In the field

For orthopedic surgeons, a patient with an unstable THA may present with early or late instability. Early dislocation has been defined in the literature as occurring within 2 years of THA [4], although Manzary considers the first year after surgery the most clinically relevant early period. Similarly, late dislocations may occur after 2 years [4] but can also appear 5–7 years later, according to Manzary. Nevertheless, it is reported that most dislocations appear within the first 3 months of surgery [5], with around 50–70% of dislocations occurring as soon as 5 weeks after THA ([5, 6] as cited in [7]). More than three quarters of dislocations are reported to occur within a year [5]. The cumulative risk of dislocation thus increases over time as a result of trauma, wear, laxity, deteriorating muscle strength, and hip-spine relationship modifications [5]. Evaluation becomes more complex when patients are referred from other centers, as the details of the primary THA may be incomplete or unavailable.

Instability has a multifactorial etiology, with several established risk factors [5]. Patient-related risk factors include female sex, advanced age, neuromuscular or cognitive disorders, alcoholism, weakness of the abductor, previous surgery to the hip or the spine, sagittal imbalance, and stiffness of the spine [5] with spinopelvic issues becoming more and more relevant as a recognized risk factor for dislocation, according to Zagra. These factors must be evaluated at each stage of the THA: preoperatively, perioperatively and postoperatively. Notably, in the preoperative phase, a detailed assessment of the risk factors allows for proper planning of the THA, with the aim of reducing or preventing instability. In contrast, surgical factors include both the surgical process and technique, surgical approach, repair of soft tissue and tensioning, impingement, as well as the choice of implant and the experience of the surgeon [5].

In addition to this, different approaches are needed for patients presenting with recurrent dislocation or those referred from another center. For referred cases, the surgeon must reconstruct the context of the primary THA, including the indication, surgical technique, and implant decisions that may only be fully known to the original surgeon. As Manzary comments, “The question raised when presented with a patient with an unstable THA is, why is this happening? We have to think about what happened intraoperatively, for example was there malpositioning of the component or was implant choice a factor. In the latter case we need to consider situations where a patient may have required an implant with extended offset but instead received one with standard offset. There may also have been intraoperative technical errors such as damage to the abductor muscle. We need to consider all of these points when we examine the patient, because they feed directly into our treatment strategy”.