27 Thumb

Russell A. Shatford, Antony Hazel, and James M. Kleinert

27 Thumb

27.1 Osteology

The skeleton of the radial side of the hand includes the trapezium, first metacarpal, and two phalanges—the proximal phalanx and the distal phalanx (▶Fig. 27.1). The thumb carpometacarpal (CMC) joint has very little inherent bony stability and relies on a complex network of ligaments. The thumb CMC joint is a complex joint, capable of perpendicular motions of flexion–extension, abduction–adduction, and rotation. For the complete description of the thumb CMC joint, please see Chapter 34 that is specifically devoted to this joint.

**Fig. 27.1** Thumb osteology. Volar view of right thumb. From *right* to *left* the bones are as follows: trapezium, first metacarpal, proximal phalanx, and distal phalanx. The groove in the trapezium that accommodates the flexor carpi radialis can be seen at the *bottom right* of the photograph.

The thumb metacarpophalangeal (MCP) joint (▶Fig. 27.2) is considered a condyloid joint though the condyles of the first metacarpal are less spherical than the other metacarpals. This less spherical shape limits lateral movement. The MCP joint is capable of flexion–extension, abduction–adduction, and rotation. Flexion ranges from 5 to 100°, with 53° being average. The radial condyle projects slightly more than the ulnar condyle, which results in pronation with flexion. ¹

**Fig. 27.2** Thumb metacarpophalangeal joint with radial collateral ligament (*bottom*) and ulnar collateral ligament (*top*).

The proper and accessory collateral ligaments ² of the MCP originate from the metacarpal head (▶Fig. 27.2). The ulnar collateral ligament (UCL) originates on the first metacarpal, approximately 4.2 mm from the dorsal surface, 5.3 mm from the articular surface, and 7 mm from the volar surface. The proper UCL inserts on the base of the proximal phalanx, approximately 9.2 mm from the dorsal surface, 3.4 mm from the articular surface, and 2.8 mm from the volar surface. The UCL is also joined by the insertion of the adductor pollicis (AP) (▶Fig. 27.3). The UCL is critical in stabilizing key pinch (▶Fig. 27.4a, b). The radial collateral ligament (RCL) originates on the metacarpal head, approximately 3.5 mm from the dorsal surface, 3.3 mm from the articular surface, and 8.1 mm from the volar surface, while the insertion of the proper RCL is 7.2 mm from the dorsal surface, 2.6 mm from the articular surface, and 2.8 mm from the volar surface (▶Fig. 27.5a, b). ³ The RCL is joined by the abductor pollicis brevis (APB) muscle at its insertion. The accessory collateral ligaments insert into the volar plate (▶Fig. 27.6). ⁴ The volar plate resists MCP joint hyperextension, originating at the volar neck of the first metacarpal and inserting into the base of proximal phalanx. The volar plate also contains the sesamoid bones. ⁵ The MCP joint capsule inserts into the dorsal base of the proximal phalanx and provides some indirect joint stability. In MCP extension, the volar plate and accessory collateral can resist ulnar and radial deviation, even in the absence of the proper collateral. Therefore, resistance testing of the proper collateral is performed with the MCP flexed. Complete laxity of the MCP in extension requires incompetence of both the proper and accessory collateral ligaments.

**Fig. 27.3** Thumb ulnar collateral ligament with adductor pollicis insertion. The adductor pollicis is inserting into the ulnar collateral ligament. The first dorsal interosseous muscle lateral head is originating from the first metacarpal.

**Fig. 27.4** The relationship between thumb and index finger during pinch. (a) In this figure the thumb and index finger interphalangeal joints are fully extended. The first dorsal interosseous muscle is dorsal to the adductor pollicis. (b) Here, the interphalangeal joints are flexed. In pinch, the first dorsal interosseous and adductor pollicis are contracted.

**Fig. 27.5** Radial collateral ligament of the thumb metacarpophalangeal joint in extension (a) and flexion (b).

**Fig. 27.6** Axial view of thumb proximal phalanx base with the volar plate to the left of the joint. The proper collateral ligaments can be seen inserting into the proximal phalanx base, while the accessory collateral ligaments can be seen inserting into the volar plate.

The thumb interphalangeal (IP) joint is a trochlear joint that acts as a hinge. ¹ The thumb proximal phalanx has two condyles, with an intercondylar notch in between that engages with the median ridge of the distal phalanx base, which provides some relative stability. The IP joint is further stabilized by the collateral ligaments and volar plate, and the insertions of the flexor pollicis longus (FPL) and extensor pollicis longus (EPL) tendons, at the volar and dorsal base of the distal phalanx, respectively. ⁶ Range of motion of the IP joint is from approximately 20° extension beyond neutral, to 80° flexion.

27.2 Myology

Thumb motion is achieved through a coordination of intrinsic and extrinsic muscles. The muscles can be defined as having a primary or secondary function, based on electromyographic data. ⁶

The intrinsic musculature of the thumb includes the APB, flexor pollicis brevis (FPB), opponens pollicis (OP), and adductor pollicis (AP) (▶Fig. 27.7a, b).

**Fig. 27.7** Thenar musculature: (a) overview, (b) detail view. From proximal to distal, the muscle mass volar to the flexor pollicis longus (FPL) tendon includes both the abductor pollicis brevis (APB, proximally) and flexor pollicis brevis (FPB, distally), with subtle separation at their origin, and separation distally by a tendinous portion, shown in more detail in the next figure. The opponens pollicis (OP) is not seen, as it is deep to the APB. Distal and dorsal to the FPL, the adductor pollicis (AP) courses from its origin, on the third metacarpal, to its insertion at the ulnar side of the thumb. The thumb pulleys are discussed later, but the first annular pulley can be seen at the level of the APB and FPB insertion, the variable annular pulley just distal to the first annular pulley, and the oblique pulley coursing from proximal ulnar to radial distal. Just distal and ulnar to the AP lies the first lumbrical, with its unipennate origin from the flexor digitorum profundus of the index, exiting the carpal tunnel, along with other digital flexor tendons. (c) This figure demonstrates the distinction between the APB (proximal and radial) and the FPB (distal and ulnar), with the OP deep, showing between the APB and FPB. (d) The actions of the FPB during thumb metacarpophalangeal joint flexion, with the muscle lax during passive flexion, are shown. (e) The APB muscle has been divided (inset) and reflected to reveal the OP muscle. (f) The FPB is separated into superficial head (elevated with scissor) and deep head, distal, and ulnar.

The APB originates from the flexor retinaculum (FR) of the wrist, flexor carpi radialis tendon sheath, trapezium, and scaphoid. The APB inserts into the radial base of the proximal phalanx, MCP joint capsule, and radial sesamoid (▶Fig. 27.7c). The APB is usually innervated by the median nerve (95%) or the ulnar nerve (2.5%) or both (2.5%). The APB muscle’s actions include abduction and flexion of the thumb metacarpal, extension of the thumb IP joint, and ulnar deviation of the MCP joint. ⁵

The FPB originates from the FR and inserts into the MCP joint capsule and also the radial sesamoid (▶Fig. 27.7d, f). The superficial head is classically innervated by the median nerve while the deep head is innervated by the ulnar nerve. The FPB muscle’s functions include MCP joint flexion, IP joint extension, and thumb pronation.

The OP originates from the FR, trapezium, and thumb CMC joint and inserts into the distal volar radial aspect of the first metacarpal (▶Fig. 27.7e). The OP muscle is usually innervated by the median nerve (83%), less frequently by the ulnar nerve (10%), and, very rarely, by dual innervation (7%). ⁵ The OP muscle’s functions include flexion and pronation of the thumb metacarpal.

The AP originates from the long finger metacarpal and inserts into the ulnar aspect of the thumb proximal phalanx base, dorsal–extensor complex, and ulnar sesamoid (▶Fig. 27.8a–c). The AP innervation arises from the ulnar nerve. The AP adducts the thumb metacarpal, flexes the MCP joint, and extends the thumb IP joint.

**Fig. 27.8** Progressive axial views of the first web space of right thumb. (a) and (b) Pronated abducted view of first web space; (c) End on view of first web space. The first dorsal interosseous muscle (lying dorsal to the adductor pollicis muscle) arises from the first and second metacarpals, with the major head arising from the ulnar aspect of the thumb metacarpal and the minor head arising from the radial aspect of the second metacarpal. The first dorsal interosseous muscle inserts primarily on the radial aspect of the index proximal phalanx, acting mainly as an abductor of the index metacarpophalangeal joint.

The extrinsic musculature consists of the extensor pollicis brevis (EPB), EPL, abductor pollicis longus (APL), and FPL.

The main thumb extensors are the EPB and EPL muscles (▶Fig. 27.9a, b). The APL muscle also has some contribution to thumb extension as seen with electromyographic analysis. ⁶ The EPB originates from the radius and interosseous membrane. The EPB tendon lies within the first dorsal compartment at the wrist along with the APL tendon, whose muscle originates from the radius, interosseous membrane, and ulna on the dorsum of the forearm (▶Fig. 27.10). The EPB tendon classically inserts into the proximal portion of the dorsum of the thumb proximal phalanx. The actions of the EPB are to extend the thumb MCP joint and abduct the thumb CMC joint. The EPB muscle also contributes to wrist radial deviation. Variations of the EPB tendon include multiple tendon slips, fusion with the APL tendon, insertion on the extensor hood or distal phalanx, and absence (5%). ⁷ ^, ⁸ The EPB lies dorsal to the APL within the first dorsal compartment pulley at the radial styloid (▶Fig. 27.11). The EPB normally shares a single compartment with the APL, but the EPB can have its own separate compartment, or subcompartment, which is associated with an increased incidence of de Quervain’s tenosynovitis, as well as an increased prevalence of distal insertion on the extensor hood or distal phalanx (▶Fig. 27.12a, b). ⁸

**Fig. 27.9** Wrist extensor tendons seen with (a) and without (b) the overlying fascia. The extensor pollicis longus tendon angles at approximately 45° around Lister’s tubercle, passes superficial to the second compartment, and, along with the extensor pollicis brevis from the first compartment, overlies the dorsum of the thumb metacarpal.

**Fig. 27.10** Lateral projection of wrist. The extensor pollicis longus and extensor pollicis brevis (EPB) overlie the first metacarpal. The extensor pollicis longus tendon lies ulnar and dorsal to the EPB tendon, and the EPB tendon lies dorsal to the abductor pollicis longus, with the EPB of highly variable size.

**Fig. 27.11** Inferior aspect of the radial extensor retinaculum, including the first dorsal compartment. The extensor pollicis brevis (EPB) tendon is seen exiting the first dorsal compartment pulley dorsal to the abductor pollicis longus tendon (at *bottom*). The extensor pollicis longus (EPL) tendon can be seen crossing superficial to the second compartment tendons (extensor carpi radialis longus and brevis). The radial artery is seen deep to the abductor pollicis longus, EPB, and EPL.

**Fig. 27.12** (a) Axial view of the dorsal compartments and extensor retinaculum, viewed from distal, with the first dorsal compartment on the *right*, the second dorsal compartment on the *top right*, the third dorsal compartment as the round oblique pulley almost within the second compartment, the 4th compartment at the *top*, the 5th compartment collapsed and not well seen, and the sixth compartment at the *left*. On the right, the first dorsal compartment is seen with a well-defined small dorsal channel through which the extensor pollicis brevis (EPB) passes (*top*) and with the larger volar channel for the abductor pollicis longus (APL) (*bottom*). (b) On the far *right*, the first dorsal compartment is also seen just dorsal to the radial artery, but this time with separate compartments for the APL (volar) and EPB (dorsal), separated by a complete septum. (c) The radial wrist (dorsal top, distal left), showing first and third dorsal compartments. (d) The radial wrist with the APL and EPB divided, showing the first dorsal compartment dorsal to the dorsal branch of the radial artery, with the artery passing deep to the APL, EPB, and extensor pollicis longus (EPL), to dive between the two heads of the first dorsal interosseous. The insertion of the brachioradialis forms part of the floor of the first dorsal compartment. (**e, f**) The APL and EPB tendons intact, without their investing fascia, but with the first dorsal compartment pulley intact. The APL muscle is volar, with its more proximal muscle belly, and the EPB is dorsal with its more distal muscle belly. (g) The muscles shown with the investing fascia still intact proximally, and the blood supply to the retinaculum. (h) Dorsal view of the wrist (distal right, radial bottom) showing Lister’s tubercle, and the EPL, with the EPL running nearly longitudinally proximal to Lister’s tubercle, then changing direction at Lister’s tubercle, angling radial and distal, distal to Lister’s tubercle.

The EPL muscle arises in the dorsal forearm, from the interosseous membrane and ulna. The EPL tendon courses alone within the third dorsal extensor compartment, changing direction at Lister’s tubercle (▶Fig. 27.12a–h). The EPL joins the dorsal aponeurosis and continues distally to insert on the dorsal distal phalanx base. The EPL muscle’s actions are to extend the IP joint and also extend the MCP joint of the thumb. The EPL also retropulses and adducts the thumb at the CMC joint.

Dorsal to the metacarpal region, the EPL and EPB tendons form interconnections (▶Fig. 27.13a, b). Proximal to the MCP joint, the dorsal aponeurosis is formed with contributions from the thenar muscular epimysium and longitudinal fibers of both extensor tendons. There are some transverse fibers from the AP muscle that continue in the MCP joint region to dorsally envelop the EPL tendon as a rough fibrous bundle, combining with contributions of fibers of APB and FPB muscles. ⁹

**Fig. 27.13** Dorsal view of thumb with exposure of proximal phalanx and first metacarpal. The extensor pollicis brevis (EPB) is volar and radial to the extensor pollicis longus (EPL) tendon, and interconnections between the two tendons are present at the metacarpophalangeal joint. The EPL tendon has a broad insertion into the distal phalanx. (a) The EPB can be seen to insert on the proximal phalanx dorsal base, while the EPL continues distally to insert on the distal phalanx dorsal base. (b) The EPB can be seen to have fibers that continue distally to insert on the distal phalanx dorsal base.

The APL inserts primarily into the radial side of the base of the first metacarpal (▶Fig. 27.14a, b). There are often multiple additional slips of the tendon insertion, including into the trapezium, dorsal aponeurosis, thenar musculature, and flexor retinaculum. As many as 14 separate APL slips have been reported.¹⁰ The APL muscle abducts the thumb at the CMC and also radially deviates the wrist. The EPB, APL, and EPL muscles are all innervated by the posterior interosseous nerve.

**Fig. 27.14** View of radial wrist (distal left, dorsal top), showing insertion of the abductor pollicis longus (APL, multiple slips) with the extensor pollicis brevis (EPB, dorsal and smaller in diameter in this specimen) continuing distally. (a) Two slips of the APL tendon are seen inserting into the base of the first metacarpal and passing directly over the radial artery. (b) The dorsal slip of the APL inserts into the first metacarpal while the volar slip inserts into the thenar musculature (*bottom*), while the EPB, lying just dorsal to the APL insertion into the first metacarpal base, continues distally, and the extensor pollicis longus lying more dorsal and ulnar, is seen crossing superficial to the second dorsal compartment proximally and continuing distally.

The FPL is a unipennate muscle with bundles of muscle fibers 40 to 50 mm long when the thumb is extended. Approximately 100 to 130 mm of tendon lies on muscle surface, and the tendon extends a similar distance beyond the musculotendinous junction to reach the insertion (▶Fig 27.15). ¹¹ With the wrist in neutral position, the FPL tendon curves around the trapezium to reach its insertion, but the course is straight with the wrist in ulnar deviation. For isometric thumb flexion, the FPL acts primarily. For isometric adduction, the FPL muscle acts secondarily. ⁶

**Fig. 27.15** Volar view of hand. The flexor pollicis longus muscle emerges from the carpal tunnel and passes along the thenar musculature to insert on the volar distal phalanx.

Classically, three constant pulleys were identified constraining the FPL tendon (▶Fig. 27.16a, b). The first “annular pulley” (A1) is located at the level of the MCP joint with dimensions of 7 to 9 mm in width and 0.5 mm thickness (▶Fig. 27.17). Proximally, two-thirds of the A1 attaches to the volar plate at the MCP joint. Distally, one-third of the A1 attaches to the base of the proximal phalanx. The second “oblique” pulley lies obliquely volar to the proximal phalanx and is 9 to 11 mm wide and 0.6 to 0.75 mm thick (▶Fig. 27.18). The orientation of the oblique pulley is ulnar proximal to radial distal. The proximal ulnar portion is associated closely with the AP tendon insertion. During pulley release for “trigger thumb,” the oblique pulley is at less risk for inadvertent release with radial, rather than ulnar, release of the A1 pulley. The third pulley, the “annular 2” (A2), is located just proximal to the FPL insertion and centered over the volar plate of the IP joint (▶Fig. 27.18). The A2 pulley is approximately 8 to 10 mm wide and 0.25 mm thick. ¹²

**Fig. 27.16** Pulley system of thumb with tendon in place (a) and then removed and replaced with a red spacer (b) to highlight pulleys. The A1 pulley in this specimen lies deep to the palmar digital crease and can be seen extending proximal and distal to the skin of the palmar digital crease that was left in situ. A relatively substantial oblique pulley is seen, approximately midway between the palmar digital crease, and the interphalangeal joint crease. The A2 pulley is relatively diaphanous in this specimen, but lies just proximal to the interphalangeal joint crease. Between the A1 pulley and oblique, lies a second transverse pulley, the variable transverse pulley. In this specimen, the oblique pulley has some minor cruciate fibers in addition to the main oblique fibers.

**Fig. 27.17** Axial view of thumb demonstrates the A1 pulley at the level of the metacarpophalangeal joint, viewed proximally.

**Fig. 27.18** Volar view of the thumb demonstrating the pulley system. The A1 pulley can be seen at the level of the MP joint and distal to the A1 is a transverse Av pulley. Between the A1 and A2 pulleys, lies a well-defined cruciate pulley, instead of the classic oblique pulley.

Cadaver dissections have suggested that the classic pulley description is incomplete. More commonly, there is an additional pulley, appearing as though the oblique pulley split at its ulnar origin and contributed another pulley between the classic A1 pulley and the oblique pulley. Although this additional pulley appears to be an offshoot or splitting of the oblique pulley, the additional pulley has been labeled the “variable transverse,” or Av pulley, even though one of the most common patterns for the Av pulley is as a second oblique pulley. The Av pulley may be absent (7%), transverse distal to the A1 (39%), oblique (39%), or transverse and fused to the A1 (16%), but in all instances the Av pulley lies between the classic A1 and classic oblique pulleys. ¹³ Even these four thumb pulley patterns are not comprehensive, and further variation is shown with a complete cruciate pulley at the oblique position (▶Fig. 27.18).

Only gold members can continue reading. Log In or Register to continue