Function and strength of electrically stimulated hip flexor muscles in paraplegia

In this study hip flexion moments and fatigue were measured in paraplegic individuals that were implanted with percutaneous intramuscular electrodes as part of their functional electrical stimulation (FES) system for walking. The largest average hip flexion moment (36% of normal) was measured at small hip flexion angles. This percentage decreased with an increase in hip flexion angle until only an extension moment was measured above 90°. Except for the sartorius, all hip flexors including the gracilis, adductor longus, tensor fasciae latae, and iliopsoas produced extension moments at large hip flexion angles. The current iliopsoas implantation technique utilizing stimulation of the second and third lumbar motor roots resulted in recruitment of the adductor longus and brevis or pectenius causing extension moment that negated any iliopsoas creating flexion component at large hip flexion angles. Even though measured moments were minimal, the paraplegic subject was able to maintain cyclic hip flexions above 40° at the rate of 30/min over 30 min. At the slower rate a much greater flexion such as required for stair climbing can be maintained for a prolonged period. A new implantation technique using soft tissue endoscopy is being developed to isolate recruitment of iliopsoas and to extend the range of hip flexion