Paper 162: Increased Expression of Tenascin-C in Osteotendinous Healing Junction under Mechanical Strain

Abstract

The developments of the fibrocartilage in musculoskeletal organs are strongly related the mechanical strain, however, the influence of mechanical strain on fibrocartilage zone regeneration and remodeling during osteotendinous junction repair are currently poorly understood (1Benjamin M. Ralphs J.R. Fibrocartilage in tendon and ligaments: An adaptation to compressive load.J Anat. 1998; 193: 481-494Crossref PubMed Google Scholar). In present study, the expression of tenascin-C and transforming growth factor – ß 1(TGFß1), two key factors involved in strength and elasticity of extracellular matrix remodeling (2Jarvinen T.A. Jozsa L. Kannus P. Jarvinen T.L. Kvist M. Hurme T. Isola J. Kalimo H. Jarvinen M. Mechanical loading regulates tenascin-C expression in the osteotendinous junction.J Cell Sci. 1999; 18: 3157-3166Google Scholar, 4Zhao Y. Young S.L. TGF-beta regulates expression of tenascin alternative-splicing isoforms in fetal rat lung.Am J Physiol. 1995; 268: 173-180Google Scholar), were examined in the healing osteotendinous junction under controlled mechanical loading through quadriceps muscles tension induced by functional electric stimulation (FES) by using our established partial patellectomy model in rabbits (5Wang W. Chen H.H. Yang X.H. Xu G. Chan K.M. Qin L. Postoperative programmed muscle tension augmented osteotendinous junction repair.Int. J Sports Med. 2007; 28: 691-696Crossref PubMed Scopus (14) Google Scholar). Standard transverse osteotomy was performed between the proximal 2/3 and the distal 1/3 of the patella, and distal 1/3 of the patella was excised. The patellar tendon was directly sutured back to the proximal remaining patella while protected with a ‘figure of eight' tension band wire. The knee was immobilized with long leg cast in 90° of knee flexion, 21 rabbits were randomly divided into two groups. The controlled mechanical strain generated from quadriceps muscle contraction induced by FES was applied on the healing patella–patellar tendon junction for 30 minutes per day, 5 days per week for 6 weeks in FES group compaired with non-mechanical loading in control group. The quadriceps muscles-patella-patellar tendon-tibia (QPPT) complex was harvested at the end of postoperative week 6 and 12 respectively for biomechanical testing (n=5) and semiquantitative histology (n=2). The samples after biomechanical testing were also used for histological quantification. Image quantification of fibrocartilage zone and proteoglycan content, semiquantitation of immunohistometry of the expression of tenascin-C and transforming growth factor – ß 1(TGFß1) in the healing osteotendinous junction, ultimate stress of (QPPT) complex were compared by two-way ANOVA between the FES group and control group at each healing time points. Statistical significance level was set at p ? 0.05. As compared with control group, better organized collagen fibers orientated along with mechanical loading axis was observed under polarized microscope to bridge the healing osteotendinous interface at both week 6 and 12. An elevated proteoglycant stainability and larger intermitted fibrocartilage zone were found in the osteotendinous healing interface in FES group compared to control group at both week 6 and 12. Semiquantitation of immunohistometry revealed that the expression levels of Tenascin-C and TGFß-1 increased in the osteotendinous healing interface in FES group compared to control group at both week 6 and 12. The decreased cross sectional area, increased failure load and ultimate strength of all healing osteotendinous interface observed with healing over time, but more significant in FES group as compared to the controls at each healing time point. However, the ultimate strength of FES group and control group only reached to 20.2±3.6% and 11.6±4.5% of the intact contralateral hind limb respectively. The failure mode of the tested healing osteotendinous complex specimens in control group was found at the initial osteotomy site, but at the sub-fibrocartilage woven bone in FES group. The dramatically increased levels of tenascin C and TGF-ß1 expression in the healing osteotendinous junction induced by mechanical strain generated from muscle tension contraction have not been reported before. The much better restoration of fibrocartilage zone in terms of morphology as well as biomechanical properties under the mechanical strain was also shown. The present study indicated that the mechanical strain has beneficial effects on osteotendinous healing processes by influencing the extracellular matrix remodeling at fibrocartilage zone. The dilemma between prolonged immobilization in order to providing a static environment for facilitating osteotendinous junction repair and the need of early functional rehabilitation remains a challenge in surgical osteotendinous junction repair clinically (3Thomopoulos S. Williams G.R. Soslowsky L.J. Tendon to bone healing: differences in biomechanical, structural, and compositional properties due to a range of activity levels.J Biomech Eng. 2003; 125: 106-113Crossref PubMed Scopus (296) Google Scholar). Findings of our study suggest that the early muscle tension for patients underwent osteotendinous junction repair should be conducted.