Advances in the Canine Cranial Cruciate Ligament, 2nd edition

22 Structure and Function

Injury 1 3 5 7

MCL Edema

Angiogenesis

Macrophages Largest Wound Region

Myofibroblasts

VEGF

Total Cells

Hematopoietic Cells

Fibromodulin

Type III Collagen

Type I Collagen (↓↓) Type I Collagen (↓↓)

Proliferation

Remodeling

Hemostasis

Inflammation

Decorin (↓↓)

Apoptosis Apoptosis

Neutrophils Mitotic Cells

T-Lymphocytes

9

Days Post-Injury

Relative Level

11 14 21 28

Figure 3.1 Process of normal, extracapsular healing by the rat medial collateral ligament. Healing involves three
complex and overlapping processes, including hemostasis and inflammation, proliferation, and remodeling. Hemostasis
and inflammation involves clot formation and the infiltration of inflammatory cells, such as neutrophils, macrophages
and T lymphocytes, immediately after injury. Proliferation is characterized by the formation of granulation tissue,
including fibroblast proliferation and angiogenesis. Remodeling is the final phase and involves cell number reduction
and scar formation. Source: Chamberlainet al. 2009. Reproduced with permission from John Wiley & Sons, Inc.

of healing and follows proliferation. The earlier
infiltration of fibroblasts, inflammatory cells,
and endothelial cells diminish to basal levels
during this stage (Chamberlainet al. 2009). This
phase of healing lasts many months in liga-
ments and results in scar-like neo-ligamentous
tissue that can still be found two years post
injury (Franket al. 1983). The cellular profile of
the remodeling ligament is somewhat similar
to uninjured tissue compared to the previous
inflammatory or proliferative phases, but
complete functional recovery may never occur.
With or without surgical intervention, the
injured MCL will heal, but it results in tissue
that is more scar-like than the native tissue and
is mechanically inferior.

Healing potential of the completely

ruptured CrCL

Unlike the extracapsular MCL, the intracapsu-

lar CrCL does not heal without early surgical

intervention. A native CrCL is a highly orga-

nized, dense connective tissue composed of

dense parallel collagen bundles, exhibiting bire-

fringence and crimping under polarized light

(Hayashiet al. 2003a). Small blood vessels and

fusiform- and ovoid-shaped fibroblasts sur-

round the collagen bundles. A synovial mem-

brane surrounds the CrCL and consists of dense

connective tissue, small fibroblasts, and some

adipocytes (Heffron & Campbell 1978; Hayashi

et al. 2003a). Healing phases are summarized