Isolated STT arthritis is less common than SLAC patterns of arthritis [43,44], and the etiology of STT arthritis is not as well understood. In Watson and Ballet's paper , SLAC wrist accounted for 57% of arthritic wrists, whereas 27% of cases occurred between the scaphoid, trapezium, and trapezoid; a combination of these two patterns occurred in 15% . Previous studies have associated STT arthritis with isolated sca-pholunate ligament disruption . Cope  demonstrated in a cadaveric study that abnormal scaphoid rotation, rotatory subluxation of the scaphoid, is prevented if the scaphotrapezial and radiocarpal ligaments are intact, even if the sca-pholunate interosseous ligament is disrupted. With disruption of all of these ligaments, the resulting rotatory subluxation of the scaphoid leads to abnormal pressures on the radioscaphoid articulation and eventual arthritis of the radiocarpal joint . Consistent with this concept of isolated scapholunate ligament injury leading to STT arthritis, Viegas and coworkers  noted that isolated STT arthritis was associated with an increased scapholunate interval, but not with a ring sign or radiocarpal arthritis. Presumably, these patients had isolated scapholunate ligament injury that led to the STT arthritis, but because the other ligaments were intact, there was no rotatory subluxation of the scaphoid or development of radiocarpal arthritis and the SLAC wrist pattern.
More recently, a study examining radiographs of 1711 patients visiting an emergency room in the United Kingdom were reviewed over a 5-month period . Isolated STT arthritis was seen in 1% of the population, was predominantly in females, and was often asymptomatic . The study authors found that the majority of patients who had STT arthritis did not have scapholunate ligament disruption, thus contesting the notion that isolated scapholunate ligament injury leads to STT arthritis. Instead, it was suggested that general degenerative disease accounted for the association between STT arthritis and isolated scapholunate ligament tears.
The initial evaluation of STT arthritis is similar to that of patients who have SLAC wrist. In patients who have STT arthritis, swelling and fullness will be noted in the anatomic snuffbox and volar radial wrist. Volar pressure on the scaphoid or flexor carpi radialis tunnel will elicit tenderness, which is exacerbated by radial deviation and gripping. Additional radiographic views include a hyperpronated view of the wrist, which may show early changes in the STT joint. These views will also allow assessment of the first carpometacarpal (CMC) joint (Fig. 6). Severe CMC arthritis can lead to involvement of the STT joint; however, the treatment of pan-trapezial arthritis differs from that of isolated STT arthritis and is not discussed here.
For patients who have symptomatic STT arthritis that is refractory to conservative treatment, surgical options include arthroscopic de-bridement, resection arthroplasty, or STT fusion. Ashwood and coworkers  have reported success with arthroscopic debridement for isolated STT arthritis, although this procedure is controversial. Ten patients who had persistent symptoms underwent arthroscopic debridement of the STT joint. Nine patients reported good or excellent results at an average follow-up of 36 months; however, as with arthroscopy for other arthritic joints, debridement offers at best only temporary relief. Most clinicians prefer STT fusion.
Reported results from STT fusion vary. Meier and colleagues  reported on 111 patients who
were treated with STT fusion from 1992 to 1997. Indications were chronic dissociation of the sca-pholunate joint (n = 15), idiopathic arthrosis of the scaphotrapeziotrapezoid joint (n = 11), Kien-bock's disease in advanced stage (n = 84), and dislocation of the trapezium (n = 1). After an average follow-up period of 4 years (range 2 to 8 years), patients showed an average wrist motion in extension and flexion of 81% of the preopera-tive range, and in radial and ulnar deviation of 68% of the preoperative range. Preoperative pain values were reduced. The average grip strength improved to 65% of the contralateral side. Good results were reached according to the modified Mayo wrist score, with a score of 66 points (71 points in arthritis of the STT joint, 62 points in Kienbock's disease, 60 points in SL-dissociation). The patients described low disability in the Disabilities of the Arm, Shoulder and Hand (DASH) scores, with an average of 27 points. At 4 years, the data showed that STT fusion was reliable and effective for treatment and pain relief, and offers reasonable functional results .
Unfortunately, although several operations may be effective at limiting rotatory subluxation of the scaphoid, few operations are able to correct scapholunate gap. This applies to both ligamen-tous reconstructions and to scaphotrapeziotrape-zoid fusion. STT/triscaphe fusion is used to stabilize the radial column of the wrist. Kleinman and colleagues  analyzed the effects of STT ar-throdesis on wrist kinematics in a series of patients. They followed 41 patients who underwent
STT fusion: 25 patients had chronic static scapho-lunate instability and 16 patients had dynamic instability. The average follow up was 56 months. Postoperative planar radiographs and cineradio-graphic examination in patients were performed. Scapholunate diastasis that was present before the operation persisted after the operation. This was noted with in ulnar deviation of the wrist. In ulnar deviation, the STT fusion mass, capitate, and hamate rotate with the hand while the lunate-triquetral unit is not physiologically "pulled" radially into the lunate fossa of the radius.
Alternatives to STT fusion include resection arthroplasty as well as pyrocarbon implants. Garcia-Elias and coworkers  reviewed a series of 21 patients who underwent distal scaphoid excision for STT arthritis. In some of the surgeries, the defect was filled with capsular or tendinous tissue, and in approximately half, the defect was not filled. Thirteen of the wrists were pain-free and 8 reported mild discomfort at an average follow-up of 29 months. Grip strength, pinch strength, and motion improved, and 15 patients returned to their previous jobs. The 6 patients who were previously unemployed reported no limitations in activities. In the past, there has been little success with prosthetic replacements for intercarpal osteoarthritis, although Pequignot and colleagues  recently reported on treating STT arthritis using a pyrocarbon implant. Fifteen cases that occurred between 1994 and 2002 were reviewed, with an average follow-up of 4 years. The study authors reported improvements in pain and grip strength, and stressed that this intervention restored mobility without the destabilization of carpal bones seen with distal scaphoid excision. In addition, they reported a low complication rate for a procedure that could be later revised to an STT fusion if necessary .
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