Introduction

In an ageing population the incidence of patients sustaining a neck of femur fracture is likely to rise. Whilst the neck of femur fracture is thought to be a pre-terminal event in many patients, there is little literature following this common fracture beyond 1 year. With improving healthcare and increasing survival rate, it is likely that a proportion of patients live to have subsequent fractures. However little is known about if these occur and what the epidemiology of these fractures are.

Aim

To investigate the effect of intraoperative wound irrigation with povidone-iodine on surgical site infection.

Posterolateral spinal fusion using autograft in adult rabbits has been reported by many groups using the Boden model. Age in general has an adverse effect on skeletal healing; although, its role in posterolateral fusion is not well understood. This study examined the influence of animal age on spinal fusion using a standard model and experimental endpoints. We hypothesised that fusion quality and quantity would be less with increasing age.

A single level posterolateral fusion between the fifth and sixth lumbar segments were performed in six-month and two-year-old New Zealand white rabbits (n=6 per group) using morcelized iliac crest autograft. All animals were sacrificed at 12 weeks following surgery. Posteroanterior Faxitron radiographs and CT scans were taken and DICOM data was analysed (MIMICS Version 12, Materialise, Belgium). Axial, sagittal, coronal and three-dimensional models were created to visualise the fusion masses. Bone mineral density (BMD) of the fusion mass was measured using a Lunar DPXL Dexa machine. An MTS Bionix testing machine was then used to assess peak load and stiffness. Sagittal and coronal plane histology was evaluated in a blinded fashion using H&E, Tetrachrome and Pentachrome stains. Assessment included overall bony response on and between the transverse processes. Radiographs and CT confirmed a more robust healing response in younger animals. Radiographic union rates decreased from 83% to 50% in the aged animals. A neo- cortex surrounding the fusion mass was observed in the younger group but absent in the aged animals. Fusion mass BMD and that of the vertebral body was decreased in the older animals (P<0.05). Tensile mechanical data revealed a 30% reduction in peak load (P=0.024) and 34% reduction in stiffness (P=0.073) in the two-year-old animals compared with the six-month-old animals. Histological evaluation demonstrated a reduction in overall biological activity in the two-year-old animals. This reduction in activity was observed in the more challenging intertransverse space as well as adjacent to the transverse processes and vertebral bodies at the decortication sites. Numerous sites of new bone formation was present in the middle of the fusion mass in the six-month-old animals while the bone graft in the two-year- old animals were less viable.

Skeletal healing is complex and mediated by both local and systemic factors. This study demonstrated that ageing leads to an impaired and delayed skeletal repair.

Where autograft is utilised, diminished graft osteoinductivity and reduced levels of growth factors and nutritional supply in the surrounding milieu explains our observations. The aged rabbit posterolateral spinal fusion model has not been previously described but would be a useful to evaluate new treatment modalities in a more challenging host environment.

Distraction osteogenesis (DO) is useful for bone lengthening and deformity correction. Unfortunately, this often requires prolonged use of an external fixator with concomitant morbidities. This study investigates whether low-magnitude, high-intensity vibrations (Dynamic Motion Therapy, DMT) can accelerate maturation of regenerate bone in DO, thus reducing the duration of external fixation. 28 NZ White Rabbits underwent a right mid-tibial osteotomy with application of an Orthofix M-103 fixator (Orthofix, Busselengo, Italy). Distraction commenced on day 3 at 0.5 mm every 12 hours for 12 days. All animals were sacrificed on day 45. Animals were randomly assigned into 4 groups:

control group;

DMT was applied with the Juvent platform (Juvent, Somerset, NJ) for 10 minutes/day. X-ray and CT scans were taken prior to mechanical testing. All specimens were processed for histology. X-rays and CT scans showed evidence of cortical remodelling and re-establishment of the medullary canal in animals treated with DMT (groups 2, 3 and 4). This was most pronounced in animals treated during the distraction and consolidation phases (group 4). Regenerate bone in the control group (group 1) was more disorganised, with a delayed union evident in 1 animal. Group 1 achieved peak torque and stiffness values of 70% and 50% of the contralateral (unoperated) tibia respectively. No significant difference was seen in peak torque and stiffness between groups 2, 3, and 4, however each was significantly higher than group 1 (P< 0.05). H& E staining revealed less porosity in the newly formed cortical bone and a more defined medullary canal in animals treated with DMT than in the control group. Low-magnitude, high-intensity vibrations appear to accelerate cortical remodelling and reestablishment of a medullary canal. Regenerate bone in animals treated with DMT was also mechanically superior. The timing of DMT therapy did not appear to be important. Further studies are required to determine the optimal timing and duration of DMT therapy.

Introduction: The majority of midshaft humeral fractures will achieve a satisfactory outcome with non-operative management. However, internal fixation is occasionally required to assist with rehabilitation, particularly in multiply-injured patients. Although the clinical risks and benefits of the locking plate and humeral nail are well known, there is a paucity of data comparing their mechanical properties.

The aim of this study was to determine the torsional and 4-point bending properties of a midshaft humeral osteotomy reconstructed with either an intramedullary nail or locking plate.

Methods: 19 fresh cadaveric humeri were DEXA scanned to ensure similar BMD. Non-destructive 4-point bending was performed on the intact bone to determine stiffness in the sagittal and coronal planes. Load was applied using an MTS MiniBionix 858 (Mechanical Testing Systems, MN) at a rate of 1 mm/min to a maximum of 450 N.

A transverse midshaft osteotomy was created and a spacer ensured a constant 3-mm gap between the bone ends. Reconstruction was performed with either

Trigen humeral nail (Smith & Nephew, TN) – 10 specimens

Non-destructive 4-point bending was repeated, and then each humerus was embedded in a low-melting point alloy proximally and distally for torsional testing. Torque was applied at 5 deg/min until failure. Maximum torque, maximum angle and stiffness were calculated.

All data were analysed with SPSS for Windows (SPSS Inc., Il) using ANOVA.

Results: One specimen in the locking plate group fractured during plate application and was excluded from the study. Non-destructive bending tests showed no significant difference in stiffness of the intact bones between the two groups.

4-point bending: the bones reconstructed with the intramedullary nail were ~50% as stiff as the intact state in both planes. There was no statistically significant difference in stiffness between the intact bones and those reconstructed with the locking plate.

Torsional testing: the locking plate specimens were 3 times as stiff as the intramedullary nail specimens (P< 0.05) and failed at twice the torque (P< 0.05).

Discussion: Humeral intramedullary nails are reported to have an advantage over plates under axial loading (Chen et al, 2002). However, this study demonstrates that locking plates are superior to intramedullary nails in torsion and four-point bending. Although the clinical situation often dictates the most appropriate management, locking plates should be considered in patients when torsional or four-point bending loads are expected to predominate in the post-operative period.

Introduction: A cosmetic deformity does not always occur after a biceps tenotomy. The anatomical restraints preventing distal excursion of the long head of biceps tendon following tenotomy have not previously been described. This study aims to evaluate the biceps sheath and its potential role as a restraint to distal excursion of the biceps following tenotomy.

Methods: Fifteen fresh cadaveric specimens were dissected free of overlying soft tissues to reveal the rotator cuff, biceps sheath and long head of biceps muscle belly and tendon. Eight specimens were used for gross anatomical analysis. Measurements of the length of the biceps sheath on the humeral (bone) side and tendon side were made using a digital caliper (Mitutoyo, Japan). The long head of biceps tendon was then released from the glenoid labrum and the excursion of the stump relative to the rim of the articular surface measured. The biceps sheaths of two specimens were used for histological analysis.

Seven specimens were used for mechanical analysis. A humeral osteotomy was performed distal to the insertion of pectoralis major, leaving intact the biceps sheath and the muscle belly of long head of biceps. The proximal humerus was attached to a custom-designed jig and the muscle belly of biceps grasped in cryogenic grips. Specimens were loaded on an MTS 858 Bionix mechanical testing machine (MTS Systems, MN) in uniaxial tension at a rate of 1 mm/sec until failure was observed.

Results: The biceps sheath surrounds the long head of biceps tendon and inserts into the bone of the proximal humerus. It is trapezoidal in cross-section, with a mean length of 75.1 mm on the bone side and 49.3 mm on the tendon side. The average excursion of the stump was to within 2.8 mm of the rim of the articular surface.

Histological examination of the biceps sheath revealed membranous tissue consisting of loose soft tissue with fat and blood vessels. Synovial tissue was also identified. The sheath was seen to loosely attach to the biceps tendon, with a more intimate attachment to the periosteum.

The mean force to pull the long head of biceps tendon out of the sheath 102.7 N (range 17.4 N–227.6 N)

Discussion: The biceps sheath is a consistent structure intimately associated with the biceps tendon. It appears to contain blood vessels which provide nutrition to the tendon, similar to the vincula of flexor digitorum pro-fundus. Mechanical testing reveals that a substantial force is sometimes required to pull the biceps tendon from the sheath. This may explain why biceps tenotomy does not routinely result in a “Popeye” biceps.

This study was undertaken to assess the contribution of pulmonary fat embolism caused by intramedullary femoral canal pressurization to the development of acute lung injury in the presence of resuscitated hemorrhagic shock. Twenty-seven NZW rabbits were randomly assigned into one of four groups: resuscitated hemorrhagic shock and fat embolism, resuscitated hemorrhagic shock, fat embolism, and control. Fat embolism was induced via intramedullary cavity with a 1–1.5 ml bone cement injection. Only the animals that underwent resuscitated shock and fat embolism displayed amplified neutrophil activation and alveolar infiltration. These findings suggest that the combination of resuscitated shock with fat embolism initiates an inflammatory response, which may play a role in the development of fat embolism syndrome.

The objective of this study was to assess the contribution of pulmonary fat embolism caused by intramedullary femoral canal pressurization to the development of acute lung injury in the presence of resuscitated hemorrhagic shock.

Only the animals that underwent resuscitated shock and fat embolism displayed amplified neutrophil activation and alveolar infiltration.

These findings suggest that the combination of resuscitated shock with fat embolism initiates an inflammatory response, which may play a role in the development of fat embolism syndrome.

CD11b mean channel florescence was only significantly elevated in the HR/FE group at two and four hours post knee manipulation. Moreover, greater infiltration of alveoli by leukocytes was only significantly higher in the HR/FE group as compared to controls.

Twenty-seven NZW rabbits were randomly assigned into one of four groups: resuscitated hemorrhagic shock + fat embolism (HR/FE), resuscitated hemorrhagic shock (HR), fat embolism (FE), and control. Hypovolemic shock was induced via carotid bleeding for one-hour prior to resuscitation. For fat embolism induction, the intramedullary cavity was drilled, reamed and pressurized with a 1–1.5 ml bone cement injection. For evaluation of neutrophil activation, blood was stained with antibodies against CD45 and CD11b and analyzed with a flow cytometer. Animals were mechanically ventilated for four hours post surgical closure. Postmortem thoracotomy was performed, and three stratified random blocks of each lung were processed for histological examination.

Our findings suggest that FE by itself does not cause lung injury, as there were no apparent differences between the control and FE animals. Only the HR/FE animals revealed a higher number of infiltrating neutrophils into alveolar spaces and greater neutrophil activation.