The Effect of Stem Design on the Prevalence of Squeaking Following Ceramic-on-Ceramic Bearing Total Hip Arthroplasty

Restrepo, Camilo MD; Post, Zachary D. MD; Kai, Brandon BS; Hozack, William J. MD

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.H.01326
Scientific Articles
Abstract

Background: The ceramic-on-ceramic bearing for total hip arthroplasty has an extremely low wear rate and demonstrates minimal inflammatory response in comparison with other bearing choices. However, acoustic emissions such as squeaking and clicking are being reported as annoying complications related to its use. The cause or causes of this phenomenon have not been determined. The purpose of the present study was to evaluate the possibility that design aspects of the femoral component may be a contributing factor to the etiology of squeaking associated with the ceramic-on-ceramic bearing total hip arthroplasty.

Methods: We retrospectively reviewed 266 consecutive patients (304 hips) who had undergone total hip arthroplasty with use of ceramic-on-ceramic bearings. The first 131 consecutive patients (152 hips) (Group 1) received a hydroxyapatite-coated stem composed of titanium-aluminum-vanadium alloy with a C-taper neck geometry and robust midsection with an anteroposterior diameter of 13 mm. The second 135 consecutive patients (152 hips) (Group 2) also received a hydroxyapatite-coated stem, but in that group the stem was composed of titanium-molybdenum-zirconium-iron alloy, with a V-40 neck geometry and a midsection with an anteroposterior thickness of only 10 mm. All 304 hips received the same cup, composed of titanium-aluminum-vanadium alloy. Demographic characteristics, such as age, sex, height, weight, and body mass index, were similar in both groups. Data regarding the presence of squeaking were obtained prospectively. Patients who were seen for clinical follow-up either expressed the squeaking phenomenon themselves or were asked about it by the physician. Patients who were not seen at a recent clinical follow-up visit were contacted by telephone and were asked specifically about squeaking that might be associated with the hip replacement. Only patients with confirmed squeaking noise were included in the present study. Postoperative radiographs, the Short Form-36 health survey, the Harris hip score, and office or telephone interviews of the patient were used to determine the overall outcome of the procedure.

Results: The prevalence of squeaking was seven times higher for patients who received the titanium-molybdenum-zirconium-iron-alloy stem (twenty-seven patients, twenty-eight hips [18.4%]) than in those who received the titanium-aluminum-vanadium-alloy stem (three patients, four hips [2.6%]); this difference was significant (p < 0.0001).

Conclusions: Our study suggests that different stem alloys, stem geometries, or neck geometries can have an impact on the frequency of squeaking following a ceramic-on-ceramic total hip arthroplasty.

Level of Evidence: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.

Author Information

1Department of Orthopaedic Surgery, Thomas Jefferson University Hospital, Rothman Institute, 925 Chestnut Street, 5th Floor, Philadelphia, PA 19107. E-mail address for W.J. Hozack: research@rothmaninstitute.com

Article Outline

Ceramic-on-ceramic bearings have many advantages for use in total hip arthroplasty. The hardness of ceramic makes it more wettable and provides a smoother surface than other bearings do. This results in wear rates as many as twenty times lower than those for metal-on-metal articulations in vitro1. In addition, particle debris from ceramic-on-ceramic hips does not generate the magnitude of inflammatory response that polyethylene does2. The particles are also more bio-inert than those from metal-on-metal articulations. Despite these advantages, ceramic-on-ceramic bearings have had a mixed experience since their introduction in the early 1970s. Early designs were plagued by catastrophic failure and were largely abandoned3. Improvements in design and ceramic quality led to a renewed interest in the 1990s and early 2000s.

However, enthusiasm for ceramic-on-ceramic bearings has been tempered recently by reports of noise, specifically, squeaking. All hard-on-hard bearings have been associated with noise4, but, unlike the noise associated with metal-on-metal articulations, ceramic-on-ceramic squeaking does not seem to abate with time. The prevalence of squeaking has ranged widely among investigators. Capello and colleagues5 reported a rate of 1%, whereas Jarrett and colleagues6 reported a prevalence of 11.4%. A recent study from Denmark7 demonstrated a rate of 20%. Data collected at the Rothman Institute8 demonstrated 3%.

The etiology of ceramic-on-ceramic squeaking has been elusive. Our hypothesis is that the audible squeak associated with ceramic-on-ceramic bearings is multifactorial but that an important contributing factor to squeaking involves specific design characteristics of the femoral component.

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Materials and Methods

Institutional review board approval was obtained for the present study. We retrospectively reviewed 266 consecutive patients (304 hips) who were managed with ceramic-on-ceramic total hip arthroplasty between 1998 and 2004. All patients had a diagnosis of degenerative joint disease of the hip and underwent total hip arthroplasty through a modified Hardinge approach. All procedures were performed by the senior author (W.J.H.) at a single institution.

Patients fell into one of two groups related to the date of surgery. Group 1 included the first 131 consecutive patients (152 hips), who were managed from 1998 to 2002. All patients in this group received an Omnifit stem (Stryker Orthopaedics, Mahwah, New Jersey), which is composed of a titanium-aluminum-vanadium alloy (Fig. 1). The Omnifit stem has a hydroxyapatite coating, a C-taper neck geometry, and a robust midsection with an anteroposterior diameter of 13 mm (Fig. 1). All of these patients received a Trident cup (Stryker Orthopaedics). The Trident cup is a titanium-aluminum-vanadium alloy and accepts a ceramic liner within a commercially pure titanium sleeve (Fig. 2). This specific design has an elevated titanium rim, which may increase the possibility of impingement and potentially could be an additional source of squeaking.

Group 2 included the second 135 consecutive patients (152 hips), who were managed from 2002 to 2004. All patients in Group 2 were managed with an Accolade stem (Stryker Orthopaedics) and the same Trident cup that was used in Group 1. The Accolade stem is made of a titanium-molybdenum-zirconium-iron alloy, with a V-40 taper neck geometry and a midsection with an anteroposterior thickness of only 10 mm (Figs. 3 and 4).

Demographic data, including age, sex, height, weight, and body mass index, were recorded prospectively for all patients (Table I).

Intraoperative data, including prosthesis type, stem size, head size, and liner size, were also recorded. All patients were managed with either a 28, 32, or 36-mm ceramic head. Head size was based on the maximum allowable size for the implanted cup. In Group 1, thirty-four hips (22.4%) received a 28-mm head, ninety-two hips (60.5%) received a 32-mm head, and twenty-six hips (17.1%) received a 36-mm head. In Group 2, twenty-seven hips (17.8%) received a 28-mm head, seventy-nine hips (52.0%) received a 32-mm head, and forty-six hips (30.3%) received a 36-mm head (Table II).

Postoperative anteroposterior and lateral radiographs were reviewed to assess the position of the acetabular component9. With use of OrthoView software (Meridian Technique, Southampton, Hampshire, United Kingdom), the anteroposterior radiographs were uploaded, the images were calibrated, and the position of the acetabular component was assessed with use of the inclination-anteversion tool from the system. This evaluation was done by an orthopaedic surgeon (C.R.) and an adult reconstruction fellow (Z.D.P.). Cup position was assessed with regard to abduction, version, and height. The stem was evaluated with regard to position and offset.

Outcome measurements, specifically, the Physical Health and Mental Health dimensions of the Short Form-36 (SF-36) Health Survey as well as the Harris hip score, were obtained preoperatively and at the time of the latest follow-up for all patients.

Data regarding the presence of squeaking were obtained prospectively. The 247 patients (282 hips; 92.8%) who were seen for clinical follow-up either expressed the squeaking phenomenon themselves or were asked about it by the physician. The 19 patients (twenty-two hips; 7.2%) who were not seen at a recent clinical follow-up visit were contacted by telephone and were asked specifically about noises that might be associated with the hip replacement. If squeaking was confirmed, the patient was asked to characterize its intensity (slightly, moderately, or highly audible), frequency (continuous, intermittent, or a single event), and the time between the date of the operation and the date of onset. Patients who had only clicking were not included in the study.

Complications, including infection, loosening, and reoperation for any reason, were recorded.

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Statistical Analysis

Demographic data as well as prosthetic femoral head size and neck length were analyzed and compared between groups of patients and between squeaking and nonsqueaking hips. All statistical tests were performed with alpha set at 0.05. The t test was performed to evaluate continuous variables (age, height, weight, body mass index, and radiographic findings), and the Fisher exact test was used to evaluate nominal values (sex, head size, and neck length). A baseline logistic regression model adjusting for the covariates of age, sex, and body mass index was performed. We tested confounding by adding several femoral variables to the baseline model individually and then tested whether it resulted in a change of odds ratio by 10%.

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Source of Funding

There was no direct external funding for this study, although one of the authors is a consultant for Stryker Orthopaedics.

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Results

The two groups did not differ significantly with regard to age, sex, height, weight, or body mass index (Table I).

On the postoperative radiographs, cup abduction, cup anteversion, cup medialization, and femoral offset were not significantly different between the two groups (Table III). Although the values for cup abduction and anteversion were high, cup malpositioning alone has been demonstrated not to correlate with squeaking8.

The only measured parameter that showed a significant difference between the two groups was the prevalence of squeaking. Three patients (four hips; 2.6%) reported squeaking in Group 1. The average time of onset in this group was 16.5 months (range, 1.2 to sixty-nine months) postoperatively. In contrast, twenty-seven patients (twenty-eight hips; 18.4%) reported squeaking in Group 2 (p < 0.0001). The average time of onset in this group was 13.2 months (range, 0.7 to seventy-seven months) postoperatively. The frequency and severity of squeaking did not change through the study period for this specific cohort. Of the thirty-two hips with squeaking, six (all from Group 2) were revised to a polyethylene liner, with complete resolution of the noise in all six cases. After logistic regression, none of the variables—age, sex, body mass index, head size, stem offset—showed a change of 10% in the odds ratio. After adjusting for the covariates, we found an association between the group and squeaking (p = 0.0001) (Table IV).

Compared with preoperative baseline values, both groups exhibited significantly increased values on the SF-36 questionnaire in terms of both the Physical Health score (with increases of 45 points in Group 1 and 47 points in Group 2) and the Mental Health score (with increases of 35 points in Group 1 and 37 points in Group 2), but there was no difference between the two groups (p = 0.956 and p = 0.987, respectively). As expected, the Harris hip score was better after surgery in both groups in comparison with the baseline values (with improvement of 27 points in Group 1 and of 25 points in Group 2), but again there was no significant difference between the two groups (p = 0.893).

All patients, including the ones who experienced squeaking, were satisfied with the result of total hip arthroplasty (except for the squeaking itself). No other orthopaedic and non-orthopaedic complications were found in either group.

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Discussion

A definitive etiology for squeaking in ceramic-on-ceramic-bearing hips has been elusive and controversial. Factors such as cup position and patient age, height, and weight have all been implicated as being associated with audible squeaking10. However, other reports and our own data have shown no association with these same factors8. The current study suggests a new explanation. We found a clear relationship between the prevalence of squeaking and the type of femoral component implanted. Patients in our series who were managed with a thicker femoral component with a C-taper neck and a stem made of titanium-aluminum-vanadium were seven times less likely to report squeaking than those with a thinner stem component with a V-40 taper neck made of a titanium-molybdenum-zirconium-iron alloy.

The current explanation for ceramic-on-ceramic squeaking is based on the phenomenon of stripe wear. Walter et al.11 first reported finding stripe wear in 2004. In a retrieval analysis, those investigators found a heavy wear pattern in a location of the head that suggested wear during activities at the extremes of motion. Specifically, their analysis showed that this wear did not usually occur during normal walking but rather occurred during rising from a seated position or other high-flexion activities. During these activities at the extremes of motion, edge loading between the ceramic head and the posterior rim of the ceramic cup occurred. The investigators concluded that it was these edge-loading activities that led to the visible wear stripe.

In a retrieval analysis, Lusty et al. reported that twelve of twelve squeaking ceramic-on-ceramic bearings had evidence of edge-loading wear, suggesting that a wear stripe is likely involved in the production of squeaking12. As a ceramic-on-ceramic bearing passes over the stripe, it could generate a vibration that produces an audible sound (Fig. 5). This explanation is consistent with the fact that ceramic-on-ceramic squeaking does not occur until an average of fourteen to eighteen months after surgery8,10. During this time, the wear stripe has not fully developed. Once a wear stripe is established, squeaking occurs. In addition, the theory that edge loading creates a wear stripe is consistent with studies that have shown an increased prevalence of squeaking in patients with malpositioned acetabular cups10. A cup in excessive retroversion, for example, would lead to increased edge loading in flexion and, subsequently, a higher prevalence of squeaking.

The basic presumption about squeaking is that the noise is due directly to vibration of the ceramic bearing. However, a study by Walter et al. demonstrated that ceramic heads and ceramic liners generally resonate at a frequency that is above the upper limit of human hearing (20,000 Hz) and well above the in vivo range of squeaking hips (400 to 7500 Hz)13. This discrepancy poses an obvious question: If ceramic heads and liners do not resonate in a range that can be heard, what is causing the audible squeaking? Further evaluation of the data from the study by Walter et al. showed that a titanium femoral stem vibrates between 2000 and 20,000 Hz, easily within the audible human range. These data, combined with our findings, suggest that the difference in the rate of squeaking in our two groups is directly related to the differences in the composition and design of the femoral components. It is our hypothesis that there is a breakdown of fluid film lubrication in the hip, with an increase in friction. This generates increased frictional energy in the form of a vibration, which is then transmitted to a flexible stem that amplifies the vibration by resonating, resulting in an audible sound.

We found no difference between Groups 1 and 2 in terms of patient-related parameters. In addition, we found no difference between the patients with and without squeaking in terms of cup or stem position. These findings are in contrast to those of some published studies10 but are consistent with others7. All procedures in the present study were performed by the same surgeon, who has performed thousands of primary total hip arthroplasties during his career. The only difference noted between groups was the prevalence of squeaking.

The stem used in Group 1 was made of a traditional titanium-aluminum-vanadium alloy. The neck on that stem had a C-taper, and the stem itself was more robust proximally. The stem used in Group 2 was made of a titanium-molybdenum-zirconium-iron alloy. That stem had a V-40 neck geometry and was much more slender proximally. One of the purported benefits of the titanium-molybdenum-zirconium-iron material is that it has a modulus of elasticity that is 30% to 40% less than that of titanium-aluminum-vanadium. Therefore, it is a more flexible material even with the same geometry. Furthermore, the titanium-molybdenum-zirconium-iron stem in our study was thinner from front to back (10 mm compared with 13 mm), thus reducing the bending stiffness in the sagittal plane by an additional 50%. These properties create the potential for less thigh pain and better stress distribution to bone, with less proximal bone atrophy. In addition, they make for a much more flexible stem. The V-40 neck is smaller than the C-taper on the titanium-aluminum-vanadium stem. The decreased cross section of the V-40 neck is another purported advantage of using titanium-molybdenum-zirconium-iron. The smaller neck diameter should lead to less impingement. However, the smaller diameter of the V-40 neck leads to a lower bending stiffness and lower resonant frequency and is more capable of amplifying vibrations generated by the ceramic-on-ceramic articulation to cause an audible squeak. The relatively high prevalence of squeaking in Group 2 is consistent with this mechanism. In contrast, the thicker C-taper neck in Group 1 has a higher bending stiffness and a higher natural frequency and is therefore less able, in theory, to amplify vibrational energy into audible resonance.

Three published studies support our proposed theory. Jarrett and colleagues reported that ten (7%) of 143 patients reported squeaking6. Of note, the stem that was used also had a thin profile with a V-40 neck and was composed of titanium-molybdenum-zirconium-iron alloy. Another study, which demonstrated a 20% prevalence of squeaking, evaluated a different femoral component, but one that was also composed of titanium-molybdenum-zirconium-iron with a V-40 neck14. In contrast, Capello and colleagues reported a 1% prevalence of squeaking in a study that evaluated a component with a C-taper that was composed of titanium-aluminum-vanadium alloy5.

In conclusion, the etiology of squeaking of a ceramic-on-ceramic-bearing hip appears to be complicated and multifactorial. Our data show a direct relationship between the prevalence of squeaking and the type of femoral component used. It is our belief that ceramic-on-ceramic continues to be a good alternative for young patients. Avoiding the use of a V-40 neck and titanium-molybdenum-zirconium-iron stem may reduce substantially the prevalence of squeaking.

NOTE: The authors thank Dr. William Walter for his invaluable input on the revision of this manuscript.

Investigation performed at the Thomas Jefferson University Hospital, Rothman Institute, Philadelphia, Pennsylvania

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 Stryker Orthopaedics. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

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