INTRODUCTION
Most hand activities require a certain amount of forearm rotation. Certainly, a loss of pronosupination may be compensated for by internally or externally rotating the humerus with the elbow semi-extended, but this implies a higher risk of developing degeneration of the rotator cuff. Without pronosupination, common tasks such as pouring water from a jar into a glass or fastening a brassiere become difficult if not impossible. Indeed, a forearm with limited pronosupination is a substantial handicap.
For a full forearm rotation, not only do both the proximal and distal radioulnar joints (DRUJ) need to be well aligned, with matching lengths and congruent cartilages, but also the soft tissue stabilizing structures need to function properly. Needless to say, the range of pronosupination is multifactorial and can be impaired as a result of distal radius misalignment, radioulnar length discrepancy, joint incongruity, and/or soft tissue (capsule and/or muscle) contracture. Consequently, there is no single treatment for all sorts of DRUJ stiffness. Its management is to be based on a thorough clinical examination and adequate radiographic investigation of the causes of the problem including properly obtained lateral radiographs and axial tomograms to assess the spatial relationship of the bones involved. Arthroscopy is an excellent tool to evaluate the status of all intracapsular soft tissues involved in pronosupination, whereas magnetic resonance imaging provides information of the extracapsular DRUJ stabilizers.
Loss of supination is often secondary to a dorsally malunited distal radius fracture. In such instances, if the triangular fibrocartilage complex (TFCC) has been stretched out or avulsed off the basistyloid fovea, the ulnar head may have been forced into a dorsally subluxed position. Such joint incongruity prevents the normal spinning and gliding of the radius relative to the ulna. Treatment in those cases essentially involves a radial corrective osteotomy.
In some instances, the cause of stiffness is an excessively long ulna as a result of trauma (shortened distal radius fracture) or a congenital defect, implying an impingement of the bone against the lunate during supination and wrist extension producing pain. In those cases, shortening of the ulna or a “wafer” resection procedure is recommended.
If the lack of rotation is due to joint incongruity secondary to trauma or cartilage degeneration, different options exist : (1) total ulnar head resection, (2) “matched ulna” resection, (3) hemiresection and fibrous interposition, (4) DRUJ fusion plus creation of a metaphyseal pseudarthrosis, (5) ulnar head implants, and (6) total DRUJ prosthesis. All these options are discussed elsewhere in this book and are not covered here. This chapter concentrates on the loss of forearm rotation secondary to soft tissue (capsular and/or muscle) contracture.
PATHOMECHANICS
To understand the consequences of specific DRUJ soft tissue contractures, it is important to analyze how the radius is prevented from rotating around the ulna beyond its normal limits.
Supination constraints: As the radius rotates from neutral toward supination, very little changes in ligament tension appear in either the palmar or dorsal radioulnar (RU) ligaments. The horizontal portion of the TFCC, consisting of the articular disc (central zone), and the two periphery RU ligaments move as a unit ( Fig. 28-1 A and B). Tension in the palmar RU ligament does not increase until a certain degree of supination is reached ( Fig. 28-1 C). At this point, the distance between the two ends of the ligament (fovea and palmar corner of the radius) start increasing until the palmar RU ligament is fully taut, at about 70 degrees of supination. If the palmar capsule were not elastic, this would be the limit of supination. The capsule is very lax, however, and allows some degree of dorsal subluxation of the radius, with the ulnar head displacing palmarward, thus decreasing tension in the anterior RU ligament ( Fig. 28-1 D). This allows further supination up to about 80 degrees until the dorsal RU ligament becomes fully taut. An important dynamic control of the final stages of supination is the pronator quadratus (PQ), which in supination becomes stretched and promotes cooptation of the joint preventing its subluxation ( Fig. 28-2 ). Indeed, the palmar RU ligament can be thought of as the primary stabilizer of the early stages of supination, whereas the dorsal RU ligament, the palmar capsule, and the PQ muscle are secondary stabilizers preventing dorsal dislocation of the radius relative to the ulna.
FIGURE 28-1
Schematic representation of the interaction that exists between the distal radioulnar joint and the surrounding soft tissues during supination . A and B, As the radius initiates a rotation around the ulna, very little changes in tension of both palmar and dorsal radioulnar (RU) ligaments appear. C, Tension in the palmar RU ligament does not increase significantly until a certain degree of supination is reached ( yellow arrow ). This tension generates a palmar translation vector to the ulnar head. D, As the ulna subluxes palmarly ( white arrow ), the dorsal RU ligament becomes taut ( yellow arrow ), preventing further displacement. The palmar RU capsule ( pink ) helps to stabilize the joint at the extreme of supination, as well as the pronator quadratus muscle ( green ).
FIGURE 28-2
The pronator quadratus muscle is fully stretched during supination, increasing its mechanical advantage as the distal radioulnar joint dynamic stabilizer. If this muscle ever suffers a disruption, it most likely occurs during supination. In pronation the muscle belly of the pronator quadratus does not offer resistance to a palmar displacement of the ulnar head. U, ulna; R, radius.
Pronation constraints: A similar phenomenon occurs during pronation: no substantial changes in tension develop in the two RU ligaments until a certain degree of pronation is achieved ( Fig. 28-3 A and B). At about 60 degrees of pronation, the dorsal ligament becomes maximally taut ( Fig. 28-3 C). This would stop pronation if not for the elastic dorsal capsule that allows some palmar subluxation of the radius relative to the ulna. As the ulna glides dorsally, there is increasing tension of the anterior RU ligament and the dorsal capsule—certainly the two ultimate constraints of pronation ( Fig. 28-3 D). In a way similar to that indicated for supination in which the PQ muscle is an effective dynamic stabilizer, the extensor carpi ulnaris (ECU) muscle plays a dynamic role in DRUJ stabilization during pronation. Indeed, as emphasized by Spinner and Kaplan, the ECU tendon is maintained in a close relation to the head of the ulna by a fibrous tunnel, independent of the rest of the extensor retinaculum. Because of this, at full pronation the ECU tendon lies medial to the ulnar head and promotes cooptation of this bone against the dorsal rim of the sigmoid cavity, thus maximizing stability ( Fig. 28-4 ). In short, the dorsal RU ligament can be thought of as the primary stabilizer of the early stages of pronation, whereas the palmar RU ligament, the dorsal capsule, and the ECU muscle are secondary stabilizers preventing palmar dislocation of the radius relative to the ulna.
FIGURE 28-3
Soft tissue interaction around the distal radioulnar joint during pronation . A and B, Rotation around the neutral position does not imply significant changes in tension of the radioulnar (RU) ligaments. C, The dorsal RU ligament becomes taut ( yellow arrow ) before reaching the extreme of pronation. With this, the ulna is forced toward the dorsum. D, As the ulna subluxes dorsally, the palmar RU ligament becomes taut, preventing further displacement. The dorsal RU capsule ( pink ) as well as the extensor carpi ulnaris tendon ( green ) stabilize the joint at the extreme of pronation.
FIGURE 28-4
Mechanism of stabilization of the distal radioulnar joint by the extensor carpi ulnaris (ECU) tendon . The ECU has its own compartment over the groove on the dorsum of the ulnar head. The sheath that covers the tendon is independent of the extensor retinaculum. In pronation, this compartment is located on the medial aspect of the bone. Therefore, the tendon in that position has an S-shaped configuration. Contracture of the ECU muscle produces a radial-directed force that compresses the joint and helps prevent a dorsal subluxation of the ulna relative to the radius.
CLINICAL FORMS OF SOFT TISSUE CONTRACTURES AROUND THE DISTAL RADIOULNAR JOINT
Contractures around the DRUJ may cause three forms of forearm limitation: (1) loss of pronation, (2) loss of supination, and (3) combined pronation and supination loss.
The third form of forearm limitation usually falls into the category of intra-articular stiffness (arthrofibrosis) and very often results from complex trauma or inflammatory disease generating intra-articular cartilage destruction and invasion by scarring fibrotic tissue. This is a very difficult condition to treat effectively, most often requiring a salvage intervention. Fortunately, it is rarely seen after a common distal radius fracture. Yet, if releasing an arthrofibrotic joint is believed to be necessary, a double palmar and dorsal approach following the guidelines proposed by Kleinman and Graham is recommended.
- 1.
Loss of pronation: Of the four structures in which scarring or contracture may theoretically affect pronation (see Fig. 28-3 D), only the dorsal capsule has been shown to be directly involved in the rare cases in which there is truly an isolated lack of pronation due to soft-tissue contracture.
The dorsal capsule may disrupt, lose its elasticity, and become thick in several ways; most often, this occurs as the consequence of an extra-articular, palmarly angulated distal radius fracture (Smith type) or in Galleazzi’s fracture-dislocation. If the fracture is not properly reduced and stabilized, particularly when the forearm is immobilized in an above-elbow cast for too long, these injuries may induce a deficit of pronation. Fortunately, plate fixation and early mobilization of these types of fractures are common practice, since the need for a secondary dorsal capsular release is almost anecdotal.
Permanent scar retraction of a partial injury to the RU ligaments producing limitation of forearm rotation is very rare. When this fails, these ligaments tend to avulse or disrupt, creating instability, but seldom stiffness. Detaching the RU ligaments to achieve increased pronosupination should be considered only exceptionally.
ECU tendinitis may result in muscle contracture and slight limitation of pronation. Reduction of forearm rotation, however, is not static but is most often the result of pain produced by the synovitic tendon when stretched during pronation. Proper treatment of the condition (splintage, corticoid injections, and eventually synovectomy) is all that is needed to recover full pronosupination.
- 2.
Loss of supination: Post-traumatic palmar capsular thickenings inducing a supination deficit are not rare. Distal radius fractures with mild dorsal displacement are particularly prone to create DRUJ capsular defects in the palm, which may eventually cause this problem. The reason for this is discussed in the text that follows.
The hyperextended carpus pulls the ulnar head anteriorly by means of the strong ulnocarpal ligaments ( Fig. 28-5 ). As the distal radius displaces dorsally, a shear stress in the DRUJ is created. If the TFCC, including the ulnocarpal ligaments, does not fail, the ulnar head promotes tearing of the palmar capsule in its attempt to sublux palmarly relative to the dorsally angulated distal radius. If there is also a supination moment involved in the injury, the fully stretched PQ muscle may not be able to resist the palmar push of the ulna and may suffer substantial elongation. Such muscle injury, however, would not have major consequences if not for the fact that this muscle is contained in its own small compartment, which the fracture fills with abundant hematoma, thus creating the conditions for a localized compartment syndrome. Increased pressure on the muscle may seriously affect its contractibility, thus inducing its later fibrotic retraction and subsequent limitation of supination.
