The palmar fascia is a triangle shaped, tough sheet of connective tissue placed deep to the skin in the palm of the hand (Fig. 2).3 Ulnarly it is limited by the hypothenar muscles and laterally by the thenar muscles. Skin displacement during grip is prevented by fibrovascular septae with loculated fat in between that link the skin to the palmar fascia. This arrangement resembles closely to the plantar fat pad.4 In addition, seven sagittal ligaments join the palmar fascia to the deep metacarpals fascia and result in 8 tunnels, 4 for the flexor tendons and 4 for the lumbricals5 distal to the central compartment of the hand. The superficial fibers of the palmar fascia fan out from palmaris longus and continue in the fingers as the pretendinous band, the spiral fibers and the lateral digital sheet. All of these structures, as well as the vertical septae that link the palmar fascia to the skin, are important in the pathogenesis of Dupuytren's contracture.6,7 The deep fibers are generally transverse and can be considered an extension of the transverse carpal ligament into the palm. The fascia that covers the thenar and hypothenar muscles,8,9 in contrast to the thick and complex palmar fascia, is thin and adherent to muscle. There is a superficial, transverse muscle that can be seen to bulge in the hypothenar eminence which originates in the palmar fascia and inserts in the skin. This is palmaris brevis.10 The function of this peculiar muscle is conjectural. On the one hand it deepens the cupping of the hand when we drink from it. Also, it contracts synergistically then the 5th MCP is flexed with the PIP and the DIP in extension and during the abduction of the 5th digit.

Fig. 2.

(a) The palmar fascia. The longitudinal fibers derive from palmaris longus tendon. Note the transverse fibers of palmaris brevis, a subcutaneous musle at the hypothenar eminence. From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.16, with permission. (b) A transverse section of the hand. The palmar fascia is located near the palmar surface. It is connected to the dermis by fibrous strands that loculate tiny fat lobules. Septae connect the deep aspect of the palmar fascia to the deep fascia that overlies the metacarpals and the interosseous muscles (the insert shows the site of the section). From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.16, with permission.

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Participants will have traced on their hands the full length of the digital flexor sheaths. They should understand the role of the restraining fibrous structures that maintain the tendons in close vicinity to bone and prevent bowstringing during flexion of the digits, the anular and cruciform pulleys.11 Although pulleys are discontinuous when the fingers are extended, with synovial tissue in between, they come together and form an almost continuous tube when the fingers are flexed (Fig. 3). The A1 pulley, being the most proximal and therefore the one that deflects the flexor tendons is the one that stands the greatest tendon/pulley pressures. Resulting swelling and chondroid changes in both the pulley and the tendon lead to nodule formation and the trigger phenomenon.12 Although patients sometimes perceive the entrapment elsewhere the trigger phenomenon is an A1 pulley affair. Because finger flexor muscles are stronger than extensors trigger fingers are usually caught in flexion. A permanent flexor deformity may result in late, unrelieved cases. An additional restraining fibrous structure is the palmar aponeurosis pulley which is comprised of transverse fibers of the palmar fascia. This restraint, which is of marginal importance in normals, helps at preventing bowstringing when the A1 or the A2 pulley is cut. The thumb has 3 anular pulleys and an oblique pulley. The thumb A1 pulley, as in the fingers, overlaps the MCP joint.13 The correct diagnosis in our patients is a trigger finger in Patient 1 and a trigger thumb in Patient 2. We would like to add that when the MCP joint ligaments are weakened, as in rheumatoid arthritis, the pull of the A1 pulley on the palmar plate and the base of the proximal phalanx in forceful finger flexion may be such as to cause palmar subluxation of the joint.

Fig. 3.

This is a simplified rendition of the fibrous digital pulleys. The proximal pulley, A1, inserts in the palmar plate and in the transverse metacarpal ligament that binds neighboring palmar plates. From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.22, with permission.

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The proximal extension of the synovial flexor tendon sheaths, which are contained in the digital flexor sheaths, will now be shown (Fig. 4). It is often surprising that the synovial sheath of the little finger connects with the ulnar bursa, a synovial expansion deep in the palm, in over 70% of cases.14 This three-layered structure, which provides a gliding surface between the long and short fingers flexors, as well as a gliding surface deep and superficial to these tendons, extends into the carpal tunnel and for about 2.5cm into the distal forearm. The synovial sheath of the long flexor of the thumb, also known as radial bursa, also traverses the palm and the carpal tunnel and extends into the distal forearm. In contrast, the synovial sheaths of the flexor tendons 2–4 end in the palmar space just short of the A1 pulley at the neck of the metacarpal bones. In Patient 3 the diagnosis is a rheumatoid flexor tenosynovitis. In this condition the swelling, which is due to both tenosynovial proliferation and effusion, involves the finger and the distal portion of the palm. Rheumatoid tenosynovitis may present few local findings but it must be suspected when a rheumatoid patient cannot actively make a full fist but passively the affected fingers can be painlessly flexed. The swelling tends to be diffuse and distend, as in our patient, the palmar cul-de-sac. Needless to say, these patients greatly improve with a well-placed tenosynovial corticosteroid injection.

Fig. 4.

This figure shows the relationship between the transverse palmar creases and the flexor synovial sheaths. Note that for the digits 2,3,4 the synovial sheaths end near the transverse creases. For the thumb and the small finger the sheaths extend to the distal forearm. The expansion of the latter in the mid palm is the ulnar bursa, a synovial structure extends to the carpal tunnel and the distal forearm. From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.24, with permission.

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The great British anatomist Frederick Wood Jones stated that creases are the joints of the skin.15 Looking at the palm there are 2 transverse creases, the distal and the proximal (Fig. 4). The distal crease, arising in the ulnar side of the hand bends distally and ends in the 2nd web space. The proximal crease begins with the longitudinal thenar crease in the 1st web space and ends short of the hypothenar eminence. An amazing phenomenon occurs when the straight fingers are bent 90 degrees at the MCP joints. Both the distal and the proximal crease come together in a continuous transverse crease. A cord placed in this crease indicates the proximal edge of the A1 pulley for the fingers 2–5. Deeper structures overlied by this cord include the flexor tendons, the palmar plates, the deep intermetacarpal ligaments that link neighboring palmar plates, and the MCP joints. Look at this region, known as region V or metacarpophalangeal by hand surgeons, from the palm, the radial side and the dorsum to get an idea of its complexity. More distally in the palmar side there is a crease where the finger appears to arise, the proximal digital crease. However, a cord placed around the finger at this crease, looked from the dorsum, crosses the mid portion of the proximal phalanx. Finally, a cord placed around the mid and the distal digital creases roughly overlaps the PIP and the DIP joints, respectively.

The palmar plates are thick and dense plates – whether they are fibrocartilaginous or not is in debate – that reinforce the volar aspect of the MCP joints (Fig. 1). While distally the palmar plates are firmly attached to the proximal phalanx, proximally they become a thin, membranous capsule.16,17 Each palmar plate is connected to the neighboring palmar plates by the deep intermetacarpal ligament. Also, sagittal bands (SB) connect the extensor tendon to the edges of the palmar plates, which also give insertion to the accessory MCP lateral collateral ligament and the A1 pulley. Thus, the palmar plates provide a true anchoring system to the fibrous skeleton of the MCP region. Together, the SBs and the palmar plate form a closed cylindrical tube that surrounds the metacarpal head. It is considered that the SBs represent the main stabilizer of the extensor tendon at the MCP joint.18 Damage of the radial sagittal fibers is one of the factors leading to ulnar deviation in rheumatoid arthritis. Palmar plates with a similar phalangeal attachment are also present in the interphalangeal joints.19

In Patient 1 the injecting needle is placed just distal to the proximal transverse crease for the index, between the proximal and distal creases for the middle finger and just distal to the distal crease for the anular and the little finger. There is no need to place the steroid within the synovial sheath in this condition. Indeed, extrasynovial injections appear to work better. The injection for the trigger thumb is quite different and the thumb sesamoids are used as a landmark. The thumb has 2 sesamoid bones which are easily palpable at the base of the thumb on the flexor side. These tiny bones transmit force from the abductor pollicis and the flexor pollicis brevis to the proximal phalanx via the volar plate. They also guide the flexor pollicis longus tendon that lies between them.20 The thumb sesamoids vary in size among people and one may be larger than the other. The sesamoids area is normally tender to palpation. The injecting needle is aimed at the sesamoids (Fig. 5). In Patient 3, with a diagnosis of rheumatoid flexor tenosynovitis, it is quite important to place the steroid within the sheath because synovial tissue is interspersed between pulleys and at both ends of the tube. An intrasynovial injection is felt by the patient as fluid extending distally along the palmar aspect of the finger.

Fig. 5.

In the trigger thumb the needle is inserted toward the sesamoid bones, which coincide with the proximal anular pulley of the thumb.

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If we overstretch the fingers the extensor tendons, prominent in the dorsum of the hand, are seen to disappear at the fingers. One of the reasons of this phenomenon is that the extensor tendon itself is anchored by sagittal fibers to the palmar cartilaginous plate that reinforces the MCP on the palmar side.21,22 A second reason is that the extensor tendon becomes embedded in the dorsal digital expansion.23–25 The dorsal digital expansion may be viewed as an isosceles triangle applied on the proximal phalanx (Fig. 6). The expansion incorporates the central tendon fibers destined to the base of the middle phalanx. In addition, it contains two previously separated extensor tendon contingents, the radial and the ulnar lateral bands, that join together prior to their destination at the base of the distal phalanx. Also, the interossei muscles as well as the lumbricals, past the deep transverse metacarpal ligament that separates them, run toward the angles of the extensor lamina and once incorporated to this structure, extend along the lateral sides in the middle and lateral conjoined tendons.21 In finger flexion the lateral bands slide palmarly over the PIP joint while in extension the tendon pull brings them closer together as to better extend the DIP joint.26 Is it possible to palpate the extensor lamina? Yes, by 2-finger palpation, one radial and one ulnar, on the dorsolateral aspect of the proximal phalanx during flexion-extension movements. Is it important? Yes, to get a dynamic idea of what it is going on.

Fig. 6.

The extensor lamina is a triangular fibrous sheath in the dorsum of the proximal phalanx. The extensor tendon is incorporated into this lamina and the interosseous muscles and the lumbrical muscles attach to its sides. From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.54, with permission.

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The interosseal muscles, both the dorsal and the palmar (Fig. 7), have their origin in the metacarpals and insert at the corners of the extensor lamina. In addition, the dorsal interossei have a point of insertion in the proximal phalanx.27,28 Both sets of muscles run dorsal to de deep intermetacarpal ligament. The longitudinal axis of the hand is comprised of the long finger and the 3rd metacarpal. Proof of this is that the 3erd digit stays still when the fingers are spread apart and when they are brought back together. While the dorsal interosseus tendons are so placed as to separate the index and the anular away from the long finger, by having 2 dorsal interossei this finger is able to separate from its own axis to the ulnar and the radial sides. The separation of the little finger is achieved primarily by the abductor digiti minimi and the separation of the thumb primarily by the abductor pollicis brevis. Are the bellies of the dorsal interossei identifiable on examination? The answer is a timid yes for the interossei of the long and anular fingers (you can feel them hardening during abduction with a finger appropriately placed on the dorsum of the hand) and a rotund yes for the index dorsal interosseus. This muscle is eminently placed, as well as distinctly developed in normal subjects, as to allow its clinical identification and functional characterization far beyond dissection.29 An experiment can be made “in vivo” by looking at the radial side of the 2nd MCP joint which is free of an overlapping finger. With the tip of a ballpen is possible to identify a point that remains still during flexion-extension movements. This is the transverse axis of the MCP joint. Now let's abduct the index. This motion brings up a strong muscle belly in the web space, which is no other than the dorsal interosseus muscle. If the free edge of this muscle is followed toward the index a tiny tendon appears to attach to the proximal phalanx (in most cases the attachment is to both bone and the dorsal lamina) about 1cm palmar to the axis point which explains its flexor action on the MCP joint. Furthermore, through the dorsal lamina the same contraction extend the interphalangeal joints. Variations are common in the dorsal interossei.30 All dorsal interossei are innervated by the ulnar nerve.

Fig. 7.

The left panel depicts the palmar interosseus muscles. These are three and given their disposition they bring the index, the anular and the little finger toward the 3rd finger which is the axis of the hand. The dorsal interosseus muscles are shown in the right panel. The middle finger has two and the anular and the index fingers have one. Their disposition is such that they separate the fingers from the 3rd finger, and move the 3rd finger to one and the other side. From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.20, with permission.

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There are 3 palmar interosseous muscles (Fig. 7), one for the index, one for the anular and 1 for the little finger.28 These muscles, similar to the dorsal counterparts, insert near the corner of the dorsal lamina, on the opposite side. With their origins and insertions facing the long finger it is easy to appreciate that they function as adductors, i.e. they bring the fingers close together. Their actions on the transverse axis of the joints are the same as in the dorsal interossei, flexion of the MCP joint and extension of the PIP and DIP joints. The palmar interossei cannot be reliably identified by palpation. Anatomical variations in these muscles are common.27 All palmar interossei are innervated by the ulnar nerve. Before leaving the interosseous muscles let's make one more experiment. Please note that adduction and abduction of the fingers have been tested in extension. How about with the MCP joints flexed 90 degrees? These motions are not possible. Is this due to the characteristics of insertion of the interosseal muscles? The answer is not, as passive motion is also canceled. The reason for the inability to abduct and adduct the fingers is the eccentric nature of the collateral ligaments of the MCP joints. They are lax in extension and taut in flexion. In rheumatoid arthritis, where damage to the MCP collateral ligaments may occur, lateral finger motion at 90 degrees of MCP flexion is a reliable indicator of this lesion.

These unique muscles that really look like earthworms have their origin in the deep flexor tendons in the palm of the hand (Fig. 8).30,31 In their way to the extensor lamina they run palmar to the deep metacarpal ligament.32 A unique characteristic of the lumbrical muscles is that, having had an origin in a flexor muscle their insertion is in the extensor lamina and therefore their main action is to flex the MCP joints while extending the PIP and DIP joints. This flexor/extensor linkage, an abundance of mechanoreceptors, plus a common innervation with the flexor digitorum profundus (index and middle finger, median nerve; ring and small finger, ulnar nerve) is telling us something in a language we still do not understand. Variations in the lumbrical muscles are frequent.39 One such variation that may cause a carpal tunnel syndrome is an origin within the carpal tunnel. An origin in the forearm has also been described.

Fig. 8.

The lumbrical muscles are shown. They are palmar, while the dorsal and the palmar interossei are dorsal, to the transverse metacarpal ligament. From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.20, with permission.

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Patient 5. De Quervain's tenosynovitis.

“A 79-year old violist presents with severe pain in the radial side of his wrist. He is due to play in a concert in 2 days. On physical examination there is a bulky trapeziometacarpal osteoarthritis. He has a markedly positive Finkelstein test. What am I supposed to do? This patient exemplifies a common clinical situation. When there are concurrent conditions, which one is causing the pain? One of his conditions is known to be rather refractory to treatment, the osteoarthritis. The other, de Quervain's tenosynovitis, is eminently treatable by a steroid infiltration. This dilemma was presented to the patient and he had no doubts about the correct course of action which was to have the 1st dorsal compartment tenosynovial sheath injected. The infiltration was successful and he was able to play at his concert”.

Continuing with our cord experiments, if we place a cord at the distal wrist crease, on the palmar side the cord indicates the proximal limit of the transverse palmar ligament and on the dorsum, the distal limit of the extensor retinaculum (Fig. 9). Thus, the extensor retinaculum is a forearm extensor tendon restraint and the transverse carpal ligament is a wrist flexor tendon restraint. This concept is critical to an understanding of the contents of the radial-most tendon compartments:first dorsal compartment, abductor pollicis longus (APL) and extensor pollicis brevis (EPB); second compartment, extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB); and third compartment, extensor pollicis longus (EPL). Moving distally, at the wrist the first compartment tendons remain the same, but they are followed by EPL and then ECRL and ECRB. The reason for this transposition is an oblique course of EPL at the wrist. Going back to the extensor retinaculum, EPL is flanked radially by a bony eminence, the dorsal tubercle of radius or Lister's tubercle, that redirects its course. The fourth compartment contains extensor indicis (EI) and extendor digitorum (ED). The fifth compartment, which is easy to locate between the distal end of ulna and the radius contains extensor digiti minimi (EDM) and the sixth and compartment, extensor carpi ulnaris. At the first compartment both APL and EPB may have multiple slips In addition, a septum and a bone ridge may be present in 30%–40% between the APL and the EPB tendons.33

Fig. 9.

The dorsal fibrous tunnels are shown. An important landmark is the dorsal tubercle of radius (Lister's tubercle) which lies radial to extensor pollicis longus (EPL). This is a frequent site of tendon rupture in rheumatoid arthritis. From A Companion to Medical Studies, Volume 1, Ed. by Passmore R and Robson JS, 2nd Edition, Oxford, Wiley/Blackwell 1976, p. 23.22, with permission.

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A unique pain syndrome may occur after heavy labor, the intersection syndrome of the forearm.34,35 Pain, tenderness and swelling occur dorso-radially in the forearm about 4 FB proximal to Lister's tubercle. A diagnostic sign is a tendon friction rub brought about by thumb abduction and flexion-extension movements of the wrist. A simple maneuver reveals the anatomy of this condition. Place 4 fingers on the wrist and distal forearm, the little finger next to the base of the 2nd and 3rd metacarpals, the anular over Lister's tubercle, and the long finger and the index proximal to the latter. Now ask the patient to gently dorsiflex the wrist. The tension of the ECRL and ECRB will be felt with the little finger and less with the other fingers. Let's now ask the patient to abduct the thumb. The APL and EPB will be tense up and this will be felt by the index but not by the other digits. Indeed, if one runs the index proximally over the radius these muscles will be felt to run obliquely over a generally longitudinal background. To summarize, APL and EPB cross superficially over ECRL and ECRL A rheumatologist with an interest in clinical anatomy should be able to make an instant diagnosis of intersection syndrome. Someone less informed may require an MRI or an ultrasonography study.