What’s the “True” Rate of Dislocation After Total Hip Arthroplasty?
The cumulative incidence of hip dislocation following total hip arthroplasty (THA) is about 50% higher than suggested by simple analysis of hospital data, according to a study published by The Journal of Bone & Joint Surgery.
Researchers from Hospital of South West Jutland in Esbjerg, Denmark, found that in the first 2 years following THA, the “true” rate of hip dislocation is 3.5% percent. “Since our results are based on a large cohort over a five-year inclusion period and include all hospital contacts in Denmark within the first two years after THA, we believe to have found the ‘true’ occurrence of dislocation within this patient group and time frame,” they said in the study.
Hip dislocation is one of the leading reasons for revision. Previous studies have reported widely varying rates of dislocation following THA, reflecting differences in study methods and patient populations.
The researchers from Denmark sought to develop a “more thorough and comprehensive method” for estimating the actual cumulative incidence of dislocation. With use of a national database – the Danish Hip Arthroplasty Register – the researchers identified 31,105 cases of primary THA for osteoarthritis performed in Denmark between 2012 and 2014.
They then used a nationwide hospital database – the Danish National Patient Register – to identify patients who underwent treatment for hip dislocation within 2 years after primary THA. The study used a 2-year window because most dislocations occur within that period.
The researchers identified 1861 dislocations in 1079 THAs, for a 2-year cumulative incidence of 3.5%. More than 40% of these patients had at least 2 dislocations. Three-fourths of initial dislocations occurred within the first 3 months postoperatively.
By linking the hip replacement registry to the national patient database, the researchers identified many dislocations that would otherwise have been missed. Several additional cases were identified by reviewing alternative procedure codes in patient files. The “true” rate of 3.5% “was a 50 percent increase compared with the correctly coded dislocations captured by administrative register-data only,” the researchers said.
The study also examined risk factors for dislocation following primary THA, finding that risk was:
- Lower in patients younger than age 65
- Higher in patients over age 75
- Lower in men than in women
- Lower in patients in better health, based on the ASA Physical Status Classification System
Several surgical factors associated with a lower risk of dislocation included:
- Cemented fixation
- Lateral surgical approach
- Larger femoral head size
- Use of dual-mobility cups
The researchers noted that most patients underwent posterior approach THA, which is more commonly used in Denmark compared with other countries.
The results suggest that rates of hip dislocation following THA – as shown by in-depth analysis of unique and comprehensive Danish health databases – are higher than suggested by administrative hospital data only. They concluded that, “Comprehensive search algorithms are needed in order to identify all dislocations so that this complication can be accurately reported in national registers.”
Hermansen LL, Viberg B, Hansen L, Overgaard S. “True” cumulative incidence of and risk factors for hip dislocation within 2 years after primary total hip arthroplasty due to osteoarthritis: a nationwide population-based study from the Danish Hip Arthroplasty Register. J Bone Joint Surg Am. 2020 Dec 18. doi: 10.2106/JBJS.19.01352. Online ahead of print.