Revision total hip replacement may be technically challenging, with component selection being one of the challenges. Modular titanium femoral components have some advantages, and our aim was to assess the medium term outcome of the use of such a component [Revitan or PFM]

We reviewed 323 patients undergoing revision with one of these femoral stems. We applied the Oxford Hip Score, the Charnley Class, and the Devane Patient Activity Level to each patient.

The average follow up time was 6.58 years. The mean Oxford score was 35.74.39.8% of the patients were Charnley Class B. 52.4% of patients had an activity score indicating a moderate level of activity ie they could participate in gardening, swimming and other leisure pursuits.

The overall outcome was good with this prosthesis. The Oxford scores were comparable with the national mean for revision THR on the NZ National Joint Register.

Data from the Australian Joint Register suggests that the revision rate for cruciate retaining [CR] prosthesis is less than for cruciate sacrificing prosthesis[PS]. We have analysed data from the NZOA joint register to see if this is the case in NZ.

Data for all PS and CR knee replacements in NZ between 1999 and 2004, and any subsequent revisions were analysed and the results compared with the AOA registry data [2008]. There were 3808 PS knees and 7152 CR knees on the AOA register, with a seven year revision rate of 3.3% and 2.1% respectively p=.002. On the NZOA register there were 1869 PS knees and 5749 CR knees, with a five year revision rate of 1.55% and 1.39% respectively p=.608

This aspect of prosthesis design did not influence the revision rate at five years.

Acoustic emission is an uncommon but well-recognised phenomenon following total-hip arthroplasty using hard-on-hard bearing surfaces. The incidence of squeak has been reported between 1% – 10%. The squeak can be problematic enough to warrant revision surgery. Several theories have been proposed, but the cause of squeak remains unknown. Acoustic analysis shows squeak results from forced vibrations that may come from movement between the liner and shell. A potential cause for this movement is deformation of the shell during insertion.

6 cadaver hemipelvises were prepared to accept ace-tabular components. A shell was selected and pre-insertion the inner shape was measured using a profilometer. The shell was implanted and re-measured. 2x screws were then placed and the shells re-measured. The results were assessed for deformation.

Deformation of the shells occurred in 5 of the 6 hemi-pelvises following insertion. The hemipelvis of the non-deformed shell fractured during insertion. Following screw insertion no further shell deformation occurred.

The deformation was beyond the acceptable standards of a morse taper which may allow movement between components, and this may produce an acoustic emission. Further in-vitro testing is being conducted to see whether shell deformation allows movement producing an acoustic emission.

Measurement of polyethylene (PE) wear in total hip joint replacement (THJR) is performed by measuring change in the position of the femoral head on post-operative radiographs. Early methods used manual measurement with calipers and concentric circles, while more recent techniques involve the use of computer assisted technology. RSA, while mainly used for measuring component migration, can also be used for measurement of PE wear. The aim of this paper is to describe two new methods for measuring PE wear;

A completely automated measurement (which eliminates user error and is 100% reproducible).

For the Automated Measurement Technique (AMT), software has been developed which locates the centre of the acetabular cup and femoral head on both the anteroposterior and lateral radiographs. No user input is required. Accuracy is ± 0.16 mm. Clinically, it has been used in a double-blinded randomized controlled trial (RCT) comparing conventional with cross-linked PE. For the Model Matching Technique (MMT), two pieces of software are combined, Ray-Tracing technology (used in the generation of animated movies), and the Genetic Algorithm (a branch of Artificial Intelligence). CAD models of an acetabular cup and femoral head are matched to post-operative films to position them in 3D space. Change in position of these models over time represents PE wear. CAD models of the patients’ pelvis and femur (built from CT scans) can be similarly used to measure femoral and acetabular component migration.

The AMT was used to measure the PE wear of 116 patients enrolled in a prospective RCT comparing conventional and cross-linked PE. At a follow-up of two to four years, cross-linked PE showed statistic ally significant lower PE wear than the conventional material. A cadaver pelvis and femur has been used to analyse accuracy of the MMT for measurement of component migration. Preliminary results show an accuracy of ± 0.22mm for component migration. The accuracy of PE wear measurement appears to be significantly less than this.

The development of new bearing surfaces to reduce wear in THJR requires new techniques of in-vivo wear measurement. These two new techniques should give important information on the performance of new bearings, and possibly allow measurement of clinical component migration without the need for bead implantation.

Hip fractures are common in the Western world and are an increasing problem as their incidence increasing and thus the cost to heath services is also increasing. While the treatment of intertrchanteric fractures has not changed significantly in the last two or three decades, our knowledge of the results of treatment of subcapital fracture as increased substantially as a result of several well conducted randomised studies in Europe. It is now established that displaced subcapital fractures in those over 60 years should not be treated by internal fixation because the reoperation rate is high and even if reoperation is not required the quality of the result is inferior to other options. Total hip replacement has the best outcome for displaced fractures, with a better quality of result and the lowest reoperation rate. Hemiarthroplasty has a poorer outcome than THR with poorer hip scores and a higher re-operation rate.

This raises the question “How are we doing in NZ” Data from New Zealand Health Information Service (NZHIS) suggests that approximately one third of sub-capital fractures in NZ are currently treated by internal fixation and that this proportion has not changed in recent years. This could be because the patients are young (unlikely) or that the majority of fractures are undisplaced [again unlikely]

It is proposed to investigate the treatment of subcapital fractures in New Zealand, by surveying the treatment given in three hospitals, Wellington, Palmerston North and Middlemore. Patients identified from the NZHIS data base as having been treated for a subcapital fracture in one of two time periods at one of the three hospitals will have their radiographs reviewed to determine whether or not the fracture was displaced. This data will be matched with the, the data from NZHIS to determine the treatment given. Re-admission for re-operation will also be accessed from NZHIS to determine the reoperation rate for those treated by internal fixation, hemiarthroplasty or total hip replacement.

Revision of a failed femoral component in the face of extensive bone loss is a major challenge. When the bone loss extends down below the isthmus it may be difficult to obtain longitudinal stability with a tapered or fully porous coated prosthesis. If subsidence occurs then recurrent dislocation can be an insoluble problem. This study reviews the use of a distally interlocked femoral component designed to address this challenging situation.

We have reviewed 21 cases in which extensive bone loss made the use of an interlocking prosthesis desirable. The average time from surgery was over four years. All patients completed an Oxford hip score and an EO-50. All radiographs were reviewed.

There were 14 males and seven females with an overall average age of 74 years at the time of surgery. Patients had had an average of two previous THR’s, and up to nine previous hip operations. One patient underwent re-revision because of subsidence related to screw cut out. There was one dislocation. Patient satisfaction was high with low Oxford hip scores compared with other revision prostheses, and good EO – 50 ratings.

This type of prosthesis offers a very satisfactory solution to difficult revision situations when bone loss makes the use of regular prostheses difficult. The prosthesis used in this study has a low offset and thus dislocation precautions should be emphasised.

We have performed an RCT of cross-linked versus non cross-linked polyethylene with 125 patients followed for five years. The study showed a dramatic reduction of wear with the cross-linked polyethylene consistent with the in-vitro studies. Because it has been recognised that hard bearings are sensitive to edge loading we were concerned that highly cross-linked polyethylene might exhibit wear properties similar to hard bearings. We have therefore analysed the wear rate as it relates to both anteversion and tilt, to compare non cross-linked polyethylene with cross-linked polyethylene. We found that there was no relationship between tilt and ante-version on any wear indices. These data suggest that, despite having different mechanical properties to non cross-linked polyethylene, cross-linked polyethylene does not exhibit increased wear with conditions that increase edge loading.

Early migration of the acetabular and femoral component after total hip replacement has shown to be a good predictor of implant failure. The only current technique available for this measurement is RSA. An entirely new technique for the measurement of component migration and polyethylene wear has been developed. Required are a single CT of the patients’ pelvis and femur, and routine serial postoperative antero-posterior (AP) and lateral radiographs.

A CT scan of the patients pelvis and proximal femur is performed either pre or post-operatively. This CT is used to build a solid model of the patients’ bony anatomy. CAD models of the femoral and acetabular component are obtained from the manufacturer and all four solid models are imported into custom software. Ray tracer (RT) technology is the computer generation of images of a solid model placed between a camera and a screen. It has been adapted to reproduce the radiological setup used to take clinical AP and lateral radiographs. The four solid models (pelvis, acetabular component, femoral component, femoral shaft) are each placed in the RT. Manipulation of each solid model is performed (6 degrees of freedom, x, y, z translation, and rotation about the x, y, z axis) using Artificial Intelligence, until an outline of the solid model generated by the ray tracer is identical to the outline of the AP and lateral radiograph of that patient. Change in relative positions of each solid model over time (pelvis acetabular component represents acetabular migration, acetabular component femoral stem represents polyethylene wear, and femoral stem femur represents femoral migration) are recorded. Validation to measure accuracy of the technique has been performed using computer models, and femoral and acetabular prostheses implanted into a cadaver.

Despite significant variations in the position of the pelvis and leg during the obtaining of post-operative radiographs, this new technique was able to measure polyethylene wear and component migration with accuracy similar to that of RSA (0.25 mm in the AP plane).

Further testing and validation is required, but this technique offers promise for the future in being able to retrospectively measure component migration and poly-ethylene wear, using a single CT scan and routine clinical postoperative radiographs.

Cement-less femoral fixation in revision hip arthroplasty offers advantages over cemented femoral revision with evidence of lower rates of both revision and impending prosthesis failure. Intermediate-term data suggests that extensively-coated stems provide reliable fixation by obtaining in-growth and stability in the healthier bone located more distally in the femoral shaft. We report the results of femoral stem revisions performed by a single surgeon at our institution using an extensively-coated, cement-less femoral component.

A retrospective review of notes and radiology was performed on all patients who underwent femoral revision by a single surgeon between January 1994 and March 2004, with a minimum follow up of 24 months. Patients were identified using a dedicated database and the New Zealand National Joint Registry. All patients were operated on using the same technique and received a Solution femoral stem (De Puy, USA). Each patient’s level of function was assessed using the Oxford Hip Score. Radiographic assessment was performed using Engh criteria for fixation and stability of porous coated implants.

67 Solution stems were inserted into 64 patients. Thirty-six patients (52%) were male. Mean age was 70.5 years (47–86). Mean follow up was 57 months (24–145). The most common indication for revision was osteolysis and/or polyethylene wear (75%). There were no failures of the femoral component requiring re-revision. 65 stems (97%) showed definite or suspected bony in-growth on radiographic review. The mean Oxford Hip Score was 27.3 (12–44).

Five cases (7.5%) developed significant complications requiring return to the operating theatre: one deep wound infection, two recurrent dislocations and two loose or mal-positioned acetabular components. The latter four cases required acetabular revision.

Previous reports have shown good results from the use of extensively porous coated cylindrical stems in revision hip arthroplasty. Our results show the Solution stem to be a reliable femoral revision stem with good medium-term results and a low rate of complications.

The purpose of this paper was to assess the incidence of pelvic osteolysis following the use of a one piece all polyethylene titanium plasma spray backed acetabular component a mean of 9.6 years following implantation.

The radiographs of 86 hips followed for a mean of 9.6 years were reviewed. All had primary total hips using a titanium plasma spray backed all polyethylene uncemented acetabular component. Radiographs were assessed for osteolysis in the three zones described by DeLee and Charnley.

There was no osteolysis seen in any cup in any of the zones. There were no loose cups and no obvious cup migration.

This acetabular component shows superior performance compared with all two piece cups in terms of the development of periacetabular osteolysis. The use of two piece cups should be reconsidered.

The management of periprosthetic femoral fractures associated with a total hip arthroplasty remains controversial. The 2003 AAOS Instructional Course Lecture states “Regardless of the method of fixation, the fracture site should be bone grafted with morcellised allograft.” We do not believe bone grafting is necessary to obtain union .

Forty six periprosthetic femoral fractures associated with a total hip were reviewed retrospectively. Follow up included chart and radiographic review, Oxford Hip Score, and SF-12. All fractures were classified acording to the Vancouver classification.

There were 31 type B fractures and 15 type C fractures. All fractures healed. The mean healing time was 15 weeks. No allograft was used. The mean Oxford Hip Score was 26, and the SF-12 33. There were a number of complications, primarily dislocation in the more severe fractures.

The results of this series indicate that bone graft is not necessary to obtain union in periprosthetic femoral fractures. The use of allograft is associated with possible disease and infection transmission and increased cost, risks that we do not believe are justified.

To document the medium term results of the use of a fluted tapered titanium femoral stem in revision total hip arthroplasty.

70 patients undergoing total hip revision using a tapered grit blasted titanium modular stem were reviewed at a mean follow up time of 47 months. No bone graqfts were used. Femoral defects were classified according to Pak and Paprosky and the femoral bone quality was assessed with the Bohm and Bischel system. Clinical function was assessed by the Oxford Hip Score. Radiographic analysis was performed in all cases.

The results of the use of this prosthesis compares favourably with other revision stems. The Oxford Hip Scores compare favourably with the results for revisions recorded in the New Zealand National Joint Register (24.3) Although technically demanding this stem offers a very satisfactory solution for revision of total hips in most circumstances.

Single stage bilateral total knee replacement is an uncommon and often controversial procedure. Some authors have reported significant complications. We have reviewed our experience with the procedure in 40 cases.

Forty patients undergoing simultaneous bilateral total knee replacement with a minimum follow up of two years were reviewed. Thirty of the patients completed an Oxford Knee score and an EQ-5D. Eight patients were lost to follow up. Two were deceased.

The age at the time of surgery ranged from 25–87 years – mean 68yrs. 8o% were done under general anaesthetic. 50% required blood transfusion in the post operative period, the average volume being 4 units. 50% had physiotherapy following discharge. There were 4 patients with delay in wound healing and 1 patient who had an infection requiring wound debridement. There were no other significant complications. The mean Oxford Knee score was 21.6, the mean score for primary unilateral knee arthroplasty for patients on the National Joint Register is 23.5. The EQ-5D scores were very satisfactory.

This study demonstrates that in our unit this procedure can be performed with minimum complications and the expectation of an excellent outcome.

We analysed factors affecting the rate of recovery from ankle fractures. Delays in return to normal functioning may relate to poorer quality and duration of sleep during recovery.

This prospective study investigates the relationship between the rate of recovery from ankle fracture and sleep disturbance, comparing ankle fractures classified using AO-Danis-Weber Classification – types A, B & C treated at Wellington Hospital, aged between 18 and 55 years. From June 2003 to October 2004 participants completed an ankle fracture questionnaire, and a general health profile at three, six and twelve months post-injury. A randomly selected subgroup was interviewed to identify specific recovery issues.

Six percent were Weber A, 56% B and 39%, C. Mean (and standard deviation) for return to normal functioning was; 5 (2); 8 (3) and 8 (7) weeks respectively, overall range – 2 to 24 weeks. Those who returned in 2 weeks had sedentary jobs, worked from home or were students, all with a high level of support by ACC. Physically demanding occupations delayed return to work. After one year, (93%) scored 85 – 90% satisfaction with their ankle performance. 97% scored highly on the SF 36, indicating positive life attitudes. 98% reported no change from their pre-fracture sleep patterns.

Rate of recovery is less predictable and sometimes more prolonged for Weber C than for A and B ankle fractures. Earlier return to work is a function of practical support in the workplace and positive health attitudes including balanced sleep patterns. Work planning and workplace assessment are significant factors.

This study examined the effect of completely disregarding dislocation precautions on the incidence of dislocation, as well as the speed of patient rehabilitation after THJR

Since 1^st March 2005, all uncomplicated primary THJR’s performed by one of the senior authors for OA have been told by their physiotherapist to do what they like, when they like, during the post-operative period. All patients were operated on through a modified direct lateral approach A representative sample of 30 patients were administered a questionnaire at their 6 week postoperative visit.

There were no dislocations. Of those patients in full-time employment, the majority had returned to work by 6 weeks. Most were able to drive between 3 and 4 weeks. Nearly all had regained their pre-operative range of movement and could put on their own shoes and socks. All claimed that being told to disregard dislocation precautions gave them more confidence in their THJR and helped with their achieving a speedy recovery from surgery.

Patients who are judged at the time of surgery to have a stable THJR articulation, benefit form being told to disregard the usual dislocation precautions, and are able to return to work and driving in a more timely manner.

The aim was to investigate whether or not the pre-operative injection of cortico-steroids into the knee influences the infection rate of a subsequent total knee replacement.

This was a case controlled study, in which it was calculated that 152 controls and 38 infected cases would give sufficient power to the study. The infection group had to have had a delay in wound healing or have had a revision for infection.

A total of 32.8% had had an injection at some time pre-operatively. The average number of injections was 2.23, with a range of 1–15. 37% were performed by a G.P., 35% by an orthopaedic surgeon, and 22% by a rheumatologist.79% had the injection within 12 months of surgery. The rate of injection was the same in the two groups. There was no significant difference in the infection rate between the two groups (OR 1.38; 95%CI 0.55–3.31)

Despite recent literature indicating that there is a 10% increase in infection in patients having steroid injections into the hip prior to THR this study does not confirm this risk in patients undergoing TKR.

The aim was to determine how periprosthetic hip and knee infection and subsequent revision impact on patient lifestyle and function. While the literature abounds with studies of outcomes of revision surgery for prosthetic infection, few studies address functional outcome and patient-based outcome measures.

This retrospective study examined a consecutive series of revision total knee and hip arthroplasties performed for infection between 1996 and 2002 by surgeons at Wellington Hospital. Eight knees and ten hips were treated with a two-stage exchange using antibiotic spacer and IV antibiotics. Two knee and seven hip patients underwent direct exchange procedures.

In 90% of knees and 65% of hips Infection was successfully eradicated after one revision. One (10%) knee and eight (47%) hips required further intervention of either surgery or antibiotic therapy. Mean Oxford Scores for knees and hips were 29.6 and 29.5 respectively. Oxford scores following revision for infection were slightly higher compared with scores following the primary procedure, indicating poorer functional outcome. EuroQol-5D responses indicated a lower level of function than that of a general population sample, with problems in the areas of mobility, usual activities, and pain/discomfort, most apparent.

While functional outcome is intrinsically related to both the amount of destruction caused by infection and the eradication of infection, absence of re-revision in itself cannot be equated with functional success. Although TKA/THA revision is a technically challenging orthopaedic procedure, patients do attain favourable results. Surgical revision of a prosthetic joint implant for infection can be associated with reasonable function and satisfaction scores.

To review the results of revision THR performed with a modular titanium tapered uncemented stem in two cohorts of patients to assess whether subsidence of this type of stem is avoidable through improved surgical technique.

The first 70 patients undergoing revision THR with this type of stem were compared with 38 patients who had their revision in the last 24 months and had a minium follow up of 12 months., with particular reference to stem subsidence. All patients were also assessed with the Oxford Hip Score. All radiographs were reviewed to measure subsidence. Identical post-operative management was used in both groups.

The mean subsidence in the first group was 11.7 mm and in the most recent group 4mm. The Oxford Hip Score in both groups was similar (20.9) which compares very favourably with the OHS score from the National joint Register for revision arthroplasty (24.3).

This comparison shows that changes in surgical technique can limit the subsidence seen with tapered stems used in revision total hip replacement. No bone grafts were used in either series, only small changes in bone preparation, and prosthesis selection were used .The outcome as determined by the OHS was similar in both groups.

The aim was to review the data and survival of patients with osteosarcoma in New Zealand from 1994 to 1999 and compare this to data retrieved from a similar review of the data and survival of patients from 1981 to1987.

Data was obtained from the New Zealand cancer registry from 1994–1999 and the raw data was retrieved from the 1981–1987 study.

There were 98 cases in the 1981–1987 cohort and 85 cases in the 1994–1999 cohort. Overall 5 year survival from osteosarcoma improved from 31.6% to 43.5% between the cohorts. The 5 year survival in patients less than 40 years with non metastatic tumours improved from 54.2% to 69.7%. When patients were stratified by age and stage there was a statistically significant improvement in survival between the 2 cohorts

The survival in patients with osteosarcoma in New Zealand has improved over the study period and is similar to that seen in the overseas literature.

To assess if highly cross-linked polyethylene is associated with less linear wear than ultra high molecular weight polyethylene in vivo.

To assess whether alteration in biomechanical characteristics of the reconstructed hip influence’s wear patterns.

A randomised prospective trial comparing conventional polyethylene with highly cross-linked polyethylene in an acetabular component was designed. Identical cemented stems were used in all cases, with a metal head. The polyethylene thickness was controlled. The trial design required 124 cases to be entered to give the study sufficient power to determine any difference in wear rates. Polyware Auto was used to assess 2D wear rate and volume.

This paper presents the preliminary results of the early patients entered into the study and looks at both 2D wear or creep at 18 months post operatively, and seeks to establish any relationships between 2D movement and biomechanical characteristics of the reconstructed hip.

There was no significant difference in the 2D wear (or creep) between the two types of polyethylene at 18 months. There was no correlation between femoral offset, cup offset, or centre of rotation offset and 2D wear (or creep).

This preliminary data shows no difference in the early wear rate of the two types of polyethylene. This is in contrast to an in vitro wear simulator study that has shown more creep in highly cross-linked polyethylene. The significance of this observation is unclear. We hope to demonstrate that as the trial progresses any difference in the performance of the two types of polyethylene should be evident.