Impacts from osteochondral graft insertion decrease chondrocyte viability

Researchers found significantly more apoptotic cells among transplanted graft samples compared with nontransplanted controls.

The impaction forces resulting from inserting osteochondral grafts can activate apoptosis and lead to diminished chondrocyte viability, according to an in vitro study.

Boris H. Borazjani, MD, and colleagues at the University of California-San Diego, measured the loading forces needed to implant osteochondral grafts in the knees of six human cadavers. From each knee, the researchers harvested four cylindrical grafts measuring 15 mm in diameter and with 10 mm of subchondral bone.

Two grafts from each set — one each from the trochlea and condyle — were implanted in the cadaver's ipsilateral knee. The other two grafts from each knee remained explanted and served as controls. Once inserted, the researchers obtained cartilage disks from each transplanted and control graft for analysis, according to the study.

Only normal, grade 1A articular cartilage was used in the study, the authors noted.

An average of 10 ± 4 impacts were required to implant each graft. Each impact had a mean 2.5 ± 1.3 kN loading force and a corresponding stress of 14 ± 7.3 MPa. The maximum impact applied had an average loading force of 3.9 ± 1.9 kN and a stress of 22.1 ± 10.8 MPa, according to the study.

Compared to control samples, the researchers found significantly decreased cell viability in transplanted samples up to 48 hours after insertion (P<.001). At 1 hour post-loading, significantly more cells had died in the superficial 500 µm of transplanted grafts compared to controls, averaging 21% vs. 9% for controls.

At 48 hours, cell death increased more than two-fold to 47% in the upper 500 µm layer of transplanted samples and extended to around 1,000 µm deep (P<.001), according to the study.

The researchers also found significantly more apoptotic cells among transplanted samples at 48 hours; 26% of loaded cells showed apoptosis compared with 9% of control samples.

"The results ... suggest that modification of graft insertion techniques may be warranted to protect graft viability. Indeed, this study has led to a change in our clinical practice in that we now minimize impact loading of grafts during insertion," the authors said.

However, "It is unknown what effects impact loading and subsequent cell death have on the function or longevity of the graft in vivo; thus additional studies are warranted," they added.

For more information:
Borazjani BH, Chen AC, Bae WC, et al. Effect of impact on chondrocyte viability during insertion of human osteochondral grafts. J Bone Joint Surg Am. 2006;88-A:1934-1943.