EFFECTS OF NAIL RIGIDITY ON FRACTURE-HEALING - STRENGTH AND MINERALIZATION IN RAT FEMORAL BONE

Citation
Se. Utvag et O. Reikeras, EFFECTS OF NAIL RIGIDITY ON FRACTURE-HEALING - STRENGTH AND MINERALIZATION IN RAT FEMORAL BONE, Archives of orthopaedic and trauma surgery, 118(1-2), 1998, pp. 7-13
Citations number
28
Categorie Soggetti
Orthopedics,Surgery
ISSN journal
09368051
Volume
118
Issue
1-2
Year of publication
1998
Pages
7 - 13
Database
ISI
SICI code
0936-8051(1998)118:1-2<7:EONROF>2.0.ZU;2-Z
Abstract
The present study was undertaken to assess the effects of the rigidity of nails on the healing of fractures as evaluated by mechanical stren gth and rate of bone mineralisation. Ten rats supplied biomechanical d ata at the start of the experiment and another 100 rats were randomly assigned to 5 groups. In 20 rats no intervention was performed, and th ey served as a reference group of normal values. Thus, 80 rats underwe nt a standardised partial osteotomy in the left femur diaphysis prior to manual fracture, reaming and intramedullary nailing. One group rece ived rigid steel nails (group I)and another, cannulated steel nails (g roup 2). Group 3 received semi-rigid titanium nails and group 4, soft polyethylene nails. Ten rats in each group were evaluated at 6 and 12 weeks after fracture, and radiographs and callus diameter measurements were performed. Dual-energy X-ray absorptiometry (DEXA) of the bones was performed, and the degree of mineralisation in the callus segment, distal diaphysis and total femur was calculated by the scanner. Subse quently, the bones were tested mechanically by a three-point bending t est in a Mini Bionix (MTS) testing system. Radiographs revealed clearl y visible fractures at 6 weeks in the intervention groups. At 12 weeks there were no signs of bridging callus in group 4, while the other gr oups presented scarcely visible osteotomies. The callus area in group 4 was significantly larger at both 6 and 12 weeks than in groups 1-3. In these groups there was a significant decrease in callus area betwee n 6 and 12 weeks. Both maximum bending load, bending rigidity and frac ture energy increased significantly in groups 1-3 between 6 and 12 wee ks, while bending load and fracture energy increased in group 4. At 6 weeks no significant differences were detected between groups 1-3 in m echanical strength. Group 4 had a significantly reduced maximum bendin g load and fracture energy at 6 and 12 weeks as well as bending rigidi ty at 12 weeks. At 12 weeks group 3 had a significantly increased maxi mum bending load and fracture energy compared with groups 1 and 2. Bon e mineral count (BMC) in the callus region in group 4 was significantl y reduced at both 6 and 12 weeks. BMC in the callus showed no signific ant differences between groups 1-3, either at 6 or at 12 weeks. BMC in the distal diaphysis was significantly reduced in groups 1 and 4 comp ared with group 2 at 12 weeks. Bone mineral density (BMD) in the callu s region revealed no significant differences between groups 1-3 at 6 w eeks, while at 12 weeks BMD was higher in group 3 than in group 1. BMD in the callus region and total femur in group 4 was significantly red uced at 6 weeks. This study demonstrates that diaphyseal fractures tre ated with titanium nails with a bending rigidity similar to the intact femur have a higher maximum bending load and fracture energy at 12 we eks than both rigidly or softly nailed fractures. BMD in the callus re gion was also highest after titanium nailing at 12 weeks. BMD in the d istal diaphysis and total femur indicates that the degree of stiffness of the nails have little influence on total bone mineralisation at 12 weeks.