CHAPTER SYNOPSIS:
This chapter focuses on isolated arthritis involving the articulation between the scaphoid, trapezium, and trapezoid. Arthritic changes at the scaphotrapeziotrapezoidal (STT) joint represent a subset of the bony pathology that can involve any of the intercarpal articulations and must be discussed with consideration given to overall carpal alignment and stability. Several entities, to include dorsal intercalary segmental instability, calcium pyrophosphate deposition arthropathy, and carpometacarpal arthritis of the thumb, have a strong correlation with STT joint arthritis and will be presented. The diagnosis, treatment options, surgical techniques, and “pearls and pitfalls” are covered.
IMPORTANT POINTS:
STT arthritis can exist in isolation, or it may coexist with other carpal instabilities and arthritis patterns.
Careful exclusion of other coexisting arthritic conditions at the carpometacarpal (CMC) joint and radioscaphoid joint is critical because surgical treatment options are vastly different for each entity.
Dorsal intercalary segmental instability (DISI) pattern has been shown to be associated with STT arthritis.
Calcium pyrophosphate deposition arthropathy (pseudogout) should be considered in the differential when isolated STT arthritis is identified.
Either a volar or dorsal approach to the STT joint works for STT fusion, and surgeon’s comfort should dictate which approach is preferred.
STT fusion provides reliable, reproducible pain relief and improved strength with minimal loss of preoperative wrist motion for isolated STT arthritis.
Distal pole of the scaphoid excision has shown good early and mid-term results with fewer complications than STT fusion, although long-term outcomes are not available.
CLINICAL/SURGICAL PEARLS:
Nonoperative treatment including medication, rest, splinting, and corticosteroid injections should be tried prior to offering surgical treatment.
Adequate preparation of the arthrodesis surfaces requires complete removal of subchondral bone.
Provisional pin fixation maintaining the scaphoid in a 55-degree flexed posture should be established and confirmed by intraoperative fluoroscopy prior to final fixation.
The distal radius provides a readily accessible source of autologous cancellous bone graft.
CLINICAL/SURGICAL PITFALLS:
If CMC or radioscaphoid arthritis coexists, STT fusion should be avoided.
If a dorsal surgical approach is used, careful identification and protection of the arborizing branches of the superficial branch of the radial nerve and the radial artery are important.
Patients must be counseled preoperatively regarding an expected loss of wrist motion following limited intercarpal fusion.
HISTORY AND SCOPE OF THE PROBLEM
With increasing understanding of wrist kinematics and carpal instability patterns, our understanding of the relationships between individual carpal bones and patterned types of carpal instability and arthritis has also progressed. Linscheid and colleagues are credited with descriptions of carpal instability patterns in 1972 in their classic Journal of Bone and Joint Surgery article, “Traumatic Instability of the Wrist: Diagnosis, Classification and Pathomechanics.” Six years later, in 1978 Crosby, Linscheid, and Dobyns described scaphotrapezotrapezoidal (STT) arthritis and several treatment modalities. Since 1978 literally hundreds of articles, chapters, and presentations have focused on the pathology of carpal instability, arthritis, and its treatment options. STT arthritis can only be fully appreciated by understanding that it represents one of many patterns of intercarpal arthritis, existing as a subset within the spectrum of carpal instabilities and carpal arthritic conditions. Recognition of the specific patterns of instability, collapse, and arthritic change within the STT articulations is paramount in directing appropriate management, both nonoperative and surgical treatment. STT arthritis can exist as an isolated entity, but it can also be associated with dorsal intercalary segmental instability (DISI), calcium pyrophosphate deposition (CPPD) arthropathy, and thumb carpometacarpal (CMC) arthritis.
In a series of 697 radiographic wrist examinations in patients older than age 50 years, Ferris and colleagues identified 63 wrists demonstrating isolated STT arthritis, for a 9% incidence. In cadaveric studies of 68 wrists, North and Eaton identified thumb CMC arthritis in 68% and associated scaphotrapezial arthritis (pantrapezial) in 34%. The study did not, however, delineate the percentage of isolated scaphotrapezial or STT arthritis, leaving Ferris’ 9% incidence in the older than age 50 population as the best indicator of purely isolated, although not necessarily symptomatic, STT arthritis.
ANATOMY
The anatomy of the scaphoid, trapezium, and trapezoid and the articulations between these three carpal bones are unique and help explain why these three bones are often involved in arthritis of the wrist. The anatomy of each bone will be examined here, and then the basic anatomy of the STT joint will be described to help the reader understand the genesis of STT arthritis.
Scaphoid
The scaphoid is unique in both its shape and its role within the carpus. Shaped like a kidney bean, or a cashew, it links the proximal and distal carpal rows by projecting further distally than the lunate or triquetrum. Covered almost completely by cartilage, the scaphoid maintains a flexed posture along its long axis as it articulates with the radius, capitate, lunate, trapezium, and trapezoid ( Figs. 6-1 to 6-3 ). Despite the resulting flexion moment arm acting on the scaphoid, strong ligamentous connections including the scapholunate ligament, the radioscapholunate ligament, and the STT ligaments maintain the normal relationships between these bones. The STT ligaments, in fact, have been recently studied by Brunelli, who noted the importance of this complex in maintaining normal scaphoid alignment. He noted that rotary subluxation (as seen in a DISI deformity) would not occur without injury to this ligament. Tenuous blood supply of the scaphoid is well documented and must be appreciated to avoid injuring it. Vessels enter the bone distally, with contributions from the superficial palmar branch of the radial artery volarly and from the dorsal carpal branch of the radial artery entering along the scaphoid’s dorsal radial ridge. This retrograde blood supply, as elegantly described by Gelberman and Menon, is one reason the proximal pole of the scaphoid can become avascular following fracture.
Trapezium
The trapezium, or greater multangular, articulates with the thumb metacarpal distally, the scaphoid proximally, and the trapezoid on its ulnar aspect ( Figs. 6-1 to 6-3 ). The distal articular surface of the trapezium is a biconcave saddle-shaped joint, which allows for the multiple planes of mobility enjoyed by the thumb metacarpal ( Fig. 6-4 ). There is less motion at the proximal articulation of the trapezium with the scaphoid and only slight motion between the trapezium and trapezoid in normal wrist kinematics. The higher mobility at the distal thumb CMC joint compared to the proximal STT joint may be one reason why CMC osteoarthritis is more common than STT arthritis. The axial forces transmitted through the thumb are transmitted through the thumb metacarpal, to the trapezium, and then to the distal scaphoid. These axial loads transmit a compressive force at the STT joint and subsequently cause the scaphoid to flex.
Trapezoid
The trapezoid, or lesser multangular, is smaller than the trapezium lying on its radial border and articulates with the bases of the index and middle finger metacarpals at the relatively immobile index and middle finger carpometacarpal joints. It also articulates with the distal pole of the scaphoid and with the ulnar aspect of the trapezium. In cadaveric examinations of arthritic wrists, STT arthritic changes commonly appear first at the distal scaphoid-trapezoidal joint then progress to the scapho-trapezial joint in an ulnar to radial fashion. Very little motion occurs between the trapezium and the trapezoid, and that particular longitudinal articulation is rarely involved in the arthritic process. However, because both the trapezium and trapezoid articulate with the distal pole of the scaphoid, both are involved in STT arthritis at their proximal articular surfaces. Therefore, to adequately address STT arthritis, both the trapezium and the trapezoid must be assessed for arthritic change at their articulation with the distal pole of scaphoid.
Clinical History
STT arthritis should be considered in any patient, especially if older than age 50 years, presenting with radial-sided wrist pain. The differential diagnoses of radial-sided wrist pain, with or without swelling, include DeQuervain’s tenosynovitis, Wartenberg’s syndrome or superficial branch of radial nerve neuritis, scaphoid fracture, radial styloid fracture, scapholunate advanced collapse (SLAC wrist), CMC arthritis, and intersection syndrome, just to name the more common etiologies. An exhaustive review of these diagnoses is beyond the scope of this chapter, but all, including STT arthritis, may present as radial-sided wrist pain. Differentiating the various diagnoses depends on clinical history, physical examination, radiographic evaluation, and adjunctive studies as needed to include bone scintigraphy, magnetic resonance imaging (MRI), or selective injections (under fluoroscopic guidance). This author has found bone scintigraphy coupled with physical examination findings to be particularly helpful in identifying isolated STT arthritis. Increased uptake at the STT joint can help identify the bony area of involvement. If a more global wrist arthrosis is present, that also can be seen on bone scanning. For soft tissue problems from tendinitis to ligament pathology, MRI can be a useful adjunct. As always, no adjunctive test can take the place of a careful history and physical examination. I have found the tip of my index finger to be an outstanding diagnostic tool for wrist pathology in my practice because the precise location of tenderness can lead the examiner to the correct diagnosis while ruling others out. For example, DeQuervain’s tenosynovitis is characterized by tenderness over the first dorsal compartment at the radial styloid, whereas a patient with isolated STT arthritis would be nontender over the radial styloid but tender more distally over the STT joint itself. Provocative maneuvers can be helpful, although there may be some overlap. Pain associated with thumb CMC joint arthritis seems to be exacerbated with forced extension and adduction of the thumb metacarpal, whereas STT arthritic pain is better elicited with forced radial deviation and abduction of the thumb. Likewise, forced ulnar deviation of the wrist while clasping the thumb (Finklestein’s test for DeQuervain’s tenosynovitis) and radial deviation of the wrist (without manipulating the thumb) do not cause significant pain with isolated STT arthritis.
Once the diagnosis seems accurate, associated conditions, including calcium pyrophosphate deposition (CPPD) arthropathy, carpal instability, CMC arthritis, and inflammatory arthritis, should be considered as well. CPPD, or pseudogout, may initially manifest as isolated STT arthritis on radiographs, with or without the classic calcification seen in the triangular fibrocartilage. Saffar believes isolated radiographic STT arthritis is specific for a diagnosis of CPPD. The diagnosis of calcium pyrophosphate deposition arthropathy is confirmed by identification of the rhomboid-shaped, positively birefringent crystals on analysis of joint fluid aspirate. If CPPD is suspected, fluoroscopic-guided aspiration of the joint can be confirmatory. Because the joint can be difficult to aspirate, a negative aspiration may not rule out CPPD, and other joints, such as the knee, should also be considered.
Abnormal carpal alignment as may be seen in carpal instability in which the scaphotrapezotrapezoid relationship is altered also may be associated with STT arthritis. In fact, untreated scapholunate ligament tears resulting in a DISI deformity, in which the scaphoid falls into an abnormally flexed posture and the lunate, or intercalated segment, tips into extension, has been clearly linked to the development of arthritis at the STT joint. This flexed posture of the scaphoid necessarily affects the distal articulation of the scaphoid with the trapezium and trapezoid. Radiographically, the DISI deformity is more apparent than any changes in the STT joint ( Fig. 6-5 ). A volar intercalary segmental instability (VISI) pattern in which the scaphoid still falls into a flexed position but, this time, in conjunction with hyperflexion of the lunate can also affect the STT joint. This author has treated a patient with a VISI deformity secondary to a scaphoid fracture that healed in a malunited volarly translated and flexed scaphoid that resulted in secondary changes at the STT joint. The patient’s wrist pain, and VISI deformity, resolved following STT fusion ( Fig. 6-6A-G ). In situations of STT joint arthritis associated with a carpal instability pattern, special attention should be paid to the radiocarpal joint, which can also develop associated arthritic changes. The presence of arthritis here is a strong contraindication for STT fusion, and alternate procedures should be considered.
