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Squeaking Hips
William L. Walter, MBBS, FRACS, PhD1; Tim S. Waters, FRCS(Tr&Orth)2; Mark Gillies, PhD1; Shane Donohoo, BEng1; Steven M. Kurtz, PhD3; Amar S. Ranawat, MD4; William J. Hozack, MD5; Michael A. Tuke, HNC, ME6
1 Sydney Hip and Knee Surgeons, Level 3, 100 Bay Road, Waverton, NSW 2060, Australia. E-mail address for W.L. Walter: bill.walter@hipknee.com.au
2 7 West Hill Way, Totteridge, London, N20 8QX, United Kingdom
3 2300 Chestnut Street, Suite 150, Philadelphia, PA 19103
4 Hospital for Special Surgery, 535 East 70th St, 6th floor, New York, NY 10021
5 Rothman Institute at Jefferson, 925 Chestnut Street, 5th Floor, Philadelphia, PA 19107-4216
6 Finsbury Orthopaedics, 13 Mole Business Park, Randalls Road, Leatherhead, Surrey, KT22 7BA, United Kingdom
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from CeramTec, Stryker, and the National Institutes of Health (Grant AR47904). In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from commercial entities (Stryker, DePuy, and Finsbury Orthopaedics). Also, commercial entities (Stryker, DePuy, and Finsbury Orthopaedics) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2008 Nov 01;90(Supplement 4):102-111. doi: 10.2106/JBJS.H.00867
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Ceramic-on-ceramic bearings for total hip arthroplasty were pioneered by Boutin in France during the 1970s1. The first generation of alumina ceramic experienced unacceptably high fracture rates2,3. In the 1980s and 1990s, advances in ceramic manufacturing produced alumina components of higher density and smaller grain size, substantially reducing the risk of fracture. The use of ceramics proliferated throughout Europe, although concerns about fracture, raised in the United States, resulted in its classification as a Class-III medical device by the U.S. Food and Drug Administration (FDA). These circumstances, coupled with the consequences of ceramic fracture, led to the dominance of polyethylene bearings for hip arthroplasty in the United States at the end of the twentieth century.
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    William L. Walter, MBBS, FRACS, PhD
    Posted on December 14, 2008
    Dr. Walter and colleagues respond to Dr. Hamilton
    Sydney Hip & Knee Surgeons

    We would like to thank Dr Hamilton for the opportunity to further clarify the subject of squeaking in joint replacements. Dr Hamilton focuses in his letter on lubrication but lubrication is only half of the equation. Squeaking in hip replacements (as in car brakes) is due to a phenomenon known in physics as a forced vibration(1). A forced vibration is comprised of a driving force and a dynamic response. In this case the driving force is a frictional driving force due to a breakdown of lubrication. The dynamic response is resonance of one of the components of the hip replacement or the bone - probably resonance of the metallic parts of the hip replacement.

    Dr Brian Hills, research on boundary lubrication in the native joint and in hard-on-polyethylene artificial joint has provided valuable insights into these bearings but has only limited relevance to the subject of squeaking in hard-on-hard bearings.

    In hard-on-hard bearings there is probably a variety of lubrication mechanisms depending on the loading conditions and joint fluid(2). Just less than 50% of ceramic-on-ceramic retrievals have no measurable wear suggesting that the bearings are always well lubricated in these patients. The remainder have evidence of edge loading wear(3). Under edge loading conditions in hard-on-hard bearings there is grain pullout indicating a breakdown of lubrication and high friction.

    The fact that more than 50% of ceramic-on-ceramic retrievals have edge loading wear, yet only 1% to 5% of these bearings squeak tells us that high friction does not always lead to squeak. Noise production as measured in the acoustic analysis also depends also on the part resonating in the audible range.

    While we respect Dr Hamilton's knowledgeable opinion, we feel that the statement that ‘orthopaedic surgeons since Sir John have paid little attention to joint lubrication’ is incorrect. In hard-on-hard bearings lubrication is the critical factor determining wear rate. Even when lubrication fails, ceramic-on-ceramic bearings have lower wear than any other bearing material combination available to surgeons today but a well lubricated ceramic-on-ceramic bearing has significant further reduction in wear. Efforts abound to improve lubrication including optimising the surface of the bearing, the clearance, the included angle of the acetabular articulation, the acetabular component position to prevent edge loading and reduce joint reactive force and the femoral component neck geometry. Joint lubrication is at the core of our efforts to improve the function of these bearings.

    We did not have the privilege of speaking personally with Sir John Charnley, so we can only judge what he knew by what he published(4). Squeaking was not the problem in Charnley’s day as it is today; the modern designs that have high rates of squeaking were not even being manufactured and squeaking was only motioned briefly in the literature. We feel, therefore, that squeaking can not have been well understood in his day.

    1. Main IG. Vibrations and Waves in Physics. 3rd ed. Cambridge: Cambridge University Press; 1993.

    2. Scholes SC, Unsworth A. Comparison of friction and lubrication of different hip prostheses. Proc Inst Mech Eng [H]. 2000;214(1):49-57.

    3. Lusty PJ, Tai CC, Sew-Hoy RP, Walter WL, Walter WK, Zicat BA. Third-generation alumina-on-alumina ceramic bearings in cementless total hip arthroplasty. J Bone Joint Surg Am. Dec 2007;89(12):2676-2683.

    4. Charnley J. Low Friction Arthroplasty of the Hip. Berlin: Springer -Verlag; 1979.

    Henry W. Hamilton
    Posted on November 24, 2008
    Squeaking Hips
    Port Arthur Health Centre,194 N. Court St., Thunder Bay, Ontario P7A 4V7 Canada.

    To the Editor:

    In the paper by Walter et al. on the subject of “squeaking hips”(1), the authors describe the subject as “poorly understood”. I would disagree with that assessment and point to the important and relevant history of investigations on the subject of joint lubrication.

    It was a squeaky Judet prosthesis (an acrylic hemiarthroplasty articulating against bone introduced in 1946) that inspired the late Sir John Charnley to investigate the failure of these prostheses. MacConnail, a professor of anatomy at Cork University had postulated that synovial joints were lubricated hydro-dynamically (by a fluid film). Up to the 1980s, mechanical engineers held to this belief. Hydrodynamic lubrication works well in engine bearings, where there is a contained lubricant, and continuous high-speed rotation. A wedge of fluid lubricant is created by the rotating axel, which can support a heavy load – as soon as the rotation stops, the wedge of fluid collapses, and the opposing surfaces come into to direct contact.

    Charnley’s research convinced him that this mechanism could not work in synovial joints where the movement is slow, intermittent and oscillating, and where “stick” does not occur. Charnley concluded that joint lubrication had to be by a boundary mechanism, but was unable to identify the lubricant. This was why Charnley experimented with polytetrafluorethylene, and later used a stainless steel on PE implants.

    The late Dr Brian Hills, an Australian paediatric respirologist with a Cambridge degree in physical chemistry took a new approach. He proposed that surfactants, and in particular surface-active- phospholipids, bonded electrostatically to mesothelial surfaces and were the universal lubricating system in the body. Hills published multiple papers on this subject over almost 20 years (2-9).

    When hard bearing surfaces move in relationship to each other lubrication may become a problem, e.g. chalk on a blackboard, the metal on metal Birmingham hip, or ceramic on ceramic. A “stick-slip” phenomenon causes vibrations, which may be audible as a squeak. It is odd that orthopaedic surgeons since Sir John have paid so little attention to joint lubrication.

    The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated.


    1.William L. Walter, Tim S. Waters, Mark Gillies, Shane Donohoo, Steven M. Kurtz, Amar S. Ranawat, William J. Hozack, and Michael A. Tuke Squeaking Hips J Bone Joint Surg Am 2008; 90: 102-11 2. Hills BA, Butler BD. Surfactants identified in synovial fluid and their ability to act as boundary lubricants. Annals Rheumat Dis. 1984; 43:641-648.

    3. Hills BA. Oligolamellar nature of articular surface. J Rheumatol. 1990;17:349-355.

    4. Hills BA. Synovial surfactant and the hydrophobic articular surface. J Rheumatol. 1996;23(Editorial):1323-5.

    5. Hills BA, Monds MK. Enzymatic identification of the load bearing boundary lubricant in the joint. Br J Rheumatol. 1998;37:137-142.

    6. Hills BA, Monds MK. Deficiency of lubricating surfactant lining the articular surfaces of replaced hips and knees. Br J Rheumatol. 1998;37:143-147.

    7. Hills BA. Boundary lubrication in vivo. Proc Instn Mech Engrs. 2000;214H:83-94.

    8. Purbach B, Hills BA, Wroblewski BM. Surface-active phospholipid in total hip arthroplasty. Clin Orthop Related Res. 2002;396:115-8.

    9. Hills BA, Crawford RW. Normal and prosthetic synovial joints are lubricated by surface-active phospholipid. A hypothesis. J Arthroplasty. 2003;18:499-505.I

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