Influence of static prosthetic alignment on standing posture and walking in transtibial amputees

The influence of three alignment parameters of a transtibial prosthesis (sa gittal foot position, plantar flexion, mediolateral foot position) on the l oad and motion of the lower extremity joints was investigated in 13 unilate ral transtibial amputees. The aim was to determine whether a correlation ex ists between static prosthetic alignment and gait pattern that would allow an optimal biomechanical prosthetic alignment. The gait pattern was measure d using kinematic, kinetic,and electromyographic methods. Statics was defin ed using the alignment apparatus L.A.S.A.R. Posture. The electromyogram of the m. vastus lateralis and m. biceps femoris was rec orded on both sides. The motion of joints is described by joint angles. Ext ernal joint moments define the mechanical loads. Alignment has almost no influence on muscle activity and joint mechanics of the contralateral leg. In contrast, prosthetic alignment affects clearly a nd systematically the load and motion of the knee joint during the stance p hase on the ipsilateral side. The sagittal foot position influences the max imal flexion angle in the stance phase. The plantar flexion of th e foot af fects th e temporal structure of knee motion. The mediolateral foot positio n causes correspondingly different varus and valgus moments acting on the k nee. Swing phase motion does not depend on prosthetic alignment. The iEMG of the m. vastus lateralis is reduced. Innervation characteristics of the m. biceps femoris on the prosthetically fitted leg has completely c hanged. The ischiocrural muscles take over the neuromuscular action of the m. gastrocnemius to compensate for the external knee extension moment durin g the second part of the stance phase. Prosthetic statics determines if the knee joint is physiologically stressed in a standing posture and during walking. Statics will be correct if the a natomical knee axis of the standing amputee is located about 15 mm posterio r to the load line in the sagittal plane. In the frontal plane,the load lin e touches the lateral patella border and strikes the middle of the foot abo ut 5 cm anterior to the adapter. During walking, attention should be paid t o performance of knee flexion in the stance phase.