Abstract
The perception that all cemented stems have reasonable assurance of success if implanted with contemporary cement technique has recently been questioned. Surface finish, stem shape, patient weight and high neck offset have been identified as factors contributing to early loosening. Small design changes to existing cemented stems have led to substantial differences in clinical performance. This study investigates the multi-factorial nature of stem loosening after a 24% early failure rate occurred within the initial three years.
Total hip arthroplasty was performed by the same surgeon on 67 patients with an average age and weight of 65 years (21-85) and 82 kg (49-127), respectively. Initial diagnosis was osteoarthritis (84%), osteonecrosis (7%), congenital dysplasia (4%), and other (5%). Modern femoral stems (Perfecta IMC) with increased lateral neck offset were implanted using contemporary cementing techniques. The stems are grit-blasted proximally, with intramedullary collar steps on the anterior/posterior surface. These design features are meant to enhance axial load transfer and stem-cement bonding. All acetabular cups were uncemented and used polyethylene (48 patients) or cobalt-chrome (20 patients) liners. Patients were evaluated with clinical and radiographic follow-up.
Revision for stem loosening was necessary in 16(24%) patients 9 to 38 months after index surgery, including 9 hips revised within the first 18 months. Radiolucencies at the cement/bone interface, stem subsidence and distal femoral osteolysis were consistently observed. Patients with loosening were significantly heavier than those with well-fixed stems (93 kg versus 78 kg, respectively). Revised hips included 7 cobalt-chrome and 9 polyethylene articulations.
It appears that several mechanical factors contributed to these early failures. Lateral offset stems with cement fixation appear to be at risk for loosening in young, heavy patients. Design features and a thin cement mantle may have resulted in increased cement stresses and cracks during the axial and torsional loading that occur with daily activities.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
