Hinge Fractures Are Underestimated on Plain Radiographs After Open Wedge Proximal Tibial Osteotomy: Evaluation by Computed Tomography

Background: Lateral hinge fracture (LHF) after medial open wedge high tibial osteotomy (MOWHTO) may not be recognized on perioperative plain radiographs. Such cases may be identified at follow-up and misdiagnosed as delayed LHF. Purpose: This study aimed to investigate the extent of LHF misdiagnosis and to determine whether patients with LHFs have inferior clinical outcomes after MOWHTO. Study Design: Case series; Level of evidence, 4. Methods: Fifty-one knees in 50 patients (36 women, 14 men; mean age, 51.8 years; range, 24-64 years) who had undergone MOWHTO with locking plate fixation between October 2013 and April 2016 were retrospectively reviewed. LHFs identified on intraoperative fluoroscopy and immediate postoperative radiographs were compared with the actual incidence based on computed tomography (CT) scans performed within 2 days of surgery. Delayed LHFs, not visible on the CT scans but found on later follow-up radiographs, were also assessed. More frequent radiographic check-ups were recommended in patients with LHFs, and weightbearing was delayed until evident callus formation was seen on follow-up radiographs for type 2 or 3 fractures. The loss of correction, the time of union, and complication rate were compared between the knees with LHF and those without LHF. Clinical outcome was measured according to the Knee Society (KS) scores. Results: Overall, 14 early LHFs (27.5%) were identified on CT scans. Of these, 7 LHFs (13.7%) were observed on perioperative radiographs, and the remaining 7 LHFs were identified on later radiographs. Delayed LHFs occurred in 2 cases (3.9%). In the 16 knees with LHF, minimal loss of correction was observed 1 month to 1 year postoperatively without statistical significance. No alignment changes were seen in the 35 knees without LHFs. In the LHF versus no LHF groups, no significant differences were seen regarding time of union (5.3 +/- 1.7 months vs 5.4 +/- 1.8 months, respectively; P = .898) and postoperative KS scores (knee score, 96.6 +/- 2.5 vs 95.3 +/- 6.4, P = .435; functional score, 94.4 +/- 9.6 vs 89.1 +/- 10.9, P = .107). No other complications occurred in either group. Conclusion: Most LHFs after MOWHTO occurred intraoperatively, but half (7/14) were not identified on postoperative radiographs. CT scans would enable detection of early LHFs that would otherwise have been mistaken for delayed LHF. However, clinical outcomes did not differ between patients with and without LHF.