Induction of chondrocyte apoptosis following impact load.

OBJECTIVE

To investigate the presence and extent of chondrocyte apoptosis following impact load of articular cartilage in an in vivo model.

DESIGN

An in vivo animal model, using a pendulum device and New Zealand White rabbits, was designed to study the effects of impact load on the development of chondrocyte apoptosis. Animals were placed into either a High Impact group or a Low Impact group, and the right medial femoral condyle was impacted with a single impact load. A sham operation was performed on the left limb, and this cartilage served as the control.

SETTING

Academic medical center.

PARTICIPANTS

New Zealand White rabbits (3 months).

INTERVENTION

Impact load to the right medial femoral condyle.

MAIN OUTCOME MEASURES

Three different methods were used to assess the presence and extent of chondrocyte apoptosis: 1) light microscopy (hematoxylin and eosin and terminal dUTP nick end labeling staining); 2) transmission electron microscopy; and 3) fluorescent microscopy with Hoechst 33342 staining. Secondary outcome measures included determination of the magnitude of impact force and time to peak force.

RESULTS

Light microscopy demonstrated chondrocytes with changes consistent with apoptosis including condensed nuclei, deep eosinophilic cytoplasmic staining, and vacuolization within the impacted specimens. Terminal dUTP nick end labeling staining-stained specimens had a high degree of positively stained cells (60%) in both injured and uninjured specimens. Transmission electron microscopy of the impacted specimens demonstrated numerous chondrocytes with changes characteristic of apoptosis, including nuclear and cellular fragmentation, volume shrinkage, and cytoplasmic vacuolization. Eleven percent of the cells in the High Impact group had changes consistent with apoptosis, versus 3% for the low impact group and <1% for the sham specimens. The High Impact group received a statistically significant greater stress than the Low Impact group. Impact group (P < 0.05), and the average time to peak force was 0.021 seconds for each impact group.

CONCLUSIONS

The current data strongly indicate that in vivo chondrocyte apoptosis can be stimulated by the application of a single, rapid impact load and that the extent of chondrocyte apoptosis is related to the amount of load applied. The contribution chondrocyte apoptosis makes to the development of posttraumatic arthritis following joint injury or intra-articular fracture still remains to be determined.