Dislocation is one of the most common complications in total hip arthroplasty (THA) and is primarily driven by bony or prosthetic impingement. The aim of this study was two-fold. First, to develop a simulation that incorporates the functional position of the femur and pelvis and instantaneously determines range of motion (ROM) limits. Second, to assess the number of patients for whom their functional bony alignment escalates impingement risk. 468 patients underwent a preoperative THA planning protocol that included functional x-rays and a lower limb CT scan. The CT scan was segmented and landmarked, and the x-rays were measured for pelvic tilt, femoral rotation, and preoperative leg length discrepancy (LLD). All patients received 3D templating with the same implant combination (Depuy; Corail/Pinnacle). Implants were positioned according to standardised criteria. Each patient was simulated in a novel ROM simulation that instantaneously calculates bony and prosthetic impingement limits in functional movements. Simulated motions included flexion and standing-external rotation (ER). Each patient's ROM was simulated with their bones oriented in both functional and neutral positions. 13% patients suffered a ROM impingement for functional but not neutral extension-ER. As a result, 48% patients who failed the functional-ER simulation would not be detected without consideration of the functional bony alignment. 16% patients suffered a ROM impingement for functional but not neutral flexion. As a result, 65% patients who failed the flexion simulation would not be detected without consideration of the functional bony alignment. We have developed a ROM simulation for use with preoperative planning for THA surgery that can solve bony and prosthetic impingement limits instantaneously. The advantage of our ROM simulation over previous simulations is instantaneous impingement detection, not requiring implant geometries to be analysed prior to use, and addressing the functional position of both the femur and pelvis.
Iliopsoas tendonitis occurs in up to 30% of patients after hip resurfacing arthroplasty (HRA) and is a common reason for revision. The primary purpose of this study was to validate our novel computational model for quantifying iliopsoas impingement in HRA patients using a case-controlled investigation. Secondary purpose was to compare these results with previously measured THA patients. We conducted a retrospective search in an experienced surgeon's database for HRA patients with iliopsoas tendonitis, confirmed via the active hip flexion test in supine, and control patients without iliopsoas tendonitis, resulting in two cohorts of 12 patients. The CT scans were segmented, landmarked, and used to simulate the iliopsoas impingement in supine and standing pelvic positions. Three discrete impingement values were output for each pelvic position, and the mean and maximum of these values were reported. Cup prominence was measured using a novel, nearest-neighbour algorithm. The mean cup prominence for the symptomatic cohort was 10.7mm and 5.1mm for the asymptomatic cohort (p << 0.01). The average standing mean impingement for the symptomatic cohort was 0.1mm and 0.0mm for the asymptomatic cohort (p << 0.01). The average standing maximum impingement for the symptomatic cohort was 0.2mm and 0.0mm for the asymptomatic cohort (p << 0.01). Impingement significantly predicted the probability of pain in logistic regression models and the simulation had a sensitivity of 92%, specificity of 91%, and an AUC ROC curve of 0.95. Using a case-controlled investigation, we demonstrated that our novel simulation could detect iliopsoas impingement and differentiate between the symptomatic and asymptomatic cohorts. Interestingly, the HRA patients demonstrated less impingement than the THA patients, despite greater cup prominence. In conclusion, this tool has the potential to be used preoperatively, to guide decisions about optimal cup placement, and postoperatively, to assist in the diagnosis of iliopsoas tendonitis.
Iliopsoas impingement occurs in between 5-30% of patients after hip arthroplasty and has been thought to only be caused by an oversized cup, cup malpositioning, or the depth of the psoas valley. However, no study has associated the relationship between preoperative measurements with the risk of impingement. This study sought to assess impingement between the iliopsoas and acetabular cup using a novel validated model to determine the risk factors for iliopsoas impingement. 413 patients received lower limb CT scans and lateral x-rays that were segmented, landmarked, and measured using a validated preoperative planning protocol. Implants were positioned according to the preference of ten experienced surgeons. The segmented bones were transformed to the standing reference frame and simulated with a novel computational model that detects impingement between the iliopsoas and acetabular cup. Definitions of patients at-risk and not at-risk of impingement were defined from a previous validation study of the simulation. At-risk patients were propensity score matched to not at-risk patients. 21% of patients were assessed as being at-risk of iliopsoas impingement. Significant differences between at-risk patients and not at-risk patients were observed in standing pelvic tilt (p << 0.01), standing femoral internal rotation (p << 0.01), medio-lateral centre-of-rotation (COR) change (p << 0.01), supine cup anteversion (p << 0.01), pre- to postoperative cup offset change (p << 0.001), postoperative gross offset (p = 0.009), and supero-inferior COR change (p = 0.02). Impingement between the iliopsoas and acetabular cup is under-studied and may be more common than is published in the literature. Previously it has been thought to only be related to cup size or positioning. However, we have observed significant differences between at-risk and not at-risk patients in additional measurements. This indicates that its occurrence is more complex than simply being related to cup position.
In 2021, Vigdorchik et al. published a large multicentre study validating their simple Hip-Spine Classification for determining patient-specific acetabular component positioning in total hip arthroplasty (THA). The purpose of our study was to apply this Hip-Spine Classification to a sample of Australian patients undergoing THA surgery to determine the local acetabular component positioning requirements. Additionally, we propose a modified algorithm for adjusting cup anteversion requirements. 790 patients who underwent THA surgery between January 2021 and June 2022 were assessed for anterior pelvic plane tilt (APPt) and sacral slope (SS) in standing and relaxed seated positions and categorized according to their spinal stiffness and flatback deformity. Spinal stiffness was measured using pelvic mobility (PM); the ΔSS between standing and relaxed seated. Flatback deformity was defined by APPt <−13° in standing. As in Vigdorchik et al., PM of <10° was considered a stiff spine. For our algorithm, PM of <20° indicated the need for increased cup anteversion. Using this approach, patient-specific cup anteversion is increased by 1° for every degree the patient's PM is <20°. According to the Vigdorchik simple Hip-Spine classification groups, we found: 73% Group 1A, 19% Group 1B, 5% Group 2A, and 3% Group 2B. Therefore, under this classification, 27% of Australian THA patients would have an elevated risk of dislocation due to spinal deformity and/or stiffness. Under our modified definition, 52% patients would require increased cup anteversion to address spinal stiffness. The Hip-Spine Classification is a simple algorithm that has been shown to indicate to surgeons when adjustments to acetabular cup anteversion are required to account for spinal stiffness or flatback deformity. We investigated this algorithm in an Australian population of patients undergoing THA and propose a modified approach: increasing cup anteversion by 1° for every degree the patient's PM is <20°.
Iliopsoas impingement occurs in 4% to 30% of patients after undergoing total hip arthroplasty (THA). Despite a relatively high incidence, there are few attempts at modelling impingement between the iliopsoas and acetabular component, and no attempts at modelling this in a representative cohort of subjects. The purpose of this study was to develop a novel computational model for quantifying the impingement between the iliopsoas and acetabular component and validate its utility in a case-controlled investigation. This was a retrospective cohort study of patients who underwent THA surgery that included 23 symptomatic patients diagnosed with iliopsoas tendonitis, and 23 patients not diagnosed with iliopsoas tendonitis. All patients received postoperative CT imaging, postoperative standing radiography, and had minimum six months’ follow-up. 3D models of each patient’s prosthetic and bony anatomy were generated, landmarked, and simulated in a novel iliopsoas impingement detection model in supine and standing pelvic positions. Logistic regression models were implemented to determine if the probability of pain could be significantly predicted. Receiver operating characteristic curves were generated to determine the model’s sensitivity, specificity, and area under the curve (AUC).Aims
Methods
Between 15% and 20% of patients remain dissatisfied following total knee arthroplasty (TKA). The SAIPH knee system (MatOrtho, Surrey, United Kingdom) is a medial ball and socket TKA that has been designed to replicate native knee kinematics in order to maximize the range of movement, stability, and function. This system is being progressively introduced in a stepwise fashion, with this study reporting the mid-term clinical and radiological outcomes. A retrospective review was undertaken of the first 100 consecutive patients with five-year follow-up following SAIPH TKA performed by the senior authors. The data that were collected included the demographics of the patients, clinical findings, the rate of intraoperative ligamentous release, patient-reported outcome measures (PROMS), radiological assessment, complications, and all-cause revision. Revision data were cross-checked with a national registry.Aims
Patients and Methods
This study aimed to characterise and qualitatively grade the severity of the corrosion particles released into the hip joint following taper corrosion. The 26 cases examined were CoC/ABG Modular (n = 13) and ASR/SROM (n = 13). Blood serum metal ion levels were collected before and after revision surgery. The haematoxylin and eosin tissue sections were graded on the presence of fibrin exudates, necrosis, inflammatory cells and corrosion products. The corrosion products were identified based on visible observation and graded on abundance. Two independent observers blinded to the clinical patient findings scored all cases. Elemental analysis was performed on corrosion products within tissue sections. X-Ray diffraction was used to identify crystalline structures present in taper debris.Objectives
Methods
We describe the clinical and radiological results
of cementless primary total hip replacement (THR) in 25 patients
(18 women and seven men; 30 THRs) with severe developmental dysplasia
of the hip (DDH). Their mean age at surgery was 47 years (23 to
89). In all, 21 hips had Crowe type III dysplasia and nine had Crowe
type IV. Cementless acetabular components with standard polyethylene
liners were introduced as close to the level of the true acetabulum
as possible. The modular cementless S-ROM femoral component was
used with a low resection of the femoral neck. A total of 21 patients (25 THRs) were available for review at
a mean follow-up of 18.7 years (15.8 to 21.8). The mean modified
Harris hip score improved from 46 points pre-operatively to 90 at
final follow up (p <
0.001). A total of 15 patients (17 THRs; 57%) underwent revision of the
acetabular component at a mean of 14.6 years (7 to 20.8), all for
osteolysis. Two patients (two THRs) had symptomatic loosening. No
patient underwent femoral revision. Survival with revision of either
component for any indication was 81% at 15 years (95% CI 60.1 to
92.3), with 21 patients at risk. This technique may reduce the need for femoral osteotomy in severe
DDH, while providing a good long-term functional result. Cite this article:
We report on 397 consecutive revision total hip
replacements in 371 patients with a mean clinical and radiological follow-up
of 12.9 years (10 to 17.7). The mean age at surgery was 69 years
(37 to 93). A total of 28 patients (8%) underwent further revision,
including 16 (4%) femoral components. In all 223 patients (56%,
233 hips) died without further revision and 20 patients (5%, 20
hips) were lost to follow-up. Of the remaining patients, 209 (221
hips) were available for clinical assessment and 194 (205 hips)
for radiological review at mean follow-up of 12.9 years (10 to 17.7). The mean Harris Hip Score improved from 58.7 (11 to 92) points
to 80.7 (21 to 100) (p <
0.001) and the mean Merle d’Aubigné and
Postel hip scores at final follow-up were 4.9 (2 to 6), 4.5 (2 to
6) and 4.3 (2 to 6), respectively for pain, mobility and function.
Radiographs showed no lucencies around 186 (90.7%) femoral stems
with stable bony ingrowth seen in 199 stems (97%). The survival
of the S-ROM femoral stem at 15 years with revision for any reason as
the endpoint was 90.5% (95% confidence interval (CI) 85.7 to 93.8)
and with revision for aseptic loosening as the endpoint 99.3% (95%
CI 97.2 to 99.8). We have shown excellent long-term survivorship and good clinical
outcome of a cementless hydroxyapatite proximally-coated modular
femoral stem in revision hip surgery. Cite this article:
Squeaking arising from a ceramic-on-ceramic (CoC)
total hip replacement (THR) may cause patient concern and in some
cases causes patients to seek revision surgery. We performed a meta-analysis
to determine the incidence of squeaking and the incidence of revision
surgery for squeaking. A total of 43 studies including 16 828 CoC
THR that reported squeaking, or revision for squeaking, were entered
into the analysis. The incidence of squeaking was 4.2% and the incidence
of revision for squeaking was 0.2%. The incidence of squeaking in
patients receiving the Accolade femoral stem was 8.3%, and the incidence
of revision for squeaking in these patients was 1.3%. Cite this article:
We report the clinical and radiological outcomes
of a series of contemporary cementless ceramic-on-ceramic total hip
replacements (THRs) at ten years in patients aged ≤ 55 years of
age. Pre- and post-operative activity levels are described. A total
of 120 consecutive ceramic cementless THRs were performed at a single
centre in 110 patients from 1997 to 1999. The mean age of the patients
at operation was 45 years (20 to 55). At ten years, four patients
had died and six were lost to follow-up, comprising ten hips. The
mean post-operative Harris hip score was 94.7 (55 to 100). Radiological
analysis was undertaken in 90 available THRs of the surviving 106
hips at final review: all had evidence of stable bony ingrowth,
with no cases of osteolysis. Wear was undetectable. There were four
revisions. The survival for both components with revision for any
cause as an endpoint was 96.5% (95% confidence interval 94.5 to
98.7). The mean modified University of California, Los Angeles activity
level rose from a mean of 6.4 (4 to 10) pre-operatively to 9.0 (6
to 10) at the ten-year post-operative period. Alumina ceramic-on-ceramic bearings in cementless primary THR
in this series have resulted in good clinical and radiological outcomes
with undetectable rates of wear and excellent function in the demanding
younger patient group at ten years. Cite this article:
The Delta Motion device (developed by Finsbury Orthopaedics, Leatherhead, United Kingdom, now manufactured by DePuy, Leeds, United Kingdom) is a pre-assembled factory fitted cup. It has been introduced to overcome some of the concerns relating to intra-operative assembly with improper seating of the liner and chipping. This device has a thinner shell and liner in comparison with other cups, allowing the use of larger sized heads which should help reduce the risk of impingement and dislocation. A drawback of the pre-assembled design is the inability to use supplementary screws to achieve stability and the difficulty in obtaining primary stability compared with a thin titanium shell. To date we are not aware of any publications reviewing the outcomes of these devices. 206 DeltaMotion cups were implanted in 195 patients, between Dec 2008 to Dec 2009 by the three senior authors. All the hips had the same stem (Osteonics) and a ceramic head was used. Data was prospectively collected and we reflect on our two year results.Introduction
Methods
Modularity is being increasingly used throughout the world for both primary and revision total hip arthroplasty. Recently there have been concerns of increased corrosion and fretting at the modular junctions. In the SROM® modular hip system, two modular junctions are the head-neck taper junction and the stem-sleeve taper junction. The aim of this study was to investigate corrosion at these junctions with the use of different bearing materials. Between 1994 and 2012, fourty-two patients were revised with SROM® stems. Reasons for revision included aseptic loosening of the cup or stem (11), periprosthetic fracture (2), osteolysis (8), dislocation (13) and other reasons (7). One was revised for stem breakage, and this was excluded from this study. We examined 41 retrieved S-ROM® comprised of 6 metal-on-metal (MOM), 12 metal-on-polyethylene (MOP), 7 ceramic-on-polyethylene (COP) and 16 ceramic-on-ceramic (COC). The orientation for all components was marked at the time of revision surgery. Both the proximal sleeve/stem and the femoral head-neck modular junctions were examined under 10X magnification, and graded by two independent observers. The head tapers were divided into 4 regions, and graded using a previously published 3 point scoring system for fretting and corrosion damage (Goldberg et al, Kop et al), for a total corrosion damage score of 12. The SROM stems were also assessed at the sleeve/stem taper junction. Each stem was divided into 8 quadrants, and graded for corrosion and fretting using the same system as the taper. In addition to severity, we also quantified area of corrosion damage of the stem at the sleeve-stem junction from 0–3, which was multiplied by the severity of damage, to give a score out of 9 for each quadrant (maximum total score of 72 for the stem). The bearing type was unknown to the investigators, so the grading was done in a blinded fashion. Corrosion scores were divided by time to account for differences in time to revision.Introduction
Methods
The practice of removing a well-fixed cementless
femoral component is associated with high morbidity. Ceramic bearing
couples are low wearing and their use minimises the risk of subsequent
further revision due to the production of wear debris. A total of
165 revision hip replacements were performed, in which a polyethylene-lined acetabular
component was revised to a new acetabular component with a ceramic
liner, while retaining the well-fixed femoral component. A titanium
sleeve was placed over the used femoral trunnion, to which a ceramic
head was added. There were 100 alumina and 65 Delta bearing couples
inserted. The mean Harris hip score improved significantly from 71.3 (9.0
to 100.0) pre-operatively to 91.0 (41.0 to 100.0) at a mean follow
up of 4.8 years (2.1 to 12.5) (p <
0.001). No patients reported
squeaking of the hip. There were two fractures of the ceramic head, both in alumina
bearings. No liners were seen to fracture. No fractures were observed
in components made of Delta ceramic. At 8.3 years post-operatively
the survival with any cause of failure as the endpoint was 96.6%
(95% confidence interval (CI) 85.7 to 99.3) for the acetabular component and
94.0% (95% CI 82.1 to 98.4) for the femoral component. The technique of revising the acetabular component in the presence
of a well-fixed femoral component with a ceramic head placed on
a titanium sleeve over the used trunnion is a useful adjunct in
revision hip practice. The use of Delta ceramic is recommended. Cite this article:
Edge loading commonly occurs in all bearings in hip arthroplasty. Edge loading wear can occur in these bearings when the biomechanical loading axis reaches the edge and the femoral head loads the edge of the cup producing wear damage on both the head and cup edge. When the biomechanical loading axis passes through the polished articulating surface of the acetabular component and does not reach the edge, the center of the head and the center of the cup are concentric. The resulting wear known as concentric wear is low in metal-on-metal (MOM) bearings, and is negligible in ceramic-on-ceramic (COC) bearings. Edge loading is well defined in COC hip bearings. However, edge loading is difficult to identify in MOM bearings, since the metal bearing surfaces do not show wear patterns macroscopically. The aims of this study are to compare edge loading wear rates in COC and MOM bearings, and to relate edge loading to clinical complications. Twenty-nine failed large diameter metal-on-metal hip bearings (17 total hips, 12 resurfacings) were compared to 54 failed alumina-on-alumina bearings collected from 1998 to 2011. Most COC bearings were revised for aseptic loosening or periprosthetic bone fracture, while most MOM bearings were revised for pain, soft tissue reactions or impingement. The median time to revision was 3.2 years for the metal hip bearings and 3.5 years for alumina hip bearings. The surface topography of the femoral heads was measured using a RedLux AHP (Artificial Hip Profiler, RedLux Ltd, Southampton, UK).Introduction
Materials and Methods
In patients with conventional metal-on-Polyethylene (MoP) hip replacements, osteolysis can occur in response to wear debris. During revision hip surgery, surgeons usually remove the source of osteolysis (polyethylene) but cannot always remove all of the inflammatory granulomatous tissues in the joint. We used a human/rat xenograft model to evaluate the effects of polyethylene granuloma tissues on bone healing. Human osteoarthritic and periprosthetic tissues collected during primary and revision hip arthroplasty surgeries were transplanted into the distal femora of athymic (nude) rats. The tissues were assessed before and after implantation and the bone response to the tissues was evaluated after 1 week and 3 weeks using micro-computed tomography, histology, and immunohistochemistry. After 3 weeks, the majority (70%) of defects filled with osteoarthritic tissues healed, while only 21% of defects with polyethylene granuloma tissues healed. Polyethylene granuloma tissues in trabecular bone defects inhibited bone healing. Surgeons should remove polyethylene granuloma tissues during revision surgery when possible, since these tissues may slow bone healing around a newly implanted prosthesis. This model provides a method for delivering clinically relevant sized particles into an
Two types of ceramic materials currently used in total hip replacements are third generation hot isostatic pressed (HIPed) alumina ceramic (commercially known as BIOLOX® Ceramic bearings revised at one center from 1998 to 2010 were collected (61 bearings). Eleven Introduction
Material and Methods
We analysed 54 alumina ceramic-on-ceramic bearings
from total hip replacements retrieved at one centre after a mean
duration of 3.5 years (0.2 to 10.6)
This systematic review of the literature summarises
the clinical experience with ceramic-on-ceramic hip bearings over
the past 40 years and discusses the concerns that exist in relation
to the bearing combination. Loosening, fracture, liner chipping
on insertion, liner canting and dissociation, edge-loading and squeaking
have all been reported, and the relationship between these issues
and implant design and surgical technique is investigated. New design
concepts are introduced and analysed with respect to previous clinical
experience.
We report a case of a male patient presenting
with bilateral painful but apparently well-positioned and -fixed
large-diameter metal-on-metal hip replacements four years post-operatively.
Multiple imaging modes revealed a thick-walled, cystic expansile
mass in communication with the hip joint (a pseudotumour). Implant
retrieval analysis and tissue culture eliminated high bearing wear
or infection as causes for the soft-tissue reaction, but noted marked corrosion
of the modular neck taper adaptor and corrosion products in the
tissues. Therefore, we believe corrosion products from the taper
caused by mismatch of the implant components led to pseudotumour
formation requiring revision.
This multicentre study analysed 12 alumina ceramic-on-ceramic
components retrieved from squeaking total hip replacements after
a mean of 23 months
Ceramic on ceramic articulations had been used since 1970s but with high failure rate. More recent third generation alumina ceramic had improved results due to better material properties to resist wear and fracture and better methods of fixation with metal back acetabular components. A new clinical problem of squeaking has emerged in the last decade and is now a relatively common occurrence in ceramic on ceramic total hip arthroplasty, with a reported incidence from less than 1% to 20% depending on the definition of the noise. We report experience with over 3000 ceramic-on-ceramic hips including the 10 year minimum follow-up of the first 301 cases.
All patients are asked on follow-up as part of a questionnaire: Has your hip ever made a squeaking noise? To date of the more than 3000 ceramic on ceramic hips that we follow, 74 hips (71 patients) responded yes to this question. Patient demographic and outcome data were analysed in all squeaking hips and compared with all primary ceramic on ceramic hips operated on at our unit.
Two acetabular components revised for psoas tendonitis, one of these subsequently had both components revised for acetabular osteolysis with femoral revision to improve anteversion. There were six other femoral component revisions: four for periprosthetic femoral fractures, one for aseptic loosening and one for transient sciatic nerve palsy. There has been one squeaking hip in this group not requiring revision due to the mild and intermittent nature of the noise. All complications occurred within the first 3 years, no further complication has arisen since. When comparing the 74 squeaking hips to the entire cohort of primary hips we found that taller, heavier and younger patients are significantly more likely to have hips that squeak. Squeaking hips have a significantly higher range of post-operative movement than silent hips. Squeaking hips have a significantly higher Harris hip score. There was no difference in the satisfaction scores between squeaking and silent hips.
We investigated factors that were thought to be associated with an increased incidence of squeaking of ceramic-on-ceramic total hip replacements. Between June 1997 and December 2008 the three senior authors implanted 2406 primary total hip replacements with a ceramic-on-ceramic bearing surface. The mean follow-up was 10.6 years. The diagnosis was primary osteoarthritis in each case, and no patient had undergone previous surgery to the hip. We identified 74 squeaking hips (73 patients) giving an incidence of 3.1% at a mean follow-up of 9.5 years (4.1 to 13.3). Taller, heavier and younger patients were significantly more likely to have hips that squeaked. Squeaking hips had a significantly higher range of post-operative internal (p = 0.001) and external rotation (p = 0.003) compared with silent hips. Patients with squeaking hips had significantly higher activity levels (p = 0.009). A squeaking hip was not associated with a significant difference in patient satisfaction (p = 0.24) or Harris hip score (p = 0.34). Four implant position factors enabled good prediction of squeaking. These were high acetabular component inclination, high femoral offset, lateralisation of the hip centre and either high or low acetabular component anteversion. This is the largest study to date to examine patient factors and implant position factors that predispose to squeaking of a ceramic-on-ceramic hip. The results suggest that factors which increase the mechanical forces across the hip joint and factors which increase the risk of neck-to-rim impingement, and therefore edge-loading, are those that predispose to squeaking.
The survivorship of contemporary resurfacing arthroplasty of the hip using metal-on-metal bearings is better than that of first generation designs, but short-term failures still occur. The most common reasons for failure are fracture of the femoral neck, loosening of the component, osteonecrosis of the femoral head, reaction to metal debris and malpositioning of the component. In 2008 the Australian National Joint Registry reported an inverse relationship between the size of the head component and the risk of revision in resurfacing hip arthroplasty. Hips with a femoral component size of ≤ 44 mm have a fivefold increased risk of revision than those with femoral components of ≥ 55 mm irrespective of gender. We have reviewed the literature to explore this observation and to identify possible reasons including the design of the implant, loading of the femoral neck, the orientation of the component, the production of wear debris and the effects of metal ions, penetration of cement and vascularity of the femoral head. Our conclusion is that although multifactorial, the most important contributors to failure in resurfacing arthroplasty of the hip are likely to be the design and geometry of the component and the orientation of the acetabular component.
Squeaking in hip arthroplasty is now well-documented but hitherto poorly understood. In this paper, we report data progressively accumulated from a series of studies undertaken by our group to investigate the mechanisms of noise production associated with ceramic-on-ceramic bearings. We reviewed demographic and radiographic data comparing squeaking with silent hips. Edge loading of the acetabular components was investigated on retrieved bearings and with finite element analysis. The squeaking sound itself was further investigated through acoustic analysis. Squeaking occurs in younger, heavier, and taller patients. We found a higher incidence of acetabular component malposition in squeaking hips and edge loading appears to be a causative factor. Finite element analysis revealed a stiffness mismatch between the shell and liner which may allow the shell to oscillate producing an audible squeak. Acoustic and modal analysis show that squeaking is due to a forced vibration and that the natural frequencies of the ceramic components are above the audible range, suggesting that resonance occurs in the metallic, not the ceramic parts. This phenomenon is related to patient factors, surgical factors, and implant factors, which may produce sound by a combination of edge loading of the ceramic and forced vibration of the acetabular shell and/or the femoral stem.
Squeaking in ceramic on ceramic bearing total hip arthroplasty is well documented but its aetiology is poorly understood. In this study we have undertaken an acoustic analysis of the squeaking sound recorded from 31 ceramic on ceramic bearing hips. The frequencies of these sounds were compared with in vitro acoustic analysis of the component parts of the total hip implant. Analysis of the sounds produced by squeaking hip replacements and comparison of the frequencies of these sounds with the natural frequency of the component parts of the hip replacements indicates that the squeaking sound is due to a friction driven forced vibration resulting in resonance of one or both of the metal components of the implant. Finite element analysis of edge loading of the prostheses shows that there is a stiffness incompatibility between the acetabular shell and the liner. The shell tends to deform, uncoupling the shell-liner taper system. As a result the liner tends to tilt out of the acetabular shell and slide against the acetabular shell adjacent to the applied load. The amount of sliding varied from 4–40μm. In vitro acoustic and finite element analysis of the component parts of a total hip replacement compared with in vivo acoustic analysis of squeaking hips indicate that either the acetabular shell or the femoral stem can act as an “oscillator’ in a forced vibration system and thus emit a squeak.
Under ideal conditions hard-on-hard bearings are assumed to be operating under conditions of fluid film lubrication with very low friction.14,15 However, if fluid film lubrication breaks down leading to dry sliding contact there will be a dramatic increase in friction. If this increased friction provides more energy to the system than it can dissipate, instabilities may develop in the form of friction induced vibrations and sound radiation16. Friction induced vibrations are a special case of forced vibration, where the frequency of the resulting vibration is determined by the natural frequency of the component parts. Running a moistened finger around the rim of a wine glass is an example of this. [Appendix]. The hypothesis of this study is that the squeaking sound that occurs in ceramic on ceramic hip replacement is the result of a forced vibration. This forced vibration can be broken down into a driving force and a resultant dynamic response17. The driving force is a frictional driving force and occurs when there is a loss of fluid film lubrication resulting in a high friction force14,15,18. The dynamic response is a vibration of a part of the device (the oscillator) at a frequency that is influenced by the natural frequency of the part16. By analyzing the frequencies of the sound produced by squeaking hip replacements and comparing them to the natural frequency of the component parts of a hip replacement this study aims to determine which part produces the sound.
We tested the following components: modular ceramic/titanium acetabular components, which included testing the titanium shell and the respective ceramic inserts both assembled according to the manufacturer’s instructions and unassembled; titanium femoral stems and ceramic femoral heads both assembled and unassembled. A range of sizes of each component was tested according to availability from our retrieval collection.
Sound files were captured and analyzed by the same method used in the in vitro analysis. Each recording was previewed in the spectral view mode which allows easy visual identification of the squeak in the sound recording. In addition all sound recordings were played, listening for the squeak. Once a squeak was identified a fast Fourier transform (FFT) was performed. We used FFT size 1024 with a Blackmann-Harris window which allowed us to easily pick out the major frequency components. All prominent frequency components were recorded at the beginning of the squeak and at several time points during the squeak if there was any change. A range was recorded for the fundamental frequency component. We were able to determine the frequency range of the recording device used by observing the frequency range of the background noise on the recording. We found that if a squeak was audible on the recording we had no difficulty determining its frequency regardless of the quality of the device used to make the recording or the amount of background noise. The mean age of the patients was 54 years (23 to 79 years), mean height was 171cm (152 to 186cm) and mean weight was 79kg (52 to 111kg). There were 17 female and 14 male patients. There were nineteen ABGII stem and ABGII cup combinations, 10 accolade stem and trident cup, 1 Exeter stem and trident cup and 1 Osteonics Securfit stem with an Osteonics cup. Ethics committee approval was obtained for this project from our institution and from the referring institutions and informed consent was gained from the patients.
Dislocation is a common reason for revision following total hip replacement. This study investigated the relationship between the bearing surface and the risk of revision due to dislocation. It was based on 110 239 primary total hip replacements with a diagnosis of osteoarthritis collected by the Australian Orthopaedic Association National Joint Replacement Registry between September 1999 and December 2007. A total of 862 (0.78%) were revised because of dislocation. Ceramic-on-ceramic bearing surfaces had a lower risk of requiring revision due to dislocation than did metal-on-polyethylene and ceramic-on-polyethylene surfaces, with a follow-up of up to seven years. However, ceramic-on-ceramic implants were more likely to have larger prosthetic heads and to have been implanted in younger patients. The size of the head of the femoral component and age are known to be independent predictors of dislocation. Therefore, the outcomes were stratified by the size of the head and age. There is a significantly higher rate of revision for dislocation in ceramic-on-ceramic bearing surfaces than in metal-on-polyethylene implants when smaller sizes (≤ 28 mm) of the head were used in younger patients (<
65 years) (hazard ratio = 1.53, p = 0.041) and also with larger (>
28 mm) and in older patients (≥ 65 years) (hazard ratio = 1.73, p = 0.016).
The outcome of total hip replacement (THR) is potentially affected by the body mass index (BMI) of the patient. We studied the outcome of 2026 consecutive primary cementless THRs performed for osteoarthritis. The mean follow-up was 6.3 years (0 to 11.71) and no patient was lost to follow-up for survival analysis. The patients were divided into two groups according to their BMI as follows: non-obese (BMI <
30 kg/m2) and obese (BMI ≥ 30 kg/m2). The obese patient undergoing surgery was found to be significantly younger (p <
0.001). The log-rank test for equality of survival showed no difference in the mid-term survival (p = 0.552) with an estimated survival at 11 years of 95.2% (95% CI 92.5 to 98.0) in the non-obese and 96.7% (95% CI 94.9 to 98.5) in the obese groups. The clinical and radiological outcome was determined in a case-matched study performed on 134 obese individuals closely matched with 134 non-obese controls. The non-obese group was found to have a significantly higher post-operative Harris hip score (p <
0.001) and an increased range of movement, but overall satisfaction with surgery was comparable with that of the obese patients. Radiological analysis of the acetabular and femoral components showed no significant differences with regard to radiolucent lines, osteolysis, ingrowth of the femoral component, the acetabular inclination angle or alignment of the femoral component. Our results suggest that the survival of cementless THR is not adversely affected by obesity. Obese patients can therefore be counselled that despite a lower clinical score, they should expect to be satisfied with the result of their THR with a mid-term survival rate equivalent to that of non-obese patients.
We evaluated 535 consecutive primary cementless total knee replacements (TKR). The mean follow-up was 9.2 years (0.3 to 12.9) and information on implant survival was available for all patients. Patients were divided into two groups: 153 obese patients (BMI ≥ 30) and 382 non-obese (BMI <
30). A case-matched study was performed on the clinical and radiological outcome, comparing 50 knees in each group. We found significantly lower mean improvements in the clinical score (p = 0.044) and lower post-operative total clinical scores in the obese group (p = 0.041). There was no difference in the rate of radiological osteolysis or lucent lines, and no difference in alignment. Log rank test for survival showed no significant differences between the groups (p = 0.167), with a ten-year survival rate of 96.4% (95% confidence interval (CI) 92 to 99) in the obese and 98% (95% CI 96 to 99) in the non-obese. The mid-term survival of TKR in the obese and the non-obese are comparable, but obesity appears to have a negative effect on the clinical outcome. However, good results and high patient satisfaction are still to be expected, and it would seem unreasonable to deny patients a TKR simply on the basis of a BMI indicating obesity.
We studied 33 third generation, alumina ceramic-on-ceramic bearings retrieved from cementless total hip replacements after more than six months in situ. Wear volume was measured with a Roundtest machine, and acetabular orientation from the anteroposterior pelvic radiograph. The overall median early wear rate was 0.1 mm3/yr for the femoral heads, and 0.04 mm3/yr for the acetabular liners. We then excluded hips where the components had migrated. In this stable subgroup of 22 bearings, those with an acetabular anteversion of <
15° (seven femoral heads) had a median femoral head wear rate of 1.2 mm3/yr, compared with 0 mm3/yr for those with an anteversion of ≥15° (15 femoral heads, p <
0.001). Even under edge loading, wear volumes with ceramic-on-ceramic bearings are small in comparison to other bearing materials. Low acetabular anteversion is associated with greater wear.