Effect of posterior cruciate ligament deficiency on in vivo translation and rotation of the knee during weightbearing flexion.

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 degrees to 105 degrees ) 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 degrees of flexion compared with the intact contralateral knees. At 90 degrees 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 degrees of flexion (P < .05). With regard to rotation, PCL deficiency caused a significantly lower varus rotation (on average, 0.6 degrees lower) at 90 degrees 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.

In vivo patellar tracking: clinical motions and patellofemoral indices.

Patellar tracking during in vivo weightbearing knee function is not well understood. This study investigated patellar tracking of eight subjects during a full range of weightbearing flexion using magnetic resonance imaging and dual orthogonal fluoroscopy. The data were reported using a clinical description based on patellar and femoral joint coordinate systems and using patellar indices based on geometrical features of the femur and patella. The mean patellar shift was within 3 mm over the entire range of flexion. The patella tilted laterally from 0 degrees to 75 degrees, and then tilted medially beyond 75 degrees of flexion. The mean tilt was within 6 degrees. Similarly, the mean patellar rotation was small at early flexion, and the mean total excursion of patellar rotation was about 8 degrees. The patellofemoral indices showed that the mean sulcus angle and congruence angle varied within 8 degrees over the entire flexion range. The mean lateral patellar displacement was within 6 mm. A consistent decrease in lateral patellar tilt and an increase in lateral patellofemoral angle were observed with knee flexion. In conclusion, patellar motion is relatively small with respect to the femur during in vivo weightbearing knee flexion. These data may provide baseline knowledge for understanding normal patellar tracking.

In vivo kneeling biomechanics after posterior stabilized total knee arthroplasty.

BACKGROUND: Kneeling is one of the activities sought by patients after total knee arthroplasty (TKA). This study investigated the six degrees of freedom (DOF) kinematics and three-dimensional (3D) contact during weight-bearing kneeling. METHODS: A total of 16 South Korean female patients (22 knees) after posteriorly stabilized (PS) TKA (LPS-Flex) were randomly recruited and had the same surgeon. The patients were imaged using a dual fluoroscopic technique while they kneeled from initial to maximum flexion. The acquired images and 3D models were then used to recreate the in vivo pose of the components. Contact was determined by locating the surface intersections in the tibiofemoral and cam/post (between the femoral cam and tibial post) articular compartments. RESULTS: Patients flexed, on average, from 107.3 degrees to 128.0 degrees during the kneeling activity. Changes in kinematics included 1.0 mm of proximal, 0.9 mm of medial, and 7.6 mm of posterior translation and 1.7 degrees of varus rotation (P < 0.04). A difference in internal tibial rotation was not detected. Articular contact moved posteriorly by 5.9 mm and 6.4 mm in the medial and lateral compartments, respectively. Contact also moved medially by 3.2 mm and 5.8 mm in the medial and lateral compartments. A decrease in articular contact was observed in both condyles, and lateral condylar lift-off increased with flexion (P = 0.0001). More than 80% of the patients demonstrated cam/post engagement, which always occurred in the distal portion of the post. CONCLUSIONS: In this patient cohort, the knee joint was constrained during the weight-bearing activity such that femoral subluxation and dislocation were not observed. Furthermore, posterior cam/post engagement occurred only in the distal portion of the tibial post, which may improve the longevity of the post. The tibiofemoral and cam/post articular contact data presented in this study further suggest that kneeling may be performed by patients after clinically successful PS TKA who feel comfortable with the activity and are free of pain.

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 degrees 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 degrees to 120 degrees and decreased beyond 120 degrees of flexion. The posteromedial bundle had a lower elevation angle than the anterolateral bundle beyond 60 degrees of flexion. The anterolateral bundle had a larger deviation angle than the posteromedial bundle beyond 75 degrees of flexion. The femoral attachment of the posterior cruciate ligament twisted externally with increasing flexion and reached a maximum of 86.4 degrees +/- 14.7 degrees at 135 degrees 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.