Effects of bone defects on elbow stability in olecranon fractures

Objective To investigate effects of different bone defects on stability of the elbow in the olecranon fracture. Methods Ten fresh cadavers with 20 upper extremities were used in the present study. Different models of bone defects in the middle olecranon were created by cutting the bone from 10 mm below the olecranon process. The 20 specimens were randomly made into intact, 3 mm defect, 6 mm defect and 9 mm defect groups. After osteotomy fixations were applied with the tension band wire. Changes in the range of motion of the elbow joint were measured. When the elbow was flexed at 30°, 60°, 90°, and 120°, a and the varus angulations in the varus test position, and observe the changes in relationship to the humeroulnar joint. Results Extension of the elbow was limited when the defect was 3 mm. X-ray showed that the extension of the elbow was obviously limited when the defect was 6 mm, with the humeroulnar joint moving resistantly, the olecranon process completely touching the surface of the trochlear and the interspace between the humeroulnar joint increasing. When the defect was up to 9 mm, the humeroulnar joint was subluxated obviously,with the trochlear notch nearly disappearing. Given the same degree of elbow flexion, the valgus angulation increased with the defect, especially when the defect was beyond6 mm (P ＜0.05). Conclusions When the bone defect at the middle olecranon reaches 6 mm, the trochlear notch radian will change, leading to an unstable elbow joint. Consequently, comminuted fractures of the middle olecranon can be treated with fixation if the defect is less than 6 mm: Otherwise bone grafting may be necessary to recover the trochlear notch radian and reduce the risk of traumatic osteoarthritis. Key words: Ulna; Fracture; Osteotomy; Elbow joint