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Changes in shape, ossification and quality of bones in children with spina bifida
Insights
Spina bifida in infants leads to reduced bone mass and altered tibia shape due to paralysis and intrauterine pressure. This condition, similar to
Area of Science:
- Orthopedics and Developmental Biology
- Pediatric Bone Health
- Biomechanical Remodeling
Background:
- Spina bifida is a congenital condition affecting spinal cord development, often leading to paralysis and limb deformities.
- Understanding bone development in affected individuals is crucial for managing associated skeletal complications.
- The influence of muscle function and mechanical forces on bone shape and mass is a key area in skeletal biology.
Purpose of the Study:
- To investigate changes in tibial shape, size, bone mass, and osteoid tissue in infants with spina bifida.
- To explore the role of muscle imbalance in long bone remodeling using an experimental rat model.
- To elucidate the combined factors contributing to tibial deformities in spina bifida.
Main Methods:
- Comparative analysis of dissected tibiae from spina bifida infants and age-matched controls.
- Experimental study involving double-labeled bone-seeking markers in rats with induced foot muscle imbalance (myotomy).
- Assessment of cross-sectional shape, cortical bone area, thickness, Haversian systems, and osteoid tissue.
Main Results:
- Tibiae from spina bifida infants with paralysis showed diminished cortical bone area, thickness, Haversian systems, and remodeling cavities.
- Significant alterations in tibial midshaft cross-sectional shape were observed, correlating with foot deformity type and paralysis.
- Experimental myotomy in rats demonstrated muscle's direct influence on tibial remodeling, altering cortical shape and center of gravity.
- Increased osteoid tissue in spina bifida bone suggests delayed mineralization ('paralytic rickets'), contributing to bone softening and fractures.
Conclusions:
- Paralysis and intrauterine pressure are key factors in producing tibial deformities in spina bifida.
- The findings suggest 'paralytic rickets' and reduced bone mass contribute to fractures in spina bifida.
- Muscle imbalance plays a role in bone remodeling, but combined mechanical and neurological factors are critical in spina bifida.
Abstract:
Changes in the cross-sectional shape, size, bone mass and amount of unmineralised osteoid tissue were studied in 17 dissected tibiae from spina-bifida babies who died with paralysis and foot deformities and in 14 tibiae from non-spina bifida controls of matching age. In addition, 12 tibiae from young experimental rats with myotomy of foot dorsiflexors and foot plantiflexors were double-labelled with bone-seeking markers and studied in order to find the role of experimental muscle imbalance in the dynamic remodelling of the developing long bones. It was found that in tibiae from spina-bifida children with paralysis the total area of cortical bone, its thickness, number of Haversian systems and number of large remodelling cavities are diminished. Significant changes in the cross-sectional shape of the midshaft of the tibia were found, ranging from the triangular shape seen in normal babies and in those with spina bifida and calcaneus-type foot deformity, to the circular shape of tibiae from babies with spina-bifida paralysis and no foot deformity or with spina bifida and equinovarus-type of deformity. Results of experimental myotomy on growing rats showed the direct influence of working muscles on the remodelling process of growing tibiae. On the side of myotomy the flat cortex resumed a bulging convex shape and the centre of gravity shifted towards the myotomised side. These principles cannot on their own explain the specific changes in the shape of human tibiae found during anatomical studies. There is, however, a common denominator in these apparently contradictory findings. This is the combined action of two factors previously reported: the combination of paralysis of the growing limb and mechanical intra-uterine pressure acting on it. The findings in the present study also indicate that they played a major role in the production of deformities. The total amount of osteoid tissue in spina-bifida paralysed bone is increased. This delay of mineralisation of newly laid-down bone matrix would lead to softening of the new bone matrix and osteoid-rich subepiphyseal and metaphyseal regions. This 'paralytic rickets', together with the diminished total bone mass found, could probably be the cause of the common spina-bifida fractures in these regions.