Comparison of mRNA levels for matrix molecules in normal and disrupted human anterior cruciate ligaments using reverse transcription polymerase chain reaction

Midsubstance samples of anterior cruciate ligaments from seven normal human cadaver knees (16-50 years old) were harvested and compared with midsubstance pieces of scarred anterior cruciate ligaments from 30 patients (15-40 years old). RNA was isolated from each ligament, and the expression of type-I collagen, type-III collagen, biglycan, decorin, lumican, and tissue inhibitor of metalloproteinase-l was evaluated by quantitative reverse transcription-polymerase chain reaction with use of p-actin as the housekeeping gene. Data for injured ligaments were further compared statistically as a function of time after injury to better define patterns of cellular expression over time. Our hypothesis was that injured ligaments would show minimal cellular activity and decreasing activity over time. The results revealed that both normal and injured anterior cruciate ligaments contain cells that express mRNA for all molecules studied. However, cells in injured ligaments express much higher, but still proportional, quantities of message for type-I collagen and type-III collagen (p < 0.000001) and higher quantities of biglycan (p < 0.02) and tissue inhibitor of metalloproteinase-l (p < 0.0003) than do cells in normal anterior cruciate ligaments. These levels remained elevated for longer than 1 year after injury. Linear regression analysis showed biglycan expression correlated with time from injury (r(2) = -0.69; p = 0.007). These results collectively demonstrate that injured human anterior cruciate ligaments contain cells that express scar-like molecules and that the injured ligaments are likely continuing to remodel matrix over time. Furthermore, they suggest that human anterior cruciate ligaments have not failed to heal due to the failure of scar formation per se. The quality and quantity of this scar remain questionable; however, the possibility of its enhancement as a healing strategy for human anterior cruciate ligaments cannot be dismissed.