Biomechanical Analysis of Nonconstrained and Semiconstrained Total Elbow Replacements: A Preliminary Report

The development of elbow arthroplasties has significantly improved the quality of life for many patients suffering from disabling elbow disorders. However, the high complication rate such as loosening and instability limits the long term use of total elbow replacement (TER). In the present study, biomechanical analyses on patients with unilateral nonconstrained (Souter-Strathclyde) and semiconstrained (Coonard-Morrey) TER subjects were performed to investigate differences of their motion patterns under unloaded and loaded conditions. In a biomechanical laboratory, each subject performed vertical and horizontal elbow flexion/extension first without and then with external loading (5 lb). The kinematic data were measured using 3D motion analysis system and the motion axis of the elbow was calculated by a well-defined mathematic model. During these tests, the upperarm was fixed with a special fixation device and their forearms fully supinated. The elbow motion patterns of the affected sides were compared with those of the normal sides and between different conditions. The results revealed that the elbows moved about a relatively fixed axis both in the semiconstrained and nonconstrained groups in the vertical flexion/extension with or without external loading, compatible with the normal elbows. However, the nonconstrained elbows were less stable during horizontal flexion/externsion motion with or without external loading and the elbow axis moved significantly, indicating of less stability. We conclude that this methodology of elbow motion analysis is acceptable and can be widely recommended for total elbow study. Moreover, the nonconstrained TER is less stable than the semiconstrained TER during the horizontal movement, which was compatible with previous clinical results. The patients with nonconstrained TER are suggested to avoid using their elbows in horizontal motion, especially in loaded conditions.