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.

Despite various forms of operative treatment, outcomes have been variable after displaced multi-fragment proximal humeral fractures. A significant number of fixation failures and avascular necrosis of humeral head occurs (up to 77 percent). Biomechanical studies on the locking proximal humeral plate indicate the locked screw-plate combination is a more stable construct than conventional implants. The purpose of this study is to evaluate the clinical and radiological outcome in patients who have undergone operative treatment using this implant.

Twenty-three patients with displaced proximal humeral fractures underwent surgery using this implant. The mean age was 63.6 years (range, 40–85). Nineteen patients were female and 4 were male. The mean follow-up duration was 22.2 months (range, 5–38). All patients had a fracture configuration that required operative treatment. Three patients were lost to follow-up leaving 20 patients available for review. Patients were assessed clinically using the Constant score, pain scale and satisfaction scale. General health was assessed using the SF-12 survey. Radiographs were assessed looking at the initial reduction to determine whether an anatomical reduction with calcar support correlated with a better outcome.

The mean constant score was 62 (32.5–85). The mean age and sex-adjusted constant score was 83 percent (46–117). The mean pain score was 26mm (100mm scale), and the mean satisfaction score was 84 percent. Patients that were 60 years or younger had a lower age and sex adjusted constant scores (78, range 58–109 percent) than those over 60 years (87, range 46–117 percent) despite a better absolute score (63 vs. 61). The Physical Component Score of the SF-12 was better in the younger age group than it was in the older group (43 vs. 38) although the Mental Component Score was lower (45 vs. 54). Overall satisfaction was also lower in those 60-years and younger (79 compared with 86 percent). This may be explained by higher social demands on younger patients. Only 3 patients sustained the injury as result of high-energy trauma. These patients were significantly younger (50, range 40–56) than the low energy trauma group (65, range 46–85). Patients that sustained high-energy trauma had a better clinical outcome with a mean constant score of 74.3 compared with 59.6 for the low energy trauma group.

Nine patients did not have adequate medical (calcar) support with the initial reduction. Four of these patients developed complications. Two patients developed AVN requiring a hemi-arthroplasty. One patient had a valgus collapse of the head fragment and screw penetration requiring removal. One patient had a non-union requiring bone grafting and re-plating.

The proximal humeral locking plate provides a good clinical outcome. The results of this study correlate with the limited data available on these implants in the literature. A clinical benefit over alternative procedures is yet to be elucidated by a randomised clinical trial. An anatomical reduction with calcar support appears to result in a lower complication rate.