The 45-year evolution of the Mathys RM monoblock cups: have the paradigm shifts been worthwhile?

INTRODUCTION: The Robert Mathys (RM) monoblock uncemented cup is a design less commonly used in primary total hip replacement. It's purported advantages over modular cemented cups are: (1) its modulus of elasticity approximating bone, thus mimicking load transmission and the biomechanical behaviour of the cup to better match stresses on the acetabulum, leading to bone-preservation; and (2) as a 1-piece cup there is absence of a mobile interface between a liner and shell, preventing backside wear. Since its inception in 1983 there have been 3 major design changes: the RM Classic, the RM Pressfit, and the RM Vitamys with the most modern polyethylene (vitamin E). METHODS: In a retrospective cohort study of the New Zealand Joint Registry, all designs of RM acetabular cup were reviewed. Data were included from1998 to 2018. All-cause revision rates, reasons for revision and the Oxford Hip Score (OHS) were assessed. RESULTS: In total 13,272 acetabular cups were included. The all-cause revision rates did not differ between the designs. Revision rates for aseptic loosening in the RM Vitamys were lower, but the follow-up was shorter and more larger heads were used. There was no difference in the OHS. CONCLUSION: All implant designs were safe. The use of larger heads led to a decrease in revisions due to dislocation. It has to be waited out whether the RM Vitamys performs superior in the long-term due to the highly cross-linked polyethylene.

How do 3D-printed primary uncemented acetabular components compare with established uncemented acetabular cups? The experience of the New Zealand National Joint Registry.

BACKGROUND: 3D-printed or additive manufactured acetabular implants are an exciting new technology being used in hip surgery with increasing frequency especially in complex acetabular reconstructions. However, the performance of acetabular components produced by this method for primary THR is unknown. METHODS: 41,272 uncemented cups in primary THR for OA were identified in the NZJR for the purposed of this study. There were 39,080 uncemented cups in the control group (15,798 Pinnacle cups, 12,724 Trident cups and 10,558 RM Pressfit cups) compared to 2192 3D-printed uncemented implants (1397 Delta TT cups, 640 Ti Por and 155 Polymax cups). All-cause revision rates and reasons for revision were examined. Kaplan-Meier survival analysis was performed. RESULTS: 3D-printed cups were inserted into younger, fitter patients with a higher mean BMI compared to those in the control group (p < 0.001). The overall all-cause revision rate for 3D-printed cups was not significantly different to the controls: 0.77/100 cys (95% CI 0.59-1) compared to 0.55/100 cys (95% CI 0.52-0.58) in the control group (p = 0.058, Hazards ratio 1.29, 95% CI 0.992-1.678). There was no difference in aseptic cup loosening or deep infection rates between either group or indeed individual implant designs. CONCLUSIONS: 3D-printed uncemented cups provide reliable survivorship and clinical results in primary THR comparable to established designs manufactured by traditional means. The theoretical concerns of increased rates of fatigue failure or deep infection are unsubstantiated.

Does surgical approach affect early outcomes following primary total hip replacement in obese patients?

AIM: The aim of this study was to assess whether obese patients undergoing primary total hip replacement (THR) via a posterior approach had superior revision rates and Oxford Hip Scores (OHS) compared to those via a lateral approach. PATIENTS AND METHODS: This is a retrospective cohort study using prospective data from the New Zealand Joint Registry applying STROBE and RECORD guidelines. Patients undergoing THR since 2010 were stratified by body mass index (BMI) into obese (BMI 30-39 kg/m2), and morbidly obese (BMI ⩾40 kg/m2) groups. All-cause revision rates, and 6-month OHS post-surgery were compared between groups. Multivariate analysis was performed. RESULTS: 12,109 unilateral THRs in obese patients were identified. The mean follow-up was 2.8 years (range 0.01-6.95 years). Univariate analysis in the BMI ⩾ 40 group showed the posterior approach had a significantly lower all-cause revision rate (0.99/100 observed component years (ocys); 95% CI, 0.65-1.44/100 ocys) than the lateral approach (1.71/100 ocys (95% CI, 0.98-2.77/100 ocys), p < 0.05). There was no significant difference in dislocation rates between the surgical approaches. OHS was statistically higher in the posterior approach group in BMI 30-39 patients (p < 0.001) but not clinically significant. Multivariate analysis showed femoral head size significantly influenced all-cause revision rates and mitigated against the increased risk associated with the surgical approach. CONCLUSION: The choice of surgical approach in obese patients conveys no advantage in overall revision rates in the short-term. Choosing an appropriate size of femoral head may be of greater importance than choice of surgical approach for obese patients in primary THR.

Outcomes following primary total hip arthroplasty with pre-existing spinal fusion surgery.

AIMS: There is inconsistent evidence on whether prior spinal fusion surgery adversely impacts outcomes following total hip arthroplasty (THA). We conducted a systematic review and meta-analysis to assess the association between pre-existing spinal fusion surgery and the rate of complications following primary THA. METHODS: We searched MEDLINE, Embase, Web of Science, and Cochrane Library up to October 2019 for randomized controlled trials (RCTs) and observational studies comparing outcomes of dislocation, revision, or reasons for revision in patients following primary THA with or without pre-existing spinal fusion surgery. Furthermore, we compared short (two or less levels) or long (three or more levels) spinal fusions to no fusion. Summary measures of association were relative risks (RRs) (with 95% confidence intervals (CIs)). RESULTS: We identified ten articles corresponding to nine unique observational studies comprising of 1,992,366 primary THAs. No RCTs were identified. There were 32,945 cases of spinal fusion and 1,752,362 non-cases. Comparing prior spinal fusion versus no spinal fusion in primary THA, RRs (95% CI) for dislocation was 2.23 (1.81 to 2.74; seven studies), revision 2.14 (1.63 to 2.83; five studies), periprosthetic joint infection 1.71 (1.53 to 1.92; four studies), periprosthetic fracture 1.52 (1.28 to 1.81; three studies), aseptic loosening 1.76 (1.54 to 2.01; three studies), and any complications 2.82 (1.37 to 5.80; three studies) were identified. Both short and long spinal fusions, when compared with no fusion, were associated dislocation, revision, or reasons for revision. CONCLUSIONS: Patients with prior spinal fusion are at risk of adverse events following primary THA. Measures that reduce the risk of these complications should be considered in this high-risk population when undergoing primary THA. These patients should also be counselled appropriately around their risks of undergoing THA. Cite this article: Bone Joint J 2020;102-B(6):664-670.

How do cemented short Exeter stems perform compared with standard-length Exeter stems? The experience of the New Zealand National Joint Registry.

BACKGROUND: The standard Exeter (Stryker) cemented stem is 150 mm long with standard offsets ranging from 37.5 mm to 56 mm. Exeter short stems of 125 mm are also available in the offsets of 37.5 mm, 44 mm, and 50 mm. In addition, smaller (125 mm or shorter) Exeter cemented stems with offsets of 35.5 mm or less are available. The aim of this study was to examine the New Zealand Joint Registry (NZJR) comparing medium-term survival rates and functional outcomes of standard-length stems with Exeter short stems of various offsets in patients undergoing primary total hip replacement. METHODS: Using the NZJR, we compared the results of 3 separate groups of patients with Exeter stems. Patients with standard 150 mm length Exeter stems (Standard) were compared with patients with Exeter 125 mm stems with regular 37.5 mm, 44 mm, and 50 mm offsets (Short 37+) and Exeter 125 mm stems with offsets of 35.5 mm and below (Short 37-). Demographic data, preoperative diagnosis, patient-reported outcome measures, and reasons for revision were compared between groups. Kaplan-Meier survival analysis and Cox multivariate regression analysis were used to examine implant survival and the influence of stem group on revision rates adjusting for gender, age, diagnosis, and surgical approach. RESULTS: There were 43,427 Exeter cemented stems in the NZJR between January 1, 1999 and 31, May 2018; 41,629 Standard, 657 Short 37+, and 1501 Short 37-. In all 3 groups, the posterior surgical approach was preferred (Standard, 76.1%; Short 37+, 94.6%; Short 37-, 76.6%; P < .001). In the Short 37- group, 94.1% were female, while in the other 2 groups, there was an equal gender ratio (P < .001). The Short 37- group was also significantly younger than the other 2 groups with 41.6% younger than 65 years compared with Short 37+ (37.2%) and Standard groups (36.9%) (P < .01). There was no difference in American Society of Anesthesiologists grade between groups. Body mass index (BMI) was significantly higher in both the Short 37- and Short 37 + groups compared with the Standard group (Standard BMI, 28.71; SD 5.72; Short 37+ BMI, 29.69; SD, 6.67; Short 37- BMI, 29.09; SD 7.07; P < .001). The all-cause revision rate for standard stems was 0.55/100 component years (cy) (95% CI: 0.52 to 0.58). The Short 37- group had a higher rate of revision compared with the Standard group (hazard ratio 1.6; 95% CI: 1.3 to 1.98; P < .001), while the Short 37+ group had a hazard ratio of 0.84 (95% CI: 0.38 to 1.88; P = .674) compared with the Standard group. Cox regression analysis controlling for age, gender, diagnosis of OA, and surgical approach did not affect these findings. However, no clinically meaningful difference between Oxford hip scores was observed. CONCLUSIONS: There was a significant difference in revision rates for aseptic loosening with standard-length Exeter stems having a lower revision rate than short Exeter stems with offsets 35.5 mm or less. The Short 37+ groups, despite comprising relatively small numbers, performed similarly to the Standard stem group.

Functional acetabular retroversion syndrome: description of a specific sub-type of FAI and results of treatment with minimally invasive PAO.

INTRODUCTION: Acetabular retroversion syndrome is associated with pincer-type femoroacetabular impingement (FAI) and results, theoretically, from an externally rotated hemipelvis. The purpose of this study was to examine our surgical experience and the clinical results of functional acetabular retroversion syndrome treated with minimally-invasive periacetabular osteotomy (PAO). METHODS: We performed a retrospective cohort study of prospectively collected data in consecutive patients who had an anteverting PAO from 01 November 2010 to 31 December 2015. All patients were followed up clinically and radiologically.Functional scores were ascertained using pre- and postoperative iHOT-12 and EQ-5D. The effect of hypermobility, smoking status and body mass index (BMI) on outcome measures was evaluated. RESULTS: 31 anteverting PAOs were performed on 27 consecutive patients. All patients were female. The mean age was 26.7 years (SD 6.7). The mean BMI was 25.8 kg/m2 (SD 5.1). 5 patients were smokers (16.1%) and 11 exhibited signs of generalised joint laxity. 23 hips had undergone prior hip arthroscopy and 1 patient had previous open FAI surgery. The minimum clinical follow-up was 2 years (mean 3.4 years; range 2-7 years). A crossover sign was present in all cases. The mean iHOT-12 score improved from 19.5 to 51 at 6 months, 64.5 at 1 year and 48 at 2 years following surgery (p < 0.05) EQ-5D improved from 0.42 preoperatively to 0.76 at 6 months and 0.69 at 1 year following surgery (p < 0.05). CONCLUSIONS: We have characterised functional acetabular retroversion syndrome (FARS) as a condition affecting young, active females which severe symptoms out of proportion to demonstrable radiographic pathology.

Does vitamin E highly-crosslinked polyethylene convey an advantage in primary total hip replacement? A systematic review and meta-analysis.

BACKGROUND: Vitamin E highly cross-linked polyethylene (HXLPE) was developed to reduce wear in total hip replacement (THR). This formal systematic review and meta-analysis aimed to provide independent synthesis of wear characteristics of Vitamin E treated HXLPE compared to HXPLE/UHMWPE. Secondary outcome measures were differences in revision rates and functional scores. METHODS: We performed a formal systematic review as per PRISMA guidelines; literature searches were conducted on 14 November 2017 (MEDLINE, Embase on Ovid, and the Cochrane Library). We included randomised controlled trials, analyses of joint registries, and case-controlled studies of primary THR comparing cups with a vitamin E HXLPE bearing with bearing surfaces made from other types of polyethylene. Initial screening was performed by 2 independent assessors; disagreement resolved in discussion with a third reviewer. Studies were evaluated using the Cochrane risk of bias tool. Data extraction permitted meta-analysis. RESULTS: 372 studies were identified on initial screening, 5 studies met the eligibility criteria. There was no significant heterogeneity between studies. There was variable risk of bias. At a mean of 35 (range 20-60) months, Vitamin E HXLPE had significant advantages over highly cross-linked polyethylene with regards total femoral head penetration (p = 0.004). Given the RSA measurement errors this may not be clinically significant.There were neither significant differences in revision rates nor Harris Hip Scores (p = 0.06). CONCLUSION: At a minimum of 3 years follow-up there was reduced total femoral head penetration for vitamin E HXLPE over HXLPE. This bearing surface does not, as yet, have clinically significant advantages in terms of revision rates or patient function over HXLPE.

Are Lipped Polyethylene Liners Associated with Increased Revision Rates in Patients with Uncemented Acetabular Components? An Observational Cohort Study.

BACKGROUND: Recurrent dislocation after THA remains a serious complication that carries with it a high risk of revision surgery. Previous studies have shown reduced dislocation rates with the use of lipped polyethylene (PE) liners in modular uncemented acetabular components, but there may be increased wear because of impingement, which may lead to aseptic loosening in the longer term; whether the aggregate benefit of lipped PE liners outweighs the risks associated with their use remains controversial. QUESTIONS/PURPOSES: We used data from the New Zealand Joint Registry to (1) compare Kaplan-Meier survival rates, (2) rates of revisions for dislocation between neutral and lipped PE liners, and (3) revision rates for aseptic loosening for the four most commonly used modular uncemented cups. METHODS: We used data from the New Zealand Joint Registry (NZJR) to identify 31,247 primary THAs using the four most commonly used uncemented modular acetabular implants from January 1, 1999 to December 31, 2018. The lipped liner group comprised 49% males (9924 of 20,240) compared with 42% (4669 of 11,007) in the neutral group (p < 0.001); 96% (19,382 of 20,240) of patients in the liner group had OA versus 95% (10,450 of 11,007) in the neutral group (p < 0.001). There was no difference in other patient characteristics such as age (mean 66.9 years), BMI (mean 29 ± 6 kg/m) and American Society of Anesthesiologists grade. The mean follow-up was 5.1 years (SD 3.9) and longest follow-up 19.3 years. The NZJR has more than 96% capture rate and data entry is a mandatory requirement of members of the New Zealand Orthopaedic Association. Kaplan-Meier survival rates were compared between 20,240 lipped and 11,007 neutral PE liners. Highly cross-linked polyethylene was used in 99% of lipped liner cups and 85% of neutral liner cups. Associated hazard ratios were calculated using a Cox regression analysis with a Kaplan-Meier revision-free estimates plot. RESULTS: The Kaplan-Meier survival at 10 years for lipped PE liners was 96% (95% confidence interval 95.4 to 96.2) and for neutral liners 95% (95% CI 94.7 to 95.9). After controlling for age, gender approach, femoral head size, and the use of image guidance, the all-cause revision risk was greater for neutral PE liners than that for lipped PE liners (HR 1.17 [95% CI 1.06 to 1.36]; p = 0.032). There was a higher risk of revision for dislocation in those with neutral PE liners than in those with lipped liners (HR 1.84 [95% CI 1.41 to 2.41]; p < 0.001) but no difference in the revision rate for aseptic acetabular component loosening (HR 0.85 [95% CI 0.52 to 1.38]; p = 0.511). CONCLUSIONS: The use of a lipped PE liner is not associated with a higher rate of aseptic loosening in patients who undergo primary THA compared with a neutral PE liner. Lipped PE liners are associated with lower rates of dislocation and lower all-cause revision rates without any increased association with revision rates for wear and aseptic loosening. LEVEL OF EVIDENCE: Level III, therapeutic study.

Safety of single-anaesthetic versus staged bilateral primary total knee replacement: experience from the New Zealand National Joint Registry.

BACKGROUND: Surgical management options for bilateral knee osteoarthritis comprise staged or single-anaesthetic bilateral total knee replacements (SABTKRs). We examined the New Zealand Joint Registry hypothesizing there would be no difference between these practices compared to unilateral total knee replacement (TKR) examining 30-day mortality, all-cause revision rate and function. METHODS: For this study, 84 946 primary TKRs were identified. We compared three groups: unilateral TKRs, all SABTKRs and all staged bilateral TKRs with intervals of 1 to 90 days, 91 days to 1 year and >1 year. Cumulative revision rates were calculated (Kaplan-Meier method). Mortality risks were compared to unilateral TKR and hazard ratios (HRs) calculated. Six-month Oxford scores were compared using analysis of variance. RESULTS: Thirty-day mortality for SABTKR was 0.219%: unilateral TKR 0.236% (HR 0.43; 95% confidence interval (CI) 0.38-0.48; P < 001). Staged TKR had lower mortality than unilateral TKR at three time interval groups unless performed within 90 days (adjusting for age and American Society of Anesthesiologists grade) TKR (<90 days HR 0.92; 95% CI 0.703-1.371; P = 0.915; 91-365 days HR 0.783; 95% CI 0.687-0.891; P < 0.001; >365 days HR 0.394; 95% CI 0.344-0.451; P < 0.001). Revision risk with SABTKR was lower at 0.43/100 component years (95% CI 0.37-0.49/100 component years) compared to unilateral 0.56/100 component years (95% CI 0.53-0.59; P < 0.05). Six-month Oxford scores were superior in SABTKR versus unilateral TKR (38.6 (95% CI 38.2-39) versus 36.9 (95% CI 36.8-37.1); P < 0.001). CONCLUSIONS: SABTKR is at least as safe as unilateral TKR or staged bilateral TKR in appropriately selected cases. Surgeons should wait at least 90 days before the second procedure.

Despite Improved Survivorship of Uncemented Fixation in Total Knee Arthroplasty for Osteoarthritis, Cemented Fixation Remains the Gold Standard: An Analysis of a National Joint Registry.

BACKGROUND: Total knee arthroplasty (TKA) numbers are increasing worldwide. While cement fixation for both femoral and tibial components is commonly used, alternatives include hybrid and uncemented TKAs. This study aimed to evaluate survivorship, revision rates, and patient-reported outcomes for cemented, hybrid, and uncemented TKAs using New Zealand Joint Registry (NZJR) data. METHODS: NZJR data relating to all TKAs performed during the 19 years up to the end of December 2017 were analyzed. Outcomes were assessed using prosthesis survivorship data (including reasons for revision) and Oxford scores at 6 months, 5 years, and 10 years postoperatively. RESULTS: A total 96,519 primary TKAs were performed during the period examined. Most (91.5%) were fully cemented with 4.8% hybrid and 3.7% uncemented. Mean Oxford scores at 6 months were highest in cemented and lowest in uncemented TKAs (P < .001). However, this was not clinically significant. There was no difference at 5 or 10 years. Ten-year survival rates were 97%, 94.5%, and 95.8% for cemented, uncemented, and hybrid TKAs, respectively. Revision rates were 0.47, 0.74, and 0.52 per 100 component years for cemented, uncemented, and hybrid prostheses, respectively. The revision rate for uncemented prostheses compared with cemented was higher (P < .001). When stratified by age group, there were differences in survival rates between cemented and uncemented groups (P = .001) and hybrid and uncemented groups (P = .038) in patients aged <55 years; between cemented and uncemented groups in those aged 55-64 years (P = .031); and between cemented and hybrid groups in those aged >75 years (P = .004). CONCLUSION: Uncemented TKAs had similar patient-reported outcomes but higher revision rates and worse survivorship compared with hybrid or fully cemented TKAs.

Does the femoral offset affect replacements? The results from a National Joint Registry.

BACKGROUND: Femoral component offset influences the torque forces exerted on a femoral stem and may therefore adversely affect femoral component survival. This study investigated the influence of femoral component offset on revision rates for primary total hip replacements (THR) registered on the New Zealand Joint Registry (NZJR). METHODS: There were 106,139 primary THRs registered, resulting in 4960 revisions for any cause. There were 46,242 THRs performed using the five commonest femoral components listed on the NZJR. A total of 41,100 were done for primary osteoarthritis of which 40,548 had all the offset information available for analysis. We defined low offset as < 42 mm, standard as 42-48 mm and high offset as > 48 mm offset and examined revision rates according to the reasons for revision. We performed survival analyses for both cemented and uncemented femoral components grouped by the different offsets. RESULTS: The all-cause revision rate was 0.54/100 component years (cys). Stems with < 42 mm offset had a revision rate of 0.58/100 cys (mean 0.58; 95% confidence interval (CI) 0.53-0.63), 42-48 mm offset 0.47 (95% CI 0.43-0.52) and > 48 mm offset 0.67 (95% CI 0.57-0.79). There was no significant difference in all-cause revision rates between varying stem offsets in uncemented stems adjusting for age and gender. In cemented stems both high and low offset stems were more likely to be revised. Uncemented stems of all offsets were more likely to undergo revision for femoral fracture. CONCLUSIONS: Femoral component offset affects the overall all-cause revision rate of the most commonly used cemented stem, but not uncemented stem designs. In cemented stems offset influences the rate of revision for loosening and periprosthetic fractures.

The use of silver coating in hip megaprostheses: a systematic review.

Retrospective studies of silver-coated hip implants have demonstrated promising results and safety profile, however, the potential benefits are so far unproven in prospective studies. Silver-coated implants may have a role in patients undergoing revision or primary surgery with a high risk of infection but as yet there are no human studies investigating silver in primary hip arthroplasty. Adequately powered robust prospective studies are needed in this area to determine if silver-coated implants would be efficacious and cost-effective. The purpose of this systematic review article is to review the current literature regarding the use of silver in hip arthroplasty. Our review showed that there is some encouraging evidence that silver coatings can reduce infection.

Is single-anaesthetic bilateral total hip replacement using cemented stems safe and appropriate? A review of four decades of practice.

BACKGROUND: Symptomatic bilateral hip osteoarthritis can be treated surgically with either staged or single-anaesthetic bilateral total hip replacement (BTHR). Today the typical candidate for BTHR is more likely to receive cementless implants. We present the experience of BTHR at our institution using cemented stems combined with cemented and uncemented sockets and, to our knowledge, the largest prospective single-centre series. PATIENTS AND METHODS: This cohort study reviews all patients (319 patients: 638 hips) having BTHR at our institution between December 1977 and December 2015. No case was lost to follow-up. Data were collected prospectively but reviewed retrospectively. Length of stay and complication rates were included, and data were compared with Hospital Episode Statistics figures for operations carried out between March 2005 and June 2014 to confirm local database validity. Patient experience and Oxford Hip Scores were obtained for a subgroup of this cohort, comparing them with patients who underwent bilateral staged operations performed within 1 year. RESULTS: The rates for mortality, deep vein thrombosis, non-fatal myocardial infarction within 6 months were each 0.3% (1 episode) and non-fatal pulmonary embolism 0.6% (2 episodes). There were no intraoperative periprosthetic fractures or readmissions within 30 days. CONCLUSIONS: Our study shows a low risk of complications when using cemented and hybrid BTHRs for selected patients and the risk of complications compares favourably with published results. Available functional scores compared favourably to a comparison group of patients undergoing bilateral staged procedures, and a positive impression on treatment experience from a subgroup of interviewed BTHR patients was noticeable.

Increased subchondral bone thickness in hips with cam-type femoroacetabular impingement.

OBJECTIVES: Increased thickness of subchondral acetabular bone with associated articular cartilage thinning in hips with femoroacetabular (FAI) cam impingement has been observed on magnetic resonance imaging (MRI). Dynamic attrition by the cam deformity moving into the acetabulum may potentiate trans-articular shear stresses thus causing these subchondral bone changes. We aimed to quantify the hypertrophic changes of subchondral acetabular bone in patients with cam-type FAI. METHODS: MRI studies were performed on an asymptomatic population of young Swiss army recruits. Subjects underwent clinical examination and completed questionnaires before undergoing an MRI of the hip. Cam deformities were graded and the dimensions of the acetabular subchondral bone quantified. Univariate linear regression was used to determine the association between the presence of cam deformities and the degree of subchondral acetabular sclerosis. RESULTS: There was a strong association between cam deformities and the thickness, area and shape of subchondral sclerosis. The main increase in hypertrophy was observed in the antero-superior acetabulum where impingement typically occurs. The subchondral sclerosis was 0.66 mm thicker in cam-type deformities than in hips without cam-type deformities (95% CI, 0.38-0.93, p value < 0.001). CONCLUSIONS: Mechanical stress in the antero-superior acetabular area is elevated in hips with a cam-type deformity. The study supports the concept that cam-type deformity induced stress leads to hypertrophy of subchondral acetabular bone in the area of impingement. This is collocated with the clinically observed cartilage damage caused by the cam mechanism.

Is single-anaesthetic bilateral primary total hip replacement still safe? A 16-year cohort study from the New Zealand Joint Registry.

BACKGROUND: The surgical management options for bilateral hip osteoarthritis comprise staged or single-anaesthetic bilateral total hip replacements (THRs). The key issue of contention in performing the latter remains safety. We compared unilateral, staged bilateral and single-anaesthetic bilateral THR with the hypothesis that there would be no difference between these three practices using mortality risk, functional outcome and revision rate as the primary outcome measures. METHODS: We performed a retrospective cohort analysis of the New Zealand Joint Registry identifying all primary THRs performed between 1 January 1999 and 31 December 2015. We report this study in accordance with STROBE and RECORD guidelines. We identified all unilateral THRs, all single-anaesthetic bilateral THRs and all staged bilateral THRs and compared the mortality risk, all-cause revision risk with Kaplan-Meier survival analysis and reasons for revision and functional outcome using the Oxford 12 scores. Analysis was adjusted for age, gender, American Society of Anesthesiologists rating score and body mass index. RESULTS: The mortality risk for single-anaesthetic bilateral THR within 3 months was 0.26% and for unilateral THR 0.75% (hazard ratio 0.35 (95% confidence interval (CI) 0.30-0.41, P < 0.001). The risk of revision in the single-anaesthetic bilateral THR group was 0.69/100 component years (95% CI 0.59-0.79/100 component years) versus 0.74/100 component years (95% CI 0.72-0.77/100 component years) in unilateral THR. Mean Oxford 12 scores at 6 months post-arthroplasty was 41.7 (95% CI 41.2-42.2) in the single-anaesthetic bilateral THR group. The best results in the staged bilateral THR group were obtained if the second procedure was delayed by at least 90 days from the first THR. CONCLUSIONS: Single anaesthetic bilateral THR is at least as safe as unilateral THR or staged bilateral THR in appropriately selected cases. Experienced surgeons can expect predictable survival rates and functional scores.

Does the type of surgical drape (disposable versus non-disposable) affect the risk of subsequent surgical site infection?

AIMS: Determine whether disposable or reusable drapes are better at reducing surgical site infection (SSI) rates. METHODS: A systematic review of the English literature from inception to 2018 with search terms relating to infection and drapes in orthopaedic and spine surgery. RESULTS: No orthopaedic or spinal surgery studies assessed the risk of SSI between reusable or disposable drapes. However, two articles, with conflicting results, compared current reusable and disposable drapes in other surgical disciplines. CONCLUSION: There is no evidence to support a difference between reusable or disposable drapes to reduce the risk of SSI in orthopaedic and spinal surgery.

The management of the painful borderline dysplastic hip.

Improved imaging and the evolution of surgical techniques have permitted a rapid growth in hip preservation surgery over the last few decades. The management of the painful borderline dysplastic hip however remains controversial. In this review, we will identify the pertinent issues and describe the patient assessment and treatment options. We will provide our own recommendations and also identify future areas for research.

The use of an Ossis custom 3D-printed tri-flanged acetabular implant for major bone loss: minimum 2-year follow-up.

INTRODUCTION: Custom 3D-printed acetabular implants are a new technology used in hip surgery with ever-increasing frequency. They offer patient-specific implants to optimise filling of bone defects and implant-bone contact, without the need for excessive bone resection. METHODS: This is a retrospective cohort study of 46 consecutive patients who underwent an Ossis unilateral custom 3D-printed acetabular implant. Clinical (Oxford Hip Score OHS-60), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Harris Hip Score (HHS) and radiological (restoration of biomechanical hip centre, osteointegration, wear, heterotrophic ossification) results were assessed. RESULTS: Patient mean age was 68 years and follow-up was 38 months (minimum 24 months). 10 patients were excluded from the outcome analysis; 2 patients died, 1 required revision for deep infection and 7 were lost to follow-up. Of the 36 patients included, 21 had severe osteolysis. 7 were revised for infection, 3 for tumoural defects, 3 for metallosis, 1 for dysplasia and 1 for trauma (Paprosky 2a [n=6], 2b [n=2], 2c [n=5], 3a [n=6], 3b [n=11], pelvic dissociation [n=6]). OHS significantly improved postoperatively (16-8-48.4 p=0.027). Postoperative functional scores were good (WOMAC 98; HHS 79). The biomechanical hip centre was restored in all patients. 1 patient had early implant migration with subsequent stabilisation. 2 patients had radiographs concerning for failure of osteointegration. 1 patient had recurrent dislocations. CONCLUSIONS: The mid-term results of the Ossis custom 3D-printed tri-flanged acetabular implant for the management of severe acetabular defects are encouraging. The improvement in functional scores and radiographic outcomes are comparable to similar designs. In addition, no cases have required revision for aseptic loosening.

Which is the best bearing surface for primary total hip replacement? A New Zealand Joint Registry study.

INTRODUCTION: We have investigated the revision rates of all bearing surface combinations for primary total hip replacement (THR) registered on the New Zealand Joint Registry (NZJR) to determine which coupling has been the most durable and successful over the last 16 years. METHODS: There were 106,139 primary THRs registered, resulting in 4,960 revisions for any cause. We examined all-cause revision rates, reasons for revision and performed survival analyses. RESULTS: Ceramic-on-highly cross-linked polyethylene (CoPx) had the lowest all-cause revision rate of 0.54/100-component-years (cys) (95% confidence interval 0.48 to 0.61). This was superior to all other hard-on-soft bearing combinations in unadjusted analysis. Furthermore, the age of patients receiving CoPx was significantly lower than for metal-on-polyethylene (mean 62.9; standard deviation [SD] 10.1 vs. 69.1; SD 9.6; p<0.001). Acetabular loosening was the reason for revision in 14.5% of CoPx, compared to 33% of MoP THRs (p<0.001). Metal-on-metal bearings had the highest revision rate of 1.43/100 cys and were significantly inferior to CoPx (p<0.001). Kaplan-Meier analysis and Cox regression analyses were performed and we adjusted the analyses to control for age, femoral head size, surgical approach and fixation. CONCLUSIONS: CoPx remained the most durable and successful coupling used in primary THR in New Zealand irrespective of age, gender or size of femoral head.

Custom 3D-printed acetabular implants in hip surgery--innovative breakthrough or expensive bespoke upgrade?

Custom 3D-printed triflange acetabular cages are a new option in the armamentarium of the revision hip surgeon. This review article defines this technology, its indications, surgical method, advantages, disadvantages, use, current published literature and future applications.