Muscle strain is one of the most common sports and occupational injuries, and ultrasound is often the first imaging performed — it's fast, dynamic, and unlike MRI can be repeated cheaply to track healing. The muscle belly and myotendinous junction are also genuinely different territory from the tendon-focused scans covered elsewhere: tendons fail at their insertion or midsubstance; muscle characteristically fails at the myotendinous junction, where the mechanical properties of muscle and tendon meet and diverge.

Where Muscle Actually Tears

The myotendinous junction is the site of most muscle strains — mechanically, it's where stiffer tendon meets more compliant, extensible muscle, and that mismatch concentrates stress there during eccentric loading. Classic examples: the hamstring near its origin or at the myotendinous junction mid-belly, the medial gastrocnemius ("tennis leg"), and the rectus femoris.

Timing changes the appearance. An injury scanned within hours looks different from the same injury scanned at 48–72 hours, when hemorrhage has organized and edema has fully developed. If possible, know how long ago the injury occurred before interpreting what you see — a "milder-looking" very acute strain can still evolve into a more significant-appearing injury over the following day or two.

Technique

Probe: High-frequency linear, 7–15 MHz for most superficial muscles; consider a curvilinear probe for deeper muscles in a larger patient, such as the proximal hamstring in a well-muscled athlete.

Position and technique: Scan in both longitudinal and transverse planes through the area of point tenderness, extending well beyond the symptomatic area to assess the injury's full extent — strains are often larger than the palpable tender zone suggests.

Dynamic assessment: Ask the patient to gently contract the muscle while scanning. A partial tear often shows the disrupted fibers separating or fluid within the defect shifting with contraction — genuinely useful for confirming a subtle finding and for assessing functional continuity of the muscle.

Compare to the contralateral side when the diagnosis or extent is uncertain — muscle echotexture and thickness vary enough between individuals that a comparison view is often the difference between a confident and an equivocal call.

Grading System

Most commonly used is a three-tier grading system, sometimes further divided:

Grade	Description	Sonographic findings
Grade I	Mild strain, minimal fiber disruption	Normal or subtly heterogeneous echotexture, mild perifascial fluid, no discrete fiber discontinuity
Grade II	Partial tear	Partial disruption of muscle fibers, a hematoma or hypoechoic gap at the tear site, some fibers remain intact
Grade III	Complete rupture	Complete discontinuity of the muscle, often with retraction of the torn ends and a large intervening hematoma

Some systems add a Grade 0 for a muscle that is clinically symptomatic (delayed-onset soreness, mild strain symptoms) but sonographically normal — a genuinely common and useful category, since a normal scan in a symptomatic athlete is itself clinically informative and should be reported as a real finding, not a non-diagnostic study.

What to Measure and Describe

Length and width of the tear — the craniocaudal extent of fiber disruption, and its width in the transverse plane.

Percentage of muscle cross-sectional area involved — a tear through 10% of the cross-section behaves very differently than one through 70%, and this is one of the more clinically actionable numbers you can provide.

Hematoma size, measured in three dimensions if possible — larger hematomas are associated with longer recovery, and serial size is a genuinely useful thing to track.

Retraction distance, for a complete tear — the gap between the two retracted muscle ends, measured with the muscle relaxed. This number matters directly for surgical planning when repair is being considered, most classically for a complete proximal hamstring avulsion.

Location relative to the myotendinous junction — proximal, mid-substance, or distal — since location affects both prognosis and, for certain muscles, treatment approach.

Specific Muscles Worth Knowing

Hamstring (biceps femoris, semitendinosus, semimembranosus): The most commonly strained muscle group in sprinting sports. The biceps femoris long head is most frequently involved. A proximal tear near the ischial tuberosity with significant retraction is the pattern most likely to prompt a surgical referral — measure retraction distance explicitly whenever this pattern is seen.

Medial gastrocnemius ("tennis leg"): Classically a tear at the myotendinous junction between the medial gastrocnemius and the underlying soleus aponeurosis, presenting as sudden calf pain, often during push-off. Always assess the deep veins of the calf in this presentation — the clinical picture can closely mimic DVT, and the two can coexist, since local hematoma and immobility both raise clot risk in the injured leg.

Rectus femoris: Prone to a specific and important variant — a central tendon (intramuscular) tear, where the injury occurs around the muscle's central aponeurosis rather than at the surface myotendinous junction. This pattern can look deceptively contained on a cursory scan while representing significant injury; scan the full course of the central tendon deliberately.

Adductor longus: Common in kicking and change-of-direction sports, typically strained near its proximal origin at the pubic bone. Note any adjacent pubic bone irregularity, which can suggest an associated osteitis pubis component in a patient with a longer symptom history.

Complications to Look For

Intramuscular hematoma vs. developing seroma or myositis ossificans: An organizing hematoma can develop peripheral calcification over 2–6 weeks, an early sign of myositis ossificans — worth specifically screening for on any follow-up scan of a significant hematoma, since it changes rehabilitation timing.

Compartment syndrome (rare but urgent): A large, rapidly expanding hematoma with significant swelling and pain out of proportion to exam findings should prompt immediate communication with the clinical team — this is a surgical emergency that ultrasound can help flag but never definitively excludes.

Re-injury at a prior scar: A previously injured muscle is at elevated risk of re-tear at the same site — note prior injury history and look specifically at the old injury location, which often shows persistent architectural change (scarring, mild fibrosis) that can be mistaken for new injury if the baseline isn't known.

Key Images to Capture

Longitudinal view through the injury site, with length of disruption measured
Transverse view at the widest point of the tear, with width and percentage cross-sectional involvement noted
Hematoma measured in two or three dimensions
Retraction distance, if a complete tear, with the muscle relaxed
Dynamic clip during gentle contraction, if performed
Contralateral comparison image, if obtained
Deep venous assessment of the calf, specifically for suspected medial gastrocnemius injury

Reporting Language

Grade II strain: "Partial-thickness tear of the biceps femoris long head at the myotendinous junction, approximately 4.2 cm craniocaudally, involving roughly 40% of the muscle cross-sectional area at its widest point. A 2.8 × 1.4 cm intramuscular hematoma is present at the tear site. Remaining muscle fibers are intact. Findings consistent with a Grade II hamstring strain."

Grade III with retraction: "Complete discontinuity of the medial gastrocnemius at the myotendinous junction with the soleus aponeurosis, with approximately 2.1 cm of retraction of the proximal muscle belly with the leg in a relaxed, neutral position. A large surrounding hematoma measures 6.3 × 3.1 × 2.8 cm. Deep veins of the calf are patent and compressible without evidence of thrombosis. Findings consistent with a complete ('tennis leg') myotendinous tear."

SonoBuddy is a reference tool for sonographers. Return-to-play and treatment decisions belong with the treating clinician and, where relevant, a sports medicine specialist.

Muscle Injury Ultrasound: Grading Strains and Tracking Return to Play