Intra-articular fractures were created in the distal end of the femur in
adult rabbits. Fractures were then reduced in three different fashions:
incomplete reduction, adequate reduction without compression of the fragments,
and ideal reduction, which consisted of reduction with strong compression of
the fracture fragments. Animals were killed at intervals ranging from seven
weeks to one year, and the cartilage fractures were studied by light,
transmission, and scanning electron microscopy, using proteoglycan stains.
Cartilage fractures that were inadequately reduced or were adequately
reduced without compression healed by fibrocartilage only. Fractures that were
reduced with compression across the fragments healed with a tissue which, by
light and electron microscopy, appeared to be hyaline cartilage, which showed
the collagen and proteoglycan orientation and relationships of normal hyaline
cartilage. The healing of these defects appears to be the result of a
proliferation of cells emanating from the region of the tidemark, and perhaps
of migration of chondrocytes from the surface into the lesion. We postulate
that compression of the cartilage surfaces either creates a physical
environment that allows certain chondrocytes to heal the defect with hyaline
cartilage, or, by coapting the surfaces, prevents ingrowth of granulation
tissue from the subchondral bone that might interfere with repair by hyaline
cartilage.
This study suggests a hitherto unappreciated capacity for hyaline cartilage
to repair structural defects.
Clinical Relevance: Accurate reduction of
intra-articular fractures with interfragmentary compression may create the
environment whereby cartilage cells may repair the cartilage fracture —
a capacity not previously thought possible in adult cartilage. The repair of
cartilage defects provides obvious benefits to the patient.