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Less lubricin found in the synovial fluid of ACL-injured joints compared to healthy knees

Injured knees had significantly higher levels of type 2 collagen compared to contralateral joints.

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SAN DIEGO — New research shows a significant decrease in lubricin in knees with an injured ACL, compared to healthy knees. The difference was greatest during the acute stages of injury, according to research presented here.

In a study of 30 patients with unilateral ACL injuries, researchers discovered significantly lower concentrations of lubricin in the synovial fluid of injured knees compared to uninjured, contralateral limbs (P<.001). They also said the decreased levels of lubricin were more prominent less than 60 days after injury compared to over 60 days postinjury.

"This increase was associated with increased levels of pro-inflammatory cytokines and an increase of synovial fluid cartilage degradation," Khaled A. Elsaid, PhD, said at the Orthopaedic Research Society annual meeting. "Lubricin is being degraded during the earliest stages following an ACL injury and is associated with an earlier indication of cartilage degradation markers."

A Western blot analysis revealed there is less full-length lubricin and more lower-molecular-weight fragments in the injured joints compared to the healthy knees.

"Also, type 2 collagen in the synovial fluid of the injured joints was significantly higher than collagen type 2 in the synovial fluid of the contralateral joint," Elsaid said.

The researchers collected lubricin samples from the synovial fluid of patients between 9 days and 1 year after injury. They excluded patients with greater than one-third damage to the meniscus, prior knee injury and arthroscopic evidence of chondral lesions.

The investigators determined the quantity of lubricin using a sandwiched enzyme-linked immunosorbent assay, or ELISA. They also performed collagen type 2 testing and a Western blot analysis to determine cartilage degradation and the full duration of lubricin.

For more information:

• Elsaid KA, Fleming BC, Oksendahl HL, et al. Synovial fluid lubricin concentrations are decreased following anterior cruciate ligament injury in humans and are associated with increased cartilage formation. #160. Presented at the Orthopaedic Research Society 53rd Annual Meeting. Feb. 11-14. 2007. San Diego.