The German pathologist Otto first described Protrusio acetabuli, (also known as ‘arthrokatadysis’,) in 1824. Hence also known as Otto Pelvis
Idiopathic, or primary protrusio acetabuli: no causative factors are found in this group
· Secondary protrusio acetabuli: The causes are as follows
ü Mycobacterium tuberculosis
ü Metastatic carcinoma (breast, prostate most common)
ü Radiation-induced osteonecrosis
ü Rheumatoid arthritis
ü Ankylosing spondylitis
ü Juvenile rheumatoid arthritis
ü Psoriatic arthritis
ü Acute idiopathic chondrolysis
ü Reiter’s syndrome
ü Osteolysis following hip Replacement
ü Paget’s disease
ü Osteogenesis imperfecta
ü Osteomalacia (very high incidence –50%)
ü Sequalae of acetabular fracture
ü Surgical error during hip Replacement
ü Trichorhinophalangeal syndrome
ü Stickler syndrome
ü Trisomy 18
ü Ehler-Danlos syndrome
ü Marfan’s syndrome
ü Sickle cell disease
The typical orientation for the joint reaction force is 69 degrees from horizontal during the stance phase of gait.
McCollum et al.. found that protrusio acetabuli occurs at 65 degrees from the horizontal and concluded that the axis of migration was nearly the same as that of the joint-reaction force during stance(1)
Eppinger’s theory: the condition is secondary to a chondrodystrophy wherein the three plates of the triradiate cartilage remain unfused, allowing protrusion of the femoral head medially into the pelvis
Inflammatory causes lead to destruction and weakening of the bone surrounding the hip with resultant migration along the joint-reaction vector
The deformity may progress until the greater trochanter impinges on the side of the pelvis
An associated varus deformity of the femoral neck is often seen
-Idiopathic protrusio presents in early adolescence, hence should be kept in the differential diagnosis of hip pain in a teenager
-Common in younger women
-Present with pain and stiffness, rarely with knee pain
-Arising from a seated position is a frequent cause of exacerbation
-The Wiberg’s center-edge angle over 40 degrees is diagnostic of protrusio acetabuli
-Normally on an AP radiograph the medial wall of the acetabulum lies 2 mm lateral to the ilioischial line in a male and 1 mm medial to this line in a female.
-If the medial wall of the acetabulum protruded medial to the ilioischial line (Kohler’s line) by 3 mm in males or 6 mm in females it favours the diagnosis of protrusio.
-May be graded as mild (1 to 5 mm), moderate (6 to 15 mm), or severe (>15 mm), with reference from the ilioischial line.
· In skeletally immature patients, with an open triradiate cartilage: surgical closure of the triradiate cartilage is done. A valgus intertrochanteric osteotomy may be combined
· In adolescent or skeletally mature patients: Valgus intertrochanteric osteotomy (VITO). This lateralises the mechanical axis of the limb. Soft tissue releases of the psoas tendon may be done.
· VITO procedure should not be performed on patients who are over age 40 years or whom have significant degenerative changes visualized on plain radiographs.
Older Adult Patients:
· Total hip Arthroplasty is the treatment of choice
The principles of THA in protrusio acetabuli are:
-Restoration of hip center at its anatomical location for proper joint biomechanics
-The intact peripheral rim of the acetabulum should be used to support the acetabular component
-Cavitary and segmental defects in the medial wall must be reconstructed with bone grafting
-The sciatic nerve will lie near the joint compared to normal patients, and should be routinely identified and protected.
-Trochanteric osteotomy may be required for exposure
-When dislocation is difficult, removal of portion of the posterior acetabular wall maybe required.
-In severe cases, the head is incarcerated into the acetabulum, such cases require osteotomy of the neck at the desired level and removal of the head is facilitated by a corkscrew or rarely as piecemeal.
-The medial wall of the acetabulum is thin or may be partly membranous, and it should not be perforated.
-Medial reaming should be avoided
-Only peripheral reaming should be done to make the acetabular dome to converge
-A protrusio cup is available which avoids medial bone grafting
-If the pelvis is osteoporotic it is better to fix an antiprotrusio cage rather than attempting to press-fit the acetabular component and causing a fracture.
1. McCollum DE, Nunley JA, Harrelson JM: Bone-grafting in total hip replacement for acetabular protrusion. J Bone Joint Surg Am 1980;62:1065-1073.
2. Ranawat CS, Zahn MG: Role of bone grafting in correction of protrusion acetabuli by total hip arthroplasty. J Arthroplasty 1986;1:131-137.
3. Van de Velde S, Fillman R, Yandow S. Protrusio acetabuli in Marfan syndrome: indication for surgery in skeletally immature Marfan patients. J Pediatr Orthop. 2005; 25:603-6.
4. Van De Velde S, Fillman R, Yandow S: The aetiology of protrusio acetabuli: literature review from 1824 to 2006. Acta Orthop Belg 2002; 72:524.
6. Dunlop CC, Jones CW, Maffulli N: Protrusio acetabuli. Bull Hosp Jt Dis 2005; 62:105