Analysis of fracture healing in osteopenic bone caused by disuse: experimental study

Abstract

Osteoporosis has become a serious global public health issue. Hence, osteoporotic fracture healing has been investigated in several previous studies because there is still controversy over the effect osteoporosis has on the healing process. The current study aimed to analyze two different periods of bone healing in normal and osteopenic rats. Sixty, 7-week-old female Wistar rats were randomly divided into four groups: unrestricted and immobilized for 2 weeks after osteotomy (OU2), suspended and immobilized for 2 weeks after osteotomy (OS2), unrestricted and immobilized for 6 weeks after osteotomy (OU6), and suspended and immobilized for 6 weeks after osteotomy (OS6). Osteotomy was performed in the middle third of the right tibia 21 days after tail suspension, when the osteopenic condition was already set. The fractured limb was then immobilized by orthosis. Tibias were collected 2 and 6 weeks after osteotomy, and were analyzed by bone densitometry, mechanical testing, and histomorphometry. Bone mineral density values from bony calluses were significantly lower in the 2-week post-osteotomy groups compared with the 6-week post-osteotomy groups (multivariate general linear model analysis, P<0.000). Similarly, the mechanical properties showed that animals had stronger bones 6 weeks after osteotomy compared with 2 weeks after osteotomy (multivariate general linear model analysis, P<0.000). Histomorphometry indicated gradual bone healing. Results showed that osteopenia did not influence the bone healing process, and that time was an independent determinant factor regardless of whether the fracture was osteopenic. This suggests that the body is able to compensate for the negative effects of suspension.

Figure 1. Fractured right hindlimb immobilized by an orthosis.

Figure 2. Positioning of the tibia to test the torsion. A: mobile device, arrow indicates the orientation of the torsion; B: tibia; C: fixed device.

Figure 3. Histological photomicrography of tibia sections stained by Trichrome Masson (A-D) and Picro-Sirus Red (E-H), original magnification 50×. Group OU2 (A) and group OS2 (B) showed lower amounts of bone formation than group OU6 (C) and group OS6 (D). Group OU2 (E) and group OS2 (F) showed lower collagen levels than group OU6 (G) and group OS6 (H). Group OU2: unrestricted rats 2 weeks post-osteotomy; group OS2: suspended rats 2 weeks post-osteotomy; group OU6: unrestricted rats 6 weeks post-osteotomy; group OS6: suspended rats 6 weeks post-osteotomy.