Bone marrow stimulation induces greater chondrogenesis in trochlear vs condylar cartilage defects in skeletally...

The aim of this study was to compare the early repair response of cartilage defects in trochlea (TR) and medial femoral condyle (MFC) at 2-3 weeks after bone marrow stimulation.

Bilateral full-thickness cartilage defects were generated in central trochlear groove and MFC of skeletally mature rabbits. Four subchondral perforations were made on each defect, either by microfracture to 2 mm deep, or by drilling to 2 mm or 6 mm deep. Rabbits were sacrificed either on Day 14 post-operatively or on Day 21. Defects were analyzed by histology, stereology, histomorphometry and micro-computed tomography (CT). Intact femurs (N = 4) served as controls.

Stromal cell density recruitment was similar in all defects, irrespective of defect location and surgical techniques used. There was a robust appearance of chondrocytes at Day 21 in TR defects with significantly higher volume fraction of chondrocytes in TR compared to MFC (P = 0.013). Chondrogenic foci were observed in marrow penetrating holes, with a significantly higher frequency and larger foci in TR vs MFC defects at Day 21 (P = 0.043 and P = 0.0014, respectively). Micro-CT analysis showed that deep drilling elicited significantly more mineralized bone fill compared to shallower perforations at 2 and 3 weeks repair (all at P ≤ 0.0008).

Bone marrow stimulation induced greater chondrogenesis in TR vs MFC defects in adult rabbits, with more chondrocytes and larger chondrogenic foci appearing in TR vs MFC on Day 21 post-operation.