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
Sources