22.765.3%, 26.767.5%, 4.660.9%, 2.861.2%, 19.464.6%, 20.960.3%, and 21.263.5%, respectively (Figure 3A). Fibrocar- tilage tissues (MM and LM) had the highest collagen content; the fibrocartilage tissues averaged together had 4.1x the collagen content of the hyaline tissues and 6.7x the collagen content of the cruciate ligaments. Among just the fibrous tissues, the collateral ligaments (MCL and LCL) and PL had higher collagen content than the cruciate ligaments (CraCL and CauCL); in particular, the collateral ligaments averaged together had 5.4x the collagen content of the cruciate ligaments. The cruciate ligaments were not significantly different from the hyaline cartilage tissues (CC and PC) in collagen content. The collagen/dry weight for CC, PC, MM, LM, CraCL, CauCL, MCL, LCL, and PL were 45.6610.3%, 46.5616.2%, 91.6616.4%, 93.5610.6%, 72.6612.1%, 86.8610.7%, 70.8616.1%, 81.769.3%, and 84.1611.6%, respectively (Figure 3B). Pyridinoline crosslink content Pyridinoline was resolved as one peak for all samples. Pyridinoline normalized to tissue wet weight (pyd/ww) for CC, PC, MM, LM, CraCL, CauCL, MCL, LCL, and PL were 0.30360.101, 0.17460.049, 0.49860.160, 0.53460.115, 0.37460.087, 0.56560.204, 0.41460.123, 0.42260.067, and 0.58560.069 nmol/mg, respectively (Figure 3C). Pyd/ww was highest in PL, while CauCL, LM, and MM samples trended Characterization of Immature Knee Joint Tissues higher compared to all other tissues. The hyaline cartilages (CC and PC) had the lowest pyd/ww. The fibrocartilage tissues averaged together had a pyd/ww 2.16x that of the hyaline cartilages, and all of the ligament tissues averaged together had a pyd/ww 1.98x that of the hyaline cartilages. Pyridinoline normalized to collagen content (pyd/col) for CC, PC, MM, LM, CraCL, CauCL, MCL, LCL, and PL were 5.6963.85, 3.6861.59, 2.2860.88, 2.1760.92, 8.3262.12, 16.0864.53, 2.2260.85, 2.0260.34, and 2.8060.42 nmol/mg, respectively (Figure 3D). Statistically, CauCL had the highest pyd/ col and CraCL the second highest, followed by the hyaline cartilages. The collateral and patellar ligaments and both menisci were not statistically different from each other and were less than the cruciate ligaments and the hyaline cartilages. CauCL had a pyd/col 1.93x that of the CraCL, 3.43x that of the hyaline cartilages, 7.22x that of the fibrocartilage tissues, and 7.59x that of the collateral ligaments. Tensile properties The Young’s moduli for CC, PC, MM, LM, CraCL, MCL, LCL, and PL were 8.464.1, 4.661.8, 25.967.0, 21.666.2, 2.161.0, 11.665.9, 13.265.8, 16.964.07, 27.562.8 MPa, respectively (Figure 4A). The UTS for CC, PC, MM, LM, CraCL, MCL, LCL, and PL were 7.062.2, 3.960.7, 15.164.5, 24.662.0, 1.460.6, 7.465.9, 10.166.4, 14.963.9, and 15.763.3 Figure 3. Collagen and pyridinoline content of joint tissues. (A) Collagen normalized to wet weight was significantly higher for the menisci, collateral ligaments, and patellar ligament. (B) Collagen normalized to dry weight was highest in the menisci and lowest in the hyaline cartilages. (C) Pyridinoline normalized to wet weight was highest for menisci, patellar ligament, and the caudal cruciate ligament. Crosslink content was lowest for patellar cartilage. (D) Pyridinoline normalized to collagen was highest for the hyaline cartilages and cruciate ligaments. Groups denoted by different letters are significantly different (p,0.05). doi:10.1371/journal.pone.0026178.g003 PLoS ONE | www.plosone.org 4 October 2011 | Volume 6 | Issue 10 | e26178