Osteochondral allograft transplantation, an approach to treating cartilage defects, is traditionally performed using size-matched condyles. However, the donor supply is limited in the U.S.
Therefore, the practice has emerged of harvesting multiple precut allograft plugs from a single donor condyle. These can be stocked by regional tissue banks/high-volume centers for off-the-shelf use. Commercial precut plugs are also available:
- 10-mm plugs harvested using a manual Osteochondral Autograft Transplant System (OATS) punch device (Arthrex, Naples, FL)
- 16-mm plugs harvested with a powered trephine device (Osteochondral Resurfacing System, JRF Ortho, Centennial, CO)
Chondrocytes are quite fragile, and even minor mechanical insults can result in substantial cell death and graft compromise. Gergo Merkely, MD, PhD, a resident in the Harvard Combined Orthopaedic Residency, Chilan B. Leite, MD, a postdoctoral research fellow in the Cartilage Repair Center of the Division of Sports Medicine at Brigham and Women’s Hospital, Christian Lattermann, MD, director of the Center and chief of the Division, and colleagues conducted a controlled laboratory study to determine the optimal technique for harvesting the plugs. They found both methods lead to significant mechanical injury at the edge of the explants compared with scalpel incision. In Cartilage, they propose a combination strategy for plug harvest.
The researchers harvested osteochondral explants from bovine and human samples using three techniques: the OATS manual punch, the powered trephine device, and a fresh scalpel blade (GEM, West Hempstead, NY). They obtained 45 explants (15 per technique) from bovine samples and 18 from human samples (six per technique).
Dead Cell Areas
Microscopic examination of the periphery of the human samples showed the dead cell area was:
- OATS punch—35.83 mm2
- Powered trephine—30.80 mm2 (P=0.065 vs. OATS)
- Scalpel blade preparation—6.10 mm2 (P<0.001 vs. both the powered trephine and OATS)
These findings confirmed previous research by other groups, and changes were similar after the harvest of bovine samples.
The powered device was the most difficult to use, as the abrupt torque and rotary action resulted in more frequent “skidding” or “walking” upon contact with the graft surface. That resulted in greater structural damage and tissue loss. The affected samples were not analyzed, but surgeons should bear the phenomenon in mind.
Dead Cell Pattern and Tissue Contour
The tissue contour and dead area at the chondral periphery of the samples also varied with different harvest techniques:
- OATS punch—Conical-shaped, regular margins; funnel-shaped pattern of chondrocyte death in which the dead area was wider at the superficial zone than the deep zone, probably attributable to the beveled cutting edge
- Powered trephine—Conical-shaped, ragged and irregular margins, and the greatest amount of tissue loss at the periphery
- Scalpel blade—More perpendicular, straight and regular margins with the least amount of cell death and tissue loss
Histologic evaluation of structural damage and tissue loss showed samples harvested with OATS or the powered trephine presented more evidence of peripheral mechanical injury than the scalpel blade samples.
The researchers propose using a combined technique for osteochondral allograft harvest in which each tissue type is prepared to the level of the subchondral plate. Specifically, a retrograde scalpel blade or a circular scalpel should be used to prepare the chondral surface, and an antegrade powered trephine should be used to prepare the bony surface.