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 . combinations include metal - on - metal , metal - on - polyethylene , ceramic - on - plastic , and ceramic - on - ceramic ( coc ) . with stable chemical inertia , reliable biocompatibility , high hardness , and a low coefficient of friction , coc bearing for tha was first introduced by boutin in france during the 1970s . 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 . 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 . there is neither a specific definition for postsurgery squeaking nor a universal categorization for the sound . kuo et al . studied 125 patients who had undergone tha , eight of whom reported squeaking noises , including clicking , grinding , and snapping . 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 . further studies have demonstrated that the fundamental frequency is approximately 1500 hz in male patients and 2500 hz in females . it should be noted that squeaking is not usually associated with abnormal feelings or functional impairment . in addition , there has been no significant difference in satisfaction between patients with squeaking and silent hips . reported occurrences of squeaking vary among different studies [ table 1 ] ; the prevalence was reported to be around 0.5% by walter et al . but 10.6% by cogan et al . 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 . 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 . studies reported occurrence of squeaking associated with coc tha coc : ceramic - on - ceramic ; tha : total hip arthroplasty . 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 , it can affect patients quality of life 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% . the estimated prevalence for revision based on a meta - analysis was approximately 0.2% . 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 . various factors have been proven to be relevant to post - tha squeaking and can be divided into three categories : patient , surgical , and implant factors . a retrospective study by mai et al . showed that patients who experienced squeaking were taller on average than that of patients who had not . 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 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 , 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 . walter et al . 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 . 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 . moreover , reduced hip center medialization and high prosthetic femoral offset were also associated with hip squeaking . thus , placement of the implants during operation may directly influence the chance of squeaking . the prosthesis design and the materials used are also thought to be contributing factors for squeaking . a study conducted by parvizi et al . 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 . 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% . 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% ) . 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 . it should be noted that a meta - analysis conducted by lee et al . , 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 . studies demonstrating risk factors associated with coc tha squeaking coc : ceramic - on - ceramic ; tha : total hip arthroplasty ; bmi : body mass index . a retrospective study by mai et al . showed that patients who experienced squeaking were taller on average than that of patients who had not . 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 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 , 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 . walter et al . 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 . 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 . moreover , reduced hip center medialization and high prosthetic femoral offset were also associated with hip squeaking . thus , placement of the implants during operation may directly influence the chance of squeaking . the prosthesis design and the materials used are also thought to be contributing factors for squeaking . a study conducted by parvizi et al . 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 . 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% . 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% ) . 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 . it should be noted that a meta - analysis conducted by lee et al . , 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 . studies demonstrating risk factors associated with coc tha squeaking coc : ceramic - on - ceramic ; tha : total hip arthroplasty ; bmi : body mass index . audible noises generated by irregular vibrations were a coeffect of impulse and amplification system . 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 and it could disappear when lubricants are introduced , indicating that the squeaking was caused by friction . 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 . proposed mechanisms of squeaking in coc tha . coc : ceramic - on - ceramic ; tha : total hip arthroplasty . as mentioned above 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 , mostly crescent - shaped , could frequently be observed during revision for tha squeaking . 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 mm / year compared to a median of 0.14 mm / year in the silent control group , representing a 45-fold increase . given the fact that hip squeaking mostly occurs several months after surgery and that the formation of stripe wear also requires some time to develop , the relationship between squeaking and stripe wear may well be speculative . 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 . 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 . 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 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 . 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 , 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 . 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 . 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 . 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 , 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 . 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 , 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 . 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 . with the fact that both femoral components and acetabular components are fixed combinations 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 . therefore , the ceramic liner could tilt out of the metal acetabular shell where the analysis of combination frequency becomes inapplicable . 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 , 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 mm / year compared to a median of 0.14 mm / year in the silent control group , representing a 45-fold increase . given the fact that hip squeaking mostly occurs several months after surgery and that the formation of stripe wear also requires some time to develop , the relationship between squeaking and stripe wear may well be speculative . 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 . 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 . 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 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 . 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 , 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 . 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 . 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 . 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 , 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 . 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 , 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 . 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 . with the fact that both femoral components and acetabular components are fixed combinations 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 . therefore , the ceramic liner could tilt out of the metal acetabular shell where the analysis of combination frequency becomes inapplicable . 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
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 .