Sports-related lower limb muscle injuries: pattern recognition approach and MRI review

Abstract

Muscle injuries of the lower limbs are currently the most common sport-related injuries, the impact of which is particularly significant in elite athletes. MRI is the imaging modality of choice in assessing acute muscle injuries and radiologists play a key role in the current scenario of multidisciplinary health care teams involved in the care of elite athletes with muscle injuries. Despite the frequency and clinical relevance of muscle injuries, there is still a lack of uniformity in the description, diagnosis, and classification of lesions. The characteristics of the connective tissues (distribution and thickness) differ among muscles, being of high variability in the lower limb. This variability is of great clinical importance in determining the prognosis of muscle injuries. Recently, three classification systems, the Munich consensus statement, the British Athletics Muscle Injury classification, and the FC Barcelona-Aspetar-Duke classification, have been proposed to assess the severity of muscle injuries. A protocolized approach to the evaluation of MRI findings is essential to accurately assess the severity of acute lesions and to evaluate the progression of reparative changes. Certain MRI findings which are seen during recovery may suggest muscle overload or adaptative changes and appear to be clinically useful for sport physicians and physiotherapists.

Keywords: Athletic injuries; Magnetic resonance imaging; Muscle; Prognosis; Return to sport.

Fig. 1

Hamstring complex muscles showing the distribution of connective tissue in each muscle belly. a Frontal view of the hamstrings (BFlh, biceps femoris long head; ST, semitendinosus; BF: biceps femoris). b Coronal section of the semitendinosus. c Open lateral view of the biceps femoris (MTJ, myotendinous junction). d Axial section of the distal part of the biceps femoris. e Coronal section of the semimembranosus (MCJ, myoconnective junction)

Fig. 2

Diagram of the distribution of connective tissue in the rectus femoris. The proximal connective tissue is distributed into the central septum, the anterior aponeurosis, and the anterior fascia; the posterior aponeurosis/fascia is an extension of the distal tendon. Axial sections (left); sagittal section (right)

Fig. 3

Diagram of the distribution of connective tissue in the soleus identifying medial and lateral fascicles, central septum and aponeurosis (coronal and axial section); only the central septum reaches the posterior aponeurosis (sagittal sections)

Fig. 4

MRI findings and patterns in acute muscle injuries of the lower limb. Tendon injuries showing elongation without a measurable tear (a1), longitudinal tear (a2), and total transverse tear with marked tendon retraction (a3). Peripheral myoaponeurotic/myofascial/myotendinous injuries showing intact aponeurosis (b1), fascial tear (b2), and tendinous complete section with hematoma and retraction (b3). Central myotendinous (septal) injuries showing intact septum (c1), fiber gap of the septum (c2), and total septal tear with loss of tension (c3). Injuries of isolated muscle fibers without disruption (d1) with architectural distortion or blurring (d2), or with measurable tear (d3)

Fig. 5

Proximal lesions of the rectus femoris. Fluid-sensitive MRI sequences showed (a) gap of the central septum with edema and loss of the pennation angle of the muscle fibers of myoconnective anchor center (axial and coronal images); gap of the aponeurosis (arrows) with interfascicular and intermuscular hemorrhage (b) (axial and sagittal images); discontinuity of the connective tissue of lesser thickness (dashed arrows) with peripheral fluid and fiber gap in the anchorage of peripheral myoconnective fibers (c) (axial and sagittal images)

Fig. 6

In the soleus, axial MR images in fluid-sensitive sequences of four different patients show edema surrounding the connective tissue injured and its discontinuity (arrows) involving different structures: (a) the posterior aponeurosis, (b) central septum, (c) medial fascicle, and (d) lateral fascicle

Fig. 7

Axial MR images in fluid-sensitive sequences in distal myoconnective injuries of the semimembranosus muscle showing muscular edema (arrows) at different levels (a and b). Edema in the deep (short arrow, c) and superficial (dashed arrow, d) zippers of the femoral biceps

Fig. 8

Axial and coronal/sagittal MR images in fluid-sensitive sequences of the proximal hamstring complex tendon. a Complete apophyseal avulsion fracture of the right ischial tuberosity with severe increase of the signal intensity at the avulsion site (dashed circles). b Complete transverse tear (dashed arrows) of the common tendon of the biceps femoris and the semitendinosus with thickening and distal retraction. c Complete avulsion of the semimembranosus proximal tendon (short arrows) with retraction. d Mixed partial rupture of the semimembranosus proximal tendon

Fig. 9

Coronal and axial MR images in fluid-sensitive sequences of the long head of the biceps femoris tendon. a Partial mixed disruption (arrows), predominantly longitudinal without loss of tendon tension. b Complete disruption with loss of tendon tension (wavy morphology, dashed short arrows), extensive interstitial edema, and intermuscular fluid

Fig. 10

Intramuscular isolated injuries of the rectus femoris. Axial and coronal/sagittal MR images in fluid-sensitive sequences. a Marginal or paraseptal muscular edema with gap of the muscle fibers (circles). b Edema, fiber distortion, and areas of tear surrounding the central septum (short arrows) without retraction. c Circumferential pattern of fibers rupture encompasses the entire central septum with loss of its tension (large arrows)

Fig. 11

Evolution of healing by MRI over a course of 15 days: hamstring myotendinous junction. Axial fluid-sensitive images at 24 h (a), 8 days (b), and 15 days (c). At 8 days, the soft scar is present with centripetal growth although with reparative pericicatricial edema that remains at 15 days (b and c, arrows)

Fig. 12

Evolution of healing by MRI over a course of 12 weeks: rectus femoris central myoconnective junction. Axial T1- and fluid-sensitive images at 1–2 weeks (a), 9 weeks (b), and 12 weeks (c) show progressive reduction of edema. a MR images show a soft fragmented callus (dashed arrow). b MR images show the callus organized and complete. It is hypertrophic, hypointense in fluid-sensitive image, and slightly heterogeneous in T1 (arrows). c MR images show a complete recovery of the tendon and peripheral musculature signal

Fig. 13

Evolution of healing by MRI over a course of 8 weeks: soleus with common aponeurosis, a normal anatomical variant, myoconnective junction. Axial T1- and fluid-sensitive images at 24 h (a), 4 weeks (b), and 8 weeks (c). a MR images show an extensive initial lesion with several foci of rupture of the lateral portion of the common aponeurosis (arrowheads). b MR images show an hypertrophic soft scar (dashed circle). c MR images show a medial re-injury in the common aponeurosis (dashed arrow)

Fig. 14

Muscle signal changes in muscle fibers, adaptive or by overload, in the recovery from distal myoconnective injury of the femoral biceps and the rectus femoris. a Axial and sagittal fluid-sensitive images show areas of hyperintensity of muscle fibers adjacent to scar in the form of feathery peritendinous interstitial edema (arrows) suggesting overload. b Axial fluid-sensitive image shows area of slightly hyperintensity of muscle fibers adjacent to scar in the form of cotton-like edema pattern (DOMS, dashed circle) suggesting adaptation