JOA - 2026-07-22 - Journal Article
Collar-Calcar Contact Reduces Risk for Early Periprosthetic Fracture and Subsidence in Dorr Type C Femora Using Collared, Fully Hydroxyapatite-Coated, Cementless Stems.
Navarro JAM, Miura Y, Oinuma K, Ninomiya T
Topics
Key Takeaway
Collar-calcar gap in collared HA-coated cementless stems was present in 4.1% of Dorr C femora and accounted for 100% of early periprosthetic fractures (18.8% vs 0%) and the majority of subsidence events (12.5% vs 0.5%).
Summary Depth
Choose how much analysis to show on this article page.
Summary
This retrospective study evaluated whether collar-calcar gap on early postoperative radiographs predicts periprosthetic fracture (PPF) and subsidence in 387 Dorr C femora receiving collared, fully HA-coated cementless stems via direct anterior approach. Full collar-calcar contact was achieved in 95.9% of hips; the 4.1% with a gap had PPF rates of 18.8% vs 0% and subsidence rates of 12.5% vs 0.5% compared to the contact group (P<0.0001 for both). All three PPFs and disproportionate subsidence occurred exclusively in the gap group, confirming collar-calcar contact as a critical intraoperative endpoint in osteopenic bone.
Key Limitation
The absolute event numbers are very small (3 PPFs, 4 subsidence cases total), limiting statistical power and the ability to control for confounders such as stem size, canal fill ratio, or surgeon experience in multivariate analysis.
Original Abstract
BACKGROUND
Collared, fully hydroxyapatite-coated stems are designed to enhance axial and rotational stability through collar-calcar contact, reducing the risk for implant subsidence and periprosthetic fracture. The purpose of this study was to address the uncertainty surrounding the use of cementless stems in Dorr C femora by evaluating the association between collar-calcar gap with periprosthetic fracture and subsidence in patients who underwent THA through the direct anterior approach.
METHODS
A retrospective analysis was performed on 6,107 total hip arthroplasties performed between September 2020 and June 2025. A total of 387 hips, with Dorr C femora, using collared, fully HA-coated stems, were included in this study. All surgeries were performed using the direct anterior approach. Radiographs were reviewed for the collar-calcar gap within 90 days postoperatively. Outcomes included the presence of PPF and/or subsidence.
RESULTS
Full collar-calcar contact was observed in 371 hips (95.9%), while gaps were present in 16 hips (4.1%). There were three PPFs that occurred exclusively with patients who had a collar-calcar gap (18.8%) and were not observed in patients who had collar-calcar contact. Subsidence was present in two hips among the contact group (0.5%) and two hips among the gap group (12.5%). The presence of a gap is associated with higher rates of subsidence and periprosthetic fracture with the collar-calcar gap group as compared to the collar-calcar contact group (P = 0.0000282; P = 0.0000584). The absolute number of events is small; however, the effect size is clinically meaningful.
CONCLUSION
The exclusive occurrence of early PPF and subsidence in the gap group underscores the mechanical importance of immediate load transfer through the collar. Our findings support intraoperative assessment of collar-calcar contact, especially in Dorr C bone, and reinforce the rationale for using collared, fully HA-coated, cementless stems when contact can be secured.