Effectiveness of physiotherapeutic management of osteoarthritic knee

Abstract

Our previous study demonstrated that two weeks of daily TENS produces a cumulative antinociceptive effect in patients with chronic low back pain (Cheing and Hui-Chan 1996). Osteoarthritic (OA) knee is a highly prevalent condition in Hong Kong, manifested by pain, muscle weakness and a limited range of knee joint movement. The present thesis consisted of three inter-related studies with the following objectives. First, we set out to investigate the baseline pain level and motor dysfunction of patients with OA knee as compared with the normal age-matched subjects in a Chinese population. Specifically, motor performance was assessed by (a) the isometric peak torque of the knee extensors and flexors; (b) the gait velocity, cadence and stride length; and (c) the range of knee movement at rest and during walking. Second, we compared the time course and possible cumulative antinociceptive effects on the intensity and unpleasantness of OA knee pain of 4 different treatment protocols over a 4-week period. The four protocols were (1) TENS for 60 min; (2) placebo stimulation for 60 min; (3) isometric exercise training for the knee extensors and flexors for 30 min; and (4) TENS for 60 min plus isometric exercise for 30 min. Third, we evaluated the relative effectiveness of the four treatment protocols in improving the motor functions of patients with OA knee. The latter was assessed as an increase in the peak torque of the knee muscles, gait performance and range of knee movement from the baseline value. Sixty-two patients, aged 50 to 70, were matched according to age, gender and body mass index before being randomly allocated to four groups. They received either (i) 60 min of conventional TENS, (ii) 60 min of placebo stimulation, (iii) 30 min of isometric exercise training for the knee, or (iv) 60 min of TENS plus 30 minutes of exercise on each workday over a 4-week period. A follow-up assessment was conducted four weeks after the treatment period stopped. Two separate, colour-coded visual analogue scales recorded the intensity (VAS INT) and unpleasantness of pain (VAS UNPL) before, during and after each treatment during the whole study period. The motor performance of both knees was evaluated in session1, session10, session20 and the follow-up session. The isometric peak torque of the knee extensors was measured at 30o, 60o and 90o of knee flexion by the Cybex II+ dynamometer system with the subjects seated. The peak torque of the knee flexors was measured at 90o. Electrogoniometers were used to measure the range of knee motion at rest (with the subject supine) and during walking. An electric foot-switch system was used to record the spatio-temporal gait parameters along a 7.5m level walkway, specifically the gait velocity (cm/s), cadence (steps/min) and stride length (cm). Our findings suggested that there was a cumulative pain reduction in the VAS INT and the VAS UNPL scores in all treatment groups over the study period (all p<0.05), except the exercise group. For the intensity of pain, the TENS group showed the greatest (45.9%) cumulative reduction in pain intensity by session20, without reaching statistical significance when compared with the other three treatment groups. It is interesting to note that the application of TENS alone improved certain motor functions such as muscle strength and gait performance. Depending on the initial knee joint angle, this group showed an average of 12.5% increase in the isometric peak torque of the knee extensors. For the spatio-temporal gait parameters, the TENS group showed an average of 9.1 to 19.7% improvement over time. Exercise training is usually recommended to restore muscle strength and gait performance. Nevertheless, our findings suggest that exercise can affect the pain level of patients with OA knee at different stage of the training. During the initial three sessions, there was about 30% increase in the knee pain. It was reduced gradually to 29.3% below the baseline level by session20. Although the placebo group showed a reduction of knee pain over time, there was negligible improvement in the motor parameters recorded. Of the 4 treatment protocols in this study, TENS plus exercise seems to be the most effective rehabilitation strategy for patients with OA knee. The addition of TENS to isometric exercise training controlled the knee pain that was aggravated by exercise during the initial sessions. By session20, there was a 29.4% pain reduction and an average of 26.6% improvement in the isometric peak torque of the knee extensors, depending on the initial knee joint position. For the temporal gait parameters, this group showed a 12.6% increase in stride length (p=0.006), a 9.3% increase in cadence (p=0.098) and a 22.4% increase in gait velocity (p=0.034) by session20. In addition, the TENS plus exercise group was the only group that demonstrated a significant gain (12.0%, p=0.000) in the functional range of motion of the knee joint during walking across all testing sessions. At the baseline recording in session1, we found some 10 to 33.3% deficiencies in the various motor functions of the patients with OA knee as compared to normal subjects. By the end of the four-week treatment period, patients in the TENS plus exercise group appeared to have restored most of their OA-related physical deficiencies.