Cranioplasty Reconstruction With Autogenous Rib Graft
Scott J. Rapp
DEFINITION
Cranial defects resulting from trauma, oncologic resection, decompressive craniotomies, osteomyelitis, congenital defects, and cranial vault expansion/remodeling for craniosynostosis may require reconstruction when the defect is large. In the young patient, defects greater than 4 cm2 will not close spontaneously, leading to gross contour irregularities and risk of intracranial herniation or injury if left unrepaired.1
Other factors that influence healing of bone include age of patient, nutritional status, previous scarring, and surgeries.
Autogenous rib inlay grafting represents a useful cranioplasty technique to provide structural rigidity to the cranial vault, maximizing bony integration while minimizing infection and resorption.
ANATOMY
The neurocranium arises from paraxial mesoderm and neural crest cells (FIG 1).
The calvaria develops through intramembranous ossification.
The cranial base develops through endochondral ossification.
A definitive diploic space forms by around age two to three and thickness varies on anatomic location.
Craniosynostosis leads to both thin calvarial wall and diploic thickness.2
FIG 1 • The neurocranium develops from both endochondral and intramembranous ossification.
Rib development occurs from paraxial mesoderm and arises from sclerotome cells within the costal process of thoracic vertebrae.
True ribs (1-7) attach to the sternum directly by their own cartilage.
False ribs (8-10) attach to the sternum by synchondrosis.
Floating ribs (11,12) do not attach to the sternum (plain film; FIG 2).
PATHOGENESIS
A critical-sized defect is one that will not heal spontaneously and leads to a fibrous nonunion.
4-cm2 gaps are considered “small” with defects greater than 5 cm in diameter or 25 cm2 considered “large.”
Healing of bone gaps in the cranial vault occur through multiple pathways:
The dura mater is an important contributor providing a primary source of osteogenic cells and the source of osteoinductive growth factors.
Bone growth occurs both centrally and peripherally within the defect.3
The periosteum, when present, provides an important source of growth factors and mesenchymal cells including osteoblasts, pericytes, fibroblasts, and periosteum-derived stem cells.
Growth factors released include BMP-2, IGF-1, and TGF-β.
Partial bone growth from the margins of the wound occurs from local osteoblasts through osteogenesis.
NATURAL HISTORY
Surgical intervention to reintroduce structural integrity within the defect may be accomplished through alloplastic, allograft, and autograft sources.
Alloplastic materials are biocompatible and hold the advantage of ease of use, ample supply, and no donor-site morbidity.
The bone substitute acts as a structural lattice, and new bone formation occurs through osteoconduction.
May provide greater mechanical strength to the repair
Useful for small defects utilizing a “spackle” technique
Larger-sized defects under 5 cm require an absorbable or titanium mesh underlay to provide support against the pulsing dura beneath.
Titanium mesh may provide intracranial protection rapidly when the defect is large.
FIG 2 • Plain film of floating ribs 11 and 12.
Alloplastic materials are not recommended in the rapidly growing pediatric skeleton and are associated with higher rates of extrusion and infection.
Infection rates have been reported to be 5 times higher than other bone grafting materials.4
Avoid using these materials in a postradiated wound bed with diminished blood supply.
Allograft materials are derived from cadaveric bone.
May be fresh or frozen bone
Most available source is demineralized bone matrix.5
Bony regeneration occurs predominately through osteoconduction but may also confer osteoinduction properties as some osteoclasts may survive the free transfer.6
Autogenous bone grafting is the current “gold standard” to correct vault defects long term.
Bony healing occurs through osteoinduction, osteoconduction, and osteogenesis—whereby the transplanted osteoblasts survive and contribute to the creation of de novo bone formation.
Indications for use include complex or large-sized defects, need for staged procedures, defects near sinuses, previous reconstruction failures, radiated tissue beds, and colonized or infected sites.
Autogenous bone grafts can become revascularized.
Most frequent autogenous sources of bone grafting to the skull include
Iliac crest
Split calvarial bone
Split rib
Parascapular osteocutaneous flap
Vascularized bone grafting based on superficial temporal vessels
The use of rib grafts as a surgical intervention was first described in 1917 by Brourt.7
Multiple ribs may be used.
Once healed, the bone is smooth and radiographically indistinct by CT imaging.8
PATIENT HISTORY AND PHYSICAL FINDINGS
Cranial defects can first be identified by physical exam and palpation.
In the young pediatric population, even large-sized defects can be observed for closure spontaneously until patients are more physically active.
Intervention is usually performed when the patient with a large skull defect becomes more mobile, exposing intracranial contents to risk for harm or herniation.
Congenital bony abnormalities requiring intervention can result from:
Cutis aplasia
Cleidocranial dysplasia
Craniofrontonasal dysplasia
Encephaloceles, gliomas
Hypophosphatasia
Hypothyroidism
Fibrous dysplasia
Elevated intracranial pressure from multisuture craniosynostosis
IMAGING
Noncontrast CT with 3D reconstructions identifies defects adequately.
Coronal cuts are useful to evaluate diploic space thickness to assess split calvarial bone grafting as an alternate option for treatment.
In complex or the multiply operated cranial vault, virtual surgical modeling may be helpful in determining calvarial thickness and location of multiple defects within an area of concern.
NONOPERATIVE MANAGEMENT
If the patient is unable to undergo surgical reconstruction for any reason and the cranial defect is such that the intracranial contents are at risk, a protective orthotic helmet may be used until comorbidities are corrected.Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
