The authors evaluate the incidence, patterns and causative factors of avascular necrosis (AVN) in patients with developmental dysplasia of the hip (DDH) and to follow up these patients to determine what their long term functional and radiological outcome is.

All patients treated for DDH by the same consultant with the subsequent development of AVN were assessed. Outcome was assessed by grading the AVN using the Kalamchi and McEwan classification at final follow up.

A group of 250 hips with DDH were treated over a 16 year period and reviewed. All hips that developed AVN were studied. AVN was seen in 15% of hips treated with closed reduction and 62% of hips after open reduction–32% of the hips treated in the open reduction group were treated elsewhere and subsequently referred.

If use of a Pavlik harness fails, children with DDH should be treated with pre reduction traction, closed reduction and spica cast after the age of 4 months. In the surgical group a capsulorrhaphy should be avoided. Poor radiological outcome at final follow up was not necessarily equivalent to a poor clinical outcome.

The search for the ideal bearing surfaces to be used in Total Hip Replacement continues. The current “best” materials are felt to be various combinations of metal, ceramics and cross linked polyethylene. This study aims to identify the best combination with the lowest side effect profile.

In February 2004 a prospective randomised trial on different bearing surfaces was started. The combinations selected were ceramic on cross linked polyethylene, ceramic on ceramic, metal on metal and ceramic on metal. Institutional ethics clearance was obtained. In all patients uncemented femoral stems are used, and an uncemented porocoated acetabular shell. 28mm Head size was selected. Blood samples have been taken to measure the metal ion concentrations in all patients. These are measured pre operatively, and repeated at intended follow up visits at 3 months, 1, 3, 5 and 10 years post operative using a graphite furnace atomic absorption spectrometer.

Between February 2004 and 2006 seventy hips have undergone total hip replacement. There are 85 patients (11 bilateral). 40% are males and 60% female. The average age at operation is 52 years (17 to 72). 46% Hips are left and 54% right. Follow up includes blood samples and the Harris Hip Score. Complications to date have been surgeon related, with three femoral components needing early revision for technical reasons. This has not affected the bearing surfaces. Ten patients have hetero-topic ossification. Cup inclination averages at 48 degrees (32 degrees to 69 degrees). Post operative blood metal ion levels are compared to the patient’s pre-operative level. To date there is no increase in the metal ion levels for the ceramic/cross linked poly ethylene and ceramic/ceramic articulations. The ceramic metal group is providing intermediate raised metal ion levels, and the highest metal ion levels are in the metal on metal articulation group. In the laboratory the ceramic on metal articulation demonstrates the least wear of all the groups studied, with metal on metal second. The high level of metal ions in the latter groups has always been of concern.

This study demonstrates a lower blood level of metal ions in the ceramic on metal group. If the in vivo wear rate in this group is as good as the laboratory wear, it becomes a very attractive bearing surface in younger active patients.

The aim of this study was to asses the results of total hip replacements using the Elite Plus femoral stem.

During the period 1995 to 2000, 212 total hip replacements were done using the Elite Plus femoral stem. These were followed up prospectively. The cohort of patients included 11 with bilateral hip replacements. 38% of patients were male and 62% were female. The average age at surgery was 61 years, with 18% being younger that 50 years at the time of surgery. All hip replacements were done using the same surgical and cementing techniques. Both cemented and uncemented cups were used in this cohort of patients.

2 patients died peri-operatively, and 22 hips were lost to follow-up. 6 hips have been revised, with 1 revision being due to sepsis and 5 due to loosening. A further 4 hips have radiographic evidence of early loosening, and 1 other hip has developed late sepsis. None of these 5 has yet been revised. Our survivorship at an average of 9 years is 97%.

The survivorship of total hip replacements using the Elite Plus femoral stem in our unit is 97% at an average of 9 years. This compares very well with the results reported in other series. We do note though that there are 5 hips that may need revision, and this would bring the survivorship down to 94%. We feel that our good results are due to careful attention to surgical and cementing techniques, and this may explain our improved results compared to previous reports.

Good short-term results with Mt Blanc uncemented acetabular cups have been previously reported. However, in the medium term, we have observed acetabular loosening related to large granulomatous lytic lesions. To determine the cause of the polyethylene load causing the granulomatous lytic lesions, we subjected six explanted Mt Blanc acetabular cups to retrieval analysis. We also reviewed the literature on polyethylene locking mechanisms in uncemented metal-backed cups and on the deformability of metal-backed cups.

We subjected the retrieved cups to stereo-photographic analysis and to dye penetration and surface scanning electron microscopy techniques. We demonstrated severe polyethylene wear and particle generation on the back surface of the polyethylene insert. This was due both to two-body sliding wear, as characterised by surface deformation and delamination of the polyethylene, and to three-body abrasive wear, as characterised by surface roughness and embedded titanium particles. The literature confirmed that the locking mechanism of the Mt Blanc cup was particularly poor and the deformability greater than in other cups tested. This confirmed the wear patterns on the back-surface of the polyethylene liner.

We caution against the use of uncemented cups that have poor locking mechanisms for the polyethylene liners and those that deform excessively. The combination of poor locking mechanisms and titanium shells is especially dangerous.

Introduction and Aims: Uni-compartmental knee replacements are an alternative to total knee replacements in the management of uni-compartmental osteoarthritis of the knee. The aim of the study was to review the results of our first 60 patients.

Method: We assessed all patients both clinically and radiologically. To expedite the radiological assessment we devised a simplified scoring system. The mean follow-up was 18 months, nine patients had bilateral procedures. The mean age was 66 years, ranging from 45 to 83 years. Eightly-six percent were female. Primary osteoarthritis was the pathology in 93% and post-traumatic arthritis in 7%.

Results: Our average range of movement increased from 113 degrees to 120 degrees post-operatively. Our complicationns included one deep venous thrombosis, one patient with bilateral tibial component loosening and three patients with loose cement particles in the joint. A full radiological assessment was done to assess positioning of the prostheses as well as the interfaces. There was an improvement in the average radiological scoring when comparing the first and the last 10 patients.

Conclusion: Uni-compartment knee replacements are an interesting alternative to total knee replacements. Patient selection is critical. There is a significant learning curve, as demonstrated by the improved radiological scoring later in the series, particularly with regard to cementing techniques. Attention needs to be paid to removing all loose cement from the joint. The complication rate remains low and the results are satisfactory.

Introduction and Aims: Aim of the study is to show whether the accuracy of alignment of a total knee pros-thesis is more dependent on the instrumentation or the skills of the surgeon.

Method: Forty patients that had total knee arthroplasties performed between September 1997 and September 1999 have been analysed. The results of prospective randomised trial using the LCS (Depuy) and IBII (Zimmer) prostheses have been analysed, as well as results using the Scorpio (Stryker) and Profix (Smith + Nephew) total knee replacement systems. Patients were evaluated according to a radiographic protocol, a modification of the Knee Society total knee arthroplasty x-ray evaluation and scoring system. All patients had long leg standing x-rays in full extension and neutral rotation. Lateral x-rays were taken in neutral rotation with a maximum of 10 degrees of flexion. The femoral varus/valgus alignment is recorded on the AP x-ray as the Alpha angle, and the tibial alignment as the Beta angle. On the lateral x-ray the Gamma angle records the femoral flexion and the Theta angle the tibial prosthesis alignment along the tibial shaft.

Results: The results were statistically analysed by the Department of Statistics at the University. Results were stratified according to both the instrumentation used and the surgeon. These showed that there was no statistical difference between the alignment of the different prostheses, irrespective of the surgeon performing the procedure.

Conclusion: From this study we concluded that no one set of instrumentation used while performing a total knee replacement was superior to another. As long the surgeon is familiar with the instrumentation the final alignment of the prosthesis will be satisfactory.

Introduction and Aims: In a radiological study we evaluated the outcome of the Chiari osteotomy as a primary method of femoral head containment in patients with Perthes’ disease presenting at the age of eight years or older. Even when Salter’s prerequisites are met, the results of a Salter osteotomy is known to be poor in this group.

Method: Thirteen patients underwent a Chiari osteotomy at a mean age of nine years and four months. The osteotomy was performed before femoral head deformity had occurred. The hip was considered to be at risk because of the late onset of the disease. Measurements were made on the pre-operative x-ray, the pre-operative arthrogram and the latest follow-up x-rays. Patients have been followed up for an average of five years and four months. On the pre-operative arthrogram there was no femoral head deformity or hinging on abduction. At the time of surgery it was too early in the disease process to assign a hip reliably to a particular classification. During the follow-up period, 12 hips manifested as a Catterall group IV. Eleven hips became Herring type B and two Herring type C.

Results: At latest follow-up all hips could be reliably graded according to the Stulberg classification. Currently, eight hips were a Stulberg type II and five a Stulberg type III, but this might change as skeletal maturity is reached. It is clear that none of the hips will be a Stulberg type IV or V, which is seen in a significant number of untreated hips at this age.

Conclusion: The Chiari osteotomy achieves a congruent hip in this specific group of patients where a poor outcome would otherwise be anticipated.

Introduction and Aims: The purpose of the study was to determine whether the addition of screws improved the fixation of the tibial base plate when using an uncemented total knee replacement.

Method: In June 1999 a prospective randomised double blind study on tibial base plate fixation was started at our institution after Ethics Committee approval. Patients were randomly allocated to either having or not having supplementary screws inserted through the base plate. To date, 138 arthroplasties have been performed and 119 are available for study. Of these, 56 have screws through the base plate and 63 do not. Assessment was of the position of the components of the prostheses, as well as the presence of any radiological lucent lines.

Results: The study is ongoing, and updated results will be presented. After a minimum of 12 months follow-up, 27 patients have some radiolucent lines at the prosthesis-bone interface on the tibial component of the knee replacement. Fourteen occurred where screws had been used and 13 when screws had not. One tibial tray subsided into the tibia without failure of fixation. No screws had been used in this case. Statistically no difference could be demonstrated between the two groups.

Conclusion: The early results of our study question the value of supplementing base plate fixation in uncemented total knee replacements, especially considering the additional cost of the screws and the potential detrimental consequences of the screws.

Introduction and Aims: Rapidly progressive lytic lesions of the calcar develop under the collar of cemented titanium femoral stems inserted in our unit. Progression of the defects slowed after reaching a critical size. Biopsies showed granulomatous lesions with polyethylene particles and multi-nucleate giant cells. The aim of the study was to determine the natural history of these lytic lesions.

Method: We developed a finite element analysis model. We determined the parameters of the FEA model, to reflect the geometry and physical characteristics of the prosthesis-bone construct and also factored in both loading and non-loading parameters. We also determined the characteristics of titanium and cobalt-chrome prostheses.

Results: We determined from the FEA model that there is some vertical displacement of the collar relative to the calcar-cement construct. This displacement is larger in the titanium than the cobalt-chrome model. The magnitude of the displacement is larger than the average polyethylene particle size. On loading and non-loading this displacement allows the development of a pump action, thus concentrating polyethylene particles under the collar of the prosthesis and leading to the granulomatous lytic lesions. The FEA studies demonstrated that the pumping action of the collar became less efficient, but did persist, as the lytic lesions increased in size.

Conclusion: We have explained the development of calcar lytic lesions under the collar of femoral stems. A pump action is present in loading and non-loading phases, sucking in polyethylene particles and allowing granulomatous lesions to form. We recommend caution when using collared femoral prostheses, more so titanium than cobalt-chrome, because of the development of calcar lytic lesions.

Introduction and Aims: Severe central fracture dislocations of the hip in the elderly can be catastrophic events. Conservative treatment yields poor results with stiff painful hips. We assessed the results of three patients treated with a total hip replacement for a central fracture dislocation of the hip, using ante-protrusio supports and bone grafts.

Method: Three elderly patients with central fracture dislocations were treated with early total hip replacement utilising ante-protrusio supports. Bone grafting was used to re-establish acetabular bone stock. Intra and post-operatively these patients had no more complications than a comparable group undergoing hip replacement for femoral neck fractures. The surgical times were longer than for routine hip replacment, and blood replacement requirements was slightly higher. Patients were mobilised early and aggressively.

Results: All became independent walkers. All regained a good range of movement. Radiologically the acetabular/pelvic fractures united and good bone-implant interfaces were obtained. There was no excessive heterotrophic bone formation. The economic assessment indicated that it was more cost-effective to treat these patients with a hip replacement than with alternative methods.

Conclusion: We regard total hip replacements in the management of acetabular fractures in the elderly as a reasonable approach, enabling our patients to mobilise early and keeping morbidity to an acceptable level. The procedure is also more cost-effective than internal fixation and delayed arthroplasty.

Introduction and Aims: Differing methods of cup fixation in total hip replacement are recommended. This prospective randomised study aims to show whether one method is superior to another.

Method: A prospective randomised double blind study was started in 1995, with Ethics Committee approval. Four different methods of cup fixation were used viz. a cemented Ogee cup, a press fit metal-backed cup with pegs, a press fit cup without pegs and a truncated screw in cup. Patient selection was confined to unilateral osteoarthritis of the hip and all other components used were standard viz cemented Elite Plus stem, 28mm ceramic head and Enduron polyethylene.

Results: One hundred and thirty-nine patients have been entered into the study, 23 were lost to follow-up leaving 116 for analysis. The cups have been radiologically assessed for acetabular orientation and the presence or absence of radiolucent lines or acetabular loosening. Follow-up ranges between one and nine years, and as the study is ongoing, updated data will be presented. Currently there are radiolucent lines appearing in zones 1, 2 and 3 of the Ogee cups, but none in the metal-backed cups. To date no cup has come loose.

Conclusion: Early results show that no method of cup fixation is superior to the other, although the radiolucent lines with the Ogee cups (cemented cups) is a cause for concern in the future.

The aim of this study was to measure polyethylene wear in uncemented metal-backed cups and compare it with cemented ultra-high molecular weight (UHMW) polyethylene cups in a controlled double-blind study.

The study group was made up of 91 patients aged 50 to 70 years undergoing THR for unilateral OA of the hip between February 1995 and July 2002. The male to female ratio was 40:60. In all patients, a cemented stem and 28-mm ceramic head was inserted, using a third-generation cementing technique and UHMW polyethylene. Patients were randomly allocated to receive either a cemented or uncemented acetabular cup. Eight patients were lost to follow-up.

Cemented cups were used in 28 patients (mean age 64 years). The mean thickness of the polyethylene was 9.6 mm (7.5 to 12.5). The mean liner thickness in the metal-backed cups was 8.9 mm (7 to 12.2). In measuring wear, baseline 3-month postoperative radiographs were compared with the most recent follow-up radiographs and Martell software was used.

The polyethylene in metal-backed cups had a mean wear rate of 0.49 mm at 4.7 years, with a mean annual wear rate of 0.12 mm. The cemented polyethylene cups had a mean wear rate of 0.45 mm at 5.3 years, with a mean annual wear rate of 0.11 mm.

The study is ongoing. Currently we conclude that there is no significant difference in the annual wear rate of polyethylene in uncemented metal-backed cups and cemented cups.

Introduction and Aims: To determine whether polyethylene wear is different comparing cemented polyethylene cups with metal-backed cups and a polyethylene insert.

Method: A sample of patients who had hip replacements between February 1995 and July 2002 have been studied. They were randomly allocated to either a cemented polyethylene cup or a metal-backed press-fit cup and polyethylene insert. All patients had a cemented stem and a 28mm ceramic head inserted. Ninety-one patients were treated, and 83 are available for analysis. The pre-operative diagnosis in all was unilateral osteoarthritis. The trial is a prospective randomised one and patients have been assessed clinically and radiologically annually. Twenty-eight patients with cemented polyethylene cups and 55 patients with uncemented metal-backed cups have been analysed. The polyethylene thickness of the cemented cups is 9.6mm on average, and the metal-backed cups had an average liner thickness of 8.9mm. Wear measurements were done using the Martell computer system.

Results: Based on measurements done on acetabular cups with the longest follow-up, the metal-backed cups have an average wear of 0.65mm, with an annual wear rate of 0.14mm. The cemented cups have an average wear of 0.64mm, with an annual average of 0.12mm. The study is ongoing and data will be updated.

Conclusion: Wear measurements were done using the three-month post-operative x-ray as the baseline and the most recent follow-up x-ray. Based on measurements done on cups with the longest follow-up, there is very little difference between the two groups. The study is ongoing and data will be updated.

Osteolysis and subsequent mechanical loosening often occurs in hip arthroplasties using polyethylene-on-ceramic (POC) bearings. This has prompted an ongoing search for alternative bearing surfaces. Ceramic-on-ceramic (COC) and metal-on-metal (MOM) prostheses are widely used, with good clinical results. Using hip simulator studies, we compared ceramic-on-metal (COM) and MOM prostheses.

We found COM pairings had 100-fold lower wear rates than MOM. The wear particles from both articulations were oval to round in shape and in the nanometer size range, with the COM producing smaller particles than the MOM. In both pairings, particle size decreased as the bearings bedded in. The volumetric particle loads were far smaller with COM bearing-surfaces than in currently-used MOM prostheses.

These findings have encouraged us to investigate the use of these novel bearing surfaces. Ethical approval has been obtained, and a prospective randomised clinical trial comparing POC, MOM, COC and COM bearing surfaces has started.

The assessment of large allografts in acetabular reconstruction surgery is notoriously difficult. Because of their invasive natures, methods such as tetracycline-labeled histological examination are not recommended. Radio-isotope studies are unreliable in assessing the degree of incorporation because labeled tissues remain hot for extended periods. CT scans are impractical because of the scatter generated by the metallic prosthetic components.

We used DEXA to assess the quality of large acetabular bone grafts immediately after surgery and at regular intervals thereafter. Software programmes were used to subtract the prosthetic components and give values for the remaining bony structure. DEXA results confirmed the initial adequacy of our grafting techniques. Serial scans showed the response of the grafts to both revascularisation and loading. Increases in high-load areas were higher than in low-load areas, reflecting the response of live bone to in vivo stresses. There were also changes reflecting the ongoing revascularisation of the grafts. These findings were born out by radiographs.

DEXA is useful in assessing the incorporation and biological responses of large allografts in revision arthroplasty.

Introduction and Aims: Many authors believe that patellar resurfacing decreases the incidence of anterior knee pain. We analysed the result of 150 of our own patients.

Method: Over the past four years we performed 150 total knee arthroplasties. None of the patellae were resurfaced, osteophytes were carefully removed, the patellae debrided, a thorough peri-patellar synovectomy and circumpatellar cautery denervation performed. All patients were examined by a consultant and a registrar to determine the site of any pain complaint. If there was any controversy a third surgeon was consulted.

Results: No patient had pain severe enough to warrant revision surgery. Only two patients had anterior knee pain, and in neither was it marked.

Conclusion: We do not know whether our favourable results are attributable to the patellar management, or due to the prosthesis used. We concede that a prospective randomised trial is necessary to determine this, but with such a low incidence of patellar complications we feel this is not ethically justified.

Over five years, 85 low-cost primary total arthroplasties (Eortopal Bulteamex) were done at a referral hospital. These were followed up for a mean of 48 months (minimum of 18 months). There were 11 revisions (13%), with four (4.7%) necessary for aseptic loosening, two (2.3%) for recurrent dislocations, four (4.7%) for sepsis and one (1.3%) for a periprosthetic fracture.

When these results were compared with the Trent Regional Arthroplasty Register, the revision rate was noted to be four times higher than in the Trent study, with aseptic revisions being twice as high and infection rates three times higher. Dislocation rates were half those in the Trent study. We concluded that our lower dislocation rate probably reflected the quality of our surgery. Our higher sepsis rate was probably related to the hospital environment, and the high aseptic loosening rate due to the quality of the ‘low-cost’ prosthesis.

We conclude that to be cost-efficient, ‘low-cost’ pros-theses must be of good quality and that the hospital environment must be optimal. This study highlights the need for an Arthroplasty Register in South Africa.

We have previously reported on early lytic lesions occurring when collared titanium prostheses are used. Previous finite element analysis studies (FEAs) showed that lytic lesions of the calcar were due to concentration of polyethylene wear particles under the collar by a ‘pumping action’. Further follow-up of these calcar lytic lesions showed that their rate of increase in size progressively slowed down. Further FEAs were performed to determine why this was so.

An FEA mesh construct was developed, incorporating the new parameters of no contact between the collar and the calcar bone. A mechanical model to determine displacement parameters was also developed. These FEA studies demonstrated that the pumping action of the collar became less efficient as the size of the lytic lesions increased. This led to less concentration of polyethylene particles under the collar and fewer granulomatous reactions. The change in the proximal prosthesis-cement-bone construct may lead to cement mantle deterioration and earlier failure. We still recommend caution when a collared prosthesis is used, and the material and geometry of the prosthesis remain important.

Complex acetabular defects after failed total hip arthroplasty (THA) remain a major challenge in revision surgery. We managed 29 patients, of whom 27 had type-III and two type-IV defects (AAOS classification).The mean age of the 16 men and 13 women was 68 years (22 to 96).

Use of a modular uncemented acetabular revision system allowed us accurately to position the construct, and then optimise the orientation of the polyethylene liner in respect of stability in the reduced hip. The modularity of the system allowed good access to do an impaction bone graft to restore the defects in the bone stock.

Our follow-up ranged from 2 to 25 months. The orientation of the acetabular construct was measured radiologically and was at 50°. Our complications included four dislocations, two transient nerve palsies, one deep infection, four deep venous thromboses and one death from a pulmonary embolism. We conclude that the use of a modular acetabular reconstruction system is promising in these extremely difficult cases.

We managed three elderly patients who had central fracture dislocations with early total hip arthroplasty (THA), using anteprotrusio supports. Bone grafting was used to re-establish acetabular bone stock.

Intraoperatively and postoperatively, these patients had no more complications than did patients undergoing THA for hip fractures. However, the surgical times were longer than for routine THA and blood replacement was slightly higher. Patients were mobilised early and aggressively. All became independent walkers and regained good range of movement. Radiologically the acetabular/pelvic fractures united and good bone-implant interfaces were established. There was no excessive heterotrophic bone formation.

We regard THA in the management of acetabular fractures in the elderly as a reasonable approach, enabling patients to mobilise early and keeping morbidity to an acceptable level.