Alexander D. Mih
DEFINITION
Scaphoid fractures account for 60% of carpal bone fractures.
Nonunions occur in up to 15% of scaphoid fractures and often result from delayed treatment, inadequate immobilization, displacement of the fracture, or proximal pole involvement or in the setting of avascular necrosis (AVN).
ANATOMY
The blood supply to the scaphoid travels in a distal to proximal direction and emanates from the radial artery. Intraosseous vessels traverse the scaphoid to supply the proximal pole.
In about 30% of scaphoids, there is either a single or no vascular channel found reaching the proximal pole.
Studies of vascularity of the distal radius have identified several sources of vascularized bone graft available for nonunion treatment.
Animal studies of vascularized bone grafts have documented a significant increase in blood flow present when compared to nonvascularized grafts.
PATHOGENESIS
Without adequate blood flow, the normal bone healing response cannot be completed. The scaphoid fracture site fills with fibrous connective tissue and motion persists at the site of the fracture.
In some cases, the bone undergoes changes of AVN with cellular death, edema, and the eventual loss of trabecular architecture.
Studies have shown that in cases in which the trabecular bone pattern has been lost, union may be difficult if not impossible to achieve.
NATURAL HISTORY
Nonunion of the scaphoid severely alters the normal carpal biomechanics and subjects the cartilage to shear forces detrimental to its survival.
PATIENT HISTORY AND PHYSICAL FINDINGS
Often patients recall injuring their wrists several years before developing pain severe enough to seek medical attention.
Patients usually complain of limited range of wrist motion and pain, often with grip or weight bearing. The patients have often significantly reduced their activity level due to persistent pain.
In most cases the patient will experience tenderness to palpation at the anatomic snuffbox (FIG 1A), the radial styloid–scaphoid joint (FIG 1B), or the distal pole of the scaphoid (FIG 1C), which is palpable on the palmar side of the wrist.
Wrists with established scaphoid nonunions have an arc of motion that is significantly reduced from the uninvolved side, primarily in extension.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Standard radiographic studies include posteroanterior (PA), lateral, and scaphoid (ulnar deviation) views (FIG 2).
Classic radiographic findings begin at the radial styloiddistal pole of scaphoid interface and proceed to involve the entire scaphoid fossa, the midcarpal joint, and eventually the entire radiocarpal articulation.
CT is essential for determining union as well as for identifying patients in whom the normal trabecular bone pattern has been lost.
MRI is useful in evaluating the scaphoid for vascularity, although definitive determination of avascularity may be difficult. Conflicting reports regarding the usefulness of gadolinium enhancement have been published over the past several years.
FIG 1 • A. Tenderness at the anatomic snuffbox is a classic finding of scaphoid nonunion. B. The radial styloid–scaphoid interface is the earliest site of degenerative change in scaphoid nonunions, and patients will often display tenderness at that location. C. The distal pole of the scaphoid is palpable at the base of the thumb on the palmar aspect of the wrist. Tenderness at this region is usually found in cases of scaphoid nonunion.
FIG 2 • A. Early radiographic appearance of scaphoid nonunion before degenerative change. B. Development of degenerative changes at the radial styloid–scaphoid interface. C. Advanced changes involving the entire scaphoid fossa.
DIFFERENTIAL DIAGNOSIS
Ligamentous injury to the wrist
Wrist synovitis
Intraosseous ganglia
Primary AVN of the scaphoid
NONOPERATIVE MANAGEMENT
Nonoperative treatment is limited for established nonunions.
Investigators have attempted the use of bone stimulators, which use either electrical stimulation or ultrasound.
There is little evidence in the literature supporting the use of these units for treatment of established scaphoid nonunions.
SURGICAL MANAGEMENT
A vascularized distal radial bone graft is indicated for scaphoid nonunions with and without evidence of avascularity.
Correction of a “humpback deformity” requires extensive mobilization of the pedicle when attempting the use of a dorsally sourced graft, and a palmar vascularized graft may be more appropriate.
For significant collapse, a nonvascular iliac crest graft may be required to create a compression-resistant construct.
When early degenerative changes are present, a radial styloidectomy should accompany the use of a vascularized distal radial graft.
The presence of more advanced degenerative joint disease or carpal malalignment is a contraindication to performing surgery to obtain bony union.
Preoperative Planning
Radiographs must be evaluated to rule out degenerative joint changes or carpal instability patterns, which are often found in established nonunions.
Positioning
The patient is placed supine on the operating table with the arm placed on an armboard.
Surgery is performed under tourniquet control.
Approach
Vascularized grafting is carried out through a dorsal approach. Anatomic studies have shown that the dorsal irrigating vessels are of greater diameter and are further from the articular surface than irrigating vessels on the palmar surface of the radius.
TECHNIQUES
VASCULARIZED DISTAL RADIUS BONE GRAFTING USING THE 1,2-INTERCOMPARTMENTAL SUPRARETINACULAR ARTERY 7
Exposure
A curvilinear incision is made over the dorsoradial aspect of the wrist, centered between the first and second extensor compartments (TECH FIG 1A).
The 1,2-intercompartmental supraretinacular artery (1,2 IC SRA) lies on the surface of the retinaculum between the first and second compartments (TECH FIG 1B).
The irrigating branch enters the distal radius and supplies bone distal and dorsal to the brachioradialis insertion.
Avoidance of exsanguination before tourniquet inflation facilitates its identification.
The first and second compartments are unroofed on their radial and ulnar aspects, respectively, to avoid damage to this irrigating vessel.
Graft Harvest
The periosteum is scored with a scalpel to outline the graft shape, which measures 1.5 cm in the longitudinal dimension and 0.5 to 0.75 cm in the transverse dimensions (TECH FIG 2A). The distal graft margin extends to a point 0.5 to 1 cm from the articular surface.
Osteotomes are used to elevate the cortical cancellous graft.
TECH FIG 1 • A. The incision is made over the dorsoradial aspect of the distal radius. B. 1,2-intercompartmental supraretinacular artery is visible between the first and second compartments (arrow).
The soft tissue envelope containing the vessel is elevated from the radial periosteum distal to the site of graft harvest (TECH FIG 2B). This can usually be accomplished with a scalpel or Freer elevator.
The 1,2 IC SRA is not dissected free; rather, it is left as part of the retinacular septum.
The tourniquet is deflated and perfusion of the vascularized bone graft is ensured (TECH FIG 2C).
Graft Placement
The joint capsule is incised in the distal portion of the incision and the scaphoid nonunion is identified.
A radial styloidectomy greatly increases the exposure of the scaphoid and eliminates the possibility of bone graft impingement.
Intervening fibrous tissue and sclerotic bone are removed from the nonunion site using rongeurs and curettes to prepare the scaphoid for graft placement.
Cancellous bone graft from the distal radius is packed proximally and distally to fill voids created by débriding sclerotic bone.
The carefully contoured vascularized graft is then rotated into the nonunion site and pressfit into position, taking care to avoid torsion of the vascular pedicle (TECH FIG 3A).
Kirschner wires are advanced from the distal pole of the scaphoid to the proximal pole to secure the graft in place (TECH FIG 3B).
The radial capsule is closed loosely with absorbable suture and the skin is closed in a routine fashion.
The pedicle must not be compressed.
The patient is placed in a short-arm thumb spica splint.
TECH FIG 2 • A. The site of the graft is scored and elevated with an osteotome. (Carpus is to the left in all parts.) B. Soft tissue sleeve containing irrigating artery is elevated from the distal radius (arrow). C.Vascularized graft is evaluated for bleeding with tourniquet deflation (arrow is at cancellous surface).
TECH FIG 3 • A. The vascularized graft is rotated into the nonunion site (arrow) and pressfit into position. B. Kirschner wire placement is percutaneous, from distal to proximal.
POSTOPERATIVE CARE
Kirschner wires are removed when healing is observed, usually 4 to 6 weeks after surgery.
CT scanning may be required to document complete healing before the patient resumes risky activities.
MRI may be useful in evaluating the scaphoid for vascularity and may be done after Kirschner wire removal.
OUTCOMES
A recent meta-analysis2 found a scaphoid union rate of 88% with the use of a vascularized bone graft. Individual series report union rates ranging from 60% to 100%.
Previous reports have shown that patients with MRI evidence of AVN or loss of trabecular bone pattern noted on CT have a decreased level of success with reconstructive surgery. Treatment is rarely successful when both findings are present.
A recent study1 has identified risk factures for failure: proximal pole AVN, radiographic degenerative changes, loss of carpal alignment, inadequate fracture fixation, tobacco use, advanced age, and female gender.
COMPLICATIONS
Failure to gain union
Progressive degenerative changes
Impingement of bone on radial styloid
Infection
REFERENCES
1. Chang MA, Bishop AT, Moran SL, et al. The outcomes and complications of 1,2-intercompartmental supraretinacular artery pedicled vascularized bone grafting of scaphoid nonunions. J Hand Surg Am 2006;31A:387–396.
2. Merrell GA, Wolfe SW, Slade JF III. Treatment of scaphoid nonunions: quantitative meta-analysis of the literature. J Hand Surg Am 2002;27A:685–691.
3. Sheetz KK, Bishop AT, Berger RA. The arterial blood supply of the distal radius and ulna and its potential use in vascularized pedicled bone grafts. J Hand Surg Am 1995;20A:902–914.
4. Shin AY, Bishop AT. Pedicled vascularized bone grafts for disorders of the carpus: scaphoid nonunion and Kienbock’s disease. J Am Acad Orthop Surg 2002;10:210–216.
5. Steinmann SP, Bishop AT, Berger RA. Use of the 1,2 intercompartmental supraretinacular artery as a vascularized pedicle bone graft for difficult scaphoid nonunion. J Hand Surg Am 2002; 27:391–401.
6. Waters PM, Stewart SL. Surgical treatment of nonunion and avascular necrosis of the proximal part of the scaphoid in adolescents. J Bone Joint Surg Am 2002;84A:915–920.
7. Zaidemberg C, Siebert JW, Angrigiani C. A new vascularized bone graft for scaphoid nonunion. J Hand Surg Am 1991;16A:474–478.