The impact of extreme genu varum and genu valgum on postoperative outcomes using mini-subvastus approach in TKA

Increasing interest in using minimally invasive approaches in TKA has led to the question: how much deformity is accepted for using MIS in TKA? A single surgeon performed 87 consecutive TKAs with mini-subvastus approach, using unconstrained prosthesis in 84 knees and constrained prosthesis in 3 knees. We conducted a prospective study in which patients were divided into two groups according to preoperative tibiofemoral axes (TFM), one group with 160°<TFM<195° and the second group with 160°≥TFM≥195°. Clinical and radiographic outcomes were compared. Postoperative ROM and knee score were improved in both groups, with similar results (p<0.01). Postoperative radiographic analyses showed that TFM was improved in both groups (p<0.01) with the coronal alignment inferior in 160°≥TFM≥195° group than the 160°<TFM<195° group. The results of this study suggest that mini-subvastus approach is a proper technique to use in primary TKA in patients with a TFM angle less than 160° and more than 195° with similar results with TFM angle between 160° and 195°, and for the use of constrained prosthesis designs with promising results. Preoperative TFM angle less than 160° and greater than 195° increases the risk of component malposition in coronal plane.