Muscle Injuries 15 Muscle Injuries 3 Jan L. Gielen, Philip Robinson, Pieter Van Dyck, Anja Van der Stappen, and Filip M. Vanhoenacker CONTENTS Box 3.1. US ● 3.1 Introduction 15 Best technique for diagnosis of strain and contusion 3.2 Anatomy, Ultrastructure and (Patho)physiology with ● Evaluation of the muscular ultrastructure Imaging Correlation 16 provides a good assessment of tear 3.3 Muscle Trauma 20 ● 3.3.1 Acute Muscle Injuries 20 Best technique for follow up of strain 3.3.1.1 Muscle Strain 20 3.3.1.2 Crush Trauma 27 3.3.2 Complications of Muscle Injury 30 Box 3.2. MRI 3.4 Delayed Onset Muscular Soreness (DOMS) 33 ● Best technique for detection of edema 3.5 Chronic Exertional Compartment ● Time dependent presentation of blood Syndrome 33 3.5.1 Defi nition, Clinical Presentation and degradation products Diagnosis 33 3.5.2 Imaging 33 3.6 Muscle Atrophy 34 Box 3.3. Standard radiography 3.7 Rhabdomyolysis 35 ● Main role is evaluation of maturity of myositis 3.8 Calcifi c Myonecrosis 35 ossifi cans and avulsion fractures 3.9 Muscle Herniation 36 ● Characteristic in calcifi c myonecrosis 3.10 Conclusion 36 Things to Remember 37 References 37 3.1 Introduction Skeletal muscle comprises the largest tissue mass in the body, accounting for 40–45% of body mass (Best and Garret 1994; Garrett and Best 1994). The J. L. Gielen, MD, PhD muscle-tendon unit (MTU) is, in essence, a mechani- Associate Professor, Department of Radiology, University cal system, that enables locomotion. Muscles are sub- Hospital Antwerp, Wilrijkstraat 10, 2650 Edegem, Belgium ject to traumatic processes that can compromise their P. Robinson, FRCR Consultant Musculoskeletal Radiologist, Department of function. Muscle trauma is common in athletes, it can Radiology, Musculoskeletal Centre, Chapel Allerton Hospital, lead to changes that may be observed on US and MRI, Leeds Teaching Hospitals, Leeds LS7 4SA, UK and that may manifest as abnormalities of muscle Van Dyck P. , MD refl ectivity respectively intensity and (ultra)structure A. Van der Stappen, MD F. M. Vanhoenacker, MD, PhD as well as volume alterations. Muscles were diffi cult Department of Radiology, University Hospital Antwerp, to image with early techniques (radiographs, com- Wilrijkstraat 10, 2650 Edegem, Belgium puterized tomography (CT) and low resolution 16 J. L. Gielen et al. ultrasound) because of low soft tissue contrast. With T1- and T2-weighted MR images (WI) with interme- the advent of high resolution ultrasound (US) and diate to slightly long T1 relaxation time and short T2 magnetic resonance imaging (MRI) it became much relaxation time. The fat along fascial and subcutane- easier to diagnose injuries primarily affecting the ous tissue planes allows identifi cation of individual soft tissues. Currently more attention is paid to trau- muscles. The axial plane is particularly helpful for matic lesions of the MTU in radiological literature outlining specifi c muscle contours to determine loca- (Campbell and Wood 2002; El-Khoury et al. 2004). tion of lesions and to compare atrophy or expansion US grading of muscle injury can be performed, and of muscle. Including the opposite side for compari- follow-up studies can assess repair of muscle tissue son may be helpful (Kathol et al. 1990). The outer and identify complications of the healing process. thicker layer or epimysium (muscle fascia) that sur- Some features such as vascularity and intralesional rounds the entire muscle belly is also refl ective on US. calcifi cation may be more easily appreciated on ultra- This thick fascia may produce a low SI cocoon around sound than MRI. the muscle belly on T1- and T2-WI MR images. This chapter reviews to the imaging relevant anat- These layers of connective tissue within the muscle omy, ultrastructure and (patho)physiology of muscle belly are called the connective tissue skeleton of the as well as the radiological characteristics of normal muscle (endo-, peri-, and epimysium). At the myoten- and injured muscle as seen on ultrasound and MRI dinous junction the contractile elements end and the with emphasis on its clinical relevance. connective tissue skeleton of the muscle belly contin- ues in endo-, peri- and epitendineum of the tendons of attachment. This transition site of connection between the contractile muscle cells and the tendon is known as the myotendinous junction (Noonan and 3.2 Garrett 1992). It is a specialized region of highly Anatomy, Ultrastructure folded membranes at the muscle-tendon interface. and (Patho)physiology The folding increases the junctional surface area by with Imaging Correlation 10–20 times, decreasing the stress per unit area. The muscle fi bre is the basic structural element of skeletal muscle; the sarcomere is the smallest con- tractile unit of muscle fi bre. The muscle fi bre is a long cell connected to the tendon or bone on which it acts. The contractile fi laments, myosin and actin fi laments, are interswitched with a minimum overlap. Greater overlap of these fi laments produces muscle shortening-contraction (Fig. 3.1). There are no end to end connections between muscle fi bres. Muscles originate from and insert on bone or dense connec- tive tissue either directly or via a tendon. A layer of fi brous connective tissue, the endomysium, surrounds each individual muscle fi bre. These fi bres are bundled into fascicles, which themselves are surrounded by a perimysium. The perimysium is easily recognized on longitudinal ultrasound as linear refl ective lines separating the hyposonant contractile fascicles (Peetrons 2002) (Fig. 3.2a, Fig 3.3a, b, d, f, g (left)). Transversely they appear as dotted refl ective areas. Thicker refl ective septa may occasionally be seen within the muscle belly, resulting in a reticular or b honeycomb pattern on transverse images ( Fornage Fig. 3.1a,b. Schematic drawing of muscle fi lament orientation. 1995) (Fig. 3.2b, Fig. 3.3c, e, g (right)). On MRI this a Normal actin and myosin fi lament orientation during rest fascicular structure is not well appreciated. Muscular (top), and maximum contraction (bottom). b Filament elonga- tissue produces a homogeneous intermediate SI on tion after strain injury grade 1 Muscle Injuries 17 RF VM VI VL TI a b Fig. 3.2a,b. Thigh muscles and tractus iliotibialis. Lateral longitudinal (a) and transverse (b) extended fi eld of view ultrasound images of the thigh muscles. Longitudinal posterior and anterior view with a total length of 40 cm on top and bottom respec- tively. The gluteus maximus (GM), vastus lateralis (VL) and vastus intermedius (VI) muscles and the tractus iliotibialis (TI) can be identifi ed on longitudinal images. The four quadriceps heads including vastus medialis (VM) and rectus femoris (RF) can be identifi ed on the transverse image. The refl ective linear lines of the perimysium are best appreciated in the localized longitudinal ultrasound images. The refl ective line between muscles corresponds to the epimysium (muscle fascia). The deep refl ective line (arrows) is formed by the cortical lining of the femur diaphysis and distal metaphysis The orientation of refl ective layers of perimy- muscles which refl ect the speed of contraction and sium on ultrasound depends on the orientation of endurance of the muscle (Garrett et al. 1984). The the muscle fi bre. Unipennate (e.g. gastrocnemius type I (slow twitch) fi bre has slow contraction and muscles) and bipennate (e.g. rectus femoris muscle) relaxation times; it is, however, resistant to fatigue muscles have muscle fi bres obliquely oriented to the and has more mitochondria and capillaries per fi bre. epimysium and myotendinous junction (Fig. 3.3a–f). Muscles active in postural activities are rich in type I In these cases, the myotendinous junction is often fi bres. The type II (fast twitch) fi bre is divided into quite large, extending a long distance into the muscle subtypes but generally the type II fi bre has lower belly. This confi guration allows for a large number mitochondrial content, functions glycolytically and of short muscle fi bres in a given cross-sectional area is better adapted to intense movement activities of (CSA), producing powerful muscles that resist elon- short duration. More tension can developed in type II gation. The angle of the muscle fi bres in relation to fi bres than in the type I fi bres. The amount of active the tendon or aponeurosis in pennate muscle types is tension that a muscle produces has been shown to be easily appreciated on ultrasound; it grows in hyper- proportional to the fi bre type content, so that muscles trophied muscles as is the case in athletes, especially with higher proportion of type II fi bres are able to in body builders (Fig. 3.3a). It is believed that resul- generate more force. Low intensity exercise selec- tant force vector parallel to the tendon diminishes tively involves type I fi bres, while more type II fi bres in angulations over 45° resulting in lower muscle are recruited as exercise intensity increases. Muscle strength. In a parallel or fusiform confi guration, biopsies from sprinters are more likely to show a the muscle fi bres are oriented with the long axis of predominance of type II fi bres, as compared with the muscle, with a smaller number of longer muscle long distance runners where type I fi bres predomi- fi bres in the same CSA. This allows a greater range of nate. It is not certain if these fi bre distributions are movement and maximum velocity of shortening, but genetically determined or are a response to training less power. ( Garrett 1990). Research in muscle biology has proved the exis- Most muscles cross one joint but some cross two or tence of different types of muscle fi bres with dis- more joints.