Objectives

This study aimed to characterise and qualitatively grade the severity of the corrosion particles released into the hip joint following taper corrosion.

Introduction

The possibility of corrosion at the taper junction of hip replacements was initially identified as a concern of generating adverse reactions in the late 1980s. Common clinical findings of failure are pain, clicking, swelling, fluid collections, soft tissue masses, and gluteal muscle necrosis identified intra operatively.

Introduction

Osteloysis following metal-on-UHMW polyethylene Total Hip Arthroplasty (THA) is well reported, as is lack of osteolysis following Ceramic-on-Ceramic (CoC)THA. Early ceramic failures did report some osteolysis, but in flawed implants. As 3rd and now 4th generation ceramic THAs come into mid- and long-term use, the orthopaedic community has begun to see reports of high survival rates and very low incidence of osteolysis in these bearings. Osteolysis reported after 3rd generation CoC THA often included metallosis due to neck rim impingement. In our department we have revised only 2 hips in over 6000 CoC THAs for osteolysis. Both had evidence of metallosis as well as ceramic wear. The technique used by Radiologists for identifying the nature of lesions on CT is the Hounsfield score which will identify the density of the tissue within the lucent area. It is common for radiologist to have no access to previous imaging, especially pre-operative imaging if a long time has elapsed.

With such a low incidence of osteolysis in this patient group, what, then, should a surgeon do on receiving a CT report on a ceramic-on-ceramic THA which states there is osteolysis? Revision of such implants in elderly patients has a high risk of morbidity and mortality.

Background

Total Hip Arthroplasty (THA) using the Direct Anterior Approach (DAA) is a muscle sparing approach which promotes early mobilisation of patients. It is a technically challenging approach shown to have a high rate of complications, especially during the learning curve. Here we present the results of 157 cases of THA via a DAA on a standard theatre table, with a minimum of 6 months follow-up.

Introduction and Aims

The 21^st Century has seen ceramic bearings become an increasingly popular choice in total hip arthroplasty due to their high wear resistance and inert wear debris without osteolysis promising a long term bearing solution. Early ceramic bearings were hindered by fracture but improved manufacturing processes and materials subsequently produced stronger ceramics. These third generation ceramics showed greatly reduced fracture rates but there is limited evidence in the literature reporting their long term survival and wear characteristics. The purpose of this study was to determine osteolysis and survival rates of Alumina ceramic bearings in cementless total hip arthroplasties with a minimum follow-up of 15 years.

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: Bone Joint J 2013;95-B:1603–9.

Introduction

Squeaking is a potential problem of all hard on hard bearings yet it has been less frequently reported in metal-on-metal hips. We compared a cohort of 11 squeaking metal-on-metal hip resurfacings to individually matched controls, assessing cup inclination and anteversion between the groups to look for any differences.

Introduction

The success of total hip arthroplasty has meant its indications have been extended to the younger more active patient. Due to the higher activity levels and increased demands of these patients, revision rates have been traditionally higher than when compared to older patients [1]. Ceramic on ceramic bearings may offer a viable long term solution as manufacturing methods have evolved resulting in improved mechanical properties, particularly of third and fourth generation ceramics. We report the outcome of primary cementless, alumina-on-alumina hip arthroplasty with a minimum 10 year follow up in 110 patients under the age of 55 years of age at time of surgery.

Introduction

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.

Introduction

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.

Introduction

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.

Edge loading commonly occurs in all bearings in hip arthroplasty. The aim of this study compares metal bearings with edge loading to alumina bearings with edge loading and to metal bearings without edge loading.

Seventeen failed large diameter metal-on-metal hip bearings (8 total hips, 9 resurfacings) were compared to 55 failed alumina-on-alumina bearings collected from 1998 to 2010. The surface topography of the femoral heads was measured using a chromatically encoded confocal measurement machine (Artificial Hip Profiler, RedLux Ltd.).

The median time to revision for the metal hip bearings and the alumina hip bearings was 2.7 years. Forty-six out of 55 (84%) alumina bearings and 9 out 17 (53%) metal bearings had edge loading wear (p<0.01). The average volumetric wear rate for metal femoral heads was 7.87 mm3/yr (median 0.25 mm3/yr) and for alumina heads was 0.78 mm3/yr (median 0.18 mm3/yr) (p=0.02).

The average volumetric wear rate for metal heads with edge loading was 16.51 mm3/yr (median 1.77 mm3/yr) and for metal heads without edge loading was 0.19 mm3/yr (median 0 mm3/yr) (p=0.1). There was a significant difference in gender, with a higher ratio of females in the alumina group than the metal group (p=0.02).

Large diameter metal femoral heads with edge loading have a higher wear rate than smaller alumina heads with edge loading. Metal-on-metal bearings have low wear when edge loading does not occur.

Aim

Alumina ceramic on ceramic bearings in total hip arthroplasty (THA) may reduce the prevalence of osteolysis due to its properties of low wear and chemical inertness. This is critical in the younger patient population as they place increased demands over a longer period. This study reports on the clinical and radiographic outcomes of a series of modern cementless ceramic on ceramic THA at a minimum of 10 years in this younger group.

Aim: Alumina ceramic on ceramic bearings have gained popularity in hip arthroplasty due to the properties of low wear, low friction and chemically inert wear debris. In a previous study, we reported the excellent clinical results of a series of cementless ceramic on ceramic primary total hip arthroplasties at a minimum of 5 years. We now present the follow up results at 10 years.

Method: Between June 1997 and February 1999, 301 consecutive, primary cementless hip arthroplasties were performed on 283 patients in our unit. The mean age of the patients was 57.8 years, with 145 (51%) being female. All of the hips received the same implant: (Osteonic ABC cup and Secure-Fit or Secure-Fit Plus stem; Stryker Orthopaedics). A third generation alumina ceramic on ceramic bearing (Biolox Forte; CeramTec) was used for articulation in all cases. All the operations were performed through a posterior approach with enhanced posterior repair, and the post-operative protocols were the same for all the patients. The clinical and radiographic outcome at 10 years were analysed.

Results: At 10 years, 7.3% had died of unrelated cause and 3% were revised. The average Harris Hip score was 94.3 points at the last follow up. Ninety six percent of patients scored an excellent or good result, with less than 3% have moderate residual pain. Radiographically, all patients assessed had evidence of stable bony ingrowth. There were nine revisions in all, four stem revisions due to periprosthetic fracture, one secondary to aseptic loosening and one to facilitate a femoral shortening osteotomy. There was one cup revision for psoas tendonitis and one for cup repositioning. This same patient subsequently underwent further revision due to acetabular osteolysis with metallosis and some ceramic wear. Overall, the survival rate of the implants was 96% at 10 years. The retrieved femoral heads showed a median wear rate of 0.2 cubic millimeters per year.

Conclusions: Alumina ceramic on ceramic bearings in cementless primary total hip arthroplasty had been shown to have good survival rate at 10 years with good function, low wear rate and no adverse radiographic changes. The one case of osteolysis may be due to ceramic wear debris or may be due to metal wear debris from the neck to rim impingement.

Background: Squeaking in hip arthroplasty is a phenomenon that was described decades ago, but has only been brought back to attention recently. It occurs predominantly in ceramic on ceramic bearings, and has a reported incidence from less than 1% to 21%. The cause and the implication of squeaking are still unknown and many factors have been suggested to contribute. This study has looked into the patient factors to investigate if any clinical features are associated with an increased risk of squeaking.

Methods: All primary total hip arthroplasties with ceramic on ceramic bearing that were performed at our unit were reviewed and all squeaking hips presented are included in the study. Patient demographics and clinical outcome data were analysed and compared with matched controls from the silent hips.

Results: Between 1997 and 2008, 3375 primary hip arthroplasties in 3182 patients with ceramic on ceramic bearing were performed in our unit. Seventy one hips (2.1%) presented with squeaking on direct questioning and self reporting. Those patients were found to be taller, heavier and younger. They also have a significantly higher post-operative range of hip motion and higher Harris hip score when compared to matched controls. There was no difference in the satisfaction score. Only 4 patients (5.6%) presented with pain as well as squeaking, and 2 (2.8%) resulted in revision surgery for problematic squeaking.

Conclusions: We present the largest series of squeaking primary hip arthroplasties with ceramic on ceramic bearing to date. A number of patient factors were found to be associated with squeaking. The taller, heavier and younger patients with more flexible and functional hips were at a higher risk, presumably because these patients put greater mechanical demands on their hips. Majority of the patients with squeaking are pain free and there is only a small risk of requiring revision surgery.

Introduction: Dislocation is the most common complication resulting in re-operation after total hip arthroplasty. This study investigates the association between acetabular prosthesis position, changes in femoral offset and leg length and the risk of dislocation.

Patients and Methods: All total hip arthroplasties performed over the past 17 years at one institution were reviewed. The posterolateral approach was used in all cases. Only hips that included all of the following were included in the study: diagnosis of primary osteoarthritis, no previous surgery, unconstrained liner. 3682 hips met the inclusion criteria. 60 hips (1.6%) sustained a dislocation. Cup inclination and version was determined from scanned radiographs using Hip Analysis Suite software (University of Chicago) in all hips that dislocated and a control group of 60 patients matched for femoral head size, sex, age at surgery, side of hip replacement, time from surgery, BMI, type of prosthesis and bearing surface. We compared femoral offset and length against the contralateral normal hip, on standardised radiographs. Therefore dislocation cases where the contralateral hip had been replaced, where arthritic changes were present, or where previous surgery had been undertaken were not included in the analysis. 24 dislocating hips were measured and compared with 48 controls matched using the same criteria as above. Radiographs were analysed using Hip Analysis Suite.

Results: There is a statistically significant difference (p=0.025) in anteversion between dislocators and matched controls. Inclination is not significantly associated with dislocation (p=0.536).

There is a relative risk of 3.0 of dislocation in cups with ≤15 degrees of anteversion compared with > 15 degrees of anteversion. This difference in dislocation is statistically significant (p< 0.01).

Increased femoral offset compared with the normal contralateral hip is statistically significantly associated with an increased risk of dislocation (p=0.03). Change in leg length is not associated with dislocation risk.

Discussion: Decreased cup anteversion is associated with an increased risk of dislocation in hips operated on via the postero-lateral approach. Our results indicate that the surgeon should aim for a minimum of 15 degrees of anteversion to reduce the risk of dislocation.

The increase in femoral offset in the prosthetic hip compared with the normal contralateral hip and its association with dislocation may be due to intraoperative attempts to compensate for an unstable hip by increasing offset. These results indicate that a surgeon should be cautious when increasing femoral offset alone to try and compensate for a potentially unstable hip. Other factors, for example acetabular version should be addressed, with readjustment of cup position intra-operatively if required.

Introduction and Aims: Good clinical outcome can be expected following cementless total knee arthroplasty (TKA) provided there is early stability and bone ingrowth. Screws give excellent initial stability but provide a path for osteolysis. Screws also cause an irregularity of the tibial component surface which limits their use as a mobile bearing component. We hypothesise that early stability can be obtained with four peripheral pegs rather than screws. We present the results of such a tibial component at a minimum of two years in a cementless mobile-bearing TKA.

Materials and Methods: We evaluated 200 knees in 173 patients. The average age at surgery was 72 years (range, 45–91 years) with 61% of cases in women. Patients were followed up for an average of 45.7 months (range 24 to 69 months). All radiographic and clinical scores were performed prospectively and recorded on a relational database. The components used were the cementless Low Contact Stress femoral component with the DuoFix MBT tibial tray (Depuy, Warsaw, Indiana, USA). The tibial tray was manufactured from cobalt-chrome with a central polished stem and four peripheral pegs. The underside, including the pegs, had a porous surface coated with 50 microns of hydroxyapatite.

Results: After excluding patients who had died, or lost to follow up, 164 cases had a minimum 2-year follow-up. None of the tibial components have required revision. One patient (0.6%) required revision of the femoral component at 22 months for failure of bone ingrowth. There was one superficial infection which resolved with intravenous antibiotics. Two patients developed deep infections (1.2%) which resolved with arthroscopic lavage and antibiotics. One patient presented with bearing spin out at 3 months following surgery, and an exchange to a thicker tibial insert was performed. Average flexion at follow up was to 110°. The patients stated that they were satisfied with their knees in 141 out of 155 cases (91%). The mean score for pain at rest was 0.9 (0–10) and for activity related pain was 1.3. The average HSS score was 86/100 with 90% good or excellent results, compared with a preoperative score of 54/100. Lucent lines were seen in one tibial zone in ten knees (7%), and two zones in three knees (2.1%). There were lucent lines in one femoral zone in 13 cases and two zones in two cases. None of the lines were progressive, and all the surviving components were bone ingrown. Osteolysis was present in a single zone around one (0.7%) tibial component. One patient showed some femoral osteolysis in one zone (0.7%) and also had patellar osteolysis in one zone. Two patients had osteolysis in a single zone of the patella.

Conclusion: This study shows that this design of mobile bearing tibial component provides good primary stability and bone ingrowth.

Previously ankylosed or surgically arthrodesed hip joints can be converted successfully to a Total Hip Replacement (THR) in order to improve patient mobility and function. We present a long term prospective cohort study of cementless revisions of previously ankylosed hips.

Sixteen hips (15 patients) with a mean age of 52 years (range 16 to 75) had ankylosed hips for a mean of 36 years (range 3.5 to 65 years). They all received a cement-less THR between August 1988 and January 2003 and were prospectively followed-up for a mean of 11 years (range 5.0 to 19 years). Two patients died during the study period of unrelated causes and none were lost to follow-up.

All patients showed improved mobility and function following the conversion of their ankylosed hips. The Harris Hip Score improved from a pre-operative mean value of 70 (Standard Error of Mean (SEM) 3.4) to a post-operative value of 83 (SEM 4.4) at the latest review, which was statistically significant (p < 0.05). There was one acetabular cup revision at 5 years post implantation for aseptic loosening. At a mean of 11 years post THR, all other femoral and acetabular components remained clinically and radiographically well fixed.

One patient with systemic ankylosing spondylitis and spontaneous bilateral bony hip ankylosis developed the unusual complication of Paget’s disease of the Left hemipelvis and proximal femur two years after successful bilateral THR surgery. His symptoms resolved following medical therapy for Paget’s disease.

We conclude that a previously ankylosed hip can be effectively converted to a cementless total hip replacement with good long term results.

Dislocation remains a common complication following total hip arthroplasty, second only to aseptic loosening as a cause of revision. Factors thought to play a role in dislocation include cup and stem alignment, soft tissue tension, surgical approach, patient factors, and design features of the prosthesis, including femoral head size.

We analysed all consecutive total hip replacements at one institution over a 17 year period. Criteria for study inclusion were hips replaced due to primary osteoarthritis with no previous surgery, femoral head sizes of 28mm and 32mm only, and at least one year from date of surgery. 3682 hips fulfilled these criteria. All procedures were carried out using a posterolateral approach with enhanced posterior repair, and a standard method of intraoperative soft tissue balance assessment.

The rate of dislocation was 1.6%. 32mm femoral head size was associated with a statistically significant lower rate of dislocation. However, after controlling for different follow-up times between 28mm and 32mm heads, this difference was no longer observed. Older age at time of surgery and decreased cup anteversion were shown to be significantly associated with an increased risk of dislocation. Ceramic on ceramic bearing surface was significantly associated with a decreased risk of dislocation, after controlling for age, bearing wear and time from surgery. Cup inclination, gender, BMI, and preoperative hip score were not related to dislocation risk.

Our dislocation rate may reflect current dislocation rates of surgeons using the posterolateral approach with posterior capsule and external rotator repair. The risk factors identified and excluded in this study are likely to be relevant to all surgeons who utilise this approach in total hip arthroplasty.

Dislocation remains a common complication following total hip arthroplasty, second only to aseptic loosening as a cause of revision. Factors thought to play a role in dislocation include cup and stem alignment, soft tissue tension, surgical approach, patient factors, and design features of the prosthesis, including femoral head size.

We analysed all consecutive total hip replacements at one institution over a 17 year period. Criteria for study inclusion were hips replaced due to primary osteoarthritis with no previous surgery, femoral head sizes of 28mm and 32mm only, and at least one year from date of surgery. 3682 hips fulfilled these criteria. All procedures were carried out using a posterolateral approach with enhanced posterior repair, and a standard method of intraoperative soft tissue balance assessment.

The rate of dislocation was 1.6%. 32mm femoral head size was associated with a statistically significant lower rate of dislocation. However, after controlling for different follow-up times between 28mm and 32mm heads, this difference was no longer observed. Older age at time of surgery and decreased cup anteversion were shown to be significantly associated with an increased risk of dislocation. Ceramic on ceramic bearing surface was significantly associated with a decreased risk of dislocation, after controlling for age, bearing wear and time from surgery. Cup inclination, gender, BMI, and preoperative hip score were not related to dislocation risk.

Our dislocation rate may reflect current dislocation rates of surgeons using the posterolateral approach with posterior capsule and external rotator repair. The risk factors identified and excluded in this study are likely to be relevant to all surgeons who utilise this approach in total hip arthroplasty.

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.

Introduction and Aims: Periprosthetic fracture is a serious complication of increasing incidence in joint replacement. Our aim was to evaluate periprosthetic fracture patterns in our series of 1152 primary hip arthroplasties using a cementless proximally hydroxyapatie coated anatomic stem and to identify risk factors from parameters measured in our assessment of these patients.

Method: All patients with periprosthetic fracture following primary total hip arthroplasty using the Anatomique Benoist Girard I (ABG I) hip system were identified. Parameters studied included time of fracture after surgery, patient age and fracture classification. The pre-operative cortical index in the fracture group was measured and compared with a group matched for age, gender, diagnosis, and body mass index.

1152 ABG I primary hip arthroplasties were performed in 1037 patients from 1991–1997. Osteoarthritis was diagnosed in 93% of cases. The average age was 65 years; there were 536 females and 501 males. Mean follow-up was 79.6 months.

Results: Thirty-two patients, 16 male and 16 female, suffered a periprosthetic fracture. Thirty-one patients were treated for osteoarthritis and one for a femoral neck fracture. We retrieved complete records on 28 patients.

The average age of the fracture group was 73 years, compared to 65 years for the whole series (p< 0.0001). The incidence of periprosthetic fracture increased with age. The relative risk for patients over 70 years for peri-prosthetic fracture is 4.7 greater (95% CI 2.14–10.21).

Distinct fractures patterns were related to time from initial surgery. Four fractures occurred within three months of surgery; these early fractures exhibited a particular pattern. The remaining 24 occurred between four and 114 months after surgery. These late fractures exhibited a different but consistent fracture pattern. Two fractures in the early group were identified immediately post-operatively. All others presented after minor low energy trauma.

The mean cortical index in the fracture group was 47% and in the matched group 51%. If the pre-operative cortical index is below 50%, the risk of periprosthetic fracture is 4.75 greater (odds ratio 4.75 CI 1.5–15.00).

All fractures were adequately classified and managed by guidelines in the Vancouver classification.

Conclusion: This study identified distinct fracture patterns related to time from surgery. Cortical index and age have predictive value in pre-operative assessment of fracture risk: cortical index below 50 and age above 70 are risk factors for periprosthetic fracture and should be considered with other parameters to minimise risk of this complication.

Introduction and Aims: Polyethylene wear and associated osteolysis is a major factor limiting arthroplasty longevity. The Duration process has the theoretical advantage of reducing wear. Our aim was to evaluate the wear rate of standard and Duration polyethylene using either metal or zirconia ceramic heads in the Anatomique Benoist Girard II hip system.

Method: Of 510 patients, 258 had appropriate radiographs for wear measurement. There were five bearing-couple groups. Group 1, 73 patients: metal (cobalt chrome) head on standard polyethylene; group 2, 73 patients: metal head on Duration polyethylene; group 3, 21 patients: (HIPed) zirconia ceramic head on standard polyethylene; group 4, 63 patients: HIPed zirconia head on Duration polyethylene; and group 5, 28 patients: non-HIPed zirconia head on standard polyethylene. All patients had 28mm heads. Sequential radiographs – at least one year after surgery and at least two years apart thereafter – were digitally scanned and images were analysed using computer software.

Results: Group 1: metal on standard polyethylene (n=73) – mean linear wear rate of 0.138 mm/yr (range 0.023–0.462 mm/yr). Group 2: metal on Duration polyethylene (n=73) – mean linear wear rate of 0.106 mm/yr (range 0.067–0.405 mm/yr). Group 3: HIPed zirconia heads on standard polyethylene (n=21) – mean linear wear rate of 0.124 mm/yr (range 0.037–0.225 mm/yr). Group 4: HIPed zirconia heads on Duration polyethylene (n=63) – mean linear wear rate of 0.120 mm/yr (range 0.001–0.427 mm/yr). Group 5: non-HIPed zirconia heads on standard polyethylene (n=28) – mean linear wear rate of 0.119 mm/yr (range 0.044–0.0330 mm/yr). Comparison of linear wear rates of standard (group 1) and Duration polyethylene (group 2) bearings with metal heads revealed a difference of statistical significance (p=0.0083), with lower annual wear rates with Duration polyethylene. Further comparison between these two groups revealed a male preponderance in the Duration group (p=0.000001). There was also a statistically significant difference in body weight between these groups, with the Duration group being heavier by a mean of 5.1 kilograms (p=0.05). There was no significant difference in wear rates between standard and Duration polyethylene bearings with HIPed zirconia heads. There was no statistically significant difference in age in our patient groups.

Conclusion: Duration polyethylene has lower linear wear rates when coupled with a cobalt chrome head. This is despite a male preponderance and higher body weight. Wear rates between standard and Duration polyethylene bearings coupled with zirconia heads were not statistically different.

Introduction and Aims: Third generation alumina ceramic-on-ceramic bearings are being increasingly used in hip replacement surgery as an alternative to polyethylene because of the unacceptably high wear of polyethylene bearings and associated osteolysis leading to failure of hip replacement. Follow-up time with these modern ceramic bearings is still short.

Method: We report the minimum five-year follow-up of our first 300 hip replacements with these bearings in 283 patients, done between June 1997 and February 1999. Three hundred ceramic-on-ceramic Osteonics Securfit or Securfit Plus stems were used with the Osteonics Securfit cup in all cases – these are cement-free and hydroxyapatite coated. The bearings were third generation alumina ceramic femoral heads and cup inserts manufactured by CeramTec. The average age was 58 years and there were 52% females. Osteoarthritis was the diagnosis in 93% and inflammatory arthritis in four percent. We used 92% 32mm bearings and eight percent 28mm bearings.

Results: Mean Harris hip score improved from 56 pre-operatively to 94 at five years. Complications included: three non-fatal and no fatal pulmonary emboli, one deep and four superficial infections. There were four revisions for periprosthetic femoral fracture, one for cup malposition and one for sciatic nerve palsy in a patient with proximal focal femoral deficiency. There were a further four re-operations for psoas tendonitis where the psoas tendon was released. There were no re-operations for bearing failure and none of the ceramic components failed catastrophically, although a small number of acetabular inserts chipped around the rim during insert and were discarded. Of particular interest is the fact that there was no osteolysis seen in any of these hips, either around the acetabulum or around the femur. The usual small lytic areas noted around the calcar and the trochanteric regions of the femur that are commonly seen with polyethylene bearings were completely absent in this group. Three of the hips squeak intermittently with vigorous activity.

Conclusion: Third generation ceramic-on-ceramic bearings have only been available for seven or eight years. Early results using these new bearings are encouraging, in that osteolysis to date has not been seen in this series. No hip in this series has been revised for failure of these ceramic implants. It will be a further five to 10 years before we can be certain how these newer bearings will perform in the long term, but the five-year results are encouraging.

Introduction This study was performed to evaluate the wear rates of Zirconia ceramic heads manufactured prior to the introduction of hot isostatic pressing, on a modular cementless polyethylene cup, and to compare this with the wear rate of a cobalt chrome head coupled with the same cup.

Methods Radiological analysis of 281 primary uncemented ABG total hip arthroplasties performed between 1991 and 1994 was carried out. Patients were divided into three groups: 203 patients with 28 mm zirconia head/polyethylene bearings, 47 patients with 32 mm zirconia ceramic head/polyethylene bearings, 31 patients with 28 mm cobalt chrome head/polyethylene bearings. Wear analysis was performed using the Martel software after digitising radiographs on a flatbed scanner. Initial radiographs were at a minimum of one year to exclude bedding in, and follow-up radiographs a minimum of two years later. Mean follow-up was 6.5 years.

Results The mean linear wear rate of the groups following age and gender matching: for 28 mm Zirconia heads 0.22 mm/yr, for 32 mm Zirconia heads 0.20 mm/yr and for 28 mm metal heads 0.14 mm/yr (p< 0.05). The patients with Zirconia heads had higher rates of osteolysis and revision than those with cobalt chrome heads.

Conclusions The reason for this increased wear rate of Zirconia on polyethylene may well be the transformation of the tetragonal stable phase of the Zirconia to the monolithic unstable phase on the surface of the material. This transformation at grain boundaries on the surface results in ceramic grain “pull-out” by the sliding action of the head against the polyethylene cup. This phenomenon may well occur as a result of the Zirconia processing; the ceramic studied was produced prior to hot isostatic pressing, which produces an inherently more stable ceramic i.e. a higher percentage of the tetragonal phase.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Purpose: We have been using the ABG cementless femoral stem since 1992 for the majority of our primary hip arthroplasty cases. This paper presents a review of our experience and results with the first 1000 ABG stems.

Method: A consecutive series of primary hip arthroplasty cases was followed prospectively beginning in 1992, with a total of 1000 cases performed before October 1996. A variety of degenerative conditions were included, and all cases were assessed using standard clinical and radiographic scoring systems, and recorded on an arthroplasty database.

Results: There were 1000 arthroplasties performed in 905 patients. Mean age at surgery was 64 years (22 to 94 years). There was a predominance of females (53%), and of right hips (58%). Mean height was 170 cms, and mean weight was 75 kgs. Diagnoses included primary or secondary osteoarthritis (93%), inflammatory arthropathy (5%), and fracture neck of femur (2%). Posterior approach was used in all but one case. A femoral fracture or stress riser was incurred in 3 cases (0.3%). A variety of acetabular components were mated with the stem, including ABG (58%), Implex one piece (20%), and ABG II no hole (20%). There were 1 deep infection, occurring acutely. There were 16 (1.6%) femoral periprosthetic fractures occurring between 2 days and 86 months after surgery, most requiring internal fixation or revision. There were 17 dislocations (1.7%) occurring between 2 weeks and 97 months after surgery. Only 1 stem has been revised for aseptic loosening, 3 for dislocation and 8 for periprosthetic fracture. At mean follow up of 60 months (24 to 108 months), average Harris Hip Score was 90/100, with 86% of patients having a good or excellent result. No additional stems were found to be loose on radiographic evaluation.

Conclusion: The design features of this anatomic, hydroxyapatite coated femoral stem provide for excellent initial stability, reliable bone ingrowth, and low intraoperative fracture rate. A small number of periprosthetic fractures occurred, most related to trauma. The proximal geometry of the implant results in low dislocation rates, despite use of the posterior approach.

Introduction: Acetabular osteolysis is common behind cups with holes (the reported incidence is 9% to 36%). Fluid pressure has been implicated in the pathogenesis of osteolysis.

Aim: To test the hypothesis that a polyethylene liner in a metal cup can act as a pump in vivo.

Methods: This study was performed during revision surgery in six cases. The components were from several manufacturers. All were ingrown uncemented cups that had osteolytic lesions associated with holes in the cup.

A cannula was placed through the capsule into the hip joint and another was placed through the periosteum and bone of the ilium into the osteolytic lesion above the ingrown cup. The continuity of these two spaces through the holes in the cup was confirmed by the injection of methylene blue. Pressure transducers were then connected to both cannulae. Measurements were taken while applying compression and distraction forces across the artificial hip joint.

Results: Compression and distraction loads produced a rise (48mmHg) and a fall (35mmHg) respectively in the pressure in the osteolytic lesion but no change in the hip joint pressure, thereby, demonstrating a pumping action. After exposing the prosthesis we were able to demonstrate 1mm to 2mm of in-out excursion of the polyethylene liner in the metal cup, which may explain the mechanism of the pumping effect.

Discussion: The polyethylene liner in the metal shell can act as a pump. Compression and distraction forces, such as occur in normal gait, produce changes in fluid pressure, which are transmitted through the holes and may cause osteolysis behind the cup.

Introduction: Osteolysis is a recognised complication in both cemented and cementless arthroplasty. This may be caused by macrophage mediated reaction to small particulate polyethylene debris. The effective joint space describes the area where polyethylene particles may travel, such as through holes in the cup, to cause a local osteolytic process.

Methods: Twenty four cases of osteolysis (in twenty three patients) requiring revision were identified from patients on whom we had performed the primary arthroplasty. These cases were compared to an overall group of 560 primary hip arthroplasty cases performed during the same time and with the same implants.

Results: The 24 index cases were revised for osteolysis. This represents 4.3% of the total group in this series of implants. Secondary loosening of the acetabular component was present in 7/24 with 13/24 cups being well fixed at the time of revision. All the cups with secondary loosening had evidence of bone ingrowth & had been undermined by the osteolytic process. In 4 cases, either a pelvic fracture or pelvic dissociation had occurred through an osteolytic lesion. In 21 cases femoral stems were revised, but none of these were loose, and none had significant osteolysis around the stems.

The average time from primary procedure to revision was 72 months. The osteolytic group was younger than the overall group at the time of index surgery (53 years vs 63 years, p< 0.0001). There were 16 females and 7 males (p = 0.06). The osteolytic group were also less likely to have an initial diagnosis of primary osteoarthritis than the control group (p=0.05). Other diagnoses in the osteolytic group included dysplasia, previous trauma and inflammatory arthropathy.

Acetabular liner thickness was assessed for all patients. The osteolytic group had a significantly higher proportion of cases with polyethylene thickness of less than 7mm (p < 0.005), and less than 6mm (p < 0.0001). There was no difference in the mean height and weight of the two groups.

Conclusion: Osteolysis is multifactorial and facilitated by screw holes in the acetabular shell that increase the “effective joint space.” Younger females with small ace-tabular components and thin polyethylene are most at risk. Alternate bearing surfaces or acetabular components without holes may alleviate this problem. These cases represent our experience with osteolytic lesions within the acetabulum requiring revision. There were no cases of cup loosening in our overall group other than the 7/24 that had been undermined by the osteolytic process. Revision to ceramic on ceramic bearing implants is our preferred method of treating this problem.

Introduction: Hip arthroplasty for dysplasia of the hip provides a challenge to all hip surgeons. The choice of prosthesis used depends on the severity of the deformity, and the challenge of acetabular reconstruction. We report a review of 105 of our cases operated since 1992 with a minimum two-year follow-up.

Methods: The data in this study has been collected and entered prospectively since 1992 on an arthroplasty database. A total of 105 cases were identified and reviewed. The indication for surgery was painful hip osteoarthritis secondary to dysplasia. All patients were reconstructed with some attempt at restoration of the hip centre, and without femoral osteotomy.

Results: There were 96 patients (10 bilateral), 66 females and 29 males whose mean age at surgery was 53 years (23 to 97 years). The mean follow-up period was 59 months (27 to 107 months). The hip was exposed via a posterior approach in 98% of cases. The majority (94%) of cases had no previous surgery. Depending on the degree of dysplasia either an ABG or S-ROM prosthesis was used.

There were 78 Crowe I & II, and 18 Crowe III & IV hips. The more dysplastic hips required the versatility of the SROM stems to avoid excessive lengthening or femoral osteotomy. These cases also had significantly more inferior reconstruction of the hip centre, and medialisation of the hip centre.

Complications occurred in 8/106 (8%) of cases, the mean time to occurrence being 25 months. The majority were dislocations 7 (7%). There were no sciatic nerve palsies. Revision was required for 5 cups and 1 stem. Clinical evaluation showed all patients were living at home and 85% had no activity restrictions. Mean Harris Hip Score was 92/100. None or mild thigh pain only was reported in 90% of cases. In 98% of cases patients were satisfied with their outcome. Radiographic evaluation showed stem ingrowth occurred in all cases. Minor osteolysis was apparent in 6% of cases. Spot welds were identified in 76% of cases. One case demonstrated pedestal formation.

Conclusion: Reconstructing hip joint mechanics is a challenge in the dysplastic hip. The use of different prostheses for the varying severity in dysplasia has been an effective approach to optimise hip mechanics. Our results using this approach with cementless implants has given excellent short term clinical and radiographic results.

Aim: To review our experience and results of the use of the ABG cementless femoral stem in younger patients; less than 50 years at the time of surgery.

Methods: A series of 82 primary hip arthroplasty cases in patients under the age of 50 years were reviewed. All cases were assessed using standard clinical and radiographic scoring systems.

Results: There were 82 arthroplasties performed in 72 patients. The mean age at surgery was 41 years (22 to 49 years). Diagnoses included primary osteoarthritis (44%), secondary osteoarthritis (42%), and inflammatory arthropathy (13%). There was one femoral peri-prosthetic fracture occurring at 69 months after surgery, associated with a large trochanteric granuloma and ace-tabular wear. There were four dislocations (4.9%). One stem has been revised, for dislocation two weeks after surgery. One other ingrown stem was removed at the time of acetabular revision for osteolysis. A total of 10 patients (14%) has required revision for osteolysis and wear in this group. At mean follow up of 72 months (37 to 109 months), average Harris Hip Score was 91/100, with 90% of patients having a good or excellent result. No stems were found to be loose on radiographic evaluation.

Conclusions: This anatomic, hydroxyapatite coated femoral stem provided excellent initial stability and reliable bone in-growth. The fixation appeared to be durable over this follow-up period. This group of young patients had a high polyethylene wear rate, as expected in high demand individuals, and higher dislocation rate than our overall experience with this implant and surgical approach.