Abstract
Outcome measures are an essential element of our industry: comparing a novel procedure against an established one requires a reliable set of metrics that are comprehensible to both the technologist and the layman.
We surmised that a detailed assessment of function before and after knee arthroplasty, combined with a detailed set of personal goals would enable us to test the hypothesis that less invasive joint and ligament preserving operations could be demonstrated to be more successful, and cost effective. We asked the simple question: how well can people walk following arthroplasty, and can we measure this?
Materials and methods
Using a treadmill, instrumented with force plates, we developed a regime of walking at increasing speeds and on varying inclines, both up and down hill. The data from the force plates was then extracted directly, without using the proprietary software that filtered it. Code was written in matlab script to ensure that missed steps were not mistakenly attributed to the wrong leg, automatically downloading of all the gait data at all speeds and inclines.
The pattern of gait of both legs could then be compared over a range of activities.
Results
Wide variation is seen in gait both before and after arthroplasty. The variables that are easiest to explain are these:
width of gait – this appears to be a pre-morbid variable, not easily correctible with surgery. (figure 1)
top walking speed – total knee replacement is associated with 11% lower top speeds than uni knees or normals (p < 0.05)
change in stride length with increasing speed: normal people increase their walking speed by increasing both their cadence and their stride length incrementally until a top stride length is reached. Patients with a total knee replacement do not increase their stride length at a normal rate, having to rely on increasing cadence to deliver speed increase. Patients with uni or bi-compartmental knee replacements increase speed like normal people.
Downhill gait: as many as 40% of fit patients with ‘well functioning’ total knee replacements choose not to walk downhill at all, while all fit patients with ‘well functioning’ partial replacements are able to do this. Those who can manage, can only manage 90% of the normal speed, unlike unis which are indistinguishable from normal (p < 0.05)
Conclusions
At higher speeds and on inclines, the presence of an intact cruciate ligament couple enables a near normal gait, following both Unicondylar knee arthroplasty and Uni + PFJ arthroplasty. Total knee arthroplasty, whether cruciate retaining or sacrificing, prevents normal gait at higher speed. An intact anterior cruciate may be an essential part of gait, playing a greater role in the swing through phase of gait. Resecting it as part of an arthroplasty may not be in the best interest of the patient's gait.
