Br J Sp Med 1994; 28(2)

Review

Magnetic resonance imaging in sports medicine - anoverview

Terence Featherstone FRCRDepartment of Radiology, Darlington Memorial Hospital and Darlington MRI Centre, Darlington, UK

As more Britons become health conscious and are involvedin a variety of sporting events, sports-related injuries are adaily occurrence. Although evaluation of bony abnormali-ties resulting from acute and chronic sports injury byconventional radiography and bone scintigraphy has beensatisfactory, the assessment of soft tissue and tendinousinjury is more difficult and imprecise. Due to its superiorcontrast sensitivity and multiplanar imaging capability,magnetic resonance imaging has already shown greatpromise in delineating soft-tissue and tendinous abnorma-lities. In addition, marrow pathology is exquisitelydisplayed.

Keywords: Magnetic resonance imaging, sports injuries

In an age of finely tuned athletes and superioron-field performances, medicine has followed suit.Gone are the days when professional sportsmen andsportswomen ignored their injuries, or relied simplyupon radiography to investigate chronic pain. Doc-tors now have access to sophisticated imagingequipment and athletes are reaping the benefits.Furthermore, increased health consciousness hasmotivated more of the general public to participate insports with a concomitant rise in sports injuries.

In recent years, particularly in the USA, magneticresonance imaging (MRI) has proved itself thepremier imaging tool in the evaluation of sportsinjuries. The technique provides excellent inherentsoft-tissue contrast allowing direct visualization ofcartilage, muscle, tendons, and other soft tissues, inaddition to bone marrow. Further advantages includeits multiplanar imaging capability, the absence ofionising radiation, and no known harmful effectsattributed to the technique.The nuclear magnetic resonance phenomenon is a

normal property of matter, initially discovered by theAmerican Physicists Bloch and Purcell in the 1940s.The physics of magnetic resonance imaging iscomplex but it is helpful to understand somebackground to the subject for the interpretation of theimages.

Address for correspondence: Dr T. Featherstone, Department ofRadiology, Darlington Memorial Hospital, Darlington, DurhamDL3 6HX, UK

(© 1994 Butterworth-Heinemann Ltd0306-3674/94/020084-06

The nuclei of many substances within the body willshow magnetic resonance, but the hydrogen nucleiare by far the most common in the human body, andwill give the biggest signal. Hydrogen nuclei can beconsidered as acting like spinning bar magnets. Sincethe hydrogen in the body is mainly in the form ofwater and fat, the information obtained from MRI isprincipally concerned with the distribution of waterand fat.

In an external magnetic field the magnetic momentof the spinning hydrogen nuclei will have a wobblingspin, known as precession. The frequency of preces-sion is dependent on the strength of the magneticfield. Once the patient is placed in a strong magneticfield a pulse of electromagnetic energy at a particularradio frequency is passed through the patientimparting energy to the nuclei which are spinning atthe same frequency. Only the nuclei that areresonating at the correct frequency will be affected.Magnetic gradients are applied in addition to themain field. These are applied in three planes, at rightangles to one another, and they decide the position ofthe slice and encode any one position within the slice,such that each point or pixel has a different radiofrequency or phase. When the radio frequency isswitched off, a signal can be detected emanating fromthe resonating nuclei. This signal is detected as acomplex wave form, but is converted by Fouriertransformation into constituent frequencies with theirrespective phases and amplitudes. The position ofthe signal on the scan will be determined from thefrequency and phase. The amplitude of the signal willdetermine the position on the grey scale with thehigher signal being shown as a brighter area. Manyfactors affect the emitted signal and hence the finalpicture. These include:

1. Proton density. This is of considerable importancesince in the absence of protons there can be nosignal.

2. Relaxation times. These are constants related to thelength of time for the signal to decay afterstimulation by the radio frequency. The T1relaxation time is relaxation between the spinningprotons and the main magnetic field and is alsoknown as the spin lattice relaxation. The T2relaxation time represents relaxation between theneighbouring protons due to interference, this isknown as the spin-spin relaxation time.

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3. Chemical shift. The hydrogen is bound differentlyin water and fat and these two forms have slightlydifferent resonant frequencies resulting in over-lapping image and edge artefacts.

4. Flow. Flowing fluid in the body, e.g. cerebrospinalfluid and blood can cause flow voids or enhance-ment, depending on the signal used.

5. Susceptibility. This is a measure of the paramagne-tic effect of a material. Some substances. e.g.melanin and methaemoglobin, possess paramag-netic properties and these can alter the localmagnetic environment, resulting in enhancementor decrease in signal. If the substance has highsusceptibility, e.g. some metallic pigments in eyemascara, the magnetic field may be substantiallydistorted causing artefacts across the image. Themost classical sequence used in MRI is known asspin echo, using 900 and 1800 radio frequencypulses. Images are produced with T1, T2 andproton density weighting. It is also possible tosuppress the signal from fat using the short tauinversion recovery (STIR) sequence with somesummation of Ti and T2 effects, giving rise toincreased lesion detection.

Magnetic resonance imaging is a safe technique, butbecause of the strong magnetic field, care is neededwith metallic implants, neurosurgical clips etc., toavoid migration or excessive tissue heating. Claus-trophobia is a problem for about 1% of patients. Thescan currently takes longer than a computed tomo-graphic (CT) examination, although major progressin improving the acquisition times is underway.While MRI is not usually needed in the diagnosis ofobvious acute injuries, its ability to delineate accu-rately the extent of certain injuries can be of value indetermining which cases require surgical interven-tion and which may be handled with conservativemethods.

Upper extremitiesThe shoulder is commonly injured in activitiesinvolving overhead movements, e.g. swimming,racquet sports and gymnastics. MRI is generallyregarded as the most appropriate noninvasive techni-que for the evaluation of rotator cuff tears andimpingement syndrome, which are the most com-mon shoulder injuries'. MRI determines the locationand size of the tears, the degree of retraction of tornedges and the status of the remaining rotator cuff.The presence of subacromial fluid is a sensitiveindicator of a tear with interruption of the tendonbeing a specific finding2 (Figure 1).MRI is limited, however, in detecting labral

abnormalities when a joint effusion is absent and CTarthrography, although more invasive, remains thegold standard in this respect'.The elbow, as the focus of stress in many sports, is

prone to injury. MRI of elbow injuries has developedslowly but its application has good potential as newcoil designs provide comfortable patient positioning.

Injuries to the hand and wrist occur frequently in awide variety of sports. Standard radiographs, CTscans and arthrography are used to evaluate the

Figure 1. A T2* GE coronal image shows fluid within thesubacromial-subdeltoid bursa and heterogeneous signalin the supraspinatus tendon indicative of a partial tear,confirmed at surgery

majority of wrist injuries, but there is a growingconsensus that MRI is accurate in detecting tears ofthe triangular fibrocartilage4.

Lower extremitiesPlayers in contact sports and activities characterizedby rapid bursts of movement such as soccer, hockey,rugby and athletics are the most likely to beassociated with injuries to the lower extremities. Theknee is the most frequently injured joint in sport5. Achronic knee injury is one of the most typical reasonsfor premature retirement from athletics.MRI has largely replaced arthrography, computed

axial tomography and ultrasonography in examina-tion of the knee because of its noninvasive highdiagnostic accuracy6. While arthroscopy can be bothdiagnostic and therapeutic, the frequency of normalarthroscopy can be decreased substantially by theroutine use of MRI7'8Normal menisci appear as black, low signal

structures, as does the posterior cruciate ligament.The anterior cruciate ligament is more vascular and isseen as a band of intermediate signal. So sensitive ismagnetic resonance to local change in water contentthat after jogging, about 50% of people can be shownto have a higher signal in their menisci with smalljoint effusions9.There is a well accepted grading system for

meniscal abnormalities ranging from grade I and IIincreases in signal intensity within the substance ofthe meniscus, representing various stages of myxoiddegeneration, to grade III changes which representcomplete tearsl0.MRI is particularly useful in determining the

presence of tears of the posterior horn of the medialmeniscus which can be difficult to see at arthroscopy(Figure 2). Cysts of both the menisci and poplitealregion are easy to diagnose in addition (Figure 3).

Tears of the cruciate and collateral ligaments arewell seen by MRm. In anterior cruciate ligament (ACL)tears a correlation of 94% with athroscopy has been

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Figure 2. A T2* GE sagittal image of the knee. The posteriorhorn of the medial meniscus should appear of uniformlow signal intensity but there is a region of linear highsignal intensity running through the meniscus extendingto the inferior articular surface (long arrow). Thesefindings indicate a meniscal tear, confirmed on arthros-copy. A joint effusion is also seen (arrow head)

reported", as compared with 78% for the anteriordrawer test and 89% for Lachman's test.

Injuries of the patellar tendon are common,particularly in jumpers. Incomplete tendon rupturecan be seen on MRI as irregular thinning, localizedthickening and hyperintense areas within the ten-don12. Disruption of the continuity of the tendonindicates complete rupture (Figure 4). MRI is indi-cated in osteochondritis dissecans since it is particu-larly useful in defining the origin of the bonefragment and is able to demonstrate if the fragmentremains attached to the underlying bone or cartil-age'3. MRI is also able to demonstrate whether thebone under the area of cartilage damage is viable ornot.Although MRI shows cortical bone as a signal void,

it is exquisitely sensitive to abnormalities seen in thebone marrow. This makes MRI an effective modalityfor demonstrating occult fractures, stress fracturesand bone contusions14. Minimally displaced im-pacted fractures may have no radiographic findings,yet be the cause of significant symptoms. Bonecontusions, or bone 'bruises' are seen at the sites of adirect blow, often in the subchondral region of anepiphysis and are thought to represent miscroscopiccompression fractures of trabecular bone. The pre-sence or absence of a so called bone 'bruise', is nowconsidered an extremely useful prognostic sign, withrespect to the degree of severity of the internalderangement of the joint. It follows that MRI is nowthe most sensitive and specific technique for the

Figure 3. Meniscal cyst. a Sagittal Ti image - the cyst can beseen as a well circumscribed area of intermediate intensityadjacent to the posterior horn of the lateral meniscus(arrow). b Sagittal T2* image - the cyst demonstrates highsignal intensity due to its fluid filled nature (arrow)

Figure 4. Sagittal GE T2* image. Acute rupture of thepatellar tendon with oedema and haemorrhage shown ashigh signal area (straight arrow). A normal ACL is also seen(small arrows)

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Figure 5. Coronal Ti weighted image demonstratingbilateral avascular necrosis (AVN) of the femoral heads in ayoung weightlifter known to have used anabolic steroids.The right femoral head shows a characteristic 'geographicmap' (arrow) indicating early AVN. The left femoral headshows a more advanced lesion with flattening andextensive marrow signal loss (arrow head)

diagnosis of avascular necrosis'5. Numerous studieshave shown that the earlier diagnosis of osteo-necrosis of the femoral head is possible using MRI(Figure 5). This diagnosis is made more important inthe sports world due to the acknowledged risks ofsteroid abuse.The ankle rivals the knee as the most frequently

injured joint in athletics. The anatomy of the anklejoint is well demonstrated by multiplanar MRI16. Themajority of ankle injuries involve the soft tissues,particularly the lateral ligament complex. Injuries ofthe ankle tendons are relatively uncommon com-pared with ligament injuries. The Achilles tendon isan exception, being a common site of injury in older

athletes. Achilles tendon injuries account for 20% ofall running injuries17.In complete rupture there is discontinuity of thetendon with high signal material visible on T2weighted images, occupying the gap. MRI before anoperation can provide information concerning thedegree of shredding, the orientation of the torn fibresand the width of the gap that is useful to the

18surgeon

Partial tears can be seen on MRI as localizedthinning or thickening of the tendon, with or withouthigh signal areas on T2 weighted images. Thecontinuity of the tendon is preserved. Tendinitis ofthe Achilles tendon is seen in a wide range ofathletes. Chronic tendinitis may cause substantialthickening of the tendon (Figure 6), with or withoutabnormal intratendinous signal intensity. The dis-tinction from a partial tear is sometimes difficult,although the history is often helpful.

Certain types of sport trauma can occur anywherein the body. Exertion related muscle pain is afrequent occurrence although its severity and signifi-cance may be difficult to assess clinically. MRI ishighly sensitive to muscle oedema and haemorrhageand, therefore, is useful in evaluating myalgia,strains, contusions, delayed onset muscle soreness,chronic muscle-overuse-syndromes and contracture.Associated injuries to the adjacent tendons, fasciaand bones may also be detected and their presencealter injury management19.The STIR sequence is particularly sensitive to

muscle pathology and often demonstrates possibletears undetectable by other sequences (Figure 7). MRIvisualizes the sequelae of muscle injuries, such asfibrosis, myositis ossificans, fatty infiltration andcompartment syndrome. MRI thus complements theclinical evaluation of muscle injuries. In addition, itssafety allows serial monitoring of exertional muscleinjuries and may provide insight into possiblerelationships among acute and chronic injuries.

Figure 6. Axial Ti image of both ankles in a weekend jogger. The left Achilles tendon (small arrows) is slightly crescentricwith rounded sides and a flattened anterior aspect. The abnormal right Achilles tendon (large arrow) is grossly widenedconsistent with chronic tendinitis

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A4'

Figure 7. Coronal STIR image of a footballer with left thighpain following a match. There is diffuse high signal in therectus femoris muscle reflecting an acute strain

SpineInjuries to the spine and spinal cord are a cause ofserious morbidity in diving, gymnastics and motorsports in particular. The incidence of quadriplegia intrampolining was sufficiently high that the event wasremoved from national and international competitivegymnastics.

Radiographic evaluation of spinal trauma remainsan important initial investigation. MRI will showassociated bone marrow oedema in fracture evalua-tion and also document the degree of spinal cordcompression and haemorrhage.

In the assessment of lumbar radiculopathy, MRIhas an accuracy of 90% which is equal or superior toCT scanning after intrathecal contrast20. A specificadvantage of MRI is its ability to show the wholelumbar spine and thoracolumbar junction includingthe conus medullaris, thereby ensuring that un-suspected proximal lesions are not overlooked,unlike axial computed tomography. MRI is usuallyrecommended in preference to computed tomo-graphy in the evaluation of spinal stenosis, thoracicdisc disease and cervical disc disease and stenosis.Further advantages are offered by MRI in theassessment of various types of disc disease. In thedegenerative disc there is an overall reduction inhydration of the annulus and nucleus pulposus toabout 70%. As the magnetic resonance image ishighly sensitive to the degree of hydration ofdifferent tissues, the degenerate disc can be seen inthe absence of morphological abnormalities (Figure 8).

SummaryMRI is a relatively new and advanced imagingmodality. Its role in studying the musculoskeletal

Figure 8. T2 weighted sagittal image of the lumbar spine ina patient with low-back pain. The CSF exhibits high signalwith a so called 'myelographic' effect. The normalintervertebral discs also exhibit high signal indicatingnormal hydration. There is marked reduction in signalintensity in the [4/5 intervertebral disc reflecting a loss ofhydration and indicating degenerative change. Significantposterior disc protrusion is also present at L4/5

system has grown rapidly in the past 5 years. Due toits ability to display the soft tissue components of themusculoskeletal system with a high level of contrastand specificity MRI has emerged as a preeminent toolin the evaluation of sports injuries. Not only accuratein assessing muscles, tendons, ligaments and cartil-age, MRI plays a key role in evaluating bone traumabecause of its sensitivity to trauma related marrowoedema. The use of MRI in sports medicine willcontinue to grow with advances in, and increasedavailability of, scanners in the UK.

References1 Crues JV, Fareed DO. Magnetic resonance imaging of

shoulder impingement. Top Magn Reson Imaging 1991; 3:39-49.

2 Farley TE, Neumann CH, Steinbach LS et al. Full thicknesstears of the rotator cuff of the shoulder: diagnosis with MRI.AJR 1992; 158: 347-51.

3 Kieft GJ, Gloem JL, Rozing PM, Obermann WR. MR imagingof recurrent anterior dislocation of the shoulder: comparisonwith CT arthrography. AJR 1988; 150: 1083-7.

4 Reicher MA, Kellerhouse LE. MRI of the wrist and hand.New York, USA: Raven Press, 1990: 92-3.

5 Kujala UM, Kvist M, Ostermann K. Knee injuries in athletes.Review of exertion injuries and retrospective study ofoutpatient sports clinic material. Sports Med 1986; 3: 447-60.

6 Heron CW. Review article: MRI of the knee. BIR 1993; 66:292-302.

7 Spiers ASD, Meagher T. Ostlere SJ et al. Can MRI of the kneeaffect arthroscopic practice? I Bone Joint Surg [BrI 1993; 75-B:49-52.

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8 Ruwe PA, Wright J, Randall RL et al. Can MR imagingeffectively replace diagnostic arthroscopy? Radiology 1992;183: 335-9.

9 Kursunoglu-Brahme S. Schwaighofer B, Gundy C et al.Jogging causes acute changes in the knee joint: an MR studyin normal volunteers. AJR 1990; 154: 1233-5.

10 Van Heuzen EP, Golding RP, Van Zanten TE et al. MRimaging of meniscal lesions of the knee. Clin Radiol 1988; 39:658-60.

11 Lee JK, Yao L, Phelps CT et al. Anterior cruciate ligamenttears: MR imaging compared with arthroscopy and clinicaltests. Radiology 1988; 166: 861-4.

12 Beltran J, Noto AM, Herman U et al. Tendons: high fieldstrength, surface coil MR imaging. Radiology 1987; 162:735-40.

13 Dipaola JD, Nelson DW, Colville MR. Characterizingosteochondral lesions by MRI. Arthroscopy 1991; 7: 101-4.

14 Lynch TC, Crues JV, Morgan FW et al. Bone abnormalities of

the knee: prevalence and significance at MRI. Radiology 1989;171: 761-6.

15 Genez BM, Wilson MR, Houk RW et al. Early osteonecrosis ofthe femoral head: detection in high risk patients with MRimaging. Radiology 1988; 168: 521-4.

16 Kier R, Dietz MJ, McCarthy S et al. MR imaging of the normalligaments and tendons of the ankle. Journal of Computed AxialTomography 1991; 15: 477-82.

17 James S. Bates B, Ostering L. Injuries to runners. Am J SportsMed 1978; 6: 40-50.

18 Keene JS, Lash EG, Fisher DR et al. Magnetic resonanceimaging of Achilles tendon ruptures. Am J Sports Med 1989; 17:333-7.

19 Fleckenstein JL, Shellock FG. Exertional muscle injuries: MRIevaluation. Top Magn Reson Imaging 1991; 3: 50-70.

20 Modic MT, Masaryk T, Boumphrey F et al. Lumbar herniateddisc disease and canal stenosis: prospective evaluation bysurface coil MR, CT and myelography. AJR 1986; 147: 757-65.

ROYAL COLLEGE OF PHYSICIANS OF LONDON

CONFERENCE ON

MEDICAL HAZARDS OF EXERCISE AND SPORTMonday 11th - Tuesday 12th July 1994

Sessions will include:

Overview of participation In sport and recreation In the UKand the most hazardous sports and recreation

Mass participation and sudden deathWater sports at home and abroad

Hazards of exposure to cold and altitudeExercise and Injury to musculoskeletal system

Other adverse effects of Intense exerciseAnabolic steroids and associated drug abuse

The risks of not taking exercise

at Royal College of PhysiciansI1 St Andrews Place, Regent's Park, London NW1 4LE

Further details from the Conference Office,Tel: 071 935 1174, ext 252/300 Fax: 071 4875218

Concessionary rates are available for this Conference

PGEA APPROVAL REQUESTED

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