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The flexor tendons of the hand are held in place by a series of connective tissue structures called pulleys. The pulley system comprises a number of annular or A pulleys. These are supported by cribriform or C pulleys which are at the level of the joints. The annular pulleys are considered more important. There are four sets of A pulleys and three sets of C pulleys. The A1 pulley lies at the level of the metacarpal phalangeal joint just distal to the C1 pulley. Other A pulleys are between the joints
he commonest pathology of the A1 pulley is a fibroma which is discussed in another section. The A2 pulley is the largest of the pulley and lies at the level of the proximal phalanx. It holds the flexor tendon in close apposition to the proximal phalanx. It is a thin connective structure that is difficult to identify on imaging. Although direct visualisation is possible particularly on ultrasound, the function of the pulley is more commonly assessed by noting the distance between the flexor tendon and the underlying bone particularly when the finger is flexed against resistance. With a functioning pulley, the flexor tendon should lie no more than a millimetre from the underlying bone. Pulley injuries are most commonly described in rock climbers. The crimp grip in particular is used by climbers to secure a hold on the underlying rock and this places great stress on the flexor tendon and pulley system. The extent of injury to the pulley system can be assessed during flexion stress on the flexor tendon by identifying the distance between the tendon and the metacarpal. If the tendon is displaced but less than 3mm than a tear of the A2 pulley is diagnosed. If the distance between the bone and the tendon is more than 4mm then a combined tear of the A2, 3 and 4 pulleys is assumed. Injuries to the cribriform or C pulleys are rare.
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There is a synovial sheath surrounding each of the flexor tendons. These are separate from the tendon sheath surrounding the flexor tendons within the carpal tunnel. Inflammatory changes within the tendon manifests with increased fluid and, with progress of disease, increased vascularity and thickening of the synovial lining. Magnetic resonance imaging in the sagittal plane with high-resolution coils are best employed for the assessment of flexor tendon disease. Gadolinium enhancement helps to identify more subtle disease and is useful for recognising associated joint involvement. On ultrasound, the earliest manifestation is the appearance of the dark halo around the tendon. This is best appreciated on axial images, especially by comparing the affected finger with those that are not involved. In long axis fluid and synovial thickening will gather in the areas between the flexor pulleys
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Pulley Injuries
Trigger Finger
UCL thumb
Jersey Finger
Mallet Finger
Sagittal Band
Central Slip
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