To illustrate this process, consider the dysfunction of the right knee of the young man (SR) with cerebral palsy spastic diplegia (Video 3). One can readily appreciate from the video presentation that his right knee is excessively flexed (bent) when his foot initially contacts the ground at "initial contact" and remains in that position while the foot is on the ground throughout "stance". This is referred to as a "crouch gait pattern." Also observe that the knee does not flex properly as the right leg moves forward in "swing", referred to as a "stiff knee pattern." Not surprisingly, a plot of his knee position as a function of the gait cycle (Figure 2) demonstrates these same findings.
Knee kinematics for an adolescent with cerebral palsy spastic diplegia (shown in Video 3). The knee is excessively flexed at initial contact (Point A, when the foot first contacts the ground at beginning of the gait cycle) and remains excessively flexed while in contact with the ground (Point B, throughout stance phase of the gait cycle). Blue band on plot signifies first standard deviation of the mean normal reference in degrees.
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Video 3. This is an adolescent male with cerebral palsy spastic diplegia. Pay particular attention to position of right knee at initial contact and throughout stance phase of the gait cycle (see also Figure 2).
Clinical examination reveals tightness of both medial and lateral hamstring muscles, suggesting that the hamstrings might be restraining the knee in a crouched position. The hamstring EMG tracing (Figure 3) indicates continuous activity throughout stance and into swing, further substantiating the hamstrings as a primary concern. Are there other abnormalities involving the pelvis, hip, or ankle that might contribute to this crouched knee gait pattern?
Knee kinematics and associated hamstrings EMG tracing for an adolescent with cerebral palsy spastic diplegia (shown in Video 3) indicating that the hamstrings are active throughout stance phase (Point A). The blue band on the knee angle plot signifies first standard deviation of the mean normal reference in degrees. Normal firing patterns are indicated by blue bars above each signal.
An examination of the hip angle plot (Figure 4) indicates a reduction of hip extension in stance that is consistent with the crouched knee position. This may also be attributed in part to hip extensor muscle weakness (seen during the clinical examination). Consequently, the inappropriate flexion of the knee at initial contact may be due to the hamstring tightness, and the excessive knee flexion in stance may be due to both the tight hamstrings and the weak hip extensors that cannot effectively pull the thigh posteriorly and thereby reduce the crouched knee position. Hip flexor muscle tightness can sometimes restrict hip extension in stance, but is not implicated in this case, as there was no evidence of a hip flexion contracture in the clinical examination. The posterior positioning of the pelvis (Figure 5) is also consistent with the hamstring tightness. Ankle position (or muscles crossing the ankle) does not contribute to the crouched knee position because excessive dorsiflexion, sometimes seen with plantar flexor weakness, is not present in this case. (Figure 6)
Knee and hip kinematics for an adolescent with cerebral palsy spastic diplegia (shown in Video 3). The excessive hip flexion in late stance (Point A, ie, the hip does not achieve extension) could either be associated with excessive knee flexion in stance or inappropriate pelvic position (anterior tilt). Blue band on each plot indicates first standard deviation of the mean normal reference in degrees.
Knee, hip and pelvic kinematics for an adolescent with cerebral palsy spastic diplegia (shown in Video 3). Posterior tilt of pelvis in stance (Point A) is consistent with hamstring tightness which tends to tether the pelvis. Consequently, the crouch gait pattern (excessive knee flexion in stance) appears to be caused by this hamstring muscle tension. Blue band on each plot indicates first standard deviation of the mean normal reference in degrees.
Knee and ankle kinematics for an adolescent with cerebral palsy spastic diplegia (shown in Video 3). The absence of excessive ankle dorsiflexion in stance (Point A) indicates that plantar flexor weakness is not contributing to his crouch gait pattern (excessive knee flexion in stance). Blue band on each plot indicates first standard deviation of the mean normal reference in degrees.
Returning to the issue of the stiff knee gait in swing, the rectus femoris muscle may be contributing because inappropriate activity (spasticity) of the rectus femoris (a knee extensor) is thought to impede knee flexion in swing. The rectus femoris spasticity observed during clinical examination, prolonged rectus femoris EMG activity in swing during gait, and the delay in the timing of the peak knee flexion in swing are all evidence in support of rectus femoris involvement. (Figure 7) The EMG tracings also demonstrate the usual lack of involvement of the vastus medialis and vastus lateralis muscles in this phenomenon.
Knee kinematics and associated EMG tracings for the rectus femoris, vastus lateralis, and vastus medialis muscles in an adolescent with cerebral palsy spastic diplegia (shown in Video 3). Delay in timing of peak knee flexion in swing (Point A), reduced range of motion of the knee in swing (Point B), and prolonged activity of rectus femoris (Point C) all serve to implicate rectus femoris spasticity as the cause of the knee kinematic anomalies in swing phase. Note absence of inappropriate activity of the two vastii muscles that were monitored. Blue band on knee angle plot indicates first standard deviation of the mean normal reference in degrees. The normal firing patterns are indicated by the blue bars above each signal.
This relatively simple example, with a focus on knee flexion/extension dysfunction, demonstrates the successful integration and use of different sources of data in this case, video recordings, joint angle plots, clinical examination results and EMG tracings. It also illustrates the appreciation of the dynamics occurring proximal and distal to the joint of interest and the consideration of the role of these two joint muscles.
A challenge in gait data interpretation is to identify the primary problems that perhaps need to be addressed and then to recognize secondary abnormalities, produced as result of the primary problems, and to appreciate compensatory mechanisms (ie, strategies the patient uses to overcome the impairment). In the case just presented, for example, the primary problem of the crouched knee (as a result of the hamstring tightness and hip extensor weakness) produced secondary "abnormalities" at the hip (reduced hip extension in stance) and pelvis (the posterior position), all of which should be resolved with hamstring intervention.
The Role of the Interdisciplinary Team
At our institution, gait data are interpreted by a team that consists of the orthopedic surgeon to whom the patient was referred and the physical therapist or kinesiologist who collected data. At times, the engineer or technician, again who collected data, or the biomechanical engineer who developed the mathematical models used to process data, is involved if there are questions of data quality or if some previously unseen walking mechanism is encountered. In general, it is important that the team have at least a rudimentary understanding of the gait model used to produce the results, in addition to a well-developed understanding of normal gait. This knowledge base, underpinned by experience gained from the examination of many pre- and post-treatment cases, is absolutely essential to produce a proper interpretation and treatment decision.
Cite this: Clinical Gait Analysis and Its Role in Treatment Decision-Making - Medscape - Sep 01, 1999.