Effects of Single-Bundle and Double-Bundle ACL Reconstruction on Tibiofemoral Forces and Joint Kinematics Under Dynamic Loading (SS-42)

Abstract

Initial biomechanical studies have determined that the double-bundle technique significantly improved upon the single-bundle method: it better resists an externally applied moment and the stress distribution between the two grafts closely matches that of the normal ACL. However, there have not been any studies to evaluate the long-term effects of double-bundle ACL reconstruction on joint contact mechanics or articular cartilage integrity. Before this can be studied however, a direct measurement of joint contact forces must be examined. This study was conducted to establish a baseline relationship between ACL reconstructive techniques on joint kinematics and compressive forces. The purpose of this study was to compare the tibiofemoral joint kinematics and contact forces between single-bundle (SBR) and double-bundle (DBR) ACL reconstructive techniques during simulated squatting using a cadaver model. Twelve matched pairs of fresh frozen human cadaver knees (7 female and 3 male) with no evidence of knee pathology were stored at −20° C following harvest. The mean age of the specimens was 58 years (range 16 – 80). The specimens consisted of the distal third of the femur and the proximal two thirds of the tibia. Threaded rods (0.5-inch diameter Stainless Steel, McMaster-Carr, Los Angeles, CA) were inserted into the intramedullary canal of the femur and tibia and secured through an epoxy resin (Smooth-Cast 300, Smooth-On Inc, Easton, PA) for attachment to a test fixture which allows for dynamic simulated squatting. Additionally, the quadriceps tendon and semimembranosus and biceps femoris hamstrings were sutured to allow attachment to the test fixture for dynamic loading. An Optotrak Image Analysis System (Northern Digital; Waterloo, Ontario) with Optotrak Digitizer software (NDI 6D Architect) was used to track the position of the tibia with respect to the femur for kinematic measurements. K-Scan thin-film pressure sensors (4000; Maximum Pressure Range: 10,342 KPa, Sensing Area: 27.9 mm x 33 mm, Sensels per square cm: 62; Tekscan Inc, South Boston, MA) were used to simultaneously measure the tibiofemoral compressive forces in both compartments of the knee. The “I-scan” software program (Tekscan, Inc., South Boston, MA) was used to gather sensor data. Measurements were made in the intact knee and after the experimental procedure at each of 11 angles (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100). For each outcome measure, two-way repeated measures analysis of variance was used to test for differences between the two experimental procedures with respect to the mean change from intact state. The model also included factors representing the effect of angle and an angle by procedure interaction. F-tests corresponding to simple effects were used to evaluate procedure differences in outcome within each angle when appropriate. One sample t-tests, which were based on the error term derived from the ANOVA, were used to evaluate significant change from intact state for each experimental procedure both across and within test angle. Analyses were performed using SAS statistical software Version 8. Statistical significance was based on p = 0.05. Rotation kinematics were different from the intact knee throughout the range of motion in the SBR group, while DBR was different at only high flexion angles while recreating proper rotation at low angles (p=0.004). In the medial compartment, both techniques successfully recreated joint contact forces (P=0.0006). In the lateral compartment, DBR failed to reapproximate native compressive forces throughout all flexion angles while SBR more closely reapproximated native compressive forces at high flexion angles. This study suggests compressive load is better restored with single-bundle than double-bundle ACL reconstruction. Joint kinematics are better restored with double-bundle reconstruction but still did not completely recreate the native ACL.