It has come to light that one significant mechanism for MOM failure may be repeated subluxation or impingement episodes leading to edge wear and release of 3^rd body particles. This MOM debris-challenge model simulates a patient who experienced one subluxation or impingement event and then continues to walk normally until the next event occurs one week later. Our model assumes that 100–200 particles (debris size 100–200 μm) would be released into the joint space at each subluxation or impingement event. The question then becomes: what is the effect of the patient walking on that single dose of particulates over the next week (or 500,000 cycles in simulator test mode).

Nine 38 mm CoCrMo bearings (DJO Inc., Texas) were run inverted in a12-station hip simulator (SWM, Monrovia, CA). The test was run in standard simulator mode (Paul gait load cycle: 0.2–2 kN, frequency 1 Hz) with the addition of 5 mg of debris particles for the first 3 Mc, followed by 10 mg of debris particles from 3–5 Mc. Commercially available CoCr (ASTM F75) and titanium alloy (ASTM F136) particles and broken polymerized bone cement particles were used in the size range 50–200 μm. Serum was changed out every 500,000 cycles and a fresh dose of debris added. All bearings were ultrasonically cleaned and examined using white light interferometry (WLI, Zygo Corp) and SEM (EVO MA15, Zeiss). Wear rates were determined gravimetrically and serum discoloration was noted at each test interval.

Titanium alloy and CoCr debris produced darkened serum within the first hour of the test and remained so for the duration (500,000 cycles). Serum color with cement debris remained an opaque golden color throughout the test run. The debris challenge provoked the largest MOM wear response using Ti6Al4V particulates (6.7 mm³/Mc), slightly milder with CoCr particulates (4.5 mm³/Mc) and minimal with PMMA particulates (0.5 mm³/Mc). Compared to bone cement debris chambers (which had wear rates comparable to non abrasive MOM bearing tests), CoCr debris created a 9-fold higher MOM wear and titanium alloy debris created a 14-fold higher MOM wear. These observations indicated that only the metal debris elicited an ‘Adverse’ wear response with MOM bearings.

Unlike conventional radiographic methods, the newly introduced EOS system provides simultaneously-synchronized anteroposterior (AP) and true-lateral (LAT) x-ray images. EOS offers considerable potential for calculating parameters such as true femoral and acetabular angular positioning, impingement sites, and also for measuring wear in polyethylene cups. In this study we used THA wear-simulation fixtures to assess 3D-wear in polyethylene cups using EOS algorithms.

There is a consensus that impingement, subluxation, and dislocation are major risks that can lead to failure in total hip arthroplasty (1). As well as producing edge-wear, such clinical events also may create additional loads of particulate debris (2). It has been suggested that the release of metal debris with collateral damage on metal-on-metal (MOM) bearings creates a particularly severe abrasive wear, hitherto not understood, and recently termed ‘micro-grooving’ (3,4). Perhaps related to this micro-grooving, large surface depressions have also been observed. These we labeled ‘Dongas’, from the South African term for a steep-sided gully created by erosion. The goal of this study was to examine Dongas found on retrieved MOM bearings and to correlate factors such as cause of revision, MOM diameter and Donga locations with respect to regions of normal and stripe wear. Our hypotheses were: (1) Dongas will be most visible in non-wear zones (NWZ) adjacent to the main-wear zone boundary (MWZ), (2) the 28 mm MOM, being inherently less stable compared to large-diameter MOM, will show a higher Donga frequency and (3) patients with subluxation or dislocation complaints will reveal a higher Donga frequency.

Five cases with 28 mm MOM, five of 34–38 mm, and five of 50–56 mm diameter were studied (N = 15). The MWZ was measured in each MOM head and the number of NWZ and MWZ Dongas recorded. Bearing damage was examined using a white-light interferometer (Zygo; 5x lens).

Dongas were mainly elliptical in shape, but sometimes highly irregular. They were commonly circumscribed by raised lips (Fig. 1). Donga “trails” were also found, appearing as a linear series of similar-sized Dongas (Fig. 2). Donga trails exhibited some variability with raised lips either lining only the opposite sides or circumscribing most of the perimeter. The Dongas were commonly found in NWZ, with less than 20% found in MWZ. For this set of 15 MOM bearings, large-diameter bearings showed the largest number of Dongas and the greatest frequency of Dongas resulted from either loose or migrating cups.

The high occurrence of dongas in the non-wear zone (supporting hypothesis-1) may be a result of particles swept into the bearing interface (2,5). The size of the Dongas and their frequent association to local micro-grooves indicated that these were the impact sites of circulating particles. Such large surface depressions (40–200 μm) have not been described previously and may be unique to MOM bearings (3,4). The observation that Dongas were most prevalent in cases with loose or migrating cups left hypothesis-2 unsatisfied. The much higher incidence of Dongas in the large-diameter MOM was surprising and negated hypothesis-3. Overall these new data relating Dongas and micro-grooves gives new credence to a hitherto unsuspected 3^rd-body abrasive wear mechanism due to repetitive subluxation or impingement.

The MOM controversy continues with many prevailing opinions as to the causes of failure in contemporary designs. There has been a great deal of focus on breakdown in fluid-film lubrication with respect to cup positioning and edge wear at its rim. However there has been very little discussion on the problems of 3^rd body abrasion. In only one study was there a description of unusually large abrasive marks on retrieved femoral heads (McKee Farrar MOM), revealing 100 μm wide scratches, attributed to circulating particles fractured during impingement episodes. With contemporary MOM devices, there is the potential for abrasion by particulates of CoCr, PMMA and Ti6Al4V. However it has been difficult to formulate a coherent simulator model for 3^rd-body abrasive wear, given the unpredictable nature of impingement damage releasing abrasive particles into the patient's hip joint. Thus this study sought to identify if metal or cement particulates were capable of creating 100 μm wide scratches as seen on retrieved MOM and develop a simulator model for 3^rd body abrasive testing on MOM bearings.

Six 38 mm CoCrMo bearings (DJO Inc., Texas) were run in a12-station hip simulator (SWM, Monrovia, CA) with cups mounted both anatomically and inverted (3 MOM each). The tests were run in standard simulator mode (Paul gait load cycle: 0.2–2 kN, frequency 1 Hz) with the addition of 5 mg of debris particles. Commercially available CoCr (ASTM F75) and titanium alloy (ASTM F136) particles and broken polymerized bone cement particles were used in the size range 50–200 μm. The simulator was run for only 10 cycles and the MOM parts removed for study. All bearings were ultrasonically cleaned and heads were examined using white light interferometry (WLI, Zygo Corp). Grooves were characterized using surface profiles to measure width, depth, and rim height. SEM imaging (EVO MA15, Zeiss) and EDS imaging (X flash detector 4010, Bruker AXS) was performed in areas of grooving and suspected transfer layers.

CoCr debris produced broad, curvilinear grooves with widths ranging from 20–170 μm, depths from 0.3–1.5 μm, raised rims, longitudinal striations and chatter marks. Titanium alloy debris produced arrays of very shallow scratches accompanying larger grooves. These larger grooves measured 20–110 μm wide and 0.4–1.9 μm deep.

EDS imaging showed the smears and islands contained the elements Ti, Al and V representative of the Ti6Al4V alloy. WLI imaging showed these metal deposits (250–900 um wide) were raised >10 um above the surface. Particularly conspicuous was evidence of considerable smearing on CoCr surfaces, with linear streaks ranging 150–300 μm wide. Bone cement debris proved incapable of grooving the CoCr surface, the only scratches observed were those comparable to normal carbide scratches.

Introduction

Femoral stem anteversion after total hip arthroplasty (THA) has always been assessed using CT scan in supine position. In this study, we evaluated the anteversion of the femoral prosthesis neck in functional standing position using EOS® technology with repeatability and reproducibility of the measurements. The data obtained were compared with conventional anatomic measurements.

In an effort to understand the role of metal ion analysis and how it relates to revision surgery and implant wear, four revised MOM cases were reviewed. The first case was revised for acute infection and is representative of the low bearing wear predicted by MOM simulator studies. Two of the four cases had apparent anterior subluxation as a result of hip hyperextension occurring with long stride gaits. The last case is a true hypersensitivity response to CoCr ions.

All four MOM prostheses were implanted by one surgeon and revised by the same surgeon approximately 6–8 years postoperatively. The implants had been positioned satisfactorily with inclination angles 45°–55° and anteversion angles 28°–42°.

Patient A (76 y/o female) with bilateral MOM hip replacements, was revised at approximately 8 years due to infection and had moderately elevated ions at the time of revision surgery (Co = 5, Cr = 2.3, Ti = 4). Only the femoral head was retrieved in this case. Retrieval analysis identified a well defined main-wear zone and one polar stripe. The CMM indicated there was minimal wear overall (form factor = 11 μm).

Patient B (33 y/o male) with bilateral MOM hip replacements, was revised at approximately 8 years due to pain, popping/catching sensations, and elevated ions (Co = 33, Cr = 17, Ti = 90). Intraoperatively, the implant was observed subluxing superiorly from the acetabular cup with anterior rotation of the leg. Both the femoral head and acetabular cup were retrieved. Retrieval analysis identified a well defined main-wear zone and multi-directional polar stripe formations similar to those reported on dislocated implants (Figure 1)[McPherson 2012, 2013]. The CMM indicated that overall wear was significant (form factor > 100 μm).

Patient C (77 y/o female) was revised at approximately 6 years due to pain, suspected implant loosening, osteolytic cysts determined by CT, and highly elevated ions (co = 164, Cr = 45, Ti = 33). Intraoperatively, there was evidence of wear including darkly stained tissue and osteolytic cysts. Both the femoral head and acetabular cup were retrieved. Retrieval analysis identified a well defined main-wear zone and one polar stripe. CMM indicated considerable wear (head form factor > 200, cup form factor >300).

Patient D (45 y/o female) was revised at approximately 6 years due to pain, apparent reactive response joint effusion, and moderately elevated ions (Co = 5, Cr = 6, Ti = 71). Only the femoral head was retrieved. Retrieval analysis identified a well defined main-wear zone and one polar stripe. Minimal wear was indicated by CMM (form factor = 21).

These four cases demonstrate distinct failure models of MOM hips and their respective metal ion results. Due to the diversity of patient location, a variety of clinical labs were utilized for this patient population. Caution should be used in interpreting metal ion analysis, as there are still no standards.

Figure 1: Retrieval analysis of stripe wear identified on femoral head from patient B.

Figure 2: Femoral head from patient C showing broader polar stripe associated with anterior subluxation in comparison to narrow polar stripe found on femoral head from patient A.

Introduction

CT based systems that are used to create custom components and custom cutting guides in total knee arthroplasty (TKA) have variable methods for accounting for the thickness of remaining cartilage that may influence component sizing and bone resection. Little information has been published about the thickness of this cartilage, especially on the posterior femoral condyles. Failure to account for this cartilage may lead to under-sizing of the femoral component, or a reduction in the posterior condylar offset that may adversely affect flexion after TKA.

Introduction

While prosthesis survival in Total Knee Arthroplasty (TKA) exceeds 90% at 10 year, failures do occur. One area of concern has been the potential for metal allergy or metal sensitivity causing persistent pain, swelling or early failure of the implant in some patients. Definitive tests for diagnosing metal allergy and metal sensitivity have not been developed and this field remains controversial. In most cases where metal sensitivity is a concern, metals such as Chromium and Nickel are implicated. Despite the lack of good diagnostic tests for identifying these patients, several orthopedic prosthesis manufacturers have developed implants made of Titanium or ceramic designed for use in patients where concerns exist regarding metal allergy. In the absence of good diagnostic tests, use of these devices in patients that self identify is one option. To date, little information has been presented about the incidence of self reported metal sensitivity in patients undergoing joint replacement. This study was undertaken to determine the incidence of self reported metal allergy or sensitivity in patients undergoing total knee arthroplasty.

Introduction

Patellar resurfacing during Total Knee Arthroplasty (TKA) is controversial. Problems unique to patellar resurfacing may be influenced by available patellar component design. These issues include; over-stuffing (the creation of a composite patellar-prosthesis thickness greater than the native patella) that may contribute to reduced range of motion; and over-resection of the native patellar bone that may contribute to post-operative fracture. Prosthesis design may play a role in contributing to these problems. Component diameter and thickness are quite variable from one manufacturer to another and little information has been previously published about optimal component dimensions. This anatomic study was performed to define the native patellar anatomy of patients undergoing TKA, in order to guide future component design.

Background

Steroid injections can be used safely to treat trigger fingers. We aimed to determine the accuracy of referring General Practitioner (GP) diagnoses of trigger finger made to an upper limb surgeon. We also aimed to determine the efficacy of a serial two steroid injection then surgery technique in the management of trigger fingers.

Range of motion (ROM) is a well recognised outcome measure following total knee arthroplasty (TKA). Reduced knee flexion can lead to poor outcome after TKA and therefore identification at an early stage is important as it may provide a window for intervention with targeted physiotherapy, closer follow-up and in resistant cases possible manipulation or arthrolysis. ROM combines both flexion and extension and in contrast to flexion, fewer studies have recognised the importance of a lack of full extension or fixed flexion deformity (FFD) following TKA. A residual FFD can increase energy cost, decrease velocity during ambulation and result in pain with knee scores more likely to be diminished than if knee extension was normal. Recognition and early detection of FFD is therefore important. Methods of assessment include by visual estimation or goniometric measurement of knee flexion angle. While goniometers are inexpensive, easy to use and provide more accurate than visual estimates of angles, they have been shown to exhibit poor inter-observer reliability. Therefore they may not be sensitive enough to consistently identify FFD and therefore distinguish between grading systems based on absolute angular limits. The aim of this study was to investigate the accuracy of standard clinical ROM measurement techniques following TKA and determine their reliability for recognising FFD.

Ethical approval was obtained for this study. Thirty patients who were six weeks following TKA had their knee ROM measured. An infrared (IR) tracking system (±1°accuracy) that had been validated against an electro-goniometer was used to give a “true” measurement of the lower limb sagittal alignment with the knee fully extended and maximally flexed while the patient was supine. The patients were also assessed independently by experienced arthroplasty practitioners using a standardised goniometric measurement technique. For goniometric clinically-measured flexion (Clin_flex) and extension (Clin_ext) linear models were generated using IR-measured flexion and extension (IR_flex and IR_ext), BMI and gender as covariables. Data for extension were categorised in none, moderate and severe postoperative FFD as per Ritter et al. 2007 and agreement in classification between the two methods was assessed using the Kappa statistic.

For the linear models for Clin_flex and Clin_ext neither BMI nor gender were significant variables. Therefore the final models were:

Clin_flex = 0.54 + 0.66∗IR_flex (r²_adj = 0.521)

Clin_ext = 0.23 + 0.50∗IR_ext (r²_adj = 0.247)

The model for Clin_flex showed that the IR and clinical measurements coincided at approximately 90° so that for every 10° increase in flexion above 90° clinical measurement only increased by 7° but for every 10° decrease in flexion below 90° clinical measurement only decreased by 7°. The model for Clin_ext showed that the IR and clinical measurements coincided at approximately 0° so that for every 10° increase in FFD angle, clinical measurement only increased by 5° but if the knee went into hyperextension this would be underestimated by the clinical measure. In identifying FFD there was moderate agreement between the two measurements (κ = 0.44). Clinically nine patients were assessed as having FFD but the IR measurements showed 18 patients having FFD, of which nine patients were not identified clinically.

When assessing knee ROM following joint arthroplasty manual goniometric measurements provided a poor estimate of the range when compared to the “true” angle as measured with a validated IR measurement tool. When the knee was held in maximum flexion there was a tendency to both underestimate and overestimate the true angle. However when the knee was held in extension there was a tendency to underestimate which we believe is important as it would underreport both the frequency and magnitude of FFD. In our study, 18 patients had a moderate FFD as identified by the IR system, only half of which were identified by goniometer measurement alone. Studies of comparisons of both visual and manual goniometry measurements of the knee in maximum flexion with lateral radiographs have shown most errors involved an underestimate of true flexion. It has been concluded that it was safer to underestimate knee flexion angle as it would result in higher pick up rate of cases being performing less well. In contrast however, underestimation while in extension is less desirable as it fails to pick-up FFD which may have benefited from intervention had they been identified. It is known that residual FFD can increase energy cost and decrease velocity during ambulation with pain and functional knee scores more likely to be reduced. Recognition and early detection is therefore important. With the use of more accurate systems to identify and measure FFD, such as the one used for this study may in turn allow more timely treatment and therefore hopefully improved outcomes.

Clinical laxity tests are frequently used for assessing knee ligament injuries and for soft tissue balancing in total knee arthroplasty (TKA). Current routine methods are highly subjective with respect to examination technique, magnitude of clinician-applied load and assessment of joint displacement. Alignment measurements generated by computer-assisted technology have led to the development of quantitative TKA soft tissue balancing algorithms. However to make the algorithms applicable in practice requires the standardisation of several parameters: knee flexion angle should be maintained to minimise the potential positional variation in ligament restraining properties; hand positioning of the examining clinician should correspond to a measured lever arm, defined as the perpendicular distance of the applied force from the rotational knee centre; accurate measurement of force applied is required to calculate the moment applied to the knee joint; resultant displacement of the knee should be quantified.

The primary aim of this study was to determine whether different clinicians could reliably assess coronal knee laxity with a standardised protocol that controlled these variables. Furthermore, a secondary question was to examine if the experience of the clinician makes a difference. We hypothesised that standardisation would result in a narrow range of laxity measurements obtained by different clinicians.

Six consultant orthopaedic surgeons, six orthopaedic trainees and six physiotherapists were instructed to assess the coronal laxity of the right knee of a healthy volunteer. Points were marked over the femoral epicondyles and the malleoli to indicate hand positioning and give a constant moment arm. The non-invasive adaptation of a commercially available image-free navigation system enabled real-time measurement of coronal and sagittal mechanical femorotibial (MFT) angles. This has been previously validated to an accuracy of ±1°. Collateral knee laxity was defined as the amount of angular displacement during a stress manoeuvre. Participants were instructed to maintain the knee joint in 2° of flexion whilst performing a varus-valgus stress test using what they perceived as an acceptable load. They were blinded to the coronal MFT angle measurements. A hand-held force application device (FAD) was then employed to allow the clinicians to apply a moment of 18Nm. This level was based on previous work to determine a suitable subject tolerance limit. They were instructed to repeat the test using the device in the palm of their right hand and to apply the force until the visual display and an auditory alarm indicated that the target had been reached. The FAD was then removed and participants were asked to repeat the clinical varus-valgus stress test, but to try and apply the same amount of force as they had been doing with the device.

Maximum MFT angular deviation was automatically recorded for each stress test and the maximum moment applied was recorded for each of the tests using the FAD. Means and standard deviations (SD) were used to compare different clinicians under the same conditions. Paired t-tests were used to measure the change in practice of groups of clinicians before, during and after use of the FAD for both varus and valgus stress tests.

All three groups of clinicians initially produced measurements of valgus laxity with consistent mean values (1.5° for physiotherapists, 1.8° for consultants and 1.6° for trainees) and standard deviations (<1°). For varus, mean values were consistent (5.9° for physiotherapists, 5.0° for consultants and 5.4° for trainees) but standard deviations were larger (0.9° to 1.6°). When using the FAD, the standard deviations remained low for all groups for both varus and valgus laxity. Introducing the FAD overall produced a significantly greater angulation in valgus (2.4° compared to 1.6°, p<0.001) but not varus (p = 0.67) when compared to the initial examination. In attempting to reach the target moment of 18Nm, the mean ‘overshoot’ was 0.9Nm for both varus and valgus tests. Standard deviations for varus laxity were lower for all groups following use of the FAD. The consultants' performance remained consistent and valgus assessment remained consistent for all groups. The only statistically significant change in practice for a group before and after use of the FAD was for the trainees testing valgus, who may have been trained to push harder (p = 0.01). Standardising the applied moment indicated that usually a lower force is applied during valgus stress testing than varus. This was re-enforced by clinicians, one third of whom commented that they felt they had to push harder for valgus than varus, despite the FAD target being the same.

We have successfully standardised the manual technique of coronal knee laxity assessment by controlling the subjective variables. The results support the hypothesis of producing a narrow range of laxity measurements but with valgus laxity appearing more consistent than varus. The incorporation of a FAD into assessment of coronal knee laxity did not affect the clinicians' ability to produce reliable and repeatable measurements, despite removing the manual perception of laxity. The FAD also provided additional information about the actual moment applied. This information may have a role in improving the balancing techniques of TKA and the management of collateral ligament injuries with regard initial diagnosis and grading as well as rehabilitation.

Finally, the results suggest that following use of the FAD, more experienced clinicians returned to applying their usual manual force, while trainees appeared to use this augmented feedback to adapt their technique. Therefore this technique could be a way to harness the experience of senior clinicians and use it to enhance the perceptive skills of more junior trainees who do not have the benefit of this knowledge.

Knee alignment is a fundamental measurement in the assessment, monitoring and surgical management of patients with osteoarthritis [OA]. In spite of extensive research into the consequences of malalignment, our understanding of static tibiofemoral alignment remains poor with discrepancies in the reported weight-bearing characteristics of the knee joint and there is a lack of data regarding the potential variation between supine and standing (functional) conditions. In total knee arthroplasty [TKA] the lower limb alignment is usually measured in a supine condition and decisions on prosthesis placement made on this. An improved understanding of the relationship between supine and weight-bearing conditions may lead to a reassessment of current surgical goals.

The purpose of this study was to explore the relationship between supine and standing lower limb alignment in asymptomatic, osteoarthritic and prosthetic knees. Our hypothesis was that the change in alignment of these three groups would be different.

A non-invasive infrared position capture system (accuracy ±1° in both coronal and sagittal plane) was used to assess the knee alignment for 30 asymptomatic controls and 31 patients with OA, both before and after TKA. Coronal and sagittal mechanical femorotibial (MFT) angles in extension (negative values indicating varus in the coronal plane and hyperextension in the sagittal plane) were measured with each subject supine and in bi-pedal stance. For the supine test, the lower limb was supported at the heel and the subject told to relax. For the standing position subjects were asked to assume their normal stance. The change in alignment between these two conditions was analysed using a paired t-test for both coronal and sagittal planes. To quantify the change in 3D, vector plots of ankle centre displacement relative to the knee centre from the supine to standing condition were produced.

Alignment in both planes changed significantly from supine to standing for all three groups. For the coronal plane the supine and standing measurements (in degrees, mean(SD)) were 0.1(2.5) and −1.1(3.7) in the asymptomatic group, −2.5(5.7) and −3.6(6) in the OA group and −0.7(1.4) and −2.5(2) in the TKA group. For the sagittal plane the numbers were −1.7(3.3) and −5.5(4.9); 7.7(7.1) and 1.8(7.7); 6.8(5.1) and 1.4((7.6) respectively. This change was most frequently towards relative varus and extension. Vector plots showed that the trend of relative varus and extension in stance was similar in overall magnitude and direction between the three groups.

Knee alignment can change from supine to standing for asymptomatic and osteoarthritic knees, most frequently towards relative varus and hyperextension. The similarities between each group did not support our hypothesis. The consistent kinematic pattern for different knee types suggests that soft tissue restraints rather than underlying joint deformity may be more influential in dynamic control of alignment from lying to standing. In spite of some evidence suggesting a difference between supine and standing knee alignment a mechanical femorotibial (MFT) angle of 0° is a common intra-operative target as well as the desired post-operative weight-bearing alignment. These results indicated that arthroplasties positioned in varus intra-operatively could potentially become ‘outliers’ (>3° varus) when measured weight-bearing. Mild flexion contractures may correct when standing, reducing the need for intra-operative posterior release. These potential changes should be considered when positioning TKA components on supine limbs as post-operative functional alignment may be different.

Background

Vitamin D deficiency may increase predisposition to a number of paediatric orthopaedic conditions and the prevalence of vitamin D deficiency is increasing in children in developed countries. The aim of this study was to determine the epidemiology of vitamin D deficiency and insufficiency in children presenting to a regional paediatric orthopaedic service. We also examined the relationships between vitamin D status, social deprivation and ethnicity

Introduction

Opponents of patellar resurfacing during Total Knee Arthroplasty (TKA) note unique complications associated with resurfacing. Problems include over-stuffing (the creation of a composite patellar-prosthesis thickness greater than the native patella) that may contribute to reduced range of motion; and creation of a patellar remnant that is too thin (in order to avoid over-stuffing) that may contribute to post-operative fracture. Factors including surgical technique, prosthesis design and patient anatomy may contribute to these problems. This study was performed to define the native patellar anatomy, and to compare the effect of differences in component thickness between manufacturers.

Background

Malnutrition has been suggested to increase the risk of falls in frail elderly. It has been hypothesised that elderly, orthopaedic trauma patients may be malnourished. We conducted an observational study to identify if this was the case.

Introduction

Problematic bone defects are encountered regularly in orthopaedic practice particularly in fracture non-union, revision hip and knee arthroplasty, following bone tumour excision and in spinal fusion surgery. At present the optimal source of graft to ‘fill’ these defects is autologous bone but this has significant drawbacks including harvest site morbidity and limited quantities.

Bone marrow has been proposed as the main source of osteogenic stem cells for the tissue-engineered cell therapy approach to bone defect management. Such cells constitute a minute proportion of the total marrow cell population and their isolation and expansion is a time consuming and expensive strategy.

In this study we investigated human bone marrow stem cells as a potential treatment of bone defect by looking at variability in patient osteogenic cell populations as a function of patient differences. We produced a model to predict which patients would be more suited to cell based therapies and propose possible methods for improving the quality of grafts.

Estrogen fluctuations have been implicated in the soft tissue injury gender-bias due to the hormones effect on the viscoelastic properties. The isolated effect of estrogen on the mechanical behaviour of human tendon is unknown. The purpose of this study was to elucidate the effect of circulating levels of estrogen on the strain properties of the human Achilles tendon.

Twenty females (18–35 years) who were using the pill together with 20 matched, non-pill users, participated in this study. Non-pill users were tested at the time of lowest (menstruation) and highest (ovulation) estrogen whilst pill users, who exhibited constant and attenuated estrogen levels, were tested at menstruation and two weeks later. At each test session, maximal isometric plantarflexion efforts were performed on a calf-raise apparatus whilst synchronous real-time ultrasonography of the triceps surae aponeurosis was recorded. Connective tissue length (Lo) of the triceps surae complex was measured and tendon strain was calculated by dividing aponeurosis displacement during plantarflexion by Lo.

Repeated measures ANOVA revealed a significant (p < 0.05) main effect of subject group with significantly higher Achilles strain rates (16.1%) in the non-pill users compared to the pill users. Augmented Achilles tendon strain was associated with higher average estrogen levels in non-pill users.

Those results suggest that higher estrogen levels diminish the joint stabilising capacity of the triceps surae musculotendinous unit and may alter the energy storage capacity of the Achilles tendon during stretch-shorten cycle activities. This may result in a higher incidence of injuries during periods of high estrogen concentration.

Hip simulator studies on MOM bearings have historically involved ‘custom’ cetabular cups. I.e. having neither beaded layers nor biological coatings.

The aim of this study was to investigate wear using such MOM bearings and evaluate the potential wear and evaluate the potential for error in the gravimetric assessment.

Six x 38 mm HC Co-Cr bearings were supplied (Global and IO International Orthopaedics). The cups were received in ‘off-the-shelf’ condition with a cast Co-Cr beaded/HA-coated backing. To remove the HA-coating, the cups were pre-soaked in lemon juice for 4 days (articular surfaces shielded). Custom plastic fixtures were machined to fit the beaded contours of the cups. Test duration was 5Mc inorbital hip simulator (Shore-Western). MOM wear was estimated from serum ion contamination. Serum samples were digested and assessed using ICP/MS (Weck Labs Inc, CA).

The majority of the HA-coating was removed from the cups after four days of soaking inlemon juice after 21 days of soaking all cup weights appeared atable (within 1 mg). Reflected-light microscopy (RLM) showed no descernible signs of HA and the total weight loss due to HA remval averaged∼400mg.

During hip simulator there was no visual evidence of lost or broken beads, 3rd body abrasion etc (Sa<30nm). Both gravimetric and metal ion analysis showed consistent wear trends for all MOM cups. The MOM with the highest wear (predicted by ion analysis) demonstrated 1.2 mm (3)/Mc)OWR) at 5Mc. In comparsion, gravimetric analysis predicted an OWR of 1.3 mm (3)Mc for the same MOM, a difference of only 8%. Soaking beaded-HA cups in lemon juice and BCS proved effective in removing the coating.

The beaded cups remained stable in weight during the wear study and caused little discrepancy in gravimetric analysis (8%).

The method described did not lead to breaking of beads, elevated 3rd-body abrasion, cup damage or distorted wear scars.

Aim

To evaluate the costs of performing revision hip and knee surgery at a District General Hospital.