Large opening gaps, unstable hinge fractures, and osteotomy line below the safe zone cause delayed bone healing after open-wedge high tibial osteotomy.

Purpose: To evaluate bone formation in the osteotomy gap after open-wedge high tibial osteotomy (OWHTO), including after plate removal, and to investigate risk factors for delayed bone healing.

Methods: Ninety-three patients (102 knees) who underwent OWHTO without bone grafting were enrolled. The osteotomy gap was divided into the lateral hinge and the four zones on anteroposterior radiographs, and we defined the zone in which trabecular bone continuity could be observed as gap filling. Bone formation in the osteotomy gap was evaluated according to this definition at 3, 6, and 12 months postoperatively; at plate removal; and at the final follow-up (mean, 62.3 ± 30.2 months). We also investigated the risk factors for delayed bone healing.

Results: The lateral hinge united at 3 months postoperatively in 92 knees (90.2%). At 1 year postoperatively, 98 knees (96.1%) reached zone 1 and 92 knees (90.2%) reached zone 2. At plate removal, gap filling reached zone 2 in all cases and progressed further without loss of correction after plate removal. Opening width over 13.0 mm [odds ratio (OR): 1.61, P = 0.02], Takeuchi's classification type II lateral hinge fracture (OR: 20.4, P < 0.01), and osteotomy line below the safe zone (OR: 8.98, P < 0.01) significantly delayed bone formation after OWHTO.

Conclusions: Gap filling progressed from lateral to medial after OWHTO without bone grafting and progressed further after plate removal. Large opening gaps, unstable hinge fractures, and osteotomy line below the safe zone cause delayed bone healing after OWHTO.