In recent years, squeaking hips have been reported in some patients with total hip arthroplasties using hard-on-hard bearing surfaces. So what exactly is the squeaking hip phenomenon? Javad Parvizi, MD, FRCS, provides the following insights:
Squeaking is purely a bearing surface–related problem, with no adverse effect on the remaining structures around the hip.
For the most part, squeaking hips occur with ceramic-on-ceramic bearing surfaces, although metal-on-metal bearings have been implicated in some cases. Specifically, audible squeaking is associated with earlier generations of ceramic bearings. Later generations of ceramic bearings have been introduced to address the issue, as well as to make the implant stronger and more fracture-resistant. To date, however, these newer design implants are available in the United States only on a limited basis.
The exact cause of squeaking is not clear, but it is likely multifactorial.
For example, femoral stems made from a particular type of titanium alloy have been associated with a much higher incidence of squeaking, compared to other femoral stems. The theory is that a softer metal with a narrower femoral neck allows for greater transmission of sound and resonance than other stems.
Neck impingement with the elevated titanium rim has also been implicated as a cause of squeaking. The impingement results in the generation of metal particles that are then transmitted to the bearing surface, resulting in patch or stripe wear that transmits audible sounds. Bearing surfaces that are too dry have also been implicated as a cause of squeaking, as has malpositioning of the acetabular component.
In most cases, the squeaking is not significant enough to warrant revision surgery.
The incidence of squeaking hips varies by institution, ranging from 1 percent to 15 percent, and the squeaking itself can either be intermittent or continuous and constant. However, revision arthroplasty with a different bearing surface—hard-on-soft—will address the problem 100 percent of the time.
Ceramics is still a great bearing surface that has withstood the test of time.
It is biologically inert, works beautifully, and is a very good joint bearing surface, especially for younger patients. However, to avoid the risk of a squeaking implant, orthopaedic surgeons should not use femoral stems made with a titanium-molybdenum-zirconium-iron alloy or with an elevated titanium rim. Hard-on-hard bearing surfaces are very sensitive to component positioning. Orthopaedic surgeons may also want to consider using the newer generation ceramic bearing, which appears to have an increased resistance to fracture and a very low rate of squeaking.