THE SCREW HOME MECHANISM IN OSTEOARTHRITIC KNEES.

Abstract

The movement of a normal knee is a complex of flex-ion-extension, translation and rotational movements. Intracapsular anatomical structures such as ACL, PCL, menisci, the bone anatomy as well as the muscles acting on the knee joint influence the screw home mechanism.

We assessed the axial rotation of the tibia during knee flexion in order to better understand the kinematic behavior of osteoarthritic knees.

We included 55 consecutive admissions (31 females and 24 males) with diagnosed osteoarthritis of the knee. All records were obtained by consultant orthopaedic surgeons using the trackers and software of a navigation knee replacement system, prior to a knee replacement surgery. All the records were obtained before any soft tissue release.

For the statistical analysis we used the Wilcoxon non parametric two sample test.

We found that the tibial rotation on knee flexion followed three distinct patterns: a) normal rotation: 26 knees (47%) with average rotation of 15.96° (range: 0.5°–34°). b) mixed internal and external rotation: 22 knees (40%) with average rotation 6.7° (range: 5°–0.5°) ^and c) reversed rotation: seven knees (13%) with average external rotation of 2.7^{° (}range:1°–4°).

Most of the tibial rotation occurs in the first 0–30° of flexion (70%) p< 0.001.

Our study confirms that osteoarthritis affects the normal kinematics of the knee joint and also suggests that the observed kinematics follow distinctive patterns.