Foveal tears and arthroscopy of the distal radioulnar joint

Relevant anatomy and biomechanics

Triangular fibrocartilage complex anatomy

The triangular fibrocartilage complex (TFCC) consists of the articular disc, the meniscus homologue, the palmar radioulnar ligament (PRUL) and dorsal radioulnar ligament (DRUL), the extensor carpi ulnaris subsheath (ECUS), the ulnar capsule, the ulnolunate ligament (ULL), and the ulnotriquetral (UT) ligament. ^, The PRUL and DRUL are the principal stabilizers of the distal radioulnar joint (DRUJ). As each radioulnar ligament extends ulnarly, it divides into two limbs: a deep limb, which attaches to the fovea on the ulna; and a superficial limb, which attaches to the ulnar styloid. Thus the TFCC has four insertions on the ulna: the palmar and dorsal superficial radioulnar ligaments (RUL), and the palmar and dorsal RUL ( Fig. 4.1 A–B). The attachment of the dorsal superficial RUL is wider than that of the dorsal deep RUL and forms the floor of the ECUS, which overlaps the fovea. The ulnocarpal ligaments, which consist of the ulnotriquetral ligament, the ulnocapitate ligament, and the ulnolunate ligament, are confluent with portions of the PRUL. The medial fibers of the ulnotriquetral ligament insert into the styloid with the palmar superficial RUL and the ulnocapitate ligament inserts into the fovea with the deep palmar RUL. In a histological study, Nakamura et al. found that the deep RUL arose vertically through Sharpey’s fibers from a broad area in the ulnar fovea and more horizontally from a narrow area at the base of the ulnar styloid. The deep RUL consists of three portions: dorsal, central, and palmar, and can be fan-shaped, V -shaped, or funnel-shaped ( Fig. 4.2 A–D). The origin of the deep RUL coincides with the axis of forearm rotation, which passes through the fovea, and allows twisting of the fibers during 180 degrees of forearm pronation and supination. The floor of the extensor carpi ulnaris sheath originates from the dorsal side of the fovea by Sharpey’s fibers. Loosely oriented fibers, corresponding to a thickened ulnar joint capsule, arise from the hyaline-like cartilage matrix at the tip of the ulnar styloid and insert onto the triquetrum without Sharpey’s fibers. The ULL and UT ligament originate not from the ulna, but from the palmar side of the TFCC. The deep RUL is the primary intrinsic stabilizer of the DRUJ. Extrinsic stability is provided by dynamic tensioning of the ECU as its tendon crosses the distal head of the ulna, the ECU sheath, dynamic support provided by the superficial and deep heads of the pronator quadratus, and the distal interosseous membrane. In an anatomical study of 30 forearm specimens, Noda et al. identified that the interosseous membrane included five ligaments: the central band, the accessory band, the distal oblique bundle (DOB), the proximal oblique cord, and the dorsal oblique accessory cord. The DOB is an inconstant isometric ligament within the distal membranous portion of the interosseous membrane (IOM) that is found in approximately 40 percent of subjects. It originates from the distal one-sixth of the ulnar shaft, at the proximal border of the pronator quadratus muscle, blends into the capsule of the distal DRUJ, and inserts into the inferior rim of the sigmoid notch, DRUL, and PRUL. Moritomo et al. showed that the distal interosseous membrane (DIOM) or the DOB (if present) act as a secondary soft tissue stabilizer of the dorsal DRUJ (DDRUJ) when the TFCC, which is the primary stabilizer of DRUJ, is torn. A residual ulnar translation deformity of the proximal radial shaft has the potential to cause DRUJ instability when a TFCC injury is also present, because it may result in detensioning of the DIOM/DOB. Correction of ulnar translation of the proximal radial shaft is critical because it restores the DIOM/DOB tension, which then firmly holds the ulnar head in the concavity of the sigmoid notch. This explains why DRUJ instability that is associated with a distal radius fracture is often corrected by rigid fixation of the fracture.

FIGURE 4.2, Different Morphology of the Deep Radioulnar Ligament.

When examined from a coronal perspective, the ulnar styloid lies relatively dorsal on the end of the ulnar head. The DRUL drapes over the dorsal aspect of the ulnar head as it converges toward the fovea, which limits the field of view through a dorsal arthroscopic portal but makes possible clear views of the sigmoid notch and the adjacent surface of the ulnar head ( Fig. 4.3 A–D). There is more room on the volar ulnar aspect of the DRUJ for insertion of an arthroscope with relatively unimpeded views of the proximal articular disk and the foveal attachments. The DDRUJ portals remain useful, however, for outflow and for instrumentation.

FIGURE 4.3, (A) Surface anatomy of the dorsal distal radioulnar joint (DDRUJ) portals. (B) Scope is in the proximal DDRUJ portal. Probe is in the DDRUJ portal. (C) View from the DDRUJ portal of the ulnar head and sigmoid notch. The dorsal superficial radioulnar ligament (RUL) (asterisk) drapes across the field of view. (D) View of the ulnar head (UH) and sigmoid notch (SN) through the DDRUJ. The probe is introduced through the volar DRUJ portal. Note the cartilage loss (asterisk) on the adjacent sides of the joint.

The foveal insertion has a greater effect on DRUJ stability than the styloid insertion. A recent in vivo motion analysis revealed that in forearm pronation, the dorsal superficial RUL and palmar deep RUL tighten, serving as restraints for DRUJ stability. In forearm supination, the palmar superficial RUL and dorsal deep RUL tighten, maintaining stability of the joint. The ulnocapitate ligament is stretched taut in wrist extension. This supports the notion that a foveal tear can be caused by excessive traction of the ulnocapitate ligament due to hyperextension of the wrist from a fall on an outstretched hand. Moritomo et al. compared the surgical and clinical findings in 15 patients who underwent an open foveal reattachment with the mechanism of injury. They found that the most common mechanism of injury (10 patients) of foveal TFCC avulsion was forced wrist extension from a fall on the outstretched hand followed by forced forearm rotation (5 patients). They hypothesized that there were at least four basic injury mechanisms of foveal avulsion: (1) forced wrist extension with forearm pronation disrupting the foveal insertion first and then the superficial dorsal limb, (2) forced wrist extension with forearm supination disrupting the foveal insertion first and then the superficial palmar limb, (3) forced forearm pronation disrupting the superficial dorsal limb first and then the foveal insertion, and (4) forced forearm supination disrupting the superficial palmar limb first and then the foveal insertion. They postulated that this theory also explained why tenderness often exists predominantly on the palmar side (positive foveal sign) following this mechanism of injury, because the ulnocapitate ligament inserts into the palmar aspect of the fovea.

Diagnosis

Kleinman has described a set of provocative maneuvers for testing the integrity of the deep fibers of the RUL. The examiner sits opposite the patient, with the patient’s elbow on the examining table in full supination and his or her fingers toward the ceiling. In this position, the dorsal fibers of the deep RUL will be under maximum tension. The examiner then pushes the distal ulna toward the patient while pulling the radiocarpal unit toward himself. This maneuver introduces a superphysiologic load into the DRUJ. It will be painless only if the dorsal fibers of the deep RUL are healthy. If inflamed, or suffering from relatively minor injury, the two forearm bones will be grossly stable on stress testing, but the patient will experience considerable pain on loading the DRUJ beyond its physiologic limits. If the deep dorsal fibers have been severely sprained and detached from the fovea, this maneuver will not only be painful but will lead to superphysiologic movement of the sigmoid notch off the seat of the ulna, resulting in subtle subluxation or even gross instability, depending on the magnitude of injury to the dorsal fibers. The palmar fibers of the deep RUL are then tested by applying a dorsally directed superphysiologic load to the distal ulna, with the forearm in full pronation. The hand-forearm unit is then pulled toward the examiner, while the examiner’s thumb pushes the ulna toward the patient. If the deep palmar fibers are either ruptured or attenuated, there will painful instability in full pronation ( Fig. 4.4 A–B). A complete foveal detachment would result in a situation in which no end point is found, demonstrating multidirectional DRUJ instability. A partial RUL tear would clinically present with a firm end point with increased excursion either in the dorsal or palmar direction. The palm press test, which presents as a floating ulnar head in the pronation position, may also help to diagnose a foveal avulsion ( Fig. 4.5 A–B) ( ). Moritomo et al. classified DRUJ instability into four levels of severity: none (same as the contralateral side), mild (more unstable than the contralateral side but not subluxated), moderate (more unstable than the contralateral side and subluxated), and severe (dislocated). Jupiter has noted that it is difficult to quantify distal radioulnar instability, and these methods suffer from subjectivity and lack of interobserver validity.

FIGURE 4.4, Distal Radioulnar Joint Instability.

A lateral radiograph may reveal dorsal or palmar translation of the distal ulna provided that it is a true lateral view of the wrist. The palmar cortex of the pisiform bone should overlie the central third of the interval between the palmar cortices of the distal scaphoid pole and the capitate head ( Fig. 4.6 A–B). This can result in a block to forearm rotation ( Figure 4.6 C). Similarly, an axial CT scan of the wrist in pronation and supination compared with the normal side can be used to assess the congruency of the DRUJ ( Fig. 4.7 A–B). MR imaging can detect these tears, which are evidenced by the presence of a high-intensity area on a T2-weighted scan of the fovea and/or pooling of dye at the fovea without a leakage to the radiocarpal joint on an arthrogram.

$FIGURE 4.7, (A) Comparative axial CT scan views of a normal right wrist and a subluxated left wrist with a recent ulnar styloid fracture demonstrating dorsal subluxation of the ulnar head relative to the sigmoid notch. (B) Axial CT scan of a distal radius fracture demonstrating dorsal subluxation of the ulnar head (UH) relative to the sigmoid notch (asterisk).$

Patients who present with ulnar-sided wrist pain and DRUJ instability with normal radiographs and with tenderness over the periphery of the TFCC are initially immobilized. Further diagnostic modalities are instituted after 2 or 3 months of immobilization if the patient continues to be symptomatic. Arthroscopy is a sensitive and specific way of assessing the deep RUL. Ruch et al. first described the hook test as a way to test the foveal insertion of the TFCC during the arthroscopic treatment of distal radius fractures. A hook probe is inserted into the prestyloid recess and traction is applied ( ). If the TFCC can be pulled upwards and radially, this is indicative of a foveal detachment ( Fig. 4.8 A–B). Similarly, Tay et al. and Atzei and Luchetti have written that if one can drag the TFCC dorsally with an arthroscopic hook probe, this is indicative of a foveal detachment. In both methods, however, one must ultimately perform a DRUJ capsulotomy or DRUJ arthroscopy to directly observe the deep RUL fibers in order to definitively make the diagnosis. Atzei proposed a classification for foveal tears by subdividing the Palmer type B lesion into 5 classes: class 1, repairable distal tear; class 2, repairable complete tear (proximal and distal); class 3, repairable proximal tear; class 4, nonrepairable; and class 5, arthritic DRUJ ( Fig. 4.9 A–D).