INTRODUCTION TO VASCULARIZED BONE GRAFTING
The advent of reconstructive microsurgery has revolutionized the management of complex skeletal defects, recalcitrant nonunions, and avascular necrosis (AVN). Unlike non-vascularized autografts, which rely on creeping substitution and are limited by the size of the defect and the vascularity of the recipient bed, vascularized bone grafts bring their own intrinsic blood supply. This preserves osteocyte viability, accelerates primary bone healing, and provides robust resistance to infection.
Among the most versatile and reliable donor sites are the Medial Femoral Condyle (MFC) Corticoperiosteal Free Flap and the Vascularized Rib Graft. The MFC flap is highly prized for its thin, pliable periosteum and dense corticocancellous bone, making it ideal for small, poorly vascularized defects such as scaphoid nonunions or Kienböck’s disease. Conversely, the vascularized rib graft, harvested via the Ostrup technique, provides a longer segment of bone suitable for mandibular reconstruction, long bone segmental defects, and complex spinal fusions.
This masterclass provides an exhaustive, step-by-step academic guide to the surgical anatomy, harvesting techniques, and postoperative management of these two critical vascularized bone flaps.
HARVESTING OF MEDIAL FEMORAL CONDYLE CORTICOPERIOSTEAL FREE FLAP
The medial femoral condyle (MFC) flap is a workhorse in upper extremity and maxillofacial reconstruction. It can be harvested as a thin corticoperiosteal flap or a thicker corticocancellous structural graft, depending on the requirements of the recipient site.
Surgical Anatomy and Preoperative Planning
The vascular supply to the MFC is robust and highly redundant, primarily derived from the Descending Genicular Artery (DGA) and the Superior Medial Genicular Artery (SMGA).
* Descending Genicular Artery (DGA): Arises from the superficial femoral artery within Hunter’s canal (the adductor canal), just proximal to the adductor hiatus. It typically divides into three branches: the saphenous branch, the muscular branch (to the vastus medialis), and the articular branch. The articular branch provides the primary periosteal supply to the MFC.
* Superior Medial Genicular Artery (SMGA): Arises from the popliteal artery and forms a rich anastomotic arcade with the DGA over the medial condyle. If the DGA is absent or hypoplastic (seen in approximately 10% of patients), the SMGA serves as a reliable alternative pedicle.
💡 Clinical Pearl: Preoperative Imaging
While routine angiography is not strictly mandatory, preoperative Computed Tomography Angiography (CTA) or Magnetic Resonance Angiography (MRA) of the lower extremity is highly recommended to map the arborization of the DGA and confirm its patency, particularly in patients with a history of peripheral vascular disease or prior knee trauma.
Patient Positioning and Preparation
- Place the patient in the supine position.
- Externally rotate and flex the operative hip, and flex the knee to approximately 60 degrees (the "frog-leg" position). Support the knee with sterile bumps.
- Apply a sterile tourniquet high on the proximal thigh. Exsanguinate the limb and inflate the tourniquet to standard pressures (typically 250 mm Hg) to ensure a bloodless surgical field during the initial dissection.
Step-by-Step Surgical Technique
1. Incision and Superficial Dissection
- Make a longitudinal incision in the distal medial thigh, centered over the interval between the vastus medialis (anteriorly) and the sartorius (posteriorly). The incision should extend from the medial joint line proximally for approximately 15 to 20 cm.
- Incise the superficial fascia and identify the deep fascia enveloping the musculature. Take meticulous care to identify and protect the saphenous nerve and the greater saphenous vein, which lie in the superficial tissues posterior to the incision line.
2. Deep Dissection and Pedicle Identification
- Incise the deep fascia. Retract the vastus medialis anteriorly and the sartorius posteriorly. This exposes the adductor magnus tendon and the floor of the adductor canal.
- Identify the descending genicular vessels (DGV) and the superior medial genicular vessels (SMGV). Note the rich arcade of vessels formed by these two systems over the periosteum of the medial femoral condyle.
- Trace the DGV proximally to confirm its caliber and suitability.
3. Flap Outline and Osteotomy
- Outline the proposed corticoperiosteal or corticocancellous flap on the medial femoral condyle. The design must center on the identified vascular network.
- Anatomical Boundaries: Limit the graft proximally at the metaphyseal-diaphyseal junction to avoid the thicker cortical bone of the diaphysis, which is harder to shape and has less cancellous vascularity. Distally, take absolute care to preserve the medial collateral ligament (MCL) and the articular cartilage of the knee joint.
- Size Limitations: The maximal safe size for an MFC corticocancellous graft is 5 × 7 cm. Exceeding this dimension significantly increases the risk of iatrogenic distal femur fracture.
- Using a sharp scalpel, incise the periosteum to the bone along the outlined template.
- Use a fine oscillating saw or sharp osteotomes to elevate the periosteum with the underlying corticocancellous bone to the exact thickness required by the recipient site.
⚠️ Surgical Warning: Thermal Necrosis
When using an oscillating saw to harvest the bone graft, continuous and copious irrigation with chilled sterile saline is mandatory. Thermal necrosis of the osteocytes will negate the primary biological advantage of a vascularized bone graft.
4. Pedicle Dissection and Harvest
- Once the bone flap is mobilized, begin the proximal dissection of the descending genicular vascular pedicle.
- Carefully ligate and divide the saphenous and muscular branches using micro-clips or bipolar electrocautery, maintaining the integrity of the articular branch supplying the graft.
- Dissect the pedicle proximally to its origin off the superficial femoral vessels in Hunter’s canal.
- Pedicle Yield: A meticulously dissected DGA pedicle will yield a vessel of 1 to 2-mm in diameter measuring approximately 7 cm in length.
- Ligate and divide the superior medial genicular vessels (SMGV) unless the surgical plan dictates using them as the primary or an adjunctive vascular pedicle.
- Deflate the tourniquet to confirm robust perfusion of the graft (evidenced by bleeding from the cancellous bone edges) prior to pedicle ligation and transfer.
HARVESTING OF VASCULARIZED RIB GRAFT (OSTRUP TECHNIQUE)
The vascularized rib graft, popularized by Ostrup, is an exceptional option when a long, curved segment of vascularized bone is required. It is uniquely suited for mandibular reconstruction, complex facial skeletal defects, and bridging massive long-bone intercalary defects.
Surgical Anatomy and Biomechanics
The rib is supplied by the posterior intercostal artery, which arises directly from the descending thoracic aorta. The artery travels in the subcostal groove along the inferior margin of the rib, accompanied by the intercostal vein and nerve.
To preserve the delicate periosteal blood supply, the rib must be harvested as a composite flap, including the inner and outer periosteum, the underlying pleura, and the adjacent intercostal musculature.
Patient Positioning and Preparation
- Anesthesia: General anesthesia with a double-lumen endotracheal tube is highly recommended. This allows for selective deflation of the ipsilateral lung, significantly reducing the risk of iatrogenic pulmonary injury during pleural dissection.
- Positioning: Place the patient in the lateral decubitus position. This allows unhindered access to the entire course of the rib, from the costovertebral junction to the anterior axillary line.
- Two-Team Approach: The lateral position facilitates a simultaneous two-team approach, where one team harvests the rib while the second team prepares the recipient site (e.g., the mandible or a contralateral limb).
Step-by-Step Surgical Technique
1. Incision and Superficial Exposure
- Identify the middle of the ninth rib (the most commonly harvested rib due to its length and the caliber of its pedicle).
- Make a skin incision directly over the ninth rib, beginning near the dorsal midline (spinous processes) and following the anatomical curve of the rib laterally and inferiorly.
- Continue the dissection through the superficial fascia. Divide the latissimus dorsi and erector spinae muscles in line with the incision. Develop a submuscular plane beneath these muscles to widely expose the rib and the surrounding superior and inferior intercostal spaces.
2. Muscle Division and Pleural Dissection
- Divide the serratus posterior inferior and the intercostal muscles near the upper margin of the selected rib.
- Carefully open the parietal pleura along this same superior line.
- Address the lower margin: Section the muscles and the pleura in the intercostal space below the rib, making the cut near the upper border of the rib immediately below.
- Critical Concept: The tissues of the interspace (intercostal muscles and parietal pleura) must be included in the composite rib graft. This wide cuff ensures the absolute integrity of the periosteal vascular system.
3. Osteotomy and Medial Mobilization
- Measure the exact required length of the graft based on the recipient site defect.
- Section the rib laterally using rib shears or an oscillating saw.
- Isolate and securely ligate the posterior intercostal vessels at the distal (lateral) end of the graft.
- Gently mobilize the rib outward. Through the transparent parietal pleura, expose the intercostal vessels medially, tracing them from their origin to the point where they disappear behind the subcostal muscle.
4. Pedicle Isolation and Disarticulation
- Dissect the vascular stalks from the overlying pleura using blunt, atraumatic dissection. Apply fine hemostats or vessel loops to the vessels near their origin at the aorta/azygos system.
- Section the intercostal nerve near the artery to prevent tethering.
- Maintaining constant visual awareness of the vascular pedicle, divide the remaining medial muscular and fascial attachments of the rib graft.
- Costovertebral Disarticulation: Disarticulate the rib at the costovertebral joint by sharply cutting through the radiate and costotransverse ligaments of the head and neck of the rib, as well as the medial intercostal muscles.
🚨 Pitfall: The Dorsal Spinal Branch
As you dissect medially toward the costovertebral joint, you must identify, divide, and securely ligate the dorsal (spinal) branch of the intercostal artery at a safe distance from the main arterial stem. Failure to secure this branch can lead to devastating epidural hematoma or compromise the main pedicle. Furthermore, extreme care must be taken to deliver the vascular pedicle safely beneath the sympathetic trunk without causing traction injury to the sympathetic chain.
5. Flap Harvest
- Apply microvascular clamps to the graft side of the pedicle.
- Ligate the central (aortic) side of the vascular pedicle securely with non-absorbable sutures or surgical clips.
- Section the vascular pedicle and transfer the composite rib graft to the recipient site.
POSTOPERATIVE PROTOCOLS AND DONOR SITE MANAGEMENT
The success of vascularized bone grafting relies heavily on meticulous postoperative care, both for the survival of the transferred flap and the minimization of donor site morbidity.
Flap Monitoring
- Clinical Assessment: If a skin paddle was included (chimeric flap), monitor capillary refill, color, and temperature hourly for the first 48 hours.
- Implantable Doppler: For buried bone flaps (like a pure MFC or rib graft), an implantable venous or arterial Doppler probe is the gold standard for continuous microvascular monitoring.
- Anticoagulation: Protocols vary by institution, but a common regimen includes intravenous Dextran 40 or subcutaneous low-molecular-weight heparin (LMWH) for 5 days postoperatively, combined with daily aspirin, to prevent microvascular thrombosis.
MFC Donor Site Management
- Closure: Close the vastus medialis and sartorius fascia over a closed-suction drain to prevent hematoma formation.
- Mobilization: The patient may begin immediate active and passive range of motion (ROM) of the knee. Weight-bearing is typically restricted to touch-down or partial weight-bearing with crutches for 4 to 6 weeks to mitigate the risk of a distal femur fracture, especially if a large (5 × 7 cm) corticocancellous block was harvested.
- Complications: Potential donor site morbidities include saphenous nerve neuropraxia (resulting in medial leg numbness), hematoma, and, rarely, patellar tracking issues if the vastus medialis is inadequately repaired.
Rib Donor Site Management
- Pleural Repair: The parietal pleura is often impossible to close primarily due to the composite nature of the harvest. A thoracostomy tube (chest tube) must be placed under direct vision prior to closure.
- Closure: Reapproximate the latissimus dorsi and erector spinae muscles meticulously in layers to prevent lung herniation and restore shoulder girdle mechanics.
- Extubation: Prior to final closure, the anesthesia team should perform a Valsalva maneuver (inflating the lungs to 30-40 cm H2O) to check for any missed parenchymal air leaks.
- Postoperative Care: Aggressive chest physiotherapy, incentive spirometry, and adequate multimodal analgesia (often via an epidural or paravertebral block) are critical to prevent atelectasis and pneumonia. The chest tube is typically removed once drainage is less than 100 cc over a 24-hour period and no air leak is present.
By adhering to these rigorous anatomical principles and precise surgical techniques, the reconstructive microsurgeon can reliably harvest both the medial femoral condyle and vascularized rib grafts, providing unparalleled biological solutions for the most challenging orthopedic defects.
