Effect of distraction length on the morphology of knee cartilage in a rat model of femoral distraction osteogenesis

TL;DR

This study shows that excessive femoral distraction in rats causes knee cartilage degeneration and osteoarthritis-like changes due to inflammation and bone remodeling.

Contribution

The study identifies a threshold for femoral distraction beyond which knee joint damage becomes irreversible, linking it to specific molecular pathways.

Findings

20 mm distraction caused severe cartilage erosion and subchondral sclerosis, unlike 10 mm distraction.

Group B showed elevated catabolic markers (IL-1β, MMP-13, RANKL) and reduced anabolic markers (COL-II, SOX9, OPG).

Excessive distraction triggers sterile inflammation and osteochondral uncoupling via IL-1β/MMP-13 and OPG/RANKL pathways.

Abstract

This study investigated the dose-dependent impact of femoral distraction length on knee joint integrity and characterized the molecular mechanisms driving cartilage degeneration in a rat distraction osteogenesis (DO) model.

Thirty-six Sprague-Dawley rats underwent femoral DO and were randomly assigned to three groups: Control (5 mm), Group A (10 mm), and Group B (20 mm). Following a consolidation phase, knee joint morphology and subchondral bone microstructure were evaluated using digital radiography and micro-computed tomography. Histological assessment included H&E, Safranin O-Fast Green, and Masson’s trichrome staining. Furthermore, immunohistochemical analysis quantified the expression of catabolic (IL-1β, MMP-13, RANKL) and anabolic (COL-II, SOX9, OPG) biomarkers in the articular cartilage and subchondral bone.

Radiographic and histological findings demonstrated successful osseointegration and physiological tolerance in the Control and Group A. Conversely, Group B exhibited severe osteoarthritis-like pathology, including cartilage erosion, proteoglycan depletion and subchondral sclerosis. Quantitative analysis confirmed significantly elevated bone mineral density and bone volume fraction in the subchondral bone of Group B (P < 0.05). Molecularly, Group B showed significant upregulation of catabolic biomarkers (IL-1β, MMP-13 and RANKL) with concurrent downregulation of anabolic biomarkers (COL-II, SOX9 and OPG; P < 0.05).

Extensive distraction (20 mm, ∼50% of original length) surpasses the physiological adaptive capacity of the knee joint, triggering irreversible degeneration via IL-1β/MMP-13-mediated sterile inflammation and OPG/RANKL-driven osteochondral uncoupling. While moderate distraction (10 mm, ∼25% length) remains compensatory, this pathological transition highlights the critical necessity of joint protection strategies when limb lengthening targets exceed ∼25% of the original bone length.

Scientific diagram illustrating distraction osteogenesis in SD rat femurs at 5 millimeters, 10 millimeters, and 20 millimeters, correlating increased distraction to histomorphological knee joint changes, subchondral bone sclerosis, and a mechanistic pathway involving mechanical overload, inflammation, and altered bone nutrient support.

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