Related Experiment Video
Updated: Jun 21, 2026
Establishment and Evaluation of a Sheep Model of Full-thickness Osteochondral Defect
Published on: April 14, 2026
Insight into the molecular pathophysiology of delayed bone healing in a sheep model
Jasmin Lienau1, Katharina Schmidt-Bleek, Anja Peters
1Julius Wolff Institut and Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Abstract:
Delayed and nonunions are still challenging problems. In this study, we examined the endogenous mRNA expression of genes regulating cartilage formation, bone formation, endochondral ossification, and bone remodeling during mechanically induced delayed bone healing in a large animal model. A tibial osteotomy was performed in two groups of sheep and stabilized with either a rigid external fixator leading to standard healing or with a rotationally unstable fixator leading to delayed healing. At days 4, 7, 9, 11, 14, 21, and 42 after surgery, total RNA was extracted from the callus. Gene expressions of several molecules functionally important for bone healing were studied by quantitative reverse transcriptase-polymerase chain reaction. The expression profiles were related to callus tissue composition, analyzed by histomorphometry. Histomorphometry demonstrated a delayed, prolonged chondral phase and a reduction in bone formation in the experimental group. There was no differential expression of Runx2 between both groups until day 42, but mRNA expression levels of BMP2, BMP4, BMP7, noggin, Col1a1, IGF1, TGFbeta1, OPN, MMP9, MMP13, TIMP3, TNFalpha, MCSF, RANKL, and OPG were lower in the delayed healing group at several time points. This study provides insight into the temporal periods during which various factors may be deficient during a compromised bone-healing situation.
Insights
This study reveals that compromised bone healing in sheep involves lower expression of key genes involved in cartilage and bone formation. Understanding these molecular deficits offers insights into treating delayed and nonunion fractures.
Area of Science:
- Orthopedics
- Biomaterials Science
- Molecular Biology
Background:
- Delayed and nonunions represent significant clinical challenges in fracture repair.
- Understanding the molecular mechanisms underlying compromised bone healing is crucial for developing effective treatments.
Purpose of the Study:
- To investigate endogenous mRNA expression of genes regulating bone healing processes during mechanically induced delayed healing.
- To correlate gene expression profiles with callus tissue composition in a large animal model.
Main Methods:
- Sheep tibial osteotomy stabilized with rigid (standard healing) or unstable (delayed healing) external fixators.
- Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to analyze mRNA expression of key bone healing genes.
- Histomorphometry to assess callus tissue composition and healing phases.
Main Results:
- Histomorphometry confirmed a delayed and prolonged chondral phase with reduced bone formation in the delayed healing group.
- Lower mRNA expression of BMP2, BMP4, BMP7, noggin, Col1a1, IGF1, TGFbeta1, OPN, MMP9, MMP13, TIMP3, TNFalpha, MCSF, RANKL, and OPG was observed at various time points in the delayed healing group.
- No significant differential expression of Runx2 was noted until day 42.
Conclusions:
- Mechanically induced delayed bone healing is associated with reduced expression of critical genes involved in cartilage and bone formation.
- This study identifies specific molecular deficiencies and temporal patterns during compromised bone healing, offering targets for therapeutic intervention.
