Transtrapezial Approach for Fixation of Acute Scaphoid Fractures: Rationale, Surgical Techniques, and Results: AAOS Exhibit Selection

Verstreken, Frederik MD; Meermans, Geert MD

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.N.01262
Scientific Articles
Abstract

Abstract: The ideal position for a screw used for scaphoid fixation is central. The purpose of this study was to compare the current volar percutaneous approaches used for scaphoid fracture fixation, explore different options to improve central screw placement, and describe our experience with the transtrapezial approach.

Author Information

1Department of Orthopaedics, Monica Hospital, Stevenslei 20, 2100 Deurne, Belgium. E-mail address: frederikverstreken@azmonica.be

2Department of Orthopaedics, Lievensberg Hospital, Boerhaaveplein 1, 4624VT Bergen op Zoom, the Netherlands. E-mail address: geertmeermans@hotmail.com

Article Outline

Of all wrist injuries, scaphoid fracture is second only to distal radial fracture with respect to prevalence. The scaphoid is the most frequently fractured carpal bone, and scaphoid fractures account for 60% of all carpal fractures and 11% of all fractures of the hand1. In different countries, the incidence has been estimated to be twenty to forty-three per 100,000 inhabitants per year1-4 or 1.47 fractures per 100,000 person-years5. Scaphoid fractures are seen more frequently in men, with an annual incidence of twenty to thirty-eight per 100,000 compared with eight to nine per 100,000 in women2,3. The age-specific incidence in men peaks between twenty and thirty years of age, after which there is a rapid decrease1.

Nonunion or malunion of the scaphoid can result in osteoarthritis, instability, chronic discomfort, and subsequent functional impairment6-12; thus, displaced waist fractures, proximal pole fractures, and fractures with loss of carpal alignment should be treated with surgery unless that is contraindicated13. Eighty percent of all scaphoid fractures occur at the waist, and the majority are nondisplaced14,15. Routine surgical treatment of acute nondisplaced fractures has been reported in young and active individuals16-18. Two recent meta-analyses demonstrated that internal fixation of nondisplaced or minimally displaced waist fractures results in better patient-reported functional outcomes, greater patient satisfaction, increased grip strength, a shorter time to union, and an earlier return to work. However, higher complication rates were reported19,20.

Because the scaphoid has a complex anatomic shape, internal fixation is technically challenging. When a standard volar percutaneous technique is used, central screw placement at the distal scaphoid pole is hindered by the trapezium. This study focuses on the transtrapezial approach for fixation of nondisplaced scaphoid waist fractures. The goals of this report are to (1) review the biomechanics of scaphoid fracture fixation, (2) present the rationale behind a transtrapezial approach, (3) describe the surgical technique of the transtrapezial approach, and (4) present the outcomes and complications of this technique as reported in the current literature and revealed by our experience.

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Biomechanics of Screw Fixation of Scaphoid Fractures

Screw Length

Placement of a headless cannulated variable-pitch screw has become common practice in the surgical management of scaphoid fractures. It is necessary to bury the implant below the level of the cartilage on both ends of the scaphoid to prevent the development of radioscaphoid or scaphotrapezial arthritis. The narrowest part of the scaphoid is at its proximal pole, and in contemporary screw designs the trailing thread diameter is larger than the leading thread diameter. Theoretically, screws with a double-threaded variable-pitch design placed through a volar approach should be longer than those placed through a dorsal approach, to the level of the subchondral surface (Figs. 1-A through 1-D)21. When a scaphoid screw is placed from a dorsal approach, there is a tendency for the surgeon to choose a shorter screw so that the screw does not become prominent and cause injury to and subsequent degeneration of the distal radial articular surface22.

In a cadaver study of simulated scaphoid waist fractures with volar bone loss, Dodds et al.22 demonstrated that less stability was conferred by short screws (screws that were 8 mm less than the scaphoid length—i.e., 4 mm from each cortex) than by long screws (screws 4 mm less than the scaphoid length—i.e., 2 mm from each cortex). Screw augmentation with a Kirschner wire improved stability when a long screw was used, although this improvement was not significant.

The ability to place a screw ≤2 mm beneath the chondral surface is determined by the screw’s design. Those with a diameter of ≥4.0 mm cannot always be buried ≤2 mm beneath the articular surface of the proximal pole21. To avoid screw prominence, screws that are available only in 2 or 2.5-mm increments are significantly shorter than those available in 1-mm increments21,22.

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Screw Position

It is easier to place screws in the desired position in the scaphoid when the screws are cannulated11. McCallister et al.23 compared the biomechanical properties of screw fixation between screws placed centrally in the proximal fragment of the scaphoid and those placed eccentrically at the proximal pole. Using single-load-to-failure conditions, they found the central position to be biomechanically superior to the eccentric position (Figs. 2-A and 2-B). The results of this biomechanical study have been translated into clinical practice. Central placement of the screw in the proximal fragment of the scaphoid is associated with significantly decreased times to union11.

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In a biomechanical model of an unstable oblique scaphoid fracture, stiffness and load to failure were similar for screws placed through the tuberosity and perpendicular to the fracture plane and screws placed in a central position in the proximal fragment24. The simulated fracture pattern used in that cadaver study accounts for only 5% of scaphoid fractures4,25. In most scaphoid waist fractures, a screw along the central axis is perpendicular to the fracture plane26.

The biomechanical properties of scaphoid screw positioning were examined in a recent study carried out at our institution. All screws were placed centrally in the proximal pole, whereas placement in the distal pole was either central or eccentric (Figs. 2-B and 2-C)27. A significantly greater force was required to generate simulated fracture displacement when the screws were positioned centrally in both the distal and the proximal fragment as opposed to centrally in only the proximal fragment. In order to optimize fixation strength when treating scaphoid fractures with a cannulated differential-pitch screw, surgeons should use a technique that allows positioning of the screw centrally throughout the scaphoid rather than centrally only in the proximal pole.

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A histomorphometric study of the scaphoid with use of micro-computed tomography (micro-CT) showed significant regional differences in the scaphoid. Because of regional variation of bone strength and stress distribution, the trajectory from the midcarpal side of the distal pole to the radial side of the proximal pole presented better bone quality than that from the radial side of the distal tuberosity to the midcarpal side of the proximal pole28. These variations can explain the biomechanical difference between central and eccentric screws at the distal pole.

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Rationale for a Transtrapezial Approach

The optimal approach for fixation of scaphoid waist fractures continues to be a subject of debate29-31. Open operative treatment, as described by Herbert and Fisher, involves insertion of a headless screw from the distal pole of the scaphoid32. Typically, a volar incision is made, a portion of the volar ridge of the trapezium is removed, and the scaphotrapezial joint is entered to allow central screw placement throughout the scaphoid.

An alternative to the open approach is a less invasive, percutaneous approach, but this is technically demanding, mainly because of the shape of the scaphoid and its position between the radius and trapezium.

A percutaneous dorsal approach has been advocated by several authors but has some disadvantages. To allow access to the central axis of the scaphoid, the wrist has to be flexed. This may cause displacement of the fracture fragments and impedes fluoroscopic control of guidewire and screw insertion. The approach also causes cartilage injury on the scaphoid at the radiocarpal joint. In our experience, the approach has led to dorsal scarring and painful impingement. A cadaver study by Adamany et al.33 showed that a dorsal approach was associated with a risk of injury to several anatomic structures, especially the posterior interosseous nerve, the extensor pollicis longus tendon, the extensor indicis proprius tendon, and the extensor digitorum communis tendon of the index finger. A clinical study of twenty-four patients by Bushnell et al.34 showed an overall complication rate of 29% (a 21% rate of major complications and an 8% rate of minor complications) when a dorsal approach was used for percutaneous scaphoid fixation.

For these reasons, a volar approach may be a better alternative but, because the trapezium is an obstacle to optimal screw placement, accurate positioning is technically demanding without opening the scaphotrapezial joint, a limitation of the volar percutaneous approach27,35-37(Table I)16,17,38-58. Different techniques resulting in either a central or an eccentric screw position at the distal pole of the scaphoid have been proposed.

In a CT study, we found that a guidewire placed through a standard volar approach, avoiding the trapezium, was eccentric at the distal and waist sections of the scaphoid37. A virtual central guidewire passing through the center of the proximal and distal poles of the scaphoid always crossed the trapezium37. In another CT study, Levitz and Ring36 showed that a screw path that avoided penetration of the scaphoid surface could not always avoid the trapezium or it lay in close proximity to the radial border of the trapezium and, as a consequence, some of the trapezium would be resected by the drill-bit. They concluded that it may often be necessary to drill or partially excise the trapezium for optimal screw placement. Leventhal et al.35 also demonstrated that access to the central axis of the scaphoid via the volar approach is not possible without resection of at least part of the trapezium or use of a transtrapezial approach.

Several techniques have been developed in an attempt to increase the clearance of the trapezium and allow more central screw placement at the distal pole of the scaphoid. These include holding the wrist in an ulnarly deviated and extended position43, partial excision of the trapezium36, using a large-bore needle as a lever to dorsally displace the trapezium58, and using a transtrapezial approach and drilling the guidewire through the trapezium48.

To gain better access to the distal pole of the scaphoid, the wrist is often held in extension and ulnar deviation (Table I). In a three-dimensional CT study, we found that a central guidewire traversed the trapezium in every patient regardless of whether the wrist was in a neutral position or in extension and ulnar deviation37. This was confirmed in another study that used CT models of scaphoids with kinematic data and demonstrated that the longitudinal axis of the scaphoid was obstructed by the trapezium in the wrist position that best uncovered the scaphoid in all but one of nine scaphoids35.

An alternative technique is to insert a large-bore needle into the scaphotrapezial joint and lever the trapezium ulnarly and volarly, potentially allowing a more central starting point on the distal pole of the scaphoid58. A cadaver study of this technique showed that eight of ten screws were positioned within the central third of the proximal pole and six of ten, within the central third of the distal pole59. Only four screws were central in both the proximal and the distal pole. This maneuver may also cause displacement of the scaphoid fragments into flexion, especially when some comminution is present at the fracture site.

The transtrapezial approach is an alternative that allows predictable access to the central axis of the scaphoid without the need to resect part of the trapezium or manipulate the wrist or scaphoid. In a cadaver study, we used radiographs to compare the standard volar percutaneous approach with the transtrapezial approach with regard to central screw placement at the distal pole27. All screws could be placed within the central one-third of the proximal pole of the scaphoid with both approaches, but all screws inserted through the transtrapezial approach were inside the central one-third of the distal pole and all screws placed through the standard volar approach were outside it (Figs. 3-A, 3-B, and 3-C)27.

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Surgical Technique of the Transtrapezial Approach

With the patient supine, the involved hand is placed on a radiolucent arm-board; no traction devices are used. General anesthesia or a brachial plexus block is administered, and a tourniquet is applied. To obtain central screw placement, the central axis of the scaphoid is determined with fluoroscopy, in both the frontal and the lateral plane, and a guidewire is placed on the skin along this axis. The central axis is then marked on the skin with a marker pen in the two planes (Video 1).

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A stab incision is made over the distal half of the trapezium, at the intersection of the two lines, after which a guidewire is drilled through the trapezium into the scaphoid. Under fluoroscopic control, the guidewire is advanced along the lines marked on the skin until it reaches the proximal cortex of the scaphoid. To determine the appropriate screw length, another, identical guidewire is drilled through the trapezium, parallel to the first guidewire, until it reaches the distal cortex of the scaphoid. The screw length is determined by measuring the difference between the two wires, and the second guidewire is removed.

To prevent the first wire from backing out, the surgeon can advance it into the distal part of the radius. Subsequently, after drilling with a 2-mm drill-bit, a cannulated differential-pitch screw is placed over the guidewire into the scaphoid, the guidewire is removed, and the final position of the screw is checked in all radiographic planes.

After the operation, a volar splint is applied and is worn for two weeks. The patient is instructed to elevate the hand for the first days to control swelling. Nonsteroidal anti-inflammatory drugs are prescribed for postoperative swelling, and pain medication is given60.

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Source of Funding

Synthes supplied the implants for this study.

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Results

Outcomes

De Vos and Vandenberghe41 reviewed the cases of forty-four patients with an acute fracture of the scaphoid that had been managed with percutaneous fixation. Their approach was through a 0.5-cm longitudinal volar incision, just distal to the scaphotrapezial joint. In most cases, a 2-mm drill-bit was introduced through the trapezium. At a mean of twenty-seven months (range, two to sixty months) postoperatively, there were two nonunions, both of Herbert B3-type fractures with a delay in diagnosis. Although the authors stated that some patients with a fracture of the proximal pole (Herbert B3) required a dorsal approach, they did not specify which approach was used in cases that went on to nonunion. The patients returned to work in a mean of forty-one days (range, ten to 120 days). At the time of follow-up, the range of flexion averaged 69.8° (98% of that on the contralateral side); extension, 80.6° (95%); ulnar deviation, 30.9° (97%); and radial deviation, 13.6° (89%). Power grip and pinch grip were, respectively, 95.9% and 95.8% of that on the contralateral side. The authors reported that, in their experience, drilling and inserting the screw through the trapezium was the best way to place the screw in the center of the scaphoid waist and to achieve compression perpendicular to the fracture line.

We conducted a clinical study of patients who had sustained an isolated, acute, nondisplaced or minimally displaced fracture of the scaphoid waist48. Forty-four patients had undergone percutaneous fixation through a transtrapezial approach, and forty-one of them were available for complete follow-up. At a mean of thirty-six months (range, fourteen to sixty-eight months), there were four good and thirty-seven excellent results according to the modified Mayo wrist score. The range of motion (mean and standard error of the mean [SEM]) was 139° ± 5.1° on the injured side and 144° ± 4.9° on the uninjured side, whereas grip strength was 57 ± 4.9 kg and 52 ± 4.2 kg, respectively. All patients had good central placement of the screw as seen radiographically. Three patients had the screw removed one year postoperatively, after consolidation of the fracture site, because the screw head was prominent distally at the scaphotrapezial joint and was mildly painful with activity; the pain resolved after the screw was removed. One patient developed type-1 complex regional pain syndrome with some residual stiffness of the small finger.

Zhang et al.61 used a transtrapezial approach in twenty-three patients with an acute stable scaphoid fracture. All fractures united, and at the time of final follow-up at a mean of ten months postoperatively all patients were pain-free with good grip power and range of wrist motion. The authors found the transtrapezial approach to be a simple, safe, and reliable method to treat acute stable scaphoid waist fractures that allowed them to place the screws along the longitudinal axis of the scaphoid more easily.

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Scaphotrapezial Joint

Use of the transtrapezial approach inevitably causes some damage to the surfaces of the scaphotrapezial joint, leading to a risk of late osteoarthritis. Degeneration can also occur at the scaphotrapezial joint after use of the standard open volar approach62-64. In a CT study (unpublished), we found that the mean surface area (and SEM) of the trapezium at the scaphotrapezial joint was 64.7 ± 3.6 mm2 (52.6 ± 3.2 mm2 in women and 76.8 ± 3.6 mm2 in men, p < 0.0001). The percentage of cartilage damage was 15.9% (range, 10.3% to 25.5%) after use of a transtrapezial approach compared with 22.3% (range, 12.9% to 36.4%) when part of the trapezium had been resected to obtain access to the center of the distal pole of the scaphoid (p < 0.0001). The former value corresponds closely to the 11% trapezial cartilage violation that was found in a cadaver study after use of a transtrapezial approach59.

In a long-term follow-up study, we specifically evaluated degenerative changes at the scaphotrapezial joint65. Of the initial cohort of forty-four patients, thirty-four were available for follow-up at a mean of 6.1 years (range, 3.7 to 8.6 years). At the time of final follow-up, we conducted a clinical examination of both hands and obtained standard posteroanterior and lateral radiographs and an additional 45° pronated oblique view to specifically assess the scaphotrapezial joints66. Degenerative changes at the scaphotrapezial joint were staged according to the modified Eaton and Glickel classification66. In twenty-nine of the thirty-four patients, the screw was seen to be placed centrally on all three views. In three patients, the screw was seen to be placed 1 mm eccentrically on one view and centrally on two views. In two patients, the screw was seen to be placed 2 mm eccentrically on two views and centrally on one view. Two patients had bilateral stage-2 osteoarthritis of the scaphotrapezial joint, and one patient had unilateral asymptomatic stage-2 osteoarthritis due to screw protrusion at the scaphotrapezial joint. Screw protrusion into the scaphotrapezial joint was noted in six cases. Because of mild pain at the scaphotrapezial joint with activity, the screw was removed in two cases.

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Discussion

Conservative treatment of nondisplaced scaphoid waist fractures is associated with a high union rate and low complication rate and is therefore the gold standard67,68. The main advantage of percutaneous fixation of these injuries is an earlier return to function, but a surgical procedure is warranted only when it allows rigid fixation of the fracture and has a very low complication rate. Percutaneous fixation of scaphoid fractures is a technically demanding procedure prone to complications. Several techniques have been proposed to facilitate screw insertion, each with its advantages and disadvantages. Some of these techniques result in an eccentric screw at the distal pole43,48,58.

Placement of a screw along the central axis of the scaphoid was shown to be biomechanically superior to a more eccentric position of the screw in an osteotomy-simulated scaphoid waist fracture model27. Central placement can be reliably achieved with the use of a transtrapezial approach, without the need to manipulate the wrist or scaphoid or resect part of the trapezium27,37.

The transtrapezial approach has some drawbacks. Passing the guidewire, drill, and screw through the trapezium damages cartilage at the scaphotrapezial joint. A study with longer-term follow-up (mean, 6.1 years) showed that this did not cause degenerative changes at the scaphotrapezial joint65.

Placement of a screw of the maximum possible length with purchase of the screw threads in the strong subchondral bone is biomechanically superior and therefore the goal in scaphoid fixation22. However, this increases the risk of screw protrusion at the radiocarpal or scaphotrapezial joint. Screw protrusion at the scaphotrapezial joint was the most common complication in a clinical study on the transtrapezial approach48,65. It occurred early in the series and is probably an indication of the learning curve associated with this technique. Screw protrusion can be avoided by thorough evaluation of the fluoroscopic images during the procedure. A pronated oblique view combined with ulnar deviation and 45° of flexion of the wrist allows the best evaluation of the scaphotrapezial joint.

Removal of a screw placed along the central axis of the scaphoid is more complex than removal of one that was inserted in a more eccentric position. If screw removal is indicated, a guidewire is reinserted through the trapezium into the screw, the trapezium is drilled, and the screw is removed. If retrograde removal of the screw is not possible, the wrist is positioned into flexion and the screw is removed antegrade through the proximal pole of the scaphoid.

In conclusion, the percutaneous transtrapezial approach to acute, minimally displaced scaphoid fractures is an accurate technique for central screw placement that has excellent clinical results. The most common complication in clinical studies has been protrusion of the screw into the scaphotrapezial joint, the risk of which might be reduced by using a 45° pronated view intraoperatively. Minimal changes at the scaphotrapezial joint have been found at the time of long-term follow-up.

Investigation performed at the Department of Orthopaedics, Monica Hospital, Deurne, Belgium

Disclosure: One or both of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or both of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Neither author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

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