 90° and 30° of flexion, respectively. Foot splint measurements did not correlate significantly with tibial rotation, overestimating rotations by a mean of 103%. Intratester and intertester intraclass correlations were significant for the skin-mounted tibial splint measurements at both flexion angles but not for foot splint measurements at either flexion angles.
Conclusion: Rotation of the foot did not accurately represent the tibial external rotation at the knee, which could be measured more accurately by an instrument resting on the skin via a molded tibial splint. These results suggest that the PTA, and not the TFA, should be used in the dial test. This would support the use of the supine position during the dial test.
Clinical Relevance: The dial test is a commonly used method for diagnosing PLC injuries. This study helps to identify the ideal position and measuring points to use for this test; measurements based on the tibia were more accurate than those that used rotation of the foot.
Background
In vitro data suggest that injury to the posterior cruciate ligament stresses the posterolateral structures of the knee, placing them at greater risk of secondary injury. However, it is not known how isolated posterior cruciate ligament deficiency affects these soft tissue stabilizers of the knee joint in vivo.
Hypothesis
Posterior cruciate ligament deficiency will alter the apparent length patterns of the lateral collateral ligament (LCL) and popliteus.
Study Design
Controlled laboratory study.
Methods
The apparent length changes in the lateral collateral ligament and popliteus muscle-tendon unit during weightbearing knee flexion were studied in 14 patients with isolated, unilateral posterior cruciate ligament deficiency using magnetic resonance imaging, dual-orthogonal fluoroscopy, and 3-dimensional modeling. Data of the injured and uninjured contralateral sides were compared.
Results
Posterior cruciate ligament deficiency caused significant increases in the apparent length of both posterolateral structures (P < .05). The differences between injured and uninjured contralateral side were greatest at 120° of knee flexion in the lateral collateral ligament (48.2 ± 6.1 mm and 51.6 ± 6.1 mm, respectively) and at 30° of knee flexion in the popliteus (101.2 ± 9.3 mm and 110.4 ± 10.2 mm, respectively).
Conclusion
Deficiency of the posterior cruciate ligament alters the length patterns of posterolateral structures in vivo and might place them at greater risk of secondary injury.
Clinical Relevance
Reestablishment of normal kinematics after posterior cruciate ligament injury is critical for restoring normal function of posterolateral structures of the knee.
Background: The effect of posterior cruciate ligament (PCL) deficiency on 6 degrees of freedom in vivo knee-joint kinematics is unclear.
Hypothesis: In addition to constraining anterior-posterior translation, the PCL also functions to constrain the medial-lateral translation and rotation of the knee during weightbearing flexion of the knee.
Study Design: Controlled laboratory study.
Methods: Eight patients with a PCL injury in 1 knee and the other intact were scanned with magnetic resonance imaging, and 3-dimensional models of the femur and tibia were created for both knees. Each knee was imaged during quasistatic weight-bearing flexion (from 0° to 105° ) using a dual-orthogonal fluoroscopic system. The translation and rotation of the PCL-deficient knee were compared with the intact contralateral control.
Results: Posterior cruciate ligament deficiency caused an increase in posterior tibial translation beyond 30° of flexion compared with the intact contralateral knees. At 90° of flexion, PCL deficiency increased posterior tibial translation by 3.5 mm (P < .05). In the medial-lateral direction, PCL deficiency resulted in a 1.1 mm increase in lateral tibial translation at 90° of flexion (P < .05). With regard to rotation, PCL deficiency caused a significantly lower varus rotation (on average, 0.6° lower) at 90° of flexion. Posterior cruciate ligament deficiency caused a decreased internal tibial rotation throughout the range of flexion, but no significant difference was detected.
Conclusions: This study quantitatively describes the effect of PCL injury on 6 degrees of freedom kinematics of the knee during quasistatic weightbearing flexion. Using the intact contralateral side as a control, we found that PCL injuries not only affect anterior-posterior tibial translation but also medial-lateral translation and rotation of the knee.
Clinical Relevance: These data provide baseline knowledge of the in vivo kinematics of the knee after PCL injury. Surgical reconstruction of the injured PCL, either using single-bundle or double-bundle technique, should not only focus on restoration of posterior stability of the knee but also the medial-lateral stability as well as the rotational stability. These findings may help to explain the long-term degenerative changes seen in PCL-deficient knees.
Background: Posterior cruciate ligament injuries are often associated with injuries to other structures. The role of the posteromedial structures of the knee in these injuries has received little attention.
Hypothesis: The posterior oblique ligament is an important restraint to posterior tibial translation in the posterior cruciate ligament–deficient knee.
Study Design: Controlled laboratory study.
Methods: Kinematic studies were performed on 10 cadaveric knees to test 3 external loading conditions at 0°, 30°, 60°, and 90° of flexion (134 N posterior tibial load, 10 N · m valgus rotation, and 5 N · m internal rotation). Resulting posterior tibial translation was determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) posterior cruciate ligament–deficient, (3) posterior cruciate ligament/superficial medial collateral ligament–deficient, (4) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament–deficient, and (5) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament/posteromedial capsule–deficient knee.
Results: When both the superficial medial collateral ligament and deep medial collateral ligament were cut in the posterior cruciate ligament–deficient knee, posterior tibial translation did not increase significantly at any flexion grade under all external loading conditions (P > .05). Additional cutting of the posterior oblique ligament increased posterior tibial translation significantly at 0°, 30°, 60°, and 90° of flexion under posterior tibial load and at all flexion angles tested under valgus or internal tibial load (P < .05). Additional cutting of the posteromedial capsule increased posterior tibial translation only at 0° and 30° in response to a valgus and internal tibial load (P < .05).
Conclusion: The posterior oblique ligament and posteromedial capsule have a significant role in the prevention of additional posterior tibial translation in the knee with posterior cruciate ligament injury.
Clinical Relevance: The posterior oblique ligament should be addressed in the patient with combined injuries to the posterior cruciate ligament and the posteromedial structures.
