At the end of 2018, the NZ Joint Registry introduced a “Surgeon Outlier” policy, whereby each year, if an individual surgeons’ lower 95% confidence interval of their revision rate, measured in revision/100 component years(r/ocys), was above the NZ mean (0.71 r/ocys), that surgeon was required to audit their results with a nominated peer. This study investigates whether outlier surgeons also have high early (1 month and 1 year) revision rates.

In 2018, 236 surgeons performed 9,186 total hip arthroplasties in NZ. At the end of 2018, 11 surgeons received notification they were outliers. Results from all surgeons for years 2016, 2017 and 2018 were combined to form the first (pre-notification) time interval, and results from years 2019, 2020 and 2021 were combined to form the second time interval (post-notification). Outlier surgeons performed 2001 total hip replacements in the first time interval and 1947 hips in the second. Early revision rates (1 month and 1 year) of both outlier and nonoutlier surgeons for both time intervals were analysed.

Non-outlier surgeons had a consistent mean early revision rate of 0.75% at one month and 1.6% at one year for both time intervals. The 11 outlier surgeons had a higher earlier revision rate of 1.35% at one month and 2.45% at one year for the pre-notification time interval. These values reduced for the post-notification time interval to a revision rate of 1.23% for one month and 2.36% for one year.

Poor joint registry results of individual surgeons are often attributed to a poor choice of prosthesis. This study shows early revision rates of outlier surgeons, where prosthesis selection has minimal influence, are also high.

A slight improvement in early revision rates of outlier surgeons since introduction of the policy shows it is working.

The Oxford hip score (OHS) at 6 months and five years of less than 27 has previously been reported as having a 5.2% chance of requiring revision of their total hip arthroplasty (THA) within 2 years. We determined whether the OHS obtained at 10 years after surgery would be a suitable screening tool in lieu of clinic visits to detect patients requiring closer monitoring.

We reviewed data from the NZ Joint Registry between January 1999 and December 2016. OHS at 10 years was available for 5,165 non-revised THA patients. Patients were separated into four categories based on their OHS: 3,483 (67%) scored 42–48, 1,023 (20%) scored 34–41, 373 (7%) scored 27–33, and 286 (5%) scored 0–26.

For patients with a 6-month OHS, revision risk within 2 years was 1.3% in the 42–48 group, 2.5% in the 34–41 group, 4.6% in the 27–33 group, and 10.2 % in the 0–27 group. If only patients with a grading of 33 or less were offered clinical follow-up, 659/5165 patients (12.7%) would require evaluation and of these, 46/659 (7%) could be expected to require revision within two years. Of those patients with an OHS > 34 not evaluated, only a small number, 72/4506 (1.6%), might require a revision.

The OHS at 10 years of patients with a THA who have a grading less than 27 is a much stronger predictor of revision than OHS at 6 months or 5 years. Use of the 10 year OHS as a screening tool for THA requires evaluation of only one in eight patients, with the chance of missing 1 in 63 patients not followed up who might require a revision.

Total hip joint replacement (THJR) for high riding congenital hip dislocation (CDH) is often performed in young patients, and presents unique problems with acetabular cup placement and leg length inequality.

A database and the NZ Joint Registry were used to identify 76 hips in 57 patients with a diagnosis of CDH who underwent THJR in the Wellington region between 1994 and 2015. Records and radiographs of 46 hips in 36 patients classified pre-operatively as Crowe II, III or IV were reviewed. Surgical technique used a direct lateral approach, the uncemented acetabular component was located in the anatomic hip center and a primary femoral stem was used in all but one hip. Whether a step-cut sub-trochanteric femoral osteotomy was performed depended on degree of correction, tension on the sciatic nerve, and restoration of leg length.

For the 36 patients classified as Crowe II or higher, the average age at operation was 44 years (26 – 66), female:male ratio was 4.5:1 and follow-up averaged 10 years (2 – 22.3). Of the 15 hips classified as Crowe IV, 10 required a step-cut sub-trochanteric femoral osteotomy to shorten the femur, but 5 were lengthened without undo tension on the sciatic nerve. Nine Crowe IV hips received a conventional proximally coated tapered primary femoral component. Oxford hip scores for 76% of patients was excellent (> 41/48), and 24% had good scores (34 – 41). All femoral osteotomies healed. Five hips have been revised, one at 2 years for femoral loosening, one at 5 years for dislocation, two at 12 years for liner exchanges, and one at 21 years for femoral loosening.

THJR using primary prostheses for CDH can provide durable long-term results.

Objectives

Our study aimed to examine not only the incidence but also the impact of noise from two types of total hip replacement articulations: ceramic-on-ceramic and ceramic-on-polyethylene.

Objectives

Our study aimed to examine if a mobile-bearing total knee replacement (TKR) offered an advantage over fixed-bearing designs with respect to rates of secondary resurfacing of the patella in knees in which it was initially left unresurfaced.

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.

The aim was to assess the wear rate of highly Cross Linked (X3) polyethylene with the use of 36mm femoral heads in total hip arthroplasty (THA). We have previously reported our early results and raised some concern regarding the potential excessive femoral head penetration rates. These results give the 2 year wear rates following this initial bedding-in phase.

There were 100 consecutive patients who had a THA with the same femoral and acetabular components using a 36mm femoral head and X3 polyethylene that were assessed prospectively. Validated computer software (Polyware) was used to assess linear and 3 dimensional wear using standardised x-rays. Examinations were performed at 2,12,18 and 24 months.

There were 40 hips that had completed the 2 year x-ray examination (average 2.4 years). The mean 2-dimensional linear wear rate was 0.17 mm/yr and the mean volumetric wear rate was 113.73 mm3/yr. Steady state wear was achieved after the 2 month and before the 1 year examination. The steady state wear rate was 0.001mm/yr. There was no difference in wear rate with the different sized cups used and wear rate was independent of liner thickness.

The early high wear rates reported have now settled into a more expected pattern of steady state wear similar to other results presented in literature with the use of smaller femoral heads. Using a 36 mm femoral head has not adversely increased the wear rates compared to smaller head sizes when used in conjunction with X3 polyethylene in the short term for THA. These results suggest that the wear rate of X3 is not compromised even with thinner liners and raise the possibility of safely using even larger head sizes with this polyethylene.

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.

Introduction: We aimed to assess a simple radiological method of predicting redisplacement of paediatric forearm fractures. The Cast Index (CI) is the ratio of sagittal to coronal width from the inside edges of the cast at the fracture site. A CI of > 0.7 was used as the standard in predicting fracture redisplacement. The cast index has previously been validated in an experimental study.

Methods: Case records and radiographs of 1001 children who underwent a manipulation under general anaesthesia for a displaced fracture of the distal forearm were studied. Redisplacement was defined as more than 15 degrees of angulation and/or more than 80 percent of translational displacement on check radiographs at 2 weeks. Angulation (in degrees) and translation displacement (in percentage) were measured on the initial and check radiographs. The CI was measured on postoperative radiographs.

Results: Fracture redisplacement was seen in 107 cases at 2 week follow up. Of the 752 patients (75%) with a CI of less than 0.7 the displacement rate was 5.58%. Of the 249 patients (25%) with a CI greater than 0.7 the redisplacement rate was 26%. The CI was significantly higher in the redisplacement group. No statistically significant difference was seen for age, sex or ethnicity. Nor were statistical differences noted in initial angular deformity, initial displacement and seniority of the surgeon. Good intra and inter observer reproducibility was observed. There was no statistical difference in patients with a cast index between 0.7 and 0.8.

Conclusion: The cast index is a simple and reliable radiographic measurement to predict the redisplacement of forearm fractures in children. Previous studies have used a CI of > 0.7 as the predictor of redisplacement although this study suggests a plaster with a CI of < 0.81 is acceptable. A high cast index is associated with redisplacement of fractures and should therefore be considered when moulding casts in distal forearm fractures.

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.

Polyethylene wear and osteolysis continue to be associated with failure of total hip arthroplasty. The advent of highly cross linked polyethylene may potentially reduce such wear.

The aim of this study was to compare the rate of wear of acetabular polyethylene using conventional cross linked versus highly cross linked polyethylene.

From June 2001 to September 2003, 119 patients were followed prospectively for up to five years on an annual basis in a double blinded, randomised trial. The mean age of patients was 59 years (range 48 to 75 yrs). The radiographs have been analyzed using previously validated measurement software to assess linear, three dimensional and volumetric wear.

The five year results show significantly reduced wear rates for highly cross linked polyethylene compared to conventional polyethylene. There was no statistically significant difference between groups with respect to age, sex, operative side, surgeon, cup abduction angle, cup anteversion or size of cup.

The reduction in wear shown after five years with the highly cross linked polyethylene is highly encouraging and is consistent with in vitro wear simulator testing. This may reduce failure of total hip arthroplasties due to wear and osteolysis over the medium to long term.

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.

The early results with highly cross-linked polyethylene have been encouraging and have increased the ability to use larger head diameters to improve the range of motion and decrease the dislocation rate, the commonest cause of early complications following total hip arthroplasty (THA). Wear rates with 32 mls heads have been satisfactory however there have been very few independent studies looking at early polyethylene wear in 36 mm heads. This study assessed the rate of polyethylene wear of a 36mm ceramic femoral head and a highly cross-linked polyethylene (X3 Stryker) liner in THA.

This prospective study reviewed 100 consecutive THAs in young patients (mean age 58 years) who had undergone THA with the same 36mm ceramic femoral head and highly cross linked polyethylene liner. All patients received the same femoral stem (ABG, Stryker) and acetabular cup (Trident, Stryker). Two surgeons performed all procedures. Patients were assessed radiologically immediately postoperatively, at 10 weeks and at one year. Validated computer software (Polyware) was used to assess both volumetric and linear wear.

At one year the mean two-dimensional linear wear rate was 0.51 mm/yr. Mean three-dimensional linear vector wear rate was 0.59 mls per year with a mean volumetric wear rate of 322.6 mms per three years. Cup size ranged from 52–62 mms and the correlation coefficient between cup size and three-dimensional linear wear rate was −0.100. The correlation coefficient between cup size and volumetric wear rate was −0.009 confirming no significant correlation between cup size and wear.

Larger size femoral heads are associated with a higher volumetric wear compared to linear wear rate when using conventional polyethylene. This study demonstrated much higher early linear wear rates compared to other studies using 28 and 32 mms heads. This higher rate may be associated with the creep phenomenon and early bedding-in in the early stages after a THA and although this is of concern these results should be interpreted with caution.

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.

The treatment of supracondylar humeral fractures in children continues to evolve. The currently fashionable treatment for displaced fractures is closed reduction and the insertion of at least two K-wires. This usually requires the patient to have a second surgery to remove the K-wires, and may result in significant scarring. The senior author has used the straight arm method to treat displaced supracondylar fractures. We have reviewed the long term results of seven children treated by the straight arm method. No patient had a scar, no patient had a cubitus varus and all children regained a full range of movement. This method offers excellent results with no risk of iatrogenic nerve injury, scarring, or second surgery.

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.