To assess tlie mRNA expression of extracellular matrix genes which might correlate with or contribute to mechanically weaker medial collateral ligament (MCL) scars in tlie ACL-deficient rabbit knee joint compared to those in anterior cruciate ligament (ACL) intact knee joints, a bilateral MCL iiijury was induced in I0 skeletally mature female NZW rabbits. As part of the same surgical procedure, the ACL was transected in one of the knees while tlie contl-alateral knee had a sham procedure. The side having the combined MCL and ACL injury was randomly assigned. After six weeks, the rabbits were euthanized. Histological assessments were performed on samples of the MCL scars from each operated knee (i7 = 3 animals) and inRNA levels for collagen type I, 111, V, decorin, biglycan, lumican, fibromodulin, TGF-P, IL-I, TNF-a, MMP-I, MMP-13. and a housekeeping gene (GAPDH) were assessed using semiquantitative RT-PCR on RNA isolated from tlie MCL scar tissue of the reiiiaining animals (n = 7 animals). Levels of mRNA for each gene were normalized using tlie corresponding GAPDH value. Results showed that the total RNA yield (per ing wet weight) in the MCL scar of the ACL-deficient knee was significantly greater than that in tlie MCL scar from the ACLintact knee. Collagen type I mRNA levels were significantly lower and mRNA levels for TNF-cc were significantly greater in the scars of ACL-deficient knees compared to scars from ACL-intact joints. There were no significant dilTet-ences between ACL-deficient and ACL-intact knees with respect to MCL scar mRNA levels for tlie remaining genes assessed. Histologically, tlie "flaw" area, which Iias been shown to correlate with niechanical properties in previous studies, was significantly greater in MCL scars from ACLdeficient knees than in the ACL-intact MCL scars. The mean number of cells/nim' in MCL scars from ACL-deficient knees was significantly greater than in MCL scars from ACL-intact knees. The present study suggests that MCL scar cell metabolism is differentially influenced by the combined injury environment.
The surgical technique adequately restored joint opening to an intact state with response to valgus stress. Agreement among surgeons when quantifying joint opening in mm was substantial. This paper addresses a technically difficult problem and provides pragmatic and practical information for surgeons who manage complicated multi-ligament knee injuries.
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