Direct and indirect biomechanical changes during gait following total knee arthroplasty

Abstract

Summary
An exploratory study which investigates the biomechanical changes following total knee arthroplasty (TKA) at the ankle knee and hip.

Conclusions
Changes directly related to the TKA were identified between the pre and postoperative assessments these were isolated to the knee. Indirect changes or adaptations were also identified at the ankle and hip between the postoperative assessments.

Introduction
Following the TKA one of the most obvious changes associated with the joint is the realignment from a varus/valgus alignment closer to neutral. The realignment and soft tissue balance have been discussed clinically at length [1] however, the magnitude of the change in in vivo biomechanical studies of gait has received little attention to date. Further study is required to document the effects of the surgery at the joints proximal and distal to the knee.

Methods
Fourteen patients were recruited all of whom were scheduled for TKA with OA graded 2-4 on the K-L scale. All patients underwent the same procedure (Zimmer NexGen CR) performed by the same surgeon. All of the patients participated in a baseline (preoperative) and three postoperative assessments conducted at six weeks, three months and six months following the procedure. Joint kinematics were measured using a 10 camera ProReflex motion capture system at 100Hz (Qualisys AB, Gothenburg Sweden), ground reaction forces were measured using 4 AMTI force plates (Advanced Mechanical Technology, Inc) at 400Hz. The segments of the lower limb were modelled in six-degrees of freedom [2]. Joint kinematics and moments were calculated for the ankle, knee and hip in the all three planes over a gait cycle.

Results
The coronal plane knee angle showed significant (p<0.01) angular realignment following the surgery of 9.7° six weeks postoperative, 10.2° at three months postoperative and 11.7° at six months post operative. Peak knee adduction moments reduced from 0.44N.m/kg to 0.19N.m/kg (p=0.02) over the same time period. No significant differences were identified in the sagittal plane knee kinematics or moments. A significant decrease in the peak knee external rotation moment in the transverse plane was identified (p<0.01) immediately following the surgery. At the ankle no significant changes were identified in the sagittal plane kinematics. Significant increases were identified in the peak plantarflexion and dorsiflexion moments between six week and six month postoperative (p=0.04 & 0.01 respectively). Peak pronation was significantly reduced between six weeks and six months (0.03). A significant increase in the hip range of motion in the coronal plane and peak external rotation were identified (p=0.03 & 0.01 respectively) between six weeks and six months post operative.

Discussion
The TKA directly resulted in a change in joint alignment, reduction in both the knee adduction and transverse plane moments. There also appear to be a number of changes which occur between six weeks postoperative and six months post operative, these appear to be compensatory mechanisms or adaptations at the ankle and hip. There is evidence of a plateau effect between six week and three months post operative, this may be partially due to the removal of the walking aids at this time.