Effects of maturation on the mechanical properties of regenerated and residual tissues in the rabbit patellar tendon after resection of its central one-third
Introduction
In recent years, the number of skeletally immature patients suffering from tears of the anterior cruciate ligament (ACL) is increasing probably due to increased participation in sport activities (Bales et al., 2004, Vaquero et al., 2005). Non-operative treatments of ACL rupture in adolescent patients tend to lead to unsatisfactory outcomes, such as persisting instability of the knee joint and associated meniscus tear (Kannus & Jarvien, 1988, Mizuta et al., 1995). Skeletally immature patients are generally able to regain knee stability and functions by ACL reconstruction surgery and then return to competitive sports activities (Aichroth et al., 2002, Gebhard et al., 2006). The central one-third portion of the patellar tendon (PT) is commonly used as an autograft for the reconstruction of the ACL, even for skeletally immature patients (Shelbourne et al., 2004, Gebhard et al., 2006).
The biomechanical properties of tendons and ligaments change during maturation (e.g., Gillis et al., 1995, Fujie et al., 2000, Yamamoto et al., 1997, Woo et al., 1990). Nonetheless, only a few studies have been carried out on the effects of maturation on the mechanical properties of healing tendons and ligaments. For example, Hefti et al. (1991) reported that the failure load of the partially transected ACL was recovered faster in immature rabbits than in mature ones. Provenzano et al. (2002) also demonstrated that the material strength of the lateral collateral ligaments underwent subfailure injury was returned to normal level faster in immature rats than in mature ones.
Previous studies have been performed on the structural properties of the healing PT after the resection of the central portion (e.g. Burks et al., 1990, Beynnon et al., 1995), the material properties of both of the tissue regenerated in the tendon defect (regenerated tissue) and the tissue remaining at both sides of the defect (residual tissue) (Miyashita et al., 1997, Tohyama et al., 2003), and the tensile properties of collagen fascicles of regenerated and residual tissues (Maeda et al., 2007). However, there have been no studies on the effects of the harvest of the central one-third PT on the mechanical properties of healing tissues in skeletally immature animals. In particular, the information of its effects on the properties of the remaining PT tissues in skeletally immature animals is useful for clinicians for the design of postoperative training regimens in immature patients after ACL reconstruction.
Therefore, the present study was performed to determine the tensile properties of regenerated and residual tissues in the PT in immature and mature rabbits after the resection of its central one-third. Our hypothesis was that immature animals regenerate tissues possessing better healing potential than mature animals from the biomechanical point of view.
Section snippets
Experimental groups and surgical procedures
A total of 30 female Japanese White rabbits were used in the present study and they were divided into three age groups: 2-month-old (2-mo, n = 11), 3-month-old (3-mo, n = 12) and 6-month-old (6-mo, n = 7) groups. Their averaged body weights were 1.9, 2.5 and 3.0 kg, respectively. A previous radiological analysis on white rabbits showed that femoral epiphyseal plate is still opened at 4–5 months, but is closed at 6 months (Woo et al., 1986). Accordingly, 2- and 3-mo groups in the present study could be
Effect of maturation
The length of the operated tendon was significantly longer in 6-mo group than in 2- and 3-mo groups, but there was no statistically significant difference between 2- and 3-mo groups (Table 1). The cross-sectional area of the operated tendon was also significantly larger in 6-mo group than in 2-mo group; however, no significant differences were observed between 6- and 3-mo groups, and between 2- and 3-mo groups. Control PTs in 6-mo group had significantly larger cross-sectional area and length
Discussion
The present study was performed to test the hypothesis that immature animals demonstrate better mechanical properties of healing tissues in the partially resected PT than mature ones. The results obtained demonstrated that the mechanical properties of regenerated and residual tissues were not significantly different between immature and mature animals (Fig. 1, Fig. 2). On the other hand, those in the normal, control PT were maturation-dependent. This indicates that the material properties of
Acknowledgement
We appreciate Mr. Tomokazu Kai for his contribution to a part of the experiments. This work was financially supported in part by the Japan Space Forum for the Ground-Based Research for Space Utilization (No. 181), and by the Grant-in-Aid for Scientific Research (A) (2) (Nos. 12308147 and 15200036) and the Program for Social Collaborative Research (Okayama University of Science) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
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- 1
Present, Division of Human Mechanical Systems and Design, Graduate School of Engineering, Hokkaido University, Sapporo, Japan.
- 2
Present, Denso Corporation, Nagoya, Japan.
- 3
Present, Department of Biomedical Engineering, School of Engineering, Okayama University of Science, Okayama, Japan.