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Study: Decreased bone mineral density in malleoli occurs within 1 year after TAA
Early periprosthetic fracture of the medial malleolus was observed and may be due to increased loading of the medial metaphysis.
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TORONTO — Following stemmed total ankle arthroplasty, patients had signs of stress shielding over both malleoli which investigators found resulted in decreased bone mineral density in the lateral and medial malleolus, as well as increased bone mineral density at the medial tibial metaphysis.
This indicated a greater than expected increase in mechanical stress from the total ankle arthroplasty (TAA), according to a presenter at the American Orthopaedic Foot & Ankle Society Annual Meeting, here.
“Our study suggested 2 years post-TAA increased bone mineral density [BMD] of the medial metaphysis in tibial regions may be due to increased mechanical stress in these areas,” Adam J. Farrier, MBChB, said. “The reduction of [BMD in] the medial and lateral malleolus regions may be due to stress shielding.”
Regions of interest imaged
Prospectively, Farrier and colleagues preoperatively collected dual energy X-ray absorptiometry (DXA) scans with the Hologic system for 23 patients with a mean age of 63.3 years who underwent TAA and repeated the scans during follow-up assessments at 1 year and 2 years postoperatively. Researchers positioned seven rectangular regions of interest on the anterior-posterior view of the first postoperative image to accommodate for implant positioning.
“Two regions of interest were then placed to coincide with each malleolus, and further regions of interest were placed proximally,” Farrier said. “Two further regions of interest were placed over the talus, region 5, and tibial shaft proximal to the implant, region 7.”
A template for analyzing the regions of interest was used for analyzing preoperative and postoperative images with the Hologic software. Data were compared using Student’s t tests. Farrier noted the BMD scan results were “expressed as a percentage of each patients’ original preoperative BMD to show the relative change over time.”
BMD changes
“Our main finding of 2 years postoperatively was a statistically significant decrease in mean BMD in the lateral malleolus,” which decreased 17% from 0.5 g/cm2 to 0.42 g/cm2, Farrier said.
He added, “Increased loading of the medial metaphysis may help explain early periprosthetic fracture of the medial malleolus which was observed in the Mobility implant (DePuy Synthes).”
The results also showed a reduction in medial malleolus BMD of 4%, in which BMD decreased from 0.67 g/cm2 to 0.64 g/cm2, as well as a 7% increase in the BMD of the medial side tibial metaphysis, however these differences were not statistically significant. Farrier noted there were no significant changes seen in the talus.
Because no further change was found in patients’ BMD from 1 year to 2 years postoperatively, he said these results suggest most remodeling occurs within the first year after TAA. – by Casey Tingle
- Reference:
- Farrier A, et al. Bone mineral density changes following total ankle replacement with an uncemented, stemmed prosthesis: A prospective cohort study. Presented at: American Orthopaedic Foot & Ankle Society Annual Meeting; July 21-23, 2016; Toronto.
- For more information:
- Adam J. Farrier, MBChB, can be reached at Freeman Hospital, Freeman Rd., High Heaton, Newcastle upon Type NE7 7DN, United Kingdom; email: adam.j.farrier@gmail.com.
Disclosure: Farrier reports no relevant financial disclosures.