Who (and Why) Risks Dislocation After Hip Arthroplasty?

Most postop hip arthroplasty dislocations occur within the first two years of surgery, according to a research team from the Yale School of Medicine. But who is most at risk and why?

The Yale team designed a study to answer that question and their result, “Incidence, Timing, and Predictors of Hip Dislocation After Primary Total Hip Arthroplasty for Osteoarthritis,” appears in the November 2022 edition of The Journal of the American Academy of Orthopaedic Surgeons.

Study co-author Stephen Gillinov, who is an M.D. Candidate at the Yale School of Medicine, explained the background of the study to OTW, “Hip dislocation after primary total hip arthroplasty (THA) is a costly and morbid complication. The true incidence of dislocation after THA in the United States is not known, due to challenges in monitoring and incomplete implementation of the American Joint Replacement Registry.”

“The present study used a large national administrative database to address this gap, by assessing the incidence, timing, and predictors of dislocation after primary THAs performed for osteoarthritis (OA).”

Using 2010 to 2020 data from the PearlDiver MHip database, the study authors looked at patients who underwent primary THA for OA (using a minimum of two years of postoperative data). They found 155,185 primary THAs, 3,630 (2.3%) of which experienced dislocation within two years. They determined that dislocation was associated with younger age (<65), female sex, body mass index <20, higher Elixhauser Comorbidity Index, cemented prosthesis, and use of metal-on-poly or metal-on-metal implants.

The team noted that their age-related finding is at odds with prior work indicating that an older patient population has been associated with an increased risk of dislocation. They say that the reason for this disparity is not clear, stating, “…but the greater incidence of dislocation in younger patients in this study could result from greater levels of initial postoperative activity or more complex presenting pathology in this specific patient population.”

“Among 155,185 primary THAs,” said Gillinov to OTW, “hip dislocation occurred within two years in 3,630 (2.3%). Among patients who experienced dislocation, 52% of first-time dislocations occurred in the first three months, 57% had more than one, and 11% experienced >5 postoperative dislocation events. Revision surgery was performed within two years of THA in 45.6% of those experiencing dislocation versus 1.8% of those who did not.”

“The 2.3% rate of dislocation that we found falls within the range of previously reported estimates from smaller, prior studies. The high rate of repeat dislocation suggests the need for particular surveillance and counseling for patients with prior episodes of hip instability.”

“Although the incidence of dislocation after THA is relatively low, the high number of THAs performed means that a large number of people are affected by this complication. Understanding the incidence, risk factors, and impact of dislocations within two years of THA should help with patient counseling and establishing treatment pathways.”