Aims

This study evaluates the association between consultant and hospital volume and the risk of re-revision and 90-day mortality following first-time revision of primary hip arthroplasty for aseptic loosening.

Aims. In metal-on-metal (MoM) hip arthroplasties and resurfacings, mechanically induced corrosion can lead to elevated serum metal ions, a local inflammatory response, and formation of pseudotumours, ultimately requiring revision. The size and diametral clearance of anatomical (ADM) and modular (MDM) dual-mobility polyethylene bearings match those of Birmingham hip MoM components. If the acetabular component is satisfactorily positioned, well integrated into the bone, and has no surface damage, this presents the opportunity for revision with exchange of the metal head for ADM/MDM polyethylene bearings without removal of the acetabular component. Methods. Between 2012 and 2020, across two centres, 94 patients underwent revision of Birmingham MoM hip arthroplasties or resurfacings. Mean age was 65.5 years (33 to 87). In 53 patients (56.4%), the acetabular component was retained and dual-mobility bearings were used (DM); in 41 (43.6%) the acetabulum was revised (AR). Patients underwent follow-up of minimum two-years (mean 4.6 (2.1 to 8.5) years). Results. In the DM group, two (3.8%) patients underwent further surgery: one (1.9%) for dislocation and one (1.9%) for infection. In the AR group, four (9.8%) underwent further procedures: two (4.9%) for loosening of the acetabular component and two (4.9%) following dislocations. There were no other dislocations in either group. In the DM group, operating time (68.4 vs 101.5 mins, p < 0.001), postoperative drop in haemoglobin (16.6 vs 27.8 g/L, p < 0.001), and length of stay (1.8 vs 2.4 days, p < 0.001) were significantly lower. There was a significant reduction in serum metal ions postoperatively in both groups (p < 0.001), although there was no difference between groups for this reduction (p = 0.674 (cobalt); p = 0.186 (chromium)). Conclusion. In selected patients with Birmingham MoM hips, where the acetabular component is well-fixed and in a satisfactory position with no surface damage, the metal head can be exchanged for polyethylene ADM/MDM bearings with retention of the acetabular prosthesis. This presents significant benefits, with a shorter procedure and a lower risk of complications. Cite this article: Bone Jt Open 2024;5(6):514–523

Background. Since the development of modern total hip replacement (THR) more than 50 years ago, thousands of devices have been developed in attempt to improve patient outcomes and prolong implant survival. Modern THR devices are often broadly classified according to their method of fixation; cemented, uncemented or hybrid (typically an uncemented acetabular component with a cemented stem). Due to early failures of THR in young active patients, the concept of hip resurfacing was revisited in the 1990's and numerous prostheses were developed to serve this patient cohort, some with excellent clinical results. Experience with metal-on-metal (MoM) bearing related issues particularly involving the ASR (DePuy Synthes, Warsaw, Indiana) precipitated a fall in the use of hip resurfacing (HR) prostheses in Australia from a peak of 30.2% in 2004 to 4.3% in 2015. The effects of poorly performing prostheses and what is now recognised as suboptimal patient selection are reflected in the AOANJRR cumulative percent revision (CPR) data which demonstrates 13.2% revision at 15 years for all resurfacing hip replacements combined; with 11 different types of hip resurfacing prostheses recorded for patients less than 55 years of age and a primary diagnosis of OA. When this data is restricted to only those prostheses currently used in Australia (BHR; Smith and Nephew, Birmingham, UK & ADEPT; MatOrtho Ltd, Surrey, UK) there is a CPR of 9.5% at 15 years for all patients. Despite these CPR results, recognition is emerging of the important distinction between MoM THR and resurfacing. Furthermore, in light of current consensus for patient selection and the surgical indications for resurfacing, a gender analysis demonstrates a CPR for females of 14.5% at 10 years compared to 3.7% for males. Similar difference for head size >50mm with 6% CPR at 10 years compared to 17.6% for head size <50mm (HR=2.15; 1.76, 2.63; p<0.001). Leading to renewed interest in resurfacing particularly in the young, active male. In addition to registry based CPR data, several studies have concluded that a true difference in mortality rates between HR and other forms of THR exists independent of age, sex or other confounding factors. We hypothesised that a difference in adjusted mortality rates between HR and other forms of THR may also be present in the Australian population. We undertook an ad hoc data report request to the AOANJRR. The data set provided was deidentified for patient, surgeon and institution and included all HR and conventional THR procedures performed for the diagnosis of primary osteoarthritis recorded in the Registry since inception in 1999. We requested mortality and yearly cumulative percent survival (CPS) of patients for primary HR and THR with sub-group analysis by the mode of fixation. There were 12,910 hip resurfacings (79% male) compared to 234,484 conventional THR (46.8% male) over the study period. When adjusted for age and gender over the 15 years of available data, there was a statistically significant difference in cumulative percent survival (CPS) between conventional THR and hip resurfacing (HR 1.66 (1.52, 1.82; p<0.001)) and between cemented THR and hip resurfacing (HR 1.96 (1.78, 2.43; p<0.001)); between uncemented THR and hip resurfacing (HR 1.58 (1.45, 1.73; p<0.001)); and between hybrid THR and hip resurfacing (HR 1.82 (1.66, 1.99; p<0.001)). When adjusted for age, gender and ASA over the 3 years data available, there was no statistically significant difference in CPS between hip resurfacing and any individual fixation type of THR. Discussion. The results demonstrate a statistically significant adjusted survival advantage for hip resurfacing compared to conventional THR and between fixation methods for THR. These findings are consistent with previous studies. While a difference in adjusted mortality rate appears to exist, we are yet to definitively determine the complex interplay of causative factors that may contribute to it

The metal on metal implants was introduced without the proper stepwise introduction. The ASR resurfacing hip arthroplasty (RHA) withdrawn due to high clinical failure rates and the large diameter head THA (LDH-THA) are also widely abandoned. Early (2 year) radiostereometry studies does not support early instability as cause of failure but more likely metal wear products. A possible advantage may be maintenance of bone mineral density (BMD). We present 5 year prospective follow up from a randomized series, aiming to report changes from baseline and to investigate links between implant micromotion, Cr & Co ions and BMD. Patients eligible for an artificial hip were randomized to RHA, Biomet LDH-THA or standard Biometric THA. 19, 17 and 15 patients completed 5 year follow-up. All followed with BMD of the femur, acetabulum and for RHA the collum. RHA and THA with whole blood Co and Co. LDH-THA only at 5 year. RHA had marker based RSA of both components, cup only for LDH-THA. Translations were compiled to total translation (TT= √(x. 2. +y. 2. +z. 2. )). Data were collected at baseline, 8 weeks, 6 months, 1, 2 and 5 years. Statistical tests: ANCOVA for TT movement, Spearman's correlation for BMD, Cr, Co and BMI to TT at 5 years. RSA: The 5 year median (25%to75%) RHA cup translations were X=-0.00(−0.49 to 0.19) Y=0.15(−0.03 to 0.20), z=0.24(−0.42 to 0.37) and TT 0.58 (0.16 to 1.82) mm. For the LDH-THA X=−0.33(−0.90 to 0.20) Y=0.28(0.02 to 0.54), z=0.43(−1.12 to −0.19) and TT 1.06 (0.97 to 1.72) mm. The TT was statistically different (p<0.05) for the two cups. The RHA femoral component moved X=0.37(0.21 to 0.56) Y=0.02(−0.07 to 0.11), z=-0.01(−0.07 to 0.26) and TT 0.48 (0.29 to 0.60) mm at 5 years. There was no TT movement from year 2. The mean (SD) acetabular BMD was diminished to 93(90–97)% for RHA and 97(93–99.9)% for THA, but LDH-THA maintained 99(95–103)%. Overall femoral BMD was unchanged at 5 years for all interventions, but both stemmed implants lost 17% at the calcar. Median (25%to75%) whole-blood Cr peaked in the LDH-THA group with 1.7 (0.9 to 3.1) followed by RHA 1.2 (0.8 to 5.0) and THA with 0.5 (0.4 to 0.7)ppb. For Co the highest levels were found in RHA with 1.6(0.8 to 4.7) followed by LDH-THA 1.2 (0.7–1.7) and THA 0.2 (0.2 to 0.6) ppb. The only correlations above +/−0.3 for TT were the RHA femoral component with a correlation of 0.47 to BMI, 0.30 to Co and Cr. The ASR cup conversely had a negative correlation of −0.60 to BMI and again, the LDH-THA cup had a negative correlation of −0.37 to Cr. In contrast to registered revision rates, we found significantly larger movement for the Biomet cup than the ASR cup. The metal ion levels were similar. The LDH-THA cup maintained the acetabular BMD best at 5 years, but the difference was small, we are limited by small numbers and the correlations between TT and the covariates showed no clear pattern

Background. Hip replacement surgery is an effective treatment, however quantitative outcome does not necessarily delineate the true picture. It is important to triangulate data methods in order to ascertain important contextual factors that may influence patient perception. Aims. The aim of the current study was to explore the patient perception on resurfacing hip arthroplasty (RHA) and mini-hip arthroplasty (MHA) in a unique cohort where each patient has received a resurfacing on one side and a mini-hip on the contralateral side using both quantitative and qualitative measures (Fig. 1). Materials and methods. We identified patients in our Practice database that had undergone RHA on one side and MHA in the opposite hip. All prostheses were implanted by two experienced surgeons using a posterior approach and followed a standard anaesthetic protocol, post-operative care and rehabilitation guidelines. The patients received Cormet 2000 hip resurfacing and MiniHip (Corin®, Ciencester, UK) implants. Data were collected pre-operatively and post-operatively at weeks 6, 12, 26 52 and annually thereafter. The data included demographic details, mHHS (modified Harris Hip Score), patient satisfaction and a qualitative semi-structured interview. Data analysis was done using both quantitative (descriptive statistics, student's t-test) and qualitative (constant comparative method of grounded theory). Results. There were 24 hips in 12 patients with mean age of 63.6 years (range 42,81) and a mean follow-up of 5.3 years (SD 4.2). The mean mHHS in pre-operative and one-year post-operative period for RHA was 50.9 (SD 22.9, range 9,71) and 82.6 (SD 11.2, range 67,91) respectively with a mean improvement of 32.9. The mean mHHS in pre-operative and one-year post-operative period for MHA was 47.83 (SD 14.6, range 20,62) and 83.2 (SD 27.3 range 53,94) respectively with mean improvement of 35.3. There was no significant difference in mHHS in the two groups (p=0.26). However, the qualitative analysis showed that a patient's perception of improvement did not always reflect the validated score improvement such as in mHHS. In 8/24 of arthroplasty cases the mHHS indicated a high return to functionality, however, interview highlighted perception of a reduction in certain aspects such as range of movement and ability to perform at a high-level such as competitive windsurfing (2/24), skiing (6/24) or martial arts (2/24). The results, therefore, suggest that the quantitative data is not sensitive enough to deduce return to function in a specialised subset of patients. The interviews indicate a marginal preference for resurfacing due to improved stability. However, the differential to the satisfaction with the mini hip was not sufficient for the potential metal ion problem to be ignored and therefore mini hip was shown to offer a reasonable bone-conserving alternative. Conclusions. Results indicate the need for more than just a quantitative score to demonstrate satisfaction and that RHA generally offers better results although when the metal ion problem is taken into account the MHA can offer sufficient function and satisfaction as an alternative

Patients from a randomised trial on resurfacing hip arthroplasty (RHA) (n = 36, 19 males; median age 57 years, 24 to 65) comparing a conventional 28 mm metal-on-metal total hip arthroplasty (MoM THA) (n = 28, 17 males; median age 59 years, 37 to 65) and a matched control group of asymptomatic patients with a 32 mm ceramic-on-polyethylene (CoP) THA (n = 33, 18 males; median age 63 years, 38 to 71) were cross-sectionally screened with metal artefact reducing sequence-MRI (MARS-MRI) for pseudotumour formation at a median of 55 months (23 to 72) post-operatively. MRIs were scored by consensus according to three different classification systems for pseudotumour formation.

Clinical scores were available for all patients and metal ion levels for MoM bearing patients.

Periprosthetic lesions with a median volume of 16 mL (1.5 to 35.9) were diagnosed in six patients in the RHA group (17%), one in the MoM THA group (4%) and six in the CoP group (18%). The classification systems revealed no clear differences between the groups. Solid lesions (n = 3) were exclusively encountered in the RHA group. Two patients in the RHA group and one in the MoM THA group underwent a revision for pseudotumour formation. There was no statistically significant relationship between clinical scoring, metal ion levels and periprosthetic lesions in any of the groups.

Periprosthetic fluid collections are seen on MARS-MRI after conventional CoP THA and RHA and may reflect a soft-tissue collection or effusion.

Currently available MRI classification systems seem to score these collections as pseudotumours, causing an-overestimatation of the incidence of pseudotumours.

Cite this article: Bone Joint J 2015;97-B:1175–82.

We compared the length of hospitalisation, rate of infection, dislocation of the hip and revision, and mortality following primary hip and knee arthroplasty for osteoarthritis in patients with Alzheimer’s disease (n = 1064) and a matched control group (n = 3192). The data were collected from nationwide Finnish health registers. Patients with Alzheimer’s disease had a longer peri-operative hospitalisation (median 13 days vs eight days, p < 0.001) and an increased risk for hip revision with a hazard ratio (HR) of 1.76 (95% confidence interval (CI) 1.03 to 3.00). Dislocation was the leading indication for revision. There was no difference in the rates of infection, dislocation of the hip, knee revision and short-term mortality. In long-term follow-up, patients with Alzheimer’s disease had a higher mortality (HR 1.43; 95% CI 1.22 to 1.70), and only one third survived ten years post-operatively. Increased age and comorbidity were associated with longer peri-operative hospitalisation in patients with Alzheimer’s disease.

Cite this article: Bone Joint J 2015;97-B:654–61.

Metal-on-metal resurfacing of the hip (MoMHR) has enjoyed a resurgence in the last decade, but is now again in question as a routine option for osteoarthritis of the hip. Proponents of hip resurfacing suggest that its survival is superior to that of conventional hip replacement (THR), and that hip resurfacing is less invasive, is easier to revise than THR, and provides superior functional outcomes. Our argument serves to illustrate that none of these proposed advantages have been realised and new and unanticipated serious complications, such as pseudotumors, have been associated with the procedure. As such, we feel that the routine use of MoMHR is not justified.

Cite this article: Bone Joint J 2014;96-B(11 Suppl A):17–21.

Introduction:. Significant proximal femoral remodeling occurs after total hip arthroplasty (THA), with regions of bone loss, and regions of hypertrophy. This study compared three implants for changes in femoral bone mineral density over 2 years following primary uncemented hip arthroplasty with a conventional stem (THA), a novel femoral neck-sparing short hip stem (NS-THA), and resurfacing hip arthroplasty (RHA). Methods:. Seventy-one patients participated in this non-randomized, prospective study. All patients had a diagnosis of osteoarthritis and underwent primary uncemented hip arthroplasty. Dual Energy XRay Absorptomitry (DXA) scans were performed at preoperative, 3–7 days post-op, 6 weeks, 6 months, one, and two years post-op. Using custom 2 cm zones, 19 zones were observed for percent changes in bone mineral density (BMD). Radiographs and Harris Hip scores were obtained at each visit. Results:. Age, gender, and BMI were found to be statistically different with fewer females and lower age in the RHA group, and a lower age in the NS-THA group. In all three groups, regions that were located proximally were shown to be the most susceptible to bone loss. Combined 2 cm zones 1C/7C, 2A/6A, and 2B/6B showed statistical significance (p < 0.05). Bone loss in the proximal regions was 8–10% lower with the femoral neck-sparing short stem, and least in the RHA group, causing little to no BMD loss in proximal regions. Radiographic outcomes and clinical results including Harris Hip scores were equal between the groups. Conclusion:. Consistent with our hypothesis, it was found that hip arthroplasty with a conventional stem resulted in the highest proximal femoral bone loss, and resurfacing arthroplasty was associated with the least bone loss. The femoral neck-sparing short stem ameliorated the bone loss seen with traditional hip arthroplasty, and approximated the bone preservation seen with hip resurfacing. The short stem neck-sparing device may provide some of the benefits of hip resurfacing, but could potentially have wider indications for use

Comparisons of blood metal ion levels of cobalt and chromium (CoCr) between metal-on-metal total and resurfacing hip arthroplasties are limited. High levels of CoCr may result in long-term adverse biological effects. We compare metal ions levels between total and resurfacing implants. 70 patients (28 males and 42 females) had a total hip arthroplasty using the Birmingham (Smith & Nephew) modular femoral component and a variety of stems, articulating with the Birmingham resurfacing component. The average age was 65.5 (±6.8) years and an average follow-up of 6.0 (±2.2) years. 170 patients (145 male and 25 female had a Birmingham resurfacing arthroplasty with an average age of 54.7 (±9.9) years and an average follow-up of 5.9 (±3.0) years. CoCr levels were measured. Bivariate correlations and independent samples t-tests were applied to determine similarities and differences within and between groups. Average ion levels in total arthroplasty patients were: Co 114.17 (±94.01) nmol/L (range 2–414); and Cr 75.12 (±68.45) nmol/L (range 10–312). Average levels in hip resurfacing arthroplasty were: Co 55.98 (±79.5) nmol/L (range 7–505); and Cr 70.77 (±87.41) nmol/L (range 5–751). Both total and resurfacing groups showed significant correlations (p<0.01) between Co and Cr levels. A significant difference was observed between the total and resurfacing group Co levels (p<0.0001). No significant difference was shown between group Cr levels (p>0.672). The average total hip replacement CoCr levels were higher than the hip resurfacing levels. While the overall activity level may be higher in the resurfacing group, possibly the incidence of stop/start frequency may be higher in the total hip replacement group. Hip resurfacing arthroplasty average CoCr levels are lower than those of total hip replacement patients. Associations between Co and Cr metal ion levels are shown within each group. Co levels differ significantly between groups where Cr does not. Long-term follow-up of CoCr levels are required

The aim of this review is to evaluate the current available literature evidencing on peri-articular hip endoscopy (the third compartment). A comprehensive approach has been set on reports dealing with endoscopic surgery for recalcitrant trochanteric bursitis, snapping hip (or coxa-saltans; external and internal), gluteus medius and minimus tears and endoscopy (or arthroscopy) after total hip arthroplasty. This information can be used to trigger further research, innovation and education in extra-articular hip endoscopy.

The December 2012 Hip & Pelvis Roundup³⁶⁰ looks at: swimming against the tide with resurfacing; hip impingement surgery; the relationship between obesity and co-morbidities and joint replacement infection; cemented hips; cross-linked polyethylene notching; whether cement is necessary in oncological arthroplasty; and how total hip replacement may result in weight gain.

Background. Hip arthroscopy is well established as a diagnostic and therapeutic tool in the native hip joint. However, its application in the symptomatic post-hip arthroplasty patient is still being explored. Aims and Methods. We have described the use of hip arthroscopy in symptomatic patients following total hip replacement, resurfacing hip arthroplasty and partial resurfacing hip arthroplasty in 24 patients (study group), and compared it with arthroscopy of the native hip of 24 patients. Results. The diagnostic yield of hip arthroscopy in symptomatic post-arthroplasty patients was 95.8% (23 / 24) and a therapeutic arthroscopic intervention resulted in relief of symptoms in 41.6% (10 / 24) of the patients. It led to revision hip replacement in a further 29.1% (7 / 24). In contrast, hip arthroscopy of the native hip (control group) had a 100% diagnostic yield and an arthroscopic therapeutic intervention was carried out in all the patients resulting in symptomatic relief in 87.5% (21 / 24). The mean operative time in the study group (59.7 mins, SD 21.1) was less than the control group (71 mins, SD 17.1, p < 0.05) but the arthroscopic approach was more difficult. Conclusion. The authors suggest the use of hip arthroscopy in well-investigated symptomatic post-arthroplasty patients with an elusive diagnosis (Fig. 1: Arthroscopic image showing a THR in situ (Furlong, JRI, London, UK) with a ceramic femoral head (yellow arrow), ceramic acetabular liner (white arrow), florid metallosis (red arrow) and corrosion on the femoral neck (green arrow) because of impingement against the margin of the acetabular component.) and also describe the technical modifications necessary with various types of hip arthroplasty

It is accepted that resurfacing hip replacement preserves the bone mineral density (BMD) of the femur better than total hip replacement (THR). However, no studies have investigated any possible difference on the acetabular side.

Between April 2007 and March 2009, 39 patients were randomised into two groups to receive either a resurfacing or a THR and were followed for two years. One patient’s resurfacing subsequently failed, leaving 19 patients in each group.

Resurfaced replacements maintained proximal femoral BMD and, compared with THR, had an increased bone mineral density in Gruen zones 2, 3, 6, and particularly zone 7, with a gain of 7.5% (95% confidence interval (CI) 2.6 to 12.5) compared with a loss of 14.6% (95% CI 7.6 to 21.6). Resurfacing replacements maintained the BMD of the medial femoral neck and increased that in the lateral zones between 12.8% (95% CI 4.3 to 21.4) and 25.9% (95% CI 7.1 to 44.6).

On the acetabular side, BMD was similar in every zone at each point in time. The mean BMD of all acetabular regions in the resurfaced group was reduced to 96.2% (95% CI 93.7 to 98.6) and for the total hip replacement group to 97.6% (95% CI 93.7 to 101.5) (p = 0.4863). A mean total loss of 3.7% (95% CI 1.0 to 6.5) and 4.9% (95% CI 0.8 to 9.0) of BMD was found above the acetabular component in W1 and 10.2% (95% CI 0.9 to 19.4) and 9.1% (95% CI 3.8 to 14.4) medial to the implant in W2 for resurfaced replacements and THRs respectively. Resurfacing resulted in a mean loss of BMD of 6.7% (95% CI 0.7 to 12.7) in W3 but the BMD inferior to the acetabular component was maintained in both groups.

These results suggest that the ability of a resurfacing hip replacement to preserve BMD only applies to the femoral side.

Introduction. Current standard cups of metal on metal resurfacing hip arthroplasty (RHA) have no dome holes and it is very difficult for surgeons to confirm full seating of these cups. This sometimes results in gap formation between the cup and acetabular floor. Although the incidence of initial gaps using modular press-fit cups with dome screw holes has been reported to range from 20 to 35%, few studies have reported the incidence of gap formation with monoblock metal cups and its clinical consequences in RHA. The purpose of this study was to investigate retrospectively the incidence of initial gap formation and whether the initial gap influences the clinical results in RHA. Material and Method. RHA was performed on 166 hips of 146 patients using the Birmingham Hip Resurfacing (BHR) (MMT, UK) between 1998 and 2007. Mean age at operation was 48.7 years (range, 19-85 years). Mean duration of follow-up was 6.9 years (2.0-10.6). Acetabular reaming was performed with the use of hemispherical reamers and the reamer size was increased up to an odd number diameter which provided tight rim fit in the antero-posterior direction. The same size hemispherical provisional cup with dome holes and slits was used to check the cavity for complete seating. If the provisional cup could not be seated on the floor, reaming was repeated with the same reamer to remove the rim bump until full seating was achieved. Acetabular cups of 1mm larger diameter were impacted into the acetabulum by a press-fit technique. After press-fit fixation, the stability of the cups was confirmed with a synchronized movement of the pelvis and the cup inserter by applying a gentle torque. Clinical evaluation was performed using WOMAC at the latest follow-up. Radiographic assessments were performed using radiographs immediately after the surgery, at 3 weeks, 3 months, 1 year, and then annually thereafter. We evaluated the height of the gap between the cup and acetabular surface, cup inclination angle, cup migration and the time to gap filling. To investigate the relationship between the magnitude of the gap and the radiographic results, the patients were divided into two groups according to the height of the initial gap; the cases with a gap of less than 3 mm on the initial radiograph were grouped into a small gap group, the cases with a gap of 3mm or more were grouped into a large gap group. We compared the changes in the height of the gap, in the cup inclination angle and the cup migration between the groups. Results. Gaps were identified in 21 of 166 hips (13%) on the postoperative radiograph. The average height of the gaps was 2.4 mm (0.56-4.5mm). Of the 21 hips with gaps, there was no revision during the follow up period. 12 of the 21 hips were classified into the small gap group, 9 of the 21 hips were classified into the large gap group. In the small gap group, there were no changes of cup inclination angle of more than 3 degrees nor was there cup migration of more than 3mm. On the other hand, in the large gap group, 6 of the 9 hips showed reductions of the cup inclination angle of more than 3 degrees with 3mm or more of migration during the initial 3 months (P<0.05). After 3 months, neither progressive angle change nor migration of the cup were observed. All acetabular components were judged to be bone ingrown at the last follow up. Conclusions. The incidence of initial postoperative gaps (13%) of this series is similar to that of modular cementless cups fixed with press-fit technique. There were no serious clinical consequences of the initial gap during the 6.9 year follow up. However, gaps of 3mm or more led to early migration of the acetabular component and change in inclination angle

Peri-articular soft-tissue masses or ‘pseudotumours’ can occur after large-diameter metal-on-metal (MoM) resurfacing of the hip and conventional total hip replacement (THR). Our aim was to assess the incidence of pseudotumour formation and to identify risk factors for their formation in a prospective cohort study.

A total of 119 patients who underwent 120 MoM THRs with large-diameter femoral heads between January 2005 and November 2007 were included in the study. Outcome scores, serum metal ion levels, radiographs and CT scans were obtained. Patients with symptoms or an identified pseudotumour were offered MRI and an ultrasound-guided biopsy.

There were 108 patients (109 hips) eligible for evaluation by CT scan at a mean follow-up of 3.6 years (2.5 to 4.5); 42 patients (39%) were diagnosed with a pseudotumour. The hips of 13 patients (12%) were revised to a polyethylene acetabular component with small-diameter metal head. Patients with elevated serum metal ion levels had a four times increased risk of developing a pseudotumour.

This study shows a substantially higher incidence of pseudotumour formation and subsequent revisions in patients with MoM THRs than previously reported. Because most revision cases were identified only after an intensive screening protocol, we recommend close monitoring of patients with MoM THR.

Background. Correct positioning of the femoral component in resurfacing hip arthroplasty (RHA) is an important factor in successful long-term outcomes. The purpose of computer-assisted navigation (CAS) in resurfacing is to insert the femoral neck guide wire with greater accuracy and to help size the femoral component, thus reducing the risk of notching at the head and neck junction. Several recent studies reported satisfactory precision and accuracy of CAS. However, there is little evidence that CAS is useful in the presence of anatomical deformities of the proximal femur, which is frequently observed in young patients with secondary degenerative joint disease. Aim. The purpose of this in vitro study was to determine the accuracy of an image-free RHA navigation system in the presence of angular deformity of the neck, pistol grip deformity of the head and neck junction and slipped upper femoral epiphysis deformity. Methods. An artificial phantom leg was used. Implant-shaft angles for the guide wire of the femoral component reamer were calculated, in frontal and lateral planes, with the computer navigation system and an electronic caliper combined with micro-CT. Results. With both normal anatomy and angular deformity we found close agreement between the CAS system and our measurement system. There was a consistent disagreement on both planes for the pistol grip deformity. In the presence of the slipped upper femoral epiphysis deformity, close agreement was found only on the frontal plane but calculation of the femoral head size was inaccurate. Conclusion. This is the first study designed to assess the accuracy of a femoral navigation system for RHA in the presence of anatomical deformity of the proximal femoral head and neck segment. Our data suggests CAS technology should not be used to expand the range of utilisation of resurfacing surgery to these cases but rather to improve the surgical outcome in those with suitable anatomy

Introduction. Sir John Charnley introduced his concept of low friction arthroplasty— though this did not necessarily mean low wear, as the initial experience with metal on teflon proved. Although other bearing surfaces had been tried in the past, the success of the Charnley THR meant that metal-on-polyethylene became the standard bearing couple for many years. However, concerns regarding the occurrence of peri-prosthetic lysis secondary to wear particles lead to consideration of other bearing surfaces and even to the avoidance of cement (although this has proven to be erroneous). Bearing combinations include polymers, ceramic and metallic materials and are generally categorised as hard/soft or hard/hard. In general, all newer bearing surface combinations have reduced wear but present with their own strengths and weaknesses, some of which are becoming more apparent with time. Bearing surfaces must have the following characteristics: low wear rate, low friction, Biocompatibility and corrosion resistance in synovial fluid. Hard/soft. Femoral head components are generally made of cobalt, chromium alloy, either cast or forged. Both alumina and zirconia ceramics have been used as femoral head materials and the hardness is thought to reduce the incidence of surface damage to the femoral head. The hard femoral heads have been traditionally matched with conventional ultra high molecular weight polyethylene. (UHMWPE) which has been produced by either ram extrusion or compression moulding. Over the past 10 years, most implant companies have moved to highly cross-linked UHMWP which in both laboratory and human RCTs have shown appreciably less wear. Hard/hard bearings – Metal-on-metal (M-O-M). The first generation of metal bearings were based on stainless steel couples but the metal on metal design by. McKee-Farrar was made from CoCrMo alloy with large head diameters. The second generation M-O-M bearing were introduced by Weber using wrought. CoCrMo alloy with low surface roughness and wear rates about 100 to 200 times less than traditional metal/UHMWPE. The re-introduction of resurfacing hip arthroplasty has been made possible by the improvement in metal technology. Concerns however exist with the long term biologic effects of metal ions, the reported incidence of sensitivity reactions to metal and the more demanding techniques required for implantation. Ceramic on Ceramic (C-O-C). Alumina ceramic bearing surfaces are extremely hard, have high wear resistance and reported low concentration of wear particles in peri-prosthetic tissues. Unlike M-O-M there is no ion release. While the reported fracture rate for ceramic couplings is extremely low their proper implantation is important to minimise impingement. There is an incidence of squeaking not seen in other bearing couples and because of the hardness of the bearing, long term concerns with stress shielding of bone remain. Clinical outcomes. Data will be presented from the Australian Orthopaedic. Association National Joint Replacement Registry on clinical outcomes of bearing surfaces. Overall metal on UHMWPE has the least revision of any bearing surface couple used with conventional hip replacement. Future trends. Further research into hard/soft bearings will look at ways to reduce UHMWPE wear without compromise of clinical results based on over 40 years use. Hard-on-hard bearings may focus on combining the best features of both. M-O-M and C-O-C couplings without fracture risk or metal iron release. When deciding which bearing surface is suitable for your patients it must be emphasised that wear reduction is only one of several considerations when taking into account the most appropriate implant

Although resurfacing hip replacement (RHR) is associated with a more demanding patient cohort, it has achieved survivorship approaching that of total hip replacement. Occasional failures from femoral neck fracture, or migration and loosening of the femoral head prosthesis have been observed, the causes of which are multifactorial, but predominately biomechanical in nature. Current surgical technique recommends valgus implant orientation and reduction of the femoral offset, reducing joint contact force and the femoral neck fracture risk. Radiographic changes including femoral neck narrowing and ‘pedestal lines’ around the implant stem are present in well performing hips, but more common in failing joints indicating that loosening may involve remodelling. The importance of prosthesis positioning on the biomechanics of the resurfaced joint was investigated using finite element analysis (FEA). Seven FE models were generated from a CT scan of a male patient: the femur in its intact state, and the resurfaced femur with either a 50mm or 52mm prosthesis head in. neutral orientation,. 10° of relative varus or. 10° of relative valgus tilt. The fracture risk during trauma was investigated for stumbling and a sideways fall onto the greater trochanter, by calculating the volume of yielding bone. Remodelling was quantified for normal gait, as the percentage volume of head and neck bone with over 75% post-operative change in strain energy density for an older patient, and 50% for a younger patient. Resurfacing with the smaller, 50mm prosthesis reduced the femoral offset by 3.0mm, 4.3mm and 5.1mm in varus, neutral and valgus orientations. When the 52mm head was used, the natural joint centre could be recreated rrespective of orientation, without notching the femoral neck. The 50mm head reduced the volume of yielding femoral neck bone relative to the intact femur in a linear correlation with femoral offset. When the natural femoral offset was recreated with the 52mm prosthesis, the predicted neck fracture load in stumbling was decreased by 9% and 20% in neutral and varus orientations, but remained in line with the intact bone when implanted with valgus orientation. This agrees with clinical experience and justifies currently recommended techniques. In oblique falling, the neck fracture load was again improved slightly when the femoral offset was reduced, and never fell below 97% of the natural case for the larger implant in all orientations. Predicted patterns of remodelling stimulus were consistent with radiographic clinical evidence. Stress shielding increased slightly from varus to valgus orientation, but was restricted to the superior femoral head in the older patient. Bone densification around the stem was predicted, indicating load transfer. Stress shielding only extended into the femoral neck in the young patient and where the femoral offset was reduced with the 50mm prosthesis. The increase in remodelling correlated with valgus orientation, or reduced femoral offset. The trend would become more marked if this were to reduce the joint contact force, but there was no such correlation for the 52mm prosthesis, when the natural femoral offset was recreated. Only in extreme cases would remodelling alone be sufficient to cause visible femoral neck narrowing, i.e. patients with a high metabolism and considerably reduced femoral offset, implying that other factors including damage from surgery or impingement, inflammatory response or retinacular blood supply interruption may also be involved in femoral neck adaptation. The results of this FEA biomechanical study justify current surgical techniques, indicating improved femoral neck fracture strength in stumbling with valgus position. Fracture risk under oblique falling was less sensitive to resurfacing. Furthermore, the results imply that reduced femoral offset could be linked to narrowing of the femoral neck; however the effects of positioning alone on bone remodelling may be insufficient to account for this. The study suggests that surgical technique should attempt to recreate the natural head centre, but still aim primarily for valgus positioning of the prosthesis, to reduce the femoral neck fracture risk

Metal-on-metal bearings have become popular in the last ten years because of a low wear rate combined with the ability to use large head sizes for conventional total hip arthroplasty (THA) and to facilitate resurfacing hip arthroplasty. Further advantages of metal-metal bearings include the fact that they are not at risk for fracture, and they can be made as modular or non-modular acetabular implants. It was recognized early that metal-on-metal implants had the potential to increase serum ion levels, and this was demonstrated in a number of studies. The significance of elevated ion levels, however, for most patients has been primarily a theoretical concern of toxicity, carcinogenesis or mutagenicity, and to date very few, if any, systemic problems related to systemic metal ions have been documented with certainty. Nevertheless, most surgeons have avoided use of the implants in patients who are likely to become pregnant, patients with renal disease, or patients with major systemic illnesses which have a high likelihood of leading to renal disease. Furthermore, most have avoided using them in patients with known dermal metal allergies, even though the connection between dermal metal allergies and metal bearings has not been established. Unexpectedly, an extremely important concern has emerged with metal bearings: the finding of local inflammatory reactions related to metal bearings. These inflammatory reactions can take several forms including pain with a milky effusion, local tissue necrosis, or large fluid collections or pseudotumors. The histology of these different reactions appears to be predominantly lymphocytic in nature and a term for at least some of these reactions has been coined “AVALS”. Whether these local reactions are primarily immunologic in nature or primarily related to dose of local metal ions or debris remains uncertain. While there is much still to be learned, it appears that certain patient populations may be at increased risk for metal reactions, possibly related to implant size (women and smaller patients). It also seems verticallyoriented implants, which create edge loading, increase wear and increase risk of local metal reactions. Perhaps the most important question is the incidence of local metal reactions, which remains to be defined. To date the problems in most series have been infrequent, less than 1 or 2 percent. However, in a few selected series the incidence has been higher, and when screening has been done for asymptomatic patients with fluid or masses around the joint, the rate has been higher in at least one reported series. Surgeons may interpret the importance of local metal reactions differently, but certainly ultimately incidence of this problem will have a very major effect on the future of these bearings