Quantitative Mapping of Matrix Content and Distribution across the Ligament-to-Bone Insertion
Lu HH (2013) Quantitative Mapping of Matrix Content and Distribution across the Ligament-to-Bone
Insertion. PLoS ONE 8(9): e74349. doi:10.1371/journal.pone.0074349
Quantitative Mapping of Matrix Content and Distribution across the Ligament-to-Bone Insertion
Jeffrey P. Spalazzi 0 1
Adele L. Boskey 0 1
Nancy Pleshko 0 1
Helen H. Lu 0 1
Alejandro Almarza, University of Pittsburgh, United States of America
0 Current address: Department of Bioengineering, Temple University , Philadelphia, Pennsylvania , United States of America
1 1 Biomaterials and Interface Tissue Engineering Laboratory, Department of Biomedical Engineering, Columbia University , New York , New York, United States of America, 2 Musculoskeletal Integrity Program, Hospital for Special Surgery , New York , New York, United States of America, 3 College of Dental Medicine, Columbia University , New York, New York , United States of America
The interface between bone and connective tissues such as the Anterior Cruciate Ligament (ACL) constitutes a complex transition traversing multiple tissue regions, including non-calcified and calcified fibrocartilage, which integrates and enables load transfer between otherwise structurally and functionally distinct tissue types. The objective of this study was to investigate region-dependent changes in collagen, proteoglycan and mineral distribution, as well as collagen orientation, across the ligament-to-bone insertion site using Fourier transform infrared spectroscopic imaging (FTIR-I). Insertion site-related differences in matrix content were also evaluated by comparing tibial and femoral entheses. Both region- and site-related changes were observed. Collagen content was higher in the ligament and bone regions, while decreasing across the fibrocartilage interface. Moreover, interfacial collagen fibrils were aligned parallel to the ligament-bone interface near the ligament region, assuming a more random orientation through the bulk of the interface. Proteoglycan content was uniform on average across the insertion, while its distribution was relatively less variable at the tibial compared to the femoral insertion. Mineral was only detected in the calcified interface region, and its content increased exponentially across the mineralized fibrocartilage region toward bone. In addition to new insights into matrix composition and organization across the complex multi-tissue junction, findings from this study provide critical benchmarks for the regeneration of soft tissue-to-bone interfaces and integrative soft tissue repair.
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Funding: This study was supported by the Wallace H. Coulter Foundation (HHL, www.whcf.org), Presidential Early Career Award (PECASE, HHL,
www.whitehouse.gov/administration/eop/ostp), NIH-NIAMS (AR052402, HHL and HSS Core Center Grant AR046121, ALB, www.nih.gov), and an NSF
graduate teaching fellowship (GK-12 0338329, JPS, www.nsf.gov). The funders had no role in study design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
The interface between soft tissue and bone is essential for
physiologic musculoskeletal motion, and serves to integrate
and minimize stress concentrations between distinct tissue
types. A functional interface with bone is especially important
for the Anterior Cruciate Ligament (ACL), the primary
tibiofemoral intra-articular ligament and joint stabilizer [1]. The
biomechanical functionality of the ACL is rooted in the
organized ligament structure, with biological fixation to bone
facilitated by complex fibrocartilaginous insertions into the
femur and tibia [13]. Specifically, the interface between ACL
and bone is divided into four distinct yet continuous tissue
regions, with region-specific distributions in cell type and matrix
composition [310]. The first region is the ligament proper, in
which fibroblasts reside in a matrix rich in types I and III
collagen. Contiguous with the ligament is the fibrocartilage
interface, which is subdivided into non-calcified and calcified
regions. The non-mineralized fibrocartilage (NFC) is composed
of fibrochondrocytes in a matrix consisting of types I and II
collagen, while hypertrophic chondrocytes within a type X
collagen-containing matrix are found in the mineralized
fibrocartilage (MFC) region, which finally transitions into bone.
This region-dependent matrix organization and the subdivision
of the interface into non-calcified and calcified regions lead to a
gradual increase in mechanical properties across the interface
regions, thereby minimizing stress concentrations and allowing
for effective load transfer from ligament to bone [3,11,12].
This complex ligament-to-bone transition, however, is not
maintained or re-established following ACL reconstruction.
Absence of this functional interface may compromise graft
stability and long-term clinical outcome [1316]. Developing an
understanding of the structure-functi (...truncated)