PURPOSE:
The purpose of this paper is to review our experience and study the feasibility and clinical results of one-stage total knee arthroplasty (TKA) for patients with osteoarthritis of the knee with extra-articular deformity.

METHODS:
Nine patients with osteoarthritis of the knee associated with extra-articular deformity underwent one-stage TKA from June 2006 to April 2010. There were two men and seven women, with an average age of 51 years (range 34-69 years); four of them had tibial deformities and five had femoral deformities. Eight of the cases resulted from malunion after fracture healing and one from femoral recurvatum. Six of the cases had uniplanar and three had biplanar deformities. The average angles of the femoral deformities were 13.3° in the coronal plane (8-22) and 11.3° in the sagittal plane (6-15); one femur had 10° external rotational deformity. Tibial deformity of 16° in the coronal plane (11-22) was noted, and one had sagittal plane deformity of 21°.

RESULTS:
All patients were followed for an average of 29 months. The average Hospital for Special Surgery (HSS) knee score improved from 18.7 points pre-operatively to 89.8 points at the time of last follow-up; the range of knee motion improved from 46.7° preoperatively to 100.6° postoperatively. The average angle of mechanical axis deviation was restored from 11.8° preoperatively to 1° postoperatively. One of the patients had unsatisfactory clinical results due to delayed union at the osteotomy site. No complications such as infection, deep vein thrombosis, ligament instability, low level or subluxed/dislocated patella or component loosening were observed. One-stage TKA with intra-articular correction of the extra-articular deformity was performed in seven patients, included proper planning, appropriate bone cuts to restore alignment and the necessary soft tissue releases to balance the knee in flexion and extension. Two patients underwent simultaneous extra-articular correctional osteotomy and TKA because the deformity was so large. Five knees that had good collateral ligamentous stability and balance received a posterior stabilised prosthesis; four knees that had ligamentous instability received a constrained condylar knee (CCK) prosthesis.

CONCLUSIONS:
One-stage TKA is a technically difficult but effective treatment for patients with osteoarthritis of the knee and extra-articular deformity. If feasible we recommend TKA with intra-articular bone resection and soft tissue balancing.





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