Overset meshing in combination with novel blended weak-strong fluid-structure interactions for simulations of a translating valve in series with a second valve

Mechanical circulatory support (MCS) devices can bridge the gap to transplant whilst awaiting a viable donor heart. The Realheart Total Artificial Heart is a novel positive-displacement MCS that generates pulsatile flow via bileaflet mechanical valves. This study developed a combined computational fluid dynamics and fluid-structure interaction (FSI) methodology for simulating positive displacement bileaflet valves. Overset meshing discretised the fluid domain, and a blended weak-strong coupling FSI algorithm was combined with variable time-stepping. Four operating conditions of relevant stroke lengths and rates were assessed. The results demonstrated this modelling strategy is stable and efficient for modelling positive-displacement artificial hearts.

Acute regional changes in myocardial strain may predict ventricular remodelling after myocardial infarction in a large animal model

To identify predictors of left ventricular remodelling (LVR) post-myocardial infarction (MI) and related molecular signatures, a porcine model of closed-chest balloon MI was used along with serial cardiac magnetic resonance imaging (CMRI) up to 5-6 weeks post-MI. Changes in myocardial strain and strain rates were derived from CMRI data. Tissue proteomics was compared between infarcted and non-infarcted territories. Peak values of left ventricular (LV) apical circumferential strain (ACS) changed over time together with peak global circumferential strain (GCS) while peak GLS epicardial strains or strain rates did not change over time. Early LVR post-MI enhanced abundance of 39 proteins in infarcted LV territories, 21 of which correlated with LV equatorial circumferential strain rate. The strongest associations were observed for D-3-phosphoglycerate dehydrogenase (D-3PGDH), cysteine and glycine-rich protein-2, and secreted frizzled-related protein 1 (sFRP1). This study shows that early changes in regional peak ACS persist at 5-6 weeks post-MI, when early LVR is observed along with increased tissue levels of D-3PGDH and sFRP1. More studies are needed to ascertain if the observed increase in tissue levels of D-3PGDH and sFRP1 might be casually involved in the pathogenesis of adverse LV remodelling.

Implementation of a Reduced Opioid Utilization Protocol for Radical Cystectomy

BACKGROUND: Radical cystectomy (RC) often requires a prolonged course of opioid medications for postoperative pain management. We implemented a Reduced Opioid Utilization (ROU) protocol to decrease exposure to opioid medications. OBJECTIVE: To determine the impact of the ROU protocol on opioid exposure, pain control, inpatient recovery, and complication rates among patients who underwent RC. METHODS: The ROU protocol includes standardized recovery pathways, a multimodal opioid-sparing pain regimen, and improved patient and provider education regarding non-opioid medications. Opioid exposure was calculated as morphine equivalent dose (MED), and was compared between RC patients following the ROU protocol and patients who previously followed our traditional pathway. Opioid-related adverse drug events (ORADEs), pain scores, length of stay, and 90-day complications, readmission, and mortality were also compared between cohorts. RESULTS: 104 patients underwent RC, 54 (52%) of whom followed the ROU protocol. ROU patients experienced a statistically significant decrease in opioid exposure in the post-anesthesia care unit (p = 0.003) and during their postoperative recovery (85.7±21.0 MED vs 352.6±34.4 MED, p < 0.001). The ROU protocol was associated with a statistically significant decrease in ORADEs after surgery. There was no significant difference in average pain scores, length of stay, readmissions, or 90-day complication or mortality rates. CONCLUSIONS: The ROU protocol decreased opioid use by 77% without compromising pain control or increasing the rate of complications. This study demonstrates the efficacy of non-opioid medications in controlling postoperative pain, and highlights the role providers can play to decrease patient exposure to opioids after RC surgery.

Anatomical study of the prostatic urethra using vinyl polysiloxane casts

BACKGROUND

There are limited studies describing the detailed nonhistologic anatomy of the prostatic urethra. We studied radical prostatectomy specimens to describe the ex vivo anatomical details of its shape and size.

METHODS

We conducted an observational study examining the prostatic urethra anatomy. Prostatic urethra casts (molds) were made using vinyl polysiloxane immediately after fresh specimens had been retrieved following prostatectomy for organ-confined prostate cancer. The following measurements were taken from the casts: anterior length, posterior length, maximal diameter, bladder neck to verumontanum, verumontanum to apex length, and prostate urethral angle (PUA). Prostate volume was calculated using the ellipsoid formula: ((p/6) × transverse × length × height).

RESULTS

Thirty-three prostatic urethral casts were obtained. The mean prostate volume was 38.59 cc. The mean PUA was 127.6°. The mean transverse, apex, and length of the prostate were 4.65, 4.06, and 3.63 cm, respectively. The mean distance from the verumontanum to sphincter was 1.2 cm. The ratio between the anterior and posterior length of the prostatic urethra was 0.82 cm and did not correlate with prostatic size (Figure 8).

CONCLUSION

The distance from the verumontanum to the apex does not change with prostate size; it is uniform with a mean length of 1.2 cm. The anterior length, posterior length, and maximum diameter of the prostatic urethra increase with prostate size. The mean difference between the anterior and posterior length is 0.8 cm and did not correlate with prostate size. Urethral angulation decreased with prostate size but was not significant. Information obtained from this study is of value designing prostatic stents and devices for benign prostatic hyperplasia.

Correction to: Solochrome cyanine: A histological stain for cobalt-chromium wear particles in metal-on-metal periprosthetic tissues

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Solochrome cyanine: A histological stain for cobalt-chromium wear particles in metal-on-metal periprosthetic tissues

Metal-on-metal (MoM) hip arthroplasties produce abundant implant-derived wear debris composed mainly of cobalt (Co) and chromium (Cr). Cobalt-chromium (Co-Cr) wear particles are difficult to identify histologically and need to be distinguished from other wear particle types and endogenous components (e.g., haemosiderin, fibrin) which may be present in MoM periprosthetic tissues. In this study we sought to determine whether histological stains that have an affinity for metals are useful in identifying Co-Cr wear debris in MoM periprosthetic tissues. Histological sections of periprosthetic tissue from 30 failed MoM hip arthroplasties were stained with haematoxylin-eosin (HE), Solochrome Cyanine (SC), Solochrome Azurine (SA) and Perls' Prussian Blue (PB). Sections of periprosthetic tissue from 10 cases of non-MoM arthroplasties using other implant biomaterials, including titanium, ceramic, polymethylmethacrylate (PMMA) and ultra-high molecular weight polyethylene (UHMWP) were similarly analysed. Sections of 10 cases of haemosiderin-containing knee tenosynovial giant cell tumour (TSGCT) were also stained with HE, SC, SA and PB. In MoM periprosthetic tissues, SC stained metal debris in phagocytic macrophages and in the superficial necrotic zone which exhibited little or no trichrome staining for fibrin. In non-MoM periprosthetic tissues, UHMWP, PMMA, ceramic and titanium particles were not stained by SC. Prussian Blue, but not SC or SA, stained haemosiderin deposits in MoM periprosthetic tissues and TSGT. Our findings show that SC staining (most likely Cr-associated) is useful in distinguishing Co-Cr wear particles from other metal/non-metal wear particles types in histological preparations of periprosthetic tissue and that SC reliably distinguishes haemosiderin from Co-Cr wear debris.

Are there clinically relevant anatomical differences of the proximal femur in patients with mild dysplastic and primary hip osteoarthritis? A CT-based matched-pairs cohort study

AIM

To investigate the three-dimensional anatomy and shape of the proximal femur, comparing patients with secondary osteoarthritis (OA) due to mild developmental dysplasia of the hip (DDH) and primary hip OA.

MATERIALS AND METHODS

This retrospective radiographic computed tomography (CT)-based study investigated proximal femoral anatomy in a consecutive series of 84 patients with secondary hip OA due to mild DDH (Crowe type I&II/Hartofilakidis A) compared to 84 patients with primary hip OA, matched for gender, age at surgery, and body mass index.

RESULTS

Men with DDH showed higher neck shaft angles (127±5° vs. 123±4°; p<0.001), whereas women with DDH had a larger femoral head diameter (46±4 vs. 44±3 mm; p=0.002), smaller femoral offset (36±5 vs. 40±4 mm; p<0.001), decreased leg torsion (25±13° vs. 31±16°; p=0.037), and a higher neck shaft angle (128±7° vs. 123±4°; p<0.001) compared to primary OA patients. Similar patterns of the three-dimensional endosteal canal shape of the proximal femur, but a high inter-individual variability for femoral canal torsion at the meta-diaphyseal level were found for DDH and primary OA patients.

CONCLUSION

Standard cementless stem designs are suitable to treat patients with secondary hip OA due to mild DDH; however, high patient variability and subtle anatomical differences in the proximal femur should be respected.

The effect of plate design, bridging span, and fracture healing on the performance of high tibial osteotomy plates: An experimental and finite element study

Objectives

Opening wedge high tibial osteotomy (HTO) is an established surgical procedure for the treatment of early-stage knee arthritis. Other than infection, the majority of complications are related to mechanical factors – in particular, stimulation of healing at the osteotomy site. This study used finite element (FE) analysis to investigate the effect of plate design and bridging span on interfragmentary movement (IFM) and the influence of fracture healing on plate stress and potential failure.

Materials and Methods

A 10° opening wedge HTO was created in a composite tibia. Imaging and strain gauge data were used to create and validate FE models. Models of an intact tibia and a tibia implanted with a custom HTO plate using two different bridging spans were validated against experimental data. Physiological muscle forces and different stages of osteotomy gap healing simulating up to six weeks postoperatively were then incorporated. Predictions of plate stress and IFM for the custom plate were compared against predictions for an industry standard plate (TomoFix).

Results

For both plate types, long spans increased IFM but did not substantially alter peak plate stress. The custom plate increased axial and shear IFM values by up to 24% and 47%, respectively, compared with the TomoFix. In all cases, a callus stiffness of 528 MPa was required to reduce plate stress below the fatigue strength of titanium alloy.

Conclusion

We demonstrate that larger bridging spans in opening wedge HTO increase IFM without substantially increasing plate stress. The results indicate, however, that callus healing is required to prevent fatigue failure.

Cite this article: A. R. MacLeod, G. Serrancoli, B. J. Fregly, A. D. Toms, H. S. Gill. The effect of plate design, bridging span, and fracture healing on the performance of high tibial osteotomy plates: An experimental and finite element study. Bone Joint Res 2018;7:639–649. DOI: 10.1302/2046-3758.712.BJR-2018-0035.R1.

Native kidney cytomegalovirus nephritis and cytomegalovirus prostatitis in a kidney transplant recipient

We present a case of cytomegalovirus (CMV) native kidney nephritis and prostatitis in a CMV D+/R- kidney transplant recipient who had completed six months of CMV prophylaxis four weeks prior to the diagnosis of genitourinary CMV disease. The patient had a history of benign prostatic hypertrophy and urinary retention that required self-catheterization to relieve high post-voiding residual volumes. At 7 months post-transplant, he was found to have a urinary tract infection, moderate hydronephrosis of the transplanted kidney, and severe hydroureteronephrosis of the native left kidney and ureter, and underwent native left nephrectomy and transurethral resection of the prostate. Histopathologic examination of kidney and prostate tissue revealed CMV inclusions consistent with invasive CMV disease. This case highlights that CMV may extend beyond the kidney allograft to involve other parts of the genitourinary tract, including the native kidneys and prostate. Furthermore, we highlight the tissue-specific risk factors that preceded CMV tissue invasion. In addition to concurrent diagnoses, health care providers should have a low threshold for considering late-onset CMV disease in high-risk solid organ transplant recipients presenting with signs and symptoms of genitourinary tract pathology.

Juvenile bovine bone is an appropriate surrogate for normal and reduced density human bone in biomechanical testing: a validation study

Orthopaedic research necessitates accurate and reliable models of human bone to enable biomechanical discoveries and translation into clinical scenarios. Juvenile bovine bone is postulated to be a potential model of normal human bone given its dimensions and comparatively reduced ethical restrictions. Demineralisation techniques can reduce bone density and alter bone properties, and methods to model osteoporotic bone using demineralised juvenile bovine bone are investigated. Juvenile bovine long bones were quantitatively CT scanned to assess bone density. Demineralisation using hydrochloric acid (0.6, 1.2 and 2.4 M) was performed to create different bone density models which underwent biomechanical validation for normal and osteoporotic bone models. All long bones were found to have comparable features to normal human bone including bone density (1.96 ± 0.08 gcm-3), screw insertion torque and pullout strength. Demineralisation significantly reduced bone density and pullout strength for all types, with 0.6 M hydrochloric acid creating reductions of 25% and 71% respectively. Juvenile bovine bone is inexpensive, easy to source and not subject to extensive ethical procedures. This study establishes for the first time, the use of its long bones as surrogates for both normal and osteoporotic human specimens and offers preliminary validation for its use in biomechanical testing.

The efficacy of rotational control designs in promoting torsional stability of hip fracture fixation

OBJECTIVES

Fractures of the proximal femur are a common clinical problem, and a number of orthopaedic devices are available for the treatment of such fractures. The objective of this study was to assess the rotational stability, a common failure predictor, of three different rotational control design philosophies: a screw, a helical blade and a deployable crucifix.

METHODS

Devices were compared in terms of the mechanical work (W) required to rotate the implant by 6° in a bone substitute material. The substitute material used was Sawbones polyurethane foam of three different densities (0.08 g/cm³, 0.16 g/cm³ and 0.24 g/cm³). Each torsion test comprised a steady ramp of 1°/minute up to an angular displacement of 10°.

RESULTS

The deployable crucifix design (X-Bolt), was more torsionally stable, compared to both the dynamic hip screw (DHS, p = 0.008) and helical blade (DHS Blade, p= 0.008) designs in bone substitute material representative of osteoporotic bone (0.16 g/cm³ polyurethane foam). In 0.08 g/cm³ density substrate, the crucifix design (X-Bolt) had a higher resistance to torsion than the screw (DHS, p = 0.008). There were no significant differences (p = 0.101) between the implants in 0.24 g/cm³ density bone substitute.

CONCLUSIONS

Our findings indicate that the clinical standard proximal fracture fixator design, the screw (DHS), was the least effective at resisting torsional load, and a novel crucifix design (X-Bolt), was the most effective design in resisting torsional load in bone substitute material with density representative of osteoporotic bone. At other densities the torsional stability was also higher for the X-Bolt, although not consistently significant by statistical analysis.Cite this article: J. D. Gosiewski, T. P. Holsgrove, H. S. Gill. The efficacy of rotational control designs in promoting torsional stability of hip fracture fixation. Bone Joint Res 2017;6:270-276. DOI: 10.1302/2046-3758.65.BJR-2017-0287.R1.

Readmission Rate and Causes at 90-Day after Radical Cystectomy in Patients on Early Recovery after Surgery Protocol

Background: Radical cystectomy (RC) is associated with high risk of early and late perioperative complications, and readmissions. The Enhanced Recovery After Surgery (ERAS) protocol has been applied to RC showing decreased hospital stay without increased morbidity.

Objective: To evaluate the specific causes of hospital readmissions in RC patients treated before and after adoption of an ERAS protocol at our institution.

Methods: We retrospectively evaluated the outcome of 207 RC patients on ERAS protocol at the Stanford University Hospital from January 2012 to December 2014. We focused on early (30-day) and late (90-day) postoperative readmission rate and causes. Results were compared with a pre-ERAS consecutive series of 177 RC patients from January 2009 to December 2011.

Results: In the post-ERAS time period a total of 56 patients were readmitted, 41 within the first 30 days after surgery (20%) and 15 within the following 60 days (7%). Fever, often associated with dehydration, was the most common reason for presentation to the hospital, accounting for 57% of all readmissions. At 90 days infection accounted for 53% of readmissions. Of all the patients readmitted during the first 90 days after surgery, 32 had positive urine cultures, mostly caused by Enterococcus faecalis isolated in 18 (56%). Readmission rates did not increase since the introduction of the ERAS protocol, with an incidence of 27% in the post-ERAS group versus 30% in the pre-ERAS group.

Conclusions: Despite accurate adherence to most recent perioperative antibiotic guidelines, the incidence of readmissions after RC due to infection still remains significant.

Effect of trunnion roughness and length on the modular taper junction strength under typical intraoperative assembly forces

Modular hip implants are at risk of fretting-induced postoperative complications most likely initiated by micromotion between adjacent implant components. A stable fixation between ball head and stem-neck taper is critical to avoid excessive interface motions. Therefore, the aim of this study was to identify the effect of trunnion roughness and length on the modular taper strength under typical intraoperative assembly forces. Custom-made Titanium trunnions (standard/mini taper, smooth/grooved surface finish) were assembled with modular Cobalt-chromium heads by impaction with peak forces ranging from 2kN to 6kN. After each assembly process these were disassembled with a materials testing machine to detect the pull-off force as a measure for the taper strength. As expected, the pull-off forces increased with rising peak assembly force (p < 0.001). For low and moderate assembly forces, smooth standard tapers offered higher pull-off forces compared to grooved tapers (p < 0.038). In the case of an assembly force of 2kN, mini tapers showed a higher taper strength than standard ones (p=0.037). The results of this study showed that smooth tapers provided a higher strength for taper junctions. This higher taper strength may reduce the risk of fretting-related complications especially in the most common range of intraoperative assembly forces.

Large-diameter total hip arthroplasty modular heads require greater assembly forces for initial stability

Objectives

Modular junctions are ubiquitous in contemporary hip arthroplasty. The head-trunnion junction is implicated in the failure of large diameter metal-on-metal (MoM) hips which are the currently the topic of one the largest legal actions in the history of orthopaedics (estimated costs are stated to exceed $4 billion). Several factors are known to influence the strength of these press-fit modular connections. However, the influence of different head sizes has not previously been investigated. The aim of the study was to establish whether the choice of head size influences the initial strength of the trunnion-head connection.

Materials and Methods

Ti-6Al-4V trunnions (n = 60) and two different sizes of cobalt-chromium (Co-Cr) heads (28 mm and 36 mm; 30 of each size) were used in the study. Three different levels of assembly force were considered: 4 kN; 5 kN; and 6 kN (n = 10 each). The strength of the press-fit connection was subsequently evaluated by measuring the pull-off force required to break the connection. The statistical differences in pull-off force were examined using a Kruskal–Wallis test and two-sample Mann–Whitney U test. Finite element and analytical models were developed to understand the reasons for the experimentally observed differences.

Results

36 mm diameter heads had significantly lower pull-off forces than 28 mm heads when impacted at 4 kN and 5 kN (p < 0.001; p < 0.001), but not at 6 kN (p = 0.21). Mean pull-off forces at 4 kN and 5 kN impaction forces were approximately 20% larger for 28 mm heads compared with 36 mm heads. Finite element and analytical models demonstrate that the differences in pull-off strength can be explained by differences in structural rigidity and the resulting interface pressures.

Conclusion

This is the first study to show that 36 mm Co-Cr heads have up to 20% lower pull-off connection strength compared with 28 mm heads for equivalent assembly forces. This effect is likely to play a role in the high failure rates of large diameter MoM hips.

Cite this article: A. R. MacLeod, N. P. T. Sullivan, M. R. Whitehouse, H. S. Gill. Large-diameter total hip arthroplasty modular heads require greater assembly forces for initial stability. Bone Joint Res 2016;5:338–346. DOI: 10.1302/2046-3758.58.BJR-2016-0044.R1.

Influence of consciousness, muscle action and activity on medial condyle translation after Oxford unicompartmental knee replacement

BACKGROUND

Quantification of the in vivo position of the medial condyle throughout flexion is important for knee replacement design, and understanding knee pathology. The influence of consciousness, muscle action, and activity type on condyle translation was examined in patients who had undergone medial unicompartmental knee replacement (UKR) using lateral video fluoroscopy.

METHODS

The position of the centre of the femoral component relative to the tibial component was measured for nine patients under different conditions. The following activities were assessed; passive flexion and extension when anaesthetised, passive flexion and extension when conscious, and active flexion, extension and step-up.

RESULTS

The position of the centre of the femoral component relative to the tibial component was highly patient dependent. The greatest average translation range (14.9 mm) was observed in anaesthetised patients, and the condyle was significantly more anterior near to extension. Furthermore, when conscious but being moved passively, the femoral condyle translated a greater range (8.9 mm) than when moving actively (5.2mm). When ascending stairs, the femoral condyle was more posterior at 20-30° of flexion than during flexion/extension.

CONCLUSIONS

The similarity between these results and published data suggest that knee kinematics following mobile-bearing UKR is relatively normal. The results show that in the normal knee and after UKR, knee kinematics is variable and is influenced by the patient, consciousness, muscle action, and activity type.

CLINICAL RELEVANCE

It is therefore essential that all these factors are considered during knee replacement design, if the aim is to achieve more normal knee kinematics.

The effect of orientation of the acetabular component on outcome following total hip arthroplasty with small diameter hard-on-soft bearings

We assessed the orientation of the acetabular component in 1070 primary total hip arthroplasties with hard-on-soft, small diameter bearings, aiming to determine the size and site of the target zone that optimises outcome. Outcome measures included complications, dislocations, revisions and ΔOHS (the difference between the Oxford Hip Scores pre-operatively and five years post-operatively). A wide scatter of orientation was observed (2sd 15°). Placing the component within Lewinnek's zone was not associated withimproved outcome. Of the different zone sizes tested (± 5°, ± 10° and ± 15°), only ± 15° was associated with a decreased rate of dislocation. The dislocation rate with acetabular components inside an inclination/anteversion zone of 40°/15° ± 15° was four times lower than those outside. The only zone size associated with statistically significant and clinically important improvement in OHS was ± 5°. The best outcomes (ΔOHS > 26) were achieved with a 45°/25° ± 5° zone. This study demonstrated that with traditional technology surgeons can only reliably achieve a target zone of ±15°. As the optimal zone to diminish the risk of dislocation is also ±15°, surgeons should be able to achieve this. This is the first study to demonstrate that optimal orientation of the acetabular component improves the functional outcome. However, the target zone is small (± 5°) and cannot, with current technology, be consistently achieved.

Pelvic position and movement during hip replacement

The orientation of the acetabular component is influenced not only by the orientation at which the surgeon implants the component, but also the orientation of the pelvis at the time of implantation. Hence, the orientation of the pelvis at set-up and its movement during the operation, are important. During 67 hip replacements, using a validated photogrammetric technique, we measured how three surgeons orientated the patient's pelvis, how much the pelvis moved during surgery, and what effect these had on the final orientation of the acetabular component. Pelvic orientation at set-up, varied widely (mean (± 2, standard deviation (sd))): tilt 8° (2sd ± 32), obliquity -4° (2sd ± 12), rotation -8° (2sd ± 14). Significant differences in pelvic positioning were detected between surgeons (p < 0.001). The mean angular movement of the pelvis between set-up and component implantation was 9° (sd 6). Factors influencing pelvic movement included surgeon, approach (posterior > lateral), procedure (hip resurfacing > total hip replacement) and type of support (p < 0.001). Although, on average, surgeons achieved their desired acetabular component orientation, there was considerable variability (2sd ± 16) in component orientation. We conclude that inconsistency in positioning the patient at set-up and movement of the pelvis during the operation account for much of the variation in acetabular component orientation. Improved methods of positioning and holding the pelvis are required.

A semi-automated measurement technique for the assessment of radiolucency

The assessment of radiolucency around an implant is qualitative, poorly defined and has low agreement between clinicians. Accurate and repeatable assessment of radiolucency is essential to prevent misdiagnosis, minimize cases of unnecessary revision, and to correctly monitor and treat patients at risk of loosening and implant failure. The purpose of this study was to examine whether a semi-automated imaging algorithm could improve repeatability and enable quantitative assessment of radiolucency. Six surgeons assessed 38 radiographs of knees after unicompartmental knee arthroplasty for radiolucency, and results were compared with assessments made by the semi-automated program. Large variation was found between the surgeon results, with total agreement in only 9.4% of zones and a kappa value of 0.602; whereas the automated program had total agreement in 81.6% of zones and a kappa value of 0.802. The software had a 'fair to excellent' prediction of the presence or the absence of radiolucency, where the area under the curve of the receiver operating characteristic curves was 0.82 on average. The software predicted radiolucency equally well for cemented and cementless implants (p = 0.996). The identification of radiolucency using an automated method is feasible and these results indicate that it could aid the definition and quantification of radiolucency.

Horses and cows might teach us about human knees

Our comparative study of the knees of horses and cows (paraphrased as highly evolved joggers and as domesticated couch-potatoes, respectively) demonstrates significant differences in the posterior sections of bovine and equine tibial cartilage, which are consistent with specialisation for gait. These insights were possible using a novel analytical measuring technique based on the shearing of small biopsy samples, called dynamic shear analysis. We assert that this technique could provide a powerful new tool to precisely quantify the pathology of osteoarthritis for the medical field.

How many different types of femora are there in primary hip osteoarthritis? An active shape modeling study

We assessed the variation in proximal femoral canal shape and its association with geometric and demographic parameters in primary hip OA. In a retrospective cohort study, the joint geometry of the proximal femur was evaluated on radiographs and corresponding CT scans of 345 consecutive patients with end-stage hip OA. Active shape modeling (ASM) was performed to assess the variation in endosteal shape of the proximal femur. To identify natural groupings of patients, hierarchical cluster analysis of the shape modes was used. ASM identified 10 independent shape modes accounting for >96% of the variation in proximal femoral canal shape within the dataset. Cluster analysis revealed 10 specific shape clusters. Significant differences in geometric and demographic parameters between the clusters were observed. ASM and subsequent cluster analysis have the potential to identify specific morphological patterns of the proximal femur despite the variability in proximal femoral anatomy. The study identified patterns of proximal femoral canal shape in hip OA that allow a comprehensive classification of variation in shape and its association with joint geometry. Our data may improve future stem designs that will optimize stem fit and simultaneously allow individual restoration of hip biomechanics.

An analysis of dislocation of the domed Oxford Lateral Unicompartmental Knee Replacement

BACKGROUND

The Oxford Unicompartmental Knee Replacement (OUKR) uses a mobile bearing to minimise wear. Bearing dislocation is a problem in the lateral compartment as the ligaments are loose in flexion. A domed tibial component has been introduced to minimise the risk of dislocation, yet they still occur, particularly medially. The aim of this mechanical study was to compare the domed and flat tibial components and to identify surgical factors that influence the risk of dislocation.

METHOD

A jig was constructed to assess the amount of vertical distraction of the lateral OUKR for a dislocation to occur. Three methods of dislocation were assessed: laterally, medially, 'over the wall' and anteriorly. The study focused on medial dislocation.

RESULTS

Significantly (p=0.02) greater vertical distraction was required to dislocate the bearing with the domed tibia rather than the flat. For medial dislocation bearing distance from the wall, femoral component external rotation and tibial rotation were associated with significantly less distraction for dislocation. With the optimal technique with the domed tibia the distraction required to dislocate the bearing medially was 6.4 mm, whereas with poor technique it was 4.6 mm.

CONCLUSIONS

This study suggests that to minimise the risk of dislocation the domed tibia should be used. The component should be implanted so the bearing is close to the wall, but does not hit it, and in flexion the femoral and tibial components should be neutrally aligned.

Does body mass index affect the outcome of unicompartmental knee replacement?

BACKGROUND

Obesity is considered to be a contraindication for unicompartmental knee replacement (UKR). The aim was to study the impact of BMI on failure rate and clinical outcome of the Oxford mobile bearing UKR.

METHOD

Two thousand four hundred and thirty-eight medial Oxford UKRs were studied prospectively and divided into groups: BMI<25 (n=378), BMI 25 to <30 (n=856), BMI 30 to <35 (n=712), BMI 35 to <40 (n=286), and BMI 40 to <45 (n=126) and BMI≥45 (n=80).

RESULTS

There was no significant difference in survival rate between groups. At a mean follow-up of 5years (range 1-12years) there was no significant difference in the Objective American Knee Society Score between groups. There was a significant (p<0.01) trend with the Oxford Knee Score (OKS) and Functional American Knee Society Scores decreasing with increasing BMI. As there was an opposite trend (p<0.01) in pre-operative OKS, the change in OKS increased with increasing BMI (p=0.048). The mean age at surgery was significantly (p<0.01) lower in patients with higher BMI.

CONCLUSIONS

Increasing BMI was not associated with an increasing failure rate. It was also not associated with a decreasing benefit from the operation. Therefore, a high BMI should not be considered a contra-indication to mobile bearing UKR.

LEVEL OF EVIDENCE

IV.

Predictive outcomes of revision total hip replacement--a consecutive series of 1176 patients with a minimum 10-year follow-up

The burden of revision total hip replacement (THR) surgery is increasing. With an increasing life expectancy and younger age of primary surgery this trend is set to continue. There are few data on the long-term outcome of revision THR. This retrospective study of 1176 consecutive revision THRs with a minimum 10-year follow-up from a University Teaching Hospital was undertaken to review implant survival and patient reported outcomes. Mean follow-up was 11 years with implant survival at 10 years of 82% (CI: 80-85). Implant survival varied between 58% (unexplained pain) to 84% (aseptic loosening) depending on the indication for revision surgery. Positive predictors of survival were age greater than 70 at the time of surgery (p=0.011), revision for aseptic loosening (p<0.01) and revision of both components or just the acetabular component (p<0.01). At the last review, mean Oxford Hip Score (OHS) was 34 (SD: 11.3) and 92% of the living patients with unrevised hips were satisfied with the outcome of revision surgery. This long term study has demonstrated that positive predictors of survival and outcome of revision THR surgery are age greater than 70 years, revision for aseptic loosening and component revision. This should aid surgeons in their counselling of patients prior to surgery.

Preoperative pain location is a poor predictor of outcome after Oxford unicompartmental knee arthroplasty at 1 and 5 years

PURPOSE

Indications for unicompartmental knee arthroplasty (UKA) vary between units. Some authors have suggested, and many surgeons believe, that medial UKA should only be performed in patients who localise their pain to the medial joint line. This is despite research showing a poor correlation between patient-reported location of pain and radiological or operative findings in osteoarthritis. The aim of this study is to determine the effect of patient-reported preoperative pain location and functional outcome of UKA at 1 and 5 years.

METHODS

Preoperative pain location data were collected for 406 knees (380 patients) undergoing Oxford medial UKA. Oxford Knee Score, American Knee Society Scores and Tegner activity scale were recorded preoperatively and at follow-up; 272/406 (67 %) had pure medial pain, 25/406 (6 %) had pure anterior knee pain, and 109/406 (27 %) had mixed or generalised pain. None had pure lateral pain. The primary outcome interval is 1 year; 132/406 patients had attained 5 years by the time of analysis, and their 5-year data are presented.

RESULTS

At 1 and 5 years, each group had improved significantly by each measure [mean ΔOKS 15.6 (SD 8.9) at year 1, 16.3 (9.3) at year 5]. There was no difference between the groups, nor between patients with and without anterior knee pain or isolated medial pain.

CONCLUSIONS

No correlation is demonstrated between preoperative pain location and outcome. We conclude that localised medial pain should not be a prerequisite to UKA and that it may be performed in patients with generalised or anterior knee pain.

Medial femoral head border is a reliable and reproducible reference for axis determination for femoral component of unicompartmental knee arthroplasty

PURPOSE

The femoral component should be implanted parallel to the mechanical axis in unicompartmental knee arthroplasty. It was hypothesised that a line between medial femoral condyle centres and medial border of femoral head will be parallel to the mechanical axis; this study set out to examine this hypothesis.

METHODS

One hundred X-rays in fifty patients were included for this study. Long-leg standing X-rays including hip and ankle with patellae facing forwards were obtained. On these films, we measured the angle, α, between mechanical axis and the line between the femoral head centre and knee centre (medial mechanical axis), and the angle, β, between the medial mechanical axis and a line between medial femoral condyle and femoral head centre.

RESULTS

The average value of α was 0.1 ± 0.5° and the average value of β 3.0° ± 0.3°. These data indicate that mechanical axis and medial mechanical axis are virtually parallel to each other.

CONCLUSION

As medial femoral head border is easily identified fluoroscopically, it is a reliable landmark for orientating the femoral component of medial UKA.

Improved fixation in cementless unicompartmental knee replacement: five-year results of a randomized controlled trial

BACKGROUND

When used for appropriate indications, unicompartmental knee replacement is associated with fewer complications, faster recovery, and better function than total knee replacement. However, joint registries demonstrate a higher revision rate for unicompartmental knee replacement. Currently, most unicompartmental knee replacements are cemented; common reasons for revision include aseptic loosening and pain. These problems could potentially be addressed by using cementless implants, with coatings designed to improve fixation. The objectives of this study were to compare the quality of fixation as well as clinical outcomes of cemented and cementless unicompartmental knee replacements at five years of follow-up.

METHODS

A randomized controlled trial was established with sixty-three knees (sixty-two patients) receiving either cemented (thirty-two patients) or cementless Oxford unicompartmental knee replacements (thirty patients). Fixation was assessed with fluoroscopic radiographs aligned to the bone-implant interface at one and five years. Outcome scores, including the Oxford Knee Score, Knee Society objective and functional scores, and Tegner Activity Score, were collected preoperatively and at six months and one, two, and five years postoperatively. At each postoperative time point, these were recorded as absolute scores and change from the preoperative score.

RESULTS

Four patients died during the study period. There were no revisions. Mean operative time was nine minutes shorter in the cementless group (p = 0.049). At five years, there was no significant difference in any outcome measure except the Knee Society functional score and the change in the Knee Society functional score, which were significantly better in the cementless group (p = 0.003 for both). There were significantly more tibial radiolucencies in the cemented group (twenty of thirty knees versus two of twenty-seven knees; p < 0.001). There were nine complete radiolucencies in the cemented group and none in the cementless group (p = 0.01).

CONCLUSIONS

Cementless fixation provides improved fixation at five years compared with cemented fixation in mobile-bearing unicompartmental knee replacements, maintaining equivalent or superior clinical outcomes with a shorter operative time and no increase in complications.

LEVEL OF EVIDENCE

Therapeutic level I. See Instructions for authors for a complete description of levels of evidence.

Ten-year RSA-measured migration of the Exeter femoral stem

The Exeter femoral stem is a double-tapered highly polished collarless cemented implant with good long-term clinical results. In order to determine why the stem functions well we have undertaken a long-term radiostereometric analysis (RSA) study. A total of 20 patients undergoing primary Exeter total hip replacement for osteoarthritis using the Hardinge approach were recruited and followed with RSA for ten years. The stems progressively subsided and internally rotated with posterior head migration. The mean subsidence was 0.7 mm (95% confidence interval (CI) 0.5 to 0.9) at two years and 1.3 mm (95% CI 1.0 to 1.6) at ten years. The mean posterior migration of the head was 0.7 mm (95% CI 0.5 to 0.9) at two years and 1.2 mm (95% CI 1.0 to 1.4) at ten years. There was no significant cement restrictor migration. The Exeter stem continues to subside slowly into the cement mantle in the long term. This appears to compress the cement and the cement bone interface, contributing to secure fixation in the long term.

Species compositions and ecology of the riverine ichthyofaunas in two Sulawesian islands in the biodiversity hotspot of Wallacea

This account of the riverine ichthyofaunas from the islands of Buton and Kabaena, off south-eastern mainland Sulawesi, represents the first detailed quantitative checklist and ecological study of the riverine fish faunas in the biological hotspot of Wallacea. The results are based on analysis of samples collected by electrofishing at a wide range of sites from July to September in both 2001 and 2002. While the fauna was diverse, with the 2179 fishes caught comprising 64 species representing 43 genera and 22 families, the catches were dominated by the Gobiidae (26 species and 25% by numbers), Eleotridae (seven species and 27% by numbers), Zenarchopteridae (three species and 22% by numbers) and Anguillidae (two species and 12% by numbers). The most abundant species were the eleotrids Eleotris aff. fusca-melanosoma and Ophieleotris aff. aporos, the anguillid Anguilla celebesensis, the zenarchopterids Nomorhamphus sp. and Nomorhamphus ebrardtii and the gobiids Sicyopterus sp. and Glossogobius aff. celebius-kokius. The introduced catfish Clarias batrachus was moderately abundant at a few sites. Cluster analysis, allied with the similarity profiles routine SIMPROF, identified seven discrete groups, which represented samples from sites entirely or predominantly in either Buton (five clusters) or Kabaena (two clusters). Species composition was related to geographical location, distance from river mouth, per cent contribution of sand and silt, altitude and water temperature. The samples from the two islands contained only one species definitively endemic to Sulawesi, i.e. N. ebrardtii and another presumably so, i.e. Nomorhamphus sp., contrasting starkly with the 57 species that are endemic to Sulawesi and, most notably, its large central and deep lake systems on the mainland. This accounts for the ichthyofaunas of these two islands, as well as those of rivers in northern mainland Sulawesi and Flores, being more similar to each other than to those of the central mainland lake systems. This implies that the major adaptive radiation of freshwater fishes in Sulawesi occurred in those lacustrine environments rather than in rivers.

Discrete mineralisation of the acetabular labrum: a novel marker of femoroacetabular impingement?

Femoroacetabular impingement (FAI) is increasingly thought to play a role in the development of hip osteoarthritis, but is difficult to define clinically and on imaging. This study investigates mineralisations of the acetabular labrum (MALs), which are small, discrete foci of dense radio-opacity within the region of the acetabular labrum. The study aims to characterise MALs and test the hypothesis that MALs are associated with FAI. CT images and radiographs of 106 hips in 66 individuals without known FAI were reviewed for the presence of MALs. The anatomical locations of the MALs in the acetabular labrum were measured. Three current radiographic markers of FAI were recorded in hips with MALs and in age- and gender-matched hips without MALs: centre-edge angle and acetabular version angle as measures of pincer impingement, and alpha angle as a measure of cam impingement. MALs were identified in 18% of hips (n=19). Hips with MAL had a larger mean alpha angle (p=0.013) than those without. MALs were found to be located anterosuperiorly and posterosuperiorly within the labrum, consistent with coup and contrecoup impingement lesion locations reported for FAI. No significant association was found between MAL and centre-edge angle or version angle. Our data demonstrate that MALs are associated with increased alpha angle and thus may be linked to cam-type FAI. MALs have not previously been associated with FAI. This correlation may give further insight into the disease process underlying hip osteoarthritis and might represent a future radiographic marker of cam-type FAI.

The hereditary predisposition to hip osteoarthritis and its association with abnormal joint morphology

OBJECTIVE

Genetic factors and abnormalities of joint morphology are important in the aetiology of hip osteoarthritis (OA). The extent to which genetic influences are manifest through joint morphology has undergone limited investigation. Using a cohort with an hereditary predisposition to end-stage hip OA and a control group with no inherited risk, we aimed to identify associations with abnormal joint morphology and clinical features.

DESIGN

One hundred and twenty-three individuals (mean age 52 years) with a family history of total hip arthroplasty (THA) (termed 'sibkids') were compared with 80 spouse controls. Morphology was assessed using standardised radiographs and cam, dysplasia, and pincer deformities defined. Regression modelling described the association of cohort with abnormal joint morphology, adjusting for confounders [age, gender, body mass index (BMI), OA, and osteophyte].

RESULTS

Sibkids had an odds ratio of 2.1 [95%confidence interval (CI) 1.3-3.5] for cam deformity. There were no differences in the prevalence of dysplasia or pincer deformities. In both groups, hips with cam deformities or dysplasia were more likely to have clinical features than normal hips [odds ratio (OR) 4.46 (1.8-11.3), and 4.40 (1.4-14.3) respectively]. Pincer deformity was associated with positive signs in the sibkids but not in the controls (OR 3.0; 1.1-8.2).

DISCUSSION

After adjustment for confounders that cause secondary morphological change, individuals with an hereditary predisposition to end-stage hip OA had a higher prevalence of morphological abnormalities associated with hip OA. Sibkids were more likely to demonstrate clinical features in the presence of pincer deformity, suggesting that the genes are acting not only through abnormal morphology but also through other factors that influence the prevalence of pain.

The association between hip morphology parameters and nineteen-year risk of end-stage osteoarthritis of the hip: a nested case-control study

Objective

Subtle deformities of the hip joint are implicated in the etiology of osteoarthritis (OA) of the hip. Parameters that quantify these deformities may aid understanding of these associations. We undertook this study to examine relationships between such parameters and the 19-year risk of total hip arthroplasty (THA) for end-stage OA.

Methods

A new software program designed for measuring morphologic parameters around the hip was developed and validated in a reliability study. THA was the outcome measure for end-stage OA. A nested case–control study was used with individuals from a cohort of 1,003 women who were recruited at year 1 in 1989 and followed up to year 20 (the Chingford Study). All hips with THA by year 20 and 243 randomly selected control hips were studied. Pelvis radiographs obtained at year 2 were analyzed for variations in hip morphology. Measurements were compared between the THA case group and the control group.

Results

Patients with THA had a higher prevalence of cam deformity than did their respective controls (median alpha angle 62.4° versus 45.8° [P = 0.001]; mean modified triangular index height 28.5 mm versus 26.9 mm [P = 0.001]) as well as a higher prevalence of acetabular dysplasia (mean lateral center edge angle 29.5° versus 34.3° [P = 0.001]; median extrusion index 0.25 versus 0.185 [P = 0.009]). Logistic regression analyses clustering by subject and adjusting for radiographic hip OA at year 2 showed that these morphologic parameters were still significantly associated with THA by year 20. The alpha angle and lateral center edge angle predicted the risk of THA independently when included in the same model.

Conclusion

This investigation describes measurements that predict the risk of THA for end-stage OA by year 20, independently of the presence of radiographic hip OA at year 2. These measurements can be made on an anteroposterior pelvis radiograph, which is an inexpensive and commonly used clinical method of investigation.

Histology of the bone-cement interface in retrieved Oxford unicompartmental knee replacements

INTRODUCTION

Radiolucent lines (RLL) are commonly seen at the cement-bone interface of knee replacements, yet are poorly understood. Although thin RLL are not associated with implant loosening or poor patient outcome there is still concern that they indicate sub-optimal fixation. The primary study aim is to characterise the histology at the cement-tibia interface in Oxford unicompartmental knee replacement (UKR). The second aim is to assess whether a correlation exists between the presence of a RLL and the type of tissue that predominates at the interface.

METHODS

The radiology and histology of retrieved specimens of the interface from around firmly fixed tibial trays in ten patients undergoing revision between 1 and 19 years after Oxford UKR were studied.

RESULTS

Pre-revision radiographs showed the presence of both full and partial RLL. On contact radiographs of 5mm thick sections of the interface the total percentage of radiolucency ranged from 0 to 90% between patients. There was no consistent pattern for the distribution of radiolucency. Histological assessment demonstrated that under every tibial component there were areas where there was direct contact and interdigitation between bone and cement. The amount of direct bone-cement contact was between 19% and 95% of the tibial tray surface area. The remaining tissue was mainly fibrocartilage but there was also fibrous tissue. The presence of radiolucency was strongly inversely correlated with the percentage of cement-bone contact.

CONCLUSION

This study demonstrates that even with partial or complete RLL seen on radiographs there is still cement-bone contact, thus indicating that there is stable fixation.

The ten-year survival of the Birmingham hip resurfacing: an independent series

Recent events have highlighted the importance of implant design for survival and wear-related complications following metal-on-metal hip resurfacing arthroplasty. The mid-term survival of the most widely used implant, the Birmingham Hip Resurfacing (BHR), has been described by its designers. The aim of this study was to report the ten-year survival and patient-reported functional outcome of the BHR from an independent centre. In this cohort of 554 patients (646 BHRs) with a mean age of 51.9 years (16.5 to 81.5) followed for a mean of eight years (1 to 12), the survival and patient-reported functional outcome depended on gender and the size of the implant. In female hips (n = 267) the ten-year survival was 74% (95% confidence interval (CI) 83 to 91), the ten-year revision rate for pseudotumour was 7%, the mean Oxford hip score (OHS) was 43 (SD 8) and the mean UCLA activity score was 6.4 (SD 2). In male hips (n = 379) the ten-year survival was 95% (95% CI 92.0 to 97.4), the ten-year revision rate for pseudotumour was 1.7%, the mean OHS was 45 (SD 6) and the mean UCLA score was 7.6 (SD 2). In the most demanding subgroup, comprising male patients aged < 50 years treated for primary osteoarthritis, the survival was 99% (95% CI 97 to 100). This study supports the ongoing use of resurfacing in young active men, who are a subgroup of patients who tend to have problems with conventional THR. In contrast, the results in women have been poor and we do not recommend metal-on-metal resurfacing in women. Continuous follow-up is recommended because of the increasing incidence of pseudotumour with the passage of time.

Improved quadriceps' mechanical advantage in single radius TKRs is not due to an increased patellar tendon moment arm

Single femoral radius TKRs have been reported to improve quadriceps' mechanical advantage, leading to enhanced patient function. An increased patellar tendon moment arm (PTMA) has been cited as the main feature leading to improved quadriceps' mechanical advantage. However, these designs often incorporate a recessed trochlea which alters the patellar mechanism and may contribute to improved quadriceps' mechanical advantage. This study simultaneously measured the PTMA using two and three dimensional methods, as well as quadriceps forces (QF), patellofemoral kinematics and tibiofemoral kinematics in a motion analysis laboratory during an open chain leg extension activity. Six cadaveric knees were tested in the normal state and after implantation of three different single femoral radius TKR designs: cruciate retaining, posterior stabilised and rotating platform posterior stabilised (Stryker, Newbury, UK). QFs in the TKRs were between 15% and 20% lower than normal between 60° and 70° flexion. The increase in PTMA was insufficient to explain the reduced QF in the TKRs. The patellar flexion angle (PFA) of the TKRs was lower than normal at knee flexion angles greater than 50°, probably as a result of the recessed trochlea. A simple patellar model demonstrated that the reduced PFA may explain a large proportion of the reduction in QF after single radius TKR.

Learning and retaining simulated arthroscopic meniscal repair skills

BACKGROUND

Previous studies of task-specific skills have suggested that a loss of technical performance occurs if the skill is not practiced for a six-month period. The aims of this study were to objectively demonstrate the learning curve for a complex arthroscopic task (meniscal repair) by means of motion analysis and to determine the impact of task repetition on the retention of this skill.

METHODS

Nineteen orthopaedic residents with experience in routine knee arthroscopy but not in arthroscopic meniscal repair were recruited into a randomized study. During the initial learning phase, all subjects performed twelve meniscal repairs on a knee simulator over a three-week period. A validated motion analysis tracking system was used to objectively record the performance and learning of each subject; the outcomes were the time taken, distance traveled, and number of hand movements. The subjects were then randomized into three groups. Group A performed one meniscal repair each month, Group B performed one meniscal repair at three months, and Group C performed no repairs during this interim phase. All three groups then returned at the six-month point for the final assessment phase, during which they carried out an additional twelve meniscal repairs over three weeks.

RESULTS

All subjects demonstrated a clear learning curve during the initial learning phase, with significant objective improvement in all motion analysis parameters over the initial twelve episodes (p < 0.0001). Although some residents had reached a learning plateau by twelve episodes, others continued to make further improvements for up to another nine episodes. Importantly, Group C did not display any loss of skill between the initial learning phase and final evaluation phase despite a six-month break in task repetition (p > 0.05).

CONCLUSIONS

In contrast to previous studies, residents did not lose any skill over a six-month interruption in task performance, and other residents took longer to produce a more consistent performance.

A low-riding patella in posterior stabilised total knee replacements alters quadriceps' mechanical advantage, resulting in reduced knee flexion moments

Abnormal in vivo Total Knee Replacement (TKR) kinetics is influenced by a range of factors, particularly by changes to the knee's geometric parameters such as the patellar tendon moment arm (PTMA). In this study, ground reaction force (GRF) measurements were combined with simultaneous fluoroscopic image measurements to investigate the relationship between abnormal TKR kinetics and geometric parameters. Nine Scorpio Cruciate Retaining (CR) TKR (Stryker, Newbury, UK), nine Scorpio Posterior Stabilized (PS) TKR and seven normal subjects performed a step-up activity on a forceplate in view of a fluoroscope. The TKR subjects were part of a larger ongoing randomised controlled trial. The maximum external knee flexion moment was 22.0% lower in the Scorpio PS group compared to the Scorpio CR group. No significant differences in PTMA were found between the groups. The Scorpio PS had a low-riding patella, with a 30.7% reduction in patellar height compared to the Scorpio CR. This was probably due to using a thick tibial insert after PCL release in the PS, and led to an 8° increase in patellar flexion angle which altered the patellar mechanism and reduced quadriceps' mechanical advantage. Consequently, PS subjects stepped-up more cautiously with a reduced knee flexion moment.

Genetic predisposition to the presence and 5-year clinical progression of hip osteoarthritis

OBJECTIVE

Genetic factors are important in the aetiology of hip osteoarthritis (OA), but studies are limited by cross-sectional design and poor association with clinically important disease. Identifying cohorts with progressive OA will facilitate development of OA biomarkers. Using a middle-aged cohort with genetic predisposition to hip OA and a control group, we compared the prevalence of clinical and radiographic hip OA and incidence of progression over 5 years.

DESIGN

123 individuals (mean age 52 years) with a family history of total hip arthroplasty (THA) ('sibkids') were compared with 80 (mean age 54 years) controls. The prevalence of radiographic OA [scored according to Kellgren & Lawrence (K&L)], clinical features, and incidence of clinical progression over a 5-year period were compared. A multivariate logistic regression model was used to adjust for confounders.

RESULTS

Sibkids had odds ratios (ORs) of 2.7 [95% confidence interval (CI) 1.1-6.3, P = 0.02] for hip OA (K&L grade ≥2), 3.4 (1.4-8.4, P = 0.008) for clinical signs, and 2.1 (0.8-5.8, P = 0.14) for signs and symptoms. Over 5 years, sibkids had ORs of 4.7 (1.7-13.2, P = 0.003) for the development of signs, and 3.2 (1.0-10.3, P = 0.047) for the development of signs and symptoms.

DISCUSSION

Compared to a control group and after adjustment for confounders, individuals with genetic predisposition to end-stage hip OA have higher prevalence of OA, clinical features, and progression. In addition to structural degeneration, the inherited risk may include predisposition to pain. Genetically-loaded cohorts are useful to develop hip OA biomarkers, as they develop progressive disease at a young age.

In vivo evaluation of edge-loading in metal-on-metal hip resurfacing patients with pseudotumours

Objectives

Pseudotumours (abnormal peri-prosthetic soft-tissue reactions) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated metal ion levels, suggesting that excessive wear may occur due to edge-loading of these MoM implants. This study aimed to quantify in vivo edge-loading in MoMHRA patients with and without pseudotumours during functional activities.

Methods

The duration and magnitude of edge-loading in vivo was quantified during functional activities by combining the dynamic hip joint segment contact force calculated from the three-dimensional (3D) motion analysis system with the 3D reconstruction of orientation of the acetabular component and each patient’s specific hip joint centre, based on CT scans.

Results

Edge-loading in the hips with pseudotumours occurred with a four-fold increase in duration and magnitude of force compared with the hips without pseudotumours (p = 0.02).

Conclusions

The study provides the first in vivo evidence to support that edge-loading is an important mechanism that leads to localised excessive wear (edge-wear), with subsequent elevation of metal ion levels in MoMHRA patients with pseudotumours.

Improved radiograph measurement inter-observer reliability by use of statistical shape models

Pre- and post-operative radiographs of patients undergoing joint arthroplasty are often examined for a variety of purposes including preoperative planning and patient assessment. This work examines the feasibility of using active shape models (ASM) to semi-automate measurements from post-operative radiographs for the specific case of the Oxford™ Unicompartmental Knee. Measurements of the proximal tibia and the position of the tibial tray were made using the ASM model and manually. Data were obtained by four observers and one observer took four sets of measurements to allow assessment of the inter- and intra-observer reliability, respectively. The parameters measured were the tibial tray angle, the tray overhang, the tray size, the sagittal cut position, the resection level and the tibial width. Results demonstrated improved reliability (average of 27% and 11.2% increase for intra- and inter-reliability, respectively) and equivalent accuracy (p>0.05 for compared data values) for all of the measurements using the ASM model, with the exception of the tray overhang (p=0.0001). Less time (15s) was required to take measurements using the ASM model compared with manual measurements, which was significant. These encouraging results indicate that semi-automated measurement techniques could improve the reliability of radiographic measurements.

The patho-anatomy of patellofemoral subluxation

Patella subluxation assessed on dynamic MRI has previously been shown to be associated with anterior knee pain. In this MRI study of 60 patients we investigated the relationship between subluxation and multiple bony, cartilaginous and soft-tissue factors that might predispose to subluxation using discriminant function analysis. Patella engagement (% of patella cartilage overlapping with trochlea cartilage) had the strongest relationship with subluxation. Patellae with > 30% engagement tended not to sublux; those with < 30% tended to sublux. Other factors that were associated with subluxation included the tibial tubercle-trochlea notch distance, vastus medialis obliquus distance from patella, patella alta, and the bony and cartilaginous sulcus angles in the superior part of the trochlea. No relationship was found between subluxation and sulcus angles for cartilage and bone in the middle and lower part of the trochlea, cartilage thicknesses and Wiberg classification of the patella. This study indicates that patella engagement is a key factor associated with patellar subluxation. This suggests that in patients with anterior knee pain with subluxation, resistant to conservative management, surgery directed towards improving patella engagement should be considered. A clinical trial is necessary to test this hypothesis.

Damage initiation and progression in the cartilage surface probed by nonlinear optical microscopy

With increasing interest in treating osteoarthritis at its earliest stages, it has become important to understand the mechanisms by which the disease progresses across a joint. Here, second harmonic generation (SHG) microscopy, coupled with a two-dimensional spring-mass network model, was used to image and investigate the collagen meshwork architecture at the cartilage surface surrounding osteoarthritic lesions. We found that minor weakening of the collagen meshwork leads to the bundling of fibrils at the surface under normal loading. This bundling appears to be an irreversible step in the degradation process, as the stress concentrations drive the progression of damage, forming larger bundles and cracks that eventually form lesions.

Effect of duration and level of supplementation of diets of lactating dairy cows with selenized yeast on selenium concentrations in milk and blood after the withdrawal of supplementation

Cows' milk containing elevated concentrations of Se provides a rich nutritional source of this essential element for meeting daily nutritional requirements or providing health benefits in humans with low immune function or at risk of cancer. An experiment involving either 2 or 6 wk of dietary supplementation with Se yeast (with the yeast supplying about 30, 40, and 60 mg of Se/d for cows supplemented for 2 wk, and about 20, 30, 40, and 60 mg of Se/d for cows supplemented for 6 wk), and 21 wk of monitoring of Se status after the withdrawal of supplementation, was undertaken between September 2008 and April 2009 using 35 multiparous Holstein-Friesian cows. Using milk and blood Se concentrations as surrogates, the research examined the time taken for Se build-up in tissue due to supplementation of lactating dairy cows with Se yeast to dissipate back to normal levels. At the end of Se supplementation, a significant relationship was found between milk Se concentration and Se intake, whereby milk Se concentration had increased by 4.5 μg of Se/kg of milk for each mg of Se eaten per day, but no effect of duration of supplementation on this relationship was observed. At the same time, both Se intake and duration of supplementation affected blood Se concentration; it increased by 3.6 μg of Se/kg of blood for each mg of Se eaten per day, and was 86 μg of Se/kg higher after 6 wk compared with 2 wk of supplementation. After the withdrawal of Se supplementation, milk Se concentrations responded quickly to the change in the quantity of Se consumed, and again, duration of supplementation had no effect on the response, but any effect that Se intake had on milk Se had completely dissipated by 4 wk. In contrast to milk, blood Se concentrations continued to be affected by both amount and duration of Se supplementation for at least 4 mo after the withdrawal of supplementation, although by 5 mo the effects of the previous supplementation treatments had virtually disappeared. The slow decline in blood Se concentrations after the withdrawal of supplementation would most likely be due to the protracted clearance of Se from the various tissues that had accumulated Se during supplementation and the rate of erythrocyte turnover. When undertaking an on-farm Se enhancement program to generate milk for the manufacture of Se-enriched milk products, post-supplementation milk Se concentrations are unlikely to create any problems at the milk factory beyond 4 wk, but the high residual blood/tissue Se concentrations that take considerably more time to dissipate may provide the potential for possible unintended consequences at the food chain/farm environment level.

Metal-on-metal bearings: the evidence so far

Lately, concerns have arisen following the use of large metal-on-metal bearings in hip replacements owing to reports of catastrophic soft-tissue reactions resulting in implant failure and associated complications. This review examines the literature and contemporary presentations on current clinical dilemmas in metal-on-metal hip replacement.

Polyethylene wear of mobile-bearing unicompartmental knee replacement at 20 years

The Oxford unicompartmental knee replacement (UKR) was designed to minimise wear utilising a fully-congruent, mobile, polyethylene bearing. Wear of polyethylene is a significant cause of revision surgery in UKR in the first decade, and the incidence increases in the second decade. Our study used model-based radiostereometric analysis to measure the combined wear of the upper and lower bearing surfaces in 13 medial-compartment Oxford UKRs at a mean of 20.9 years (17.2 to 25.9) post-operatively. The mean linear penetration of the polyethylene bearing was 1.04 mm (0.307 to 2.15), with a mean annual wear rate of 0.045 mm/year (0.016 to 0.099). The annual wear rate of the phase-2 bearings (mean 0.022 mm/year) was significantly less (p = 0.01) than that of phase-1 bearings (mean 0.07 mm/year). The linear wear rate of the Oxford UKR remains very low into the third decade. We believe that phase-2 bearings had lower wear rates than phase-1 implants because of the improved bearing design and surgical technique which decreased the incidence of impingement. We conclude that the design of the Oxford UKR gives low rates of wear in the long term.