Summary

Postoperative varus-valgus stability and clinical outcomes of Unrestricted KA-TKA for severe varus deformity were as favorable as those for mild varus deformity.

Abstract

Objective

Unrestricted Kinematic Alignment (KA) Total Knee Arthroplasty (TKA) aims to reproduce each patient's joint morphology and ligament balance. It is expected to achieve good varus-valgus stability and clinical outcomes postoperatively, regardless of preoperative deformity severity. However, outcomes in cases of severe varus deformity are still unclear due to the limited number of cases. Given the higher prevalence of severe varus deformity in Japan compared to Western countries, this study focused on varus-valgus stability and compared knees with severe varus deformity to those with mild varus deformity.

Methods

Among 160 knees (133 patients) who underwent Unrestricted KA-TKA and were followed for over six months, valgus knees with a preoperative HKA angle > 0° were excluded. We retrospectively compared the severe varus group (HKA angle < -15°) with the mild varus group (HKA angle between -15° and 0°). The surgeries were performed using a calipered technique without restricting the bone cutting angle, with GMK Sphere or Attune implants. Pre- and postoperative HKA angles, mLDFA, and mMPTA were measured using standing full-length X-rays. Postoperative stability was assessed using varus-valgus Telos stress X-rays at three months. Clinical outcomes, including range of motion (ROM), KOOS scores, and complications, were evaluated preoperatively and at six months postoperatively. The Mann-Whitney U test and Chi-square test were used for statistical comparisons (p < 0.05).

Results

The severe varus group consisted of 26 cases (29 knees; 5 males, 21 females, mean age 74.1 years), and the mild varus group had 80 cases (93 knees; 13 males, 67 females, mean age 72.8 years). The preoperative/postoperative HKA angles were -19.2°/-5.3° (severe varus group) and -7.9°/-1.7° (mild varus group). The mLDFA was 89.9°/88.9° preoperatively and postoperatively in the severe varus group and 87.2°/86.8° in the mild group. The mMPTA was 80.0°/83.7° preoperatively and postoperatively in the severe varus group, and 84.3°/85.1° in the mild group. All parameters were significantly more varus in the severe group both pre- and postoperatively.
Postoperative stability showed no significant difference between the severe and mild varus groups in varus stress (3.9° vs. 3.3°) or valgus stress (-3.3° vs. -3.0°). Extension ROM improved from -10° to -1° in the severe group, and from -9° to -1° in the mild group. Flexion ROM improved from 110° to 122° (severe) and 118° to 125° (mild). KOOS scores (Symptom, Pain, ADL, Sports, QOL) for the severe/mild groups were 51.4/51.1, 44.4/45.1, 53.5/53.7, 11/15, and 17.5/23.6 preoperatively, and 76.8/83.2, 79.2/78.4, 78.3/73.9, 30/23.8, and 65.6/54.8 postoperatively. No significant differences were found in complications, including infection (0 in both), pulmonary embolism (0 in both), sinking (0 in both), or patellar dislocation (0 in severe, 2 in mild).

Conclusion

Postoperative varus-valgus stability and clinical outcomes of Unrestricted KA-TKA for severe varus deformity were comparable to those for mild varus deformity. Restoring the preoperative varus alignment through unrestricted prosthesis placement may improve varus-valgus stability. Unrestricted KA-TKA is considered an effective surgical option, even for severe varus deformities.