A thorough understanding of the osseous and ligamentous anatomy of the wrist is a fundamental requirement for any clinician attempting to understand and treat maladies of the carpus and distal radioulnar joint. With this information, the health professional can apply the normal anatomy to normal mechanics, begin to unravel the pathways of pathomechanics, and formulate a treatment plan that is anatomically and mechanically sound. Additionally, as more detailed imaging modalities become available, more detailed understanding of anatomy will be required. 3,7,18 Although the number of ligaments identified in the wrist is large, there are patterns and conventions that make the task of learning the anatomy more palatable. Unfortunately, there have been apparent controversies that have led to confusion over the names and composition of the ligaments. 2,4–6,11,16 Despite these controversies, however, there are schemes of descriptive anatomy of the carpal ligaments that in general are agreed on, which will be used in the current study. When faced with interpretive controversies, the author likes to remember the wise words of a trusted friend and colleague who advised me that the anatomy does not change, only our descriptions of anatomy change (Julio Taleisnik, MD, verbal communication 1996).
The term ligament literally means to bind, which probably oversimplifies the roles of major articular ligaments. However, because this is the role that is most easily appreciated and grossly demonstrable, it is the role that will be assumed in the current study. The majority of ligaments in the wrist actually are incorporated into the joint capsule, although specific exceptions will be found entirely within the joint space proper. Likewise, the majority of the wrist ligaments have a typical histologic composition, consisting of longitudinally oriented groupings of collagen fibers called fascicles. These fascicles course throughout the length of the ligament, and are collinear with the gross orientation of the ligament. They are surrounded by loose areolar connective tissue transmitting small caliber nerves, arterioles and venules, and together form what is called the perifascicular space. 4 Near the deep and superficial boundaries of the ligament, the perifascicular spaces coalesce and are limited by a layer of synoviocytes (called the synovial stratum) and nonfasciculated collagen fibers oriented in various planes (called the fibrous stratum), respectively. 4 At the lateral edge of the ligament, the fibrous and synovial strata converge to virtually encapsulate the ligament, forming what is called the epiligamentous sheath. 4 This sheath essentially isolates a specific ligament from contiguous ligaments, the joint space, and extracapsular structures. As will be reported in the detailed descriptions of the individual ligaments, variations in tissue type will be found throughout the carpal ligaments.
The ligaments of the wrist can be categorized by generic divisions (intrinsic versus extrinsic), by location (palmar versus dorsal, radiocarpal versus midcarpal), or by function (guiding, constraining). 2,16 The use of these classifications is left to the surgeon as a means of simplifying the task of understanding the overall scheme of ligamentous connection in the carpus and distal radioulnar joint. One aspect that might provide some usefulness is a simple convention in nomenclature. Assuming that the ligament in question is indeed spanning a joint between two or more bones, the name assigned to that ligament includes its major attachment ordered either proximal to distal or radial to ulnar. As examples, the ligament between the radius, scaphoid, and capitate is the radioscaphocapitate ligament, the ligament between the triquetrum and hamate is the triquetrohamate ligament, and the ligament between the scaphoid and lunate is the scapholunate ligament. Additional information can be gained by applying appropriate adjectives, such as short and long radiolunate ligaments, dorsal trapezocapitate ligament, and deep capitohamate ligament. Finally, the terms palmar and dorsal are used because the region of the wrist is covered anteriorly by the glabrous skin of the palm of the hand.
For purposes of description, the individual ligaments will be grouped by region to include palmar radiocarpal, ulnocarpal, dorsal radiocarpal and intercarpal, palmar midcarpal, proximal interosseous, distal interosseous, and distal radioulnar ligaments. Although one easily could identify more ligaments in the wrist than those described, the ligaments included in the current study currently are considered to be the major stabilizers in the wrist.
Palmar Radiocarpal Ligaments
There are four palmar radiocarpal ligaments. 2,6 Each has a proximal attachment to the radius and a distal attachment to one or more carpal bones. The combined attachments to the radius span the entire width of the palmar rim of the distal radius. The most radial ligament is the radioscaphocapitate ligament 2,6,16 (Figs 1,2). The radioscaphocapitate ligament originates from the distal radius in the zone from the tip of the radial styloid process to approximately the middle of the scaphoid fossa. It forms the entire radial radiocarpal and part of the palmar radiocarpal joint capsule. It attaches to the proximal cortex of the distal pole of the scaphoid and supports the waist of the scaphoid as it enters the midcarpal joint. Here, it interdigitates with fibers from the ulnocapitate ligament and the palmar scaphotriquetral ligament. It is estimated that only 10% of its fibers actually inserts into the palmar cortex of the body of the capitate, but this is sufficient to warrant the inclusion of the capitate into its name. Often, there is a triangular depression in the deep surface of the ligament as it approaches the scaphoid, which reflects the hemicircumferential attachment of the ligament to the entire proximal surface of the distal pole of the scaphoid. Immediately ulnar to the radioscaphocapitate ligament is the long radiolunate ligament 2,6 (Figs 1–3). The long radiolunate ligament has been described previously as coursing as far ulnarly as the triquetrum. 11 However, a recent study has shown that the ligament take its proximal attachment from the palmar rim of the radius spanning the remaining aspect of the scaphoid fossa, traverses the radiocarpal joint anterior to the proximal pole of the scaphoid (without attaching to it), to attach to the lunate at the radial aspect of it’s palmar cortex. 6 It is a true capsular ligament and is separated from the radioscaphocapitate ligament by the interligamentous sulcus. The radioscapholunate ligament is found just ulnar to the long radiolunate ligament (Figs 1–3). The radioscapholunate ligament is not a true ligament in a mechanical or histologic sense. 2–5 It may be considered a mesocapsule extending from the palmar radiocarpal joint capsule. Studies of wrists from adults and fetuses have shown that it contains terminal branches of the anterior interosseous nerve and vessels emanating from the distal radial arch. 4,5 It appears to pierce the palmar radiocarpal capsule, then travels vertically dorsally until it integrates with the scapholunate interosseous ligament. 4 Histologically, the radioscapholunate ligament does not have a fasciculated pattern to the collagen fascicles and carries a very high concentration of small caliber nerves and vessels. 4,5 Immediately ulnar to the radioscapholunate ligament is the short radiolunate ligament 2,6 (Figs 1–3). The short radiolunate ligament originates proximally from the entire width of the lunate fossa region of the distal radius and attaches distally onto the radial half of the palmar cortex of the lunate. Thus, the lunate has a substantial connection to the radius via the long and short radiolunate ligaments. If not for the interruption by the radioscapholunate ligament, the lunate would be connected to the radius by a thick sheet of ligament spanning from the ulnar margin of the lunate fossa radially to the midpoint of the scaphoid fossa. This feature may explain why the lunate tends to remain with the radius in the face of a complete perilunate dislocation.
There are three identified ulnocarpal ligaments spanning the space between the distal ulna and the carpus on the anterior and ulnar aspects 2,9,10 (Fig 1). The dorsal capsule between the ulna and the carpus is reinforced partially by the dorsal radiocarpal ligament. Thus, there is little dorsal reinforcement of the joint capsule between the ulna and the carpus. The ulnocapitate ligament is the only ulnocarpal ligament that attaches directly to the ulnar head 2,9 (Fig 1). It is the most superficial of the three ulnocarpal ligaments. It attaches to the fovea region of the ulnar head, which is a slight depression at the base of the ulnar styloid process. The fovea also is a point of attachment for the dorsal and palmar radioulnar ligaments. 2,9,10 From the fovea, the ulnocapitate ligament passes distally, just anterior to the junction between the other ulnocarpal ligaments, until it reaches the lunotriquetral joint. Here, it reinforces the palmar region of the lunotriquetral interosseous ligament, emerges into the midcarpal joint space, and passes radially to interdigitate with the fibers of the radioscaphocapitate ligament. As with the radioscaphocapitate ligament, only approximately 10% of the fibers of the ulnocapitate ligament actually attach to the body of the capitate. The ulnocapitate ligament may function as an ulnar anchor of the carpus. The ulnolunate and ulnotriquetral ligaments form the anterior and ulnar aspects of the ulnocarpal joint capsule 2,9,10 (Fig 1). There is no clear demarcation between the ulnolunate and ulnotriquetral ligaments, the distinction between the two being made only by their distal attachments. Both ligaments originate proximally from the palmar radioulnar ligament, thus attaching indirectly to the ulna. This arrangement probably facilitates the independent of forearm rotation and wrist motion without compromising ulnocarpal stability. The ulnolunate ligament is continuous with the short radiolunate ligament, and attaches to the palmar cortex of the lunate just as the short radiolunate ligament does. The ulnotriquetral ligament attaches to the proximal and ulnar surfaces of the triquetrum and may have some proximal fibers attaching to the ulnar styloid process. It often has two perforations, the prestyloid process and the pisotriquetral orifice.
Dorsal Radiocarpal and Dorsal Intercarpal Ligaments
The dorsal wrist capsule is reinforced primarily by two large ligaments spanning the radiocarpal and midcarpal joints 2,13,16,17 (Fig 4). As will be discussed, dorsal interosseous ligaments connect the individual carpal bones within each carpal row. The dorsal wrist joint capsule in those areas not reinforced by ligament is extremely elastic. The dorsal radiocarpal ligament originates proximally from the dorsal rim of the distal radius, spanning the distance between the dorsal rim of the sigmoid notch to the level of Lister’s tubercle (Fig 4). It passes obliquely distally and ulnarly to attach to the dorsal cortices of the lunate and the triquetrum. It has a somewhat trapezoidal shape, tapering as it passes toward the triquetrum. The dorsal intercarpal ligament also attaches to the dorsal tubercle of the triquetrum and passes radially in two bands (Fig 4). The proximal band attaches to the dorsal ridge and radial surface of the distal pole of the scaphoid and the distal band attaches to the dorsal cortex of the triquetrum. The dorsal radiocarpal and dorsal intercarpal ligaments change their relative orientation substantially as the wrist flexes and extends, such that the intersection angle between them at the triquetrum is acute in extension and becomes almost orthogonal as the wrist palmar flexes. 2,17 It is thought that this arrangement stabilizes the scaphoid to the radius indirectly through a linkage system as opposed to a direct connection, an arrangement that theoretically enhances mobility of the scaphoid without compromising motion. 17 The is a variable presence of a ligamentous reinforcement of the dorsal joint capsule between the triquetrum and hamate, often confused with the distal extension of the extensor carpi ulnaris tendon subsheath. When present, it simply is called the dorsal triquetrohamate ligament 2 (Fig 4).
Palmar Midcarpal Ligaments
The four palmar midcarpal ligaments course from the scaphoid and triquetrum to the distal row 2,16 (Fig 1). There are no direct connections between the lunate and the distal row. The central ⅓ of the palmar midcarpal joint capsule is composed of the interdigitating fibers of the radioscaphocapitate and ulnocapitate ligaments. Referred to as the arcuate ligament, these transversely oriented interdigitating fibers support the head of the capitate without directly attaching to it, thus forming a supporting structure similar to a labrum. 16 This arrangement theoretically enhances midcarpal motion, by virtue of the centrally unconstrained capitate head, while providing stability between the proximal and distal rows at the ulnar and radial columns. Beginning radially, the scaphotrapeziotrapezoid ligament attaches to the radial and ulnar cortices of the distal pole of the scaphoid. From here, the scaphotrapezial band forms a V-shaped structure, with its apex proximally, and attaches to the palmar and radial aspect of the trapezium 2,8,16 (Fig 1). The scaphotrapezoid band forms a linear connection between the ulnar cortex of the scaphoid and the palmar surface of the trapezoid. The palmar capsule of the scaphotrapeziotrapezoid joint has little ligamentous reinforcement. The scaphocapitate ligament attaches to the distal pole of the scaphoid and passes obliquely ulnarly and distally to attach to the palmar cortex of the body of the capitate 2,16 (Fig 1). The fibers of the scaphocapitate ligament parallel the orientation of the radioscaphocapitate ligament. From a palmar perspective, this arrangement gives a false impression that the radioscaphocapitate ligament invests heavily into the capitate directly. The triquetrocapitate ligament attaches proximally to the distal and radial corner of the triquetrum and passes distally to attach to the ulnar cortex of the capitate body 2,16 (Fig 1). The triquetrohamate ligament attaches to the distal margin of the palmar cortex of the triquetrum, just ulnar to the triquetrocapitate ligament, and passes directly distally to attach to the palmar cortex of the body of the hamate (Fig 1). 2,14 Generally, the triquetrocapitate and triquetrohamate ligaments form exact images of the scaphotrapeziotrapezoid and scaphocapitate ligaments.
Proximal Interosseous Ligaments
There are two proximal interosseous ligaments: the scapholunate and lunotriquetral interosseous ligaments 2,15,16 (Figs 1–4). Both ligaments are similar in general characteristics but have specific differences. The proximal interosseous ligaments cover the dorsal, proximal, and palmar aspects of their respective joints, leaving the distal aspect of each joint open to communicate with the midcarpal joint. Both ligaments have histologic characteristics, which justify division into dorsal, proximal, and palmar regions. Both ligaments are deep in the joint, separated from and covered palmarly and dorsally by the joint capsule.
The dorsal region of the scapholunate interosseous ligament is the thickest region and is a true ligament composed of transversely oriented collagen fascicles 1 (Fig 3). The palmar region of the scapholunate interosseous ligament also is a true ligament, but is thin and oriented obliquely from palmar to dorsal progressing from the scaphoid to the lunate. It is completely independent form the more superficial long radiolunate ligament. The proximal region is composed of fibrocartilage, with no collagen orientation, blood vessels, or nerves. There often is a meniscal projection distally into the joint cleft. It is covered partially be the radioscapholunate ligament palmarly.
The palmar region of the lunotriquetral ligament is a true ligament and is the thickest region of the ligament: it is composed of transversely oriented collagen fascicles with interweave with fibers of the ulnocapitate ligament. 15 The dorsal region also is a true ligament, but is thinner than its palmar counterpart. These fibers pass transversely across the lunotriquetral joint and are covered by, but independent from, the overlying dorsal radiocarpal ligament. The proximal region is composed of fibrocartilage, with no collagen orientation, blood vessels, or nerves. There often is a meniscal projection distally into the joint cleft. Passing along the distal margins of the dorsal surfaces of the scaphoid, lunate and triquetrum is the scaphotriquetral ligament 2 (Fig 3). This ligament is a distal extension of the scapholunate and lunotriquetral interosseous ligaments, creating essentially a labral extension into the dorsal midcarpal joint.
If one considers the pisiform to be a carpal bone, rather than a sesamoid bone in the flexor carpi ulnaris tendon, a description of the ligaments attaching to the pisiform will be offered. The pisotriquetral ligament is a horseshoe-shaped ligament which connects the radial, distal, and ulnar edges of the pisotriquetral joint. The proximal aspect of the pisotriquetral joint is open for communication with the radiocarpal joint through the pisotriquetral orifice in the ulnotriquetral ligament. The radial fibers of the pisotriquetral ligament are reinforced by fibers of the ulnocapitate ligament. The pisohamate ligament is a direct extension of the flexor carpi ulnaris tendon, extending from the palmar surface of the pisiform to the hook of the hamate.
Distal Interosseous Ligaments
There are three distal interosseous ligament systems connecting the trapezium, trapezoid, capitate, and hamate 2,14,16 (Figs 1,4,5). As with the proximal interosseous ligament systems, there are several similarities between the specific ligaments. Each ligament consists of at least a dorsal and a palmar region, each composed of a nearly continuous sheet of ligament oriented transversely. The dorsal and palmar trapeziotrapezoid ligaments span virtually the entire length of the dorsal and palmar joint edges, extending substantially onto the respective cortices of the bones (Figs 1,4,5). The dorsal and palmar trapezocapitate ligaments are similar to the trapeziotrapezoid ligaments; however, because of the proximal extension of the capitate neck and head, the ligaments insert only onto the body of the capitate (Figs 1,4,5). In addition to the dorsal and palmar ligaments, there is a strong deep trapezocapitate ligament, which crosses the central region of the joint in an angled notch found in the mutually articulating surfaces (Fig 5). The dorsal and palmar capitohamate ligaments likewise are similar to the dorsal and palmar trapeziotrapezoid and trapezocapitate ligaments, again crossing only the distal half of the joint because of the proximal extensions of the pole of the hamate and the head and neck of the capitate 14 (Figs 1,4,5). As with the trapezocapitate ligament complex, the deep capitohamate ligament is found in a square-shaped depression at the anterior and distal margin of the capitohamate joint (Fig 5). This is a large ligament, which measures approximately 5 × 5 mm in cross section, with distal extensions to the third and fourth metacarpal bases. 14
Distal Radioulnar Joint Ligaments
The ligaments of the distal radioulnar joint must be considered in the context of their contribution to the triangular fibrocartilage complex and the ulnocarpal ligament complex. 2,10 The triangular fibrocartilage complex is a complex arrangement of fibrocartilage, ligament, and joint capsule connecting the distal radius, distal ulna, and the ulnar aspect of the carpus that, under normal circumstances, separates the distal radioulnar joint from the radiocarpal joint. The true ligamentous aspect of the triangular fibrocartilage complex consists primarily of the dorsal and palmar radioulnar ligaments (Figs 1,4). The dorsal radioulnar ligament attaches to the dorsal rim of the distal radius at the level of the sigmoid notch and courses obliquely ulnarly and anteriorly to insert with the palmar radioulnar ligament into the fovea of the ulnar head and the ulnar styloid process. The most superficial fibers of the dorsal radioulnar ligament separate from the remaining fibers of the ligament to contribute to the formation of the extensor carpi ulnaris tendon subsheath (Fig 4). The palmar radioulnar ligament attaches radially to the palmar rim of the distal radius at the level of the sigmoid notch and courses obliquely ulnarly and dorsally to attach with the dorsal radioulnar ligament to the fovea of the ulnar head and the ulnar styloid process (Fig 1). The most superficial fibers of the palmar radioulnar ligament turn distally to form the ulnolunate and ulnotriquetral ligaments described above. Between the palmar and dorsal radioulnar ligaments is a triangular wafer of fibrocartilage called the triangular articular disc. Just proximal to the dorsal radioulnar ligament is a strong ligament emerging from the dorsal rim of the distal radial metaphysis called the dorsal radial metaphyseal arcuate ligament 2 (Fig 4). It merges with the dorsal radioulnar ligament and reinforces the extensor carpi ulnaris tendon subsheath.
The foundation of understanding function in the human body is a clear understanding of anatomy. Without this foundation, any hope of understanding normal and pathologic function is minimal. This axiom is generously applicable to the wrist, where the motions, load distributions, and mechanical demands are extremely complex. The ligaments of the wrist have the responsibility of balancing the constraints that are necessary to maintain stability while at the same time, allowing the generous range of motion that a healthy individual enjoys. There may be other functions to this array of ligaments, such as proprioceptive interactions with the nervous system, but these theoretical concerns are beyond the scope of the current study.
By understanding not only the gross, but also histologic anatomy of the wrist ligaments, one can begin to appreciate differences in clinical conditions and project their prognosis. For example, it is not unusual for fibrocartilage to degenerate with aging without imparting significant instability to the joint. 12 The condition may cause pain, but the joint remains clinically stable. Such is the case with defects in the triangular fibrocartilage complex and then proximal regions of the scapholunate and lunotriquetral interosseous ligaments. 12 Beginning in the individual’s fourth decade of life, a progressive increase in the incidence of atraumatic degeneration occurs in these structures. By knowing the anatomy of this region, one can begin to understand why these individuals must be differentiated from those who suffer a traumatic disruption to plan appropriate treatment and predict clinical outcomes.
Another benefit of gaining a detailed understanding of the anatomy of the wrist ligaments is in the field of diagnostic imaging. With escalating technology available in imaging, including high resolution magnetic resonance imaging and arthroscopy, the line between the interpretation of normal and abnormal conditions becomes less distinct. At the foundation of these distinctions is a clear understanding of normal anatomy, including a catalogue of normal variations. There are those who may think that anatomy is somewhat of a dead science, that everything has been described ad nauseum, and that there is nothing new to be gained. It should be clear to the reader, however, that this is far from true. As each clinical question regarding the musculoskeletal system arises, the careful clinician should be requiring more and more detailed descriptions of relevant anatomy. Only then can the clinical outcomes be advanced to a higher level.
This work is dedicated to the memory of Prof. Dr. Johann (Hans) M.F. Landsmeer, Professor Emeritus of Anatomy and Embryology at the Universiteit te Leiden, The Netherlands. He provided me with the tools and the inspiration for anatomic investigations. He educated all who read his work and touched all who knew him personally. He will be forever missed and fondly remembered.
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Michael J. Botte, MD; and James R. Doyle, MD Guest Editors