Adverse Event Rates and Classifications in Medial Opening Wedge High Tibial Osteotomy

Background: Previously reported complications in medial opening wedge (MOW) high tibial osteotomy (HTO) vary considerably in both rate and severity. Purpose: (1) To determine the rates of adverse events in MOW HTO classified into different grades of severity based on the treatments required and (2) to compare patient-reported outcomes between the different adverse event classifications. Study Design: Case series; Level of evidence, 4. Methods: All patients receiving MOW HTO at a single medical center from 2005 to 2009 were included. Internal fixation was used in all cases, with either a nonlocking (Puddu) or locking (Tomofix) plate. Patients were evaluated at 2, 6, and 12 weeks; 6 and 12 months; and annually thereafter. Types of potential surgical and postoperative adverse events, categorized into 3 classes of severity based on the subsequent treatments, were defined a priori. Medical records and radiographs were then reviewed by an independent observer. The Western Ontario and McMaster Universities Arthritis Index (WOMAC) scores were compared in subgroups of patients based on the categories of adverse events observed. Results: A total of 323 consecutive procedures (242 males) were evaluated (age, mean +/- standard deviation, 46 +/- 9 years; body mass index, mean +/- standard deviation, 30 +/- 5 kg/m(2)). Adverse events requiring no additional treatment (class 1) were undisplaced lateral cortical breaches (20%), displaced (>2 mm) lateral hinge fracture (6%), delayed wound healing (6%), undisplaced lateral tibial plateau fracture (3%), hematoma (3%), and increased tibial slope >= 10 degrees (1%). Adverse events requiring additional or extended nonoperative management (class 2) were delayed union (12%), cellulitis (10%), limited hardware failure (1 broken screw; 4%), postoperative stiffness (1%), deep vein thrombosis (1%), and complex regional pain syndrome (CRPS) type 1 (1%). Adverse events requiring additional or revision surgery and/or long-term medical care (class 3) were aseptic nonunion (3%), deep infection (2%), CRPS type 2 (1%), and severe hardware failure with loss of correction (1%). Additional surgery rate was 3%. Class 1 and 2 adverse events did not affect patient-reported outcomes at 6, 12, or 24 months postoperatively. Patients with class 3 adverse events had significantly lower total WOMAC scores at 6 months but not at 12 or 24 months postoperatively. Conclusion: The most common adverse event in MOW HTO requiring extended nonoperative treatment (class 2) is delayed union (12%). The rate of severe adverse events requiring additional surgery and/or long-term medical care (class 3) is low (7%).