The effect of storage medium tonicity on osteochondral autograft plug diameter

The purpose of this study was to investigate the effect of differing storage medium on osteochondral plug diameter.

Four storage conditions were evaluated: air, hypotonic solution (sterile water), isotonic saline solution (0.9% sodium chloride), and hypertonic saline solution (3.0% sodium chloride). Four osteochondral plugs were acquired (4.5-mm harvesting system) from each of 10 fresh calf femurs and randomized to 1 of 4 storage media (N = 40). Micro-computed tomography was used to evaluate the precise diameter of each plug. After a time 0 scan, each plug was placed in a designated storage medium and rescanned at 3 time points over approximately 1 hour. A region of interest was identified from approximately 1 to 6 mm proximal to the tidemark. Custom software automatically calculated the diameter of each plug.

The time 0 plug diameter (mean ± 95% confidence interval) for all specimens was 4.66 ± 0.01 mm. There were no significant differences between any of the groups at the baseline scan. There were also no significant differences between the time 0 and subsequent scans of the unsubmerged specimens. However, all of the liquid solutions (hypertonic, isotonic, and hypotonic) resulted in a significant increase in diameter from their baseline scans (P < .05), indicating that a cause may be increased extracellular matrix fluid pressure.

Placing an osteochondral plug in a liquid solution increased the diameter of the subchondral bone. Size increase from the storage medium appeared to level off within 14 minutes after placement in solution.

Increases in diameter of the plug may alter the ease of insertion of the graft, possibly increasing contact pressure on cartilage during plug implantation.