Abstract
Total knee replacement (TKR) is an established treatment for end stage joint disease of the knee. Trabecular metal is one of the design experiments seeking to improve the bone-implant interface and wear patterns in order to increase the longevity of primary joint replacements and reduce the revision burden. Uncemented implants retain bone stock, reduce third body wear, and require a shorter operative time. Although only 4% of knee replacements currently being implanted are uncemented TKRs, there has been considerable recent interest in uncemented designs with a hope of improving the survival time of primary implants. National Joint Registry data has been less favourable of uncemented designs thus far. We report our experience with these comparative implants and present our functional and radiological mid-term results.
Trabecular metal is made of tantalum. It has an interconnecting 3-dimensional lattice structure which is 80% porous. It closely resembles the microstructural architecture of cancellous bone. Bone grows into the porous structure creating a strong bond between bone and implant. In this design, the tibial pegs are seated in a peripheral position, in denser cancellous bone when compared with a central peg. Tantalum offers an appropriate modulus of elasticity, reducing the likelihood of component lift-off and stress shielding.
Over a 4.5 year period, between April 2007 and December 2011, 132 knees in 127 patients with a diagnosis of end stage osteoarthritis, underwent TKR at a single hospital (CMH), performed by a single surgeon (JH). All surgeries were performed with a thigh tourniquet, medial parapatellar approach, antibiotic and VTE prophylaxis, patellar resurfacing, and rapid recovery rehabilitation. 86 cemented TKRs in 78 patients (mean age 76 years), and 66 uncemented TKRs in 49 patients (mean age 68 years). All components were standard NexGen (Zimmer) implants. Follow-up was a mean of 40 months (range 6–87 months).
We analysed the patient postoperative routine standing and recumbent anterior-posterior and lateral radiographs using the knee society TKA scoring system. All linear measurements were made using a PACS viewing system and analysed by 2 of the authors independently. There was no significant radiological lucent lines, and no single KSS > 4. Patients completed Oxford Knee Scores and Knee Society Scoring questionnaires to evaluate their functional outcomes. The mean OKS was 41, and KSS 89. In this period there were revisions in 3 cemented prostheses and 2 uncemented prostheses. 2 revisions were for infection, 2 for peri-prosthetic fracture following trauma, and 1 for unexplained pain.
The uncemented TKR performs equally as well as its cemented counterpart in our experience, both clinically and radiologically, at mid-term follow-up of up to 7 years (mean 3.3 years).
