The squeaking hip is a multifactorial concern

Rim impingement, microseparation, subluxation are all suspects in the sound generation.

Issue: April 2008

ByJose A. Rodriquez, MD

In an article currently in press, Jarrett et al collected data on 149 hips in 143 patients at an average age of 56 years, ranging from 23 to 78 years and an average body mass index of 34, all with ceramic hip implants. They noted that 15 patients reported squeaking hips, which is an 11.4% prevalence. Walking, bending, stair climbing and sexual activity were the initiating events. The average cup abduction and anteversion was the same in squeakers and non-squeakers and well within what we consider acceptable (Figure 1). In retrieved specimens from this study, we have seen significant stripe wear evident, with intragranular fractures, grain pullout and a small amount of metal staining centrally. In addition, there was evidence of impingement of the femoral neck on the acetabular rim, with metal wear.

Jose A. Rodriquez

Impingement and squeaking

Based on these observations, it is clear that impingement is a recurring theme in hard-on-hard bearing dysfunction. The association between rim impingement and squeaking was first presented in 2003 by Eichman et al in association with excessive socket anteversion. Moreover, Christensen and Jacobs have recently shown that there is a significant predisposition toward squeaking with ligamentous laxity, which is also a predisposition for rim impingement.

A squeak can be thought of as basically a vibration within an audible range. We can break it down as a friction which causes the vibration which can then be amplified or dampened.

Squeaking was first proposed as having a “dry-joint” etiology by Reiker et al in describing a metal-on-metal slip-stick mechanism resulting in vibration and squeaking. An appropriate fluid film is a necessary part of a low wear hard-on-hard bearing. Disrupting that fluid film can lead to abnormal articulation and accelerated wear.

Walter and colleagues presented a series of 12 squeaking ceramic retrievals demonstrating a very significant difference in the amount of wear measured from the stripe-wear region in squeakers compared to the stripe wear present in silent ceramic retrievals.

Fluid film is required for lubrication. The stripe wear has the opportunity to disrupt that fluid film and create the initial friction. This has been demonstrated in vitro by Nevelos et al. Using an in-vitro technique to reproduce femoral head–socket microseparation, they have been able to reproduce the characteristic appearance of the stripe wear that is found in vivo.

Figure 1: The average cup abduction and anteversion was the same in squeakers and non-squeakers
The average cup abduction and anteversion was the same in squeakers and non-squeakers and well within what is considered acceptable.

Figure 2: The smaller of the two sockets squeaked
Of the two socket diameters that fit a given liner size, only the smaller of the two sockets squeaked. The thicker sockets did not squeak.

Images: Rodriquez J

Vibration and amplification

The next question is what is vibrating? Walter and colleagues have recorded the squeaking sounds made be ceramic-ceramic couples, and subjected the recordings to acoustic analysis. The data indicated that the measured frequency of the squeaks is between 400 Hz and 7.5 KHz and that is within the natural resonant frequencies of the socket and the stem, but not the ceramic components. These findings suggest that it is the stem and shell that are resonating and vibrating and thereby creating the sounds that we hear. The ceramics resonate well above the audible range.

The final issue is amplification. It would appear that each implant system has a specific resonance. Data in the Jarrett et al study show that of the two socket diameters that fit a given liner size, only the smaller of the two sockets squeaked. The thicker sockets did not squeak (Figure 2).

Therefore, a scenario can be imagined where rim impingement can create microseparation which can lead to stripe wear. The titanium wear debris generated may influence this as well. The stripe wear creates diminished fluid film integrity, which leads to friction between the ceramic components. The friction creates vibration within the metal components. Amplification of the vibration is influenced by the specific geometry of the metal components, and the associated resonant frequencies.

Prevention

What can we do to prevent this phenomenon? Clearly we can minimize impingement by optimizing our implant position. We have to be careful of ligamentous laxity, wherein we will not be able to reliably and reproducibly diminish rim impingement. In cases where the extent of ligamentous laxity will necessitate rim impingement, a soft bearing may be more tolerant of it. We can also seek to minimize the initial friction. Stewart et al have published in-vitro data suggesting that the wear stripe in a Delta-Delta (DePuy Orthopaedics) ceramic created with the microseparation technique is significantly less than with Alumina-Alumina. As such, we would expect a lower prevalence of squeaking with a Delta-Delta wear couple. And finally, we can minimize amplification by choosing a proper socket-stem couple to minimize this problem.

For more information:

Jose A. Rodriquez, MD, can be reached at Lenox Hill Hospital, 130 East 77th St., William Black Hall, 11th floor, New York, NY 10021; 212-434-4799; e-mail: josermd@aol.com. He is a consultant with DePuy, a Johnson & Johnson Company, Exactech and Stryker Orthopaedics.

References:
Christensen CP, Jacobs C. Patient- and Surgery-related factors of squeaking and non-squeaking ceramic-on-ceramic total hip arthroplasties. Poster #PO27. Presented at the American Academy of Orthopaedic Surgeons 75th Annual Meeting. March 5-9, 2008. San Francisco.
Eichman TH, Clarke IC, Gustafson GA. Squeaking in a ceramic-on-ceramic total hip. Proceedings of the 8th Biolox Symposium, March 2003. Berlin.
Jarrett CA, Ranawat AS, Bruzzone M, et al. The squeaking hip: an under-reported phenomenon of ceramic-on-ceramic total hip arthroplasty. J Bone Joint Surg. In Press.
Nevelos J, Ingham E, Doyle C, et al. Microseparation of the centers of alumina-alumina artificial hip joints during simulator testing produces clinically relevant wear rates and patterns. J Arthroplasty. 2000;15;793-795.
Rieker CB, Kottig P, Schon R, et al. Clinical Wear Performance of Metal-on-Metal Hip Arthroplasties. Alternative Bearing Surfaces in Total Joint Replacement, ASTM STP 1346, Jacobs JJ, Craig TL, Eds., American Society for Testing and Materials. 1998.
Rodriquez JA. The squeaking hip: A cause for concern — affirms. Paper #22. Presented at the 24th Annual Meeting of Current Concepts in Joint Replacement Winter 2007. Dec. 12-15, 2007. Orlando.
Stewart TD, Tipper JL, Insley G, et al. Long-term wear of ceramic matrix composite materials for hip prostheses under severe swing phase microseparation. J Biomed Mater Res B Appl Biomater. 2003;66(2):567-573.
Walter WL, O’Toole GC, Walter WK, et al. Squeaking in ceramic-on-ceramic hips: The importance of acetabular component orientation. J Arthroplasty. 2007;22:496-503.