97 baseball players from high school, universities and companies were subjected to this study in order to attempt to clarify the relationship between derangement of the elbow joint and lateral instabilitly by measuring various conventional parameters and the degree of lateral instability.
From the survey by questionnaire, 29 out of 97 players complained of elbow pain, paticularily on the medial side of the joint. The painful phases of the throwing motions were the acceleration phase (23 players, 61%) and release phase (7 players, 46%) . The hyperexten sion of the elbow on the dominant side was significantly smaller than that observed on the undominant side. X-ray examination revealed osteophyte formation at the tip of olecranon and medial joint space.
On the application of 63 kg⋅cm torque force, the varus deflection angle for the dominant side was 8.3° and that for the undominant side was 8.8°. The valgus angle for the dominant side was 12.2° and that for the undominant side was 10.8°. The varus stiffness (kg⋅cm/angle) was 9.5 for the dominant side and 8.4 for the undominant side. Valgus stiffness were 6.3 for the dominant side and 9.2 for the undominant side.
Thses results indicate that the lateral side become stiffer and medial side become looser in the dominant elbow than in the undominant one.
The unphysiological valgus stress at the acceleration phase would induce the osteophyte formation as well as the elongation of the medial collateral ligament on the medial side of the elbow. At the same time the impigement of the olecranon at follow through phase, would induce the osteophyte formation around the olecranon. Thses two factors would considerably influence the range of motion and the instability of the elbow joint.