Objective: To assess the inßuence of bone density on the þxation strength of bicondylar tibial plateau fractures. Method: Sixteen cadaver tibias were randomised into two groups to receive either dual plating or ring external þxation to stabilise a bicondylar tibial plateau fracture created with a standard method. The randomisation was stratiþed by BMD measured by DXA (above and below the mean). Cyclic axial compression tests were performed with increasing peak loads. Inter-fragmentary shear displacements were measured using four extensometers. Failure was deþned as over 3mm displacement. Results: There was a strong correlation between failure load and BMD [r=0.81, P< 0.001]. The mean failure load of the low BMD group (2701 N) was signiþcantly less than that with the high BMD (4530 N) [t-test=0.003]. The failure loads of the two þxation groups were not signiþcantly different (3520 N for the dual plating and 3710 N for the external þxation) [t-test=0.78]. BMD had a signiþcant effect on the failure load in the dual plating group [t-test=0.03], but not in the external þxation group [t-test=0.1]. Discussion: Failure of þxation has been reported as a common complication of bicondylar tibial plateau fractures with a rate as high as 30%. Osteoporosis and poor bone quality are considered important contributory factors. In our study this inßuence was evident with plating, but not with ring þxation. Ring þxation may be the preferred method of þxation for tibial plateau fractures in the elderly and osteoporotic patients.

Experience has shown that oblique fractures can be slow to heal and this has been attributed to excess shear at the fracture site. We routinely treat fractures with hybrid external fixation. In previous studies, olive wires placed through the fracture site reduced shear and this has improved healing times. When the fracture is oblique in the sagittal plane, anatomical constraints prevent the use of olive wires and a new solution is required.

A sawbone tibia with a distal sagittal plane oblique fracture (70° obliquity) was stabilised with a Sheffield Hybrid Fixator. In a pilot study various methods of fixation were tested and six were chosen for further testing. Since the pull-out strength of threads in the plastic bone was poor, olive wires cut behind the olive were used as a mechanically equivalent model for the push-pull system. Seventy degree steerage pins could not be used so 25° pins were tested instead. Cyclic compressive forces (at 10mm/min) of up to 200N axially and in four off-axis positions were applied using a universal testing machine. Fracture site linear motion in three dimensions was measured using an inter-fragmentary motion device, sampled at 100Hz. A standard frame was tested before and after each adaptation and all six methods were applied sequentially to each model.

The results suggest that: I) Arched wires are effective especially under greater bends, 2) Push-pull wires are effective and provide a minimally disruptive solution, 3) Steerage pins are effective especially at steeper obliquities but this may not always be practical, and 4) Placing a half pin in the distal fragment is beneficial but less effective than the use of 2 transverse half pins acting in a compression system (Hutson technique).

Previous studies in animal models of limb lengthening have shown a wide spectrum of histopathological changes during distraction phase. Much less is known about the structural response of muscle during the consolidation phase. This study aimed to observe and score changes in morphology, weight, length and maximal perimeter of gastrocnemius during the distraction and consolidation phases.

Thirty two immature New Zealand white rabbits were divided into two equal groups: lengthening and sham. In each group, half of the rabbits were killed at the end of lengthening and half 5 weeks later. A bilateral external fixator was applied to tibia and a mid-diaphysis osteotomy performed. The lengthening rate was 0.4 mm twice daily with an initial delay of 7 days. 30% lengthening was achieved in 4 to 5 weeks. After sacrifice, the whole gastrocnemius was taken from its attachments. Its weight, length and maximal perimeter were measured. At the middle of belly, a specimen 0.5cm in length was taken from the medial gastrocnemius for H& E and Masson trichrome staining. A scoring system was used to achieve a semi-quantitative analysis of the histopathological changes in gastrocnemius.

No abnormal changes were observed in the sham side. Degeneration, atrophy and endomysial fibrosis were all found in the lengthened side. The scores of histopathological changes between the end of lengthening and 5 weeks later showed a decreasing trend, but no significant difference. The weight and perimeter decreased and length increased in the lengthening side. The weight, perimeter and length of gastrocnemius in both lengthening and control sides increased at 5 weeks after the end of lengthening.

Muscular atrophy, as shown by a decrease in weight, perimeter and muscle fibre size, occurred and might be due to the combined effect of continuous muscle stretching and inactivity. Continuous stretching of muscles beyond a certain point produced damage. Some studies reported that damage to muscle fibres, which has been shown as degeneration and fibrosis in this study, can release and activate satellite cells. As myoblast precursors, satellite cells become myoblasts, which proliferate and fuse into the microlesioned areas, regenerating and repairing myofibrils. Also, the immature muscles have more active abilities of proliferation, regeneration, growth and healing. In this study gastrocnemius growth shown by an increase in weight, perimeter and length occurred during the consolidation phase of 5 weeks. The mean scores of histopathological changes in gastrocnemius decreased during consolidation period, indicating some recovery of damage to muscle. It is not clear whether this reflects a normal response, which would have been seen in other studies had samples been taken later or whether it is a unique response of the immature animal.