Aims

Accurate and precise acetabular reaming is a requirement for the press-fit stability of cementless acetabular hip replacement components. The accuracy of reaming depends on the reamer, the reaming technique and the bone quality. Conventional reamers wear with use resulting in inaccurate reaming diameters, whilst the theoretical beneficial effect of ‘whirlwind’ reaming over straight reaming has not previously been documented. Our aim was to compare the accuracy and precision of single use additively-manufactured reamers with new conventional reamers and to compare the effect of different acetabular reaming techniques.

Aims

The aim of this study was to establish the incidence of developmental dysplasia of the hip (DDH) diagnosed after one-year of age in England, stratified by age, gender, year, and region of diagnosis.

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. The need for a novel, cost effective treatment option for osteochondral defects has therefore never been greater.

As an emerging technology, three-dimensional (3D) bioprinting has the capacity to deposit cells, extracellular matrices and other biological materials in user-defined patterns to build complex tissue constructs from the “bottom up”. Through use of extrusion bioprinting and fused deposition modelling (FDM) 3D printing, porous 3D scaffolds were successfully created in this study from hydrogels and synthetic polymers. Mesenchymal stem cells (MSCs) seeded onto polycaprolactone scaffolds with defined pore sizes and porosity maintained viability over a 7-day period, with addition of alginate hydrogel and scaffold surface treatment with NaOH increasing cell adhesion and viability. MSC-laden alginate constructs produced via extrusion bioprinting also maintained structural integrity and cell viability over 7 days in vitro culture. Growth within osteogenic media resulted in successful osteogenic differentiation of MSCs within scaffolds compared to controls (p<0.001). MSC spheroids were also successfully created and bioprinted within a novel, supramolecular hydrogel with tunable stiffness.

In conclusion, 3D constructs capable of supporting osteogenic differentiation of MSCs were biofabricated via FDM and extrusion bioprinting. Future work will look to increase osteochondral construct size and complexity, whilst maintaining cell viability.

Current strategies for bone repair have accepted limitations and the search for synthetic graft materials or for scaffolds that will support ex vivo bone tissue engineering continues. Bioprospecting has led to increased interest in potential applications for marine organisms and their by-products and biomimetic strategies have led to the investigation of naturally occurring porous structures as templates for bone growth. As a rich source of mineralising porous organisms, our seas and oceans could provide new directions for bone tissue engineering that may enhance in vivo and ex vivo bone formation.

Introduction

Tibial component malrotation is associated with pain, stiffness and altered patellofemoral kinematics in total knee arthroplasty (TKA). However, accurately measuring tibial component rotation following TKA is difficult. Proposed protocols utilizing computed tomography (CT) are not well validated and can be time consuming. This study aimed to; 1) Validate and compare the reproducibility of the Berger (2D-CT) and Mayo (3D-CT) protocols; 2) Validate a simple, and potentially rapid screening measurement using an anatomical distance on 2D axial CT- the Centre of Tibial Tray to Tibial Tubercle (CTTT) distance.

We aimed to demonstrate the clinical safety of a novel anatomic cementless ceramic hip resurfacing device. Concerns around the safety of metal on metal arthroplasty have made resurfacing less attractive, while long term function continues to make the concept appealing. Biolox Delta ceramic is now used in more than 50% of all hip arthroplasties, suggesting that it's safety profile is acceptable. We wondered if a combination of these concepts might work?

The preclinical testing of anatomic hip resurfacing device developed by our group was presented last year. A twenty patient safety study was designed. Patients had to be between the ages of 18 and 70. The initial size range was restricted to femoral heads between 46 and 54, representing the common sizes of hip resurfacing. The primary outcomes were clinical safety, PROMs and radiological control. Secondary outcomes include CTRSA and metal ion levels.

20 patients were recruited, aged 30–69. 7 were women and 13 were men. There were no operative adverse events in their operations undertaken between September 2017 and February 2018. One patient had a short episode of atrial fibrillation on the second postoperative day, and no other complications. At three months the median oxford hip score had risen from 27 (range 14–38) to 46 (31–48). Cobalt and chromium levels were almost undetectable at 3 months. Fixation appeared satisfactory in all patients, with no migration detected in either component. CTRSA is in process.

The initial safety of a novel cementless ceramic resurfacing device is demonstrated by this data. The 10 year, 250 case efficacy study will continue in 5 other European centres.

Performance of metal-on-metal (MOM) bearings was of great interest until recently. Major concerns emerged over high incidence of MOM-wear failures and initially there appeared greater risks with MOM total hip arthroplasty (THA) designs compared to resurfacing arthroplasty (RSA). Impingement of the metal neck against the THA cup was likely the differentiating risk. There is a major difference between RSA and THA in (i) size of femoral necks and (ii) risk of THA metal necks impinging on metal cups. For example, a 46mm THA with 12.5mm neck, a 3.68 head:neck (H/N) ratio, provides a suitably large range-of-motion (ROM). In contrast, an RSA patient with retained 31mm size of natural neck would only have H/N = 1.48, indicating even less ROM than a Charnley THA. However, the enigma is that RSA patients have as good or better ROM in majority of clinical studies. We studied this apparent RSA vs THA dilemma by examining MOM retrievals for signs of adverse impingement. We previously described CoCr stripe wear in failed THA bearings, notably alignment of polar and basal wear stripes coincident with the rim profiles of the cups (Clarke 2013). Our governing hypothesis was that RSA patients had to routinely sublux their hips to get ROM comparable to THA. Our THA impingement studies showed polar stripes within 15o of the polar axis in large heads. For the various RSA diameters, we calculated that wear stripes angled 40o from the femoral axis could indicate impingement with no subluxation, whereas smaller angles would indicate routine subluxation of RSA femoral-shell from cup. We compared explanted RSA (N=15) and THA (N=15) bearings representing three vendors (42–54mm diameters). Wear maps and head-stripes were ink-marked for visualization, photography, and analysis. Wear areas were calculated using spherical equations and wear-stripe angles measured by computer graphics.

The results showed that RSA femoral shells had wear areas circular in shape with areas varying 1,085- 3,121mm2. These averaged 14% larger than in matched THA heads but statistically significant difference was not proven. Polar stripes were readily identifiable on femoral components, 75% for RSA cases and 100% for THA. These contained identical linear scratches and all were sited within 30o of neck axis, confirming our hypothesis that RSA patients had to sublux their hips to achieve same motion as THA. Examination of cup wear areas revealed all showed ‘edge-loading’, but RSA cups had a significantly greater degree.

Retrieval studies are limited by uncontrolled case sources, varied brands, and small numbers. In this study, we were able to match RSA and THA cases by vendor and diameter. The RSA retrievals revealed polar stripes identical to THA by site, topography and inclination to femoral-neck axis. This confirmed our starting hypothesis and explained the large clinical ROM available in RSA patients. The larger wear areas on RSA femoral shells, although not statistically significant, and the larger ‘edge loading’ sites in RSA cups appeared as further support for routine subluxation of femoral-shells during hip impingement.

Failed total hip arthroplasty (THA) can require novel designs of revision implants that present unique risks as well as benefits. One of our patients endured a series of hip and knee revisions. In her twenties, she experienced a failed THA, became infected and all implants removed. In her early fifties (2008), she had a proximal femoral replacement incorporating a FreedomTM cup (Biomet, Warsaw, IN). She lacked hip musculature, was a dislocation risk, and cup constraint was necessary. Our choice of Freedom cup provided a 36mm head for enhanced stability and range-of-motion, plus the polyethylene liner was not as encompassing as other constrained designs, and the external clamping ring came pre-installed. This unique design allows for ease of head insertion during surgery. Our patient also had a CompressTM fixator combined knee-arthroplasty (Biomet). This knee fixation failed in 2013 and we installed a total femur combined hinge-knee arthroplasty. The Freedom cup was kept and post-op results were satisfactory.

Follow-up appeared satisfactory in 2014. Some liner eccentricity was apparent but the patient had no complaints. Radiographs in February 2016 indicated cup's locking-mechanism was possibly failing but patient had no complaints. By December follow-up of 2016, the patient claimed she had 3 falls, and her x-rays indicated a displaced head and dislodged liner. At revision, the liner appeared well-seated inside the acetabular shell. However, about 50% of the polyethylene rim was missing and the large detached circumferential fragment represented the other 50%. A new Freedom liner was installed and her follow-up appears satisfactory to date.

The fractured liner was sectioned through the thinnest wall (under detached rim fragment). The most critical design section was at site of the external locking ring, this wall thickness appearing < 3mm, whereas eccentric cup dome was 7.5–8mm thick. Under the detached rim fragment, wall thickness had been reduced (in vivo) to < 1mm. Given the robust rim profile, it seemed unlikely that the liner could have been spinning. The more likely scenario was that with repeated impingement, attempted subluxations by the femoral head stressed the contra- polyethylene rim, resulting in cold flow, thinning, and rim fragmentation. Two exemplar liners were compared, one similar to our patient's and one in a thicker design. Comparison of the sectioned retrieval to the new liners confirmed major loss of circumferential polyethylene.

Our learning experience was threefold; (i) if we had been aware of the thin wall limitation, possibly we could have inserted the thicker liner (larger shell), (ii) we could have been more alert to the impending liner failure (x- ray imaging), and (iii) positioning the cup in a more horizontal orientation may have been an alternate solution, i.e. more coverage (but perhaps more impingement). Use of a 32mm head would have facilitated a thicker liner but this option was unavailable. In conclusion, it was notable that this constrained liner functioned very well for 7 years in our complex case and was easily revised at 8 years to another Freedom liner.

Expectations for ceramic-on-metal (COM) bearings included (i) optimal lubrication due to smoother ceramic heads (ii), reduction of metal ions due to elimination of CoCr heads, and (iii) ‘differential hardness’ reducing adhesive wear and squeaking (Firkins 2001, Williams 2007). Additional benefits included (iv) use of heads larger than for ceramic-on-ceramic (COC), (v) reduction in taper corrosion and (vi) simulator studies clearly demonstrated metal ions and wear both reduced compared to MOM (Firkins 2001, Williams 2007, Ishida 2007). However, contemporary ‘3rd body wear’ paradigms focused only on metal debris size range 0.025–0.035um (Firkins 2001). Thus, neglected was the effect of hip impingement, provoking release of large metal particles sized 20–200um (Clarke 2013). In this study, we compared COM retrievals using hypotheses that adverse COM cases would demonstrate a combination of (a) steeply inclined cups, (b) liner “edge-loading”, (c) Ti6Al4V contamination on ceramic, and (d) evidence of 3rd-body CoCr wear by large particles.

As a case example, this 51-year old female had her metal-polyethylene (MPE) bearing revised to COM in June 2011. She reported no symptoms 1-year post-op, but scans revealed a palpable mass in the inguinal region of left hip. By March 2013 the patient reported mild pain in her hip, which progressed to severe by April 2014. Scans showed a solid and cystic iliopsoas bursitis while cup position had changed from 43o to 73o inclination. Revision was performed in June 2014, her joint tissues were found extensively stained due to metal contamination, and histology described formation of a large pseudotumor.

Analysis of retrieved components was by interferometry, SEM and EDS. Detailed maps were made of wear areas in heads and cups and volumetric wear was determined by CMM techniques. This adverse COM example revealed large diametral mismatch (595um) compared to COM controls (75–115um). The ceramic head had a broad polar stripe of CoCr contamination, roughness 0.1–0.3um high. Equatorial ceramic areas showed arrays of thin metal smears that demonstrated elemental Ti and Al. The CoCr liner revealed wear area into cup rim, as “edge loading”, and also featured a focal rim-defect over 18o circumferential arc. Liner scratches were 20um wide and larger, and wear-rate of CoCr liner averaged approximately 50mm3 per year. In contrast, ceramic head had minimal wear.

Our study highlights the underappreciated risk of impingement by metallic prosthetic components. Prior studies of ceramic heads showed black metallic smears. With COM we can anticipate that the broad polar smear will be CoCr alloy (wear of liner on head). However, Ti6Al4V smearing on ceramic heads is a notable signpost indicating impingement by the Ti6Al4V acetabular shell. The femoral neck (Ti6Al4V: CoCr), may also be damaged. Release of large metal particles, 1500-times larger than prior predictions, provoke a particularly adverse ‘3rd body wear’ (Halim, 2015). Such cases confirm our four hypotheses, that COM bearings will then fail in a way similar to MOM. In contrast, COC bearings are immune to such impingement and 3rd-body metal damage.

Metal-on-metal (MOM) and ceramic-on-metal (COM) studies in total hip arthroplasty (THA) documented adverse wear termed “edge loading”. Laboratory simulations necessitated cups steeply inclined to produce edge- loading, whereby cup rims could attenuate the normal wear patterns. Size of cup wear-pattern was therefore key in defining edge-loading. From prior simulator studies (‘Anatomic’ test: ISO-14242), we could demonstrate a linear relationship between size of cup wear-patterns and MOM diameters, cup wear-areas decreasing from 18% to 8%. However, retrieval studies (COM/ MOM) showed cup wear-patterns in vivo were much larger, typically covering 50–55% cup surfaces (Clarke 2013: Koper 2015). In prior MOM Anatomic simulator study (head oscillating, cup fixed), we noted areas worn on 60mm heads and cups averaging 1,668mm2 and 442mm2, respectively (Bowsher 2009). Thus, ratio ×3.77 described distributed area worn on heads relative to focal area worn in cups. In the orbital simulator, the only way to achieve larger cup wear areas was to reverse the component positions, i.e. cups oscillating, heads fixed. The overall goal for this project was to develop an understanding of how such edge-loading affected adverse-wear performance of THA in simulators.

60mm MOM (DJO, Austin TX) were chosen comparable to our prior study (Bowsher 2009) and cups were mounted inverted (oscillating) under fixed heads. Adaptors were machined to incline cup faces at 17o and 27o and, with the simulator's +/−23° motion, they experienced 40oand 50o cyclic peak oscillations, respectively. The orbital simulator was identical to that of prior study as was the test protocol (Bowsher 2009). Wear patterns on components were assessed visually and microscopically, taped and colored red to aid photography.

The 40° and 50° tests produced circular cup wear patterns that came progressively closer to the rims without actually producing edge-loading, creating average wear area of 1,663mm2. These proved identical to wear areas on heads (orbiting) in prior Anatomic test (1,668mm2). Using the hemispherical-area datum of 5,655mm2 for 60mm MOM, our test produced cup wear patterns with desired 29.4% coverage.

The value of ISTA conferences is that by definition these bring new arthroplasty ideas and technologies to the forefront. The international guideline for simulators (ISO-14242) has proven useful for standard ‘Anatomic’ cup tests that do not require edge-loading conditions. However, ours is the 1st simulator study to; (i) predict the size of THA wear patterns, (ii) show that ratio of head: cup wear-areas average ×3.8 in favor of mobile component, and (iii) demonstrated cups can be run Inverted to produce more clinically-relevant wear patterns that in edge- loading studies. The new learning experience was that studies of edge-loading in THA cups need to consider the ‘Inverted’ test in order to simulate clinically relevant tribo-mechanical parameters. Compared to Anatomic test, the Inverted-cup test has the advantage of (iv) producing larger cup wear areas, (v) clinically-relevant attenuation of wear patterns at cup rim, and (vi) intermittent edge-loading (instead of constant loading) judged likely to apply to a larger patient population at risk.

Hip resurfacing remains a safe and effective option according to registry data. Results in women were less reliable, in part owing to soft tissue impingement. Biolox Delta ceramic bearing couples are now in widespread use with very low complication rates. We set about merging these three elements to develop a novel hip resurfacing arthroplasty.

Contours of both acetabular and femoral components were generated from biometric data, adapted to the constraints of ceramic machining, to ensure that radii blended from the bearing surface avoiding any sharp boundaries. Plasma spray coating with titanium and hydroxyapatite direct onto ceramic was developed and tested using shear, tensile and taber abrasion testing. Wear testing was carried out to 5 million cycles according to the ASTM. Destructive testing was carried out in a variety of test conditions and angles.

Cadaveric testing demonstrated stability using a single use disposable instruments for both conventional and patient specific procedures. Very low dose CT enabled the entire interface to be observed as the Ceramic is radiolucent, enhancing migration analysis, which will be undertaken at 4 intervals to confirm stability. Functional scores and gait analysis will be used in the safety study.

The CE study recruitment is underway, with first in human trials starting in summer 2017. PMA submission will follow the safety study. Commercial release of the device in Europe is unlikely before 2019, and in the USA may not be until 2027. The path to novel device development in 2017 is very costly in time and money.

Aims

Our aim in this study was to describe the long-term survival of the native hip joint after open reduction and internal fixation of a displaced fracture of the acetabulum. We also present long-term clinical outcomes and risk factors associated with a poor outcome.

Hip simulator studies with ceramic-on-metal (COM) predicted less wear than metal-on-metal (MOM: Isaac. 2009). While clinical evidence is scant, two COM case reports described pseudotumors with adverse cup positioning (Deshmukh 2012, Koper 2014). It would appear that our Korean case report is the first to describe pseudotumor formation in well-positioned COM arthroplasty and including detailed failure analysis. A 50-year old female (active salesperson) had bilateral avascular necrosis of her femoral heads. A left metal-on-polyethylene (MPE) hip was performed at outside institution in 2003. At our 3-yrs evaluation, radiographs showed well-functioning MPE hip. Five years later she complained of gradual left-hip pain (2011). Radiographs and CT scan demonstrated wear, osteolysis and loosening of both components. The revision in 2011 was by COM (Fig. 1), using S-ROM stem/sleeve, 36mm ceramic head (Biolox-delta), a CoCr liner and 54mm shell (Pinnacle: Depuy Inc). Cup inclination and anteversion were considered appropriate at 45° and 20° respectively; femoral anteversion of 15° was also appropriate.

At 1-yr follow-up patient complained of mild discomfort in left COM hip (2012). Range of motion was painless and normal. Examination revealed a soft, non-tender swelling (2×3cm) in left inguinal region with no inflammation and radiographs were normal (Fig. 1a). One month later the patient complained of left hip pain, the previously noted swelling had increased in size, and she started to limp. Radiographs showed cup migration with increased inclination. CT scans showed a circumscribed lesion extending into iliopsoas region (Fig 2). Serum cobalt and chromium levels were high at 2.4 and 22.5µg/ L, respectively.

At revision the pseudotumor and surrounding inflamed synovium was excised. The cystic soft-tissue swelling (stained black) extended into the joint (Fig. 2a). The ceramic head showed a large “black stripe” across the dome (Fig 2b). The cup was loose while the femoral stem was well fixed. Operative cultures of soft tissues and joint fluid were negative for infection while histopathology was consistent for metallosis (Fig. 3). Aggressive debridement was carried out, acetabular defects were filled with bone graft. Revision incorporated 32mm ceramic head (Biolox-delta), highly cross-linked liner and 52mm trabecular-metal shell (Depuy). Functionally the patient has continued to improve. By 6 months, serum ion concentrations decreased to Co:1.3 and Cr:2.54µg/ L with most recent ion levels lower still (Co:0.66 and Cr:0.42µg/ L).

Ceramic head surfaces showed normal wear appearance. The large gray stripe identified on the highly polished dome contained Co and Cr metal-transfer from the CoCr liner (Fig. 2b). Thin gray stripes on equatorial head regions (x4 rougher than dome) represented contamination by Ti, Al and V, typical of adverse impingement against Ti6Al4V neck (Clarke 2013). There was a 100–150um defect on rim of CoCr liner as a result of impingement. Cup out-of-roundness was 476um compared to only 7um for ceramic head, thus cup wear dominated at 25–30mm³ volume. This case report was illustrative of the unpredictable and seldom diagnosed risk of habitual cup-to-neck impingement and the risk of relying on pristine simulator studies to predict outcomes in novel THA bearings.

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There will be occasions when standards and guidelines stymie the development of new methods. For example, the majority of simulator studies utilized the international guideline specifying that cups will be positioned “Anatomically” (ISO-14242), i.e. acetabular liner is positioned above oscillating femoral head (Fig. 1). This can be disadvantageous for studies of “edge wear” in steeply inclined cups (Williams 2008, Leslie 2009, Angadji 2009). Importantly, such an “Anatomical” cup is fixed with respect to the resultant load-axis (Fig. 1d: R). This produces a constant edge-wear throughout the simulator's cycle. Our supposition was that it is more likely patients experience edge-wear intermittently, i.e. at extremes of motion. This intermittent effect can be best replicated with the cup mounted “Inverted” (Fig. 2), the rotating cam allowing precise selection of edge-wear at extreme of motion (Fig. 2c). An advantage of this method is that the wear-pattern in the orbiting cup is now much larger (Bowsher, 2009: x3.8 ratio), making edge-wear easier to achieve. Our hypotheses were that (1) the Inverted test would provide both “normal” and “edge wear” as defined (Clarke, 2015: steep-cup algorithm), (2) MOM wear rates under edge-wear condition would be greater than in standard simulator tests (Bowsher 2016) and (2) intermittent edge-wear of MOM cups (Inverted) would be less severe than in prior Anatomical tests (Williams 2008, Leslie 2009, Angadji 2009).

The 60mm MOM bearings (DJO, Austin TX) were selected on the basis of prior Anatomical study (Bowsher, 2009), were run with cups Inverted, using identical test methods as before, in the orbital simulator. Wear-rates in 60mm heads revealed both run-in and steady-state wear phases (Fig. 3a). The weight-loss method showed perturbations due to protein contaminants but these appeared of minor concern over 10-million cycles. One cup was damaged during set-up, did not recover, and was not included in the analysis (Fig. 3b). Cup wear rates over 10-million cycles appeared very stable with excellent consistency (Fig. 3c). By end of test, the edge-wearing cups averaged 3.7 times higher wear than mating heads. Overall MOM wear averaged 1.6mm³ per million cycles. Apart from the first 100,000 cycles of run-in, no lubricant changed color during entire test.

In this first study of its kind, we demonstrated both normal and edge-wear wear-patterns in accordance with predictions of the steep-cup algorithm (Clarke 2015), satisfying hypothesis #1. Wear rates with Inverted cups averaged 2.7 times greater wear than those in similar Anatomical study (Bowsher, 2009), satisfying hypothesis #2. The 60mm MOM wear rates Inverted were mid-range to those in the prior steep-cup Anatomical tests (range 1.3 – 1.9mm³ per 10⁶ cycles). This neither satisfied nor eliminated hypothesis #3, perhaps due to confounding effects, i.e. different designs, MOM diameters and methods. In conclusion, the Inverted test in the simulator appears to offer considerable merit, perhaps analogous to patients who experience edge-wear only intermittently. In contrast the Anatomical test mode appears analogous to patients with mal-positioned cups, who therefore walk on the cup rim constantly throughout their gait cycle.

Despite 46 years clinical experience with ceramic-on-ceramic (COC) hip bearings, there is no data on what constitutes a successful long-term wear performance. There have been many studies of short-term failures (Dorlot, 1992; Nevelos, 2001, Walters, 2004). One retrieval study using optical-CMM technology (OCM) documented volumetric wear-rates ranging up to 7mm³/year on femoral heads (Esposito 2012). It was noted that 83% of these revisions showed stripe damage within 3–4 years. The supposition would appear to be that these were bearing-related failures.

Our selected COC case for this study was particularly interesting, a female patient having her index surgery performed at age 17 and revised at age 49 (following onset of hip pain). This patient led an active lifestyle, went dancing multiple times per week, and was mother to three children. The 38mm Autophor^TM THA (left hip) was eventually revised due to the cup painful migrating (Fig. 1: 32-years follow-up). Radiographs showed cup inclination at approximately 19^°. Impingement marks were noted on the CoCr neck and collared stem (Fig. 2). Implant geometry and form factors were analyzed by standard contour measurement (CMM) while SEM and EDS imaging provided wear topography and evidence of metal contaminants. Linear and volumetric wear in head and cup were studied by OCM at Redlux (Southampton, UK).

The head's main wear-pattern consisted of two overlapping circular areas (Fig. 3). The narrowest margin made by the wear-pattern was used to define the superior aspect of the head. By light microscopy, the superior main-wear zone covered 1490–1680mm² area while the total bi-lobed area covered larger 2170mm² area. OCM analysis delineated the same bi-lobed appearance of head wear with the superior worn area assessed at 1365mm². The cup revealed a more extensive wear pattern that circumnavigated its surface. The black staining identified by EDS imaging in the cup revealed Co and Cr elements. By OCM technique the head volumetric wear was 179 mm³ and the cup was 214mm³ (Fig. 4), i.e. 20% greater than head. Volumetric wear-rate averaged 12.3mm³ per year for this pioneering alumina ceramic.

This first demonstration of long-term, COC volumetric wear provides the foundation for retrieval and simulator studies alike. Our patient represented a “worst-case” scenario for hip-replacement surgery, due to extreme youth and long-term sporting life. While the superior wear pattern was not totally contained within the cup (Fig. 3), her implant positioning was clearly adequate. Nevertheless both cup edge-wear and CoCr contamination indicated this patient experienced habitual impingement, i.e. alumina cup rim wearing against CoCr femoral neck (Fig. 2). The head wear-pattern was distinctly bi-lobed but OCM images showed the majority of wear was in the superior hemisphere as noted in MOM retrievals (Clarke, 2013). The head wear-rate in this pioneering “Mittelmeier” THA averaged 5.6mm³/year over 32-years of follow-up. This appeared directly comparable to ceramic head wear measured with the same OCM-technique in modern ceramic THA (Esposito, 2012: 0.1 to 7mm³/year). This indicated to us that COC wear rates of the order 10–14mm³/year represented an acceptable “normal” level of performance in young and active individuals.

Introduction

Active patients may benefit from surgical repair of the achilles tendon with the aim of preserving functional length and optimising push-off power. A mini-open device assisted technique has the potential to reduce wound complications, but risks nerve injury. We present the largest published series of midsubstance achilles tendon repairs using the Achillon® device.

Patients with osteoarthritis (OA) of the knee commonly alter their movement to compensate for deficiencies. This study presents a new numerical procedure for classifying sit-to-walk (STW) movement strategies.

Ten control and twelve OA participants performed the STW task in a motion capture laboratory. A full body biomechanical model was used. Participants were instructed to sit in a comfortable self-selected position on a stool height adjusted to 100% of their knee height and then stand and pick up an object from a table in front of them. Three matrices were constructed defining the progression of the torso, feet and hands in the sagittal plane along with a fourth expressing the location of the hands relative to the knees. Hierarchical clustering (HC) was used to identify different strategies. Trials were also classified as to whether the left (L) and right (R) extremities used a matching strategy (bilateral) or not (asymmetrical). Fisher's exact test was used to compare this between groups.

Clustering of the torso matrix dichotomised the trials in two major clusters; subjects leaning forward (LF) or not. The feet and hands matrices revealed sliding the foot backward (FB) and moving an arm forward (AF) strategies respectively. Trials not belonging in the AF cluster were submitted to the last HC of the fourth matrix exposing three additional strategies, the arm pushing through chair (PC), arm pushing through knee (PK) and arm not used (NA). The control participants used the LF+FBR+PK combination most frequently whereas the OA participants used the AFR+PCL. OA patients used significantly more asymmetrical arm strategies, p=0.034.

The results demonstrated that control and OA participants favour different STW strategies. The OA patients asymmetrical arm behaviour possibly indicates compensating for weakness of the affected leg. These strategy definitions may be useful to assess post-operative outcomes and rehabilitation progress.

One of the most common bacteria in orthopaedic prosthetic infections is Staphylococcus Aureus. Infection causes implant failure due to biofilm production. Biofilms are produced by bacteria once they have adhered to a surface.

Nanotopography has major effects on cell behaviour. Our research focuses on bacterial adhesion on nanofabricated materials. We hypothesise that surface nanotopography impacts the differential ability of staphylococci species to adhere via altered metabolomics and may reduce orthopaedic implant infection rate.

Bacteria were grown and growth conditions optimised. Polystyrene and titanium (Ti) nanosurfaces were studied. The polystyrene surfaces had different nanopit arrays, while the Ti surfaces expressed different nanowire structures. Adhesion analysis was performed using fluorescence imaging, quantitative PCR and bacterial percentage coverage calculations. Further substitution with ‘heavy’ labelled glucose into growth medium allowed for bacterial metabolomic analysis and identification of any up-regulated metabolites and pathways.

Our data demonstrates reduced bacterial adhesion on specific nanopit polystyrene arrays, while nanowired titanium showed increased bacterial adhesion following qPCR (P<0.05) and percentage coverage calculations (P<0.001). Further metabolomic analysis identified significantly increased intensity counts of specific metabolites (Pyruvate, Aspartate, Alanine and Carbamoyl aspartate).

Our study shows that by altering nanotopography, bacterial adhesion and therefore biofilm formation can be affected. Specific nanopatterned surfaces may reduce implant infection associated morbidity and mortality. The identification of metabolic pathways involved in adhesion may allow for a targeted approach to biofilm eradication in S. aureus. This is of significant benefit to both the patient and the surgeon, and may well extend far beyond the realms of orthopaedics.

We present the 2 year results for the first 54 patients after Selective Dorsal Rhizotomy (SDR) delivered in Bristol, concentrating on change in Reimers' migration index.

Eligible patients are selected at the SDR multidisciplinary meeting. Physiotherapy assessment is performed pre-operatively and at 6, 12 and 24 months post-surgery. Data collected includes GMFCS, Gross Motor Function Measure (GMFM) 88 and Modified Ashworth score for spasticity for major lower limb muscle groups, amongst other data. Pelvic radiographs are taken pre-operatively and at 2 years post-operatively. Reimers' migration index was measured using the hospital picture archiving and communication system (PACS).

The mean age was 7.2 (3.9–17.5) at the time of surgery. Pre- and post-operative pelvic radiographs were available for 30 patients (60 hips). 57% (n=34) hips showed an increase in migration percentage (mean 5.4%, range 0.1–17.5%) and 43% (n=26) hips showed a decrease (mean 4.0%, range 0–15.5%). Overall no significant difference was found in Reimers' migration index at 2 year follow up (mean increase 1.3% (95% CI −0.3–3.0), p=0.12).

There was an improvement in GMFCS category (by 1 grade) for 9 patients and a worsening for 1 patient at 2 year follow up. The Modified Ashworth score for spasticity improved in all patients. There was a mean improvement of 1.7 in the hip adductors and 2.4 in the ankle plantar flexors.

There was a statistically significant improvement in the GMFM 88 D and E domains of 14.7 (95% CI 11.3–18.1), p<0.0001 and 11.4 (95% CI 7.4–15.7), p<0.0001 respectively.

We found no evidence that SDR leads to worsening hip subluxation at 2 year follow up. All patients had improvement in lower limb spasticity. Overall there was a statistically significant improvement in function, as shown by GMFM 88 domains for standing, walking, running and jumping.