TUESDAY, Dec. 29, 2020 (HealthDay News) — The “true” cumulative incidence of dislocation after primary total hip arthroplasty (THA) may be as high as 3.5 percent, according to a Danish study published online Dec. 18 in the Journal of Bone & Joint Surgery.

Lars L. Hermansen, M.D., Ph.D., from Odense University Hospital in Esbjerg, Denmark, and colleagues used the Danish Hip Arthroplasty Register to identify 31,105 primary THAs indicated for primary osteoarthritis performed from 2010 to 2014 with two years of follow-up data to assess the cumulative incidence of hip dislocation (revisions and closed reductions) after primary THA.

The researchers found there were 1,861 dislocations in 1,079 THAs, corresponding to a two-year cumulative incidence of 3.5 percent. Compared with the correctly coded dislocations captured by administrative register data only, this number represents a 50 percent increase. Three-fourths of initial dislocations occurred within the first three months postoperatively. Risk for dislocation was lower among patients who were younger than 65 years of age (odds ratio [OR], 0.70) and higher among those who were older than 75 years of age (OR, 1.32) versus those aged 65 to 75 years. There was also a lower risk among men (OR, 0.86) and those with cemented fixation (OR, 0.71) and a lateral approach (OR, 0.28). There was a higher risk for dislocation seen with a head size of 32 mm (OR, 1.27) compared with 36-mm heads. Dual-mobility cups were associated with a reduced risk for dislocation (OR, 0.13).

“Comprehensive search algorithms are needed in order to identify all dislocations so that this complication can be accurately reported in national registers,” the authors write.

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