Otto Pelvis, also known as primary protrusio acetabuli, was first described by German pathologist Otto in 1824. It is characterized by medial protrusion of the acetabulum. There are two types: primary, which remains a diagnosis of exclusion, and secondary. Clinical features include a marked female predilection and bilateral involvement. Radiographs can identify protrusio using Kohler's line or central edge angle. Management depends on age and degeneration, ranging from valgus osteotomy in younger patients to total hip arthroplasty with grafting in older patients. Surgical techniques aim to restore the hip center through lateralization and reconstruction of bone defects.

1. OTTO PELVIS
Dr. Pratik Dhabalia
Resident in Orthopedics
Dr DY Patil Hospital, Navi Mumbai

2. • The German pathologist Otto
• first described Protrusio acetabuli in 1824.
• also known as ‘arthrokatadysis’
• Hence also known as Otto Pelvis

3. Protusio Acetabuli
Two types:
1. Primary Protusio AKA Otto pelvis AKA arthrokatadysis
2. Secondary Protusio

4. ETIOLOGY
PRIMARY PROTUSIO ACETABULI
• Remains a diagnosis of exclusion
• As such many of the cases reported in the past may have in fact been
secondary to undiagnosed conditions.
• Following three headings:
An inflammatory or destructive condition of the hip joints;
A qualitative deficiency of acetabular bone;
A developmental abnormality or growth disturbance.

5. Secondary protusio acetabuli

6. Clinical Features
• Marked female predilection
• More common in middle aged persons
• The condition is characteristically bilateral
• Typically, patients with primary protrusio acetabuli present with increasing
stiffness rather than pain
• Deepening of the acetabulum leads to painful limitation of abduction as
the femoral neck impinges on the superior acetabular margin
• Further progression leads to adductor spasm, and fixed flexion deformities
develop
• Untreated, the patient ultimately develops ankylosis of the affected hip.

7. RADIOGRAPHS
Kohler’s Line
• Protrusio acetabuli is identified on anteroposterior (AP) radiographs
of the pelvis with an acetabular line projecting medial to the ilioischial
line 3 mm in males or 6 mm in females.

8. If central edge angle is greater than 40 degrees protrusio is present.
Radiographic differences between protrusion hips and the OA group:
• In the protrusio group, the medial joint space was decreased and the superior joint space was
increased when compared to the OA group.
• All hips in the protrusio group had an ilioischial line lateral to the acetabular fossa, whereas the
opposite was observed in the hips of the OA group.
• The posterior rim was lateral to the center of rotation in greater percentage of the hips in the
protrusion group than in the OA group.
• Parameters that measure lateral coverage, center edge, and Sharp’s angle were greater in the
protrusion group compared to the OA group.
• The center of rotation of the femoral head was lower than the tip of the greater trochanter in
93% of cases in the protrusion.
• The OA group, in contrast, had a center of rotation of the femoral head lower than the tip of the
trochanter in 69% of the hips.
• The neck-shaft angle of the protrusio group was substantially Less than OA group.

10. ACETABULAR TEAR DROP

12. MANAGEMENT
• The management of protusio acetabuli depends on age and degree of degenerative
change.
• In the young, skeletally immature patient with progressive secondary protrusio aceTabuli,
early surgical fusion of the triradiate cartilage with or without valgus intertrochanteric
oste- otomy is appropriate.
• As it is not possible to anticipate which patients with primary protrusio acetabuli in the
younger age group will progress to a severe deformity, fusion of the triradiate cartilage
cannot be recommended for primary protrusio acetabuli.
• Valgus intertrochanteric osteotomy is recommended in skeletally mature patients with
no degenerative change under 40 years of age.
• Over 40 years, this procedure can still be carried out in patients with no degenerative
changes in their hip joint and who are capable of undertaking the associated
rehabilitation. In older patients, total hip arthroplasty with medial bone grafting and
meticulous attention to returning the hip joint to its anatomical center is the procedure
of choice.

13. Joint Preserving Surgery
• For young adult without arthritic changes.
• Valgus intertrochanteric proximal femoral osteotomy.
• Rarely arthrodesis for young with heavy manual work.
Joint Replacement in Protrusio
• Joint replacement surgery may be necessary in the case of severe pain or
substantial joint restriction
• A lot of intraoperative problems may be encountered in protrusion hips.
Hence, it is called as “Problem in depth”.
• Protrusio is matter of concerns. The concerns are both mechanical and
biological.

14. Mechanical Concerns
• Bone can be inherently structurally impaired to provide stable
prosthesis fixation
• Preoperative limitation of movement range can be problematic for
exposure and dislocation of hip
• Higher risk of impingement leading to subluxation or dislocation, or
wear
• Limb length discrepancy is a problem
• Abducter insufficiency.

15. Biological Concerns
• Failure to achieve ingrowth into porous implant
• In case of cemented acetabulum there may be lack of stable interface with
cement.
Correction of protrusio is important and objectives of total hip arthroplasty in a
protrusio are as follow:
• Strengthen medial wall and restore acetabular integrity
• Lateralize acetabular component to restore hip biomechanics and center of hip
rotation
• Ensure acetabular component coverage
• Secure rigid prosthesis fixation
• Reconstruct the defect.

16. TREATMENT OPTIONS
Restoration of the hip center can be accomplished by a variety of surgical techniques.
• Cement augmentation
• Bone grafts:
Auto or allografts
With bipolar prosthesis
With cementless
• Support rings
Burch-Schneider’s ring
Müller’s ring.
• Surgical technique of total hip arthroplasty is demanding in case of protrusio. Careful preoperative planning and evaluation is vital
for successful outcome.
• The aim in protrusio surgery is to achieve two important objectives:
1. Restitution of bone stock
2. Lateralization of the hip center to the anatomic position to maximize the chances of successful long-term outcome.