Abstract
Introduction
Proximal short stems have gained in popularity for perceived bone preservation but more recently, physiological loading. We report the medium term success of a calcar loading, short stem in a large cohort from a single unit with multiple surgeons.
Patients/Materials & Methods
Prospectively collected sequential data, with no loss to follow-up, was retrospectively analysed from our own local database. Demographic data was assimilated to collect age, sex, BMI smoking history. Revision cases were analysed for cause and a PTIR and Kaplan Meier Curve constructed to quantify survival. Radiographs reviewed in 100 of the oldest (2009 to 2011) cases to look specifically for calcar resorption and stem sink. Imatri software was used for calculations: sink was categorised into greater or less than 0.5cm; calcar resorption was estimated using maximal osteotomy surface change of slope. Patient pre-operative and post-operative outcome scores (using Harris Hip, Charnley and Oxford scales) were extracted from the database.
Results
752 cases (in 685 patients) were identified: 313 male, 372 females with a combined average age of 61 (19 to 84); and, an average BMI of 29 kg/m2; (18–49); and, 4% were noted to be smoking on their last assessment with a maximum implantation of 9 (average 4.2) years. 74% (556) of cases utilised a 36mm Solid Ceramic head but 28, 32, 40 and 44mm heads in CrCo and TiN were also used. The majority (84%) of cases were performed for Osteoarthritis (Inflammatory arthropathy was a relative contraindication); but, 22 cases were performed for revision from a resurfacing arthroplasty. 17 patients were noted to have died (all more than 90 days post-operatively). 14 cases were revised for any cause (1.8%): 5 for cup related reasons (including dislocation); 4 deep infection, 2 for failure of fixation; 3 for periprosthetic fracture. All failures occurred within the first 4.5 years and all within the first 100 cases for each surgeon. The KM survival curve gave a 5 year survival (185 at risk) of 96.1% all causes and 99.1% for femur only. The PTIR (non-competing) was 6.5 (per 1000 years exposed) and 6.3 (competing). No reported cases of thigh pain were observed; one ceramic on ceramic bearing reported transient but recurrent squeak within the first 2 years before settling. Average sink was less than 1mm but greater than 0.5cm in 5 cases (2 of which required revision for non-fixation). All sink occurred within the first 6 months. Calcar resorption was only noted in 3 cases and was greater than 45° from the prosthesis bone interface.
Discussion
Our results are similar to unpublished, smaller outcomes of the same stem in other centres. Two relatively new modes of failure were noted with sink and early periprosthetic fracture accounting for 56% of stem related failures. In this novel designed stem, there appears to be a narrow window between under and over-sizing with the methods of failure of sink or fracture probable.
