Overview
- Scaphoid non-union management requires graft selection matched to the biological environment at the non-union site: the degree of avascular necrosis (AVN), the presence of humpback deformity, defect size, and proximal pole vascularity.
- This note covers the comparative properties of autograft, allograft, and synthetic bone substitutes, and the indications and risks of rhBMP-2.
- The Russe classification, Herbert screw mechanics, and Matti-Russe operative anatomy are assumed as background knowledge.
Scaphoid Blood Supply, Implications for Graft Selection
- Approximately 70-80% of the scaphoid's blood supply enters via the dorsal ridge through a branch of the radial artery at the waist, supplying the proximal 70-80% of the bone in a retrograde fashion.
- The distal pole receives an independent volar supply via the scaphoid tubercle.
Consequences:
- Proximal pole non-unions carry inherently compromised vascularity.
- Purely osteoconductive grafts will fail without an osteogenic or osteoinductive stimulus when AVN is present.
- Vascularity is best assessed intraoperatively by the presence or absence of punctate bleeding; MRI signal loss on T1 and CT sclerosis/fragmentation support pre-operative diagnosis.
Bone Graft Mechanisms
All grafts act through one or more of three mechanisms:
- Osteogenesis: direct new bone by viable transplanted cells (osteoblasts, osteoprogenitor cells)
- Osteoinduction: recruitment and differentiation of host mesenchymal stem cells (MSCs) via endogenous growth factors (BMPs, TGF-β, FGF, PDGF)
- Osteoconduction: passive scaffold permitting ingrowth of host vasculature and osteogenic cells
Comparative Properties by Graft Type
| Property | Cancellous Autograft | Corticocancellous Autograft | Cortical Autograft | Cancellous Allograft | Cortical Allograft | DBM | Calcium Phosphate Ceramics | BMP-2/ACS |
|---|---|---|---|---|---|---|---|---|
| Osteogenesis | ++ | + | + | − | − | − | − | − |
| Osteoinduction | + | ± | ± | + | ± | +++ | − | +++ |
| Osteoconduction | ++ | ++ | + | ++ | ± | ++ | +++ | + (carrier-dependent) |
| Mechanical strength | + | ++ | ++ | + | ++ | − | ++ | − |
| Vascularity | − | − | − | − | − | − | − | − |
| Donor site morbidity | Yes | Yes | Yes | No | No | No | No | No |
| Disease transmission | No | No | No | Low | Low | Low | No | No |
Vascularised autograft adds vascularity (++) and maintains osteogenesis (++) and mechanical strength (++), see dedicated section below.
(DBM = demineralised bone matrix; ACS = absorbable collagen sponge)
Autograft
Harvest Sites
| Site | Graft Type | Volume | Key Advantage | Key Morbidity |
|---|---|---|---|---|
| Iliac crest (anterior) | Cancellous ± corticocancellous | Large | Highest MSC concentration; optimal osteogenic source | Chronic donor pain ~15-30%; lateral femoral cutaneous nerve injury; haematoma |
| Distal radius (volar) | Cancellous | Moderate | Same operative field; no additional incision | Limited volume; distal radius fracture if over-harvested |
| Olecranon | Corticocancellous | Small-moderate | Low morbidity; convenient | Limited volume |
| Proximal tibia | Cancellous | Moderate | Low morbidity | Separate tourniquet; rare fracture |
- The iliac crest is the optimal source for MSCs and embedded endogenous BMPs.
- It remains the reference standard for scaphoid non-union grafting.
Cancellous vs. Corticocancellous Autograft
Systematic review data (all non-vascularised grafts) demonstrate:
| Parameter | Cancellous Only | Corticocancellous |
|---|---|---|
| Time to union | ~11 weeks | ~16 weeks |
| Carpal alignment correction | Inferior | Superior |
| Best indication | Stable waist non-union; proximal pole non-union without major deformity | Humpback deformity requiring structural correction (Fisk-Fernandez wedge) |
| Structural support | Requires screw fixation | Provides some intrinsic column support |
- In the Matti-Russe inlay technique, a volar cortical strut graft is used either alone or in combination with K-wires.
- In the Fisk-Fernandez technique, a volar distal radius or iliac crest corticocancellous wedge graft is customised to correct scaphoid malalignment and carpal alignment simultaneously.
- Even in the setting of proximal pole AVN, corticocancellous iliac crest autograft with rigid screw fixation has achieved union rates approaching 100% in small series, challenging the older view that non-vascularised grafts invariably fail with AVN.
- The critical prerequisite is adequate proximal fixation providing both stability and compression.
Distal Radius Autograft
- Practical for same-field harvest; volume is limited and it is best suited to stable waist non-unions without major structural defect or AVN.
- Used in both the Fisk-Fernandez wedge and as a cancellous supplement in the Russe-type approach.
Vascularised Bone Grafts (Autograft Subtype)
- Vascularised grafts bring an independent arterial supply to the non-union site.
- They function as both a structural and vascular augment in the setting of mechanical malalignment and as a regenerative augment in proximal pole non-unions with compromised healing capacity.
- Their use is controversial; most indications centre on waist non-unions with suspected AVN or proximal pole non-unions with established AVN.
Pedicled Options
| Graft | Pedicle | Approach | Indication |
|---|---|---|---|
| 1,2 Intercompartmental supraretinacular artery (1,2 ICSRA), Zaidemberg | Branch of radial artery | Dorsal | Proximal pole AVN; waist non-union with AVN |
| Volar distal radius | Volar carpal artery | Volar | Waist non-union with AVN |
| Pronator quadratus, Braun/Kawai-Yamamoto | Anterior interosseous artery | Volar | Proximal pole; waist with AVN |
| 4th/5th extensor compartment artery | Branch of anterior interosseous | Dorsal | Waist/proximal pole AVN |
| Distal ulna | Ulnar artery branch | Ulnar/dorsal | Alternative when radial options unavailable |
Free Vascularised Graft: Medial Femoral Condyle
- The medial femoral condyle (MFC) free flap, based on the superomedial genicular artery, provides corticocancellous bone with reliable periosteal vascularity.
- Recent series suggest potentially superior union rates compared to pedicled distal radial grafts for AVN cases.
Indications:
- Recalcitrant proximal pole non-union with AVN after failed prior grafting
- Large defect requiring both structural and vascular augmentation
- Prior radial surgery or compromised radial artery precluding pedicled radial options
Limitations: microsurgical expertise required; second operative field; longer operative time.
Outcomes: Vascularised vs. Non-Vascularised Grafts
Meta-analytic data (Merrell, Wolfe, and Slade, 36 eligible reports from 1121 articles):
| Clinical Scenario | Non-Vascularised Graft + Screw | Vascularised Graft | K-wire + Wedge Graft |
|---|---|---|---|
| Non-union without AVN | ~94% union | Not routinely required | ~74% |
| Non-union with AVN | ~47% union | ~88% union | , |
- Union rates for pedicled distal radial grafts range from 27% to 100% across published series, with poor results at the lower end concentrated in AVN cases.
- The MFC free flap has shown superior rates in AVN compared to pedicled radial options in more recent series.
Allograft
Types
| Type | Properties | Role in Scaphoid Non-union |
|---|---|---|
| Cancellous allograft | Osteoconductive; minimal osteoinduction if processed; no osteogenesis | Rare primary use; possible extender |
| Cortical allograft | Structural; slow remodelling; poor osteoinduction | Structural scaffold adjunct only |
| Demineralised bone matrix (DBM) | Osteoinductive (BMP exposure) + osteoconductive; available as gel/putty/strips | Adjunct; not structural; not a primary graft substitute |
| Whole scaphoid allograft | Structural replacement; high non-union risk | Salvage only for fragmented proximal pole where reconstruction not feasible |
Why Allograft is Rarely the Primary Choice
- The small bone volumes required are readily met by autograft harvest.
- Allograft lacks viable osteoprogenitor cells, most critical when the biological environment is compromised.
- Processing (freeze-drying, irradiation) degrades growth factors, reducing osteoinductivity.
- No published level I evidence supports allograft equivalence to autograft in scaphoid non-union.
DBM may supplement autograft as an osteoinductive adjunct or serve as a BMP-2 carrier but should not substitute for autograft where regenerative capacity is the primary requirement.
Regulatory and Consent Considerations
- In Australia, allograft is regulated by the TGA and must be sourced from accredited tissue banks.
- Residual risks include viral transmission (HIV estimated <1 per million with current screening) and theoretical prion transmission.
- These must be disclosed in consent.
- Use in elective non-union surgery where autograft is readily available requires explicit justification.
Synthetic Bone Substitutes
Classification
| Class | Examples | Mechanism | Role in Scaphoid Non-union |
|---|---|---|---|
| Calcium sulphate | , | Osteoconduction; rapid resorption (weeks) | Void filler only; no structural role |
| Calcium phosphate (HA, β-TCP, biphasic) | Chronos (β-TCP), Vitoss | Osteoconduction; variable resorption | Adjunct void filler; not primary graft |
| Bioactive glass | , | Osteoconduction; bonds to host bone | Experimental; no scaphoid-specific evidence |
| Demineralised bone matrix | Grafton, Osteoset | Osteoinduction + osteoconduction | Adjunct only; not structural |
| Bone marrow aspirate (BMA) | , | Osteogenesis (MSC-dependent) | Adjunct to scaffold; not standalone |
| Composite grafts | DBM + calcium phosphate | Combined osteoconduction + osteoinduction | Potential adjunct when autograft limited |
| BMP-2 on carrier | INFUSE (rhBMP-2/ACS) | Osteoinduction +++ | Off-label; see section below |
- Synthetic substitutes lack osteogenesis and do not replicate iliac crest autograft.
- Their role is as extenders when autograft volume is insufficient, as carriers for biological agents, or as void fillers with adequate fixation.
BMP-2: Indications and Risks
Biology
Recombinant human BMP-2 (rhBMP-2) is a member of the TGF-β superfamily and the most potent osteoinductive agent in clinical use. It binds BMP receptors on MSCs, activating the SMAD 1/5/8 signalling cascade and driving osteoblastic differentiation:
$$\text{MSC} \xrightarrow{\text{BMP-2} \to \text{SMAD 1/5/8}} \text{Osteoprogenitor} \to \text{Osteoblast} \to \text{New bone}$$
The commercial product (INFUSE) delivers rhBMP-2 at 1.5 mg/mL on an absorbable collagen sponge (ACS) carrier.
Regulatory Status and Approved Indications
rhBMP-2 (INFUSE) TGA-listed indications in Australia:
- Anterior lumbar interbody fusion (ALIF) at L2-S1 in skeletally mature patients
- Open tibial shaft fractures treated with intramedullary nailing
- Use in scaphoid non-union is off-label.
- Informed consent must specifically address the off-label nature; RACS/AOA guidance on off-label use of therapeutic goods applies.
Theoretical Indications in Scaphoid Non-union
Off-label consideration may be justified when:
- Recalcitrant non-union after ≥2 failed conventional procedures
- Severe biological compromise (established AVN, irradiated field) critically depleting osteogenic cell population
- Patient factors precluding autograft harvest (iliac crest pathology, systemic illness limiting operative time)
- Large defect requiring augmentation of limited autograft supply
Optimal use: combine with rigid headless compression screw fixation and supplementary cancellous autograft (osteogenic cells alongside osteoinductive stimulus); do not use as sole graft substitute.
Risks and Adverse Effects
| Risk Category | Specific Adverse Effect | Mechanism / Comment |
|---|---|---|
| Inflammatory | Early osteolysis; soft tissue swelling | Supraphysiological dosing triggers local inflammatory cascade; especially problematic in constrained spaces (wrist) |
| Ectopic ossification | Heterotopic bone formation in radiocarpal/midcarpal joint | Off-target BMP signalling; can cause permanent stiffness |
| Wound complications | Seroma; wound dehiscence | ACS acts as fluid reservoir; excessive swelling in tight dorsal/volar wrist incisions |
| Tendon irritation | Flexor (volar approach) or extensor (dorsal approach) adhesions | Proximity of tendons to graft site in the wrist |
| Carpal tunnel | Elevated carpal tunnel pressure | Inflammatory oedema from ACS/BMP reaction |
| Oncological | Theoretical cancer risk | Post-market surveillance (AMPLIFY trial) raised concern; subsequent analyses suggest confounding; current consensus is no proven carcinogenic risk at approved doses |
| Immune / allergic | Anti-BMP-2 or anti-bovine collagen antibodies | May limit efficacy on re-exposure; rare anaphylaxis |
| Resorption paradox | Initial net bone resorption before formation | Dose-dependent; small-bone applications risk net bone loss in early phase |
| Bone quality | Woven, poorly mineralised bone | Rapidly formed bone may be architecturally inferior to lamellar autograft-derived bone |
| Cost | Significant cost premium | Not PBS-subsidised for this indication; economic justification requires careful case selection |
BMP-2 in the Constrained Wrist Environment
- The wrist capsule is immediately adjacent to the graft site on both volar and dorsal approaches.
- Inflammatory swelling from the BMP-2/ACS reaction can cause flexor or extensor tendon irritation and adhesions, carpal tunnel pressure elevation, and ectopic bone in the radiocarpal or midcarpal joint.
- Cautious, low-dose supplementary use is strongly preferred over BMP-2 as a sole graft substitute.
Decision Framework: Graft Selection
| Clinical Scenario | Recommended Graft Strategy |
|---|---|
| Stable waist non-union, no AVN, no deformity | Cancellous iliac crest or distal radius autograft + headless compression screw |
| Waist non-union + humpback deformity, no AVN | Corticocancellous iliac crest autograft (Fisk-Fernandez wedge) + headless compression screw |
| Proximal pole non-union, viable proximal fragment | Corticocancellous iliac crest autograft + antegrade headless screw (dorsal approach) |
| Proximal pole non-union with AVN | Vascularised bone graft (pedicled 1,2 ICSRA or MFC free flap) ± cancellous autograft augment |
| Recalcitrant non-union, failed ≥2 procedures | MFC free flap preferred; BMP-2 off-label adjunct with autograft as last resort |
| Unable to tolerate autograft harvest | DBM + BMA as adjunct to synthetic scaffold; counsel regarding inferior biology |
Outcomes Summary
| Fixation / Graft Method | Union Rate |
|---|---|
| Non-vascularised graft + headless compression screw | ~94% |
| Vascularised graft in AVN | ~88% |
| Non-vascularised graft in AVN | ~47% |
| K-wire + wedge graft | ~74% |
| Corticocancellous iliac crest + screw (proximal pole, including AVN cases) | Up to ~100% (small series) |
Time to union: cancellous autograft ~11 weeks; corticocancellous autograft ~16 weeks.
CT confirmation is the gold standard for assessing union; plain radiographic assessment is unreliable.
Complications of Bone Grafting in Scaphoid Non-union
| Complication | Notes |
|---|---|
| Persistent non-union | ~6-20% depending on AVN status and fixation adequacy |
| Donor site pain (iliac crest) | 15-30% at 1 year; chronic pain ~10% |
| Lateral femoral cutaneous nerve injury | ~5-10% with anterior iliac crest harvest |
| Ectopic bone (BMP-2) | Variable; higher with excessive dosing or in constrained spaces |
| Hardware prominence / screw back-out | Secondary removal required in ~5% |
| SNAC wrist progression | Inevitable if symptomatic non-union untreated; staged salvage required |
| Carpal tunnel syndrome | Volar approach with significant swelling |
Outcome Measures
| Measure | Application |
|---|---|
| Patient-Rated Wrist Evaluation (PRWE) | Most responsive PROM for wrist-specific pain and function |
| DASH / QuickDASH | Upper limb disability; widely validated |
| Grip strength (% of contralateral) | >85% considered good outcome |
| Wrist range of motion (% of contralateral) | Flexion-extension arc; radial-ulnar deviation |
| CT-confirmed union | Gold standard imaging endpoint |
| Time to union | Surrogate endpoint; cancellous ~11 weeks vs. corticocancellous ~16 weeks |
Paediatric Considerations
Scaphoid non-union is uncommon in the skeletally immature. When grafting is required:
- Avoid iliac crest harvest near the ASIS apophysis in patients under ~14 years, risk of growth disturbance and pelvic deformity
- BMP-2 is contraindicated in skeletally immature patients (potential adverse effects on physes and long bone development)
- Distal radius autograft is preferred as harvest site in younger patients
- Higher union rates with conservative management reduce the frequency of surgical grafting in children compared to adults