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Cited by 398Knee injuries and reconstruction techniquesTendon Structure and TreatmentOsteoarthritis Treatment and Mechanisms

Histological Changes in the Human Anterior Cruciate Ligament After Rupture*

MURRAY, M. M., MARTIN, S. D., MARTIN, T. L., SPECTOR, M.·2000·The Journal of Bone and Joint Surgery-American Volume
DOI 10.2106/00004623-200010000-00004
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Abstract

BACKGROUND: Four phases in the response to injury of the ruptured human anterior cruciate ligament are observed histologically; these include an inflammatory phase, an epiligamentous repair phase, a proliferative phase, and a remodeling phase. One objective of this study was to describe the histological changes that occur in the ruptured human anterior cruciate ligament during these phases. Myofibroblast-like cells that contain alpha-smooth muscle actin are present in the midsubstance of the intact human anterior cruciate ligament. A second objective of this study was to determine whether an increased number of myofibroblast-like cells is found in the midsubstance of the ruptured human anterior cruciate ligament because it was thought that those cells might be responsible in part for the retraction of the ruptured anterior cruciate ligament. In the early phase of this study, it was found that the number of myofibroblast-like cells in the midsubstance of the ruptured anterior cruciate ligament was actually decreased, and this hypothesis was abandoned. During the epiligamentous repair phase, synovial tissue was formed that covered the ends of the ruptured anterior cruciate ligament. Most of the synovial lining cells were myofibroblast-like cells that contained alpha-smooth muscle actin. The primary objective of this study was to determine the location and the characteristics of the alpha-smooth muscle actin-containing myofibroblast-like cells that appear in the human anterior cruciate ligament following rupture. METHODS: Twenty-three ruptured and ten intact human anterior cruciate ligaments were evaluated for cellularity, nuclear morphology, blood vessel density, and percentage of cells containing a contractile actin isoform, alpha-smooth muscle actin. The histological features of the synovial and epiligamentous tissues were also described. RESULTS: At no time after rupture was there evidence of tissue-bridging between the femoral and tibial remnants of the anterior cruciate ligament. The ruptured ligaments demonstrated a time-dependent histological response, which consisted of inflammatory cell infiltration up to three weeks, gradual epiligamentous repair and resynovialization between three and eight weeks, and neovascularization and an increase in cell number density between eight and twenty weeks. Compared with the intact ligaments, there was a decrease in the percentage of myofibroblast-like cells containing alpha-smooth muscle actin within the remnant of the ligament. However, many of the epiligamentous and synovial cells encapsulating the remnants contained alpha-smooth muscle actin. CONCLUSIONS: After rupture, the human anterior cruciate ligament undergoes four histological phases, consisting of inflammation, epiligamentous regeneration, proliferation, and remodeling. The response to injury is similar to that reported in other dense connective tissues, with three exceptions: formation of an alpha-smooth muscle actin-expressing synovial cell layer on the surface of the ruptured ends, the lack of any tissue bridging the rupture site, and the presence of an epiligamentous reparative phase that lasts eight to twelve weeks. Other characteristics reported in healing dense connective tissue, such as fibroblast proliferation, expression of alpha-smooth muscle actin, and revascularization, also occur in the ruptured human anterior cruciate ligament. CLINICAL RELEVANCE: Unlike extra-articular ligaments that heal after injury, the human intra-articular anterior cruciate ligament forms a layer of synovial tissue over the ruptured surface, which may impede repair of the ligament. Moreover, a large number of cells in this synovial layer and in the epiligamentous tissue express the gene for a contractile actin isoform, alpha-smooth muscle actin, thus differentiating into myofibroblasts. These events may play a role in the retraction and lack of healing of the ruptured anterior cruciate ligament.

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Authors
MURRAY, M. M., MARTIN, S. D., MARTIN, T. L., & SPECTOR, M.
Affiliations
Brigham and Women's Hospital (US)
ORCID
Venue
The Journal of Bone and Joint Surgery-American Volume
Publisher
Ovid Technologies (Wolters Kluwer Health)
Published
2000-10
Volume
82
Issue
10
Pages
1387-1397
ISSN
0021-9355 (ISSN-L)
DOI
10.2106/00004623-200010000-00004
OpenAlex
W2232494399
Cited by
398
References
34
Citations by year
2026: 12 · 2025: 24 · 2024: 23 · 2023: 11 · 2022: 19 · 2021: 17 · 2020: 28 · 2019: 24 · 2018: 12 · 2017: 25 · 2016: 17 · 2015: 14 · 2014: 19 · 2013: 28 · 2012: 17
FWCI
5.77
Type
journal article
Language
en
Open access
closed
Locations
  • Journal of Bone and Joint Surgery (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Health Sciences › Medicine › Surgery › Knee injuries and reconstruction techniques
  • Health Sciences › Medicine › Orthopedics and Sports Medicine › Tendon Structure and Treatment
  • Health Sciences › Medicine › Rheumatology › Osteoarthritis Treatment and Mechanisms
Keywords
anterior cruciate ligament rupture, ligament healing, myofibroblast-like cells, alpha-smooth muscle actin, synovial lining, neovascularization, inflammatory phase, proliferative phase, ligament histology, cellularity, blood vessel density
MeSH terms
Anterior Cruciate Ligament Injuries, Actins, Adult, Female, Humans, Immunohistochemistry, Male, Rupture, Synovial Membrane, Time Factors, Wound Healing, Anterior Cruciate Ligament, Neovascularization, Physiologic

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