Laboratory Studies
Hamstring strain is diagnosed primarily by physical examination and history. Lab studies are not of significant assistance in making the diagnosis.
Imaging Studies
The diagnosis is typically clinical, but some imaging studies may helpful if the clinical picture is unclear. [11]
Radiographs can rule out an avulsion injury from the ischial tuberosity or other fractures, but they generally are not otherwise of significant help.
Ultrasonographic studies may aid the physician when confirming the diagnosis of hamstring strain, but they do not always indicate definitive results. The quality of the study is related to the expertise of the technician and the cooperation of the patient.
When a confirmation or grading of a hamstring strain is necessary, magnetic resonance imaging (MRI) is the most sensitive test used when considering the diagnosis of hamstring strain, but it should be used sparingly because of the cost and patient discomfort. [3] Some data suggest that MRI is helpful when attempting to predict return in a high-performance athlete in combination with supporting clinical evidence. Studies have shown that more than 6 weeks' delay before return to sport has been reported with the following:
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Complete transection
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Involvement of 50% of cross-sectional muscle
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Ganglionlike fluid collections
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Hemorrhagelike signal
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Distal myotendinous tears
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Deep muscle tears
Other Tests
For higher-level athletes, isokinetic muscle-strength testing may quantify muscle weaknesses or imbalances that may lead to a chronic injury or recurrence. [12]
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Normal sagittal alignment permits the knee to lock in full extension, aided by powerful quadriceps and an intact extensor mechanism. The ground reaction force passes anterior to the "center of rotation" of the knee, while the posterior cruciate ligament, posterior capsule, hamstrings, and gastrocnemius provide a tension band effect.
