What are the indications, differences, and long-term stability of Bilateral Sagittal Split Osteotomy (BSSO) versus Intraoral Vertical Ramus Osteotomy (IVRO) for patients with jaw deformities or malocclusions?

BSSO vs IVRO: Indications, Differences, and Long-Term Stability

Direct Answer

For mandibular setback in orthognathic surgery, BSSO with rigid internal fixation is the preferred technique for most skeletal Class III corrections requiring moderate setback (<10mm), while IVRO without fixation should be selected for severe setbacks (>10mm), flat gonial angles, or rotational mandibular asymmetry where condylar repositioning is advantageous. Both techniques demonstrate comparable horizontal relapse rates (approximately 25-40%), but differ fundamentally in their relapse direction patterns and TMJ effects 1, 2.

Key Technical Differences

Surgical Technique

• BSSO involves a sagittal split of the mandibular ramus with rigid internal fixation using plates and screws, maintaining direct bony contact between proximal and distal segments 1, 3
• IVRO creates a vertical cut through the ramus without fixation, allowing the condylar segment to seek its physiologic position through muscular guidance and intermaxillary fixation 4, 3

Fixation Methods

• BSSO utilizes semi-rigid or rigid internal fixation to stabilize the osteotomy 2
• IVRO relies on no internal fixation, depending instead on intermaxillary fixation during healing 2

Specific Indications

BSSO is Indicated For:

• Moderate mandibular setback (<10mm) 3
• Cases requiring precise positional control of the distal segment 1
• Patients with normal or steep gonial angles 3
• Translational mandibular asymmetry where bilateral SSRO can be performed 4

IVRO is Indicated For:

• Severe mandibular setback (>10mm) where BSSO would create excessive bone gaps 3
• Flat gonial angle anatomy 3
• Severe rotational mandibular asymmetry (unilateral IVRO on short side combined with contralateral SSRO) 4
• Cases where condylar repositioning is desired to improve TMJ function 4
• Patients at risk for condylar displacement or TMJ disorders with BSSO 4

Long-Term Stability Comparison

Horizontal Relapse (1-Year Follow-up)

• BSSO group: 24.9-28.1% relapse at B-point; 40.9% at pogonion 1, 2
• IVRO group: 22.1-27.7% relapse at B-point; 40.6% at pogonion 1, 2
• The horizontal relapse percentages are essentially equivalent between techniques 2

Critical Difference: Direction of Relapse

• BSSO: Mandible displaces forward and upward during relapse 1
• IVRO: Mandible displaces backward and downward during relapse 1
• This directional difference is clinically significant for treatment planning and predicting final outcomes 1

Maxillary Stability in Bimaxillary Surgery

• When combined with Le Fort I osteotomy, the maxilla displaces posteriorly and inferiorly in both BSSO and IVRO groups 1
• Maxillary relapse: 23.5-26.6% regardless of mandibular technique 1
• Excellent stability observed when maxilla is moved upward and forward in long-face Class III patients 5
• Moderate relapse occurs when maxilla is moved down and forward with mandibular setback 5

Factors Affecting Stability

Magnitude of Movement

• The magnitude of setback significantly accounts for relapse in both techniques 1
• Larger movements correlate with greater relapse potential 1

TMJ Considerations

• BSSO may cause large bone gaps and condylar displacement in severe rotational asymmetry, increasing TMJ disorder risk 4
• IVRO allows displaced or rotated condylar segments to return to physiologic position, potentially improving TMJ function 4
• Unilateral IVRO combined with contralateral SSRO avoids mediolateral flaring and condylar dislocation in asymmetry cases 4

Clinical Decision Algorithm

Step 1: Assess Setback Magnitude

• If <10mm → Consider BSSO 3
• If >10mm → Prefer IVRO 3

Step 2: Evaluate Mandibular Morphology

• Flat gonial angle → IVRO 3
• Normal/steep gonial angle → BSSO acceptable 3

Step 3: Determine Asymmetry Type

• Translational asymmetry → Bilateral SSRO 4
• Severe rotational asymmetry → Unilateral IVRO (short side) + contralateral SSRO 4

Step 4: Consider TMJ Status

• Pre-existing TMJ disorder or high risk for condylar displacement → IVRO 4
• Stable TMJ → Either technique acceptable 4

Common Pitfalls and Caveats

Critical Warning About Relapse Direction

• Do not assume both techniques will relapse in the same direction - BSSO relapses forward/upward while IVRO relapses backward/downward, requiring different overcorrection strategies 1

Bimaxillary Surgery Considerations

• When performing double-jaw surgery, recognize that maxillary stability affects mandibular position 5
• Vertical maxillary changes significantly impact both vertical and anteroposterior mandibular positions 5
• Plan for moderate relapse in both jaws when combining forward maxillary movement with mandibular setback 5

Fixation Implications

• BSSO requires meticulous rigid fixation technique to achieve reported stability 2
• IVRO without fixation achieves comparable horizontal stability but requires adequate intermaxillary fixation period 2

Patient Selection Error

• Avoid using BSSO for severe setbacks (>10mm) as excessive bone gaps compromise stability and increase TMJ complications 3
• Do not use bilateral SSRO for severe rotational asymmetry without considering unilateral IVRO alternative 4