A new exercise protocol for improving diagnostics of short hamstring muscle-tendon length in patients with a central neurological lesion

Crouch gait is a common gait pathology in patients with central neurological lesions (CNL)1–3. However, diagnosing the underlying cause of crouch gait can be challenging as it may stem from various factors, including short hamstring muscle-tendon length (HMTL), weak hip flexor muscles, poor balance or hip and knee joint mobility deficits4. Currently, diagnosing short HMTL involves a physical exam and 3D clinical gait analysis while walking at comfortable and fast speeds to determine if a patient's HMTLmax is shorter than that of healthy controls5–8. Fast walking speeds are thought to provoke larger HMTLmax through increased step length. However, patients might be unable to increase step length due to musculoskeletal impairments other than HMTLmax (e.g., spasticity or weak hip or ankle muscles), resulting in false positive diagnoses of short HMTLmax. To address this diagnostic limitation, we established the clinical validity of a new exercise protocol in determining HMTLmax in patients with CNL. Does the new exercise protocol provoke larger HMTLmax compared to the current gold standard in patients with a CNL and healthy young adults? Retrospective data analysis of CNL patients who performed the new protocol during usual clinical care and a prospective experimental study in healthy young adults were conducted. The new exercise protocol included: walking at comfortable speed, walking as fast as possible, walking with large steps, and performing a functional popliteal angle test slowly and as fast as possible. The functional popliteal angle test was performed standing on one leg and generating a hip flexion-knee extension motion with the contralateral leg. 3D marker position data, ground reaction forces, and sEMG data were acquired. Standard OpenSim workflows were used to compute HMTLmax. Sub-group analyses were performed for patients with crouch gait without increased anterior pelvis tilt (CR), crouch gait with increased anterior pelvis tilt (CR-AT), and without crouch gait but increased anterior pelvis tilt (AT). Patients and healthy controls used largest HMTLmax during the functional popliteal angle tests, followed by walking with large steps, walking fast and at comfortable speeds. Compared to the healthy group, the CR-AT and AT groups showed higher HMTLmax in all exercises, while the CR group had lower HMTLmax. Using the current gold standard, 10 out of 35 limbs with crouch gait and/or increased pelvis tilt were diagnosed with short HMTL whereas only 3 limbs were diagnosed with short HMTL according to the new protocol. Functional popliteal angle tests and walking with large steps provoke larger HMTLmax as compared to walking as fast as possible in patients with a CNL and healthy controls. To minimize false positive diagnoses these exercises clinicians should consider incorporating these exercises into the diagnostics of short HMTL. Future activities will incorporate diagnostics of hamstring muscle spasticity.