Do estrogen and alendronate improve metaphyseal fracture healing when applied as osteoporosis prophylaxis?

Abstract

Osteoporosis is accompanied by predominantly metaphyseal fractures with a delayed and qualitatively reduced healing process. This study addressed the question of whether fracture healing in the context of osteoporosis prophylaxis is improved with estrogen (E) or alendronate (ALN). Thirty-six ovariectomized and 12 sham-operated 12-week-old rats received soy-free (osteoporotic C, sham), E-, or ALN- supplemented diets. After 10 weeks, a metaphyseal tibia osteotomy and standardized T-plate fixation were performed. After a 5-week healing process, the fracture callus was evaluated qualitatively by biomechanical bending test and quantitatively in microradiographic sections. The time course of callus formation was examined using fluorochrome-labeled histological sections. Administration of E improved the biomechanical properties of callus (stiffness [N/mm]: sham: 110.2 + or - 76.07, C: 41.28 + or - 33.70, E: 85.72 + or - 47.24, ALN: 72.07 + or - 34.68). The resistance to microfracturing seen in E-treated animals was significantly enhanced and even superior to sham (yield load [N] sham: 27.44 + or - 9.72, C: 21.04 + or - 12.47, E: 42.85 + or - 13.74(Delta), ALN: 25.28 + or - 6.4(.)) (* P < 0.05 vs. sham group, (Delta) P < 0.05 vs. C group, (*) P < 0.05 vs. E group). Trabecular bone in particular was improved, indicating the presence of physiological endosteal bridging (Tr.Dn [%] sham: 10.53 + or - 18.9, C: 1.01 + or - 0.14, E: 24.13 + or - 34.09(Delta), ALN: 3.99 + or - 8.3(.)). ALN did not help bone healing, as shown by mechanical tests. Compared to the C group, statistically, ALN did not show worse properties. The induction of callus formation under ALN treatment was slightly delayed (Tt.Cl [mm(2)] sham: 3.68 + or - 0.66, C: 3.44 + or - 0.42, E: 3.69 + or - 0.58, ALN: 3.06 + or - 0.56). Osteoporotic metaphyseal fracture healing was qualitatively and quantitatively improved by E prophylaxis. The process of fracture healing occurred nearly physiologically (shamlike). Notably, ALN hardly improved metaphyseal callus properties when assessed as osteoporosis prophylaxis, but to a lesser extent than E.

Fig. 1

Biomechanical testing of callus formation. Stiffness was not significantly enhanced in the estrogen (E)-treated group; changes in the alendronate (ALN)-treated group did not reach sham values. Yield load in the E group was significantly improved compared to the osteoporotic C (C) group, and superior to sham group. The ALN group was slightly enhanced compared to C. P values of <0.05 were considered to be significant (* P < 0.05 vs. sham, ^∆ P < 0.05 vs. C, ^• P < 0.05 vs. E)

Fig. 2

Quantitative evaluation of microradiographic sections. Trabecular structure was significantly enhanced in the estrogen (E)-treated group compared to the osteoporotic C (C) group, surpassing levels observed in the sham group. Alendronate (ALN) was slightly improved compared to C. Callus density was enhanced under E treatment and less under ALN supplementation. P values of <0.05 were considered to be significant (* P < 0.05 vs. sham, ^∆ P < 0.05 vs. C, ^•  P < 0.05 vs. E)

Fig. 3

Intravital fluorochrome labeling. Most of the callus was created during the early, calcein green (CG)-labeled period in endosteal and dorsal regions. P values of <0.05 were considered to be significant (* value differs significantly from CG area of same group; ^∆ value differs significantly from alizarin red area of same group). The last chart presents the total callus for all stained periods

Fig. 4

Corresponding microradiographic and fluorescence-labeled sections. Compared to physiological healing in the sham group, callus formation in the osteoporotic C (C) group was enhanced, but unstructured and less dense. Estrogen (E) administration induced less callus formation, but the callus present was very compact and dense, with increased amounts of trabecular structure. The alendronate (ALN) group displayed fewer and unconstrained calluses and trabeculas

Fig. 5

Examples of Quantimet-based evaluation of microradiographic (a: native picture, b cortical structure, c callus areas, d trabecular structure) and fluorescence-labeled sections (a native picture, b cortical structure, c calcein green-labeled callus, d alizarin red–labeled callus, e tetracycline-labeled callus, f entire callus area)

Fig. 5

Examples of Quantimet-based evaluation of microradiographic (a: native picture, b cortical structure, c callus areas, d trabecular structure) and fluorescence-labeled sections (a native picture, b cortical structure, c calcein green-labeled callus, d alizarin red–labeled callus, e tetracycline-labeled callus, f entire callus area)