Does low-constraint mobile bearing knee prosthesis give satisfactory results for severe coronal deformities? A five to twelve year follow up study

Purpose Severe varus and valgus knee deformities traditionally are replaced with constrained implants, with a number of disadvantages. We present our results in this challenging group using a low constraint deep-dish mobile bearing implant design. Methods One hundred fifty-four patients (170 arthroplasties) who underwent primary TKA using a deep-dish, mobile bearing posterior-stabilized implant for severe varus (HKA < 170 degrees) or valgus (HKA > 190 degrees) deformity between 2004 and 2009 were evaluated at a mean of 6.6 years post-operatively (minimum of 5 years). Results Alignment improved from a pre-operative mean (+/- SD) varus deformity of 167.4 degrees (+/- 2.6 degrees) and a mean (+/- SD) valgus deformity of 194.1 degrees (+/- 4.0 degrees) to an overall mean (+/- SD) post-operative mechanical alignment of 178.6 degrees (+/- 3.2 degrees). Twenty-three patients had post-operative varus alignment, five patients had post-operative valgus alignment and 134 knees were in neutral alignment (within 3 degrees spread). Clinical scores at final follow-up were excellent (IKS score 93.8 (+/- 7.4) and function score 82.4 (+/- 20.2)). Three patients were reoperated upon: one deep infection, one periprosthetic fracture and one revision at 144 months for aseptic loosening of the femoral component. No patient was revised for instability or implant failure. The survival rate at five years was 99.4% and at ten years 98.6%. Conclusions Satisfactory outcomes can be achieved in patients with substantial varus or valgus deformities using low constraint deep-dish mobile bearing implant, standard approach and appropriate soft tissue releases.