Abstract
Introduction
Our primary hypothesis was simple: does gait on a downhill gradient distinguish between types of knee arthroplasty? Our secondary hypotheses were these: are stride length and other kinematic variables affected by cruciate ligament integrity following knee arthroplasty?
Participants
Ethical approval was sought and gained prior to commencement of the study. 52 subjects were tested on the instrumented treadmill, 3 groups (UKA, TKA, and young healthy control) of 19, 14, and 19 respectively. The two high performing arthroplasty groups were recruited from a database of patient related outcome measures (PROMs) and were chosen based on high Oxford knee scores (OKS) with a minimum 12 months post hip arthroplasty.
Gait Analysis
Gait performance was tested on a validated instrumented treadmill (Kistler Gaitway®, Kistler Instrument Corporation, Amherst NY)[22, 23]. The rear of the treadmill was ramped with 30 cm axle stands in order to create a 7 degree decline for downhill walking (figure 1). The speed was increased incrementally. Hof scaling and body weight normalising was also applied to the outputted mechanical data to correct for leg length and mass differences, respectively.
Results
Patient Related Outcome Measures
Both arthroplasty groups outcome scores were substantially better than the average reported by national joint registries.
Treadmill Gait Analysis
When walking fast downhill, UKA patients walked 15% faster than the TKA patients (1.75 vs 1.52 m/sec p=0.000) despite having the same cadence (134 vs 135step/min) (figures 2,3,4). The 15% difference in speed was largely due to the reduced mean step (p=0.001) and stride lengths (p=0.000) seen in the TKA patients. These finding persisted after Hof scaling, which normalised speed for leg length (p=0.000).
The values are indicated as means ± standard deviation; †significant difference between implant versus control (p <0.05); ‡significant difference between implant groups (p<0.05);H=normalized to leg length; BW=normalized to body weight.
Discussion
The UKA group walked 15% faster than the TKA, with stride length almost matching the normal controls. The presence of intact cruciate ligaments allow a normal and co-ordinated swing phase, enabling the more normal stride, while the absence of the anterior cruciate ligament contributes to the reduction of knee flexion in swing phase, and thus the shorter stride length.
