Short summary

Hip dislocation after primary Total Hip Arthroplasties (THA) continues to represent one of the leading causes of revision hip surgery. The present study aims to uncover the "true incidence" of hip dislocation in Denmark and identify the subjective difference between THA patients with/without dislocation by use of Patient Reported Outcome Measures (PROMs). The study will be of great value for the clinician, when THA patients faced with dislocations need information about what to expect afterwards and when deciding whether to revise or continue conservative treatment.

Rationale

Since the establishment of the Danish Hip Arthroplasty Registry (Dansk Hoftealloplastik Register - DHR) in 1995, there has been a steadily increasing activity in means of both primary and revision hip surgery. Due to the expanding population and increasing amount of elderly, there is no reason to believe that this trend will change either in Denmark or rest of the world. More patients are also younger at the time of primary surgery, which results in increased demands to the THAs.

Several approaches for visualizing the hip joint prior prosthesis insertion have been described and continuously modified. According to the DHR, more than 97% of primary THAs in Denmark were inserted using the posterior approach in 2015, as is the case in the preceding years. Although the implant survival has reached impressive levels through the last decades, complications do still occur, creating significant burden to the individual patient. In the first postoperative years, hip dislocation remains one of the most common reasons for revision. Incidence of hip dislocation in patients operated through the posterior approach ranges from 1-10% in the literature, and larger scale studies are lacking. Earlier registry studies of THA patients have focused on rate of revision due to recurrent dislocation and not incidence of dislocation.

After experiencing a hip dislocation, the probability of the second and further dislocations is much higher than the first episode. Reported incidences for recurrent dislocations ranges from 10% to more than 60%. The treatment algorithm after reduction of the first hip dislocation is non-operative and conservative including movement restrictions and braces. This is often repeated after the second dislocation, and if additional dislocations appear, salvage surgery targeting the underlying issue is often conducted.  Very few studies have actually reported functional and more subjective patient outcomes after a single or more dislocations.

Despite many years of data collection within the DHR, we are not aware of the actual extent of hip dislocation in primary THA patients as well as the personal experience and influence on quality of life and hip function.

This project aims to investigate dislocations after primary THA in terms of incidence, patient reported outcomes and also the outcome after revision due to recurrent dislocation.

This will be the first study to reveal the actual extent of this specific complication in a large population. It will give our surgeons knowledge of the current standards -both on a national and hospital level. Depending on the results and comparisons to relevant countries, we will be able to either substantiate or forced to rethink our current procedures. This applies to both surgical access and use of specific components. Knowledge about the patient's own perception of both general health and more hip-related issues after experiencing a hip dislocation is lacking. Hip surgeons need this information in order to incorporate it with other objective aspects, when advising patients with their first hip dislocation. Due to the large study population, this study will provide solid information of what to expect after a hip dislocation and be the largest study ever conducted within this topic. Depending on the results, this study may change the path we choose to advise for our patients after single or recurrent dislocations. 

Description of the cohort

Retrospective, we include patients with the diagnosis "primary/idiopathic hip OA". Patients are identified by data extraction from the DHR. From 2010-2014 an average of 9000 patients/year received a primary THA and about 80% of these patients were diagnosed with idiopathic/primary arthritis. Therefore, we tend to include approximately 36.000 patients. Patients are followed up for 2 years after index surgery to identify events of hip dislocation. Hereafter, these patients and identified controls (THA patients without hip dislocations) will be evaluated by means of quality of life and subjective hip function. 

Data and biological material

Patients are identified by the DHR. Patient characteristics and relevant information regarding hospital and specific surgical components are also available. Supplemental patient characteristics are sought in the Danish Anaesthesiologists Database.

Patients - both cases and controls - are evaluated both generic (EQ-5D) and hip specific (Hip Osteoarthritis and Outcome Score, HOOS).

Publications associated with the project

The Orthopaedic Research Unit, Odense University Hospital

• Professor Søren Overgaard, Head of Research, MD, DmSci.
• Bjarke L. Viberg, MD, Post.doc.

Department of Orthopaedics, Hospital of South West Jutland, Esbjerg

• Lars T. Hansen, MD