Introduction

Total knee arthroplasty is an established and successful operation. In up to 10% of patients who undergo total knee arthroplasty continue to complain of pain [1]. Recently computerised tomography (CT) has been used to assess the rotational profile of both the tibial and femoral components in painful total knee arthroplasty.

Purpose

Patients with ankylosing spondylitis (AS) are vulnerable to cervical spine injury following relatively minor trauma. The authors present a retrospective review to determine the characteristics, treatment and outcome following cervical spine injury in these patients.

Purpose

Patients with ankylosing spondylitis (AS) are vulnerable to cervical spine injury following relatively minor trauma. The authors present a retrospective review to determine the characteristics, treatment and outcome following cervical spine injury in these patients.

Patients with spinal injuries are very vulnerable to early complications or secondary spinal cord injuries before and during transfer, which may delay their rehabilitation. We designed transfer guidelines following concerns raised in a pilot study of the transfer of 16 patients. We then examined the effectiveness of the guidelines in 100 consecutive patients and completed the cycle by re-auditing a further 254 consecutive admissions after incorporating changes from the initial audit.

The transfer guidelines addressed ten areas of clinical concern. We recorded a 50% improvement in airway monitoring and management. There was also improvement in anti-ulcer therapy and thromboprophylaxis (from 50% to 96%). We saw a 50% improvement in the use of appropriate support staff during the transfer.

The re-audit showed that initial improvements were maintained and further improvements were noted in the transfer of relevant documentation and investigations. Improvement was also noted in the use of a vacuum mattress for the transfer of spinal injury patients and subsequently reduced incidence of pressure sores by a statistically significant level, which helped in the early rehabilitation of these patients. The majority of transfers were safe.

The transfer guidelines were easy to use and improved patient care by ensuring that common problems had been addressed before and during transfer. This system reduced the risk of preventable complications during inter-hospital transfer. There may be wider application of similar guidelines to other trauma patients who require inter-hospital transfer, where there is a possibility of preventable secondary injury.

After spinal cord injury (SCI) rapid muscle atrophy and extensive bone loss occur in the paralysed limbs resulting in increased fracture incidence (mostly at the epiphyses in the distal and proximal tibia and distal femur). We investigated whether re-introducing mechanical loading of the lower-limb bones in chronic SCI through exercise could induce bone formation, in accordance with Wolff’s Law.

We present cross-sectional data from the Scottish paraplegic population illustrating the time course of bone loss after SCI, and review case studies describing musculoskeletal changes following lower-limb exercise interventions in chronic SCI. Reference data were obtained from 47 subjects with SCI at neurological levels T2 to L2, ranging from 6 months to 40 years post-injury. We used peripheral Quantitative Computed Tomography (XCT3000, Stratec, Germany) to scan 4 sites in the tibia and 2 in the femur, and evaluated trabecular, cortical, and total bone data, and soft-tissue parameters. Here, we focus on trabecular bone mineral density (BMDtrab) at the epiphyses, which provides an indicator of bone integrity. The same scans were performed pre- and post-training in chronic paraplegics who undertook a period of lower-limb exercise training (body-weight-supported treadmill training (BWSTT) or electrically-stimulated leg cycle (FES-cycle) training); these results are reviewed.

The temporal pattern of bone loss is characterised by exponential decline in BMDtrab, reaching steady-state at 100 mg/cm3 in the distal tibia after 7 years and at 130 mg/cm3 in the distal femur after 3 years. A subject with incomplete SCI (18 years post-injury) showed an increase in BMDtrab in the distal tibia following 5-months BWSTT. In a separate study, subjects with complete SCI had varying responses to FES-cycle training.

Bone loss appears to plateau after 7 years post-SCI. The effectiveness of physical interventions aimed at reversing bone loss in chronic SCI seemingly depends on the details of the associated bone-loading patterns.

Morsellised cortico-cancellous bone (MCB) is used extensively in impaction grafting procedures, such as the filling of cavitory defects on the femoral and acetabular sides during hip arthroplasty. Several experimental studies have attempted to describe the mechanical behaviour of MCB in compression and shear, and it has been found that it’s properties can be improved by washing and rigorous impaction at the time of surgery. However their focus has not been on the development of constitutive models that can be used in computational simulation.

The results of serial confined compaction tests are presented and used to develop constitutive models describing the non-linear elasto-plastic behaviour of MCB, as well as its time dependent visco-elastic behaviour. It is found that the elastic modulus, E of MCB increases linearly with applied pressure, p, with E achieving a value of around 30 MPa at a pressure of around 1 MPa. The plastic behaviour of MCB can be described using a Drucker Prager Cap yield criterion, capable of describing yielding of the graft in shear and compression. The time dependent visco-elastic behaviour of MCB can be accurately modelled using a spring and dashpot model that can be numerically expressed using a fourth order Prony series. The role of impaction in reducing subsequent plastic deformation was also investigated. The developed relationships allow the constitutive modelling of MCB in finite element simulations, for example of the acetabular construct following impaction grafting. The relationships also act as a gold standard against which to compare synthetic graft and graft extender materials.

Introduction: Tibial component loosening is a common mode of failure in modern total knee arthroplasty and is thus a common cause for revision knee surgery. Direct bone ingrowth of press fit knee prosthesis has been deemed an important prerequisite for long-lasting implant fixation and thus clinical success in both primary and revision TKA whether for cemented or uncemented stems. To achieve good long term biological stabilization, initial secure mechanical stability, (i.e. minimising tibial tray and stem motion with respect to the tibia,) is vital. A lack of initial stability can lead to resorption of bone at the implant-tissue interface and can consequently result in loosening and failure of the prosthesis. Obtaining adequate tibial fixation is difficult in revision patients as often there is insufficient bone stock in the proximal tibia. A longer stem is often recommended with revision surgery as a central stem should guide the migration of the tibial component so that it occurs predominantly along the vertical axis, thus minimising the risk of recurrent malalignment and loosening due to tilting of the tibial tray. It is also thought that the presence of a third rigid peg helps to reduce inducible displacements by anchoring the new implant in robust cancellous bone. However there is no consensus on the length of central stem should be to achieve the best load transfer and fixation and although the use of long stems on the tibial component is advocated, in revision TKA involving bone grafting and augmentation. The effect of the tibial stem length in other cases has received contradictory evaluations. This research deals with an experimentally evaluate the effect that central stem lengths on the initial micromotion of the tibial tray in two revision tibial defects. This is being investigated by measurement of the bone-implant interface motion of the tibial stem.

Method: Composite bones were resected with an extramedullary jig. Three common revision defects were compared 1) no defect requiring no repair(primary); 2) T1 defect requiring bone impaction grafting; 3) T2A requiring augmentation. Three stem configurations were analysed in conjunction with these defects 1) no stem; 2) short 40mm stem; 3) long 80mm stem. Four LVDTs were positioned anteriorly, posteriorly, medially and laterally around the tray and were used to measure the movement of the tibial tray with respect to the tibia. The bones were potted and subjected to axial loading simulating 1– 6 times body weight for 3500 cycles at 1 Hz.

Results: The longer stemmed press fit implants were associated with slightly higher levels of micromotion compared to the “no stem press fit” trays in the primary and T2A defects. This could be due to the fact that cutting errors are accentuated by a longer stem and can cause increased levels of posterior lift off. For bone impaction grafting it seems that a stem sufficiently long to by-pass the defect should be used. The proximal surface cemented trays presented more stable fixation with the inducible displacement between the no stem and stemmed groups being negligible. Subsidence of the tibial tray was reduced marginally by using a longer stem.

Morsellised bone graft is used extensively in revision arthroplasty surgery. The impaction technique at the time of surgery has a significant effect on the subsequent elastic and inelastic properties of the bone graft bed. Differences in values reported in the literature for the mechanical properties of morsellised cortico-cancellous bone (MCB) can be attributed to the different loading histories used during testing. We performed serial confined compaction tests to assess the optimum compaction strategy. Compaction of the samples was carried out using repeated standardised loading cycles. Optimal preparation of MCB is dependant on the force and frequency of compaction. The maximum compactive pressure the samples were subjected to was 3 N/mm² based on the clinical experience of Ullmark & Nilsson¹ in MCB preparation at the time of surgery. This paper presents the Young’s Modulus, E, vs. number of compaction cycles and inelastic strain, ^ie, vs. number of compaction cycles curves for MCB. Qualitative and quantitative descriptions of the material behaviour of MCB are developed. The importance of frequent percussive episodes prior to implant insertion is illustrated.

MCB was also found to exhibit significant visco-elastic response, with stress relaxation under displacement controlled loading continuing for several hours following initial load application. Bone graft substitutes do not at present exhibit a similar beneficial shock absorbing visco-elastic response.

Our experiments indicate that the material properties of MCB are dependent on the force of impaction and the number of impactions applied with a hammer at the time of surgery. A minimum of 10 to 20 compaction episodes, or hammer blows are required for MCB to achieve 60 to 70% of its long term predicted stiffness.