THE EFFECTS OF PAIN ABOLITION AND SURGERY ON INTRA-OPERATIVE KNEE RANGE OF MOTION DURING TOTAL KNEE ARTHROPLASTY

Abstract

Introduction: Range of motion (ROM) is an important measure of the success of knee Arthroplasty. The extent to which pain relief contributes to improvements in knee ROM in total knee Arthroplasty (TKA) patients is unknown. This prospective study assessed the separate effects of pain abolition and surgery on ROM in a group of 141-osteoathritic patient’s undergoing TKA. Pain had a significant inhibitory effect on knee ROM. Improvements in ROM following TKA may be primarily due to pain relief.

Methods: 141 randomly selected patients underwent LCS total knee arthroplasty (De Puy). A single surgeon performed all operations, using an identical surgical technique. Passive flexion and extension were measured when awake, under anaesthesia, and post-operatively under anaesthesia.

Paired t-tests were used to test for significant differences between the measurements. Independent samples t-tests were used to test for significant differences between the changes in flexion, extension and ROM between the time points tested.

Results:

• When awake the mean flexion was 116.8°, extension 3.8°, and ROM 113.0°

• When anaesthetised pre-op, the flexion was 130.2°, extension 0.8°, and ROM 129.4°.

• When anaesthetised post-op the flexion was 133.8°, extension 0.2°, and the ROM 133.5°.

Knee flexion (p < 0.0001) and range of motion (p < 0.0001) were significantly greater and knee extension (p < 0.0001) was significantly reduced following anaesthesia only. A further significant increase in knee flexion (p < 0.0001) and range of motion (p = 0.00014) was observed post –operatively under anaesthetic. However knee extension did not significantly increase further (p = 0.29). The average improvement in range of motion once anaesthetised was 16.4° (SD = 13.1°) with the majority of this improvement due to an increase of flexion (average increase of 13.4° (SD = 11.9°) rather than an increase in extension (average increase of 3.0° (SD = 4.2°).

The combined effect of surgery and anaesthetic was 20.5° (SD = 12.3°), with the majority of this improvement due to an increase of flexion (average increase of 17° (SD = 8.5°) rather than an increase in extension (average increase of 3.6° (SD = 6.0°).

Discussion: Pain abolition resulted in a mean increase of 16.4° in the range of motion, and both TKA combined with pain abolition further increased significantly the range of motion to a mean of 20.5°. This study suggests that improvements in ROM following total knee arthroplasty are primarily due to reduction in the symptoms of pain and that other factors such as surgical technique and prosthesis design can further increase ROM.

Future studies should record the measurements of passive flexion, extension and range of motion in the anaesthetised patient, as this will allow objective assessment of changes in range of movement.