by Dan Santa Maria, MD
with special thanks to
Gordon Bosker, C.P.O.
Participating in sports provides the athlete with a sense of self worth, social contacts, aerobic conditioning and the ability to move quickly to evade danger or assist loved ones.
In the past, the aim of medical and prosthetic treatment of the amputee was merely functional ambulation. Recent advan-ces in prosthetics and an expansion of our knowledge of amputee biomechanics have made running and participation in sports a possibility for these individuals.
Hydraulic knees (complete with pistons that allow for control of friction in both swing and stance) are added to the prosthesis of above knee (transfemoral) amputees and allow amputees to run at variable cadences that would previously have been impossible with the old constant friction knee units. Even hydraulic knee units are unable to provide a smooth knee flexion like that which occurs in the sound limb with heel strike (initial contact). Much work needs to be done in this area in the future.
Both above and below the knee runners have embraced dynamic response feet which resemble a large metal “J” in appearance and function like a spring, imperfectly reproducing the power generation of the gastrocnemius and soleus in terminal stance. J.M. Czernieki defined spring efficiency as the amount of energy generated, divided by energy absorbed by a prosthetic foot. The newer dynamic response models were found to have twice the spring efficiency of the standard SACH (solid ankle cushion heel) feet but less than half of that of the sound limb with an intact gastrocnemius. However, there has been a good deal of controversy about these “feet” given the sparse literature supporting their use. Some argue that they confer no greater advantage than the old wood and foam SACH feet while others go as far to argue that they provide an unfair advantage to the amputee athlete over their able bodied peers.
A study investigating dynamics (mechanical work) of amputee running revealed that amputees absorbed and generated less energy in the prosthetic (amputated) limb even in muscles that were intact and uninjured such as the quadriceps in below the knee amputees, suggesting again that even with sound prosthetic components the amputee athlete tends to use their prosthetic limb passively and with less confidence which may limit their performance in sports.
Despite these limitations, amputee athletes continue to push the boundaries of performance as evidenced by Paul Martin, who placed 89th in a field of approximately 1,500 triathletes in the Iron Man competition. Oscar Pistorius, a bilateral congenital amputee sprinter holds the world Paralympic 100 meter record with a time of 10.91 seconds, and plans to try out for the upcoming Olympics (but may be stymied by the dynamic response foot controversy). The talent and perseverance of athletes such as these and new insights into the biomechanics of amputee running should inspire further research and im-provements in prosthetic technology.
Dan Santa Maria, MD is a completing his fourth and final year of training in Physical Medicine and Rehabilitation at the UTHSCSA. His professional interests include electrodiagnostic medicine, biomechanics, sports and musculoskeletal medicine. After graduation he plans to complete a fellowship in sports medicine and remain at the Health Science Center as junior faculty.
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