Incidence, Patterns, and Risk Factors for Aseptic Loosening in a Hydroxyapatite-Coated Cementless Stem: A Single-Centre Cohort Analysis and Case Series

Cementless Total Hip Arthroplasty (THA) is widely practised in North America for successfully relieving symptoms of degenerative hip disease. There have been reports of “stripped” Corail femoral stems (DePuy Synthes), where no/little hydroxyapatite (HA) coating remained on the stem when retrieved during revision THA for aseptic loosening of the stem. This unique phenomenon prompted us to investigate incidence and potential risk factors of aseptic stem loosening in patients in our centre. We identified all the primary THA patients from 2006 and 2021 who received Corail femoral stems (primary cohort) as well as all patients who had their Corail removed (revision cohort). We further identified demographic data, implant and revision data from our clinical database. We used Cox proportional hazards models to estimate the hazard ratios (HRs) of the association between these factors and revision for aseptic loosening of the stem, while censoring at death, end of follow-up, or other reasons for revision. For the revision cohort we retrieved all serial radiographs of the hip between the primary and revision surgery and measured the proximal-distal length of radiolucency based on Gruen zones and canal fill. We measured progression in radiolucency using templating software. We also used preoperative radiographs to determine the Dorr classification. Over 15 years, 3,876 patients were implanted with Corail stems, out of which 27 were revised for aseptic loosening and 91 for other indications. Patients with later aseptic loosening were younger at their primary surgery and a higher proportion was male. BMI was similar between these groups. Patients younger than 50 years were at higher risk of aseptic loosening for “stripped” stems compared to older patients (crude HR 2.83; 95% CI 1.04–7.74). Patients taller than 180 cm were more frequently revised for loosening compared to shorter patients (crude HR 2.20; 95% CI 0.81–6.01). The risk of aseptic loosening was also higher for smaller stems (size 9 and down; crude HR 9.78; 95% CI 4.14–23.09) and collarless stems (HR 4.91; 95% CI 1.78–13.53). Metal on Metal bearings were at significantly higher risk of aseptic loosening compared to other bearings (crude HR 10.90; 95% CI 4.47–26.56). Radiographic analysis exhibited complete osseointegration of the stem by one year for patients that were later revised for aseptic loosening. Osseointegration was concentrated over the metaphyseal region and not well appreciated distally. Loosening was insidious and progressive. Over 62% patients had loosening of both medial and lateral cortices, but it was more pronounced over the lateral aspect of the implant. No statistically significant association was noted between Dorr type, fill of the canal by the stem and loosening. This study underscores the elevated risk of mid-term loosening in previously well-integrated HA-coated stems. This risk appears to be more pronounced in younger, taller patients with smaller collarless stems and metal-on-metal bearings. Although metal-on-metal bearings are not commonly used anymore, the other risk factors remain relevant.