Background

It has become increasingly important to conduct studies assessing clinical outcomes, reoperation rates, and revision rates to better define the indications and efficacy of lumbar spinal procedures and its association with symptomatic adjacent segment degeneration (sASD). Adjacent segment degeneration (ASD) is defined as the radiographic change in the intervertebral discs adjacent to the surgically treated spinal level. SASD represents adjacent segment degeneration which causes pain or numbness due to post-operative spinal instability or nerve compression at the same level. The most common reason for early reoperation and late operation is sASD, therefore is in our best interest to understand the causes of ASD and make steps to limit the occurrence.

The primary aim of this study was to compare the clinical outcomes of osteoid osteoma (OO) between the group of patients with the presence of nidus on biopsy samples from radiofrequency ablation (RFA) with those without nidus. Secondly, we aimed to examine other factors that may affect the outcomes of OO reflecting our experience as a tertiary orthopaedic oncology centre.

We retrospectively reviewed 88 consecutive patients diagnosed with OO treated with RFA between November 2005 and March 2015, consisting of 63 males (72%) and 25 females (28%). Sixty-six patients (75%) had nidus present in their biopsy samples. Patients’ mean age was 17.6 years (4-53). Median duration of follow-up was 12.5 months (6-20.8). Lesions were located in the appendicular skeleton in seventy-nine patients (90%) while nine patients (10%) had an OO in the axial skeleton. Outcomes assessed were based on patients’ pain alleviation (partial, complete, or no pain improvement) and the need for further interventions.

Pain improvement in the patient group with nidus in histology sample was significantly better than the group without nidus (OR 7.4, CI 1.35-41.4, p=0.021). The patient group with nidus on biopsy demonstrated less likelihood of having a repeat procedure compared to the group without nidus (OR 0.092, CI 0.016-0.542, p=0.008). Our study showed significantly better outcomes in pain improvement in appendicular lesions compared to the axially located lesions (p = 0.005). Patients with spinal lesions tend to have relatively poor pain relief than those with appendicular or pelvic lesions (p=0.007).

Patients with nidus on histology had better pain alleviation compared to patients without nidus. The histological presence of nidus significantly reduces the chance of repeat interventions. The pain alleviation of OO following RFA is better in patients with appendicular lesions than spinal or axially located lesions.

Objectives

Investigate the incorporation of an antibiotic in bone cement using liposomes (a drug delivery system) with the potential to promote osseointegration at the bone cement interface whilst maintaining antibiotic elution, anti-microbiological efficacy and cement mechanical properties.

Prosthetic joint infection and aseptic loosening are associated with significant morbidity. Antibiotic loaded bone cement is commonly used and successfully reduces infection rates; however, there is increasing resistance to the commonly used gentamicin.

Previous studies have shown gentamicin incorporated into bone cement using liposomes can maintain the cement's mechanical properties and improve antibiotic elution.

The phospholipid phosphatidyl-l-serine has been postulated to encourage surface osteoblast attachment and in a liposome could improve osseointegration, thereby reducing aseptic loosening.

Preliminary clinical isolate testing showed excellent antimicrobial action with amoxicillin therefore the study aims were to test amoxicillin incorporated into bone cement using liposomes containing phosphatidyl-l-serine in terms of antibiotic elution, microbiological profile and mechanical properties.

Background

Devices are frequently used to gain sufficient purchase in a bone so that the bone itself can be manipulated to move or rupture soft tissue attachments. During hip surgery, several different extraction corkscrews are available to remove the femoral head, each with a different screw design with no evidence to suggest which is most effective. Additionally during the use of corkscrew devices, often due to the low bone density, stripping of the screw threads out of the femoral head can occur prior to its extraction, thus requiring reinsertion. The aims of this project were to measure the primary pullout and reinsertional forces of five commercially available corkscrews.

Aim

Compare clinical outcomes following staged revision arthroplasty for periprosthetic joint infection (PJI) secondary to either multidrug resistant (MDR) bacteria or non-MDR (NMDR) bacteria.

25–40% of unicompartmental knee replacement (UKR) revisions are performed for unexplained pain possibly secondary to elevated proximal tibial bone strain. This study investigates the effect of tibial component metal backing and polyethylene thickness on cancellous bone strain in a finite element model (FEM) of a cemented fixed bearing medial UKR, validated using previously published acoustic emission data (AE).

FEMs of composite tibiae implanted with an all-polyethylene tibial component (AP) and a metal backed one (MB) were created. Polyethylene of thickness 6–10mm in 2mm increments was loaded to a medial load of 2500N. The volume of cancellous bone exposed to <−3000 (pathological overloading) and <−7000 (failure limit) minimum principal (compressive) microstrain (µ∊) and >3000 and >7000 maximum principal (tensile) microstrain was measured.

Linear regression analysis showed good correlation between measured AE hits and volume of cancellous bone elements with compressive strain <−3000µ∊: correlation coefficients (R= 0.947, R2 = 0.847), standard error of the estimate (12.6 AE hits) and percentage error (12.5%) (p<0.001). AP implants displayed greater cancellous bone strains than MB implants for all strain variables at all loads. Patterns of strain differed between implants: MB concentrations at the lateral edge; AP concentrations at the keel, peg and at the region of load application. AP implants had 2.2 (10mm) to 3.2 (6mm) times the volume of cancellous bone compressively strained <−7000µ∊ than the MB implants. Altering MB polyethylene insert thickness had no effect. We advocate using caution with all-polyethylene UKR implants especially in large or active patients where loads are higher.

Introduction

Bone tumours of the foot are rare, representing 3–6% of all bone tumours. Of these 15–25% are thought to be malignant. Obtaining clear surgical margins remains an important factor in improving outcome from tumours. However, the anatomical complexity of the foot can lead to an inadequate resection, particularly if the operating surgeon is attempting to preserve function. The aim of this paper is to identify the clinical course of patients suffering from malignant bone tumours of the foot.

Joint registries report that 25–40% of UKR revisions are performed for pain. Proximal tibial strain and microdamage are possible causes of this “unexplained” pain. The aim of this study was to examine the effect of UKR implant design and material on proximal tibial cortical strain and cancellous microdamage.

Composite Sawbone tibias were implanted with cemented UKR components: 5 fixed bearing all-polyethylene (FB-AP), 5 fixed bearing metal backed (FB-MB), and 5 mobile bearing metal backed implants (MB-MB). Five intact tibias were used as controls. Tibias were loaded in 500N increments to 2500N. Cortical surface strain was measured using digital image correlation (DIC). Cancellous microdamage was measured using acoustic emission (AE), a technique which detects elastic waves produced by the rapid release of energy during microdamage events.

DIC showed significant differences in anteromedial cortical strain between implants at 1500N and 2500N in the proximal 10mm only (p<0.001) with strain shielding in metal backed implants. AE showed significant differences in cancellous microdamage (AE hits), between implants at all loads (p=0.001). FB-AP implants displayed significantly more hits at all loads than both controls and metal backed implants (p<0.001). FB-AP implants also differed significantly by displaying AE hits on unloading (p=0.01), reflecting a lack of implant stiffness. Compared to controls, the FB-AP implant displayed 15x the total AE hits, the FB-MB 6x and the MB-MB 2.7x. All-polyethylene medial UKR implants are associated with greater cancellous bone microdamage than metal backed implants even at low loads.

Introduction

We present our experience of the coned hemi-pelvis (‘ice-cream’ cone) implant, using an extended posterior approach to the hip joint, in the management of pelvic bone loss and pelvic discontinuity.

Aim/Purpose

Review our unique experience in the management of 29 consecutive casualties who survived open pelvic fractures following a blast mechanism.

The aim of this study is to review our unique experience in the management of 29 consecutive casualties who survived open pelvic fractures following a blast mechanism, in order to determine the injury pattern, clinical management and outcome of these devastating injuries.

All patients were serving soldiers who were injured whilst on operations in Afghanistan. The median New Injury Severity Score (NISS) was 41. Mean blood requirement in the 1^st 24 hours was 60.3 units. In addition to their orthopaedic injury, 6 (21%) had an associated vascular injury, 7(24%) had a bowel injury, 11 (38%) had a genital injury and 7(24%) had a bladder injury. 8 (28%) fractures were managed definitively with external fixation, and 7 (24%) fractures required ORIF. Of those patients who underwent ORIF, 4 (57%) required removal of metalwork for infection. Faecal diversion was performed on 9 (31%) casualties. Median length of stay was 70.2 days, and mean total operative time was 29.6 hours. At a mean 20.3 months follow-up, 24 (83%) were able to ambulate, and 26 (90%) had clinical and radiological evidence of pelvic ring stability.

The “Global War on Terror” has resulted in incidents that were previously confined exclusively to conflict areas can now occur anywhere, and surgeons who are involved in trauma care may be required to manage similar injuries from terrorist attacks. Our study clearly demonstrates that the management of this injury pattern is extremely resource intensive with the need for significant multi-disciplinary input. Given the nature of the soft tissue injury, we would advocate an approach of minimal internal fixation in the management of these fractures. With the advent of emerging wound and faecal management techniques, we do not believe that faecal diversion is mandated in all cases.

This study was undertaken to assess for equivalence or superiority in tendon reconstruction techniques. This is an in vitro analysis of several, different, reconstruction techniques for chronic Achilles tendon ruptures. The surgical techniques have been borne out of surgical preference rather than biomechanical principles with little published research into their comparability. Surgical preferences are a result of the supposed benefits of reduced operative time, single operative incision and decreased morbidity. An animal model, after human cadaveric tissue dissection to guide the specimen construction, was used to compare the different techniques using bovine bone and tendon and tested using a material testing machine. Ultimate load to failure was recorded for all specimens and statistical analysis of the results was undertaken.

A statistically significant difference was shown between all the techniques by analysis of variance. This will guide clinical application of these techniques. The use of bone tunnels, through which the flexor hallucis longus tendon can be passed, were found to be biomechanically superior, with regard to ultimate load to failure, to either bone anchors or end-to-end tendon suture techniques. Interference screws were found to have a large range in their ultimate load suggesting a lack of consistency in the results. The mean of the bone tunnel group (482.8N, SD 83.6N) is significantly (p < 0.01) higher than the mean of the bone anchor group (180.2N, SD 19.3N), which is, in turn, significantly (p < 0.01) higher than the mean of the Bunnell group (73.7N, SD 20.9N). This study is larger than any previous study found in the literature with regard to number of study groups and allows the techniques to be compared side by side.

Background

Patients with fractured neck of femur have historically received less attention than they deserve and have high morbidity and mortality. Literature suggests that speed to theatre reduces length of in-patient stay and complications.

The fixation of comminuted femoral fractures with intramedullary nails is commonplace but there remains little work on the mechanical ability of the different diameters of nail available to resist bending. What previous work there is has produced conflicting conclusions. The bending stiffness against the intramedullary nail diameter and the extent of the comminuted fracture is clinically important due to the impact on fracture healing and implant failure.

Intramedullary nails of differing diameters (10 mm, 11 mm and 13 mm) were loaded axially in fourth generation composite femurs with increasing mid shaft bone defects, namely 3cm, 5cm, 8cm and 10cm bones. The loading versus the displacement was recorded for each nail.

A one-way ANOVA analysis demonstrated a significant difference between intramedullary nail diameters and the bending stiffness, with p values of less than 0.012; 3cm mean 12.26 (CI 9.06-15.46) mm, p=0.012; 5 cm mean 10.63 (CI 8.35-12.92) mm, p=<0.001; 8 cm mean 11.04 (CI 8.35-13.74) mm, p=<0.001; 10 cm mean 11.68 (CI 7.86-15.50) mm, p=<0.001. For the 11 mm diameter intramedullary nail, failure occurred at around two times the body weight of an average individual or 1400 to 1800 N. A repeated measure ANOVA analysis of the effect of the increasing bone defect showed a mixed picture, with a significant difference between the 5 cm and 8 cm gap and only a trend towards significance between 5 cm and 10 cm.

Caution should be advised when considering using a cannulated femoral intramedullary nail in a patient with a fracture gap of greater than 5 cm. Further, the mechanical effect of comminuted fractures treated with nails suggests reduced stiffness with increasing length of fracture gap although the picture is complex and explains the divergence of research conclusions.

One reason why NICE (National Institute for Clinical Excellence) does not support operations by the NHS to heal hyaline cartilage lesions using a patients own cells is because there is no clear evidence to show that these operations are beneficial and cost-effective in the long term. Specifically, NICE identified a deficiency of high quality cartilage being produced in repaired joints. The presence of high quality cartilage is linked to long-lasting and functional repair of cartilage. The benchmark for quality, NICE stipulate, is repair cartilage that is stiff and strong and looks similar to the normal tissue surrounding it, i.e. mature hyaline articular cartilage.

Biopsy material from autologous cartilage implantation surgical procedures has the appearance of immature articular cartilage and is frequently a mixture of hyaline and fibrocartilage. Osteoarthritic cartilage, in its early stages, also exhibits characteristics of immature articular cartilage in that it expresses proteins found in embryonic and foetal developmental stages, and is highly cellular as evidenced through the presence of chondrocyte clusters. Therefore, an ability to modulate the phenotype and the structure of the extracellular matrix of articular cartilage could positively affect the course of repair and regeneration of articular cartilage lesions. In order to do this, the biochemical stimuli that induce the transition of an essentially unstructured amorphous cartilage mass (immature articular cartilage) to one that is highly structured and ordered, and biomechanically adapted to its particular function (mature articular cartilage) has to be identified.

We show for the first time, that fibroblast growth factor-2 and transforming growth factor beta-1 induce precocious maturation of immature articular cartilage. Our data demonstrates that it is possible to significantly enhance maturation of cartilage tissue using growth factor stimulation; consequently this may have applications in transplantation therapy, or through phenotypic modulation of osteoarthritic chondrocytes in diseased cartilage in order to stimulate growth and maturation of repair tissue.

Patient specific knee modelling has the potential to help understand the development of the mechanically induced degenerative disease, Osteoarthritis. A full joint contact model of the knee involves modelling the bones, ligaments, articular cartilage (AC) and meniscus, as well as, the kinematics and geometry of real joints. These finite element models will inevitably require great computational resource to run and it is desirable to find resource effective material model formulations which can accurately describe the mechanical behaviour of the soft tissues. Biphasic models (BIMs) have long been established as an effective formulation for modelling AC. However, the swelling behaviour caused by changes in the ionic phase is a major recovery mechanism and is neglected in the BIMs. It is therefore believed that BIMs alone are insufficient to fully describe the mechanical behaviour of AC. Instead, a thermal analogy method which is generically a BIM that includes the swelling behaviour has been thought to be suitable and has been validated against literature data using material parameters optimized to match the numerical and experimental results. To ensure the model is suitable for patient specific modelling where it will have the ability to reflect the individual AC material properties of the patients in the mechanical behaviour it predicts, two experiments have been planned and are currently being carried out using bovine AC. The first experiment is to investigate the diffusivity of the tissue in solutions of different molarity by measuring the change in tissue weight over time. Eleven explants are taken from the same bovine articular joint using a 6mm biopsy punch and are left in 10mM of PBS overnight to ensure ionic equilibrium has been reached before experiments are carried out. The explants are then placed in PBS solutions of molarities ranging from 0mM to 10mM and weighed at regular time intervals. In the final stage, the explants are then lyophilized and weighed for determining the volume of water in the tissues. Using Archimedes principle, the change in porosity of the tissue is found. A preliminary study has shown that explants submerged in a solution of 5mM has an approximately 4% change in weight after the first 24h and a further 1.73% change in the following 24h. Control specimens left in a solution of 10mM had a 0% change in weight. The second experiment is to carry out mechanical loading on the AC specimens while submerged in a solution of different ion concentrations. Experiments with various loading conditions are being investigated to explore their efficacy for validation. Preliminary compression tests have been carried out where steps of 1% strain was applied, giving a total of 10% strain. Between each step, strain was held constant until full relaxation has been achieved. The reaction force measured from the second experiment in conjunction with data collected from the first experiment will be compared to results predicted in the numerical model. This will allow the determination of whether thermal analogy is adequate or whether more complex triphasic models need to be considered. Furthermore, the development of these experimental methods will contribute to the validation of other AC material models in the future.

Introduction

Iatrogenic proximal femur hoop-stress fracture is a recognised complication of uncemented hip arthroplasty. It has a reported incidence of two to three percent and increases patient morbidity. We describe a novel technology that predicts fracture in real-time by less than one minute.

Excessive implant migration and micromotion have been related to eventual implant loosening. The aim of this project is to develop a computational tool that will be able to predict the mechanical performance of a cementless implant in the presence of uncertainty, for example through variations in implant alignment or bone quality. To achieve this aim, a computational model has to be developed and implemented. However, to gain confidence in the model, it should be verified experimentally. To this end, the present work investigated the behavior of a cementless implant experimentally, and compared the results with a computational model of the same test setup.

A synthetic bone (item 3406, Sawbones Europe AB, Sweden) was surgically implanted with a Furlong cementless stem (JRI, Sheffield, UK) in a neutral position and subjected to a compression fatigue test of −200 N to −1.6 kN at a frequency of 0.5 Hz for 50000 cycles. Measurements of the micromotion and migration were carried out using two linear variable differential transducers and the strain on the cortex of the femur was measured by a digital image correlation system (Limess Messtechnik & Software Gmbh).

A three-dimensional model was generated from computed tomography scans of the implanted Sawbone and converted to a finite element (FE) model using Simple-ware software (Simpleware Ltd, Exeter, UK). Face-to-face elements were used to generate a contact pair between the Sawbone and the implant. A contact stiffness of 6000 N/m and a friction coefficient of 0.3 were assigned. The analysis simulated a load of −1.6 kN applied to the head of the implant shortly post implantation. The motions and strains recorded in the experiment were compared with the predictions from the computational model. The micromotion (the vertical movement of the implant during a single load cycle), was measured at the proximal shoulder, at the distal tip of the implant and at the bone-implant interface. The maximum value calculated proximally using FE was 61.3 μm compared to the experimental value of 59.6 μm. At the distal end, the maximum micromotion from FE was 168.9 μm compared to 170 μm experimentally. As a point of reference, some authors have suggested that in vivo, fibrous tissue formation may take place at the bone-implant interface when the micromotion is above 150 μm. The maximum micromotion found computationally at this interface was 99 μm which is below the threshold value defined. The longitudinal strain over the surface of the bone was variable and reached values of up to 0.15% computationally and 0.4% experimentally; this may be related to the coordinate systems used. However, it was noted that digital image correlation identified qualitatively similar strain patterns, and has great potential for measuring low level surface strains on bone.

In conclusion, the good correlation between the computational modelling and experimental tests provides confidence in the model for further investigations using probabilistic analyses where more complex configurations (for example change in implant alignment) can be analyzed.

Background: Stress shielding in the proximal femur is a widely recognized sequel of total hip replacement. It is due to a discrepancy in the stiffness between the implant and the proximal femur. The strain characteristics of implants of differing materials on the femur have previously been demonstrated in the laboratory using strain gauges and photo-elastic techniques. These are however relatively crude techniques giving limited results. Finite element analysis has also been used, but this provides only a theoretical analysis. Digital Image Correlation is an extremely accurate technique for strain analysis previously used in micro and nano engineering research.

Methods: A stainless steel, a titanium, and a carbonfibre reinforced plastic (CFRP) femoral prosthesis of the same dimensions, were implanted without cement into 5 prosthetic femora. A 1kN load was applied using a compression device. The process was repeated with 5 other prosthetic control femora. Digital Image Correlation was used to give an extremely detailed 2D strain map of inner cortex of the proximal femora during laboratory simulated static physiological loading conditions.

Results: All implants caused stress shielding in the proximal calcar area. In Gruen zones 6–4, both the stainless steel and titanium implants caused statistically significant stress shielding, whereas the femora implanted with the CFRP prosthesis did not show a statistically different strain pattern from the control group. There was a reduction in strain experienced by the medial cortex of the femora beyond the tip of all of the implants.

Conclusion: Digital Image Correlation is a novel method for strain measurement within Orthopaedic research which produces extremely accurate strain maps and data that can be reliably used for statistical analysis. Using this technique, this laboratory based investigation indicates that a carbon-fibre reinforced plastic stem is a good candidate to avoid stress shielding in total hip replacement surgery.

Aim: To reduce the amount of blood wastage in our unit.

Method: In 72 patients, the number of blood units cross-matched and the haemoglobin/haematocrit fall were audited for primary total shoulder replacement (n=44), primary hemiarthroplasty (n=21), and revision shoulder replacement (n=7) over twelve months (January 2008 to December 2008). The amount of crossmatched blood was compared to the amount of blood transfused, pre-operative haemoglobin and fall in haemoglobin/haematocrit.

Results: 23 of 44 primary total shoulder replacements and 5 of 21 hemiarthroplasties were crossmatched 55 units preoperatively. 4 of the 7 revision arthroplasties were crossmatched 7 units preoperatively. No units were transfused. 4 patients were later transfused 2 units each for symptomatic low haemoglobin at day 3–5 postoperatively from postoperatively crossmatched blood. No correlation existed between preoperative haemoglobin and number of units blood ordered. A haemoglobin reduction of ~2.5 g/dl was seen for both primary and revision surgery. There was significant correlation between low preoperative haemoglobin and need for transfusion (p< 0.05). Nearly all patients in whom blood was crossmatched rather than group and saved, belonged to one consultant. No patients had an adverse outcome due to a lack of immediately available cross-matched blood.

Conclusion: A large amount of blood was crossmatched and no units used in primary and revision shoulder replacement surgery. We recommend group and save only in primary shoulder arthroplasty and crossmatch of 2 units for revision shoulder surgery. Providing pre-operative haemoglobin is > 11.5 g/dl, group and save is safe even for revision shoulder arthroplasty. Wastage of blood could be reduced to zero in our unit. We recommend regular audit as a tool to ensure compliance with guidelines, and for clinical governance purposes ensuring guidelines remain best practice.