Clinical case: Dupuytren's contracture

Objectives

• The overall goal of treatments for Dupuytren’s disease. What is meant by Percutaneous Needle Aponeurotomy (PNA). Other treatments for the condition.
• The anatomical/functional differences between the flexor digitorum superficialis and profundus.
• The synovial and fibrous digital sheaths of the hand. What is meant by trigger finger.

Treatments for Dupuytren's disease and percutaneous needle aponeurotomy

The goal of treatments for Dupuytren’s disease is to lessen the contractures and any discomfort caused by the condition. The treatment involves removing or breaking apart the cords of fibrous material that characterize the condition. Percutaneous Needle Aponeurotomy (PNA; needling) is a technique that uses a needle, inserted through the skin, to puncture and disrupt the cords of tissue that are causing the deformity. Contractures often recur but the procedure can be repeated. The primary advantages of PNA are that there is no incision, it can be done on multiple fingers simultaneously, and usually very little physical therapy is needed afterward. The main disadvantage is that there is a risk of nerve or tendon damage (as in this case).

Dupuytren’s disease can also be treated by enzyme injections that soften and weaken the fibrosis, which allows for manipulation that may be able to disrupt the cords and allow the fingers to extend. A third option for patients with advanced disease is to have the palmar fascia surgically removed. The primary advantage to surgery is that it results in a more complete and longer-lasting treatment than that provided by the two prior approaches (although in the case of this patient, the condition did recur in one hand after surgery). The main disadvantages are that physical therapy is typically needed after surgery, and recovery can be prolonged.

Differences between the flexor digitorum superficialis and profundus muscles

The FDS has two heads of origin - the humeroulnar (medial epicondyle of humerus) and radial heads, and from these heads four long tendons arise near the wrist and traverse the carpal tunnel. The tendons traverse across the palm and run along the ventral aspects of the digital rays to attach to the anterior margins on the bases of the middle phalanges of the four fingers. These tendons split (Camper's Chiasm) as they terminate to allow for passage of the FDP tendons (Figure 2). The FDS is innervated by the median nerve. The primary function of the FDS is flexion of the middle phalanges of the fingers at the PIP joints; however this muscle will also act to flex the MCP and wrist joints.

The FDP originates in the upper 3/4 of the anterior and medial surfaces of the ulna, interosseous membrane and deep fascia of the forearm. The muscle splits into four tendons for the fingers, passes through the carpal tunnel and palm to insert into the palmar base of the distal phalanx of each of the four fingers. The FDP lies deep to the superficialis, but attaches more distally by passing through the superficialis tendons. The medial part of the muscle (which flexes the 4th and 5th digits) is innervated by the ulnar nerve (C8, T1) whereas the lateral aspect (which flexes the 2nd and 3rd digit) is innervated by the median nerve, specifically its anterior interosseous branch (C8, T1). FDP is a flexor of both IP joints, the MCP, and the wrist joints. The lumbrical muscles of the hand arise from the radial side of each of the FDP tendons. Thus, this flexor muscle acts to assist the lumbrical muscles in their role as extensors of the IP joints. The force generated by the FDP at the more distal joints is controlled by wrist position. Flexion of the wrist causes muscle shortening, reducing the ability to generate tension distally. Extension of the wrist allows for more powerful digital flexion at the distal joints.

Synovial and fibrous digital sheaths of the hand

The flexor tendons as they enter the palm are retained in place by fascial retinacula, and are invested by synovial sheaths, which facilitate free movements of the tendons. Three synovial sheaths are located anterior to the wrist:

1. a common synovial flexor sheath the envelops all of the superficialis and profundus tendons;
2. a sheath that surrounds the tendon of the flexor pollicis longus; and,
3. the flexor carpi radialis, which has a has a short sheath.

Untreated infection of the synovial sheaths is liable to impair hand function. The common and pollical sheaths are often referred to clinically as the ulnar and radial bursae, respectively. The sheath that envelopes the FDS and FDP extends distally about midway along the metacarpal bones, where it ends in blind diverticula around the tendons to the index, middle, and ring fingers.

Once the flexor tendons emerge from the common flexor sheath they continue distally without a synovial sheath for a short distance (1 to 3 cm) until they become enveloped by their own tendon sheaths. These synovial tendon sheaths begin at the level of the metacarpal heads and extend to the distal phalanges. Synovial sheaths provide tendons with a large degree of freedom of movement. The fibrous digital sheaths on the palmar surface of the fingers keep the long digital flexor tendons in place during movements of the fingers. The fibrous sheaths are divided into the annular ligaments of the fingers, often referred to as A pulleys and less frequently vaginal ligaments, and the three cruciate pulleys. The annular and cruciate ligaments facilitate the flexor mechanism of the hand and wrist, preventing bowstringing upon contraction of the muscle.

Sometimes one or more of the flexor tendon becomes irritated and inflamed (swells), reducing the space for the tendon to move within its fibrous sheath (tunnel). The swelling may result in the development of a nodule that causes a snap or audible pop as the nodule moves within the sheath when the finger(s) is flexed. This is called trigger finger or stenosing tenosynovitis.