Knee joint kinematics in gait and other functional activities measured using flexible electrogoniometry: how much knee motion is sufficient for normal daily life?
Introduction
Many orthopaedic and physical therapy techniques aim to restore joint motion and hence promote rehabilitation of functional activities. These techniques are designed to restore pain free and unrestricted movement to joints on the assumption that patients will subsequently exhibit better functional ability and less impairment and disability. However the scientific evaluation of these techniques has been limited by the lack of appropriate knowledge regarding the kinematics of the knee during normal functional activity and an appropriate method for measuring knee kinematics in clinical practice.
For the knee, a number of clinical rating scales exist which use a series of standard questions and basic clinical measurements to evaluate knee function. Two commonly used examples of these types of scores are the WOMAC scale [1] and the American Society of Orthopaedic Surgeons Clinical Rating System [2]. These type of clinical rating scale provide a simple and inexpensive method of assessment, suitable for routine use in a busy clinical environment. However these scales are subjective, involving both the clinician and patient, they often lack sensitivity to post-intervention rehabilitation and the clinical significance of the results in relation to the restoration of knee joint movement is often unclear [3]. While valuable as measures of the outcome of surgery these scores shed little light on the resulting knee joint kinematics and the functional ability of the patients following rehabilitation.
Measurements of active and passive joint range are often employed to indicate the status of a joint [4]. These measures are usually recorded while lying in a supine position or while sitting (both non-weight bearing activities) and exhibit poor inter-rater reliability [5]. Moreover the active or passive range of motion has not been shown to reflect the joint movement exhibited by the patients during functional activities performed as part of normal daily life [4]. To evaluate the dynamic behaviour of a joint, we would suggest that the motion of the joint must be recorded during a number of real life functional activities.
Sophisticated motion analysis systems are available [6], [7] which employ force plates, cameras, E.M.G. and computerised recording equipment to record the patients movements in a clinical laboratory. These systems are capable of providing a full biomechanical model of motion including predictions of joint loads and phasic muscle actions [8]. Such techniques provide valuable data for the design of implants and surgical techniques and expand our understanding of the mechanics of normal and pathological human movement [9], [10]. Such systems are invaluable in the clinical assessment of complex pathologies and disabilities such as cerebral palsy [11]. However they are expensive and time consuming to conduct and have therefore only been used to study small numbers of patients in specialist centres performing a single functional activity.
To respond to the increasing demand for evidence based practice and the optimisation of clinical effectiveness, the rehabilitation specialist requires a method of establishing the dynamic behaviour of a joint, during a number of functional activities, routinely in the clinical environment. The data provided by these assessments will, we believe, be a more appropriate reflection of the effect of treatment on the kinematics of the joint and the patients functional ability than either clinical rating scores or the biomechanical evaluation of a single functional activity.
Flexible electrogoniometry [3], [12], [13] offers the opportunity to investigate joint kinematics during a number of functional activities routinely in the clinical environment. This method is inexpensive, portable, comfortable to wear and relatively simple to operate [13]. The results are immediately available and can be shown to the patient at the time of testing. The authors have used flexible electrogoniometers to evaluate a number of clinical issues over the past decade. These include the rehabilitation of total hip replacement patients [3], [13]; the influence of computerised kinematic biofeedback on patient performance following total knee joint replacement [14]; the use of therapeutic electrical stimulation in the treatment of hemiplegic cerebral palsy [4], [15]; the stair climbing ability of elderly patients following fractured neck of femur [16] and the functional performance of knee replacement patients with and without patella resurfacing during a range of functional activities.
In all of these studies we have encountered a lack of data describing normal knee kinematics. In particular, describing normal knee kinematics during a number of functional activities in a group of elderly normal subjects. This project therefore aimed to record the knee kinematics of a group of elderly normal subjects in a range of functional activities. This paper reports the patterns and ranges of motion found in different functional tasks and explores the relationships between them.
Section snippets
Method
Twenty elderly normal subjects were recruited and informed consent was obtained from all subjects. The study was granted ethical approval by the ethics committee of Lothian Health. The sample was one of convenience, subject being recruited using informal contacts and recruitment posters. The normal subjects had a mean age of 67 (S.D. 8, range 49–80). There were 16 female and four male subjects. The average mass of the subjects was 68 kg (S.D. 11, range 54–90) and the average height 1.63 m (S.D.
Results
Table 1 shows the mean, minimum left knee joint angle, maximum left knee joint angle and excursion (maximum–minimum) of the left knee joint, for the group of normal elderly subjects (n=20) during the eleven functional tasks. The table also includes the standard deviation and group maximum and group minimum value. Table 2 shows the average knee joint excursion, standard deviation and 95% confidence limits for the normal elderly group, for the left and right knees and for the mean of both knees.
Discussion
According to the data provided by the American Academy of Orthopaedic Surgeons [17] the normal human knee has a passive range of motion from 10 degrees hyperextension through to 134 degrees of flexion during static examination. This gives a total knee excursion of 144 degrees. The active range of motion measured in the normal group presented in this study was 138 degrees. For the functional tasks measured using electrogoniometry the excursion of the knee varied from 61.6 to 131.3 degrees. It
Conclusions
The electrogoniometer system proved to be a useful measurement system which gave joint angles of similar magnitude to those reported for gait and stair climbing. It was able to detect small but meaningful differences in the performance of the group between functional tasks for example between gait and walking up and down slopes. Provide care is taken to handle and mount the electrogoniometers appropriately the system is capable of giving meaningful clinical data with a high degree of cost and
Acknowledgements
This work was supported by a Knee Research Fellowship awarded to C. Myles by Depuy International Limited as part of a larger study of osteoarthritis and knee replacement with and without patella resurfacing.
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