D. J. Wilson, MD, FRCP, FRCR
Senior Clinical Lecturer University of Oxford, Consultant Radiologist, Department of Radiology, Nuffi eld Orthopaedic Centre and John Radcliffe Hospital, NHS Trust, Windmill Road, Headington, Oxford OX3 7LD, UK
Injuries of the Ligaments and Tendons 19 19
in the Ankle and Foot
David J. Wilson
Box 19.1. CT
● High radiation dose
● Poor soft tissue contrast
● Not indicated in the assessment of ligament injuries
Box 19.2. Radiography
● Not indicated in ligament injuries
Box 19.3. Ultrasound
● Excellent tool for assessing the superfi cial soft tissues
● Allows stress testing of ligaments
● Quick, easy and cheap
● Patient friendly
● Dynamic and Doppler imaging useful
● Direct interaction with patient often helpful
Box 19.4. MRI
● Excellent tool for assessing joint, bones and soft tissues
● Sensitive and specifi c for most ligament injuries
● Expensive and not very patient friendly
● Shows associated bone disease
● Easier to interpret than US for the inexperi- enced
● May not show dynamic instability
C O N T E N T S
19.1 Introduction 322
19.2 Mechanisms of Ankle Injury 323
19.3 Inversion Injuries of the Ankle 323 19.3.1 Ultrasound 323
19.3.2 MRI 326
19.4 Eversion Injuries of the Ankle 327 19.4.1 Ultrasound 327
19.4.2 MRI 327
19.5 Foot Injuries 328 19.5.1 Spring Ligament Tears 328 19.5.2 Plantar Fascia Injuries 328 19.5.3 Turf Toe 328
19.6 Stress Injuries 329 19.6.1 Ultrasound 330 19.6.2 MRI 332
19.7 Variations of Normal 333
19.8 Image Guided Injections 334 19.8.1 Treatment of Neovascularity 334 19.9 Conclusion 334
Things to Remember 335 References 335
and nature of the injury and the safety of early mobil- isation.
A prerequisite for understanding traumatic ankle pathology is a thorough knowledge of the anatomy of the ankle ligaments. This is summarized in Fig- ures 19.1 and 19.2.
19.2
Mechanisms of Ankle Injury
The most common injury to the ankle is due to an inversion stress. The majority of these events will lead to tearing of the anterior lateral soft tissue structures including the talofi bular and tibiofi bular ligaments. Severe injuries and those injuries occur- ring in the older age group with less resilient bones may fracture.
Fig. 19.1. Ligaments of the lateral side of the ankle
Fig. 19.2. Ligaments of the medial side of the ankle
19.1
Introduction
Acute injuries to the ankle and foot present a substan- tial portion of cases of sporting injuries. Running, twisting and turning activities all present the athlete with continued risk of an injury which might range from a simple ankle sprain to a career threatening injury. To place imaging in its proper context one must understand that the vast majority of injuries to the ankle are dealt with by the athlete alone and resolve spontaneously. Only the minority of all are presented to a clinical team and of these an even smaller minority require any form of investigation or decisive management.
The issues that we must address is fi rst how this triage process occurs to ensure that those with rela- tively minor injuries are not over investigated, but also to establish need for investigation in those who may dismiss their injuries as trivial when early intervention might prevent medium to long-term disablement.
Changes in the availability, quality and under- standing of the imaging appearances of tendon ligament injuries have made a substantial impact on any management of sporting trauma. On many occasions a substantial increase in information has not yet been met by a signifi cant alteration in clinical practice. It may be that as time goes by our increased knowledge of the nature and type of injury will allow us to divide patients into those who require newer and novel forms of treatment from those who are unlikely to benefi t (Bencardino et al. 1999;
Lazarus 1999; Schlegel et al. 1999; Bleakney and White 2005). In this chapter I will not only deal with the current state-of-the-art knowledge but also address the potential of imaging to act as a tool for the clinical investigator looking towards novel forms of management.
The vast majority of soft tissue injuries will settle
spontaneously with rest, elevation, analgesia and
treatment with ice packs and indeed many minor
injuries require no active management. Initial man-
agement will include plain fi lms to exclude fracture
when there is bone tenderness. If the individual’s
occupation or sporting career do not depend on early
use of the injured limb then it is often reasonable to
treat conservatively. However, there will be occasions
where the high performance athlete and those whose
occupation depends on early activity, may warrant
more complex investigation to determine the extent
then start to fail. The talofi bular ligament being the fi rst and most common to rupture; this is a relatively thin structure and susceptible to minor inversion injuries. The anterior tibiofi bular liga- ment which has two discrete segments and arguably three components may tear partially or completely.
Only in the more severe injuries does calcaneo- fi bular ligament tear. This ligament is three to fi ve times thicker than the anterior lateral ligamentous structures and its rupture very commonly leads to long-term instability. It is much more likely that a surgeon would consider repair of injuries to this ligament, both in the sporting and the non-sport- ing individuals.
The distal fi bula is prone to fracture. If there is a rotatory element to the injury, spiral fractures may occur or if there is simply pure inversion, avulsion of the tip of fi bula may result. The incidence of frac- tures increases with age. There is a good evidence of clinical examination with a careful palpation will adequately exclude bony injury and obviate the need for examination by plain fi lm. Should there be doubt or suspicion then plain radiographs will normally be more than suffi cient to identify and classify the type of fracture. Depending on the nature of the fracture assumptions may be made about the integrity or damage to ligamentous structures.
The peroneus brevis tendon inserts onto the proximal part of the fi fth metatarsal. Severe inver- sion injuries may lead to injuries of this tendon or, perhaps more commonly, avulsion fractures of the proximal fi fth metatarsal. Clinical suspicion of this injury should be raised when there point ten- derness. The fi rst investigation should be a plain radiograph.
Direct imaging of the ligamentous structures is best achieved with either ultrasound or MRI (Figs. 19.3 and 19.4).
19.3.1 Ultrasound
Ultrasound has a very high line pair resolution when compared to MR, provided that it is used for super- fi cial structures. Around the foot and ankle all the ligaments and tendons are superfi cial and therefore very well visualised in fi ne detail with high resolution ultrasound. The signs of ligamentous injury on ultra- sound are failure to identify the normal structures, thickening of the normal ligament, adjacent haem- orrhage and edema, synovial or soft tissue hyper- Eversion injuries are much less common. However,
the same rules apply and the imaging assessment is very similar.
Direct axial loading injuries typically from a fall from a height or descending from a jump are more likely to cause compression fractures in the tibia, talus and the calcaneus. This chain of bones may take the whole body weight. Paradoxically falls of less than 30–40 cm in height may produce much greater stress on this complex than a fall where the indi- vidual has time to react to the sensation of descent by contracting muscles in the lower limb. We will all have experienced the shock of impact that occurs when we mistakenly think that we have reached the bottom of the staircase and then take an additional step. The descent of a step is insuffi cient height for the nerve conduction to occur from labyrinth to cerebral cortex and downward to the motor pathways. The cli- nician may mistakenly imagine that a descent from a modest height will not lead to an injury.
Repetitive strain most commonly causes stress injuries in the forefoot and particularly the second metatarsal. In this chapter we will discuss the inves- tigation and assessment of patients with potential stress injury. Tears of the Achilles tendon are in many circumstances a form of stress injury. Whilst an acute hyperextension force may lead to a tear in the tendon, it is far more common that the force involved is rela- tively minor. The previous minor injuries and repeti- tive strain seem to predispose this ligament to par- tial and full thickness tears. In this area imaging has made a signifi cant impact in management protocols (Linklater 2004). Unfortunately not all clinical cen- tres have taken advantage of these changes and clini- cal teams should study this advancing area in detail.
19.3
Inversion Injuries of the Ankle
The nature of the damage in an inversion injury will
depend on the velocity of the impact, the weight
of the individual, the age of the patient and weak-
nesses generated by previous injuries. If there are
elements of rotation to the inversion, this may affect
different parts of the ligamentous and bony com-
plex. In simple terms an inversion injury initially
leads to stretching and minor intra substance tears
of the lateral and anterior lateral ligamentous struc-
tures (Fig. 19.1). In younger patients the ligaments
trophy (Fig. 19.5). In the repair stages granulation tissue and reactive synovitis may lead to new blood vessels which can be identifi ed on power Doppler imaging. Because the anatomy of the lateral liga- mentous structures is complex, imaging in multiple planes will be necessary. A clear understanding of the normal location of the ligaments is essential to interpret the signifi cance of their absence. Compari- son should be made with the normal and unaffected limb to be certain that a ligament is truly absent.
Dynamic stressing of the ligament by either passive or active inversion of the foot and ankle increases the sensitivity of ultrasound in detecting injuries of the ligaments. Paradoxical motion is when one bone moves away from the other in a location where it should be tethered. In an acute injury, the pressure involved should be very mild and should not cause the patient signifi cant discomfort. Even minor degrees of movement are often suffi cient to confi rm a full tear of the ligament. In the case of chronic instability where the local pain has settled, the stress applied may be more vigorous, however it is recommended that the movements involved again are small, as care- ful observation of relatively mild motion is usually more sensitive than dramatic degrees of stress. Soft tissue edema and synovitis are demonstrated by alteration in the tissue contour with thickening of the tissue planes. Soft tissue edema is refl ected by a reduction in the echo pattern (hypo-echogenicity) and scar tissue which will be seen as a more refl ective material. Synovial tissue within the mortise joint or anterolateral gutter may hypertrophy particularly in chronic ankle strain. This may lead to a mass effect in the anterolateral gutter (Fig. 19.6). This so-called synovitic lesion may in turn impinge against the adja- cent bony structures and cause signifi cant dysfunc- tion (“anterolateral impingement syndrome”). This is typically seen in professional footballers and those whose activity leads to rapid turning and kicking motions (Linklater 2004; Robinson and White 2005). This area is diffi cult to examine by imaging as the synovitic mass may sit deep within the antero- lateral gutter. It has a similar appearance on MRI to adjacent soft tissues (Fig. 19.6). The accuracy of MRI in detecting lesions that are clearly identifi ed at subsequent arthroscopy is, however, poor. Recently it
Fig. 19.3. Normal calcaneo-fi bular ligament on a composite ultrasound image
Fig. 19.4. Normal calcaneo-fi bular ligament. Axial FSE T2-weighted MR image of the calcaneo-fi bular ligament, the foot is held in an equinus position
has been demonstrated that ultrasound examination with the addition of a dynamic compression of the fi bular against the tibia is a more accurate technique in detecting synovitic lesions (Fig. 19.6). The lesion is seen as a mushroom shaped object which emerges from the anterolateral gutter on a compression of the two bones. There is a high correlation between this appearance and arthroscopic fi ndings.
Repetitive injury to joints may also be associated with pigmented villonodular synovitis (PVNS). This is a benign but locally aggressive tumour of a single joint that is seen more commonly in those who have been athletically active. It should be considered in those with a destructive monarthropathy and when MRI shows signal distortion that suggests hemosid- erin deposition (Fig. 19.7) in a joint (Saxena and Fullem 2004).
Fig. 19.5. Ruptured talo-fi bular ligament. Axial ultrasound.
There should be a band of echogenic fi bres running horizon- tally across the image, the examiner must know where to fi nd this structure to be sure that it is absent
Fig. 19.6a–c. Anterolateral gutter pain and swelling are symp- toms of a synovitic lesion (anterolateral impingement syn- drome). This axial MRI (a) shows a low signal mass adjacent to some joint fl uid and absence of the anterior talo-fi bular ligament. Ultrasound examination shows a bulging mass and no ligament (b). When the tibia is pressed towards the fi bula this mass pushes out in an anterior direction (c)
a
b
c
ning along the plane of this ligament may be more precise. Much more diffi cult is the calcaneofi bular ligament (Figs. 19.4 and 19.8). This is unfortunate as it is the most structurally important and there- fore where we would like to image most accurately.
The calcaneofi bular ligament runs in oblique plane from the calcaneus running anteriorly and superi- orly to the fi bula. The angle varies with individuals and the shape of the hind foot. It is very diffi cult to judge the inclination of the best imaging plane to produce a true axial of this ligament. It is common that axial images will show the ligament on multiple slices and it is diffi cult to follow its integrity even with MIP reconstructions. Alternative strategies are to place the foot in an equinus position, which elevates the calcaneus, making the calcaneofi bular ligament a more horizontal structure (Figs. 19.4).
In this position a true axial is more likely to show the calcaneofi bular ligament in its full length but this may be a diffi cult position for the patient to achieve and hold, particularly if the ankle is pain- ful. Therefore it may be easier to examine the foot
Fig. 19.7. PVNS. Sagittal gradient T2* MR image shows low signal intensity areas with blooming artefact (due to hemo- siderin deposition) at the tibiotalar joint, subtalar joint and along the course of the fl exor hallucis longus tendon (image courtesy of F. Vanhoenacker)
Fig. 19.8. Complete rupture of the calcaneo-fi bular ligament.
Axial FSE T2-weighted MR image shows fl uid from the joint fi lling the space where the ligament should be
19.3.2 MRI
This is commonly used in the assessment of the lateral ligamentous structure (Van De Perre et al.
2004). T1 weighted images are particularly useful at demonstrating the normal anatomy. Ligaments will appear black against the adjacent fat which will be white. In case of injury, T2 weighted images will show edema in the soft tissues and if fat suppression is used then this can easily be differentiated from fatty structures. Therefore T2 weighted images with fat suppression, or perhaps more sensitively, Fast STIR images should be employed (Morrison 2003;
Narvaez et al. 2003a, b).
Because the anatomy of the lateral complex is
variable, the choice of imaging planes is diffi cult
(Zoga and Schweitzer 2003). True axial images
are particularly useful for looking at both the ante-
rior and posterior tibiofi bular ligaments. The ante-
rior talofi bular ligament will also be seen on most
axial images although arguably an oblique axial run-
in a neutral position and incline the imaging plane with the anterior margin more cranial. The diffi - culty is how to assess the degree of angulation that would be required for an individual. Careful pal- pation of the ankle and judgement of the imaging plane by the examining technician or radiographer may assist. True 3D volume imaging of this region has an advantage that reconstructions can be made in different planes. However, 3D volume is most effectively achieved using gradient echo imaging and the contrast between the ligament and the adja- cent structure is not as effective as it is on spin echo imaging. Therefore 3D volume images are more dif- fi cult to interpret.
19.4
Eversion Injuries of the Ankle
The fi rst structure to fail in an eversion injury is the medial collateral complex (Fig. 19.2). This is a del- toid (triangular) shape. Whilst it may be anatomi- cally described as being divided into the tibiotalar and tibiocalcaneal components, dissection is more likely to show a continuous sheet of ligaments. Avul- sion injuries of the medial malleolus are a common accompaniment and these will be associated with point bony tenderness. Impaction of the everted hind foot against the fi bula may cause fractures of lateral structures or diastasis of the tibia from the fi bula with rupture of the intra-osseous membrane and the anterior and posterior tibiofi bular ligament.
When fractures and complex injuries of this type occur it may be useful to assess the functional sta- bility with the patient under a general anaesthetic using stress radiographs. In the setting of an acute injury stress views are not indicated as pain inhibi- tion will prevent abnormal motion and this type of examination would be exceptionally painful. Direct imaging of the medial collateral complex may be performed with either ultrasound or magnetic reso- nance imaging.
19.4.1 Ultrasound
Ultrasound examination has the advantage that it is fast and easy to perform, although experience is required for correct interpretation. The ligament
should be examined in all its sub-components including the anterior, middle and posterior por- tion. Sprains and tears may affect part, or all, of the ligament. A clear understanding of the anatomy is important as the operator should be able to reli- ably fi nd the normal medial collateral complex in order that its absence can be defi nitely detected.
Absence of the ligament itself is the primary sign of a rupture. Loss of clarity, thickening, adjacent edema and haematoma are supplementary signs.
Perhaps most useful is to perform dynamic stress.
Even in the relatively acute injury, very mild degrees of stress will show alterations in the dynamics of the collateral ligament. The bones will move in a paradoxical direction with no tethering. Compari- son can be made with the normal unaffected side to assess the normal degree of ligamentous laxity in individual patients. When examining with dynamic stress it should never be necessary to cause dis- comfort; however in a more acutely injured ankle a degree of stress applied is very mild. Power Doppler imaging allows the examination of the soft tissues for vessel injection which is an indication of a repair process.
19.4.2 MRI
Magnetic resonance imaging is best achieved using a combination of T1- and T2-weighted images. Ide- ally the T2-weighted images should be with either spectral fat suppression or a Fast STIR sequence.
For the medial collateral complex a true coronal plane is ideal. The signs of ligamentous injury are absence of the normal ligaments, edema, thicken- ing and associated haematoma. MRI has the addi- tional advantage that it will show edema in the bone at the site of the insertion of the ligament if there has been an insertion strain (Trappeniers et al. 2003). Avulsion injuries may be surprisingly diffi cult to detect on MRI. They are identifi ed as edema in the fragments of bone and low signal lines at the fracture site. Care must be taken in analysing the image and reference made to plain radiographs. When there is doubt and other inves- tigations are not available it may be appropriate to perform plain radiographs and/or CT examination.
The importance of detecting bony avulsion is that
they are often much pure easier to repair surgically
and is clinically diffi cult to differentiate avulsion
from ligamentous injury.
19.5
Foot Injuries
19.5.1
Spring Ligament Tears
MRI is really the only practical way of detecting spring ligament tears. It will also allow diagnosis of concomi- tant injury or other ligaments as these are common.
Surgical repair is possible and effective (Fig. 19.9). A gap in the ligament, edema, irregularity, changes in calibre and associated tendinosis of the posterior tibial tendon are all signs associate with surgically proven tears (Balen and Helms 2001; Toye et al. 2005).
19.5.2
Plantar Fascia Injuries
Most patients with symptoms that arise from the plantar fascia have chronic insertion pain at the medial aspect of its calcaneal insertion. Tenderness and swelling in this region are fairly specifi c clinical signs. US and MRI (Fig. 19.10) are useful as they show thickening (>4 mm depth is abnormal), edema and insertional enthesites (Theodorou et al. 2002; Sabir et al. 2005). US guided injection of local anaesthetic and steroid may be and effective therapy. There are advocates of shock wave therapy, “dry needling” and autologous blood injection; currently there is little scientifi c evidence to indicate the best method (Kane et al. 2001; Zhu et al. 2005). Acute tears are uncom- mon and appear as defects in continuity on MR or US (Saxena and Fullem 2004).
19.5.3 Turf Toe
This is a condition that principally affects Ameri- can Football and Australian Rules football players. It results from the use of light footwear, hard surfaces and a hyperextension injury. The injuries that result are rupture of the plantar plate to the fi rst metatar- sophalangeal joint associated with separation and sometimes fractures of the sesamoid bones (Ashman et al. 2001; Mullen and O’Malley 2004). MR will show edema and discontinuity in the fascia on sagit-
Fig. 19.9. Ruptures of the spring ligament may be repaired by surgery (image courtesy of Mr R. Sharp FRCS)
Fig. 19.10a,b. Plantar fascia rupture. a Sagit- tal T2 FSE fat sup- pressed MR images of the hind foot of an elite triple jumper who sustained an acute injury of the plantar fascia. b Note the edema at the calcaneal insertion and the dis- ruption of continuity best seen on the coro-
nal image a b
tal images. Fractures of the sesamoids as less obvious on MRI and careful examination of the plain fi lms (Fig. 19.11). or CT may be required. US will show any fracture and may also demonstrate dynamic opening of the gap (Fig. 19.12).
Fig. 19.11. On a lateral radiograph separation of the sesamoid in a sagittal direction demonstrates that there has been a soft tissue plantar plate rupture (image courtesy Mr R. Sharp FRCS)
Fig. 19.12. Athletes with Turf Toe present with pain and swell- ing over the plantar aspect of the fi rst MTP joint (cross sign on the plantar aspect of the foot)
19.6
Stress Injuries
Stress fractures will be dealt with elsewhere in Chap. 7 of this book. Stress injuries to ligaments and tendons occur due to repetitive loading ( Sijbrandij et al. 2002; Chambers 2003; Wilder and Sethi 2004). It is argued that it is more likely in the ath- lete who does not warm up or stretch in advance of exercise. It certainly is much more common as age advances and the strength and integrity of the ligaments and tendons diminishes. It can be argued that the majority of cases of chronic tendinosis are simply results of multiple small injuries to the tendon which leads to partial and incomplete repair.
This leads to thickening and enlargement of the tendon with pain, a moderate level of paratenonisis and new vessel growth into the tendon as part of the repair process. Overuse of tendons may lead to infl ammatory changes in the synovium that lines the sheaths where the tendons run around corners, par- ticularly under the malleoli and, to a lesser extent, in the anterior part of the ankle. Here the disease is in the tendon sheath itself and the term tenosynovitis is reasonably used.
There is some confusion of terminology. For the purposes of this discussion we use the term tendino- sis to indicate a chronic abnormality of the tendon substance itself. Paratenonitis means edema and swelling in the soft tissues adjacent to the tendon, this being discreet from abnormalities of the synovial sheath seen where tendons make acute angles around a joint. Tenosynovitis is swelling and abnormality of the synovium within the tendon sheath, which is often associated with increased quantities of fl uid in that sheath. In itself it does not necessarily indicate a disease of the tendon proper. However, tenosynovitis may be seen in association with tendinosis.
Degeneration within the tendon and mucoid change is part of the process of tendinosis. This may be subdivided into chronic thickening, vessel injec- tion (Fig. 19.13), internal splits and tears and eventu- ally complete tendon rupture.
Plain radiographs have little role in the assess-
ment of tendon disease, with the exception of avul-
sion injuries of a tendon insertion. The two common
injuries that of this type that may occur around the
ankle are avulsion of the proximal pole of the fi fth
metatarsal due to the peroneus brevis tendon avul-
sion and avulsion of the posterior superior aspect of
the calcaneus by the Achilles tendon.
19.6.1 Ultrasound
Ultrasound is probably the best method of initially assessing tendons. The tendon should be examined in a longitudinal and axial plane. Where the tendons run around corners it will be necessary to rotate the probe so that it follows the tendon. In the fi rst instance this is often easiest to image in a plane axial to the tendon, reserving a sagittal image until the examiner has a clear idea of the route of the tendon in the patient being examined. Ultrasound is extremely effective at demonstrating fl uid around the tendon and in differ- entiating synovial thickening from free fl uid. Blood vessel injection is easily demonstrated using Power Doppler. Power Doppler is more effective than con- ventional Colour Doppler imaging at demonstrating the low fl ow rate in vessels that grow into tendons and synovium.
Examination of tendons using ultrasound must include a dynamic assessment. Moving the tendon actively (muscle contraction) or passively (the exam- iner moves the limb) may give different information as these actions apply force to different ends of the tendon. When the tendon is more of a supporting structure (for example tibialis posterior), loading strain may be applied by standing or pressing on the limb to pull on the tendon. Dynamic examina- tion should be performed routinely. Movement will differentiate between full and partial thickness tears.
Partial tears may open under load when they are
diffi cult to identify on static imaging but they will not separate or show paradoxical movement of the tendon ends.
Longitudinal and internal splits within tendons may only be visible on the axial view and may be diffi cult to assess on sagittal planes (Figs. 19.14 and 19.15). Impingement of tendons against bony spurs and osteophytes may only be demonstrated on dynamic imaging. In general the amount of fl uid in the tendon sheath should not exceed the size of the tendon itself. Therefore the cross sectional diameter of the fl uid should be less than the diameter of the tendon. The exception to this rule is fl exor hallucis longus. In a signifi cant proportion of the normal population (around 50%) there is a communica- tion between the mortise joint and the fl exor longus tendon sheath. This means that small quantities of fl uid within the joint may extrude into the fl exor hal- lucis tendon and give the impression that there is a disease of the tendon. The amount of fl uid in the tendon sheath may exceed the size of the tendon itself by many times. In these cases care should be taken to examine the tendon in detail to look for tendino- sis. The presence of fl uid around the fl exor hallucis longus tendon as a result of communication with the mortise joint suggests that there is a joint disease.
There should be no blood vessels identifi able within normal tendons. The presence of neovascular- ity is a specifi c sign of disease and attempted repair.
Full rupture of a tendon presents with pain and disability. There are many occasions from which these
Fig. 19.13a–c. Chronic Achilles tendinosis is seen as a het- erogeneous signal area of irregular thickening on MRI (a,b) whilst using Doppler US vessels are seen to enter the tendon (c)
a
c
b
tears are diffi cult to diagnose clinically. In particular, injury to the tibialis posterior tendon may present with confusing clinical features.
Identifi cation of a full rupture of a tendon is best achieved with ultrasound and a dynamic stress
(Fig. 19.16). This is particularly true of the Achil- les tendon where the clinical team will be decid- ing whether to treat the patient conservatively with immobilisation in an equinus position or by surgi- cal procedure (Bleakney and White 2005). In the patient with an acute Achilles injury the clinical ques- tions are fi rstly whether the injury is to the tendon or the musculotendinous junction. Injuries to the muscular tendonous junction are much more likely to settle spontaneously. Having determined that the injury is in the tendon proper, locating the tear with respect to a fi xed anatomical point is important. Sur- gical repair of tendon ruptures is now commonly performed through small incisions which need to be precisely localised by imaging. The imager should fi nd the rupture and identify its location from a fi xed reference point. In the case of the Achilles tendon it is best to choose the posterior superior aspect of the calcaneus, as this is one that can be palpated clini- cally. Reference should then be made to the position of the tear with relationship to this bony landmark when the patient’s foot is in a defi ned position, for example a true neutral position. If the patient is shortly to undergo surgery it is reasonable to mark
Fig. 19.15. A split of the peroneus brevis allows the longus tendon to enter the defect and is seen a three oval low signal areas on axial MRI
Fig. 19.14a–c. Longitudinal splitting of the peroneus brevis tendon. Using ultrasound a longitudinal split in the peroneus brevis tendon is seen as a dark (hypoechoic) area. In this case the central split (a) extends into a ganglion adjacent to the tendon (b). Both are seen well on the sagittal view (c) a
c
b
the tears on the skin with an indelible marker, again indicating the position the joint was in at the time this marking took place.
At corners tendons are held by retinaculae which are fi brous pulleys. These structures guide the tendon movement and prevent bow string- ing. The retinaculae are very thin and diffi cult to image but injury may be implied. Movement of the tendon away from its normal position and sublux- ation in varied positions are the specifi c sign. US (Fig. 19.17) is arguably more effective in this type of case and MRI has a signifi cant error rate (Saxena and Fullem 2004).
Chronic tendinosis probably represents multiple small partial tears and incomplete or unfi nished repair. Focal thickening, heterogeneity, loss of a clear tendon margin and vascular ingrowth are all imaging features (Fig. 19.13). However athlete with particular training regimes may show focal changes in tendons and edema in bones as part of the response to the loads imposed on the tendon. These changes are asymptomatic and symmetric (Lohman et al. 2001;
Magnusson and Kjaer 2003).
19.6.2 MRI
Axial and sagittal images are the most useful. Axial planes are the most effective at assessing the tendon integrity as these can be performed serially through- out the length of the potentially injured area. Where a tendon runs around a corner, for example the pero- neal tendons or the tibialis posterior and the fl exor digitorum longus tendons, then the axial images will need to be supplemented by a coronal view to show a true axial of the tendon through the majority of its length. Sagittal images are more diffi cult to achieve as tendons tend to course in oblique routes and may traverse several slices. 3D volume imaging may be useful but there can be problems in the contrast between the tendon and the adjacent structures as 3D imaging is most commonly achieved using gra- dient echo sequences. Tenosynovitis will be seen as edema around the tendon seen as high signal on T2 weighted images. Using conventional MRI it is not possible to differentiate the synovial thickening from free fl uid. If intravenous Gadolinium DTPA is
Fig. 19.16a,b. Tear in the mid portion of the Achilles tendon on ultrasound with extended fi eld of view shows (a). Dynamic stress achieved by moving the toes up and down by about one centimetre shows the gap open and close confi rming that this is a full thickness tear (b)
a
b
Fig. 19.17a,b. The peroneal tendons lie beneath the distal fi bu- lar and appear as two round structures on this axial ultra- sound image (a). In (b) both tendons are seen to sublux into a position superfi cial to the tip of the fi bula. The retinaculum is therefore defi cient
a
b
given, the increased signal that occurs within most areas of synovitis will assist. However some forms of synovitis have a relatively low fl ow particularly if they are chronic and there may be continued diffi culty in making this differentiation. Note that ultrasound is not limited by these circumstances and does not require contrast agents to differentiate fl uid from synovitis. Hence, ultrasound may be a very useful supplement to an MRI examination. Internal degen- eration within tendons may be seen as increasing on T1-weighted images due to mucoid change. Inter- nal splits and tears are seen as lines on T1-weighted images and/or edema within the tendon. MRI is a little less sensitive to this diagnosis when compared to ultrasound. Full thickness tears and retraction are relatively easy to identify on MRI, but partial tears, or tears without retraction may be diffi cult to assess (Fig. 19.18). When there is doubt dynamic imaging should be performed and this is best achieved by a supplementary ultrasound examination. MRI and CT have both been used to image dynamically but this is a more complex and cumbersome method (Renard et al. 2003).
19.7
Variations of Normal
Around the ankle and hind foot there are a number of common variants. Some of the normal varia- tions in alignment of tendons and ligaments have been described above. Additional muscles have been described, peroneus tertius, peroneus quartus and accessory soleus (Fig. 19.19) being the most common.
Fig. 19.18. Torn Achilles tendon on a sagittal fat suppressed proton density MR image. The defect is shown but it is uncertain whether there are any residual intact fi bres as the tendon ends are not very far apart
Fig. 19.19. An accessory soleus muscle appears as a very low insertion of the soleus onto the anterior surface of the Achil- les tendon
The hallmarks of an accessory muscle are that it is usually bilateral (but not always), the muscle will have a pennate or fi brillar structure on ultrasound and it will contract normally. Some so-called acces- sory or additional muscles are simply variations in the structure of a normal muscle. It may be argued, for example, that the accessory soleus is simply a very low insertion of the normal soleus belly. The plantaris muscle and tendon is a common variant. It arises from a small muscle belly in the medial side of the proximal calf next to or within the medial head of gastrocnemius. The plantaris tendon runs parallel to the Achilles tendon. It may insert in the calcaneus, but equally it may insert at any point along the Achilles tendon. In patients who not have an identifi able sepa- rate plantaris tendon, it is likely that the muscle belly and tendon are embryologically part of the Achilles.
This may produce a dent or bump on the Achilles
tendon surface. The plantaris tendon is very useful
when tendon transfers and transplants are being con-
sidered. Pre-operative identifi cation of the plantaris
may be achieved either using ultrasound examina- tion or MRI.
There are rare occasions when accessory muscles may become injured or painful. In these circum- stances it may be diffi cult to differentiate these from soft tissue masses or a tumour. In these circum- stances comparison with the normal side is especially useful.
19.8
Image Guided Injections
Injection of a local anaesthetic against topical ste- roid is a common means of treating chronic injuries in and around the ankle. There are a number of haz- ards. Unguided injections may penetrate the tendon and cause further damage. The adjacent neurovas- cular structures may be damaged. Numbing and temporary anaesthesia of a tendon or ligament may allow the patient to perform actions which produce excess loading and lead to rupture of the tendon or ligament. This is a particularly serious risk in those tendons which are weight bearing which includes the majority of those in and around the ankle. Local anaesthetic and steroid injections should only be given to tendons in and around the ankle when careful consideration has been given to the risk of rupture. It is wise to perform initial imaging to ensure that the disease is not within the tendon itself (tendonosis). In those patients where there are partial tears, longitudinal splits, mucoid degen- eration or thickening of the tendon considerable care should be taken before considering injection of that region. It is relatively safe to inject patients who have pure tenosynovitis and a normal tendon.
On the other hand if a ligament or tendon is fully ruptured, then there is unlikely to be any worsen- ing due to an injection procedure. If consideration is being made to giving injections in patients with tendon abnormalities, then the patient should be carefully consented for the risk of rupture. A sur- geon who would be involved in a repair should be consulted and consideration should be given to immobilising the limb for one or two weeks in a lightweight splint. Certainly the patient should be non-weight bearing for several days after the injec- tion if a splint is not provided. Image guidance using ultrasound is the most effective method of placing needles in a location that does not damage adja-
cent structures. The needle should be introduced as close to 90q to the incident ultrasound beam as possible, as this gives the best visualisation of the needle track (Fig. 19.20). The needle tip can be followed and the injectate observed as it fl ows into the target tissue.
Fig. 19.20. Ultrasound guided intervention. Ultrasound is the ideal means of guiding needles into tendon sheaths. A needle is introduced at almost 90q to the ultrasound beam and moved up to the tibialis posterior tendon sheath
19.8.1
Treatment of Neovascularity
It has been suggested that either dry needling of areas of neovascularity and tendinosis or alterna- tively the direct injection of autologous blood (drawn from the patient by venesection) will accelerate heal- ing. As yet there are no randomised control trials to assess this technique and it must at present be regarded as experimental. Other authors have sug- gested the injection of sclerosing agents at the base of the neovascularity; similarly this is an experimental procedure.
19.9 Conclusion
Ultrasound and MRI now provide us with tools to
assess and quantify the nature of tendon and liga-
ment disease around the ankle. They are playing an
increasing role in prognosis, management and treat-
ment for those patients with ankle injuries.
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