Hip Squeaking after Ceramic-on-ceramic Total Hip Arthroplasty.

OBJECTIVE: The present study aimed to review the characteristics and influencing factors of squeaking after ceramic-on-ceramic (CoC) total hip arthroplasty (THA) and to analyze the possible mechanisms of the audible noise. DATA SOURCES: The data analyzed in this review were based on articles from PubMed and Web of Science. STUDY SELECTION: The articles selected for review were original articles and reviews found based on the following search terms: "total hip arthroplasty", "ceramic-on-ceramic", "hip squeaking", and "hip noise."
RESULTS: The mechanism of the squeaking remains unknown. The possible explanations included stripe wear, edge loading, a third body, fracture of the ceramic liner, and resonance of the prosthesis components. Squeaking occurrence is influenced by patient, surgical, and implant factors.
CONCLUSIONS: Most studies indicated that squeaking after CoC THA was the consequence of increasing wear or impingement, caused by prosthesis design, patient characteristics, or surgical factors. However, as conflicts exist among different articles, the major reasons for the squeaking remain to be identified.

INTRODUCTION

Total hip arthroplasty (THA) is an effective therapeutic method for advanced hip diseases that can restore the physical function of the hip joint and improve the quality of life in most patients. Common materials used for THA include metal, polyethylene, and bioceramics. Combinations include metal-on-metal, metal-on-polyethylene, ceramic-on-plastic, and ceramic-on-ceramic (CoC).[1] With stable chemical inertia, reliable biocompatibility, high hardness, and a low coefficient of friction, CoC total hip implants have been popularized in recent years.[23]

CoC bearing for THA was first introduced by Boutin in France during the 1970s.[4] With the application of third- and fourth-generation ceramic total hip bearing surfaces, CoC implants are currently widely utilized in THA.

However, even with the application of new ceramic surface materials, various clinical problems still exist with CoC hip prostheses. One such problem is postsurgery squeaking, which affects patients’ quality of life. Recent research has shown that the incidence of noise emanating from CoC-bearing THAs is nearly three times more frequent than the noise that emanates from ceramic-on-polyethylene hip implants.[5] Nevertheless, explanations for hip squeaking are still limited.

CHARACTERISTICS OF SQUEAKING

There is neither a specific definition for postsurgery squeaking nor a universal categorization for the sound. Kuo et al.[6] studied 125 patients who had undergone THA, eight of whom reported squeaking noises, including clicking, grinding, and snapping. Jarret et al.[7] described the sound as clicking, popping, clunking, and grinding. In terms of sound analysis, the noise is composed of a series of sounds with individual frequencies, with a fundamental frequency between 400 and 7500 Hz.[8] Further studies have demonstrated that the fundamental frequency is approximately 1500 Hz in male patients and 2500 Hz in females.[9]

It should be noted that squeaking is not usually associated with abnormal feelings or functional impairment.[1011121314] In addition, there has been no significant difference in satisfaction between patients with squeaking and silent hips.[15]

OCCURRENCES OF SQUEAKING

Reported occurrences of squeaking vary among different studies [Table 1]; the prevalence was reported to be around 0.5% by Walter et al.[8] but 10.6% by Cogan et al.[22] Another study showed that the prevalence could reach up to 24.6%.[29] Such variation could be ascribed not only to the difference in sample sizes among the studies but also to inevitable subjective bias due to a lack of unified scales for noise assessment. Owen et al.[30] summarized studies of squeaking after THA over recent years where 545 of 15,131 cases reported squeaking, with an average incidence of 4.2%. In these studies, the incidence rate was 1.2% in self-reported studies, but as high as 4.5% in scale-based ones, which is convincing evidence for the existence of subjective bias.

Table 1

Studies reported occurrence of squeaking associated with CoC THA

Authors	Year	Hip joints (n)	Squeaking (%)
Walter et al.[8]	2008	2397	0.5
Restrepo et al.[12]	2008	1056	2.8
Capello et al.[16]	2008	380	0.8
Keurentjes et al.[17]	2008	43	20.9
Jarrett et al.[7]	2009	149	10.7
Boyer et al.[18]	2010	76	1.3
Choi et al.[19]	2010	173	4.6
Mai et al.[20]	2010	320	17.2
Sexton et al.[15]	2011	2406	3.1
Schroder et al.[21]	2011	375	2.4
Cogan et al.[22]	2011	265	10.6
Parvizi et al.[23]	2011	1745	5.6
Nikolaou et al.[24]	2012	34	8.8
Haq et al.[25]	2012	1002	1.5
Chevillotte et al.[26]	2012	89	5.6
McDonnell et al.[27]	2013	208	20.7
Kiyama et al.[28]	2013	183	12.0
Owen et al.[29]	2014	69	24.6
Owen et al.[30]	2014	16,828	4.2
Aoude et al.[31]	2015	140	0.7

CoC: Ceramic-on-ceramic; THA: Total hip arthroplasty.

The onset of squeaking was usually 14–40 months after THA surgery.[1011151729] Although there was barely any evidence indicating a relationship between squeaking and osteolysis, heterotopic ossification, and other postsurgery biomechanical problems, such as instability and functional limitations,[1113143233343536] it can affect patients’ quality of life[202137] and in some cases, lead to revision surgery. In different studies of patients who had received CoC THA, the incidence of revision surgery for post-THA squeaking ranged between 0 and 4.7%.[17] The estimated prevalence for revision based on a meta-analysis was approximately 0.2%.[30] However, the real proportion could be far higher, taking into account both patients on the waiting list or those about to undergo the second operation.

RISK FACTORS OF SQUEAKING

Various factors have been proven to be relevant to post-THA squeaking and can be divided into three categories: patient, surgical, and implant factors.[10]

Patient factors

A retrospective study by Mai et al.[20] showed that patients who experienced squeaking were taller on average than that of patients who had not. Sexton et al.[15] reported that the tendency for squeaking to occur was higher in younger, heavier, and taller patients. However, a retrospective meta-analysis by Stanat and Capozzi[38] demonstrated that squeaking was solely based on body mass index (BMI); patients with a higher BMI were at a higher risk for squeaking while no significant relevance was found between squeaking and patients age, gender, height, weight, or procedural laterality.

In addition, limb length shortening and rheumatoid arthritis were also common factors for hip noise,[1125] and patients with squeaking hips experienced more physical activities with a significantly wider range of hip joint movement, especially in terms of internal and external rotation range.[15]

Surgical factors

Implant position and orientation can play a key role in causing hip squeaking. Walter et al.[10] proved that high or low anteversion and inclination of the acetabular component were associated with squeaking. In patients without squeaking, 94% of the implants were installed with 25° ± 10° anteversion and 45° ± 10° inclination while only 35% of squeaking hips were within this range. Neck-socket impingement and edge loading caused by an improper component position were possible explanations for the relationship between acetabular component orientation and squeaking.[39] In addition, increased cup anteversion and inclination were found to be associated with anterior edge loading while insufficient anteversion and inclination were associated with posterior edge loading.[1040] Moreover, reduced hip center medialization and high prosthetic femoral offset were also associated with hip squeaking.[1528] Thus, placement of the implants during operation may directly influence the chance of squeaking.

Implant factors

The prosthesis design and the materials used are also thought to be contributing factors for squeaking. A study conducted by Parvizi et al.[23] reported squeaking in 92 of 1507 enrolled patients (6%), all of whom had received implants with an elevated rim. The noise could be either a consequence of rim impingement when the lubricating layer was compromised by fallen fragments into the space between friction pairs or a direct effect of friction at the impingement site. In addition, the impingement also increased the chance of mismatch and edge loading, resulting in further damage of the bearing surfaces.[12324142]

Some reports mentioned that specific hip joint prosthesis pairs could lead to more frequent squeaking. Stryker Trident acetabular cups paired with Stryker Accolade femoral stems showed a dramatically higher average incidence of squeaking, i.e., up to 35.6% compared with non-Stryker designs in which the incidence was only 3.6%.[11] This higher incidence is possibly due to the unique design of the Stryker system, which features a high rim and short femoral neck.

The incidence of squeaking was also reported to be related to the materials of the femoral stem but not its design. The prevalence was seven times higher for patients who had received titanium-molybdenum-zirconium-iron alloy stems (18.4%) than for those who had received titanium-aluminum-vanadium alloy ones (2.6%).[43] This phenomenon implies that the specific composition of the material and structure could influence the stiffness and fundamental frequency of the prosthesis, which has a greater tendency to induce resonance during hip joint movements, thus resulting in audible squeaking.[2844]

It should be noted that a meta-analysis conducted by Lee et al.,[45] which included 132 recent studies on squeaking, showed that among numerous factors, the only significant one was the abduction angle, which was positively related to squeaking incidence. A significant difference existed among results of published studies and potential factors related to hip squeaking in the available literature are listed in Table 2.

Table 2

Studies demonstrating risk factors associated with CoC THA squeaking

Authors	Relevant factors	Irrelevant factors
Mai et al.[20]	Height, neck geometry, V40 neck/Trident combination and C-taper/Trident combination	Age, gender, weight, BMI, indication, head size, acetabular component
Sexton et al.[15]	Height, weight, age, femoral offset, inclination, anteversion, medialization	Femoral head size, BMI
Stanat and Capozzi[38]	BMI	Age, gender, height, weight, procedural laterality
Walter et al.[10]	Height, weight, age, anteversion, inclination, impingement, edge loading
Eickmann et al.[39]	Neck-socket impingement
Kiyama et al.[28]	Age, obesity, cup lateralization, Accolade stem, shortened head length, activity level	Loosening of prosthesis
Parvizi et al.[23]	Neck impingement, Trident acetabular cup
Restrepo et al.[12]	Edge loading, stripe wear, the kinematics of the hip implant	Acetabular component positioning, intervention, abduction, femoral head size, type of femoral stem, impingement, age, height
Rodríguez et al.[41]	Rim impingement, lubrication disruption, Trident cup with Accolade stem
Yang et al.[32]	Elevated titanium rim
Swanson et al.[11]	Combination of Stryker Trident cup and Accolade stem, short femoral neck length, rheumatoid arthritis	Age, sex, height, activity level, acetabular component size, femoral head size, BMI, laterality, femoral offset
Restrepo et al.[43]	Accolade stem	Age, height, weight, BMI, abduction, anteversion
Restrepo et al.[44]	Type of motion activity	Pain
Lee et al.[45]	Abduction angle	Age, gender, BMI, anteversion, head size, type of femoral stem and acetabular cup
McDonnell et al.[27]	Range of motion, inclination, anteversion, head size, ligament laxity	Age, height, weight, BMI, gender, stem type
Chevillotte et al.[46]	Trident acetabular cup, anteversion	Age, gender, height, weight
Haq et al.[25]	BMI, acetabular opening angle, limb length shortening	Age, acetabular anteversion
Hothan et al.[47]	Stem design, assembled stem, axial load	Cup design, bearing clearance
Bernasek et al.[48]	Gender, inclination
Choi et al.[19]	Head size, gender	Age, height, weight, BMI, cup size, neck length, abduction

CoC: Ceramic-on-ceramic; THA: Total hip arthroplasty; BMI: Body mass index.

MECHANISMS OF POSTTOTAL HIP ARTHROPLASTY SQUEAKING

Audible noises generated by irregular vibrations were a coeffect of impulse and amplification system.[49] Proposed mechanisms of squeaking in CoC THA are shown in Figure 1. Most studies so far have implied that post-THA squeaking is the result of disruption of the lubrication between bearing surfaces[37435051] and it could disappear when lubricants are introduced,[52] indicating that the squeaking was caused by friction. Therefore, the impulse is mainly abnormal friction force. Most studies so far have focused on factors that would modify the nature of friction pairs, thus generating abnormal friction, while some recent studies have turned to the amplification system, that is, the resonance of the implants.

Figure 1

Proposed mechanisms of squeaking in CoC THA. CoC: Ceramic-on-ceramic; THA: Total hip arthroplasty.

Mechanisms of impulse

As mentioned above, hip squeaking will not occur under normal lubricating conditions. However, the fluid film lubrication can be disrupted by increased surface roughness (stripe wear), abnormal behaviors in the hip prosthesis (edge loading and microseparation), particulate debris between bearing surfaces (a third body), and direct destruction of implants (fracture), thus leading to direct contact of the prosthesis’ bearing surfaces and the generation of noise when relative movement occurs.

Stripe wear

Stripe wear, mostly crescent-shaped, could frequently be observed during revision for THA squeaking. The wear rate of the ceramic surface increased significantly in this area. It was reported that the median wear rate of the combined implant (femoral heads and acetabular components) of noisy CoC bearings with stripe wear was 6.7 mm3/year compared to a median of 0.14 mm3/year in the silent control group, representing a 45-fold increase.[53] The prevalence of squeaking clearly increased with the occurrence of stripe wear.[54] Given the fact that hip squeaking mostly occurs several months after surgery[55] and that the formation of stripe wear also requires some time to develop, the relationship between squeaking and stripe wear may well be speculative.

Edge loading

Because of the process and technology of implant production, the ceramic liner was not a continuous smooth surface, but rather one with hard edges at the margin of the bearing surface that sat a couple of millimeters recessed from the face of the implant.[49] The friction pairs were uniformly forced when the femoral head moved normally inside the liner. However, under certain circumstances, the contact point between the femoral head and the liner would move over the hard edge, leading to an increase in stress (referred to as edge loading), hence causing stripe wear.

Some researchers suspected that edge loading might be related to impingement between the femoral neck and acetabular cup. Restrepo et al.[12] studied five patients (with six THA hip joints) who had undergone revision surgery for squeaking, posteroinferior neck-rim impingement, as evidenced by indentation in the rim, was observed in four of these acetabular components. The prevalence of impingement was 7 of 12 according to Walter et al.[53] The impingement would lead to dislocation of the femoral head, which could result in an altered distribution of surface stress and consequent edge loading. It should be noted, though, that not all stripe wear cases demonstrated edge impingement.

Microseparation was one of the hypotheses for edge loading.[56] Separation between bearing surfaces during swinging of the artificial hip joint could lead to edge loading when the patient's leg touches the ground. One experiment in vivo proved the existence of microseparation,[57] which could be a consequence of lowered joint stability due to post-THA reduction of soft tissues, such as articular capsules, ligaments, and muscles. However, some researchers have argued that edge loading would not take place with normal walking, but rather only where the hip is flexed, such as when the patient is rising from a chair or climbing a high step.[40]

Third body

Friction force, except for the contact force, is also modified by the friction coefficient. Alternation of the lubrication fluid status could directly lead to a change of the friction coefficient, and increasing the friction coefficient could ultimately result in unstable vibration and an audible noise. It was reported that impingement between the femoral neck and acetabular cup could presumably be caused by malposition, or that improper design of the implants could produce third bodies.[1139] Metal debris from impingement could fall inside the bearing surface and disrupt the lubrication film, which would bring about an increased wear rate of the ceramic surfaces, thus producing ceramic debris. Third bodies composed of both metal and ceramic debris further facilitate abrasion of the joint bearing surfaces. Chemical identification with microanalysis proved the presence of ceramic particles in the synovial fluid of squeaking hips.[58] Experiments in vitro also indicated that the friction coefficient could be dozens of times higher than normal situations with the existence of a third body as well as of edge loading,[59] implying a relationship between third bodies and abnormal friction.

Fractures of ceramic liner

Along with wearing, fractures of the ceramic liner could also lead to modified nature of friction surfaces. Abdel reported four cases with audible hip squeaking,[60] all with fractured ceramic liners. It was remarkable that all these patients also had complaints of sharp pain.

Amplification system - resonance

Most current studies of THA squeaking have focused on mechanisms of impulse while investigations were limited to the amplification system or resonance factors. Considering the composition of ceramic hip prostheses, the components responsible for resonance could be either one single part (metal cup, ceramic liner, ceramic femoral head, and femoral stem) or combinations of parts, such as acetabular components (pelvic bone, metal cup, and ceramic liner) or femoral components (ceramic head, metal stem, and femur).

Resonance does not occur unless the vibration frequency approximates the natural frequency of vibration components. It was reported that frequency of squeaking was between 400 and 7500 Hz,[8] which indicated that the natural frequency of components contributing to audible squeaking should be within this range. For single parts, experiments reported that both femoral stem and metal cup were eligible.[86162] However, when it comes to combined components, only the natural frequency of femoral components (head + stem + femur) was within this range. A finite element model of pelvis + stem + femur showed that the bending and torsion of the femoral component at lower frequencies may be the source of unstable vibrations for squeaking.[61]

With the fact that both femoral components and acetabular components are fixed combinations, it seems plausible to conduct an analysis of combination frequency. However, the stiffness of individual parts in combined components is not identical and the metal cup might be deformed with edge loading; hence, the shell-liner taper system could be uncoupled as reported by Walter et al.[8] Therefore, the ceramic liner could tilt out of the metal acetabular shell where the analysis of combination frequency becomes inapplicable.

CONCLUSIONS

So far, most published evidence indicates that squeaking after CoC THA is the consequence of increasing wear or impingement related to prosthesis design, patient, and surgical factors, which influence the frictional driving force and dynamic response. However, the major reasons for squeaking remain to be identified as conflicts still exist among certain studies. Future research should focus on investigations of in vivo conditions, reasonable methods of in vitro stimulations, and follow-up tactics and scales, which are critical for improving reproducibility among individual studies.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.