- See:
Bone Grafting for Acetabular Defects:
- Discussion:
- it is probably the result of remodeling of weak, medial acetabular bone after multiple, recurring stress fractures.
- intrapelvic protrussion of the acetabulum may be primary or secondary;
- protrusio acetabuli is not found only in inflammatory arthritides;
- most cases are in patients with osteoarthritis.
-
primary protrusio: Otto Pelvis (Arthrokatadysis)
- primary protrusio acetabuli characterized by progressive protrusio in middle aged women;
- is bilateral in 1/3 of pts & causally related to osteomalacia
- large cortical-cancellous bone grafting may be required using pt's femoral head in a primary arthroplasty as well as a large
acetabular component;
- primary form, Otto pelvis (arthrokatadysis), involves both hips, occurs most often in females, & causes pain & limitation of motion at a relatively early age;
- varus deformity of femoral neck & arthritic changes are common;
-
secondary protrusio:
- secondary form may be caused by femoral head prosthesis, cup arthroplasty, septic arthritis, central fracture dislocation, or
THR, & may be present bilaterally in
paget's,
marfan's,
RA,
AS, &
osteomalacia;
- deformity may progress until femoral neck impinges on side of pelvis;
- often, because of medial migration of the femur, the sciatic near is nearer the joint than normally;
- Radiographic Diagnosis:
- Kohler's line:
- relationship of femoral head to ilioishial line;
- if femoral head is medial to Kohler's line, then protrusio is present;
- Center Edge Angle of Wiberg;
- if CE angle is greater than 35 deg, protrusio is present;
- Considerations in THR:
- template preoperative
leg length inequality;
- realize that adaptive soft tissue changes may not allow full restoration of leg length inequality;
-
component selection:
-
acetabular component design
- ideally component should contain a "peripheral flare" rather than a true hemisphere inorder to prevent progressive medialization of the component;
- peripherally placed screws may also prevent medialization;
- Surgical Technique:
- in some pts such as those w/ protrusio, neck should be divided & head removed from acetabulum in a retrograde fashion rather than risk fracture;
- medial wall of the acetabulum is usually thin or may be partially membranous, and should not be penetrated;
- failure to restore normal lateral offset may cause the greater trochanter to inpinge off of the anterior edge of the acetabulum (leading to posterior instability);
-
reaming technique:
- it is essential not to deepen the acetabulum while reaming;
- surgeon should ream inorder to obtain good peripheral fit;
-
bone grafting: bone grafting for acetabular defects:
- w/ bone grafting a noncemented cup be placed in a more lateral and anatomic position and secured with acetabular screws;
- in young pt w/ acetabular protrusion secondary to longstanding inflammatory arthritis, most authorities advise strengthening thin and medially
displaced medial wall of the acetabulum w/ placement of a block cancellous autograft taken from the femoral head of the patient;
- large cortical-cancellous bone grafting may be required using pt's femoral head in a primary arthroplasty as well as large acetabular component;
- in the report by E. Garcia-Cimbrelo (JBJS Br 2000):
- authors followed 148 primary THR with acetabular protrusion between 1972 and 1990;
- 62 with a mild protrusion were classified as group 1, 54 with moderate or severe protrusion as group 2 and 32 with moderate and severe protrusion which required bone grafts as group 3;
- mean follow-up was 18.3 years (3 to 24) for group 1, 17.4 years (8 to 22) for group 2 and ten years (8 to 13) for group 3.
- there were 31 revisions of the cup, 12 in group 1 and 19 in group 2;
- according to the Kaplan-Meier analysis the overall rates at 20 years were 21 ± 10.79% in group 1 and 37 ± 11.90% in group 2;
- there were 43 radiological loosenings: 22 in group 1, 21 in group 2 and none so far in group 3, at ten years;
- overall loosening rates at 20 years were 42 ± 14.76% in group 1 and 49 ± 19.50% in group 2;
- grafts were well incorporated in all group-3 hips, and the bone structure appeared normal after one year;
- the distance between the centre of the head of the femoral prosthesis and the approximate true centre of the femoral head was less
in group 3 than in groups 1 and 2 (p < 0.01);
- better results were obtained in moderate and severe protrusions reconstructed with bone grafting than in hips with mild protrusion which were not grafted.
- weakness of this study is that the authors were including patients back from the 1970's and 1980's that had insertion of early press fit designs;
- authors did not specify how many cups contained a peripheral flare and how many had screw augmentation;
- ref: Loosening of the cup after low-friction arthroplasty in patients with acetabular protrusion.
The Importance of the position of the cup. E. Garcia-Cimbrelo, A. JBJS [Br] 2000;82-B:108-15.
Radiographic measurements in protrusio acetabuli.
Bone-grafting in total hip replacement for acetabular protrusion.
A technique for removing an intrapelvic acetabular cup. P. Grigoris et al.
JBJS. Vol 75-B. 1993. p 25-27.
Bone-grafting in total hip arthroplasty for protrusio acetabuli. A follow-up note.
Intrapelvic migration of total hip prostheses. Operative treatment
NS Eftekhar and O. Nercessian.
JBJS. Vol 71. 1989 p 1480-1486.
Protrusio Acetabuli: Diagnosis and Treatment.
