- See:
acetabular component
- Loosening of Uncemented Acetabular Components: (
press fit acetabular components)
- normal bone ingrowth:
- generally for bone ingrowth to occur, the component must lie with 50 micrometers of the acetabulum, inorder for host bone ingrowht to occur;
- as noted by RD Bloebaum et al 1997, bone ingrowth into component averages only 12%, eventhough 84% of the cup surface was in contact w/ periprosthetic bone;
- bone ingrowth was found to be uniform in all zones, most likely due to the uniform distribution of stresses from the metal backing;
-
radiographic signs of ingrowth fixation: (from
Moore, Milan S MD et al.
- 97 percent of the cups with three or more of these signs were determined to be stable at the time of revision surgery
-
in contrast, 83% of the cups with two or fewer signs were loose.
- five radiographic signs of stable cup fixation:
- absence of radiolucent lines
- presence of a superolateral buttress
- medial bone stress-shielding
- radial trabeculae
- inferomedial buttress
-
radiographic signs of loosening: (see
radiographic techniques for eval of acetabulum)
- radiolucent lines that initially appeared after two years
- progression of radiolucent lines after two years
- radiolucent lines in all three zones
- radiolucent lines 2 mm or wider in any zone
- migration
- loosening is present w/ more than 2 mm of migration (either horizontal or vertical);
- continuous radiolucent line;
- note that peripheral radiolucent lines which are non-continuous are commonly found in press fit acetabular components and are often not progressive;
- of note, postoperative gaps are net necessarily associated with subsequent presence of radiolucent lines, progressive radiolucent lines, or socket-loosening;
- references:
-
Comparison of Preoperative Radiographs and Intraoperative Findings of Fixation of Hemispheric Porous-Coated Sockets.
- Loosening of Cemented Acetablar Components: (
cemented acetabular component)
- radiolucency upto 2 mm wide with or without a surrounding fine line of density may develop in
one or more of the the three zones about cement mass in the pelvis;
- as in the femur, radiolucency is produced by the dense fibrous membrane and in some areas, fibrocartilage
that forms about the surface of the cement and the surrounding shell of reactive bone;
- loosening commonly occurs at the stem cement interface, but it rarely occurs at the cup cement interface;
-
risk factors for loosening:
- as noted by S. Kobayashi et al 1997, the most important factor for loosening is rapid wear of the
polyethylene (more than 0.2 mm per year), followed by atrophic osteoarthritis (DJD w/o osteophytes);
-
definite loosening:
- migration of component of more than 5 mm;
- crack in cement mantle;
-
probable loosening:
- continuous radiolucent line > 1-2 mm wide at the bone cement interface;
- as pointed out by Hodgkins et al 1988, the finding of a continuous radiolucent
line about the acetabular component indicates loosening in 94% of patients;
-
possible loosening:
- non circumferential radiolucency which extends at least 50% around the bone cement interface;
-
implications of loosening:
- even w/ radiographic loosening, only 10% of these hips will require revision;
- Effect of Femoral Head Size:
- higher frequency of isolated acetabular loosening was associated with use of a 32-mm femoral head.
- increased loosening rate of acetabulum w/ larger femoral head diameter may reflect thinner
poly
and higher frictional torsional stresses transmitted to the
acetabular component;
- w/ smaller femoral heads, the frictional forces are less and the
polyethylene is thicker;
Postmortem Analysis of Bone Ingrowth into Porous Coated Acetabular Components.
RD Bloebaum PhD, NL Mihalopoulus, JW Jensen, and LD Dorr MD.
JBJS Vol 79-A, No 7, Jul. 1997. p 1013.
Factors affecting aseptic failure of fixation after primary Charnley Total Hip Arthroplasty.
S. Kobayashi et al. JBJS. Vol 79-A. No 11. Nov 1997. p 1618.
Loosening of cobalt chrome beads from a porous-coated acetabular component. A report of ten cases.
The acetabular teardrop and its relevance to acetabular migration.
Total hip acetabular component position affects component loosening rates.
Aseptic loosening in metal-backed acetabular components for total hip replacement. A minimum five-year follow-up.
Bead loosening from a porous-coated acetabular component. A follow-up note.
Early and late loosening of the acetabular cup after low-friction arthroplasty.
Migration of Acetabular Components, Inserted with and without Cement, in One-Stage Bilateral Hip Arthroplasty.
A Controlled, Randomized Study Using Roentgenstereophotogrammetric Analysis.
Early failure of acetabular components inserted without cement after previous pelvic irradiation.
The histology of the radiolucent line.
Acetabular revision in total hip replacement with a press-fit cup.
A Comparison of Radiographic and Scintigraphic Techniques to Assess Aseptic Loosening of the Acetabular Component in a Total Hip Replacement.
Radiographic Signs of Osseointegration in Porous-coated Acetabular Components.
