CHAPTER 10 • MUSCLE AND TENDON INJURY AND REPAIR 59- The insertion of tendons onto bone is usually via four
zones: tendon, fibrocartilage, mineralized fibrocarti-
lage, and bone.
•Tendons that bend at acute angles (flexor tendons in
the hand) are enclosed in a distinct sheath that acts as
a pulley (Wood et al, 2000). Synovial fluid within the
sheath assists in tendon gliding. Tendons that are not
enclosed in a sheath (Achilles tendon) are covered by
a paratenon.
•Mechanical forces affect the characteristics of tendon.
Tendons subjected to tensile loads have smaller
densely packed collagen fibrils, increased collagen
synthesis, smaller proteoglycans (Decorin), and a
higher collagen to proteoglycan ratio. Tendons sus-
taining compressive loads exhibit increased proteo-
glycan levels, larger proteoglycan molecules, and
larger less dense collagen fibrils (Hyman and Rodeo,
2000). - Aging also affects the material characteristics of
tendon with decreased collagen synthesis, increased
collagen fibril diameter, decreased proteoglycan con-
tent, decreased water content, and decreased vascular-
ity. This results in a stiffer, weaker tendon (Hyman
and Rodeo, 2000).
CHRONIC TENSILE OVERLOAD INJURIES
TERMINOLOGY
- There is significant confusion regarding the terminology
of chronic tendon injuries. Tendinitis, tendonitis, and
tendinosis are frequently used terms to describe the clin-
ical picture of pain, swelling, and stiffness in a tendon.
•Terminology based on pathology has been proposed
(Jarvinen et al, 1997):
a. Paratenonitis: Inflammation of the paratenon or
tendon sheath. Peritendinitis and tenosynovitis are
included in this category.
b. Paratenonitis with tendinosis: Tendon degeneration
with concomitant paratenon inflammation
c. Tendinosis: Tendon degeneration without inflam-
mation
d. Tendinitis: Inflammation within the tendon - Tendinopathyhas been proposed as a generic term
describing the clinical picture of pain, swelling, and
impaired performance (Maffulli, Kahn, and Puddu,
1998).
ETIOLOGY
- The etiology of chronic tendon injuries is multifacto-
rial and involves a combination of intrinsic and extrin-
sic factors.
•Important intrinsic factors include anatomic abnor-
malities(malalignment, muscle weakness/imbalance,
decreased flexibility, and joint laxity), age, gender,
weight, and predisposing diseases (Almekinders,
1998; Kannus, 1997).
•Important extrinsic factors include excessive mechan-
ical load (frequency, duration, and intensity), training
errors (over training, rapid progression, fatigue, run-
ning surface, and poor technique), and equipment
problems (footwear, racquets, and seat height)
(Almekinders, 1998; Kannus, 1997).- There are very few well-controlled studies that exam-
ine the etiologic factors involved in chronic tendon
injuries.
PATHOPHYSIOLOGY- Repetitive load on a tendon that results in 4–8% strain
causes microscopic tendon fiber damage. Continued
load on the tendon at this level overwhelms the
tendon’s ability for repair. Damage occurs to the col-
lagen fibrils, the noncollagenous matrix, and
microvasculature (Hyman and Rodeo, 2000). - Cellular damage results in inflammation of the sur-
rounding paratenon (paratenonitis). Tissue edema,
fibrin exudate, and capillary occlusion result in local
tissue hypoxia. Audible crepitation may be noted on
examination (Kannus, 1997). - The paratenon becomes thickened as fibroblast prolif-
eration and fibrotic adhesions develop. This results in
decreased tendon gliding and triggering. - Intrinsic tendon damage (tendinosis) may occur with
continued tendon overload. Tendon degeneration may
appear as a number of histologic entities (hypoxic
degeneration, mucoid degeneration, fiber calcifica-
tion, and the like) (Kannus, 1997). - The causal link between initial inflammation (paratenon-
itis) and tendon degeneration (tendinosis) is unclear.
Researchers have demonstrated that chronic paratenoni-
tis can result in tendon degeneration in an animal model
(Backman et al, 1990); however, a large clinical study
showed no previous evidence of paratenonitis in over
60% of patients who sustained an Achilles tendon rup-
ture (Kannus and Jozsa, 1991). The initial paratenonitis
may be causative factor for tendon degeneration or may
coexist independently. - The exact cellular mechanism of tendon degeneration
has not been completely defined. Important factors
include tissue hypoxia, free radical induced tendon
damage, and tissue hyperthermia (Kannus, 1997).
DIAGNOSIS- The history often reveals repetitive mechanical over-
load. The athlete will usually be involved in either an
endurance sport (running, cycling, and swimming) or
a sport that requires repetition of a specialized skill
(tennis, basketball, and baseball) (Hess et al, 1989).