Definition and validation of a system for classifying the undersized Corail femoral stem in total hip arthroplasty

Abstract

Introduction: The uncemented total hip arthroplasty relies on a secure initial fixation of the femoral stem to achieve osseointegration. Undersizing of the femoral implant compromises this. Surgeons routinely review postoperative radiographs to assess appropriate sizing, but existing methods of assessment lack standardisation. We present a system of accurately and reliably classifying radiological undersizing, which will help us better understand the factors that might have led to undersizing. Aim: To describe and evaluate a classification system for assessing radiological undersizing of the uncemented stem in hip arthroplasty. Method: We conducted a retrospective review of 1,337 consecutive hip arthroplasties using the Corail stem. Two independent investigators reviewed post-operative radiographs and classified them as either appropriately sized or undersized. Undersized stems were sub-categorised into four subtypes: uniformly undersized, varus undersized, valgus undersized or ‘cocktail-glass’ undersized. Inter- and intra-observer agreement was determined. The accuracy of our classification system was validated by comparison with digital re-templating. We further assessed patient demographics and stem size in relation to sizing. Results: 1 in 5 cases (19.75%) were deemed radiologically undersized. The commonest subtypes of undersizing were uniformly (47%) and varus (39%) undersized. When assessing sizing and subtype categorisation, inter-observer agreement was 89–92% and intra-observer agreement 86%. Classification decisions showed 92% and 97% accuracy for uniformly undersizing and varus undersizing respectively when validated against digital re-templating. Age, gender and smaller stem size were significantly associated with radiological undersizing. The Corail KLA model (125° neck) was found to have a higher incidence of stems undersized in varus. Conclusions: This study describes and validates a classification system for the analysis of radiological undersizing.

Collared versus collarless hydroxyapatite-coated stems for primary cementless total hip arthroplasty; a systematic review of comparative studies. Is there any difference in survival, functional, and radiographic outcomes?

“…Also, orthopaedic surgeons who use collared stems to prevent subsidence may unconsciously opt for smaller stem sizes in osteoporotic femurs to avoid intraoperative fracture. However, an undersized stem may increase the risk of subsidence and revision due to AL in the long-term [ 29 , 30 ]. Surgeons using collarless stems may opt for the largest stem size to avoid subsidence, increasing the PPF risk [ 13 , 22 ].…”

“…Both collared and non-collared stems must be implanted at the appropriate size to ensure proper osseointegration. An undersized collared stem cannot rely on a collar’s protective role to osseointegrate [ 30 ].…”

“…On the other hand, a surgeon using a collared, uncemented stem could choose a slightly smaller stem size and still rely on the collar to prevent subsidence. Additionally, this approach could potentially lower the PPF risk [ 30 ]. Besides, the collared and collarless stems were traditionally used for different age populations, making direct comparisons between these two stem groups in registry results challenging.…”

Does Proximal Femoral Morphology Impact Morbidity and Mortality? A Cohort Study of Uncemented Hemiarthroplasties in the Treatment of Femoral Neck Fractures

“…This has 95% coverage for the entire country. The radiographs were analyzed for stem alignment, Dorr classification on preoperative radiographs [7] , and gross undersizing [8] . This corresponded to a uniformly contiguous margin around the stem.…”

Small design modifications can improve the primary stability of a fully coated tapered wedge hip stem

“…The increased risk for smaller sizes might be caused by a mismatch between the metaphyseal-diaphyseal geometry of the stem design and the anatomy of the human femur [ 9 , 10 ]. The surgeon can get the impression of sufficient stem primary stability during implantation due to distal (diaphyseal) contact and fixation of the stem, even so no sufficient stability has been achieved in the proximal (metaphyseal) region [ 11 , 12 ].…”