32 Compartments of the Hand

Ethan W. Blackburn

32 Compartments of the Hand

32.1 Introduction

A thorough knowledge of the discrete myofascial compartments of the hand is critical when a surgeon is confronted with a severely injured hand with possible compartment syndrome. The causes of compartment syndrome of hand are numerous, ranging from restrictive dressings to industrial accidents. ¹ Surgeons must have a high level of clinical suspicion even after seemingly innocuous injuries such as injection injury or careless intraoperative positioning. Failure to diagnose compartment syndrome of the hand can lead to intrinsic muscle necrosis, followed by fibrosis and loss of function. Litigation often stems from missed compartment syndrome with an average malpractice award of 280,000. ² Understanding the anatomy and variability of the hand compartments is required for prompt and effective treatment of this potentially devastating problem.

Studies have supported the presence of distinct myofascial compartments of the hand, and much of the contemporary teaching for treating compartment syndrome is founded on this. ³ It should be noted that some research supports little to no tough fascial tissue surrounding these compartments. ⁴ While anatomical studies are controversial, clinical studies documenting the results of neglected compartment syndrome support prompt and aggressive treatment. ⁵ Until further research is available, we recommend aggressive treatment with surgical decompression when clinical suspicion is high. As Ortiz and Berger pointed out, fasciotomy wounds may present a cosmetic challenge, but this is far outweighed by the potential dysfunction of an undiagnosed hand compartment syndrome. ⁶

Hand compartments are enclosed spaces by connective tissue or bone. Typically, the hand has been divided into six spaces (▶Fig. 32.1 and ▶Fig. 32.2): the thenar, hypothenar, adductor, interosseous, carpal tunnel, and digit. It should be noted that some surgeons refer to each volar and dorsal interosseous muscle as a separate space.

**Fig. 32.1** Dorsal view of the hand with skin and subcutaneous tissues and finger extensors removed. From left the right, the first through fourth dorsal interossei (*), and the abductor digiti minimi (A) are visualized.

**Fig. 32.2** Volar view of the hand with skin, subcutaneous tissues, palmar aponeurosis, and flexor tendons removed. The hypothenar compartment (A), carpal tunnel (B), and thenar compartment (C) are visualized. The median nerve has been transected proximal to the carpal tunnel, and the palmar cutaneous branch of the median nerve was removed with subcutaneous tissues.

32.1.1 Thenar Compartment

The thenar compartment contains the flexor pollicis brevis, abductor pollicus brevis, and the opponens pollicus. These muscles are innervated primarily by the recurrent branch of the median nerve with variable contributions of the deep branch of the ulnar nerve. ⁷ The thenar fascia extends from the palmar surface of the thumb metacarpal, surrounds the muscles, and inserts back onto the thumb metacarpal. ¹ In 52% of cadaveric hands, a second discrete compartment is found within the thenar group. ⁸ The flexor pollicus brevis was found to be an isolated compartment in 38% of hands, while the abductor pollicus brevis as confined space was found in only 10% of cadaveric specimens.

32.1.2 Adductor Compartment

The adductor pollicis is the largest and most powerful thenar muscle. ⁷ Its transverse head spans between the thumb and third metacarpal while its oblique head commonly originates from the third and fourth metacarpal (▶Fig. 32.3). The deep branch of the ulnar nerve with the deep palmar arch and associated veins pierce a space formed between the two heads. DiFelice et al reported the adductor was a separate space in 71% of hands while 19% of the time it was combined with the first dorsal interosseous. ⁸ These authors found the adductor pollicus and the first dorsal interosseous space continuous with the midpalmar space in 5% of specimens. Isolated chronic compartment syndrome of the first dorsal interosseous has been reported. ⁹ ^– ¹¹

**Fig. 32.3** Dorsal radial view of the hand with skin, subcutaneous tissues, and extensor tendons removed. The first dorsal interosseous (A) and adductor pollicus (B) are visualized.

32.1.3 Interossei

The dorsal interossei are finger abductors away from the axis of the third ray, while the volar interossei adduct the fingers. ⁷ Both muscle groups are metacarpophalangeal joint flexors and proximal interphalangeal joint extenders. The three volar interossei are bipennate muscles that arise from the second, fourth, and fifth metacarpal, pass volar to the deep transverse metacarpal ligament, and insert onto the dorsal apparatus. The radial head of the first dorsal interossei arises from the ulnar aspect of the first metacarpal, while the ulnar head arises from the radial aspect of the second metacarpal. These tendons have a primarily bony insertion onto the base of the second proximal phalanx. The radial artery and vena comitans pass through a gap between the two origins of this muscle. The second, third, and fourth dorsal interossei originate from their adjacent metacarpals and pass volar to the deep transverse metacarpal. They insert into proximal phalanx and dorsal apparatus. The second dorsal interossei inserts onto the radial aspect of the middle finger, the third on the ulnar aspect of the middle finger, and the fourth on the ulnar aspect of the ring finger. These muscles flex the metacarpophalangeal joints and extend the proximal interphalangeal joints. The second and third dorsal interossei are responsible for the radial and ulnar deviation of the middle finger, and the first and forth abduct the index and ring fingers relative to the third ray, respectively.

The interosseous compartments have been the subjects of considerable debate in several studies. Halpern and Mochizuki examined the interossei by removing the dorsal skin, injecting Renografin dye followed by radiographic evaluation and dissection. ³ The authors discovered that the dye injected into the dorsal interossei did not extravasate into the volar interossei and thus concluded that these muscles resided in separate compartments. More recent studies have reexamined these results with several modifications to the study design. Guyton et al left the skin intact and used continuous pressure monitoring with real-time computed tomography to visualize the injected contrast in the second dorsal interosseous. ⁴ These authors demonstrated that the barrier between volar and dorsal interossei became incompetent at only 15 mm Hg. Contrast was visualized spreading to adjacent interossei at pressures less than 35 mm Hg.

DiFelice et al demonstrated significant variability in the interosseous spaces. ⁸ The first dorsal interosseous was a separate space in 76% of hands, and it was combined with the adductor pollicus in 19% hands, with this space continuous with the midpalmar space 5% of the time. The second, third, and fourth interosseous groups were separate compartments in 48, 29, and 57% of hands, respectively. The second interosseous group was in separate volar and dorsal compartments in 48% of specimens. The third and fourth dorsal and volar interossei were separate compartments 67 and 38% of the time, respectively. All interossei spaces opened into the midpalmar space or the carpal canal 4 to 5% of the time.

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