Opening wedge high tibial osteotomy using a monoaxial dynamic external fixator

Purpose: To prospectively assess midterm results in 37 patients (41 knees) who were treated with opening wedge high tibial osteotomy (OW-HTO) with the use of a monoaxial dynamic external fixator (MDEF) for medial knee osteoarthritis. Methods: Clinical and subjective evaluations were performed using the IKDC and KOOS evaluation forms and the modified Knee Society Clinical Rating System (KSS). Pin tract infections were evaluated according to Checketts–Otterburns classification. Radiographic evaluation included long-standing AP lower limb, standard lateral, Rosenberg and Merchant views. Results: Thirty-six patients (40 knees) were evaluated at a mean follow-up period of 7 years. Ten patients (25 %) developed a minor pin tract infection. Subjective KOOS and IKDC scores showed statistically significant improvement. Clinical evaluation with IKDC and KSS forms showed no patient with instability or a range-of-motion deficit worst than pre-operatively. At MDEF removal, the mechanical axis was on average 4.5° valgus; anatomical axis 6.8° valgus; the Mikulicz’ line crossed the tibial plateau on average at 64 % of the width of the tibial plateau measured from medial; the posterior slope 5°; the metaphyseal varus 4.3°; and the Insall/Salvati ratio 1.02. At latest follow-up, five patients had a loss of correction of 1°–2° on mechanical axis and one patient had a loss of correction of 3° on mechanical axis and 4 % of mechanical axis on tibial plateau. Conclusions: The use of a MDEF to perform an OW-HTO showed a good maintenance of correction achieved with satisfactory midterm outcome results in all patients but three who underwent total knee replacement. The only severe post-operative complication was one case of non-union in a heavy smoker. Level of evidence: Prospective and therapeutic study, Level IV.