Patient education programmes prior to hip and knee arthroplasty reduce anxiety and create realistic expectations. While traditionally delivered in-person, the Covid-19 pandemic has necessitated change to remote delivery. We describe a ‘Virtual Joint School’ (VJS) model introduced at Ysbyty Gwynedd, and present patient feedback to it.

Eligible patients first viewed online educational videos created by our Multi-Disciplinary Team (MDT); and then attended an interactive virtual session where knowledge was reinforced. Each session was attended by 8–10 patients along with a relative/friend; and was hosted by the MDT consisting of nurses, physiotherapists, occupational therapists, and a former patient who provided personal insight. Feedback on the VJS was obtained prospectively using an electronic questionnaire.

From July 2022 to February 2023, 267 patients attended the VJS; of which 117 (44%) responded to the questionnaire. Among them, 87% found the pre-learning videos helpful and comprehensible, 92% felt their concerns were adequately addressed, 96% felt they had sufficient opportunity to ask questions and 96% were happy with the level of confidentiality involved. While 83% felt they received sufficient support from the health board to access the virtual session, 63% also took support from family/friends to attend it. Only 15% felt that they would have preferred a face-to-face format. Finally, by having ‘virtual’ sessions, each patient saved, on average, 38 miles and 62 minutes travel (10,070 miles and 274 hours saved for 267 patients).

Based on the overwhelmingly positive feedback, we recommend implementation of such ‘Virtual Joint Schools’ at other arthroplasty centres as well.

Meniscal root tears can result from traumatic injury to the knee or gradual degeneration. When the root is injured, the meniscus becomes de-functioned, resulting in abnormal distribution of hoop stresses, extrusion of the meniscus, and altered knee kinematics. If left untreated, this can cause articular cartilage damage and rapid progression of osteoarthritis. Multiple repair strategies have been described; however, no best fixation practice has been established. To our knowledge, no study has compared suture button, interference screw, and HEALICOIL KNOTLESS fixation techniques for meniscal root repairs. The goal of this study is to understand the biomechanical properties of these fixation techniques and distinguish any advantages of certain techniques over others. Knowledge of fixation robustness will aid in surgical decision making, potentially reducing failure rates, and improving clinical outcomes.

19 fresh porcine tibias with intact medial menisci were randomly assigned to four groups: 1) native posterior medial meniscus root (PMMR) (n = 7), 2) suture button (n = 4), 3) interference screw (n = 4), or 4) HEALICOIL KNOTLESS (n = 4). In 12 specimens, the PMMR was severed and then refixed by the specified group technique. The remaining seven specimens were left intact. All specimens underwent cyclic loading followed by load-to-failure testing. Elongation rate; displacement after 100, 500, and 1000 cycles; stiffness; and maximum load were recorded.

Repaired specimens had greater elongation rates and displacements after 100, 500, and 1000 cycles than native PMMR specimens (p 0.05). The native PMMR showed greater maximum load than all repair techniques (p 0.05). In interference screw and HEALICOIL KNOTLESS specimens, failure occurred as the suture was displaced from the fixation and tension was gradually lost. In suture button specimens, the suture was either displaced or completely separated from the button. In some cases, tear formation and partial failure also occurred at the meniscus luggage tag knot. Native PMMR specimens failed through meniscus or meniscus root tearing.

All fixation techniques showed similar biomechanical properties and performed inferiorly to the native PMMR. Evidence against significant differences between fixation techniques suggests that the HEALICOIL KNOTLESS technique may present an additional option for fixation in meniscal root repairs. While preliminary in vitro evidence suggests similarities between fixation techniques, further research is required to determine if clinical outcomes differ.

Major orthopaedic fractures are an independent risk factor for the development of venous thromboembolism (VTE), which are significant causes of preventable morbidity and mortality in trauma patients. Despite thromboprophylaxis, patients who sustain a pelvic or acetabular fracture (PA) continue to have high rates of VTE (12% incidence). Thrombelastography (TEG) is a whole-blood, point-of-care test which provides an overview of the clotting process. Maximal amplitude (MA), from TEG analysis, is the measure of clot strength and values ≥65mm have been used to quantify hypercoagulability and increased VTE risk. Therefore, the primary aim was to use serial TEG analysis to quantify the duration of hypercoagulability, following surgically treated PA fractures.

This is a single centre, prospective cohort study of adult patients 18 years or older with surgically treated PA fractures. Consecutive patients were enrolled from a Level I trauma centre and blood draws were taken over a 3-month follow-up period for serial TEG analysis. Hypercoagulability was defined as MA ≥65mm. Exclusion criteria: bleeding disorders, active malignancy, current therapeutic anticoagulation, burns (>20% of body surface) and currently, or expecting to become pregnant within study timeframe.

Serial TEG analysis was performed using a TEG6s hemostasis analyzer (Haemonetics Corp.) upon admission, pre-operatively, on post-operative day (POD) 1, 3, 5, 7 (or until discharged from hospital, whichever comes sooner), then in follow-up at 2-, 4-, 6-weeks and 3-months post-operatively. Patients received standardized thromboprophylaxis with low molecular weight heparin for 28 days post-operatively. VTE was defined as symptomatic DVT or PE, or asymptomatic proximal DVT, and all participants underwent a screening post-operative lower extremity Doppler ultrasound on POD3. Descriptive statistics were used to determine the association between VTE events and MA values. For the primary outcome measure, the difference between the MA threshold value (≥65mm) and serial MA measures, were compared using one-sided t-tests (α=0.05).

Twenty-eight patients (eight females, 29%) with a mean age of 48±18 years were included. Acetabular fractures were sustained by 13 patients (46%), pelvic fractures by 14 patients (50%), and one patient sustained both. On POD1, seven patients (25%) were hypercoagulable, with 21 patients (78%) being hypercoagulable by POD3, and 17 patients (85%) by POD5. The highest average MA values (71.7±3.9mm) occurred on POD7, where eight patients (89%) were hypercoagulable. At 2-weeks post-operatively, 16 patients (94%) were hypercoagulable, and at four weeks, when thromboprophylaxis was discontinued, six patients (40%) remained hypercoagulable. Hypercoagulability persisted for five patients (25%) at 6-weeks and for two patients (10%) by three months.

There were six objectively diagnosed VTE events (21.4%), five were symptomatic, with a mean MA value of 69.3mm±4.3mm at the time of diagnosis. Of the VTE events, four occurred in participants with acetabular fractures (three male, 75%) and two in those with pelvic fractures (both males).

At 4-weeks post-operatively, when thromboprophylaxis is discontinued, 40% of patients remained hypercoagulable and likely at increased risk for VTE. At 3-months post-operatively, 10% of the cohort continued to be hypercoagulable. Serial TEG analysis warrants further study to help predict VTE risk and to inform clinical recommendations following PA fractures.

Aims

The aim of this study was to surveil whether the standard operating procedure created for the NHS Golden Jubilee sufficiently managed COVID-19 risk to allow safe resumption of elective orthopaedic surgery.

In the vast majority of patients, the anatomical and mechanical axes of the tibia in the coronal plane are widely accepted to be equivalent. This philosophy guides the design and placement of orthopaedic implants within the tibia and in both the knee and ankle joints. However, the presence of coronal tibial bowing may result in a difference between these two axes and hence cause suboptimal placement of implanted prostheses. Although the prevalence of tibial bowing in adults has been reported in Asian populations, to date no exploration of this phenomenon in a Western population has been conducted. The aim of this study was to quantify the prevalence of coronal tibial bowing in a Western population.

This was an observational retrospective cohort study using anteroposterior long leg radiographs collected prior to total knee arthroplasty in our high volume arthroplasty unit. Radiographs were reviewed using a Picture Archiving and Communication System. Using a technique previously described in the literature for assessment of tibial bowing, two lines were drawn, each one third of the length of the tibia. The first line was drawn between the tibial spines and the centre of the proximal third of the tibial medullary canal. The second was drawn from the midpoint of the talar dome to the centre of the distal third of the tibial medullary canal. The angle subtended by these two lines was used to determine the presence of bowing. Bowing was deemed significant if more than two degrees. The position of the apex of the bow determined whether it was medial or lateral. Measurements were conducted by a single observer and 10% of measurements were repeated by the same observer and also by two separate observers to allow calculation of intraclass correlation coefficients (ICCs).

A total of 975 radiographs consecutively performed in the calendar years 2015–16 were reviewed, 485 of the left leg and 490 of the right. In total 399 (40.9%) tibiae were deemed to have bowing more than two degrees. 232 (23.8%) tibiae were bowed medially and 167 (17.1%) were bowed laterally. The mean bowing angle was 3.51° (s.d. 1.24°) medially and 3.52° (s.d. 1.33°) laterally. Twenty-three patients in each group (9.9% medial/13.7% lateral) were bowed more than five degrees. The distribution of bowing angles followed a normal distribution, with the maximal angle observed 10.45° medially and 9.74° laterally. An intraobserver ICC of 0.97 and a mean interobserver ICC of 0.77 were calculated, indicating excellent reliability.

This is the first study reporting the prevalence of tibial bowing in a Western population. In a significant proportion of our sample, there was divergence between the anatomical and mechanical axes of the tibia. This finding has implications for both the design and implantation of orthopaedic prostheses, particularly in total knee arthroplasty. Further research is necessary to investigate whether prosthetic implantation based on the mechanical axis in bowed tibias results in suboptimal implant placement and adverse clinical outcomes.

The meniscus is comprised largely of type I collagen, as well as fibrochondrocytes and proteoglycans. In articular cartilage and intervertebral disc, proteoglycans make a significant contribution to mechanical stiffness of the tissue via negatively charged moieties which generate Donnan osmotic pressures. To date, such a role for proteoglycans in meniscal tissue has not been established. This study aimed to investigate whether meniscal proteoglycans contribute to mechanical stiffness of the tissue via electrostatic effects.

Following local University Ethics Committee approval, discs of meniscal tissue two millimetres thick and of five millimetres diameter were obtained from 12 paired fresh frozen human menisci, from donors < 6 5 years of age, with no history of osteoarthritis or meniscal injury. Samples were taken from anterior, middle and posterior meniscal regions. Each disc was placed within a custom confined compression chamber, permeable at the top and bottom only and then bathed in one of three solutions − 0.14M PBS (mimics cellular environment), deionised water (negates effect of mobile ions) or 3M PBS (negates all ionic effects). The apparatus was mounted within a Bose Electroforce 3100 materials testing machine and a 0.3N preload was applied. The sample was allowed to reach equilibrium, before being subjected to a 10% ramp compressive strain followed by a 7200 second hold phase. Equal numbers of samples from each meniscus and meniscal region were tested in each solution. Resultant stress relaxation curves were fitted to a nonlinear poroviscoelastic model with strain dependent permeability using FEBio finite element modelling software. Goodness of fit (R2) was assessed using a coefficient of determination. All samples were assayed for proteoglycan content. Comparison of resultant mechanical parameters was undertaken using multivariate ANOVA with Bonferroni adjustment for multiple comparisons.

36 samples were tested. A significant difference (p < 0 .05) was observed in the value of the Young's modulus (E) between samples tested in deionised water compared to 0.14M/3M PBS, with the meniscus found to be stiffest in deionised water (E = 1.15 MPa) and least stiff in 3M PBS (E = 0.43 MPa), with the value of E in 0.14M PBS falling in between (0.68 MPa). No differences were observed in the zero strain permeability or the exponential strain dependent/stiffening coefficients. The viscoelastic coefficient and relaxation time values were not found to improve model fit and were thus held at zero. The mean R2 value was 0.78, indicating a good fit and did not differ significantly between solutions. Proteoglycan content was not found to differ with solution, but was found to be significantly increased in the middle region of both menisci.

Proteoglycans make a significant electrostatic contribution to mechanical stiffness of the meniscus, increasing it by 58% in the physiological condition, and are hence integral to its function. It is important to include the influence of ionic effects when modelling meniscus, particularly where fluid flow or localised strain is modelled. From a clinical perspective, it is critical that meniscal regeneration strategies such as scaffolds or allografts attempt to preserve, or compensate for, the function of proteoglycans to ensure normal meniscal function.

Introduction

Virtual fracture clinics (VFCs) are being increasingly used to offer safe and efficient orthopaedic review without the requirement for face-to-face contact. With the onset of the COVID-19 pandemic, we sought to develop an online referral pathway that would allow us to provide definitive orthopaedic management plans and reduce face-to-face contact at the fracture clinics.

Introduction

Hip arthroplasty is considered common to patients aged 65 and over however, both Jennings, et al., (2012) and Bergmann (2016) found THA patients are substantially younger with more patients expecting to return to preoperative activity levels. With heavier, younger, and often more active patients, devices must be able to support a more demanding loading-regime to meet patient expectations. McClung (2000) demonstrated that obese patients can display lower wear-rates with UHMWPE bearing resulting from post-operative, self-induced reduced ambulatory movement, thus questioning if obese kinematics and loading are indeed the worst-case.

Current loading patterns used to test hip implants are governed by ISO 14242-1 (2014). This study aimed to characterize a heavy and active population (referred to as HA) and investigate how the gait profile may differ to the current ISO profile.

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.

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.

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.

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.

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.

This study presents an unusual recurrent case of pigmented villonodular synovitis (PVNS) around a ceramic-on-metal (COM) hip retrieved at 9-years. PVNS literature relates to metal-polyethylene and ceramic-ceramic bearings. Amstutz reported 2 cases with MOM resurfacing and Xiaomei reported PVNS recurring at 14 years with metal-on-polyethylene THA. Friedman reported on PVNS recurrence in a ceramic THA. Ours may be the first reported case of recurrent PVNS of a ceramic-on-metal articulation.

This young female patient (now 38-years of age) had a total hip replacement in 2006 for PVNS in her left hip. In her initial work-up, this case was presumed to be a pseudotumor problem, typical of those related to CoCr debris with high metal-ion concentrations. She had an CoCr stem (AML), 36mm Biolox-delta head (Ceramtec), and a Pinnacle acetabular cup with CoCr liner (Ultramet, Depuy J&J). This patient had no concerns regarding subluxation, dislocation or squeaking. Three years ago she complained of mild to moderate groin and thigh pain in her left hip. This worsened in the past year. She noticed increased swelling now with an asymmetry to her right hip. She went to the emergency room in Dec-2014 and was referred to a plastic surgeon. In our consult we reviewed MARS-MRI and CT-scans that demonstrated multiple mass lesions surrounding the hip. Laboratory results presented Co=0.7, Cr=0.3 ESR=38 and Crp=0.3.

At revision surgery, the joint fluid was hemorrhagic/bloody with hemosiderin staining the soft tissues. Multiple large 4–5×5cm nodules were present in anterior aspect of the hip as well as multiple nodules surrounding posterior capsule and sciatic nerve. Pathology demonstrated a very cellular matrix with hemosiderin-stained tissue and multiple giant cells, which was judged consistent with PVNS. The trunnion showed no fretting, no contamination and no discoloration. The superior neck showed impingement due to low-inclination cup. There was minimal evidence of metal-debris staining the tissues. There was a large metallic-like stripe across the ceramic head.

This is a particularly interesting case and may be the first reported recurrent PVNS around a ceramic-on-metal bearing (COM). Data is scant regarding clinical results of COM bearings and here we have a nine-year result in a young and active female patient. She was believed to have a metalosis-related pseudotumor yet her metal-ion levels were not alarmingly high and there was no particular evidence of implant damage or gross wear products. In addition, the CoCr trunnion appeared pristine. Our work-up continues with analyses of wear and histopath-evidence. This case may demonstrate the need for a broadening of the differential diagnosis when dealing with hip failures.

The treatment of patients with osteoarthritis of the knee and associated extra-articular deformity of the leg is challenging. Current teaching recognises two possible approaches: (1) a total knee replacement (TKR) with intra-articular bone resections to correct the malalignment or (2) an extra-articular osteotomy to correct the malalignment together with a TKR (either simultaneously or staged).

However, a number of these patients only have unicompartmental knee osteoarthritis and, in the absence of an extra-articular deformity would be ideal candidates for joint preserving surgery such as unicompartmental knee replacement (UKR) given its superior functional outcome and lower cost relative to a TKR [1).

We report four cases of medial unicondylar knee replacement, with a simultaneous extra-articular osteotomy to correct deformity, using novel 3D printed patient-specific guides (Embody, UK) (see Figure 1). The procedure was successful in all four patients, and there were no complications. A mean increase in the Oxford knee score of 9.5, and in the EQ5D VAS of 15 was observed.

To our knowledge this is the first report of combined osteotomy and unicompartmental knee replacement for the treatment of extra-articular deformity and knee osteoarthritis. This technically challenging procedure is made possible by a novel 3D printed patient-specific guide which controls osteotomy position, degree of deformity correction (multi-plane if required), and orientates the saw-cuts for the unicompartmental prosthesis according to the corrected leg alignment.

Using 3D printed surgical guides to perform operations not previously possible represents a paradigm shift in knee surgery. We suggest that this joint preserving approach should be considered the preferred treatment option for suitable patients.

Use of “CPR” distance has proven clinical utility in stratifying risks of “steep cups” in MOM failures.[1, 4] The CPR indice has been defined as distance between point of intersection of the hip reaction force (Fig. 1: vector-R in contact patch) and closest point on the inner cup rim.[4] However, the CPR indice has limitations. It assumes that, (1) the hip load-vector (R) will be angled 10°-medial in all patients, (2) the contact patch will be same size in all patients, and (3) the contact patch will be invariant with increasing MOM diameter. In contrast it is known from retrieval studies that larger MOM bearings created much larger wear patches.[3] Furthermore, the size of cup wear-patches in MOM bearings can now be estimated with some certainty using simulator wear data.[2] Our objective was to develop an algorithm that would predict (i) contact-patch size for all cup designs and diameters, (ii) determine actual margin of safety (Fig. 1: MOS) for different laterally-inclined cups, and (iii) predict critical test angles for “steep” cup studies in hip simulators.

The ‘CPR-distance’ (Fig. 1) is subtended by the CPA angle, but the true margin of safety is the distance from edge of wear patch to cup rim, indicated here by MOS angle. In this algorithm the wear-patch size (CAP angle) is a key parameter, as derived from MOM wear data (Fig. 2). The CAP angles decrease with increasing MOM diameter, as defined by strong linear trend (R=0.998). The key 2nd parameter is cup inclination angle that juxtaposes the wear-pattern to the cup rim (CCI). For hemispherical cups the critical inclination is given by CCI = 90 – CAP/2, where articulation angle ABA = 180o. The cup bearing-surface is typically reduced < 180o(sub-hemispherical profile, instrumentation groove, rim bevel, etc). These effects are grouped under ‘rim-detail’, as defined by RD = (180-ABA)/2 (Fig. 1). Thus critical inclination any cup is given by CCI = 90o – (CAP/2) – RD = (ABA – CAP)/2. The margin-of-safety (Fig. 1) is then represented by the equation MOS = 100 – (CIA + CAP/2 + RD).

Applicability of the new algorithm can be visualized with a 48mm MOM (cup ABA=160o) run in a standard simulator test (Fig. 3). The algorithm predicts that with cup at 40o inclination there is good margin of safety (11.8o), representing a 5mm distance. This would become much reduced at CIA = 50o, while true edge-wear appears at the 60o test inclination (Fig. 3. EW = −8.2o). For clinical comparison with ‘CPR-distances’, the algorithm shows that positioning the wear patch 10o-medial (Figs. 1, 3) has margin of safety averaging 11.5 mm (MOS) less than was predicted by the CPR indice. While CPR has shown clinical utility, it is believed that compensating for actual size of cup wear-patterns provides a more realistic risk assessment for different MOM diameters in different cup positions. Thus the new algorithm permits accurate depiction of cup wear-patterns for use in both clinical and simulator studies.

Introduction

Patient Specific Instrumentation (PSI) has the potential to allow surgeons to perform procedures more accurately, at lower cost and faster than conventional instrumentation. However, studies using PSI have failed to convincingly demonstrate any of these benefits clinically. The influence of guide design on the accuracy of placement of PSI has received no attention within the literature.

Our experience has suggested that surgeons gain greater benefit from PSI when undertaking procedures they are less familiar with. Lateral unicompartmental knee replacement (UKR) is relatively infrequently performed and may be an example of an operation for which PSI would be of benefit. We aimed to investigate the impact on accuracy of PSI with respect to the area of contact, the nature of the contact (smooth or studded guide surfaces) and the effect of increasing the number of contact points in different planes.