November 12, 2014
1 min read

Most dislocated hips placed within ‘safe zone’ during THA, study finds

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DALLAS — During their minimum 2-year follow-up, researchers here reported a 1.9% rate of subsequent dislocation after total hip arthroplasty in a contemporary practice and noted 58% of these cases had an acetabular socket position within the Lewinnek safe zone.  

“Most contemporary total hip arthroplasties that dislocate are within the Lewinnek safe zone,” Matthew P. Abdel, MD, said during his presentation at the American Association of Hip and Knee Surgeons Annual Meeting. “Cup position for some patients certainly lies outside this safe zone. Most importantly, new technologies will need better targets to hit prior to them being clinically relevant or economically feasible.”

Matthew P. Abdel

Abdel and colleagues conducted a retrospective review of the Mayo Clinic’s total joint registry and identified 12,000 primary total hip arthroplasties (THAs) performed between 2003 and 2012 that had a minimum 2-year follow-up. Of these, 224 THAs (1.9%) had dislocated. The mean time from index THA to dislocation was 18 months.

The mean cup inclination for the dislocated THAs was 44°, with 84% of patients having had their socket with in the Lewinnek safe zone for cup inclination of 40° ± 10°. The mean anteversion for the dislocated THAs was 15°, with 69% of patients having had their cup within the Lewinnek safe zone for anteversion of 15° ± 10°.

“When looking at combined safe zone for inclination and anteversion, 58% of patients who dislocated their THA were considered to be in the safe zone,” Abdel said.

Given the 1.9% prevalence for dislocation, if an ideal technology that guaranteed socket position within the safe zone was available and 40% of dislocated THAs outside of the safe zone could be prevented by hitting the target, 60 patients would need to be treated to prevent one additional dislocation, according to Abdel.

“This is in a best-case scenario and makes several assumptions,” he said, including that the 100% accurate technology is available to hit the safe zone, and that hitting the safe zone would eliminate those dislocations. — by Gina Brockenbrough, MA


Abdel MP. Paper #24. Presented at: American Association of Hip and Knee Surgeons Annual Meeting. Nov. 7-9, 2014; Dallas.

Disclosure: Abdel has no relevant financial disclosures.