Clinical History: A 20 year-old collegiate football running back presents with severe pain and inability to bear weight following an acute hyperextension injury to his great toe. Fat-suppressed T2-weighted (1a) sagittal and (1b) coronal (short axis) images are provided. What are the findings? What is your diagnosis?
Grade 3 Turf Toe injury.
Injuries to the metatarsophalangeal region of the great toe were once considered relatively uncommon, but now are recognized as a frequent cause of morbidity and lost playing time in the athlete, particularly among American football players. The term “Turf Toe” was first coined by Bowers and Martin1 in a 1976 article describing capsuloligamentous sprains at the first metatarsophalangeal joint sustained by collegiate football players on artificial turf. Although the hardness and reduced shock absorption of artificial surfaces have impacted the frequency of this injury, it is also recognized that the use of softer soled shoes on artificial turf, allowing greater speed and traction for the athletes, have also had a major contribution, as hyperextension is more likely with these shoes as compared to the harder soled cleats utilized on natural grass. The frequency of turf toe among professional football players is estimated at 30-45%2,3. Although many clinicians originally felt that turf toe represented a relatively minor capsular sprain, the term is now used to describe a wide spectrum of injuries with greatly varying levels of severity4.
Anatomy and Pathophysiology
Although primarily a hinge joint that flexes and extends, motion at the great toe metatarsophalangeal joint includes rotary and sliding components. The relatively small and shallow articular surface of the proximal phalanx provides little intrinsic stability relative to the metatarsal head. The great toe withstands 40-60%
of body weight during normal gait, and this load increases several fold with running or jumping5. The toe’s ability to withstand this degree of stress and instability at the metatarsophalangeal joint is dependent upon anatomy that can be referred to as the capsuloligamentous-sesamoid complex.
The paired medial and lateral sesamoids are critical components of normal function at the joint, reducing friction and providing vital shock absorption at the great toe. Much of the complex anatomy at the metatarsophalangeal joint is related to the sesamoids. The sesamoids are embedded in a firm fibrous structure known as the plantar plate, which at its proximal aspect blends with the capsule about the plantar aspect of the distal metatarsal. Distally, the plantar plate attaches to the base of the proximal phalanx, where a small recess is often found. The plantar plate is relatively thin centrally, where it overlies the flexor hallucis longus. The posterior midline aspect of the plantar plate, lying between the sesamoids, may be referred to as the intersesamoidal ligament. At its periphery, where it attaches to the sesamoids, the plantar plate significantly thickens, and these regions are often referred to as the sesamoid phalangeal ligaments. It should be noted that the designation of the intersesamoidal and sesamoid phalangeal regions as “ligaments” is primarily semantic, as these regions are composed of the same type of fibrous tissue as the central plantar plate. The designations are analogous to the use of the terms dorsal and volar radioulnar ligaments to refer to the thicker peripheral regions of the triangular fibrocartilage at the wrist.
The collateral ligament complexes include main collateral ligaments and accessory sesamoid ligaments, the latter extending from the metatarsal head to the periphery of the respective sesamoids. The medial and lateral heads of the flexor hallucis brevis tendons attach to the sesamoids proximally. The abductor hallucis tendon attaches firmly to the medial aspect of the medial sesamoid with distal contributions blending with the capsule and the plantar plate. Laterally, the transverse and oblique heads of the adductor hallucis form a unified tendon that attaches to the lateral aspect of the lateral sesamoid with distal continuation to the joint capsule. The flexor hallucis longus tendon courses between the sesamoids as it extends to the distal phalanx, but does not actually attach at any point to the sesamoids.
The most common mechanism of injury in turf toe is a hyperextension event with the foot in mild dorsiflexion6. A frequent scenario involves a lineman engaged in a block who is injured when another player then falls upon the planted foot, driving the toes downward and hyperextending the great toe. Depending upon the vectors of force, any component of the capsuloligamentous-sesamoid complex can be injured. Associated valgus or varus forces result in a greater likelihood of injuries to the medial and lateral supporting components, respectively.
Normal MR Anatomy
The important anatomical components of the capsuloligamentous-sesamoid complex are well visualized on high quality MR images7. The plantar plate is seen as a thin low signal intensity structure on all pulse sequences, with its central portion being best visualized in the sagittal plane (6a). A normal synovial recess is often present at the distal insertion, typically appearing relatively small and smooth, and never full thickness in the normal plantar plate (7a). The thicker periphery of the plantar plate which comprises the sesamoid phalangeal ligaments is easily demonstrated in the sagittal plane (8a). Coronal (short axis) images may also provide visualization of the central plantar plate, though visualization is more difficult except for in cases where the plantar plate is thicker than typical. Thicker components such as the sesamoid phalangeal ligaments and the intersesamoidal ligament are well seen in the coronal plane.
Coronal images at the level of the sesamoids are utilized to confirm the normal position of the sesamoids relative to their facets along the plantar surface of the metatarsal head (9a). The low signal intensity band between the sesamoids, overlying the flexor hallucis longus tendon at this level, represents the intersesamoidal ligament. Contributions to the sesamoids from the abductor and adductor hallucis tendons as well as the sesamoid accessory ligaments are visible in this plane.
Though overall of the least value in the evaluation of turf toe, axial images (long axis) are useful in the assessment of sesamoid position, the peripheral sesamoid attachments, and for visualization of plantar musculotendinous injuries (10a).
MR Appearance of Turf Toe
Initial reports on the use of MR in the evaluation of turf toe described defects, swelling and/or edema in the region of the plantar capsule in patients with injury to the great toe metatarsophalangeal joint8,9. Advances in MR technology and knowledge of anatomy have subsequently led to a much more detailed approach to the evaluation of turf toe, such that numerous types and variations of injuries to the capsuloligamentous-sesamoid complex can be specifically described10.
Although clinical studies of turf toe have postulated that tears of the plantar capsule would predominate at a weaker attachment site upon the metatarsal head, our experience and published MR studies suggest that proximal capsular injuries are relatively uncommon (11a). Of patients who present for MR imaging, distal tears of the plantar plate and sesamoid phalangeal ligaments predominate (12a,13a).
With increasingly severe injuries, discrete defects within the plantar plate or sesamoid phalangeal ligaments may not be apparent. Rather, normal structures may simply be replaced by diffuse soft tissue thickening and edema (14a). In cases of extensive sesamoid phalangeal ligament disruption, proximal migration of the sesamoids is frequently apparent (15a).
The same forces that cause soft tissue injuries in turf toe also place osseous structures at risk, primarily the sesamoids. The role of the sesamoids in shock absorption at the toe and their plantar position result in a greater tendency for injury to the sesamoids relative to the metatarsal head or proximal phalanx11. The medial sesamoid is at greater risk as it is under a more direct weightbearing load12, but either sesamoid may be injured either acutely or due to the chronic repetitive stress that occurs in patients prone to turf toe (16a,17a).
In cases of turf toe with significant sesamoid migration, tendinous and capsular injuries are virtually obligatory, and should be carefully assessed. For the sesamoids to migrate proximally, the integrity of the attachments of the ipsilateral capsule, abductor or adductor hallucis tendons, and the accessory sesamoid ligament are quite likely compromised (18a).
Capsular and tendinous avulsions at the great toe may also occur in the absence of sesamoid migration. The most common clinical scenario is in cases where a hyperextension and valgus load are placed upon the toe, resulting in medial soft tissue injuries (19a,20a). In such cases, the plantar plate may remain intact, and the abnormalities may easily be missed if not carefully assessed as part of a thorough search pattern.
Management of Turf Toe
The wide spectrum of injuries in athletes with turf toe necessitates variability in the treatment approach. In 1994, Clanton and Ford proposed a clinical grading system for turf toe which remains useful for estimating severity of injury13. Patients with grade 1 injury have tolerable pain and minimal swelling, and are often able to finish the game or practice. These patients are felt to have a stretch injury or mild sprain of the capsuloligamentous complex. Patients with grade 2 injuries are thought to have partial tears, and present with swelling, pain, and guarding against dorsiflexion. Patients with grade 3 injury are felt to have complete tears, generally presenting with severe pain and often being unable to bear weight on the toe. Grade 3 injuries are those that are most likely to benefit from MR imaging in order to clearly delineate the extent and type of injury that has been sustained.
Most turf toe is managed non-operatively, with grade 1 injuries typically requiring little loss of playing time. Treatment measures including ice, elevation, and NSAIDS are generally effective. Higher grade injuries may require a walking boot or immobilization, with return to play dictated by the lack of pain with dorsiflexion, followed by pain-free running prior to progression to cutting or other more aggressive maneuvers. Early surgery for turf toe is indicated when large tears are present, in cases of joint instability, or when sesamoid diastasis or migration is present14. Osteochondral lesions and loose bodies are also indications for operative intervention. Defects in the plantar plate and sesamoid phalangeal ligaments are typically amenable to primary repair.
Another subset of patients benefitting from surgery includes athletes who fail conservative therapy. These patients may present months after injury with complaints of increased intensity and duration of pain following activity. MR in these patients is able to confirm significant anatomical lesions that require operative repair (R). Such delayed surgeries may be more challenging, as scarring and shortening of retracted structures often occur.
Turf toe, once felt to represent a minor injury of the great toe metatarsophalangeal joint, is now recognized as encompassing a wide spectrum of abnormalities with markedly varying severities. Turf toe is a quite common cause of morbidity and reduced playing time in competitive athletes, and has even proven career-ending in professional football players. MR’s ability to assess and characterize the abnormalities that exist in turf toe allows an accurate diagnosis to be made, providing valuable guidance in the determination of the need for operative repair. The use of MR in the evaluation of severe turf toe may facilitate earlier detection of injury patterns likely to require surgery, thereby avoiding prolonged morbidity and more challenging surgery that may result from diagnostic delays.
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