Objective: To evaluate bone formation in the osteotomy gap after opening-wedge high tibial osteotomy (OWHTO) and to investigate risk factors for delayed bone healing.
Methods: Fifty-seven knees in 51 patients (mean age, 62.7±9.7 years) who underwent OWHTO were enrolled in this study. We divided the osteotomy gap into the lateral hinge and four zones on anteroposterior radiography, and defined the zone in which trabecular bone continuity can be seen as gap filling. According to this definition, bone formation in the osteotomy gap was evaluated at 3, 6, and 12 months postoperatively, in addition to when they had plate removal, and at the final follow-up (mean, 60.8±21.5 months). We also investigated the following factors affecting bone formation including age, body mass index, diabetes mellitus, postoperative femorotibial angle (FTA), opening width, lateral hinge fracture, and direction of the osteotomy line.
Results: The mean FTA changed significantly from 180.0°±2.2° preoperatively to 168.6°±1.8° postoperatively. This correction was maintained at the last follow-up. The lateral hinge united at 3 months postoperatively in 49 knees (86.0%). At one year postoperatively, gap filling in 55 knees (96.5%) reached to zone 1 and in 48 knees (84.2%) to zone 2. At plate removal, gap filling reached to zone 2 in all cases, and progressed further without loss of correction after plate removal. Presence of a lateral hinge fracture (Takeuchi classification type 2) and an osteotomy line below the safe zone, both significantly delayed bone formation.
Conclusion: Bone formation progressed from the lateral to medial direction after OWHTO. The presence of a lateral hinge fracture (Takeuchi classification type 2) and an osteotomy line below the safe zone were both risk factors for delayed bone formation.
