FORCE PLATE ANALYSIS OF KNEELING ABILITY AFTER KNEE ARTHROPLASTY

Abstract

Introduction: Force plate analysis of contact areas and pressure has been used in the fields of podiatry and foot surgery. We used this tool in assessing normal subjects and knee replacement patients kneeling.

Aim: We analysed contact areas and pressures over the front of the knee during different kneeling positions.

Methods: Twenty three normal subjects and 33 knee replacement patients were included in this study. The patients were selected according to age and kneeling ability and the absence of involvement of other joints. They had unilateral or bilateral Total (TKR) or Unicompartmental knee replacements (UKR).

Target points were identified on the plate and patients were asked to place their tibial tuberosity on the target sites.

Patients and normal subjects’ data of load, contact area and pressure were recorded with knee at 90 degrees. A second reading was taken with subjects kneeling in their maximum flexion comfortable position. Foot position during kneeling was recorded in each case.

Results: Average age was 48.3 years for the normal group and 65.5.2 for the replaced knee group. Average range of motion was 141 degrees for the normal group and 115 degrees for the replaced knees group.

In the normal group, there was a significant positive correlation between body mass and kneeling load at both 90 degrees and maximum flexion. Kneeling pressure was never identical in both knees in all groups. There was no significant difference of peak pressures and contact areas between the normal and UKR group.

The angle of flexion affected the contact pressures as going from 90 degrees to higher flexion with the body weight still actively supported increases contact pressure, which then dropped to lowest level in maximum flexion when the body weight was supported by the calf. Peak loads were usually in the region of the tibial tuberosity.

Conclusion: Kneeling may be a sided activity with each individual having a dominant knee. The UKR group showed more normal kinematics in comparison with the TKR group.

Maximum contact pressures decreased in knees able to achieve full flexion. As kneeling flexion angle increases, the contact area decreases and while the thigh is off the calf and the peak pressure increases. Contact pressure dropped to below 90 degrees level whenever full flexion was achieved.