Scaphoid Nonunion

Scaphoid nonunion is failure of a scaphoid fracture to heal, typically defined as absence of radiographic union at 6 months despite treatment, or the presence of an established nonunion pattern. Between 5 and 15% of all scaphoid fractures progress to it.

Who is at risk. The rate is higher with:

• Proximal pole location, with its poor blood supply: nonunion in up to 30%
• Displacement greater than 1mm
• Delayed presentation or treatment, greater than 4 weeks, and the missed diagnosis
• Smoking, the major modifiable factor, with a 2-3x increased risk
• NSAID use, which inhibits healing
• AVN at the outset
• Poor compliance with immobilisation

Natural history. Degeneration is progressive and time-dependent, not immediate. In Mack's series, changes were confined to the scaphoid at a mean of 8.2 years, radioscaphoid arthritis appeared at 17 years and generalised wrist arthritis at 31.6 years, and roughly half the series (23 of 47) had no wrist arthritis at review. Few nonunions stayed undisplaced, stable and arthritis-free beyond 10 years, and displacement and carpal instability (lunate dorsiflexion 10 degrees or more) predicted the severity.

Children. Scaphoid nonunion in the skeletally immature child or adolescent behaves differently from the adult, carries a better prognosis, and is a distinct examinable scenario.

• Paediatric scaphoid fractures are more often distal-third or avulsion injuries than waist fractures, and are frequently missed or treated late, which is the main driver of the (uncommon) nonunion
• The child's robust periosteal vascularity and remodelling mean a trial of immobilisation in a cast can still unite an established nonunion in a way it rarely would in an adult, so consider a cast trial first; AVN and SNAC are comparatively rare
• Persistent nonunion is treated with debridement, bone grafting (usually non-vascularised distal radius or iliac crest) and fixation with a screw or K-wires sized to the small bone, with high union rates (often over 90%) and good remodelling
• Vascularised grafts are rarely needed because proximal pole AVN is uncommon in this group; reserve them for the rare avascular or revision case

The bone. The largest carpal bone in the proximal row, the scaphoid spans both carpal rows and acts as the kinematic link between them. About 80% of it is covered by articular cartilage, which limits its periosteal blood supply.

The blood supply. The dorsal scaphoid branch of the radial artery enters at the dorsal ridge at the waist and supplies 70-80% of the bone, most of it by retrograde flow. Palmar branches from the superficial palmar arch enter at the scaphoid tubercle and supply the distal pole and tuberosity, the remaining 20-30%. Any direct supply to the proximal pole is variable and reaches only a small portion of it: only 20-30% of the proximal pole has any direct blood supply.

Why it matters. Because the flow is retrograde, the proximal pole is at the highest AVN risk, and a waist fracture interrupts the main supply to it.

The strut fails. The scaphoid normally acts as a strut connecting the proximal and distal carpal rows. When it fails to unite, the nonunion site loses its structural integrity and the scaphotrapezial ligament pulls the distal fragment into flexion. The scaphoid angulates dorsally through the nonunion, and the dorsal convexity is the humpback.

Measuring the humpback. The lateral intrascaphoid angle is measured on a lateral radiograph or sagittal CT, between lines drawn along the axes of the proximal and distal poles. Normal is less than 35 degrees. Greater than 45 degrees is a significant humpback, and it must be corrected with a wedge graft for union to succeed.

The carpus follows. Normally the scaphoid's flexion tendency is balanced by the lunate, which sits in neutral, and the scapholunate angle is 30-60 degrees. In a nonunion the scaphoid collapses into flexion and the lunate, attached to the proximal fragment, extends. This is dorsal intercalated segment instability (DISI): the scapholunate angle rises above 60 degrees and load is distributed abnormally across the wrist.

Where it ends. Those abnormal mechanics end in SNAC wrist (Scaphoid Nonunion Advanced Collapse), the usual endpoint of a displaced, unstable nonunion left untreated. The arthritis appears in a fixed order, typically over years to decades, and faster with displacement and carpal instability.

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Slade-Geissler. Alongside Herbert, the Slade-Geissler classification grades the nonunion by the degree of healing and sclerosis seen arthroscopically and on CT. The grade maps onto whether a percutaneous or arthroscopic approach is feasible, or whether open structural grafting is required:

• Grades I-II (delayed union, fibrous union without sclerosis): minimal pathology, amenable to percutaneous headless compression screw fixation alone, with no formal graft
• Grades III-IV (progressive minimal-to-comprehensive sclerosis at the nonunion): arthroscopic-assisted debridement and bone grafting with percutaneous screw fixation can achieve union while avoiding an open approach and preserving blood supply
• Grades V-VI (cyst formation and resorption, then a wide gap with humpback and carpal collapse): the deformity and bone loss demand open reduction with a structural (wedge) graft, and an avascular proximal pole demands a vascularised graft

The arthroscopic trade. Arthroscopic-assisted grafting is soft-tissue-sparing and protects the dorsal blood supply, with union rates comparable to open surgery in selected nonunions: lower-grade, without humpback, with a vascular pole. It is not appropriate where a humpback must be corrected, and the Slade-Geissler grade is the practical tool for choosing between percutaneous, arthroscopic and open surgery.

History. Presentation is often delayed, with chronic wrist pain, and the injury may be remote enough to have been forgotten. The patient reports pain with gripping and loading the wrist, weakness with reduced grip strength, and loss of motion.

Look and feel. Swelling is often minimal in chronic cases, though dorsal wrist fullness may be present; compare with the contralateral side and assess the overall posture of the wrist. Palpate for tenderness in the anatomical snuffbox, over the scaphoid tubercle on the volar side and over the dorsal scaphoid, and check for crepitus.

Provocative tests.

• Scaphoid shift (Watson) test: a painful clunk with radial deviation
• Thumb compression: pain with axial load through the thumb
• Grip strength, compared with the contralateral side

Movement. Wrist flexion, extension and radial deviation are decreased; ulnar deviation may be relatively preserved.

Radiographs. A four-view series:

Across the series, a nonunion shows a gap at the fracture site with sclerotic margins, cystic change and bone resorption, the humpback and DISI on the lateral, and SNAC changes once it is advanced.

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CT is the gold standard for judging union or nonunion, and essential for surgical planning. Sagittal reconstructions measure the humpback, and the scan shows cystic change and sclerosis and stages any SNAC arthritis.

MRI is essential for AVN assessment, because it determines the graft. T1 sequences show the marrow signal and gadolinium enhancement confirms vascularity; absent enhancement of the proximal pole suggests AVN.

Bone scan is less commonly used now. Decreased uptake suggests AVN, but the test is non-specific.

The goals, in order:

1. Achieve union, the primary goal
2. Restore anatomy: correct the humpback and restore length
3. Prevent SNAC progression
4. Maintain or restore function: motion and grip strength

Who needs surgery. Virtually all symptomatic scaphoid nonunions, asymptomatic nonunions in young patients (to prevent SNAC), and those with progressive arthritic change. Relative contraindications are SNAC Stage 3-4, where salvage procedures are indicated instead, severe comorbidities that preclude surgery, and patient preference after informed discussion.

The work-up. Each step feeds the decision:

1. History and examination: symptom duration and prior treatment
2. Plain radiographs (4 views) to confirm the nonunion
3. CT for nonunion detail and bone quality
4. MRI with gadolinium for AVN
5. A check for SNAC changes, which decides whether salvage is needed

Together they place the nonunion by Herbert D type, location, SNAC stage if arthritis is present, and degree of humpback (the intrascaphoid angle), and that complete assessment guides the treatment.

The decision. Graft selection is the most critical decision in scaphoid nonunion surgery. It rests on the vascularity of the proximal pole and on the deformity; once SNAC arthritis is present, the answer is a salvage procedure chosen by stage.

Failed prior surgery. Consider a free vascularised graft (MFC); staged procedures may be needed, and the risk of a poor outcome is higher. Careful patient selection and realistic expectations are essential.

Algorithm

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The principles, whatever the graft.

1. Debride the nonunion, sclerotic bone included, to punctate bleeding
2. Correct the humpback deformity with a structural graft
3. Insert the appropriate graft
4. Fix with a headless compression screw, the preferred fixation
5. Immobilise for 8-12 weeks

Persistent nonunion. Identify the cause (inadequate graft, AVN, poor fixation, smoking) and address the modifiable factors before revising:

• A failed non-vascularised graft is revised with a vascularised graft
• After a failed pedicled VBG, consider a free vascularised (MFC) graft
• If SNAC is advanced, salvage procedures, chosen by stage as in the SNAC classification

Judging union. Serial CT is the best way to assess union. Bridging trabeculae indicate healing and complete bridging is union, which may take 12 weeks or more in VBG cases.

What drives the result. Union rates are lower with AVN, and a chronic nonunion does worse than an acute one. Outcome also turns on addressing the humpback, choosing the appropriate graft, and smoking cessation.

Function. Prognosis is excellent if union is achieved: most patients get pain relief and return to normal function. Grip strength and range of motion reach 70-85% of the contralateral side, and return to work or sport comes at 4-6 months if the scaphoid unites.

Global Epidemiology

The scaphoid is the most commonly fractured carpal bone, and nonunion is the dominant late complication that drives carpal collapse and arthritis worldwide.

Incidence rises with social deprivation and shows summer seasonality, reflecting the high-energy sporting and occupational mechanisms typical of the young male population at risk (Garala 2016).

Guideline and Society Guidance, Side by Side

There is no single high-level (Level I) guideline dedicated to scaphoid nonunion; recommendations are drawn from society resources and pooled evidence, which broadly agree.

Registry Evidence

Unlike arthroplasty, scaphoid nonunion is not tracked by national joint registries (NJR, AJRR, AOANJRR, SHAR, NZJR), which capture hip, knee and other joint replacements rather than carpal reconstruction. The best population-level evidence therefore comes from epidemiological cohorts (Garala 2016) and large pooled systematic reviews (Duncumb 2022) rather than implant registries.

Global Practice Variation