Joint line elevation after TKA is higher in patients with metaphyseal deformity: a prospective study

Joint level restoration is crucial for the success of total knee arthroplasty. The aim of this study was to evaluate joint line estimation methods between two patient groups with mild to moderate or advanced varus deformities.

Patients were classified according to the Parvizi Classification as Type IA or Type M. Measurements were taken of distances from the fibular head, medial and lateral epicondyles, and adductor tubercle to the joint line, and the adductor ratio (AR) was calculated. Joint line elevation was measured postoperatively. Two years after surgery, the Hospital for Special Surgery (HSS) scores were recorded at the end of 2 years postoperatively.

Evaluation was made of 68 patients, comprising 58 (85.3%) females and 10 (14.7%) males with a median age of 65 years (IQR: 25-75; 62-69). Although preoperative AR values were significantly lower in the Type M group (p < 0.001), no significant intraoperative AR difference was found (p = 0.829). The medial epicondyle to joint line and lateral epicondyle to joint line distances showed consistency between measurements in all groups. Joint elevation was significantly higher in the Type M group (3.5 mm (IQR 3.1-3.8) than the Type IA group (2.1 mm (IQR 1.6-2.6) (p < 0.001). Preoperative and postoperative HSS were found to be similar in both groups (p = 0.995 and p = 0.374, respectively).

While Type IA gonarthrosis did not significantly affect joint line estimation and the Adductor Ratio (AR) showed inconsistency in Type M gonarthrosis, a key finding was the significantly higher joint line elevation observed in Type M compared to Type IA patients. Importantly, this increased elevation did not result in a significant impact on HSS functional scores at two years post-surgery.