Recreational and competitive running is increasing in popularity worldwide and in all age groups, and running injuries are becoming more prevalent. Symptoms and clinical exam can be nonspecific and suggest a wide differential diagnosis. Imaging, especially MR, can help diagnose injury, determine the location, severity and extent of injury thereby providing prognostic information, exclude diagnoses, and help direct the type and timing of treatment, making it invaluable in the workup of the injured athlete. This session will help familiarize the participant of the common lower extremity injuries, relevant anatomy and pathogenesis of injury in track and field athletes and the MR imaging findings seen in these patients.
Recreational and competitive running is increasing in popularity worldwide and in all age groups, and running injuries are becoming more prevalent. Symptoms and clinical exam can be nonspecific and suggest a wide differential diagnosis. Imaging, especially MR, can help diagnose injury, determine the location, severity and extent of injury thereby providing prognostic information, exclude diagnoses, and help direct the type and timing of treatment, making it invaluable in the workup of the injured athlete.
Muscle and tendon injuries Lower extremity muscle injuries are common in runners. Muscles that cross two joints, have a high proportion of fast twitch/type II muscle fibers and undergo eccentric contraction are most prone to strain injury. There are three muscle-tissue interfaces susceptible to injury. The central intramuscular myotendinous junction that runs the length the muscle, the myotendinous junction at the end of the muscle – tendon unit, and the myofascial junction between the muscle and the overlying fascia1. The most commonly strained lower extremity muscles in runners include the hamstring muscle group, rectus femoris and gastrocnemius. An MR grading system for muscle injury describes grade 1 as feathery edema at the myotendinous junction, grade 2 as a focal myotendinous junction tear and grade 3 as a complete myotendinous junction tear. The hamstring muscle group extends the hip, flexes the knee, and is capable of explosive force. Hamstring injuries account for 50% of strain injuries in sprinters and 20% of injuries in middle distance and long-distance runners. Injuries can occur secondary to sudden hip flexion with knee extension which is common in sprinters. Strains can occur when rapid deceleration, acceleration, or changes in direction are required2. Tensile overload can result in acute injury which can occur anywhere along its length from its origin to its insertion and anywhere along the myotendinous junction3. The biceps femoris muscle is reported to be the most commonly strained muscle of the hamstring muscle group. The rectus femoris muscle flexes the hip and extends the knee. It is the only quadriceps muscle that crosses two joints and it eccentrically contracts in the early swing phase of sprinting4. Rectus femoris muscle strains are common in runners. Rectus tendon origin tear and tendinopathy can be seen in sprinters5. The gastrocnemius muscles play a role in “fast movements” such as running and jumping and as such have a higher proportion of fast twitch/type II muscle fibers6. Gastrocnemius muscles cross two joints and act to plantarflex the foot at the ankle and flex the knee. Rectus injuries at the myofascial junction (periphery) have been found to recover quicker than those involving the central tendon7.
Tendons may undergo degeneration as a result of chronic overuse; this is referred to as tendinosis or tendinopathy8. Regardless of location, MR imaging of tendinopathy reveals alterations in size (enlarged) and signal (increased within and around the tendon). This process of degeneration weakens the underlying tendon, predisposing it to tear. High hamstring tendinopathy is much less common than myotendinous strains and is an uncommon overuse injury in middle- and long-distance runners9. Achilles tendinopathy reportedly affects up to 11% of runners. The Achilles tendon is subject to both cyclic loading and torsional force with running10 ,experiencing a force of 6-8 times body weight at the end of the stance phase11.
Aponeurotic related injuries The iliotibial band (or tract) and the muscles associated with it transmit forces from the hip to the knee, assist in extension, abduction and lateral rotation of the hip and contribute to knee stability12. Overuse injuries resulting in traction related injury and tearing of the proximal iliotibial band are increasingly being recognized in athletes13, though pathology here may also be the result of acute trauma, degeneration, or inflammatory causes. Iliotibial band syndrome is a common cause of lateral knee pain in runners, and is thought be related to the repetitive friction of the iliotibial band over the lateral femoral condyle resulting in chronic inflammation and pain14. The plantar fascia (aponeurosis) plays an important biomechanical role in the static and dynamic stability of the longitudinal arch of the foot15. The central cord is the largest and most important biomechanically. The plantar fascia is best assessed on sagittal and coronal images of the ankle and is manifest as increased T2 signal and fascial enlargement on MR imaging; this is commonly accompanied by perifascial edema and reactive marrow edema at its calcaneal attachment. Focal tears in the fascia can also be detected on MR.
Stress injuries of bone Stress injuries of bone represent a spectrum of injuries which can progress from stress lesions to frank fractures. Cyclic submaximal loading of bone results in bone weakening secondary to osteoclastic bone resorption that outpaces osteoblastic new bone formation. With continued loading, trabecular microfractures and ultimately frank fractures can develop10. Stress fractures occur in up to 37% of runners 10 and are most common in the tibia, tarsal navicular, metatarsals, femur, fibula and pelvis16. MR imaging is can detect stress injuries in their early stages when intervention can prevent frank fractures from developing. High risk stress injuries require immediate diagnosis and aggressive treatment.
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