Predicting the need for medial augmentation for primary total knee arthroplasty with varus deformity.

Objectives: This study aims to compare the radiographic results with and without postoperative metal augmentation in varus knee patients with primary total knee arthroplasty (TKA) with a hip-knee-ankle (HKA) angle >10° and to determine a cut-off value using radiographic parameters to predict the need for metal augmentation.

Patients and methods: Between October 2022 and April 2024, a total of 87 knees (51 right and 36 left) of 82 patients (11 males, 71 females; mean age: 68.7±8 years; range, 53 to 86 years) who underwent primary TKA were retrospectively analyzed. The patients were divided into two groups as patients who underwent primary TKA with and without tibial metal augmentation. There were 39 patients and 42 knees in the group with metal augmentation and 43 patients and 45 knees in the group without metal augmentation. The HKA angles and amount of preoperative planned tibial resection (ETR) were evaluated. Cut-off values for preoperative HKA angle and ETR were determined using receiver operating characteristic (ROC) analysis.

Results: The mean pre- and postoperative HKA angles were 18.98±4.42° and 6.58±3.48°, respectively and the mean ETR was 13.91±3.02 mm. Both groups were comparable in terms of postoperative HKA angles p=0.283). The mean preoperative HKA and ETR were significantly higher in TKAs with augmentation (p<0.001 for both). The probability of needing augmentation was approximately six times higher in knees with a preoperative HKA angle of >20.6° (OR=5.909, 95% CI: 2.065-16.91, p<0.001) or ETR of >12.52 mm (OR=5.816, 95% CI: 2.202-15.359, p<0.001).

Conclusion: In TKA with advanced varus deformity, tibial metal augment is a method that can be used to provide soft tissue balance. The need for metal augmentation should be kept in mind, particularly if the preoperative evaluation indicates that the HKA angle exceeds 20.6° or ETR exceeds 12.5 mm.