To Collar or Not to Collar

Total hip replacement is one of the most successful surgeries in modern medicine, and implant designs are constantly evolving to provide better results. In recent years, orthopedic surgeons have increasingly favor "collared" femoral stems, which feature a small metal ledge that rests on the top of the thigh bone. These collared designs offer excellent mechanical stability and significantly lower the risk of early bone fractures around the implant. However, a recent study by our group highlights a specific complication we need to watch out for as these implants gain popularity: iliopsoas impingement (IPI).

IPI occurs when a tendon in the front of the hip rubs painfully against a prominent edge of the hip implant. The use of collared stems grew substantially, by an average of 9.4% annually from 2020 onward, at our institution of interest. Alongside this growth, there was a notable rise in patients requiring a minor secondary surgery to release the irritated tendon.

Our study identified a clear culprit: collar overhang. When the metal collar extends more than 2 mm beyond the patient's natural bone, it can irritate the surrounding soft tissues. Our research found that a specific type of implant—those with a constant length collar (CLC)—was disproportionately responsible. While CLC implants made up only 19.6% of the collared stems used in the study period, they accounted for 51.7% of the tendon irritation cases requiring surgery.

This issue predominantly affects patients with smaller bone structures. Because the CLC collar length remains unchanged and does not shrink for smaller implant sizes, it is more likely to stick out and cause friction in a smaller thigh bone.

The Bottom Line: For patients, this emphasizes the importance of personalized surgical planning. While collared stems provide fantastic stability, we must carefully match the implant's geometry to your unique anatomy, potentially opting for size-specific collars or collarless designs if you have a smaller bone structure. By paying close attention to these sizing details, we can maximize the benefits of these modern implants while keeping you active and pain-free.

Check out the study for yourself Here.