Front Matter

68 Canine Sports Medicine and Rehabilitation

(Sharpey’s fibers) that blend with the perios­
teum and are anchored directly into cortical
bone. Fibrocartilaginous entheses contain a
zone of fibrocartilage at the tendon or ligament
attachment site that serves as a transition zone
between the parallel collagen fibers of the ten­
don/ligament and the bone matrix (Figure 3.21).
As in the deeper zones of articular cartilage,
enthesial fibrocartilage contains deep mineral­
ized and more proximal nonmineralized
regions that are separated by a tidemark.
The interface between the bone matrix and the
deep mineralized zone of the enthesial fibrocar­
tilage has an irregular and wavy configuration
that presents an extensive surface area along
which collagen fibrils cross to merge with the
bone matrix.
Entheses form a transition between two
structures (tendon/ligament and bone) that dif­
fer greatly in mechanical properties and that are
adapted to resist different forms of loading (ten­
sile loads for tendon/ligament, and compressive
loads for bone) (Thomopoulos et  al., 2003).

Entheses are also subjected to multidirectional

stresses since conditions of load are often pre­

sent throughout the full range of motion of an

associated joint. The structure of fibrocartilagi­

nous entheses in particular has evolved to dis­

sipate the complex stresses that would otherwise

concentrate at the osteotendinous or osteoliga­

mentous interface. The complex patterns of

loading and high‐intensity stresses that occur at

many entheses during locomotion underlie the

susceptibility of these structures to both acute

injury and chronic pathology (Shaw & Benjamin,

2007; Slobodin et al., 2007).

Figure 3.21 Histological appearance of a
fibrocartilaginous enthesis. Collagen fibers within the
body of the tendon (T) transition through a zone of
fibrocartilage before intercalating into the collagen
structure of the bone matrix (B). Multiple tidemarks
(white arrow) and chondrocytes isolated with lacunae
(black arrow) are present within the fibrocartilage zone.

Case Study 3.2 Calcanean tendon repair

Signalment: 4 y.o. F/S Chesapeake Bay Retriever.

Presented for evaluation of right pelvic limb

lameness.

History: Patient showed intermittent performance

deficits while hunting for 3 months; lameness

worsened acutely during recent training.

Examination: II‐III/IV right pelvic limb lame with

plantigrade stance, 170‐degree standing angle at

stifle. Right calcanean tendon thick and mildly

painful on palpation just proximal to insertion.

Ultrasonographic examination: fiber disorganiza-

tion consistent with tendon rupture and

enthesiopathy.

Treatment: Surgical reattachment of tendon to

calcaneus. For 12 weeks postoperatively, tarsus was

maintained in extension with dynamic supportive

bracing. Patient received regular hydrotherapy. Site

treated daily with low‐level laser. Low‐intensity

pulsed ultrasound treatment once every 3 days.

Local injections of platelet‐rich plasma performed

at 1, 2, and 4 weeks postoperatively. Six months

postop., patient’s function improved; however,

lameness developed consistently after moderate

exercise. Standing angles of stifle and tarsus:162

and 129 degrees, respectively. The gastrocnemius

insertion remained palpably thick.

Discussion: This case highlights the extraordinary

difficulty associated with management of enthesial

disruptions. Fibrocartilaginous entheses are highly

specialized structures that dissipate multidirec-

tional stresses at osteotendinous junctions. Surgical

reattachment of tendons produces a mechanically

inferior fibrous enthesis that is incapable of resist-

ing large and complex osteotendinous loads.