Influencing factors on swing phase ground clearance in transfemoral prostheses - A biomechanical study

Prosthetic fittings for persons with a transfemoral amputation should provide adequate ground clearance (GC) during prosthetic side swing to minimize the risk of stumbling or falling. Insufficient ground clearance often leads to compensatory movements that consequently influence gait biomechanics negatively.

How do different prosthetic components and alignment of a transfemoral prosthesis affect prosthetic side GC and compensatory strategies during level walking?

Eight persons with transfemoral amputation were enrolled. Three different knee joints (one monocentric and two polycentric) as well as two prosthetic feet (with and without passive dorsiflexion) were investigated. For prosthetic alignment, ap-position of the knee and foot as well as prosthesis length were varied. Kinematic and kinetic parameters were recorded with a 12-camera optoelectronic system and two force plates embedded in a 12-m walkway. The measurements were performed during level walking with self-selected slow, mid and fast gait speed.

Several consistent effects were observed. GC increased with higher prosthetic swing knee flexion angle, a more anterior knee position and more posterior foot position. The individual swing phase control of the investigated knee joints showed a higher impact on GC than by geometric shortening effects of the polycentric knee joints. Passive ankle dorsiflexion enhanced GC, but the more anterior position of the foot (recommended by the manufacturer) eliminates this effect. Shortening of the prosthesis did not affect GC consistently but resulted in negative impact on the pelvis and trunk. To compensate for a lack of GC, vaulting was primarily observed.

The findings provide experts with a comprehensive overview of relevant factors influencing ground clearance. The importance of prosthetic alignment and prosthetic knee swing phase control was particularly evident. This can help to optimize the prosthetic fitting to the needs of the user and to reduce unnatural compensatory strategies.