Movement of the knee in osteoarthritis: The use of electrogoniometry to assess function

Movement of the knee in osteoarthritis: The use of electrogoniometry to assess function

Walker, C R C

THE USE OF ELECTROGONIOMETRY TO ASSESS FUNCTION

We used electrogoniometers to measure the range of movement (ROM) of the knee during various

activities, comparing 50 patients with osteoarthritis of the knee (OA) with 20 healthy age- and sex-matched subjects.

The minimum and maximum joint angles and the ranges of excursion of the patient and control groups were tested for significant differences, using an unrelated Student’s t-test with pooled variance. Knee flexion in patients with OA was significantly reduced during all activities (p

Electrogoniometry of the ROM of the knee provides a reliable, accurate and objective measurement of knee function.

J Bone Joint Surg [Br] 2001;83-B: 195-8.

Received 27 September 1999; Accepted 6 June 2000

Knee scoring systems attempt to measure the outcome of treatment objectively. Some concentrate mainly on levels of pain and disability1 and others on joint stability;2 all attempt to measure functional outcome, and most include questions relating to daily activities or sports. Patients’ responses, however, coloured by their expectations, are often too subjective to yield a satisfactory measurement.

For example, the hopes of a patient undergoing total knee replacement (TKR) are very different from those of an athlete having reconstruction of an anterior cruciate ligament.

We used electrogoniometers to compare the range of movement (ROM) in osteoarthritic and normal knees during a range of typical daily activities.

Materials and Methods

We included in the study 50 patients (24 women and 26 men) awaiting TKR for unilateral or bilateral osteoarthritis (OA) of the knee. The mean American Knee Society score was 41 and the mean functional score was 58 (Table I). We excluded patients with inflammatory polyarthritis or disorders affecting movement of the hip or gait, or if they had previously undergone major surgery on the knee. We obtained the approval of the Ethics Committee, and all patients gave written consent. Patients continued taking prescribed analgesics or non-steroidal anti-inflammatory medication throughout the study. We compared these patients with a control group of 20 age-matched volunteers, 16 women and four men, who had no knee symptoms or clinical evidence of OA.

Using two flexible electrogoniometers (M180 Twin Axis; Penny & Giles Biometrics Ltd, Blackwood, Gwent, UK) we measured movement in the sagittal plane in all knees. The electrogoniometers had no fixed centre of rotation. They were easy to attach and did not obstruct movement of the knee. A switch attached to the sole of the foot made it possible to determine the time that the knee took to complete its arc. Using repeat static and dynamic calibration and external validation against a Vicon 370 motion analysis system (Vicon 370 Clinical; Oxford Metrics, Oxford, UK), we confirmed that the results were both reproducible and accurate and that this system was precise enough to record the ROM of knees in vivo to within 2 deg.

Patients and control subjects undertook 11 functional activities, which fell into two types. Type-A activities involved cyclical movement and low excursion ranges including level walking, ascending and descending a slope, climbing and descending stairs. Type-B activities involved large excursion ranges such as sitting down and rising from a low chair, sitting down and rising from a standard chair, and getting into and out of a bath.

The location of tests and the equipment remained constant throughout the study. Ascending and descending a slope were measured on a 5 deg incline and stair-climbing on 165 mm high steps. The low chair was 380 mm high and the standard chair 460 mm. The height of the sides of the bath measured 590 mm. Measurements of the static ROM were obtained with subjects lying supine on an examination couch and actively flexing or extending their knees.

They were recorded on a lightweight data-logger, down– loaded on to a PC and imported into Excel for Windows. The maximum knee flexion recorded during an activity was termed the maximum joint angle and the maximum extension was termed the minimum joint angle. The angle between the minimum and maximum joint angles was described as the excursion range. Using the foot-switch or the joint angle data, we isolated one cycle of each functional activity, and determined the maximum and minimum joint angles and excursion ranges of each. From the data obtained for all 11 functions for all subjects, we calculated the mean, SD and maximum and minimum values for patients and control subjects (Table II). Using an unrelated Student t-test with pooled variance, we tested the maximum and minimum joint angles and excursion range for significant differences between the OA and control groups. Because 11 Student t-tests were conducted for each outcome variable, the method of Bonferroni was applied and the p value reduced from p = 0.05 to p = 0.004.

Results

Table II shows the joint angles recorded for patients and control subjects. When descending stairs, patients extended their knees more than the control subjects, and the difference between the minimum joint angles of the OA and control groups was significant. No other activities produced significant differences in minimum joint angles. Control subjects at walking level had a maximum joint angle of over 60 deg, which was similar on slopes. Climbing or descending stairs required maximum joint angles of 90 deg to 100 deg, and sitting down in and rising from a low chair over 100 deg . A maximum joint angle of more than 130 deg was needed for getting into and out of a low bath. During all 11 functions the maximum joint angles and excursion ranges of OA patients were significantly reduced. The greatest maximum joint angle recorded was 80 in the patient group and 138 deg in the control group. When getting into and out of a bath, patients with OA displayed only 60% of normal knee flexion, while in all other activities it was 70% to 80%.

TKR had been performed on the contralateral knee in 14 patients. The contralateral knee was normal in 21 and osteoarthritic in 15. Table III shows the total ROM of the contralateral knees during the 11 functional activities.

Table IV compares the static ROM, measured with subjects lying supine, with the maximum functional ROM measured during the various activities. In the control group, the mean static measurements of ROM approached those of the mean functional values, but the coefficient of determination (r^sup 2^) between functional and static total excursion was 0.6, indicating that variation in the functional angles accounted for 60% of variation in the static angles (Fig. 1). There were wide differences between the static and functional measurements of ROM of the osteoarthritic patients and the control group. There was also wide variation in the measurements of individual patients. The coefficient of determination between the functional and static total excursion in the patient group was 0.59.

Discussion

Many studies have assessed the ROM of the normal knee during various activities,3-7 but none has compared age– matched groups of normal and OA knees. Our findings illustrate the restrictions imposed on patients by lack of knee flexion and the functional effects of treatment, particularly TKR.

For level walking, a maximum joint angle of about 65 deg is required. Although the mean static ROM in patients with OA was 98 deg, during level walking a mean functional ROM of only 48 deg was exhibited. This indicates that load-bearing inhibits joint movement; it seems that patients feel less pain on walking if the knee is braced and held stiff. The effects of load-bearing are even more marked in stair-climbing, during which the mean range of excursion was 800 in the control group and only 62 deg in those with OA. Getting out of a bath normally requires 130 deg of knee flexion, but a patient with an OA knee uses only 74 deg. These differences suggest that people with OA of the knee develop ways of compensating, and modify their behaviour to reduce the demands on their knees. We observed that they executed tasks hesitantly, moving more slowly and less fluidly than the control subjects. They used rails to negotiate stairs and supported their weight on their arms when getting in and out of chairs and baths, lowering themselves slowly at first, and then suddenly letting their bodies drop.

Static non-load-bearing measurements of ROM are a major component of knee scoring systems used to assess outcome after TKR, but are clearly not a true reflection of knee function. They give an indication of the potential ROM, but it is apparent that patients with OA do not fully use this. The component of knee-scoring systems which deals with functional ability usually takes the form of the patients’ own evaluation of ability to walk certain distances, climb stairs or manage low chairs. Present knee– scoring systems offer no way of objectively measuring knee function during these activities. Electrogoniometry accurately measures the functional ROM during load-bearing in activities such as level walking, stair-climbing, and rising from a chair. The functional ROM before and after TKR can therefore be compared to obtain an objective assessment of function after treatment.

Further studies are under way using electrogoniometry both to assess the functional outcome after TKR for OA and to compare the outcome of TKR procedures in which the patella is resurfaced with those in which it is not.

Electrogoniometry is relatively inexpensive, can be performed in a normal clinical setting with minimal inconvenience to the patient, and may prove to be a valuable objective tool for comparative evaluation of different prostheses or surgical techniques for TKR.

One or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition benefits have also been or will be directed to a research fund, foundation, educational institution, or other non-profit institution with which one or more of the authors is associated.

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C. R. C. Walker, C. Myles, R. Nutton, P. Rowe

From Southern General Hospital, Glasgow and Princess Margaret Rose Orthopaedic Hospital and Queen Margaret College, Edinburgh, Scotland

C. R. C. Walker, FRCS (Tr & Orth), Consultant Orthopaedic Surgeon Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF, UK.

C. Myles, BSc, Research Physiotherapist R. Nutton, MD, FRCS, Consultant Orthopaedic Surgeon Princess Margaret Rose Orthopaedic Hospital, 41-43 Frogston Road West, Fairmilehead, Edinburgh EH10 7ED, UK.

P. Rowe, PhD, Senior Lecturer Department of Physiotherapy, Queen Margaret College, Edinburgh, UK.

Correspondence should be sent to Mr C. R. C. Walker.

Copyright British Editorial Society of Bone & Joint Surgery Mar 2001

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