Influence of mechanical unloading on histological changes of the patellar tendon insertion in rabbits

The purpose of this study was to clarify the influence of mechanical unloading on histological changes of the patellar tendon (PT) insertion in rabbits.

The PT was completely released from stress by drawing the patella toward the tibial tubercle with a stainless steel wire installed between the patella and tibial tubercle (mechanical unloading group, n=28). The animals of the sham group underwent the same surgical procedure; however, the wire was not tightened (n=28). The average thickness of the Safranin O-stained glycosaminoglycan (GAG) area, chondrocyte apoptosis rate and chondrocyte proliferation rate of the cartilage layer at the insertion were measured at one, two, four, and six weeks.

The chondrocyte apoptosis rate in the mechanical unloading group was significantly higher than that in the sham group at one and four weeks (p<0.05). The chondrocyte proliferation rate in the mechanical unloading group was significantly lower than that in the sham group at four and six weeks (p<0.05). The average thickness of the GAG-stained area in the mechanical unloading group was significantly lower than that in the sham group at six weeks (p<0.05).

Mechanical unloading significantly affected the increase in the chondrocyte apoptosis rate, decrease in the chondrocyte proliferation rate, and decrease in the GAG layer thickness at the PT insertion for up to six weeks in rabbits.

We suggest that more than 6 weeks of mechanical unloading should be avoided to prevent degeneration at the PT insertion.