Stress-relaxation plates and the remodeling of callus and cortex under the plate in rabbits.
OBJECTIVE
To study the influence of a stress-relaxation plate on the remodeling of callus and cortex under the plate.


METHODS
The bilateral tibia diaphysis of New Zealand rabbit were osteotomized and fixed with stress-relaxation plate (SRP) and rigid plate (RP), respectively. Polarized light microscopy and transmission electron microscopy (TEM) were used to study the remodeling of callus and the cortex under the plate from 4 to 24 weeks postoperatively.


RESULTS
Polarized light microscopy: the structural changes of callus and cortex beneath the plate are similar in the SRP and RP groups at the early postoperative stage, manifesting an alignment disorder of collagen fibers with a weak birefringence in the callus and absorption cavities in the cortex under the plate. After the twelfth postoperative week, the SRP group showed callus starting to transform to lamellar bone and absorption cavities in the cortex under the plate becoming smaller. By contrast in the RP group the absorption cavities in the callus and cortex under the plate became larger and the whole layer of cortex was cancellated. TEM: the active osteoclasts appeared in both SRP and RP groups in the period from 4 to 8 weeks postoperatively. In the SRP group, many functionally active osteoblasts could be seen on the surface of the bone, while in the RP group, the osteoblasts were not very active. By 24 weeks postoperatively, the shape of osteocytes were normal but the number of the osteoclasts were small in the SRP group. In the RP group, the osteoclasts became more active and osteocytic osteolysis was manifested.


CONCLUSIONS
Fixation with SRP not only enhanced callus remodeling, but also abated the degree of osteoporosis in the cortex under the plate. This approach may lead to an improved osteosynthetic apparatus.
Zhang
X
X
Department of Orthopaedic Surgery, Shanghai Sixth People's Hospital, Shanghai 200233, China.
Bao
K
K
Dai
K
K
D000818:Animals; D001860:Bone Plates; D016723:Bone Remodeling / Q000502:physiology*; D002146:Bony Callus / Q000473:pathology / Q000503:physiopathology* / Q000648:ultrastructure; D017102:Fracture Healing / Q000502:physiology; D008854:Microscopy, Electron; D008859:Microscopy, Polarization; D010006:Osteoblasts / Q000502:physiology; D010011:Osteocytes / Q000502:physiology; D010012:Osteogenesis / Q000502:physiology; D011817:Rabbits; D013314:Stress, Mechanical; D013978:Tibial Fractures / Q000503:physiopathology