Good stability but high periprosthetic bone mineral loss and late-occurring periprosthetic fractures with use of uncemented tapered femoral stems in patients with a femoral neck fracture

Abstract

Background and purpose: We previously evaluated a new uncemented femoral stem designed for elderly patients with a femoral neck fracture and found stable implant fixation and good clinical results up to 2 years postoperatively, despite substantial periprosthetic bone mineral loss. We now present the medium-term follow-up results from this study.

Patients and methods: In this observational prospective cohort study, we included 50 patients (mean age 81 (70-92) years) with a femoral neck fracture. All patients underwent surgery with a cemented cup and an uncemented stem specifically designed for fracture treatment. Outcome variables were migration of the stem measured with radiostereometry (RSA) and periprosthetic change in bone mineral density (BMD), measured with dual-energy X-ray absorptiometry (DXA). Hip function and health-related quality of life were assessed using the Harris hip score (HHS) and the EuroQol-5D (EQ-5D). DXA and RSA data were collected at regular intervals up to 4 years, and data concerning reoperations and hip-related complications were collected during a mean follow-up time of 5 (0.2-7.5) years.

Results: At 5 years, 19 patients had either passed away or were unavailable for further participation and 31 could be followed up. Of the original 50 patients, 6 patients had suffered a periprosthetic fracture, all of them sustained after the 2-year follow-up. In 19 patients, we obtained complete RSA and DXA data and no component had migrated after the 2-year follow-up. We also found a continuous total periprosthetic bone loss amounting to a median of -19% (-39 to 2). No changes in HHS or EQ-5D were observed during the follow-up period.

Interpretation: In this medium-term follow-up, the stem remained firmly fixed in bone despite considerable periprosthetic bone mineral loss. However, this bone loss might explain the high number of late-occurring periprosthetic fractures. Based on these results, we would not recommend uncemented femoral stems for the treatment of femoral neck fractures in the elderly.

Figure 1.

Diagram of patient flow through the study. The patient flow up to the 1-year follow-up is presented in more detail in a previous paper (Sköldenberg et al. 2011).

Figure 2.

Graphs showing periprosthetic bone remodeling in zones 1–7 with median percentage change in bone mineral density (BMD) around the implant.* p ≤ 0.05 compared to the 2-year follow-up (Wilcoxon signed-rank test).

Figure 3.

Periprosthetic postoperative BMD (x-axis) plotted against percentage change in BMD around the implant (zones 1–7) (y-axis) at 4 years.

Figure 4.

Example of a late-occurring periprosthetic fracture. a. Postoperatively. b. 2-year follow-up with radiographic signs of stress-shielding (arrows) including calcar atrophy and hypoattenuation of bone mass in the greater trochanter and diaphysis. At 2 years, the total decrease in BMD around the stem was –16% compared to the postoperative value. c. The periprosthetic fracture that was sustained after a low-energy trauma at 2.2 years. d. The healed fracture at 2.7 years, treated with protected weight bearing.