Siegel, K Lohmann, Kepple, TM, Stanhope, SJ; National Institutes of Health, Bethesda, MD. karen_siegel@nih.gov.

PURPOSE: The ability to extend the knee is critical to preventing limb collapse during upright activities. The purpose of this case report was to describe subjects with unilateral quadriceps femoris weakness who each used a different compensatory strategy to produce knee extension during gait. SUBJECTS: Subjects were 3 males with less than anti-gravity strength in the quadriceps femoris and a variable pattern of weakness elsewhere in the lower extremity. Subject 1 (16 yrs) was 1 year post limb salvage surgery for an osteosarcoma of the left distal femur. Subject 2 (29 yrs) was 5 months post excision of a soft tissue sarcoma of the right pubic ramus complicated by a femoral nerve injury. Subject 3 (54 yrs) was diagnosed with amyotrophic lateral sclerosis more severely affecting the left lower extremity. METHODS AND MATERIALS: Subjects walked barefoot at a self-selected speed without assistive devices. Gait analysis of the pelvis and bilateral lower extremity segments was performed with a 6 camera, 2 force platform 3D motion capture system. ANALYSES: Joint moments were computed from the motion capture data. A musculoskeletal model was used to assess the relative ability of each lower extremity joint moment and gravity to accelerate the knee during the early stance phase of gait. RESULTS: Results are ipsilateral to the side of the quadriceps femoris weakness unless otherwise stated. Subject 1 generated knee extension almost exclusively via the hip extensor moment (94%). Subject 2 relied less on the hip extensor moment (39%) and more on the ankle plantar flexor moment (61%) to create knee extension. For Subject 3, the ipsilateral hip extensor moment (24%) and the contralateral ankle plantar flexor moment (67%) assisted knee extension. CONCLUSIONS: A variety of adaptive strategies both within and across limbs can produce knee extension during gait. The strategy selected by each subject likely was influenced by both their total pattern of impairments and the effectiveness of the available compensations. Knowledge about the type and effectiveness of the strategies used by these subjects to compensate for quadriceps femoris weakness assisted the selection of treatment interventions for these individuals. FUNDING SOURCE: No external funding supported this study and the authors have no financial interest in the outcome.

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