Tendon
Tendons attach muscle to bone and are composed of dense, regularly arranged fascicles, or groups of collagen bundles. The fascicles are surrounded by an epitenon and are closed within the paratendon (tendon sheath). The predominant cells are fibroblasts producing mostly type I collagen (85 per cent dry weight of tendon). Tendons transmit load from muscles to the bone and the collagen fibres tend to orientate themselves along stress lines. The collagen laid down in a healing tendon initially has a haphazard arrangement but when subjected to physiological strains the orientation returns to normal, with restoration of the mechanical properties of the tendon.
Tendon pathology may be divided into three types:
• paratendinitis;
• paratendinitis with tendinosis;
• pure tendinosis.
Paratendinitis
is inflammation of the investing paratenon and may be diagnosed by eliciting
tenderness around the full circumference of the tendon, the site of which does
not move with the underlying tendon (Fig. 29.4). It is an extremely painful
condition. Paratendinitis usually responds well to anti-inflammatory medication,
local physical therapies such as friction massage and ultrasound, and
occasionally an injection of local anaesthetic and corticosteroid into the
paratenon (not into the tendon itself). If the paratendinitis becomes
chronic it may be necessary to strip surgically the injured paratenon from the
tendon.
Tendinosis is a more sinister condition
both to diagnose and to treat. It is usually asymptomatic and is present in an
increasing proportion of all tendons with advancing age. The term covers a wide
variety of pathological processes: hyaline degeneration, a decrease in the
normal cell population and alterations in the matrix.
Treatment
for tendinosus is difficult and patients should be warned against the likelihood
of a ‘quick fix’. Physical therapies aimed at improving the blood supply
to the degenerate areas are only moderately successful. Rehabilitation
programmes
should start with complete rest and only progress within the limits of pain.
More recently the emphasis has been on eccentric loading and enhanced
proprioceptive feedback to improve tendon healing. Surgical treatment for
tendinosis is controversial but a distinction should be made between surgery to
remove aggravating mechanical factors, for example subacromial decompression of
the rotator cuff tendon, which has a good success rate, and surgery to the
tendon itself which is less rewarding. However, encouraging results have been
obtained after percutaneous, longitudinal tenorrhaphy of the Achilles tendon,
although the risk of precipitating tendon rupture is always present.
Tendon
rupture
Rupture is the end point of tendinosis in that there is histological
evidence of degeneration present within every tendon that has ruptured. It seems
that closed injury cannot rupture a normal tendon, failure always
occurring at the musculotendinous junction in this instance.
The
principles of treatment of a ruptured tendon are similar to those for treating
fractures, namely to restore anatomy and maintain it whilst healing occurs.
Tendon ends need to be apposed in order to minimise the gap that must be bridged
by fibrous tissue. The larger the gap the greater the volume of scar tissue
which has inferior biomechanical properties. A large tendon gap also decreases
muscle strength by lengthening the musculotendinous unit and reducing the
efficiency of its contractions.
Plantar flexing
the ankle usually brings the tendon ends together after rupture of the Achilles
tendon. Failure to produce tendon apposition may account for the relatively high
rate of tendon re-rupture and weakness of calf muscle power in nonoperatively
treated patients. In several instances the tendon ends can never be apposed by
closed means; examples of this include rupture of the distal insertion of the
biceps tendon on to the radial tuberosity and tears of the rotator cuff tendon.
Surgery is then required to restore the anatomy whilst preserving the blood
supply wherever possible. One advantage of surgical repair of a ruptured tendon
is that a graduated rehabilitation programme to maintain muscle function and
joint range of motion can be started within a week of surgery.