gms | German Medical Science

Objectives: Most of the fracture models developed in small animals performed unilateral though it is well known, that weight bearing and biomechanical stimulation are essential for adequate bone healing. This involves the partial or full loading of the affected limb.

We hypothesized that animals with unilateral osteotomy would not load the injured limb and this would lead to a disturbance of healing processes. We compared the healing of tibia osteotomy performed bilaterally or unilaterally in ovariectomy induced osteopenic rats.

Methods: Thirty-two 3-month old female Spague-Dawley rats were ovariectomized. After 9 weeks, half of the rats underwent transverse unilateral (right limb) osteotomy of tibia metaphysis (UL group). The other rats were osteotomized bilaterally (BL group). A 5-hole, T-shaped titanium plate fixed the osteotomized tibia with the aid of four screws at the ventromedial aspect. Body weight, water and food intake were recorded on a weekly basis. Pain and function of hind limbs were assessed using a score. After 5 weeks of healing, tibiae were analyzed by micro-CT, biomechanical and histological analyses. In muscles (gastrocnemius (MG), soleus (MS) and longissimus (ML)) fiber morphology, capillary density and metabolic enzyme activity were investigated. The differences between 2 groups (UL, BL) were compared using t-test (P<0.05).

Results and Conclusion: Weight of body and adrenal glands, water and food intake did not differ significantly between the two groups. This indicates that the stress and pain experienced by rats were also not different.

In the UL group, rats started to load the osteotomized limb from the week 3 onward, whereas in the BL group, rats used both hind limbs after recovering from anesthesia (day 2 onward). No-bridging of osteotomy gap was observed in 20% of UL rats and in 4% of BL rats. A partial osteotomy bridging with soft callus was found in 20% of UL rats and in 14% of BL rats. The bridging of osteotomy with the hard callus was observed in 60% of UL rats and in 82% of BL rats. Callus volume and bone volume fraction were significantly lower in UL group than in BL group (32 vs. 48 mm3 and 30 vs. 43%, respectively).

The adequate fracture healing requires loading of the bone and biomechanical stimulation. Therefore, the bone healing was significantly delayed and disturbed in UL group due to not usage of the operated hind limb. In contrast, the healing in BL rats was in progress since they started the normal movement using four limbs within the first days after osteotomy.

Weight of MG and MS of the left hind limb (not operated) was significantly higher in UL group than that of operated hind limbs in both groups and intact rats from other studies. This demonstrates a training effect of uninjured hind limb due to the disuse of the osteotomized contralateral hind limb.

Thus, for the experimental studies on bone healing in rat, it is advisable to perform bilateral osteotomy.