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.
Keywords: External fixator; Hemicallotasis; High tibial osteotomy; Knee; Opening wedge; Osteoarthritis.