Abstract
Introduction/purpose: Cementless femoral fixation in TKA varies regarding philosophy of design, materials, and surgical technique. This study evaluates autograft enhancement with AML (porocoated) stems. Impaction autograft (head reamings) enhances cortico-cancellous fit in canals of different geometry, preserves bone, decreases potential for stress shielding and seals the stem from wear particles.
Materials/methods: Clinical/radiologic evaluation of 110 AML prostheses (proximal/extensive porous-coated) with 4- to 11-year (mean 6.9) follow-up was performed. Demographics included 68 females, 42 males, age 34–90 (mean 66). Diagnoses included OA (86), RA (16), other (8). Key surgical points included: 1) stem matching/sizing to proximal cortical contact; 2) head/neck reaming with acetabular graters; 3) autograft delivery (distal-lateral) prior to partial stem insertion and proximal-medial prior to prosthetic seating.
Results: Femoral stem fixation was successful in 98%. Autograft fill was visualized radiographically within the first 6 weeks. Stem fit-fill ratios were .63 proximally and .73 distally, suggesting that most stems were stabilized via cortico-cancellous bone. The 2 fixation failures (1 stem fracture, 1 aseptic loosening) occurred in large males with undersized stems. Radiologic stability was noted in 95%. There were 6 cases of proximal osteolysis secondary to wear without distal extension, and no lucency > 2mm. Mean subsidence was.6mm. There were 10 acetabular failures secondary to wear/loosening and 1 traumatic neck fracture. There were no infections.
Conclusion: The technique of impaction autograft using femoral head reamings is a biological (osteoinductive-osteoconductive), practical, and simple treatment method to accommodate and fill femoral canal voids frequently encountered in THA. Large, stiff stems (with distal fixation) can be avoided with less risk of technical problems and long-term bone loss secondary to stress shielding. The technique can be utilized, with variation, in any current cementless femoral stem.
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.
