In general skeletal muscle attaches to bone via a muscle tendon bone complex (figure 1),
the type of injury varies with age,
muscle and skeletal maturity,
type of sporting activity and mechanism of injury.
Intrinsic or Distraction Injuries:
Intrinsic or distraction injuries occur with forced muscle contraction and are common in running sports requiring sudden acceleration,
weightlifters and gymnasts (ref).
Injury occurs from sudden eccentric contraction while the muscle is being lengthened during activity.
Predisposing factors which increase risk of this type of injury include: muscle origin and insertion across two joints,
eg rectus femoris,
biceps femoris and medial gastrocnemius muscles: perform eccentric contraction and have a high percentage of fast twitch,
type II muscle fibres used in rapid acceleration.
The injury occurs at the myotendinous junction or along the internal aponeuroses.
There maybe a strain injury,
partial tear or complete muscle rupture.
(figure 2)
Apophyseal Injuries:
In children and adolescents the weakest link in the muscle-tendon-bone complex is the attachment of the tendon to the non-ossified cartilage of the apophysis.
(figure 3)
Sudden acute apophyseal injuries occur with violent traction tension applied to apophysis from sudden muscle contraction.
The apophysis can partially or completely detach,
occasionally with complete functional loss.
These injuries are most common in the adolescent pelvis and the majority involve the ischial tuberostiy,
anterior inferior iliac spine (AIIS) or anterior superior iliac spine (ASIS).
Pelvic hip apophysitis most commonly affects adolescents between 14 and 18 years of age and usually affects runners,
sprinters,
dancers and football players.
Diagnosis usually apparent on XR (figure 4) but can be diagnosed on US,
especially if occuring at an unexpected site (figure 5).
MRI may be helpful if the XR appearances are unusual (figure 6) or require further clarification (figures 7 & 8).
Occassionally CT may be employed if the injury is deemed to be more complex (figure 9).
Chronic Traction apophysitis results from repetitive traction trauma on the attachment of the tendon to the apophysis,
with no time for recovery from the insult before it happens again.
This leads to progressive insertional tendinopathy and microtears within the cartilage,
progressing to osteochondral fragmentation.
The knee is the most common site for traction apophysitis in adolescents,
with Osgood-Schlatter's occuring at the distal patella tendon insertion (figure 10) on the tibial tuberosity apophysis and Sinding-Larsen Johansson syndrome at the proximal origin of the tendon form the patella.
The pelvis is also a common location for chronic traction apophysitis,
which may follow non union of the avulsed bone (figure 11).
Tendon Injuries:
These injuries usually occur once the tendon attachment to the apophysis has fused,
frequently in older adults and acute tears are common in racquet sports.
Acute injury results in partial or full thickness tears that almost exclusively occur in tendons that are abnormal and tendinopathic with mucoid degeneration.
Partial thickness tears demonstrate incomplete disruption of tendon fibres and often extend to the tendon surface.
Complete full thickness tears involve the entire cross section of the tendon with retraction and a tenon gap filled with haematoma and debris.
(figure 12).
Chronic overuse tendinopathy is also more common in adults but may occasionally be seen in sporting children ( figures 12 &13).