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Long, smooth taper with MoM hip bearing associated with less material loss
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LAS VEGAS — The metal-on-metal hip bearing that was once most widely used in the United States was found in a recently presented study to lead to increased material loss at its taper junction when paired with shorter, rougher stem trunnions.
Harry S. Hothi, BEng, MSc, PhD, told Orthopaedics Today Europe he and his colleagues conducted a retrieval study to determine which type of material and style of head-stem junction lost the most material volume per year.
“The London Implant Retrieval Centre combines clinical and engineering expertise to identify the surgical, implant and patient factors that lead to failure of orthopaedic implants. In this case control retrieval study involving a single metal-on-metal (MoM) bearing design paired with two different stem types, we demonstrated that shorter and rougher stem trunnions led to greater material loss at the head-stem taper junction,” Hothi said.
One bearing, two stems
Hothi and colleagues’ study, which had a case control design, analyzed 60 surfaces of a single design of a modular MoM total hip replacement prosthesis made of cobalt-chromium, the DePuy Synthes Pinnacle bearing. The bearing was paired with two titanium stems of differing taper types manufactured by DePuy Synthes; either 11/13 or 12/14. The 11/13 stems were the S-ROM and the 12/14 stems were the Corail.
The researchers matched the hips by head size of 36 mm, as well as by patient age and gender, time to revision and head-neck length of either 36 mm +6 mm or 36 mm +5 mm.
Using methods they previously published, Hothi and colleagues measured the volume of material lost for each of the bearings and on the taper surfaces. They also analyzed the significance of the differences in material loss per year between the two stem groups using an independent samples t-test.
Corail taper lost more material
The annual median taper material loss rate was significantly greater for the Corail stems than the S-ROM stems at 0.238 mm3/year and 0.0132 mm3/year, respectively (P = .042).
“The tapers with Corail stems had greater material loss rates than with the S-ROM stems. These findings are in agreement with previous retrieval work. The Corail trunnions in this study had a rougher surface topography leading to imprinting of the taper surface and greater observed corrosion. They were set fully inside of the taper allowing toggling of the trunnion to occur in the high-wearing cases. At this stage, it is unclear if the toggling was due to surgical misassembly or poor manufacturing and this is an area of future work,” Hothi said. – by Robert Linnehan
- Reference:
- Hothi H, et al. Paper #871. Presented at: American Academy of Orthopaedic Surgeons Annual Meeting; March 24-28, 2015; Las Vegas.
- For more information:
- Harry S. Hothi, BEng, MSc, PhD, can be reached at Institute of Orthopaedics and Musculoskeletal Science, University College London and Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, United Kingdom; email: h.hothi@ucl.ac.uk.
Disclosure: Hothi reports no relevant financial disclosures.