Loading Patterns of the Posterior Cruciate Ligament in the Healthy Knee: A Systematic Review

Abstract

Background: The posterior cruciate ligament (PCL) is the strongest ligament of the knee, serving as one of the major passive stabilizers of the tibio-femoral joint. However, despite a number of experimental and modelling approaches to understand the kinematics and kinetics of the ligament, the normal loading conditions of the PCL and its functional bundles are still controversially discussed.

Objectives: This study aimed to generate science-based evidence for understanding the functional loading of the PCL, including the anterolateral and posteromedial bundles, in the healthy knee joint through systematic review and statistical analysis of the literature.

Data sources: MEDLINE, EMBASE and CENTRAL.

Eligibility criteria for selecting studies: Databases were searched for articles containing any numerical strain or force data on the healthy PCL and its functional bundles. Studied activities were as follows: passive flexion, flexion under 100N and 134N posterior tibial load, walking, stair ascent and descent, body-weight squatting and forward lunge.

Method: Statistical analysis was performed on the reported load data, which was weighted according to the number of knees tested to extract average strain and force trends of the PCL and identify deviations from the norms.

Results: From the 3577 articles retrieved by the initial electronic search, only 66 met all inclusion criteria. The results obtained by aggregating data reported in the eligible studies indicate that the loading patterns of the PCL vary with activity type, knee flexion angle, but importantly also the technique used for assessment. Moreover, different fibres of the PCL exhibit different strain patterns during knee flexion, with higher strain magnitudes reported in the anterolateral bundle. While during passive flexion the posteromedial bundle is either lax or very slightly elongated, it experiences higher strain levels during forward lunge and has a synergetic relationship with the anterolateral bundle. The strain patterns obtained for virtual fibres that connect the origin and insertion of the bundles in a straight line show similar trends to those of the real bundles but with different magnitudes.

Conclusion: This review represents what is now the best available understanding of the biomechanics of the PCL, and may help to improve programs for injury prevention, diagnosis methods as well as reconstruction and rehabilitation techniques.

Fig 1. The 2009 PRISMA flowchart for the systematic review.

Fig 2. Binned scatter plot and weighted polynomial regression lines of all reported strain data for the AL, PM and mid-PCL bundles during passive knee flexion (R² of 0.68, 0.04 and 0.46 respectively).

Each circle shows the mean of the data extracted from the individual studies, where the size of the circle represents the number of knees tested and the numerical labels detail the reference numbers from which data were extracted. Data points with strains of less than -25% or greater than +45% are not shown (resolution of bins: ±2%).

Fig 3. Strain of the virtual mid-PCL bundle during passive knee flexion, separated according to the assessment categories used.

Articles in this graph included all data available for the mid-PCL: in vivo studies [31, 32], in vitro studies [19, 32, 51, 61, 82, 90], and modelling studies [35, 84, 92]. Experimental data were weighted based on the number of knees tested. Error bars show the Standard Error of Mean.

Fig 4. Strain of the real and virtual bundles of the PCL during passive knee flexion.

Data were weighted based on the number of knees tested. Articles included in this graph: Studies on real bundles [26, 49] and studies on virtual bundles [19, 22, 24, 25, 27, 29, 51, 60, 61, 73, 82].

Fig 5. Average force patterns of the PCL during knee flexion with and without Posterior Tibial Load (PTL).

Included articles in this graph: in vitro force in passive flexion [, , , , , –89, 91], in situ force in passive flexion [9], modelling force in passive flexion [36, 75, 84], in vitro force with 100 N PTL [, , , –88, 96, 97], in situ force with 100 N PTL [17] and in situ force with 134 N PTL [, , , , –95, 98, 105].

Fig 6. Average experimental strain patterns of the virtual PCL bundles during passive and active knee flexion.

Included articles in this graph: Studies on passive flexion [19, 22, 24, 25, 27, 29, 51, 60, 61, 73, 82] and studies on forward lunge [14, 30, 33, 57].