Hand Surgery
1st Edition

75
Scaphotrapeziotrapezoid and Scaphocapitate Fusions
Peter D. Burge
Scaphocapitate (SC) fusion was first described by Sutro in 1946 for scaphoid nonunion (1). Seven cases in which both poles of the fractured scaphoid were fused to the capitate were reported by Helfet (2). Peterson and Lipscomb (3) described scaphotrapezial fusion in three cases of degenerative arthritis and one case of scaphotrapeziotrapezoid (STT) fusion for traumatic arthritis with scaphoid subluxation. They reasoned that because individuals with congenital carpal fusions have wrists that are functionally normal, surgically created fusions should be compatible with good function. However, this assumption ignores subtle developmental changes in articular surface shape and ligament anatomy that may compensate for congenital absence of motion at an intercarpal joint; the normal wrist may behave differently after surgical intercarpal fusion in adult life. STT fusion in 13 patients was described by Watson and Hempton in 1980 (4). Although enthusiasm has been tempered in recent years by better understanding of complication rates and by concern that restriction of motion of the scaphoid may lead to abnormal loading of articular cartilage and premature degenerative arthritis, STT and SC fusions remain useful techniques for certain wrist disorders.
ANATOMY
The scaphoid has a concave oval facet articulating with the radial surface of the head of the capitate and a convex distal surface that in 80% of wrists is divided by a central ridge, giving separate facets that articulate with the trapezium and trapezoid (5). The trapezoid has flat radial and ulnar surfaces that articulate with the trapezium and capitate, respectively; it is bound tightly by ligaments to these bones. The slightly concave proximal surface articulates with the distal pole of the scaphoid. The flat radial surface of the distal capitate articulates with the trapezoid and is continuous with the convex lateral surface of the capitate head, which articulates with the scaphoid (Fig. 1).
The scaphotrapezial ligament runs distally from the radiopalmar aspect of the scaphoid distal pole to insert along the trapezial ridge and to the radial aspect of the trapezium.
The SC ligament arises between the trapezoid and capitate facets of the scaphoid on its palmar surface and attaches to the palmar surface of the waist of the capitate (Fig. 2). The capitate–trapezium ligament passes from the radiopalmar aspect of the trapezium into the palmar waist of the capitate and is not attached to the trapezoid. It may serve to support the distal pole of the scaphoid, and it reinforces the palmar aspect of the STT joint capsule (6). The trapeziotrapezoid and trapezoid–capitate joints appear to allow virtually no movement.
BIOMECHANICS
The bones of the distal carpal row are linked to each other and to the bases of the index and middle metacarpals by stout ligaments that permit very little movement; for practical purposes, the distal row may be regarded as a fixed unit that is firmly joined to the metacarpals. The proximal row is mobile and lacks tendon or muscle attachments—it is “a prisoner of circumstance,” and the positions of its bones are determined by their shape, by the ligaments that hold them to each other and to the adjacent rows, and by externally applied forces. Carpal instabilities are abnormal motions of the bones of the proximal row, either singly or in combination.
The proximal row flexes during radial deviation of the wrist and extends during ulnar deviation. Put simply, the scaphoid flexes during radial deviation so as to accommodate to the decreasing space between the distal row and the radius. In ulnar deviation, the helicoidal slope of the triquetrohamate joint drives the triquetrum into extension, and this motion is transmitted to the lunate and thence to the scaphoid through the lunotriquetral and scapholunate interosseous ligaments. In scapholunate instability (and its bony analogue scaphoid nonunion), the excessive flexion of the scaphoid leads to carpal collapse, and to excessive loading
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and loss of articular congruity in the elliptical radio-scaphoid joint. The end stage is the scapholunate advanced collapse pattern of degenerative arthritis (7). A primary aim of both STT and SC fusions is prevention or correction of excessive scaphoid flexion.
FIGURE 1. The scaphotrapeziotrapezoid joint forms an inverted T. The trapezoid–capitate and trapeziotrapezoid joints are relatively immobile. C, capitate; S, scaphoid; Td, trapezoid; Tm, trapezium.
STT motion is a simple rotational movement about a single axis that passes through the radiopalmar aspect of the distal scaphoid and the waist of the capitate (Fig. 2) (6) and is essentially the same in both flexion/extension and radial/ulnar deviation of the wrist. This rather simple pattern of motion contrasts with the complex behavior of the scaphoid with respect to the radius during radial/ulnar deviation and flexion/extension of the wrist. Because the trapezium–trapezoid and trapezoid–capitate joints are immobile, fusion of the scaphoid to the trapezoid has biomechanical effects very similar to those of SC fusion.
FIGURE 2. The axis of rotation of the scaphotrapeziotrapezoid (STT) joint passes through the waist of the capitate (C) and the radiopalmar aspect of the distal scaphoid (S). S-C, scaphocapitate; S-Tm, scaphoid-trapezium; Td, trapezoid; Tm, trapezium. (From Moritomo H, Viegas SF, Elder K, et al. The scaphotrapezio-trapezoidal joint. Part 2: a kinematic study. J Hand Surg [Am] 2000;25:911–920, with permission.)
STT fusion alters loading and contact areas in the radio-scaphoid joint (8). STT motion is crucial to the adaptive positioning of the scaphoid during radial and ulnar deviation of the wrist. An appreciation of the way that STT and SC fusions alter the motion, loading, and congruity of the radiocarpal joint, especially with respect to the scaphoid and its relationship with the radius, is fundamental to understanding the rationale of these procedures and their effect on the wrist. The normal pattern of motion of the scaphoid allows it to remain congruent with the radius in the face of the constantly changing relationship between the distal carpal row and the elliptical scaphoid fossa of the radius. This adaptive mechanism is lost when motion of the scaphoid is restricted by its fusion to the distal row. The flexion–extension component of scaphoid movement decreases, and the scaphoid rotation axis approaches the axis of the capitate, causing it to behave like a bone of the distal row. The loss of scaphoid flexion during radial deviation of the wrist increases stress in the radioscaphoid joint during radial deviation, and there is corresponding stress on the scapholunate ligaments in ulnar deviation because the scaphoid is unable to extend (9). Simulated STT and SC fusions increased loading in the radio-scaphoid joint (Fig. 3) (8,10). These kinematic changes have
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given rise to concern that STT and SC fusions predispose to degenerative arthritis in the radioscaphoid joint. Radio-scaphoid impingement has been observed after STT fusion, and routine radial styloidectomy has been advocated (11).
FIGURE 3. Average peak pressures at the radioscaphoid, radio-lunate, and ulnolunate joints in intact wrists and after simulating the following operations: scaphotrapeziotrapezoid (STT) fusion, scaphocapitate (SC) fusion, capitate–hamate (CH) fusion, capitate shortening (C-short) plus CH fusion, and ulnar lengthening/radial shortening (4 mm). *, p <.05; **, p <.005 compared with intact (Tukey test). (From Horii E, Garcia-Elias M, Bishop AT, et al. Effect on force transmission across the carpus in procedures used to treat Kienböck’s disease. J Hand Surg [Am] 1990;15:393–400, with permission.)
The effect of STT fusion and SC fusion on wrist motion was simulated in cadaver wrists by fixation with two Herbert screws (9). STT fusion reduced the range of flexion–extension by 22 degrees, and SC fusion reduced it by 18 degrees. Radial deviation and ulnar deviation were reduced by 20 degrees and 26 degrees, respectively. Clinically, stiffness due to preexisting disease or to immobilization after surgery may further restrict motion after intercarpal fusion. The average range of motion in the flexion/extension plane in 13 reports of STT fusion was 62% of normal (12). SC fusion reduced wrist extension on average by 28 degrees, flexion by 40 degrees, radial deviation by 14 degrees, and ulnar deviation by 14 degrees (13). The range of motion reached a plateau after approximately 6 months (13) and strength after approximately 1 year.
The arc and range of wrist motion are affected by the position of fusion of the scaphoid with respect to the distal carpal row. Radioscaphoid angle and wrist motion were measured in cadaver wrists before and after simulated STT and SC fusions with the scaphoid in extended, neutral, and flexed positions with respect to the long axis of the radius (14). Radial deviation and wrist extension increased as the scaphoid became more flexed; ulnar deviation and flexion increased as the scaphoid became more extended. The optimum radioscaphoid angle for maximum wrist motion was 41 degrees to 60 degrees for STT fusion and 30 degrees to 57 degrees for SC fusion.
INDICATIONS
The specific indication for STT fusion is degenerative arthritis of the STT joint (Table 1). SC fusion has been advocated for isolated SC arthritis (13) and for resistant scaphoid nonunion (1,2). Both STT fusion and SC fusion have been advocated for chronic static scapholunate instability and for Kienböck’s disease; for these two indications, SC fusion is probably equivalent functionally to STT fusion because fusion of the scaphoid to the trapezoid effectively links the scaphoid rigidly to the capitate through the relatively immobile trapezoid–capitate joint.
Degenerative Arthritis
Causes of STT arthritis include previous trauma and calcium pyrophosphate deposition disease, but most cases are idiopathic (Fig. 4). Scaphotrapezial arthropathy was present on radiographs of 44% of 160 wrists that showed chondrocalcinosis of the triangular fibrocartilage and in 14% of age- and sex-matched controls without chondrocalcinosis (15). The prevalence of isolated STT osteoarthritis was 2% of 143 postmenopausal females with distal radial fractures (16). The STT arthritis that accompanies advanced trapeziometacarpal arthritis is best treated by trapezial excision arthroplasty with or without ligament reconstruction.
TABLE 1. INDICATIONS FOR SCAPHOTRAPEZIOTRAPEZOID FUSION
Isolated scaphotrapeziotrapezoid degenerative arthritis
Scapholunate instability
KienbÖck’s disease
FIGURE 4. Degenerative arthritis of the scaphotrapeziotrapezoid joint.
Many cases of isolated STT arthritis respond to nonoperative treatment with splintage, activity modification, and steroid injection. Fusion is reserved for the minority of cases that fail to respond to these measures. Relief of pain is generally good (17,18).
Excision arthroplasty by removal of the distal pole of the scaphoid (19) is an alternative to STT fusion. Advantages include shorter immobilization and recovery times and probably also a lower complication rate. However, excision of the distal pole of the scaphoid resulted in a dorsiflexion intercalated segment instability pattern of carpal malalignment in 12 of 21 wrists (19). Although malalignment appeared to cause no symptoms, its long-term consequence is unknown.
Kienböck’s Disease
Management of Kienböck’s disease has centered on techniques that reduce loading of the lunate. Biomechanical studies using pressure-sensitive film (20) and theoretical models (21) have shown that both STT fusion and SC fusion reduce loading of the radiolunate joint but at the expense of overloading adjacent joints, particularly the
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radioscaphoid joint (Fig. 3) (10). Radial shortening, however, produced a 45% reduction in loading, with only moderate changes in force at the radioscaphoid joint.
Alignment of the scaphoid influences the unloading effect of STT fusion. A neutral or extended position unloads the radiolunate joint regardless of the condition of the lunate (20); the load is shifted to the radioscaphoid joint. However, fusion in a flexed position does not affect lunate load.
The lack of controlled studies hampers the comparison of the results of different procedures in a condition such as Kienböck’s disease for which the symptoms are variable and correlate poorly with the radiographic appearance. However, STT fusion and SC fusion have been used with apparent benefit in Kienböck’s disease (22,23,24,25 and 26). STT fusion combined with lunate excision and replacement with rolled tendon gave good relief of pain but less satisfactory range of motion in 12 of 15 wrists at an average of 57 months (27). Stage IIIB was believed to be the specific indication for this procedure, which corrected the flexed posture of the scaphoid. However, progressive radioscaphoid osteoarthritis was the chief cause of poor results and required total wrist fusion in two cases. SC fusion gave good pain relief in 10 of 11 patients at an average of 3 years after SC fusion; the lunate was left in situ (25).
The potential for inducing radioscaphoid degenerative arthritis remains a concern with regard to STT and SC fusions. As joint-leveling procedures such as radial shortening are probably more effective in unloading the radiolunate joint and do not greatly increase radioscaphoid loading (10,28), these procedures are preferred over STT fusion and SC fusion in the ulnar minus wrist. Other reasons for preferring radial shortening osteotomy to limited carpal fusion include its simplicity, lower potential for reducing wrist motion, lower complication rate, and more rapid rehabilitation. However, STT fusion or SC fusion may have a place in cases with neutral or positive ulnar variance.
Scapholunate Instability
STT fusion was first used in the treatment of chronic rotatory subluxation of the scaphoid by Peterson and Lipscomb in 1967 (3). Several subsequent studies have suggested that fusion of the STT joint maintains the height of the radial side of the carpus and prevents the scaphoid flexion and rotatory subluxation that lead to pain and weakness in chronic static scapholunate instability (29,30 and 31). However, carpal mechanics remain abnormal, and the load-sharing function of the lunate is not restored. Using pressure-sensitive film, Viegas et al. (8) showed that excessive scaphoid loading after simulated perilunate instability was exaggerated by STT and SC fusions (Fig. 5). It may be noted that the effect of fusions on scaphoid loading was much greater in wrists after simulated perilunate instability (Fig. 5) (8) than in normal wrists (Fig. 3) (10).
STT fusion does not close the scapholunate diastasis; indeed, the scapholunate interval may open farther during ulnar deviation as the STT fusion mass, capitate, and hamate rotate with the hand into ulnar deviation, and this may be associated with persistent ulnar translation of the carpus. In flexion, the proximal pole of the scaphoid may shift dorsally, where it may impinge on the dorsal rim of the distal radius. Despite these abnormal motion patterns, good medium-term results have been reported, with little evidence of degenerative arthritis at an average follow-up of 56 months. Poor results were associated with failure to correct the flexed posture of the scaphoid. Whether the adverse load-shifting effects of STT and SC fusions lead to degenerative arthritis is a question that will be answered only by longer-term follow-up studies (32).
FIGURE 5. Histogram comparing overall scaphoid and lunate high-pressure contact areas as a ratio of the available joints surface area (HPA/AA) for wrists in the normal and the destabilized state as well as for destabilized wrists after various types of intercarpal fusion. CL(n), capitate lunate fusion with the lunate in a neutral posture relative to the capitate; III, stage III perilunate instability; N, normal; SC, scaphocapitate fusion; SL, scapholunate fusion; SLC, scapholunocapitate fusion; STT(e), scaphotrapeziotrapezoid fusion with the scaphoid vertically orientated. (From Viegas SF, Patterson RM, Peterson PD, et al. Evaluation of the biomechanical efficacy of limited intercarpal fusions for the treatment of scapho-lunate dissociation. J Hand Surg [Am] 1990;15:120–128, with permission.)
CONTRAINDICATIONS
Degenerative arthritis of the radioscaphoid joint is a definite contraindication to STT fusion. The radiographic signs may be subtle and include loss of articular cartilage height, subchondral sclerosis, and “beaking” of the radial styloid. These changes may progress rapidly after STT fusion, despite correct alignment of the scaphoid.
OPERATIVE TECHNIQUE
The technical principles set out by Watson and Hempton (4) have been amplified in the light of experience, especially in view of the relatively high complication rate encountered
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in some studies (33,34) (see Complications). They can be summarized as follows:
  • Protection of dorsal sensory nerve branches
  • Maintenance of intercarpal distances
  • Correct scaphoid alignment
  • Preparation of healthy cancellous bone surfaces
  • Use of bone graft (usually from the distal radius)
  • Stable fixation with buried implants
  • Protection by cast or splint until union
Scaphotrapeziotrapezoid Fusion
A transverse incision, as recommended by Watson and Hempton (4), with a second, more proximal transverse incision for harvesting bone graft from the dorsum of the distal radius, has cosmetic advantages over a longitudinal approach, although the latter may be necessitated by previous wrist surgery. Branches of the superficial radial nerve are sought and protected. The dorsal branch of the radial artery is mobilized and retracted, with any small carpal branches coagulated and divided. Retracting the tendons of the first and second dorsal compartments to either side, a longitudinal incision is made in the capsule of the scaphotrapezial joint (Fig. 6). The joint is identified as an inverted T, and the capsule is reflected off the bones to expose the joint surfaces fully.
FIGURE 6. A,B: Transverse approach to the scaphotrapeziotrapezoid joint. MC, metacarpal. (From Ruby LK. Arthrotomy. In: Cooney WP, Linscheid RL, Dobyns JH, eds. The wrist. Diagnosis and operative treatment. St. Louis: Mosby, 1998, with permission.)
At this stage, any excessive flexion of the scaphoid can be corrected, and provisional fixation with Kirschner wires is achieved. It is advisable to check the alignment with intraoperative radiographs, using radiographs of the opposite
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wrist for comparison if necessary. Alignment of the scaphoid must avoid excessive flexion. The optimum position of the fused scaphoid—i.e., the position that maximized wrist motion in simulated fusions of cadaver wrists—was a radioscaphoid angle between 41 degrees and 60 degrees (14). Failure to ensure correct alignment of the scaphoid has been associated with persistent pain (33).
FIGURE 7. A: Articular surfaces are removed and three pins have been “preset” in retrograde fashion. B: Cancellous bone graft had been packed between the bones, the external shape of the three-bone unit is maintained, and the pins are driven across the arthrodesis sites. (From Watson HK, Hempton RF. Limited wrist arthrodeses. I. The triscaphoid joint. J Hand Surg [Am] 1980;5:320–327, with permission.)
The dorsal 70% of the articular surfaces of the STT joint is then excised to expose cancellous bone. Leaving the palmar 30% of the articular surfaces intact maintains the appropriate intercarpal distances; if the entire surface is removed, the handle of a small elevator can be used to maintain the correct intercarpal separation as the pins are inserted (Fig. 7) (4). Cancellous bone taken from the distal radius in the vicinity of Lister’s tubercle, via a separate transverse incision if necessary, is then packed between the prepared surfaces. A radial styloidectomy may be performed if desired (11). No more than 3 to 4 mm of the styloid should be removed to avoid damage to radiocarpal ligaments and the consequent risk of ulnar translation of the carpus (35,36).
Alternative bone grafting techniques include the dowel method (37), using a precision tube saw to prepare the graft bed (centered on the junction of scaphoid, trapezium, and trapezoid) and a slightly larger saw to obtain, from the iliac crest, a matching dowel graft that fits tightly into the bed. A similar method can be used with distal radial graft (38). The iliac crest tends to provide a stronger graft, but the lower morbidity of the distal radial donor site is preferred by patients.
For fixation, Kirschner wires have the virtue of simplicity but require later removal. Three or four wires are required; they should cross the joints to be fused (4), and it may be helpful to pin the scaphoid to the capitate; however, pins should not cross other joints. The decision to bury the tips subcutaneously or leave them percutaneously is influenced by the consequences of infection of pin tracks that traverse the joint spaces of the wrist—septic arthritis is a potentially disastrous result of pin track sepsis. For this reason, the author buries subcutaneously the ends of all pins that cross the synovial cavity of the wrist joint and accepts the need to remove them in due course.
Passage of pins and screws through any but the dorsal incision entails risks to the superficial radial nerve branches and to the dorsal branch of the radial artery. The author makes an incision large enough to permit blunt dissection down to the joint capsule, as for a wrist arthroscopy portal, and uses an appropriately sized drill guide to protect the soft tissues. The anatomic study of Steinberg et al. (39) is helpful in planning the placement of wires. An equal degree of care is required when removing them.
Alternative methods of fixation include screws and staples (Fig. 8). Screws can generally be left in place indefinitely; unlike Kirschner wires, there is no pressure to remove them, and this can be an advantage if union is slow (Fig. 9). The use of screws is influenced by considerations of access; it may be difficult to achieve the correct angle of attack through the dorsal incision, necessitating a separate radial incision or stab incisions, with the inherent risk to the superficial radial nerve and the dorsal branch of the radial artery. Staples have the advantage that they can be inserted directly through the dorsal approach, avoiding any
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risk to dorsal sensory nerves, although the literature contains little about their use in STT and SC fusions.
FIGURE 8. Fixation techniques for scapho-trapeziotrapezoid and scaphocapitate fusions. A,D: Kirschner wires. B,E: Staples. C,F: Herbert screws.
Most authors recommend immobilization for 8 to 12 weeks. The extent of the cast varies from a simple short arm cast to a long arm cast including the metacarpophalangeal joints of the index and middle fingers (4). A long cast for an initial period of 4 to 6 weeks and a short cast thereafter is a reasonable regimen. Thereafter, graduated progression is made through active range-of-motion exercises and subsequent strengthening exercises, with the maximum range of motion reached at approximately 6 months postoperatively.
Scaphocapitate Fusion
SC fusion can be performed through a transverse or longitudinal skin incision. The joint capsule is opened in the interval between the third and fourth dorsal compartments, protecting superficial radial nerve branches. The adjacent surfaces of the capitate and scaphoid are prepared as for STT fusion (see Scaphotrapeziotrapezoid Fusion), preserving the palmar 30% of the surfaces to maintain the correct intercarpal relationship. Kirschner wires are driven from the radial surface of the scaphoid into the capitate, with the scaphoid having been positioned at approximately 45 degrees to the long axis of the wrist (Fig. 10). Alternatively, headless screws such as the Herbert and Acutrak screws may be placed across the SC joint. Staples may also be used. Cancellous bone graft from the distal radius is packed into the prepared bone surfaces. The wound is closed, and the limb is immobilized for 8 to 12 weeks, as for STT fusion. However, if secure screw fixation is achieved, the period of immobilization may be shortened.
Results
A review of the literature on intercarpal arthrodesis (12) identified 258 patients in 13 reports of STT fusion, which was performed for a variety of disorders. The average follow-up period was 38 months. Using strict criteria for definition of postoperative pain, 49% of wrists were painful at final follow-up. In this study, any complaint related to pain was recorded as positive,
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but not all cases with mild postoperative pain had poor results. The average range of motion was 62% of the normal flexion/extension arc, and the average grip strength was 74% of normal. Several studies reported cases of radioscaphoid arthrosis developing after STT fusion. Approximately one-third of 258 patients required further operations to treat complications or persistent pain. These procedures included bone grafting, total wrist arthrodesis, proximal row carpectomy, and radial styloidectomy. The results in cases of STT arthrosis were similar to the results in other disorders. The reviewers agreed with Tomaino et al. (40) that postoperative function was more dependent on pain relief than on residual movement. The short average follow-up in the reviewed papers (36 months) emphasizes the paucity of long-term data on which advice to patients can be based.
FIGURE 9. A,B: Fusion of the sca-photrapeziotrapezoid joint with Kirschner wires, supplemented by a Herbert screw passed between the trapezium and trapezoid. C,D: The appearance after 2 years.
Data on the results of SC fusion are more limited. Seven of 17 patients (13) had persistent pain with heavy use. The average loss of flexion/extension was 68 degrees, and grip strength averaged 74% of the unoperated side. SC fusion for Kienböck’s disease using two lag screws (25) gave complete pain relief in 10 of 11 patients at an average of 36 months with a 64-degree arc of flexion/extension and grip strength 72% of the unoperated side. Two patients required second operations to achieve union.
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FIGURE 10. An anteroposterior radiograph demonstrates successful scaphocapitate fusion using power staples.
COMPLICATIONS
The complication rate of STT fusion has remained significantly higher than other wrist procedures (33,34,41,42 and 43). A review of 13 papers that described 258 patients (12) found a complication rate averaging 43% in those studies in which it was reported, including 13% nonunion. Kleinman and Carroll (33) had 52% complications in 47 wrists. In another series, it was 53% of 40 cases (34). Complications included pin track infection, osteomyelitis, radial styloid impingement, nonunion, and dorsal sensory nerve problems (Table 2). Attention to details of operative technique and to positioning of the scaphoid can do much to minimize the risk of complications. The optimum position of the fused scaphoid—i.e., the position that maximizes wrist motion—is a radioscaphoid angle between 41 degrees and 60 degrees (14). Ulnar translation of the lunotriquetral unit occurred in two of 47 cases treated by Kleinman and Carroll (33). Both were associated with ulnar-sided wrist pain and required total wrist fusion.
TABLE 2. COMPLICATIONS OF SCAPHOTRAPEZIOTRAPEZOID FUSION
Nonunion
Pin track sepsis
Septic arthritis
Osteomyelitis
Radial styloid impingement
Dorsal sensory nerve impairment
Radioscaphoid arthrosis
Radial styloid impingement was reported in 31 of 91 patients at an average of 23 months after STT fusion (11). Impingement was characterized by radial wrist pain on flexion or by limited radial deviation; the symptoms were relieved by radial styloidectomy. These authors recommended routine partial radial styloidectomy at the time of STT fusion.
Complications of SC fusion included nonunion in 2 of 17 patients (13).
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