This study aimed to examine the changing trends in the causes for early revision of total hip replacements (THR) in one country over fifteen years to assess whether changes in arthroplasty practices have changed revision patterns.

The cause for revision within one year was extracted from the New Zealand Joint Registry for the period of January 1999 to December 2013. The results were grouped into three periods of 5 years (Period 1=1999–2003, Period 2=2004–2008 and Period 3 = 2009–2013). The causes were compared across the three periods and were adjusted for age, gender and ASA grade.

The rate of early revisions (within one year) rose from 0.86% to 1.30% per year. There was significant rise in revision for deep infection (14% increased to 21% of all causes, p<0.001) and femoral fracture (5% increased to20%, p<0.001), whereas revision for dislocation decreased (55% decreased to 35%, p<0.001). Adjusting for age and gender femoral fracture and deep infection rates remained significant for both (p<0.05). Adjusting for age, gender as well as ASA only remained significant for infection (P<0.05).

The reduction in revision for dislocation followed the registry trend for the use of larger femoral heads and cross linked polyethylene. The rise in early periprosthetic femoral fracture rates was directly associated (p<0.001) with the increased use of uncemented femoral prostheses. The worrying increase in infection rate was unexplained on the basis of registry data alone. It was related to ASA grade but the overall ratios of ASA grades remained consistent over the 15 years.

Method.

We prospectively investigated the radiological outcomes of the uncemented Oxford medial compartment arthroplasty in 231 consecutive patients performed in a single centre with a minimum two year follow up.

There has been recent interest in the treatment of Dupuytren's disease by minimally invasive techniques such as needle fasciotomy and collagenase injection, but only few studies have reported the outcomes following open fasciotomy. This study attempts to address this gap, with a retrospective analysis of a large series of patients who underwent an open fasciotomy by a single surgeon over a five-year period. The aim of the study was to determine the requirement for re-operation in the cohort and to analyse the revisionary procedures performed.

Theatre coding data was used to identify a consecutive series of patients who underwent open fasciotomy over a five-year period between 2000 and 2005. Within this group medical records were obtained for those patients who underwent a secondary procedure for recurrence. All procedures were carried out by a single surgeon in a regional hand unit using an unmodified open technique.

A total of 1077 patients underwent open fasciotomy for Dupuytren's disease. Of these, 865 (80.3%) were male and 212 (19.7%) were female. The mean age at initial surgery was 64.4 years (range 21.7 to 93.7 years) for males and 68.3 (range 43.6 to 89.8 years) for females. Of the 1077 patients who underwent open fasciotomy, 143 patients (13.3%) subsequently underwent a second procedure for recurrence.

The medical records were available for 97 patients. The median time to re-operation in this group of patients was 42.0 months (95% CI, 8.3 to 98.0 months). The most common revision procedure being dermofasciectomy (54.2%), followed by fasciectomy (32.6%) and re-do open fasciotomy (13.2%). Mean pre-operative total extension deficit was 88 degrees (range 30–180 degrees) with intra-operative correction to a mean of 9.5 degrees (range 0–45 degrees).

There is no standard definition for recurrence after Dupuytren's surgery. We have looked at the rate of revision surgery after open fasciotomy, in a relatively fixed population serviced over a 5-year period by a single hand surgeon. A low re-operation rate has been identified, with good intra-operative correction achieved by secondary surgery.

Tibiotalocalcaneal (TTC) arthrodesis using a retrograde nail is a common salvage procedure for a range of indications. Previous work has suggested subtalar joint preparation is unnecessary to achieve satisfactory results. We examine the incidence of symptomatic subtalar nonunion following tibiotalocalcaneal fusion in a series of patients, all of whom had full preparation of the subtalar joint, and consider the possible contributing factors.

We performed a retrospective review of all patients who underwent TTC arthrodesis from 2004–2010. All fusions were performed by the same surgeon with full preparation of both tibiotalar and subtalar joints.

61 TTC arthrodeses were performed in 55 patients (mean age = 59 years) using an intramedullary retrograde nail. Mean follow-up was 18 months (6–48 months). Fifty-six ankles (92%) achieved satisfactory union. Five patients (8%) had symptomatic non-union: 4 patients of the subtalar joint - with 3 patients undergoing revision subtalar arthrodesis and 1 patient of the tibiotalar joint. Nine patients required removal of the calcaneal screw (16%) – all had evidence of isolated subtalar nonunion prior to metalwork failure. Eight of these patients achieved asymptomatic union following screw removal.

Subtalar nonunion following TTC fusion has resulted in recent changes to nail design to increase stability across the subtalar joint. Our results demonstrate a favourable overall nonunion rate with isolated subtalar nonunion making up the majority of cases. We also observed a significant rate of distal screw loosening, also associated with subtalar nonunion prior to screw removal, the significance of which merits further investigation.

Despite a large body of literature the optimal choice of bearing surface for total hip arthoplasty (THA) remains controversial. To avoid the brittleness and squeaking noted with ceramic-on-ceramic and the metal ion release associated with metal-on-metal (MOM) articulations, a novel hybrid coupling of ceramic-on-metal (COM) has been introduced. The purpose of this study was to compare changes in serum metal ion levels and the functional performance of COM and MOM bearing combinations.

Eighty-six patients (86 hips) undergoing THA between April 2009 and October 2010 were randomized to COM or MOM bearing couplings. All received identical uncemented acetabular shells and femoral components from two experienced surgeons using the same operative technique.

Demographic and peri-operative data were recorded. Serum cobalt and chromium levels, renal function and disease specific outcome scores (Oxford Hip, Harris Hip, UCLA activity) were assessed at baseline, 6 and 12 months post-operatively. Patients and outcome assessors remained blinded.

Mean age of the total cohort was 62.5 years. Randomization successfully matched groups for age, Body Mass Index, baseline serum Cobalt and Chromium levels, and pre-operative functional performance scores. One-year data is currently available for 25 of 44 COM and 26 of 42 MOM patients. No significant difference in serum cobalt (P value = 0.81) and chromium (P value = 0.66) levels between groups was noted. Improvements in outcome scores (Oxford Hip, Harris Hip, UCLA activity) were equivalent (P values 0.16 – 0.46).

At 1-year, COM and MOM hip arthroplasty articulations appear equivalent in terms of function and serum metal ion levels. Data collection out to 5-years post-surgery continues.

There has been limited research examining the effect training of orthopaedic trainees may have on patient outcomes. This paper aims to determine if there is a difference in revision rate and functional outcomes of total hip joint replacement performed by consultants compared to those performed by supervised and unsupervised trainees.

We reviewed all patient data since 2000 from the New Zealand National Joint Registry in patients undergoing total hip joint replacement (THJR) comparing the outcomes with the experience of the primary surgeon. The outcome measures were revision hip replacement and the Oxford Hip score at six months. We compared the reason for revision controlling for factors such as ASA, age and the index diagnosis. We also compared the six-month Oxford scores with the experience of the primary surgeon.

There were 35415 patients who underwent elective THJR, 30344 of which were performed by a consultant, 2982 by a supervised registrar and 1067 by an unsupervised registrar. There was an overall revision rate (RR) of 0.77 per 100 component years. The RR was 0.75 (95% CI 0.67–0.82) for consultants, 0.97 (95% CI 0.72 – 1.28) for supervised trainees and 0.70 (95% CI 0.36 – 1.22) for unsupervised trainees. There was no significant difference in revision rates between consultants and supervised trainees (p<0.077) or unsupervised trainees (p< 0.30). The most common cause for revision surgery was dislocation, occurring in 39% of cases. This was more common in supervised and unsupervised trainees (48% and 50%) however there was no significant difference between the three groups (p-value 0.24). The other causes for revision were; loosening of the acetabular or femoral component, deep infection, pain and fracture with no significant difference between the three groups. The mean OHS was higher for consultants at 40.7 compared to 38.95 and 38.23 for supervised and unsupervised trainees respectively (p <0.001)

The results of this study show no significant difference in the revision rate of THJR performed by trainees when compared to their consultants. Orthopaedic consultants do appear to have slightly better (1–2 points) OHS. These results are reassuring and show orthopaedic training does not adversely compromise patient outcomes.

Cell-scaffold based cartilage tissue engineering strategies provide the potential to restore long-term function to damaged articular cartilage. A major hurdle in such strategies is the adequate (uniform and sufficient) population of porous 3D scaffolds with cells, but more importantly, the generation of engineered tissue of sufficient quality of clinically relevant size. We describe a novel approach to engineer cartilage grafts using pre-differentiated micro-mass cartilage pellets, integrated into specifically designed 3D plotted scaffolds.

Expanded (P2) human nasal chondrocytes (HNCs) or bone marrow-derived mesenchymal stem cells (MSCs) from 3 donors (age 47–62 years) were micro-mass cell pellet cultivated at 5 × 105 cells/pellet for 4 days. Subsequently, pellets were integrated into degradable 3D Printed polymer (PEGT/PBT) scaffolds with 1mm fibre spacing. Constructs were cultured dynamically in spinner flasks for a total of 21 days. As a pellet-free control, expanded HNCs were spinner flask seeded into PEGT/PBT fibre plotted scaffolds. Constructs were assessed via histology (Safranin-O staining), biochemistry (glycosaminoglycan (GAG) and DNA content) and collagen type I and II mRNA expression.

After 4 days, micro-mass cultured pellets could be successfully integrated into the fibre plotted scaffolds. DNA content of pellet integrated constructs was 4.0-fold±1.3 higher compared to single seeded constructs. At day 21, cartilage tissue was uniformly distributed throughout pellet integrated scaffolds, with minimal cell necrosis observed within the core. GAG/DNA and collagen type II mRNA expression were significantly higher (2.5-fold±0.5 and 3.1-fold±0.4 respectively) in pellet versus single cell seeded constructs. Furthermore, compared to single cell, the pellet seeded constructs contained significantly more total GAG and DNA (1.6-fold±0.1 and 3.1-fold±1.0 respectively).

We developed a novel 3D tissue assembly approach for cartilage tissue engineering which significantly improved the seeding efficiency (∼100%), as well as tissue uniformity and integrity compared to more traditional seeding approaches using single cell suspensions. Furthermore, the integration of micro-mass cell pellets into 3D plotted PEGT/PBT scaffolds significantly improved the amount and quality of tissue engineered cartilage.

Bone mineral density (BMD) and bone mineral content (BMC) have not been previously assessed in unicompartmental knee replacement (UKR). We studied the early bone changes beneath the uncemented Oxford medial UKR. Our hypothesis was that this implant should decrease the shear stresses across the bone-implant interface and result in improved BMD and BMC beneath the tibial component.

Using the Lunar iDXA and knee specific software we developed 7 regions of interest (ROI) in the proximal tibia and assessed 38 patients with an uncemented Oxford UKR at 2 years. We measured the replaced knee and contralateral unreplaced knee using the same ROI and compared the BMD and BMC. The initial precision study in 20 patients demonstrated high precision in all areas.

There were 12 males and 16 females with an average age of 65.8 years (46–84 years). ROI 1 and 2 were beneath the tibial tray and had significantly less BMC (p=0.023 and 0.001) and BMD (p=0.012 and 0.002). ROI 3 was the lateral tibial plateau and this area also had significantly less BMC (p=0.007) and BMD (p=0.0001). ROI 4 and 5 immediately below the tibial keel had no significant change. These changes were independent of gender and age.

These results were surprising in that the universal loss of BMC and BMD suggested that bone loading of the proximal tibia was not improved even after a UKR. The better BMD and BMC adjacent to the keel confirms other studies that show improved bone in-growth around keels and pegs in the uncemented tibial component. A prospective longitudinal study has been developed to compare BMD and BMC changes over time to see whether these changes are dynamic.

C-type natriuretic peptide is the most abundant natriuretic peptide in the central nervous system. It has been implicated in neurogenesis and may have a significant role in spinal regeneration. We postulated that the spinal concentration of CNP would be reflected in the plasma concentrations of both CNP and the pro-hormone (NTproCNP) and this may be an indicator of repair potential in spinal injuries.

Concurrent plasma and CSF concentrations of CNP forms were measured in 51 subjects undergoing spinal anaesthesia for elective total hip and knee replacement. Associations with CNP activity and metabolism in CSF were sought by measuring CSF levels of cGMP and neprilysin respectively.

Elevated concentrations of NTproCNP (1045±359 pmol/L) were found in CSF and greatly exceeded those of CNP (7.9±3.2 pmol/L). The ratio of NTproCNP to CNP in CSF (145±55) was much higher than in plasma (31±27). A significant inverse relation was found between plasma and CSF CNP concentrations (r=−0.29, p<0.05). cGMP and neprilysin were unrelated to CNP levels in CSF

Despite markedly elevated levels of NTproCNP in CSF, it is unlikely that these contribute to systemic levels in healthy adults. Identifying NTproCNP as the dominant CNP form in CSF opens up the possibility of its use in future studies exploring CNP regulation within the CNS and possible applications in diagnosis and monitoring of healing in patients with spinal cord injury.

Determine if debridement, rather than staged revision is a more effective strategy in some patient subgroups with infected arthroplasty

We compiled a database comprising 154 proven infected knee replacements and 144 infected hip replacements in Christchurch over the last 10 years. This has given us the largest series in the literature. Cross referencing this database with the joint registry enabled us to compare the treatment of both acute and chronic infection in hip and knee arthroplasty with regard to both functional outcome and re-revision rate.

Patients treated with debridement had no statistically significant difference in re-revision rate or functional score when compared with patients undergoing staged revision.

Orthopaedic surgeons justifiably aim to eradicate infection in arthroplasty patients. A prosthesis retaining management strategy may be justifiable, especially in certain patient groups in whom multiple operations are best avoided.

Assessing the efficacy of cervical orthoses in restricting spinal motion has historically proved challenging due to a poor understanding of spinal kinematics and the difficulty in accurately measuring spinal motion. This study is the first to use an 8 camera optoelectronic, passive marker, motion analysis system with a novel marker protocol to compare the effectiveness of the Aspen, Aspen Vista, Philadelphia, Miami-J and Miami-J Advanced collars. Restriction of cervical spine motion was assessed for physiological and functional range of motion (ROM).

Nineteen healthy volunteers (12 female, 7 male) were fitted with collars by an approved physiotherapist. ProReflex (Qualisys, Sweden) infra-red cameras were used to track the movement of retro-reflective marker clusters attached to the head and trunk. 3-D kinematic data was collected from uncollared and collared subjects during forward flexion, extension, lateral bending and axial rotation for physiological ROM and during five activities of daily living (ADLs). ROM in the three clinical planes was analysed using the Qualisys Track Manager (Qualisys, Sweden) 6 Degree of Freedom calculation to determine head orientation relative to the trunk.

For physiological ROM, the Aspen and Philadelphia were more effective at restricting flexion/extension than the Vista (p<0.001), Miami-J (p<0.001 and p<0.01) and Miami-J Advanced (p<0.01 and p<0.05). The Aspen was more effective at restricting rotation compared to the Vista (p<0.001) and Miami-J (p<0.05). The Vista was least effective at restricting lateral bending (p<0.001). Through functional ROM, the Vista was less effective than the Aspen (p<0.001) and other collars (p<0.01) at restricting flexion/extension. The Aspen and Miami-J Advanced were more effective at restricting rotation than the Vista (p<0.01 and p<0.05) and Miami-J (p<0.05). All the collars were comparable when restricting lateral bending.

The Aspen is superior to, and the Aspen Vista inferior to, the other collars at restricting cervical spine motion through physiological ROM. Functional ROM observed during ADLs are less than those observed through physiological ROM. The Aspen Vista is inferior to the other collars at restricting motion through functional ROM. The Aspen collar again performs well, particularly at restricting rotation, but is otherwise comparable to the other collars at restricting motion through functional ranges.

Objective

To compare the effectiveness of the Aspen, Aspen Vista, Philadelphia, Miami-J and Miami-J Advanced collars at restricting cervical spine movement in the sagittal, coronal and axial planes.

The purpose of this study was to investigate the surgical options for unicompartmental osteoarthritis (OA) in younger patients by comparing the survivorship and functional results of Total Knee Replacement (TKR) following osteotomy with the results for both primary TKR and revision of Unicompartmental Knee Replacement (UKR) to a TKR, and thereby recommend the most appropriate index procedure for this group of patients.

We reviewed the revision rate and functional outcome of all patients who had a total knee replacement (TKR) following an osteotomy or Unicompartmental Knee Replacement (UKR) on the New Zealand Joint Registry. We used this data to compare the results to primary TKR scores, including comparison of age-matched subgroups.

There were 711 patients who had undergone TKR as salvage for a failed osteotomy with a revision rate of 1.33 revisions per 100 component years and a mean Oxford knee score (OKS) of 36.9. 205 patients had failed UKR converted to TKR with a revision rate of 1.97 revisions per 100 component years and a mean OKS of 29.1. The revision scores of TKR for both failed osteotomy and failed UKR were significantly poorer than following primary TKR (p← 0.05). The mean OKS following revision of a UKR was significantly poorer than both primary TKR (p←0.001) and TKR for a failed osteotomy (p←0.001). There was no significant difference in mean OKS between primary TKR and TKR for a failed osteotomy, even amongst patients younger than 65 years (p=0.8).

This study has shown that if a surgeon is choosing between an osteotomy and a UKR in the younger patient than the better for any subsequent revision procedure will be achieved with an osteotomy. Revision of a failed osteotomy to a TKR has improved functional results compared to revision of a failed UKR. However, both yield poor survivorship rate compared to primary TKR.

We prospectively reviewed patients who had undergone a Revision Total Knee Replacement (TKR) to a mobile-bearing arthroplasty. We wanted to assess functional outcome and survival, and to determine whether the perceived advantages of a mobile-bearing arthroplasty could be expanded to the revision situation.

We divided the patients into two groups. Group 1 consisted of 40 patients who were revised to a rotating platform, with or without stems and augments, and group 2 consisted of 41 patients revised to a varus-valgus constrained mobile-bearing device that still allowed rotation of the bearing. All were assessed with Knee Society Knee Scores, WOMAC, and New Jersey Knee Scores and standard radiographs by an independent examiner.

Group 1 had an average age of 71 years at revision and a follow-up of 5–9 years. Seventy-six percent had excellent or good results with 89% survival at 9 years. Group 2 had an average age of 71 years at revision and a follow-up of 2–5 years. The patient satisfaction score was 8/10 and the normality score was 6.8/10. There was only one case of instability in both groups in a patient with a patellar fracture.

A mobile-bearing TKR can be used in the revision situation with acceptable clinical results and patient outcome without compromising the stability or survivorship in the short-term. It has proved to be a “patellar-friendly” procedure with reduced re-operation for patellar complications; however longer-term studies are required to determine whether the rates of polyethylene wear are reduced by the use of a more congruent articulation.

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.

Replacement of damaged or diseased tissues with permanent metal implants based on stainless steel, cobalt chrome and titanium alloys has been at the forefront of classical biomaterials research and the orthopaedic medical device industry for decades. Biodegradable polymers have also reached the market but often have limited capacity in load bearing orthopaedic applications due to their low stiffness and poor mechanical properties. The development of biodegradable metals based on magnesium (Mg) could be heralded as a major breakthrough in the field of orthopaedic surgery. Degradable implants eliminate the time and cost associated with a secondary surgery to remove hardware, and reduces the period the implant is exposed to instability, fibrous encapsulation, stress shielding and inflammation. The metabolism of Mg and its excretion via the kidneys is a natural physiological process that is well understood, however, controlling the rapid degradation of Mg biomaterials in vivo is a major challenge yet to be resolved for the safe and effective use of Mg in orthopaedic implants.

In this study, we describe a novel manufacturing method for fabricating Mg/Mg alloy implants, as well as the development of an in vitro method for screening Mg/Mg alloy degradation rate by considering both their electrochemical corrosion behaviour and biological characteristics.

A range of Mg alloys with varying amounts of calcium (0.8–28%) and zinc (3–10%) were cast and then machined into Ø4mm and 15mm discs for biocompatibility (HETCAM) and parallel in vitro testing. Alloys were placed in various simulated body fluid (SBF) solutions in vitro (7–28 days) to determine effect of alloy composition on degradation rate. These potentiostatic and potentiodynamic tests were designed to simulate, to varying degrees, the in vivo environment, with the crucial factors (e.g. temperature, pH, serum proteins, CO2 level) controlled to ensure consistency across the test methods. The mechanisms of corrosion on the Mg/Mg alloy microstructure and the effect of protein adsorption all played key roles in dictating the corrosion of alloys in vitro. Specifically the inclusion of physiological levels of serum proteins decreased the corrosion rate up to 600% over more standard SBF solutions described in literature.

This work provides an improved understanding of the effects of corrosion variables on Mg alloys, while making major steps towards deciding the most appropriate screening tests for new alloys for their use as a biomedical material prior to moving to in vivo animal studies.

The aim of this study was to examine the results of medial opening wedge high tibial osteotomies in which TRISOITE (hydroxyapatite tricalcium phosphate composite) wedges have been used as bone graft substitute and to compare the histological results with the clinical outcome.

There were 36 medial opening wedge high tibial osteotomy performed in 33 patients with a mean age of 45 years. Medial compartment osteoarthritis with varus alignment was the indication in 32 patients. All were followed to union with a minimum follow up of 6 months (average 50 months).

The surgical technique involved creating an oblique upper tibial osteotomy at an angle of 60 degrees from distal-medial to proximal lateral, passing distal to the insertion of the patellar ligament and preserving the lateral cortex. The osteotomy was opened to the desired angle of correction and preformed Triosite wedges were inserted. Stabilisation was obtained with a contoured titanium T-plate (ENZTEC). Re-operation was required for metal removal or conversion to total knee replacement in 10 cases. All of these patients had a biopsy of the osteotomy site.

The clinical notes and x-rays were retrospectively reviewed. One patient developed a superficial infection post-operatively which was successfully treated with intravenous antibiotics. Bone grafting was required to achieve union in 1 case (2.8%). There were no cases of varus deformity recurrence as a result of graft collapse. Biopsies provided microscopic evidence of bony incorporation around the tricalcium phosphate with bone healing. Three patients were converted to total knee replacement with no problems at the osteotomy site.

Triosite wedges appear to be a reliable synthetic bone graft substitute to act as a scaffold for bone healing in opening wedge osteotomies. They reduce the morbidity associated with iliac crest bone graft.

This study reviewed the revision rate of fully cemented, hybrid and cementless primary total knee replacements (TKR) registered in the New Zealand Joint Registry from 1999 to May 2008 to determine whether there was any significant difference in the survival and reason for revision with these different types of fixation.

The percentage rate of revision was calculated per 100 person years (HPY) and compared to the reason for revision, type of fixation and the patient’s age.

Of the 28707 primary TKR registered, 522 underwent revision procedures requiring change of at least one component with a survival rate of 0.44 HPY (1.8%). The majority of revisions were for pain (153) followed by deep infection (133) followed by loosening of the tibial component (98). Overall the rate of tibial loosening was 0.07 HPY (0.3 %) in the cemented group vs 0.25 HPY (1%) in the cementless group (p < 0.001). There was no significant difference in the type of fixation used for the femoral component, but there was a significant difference in the different types of fixation when revised for pain, with the uncemented tibia performing the poorest. There was no significantly difference in the younger patient (< 55 years) with respect to tibial loosening (p=0.92).

Failure of the uncemented total knee replacement was due to pain and tibial loosening although the results in patients under 55 years were similar in all fixation groups. There was no difference in the fixation method of the femoral component.

To ascertain whether there is any relationship between the Oxford 12 scores gained six months post surgery and early revision for primary hip and knee arthroplasty.

The six month post surgery Oxford 12 scores were retrieved from the National Joint Registry (NJR) for the seven year period ending 31^st December 2006. These were analysed in relation to revision of primary hip and knee procedures using three methods of statistical analysis; logistic regression, receiver operating characteristic (ROC) curve and direct plotting of groups of scores against the proportion of hips revised for that same group.

Logistic regression: For every one unit increase in the Oxford score there was an 11% increased risk of revision (hips) and 12% (knees) within the first two years of surgery, 5 and 6% respectively between two and four years and 3 and 4% risk respectively between four and six years (p> 0.001).

The ROC Curve Analysis: demonstrated that a patient with a score greater than 20 (hips) or 28.5 (knees) or 24 (uni knees) has eight times the risk of needing a revision within two years compared to a person with a score equal or less than the above numbers. Alternatively the ROC analysis predicted 73% of the revisions within three years for all three arthroplasty groups.

Plotting Scores Against Revisions: Plotting scores in groups of five demonstrated an incremental increase in the risk during the first two years. A person with a score greater than 40 has; for hips 24 times, knees 27 times and uni knees 69 times the risk of a revision within two years compared to a person with a score between 16 and 20.

Monitoring of the six month post surgical Oxford 12 score is another tool in the surgeon’s armamentarium for deciding which patients need closer monitoring following arthroplasty surgery.

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.