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Using a Knee Arthrometer to Evaluate Tissue-specific Contributions to Knee Flexion Contracture in the Rat

Normal knee range of motion (ROM) is critical to well-being and allows one to perform basic activities such as walking, climbing stairs and sitting. Lost ...

The Ottawa Hospital Rehabilitation Centre

A linear piston hydraulic angular-velocity-based control knee joint was designed for people with knee-extensor weakness to engage knee-flexion resistance when knee-flexion angular velocity reaches a preset threshold, such as during a stumble, but to otherwise allow free knee motion. During mechanical testing at the lowest angular-velocity threshold, the device engaged within 2 degrees knee flexion and resisted moment loads of over 150 Nm. The device completed 400,000 loading cycles without mechanical failure or wear that would affect function. Gait patterns of nondisabled participants were similar to normal at walking speeds that produced below-threshold knee angular velocities. Fast walking speeds, employed purposely to attain the angular-velocity threshold and cause knee-flexion resistance, reduced maximum knee flexion by approximately 25 degrees but did not lead to unsafe gait patterns in foot ground clearance during swing. In knee collapse tests, the device successfully engaged knee-flexion resistance and stopped knee flexion with peak knee moments of up to 235.6 Nm. The outcomes from this study support the potential for the linear piston hydraulic knee joint in knee and knee-ankle-foot orthoses for people with lower-limb weakness.

Mechanical and biomechanical analysis of a linear piston design for angular-velocity-based orthotic control.

Joint contractures alter the mechanical properties of articular and muscular structures. Reversibility of a contracture depends on the restoration of the elasticity of both structures. We determined the differential contribution of articular and muscular structures to knee flexion contractures during spontaneous recovery. Rats (250, divided into 24 groups) had one knee joint surgically fixed in flexion for six different durations, from 1 to 32 wk, creating joint contractures of various severities. After the fixation was removed, the animals were left to spontaneously recover for 1 to 48 wk. After the recovery periods, animals were killed and the knee extension was measured before and after division of the transarticular posterior muscles using a motorized arthrometer. No articular limitation had developed in contracture of recent onset (≤2 wk of fixation, P > 0.05); muscular limitations were responsible for the majority of the contracture (34 ± 8° and 38 ± 6°, respectively; both P < 0.05). Recovery for 1 and 8 wk reversed the muscular limitation of contractures of recent onset (1 and 2 wk of fixation, respectively). Long-lasting contractures (≥4 wk of fixation) presented articular limitations, irreversible in all 12 durations of recovery compared with controls (all 12 P < 0.05). Knee flexion contractures of recent onset were primarily due to muscular structures, and they were reversible during spontaneous recovery. Long-lasting contractures were primarily due to articular structures and were irreversible. Comprehensive temporal and quantitative data on the differential reversibility of mechanically significant alterations in articular and muscular structures represent novel evidence on which to base clinical practice. 

Quantitative and temporal differential recovery of articular and muscular limitations of knee joint contractures; results in a rat model.

Knee flexion contractures prevent the full extension of the knee joint and cause disability. The etiology is not well defined. Extended periods of immobilization of joints lead to contractures difficult to completely reverse by rehabilitation treatments. Recovery of the complete range of motion without intervention has not been studied but is of importance to optimize clinical management. This study was designed to quantify the spontaneous reversibility of knee flexion contractures over time.

Louis Goudreau

The Ottawa Hospital Rehabilitation Centre

Using a Knee Arthrometer to Evaluate Tissue-specific Contributions to Knee Flexion Contracture in the Rat