Scaphoid Nonunion — Vascularised Bone Graft (1,2-ICSRA and Medial Femoral Condyle)

Surgical Indications

Absolute Indications for Vascularised Bone Graft

• Established scaphoid nonunion with proximal pole avascular necrosis (AVN) confirmed by MRI or intraoperative assessment
• Failed prior conventional (non-vascularised) bone grafting with persistent nonunion
• Humpback deformity with greater than 3 mm scaphoid shortening or DISI greater than 15 degrees requiring structural correction
• Proximal pole nonunion with sclerotic, cystic changes and poor bleeding points after tourniquet release

Relative Indications

• Nonunion greater than 2 years duration with established proximal pole AVN
• Smoker or patient with vascular risk factors where conventional graft has lower expected success
• High-demand patient (athlete, manual worker) where rapid revascularisation and union are prioritised
• Revision of failed percutaneous screw fixation with bone loss and AVN

When Non-Vascularised Graft Is Sufficient

• Waist nonunion without proximal pole AVN and minimal deformity (less than 2 mm shortening, DISI less than 10 degrees)
• Distal pole nonunion (excellent vascularity)
• Acute displaced fractures treated with ORIF plus cancellous graft (not nonunion)
• Paediatric scaphoid nonunion (robust healing potential)

Contraindications

Absolute:

• Advanced SNAC wrist Stage III or IV (capitolunate or radiolunate arthritis) — reconstruction will not address the arthritic pain
• Active infection at the wrist or donor site
• Patient unable or unwilling to comply with prolonged immobilisation and rehabilitation

Relative:

• Severe osteoporosis or bone loss precluding stable screw fixation
• Ipsilateral knee pathology precluding MFC harvest (consider alternative donor)
• Heavy smoker unwilling to cease — counsel on markedly reduced union rates

Evidence for Vascularised versus Non-Vascularised Grafting

1,2-ICSRA Pedicled Graft Outcomes

• Union rates 80-95 percent in most series for proximal pole nonunion with AVN
• Time to union typically 8-16 weeks when the pedicle remains patent
• Key technical factor: preservation of the pedicle throughout elevation and inset; tension or kinking is the most common cause of failure
• Humpback correction is limited by graft size — greater than 3 mm volar wedge often requires MFC instead

Medial Femoral Condyle Graft Outcomes

• Union rates 85-100 percent even in severe AVN and large defects
• Can correct greater than 5 mm length loss and severe humpback
• Requires microsurgical expertise for free transfer or careful pedicle dissection for volar pedicled variant
• Donor-site morbidity (knee pain, instability) reported in 10-20 percent at one year

Key Evidence

Scaphoid Vascular Anatomy

Extrinsic Blood Supply

• The scaphoid receives blood supply from the radial artery via dorsal and volar branches
• The dorsal branch enters through the dorsal ridge at the waist and supplies the proximal 70-80 percent of the bone in retrograde fashion
• The volar branch enters at the distal tubercle and supplies only the distal 20-30 percent
• The proximal pole is therefore a vascular watershed — dependent on retrograde flow from the waist vessels

Clinical Implication for Nonunion

• A fracture at the waist or proximal pole disrupts the retrograde supply to the proximal fragment
• Proximal pole AVN occurs in 30-50 percent of waist nonunions and greater than 80 percent of proximal pole nonunions
• The presence of AVN is the single most important predictor that conventional grafting will fail

1,2-ICSRA Pedicle Anatomy

Course and Landmarks

• The 1,2-ICSRA arises from the radial artery 2-3 cm proximal to the radiocarpal joint
• It travels distally in the groove between the first and second extensor compartments, superficial to the extensor retinaculum
• At the level of the snuffbox it anastomoses with the radial artery or its dorsal carpal branch, allowing retrograde flow
• The pedicle length is typically 2-4 cm — sufficient to reach the proximal pole when the graft is inset

Bone Block Harvest

• The graft is harvested from the dorsal distal radius between the first and second compartments
• Typical dimensions 1.5 cm by 1 cm by 1 cm corticocancellous block
• The pedicle must be dissected free of the retinaculum while preserving the periosteal and nutrient vessels to the bone block
• The graft remains attached only by the pedicle until inset into the prepared scaphoid bed

Anatomic Variability

• In 5-10 percent of wrists the 1,2-ICSRA is hypoplastic or absent
• The 2,3-ICSRA or fourth extensor compartment artery may be used as alternatives when the 1,2 vessel is inadequate
• Always inspect and confirm pedicle quality before committing to graft elevation

Medial Femoral Condyle Graft Anatomy

Vascular Pedicle

• The descending genicular artery arises from the superficial femoral artery just proximal to the adductor hiatus
• It gives articular branches to the medial femoral condyle and a saphenous branch
• Pedicle length 6-8 cm with vessel diameter 1.5-2.5 mm — suitable for microsurgical anastomosis
• The graft can be harvested as a corticocancellous block up to 3 by 2 cm with or without cartilage

Volar Pedicled Variant

• The descending genicular artery can be dissected distally to allow a pedicled transfer through the interosseous membrane or a subcutaneous tunnel to the volar wrist
• Avoids microsurgery but requires careful pedicle routing to prevent kinking at the elbow or forearm

Advantages for Scaphoid Reconstruction

• Large structural graft can be shaped to correct severe humpback and restore length
• Cancellous portion provides rapid revascularisation of the proximal pole
• Can be combined with internal fixation using a headless compression screw

Carpal Kinematics — Humpback and DISI

Normal Scaphoid Alignment

• On a true lateral radiograph the scaphoid long axis forms an angle of 30-60 degrees with the radius
• The lunate is colinear with the radius (radiolunate angle 0-15 degrees)

Humpback Deformity

• Distal fragment flexes volarly while the proximal fragment extends with the lunate (DISI)
• Scaphoid length shortens by 3-8 mm
• DISI greater than 15 degrees and scaphoid shortening greater than 3 mm are thresholds for corrective grafting

Consequences of Uncorrected Deformity

• Persistent DISI leads to abnormal load distribution across the radioscaphoid and scaphocapitate joints
• Even with solid union, uncorrected humpback predicts progressive SNAC arthritis within 5 years
• Correction of length and alignment at the time of grafting is therefore mandatory

Positioning and Preparation

Patient position: Supine, arm abducted 90 degrees on hand table. For dorsal 1,2-ICSRA graft the forearm is pronated; for volar approaches the forearm is supinated. A tourniquet is applied to the upper arm and inflated to 250 mmHg after exsanguination.

Anaesthesia: Regional (axillary or supraclavicular block) or general anaesthesia. WALANT is not suitable for vascularised grafting because patient movement risks pedicle injury.

Fluoroscopy: Mini C-arm positioned to obtain true posteroanterior, lateral, and scaphoid views throughout the procedure. The surgeon must be able to confirm reduction, graft position, and screw placement without repositioning the arm.

Consent: Discuss union rate 80-95 percent for 1,2-ICSRA and 85-100 percent for MFC, risk of pedicle failure (5-10 percent), donor-site morbidity (knee pain, instability for MFC), persistent nonunion requiring salvage, progression to SNAC despite union, and the need for prolonged immobilisation (8-12 weeks).

Dorsal 1,2-ICSRA Pedicled Graft — Step-by-Step

Step 1: Exposure of the Scaphoid Nonunion

A longitudinal dorsal incision is made over the snuffbox, centred between the first and second extensor compartments. The dorsal sensory branch of the radial nerve is identified and protected. The extensor pollicis longus tendon is retracted radially. The joint capsule is opened longitudinally over the scaphoid waist and proximal pole. The nonunion site is exposed and fibrous tissue is excised until healthy bleeding bone is seen on both sides. The proximal pole is curetted and inspected for bleeding points after tourniquet release.

Step 2: Exposure and Confirmation of the 1,2-ICSRA Pedicle

The interval between the first and second extensor compartments is developed. The 1,2-ICSRA is identified running superficial to the extensor retinaculum. The vessel is traced proximally to its origin from the radial artery and distally to its anastomosis in the snuffbox. The pedicle is mobilised with a 5-10 mm cuff of retinaculum and periosteum to protect the nutrient vessels.

Step 3: Harvest of the 1,2-ICSRA Graft

A 1.5 by 1 cm corticocancellous graft is outlined on the distal radius between the first and second compartments, centred over the pedicle. The periosteum is incised and the graft is elevated with osteotomes, preserving the pedicle attachment. Cancellous bone is curetted from the donor site and saved for packing around the graft. The pedicle is ligated proximally and the graft is left attached only by the retrograde pedicle.

Step 4: Preparation of the Scaphoid Bed and Humpback Correction

The nonunion is prepared with a high-speed burr or curettes to create a rectangular or trapezoidal defect. For humpback deformity, the distal fragment is extended and the proximal fragment flexed to correct DISI. A volar trapezoidal wedge graft is shaped from the harvested block so that the volar height is 3-5 mm greater than the dorsal height. The graft is impacted into the defect and temporarily stabilised with 1.1 mm K-wires.

Step 5: Headless Compression Screw Fixation

A 3.0 or 4.0 mm headless compression screw is selected based on measured scaphoid length. The screw is inserted from distal-volar to proximal-dorsal under fluoroscopic guidance. The screw threads must engage both the distal and proximal fragments with at least 5 mm of thread purchase in each. The graft is packed around the screw with additional cancellous bone. Final fluoroscopic views confirm correction of DISI, restoration of scaphoid length, and screw position within the central axis.

Step 6: Pedicle Inspection and Wound Closure

The pedicle is inspected under loupe magnification to confirm it lies without tension or kinking. The capsule is closed loosely over the graft. Skin is closed with 4-0 nylon. A bulky dressing and short-arm thumb spica cast are applied.

Medial Femoral Condyle Graft — Key Technical Points

When to Choose MFC over 1,2-ICSRA

• Scaphoid shortening greater than 4 mm or humpback requiring greater than 5 mm volar wedge
• Proximal pole fragmentation or bone loss too large for the 1,2-ICSRA block
• Failed prior 1,2-ICSRA graft with persistent nonunion

Free MFC Technique

The graft is harvested from the ipsilateral or contralateral medial femoral condyle through a longitudinal incision over the medial epicondyle. The descending genicular artery and vein are dissected to their origin. The graft is elevated with a cuff of periosteum and muscle. Microvascular anastomosis is performed end-to-side to the radial artery and vein in the snuffbox or end-to-end to the dorsal carpal branch. The graft is shaped and inset exactly as described for the pedicled graft, followed by headless screw fixation.

Volar Pedicled MFC Variant

The descending genicular pedicle is dissected distally and routed through the interosseous membrane or a subcutaneous tunnel to the volar wrist. The graft is inset through a volar Henry approach. This avoids microsurgery but requires meticulous pedicle routing to prevent kinking at the elbow.

Post-operative Protocol

Immobilisation

• Short-arm thumb spica cast for 8-12 weeks (non-weight-bearing on the hand)
• For MFC free graft, immobilisation is extended to 10-14 weeks because of the larger construct
• Serial radiographs at 2, 6, 10, and 14 weeks to assess graft incorporation and screw position

Rehabilitation

• Week 0-8: protected active range of motion of the fingers and thumb only; no wrist motion
• Week 8-12: removable splint, gentle active wrist motion begins when radiographic bridging appears
• Week 12-16: progressive strengthening, proprioception, and grip exercises
• Return to heavy manual work or sport: 4-6 months when CT confirms solid union and full strength recovered

Monitoring for Union

• Clinical: resolution of snuffbox tenderness, improved grip strength
• Radiographic: bridging trabeculae on at least two views, no lucency around the screw
• CT at 12-16 weeks if radiographs are equivocal — gold standard for confirming union before advancing rehabilitation

Outcomes and Prognostic Factors

Union Rates

• 1,2-ICSRA pedicled graft: 80-95 percent in most series when pedicle remains patent
• MFC graft: 85-100 percent even in severe AVN and large defects
• Time to union: 8-16 weeks (1,2-ICSRA); 10-20 weeks (MFC)

Factors Associated with Failure

• Persistent smoking (union rate drops to 60-70 percent)
• Severe humpback not corrected at surgery
• Inadequate debridement leaving sclerotic bone at the nonunion site
• Pedicle kinking or tension intraoperatively
• Advanced SNAC (Stage II or greater) at the time of grafting

Long-term Wrist Function

• Successful union with corrected alignment restores 70-85 percent of contralateral grip strength and 60-80 percent of wrist motion
• Patients with uncorrected DISI or residual shortening have significantly worse functional scores and higher rates of secondary surgery for SNAC