Periacetabular Osteotomy (PAO)

Synonyms: Bernese osteotomy, Ganz osteotomy

Introduced by: Dr. Reinhold Ganz in 1984 in Bern, Switzerland

Definition:

• Triplanar peri-acetabular osteotomy
• For adults & adolescents with dysplastic hips
• That require correction of congruency & containment to the femoral head

Outcome of 1st Ganz cohort in 30 years followup:

Authors	Follow-up	Journal	No. of patients (hips)	Survivorship
K.A Sienbrock et.al.	10 years	CORR 1999	63 (75)	80-90%
Simon D et.al.	20 years	CORR 2008	58 (68)	60%
T. Lerch et.al	30 years	CORR 2017	63 (75)	30%

Advantages of Periacetabular Osteotomy (PAO):

1. Posterior column preserved
2. Fragment perfusion maintained
3. Large acetabular fragment
4. Close-to-joint osteotomy:
   • Allows medialization
   • True pelvis dimensions maintained
5. Good improvement in CE angle (avg. 31 degrees correction)

Indications:

1. Age: 10-35 years
2. Osteoarthritis: Tonnis grade 0-1; grade 2 (selected cases only)
   • PAO more cost-effective if no complications

No signs of OA + No previous surgeries + Age <30 years = Success rate almost 100% at 15-22 years followup

For Tonnis Grade 3 OA: Total hip arthroplasty is more cost-effective

Osteotomy sequence	Important points
1. Incomplete ischial	Infracotyloid groove towards ischial spine Risk – Sciatic nerve at lateral wall
2. Complete superior ramus	Medial to pectineal eminence & directed medially Risk – Obturator NV bundle
3. Supra-acetabular iliac	Between ASIS & AIIS to 1 cm proximal to pelvic brim
4. Retro-acetabular iliac	Continue cut 3 towards posterior column – 4 cm distal to pelvic brim Risk – Sciatic n. posteriorly
5. Fracture controlled	Connect cut 1 + cut 4

Fragment mobilization, reorientation and fixation

Aim:

1. Adequate acetabular roof angle (0-10 degrees)
2. No cross-over sign
3. Femoral head sitting neutrally

Fragment movement: Usually flexed & adducted for “classic dysplasia” but must be individualized

Intraoperative pearls and pitfalls

1. Preserve posterior column continuity for stability.
2. Use fluoroscopy extensively for blind cuts (ischial, posterior) to avoid joint penetration or incomplete mobilization.
3. Common risks: Intra-articular extension, neurovascular injuries

References:

1. Bernese periacetabular osteotomy, K A Siebenrock, E Scholl, M Lottenbach, R Ganz. Clin OrthopRelatRes 1999
2. Mean 20-year Follow-up of Bernese Periacetabular Osteotomy. Simon D. Steppacher, Mortiz Tannast, Reinhold Ganz, K.A Siebenrock. Clin OrthopRelatRes (2008)
3. One-third of Hips After Pericetabular Osteotomy Survive 30 Years With Good Clinical Results, No Progression of Arthritis, or Conversion to THA. Till Dominic Lerch, Simon Damian Steppacher, Emanuel Francis, MortizTannast, K.A Siebenrock. Clin OrthopRelatRes (2017)
4. Rodrigues VB et al. Periacetabular hip osteotomy for residual dysplasia. Rev Bras Ortop. 2018;53:332–6.