▪ Rationale and Basic Science Pertinent to the Procedure

Excision of the distal pole of the scaphoid has been recommended for the treatment of a variety of scaphoid-trapezium-trapezoid (STT) dysfunctions. The encouraging results of resection-interposition arthroplasties in other joints promoted its use in this articulation as well.1 ^, 2 Nevertheless, as more experience was collected, the more evident it became that this is not a procedure to be used without caution.3 ^, 4 Indeed, excising the distal scaphoid may have adverse mechanical consequences if it is not properly done and for the right indications.

The proximal carpal row is an intercalated segment between the distal row and the radius, implying a multilevel linkage that allows greater mobility to the wrist than if it was a single-level articulation. Under load, such a longitudinal link connection would collapse in a zig-zag fashion, were it not for the presence of several stabilizing mechanisms, the most important of which may be described as follows. When the trapezium is axially loaded, the obliquely oriented scaphoid always tends to rotate into flexion. Contrarily, when the hamate is pushed proximally, the triquetrum tends to rotate into extension. The reason for this can be found in the fact that the triquetrum-hamate joint has a dorsal inclination inducing the hamate to slide dorsally under load. The bone does not sublux, however, because it is strongly connected to the palmar-distal edge of the triquetrum by the palmar triquetrum-capitate-hamate (TqCH) ligament. Such a strong connection constrains the dorsal subluxing tendency of the hamate by promoting an extension moment to the triquetrum, which neutralizes the flexion moment initiated by the scaphoid. With this, a stable equilibrium is achieved.5 Obviously, such balanced alignment of carpal bones is only possible if the linkages connecting the different elements of this “midcarpal ring” are intact.6

The system could be compared with a spring with two (lateral and medial) prongs extending distally toward divergent directions.4 When compressed by the distal carpal row, the angle between the two arms of the spring is likely to increase until the coiled portion of the spring is blocked and maximal stability is achieved ( Fig. 33.1A ). According to this concept, if the “scaphoid” arm is shortened, it will lose its mechanical advantage, and the “triquetral” arm will predominate, promoting a rotation of the spring in a dorsal direction ( Fig. 33.1B ). Such dorsal rotation is likely to progress until the shorter scaphoid arm is able to hold again the trapezium and a new balance is attained ( Fig. 33.1C ). In fact, excision of a portion of the distal scaphoid decreases the scaphoid influence to the overall wrist stability and the ulnar column takes control of the proximal row inducing its rotation into extension: the so-called carpal instability nondissociative with dorsal intercalated segment instability (CIND-DISI).7 Based on this, it is obvious that a partial distal scaphoidectomy should not be regarded as a harmless intervention.4

By excising a portion of the distal scaphoid an abnormal mechanical environment is created with substantial alteration of the pathways along which forces are transferred. Whether or not the wrist will be able to adjust to this new situation and allow acceptable function will depend on several factors: (1) the size of the scaphoid being removed, (2) the ability of the remaining capsuloligamentous structures to absorb the forces generated by the dorsally subluxing capitate and hamate bones, (3) the status of the cartilage in those areas that will be loaded by the subluxing bones, and (4) the capacity of specific muscles to cope with its dynamic role in the stabilization of the surgically induced carpal malalignment.

▪ Indications

Distal scaphoid excision should be indicated only as a salvage procedure when the morbidity of other alternatives is unacceptably high. There are two major indications for such an approach: (1) treatment of selected scaphoid nonunions in low demand patients, and (2) treatment of symptomatic STT degenerative osteoarthritis without dorsal midcarpal instability. Not discussed in this chapter is when the distal scaphoid is excised in patients with a radioscapholunate fusion to unblock the midcarpal joint and allow a more physiological function.4

▪ Contraindications

After excising the distal pole of the scaphoid, most of the load across the STT articulation will be transferred to the central portion of the midcarpal joint.4 Consequently, the scapholunocapitate (SLC) ball-and-socket articulation may suffer from overload when the scaphoid has been partially resected. The procedure, therefore, is not indicated when there are arthritic changes, incongruency, or instability at the SLC joint.13 Very often, the consequence of resecting the distal scaphoid in advanced STT arthritis with dorsal midcarpal instability (DISI pattern of misalignment) is the development of a painful dorsal subluxation of the capitate. Certainly, if an STT degenerative arthritis exhibits substantial DISI before surgery, the condition will be better treated by an STT fusion, a midcarpal fusion, a proximal carpal row, or a radioscapholunate fusion plus distal scaphoidectomy.

▪ Surgical Technique

Distal Scaphoid Nonunion

A longitudinal, zig-zag, or lazy S dorsoradial incision over the scaphoid snuffbox is usually used. The sensory branches of the radial nerve need to be gently retracted and protected throughout the procedure. Deep in this area, under a thin layer of fascia, the radial artery is to be identified and protected. This approach may also be used to perform a radial styloidectomy should an osteophyte in this location be part of the problem. A transverse dorsal incision at the STT level is usually adequate to expose the distal scaphoid. Bone excision is facilitated by inserting a K-wire into the fragment and rotating it to incise its palmar soft tissue attachments ( Fig. 33.2C ). Special attention needs to be paid not to damage the palmar radioscaphocapitate ligament, located palmarly just in contact with the anterior concavity of the scaphoid. Whenever possible, the ligament fibers that connect the lateral corner of the scaphoid tuberosity to the lateral aspects of the trapezium and trapezoid (STT ligaments) should also be preserved.

Once the distal scaphoid has been removed, it is essential to test the stability of the distal row relative to the proximal scapholunate socket ( Fig. 33.2 ). Should the midcarpal “posterior drawer’s test”14 demonstrate substantial subluxation of the capitate, a combined stabilizing procedure, such as an STT fusion or a more extended midcarpal arthrodesis, should be added. If instead, there is more instability at the radiocarpal articulation, a radioscapholunate fusion is recommended.15 Checking for residual instability after resection of the distal scaphoid is particularly important in heavy manual workers ( Fig. 33.2 ). Mild dorsal instabilities in low demand patients may respond well by interposing a bulky “anxovy” of the palmaris longus tendon in the defect, plus a dorsal midcarpal capsulodesis.3 The goal of the fibrous interposition in such cases is to prevent excessive extension of the scaphoid, and through it, of the entire proximal row. Certainly, if the scaphotrapezial gap is tightly filled with fibrosis, the scaphoid extension may somehow be minimized. This, in association with a distally based capsular flap that is to be tightly sutured onto the dorsal edge of the scapholunate joint, has proven a certain efficacy in avoiding dorsal midcarpal instability. If the posterior drawer’s test rules out any form of residual radiocarpal and/or midcarpal instability, the defect may be left empty behind the repaired capsule. Except for the cases requiring an associated partial fusion, resection arthroplasties necessitate no more than 4 weeks of immobilization, the time needed for proper cap-sular healing.

The early aim of hand therapy in such cases is to regain motion, not grip strength. No muscle strengthening exercises should be promoted during the first 3 months after surgery, and even then no gripping activities should be performed with the wrist flexed, but always extended. Indeed, any axial force with the wrist in flexion would promote excessive compressive load of the capitate against the dorsal lip of the lunate thus inducing the appearance of further DISI malalignment and dorsal midcarpal subluxation. In fact, these patients should always be advised to avoid contact sports and to wear a removable, slightly extended splint for all activities implying any force or torque to the operated wrist for the first 6 months after surgery.

Related posts:

42 Arthroscopic Styloidectomy for Scaphoid Nonunion Advanced Collapse Wrist 41 Total Wrist Fusion versus Denervation for Chronic Scaphoid Nonunion 38 Corrective Osteotomy for Scaphoid Malunion 37 Proximal Row Carpectomy for Scaphoid Nonunion 35 Pyrocarbon Scaphoid Implant Allowing Adaptive Mobility in Proximal Scaphoid Pseudarthrosis 34 Arthroscopic Distal Scaphoidectomy

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