Primary total hip arthroplasty using a short bone-conserving stem in young adult osteoporotic patients with Dorr type C femoral bone.

BACKGROUND

Dorr type C femoral bone exhibits a wide, stovepipe-shaped femoral canal, and thin cortices in the proximal femur. Dorr C bone combined with severe osteoporosis is an important challenge in primary hip arthroplasty. In this study, we assessed the effects of short metaphyseal fitting cementless stems on preformatted primary total hip arthroplasties in young adult osteoporotic patients with this femoral presentation.

METHODS

A total of 42 hip arthroplasties were performed in 35 young patients (range 20 to 36 years) using a short Tri-lock bone preservation metaphyseal-fitting cementless femoral component between 2012 and 2017. The mean age at surgery of the 27 male (33 hips) and 8 female (9 hips) patients was 27.5 years (range 20.3 to 35.8 years). The mean body mass index (BMI) was 20.2 kg/m (range, 16.8-23.2 kg/m). According to Dorr's criteria, all 42 femora were classified as type C bone and all femurs suffered from severe osteoporosis (Singh index ≤ 3).

RESULTS

The mean follow-up period was 5.5 years (range 3.0 to 8.0 years). The clinical and functional results improved for the Harris hip score, WOMAC, and UCLA activity scores. The Harris Hip score improved from 48.0 ± 8.0 (range 38.0 to 61.0) preoperatively to 87.0 ± 9.0 (range 77.0 to 92.0) at 12 months after surgery and 91.0 ± 8.0 (range 85.0 to 98.0) at final follow-up. The preoperative UCLA activity score was 3.0 ± 0.5 points (range, 1.0-4.0 points), which significantly improved to 7.5 ± 0.7 points (range 6.0 to 8.0 points) at the final follow-up. No patient exhibited thigh pain at the final follow-up. The mean stem-to-canal fill percentages were 97% ± 2.1% (anteroposterior view at midstem). For stem alignment, 40 hips (95.2%) of the femoral stem were positioned neutrally to 3° of varus with reference to the femoral shaft axis. The remaining two were positioned at 4° varus to 4° valgus. Radiographic evaluation showed good osteointegration of the implants in follow-up.

CONCLUSIONS

Based on the tapered-wedge design and proximal porous coating, the shortened tapered conventional stem can achieve reliable stability through neck filling and metaphyseal fixation, which does not depend on the isthmus hoop stress. This stem was suitable in severe osteoporotic patients with type C bones in young adults who presented with a correspondingly straightened femoral canal with a wide isthmus and thin cortex.