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THA instability prevention has come a long way with further to go
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Since the time right after the introduction of total hip arthroplasty, postoperative instability that leads to dislocation of the reconstructed hip has been a challenge.
Originally, orthopaedic surgeons considered the problem of total hip arthroplasty (THA) dislocation to be related to the lack of a tense soft tissue scar. They thought it was best to manage these patients by keeping them in bed for a long time and limit hip motion. Later in the recovery period, it was commonplace to immobilize patients in bandages long-term to restrict excessive hip motion. However, over time it was learned that a detailed preoperative examination to determine hip joint offset and component positioning was an important tool to minimize the risk of hip dislocation.
Today’s patients
Today, THA patients are extremely active. Everyone accepts that THA is typically a quick and safe procedure that quickly puts patients “back in business.” In fact, some younger patients can return to work a few weeks after surgery.
Therefore, I find that today’s challenge related to hip instability is that we still have to compromise with and educate our patients. We must let them know that this complication is probably the main reason why THAs fail and although we do our best to create a stable joint postoperatively, we cannot guarantee that hip dislocations will not occur.
We should also focus on educating hip patients about safety procedures to prevent dislocation so they do not expect to perform all of their activities without caution after discharge. This is important information to convey to patients early and often, because dislocation of a replaced hip can be the start of a long and complicated ride.
Recent developments
Several recent THA developments have helped reduce the risk of THA dislocation. Hard bearings and improved wear of polyethylene acetabular inserts have made it possible to insert larger femoral heads into the THA prosthesis. In fact, conventional THA sometimes now allows use of 44-mm diameter or larger heads with 6-mm polyethylene inserts, and this strategy may help prevent a dislocation.
One reason why metal-on-metal bearings were introduced was to increase the stability of THA in patients and reduce the dislocation risk by increasing the jumping distance of the joint in a situation that could result in dislocation. In the past, that change alone may have led to a dislocation after an unintended motion, but today the hip forces that occur with such risky activities are transmitted to the implant-bone interface. This produces a different failure mechanism — either extrusion of an uncemented acetabular component or a fracture around the femoral stem, both of which require another, possibly more challenging surgery.
The collaborative registries of the Nordic Arthroplasty Register Association show that early revisions due to proximal femoral fractures, mainly in elderly patients with non-cemented stems, are increasing. The best explanation for the phenomenon is the use of larger femoral heads. This just goes to show that larger femoral heads in THA are not a panacea by any means and no solution is without a consequence in another area. In the end, hip instability after THA remains an important challenge with several closely related aspects that the orthopaedist must consider.
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- Per Kjaersgaard-Andersen, MD, is Chief Medical Editor of Orthopaedics Today Europe. He can be reached at Orthopaedics Today Europe, 6900 Grove Road, Thorofare, NJ 08086, USA; email: orthopaedics@healio.com.
Disclosure: Kjaersgaard-Andersen has no relevant financial disclosures.