Reversed Vascularized Second Metatarsal Flap for Thumb Hypoplasia Reconstruction

0
0
0

Reversed Vascularized Second Metatarsal Flap for Reconstruction of Manske Type IIIB and IV Thumb Hypoplasia with Reduced Donor Site Morbidity

Thumb hypoplasia represents a spectrum of congenital anomalies ranging from minor underdevelopment to complete absence of the thumb. Manske type IIIB and IV hypoplastic thumbs are characterized by proximal metacarpal deficiency, instability at the carpometacarpal (CMC) joint, and severe functional impairment. Traditional management for these complex cases involves index finger pollicization, which sacrifices the digit to create a neo-thumb. While pollicization offers reliable functional outcomes, parental reluctance to amputate a healthy finger—particularly in cultures where hand mutilation carries significant stigma—has driven the search for reconstruction techniques that preserve all five digits. This study presents a novel approach using a reversed vascularized second metatarsal composite flap to reconstruct the skeletal framework of the thumb while minimizing donor site morbidity.

Surgical Technique and Rationale

The procedure addresses two critical challenges in Manske IIIB/IV thumb reconstruction: (1) restoration of CMC joint stability and metacarpal structure, and (2) provision of adequate soft tissue coverage for the underdeveloped thenar region. The second metatarsal was selected due to its anatomical similarity to the thumb metacarpal, reliable vascular supply, and growth potential in pediatric patients.

Stage 1: Flap Harvest and Thumb Reconstruction

  1. Hand Preparation: A radial longitudinal incision exposed the hypoplastic first metacarpal remnant and radial styloid. The abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons were detached from their abnormal insertions for later reattachment. The CMC joint space was created by releasing underdeveloped ligaments and soft tissues.
  2. Osteocutaneous Flap Design: A 1.5–2.2 cm × 3.0–5.8 cm elliptical skin paddle was marked over the second metatarsal. The flap included:
    • 4–5 cm segment of second metatarsal bone with distal articular head
    • Dorsalis pedis artery and great saphenous vein as pedicle
    • Periosteum and periarticular soft tissues
  3. Donor Site Reconstruction: The adjacent third metatarsal was split longitudinally (50–60% width) and transposed to fill the second metatarsal defect. Kirschner wires (0.8 mm) and absorbable sutures stabilized the construct, preserving foot architecture.
  4. Flap Inset: The metatarsal was reversed 180°, positioning the distal articular head proximally to articulate with the trapezium or second metacarpal base. Two intramedullary K-wires provided fixation. The APL/EPB tendons were reattached to the neo-CMC joint capsule. Microvascular anastomosis connected the dorsalis pedis artery to the radial artery (n=7) or common digital artery (n=8), with venous outflow via the great saphenous-to-cephalic vein system.

Stage 2: Functional Enhancements

At 4–6 months postoperatively, secondary procedures were performed:

  • Ring finger flexor digitorum superficialis transfer for thumb opposition (n=9)
  • Z-plasty/web space release (n=6)
  • Fat grafting to augment thenar contour (n=5)

Clinical Outcomes

The series included 15 patients (10 male, 5 female; median age 4.2 years) with 7 Manske IIIB and 8 type IV thumbs. Follow-up averaged 19.2 months (12–34 months).

Functional Results

  • Kapandji Score: Improved from 0 to 6.7 (range 3–10)
  • Pinch Strength: Increased from 0 to 1.5 kg (range 0.5–5.0 kg)
  • Daily Activities: 13/15 patients achieved pulp-to-pulp pinch for small object manipulation; 11/15 could grip large items (>5 cm diameter)

Radiographic Findings

X-ray demonstrated:

  • Metatarsal flap survival in 14/15 cases (93.3%)
  • Continuous bone growth at 6-month follow-up (mean 2.1 mm/year longitudinal growth)
  • Stable CMC joint alignment without subluxation

Donor Site Evaluation

All patients maintained normal foot function:

  • No gait abnormalities or metatarsalgia
  • Preserved range of motion in second/third toes
  • Radiographic union at split metatarsal site by 3 months

Complications

  • Partial Flap Necrosis (1 case): Managed with pedicled radial forearm flap and iliac crest bone graft
  • Marginal Skin Necrosis (2 cases): Healed conservatively

Critical Analysis

Advantages Over Pollicization

This technique addresses three parental concerns associated with pollicization:

  1. Digit Preservation: Maintains five-digit hand configuration
  2. Aesthetic Outcome: Provides natural-looking thumb with nail plate and phalangeal proportions
  3. Growth Potential: Vascularized epiphyseal transfer enabled 78% of expected metacarpal growth at 2-year follow-up

Technical Innovations

  1. Reverse Flap Orientation: Positioning the metatarsal head proximally created a stable pseudoarthrosis with the trapezium, mimicking native CMC joint biomechanics.
  2. Third Metatarsal Splitting: The “V-shape” osteotomy preserved vascularity through the arcuate artery branch, preventing donor site collapse.
  3. Staged Rehabilitation: Early postoperative bracing (6 weeks) followed by active mobilization optimized functional recovery.

Limitations

  • Microsurgical Complexity: 4–7 hour operative time requires experienced teams
  • Residual Functional Deficits: Reconstructed thumbs achieved 64% of age-matched pinch strength
  • Growth Discrepancy: Metatarsal growth rate (2.1 mm/year) lagged behind normal thumb metacarpal (2.8 mm/year)

Parental Perception

A 10-point Visual Analog Scale (VAS) revealed:

  • Aesthetic Satisfaction: 8.2/10
  • Functional Improvement: 7.6/10
  • Willingness to Recommend: 8.9/10

Despite functional limitations compared to pollicization, 14/15 families preferred this reconstruction to digit ablation.

Conclusion

The reversed vascularized second metatarsal flap represents a viable alternative for Manske IIIB/IV thumb reconstruction in patients prioritizing digit preservation. By combining microsurgical precision with innovative donor site management, this approach achieves:

  • Functional thumb with opposition capability
  • Physiological bone growth
  • Minimal foot morbidity
  • Psychologically acceptable five-digit hand

Long-term studies are needed to evaluate skeletal maturation and degenerative joint changes. However, preliminary results suggest this technique fulfills an important niche in congenital hand reconstruction.

https://doi.org/10.1097/CM9.0000000000000477

Was this helpful?

0 / 0