Sagittal Split Osteotomy (SSO / BSSO)

Indications

• Mandibular prognathism (Class III malocclusion) - mandibular setback
• Mandibular retrognathia (Class II malocclusion) - mandibular advancement
• Mandibular asymmetry - with appropriate preoperative planning
• Open bite correction - through autorotation
• Obstructive sleep apnea (OSA) - as part of maxillomandibular advancement (MMA); the sagittal-split mandibular osteotomy combined with Le Fort I is the standard MMA approach. [Cummings Otolaryngology] reports MMA success rates of ~85.5% (AHI reduction >50% with final AHI <20/h)
• Combined bimaxillary deformities (e.g., Class III with crossbite) - often paired with Le Fort I maxillary osteotomy

Limitations / When to Choose Alternatives

• Setbacks >7-8 mm can be technically difficult with BSSO; consider intraoral vertical ramus osteotomy (IVRO) instead
• Large advancements in skeletally immature patients or those with poor soft tissue envelopes: mandibular distraction osteogenesis is preferred

Surgical Anatomy

• Inferior alveolar nerve (IAN) - runs through the mandibular canal in the ramus/body
• Inferior alveolar artery - accompanies the nerve
• Masseteric artery - from the medial surface of the ramus
• Lingual nerve - at the medial surface of the ramus superiorly

• The proximal segment carries the condyle and coronoid process
• The distal segment carries the teeth and the anterior mandible

Surgical Technique (Obwegeser-Dal Pont)

1. Incision and Exposure

• Intraoral incision along the anterior aspect of the mandibular ramus
• Subperiosteal dissection exposing the medial and lateral ramus surfaces
• Identification and protection of the IAN as it enters the mandibular foramen

2. Osteotomy Cuts (three cuts)

1. Medial (lingual) horizontal cut - made above the mandibular foramen, along the medial ramus using a reciprocating saw or fissure bur
2. Lateral (buccal) vertical cut (Dal Pont modification) - extends down the lateral cortex of the mandibular body into the molar region, providing a larger bony overlap for fixation
3. Inferior border cut - connects the medial and lateral cuts along the inferior border of the ramus

3. Splitting

• Osteotomes are gently placed to split the bone along the sagittal plane
• The IAN should lie within the distal (tooth-bearing) segment after the split
• The surgeon carefully teases the nerve free if it remains attached to the proximal segment

4. Repositioning

• The mandible is moved to the planned position (based on preoperative model surgery or virtual planning)
• Intermaxillary fixation (IMF/MMF) with the dental splint maintains occlusion

5. Fixation

• Rigid fixation with:
  • Bicortical screws (positional or lag screws) - most stable, allows early jaw mobilization
  • Miniplates - used in some protocols
• Proper condylar seating during fixation is critical to prevent relapse and TMJ complications

Fixation Methods

Complications

Neurosensory Disturbance (Most Common)

• Inferior alveolar nerve (IAN) injury is the most significant and common complication
• Incidence of some long-term neurologic deficit: 10-30% (symptomatic or asymptomatic)
• Nerve transection: 2-3.5%
• When combined with osseous genioplasty, nearly 70% of patients have some neurosensory deficit at 1 year
• Mechanisms: direct saw/chisel/drill injury, hematoma, nerve compression during fixation, stretching during segment manipulation
• Injury types: neuropraxia, axonotmesis, neurotmesis
• Most deficits are temporary; permanent hypoesthesia/paresthesia of lower lip and chin can occur
• A 2026 systematic review (PMID: 40983111) confirmed persistent neurosensory disturbance at 1 year is a significant concern, with identifiable risk factors

Lingual Nerve Injury

• Less common since shift to screw fixation
• ~3% long-term deficit reported in some series
• Usually spontaneously resolves

Unfavorable/Bad Split

• Fracture of the proximal segment (condyle/coronoid fracture) or coronoid process
• Can occur with thin rami, incomplete osteotomy, or excessive force
• Requires revision or alternative fixation

Condylar Complications

• Condylar malposition from inadequate seating during fixation - leads to relapse, open bite, malocclusion
• Condylar resorption (idiopathic) - particularly in young females, patients with pre-existing TMJ disease
• Worsening of TMJ symptoms

Other Complications

• Hemorrhage - from IAN artery or masseteric artery
• Infection - relatively uncommon (intraoral approach)
• Avascular necrosis - rare
• Relapse - particularly with large movements; related to fixation quality, muscle tension, and condylar positioning
• Malocclusion (open bite) - often from inadequate fixation or condylar malposition

Clinical Example (Cummings Otolaryngology)

• Le Fort I maxillary osteotomy with advancement
• Bilateral sagittal split ramus osteotomy of the mandible with setback and rotation
• Asymmetric advancement genioplasty

BSSO vs. IVRO (Intraoral Vertical Ramus Osteotomy) for Setback

Key Points Summary

• BSSO is the gold standard for mandibular repositioning in orthognathic surgery
• Rigid fixation with bicortical screws has largely replaced wire osteosynthesis, improving stability and eliminating prolonged IMF
• Neurosensory disturbance of the IAN is the most common clinically significant complication
• Proper condylar seating during fixation is the single most important technical step to prevent relapse
• Timing: performed after facial skeletal growth completion (females ~16-17 years; males ~17-19 years)
• Often combined with Le Fort I osteotomy (bimaxillary surgery) for complex dentofacial deformities and as part of maxillomandibular advancement for OSA