Disorders of the Fingers and Hand

Introduction

This section will be divided into abnormalities that occur on the flexor side and those that occur on the extensor side of the fingers. Each section will deal separately with disorders of tendons and ligaments and retinacula. The flexor and extensor tendons of the hand are divided into zones to help describe and plan the treatment of injuries. The extensor zones are numbered 1 to 7, with the odd numbers overlying joints, beginning distally. Zone 1 is therefore the area overlying the distal interphalangeal joint (DIPJ) and zone 7 is overlying the wrist. The even-numbered zones lie between the joints. On the flexor side, there are 5 zones, also numbered from distal to proximal.

Flexor Tendons

Anatomy and Clinical Aspects

There are two flexor tendons to each finger: one superficial and one deep. Each arises from the corresponding flexor digitorum superficialis and flexor digitorum profundus muscle belly.

Key Point

The superficialis tendon is the superior of the two finger tendons but it inserts first at the base of the middle phalanx. In order to achieve this, the tendon splits and sends a medial and lateral slip one each side of the profundus tendon to their respective insertions in the proximal part of the middle phalanx.

The profundus tendon continues distally to insert on the volar aspect of the distal phalanx. The two tendons are contained within a common sheath. Vascular supply is from the adjacent digital arteries, with the vascular pedicle, or vincula, invaginating the tenosynovium as the tendovaginum.

Disorders of the tendon and tendon sheath, as with tendons elsewhere, include tenosynovitis, tendinosis and tendon rupture. Tenosynovitis refers to inflammation on the tendon sheath. The term tendinosis is sometimes used for intratendinous mucinous degeneration, which is not associated with symptoms. Tendinopathy is a similar term, but in the same context indicates that symptoms are present. Others use the term tendinosis regardless of whether symptoms are present or not.

Tenosynovitis

Key Point

A synovial sheath surrounds the two flexor tendons in the finger. These are separate from the tendon sheath surrounding the flexor tendons within the carpal tunnel.

Flexor tenosynovitis may occur as a misuse injury in sport. Increased fluid and synovial thickening within the tendon sheath can give rise to the classical ‘sausage digit’ appearance. This pattern is particularly associated with seronegative arthropathy, most typically psoriatic arthropathy. The soft tissue manifestations of psoriatic arthropathy may precede the appearance of the typical psoriatic rash, so the absence of a rash does not exclude the diagnosis. The differential diagnosis of sausage digit includes infective tenosynovitis, although this is uncommon. The history of trauma, particularly a biting injury and a human bite, is often the worst, should be sought. Infection can be acute or chronic. Chronic infection in the tendon sheath is less often accompanied by heat and redness. In these cases tuberculous dactylitis should be suspected. Yaws and syphilis are other uncommon causes.

Practice Tip

Patients with tenosynovitis may initially complain of stiffness and inability to form a fist and not infrequently arthritis is suspected.

Inflammatory changes within the tendon manifest as increased fluid and, with progress of the disease, thickening of the synovial lining and increased Doppler signal.

Practice Tip

The earliest ultrasound finding is the appearance of the dark halo around the tendon.

This is due to a thin rim of fluid that comes between the tendon and tendon sheath (Fig. 15.1). This sign is best appreciated on axial images, especially by comparing the affected finger with those that are not involved.

Figure 15.1 Transverse section of flexor tenosynovitis of third finger. Note a thickened low-reflective halo around the otherwise normal tendon. Compare with the adjacent flexor tendon.

As the amount of fluid increases, the tendon sheath becomes increasingly distended (Fig. 15.2). In long axis fluid and synovial thickening will not be evenly distributed along the length of the tendon (Fig. 15.3), but will be initially constrained in the areas of the flexor pulleys, creating a lobulated appearance. This should not be misinterpreted as multiple ganglia. As the disease progresses, the degree of synovial thickening (Fig. 15.4) and Doppler activity increases (Fig. 15.5). At this stage associated tendinopathy is common and vascular ingrowth is identified within the substance of the tendon itself, alongside accompanying intratendinous matrix changes.

Figure 15.2 Flexor tenosynovitis. Fluid surrounds the tendon apart from where the tenovaginum attaches. Note the slight thickening of the synovial lining of the tendon sheath.

Figure 15.3 Long axis of flexor tenosynovitis. Note the rind of low-signal material around the tendon. It has an undulating appearance where the sheath is constrained by the flexor pulleys.

Figure 15.4 Flexor tenosynovitis. Note the sharp reflective margin of the flexor tendon.

Figure 15.5 Transverse section of wrist extensor tenosynovitis. Increased Doppler activity indicates the areas of active inflammation.

Tendon Rupture

Rupture of the flexor tendon may affect either the superficial or profundus tendon, although the latter is more common.

Key Point

The commonest site of flexor profundus tear is just proximal to its insertion into the base of the distal phalanx.

This injury is referred to as a jersey finger or rugby finger, reflecting a common cause of injury. The profundus tendon of the ring finger is the most commonly affected by the jersey pull injury. The injured player attempts to grab his opponent by the jersey but only manages to gain purchase with the tip of the finger, which is then forcibly extended. The insertion of the profundus tendon is avulsed from the underlying bone with a small bony fragment attached, or a small stump of tendon remains attached to the distal phalanx (zone 1 injury) and the remainder of the tendon retracts proximally (Fig. 15.6). The index finger is involved in 75%.

Figure 15.6 Flexor tendons at the level of the palm. The superficial flexor tendon is intact. There is a tear of the profundus tendon that is retracted.

Clinically there is localized tenderness, pain and swelling and inability to flex the DIPJ. The latter can be assessed during the ultrasound by fixing the proximal interphalangeal joint (PIPJ). Additionally, during finger flexion there will be dysynchronous movement between the proximal and distal portions of the ruptured profundus tendon. Gentle finger movements are also helpful to distinguish between partial and complete tears. Synchronous movement between proximal and distal components of a suspected tear excludes a complete rupture in the acute phase.

Practice Tip

The flexor tendons are less strongly attached to the surrounding structures and thus the degree of retraction is often quite large.

Ultrasound is useful not only to confirm the presence of tendon rupture, but also to identify the precise location of the tendon ends. This can be useful for surgical planning as more precise identification of the tendon ends reduces the need for extensive exploratory surgery. Two small incisions can be made at the locations identified by ultrasound, thus minimizing the risk of postoperative adhesions.

The location of flexor tendon rupture can also be reported using the zones method. Zone 1 covers the segment between the superficialis and the profundus insertions. Zone 2 is the area between the superficialis insertion and the distal palmar crease. In this segment the profundus and superficialis tendon lie in close proximity. Zone 3 is between the level of the A1 pulley and the flexor retinaculum. Zone 4 covers the section of flexor tendon within the flexor retinaculum and zone 5 that portion proximal to it. Jersey finger has its own classification as there is often a small bony avulsion fragment attached to the tendon which influences the degree of retraction encountered. If a large bony injury is involved, retraction proximal to the A4 pulley is uncommon. This is designated a type 3 lesion. In the rare type 4 lesion the profundus tendon may itself be avulsed from the avulsed bony fragment. Retraction of the tendon into the palm is designated a type 1 and retraction to the level of the PIPJ a type 2, completing the spectrum of lesions.

As it is required to cross fewer joints than its deeper counterpart, closed rupture of the superficialis tendon is uncommon but can occur due to forced extension against a contracted muscle. It is also less prone to abrasion against the carpal bones. Open tendon lacerations are a more common cause of superficial flexor tendon rupture and most frequently involve the midsubstance of the tendon.

Flexor Pulleys

Anatomy

The flexor tendons of the hand are held in place by a series of connective tissue retinacula that are formed by condensations of the fibrous sheath. They are arranged into annular and cruciate configuration, referred to as the A and C pulleys (Fig. 15.7). The pulley system is important for keeping the flexor tendons close to the phalanges to maximize their ability to flex the fingers. Clinically, the annular A pulleys are by far the most important and these are numbered A1–5. The A1, A3 and A5 are at the level of the metacarpalphalangeal, PIP and DIP joints respectively. They are on the convexities of the flexor tendons and are thus less prone to injury. The A2 pulley is at the level of the midportion of the proximal phalanx and the A4 pulley at the midportion of the middle phalanx (Fig. 15.8). These are on the concavity of the flexor tendon and are more prone to injury.

Figure 15.7 Schematic diagram of the annular pulleys. Five sets are present. A1, A3 and A5 are at the level of the articulations on the convexity of the tendon. A2 and A4 are on the tendon concavities and are the most prone to injury.

Figure 15.8 The normal A4 pulley is a low-signal, thin structure surrounded by a rim of more reflective connective tissue. The A2 and A4 pulleys overlie the tendon at its most concave portion.

The A2 is the largest of the pulleys. It can be visualized directly on ultrasound and note is made of any associated injury. Functionally, it is tested by noting the distance between the profundus tendon and the underlying bone when the finger is flexed against resistance. With a functioning pulley, the flexor tendon should show minimal separation from the underlying bone.

Pulley Injury

The classic injury leading to pulley rupture is typified by the crimp grip of rock climbers. Hyperextension occurs at the metacarpalphalangeal joint and flexion at the IPJ. If the weight supported by the fingers in this position is suddenly increased beyond the restraining ability of the pulley system, rupture occurs. The flexor tendons are pulled away from the phalanges and shorten. This is called bowstringing. The middle and ring fingers are the most vulnerable. There is some disagreement as to which pulley ruptures first, although most commonly the injury is said to begin at the distal portion of the A2 pulley. It then progresses through A4 with progressive bowstringing of the flexor tendon (Fig. 15.9).

Figure 15.9 With increasing strain, the A2 pulley ruptures. The flexor tendon separates from the proximal phalanx with bowstringing.

Key Point

The degree of bowstringing measured by the separation of the flexor tendon from the underlying bone gives a clue on which pulleys are involved.

A small gap (<3 mm) suggests isolated A2 injury and gaps more than 5 mm suggest multiple pulley involvement. The A1 pulley is rarely involved in this injury. Injuries to the cribriform or C pulleys are reported, but not common.

Ultrasound Imaging of Pulley Rupture

Injury to the pulley itself may be visualized by both ultrasound and MRI (Fig. 15.10). Ultrasound offers an advantage over MRI in that the pulley can be stressed dynamically. The patient places the back of their hand on the examination couch and the probe is placed in long axis overlying the A2 pulley. A free finger of the examiner’s hand is placed on the distal phalanx of the finger being examined, restraining it as the patient flexes (Fig. 15.11

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