[Value of virtual reality technology in preoperative planning of transtrochanteric curved varus osteotomy for avascular necrosis of femoral head in adults].

Objective: To research the value of virtual reality (VR) technology in the preoperative planning of transtrochanteric curved varus osteotomy for avascular necrosis of the femoral head (ANFH) in adults.

Methods: Between June 2018 and November 2018, 7 patients (11 hips) with ANFH, who were treated with transtrochanteric curved varus osteotomy, were enrolled in the study. There were 4 males (7 hips) and 3 females (4 hips) with an average age of 31.9 years (range, 14-46 years). Among them, 3 patients were unilateral ANFH and 4 patients were bilateral ANFH. There was 1 patient (1 hip) of traumatic ANFH, 2 patients (4 hips) of alcohol-induced ANFH, 2 patients (3 hips) of hormonal ANFH, and 2 patients (3 hips) of idiopathic ANFH. All hips were Association Research Circulation Osseous (ARCO) stage Ⅲ. There were 5 hips for Japanese Investigation Committee (JIC) type C1 and 6 hips for type C2. There were 5 hips for China-Japan Friendship Hospital (CJFH) type L1,1 for type L2, and 5 for type L3. The disease duration ranged from 5 to 12 months (mean, 8 months). Preoperative Harris score was 53.91±7.66. The neck-shaft angle ranged from 128 to 143° (mean, 133.9°). VR technology was adopted for the preoperative planning. CT data were imported into the software to construct the morphology of necrotic area, and the transrtrochanteric varus osteotomy was simulated. The varus angle was designed according to the integrity rate of femoral head. The planned varus angle was 6 to 16° (mean, 9.7°). The transtrochanteric curved varus osteotomy was performed according to the preoperative planning, and the varus angle and loading area were confirmed under fluoroscopy. If the planned varus angle was too small, it would continue to increase under the fluoroscopy until a satisfactory varus angle. Postoperative changes of the neck-shaft angle were calculated and compared with the preoperative planned varus angle (error). The hip function was assessed by using the Harris score.

Results: All incisions healed by first intention. All patients were followed up 6-11 months with an average of 8 months. The X-ray film at 2 days after operation showed that the neck-shaft angle was 112-135° (mean, 123.4°). The difference of the neck-shaft angle between pre- and post-operation was 6-16° (mean, 11.0°). Among them, the difference of the neck-shaft angle was consistent with planned varus angle in 5 hips, while the error of the remaining 6 hips was 1-4°. There was 1 patient (1 hip) of osteotomy nonunion at 4 months after operation, 1 patient (1 hip) of proximal femur fracture at 2 months after operation. The rest 5 patients (9 hips) obtained union at the osteotomy. At last follow-up, the Harris score was 82.18±16.35, showing significant difference when compared with preoperative score ( =-5.195, =0.000).

Conclusion: VR technology is a brand-new preoperative planning method for transtrochanteric curved varus osteotomy in treating ANFH.