Pelvic Osteotomies — A Comparative Overview

Why Operate on the Pelvis in Dysplasia

In developmental dysplasia of the hip (DDH) and residual acetabular dysplasia, the acetabulum provides deficient anterolateral cover of the femoral head. This concentrates load over a small contact area, produces high cartilage contact stress, and drives premature osteoarthritis. Pelvic osteotomies aim to either reorient or reshape the native socket (reconstructive intent) or, where this is not possible, increase the weight-bearing area with a buttress (salvage intent).

The Three Families of Pelvic Osteotomy

1. Redirectional Osteotomies

The acetabulum is of essentially NORMAL shape but malpositioned. The osteotomy reorients the entire intact socket over the head to improve cover. They require a congruent, reducible, near-spherical joint.

• Salter (single innominate) — one supra-acetabular iliac cut, hinging on the symphysis pubis
• Triple innominate (Steel / Tönnis) — ilium, pubis and ischium divided, freeing the fragment
• Periacetabular osteotomy (PAO; Ganz / Bernese) — multiple juxta-articular cuts freeing the acetabulum while preserving the posterior column

2. Reshaping / Volume-Reducing Osteotomies

These bend the acetabulum around the triradiate cartilage, which acts as the hinge — so an OPEN triradiate is mandatory. They reduce acetabular volume and increase cover by changing socket shape.

• Pemberton (pericapsular) — cut curves down to the triradiate; hinges on the triradiate, rotating the acetabular roof
• Dega (transiliac/incomplete) — incomplete iliac osteotomy with a posterior cortical hinge; flexible direction of correction

3. Salvage Osteotomies

Used when the joint is incongruent and cannot be made congruent. They do NOT reorient hyaline cartilage; instead they increase the load-bearing surface, which undergoes fibrocartilage metaplasia.

• Chiari — medial displacement osteotomy just above the acetabulum; the iliac wing becomes a buttress and the hip centre is medialised
• Shelf / Staheli (slotted acetabular augmentation) — extra-articular bony shelf laid over the capsule to extend lateral cover

Key Decision Drivers (memorise these)

Combination with Femoral Osteotomy

Pelvic osteotomies are frequently combined with a proximal femoral osteotomy (varus derotation osteotomy, VDRO) when there is coexisting femoral deformity — excessive anteversion, coxa valga, or to improve concentric reduction and head-neck offset. The pelvic side corrects acetabular deficiency; the femoral side corrects proximal femoral morphology. In high dislocations a femoral shortening osteotomy may be added to reduce the head safely and lower the risk of avascular necrosis.

Salter Single Innominate Osteotomy

Principle: A single straight cut across the ilium from the sciatic notch to the AIIS region; the distal acetabular fragment is hinged on the symphysis pubis and rotated anterolaterally and downward to improve anterolateral cover. A bone graft wedge (from the iliac crest) is interposed and fixed with K-wires.

• Mechanism of correction: Rotation about the symphysis — therefore the symphysis must be mobile (young child).
• Effect: Improves anterolateral cover, does NOT change acetabular volume; correction is limited (roughly 15-25 degrees of cover).
• Age window: Approximately 18 months to 6 years (mobile symphysis, before the deformity is fixed).
• Caveats: Can slightly lengthen the limb; requires a concentrically reducible, congruent joint.

Triple Innominate Osteotomy (Steel / Tönnis)

Principle: Three cuts — ilium, superior pubic ramus and ischium — completely free the acetabular fragment, which can then be redirected more freely than the symphysis-tethered Salter.

• Advantage over Salter: Greater, more multiplanar correction because the fragment is fully mobilised.
• Indication: Older child or adolescent with a closing or recently closed triradiate who needs more correction than a single innominate cut provides, with a congruent joint.
• Tönnis (juxta-articular) modification: Cuts placed closer to the acetabulum allow greater correction with less fragment displacement and better medialisation than the classic Steel.
• Caveats: The freed fragment is less inherently stable; the posterior column is divided (unlike the PAO).

Periacetabular Osteotomy (PAO; Ganz / Bernese)

Principle: A series of controlled juxta-articular cuts (incomplete iliac/supra-acetabular, pubic, ischial and a posterior retroacetabular cut) free the acetabulum as a single fragment while preserving the posterior column. The fragment is reoriented in all planes and rigidly fixed (screws).

• The modern adult/adolescent dysplasia operation. Performed through a single anterior (modified Smith-Petersen/ilioinguinal) approach.
• Why it is powerful:
  • Multiplanar correction — improves anterior and lateral cover, corrects version
  • Posterior column intact — pelvic ring continuity maintained, allowing early protected weight-bearing and stable fixation
  • Acetabular blood supply preserved — the fragment retains its vascularity
  • True pelvis undistorted — preserves the birth canal in women of childbearing age
• Requirement: CLOSED triradiate cartilage — never in the skeletally immature hip (would arrest acetabular growth and devascularise it). Needs a congruent, spherical, well-preserved joint with minimal arthritis.

Reshaping (Volume-Reducing) Osteotomies — Open Triradiate Hinge

Pemberton (Pericapsular) Osteotomy

Principle: A curved supra-acetabular cut is carried down anteriorly and posteriorly to the triradiate cartilage, which acts as the hinge. Levering the acetabular roof down and laterally rotates the roof over the head, reducing acetabular volume and increasing cover.

• Hinge: Triradiate cartilage — therefore an OPEN triradiate is mandatory.
• Effect: Changes acetabular SHAPE and reduces volume — useful when the acetabulum is capacious/large relative to the head.
• Caveats: Can create incongruity or joint stiffness if the head is large or the joint is not truly congruent; technically demanding; may stress the triradiate (theoretical growth-arrest concern).

Dega (Transiliac / Incomplete) Osteotomy

Principle: An incomplete transiliac osteotomy that leaves the posterior (and often medial) iliac cortex intact as a hinge, with the inferior limb directed toward (but not through) the triradiate/sciatic notch region. Bone graft wedges control the direction of correction.

• Hinge: Posterior/medial iliac cortex (and triradiate) — open triradiate preferred.
• Advantage: The direction of correction is adjustable (anterior, lateral or posterior cover) by varying graft placement — versatile for global or posterior deficiency (e.g. neuromuscular dysplasia).
• Relationship to Pemberton: Both bend the acetabulum about a hinge; Dega leaves more cortex intact and is more flexible in correction direction.

Salvage Osteotomies — Fibrocartilage Cover for the Incongruent Hip

Chiari Medial Displacement Osteotomy

Principle: A curved osteotomy of the ilium just above the acetabular margin/capsular insertion; the distal fragment (with the acetabulum) is displaced medially, so the overhanging iliac wing/capsule becomes a bony buttress over the head. The interposed capsule undergoes fibrocartilage metaplasia.

• Effect: Increases weight-bearing area, medialises the hip centre (reducing the lever arm and joint reaction force).
• Indication: Incongruent, subluxated, painful hip where redirection cannot restore congruency.
• Caveats: Fibrocartilage (not hyaline) cover; over-medialisation narrows the pelvis; risk to the sciatic nerve and joint penetration with a mis-directed cut.

Shelf / Staheli (Slotted Acetabular Augmentation)

Principle: An extra-articular bony shelf is created by slotting cortical/cancellous graft into the ilium just above the acetabular rim, extending the lateral roof over the capsule. The Staheli "slotted" technique anchors graft in a trough at the acetabular margin.

• Effect: Augments lateral cover; the capsule beneath undergoes fibrocartilage metaplasia.
• Indication: Incongruent hip or as an adjunct to other procedures; useful when the acetabular rim cannot be reoriented.
• Caveats: Graft resorption or fracture; non-hyaline cover; relies on a good capsule.

A Practical Selection Algorithm

Step 1 — Is the joint congruent and reducible?

• No (incongruent, irreducible) → SALVAGE (Chiari or shelf/Staheli)
• Yes → proceed to step 2 (reconstructive options)

Step 2 — Is the triradiate open or closed?

• Open (skeletally immature):
  • Young child, limited correction, mobile symphysis → Salter
  • Need to reduce acetabular volume / reshape roof → Pemberton or Dega
• Closing / recently closed, more correction needed in an older child → Triple innominate
• Closed (adolescent / adult), congruent spherical joint → Periacetabular osteotomy (PAO)

Step 3 — Is there coexisting femoral deformity?

• Excessive anteversion / coxa valga / high dislocation → add proximal femoral osteotomy (VDRO ± shortening) to the pelvic procedure.

Approach and Generic Technical Principles

• Approach: Most pelvic osteotomies use an anterior approach (Smith-Petersen / modified ilioinguinal / bikini incision for PAO). Identify and protect the LFCN near the ASIS.
• Imaging: Intra-operative fluoroscopy confirms cut position, fragment reorientation, and that no cut has entered the joint (especially the PAO retroacetabular cut and Chiari).
• PAO fragment targets: Aim for an anterior centre-edge angle and lateral centre-edge angle in a normal range, a horizontal sourcil (acetabular index normalised), and avoid retroversion / overcoverage (which causes secondary impingement). Confirm head-neck offset and treat impingement (osteochondroplasty) if present.
• Fixation: Salter — K-wires + interposition graft; triple — screws/wires; PAO — multiple screws into the fragment; Pemberton/Dega — graft wedges (often without internal fixation in young children, spica immobilisation).
• Immobilisation/weight-bearing: Young children typically need a hip spica (Salter, Pemberton, Dega); the PAO permits early protected weight-bearing because the posterior column/pelvic ring is preserved.