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Division of MSK Imaging, McMaster University, Staff MSK Radiologist: Hamilton General Hospital, Hamilton Health Sciences, 237 Barton St.E, Hamilton, Ontario L9L 2X2, Canada
Sports Imaging has dramatically increased in the past decade with increasing number of adolescents, young and middle-aged adults participating in non-competitive/hobby sports. Therefore, sports injuries are no longer confined to elite athletes. Furthermore, newer forms of sports such as mountain climbing, pickle ball and curling etc. are gaining popularity. Majority of the injuries in sports medicine are from musculoskeletal trauma. Therefore, it is imperative that the musculoskeletal radiologist becomes familiar with various sports related injury patterns as these are commonly encountered in daily practice. This update aims to briefly encapsulate the major aspects of sports imaging. It includes the imaging manifestations of various types of musculoskeletal injuries on different modalities (commonly US and MRI) and briefly mentions the various image guided interventions, performed both on the sports field and in the hospital setting.
Sports injuries occur in both, the elite competitive athletes, and non-competitive players. The various sports injuries and their patterns vary according to the age of the athlete,
for example, between swimmers and soccer players, the pattern of injuries is different, based on the biomechanics of the two sports. In recent times, when the COVID 19 pandemic has changed our lives and imposed so many limitations on our social interactions, people have engaged in sports with family members and friends for recreation and stress relief. This sudden increase in recreational sports including badminton, tennis, golf, running and jogging by otherwise sedentary people has made them vulnerable to injuries.
Sports physicians, orthopedic surgeons and radiologists need to be familiar with the various patterns of injuries within the wide panorama of sports (Fig. 1, Fig. 2). This is to arrive at an accurate diagnosis and provide timely and effective management, be it surgical or conservative. The primary aim in sports injuries sustained by elite athletes is to limit the immediate as well as long-term effects of injury and hasten return to play, while being cognisant of the risk of re-injury. This delicate balance requires a deep understanding of the sport, injury patterns, use of the appropriate imaging modality to assess the extent of tissue damage, provide standardized reports with clinically necessary information and liaise closely with the sports medicine physician to help provide adequate and timely management. Often, there is need for follow up imaging to assess improvement/healing of the injured tissue. This can be following conservative management or post surgical treatment, in order to make a decision on return to play. There are myriad classifications in recent literature on extent of injury and injury patterns for various sports and their imaging characteristics. This sports update, however, briefly describes the type of sports injuries that can affect the various tissues in musculoskeletal (MSK) system (muscle-tendon -bone unit, neural and vascular); the currently utilized modalities to diagnose the injuries; the chief imaging characteristics; and a short note on the latest research in MSK sports imaging.
Fig. 1Spectrum of sports injuries with commonly injured parts of the body.
The muscle is the primary motor that sets into action the muscle-tendon- bone unit, thereby affecting movement and locomotion. It is commonly injured in athletes. Muscle injuries represent more than thirty percent of sports injuries.
According to the muscle architecture, muscles can be classified as strap muscles (parallel muscle fibres inserting on a broad marginally located tendon such as pronator quadratus, hamstrings), fusiform muscles (converging muscle fibres on the tendon, for example biceps brachii), and pennate muscles (long peripheral myotendon running along the entire muscle center). The pennate muscles can be unipennate, bipennate or multipennate (Fig. 3). In these muscles, the myotendons course through the muscle with the muscle fibres aligned at an angle to the myotendon (pennation angle), altering the forces on the muscle tendon complex and thereby affecting the type of injury. The pennation angle creates increased force per unit area (such as in the deltoid, pectoralis major, infraspinatus, subscapularis)) and one or more muscle myotendon subunits can be injured.
Fig. 3Diagram showing unipennate, bipennate and multipennate muscles depicting the varying direction of their muscle fibres (red) and varying characteristics of the myotendons (white).
Strain is caused by indirect stretching, most commonly affecting unipennate muscles (most often injured are the biceps femoris, rectus abdominis and gastrocnemius in that order). An intramuscular contusion is caused by a direct blow injury compressing the muscle/muscles against the bone, with greater force exerted by smaller striking objects than larger flatter ones (intramuscular quadriceps contusions). A muscle laceration is from a penetrating injury, usually from the sharp edge of a broken bone resulting in discontinuity of muscles fibres, usually with an associated hematoma. In compartment syndrome, there is acutely elevated pressure within the injured muscle compartment. This is due to marked tightening of the compartment from bulging muscles, from muscle edema, peri-muscular and intermuscular fluid and intracompartmental hemorrhage. This is a surgical emergency and usually urgent surgery is undertaken before imaging is performed.
2.3 Location of the injury
The anatomical site of injury is crucial as it could affect weight bearing, restrict the range of movements and locomotion, as with injuries of the lower limb when compared to the upper limb. The type of sports also dictates the time to return to play. For example, a hamstring muscle tear affects a soccer athlete's return to play to a greater degree than a similar injury in a swimmer.
2.4 Involvement of myofascial, myotendinous or intramuscular tendons
The healing of injured myofascial, myotendinous or intramuscular tendon takes longer than an intramuscular tear, for example, an intramuscular hematoma of the gastrocnemius muscle belly heals faster than a myotendinous or aponeurotic tear.
2.5 Retraction of fibres
The greater the degree of retraction of the muscle fibres in a muscle tear, the longer is the healing time. Also, greater the degree of retraction of the torn end of the tendon from its bony attachment or greater degree of separation between the proximal and distal ends of the torn tendon; the more complex is the surgery. For example, the greater the gap between the retracted torn end of the ruptured long head of distal biceps tendon from the radial tuberosity, wherein the lacertus fibrosis is injured, the more difficult is the surgery.
2.6 Extent of muscle edema
The extent of muscle edema in the long and short axis plane helps to determine the extent of injury and thereby the return to play.
2.7 Fresh or re-injury
Return to play is delayed in re-injuries compared to fresh injuries.
2.8 Range of sub-acute and chronic injuries
In the rehabilitation of an athlete with an acute injury, the extent of fibrosis, muscle atrophy, muscle denervation and heterotopic ossification are the various factors that will affect long-term management and performance. While clinical classification systems primarily emphasize acute forms of muscle trauma, MSK radiologists also need to be familiar with a range of sub-acute and chronic injuries that can result in persistent symptoms and functional limitation of the athlete.
2.9 Imaging features
Both Ultrasound (US) and Magnetic Resonance Imaging (MRI) are used to assess muscle injuries. US is inexpensive, easily accessible, can be used for rapid assessment of the MSK sports injury on the field and in evaluating continuation of same day play and return to play. For example, US can depict an intramuscular hematoma and its evolution, muscle fibre disruption and extent of tear, muscle healing, fibrosis, remodelling and dynamic assessment of muscle contraction. US can also be used for guided injections, for example, steroid/local anesthetic injections on the field at the time of injury to facilitate completion of a game or platelet rich plasma (PRP) injection into muscle tears in high end athletes in the hospital setting. The disadvantages of US include its inability to depict injuries of deep-seated muscles, depict the entire muscle in relation to the region of interest and denervation edema. Also, US is operator dependent and has a steep learning curve. In comparison, MRI has the advantage of greater contrast resolution, is useful for assessing deep-seated muscles, can depict denervation patterns and depict the entire region of interest including adjacent bones and joints. MRI is also used to evaluate muscles pre and post exercise for chronic compartment syndromes. However, unlike US, it cannot be used for on the field imaging, is not routinely used for image-guided interventions, is expensive and not easily accessible.
These types of injuries and their evolution are well imaged by US and MRI. They are treated conservatively with elevation, cooling, compression banding and rehabilitation. US guided aspiration and injection of steroid, PRP and surgery are not yet substantiated with enough evidence. Fluid is seen as an anechoic collection within the muscle on US and it appears T1 hypointense and T2 hyperintense on MRI. Both imaging modalities can demonstrate debris and peripheral flow on doppler US and peripheral contrast MR enhancement, as the hematoma evolves.
2.9.2 Sprains and tears
Sprains and tears are well depicted on high resolution US and MRI (Fig. 4). High resolution US probes (transducer frequencies ranging from 5 to 13 and 27 MHz) have greatly improved the resolution of tissues. 3 T MRI provides greater resolution of muscle architecture (myoconnective/myofascial/myotendon tissues) and extent of muscle injuries when compared to 1.5 T. The greater the extracellular matrix involved, greater is the connective tissue damage, and greater the functional impairment and prognosis. The larger the gap between torn ends of the muscle-myotendon- tendon complex, the worse the prognosis and this directs management decisions, whether conservative or surgical.
Fig. 4Coronal T2W MR image showing an acute pectoralis major tendon avulsion injury in a professional weightlifter. The sternal head is retracted with diffuse muscle edema (yellow arrow) and a large haematoma (red arrow) between the retracted torn end of the tendon and its humeral attachment.
They are FC Barcelona-Aspetar-Duke classification, Munich consensus statement and British Athletics Muscle Injury classification. These classifications are based on the site of injury (proximal, middle, distal), involved anatomical structure (muscle fibres, tendon, aponeurosis, fascia), the various MRI features discussed above (edema, disruption of muscle fibres, intramuscular hematoma, tendon retraction, intermuscular fluid), and the size of the abnormality (length and cross sectional area of edema, area of disruption of muscle fibres and area of muscle discontinuity). The British Athletics Muscle Injury Classification based on MRI findings is given in Table 1.
Intravenous (IV) contrast enhancement is used in MRI to assess hypoperfusion of muscles, peripheral enhancement in hematomas and myonecrosis. Peri-fascial, intramuscular and intermuscular fluid in muscle injury is well depicted by MRI irrespective of the muscle depth and is therefore more reliable than US. Plain radiography and CT play an important role in assessment and diagnosis of post-traumatic heterotopic ossification. Myonecrosis can also be diagnosed on US and MRI, albeit with wider differentials.
There is no current evidence that MRI can predict return to play and risk of re-injury, based on normalization of the post injury abnormal MR signal intensities and structural recovery. Functional recovery precedes structural recovery and is decided by the sports medicine physicians.
This can be seen in asymptomatic and symptomatic athletes after a bout of vigorous exercise. Cotton-like pattern of diffuse edema without distortion of architecture is seen in the affected muscles.
Acute compartment syndrome is a surgical emergency treated with fasciotomy. Imaging is very rarely indicated. However, imaging is often helpful in chronic compartment syndromes and exercise induced compartmental syndrome.
This occurs when there is a focal defect in the fascia, from a fracture, penetrating injury during sports, post surgery, chronic thinning of the fascia or chronic compartment syndrome. The common examples are at the anterior and lateral compartments of the leg, wherein, the tibialis anterior and peroneal muscles herniate through the overlying deep fascia. Typically, the bulge appears on contraction of the muscle and therefore is best visualized on dynamic US.
There is a lot of research being conducted on Diffusion Tensor Imaging (DTI), MR elastography, T2-weighted mapping, Positron Emission Tomography (PET) and dual energy CT.
The diagnostic value of intracompartmental pressure measurement, magnetic resonance imaging, and near-infrared spectroscopy in chronic exertional compartment syndrome: a prospective study in 50 patients.
These novel modalities will play a greater role in imaging muscle injuries in the future, which will then be applicable to sports imaging. Determination of severity of muscle-myotendon injury will help determine the time to heal, complete return to play, graded return to play and risk of re-injury adding strength to the functional assessment conducted by the sports physician.
Tissue softness or hardness is measured on sonoelastography using the principle of strain caused by tissue compression. The tissue becomes harder with disease and these changes can be detected using US. Sonoelastography has the potential to be used in Achilles tendinosis, lateral epicondylitis, patellar tendinopathy and rotator cuff tendinopathy.
Tendons appear hypointense on T1 and T2 till late in tendinosis. With Ultrashort echo time, MRI signal acquisition starts at less than 100 μs after excitation. It picks up intra-tendinous changes early on by generating image contrast with off-resonance saturation. It can improve visualization of the enthesis architecture and demonstrate changes of tendinosis early on.
2.10.3 Dynamic contrast-enhanced MRI
Early enhancement rates are calculated and can be used in diagnosing tendinosis and response to treatment in high-end athletes.
3. Tendon injuries
Structurally, a healthy tendon comprises of parallel type 1 collagen fibres with intervening connective tissue (endotenon) and a surrounding tendon sheath or connective tissue layer (paratenon). Blood supply to tendons is from the myotendon, bone or from the tendon sheath/paratenon.
Normal tendons appear echogenic on US with the connective tissue appearing hypoechoic. The tendons are of low signal on T1 and T2 MRI. Tenosynovitis demonstrates bright T2 signal around the tendon, from fluid within the tendon sheath, for example, tendons in the hand and wrist. Mild inflammatory hyperintense signal is also seen around tendons that lack a tendon sheath. This is termed paratenonitis, for example, in case of the Achilles tendon. When tendons degenerate, they are replaced with type 3 collagen fibres. Such degenerate tendons appear hypoechoic on US, show intermediate T1 signal and inhomogenously hyperintense T2 signal which is less than that of fluid. Sports injuries can occur in healthy tendons of young adults or on a background of tendinosis in older individuals. Tendons attach to bone by fibrous connective tissue. When the tendon attachment is at the diaphysis and metaphysis of long bones, then it is termed enthesis. When the attachment is at epiphysis, apophysis and small bones, then it is fibrocartilaginous enthesis. Avulsion injuries occur at bony attachments.
Tendon injuries related to sports can be the result of avulsion of the tendon from its bony attachment such as distal biceps tendon from the radial tuberosity, Achilles tendon from the calcaneus, quadriceps tendon from its patellar attachment and hamstring tendon avulsion from the ischial tuberosity. They can also occur as tears at the myotendon such as myotendons of the quadriceps and hamstrings and medial and lateral heads of gastrocnemius or tears of the medial and lateral gastrocnemius aponeurosis.
Tendon injuries are purely connective tissue lesions. They can occur as stretch or elongation injuries, partial thickness tears or full thickness complete tears. With stretch injuries, there is only slight signal change of the tendon with surrounding peri-tendinous high T2 signal. With partial thickness tears, there is varying degree of disruption of tendon fibres (Fig. 5). With complete tears/ruptures, there is a gap between the torn ends of the tendon or tendon retraction from its bony attachment, with an intervening hematoma (Fig. 6). The diagnosis of tears can be made with US or MRI. The resolution of US is greater than MRI for superficial tendons and it is better at diagnosing the extent of partial thickness tears such as of the distal biceps tendon and Achilles tendon. Furthermore, dynamic assessment is possible with US. This dynamic assessment helps to differentiate high-grade partial thickness tears from full thickness tears. For example, lateral manoeuvre of the distal biceps or flexor/extensor tendons of the fingers wherein, lack of movement of the proximal portion of the tendon on passive movement of the elbow or finger, respectively, indicates a full thickness complete tear. The degree of separation of the tendon from bone or between two torn ends can be assessed in the neutral position and on dynamic manoeuvres, such as, in neutral and plantar flexion at the ankle, with Achilles tendon ruptures, the extent of intervening gap in these two positions contributes to decision making and prognosis of the injury. However, for deep-seated tendons like the hamstrings, MRI is necessary to accurately assess the extent of injury, the location and extent of retraction of the torn end of the tendon.
Fig. 5US long axis image of the right medial elbow in a patient with non- professional Golfer’s elbow. There is common flexor tendinosis (with loss of the normal fibrillary appearance, focal hypoechogenicity and thickening of the tendon). An intrasubstance partial-thickness tear (red arrow) is seen as a anechoic area within the zone of tendinosis. ME- medial epicondyle.
Fig. 6Longitudinal axis US image of left elbow joint depicting an acute triceps tendon rupture in a soccer player. The triceps tendon is retracted with an avulsed bone fragment attached to it (yellow arrow). An intervening haematoma (red arrow) is noted between the retracted torn end of the tendon and the olecranon. O-olecranon process.
Internal derangement of joints, injuries of the articular cartilage (chondromalacia, delamination, tears, and defects), osteochondral lesions, subchondral bone plate fractures, stress injuries related to sports are all optimally diagnosed with MR imaging. Prior to MR imaging, plain radiographs are still mandatory to assess and exclude fractures, osteochondral lesions, intra-articular mineralized bodies, subluxation and dislocations.
Extraarticular ligaments can be evaluated with US. The commonly imaged sports injuries are the anterior talofibular ligament (ATFL) following ankle injuries and the collateral ligaments of the knee and elbow. In acute sprains, there is diffuse hypoechogenicity of the ligament on US with surrounding fluid. In MR images, the ligament appears hypointense on T1, hyperintense on T2 and surrounding bright T2 fluid is seen. Partial thickness tears are detected as focal areas of thinning and hypoechogenicity of the ligament on US, and as focal partial thickness defects on MRI, both on T1 and T2 (Fig. 7). Full thickness tears are seen as discontinuity of the ligaments, with ligamentous disruptions equally well seen on US and MRI. The peri-ligamentous fluid disappears as the ligament heals with fibrous tissue filling the areas of ligamentous defects. The healed ligament appears thickened but there could be laxity of the ligament on dynamic imaging with US due to loss of tensile strength.
Fig. 7Coronal Proton Density fat-saturated MR image in a football player showing marrow edema in the medial femoral condyle (yellow arrow) and partial tear of the medial collateral ligament (red arrow).
MR arthrography (wherein diluted gadolinium is injected into joints prior to MR imaging) of various peripheral joints is very popular and a highly utilized technique in accurately assessing labral, intra articular ligamentous and capsular injuries despite the advent of 3T MRI (Fig. 8, Fig. 9).
Fig. 8Axial T1-weighted fat-saturated hip MR arthrogram image showing a partial thickness tear of the anterosuperior acetabular labrum (red arrow) in a varsity soccer player. Also noted is a femoral neck small anterior bump (yellow arrow), possibly an early CAM type of femoroacetabular impingement.
Fig. 9Coronal T1-weighted fat-saturated wrist MR arthrogram image showing a peripheral tear of the triangular fibrocartilage including styloid attachment (red arrow) and partial thickness tear of the scapholunate ligament (yellow arrow) following an acute skiing injury in a young non-professional skier.
Fractures and dislocations are best evaluated with plain radiography. However, subtle fractures and clinically suspected occult fractures are evaluated on CT, scintigraphy and MRI. 3D CT reformats help to assess malalignment, dislocations and fracture orientation for surgical planning. MRI including newer sequences such as Dixon and in and out of phase imaging can be used to assess marrow edema in occult fractures and stress fractures. There is research and early evidence of dual energy CT being used to detect occult fractures.
Peripheral nerves can be imaged both with US and MRI. US has superior spatial resolution when compared to MRI for superficially located peripheral nerves. In the long axis plane, nerves appear as parallel alternating linear hypo and hyperechoic lines from nerve fascicles with endo, peri and epineurium respectively. In the short axis plane, the nerve appears as speckled hypoechoic dots (nerve fascicles) with intervening hyper echogenicity (connective tissue) and echogenic rim (epineurium). In neuritis, the neural fascicles are thickened and hypoechoic on US with resultant fusiform thickening of the nerve and this entity is often seen in athletes, due to overuse. As the severity of the neuritis increases, the entire nerve becomes hypoechoic with loss of the neuro fascicular appearance, there is doppler hyperemia and a rim of perineural hyperechogenicity (from the rind of perineurium) develops (Fig. 10). Unlike superficially located peripheral nerves, the deep-seated nerves and brachial plexus are optimally assessed on MRI and MR neurography, appearing bright on T2 images in neuritis. Avulsion of nerve roots of the brachial plexus is well assessed on 3T MRI and MR neurography. Nerve disruptions (transections) and post-traumatic neuromas can be assessed using US and MRI, based on the location and depth of the nerves.
Fig. 10Longitudinal axis (a) and transverse axis (b) US images of the median nerve in a badminton player with carpal tunnel syndrome showing thickened hypoechoic median nerve with loss of the fascicular appearance (red arrow), perineural echogenicity and mild doppler hyperemia (yellow arrow).
MSK radiologists are often called onto the field to perform a quick ultrasound to assess extra articular soft tissue injuries and are frequently asked to inject the injured tissues to mask the pain for completion of the game. These injections are usually local anesthetic and steroid and are injected under ultrasound guidance at the site of injury. Steroid injections into joints, tendon sheaths for tenosynovitis and around peripheral nerves for neuritis; PRP injection into muscle tears, joints, injured tendons, fascia and ligaments; aspiration of hematomas; botox injections; peri-neural hydrodissections with local anesthetics, steroid, dextrose and PRP, steroid injections around injured pulleys are the various interventions performed by MSK radiologists for sports related injuries. Stem cell injections into joints for cartilage regeneration, into muscle tears and into tendons for tendonitis are gaining popularity in competitive athletes though there is no definitive evidence in literature. PRP injections are still popular despite lack of definitive scientific evidence regarding their effectiveness. Fenestration (dry needling) of tendons takes a longer time to heal, oftentimes 8–12 months and therefore is not the first choice in return to play athletes. Sacro-iliac joint injections and pyriformis blocks (using steroid and local anesthetic or lately botox for pyriformis blocks) are easier to perform using CT fluoroscopy guidance as there is dynamic visualization of the needle tip as it approaches the deep seated target on thin axial CT images. However, fluoroscopy guided injections are still being performed in many centers, across the globe.
Increasingly, MSK radiologists are an integral part of the sports physician's team and are involved in making crucial decisions for the athlete's well being, while balancing return to play and continuation of sports. Familiarity with the mechanisms of injury in the specific sport, the various types of sports related tissue injuries of the musculoskeletal system and their imaging features are mandatory for interpreting sports injuries by MSK radiologists. Furthermore, expertise in various image guided interventions for sports injuries, both on the field and in the hospital setting are imperative for MSK subspecialty radiologists, in order to administer timely, appropriate and state of the art evidence based care of their athletes.
Sources of support
NIL.
Declaration of competing interest
None.
Acknowledgements
The authors would like to acknowledge the work of Ms Akhila Rachkonda, BMsc, Year 3 MD Student, Flinders Medical Centre, Bedford Park, Adelaide, South Australia 5042, Australia who has contributed diagrams in the manuscript.
The diagnostic value of intracompartmental pressure measurement, magnetic resonance imaging, and near-infrared spectroscopy in chronic exertional compartment syndrome: a prospective study in 50 patients.
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