Effect of impact on chondrocyte viability during insertion of human osteochondral grafts

Background: Osteochondral grafts, used to treat chondral and osteochondral defects, require high insertional forces that may affect the viability of chondrocytes in the graft. The objectives of this study were to (1) measure the loading impact during insertion of osteochondral grafts, (2) evaluate the effect of insertional loading on chondrocyte viability, and (3) assess this effect on chondrocyte apoptosis and activation of caspase-3. Methods: The distal parts of twelve fresh femora from six adult human cadavers were harvested within seventy-two hours after the death of the donor. From each femur, four 15-mm-diameter cylindrical osteochondral grafts were isolated; two of these grafts (a total of twenty-four grafts in the study) were transplanted with standard impact insertion into recipient sockets in the other condyle of the ipsilateral femur. The other two grafts served as unloaded controls. Loads were measured during the insertion of ten of the twenty-four transplanted grafts. Full-thickness cartilage disks were then removed from the grafts, incubated for up to forty-eight hours, and analyzed for cell viability, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling)-positive reactivity, and caspase-3 activation, each as a function of the depth from the articular surface. Results: The insertion of an osteochondral graft was characterized, on the average (and standard deviation), by 10 4 impacts, each generating 2.4 +/- 0.9 kN of load and 13.3 +/- 4.9 MPa of stress for a duration of 0.57 +/- 0.13 ms with a 0.62 +/- 0.25 N.s impulse. Impact insertion increased cell death in the superficial 500 mu m to 21% at one hour (p < 0.001) and 47% at forty-eight hours (p < 0.001) and also increased cell death in deeper layers at forty-eight hours. Some cell death was due to apoptosis, as indicated by an increase in caspase-3 activation at eight hours (p < 0.01) and TUNEL-positive cells at forty-eight hours (p < 0.05) in the superficial 500 mu m of impacted cartilage. Conclusions: Impact insertion of osteochondral grafts generates damaging loads that cause chondrocyte death, particularly in the superficial zone, mainly as a result of apoptosis mediated by the activation of caspases. Clinical Relevance: Chondrocyte death that occurs during impact insertion of osteochondral grafts may lead to compromised function. Understanding the mechanisms and consequences of such impact loading may provide insights into potential therapeutic interventions, or lead to changes in the insertion technique, to decrease the cell injury associated with impact loading.