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

• Mechanical unloading increased the chondrocyte apoptosis rate at the patellar tendon insertion.
• Mechanical unloading reduced the chondrocyte proliferation rate at the insertion.
• Mechanical unloading reduced the glycosaminoglycan layer thickness at the insertion for up to 6 weeks.

BackgroundThe purpose of this study was to clarify the influence of mechanical unloading on histological changes of the patellar tendon (PT) insertion in rabbits.Materials and methodsThe 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.ResultsThe 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).ConclusionMechanical 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.Clinical relevanceWe suggest that more than 6 weeks of mechanical unloading should be avoided to prevent degeneration at the PT insertion.