Introduction: Over the last 10 years minimally invasive plate osteosynthesis (MIPO) has gained more and more popularity over the conventional open surgical approach (ORIF). Numerous clinical case collection studies reported the MIPO technique as a good, alternative method. While MIPO offers some advantages over ORIF, it also has significant drawbacks, such as more demanding surgical technique and increased radiation exposure. In an attempt to compare these approaches, a previous animal study 1 did not show any significant differences in fracture healing outcome. Using a new developed, standardised severe trauma model on the sheep femur 2, this study examines the effects of the surgical approaches on fracture healing.

Methods: 24 sheep (Merino wethers, mean age 5.6years, mean weight 39.1kg) underwent the trauma model 2 with a severe soft tissue damage and a multifragmentary, distal femur fracture as well as initial stabilisation with an external fixator. After five days of soft tissue recovery, the animals were definitively operated with an internal fixator (LCP) randomised either by a minimally invasive or open approach. The sheep were sacrificed after 4 and 8 weeks (two groups), mechanical testing performed and statistically analysed with ANOVA test.

Results: After 4 weeks, torsional rigidity is significantly higher in the MIPO group (30.1r10.6(SD)%) of fractured to intact bones, p< 0.05) compared to ORIF group (9.8r12.4(SD)%), while ultimate torque also shows increased values for MIPO technique (p=0.11). After 8 weeks, the differences in mechanical properties levelled out, but still higher values for the MIPO group (p=0.36/p=0.26).

Conclusion: In the early stage of fracture healing, minimally invasive plate osteosynthesis shows advanced healing pattern compared to open fixation technique. This advantage seems to level out over time.

Introduction: It has long been recognised that static plain x-rays are a sub-optimal method for the assessment of lumbar fusion. Blumenthal and Gil showed that radiographic assessment of fusion corresponded with operative findings only 69% of the time. Santos et al suggest that both plain x-rays and flexion/extension x-rays overestimate the fusion rate when compared to helical computed tomography (CT). To date there has been no correlation of CT assessment of fusion with surgical exploration. In this study we present an animal model of lumbar spine pseudarthrosis and compare three imaging modalities with micro-cut CT scanning and cadaveric assessment.

Methods: Approval was gained from the QUT animal ethics committee. Eleven mixed bred ewes were assigned to either a fusion group or an intentional pseudarthrosis (IP) group. A dorsal approach to the facet joints of L2/3 was made. The facet joints were destabilised by resecting the articulating surfaces with a rongeur. In the fusion group, the spinous processes of the destabilised segment were wired tightly together and a bone graft harvested from the iliac crest was placed into the joint space. In the IP group the bone graft bed was prepared similarly except that a small proportion of the articulating surface was left intact and a 1.0 cm2 roll of oxidised cellulose was placed into the facet joint space bilaterally. In the IP group the spinous processes were wired around an interspinous spacer which was later removed to create a similar degree of laxity in the fixation of each of the IP specimens. The animals were sacrificed at 6 months and static and dynamic lateral radiographs obtained. The spine was removed en bloc, and high speed fine cut (2mm) CT Scanning performed. The specimens were individually assessed for fusion by micro-cut CT scanning. Eight independent, blinded orthopaedic surgeons, were asked whether they considered the spine to be fused based on

plain x-ray

These results were correlated with a fusion rate based on the micro CT. The specificity and sensitivity of these radiological measures in diagnosing pseudarthrosis and inter-rater reliability using Fleiss’ Kappa scores for each method were calculated.

Results: For assessing pseudarthrosis identified by microCT the plain film sensitivity was 0.41 and the specificity was 0.47. For assessing pseudarthrosis with plain and flexion extension xrays the sensitivity was 0.55 and the specificity was 0.33. For assessing pseudarthrosis with plain flexion extension xrays and CT the sensitivity was 0.81 and the specificity was 0.88. The Kappa score for plain films was 0.15, for flexion extension was 0.07 and CT was 0.54.

Discussion: This study suggests that plain radiographs and flexion extension radiographs are an unreliable measure of posterior lumbar fusion. The current clinical gold standard for assessment of fusion (CT) was able to correctly identify non-union in 80% of cases. Whilst no alternatives to structural assessment of the fusion mass with CT currently exist it is important to recognise the limitations of this technique.

Introduction Cement leakage into adjacent structures is the main complication during vertebroplasty. The majority of these leaks are asymptomatic, but pulmonary cement embolism has been reported to cause cardiovascular disturbances and even death (1,2). Furthermore, the use of calcium phosphate (CaP) cements for vertebroplasty may aggravate cardiovascular deterioration in the event of cement embolism by stimulating coagulation [3].

The cardiovascular effects of pulmonary cement embolism were investigated using an animal model.

Methods In 18 skeletally mature sheep, 2.0ml cement was injected into the pulmonary trunk during general anaesthesia (approved by Animal Ethics Committee). Three different cements were used: 1) PMMA (Simplex P, Stryker); 2) PMMA with 10% hydroxyapatite (PMMA & HA) (Vertecem, Synthes); 3) Experimental injectable CaP cement (Synthes). The following cardiovascular parameters were recorded continuously (endpoint: 60min post-injection): arterial, central venous, pulmonary arterial pressures and cardiac output. Blood gases and coagulation parameters (antithrombin, D-dimer, prothrombin fragments I & II) were measured pre-injection, 10, 30 and 60min post-injection. Postmortem, lungs were removed intact and submitted to computer tomography (CT) imaging.

Results There were no fatalities. After 1min, mean pulmonary arterial pressure had increased by 9%, 14% and 21% from pre-injection value in the PMMA, PMMA & HA and CaP group respectively. Differences in pulmonary arterial pressure between the three material groups were not statistically significant. Pulmonary arterial pressure stayed elevated for the duration of the experiment (i.e. 60min post-injection). There were no other significant changes in cardiovascular, blood gas or coagulation parameters from pre- to post-injection values. Three dimensional reconstructions of the CT images showed a tendency of the CaP cement to break up into multiple smaller pieces whereas the two other cements did not.

Discussion Cement embolism led to mild pulmonary hypertension in all material groups. Present results are in contrast to earlier reports (pig model) of fulminant cardiovascular deterioration after CaP cement embolism (3). Present changes were not as severe and there was no evidence of thromboembolism. This discrepancy may have been due to differences in the cement formulations or the animal model.

Pulmonary hypertension was more severe in the CaP cement group. This may have been due to the disintegration of the CaP cement resulting in blockage of more pulmonary vessels compared to the PMMA cements.

Introduction and Aims: Cyclic pneumatic pressure applied to the musculature proximal to a fracture of the distal radius has been shown to produce compressive loading of the fracture. The aim of this randomised controlled in vivo study in an ovine model was to investigate the effect of the pneumatic pressure on fracture healing.

Method: Thirty-seven sheep underwent a transverse osteotomy of the right radius. All sheep were managed in a plaster cast and splint to ensure non-weight bearing during rehabilitation. Nineteen of the sheep were randomised to receive cyclic loading by the application of a pressure cuff around the muscles of the proximal forearm deep to the cast. The other 18 sheep acted as controls. The sheep in the experimental group received 120 cyclic loads over two 10-minute sessions each day starting one week post-osteotomy. Sheep from both groups were sacrificed at either four or six weeks. X-rays, ultrasonography, biomechanical testing and histomorphometry were used to assess differences between the groups.

Results: The area of periosteal callus on lateral and antero-posterior x-ray, the peak torsional strength, the fracture stiffness, the energy absorbed over the first 10 degrees of torsion and histomorphometric analysis all showed that the fractures in the group treated with the cyclic pneumatic pressure achieved the same level of union at four weeks as the control group fractures at six weeks (not significantly different p> 0.05). The density of the woven bone in the periosteal callus of the treated sheep was significantly greater than the controls (p< 0.01). Ultrasonography showed no significant difference (p> 0.05) in the amount of muscle wasting between the treated group and the control group.

Conclusion: This study has shown that the rate of healing is enhanced when cyclic pneumatic pressure is applied to the musculature proximal to a transverse fracture of the distal radius in an adult sheep model. There is potential for this treatment to be used in a human population.

Introduction & aims: Quadriceps muscle wasting is common in patients with osteoarthritis (OA) of the hip and knee. Previous studies,using ultrasound and performing biopsies, have demonstrated quadriceps muscle fibre atrophy. Thigh girth measurements are quoted in textbooks as a means of quantitatively assessing muscle bulk. This study has looked at these measurements in patients with hip and knee OA to see if these measurements are useful.

Method: 87 patients (mean age 62, range 36–87) with a diagnosis of OA were seen in the pre-assessment clinic. 47 were awaiting total hip replacement (THR) and 40 were awaiting total knee replacement (TKR).All were awaiting primary arthroplasty and had not had previous joint surgery. Thigh girth measurements were taken at 2 points corresponding with one-third and two-thirds of the length between the anterior superior iliac spine and the tibial tuberosity. These measurements were taken for both thighs. The observed differences were analysed with normal probability plots and paired Student’s t-tests.

Results: No significant difference in thigh girth could be detected in patients awaiting total knee replacement. Girth was significantly reduced in the thigh on the side of planned THR. This difference was apparent when measured both proximally and distally.

Conclusion: Measurements of thigh girth were not useful indicators of quadriceps wasting in patients awaiting TKR. Patients awaiting THR should have thigh girth measured, those with reduced thigh girth on the side of planned arthroplasty may have quadriceps atrophy and can then be referred for physiotherapy prior to surgery.

Introduction: Vertebroplasty using polymethylmethacrylate (PMMA) is an established technique in the treatment of osteoporotic fractures of the vertebra. Complications of vertebroplasty associated with PMMA leakage can include damage to the spinal cord. Previous studies have sought to investigate thermal changes in the paravertebral region, but used smaller volumes of cement than are used clinically¹, or used in vitro experimental techniques.² We have designed an in vivo sheep model to investigate the thermal changes after injection of clinically relevant volumes of PMMA, and to measure change in cord function associated with PMMA extrusion.

Methods: Five sheep were anaesthetised and 1.0ml of PMMA was injected into the spinal canal at the L1 level, with measurement of the temperature by thermocouple. The L2 to L5 vertebral bodies were then exposed and 9 thermocouples placed at points in and around the vertebra (superior and inferior endplate, disc above and below, central body, posterior wall, and spinal canal) to measure paravertebral temperature for a 10- minute period after injecting 6.0mls of PMMA. All animals were then humanely euthanased, and the T12 to L2 vertebrae harvested to examine the effect of temperature on the vertebral body and spinal cord using light microscopy.

Results: The experiments showed significant increases in the paravertebral temperature, especially at the end-plates (mean temperature 51.7°C, mean increase in temperature +16°C). This is contrary to studies using small cement volumes or in vitro conditions. Intradiscal and posterior wall temperature did not significantly rise. Spinal canal temperature reached a mean 75.4°C in the presence of “extruded” cement. Microscopic examination showed thermal damage to the spinal cord.

Discussion: The experiments indicate that neurological complications associated with vertebroplasty are likely to be thermally mediated, and that the analgesic effects of vertebroplasty are likely to be, at least in part, due to thermal damage to endplate neurological structures.