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 µm 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 µm 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.