Kinematics and laxity of the Souter-Strathclyde total elbow prosthesis

The motion pattern and laxity of 8 cadaveric elbows were recorded with a 3-dimensional electromagnetic tracking device before and after the Souter-Strathclyde total elbow prosthesis was implanted. The Souter-Strathclyde prosthesis replicates the valgus-varus motion pattern of the intact elbow but causes a significant internal rotation of the ulnar shaft of 8.9° ± 4.1° (P <.0005) at 110° of elbow flexion. One of the reasons for this unphysiological motion pattern is positioning of the humeral component in a mean of 5.4° ± 6.4° of external rotation compared with the intact elbow (P =.05). This positioning is related to the design of this device. The Souter-Strathclyde elbow prosthesis has a mean maximum valgus-varus laxity of 6.5° ± 1.5° compared with 4.3° ± 2.3° for the intact elbow (P =.004). This implant is more constrained than previously tested devices, which may explain its relatively higher loosening rate. (J Shoulder Elbow Surg 2000;9:127-34.)