Biomechanical Evaluation of Cemented Composite Beam and Cementless Collared and Collarless Triple Taper Femoral Stems With and Without Prophylactic Calcar Wiring

Abstract

Background: Cemented composite beam (CB) stems are associated with less risk of periprosthetic femoral fractures (PPFxs) after total hip arthroplasty. An alternative to cementing that has grown interest and has been associated with reduced early PPFx, is the use of collared cementless stems (collared). This biomechanical study aimed to compare peak torque to failure among CB and cementless stems.

Methods: There were seven CB stems, 15 collarless cementless stems (collarless) (eight with and seven without calcar wiring), and eight collared stems were implanted into standard sawbones. A servo-hydraulic test machine applied load of 2,000 N and an internal rotation of 40° per second until failure. The peak torque to failure was measured. Assuming a SD of 14.8 Nm in peak torque, a sample size of seven specimens per group was determined to provide 90% power to detect a difference of at least 30 Nm between the groups. Comparisons were performed using two-sample t-tests, and noninferiority was evaluated with a noninferiority margin of -25 Nm.

Results: The mean peak torque to failure was 102.9 Nm ± 15.6 for collared stems, 87.2 Nm ± 14.1 for collarless stems and 205.3 Nm ± 26.9 for CB stems. There was a significant difference at peak torque to failure between CB stems and the two types of cementless stems (P < 0.001). There was no significant difference between collared and collarless stems (P = 0.090). The peak torque to failure for calcar-wired collarless stems was 92.7 Nm ± 11.4, which was not inferior to a cementless collared stem (P = 0.041).

Conclusions: In this biomechanical study, the peak torque to failure was significantly higher in CB stems compared to both collarless and collared stems. Addition of the calcar to the collarless stem led to noninferior torque to failure compared to the collared stem. These data support the use of CB stems as the best surgical strategy to decrease early PPFx.

Keywords: cemented stems; collared cementless stems; collarless cementless stems; periprosthetic fractures; torque to failure.