Background

Patellar instability is a complex, multi-factorial disorder. Radiological assessment is regarded as an important part of the management of this population. The purpose of this study was to determine the intra- and inter-rater reliability of common radiological measurements used to evaluate patellar instability.

Purpose

Great expense is accumulated in investigation and management, often with poor outcome, of a patient with a painful TKR. We aim to produce guidelines for their investigation and careful, successful management.

ARMD (Adverse Reaction to Metal Debris) is an increasingly recognised complication of metal on metal hip replacements. The MHRA (Medical and Healthcare Related Devices Agency) have advised a blood cobalt or chromium level above 7 mg/L is a threshold for further investigation, stating that “low levels are reassuring and strongly predict not having an adverse outcome”. Cross-sectional imaging should be performed when levels are above 7 mg/L. We have performed a study investigating the specificity and sensitivity of chromium and cobalt metal ion levels as a screening measure for ARMD.

79 ASR hip replacements were performed at our hospital and 75 (95%) of these underwent a Metal Artefact Reduction Sequence (MARS) MRI scan. All patients (64 hips) who had not undergone revision were invited to take part in this study. 57 patients with 62 hip replacements completed hip and activity scores, had blood cobalt and chromium ion level measurements and 3D-CT to measure acetabular component position.

Acetabular component inclination (>50 degrees), small head size (< 51mm) and female gender were significantly correlated with raised chromium (Cr) and cobalt (Co) ion levels. An ARMD was detected using MRI in 18 (29%) of the hips in this study. The incidence of ARMD was significantly higher when chromium concentration was above 7 mg/l (p = 0.02). Chromium ion levels >7 mg/L had a sensitivity of 56% and specificity of 83% for ARMD, and cobalt ion levels >7 mg/L 56% and 76% respectively. 40 patients had cobalt levels <7 mg/L and 33 had chromium levels <7 mg/L, but 8 of these had an ARMD on MRI. All 8 patients had minimal symptoms (Oxford Hip Score ≥ 44 out of 48).

The Medicines and Healthcare Products Regulatory Agency (MHRA) has recommended that cobalt and chromium levels be measured in patients with a metal-on-metal hip replacement and cross-sectional imaging performed when these levels are above 7 μg/L. This study has shown that by using this threshold, in patients with this implant combination, the sensitivity and specificity for the detection of ARMD is low and patients with soft tissue disease may be missed. Furthermore the presence of MRI detected ARMD, in the absence of significant clinical symptoms and with metal ion levels <7 μg/L is of concern.

MoM implants at risk of failure are associated with raised cobalt and chromium levels. However metal ion analysis alone is not reliable as a screening tool for ARMD, which is often clinically “silent”. We recommend the routine use of MARS MRI as the safest method of ARMD diagnosis in patients with MoM implants.

Allogeneic blood transfusion is associated with many complications and significant cost. The RD&E has looked at the use of autologous drains after our study of 100 cases showed an improved post-operative haemoglobin and reduced length of stay. There is a need to identify those patients of increased need for an autologous drain, in order to decrease the frequency of allogeneic transfusion. In 2007 a protocol was drawn up using information from our study of 191 cases which showed an average haemoglobin drop post-operatively of 3.05g/dl and average intra-operative blood loss of 285 ml. This protocol gives the surgeon triggers for autologous drain use; preoperative haemoglobin of <13g/dl, intra-operative blood loss of >400ml, tourniquet use, patient weight <50kg and patients refusing donated blood.

In 2007-08, 65% of a further 275 cases analysed met the triggers for use of an autologous system. The remaining patients received low vacuum drains. Of the 275 patients, only 2 (<1%) of those who did not fulfil the criteria for an autologous drain required allogeneic blood, compared with 43 patients (24%) of those deemed high risk of transfusion, and assigned autologous drains. The protocol was therefore deemed to be successful in identifying those patients who required additional support and expenditure to minimise allogeneic blood transfusion.

Analysis of this data led to recommended changes to the protocol in order to maximise the efficiency of the autologous drain use. In 2010 a further patient cohort studied showed a reduction in allogeneic blood transfusion to <10% of those receiving autologous drains, and an increase to 5% of those with low vacuum drains.

Due to the increased cost of autologous drains (£68) compared with the low vacuum systems (£32), and the cost of allogeneic units at £141, the expenditure per patient was calculated and shown to fall from £92 in 2007 to £78 in the 2010.

In conclusion, this protocol allows the clinician to appropriately target the use of the more expensive autologous drains to those of increased risk of transfusion. This protocol helps to minimise unnecessary allogeneic blood transfusion risks, and this has been shown to be more cost effective.

Weight-bearing is a known stimulus for bone remodelling and a reduction in weight-bearing is associated with reduced bone mineral density (BMD) in affected limbs post lower limb fracture. This study investigated short and long-term precision of a method for measuring relative left/right weight-bearing using two sets of identical calibrated scales. The effect of imbalance on BMD at the hip and on lower limb lean tissue mass (LLTM) was also assessed.

46 postmenopausal women, with no history of leg or ankle fracture, were measured three times whilst standing astride two scales (Seca, Germany). 34 of the participants were re-measured after 6 months by the same method. Bilateral hip and total body dual x-ray absorptiometry measurements were performed using a GE Lunar Prodigy (Bedford, MA). Precision errors in weight-bearing measures were calculated using the root mean square coefficient of variation (RMSCV%). The correlations at the first visit between left/right differences in weight-bearing and differences in BMD and LLTM were calculated.

The short-term RMSCV% for left and right weights were 4.20% and 4.25% respectively and the long-term RMSCV% were 6.91% and 6.90%. Differences in left/right weight-bearing ranged from 0 to 24% (SD 8.63%) at visit 1 and 0 to 30% (SD 10.71%) at visit 2. Using data from visit 1, the relationship between hip BMD differences and left/right weight-bearing differences were investigated, with no significant correlations found. However, a weak, but statistically significant correlation of r=0.35 (p=0.02) was found for differences in LLTM and left/right weight-bearing differences.

In conclusion, left/right weight-bearing measured using two scales is a precise method for evaluating differences in weight-bearing in the short and long-term. Differences in left/right weight-bearing in this population varied by up to 30%. Participants showed a high degree of consistency in their long-term balance in a natural standing posture. Inequalities in left/right weight-bearing did not correlate significantly with BMD at the hip, but demonstrated a weak but statistically significant correlation with lean tissue mass.

Background and Objectives

Triangular fibrocartilaginous complex (TFCC) tears are common sources of ulna sided wrist pain and resultant functional disability. Diagnosis is based on history, clinical examination and radiological evidence of a TFCC central perforation or radial/ulna tear. The purpose of this study is therefore to evaluate the diagnostic accuracy of Magnetic Resonance Imaging (MRI) and Magnetic Resonance Arthrography (MRA) in the detection of TFCC injury in the adult population.

Purpose

To calculate the cost of investigation of a painful Total Knee Replacement (TKR) to the hospital trust and Primary Care Trust (PCT).

Introduction: Although good mid-term results have been reported with some metal on metal hip replacements, reported complications due to metal on metal (MOM) related reactions are a cause for concern. We have assessed the clinical outcome and MRI metallic artefact reduction sequence (MARS) findings in a consecutive series of patients with a large head metal on metal hip replacement.

Methods: 62 ASR XL Corail THRs and 17 ASR resurfacings were performed at our hospital between 2005 and 2008. All patients were reviewed and assessed with an Oxford hip score (OHS), a plain radiograph and a MRI imaging was obtained on 76 (96%) hips. Implant position was assessed using Wrightington cup orientation software.

Results: At a mean follow up of 32 months, 9 (15%) ASR XL Corail THRs, and 2(12%) ASR resurfacings had been revised. 10 revisions were performed for MRI confirmed MOM related pathology. Histology confirmed a MOM reaction in all 10 cases.

Of the 76 hips that were MRI scanned, 27 (36%) had typical features of a MOM reaction. These were classified as mild in 10 (13%), moderate in 13 (17%) and severe in 4 (5%).

78 patients completed an OHS and the mean score was 21. The mean OHS was 29 pre-operatively in those that had been revised, 25 in patients with abnormal MRI findings and 20 in those with a normal MRI. 10 patients with abnormal MRIs had a near perfect OHS (15 or less)

Conclusions: The ASR XL Corail THR has an unacceptably high early failure rate. MARS MRI is able to detect metal debris related soft tissue pathology around metal on metal THRs. These lesions are sometimes asymptomatic. We suggest that MARS MRI evaluation should form part of the routine evaluation of all metal on metal THRs, and in particular of this implant.

We describe our technique and the early results of compaction morselised bone grafting (CMBG) for displaced tibial plateau fractures using fresh frozen allograft. This technique has been performed by the senior author since July 2006 on eight patients.

Clinical and radiological follow-up was performed on seven remaining patients at an average 12 months (range 4–19) following surgery. One patient died of an unrelated cause three months following surgery. One patient underwent a manipulation under anaesthesia at three months for knee stiffness. One patient developed a painless valgus deformity and underwent corrective osteotomy at 15 months. The height of the tibial plateau on radiographs has been maintained to an excellent grade (less than 2 mm depression) in all but one patient.

CMBG using fresh frozen allograft in depressed tibial plateau fractures provides structural support sufficient to maintain the height of the tibial plateau, is associated with few complications in complex patients with large bone loss and has theoretical advantages of graft incorporation and remodelling.

We have analysed the early functional results in patients who have had the NRG total knee replacement at the Princess Elizabeth Orthopaedic Centre, Exeter. This is a new modern design designed for high function. We analysed a total of 54 knees (47 patients) operated between September 2005 and October 2007. The follow up ranged from 9 to 25 months averaging 16 months. Thirty eight percent of the patients were male and 62% female. The age of the patients ranged from 42 to 90 (average 72).

The Oxford knee score and satisfaction score were documented at 6 weeks, 6 months, I year and 2 years. The range of movement was also noted. Ninety eight patients had the highest satisfaction score of 3 at the one year follow up. The average Oxford knee score pre-operatively was 45 and the average was 30 at 6 weeks and 6 months and 20 at 1 and 2 year follow up. Seventy four percent of the patients had post operative knee flexion of more than 100 degrees. The average post operative value added flexion was 14 degrees.

We conclude the early results of the NRG knee replacement are very encouraging with very good patient satisfaction scores and post operative flexion of the knee.

The 4th England and Wales NJR showed that 83% of total knee replacements were cemented (47,626 knees). This study aimed to compare modern techniques of cementation of the proximal tibia in an experimental model against tourniquet-less knee replacement surgery with cancellous bone suction and a cement gun.

A metal box was constructed to approximate the proximal tibia and open cell sawbone simulated the tibia with simulated blood flow and bone suction. Each sample was prepared in an identical fashion except for the cementing technique. The techniques compared were of

Tourniquet,

Samples were subsequently sectioned, polished and the cemented area measured using a planimeter.

ANOVA testing demonstrated that the techniques were significantly different (p< 0.0001). Bonferroni Comparison demonstrated that the Exeter technique gave significantly better cement penetration for central and lateral measurements (p< 0.0001 and p< 0.0001) compared to all other methods.

The authors believe that our technique of cementation of the proximal tibia offers an easy and reproducible way of getting good quality cementing of the tibial component in total knee replacement and this is borne out by our experimental model.

Metal-on-metal total hip replacement has been targeted at younger patients with anticipated long-term survival, but the effect of the production of metal ions is a concern because of their possible toxicity to cells. We have reviewed the results of the use of the Ultima hybrid metal-on-metal total hip replacement, with a cemented polished tapered femoral component with a 28 mm diameter and a cobalt-chrome (CoCr) modular head, articulating with a 28 mm CoCr acetabular bearing surface secured in a titanium alloy uncemented shell.

Between 1997 and 2004, 545 patients with 652 affected hips underwent replacement using this system. Up to 31 January 2008, 90 (13.8%) hips in 82 patients had been revised. Pain was the sole reason for revision in 44 hips (48.9%) of which 35 had normal plain radiographs. Peri-prosthetic fractures occurred in 17 hips (18.9%) with early dislocation in three (3.3%) and late dislocation in 16 (17.8%). Infection was found in nine hips (10.0%).

At operation, a range of changes was noted including cavities containing cloudy fluid under pressure, necrotic soft tissues with avulsed tendons and denuded osteonecrotic upper femora. Corrosion was frequently observed on the retrieved cemented part of the femoral component. Typically, the peri-operative findings confirmed those found on pre-operative metal artefact reduction sequence MRI and histological examination showed severe necrosis.

Metal artefact reduction sequence MRI proved to be useful when investigating these patients with pain in the absence of adverse plain radiological features.

There are many reports in the literature about the benefits of computer-aided surgery with regards to improved limb alignment, reduced blood loss and embolic events but surgeons remain sceptical about its routine use because of availability, cost and time implications. To maximise these benefits and overcome the distractions, a modified navigation technique has been developed after evaluation of the standard measurements.

The true varus/valgus angle of the distal femoral cut achieved with navigation is unknown but represents presumed accurate alignment with regards to the mechanical axis through the femoral head. With placement of the femoral tracker in the medial supracondylar region clear of the intramedullary canal, the navigated cut was correlated with the cut placement determined with the standard intramedullary jig in 10 patients undergoing knee replacement. In addition, jigged femoral rotation was checked with the tracker placement. Tibial slope, varus/valgus angle and rotation were determined using surgeon placement of an external alignment jig and confirmed with tracker placement.

The navigated distal femoral cut ranged from +3 degrees to −2 degrees when measured against the distal cutting block stabilised over an intramedullary rod. The femoral rotation was within 1 degree of the trans-epicondylar line as outlined by navigation when a 3 degree externally rotated jig was used. All of the tibial measurements were within 0.5 degrees of the navigated planned positions.

The femoral cuts are presumed to be accurately determined with navigation as judged from long-leg alignment x-rays but this study highlights the potential error if a fixed valgus cut angle with alignment jigs is used. Tibial preparation, however, was accurately predicted by the surgeon using a traditional external alignment jig. Bone preparation time was reduced to 4 minutes (modified technique) compared to 12 minutes (full navigation, p< 0.05).

With this information, computer-aided navigation is now routinely used to determine the distal femoral cut only and an external alignment jig is used for tibial preparation without navigation. The reduction in blood loss and embolic events and improved limb alignment is now achieved with a reduction in preparation time over full navigated techniques. Use of the pinless surface mounted femoral jig alone highlights these advantages further.

60 out of total series of 643 metal-on-metal hip replacements, carried out over the last nine years, have so far required revision, 13 for peri-prosthetic fracture and 47 for extensive, symptomatic, peri-articular soft-tissue changes.

Dramatic corrosion of generally solidly fixed, cemented stems has been observed and is believed to have resulted in the release of high levels of cobalt chrome ions from the stem surface. The contribution of the metal-to-metal articulation is, as yet, unclear.

Not including the fracture cases, plain films have demonstrated little or no abnormality to account for patients’ progressive symptoms. MRI scanning, on the other hand, utilising a technique designed to minimise implant artefact, has correlated very closely with findings at the time of revision surgery.

The histological changes, typified by extensive lymphocytic infiltration and a severe vasculitis leading to, in some cases, extensive tissue necrosis are demonstrated and discussed.

The failure of any of the existing protective mechanisms or regulatory restrictions to identify and limit the exposure of large numbers of patients to unsatisfactory implants has again been demonstrated.

Introduction: Diaphyseal fracture at a cortical perforation is the commonest postoperative complication of hips revised with impacted morsellised bone. To reduce fracture risk, surgeons can apply mesh, augment the bone with plate or strut graft, or bypass the perforation with a longer stem. No biomechanical data exists to choose between these alternatives. The objective of this study was to compare the above methods of cortical repair in terms of (i) bone fracture risk and (ii) stem migration.

Methods: Fourteen large composite femora (Sawbones, Malmö, Sweden) were prepared to simulate cavitary defects. An 18×40 mm lateral cortical perforation was made in 12 diaphyses. These diaphyses were repaired with mesh only, mesh and plate, or mesh and strut graft (n=4 each). Strut graft and plate were fixed with cables. Porcine cancellous bone was morsellised and impacted into each cavitary defect. Simplex P bone cement was injected. In the 12 femora with repaired perforation, a standard or a long Exeter prosthesis, bypassing the perforation 2 cortical diameters, was implanted. Thus, 6 methods of defect repair were created (mesh, plate and strut, combined with either long or short stem, each n=2). Standard stems impaction-grafted in the two femora without perforation served as control (n=2). Femora were placed in a testing machine and loaded at 1 Hz with 100 cycles of joint and abductor force. Peak joint force was 2,500 N. Strain amplitudes at the perforation and stem migration were determined. Statistical analysis was by 2-way and 1-way ANOVA, and the Student-Newman-Keuls (SNK) post-hoc test.

Results: Stem length did not affect average defect strain if used with plate or strut graft (2x2 ANOVA, p=0.62). Four combinations remained for further analysis: standard stem with mesh, long stem with mesh, plate, and strut graft, with defect strains of 5250, 3620, 2940, and 2480 μstrain. In controls, strains were 1750 μstrain. Defect strains differed significantly (ANOVA, p=0.0004), with strains for standard stems with mesh significantly higher than all other groups, those for long stems with mesh significantly higher than controls, and those for plate or strut graft no different from controls (SNK). Maximum permanent subsidence was 0.71 mm and retroversion 1.6°. For repaired perforations, stem length did not affect subsidence (p=0.96), but repair method did (p=0.03, both 2-way ANOVA). For further analysis, subsidence of the three repair methods (mesh, plate and strut graft with subsidence of 0.24, 0.47 and 0.19 mm, resp.) was compared with that of controls (0.52 mm). Subsidence differed significantly (ANOVA, p=0.02), and stems with strut graft subsided significantly less than those with plate or controls (SNK). Permanent retroversion was similar for each group.

Dicussion: Non-reinforced defects with a standard stem generated high defect strain amplitudes. A long stem bypassing the defect reduced these strains by 30%, and might suffice in case of otherwise strong cortex. In other cases, augmentation of the perforated diaphysis with either strut graft or plate needed to minimise fracture risk. Stem migration in reconstructed perforated diaphyses was always less than control cases, suggesting stem migration is no specific problem in reconstruction.

Introduction: Bio mechanical tests under realistic loading conditions of prostheses in bone can help to improve the design of joint implants. Cadaveric bones are most realistic but highly variable and difficult to obtain and conventional bone models have been used so far. Stereo lithography (SLA) techniques are used in industry to generate 3-D rapid prototypes. These techniques could serve to produce bones with complex geometries, but the material used is less stiff than cortical bone.

Aim: The purpose of the study was to answer the following two questions? 1. Does stability of and cortical strains around implants in SLA-made bones matched those of conventional artificial bones? 2. Whether increasing cortical wall thickness brings these variables closer?

Methods: Four artificial cortical shells of proximal tibiae were made from resin (SL5170, 3D systems Europe Ltd., Hemel Hempstead, UK) using SLA process. Two third generation large composite tibiae #3302 (Sawbones Europe AB, Malmö, Sweden) were chosen and the polyurethane foam that represents the cancellous bone was removed. All six cortices were filled with polyurethane foam (Tripor 224, ABL (STEVENS), Cheshire, UK) with an average compressive modulus of 53.9±7.2 SD MPa. The tibiae were prepared to receive a standard size cemented tibial tray for all models. The models were loaded with 100 cycles of 2000 N at 1 Hz along the longitudinal axis, separately on the lateral and on the medial condyle. Medial cortical strain and tray migration during load was determined.

Results: Cyclic loading gave a general pattern of cyclic movements, superimposed on a very small permanent movement. The first cycle gave most permanent displacement, after which further migration occurred at a decreasing rate. Permanent and cyclic migration of all four trays implanted in SLA-made tibiae fell within the range of those implanted in conventionally available tibiae. Strains at the proximal medial cortex were low and on the same order for all six tibiae. Strains more distally were approximately inversely proportional to the material stiffness and cortical thickness of the tibiae.

Conclusion: The study concludes that migration of tibial trays in all SLA models was with in the range of those in conventional models. Hence these models can be used to test early mechanical stability of joint implants despite their lower stiffness. The small difference may be related to load bearing mechanism of tibial trays which is largely through cancellous bone and not cortical bone. The low strains at the proximal cortex in this study also suggest that the cortex carried little direct load. The polyurethane foam representing cancellous bone in our study was identical for each tibia, which may explain that movements of the trays were comparable. Distal cortical strains reflected the stiffness of the tibiae and were directly influenced by cortical thickness.

The use of impaction bone grafting during revision arthroplasty of the hip in the presence of cortical defects has a high risk of post-operative fracture. Our laboratory study addressed the effect of extramedullary augmentation and length of femoral stem on the initial stability of the prosthesis and the risk of fracture.

Cortical defects in plastic femora were repaired using either surgical mesh without extramedullary augmentation, mesh with a strut graft or mesh with a plate. After bone impaction, standard or long-stem Exeter prostheses were inserted, which were tested by cyclical loading while measuring defect strain and migration of the stem.

Compared with standard stems without extramedullary augmentation, defect strains were 31% lower with longer stems, 43% lower with a plate and 50% lower with a strut graft. Combining extramedullary augmentation with a long stem showed little additional benefit (p = 0.67). The type of repair did not affect the initial stability. Our results support the use of impaction bone grafting and extramedullary augmentation of diaphyseal defects after mesh containment.