Bilateral Sagittal Split Osteotomy (BSSRO)
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Direct answer
Split each mandibular ramus lengthwise into a condyle-bearing proximal segment and a tooth-bearing distal segment, and the mandible can be advanced or set back as the occlusion demands — that is the bilateral sagittal split osteotomy, described intraorally by Obwegeser in 1957 and extended towards the mandibular body by Dal Pont in 1961 to widen the bony contact. Three corticotomies define the split: a medial horizontal cut just above the lingula, a buccal vertical cut at the second molar, and a connecting cut along the anterior border of the ramus; chisels then cleave the cortex so the inferior alveolar canal unroofs and travels with the distal segment. Fixation is by bicortical lag screws or a monocortical plate per side. Altered sensation of the lower lip from inferior alveolar nerve involvement is the complication every patient must be consented about.
What you must remember
- Eponym layer: Obwegeser, 1957 — the intraoral sagittal split; Dal Pont, 1961 — moving the buccal cut anteriorly to the second molar region, increasing the split surface and hence the stability of large advancements.
- The three cuts: medial horizontal corticotomy running from just behind the lingula along the medial ramus, staying above the mandibular foramen; buccal vertical corticotomy at the second molar from the external oblique ridge down to (and often through) the lower border; connecting corticotomy along the external oblique ridge between them.
- The split itself: progressive thin and wide osteotomes split the cancellous bone along the canal; the nerve normally remains with the distal (tooth-bearing) segment as the proximal segment's lingual cortex peels away.
- Fixation options: bicortical position or lag screws (two to three per side, placed through a transbuccal trocar) — rigid, or a monocortical miniplate along the external oblique ridge — forgiving, with equivalent stability in most comparative series.
- Complications register: transient altered lower lip sensation in a substantial share of patients early on, with most recovering and a small minority persistent; bad splits (fracture of the lingual plate, condylar neck or an unfavourable proximal segment); haemorrhage from the medial pterygoid region; condylar sag producing an immediate malocclusion or open bite; relapse with large advancements and especially high mandibular plane angles; rare facial nerve and TMJ injury.
- Indications: mandibular deficiency (advancement, with or without genioplasty), mandibular prognathism (setback), and asymmetry corrections, nearly always after presurgical orthodontic decompensation.
- Advantage over vertical subsigmoid osteotomy: a broad osseous interface for healing and immediate rigid fixation — the reason BSSRO displaced the vertical ramus osteotomy for advancement.
The operation in sequence
A 24-year-old with mandibular prognathism and completed presurgical orthodontics is listed for bilateral sagittal split osteotomy setback. Through an incision along the external oblique ridge ascending onto the anterior ramus, the medial ramus is exposed above the lingula and the temporalis insertion stripped from the anterior border. The medial horizontal corticotomy is placed just above the lingula, staying above the mandibular foramen; the saw then follows the anterior border down the external oblique ridge, and the buccal vertical cut drops at the second molar towards the lower border. Splitting follows with osteotomes worked systematically along the corticotomy, lifting the nerve off the proximal segment if it adheres. Both sides are split before the mandible is set into the final splint; maxillomandibular fixation holds the occlusion while the condyles are seated passively in the fossae, and screws are placed through the trocar. Elastics guide the occlusion afterwards, and lip sensation is documented daily.
Where students slip
The question examiners reach for is which segment carries the nerve: the distal, tooth-bearing segment — the canal splits to the distal side — and the candidate who answers "the condylar segment" has reversed the anatomy and usually the whole operation. The second is the Obwegeser-Dal Pont distinction: Dal Pont's contribution was anterior extension of the lateral cut, increasing the surface area of bone interface — answers crediting Dal Pont with the entire operation or with the medial cut are common and wrong. Third is the bad split question: an unfavourable fracture of the lingual plate or condylar neck recognised intraoperatively and managed by fixation of the fragment rather than panic — examiners look for recognition before management. In Indian exams, BSSRO appears as "sagittal split osteotomy — indications, technique, complications", with marks clustering around the three cuts, the nerve, and the consent point about usually temporary lip paraesthesia.
Frequently asked questions
Who described the sagittal split osteotomy and its key modification?
Obwegeser described the intraoral procedure in 1957; Dal Pont modified it in 1961 by extending the lateral corticotomy anteriorly to increase bony contact and stability.
With which segment does the inferior alveolar nerve travel?
The distal, tooth-bearing segment, as the canal unroofs during the split; adhesions to the proximal segment are gently released to avoid traction injury.
What is a bad split?
An unplanned unfavourable fracture — of the lingual plate, the condylar neck, or the proximal segment — during the osteotomy, managed by identifying and fixating the fragment on the table.
How is the osteotomy fixed?
Bicortical position or lag screws (two or three per side through a transbuccal trocar) or a monocortical miniplate, both providing stability for early jaw function.
What must every patient be consented about?
Altered sensation of the lower lip and chin — common early, usually temporary, occasionally persistent — besides bleeding, infection, bad split, condylar sag, relapse and the need for orthodontics.