Suspension of the Below-Knee Prosthesis: Comparison of Supracondylar Clip and Cuff
DAVID LYTTLE, BSc, MB, FRCS(C)*Winnipeg, Manitoba
Suspension prevents the prosthesis from slipping, minimizes shear and enhances stability. The thigh corset provides superior security against losing one's prosthesis, but few activities demand such security. Some gymnasts prefer a silastic sleeve even though frequent replacements are needed and it causes venous congestion. Most adolescents opt for the supracondylar cuff; suspension is well maintained even when sitting, the brim can be trimmed low, and friction at the femoral condyles is minimal. A cuff applied too tightly impairs circulation, and dexterity is required to adjust the Velcro. We prefer the supracondylar/suprapatellar clip (SP/SC), sometimes with a foam liner with wedged brim or a removable medial wedge. Although skiers may believe a thigh corset avoids losing suspension on the slopes, a PTB prosthesis with SC/SP suspension is satisfactory in mud and snow. Involuntary release when in flexion is probably a safety feature during falls. The SP/SC clip offers excellent rotational stability for quick turns when ice skating and, for a first prosthetic fitting, it enforces a good gait, prohibiting knee extension beyod the desirable 5 deg. of flexion. Undesirable friction at the brim and a bump in one's trousers at the knee when sitting are the principal objections. Four patients had standardized stresses applied to both knees under X-ray control. Joint-line separation was slightly greater on the amputated than on the sound knee. The fibula scissored behind the tibia to allow more apparant varus positioning of the prosthesis than actual knee-joint strain.
*Department of Rehabilitation Engineering, Health Sciences Centre, 633 Wellington Crescent, Manitoba, R3M 2A8, Canada