Imaging of the fingers has come a long way in the past decade. Higher field strength MR scanners, specialized coils and advances in scanner and coil technology allow very high resolution imaging of the small structures of the hand. MRI is routinely used to diagnose injury, determine the location, severity and extent of injury and help direct the type and timing of treatment. At the conclusion of this activity, participants will understand the basic challenges of MR imaging of the fingers, know the basic MR imaging strategies for imaging the fingers, and know the important anatomy and common pathology encountered in MR finger imaging.
Imaging of the hand and fingers has come a long way in the past decade. Higher field strength MR scanners, specialized coils and advances in scanner and coil technology allow very high resolution imaging of the small structures of the hand. MRI is routinely used to diagnose injury, determine the location, severity and extent of injury and help direct the type and timing of treatment.
High spatial resolution is needed to evaluate the small structures, imaging planes and field of view must be chosen based on the site and type of suspected pathology and knowledge of the complex anatomy is requisite for successful MR imaging of the hand. Higher field strength (1.5T at a minimum, 3T ideally) MR scanners coupled with dedicated coils and isocenter imaging provide the high detail images necessary for evaluation. The field of view used should be as small as possible (tendon injuries are an exception, and larger field of view is necessary to identify retracted tendons) and include a digit on either side of the digit to be evaluated. Imaging planes must be prescribed in reference to the digit. Anatomic (T1 and proton density) and fluid sensitive (fat suppressed T2, PD, STIR) sequences are most helpful in evaluating pathology.
Injuries at the distal interphalangeal (DIP) joint:
Mallet finger: Injury of the terminal extensor tendon. The mechanism is forced flexion of an extended DIP joint. Sagittal and axial imaging planes best depict the injury. Injury to the terminal extensor tendon can result in swan neck deformity.
Jersey finger: Injury of the flexor digitorum profundus tendon at the DIP joint. The ring finger is most commonly affected. The mechanism is forced extension of an actively flexed DIP joint. Sagittal and axial imaging planes best depict the injury. Flexor digitorum profundus tendon requires surgical treatment.
Injuries at the proximal interphalangeal (PIP) joint:
Injuries at the proximal interphalangeal (PIP) joint result from a common mechanism of PIP injury (simultaneous hyperextension and axial compression) and include volar plate injury, central slip injury, collateral ligament injury and joint dislocation. Volar plate injury: There are best seen on sagittal images and can be purely soft tissue or associated with fractures. Fractures which involve greater than 40-50% of the articular surface are at risk for destabilizing the collateral ligaments1. Central slip injury: The central slip is central portion of the trifurcated extensor tendon which inserts on the dorsal aspect of the middle phalanx. It is best seen on the sagittal and axial images. If left untreated, these injuries can result in a boutonniere deformity which develops weeks after the initial injury.
Injuries at the metacarpophlanageal (MCP) joint:
Sagittal band injury: Envelops the extensor tendon and provides primary restraint to radial/ulnar deviation of the tendon at the dorsum of the MCP joint. Sagittal band injury can occur after relatively minor trauma in the elderly, be seen in the setting of rheumatoid arthritis or be injured as a result of a direct blow in boxing (“boxer’s knuckle”). This injury most commonly involves the third (long) digit. It is best seen on the axial images.
Collateral ligament injury: There are two collateral ligaments on either side (radial (RCL) and ulnar (UCL)) of the joint- the accessory and proper collateral ligaments. The proper collateral ligament is most important for joint stability. Thumb metacarpophalangeal collateral ligaments are most often injured. Thumb UCL can be injured as a result of sudden/forceful radial deviation of proximal phalanx. Healing can be impaired if the torn ligament is displaced superficial to the adductor aponeurosis (aka Stener lesion). Collateral ligament injury is best seen on coronal and axial images.
Digital annular pulley injuries:
There are 5 digital annular pulleys, designated A1 through A5 from proximal to distal. A2 and A4 are most important to prevent flexor tendon bowstringing2. Biomechanically significant injuries can result in loss of digital motion and power. The “crimp grip” used by climbers puts strain on the digital pulleys which can result injury. Annular pulleys are best seen on the axial and sagittal images.
Tendon lacerations:
Tendon lacerations are open tendon injuries. Flexor tendon injuries are classified into 5 zones (Zone I distal to the insertion of flexor digitorum superficialis tendon, zone II from the A1 annular pulley (MCP joint) to the insertion of flexor digitorum superficialis tendon, zone III from the carpal ligament to the A1 annular pulley, zone IV within the carpal tunnel, and zone V proximal to the carpal tunnel. Tendon lacerations are best assessed on sagittal and coronal images, and proximal tendon retraction necessitates larger field of view of imaging.
1. Prucz RB, Friedrich JB. Finger joint injuries. Clin Sports Med. 2015;34(1):99-116.
2. Zafonte B, Rendulic D, Szabo RM. Flexor pulley system: anatomy, injury, and management. J Hand Surg. 2014;39(12):2525-2532; quiz 2533.