Sagittal Split Osteotomy

The sagittal split osteotomy is the workhorse procedure for repositioning the mandible in orthognathic surgery. Through an intraoral incision, the ramus and posterior body of the mandible are split in a sagittal plane so that the tooth-bearing distal segment can be advanced or set back while a broad cancellous overlap between the segments promotes bony healing.

Definition

The sagittal split osteotomy is a mandibular ramus osteotomy in which medial and lateral horizontal cuts are connected by a sagittal cut along the ascending ramus and body, allowing the mandible to be split lengthwise into proximal (condyle-bearing) and distal (tooth-bearing) segments that are then repositioned and fixed.

Scope

This topic covers the rationale, technical principles, and characteristic outcomes of the bilateral sagittal split osteotomy (BSSO), including the broad bone contact that aids union, fixation, and its signature complication — inferior alveolar nerve disturbance. It is a reference description of the technique and its evidence base, not operative instruction.

Core questions

• How does the sagittal geometry of the cut create the broad cancellous bone overlap that favours healing in both advancement and setback?
• Why is the inferior alveolar nerve at risk during the split, and how often is sensory disturbance lasting?
• How are the proximal and distal segments related so that the condyle is seated correctly while the occlusion is set?

Key concepts

• Proximal (condylar) and distal (tooth-bearing) segments
• Medial and lateral cortical cuts joined by a sagittal split
• Cancellous bone overlap and bony union
• Rigid internal fixation versus wire fixation
• Inferior alveolar nerve and neurosensory disturbance
• Mandibular advancement and setback
• Bad split (unfavourable fracture)

Mechanisms

A horizontal cut is made on the medial ramus above the lingula, a vertical or oblique cut on the lateral cortex of the body, and the two are joined by a sagittal osteotomy. Controlled splitting separates the mandible into a proximal segment carrying the condyle and a distal segment carrying the teeth. Because the cut planes overlap broadly in cancellous bone, the segments can be advanced or retruded while retaining contact, and the surfaces heal by direct bony union, usually under rigid plate-and-screw fixation. The inferior alveolar nerve runs within the split zone, so the technique balances adequate mobilisation against protection of the nerve (Wyatt, 1997; Trauner & Obwegeser, 1957).

Clinical relevance

The sagittal split osteotomy illustrates how a single intraoral osteotomy can produce versatile, stable mandibular movement, and how procedure design interacts with a named anatomical risk. It is presented to explain technique and outcomes; it is not a recommendation for or against surgery in any individual.

Epidemiology

Neurosensory disturbance of the inferior alveolar nerve is the characteristic morbidity of the procedure. Systematic reviews find that altered sensation is common in the early post-operative period and then declines over months, though a proportion of patients report some persistent change, with reported frequencies varying by assessment method and follow-up interval (Antonarakis, 2012; Colella, 2007).

History

Trauner and Obwegeser introduced the intraoral sagittal split of the ramus in 1957, replacing extraoral approaches and making mandibular repositioning more predictable and scar-free. Dal Pont later modified the lateral cut to increase bony contact, and subsequent authors refined the cuts and the move to rigid internal fixation, as summarised in technical reviews (Wyatt, 1997).

Debates

Rigid internal fixation versus wire fixation and nerve outcome

Plate-and-screw rigid fixation allows earlier function but bicortical screws placed near the canal have been linked in some series to greater nerve disturbance, so the trade-off between stability and neurosensory safety remains a point of discussion.

Key figures

• Hugo Obwegeser
• Richard Trauner
• Giulio Dal Pont

Seminal works

• trauner-obwegeser-1957
• wyatt-1997

Frequently asked questions

Why is the sagittal split osteotomy so widely used for the mandible?

Its lengthwise split creates a broad overlap of cancellous bone that stays in contact whether the jaw is advanced or set back, giving a versatile, intraoral procedure that heals reliably with plate-and-screw fixation.

What is the most common problem after the operation?

Altered sensation in the lower lip and chin from handling of the inferior alveolar nerve, which lies in the path of the split. It is common early on, usually improves over months, and persists to some degree in a minority of patients.