BMP Use in the Craniofacial Skeleton
James P. Bradley
Kristen S. Yee
DEFINITION
Synthesized recombinant human bone morphogenetic proteins (BMPs) have osteoinductive activity (ability to induce new bone formation) for use in the craniofacial skeleton and may replace bone grafts, which have a high morbidity, and alloplastic grafts, which are incompatible with the growing skeleton.
Craniofacial operative procedures that utilize BMP-2 and a resorbable matrix include (a) alveolar cleft repair (both primary and secondary), (b) cranial vault defect reconstruction, and, less commonly, skeletal reconstruction, like (c) mandibular defect repair with supportive crib or (d) rare Tessier cleft repair.
ANATOMY
Alveolar cleft defects may be unilateral or bilateral and are thought of as three dimensional (3D) trapezoid shapes that span from the floor of the nose (superiorly), to the alveolar ridge (anteriorly), to the bottom of the gingiva or adjacent tooth root with attached gingiva (inferiorly), and to the incisor foramen (posteriorly) (FIG 1A,B).
Cranial vault defects vary in size and location and may be complete or incomplete; these defects have varying degrees of intervening scar from the deep dura to the more superficial periosteum, galea, or skin. Reconstructions of skull defects near the frontal sinuses or other areas lined with mucosal membranes are fraught with infectious problems.1
FIG 1 • Intraoperative image of right cleft lip and palate patient during primary lip, nose, and GPP with BMP-2 repair. A. The alveolar defect is represented anatomically as a 3D trapezoid that extends from the floor of the nose (superiorly), to the alveolar ridge (anteriorly), to the bottom of the gingiva or adjacent tooth root with attached gingiva (inferiorly) and to the incisor foramen (posteriorly). B. The BMP-2-impregnated collagen gel fills the alveolar defect after deep mucosal flaps are closed. Careful soft tissue closure over the implant is then performed.
Mandibular defects also vary in size and location and present after tumor resection or as a result of complications of trauma (including nonunion and osteomyelitis).2 They may be separated into anterior (symphyseal, parasymphyseal), lateral (body, ramus), or posterior (condylar).
Rare Tessier clefts are associated with bony defects in the facial skeleton based on defined embryologic zones numbered from 0 to 14 (FIG 2). Skeletal defects correlate with overlying soft tissue deficits and may extend from the maxilla, through the maxillary sinus, into the orbit and/or into the cranium. These skeletal defects benefit from bony reconstruction.
PATHOGENESIS
Congenital: Facial clefts (common, cleft lip and palate, and rare, Tessier-numbered clefts) occur due to failure of fusion of facial embryologic elements.
FIG 2 • Tessier classification of craniofacial clefts. Skeletal locations of numeric clefts are depicted on the right side of the face, and soft tissue landmarks are outlined on the left side of the face. Facial clefts are numbered 0 through 7, and cranial clefts are numbered 8 through 14. A mandibular midline facial cleft is number 30.
Oncologic: Tumors in the craniofacial skeleton may arise from a variety of pathologies involving bone or adjacent soft tissue.
NATURAL HISTORY
Alveolar clefts that are not repaired (or poorly repaired) can have several consequences.
A persistent oronasal fistula may result in poor speech and difficult hygiene.
Insufficient or absent bone may prevent eruption of teeth in the cleft area and also result in malocclusion due to maxillary arch collapse.
Discontinuity of the maxillary arch increases difficulty of a future Le Fort I advancement.
Lack of bone under the nasal base results in nasal asymmetry.
Large cranial defects necessitate the use of helmets to protect the brain and may result in the “syndrome of the trephine”— neurologic cognitive deficits related to disruption of equilibrium of intracranial pressure secondary to exposure of the brain to atmospheric pressure.5
Unrepaired mandibular defects can result in difficulties with mastication and speech and an “Andy Gump” deformity, characterized by severe retrognathia and the appearance of an absent chin from contraction of the soft tissues over the area with missing bone.
Rare Tessier craniofacial clefts repairs that do not receive adequate skeletal support will result in soft tissue collapse and progressive worsening of the deformity over time.
PATIENT HISTORY AND PHYSICAL FINDINGS
Alveolar cleft: An alveolar defect can be associated with nasal regurgitation and poor feeding when associated with a cleft palate or oronasal fistula; a gap or notch in the alveolar ridge is seen on examination.
Cranial defect: The history may include head trauma or prior intracranial hemorrhage necessitating decompressive craniotomy; the edges of the bony defect are palpable, and with long-standing, large defects, the skin may be contracted into the depression (sunken skull deformity).
Mandibular defect: The patient’s history includes prior mandibular surgical resection. The patient may report problems with mastication, oral competence, or pain. Malocclusion and soft tissue collapse can be seen on exam.
Rare craniofacial cleft: Larger clefts can be noted on prenatal ultrasound and consultation may be planned before delivery; findings vary depending on the site and severity of the cleft. Careful examination of the eye and lid structures, and nasal and oral cavities should be performed, particularly when the cleft is adjacent to these structures.
IMAGING
Alveolar cleft: Although imaging should be used sparingly in infants and children due to risks of radiation exposure, a CT scan can be useful to assess the volume of the defect and the graft “take” after surgery (FIG 3). Routine records for secondary alveolar grafting include a panorex and periapical films.
Cranial defect: A CT scan (1-mm cuts from the apex to the hyoid) with 3D reconstruction gives an accurate assessment of the defect size and location, as well as record of brain pathology, including ventricular size. In addition, a 3D CT scan model may be helpful for intraoperative resorbable plate shaping.
Mandibular defect: A CT scan with 3D reconstruction, with or without model reconstruction, acts as a road map for reconstruction and guide for creation of custom-made supportive cribs (FIG 4).
Rare Tessier clefts: A CT scan with 3D reconstruction is of paramount importance with these cases because of the unique skeletal abnormalities that occur within Tessiernumbered regions that the outward soft tissue findings only partially suggest.
SURGICAL MANAGEMENT
Alveolar cleft: Primary alveolar cleft closure at the time of cleft lip or palate repair with gingivoperiosteoplasty (GPP) and BMP-2 is possible after presurgical molding approximates alveolar segments within 2 mm (FIG 5A,B). Secondary alveolar closure may be performed after orthodontic palatal expansion at approximately age 6 to 10 years of age.
FIG 3 • CT scan with axillary cuts of a patient with right cleft lip and palate. A. Preoperative image shows the alveolar defect. B. Postoperative image 6 months after gingivoperiosteoplasty (GPP) and BMP-2 grafting shows bony healing and closure of the alveolar defect. 3D CT scan of a patient with right cleft lip and palate. C. Preoperative image shows the alveolar defect. D. Postoperative image 6 months after GPP and BMP-2 grafting shows bony healing and closure of alveolar defect.
Cranial defect: Bilaminar resorbable matrix with BMP-2 reconstruction is an alternative to titanium, alloplastic, or autologous bone reconstruction (FIG 6A,B). Each of these techniques provides structural support to protect the underlying brain. The bilaminar resorbable matrix with BMP-2 reconstruction has the added benefit of decreased donor-site morbidity and eventual resorption of all foreign material.6Related posts:
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