To the best of our knowledge, this is the first in vivo evaluation of the elbow joint contact area in pitchers with symptomatic valgus instability with elbow valgus stress. The present study demonstrated that the elbow joint contact area differed between the dominant side with symptomatic valgus instability and the non-dominant side without valgus instability. In the pitchers with symptomatic valgus instability with elbow valgus stress, the contact area of the radiocapitellar joint was translated laterally, and that of the ulnohumeral joint was translated posteriorly. The results indicate that, in pitchers with symptomatic valgus instability, stress is most highly concentrated in the lateral part of the radiocapitellar joint and the posterior part of the ulnohumeral joint with elbow valgus stress.
The elbow joint contact area has been recorded in vitro and in vivo using various devices, such as radiographys17, cameras18, and CT scans19. In addition, various experimental methods have been used to study elbow joint contact area, including silicon casting20, cartilage staining21, pressure-sensitive film technique22, and CT scans23. However, these studies were based on 2-dimensional images. Furthermore, in in vitro cadaveric studies, the lack of soft tissue tensioning may have affected the normal joint kinematics. In recent years, the in vivo 3D joint contact area has been measured using noninvasive techniques24. Using these in vivo 3D methods, Omori et al.13 reported that in the neutral position, the contact area of the radiocapitellar joint was 332.5 ± 11.9 mm2 and that of the ulnohumeral joint was 1059 ± 40.2 mm2. In the present study, the contact areas of the radiocapitellar joint and the ulnohumeral joint with and without elbow valgus stress were investigated using in vivo 3D methods. The current results of the non-dominant elbow without valgus stress are comparable to those of previous reports.
Although several cadaveric studies have analyzed the distribution of the joint contact area through the elbow joint3,4, in vitro cadaveric studies lack soft tissue tensioning and internal force applied to the elbow joint which may affect the normal joint kinematics. Thus, 3D CT was used to evaluate changes in contact area through the elbow joint in pitchers with symptomatic valgus instability with elbow valgus stress in the present study, and the biomechanical characteristics of the articular surfaces of the elbow under the in vivo loading conditions were clarified. The present study showed that, in pitchers with symptomatic valgus instability, the radiocapitellar joint contact area was translated laterally, and the ulnohumeral joint was translated posteriorly with elbow valgus stress. Ahmad et al.4 reported that medial ulnar collateral ligament deficiency alters the contact area and pressure between the posteromedial trochlea and the olecranon in cadaveric specimens. Change in the contact area was found to occur in pitchers with symptomatic valgus instability with in vivo loading conditions. Furthermore, in pitchers with symptomatic valgus instability with elbow valgus stress, it was shown that the elbow joint contact area of the ulnohumeral joint was translated posteriorly, and that of the radiocapitellar joint was translated laterally.
Posterior elbow joint cartilage injuries are typical in pitchers with symptomatic valgus instability, and they are a severe problem for adolescent pitchers25. Osbahr et al.26 reported that UCL deficiency rises contact pressures, reduces contact area, and transfers the contact point medially onto the medial crista of the posterior humeral trochlea, may cause chondromalacia at this location. In the early acceleration phase of the throwing motion with the elbow flexed to 90°, the results demonstrate that valgus laxity potentially resulting in abnormal contact through increased contact pressures across the posteromedial elbow between the medial tip of the olecranon and the medial crista of the humeral trochlea. In addition, congruency of the ulnohumeral joint changed, since there was a significant medial shift of the olecranon on the posterior humeral trochlea with the elbow flexed to 90° after sectioning the anterior bundle of the ulnar collateral ligament. The present results of pitchers with symptomatic valgus instability, showing posterior translation in ulnohumeral joint contact with elbow valgus stress, suggest that the posterior elbow cartilage disorder is produced by long-term pitching activities with elbow valgus instability.
The present study had several limitations. First, the contact areas of the radiocapitellar and ulnohumeral joints were estimated from the joint space width distribution at these joints. Although the methods used in the current study allowed comparisons between the symptomatic and non-dominant elbows using the threshold levels reported in the literature to define the contact areas, absolute values of the contact area need to be confirmed by a validation study. Second, the positions of the elbow joint under stress were not true dynamic positions. Nonetheless, the elbows consistently showed a characteristic pattern of elbow kinematic changes and these results appear to successfully represent the elbow kinematics of the symptomatic elbow valgus instability condition.
In conclusion, symptomatic UCL deficiency was associated with a characteristic lateral shift on the anterior part of the capitellum and a posterior shift on the trochlea. These alterations of contact areas could explain the cartilage injury at the posterior trochlea in pitchers with UCL deficiency.