Although epidemiology and clinical history can help to distinguish strains of the soleus and gastrocnemius, it is the physical exam that allows us to isolate the site and severity of injury. To localize strains to the gastrocnemius or soleus, a combination of palpation, strength testing, and stretching is required.
Palpation of the calf should occur along the entire length of the muscles and the aponeuroses. It is necessary to identify tenderness, swelling, thickening, defects, and masses if present. Gastrocnemius strains typically present with tenderness in the medial belly or the musculotendinous junction. In soleus strains the pain is often lateral . A palpable defect in the muscle helps in localization and suggests more severe injury.
The origin of the gastrocnemius and soleus are anatomically distinct arising from above and below the knee respectively. This allows the examiner to isolate the activation of the muscles by varying the degree of knee flexion. With the knee in maximal flexion the soleus becomes the primary generator of force in plantar flexion. Conversely with the knee in full extension the gastrocnemius provides the greater contribution . This relationship allows for more accurate strength testing of the individual calf muscles and enables the clinician to better delineate which muscle has been injured.
A similar approach is used to test pain and flexibility with passive ankle movements and stretching. In this case, the knee is again placed in maximal extension and then subsequently in flexion while the ankle is passively dorsiflexed to cause relative isolated stretch of the gastrocnemius and soleus respectively. Use of this technique for clinical isolation of the gastrocnemius and soleus is key to determining the site of injury and guiding rehabilitate stretching and strengthening exercises as described below.
Additional testing that can be used during evaluation of calf strain includes the Thompson test for complete disruption of the Achilles tendon, circumferential calf measurements to quantify asymmetry and functional movements. These movements may include hopping, running, and jumping in order to illicit more sublet calf muscle dysfunction.
It should be noted that concomitant tears of both the soleus and gastrocnemius are possible. This can complicate the clinical picture. Coexisting strains of the gastrocnemius and soleus were found in 17% of calf strains in one radiology study .
Although a diagnosis can usually be made on clinical grounds as outlined above, the use of imaging can help if the diagnosis is in doubt. Imaging may also be useful in diagnosis and grading of calf injuries in elite athletes because of unique financial and strategic consequences of return to play decisions .
Except in rare situations, MRI and musculoskeletal ultrasound (MSK US) are the two choices for imaging. Both can be used to confirm strain, localize the injured muscle and determine extent of injury. Screening MRI usually consists of T1 and T2 series with occasional addition of fluid sensitive fat suppressed sequences. Contrast agents are not routinely recommended [5, 12].
MSK US is preferred by some institutions and authors [5, 8]. It may be particularly useful when used as part of the initial clinical exam by the sports medicine physician when severe pain and swelling limit clinical testing. Ultrasound may also be valuable in early triage of calf injuries or complaints when a wider differential is in play. Ultrasound has advantages of cost, portability, speed, and ease of use compared to MR when in the hands of an experienced operator.