Heterotopic ossification (HO) refers to the pathological process of new bone formation within the soft tissue or outside the intra-articular bone. It commonly occurs in patients with severe trauma or bone morphogenetic protein (BMP) receptor gene mutation.Heterotopic ossification of elbow joint is one of the main reasons for limited elbow function. Distal humeral fracture is a common injury of elbow joint. It has been reported that the incidence of heterotopic ossification after operation of distal humeral fracture is about 45%, and the influence factors are numerous. Which of the many influence factors plays a major role? Whether indomethacin is effective for preventing heterotopic ossification of elbow joint? Currently, there is no consistency among the reported literatures. Objective To investigate the influence factors of heterotopic ossification after open reduction and internal fixation for distal humeral fractures in adults.

From December 2014 to December 2017, 138 patients (139 elbows) who underwent open reduction and internal fixation for distal humeral fractures were retrospectively reviewed. The heterotopic ossification was evaluated with X-rays, and the elbow joint function were also assessed using Mayo score and DASH score. Univariate and multivariate Logistic regression analysis were performed for gender, age, injury side, fasting blood glucose on admission, body mass index (BMI) , AO/OTA classification of fracture, whether to perform olecranon osteotomy during operation and whether to take indomethacin after operation.

The mean age of 138 patients was (45.32±15.02) years (18-69 years) , the mean age of 56 males was (39.43±14.46) years (18-69 years) , and the mean age of 82 females was (49.07±14.07) years (18-69 years) . According to AO/OTA classification, there were 5 cases of type B1 fractures, 6 cases of type B2 fractures with 1 case of olecranon osteotomy included, 48 cases of type B3 fractures with 28 cases of olecranon osteotomy included, 12 cases of type C1 fractures, 37 cases of type C2 fractures with 21 cases of olecranon osteotomy included, and 31 cases of type C3 fractures with 31 cases of olecranon osteotomy included. The mean time from injury to operation was (7.06±5.36) days (2-56 days) , and the mean operation time was (124.94±44.24) minutes (40-280 minutes) . Oral indomethacin was not taken among 50 cases (51 elbows) , but it was taken among 88 cases (88 elbows) . The mean postoperative follow-up time was (14.26±3.83) months (12-25 months) . All the incisions healed in the first stage after operation without infection and poor healing. All the distal humeral fractures as well as olecranon osteotomy healed without delay, nonunion or internal fixation loosening. At the last follow-up, the mean range of elbow flexion and extension was 99.35°±28.72° (135°-0°) , the mean Mayo score was (91.71±9.36) points (60-100 points) , and the mean DASH score was (6.71±8.25) (2.88-41.66 points) . At the last follow-up, one patient's forearm rotation was slightly restricted, with 50°of pronation and 30°of supination. The rest of the patients had normal forearm rotation. Univariate Logistic regression analysis revealed statistical differences in age (P=0.009) , fasting blood glucose on admission (P=0.005) , ulna olecranon osteotomy (P=0.016) , operation time (P=0.016) , and fracture classification (P=0.049) . Type C3 fractures had a higher incidence of heterotopic ossification than other types (P=0.049) . There was statistical difference of time from injury to operation between≤6 d and > 6 d (P=0.058) . There was no significant difference in whether oral indomethacin was taken (P=0.424) . Multivariate Logistic regression analysis revealed that there were statistical differences in whether or not to perform olecranon osteotomy and fasting blood glucose,respectively (P=0.024,P=0.016) .

The main factors causing the formation of heterotopic ossification of elbow joint after open reduction and internal fixation for distal humeral fractures were olecranon osteotomy and fasting blood glucose, while whether or not to take oral indomethacin after operation was not. The trauma of complex fracture is usually severer, and the olecranon osteotomy is often required to facilitate the anatomical reduction and internal fixation of articular surface and thus the incidence of heterotopic ossification is higher.