Total knee arthroplasty in severe valgus deformity: interest of combining a lateral approach with a tibial tubercle osteotomy.

INTRODUCTION: Among the patients requiring total knee arthroplasty (TKA), approximately 10-15% presents with a valgus deformity (VD). Severely deformed valgus knees represent a surgical challenge. The purpose of this study is to evaluate the results of TKA in grade II and III valgus knee deformities (Ranawat classification), focusing on axis correction, by using a lateral parapatellar capsulotomy combined with tibial tubercle osteotomy.

HYPOTHESIS: The lateral approach in combination with a tibial tuberosity osteotomy is highly beneficial in the treatment of severe valgus knees in patients undergoing primary TKA, for correction of anatomical axis.

PATIENTS AND METHODS: Between January 1995 and December 2001, 33 patients with severe VD, grade II and III, were treated with TKA by one surgeon. Twenty-six patients (19 male, seven female) with mean age of 72 years (57-79) were dealt with a resurfacing posterior stabilized design; whereas in seven cases, a constrained type implant was used. These seven patients were excluded from the study. Two more patients were lost for follow-up and were also excluded. The axis deviation of the remaining 24 patients ranged from 15 to 35 degrees, (average 23°). A lateral parapatellar arthrotomy, in combination with tibial tubercle osteotomy was used. Patients' clinical evaluation - using the International Knee Society (IKS) score - with simultaneous radiological assessment was performed yearly after the operation; and for a mean follow-up time of 11.5 years (8 to 15 years).

RESULTS: The mean IKS score improved from 44 points (34 to 52) preoperatively, to 91 points (68 to 100) postoperatively, at the last follow-up. In terms of alignment parameter, only two knees had a residual valgus deviation greater than 7° (ideal range : 3-7°). One knee exhibited a 9° valgus, and another one 10°, according to anatomical axis measurments. In one case, there was a 5mm proximal migration of the osteotomised tuberosity fragment, due to breakage of the screw. However, the final outcome was not affected. There were no cases of tibial tubercle's non-union; neither of delayed instability.

CONCLUSION: The lateral approach is a useful approach in the treatment of severe valgus knee deformity in patients undergoing primary TKA. Anatomical axis restoration is facilitated, as the contracted structures are easily accessed and, in severe cases, the patellar alignment may be achieved by displacing the osteotomised tubercle. However, careful fixation of the tuberosity is mandatory.

LEVEL OF EVIDENCE: Level IV, prospective study of case series.