INTRODUCTION Is a radiographically demonstrable change in the
mechanical integrity of the load-carrying cemented femoral
component, specifically, fractured cement and an intersurface gap
that produces a radiolucent zone in the cement-stem or cement-bone
interface. Usually, loosening of a total hip prosthesis is
accompanied by increasing pain, and by distinct radiological
changes. Second most common indication for revision of total hip
arthroplasty.
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CAUSES Septic (Infections) Aseptic Theories proposed -
Sensitivity to wear debris caused by motion of an improperly fixed
implant. - Improper techniques. - Improper implants.
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SYMPTOMS A painful hip that restricts the patients daily
activities severely. Start up pain Lasting and / or increasing pain
in the hip. Stiffness (restriction of movements). NOTE: Patients
with well functioning total hips may have signs of loosening
whereas there are patients with loose painful and stiff hip joints
who do not have signs of loosening on plain radiographs.
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DIAGNOSIS Periodic radiographic inspection of the implants,
cement, bone and the interfaces. Special X-ray method called X-ray
stereofotogrammetry. Zones as described by Gruen et al and DeLee
and Charnley.
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FEMORAL LOOSENING Standardized techniques and positioning of
the limb to be used while taking radiograph. Cemented femoral
components list of radiographic changes diagnostic of loosening. 1.
Radiolucency between the superolateral one third of the stem and
the adjacent cement mantle, indicating debonding of the stem from
the cement and possible early deformation of the stem.
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FEMORAL LOOSENING(cntd..) 2. Radiolucency between the cement
mantle and surrounding bone. 3. Subsidence of the entire cement
mantle and stem or migration of the stem into the cement mantle,
resulting in a more distal position of the collar or platform in
relation to the proximal surface of the cement and the femoral
neck. 4. Change of the femoral stem into a more varus
position.
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FEMORAL LOOSENING(cntd..) 5. Areas of rarefaction or
fragmentation of the cement, especially between the superomedial
aspect of the stem and the femoral neck or in areas of thin cement
mantle. 6. Fracture of the cement mantle, most commonly near the
tip of the stem. 7. Deformation of the stem in the anteroposterior
or lateral radiographs. 8. Incomplete or complete failure
(fracture) of the stem
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FEMORAL LOOSENING
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INNOCENT vs OMINOUS RADIOLUCENT LINES
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FEATURES AND CAUSES OF INNOCENT RADIOLUCENT LINES Thin less
than 2 millimeters thick Do not change on serial radiographs Can be
due to cancellous bone that was not completely removed at surgery.
Normal age related expansion of femoral canal and thinning of the
femoral cortex.(0.33 mm/yr and 0.14 mm/yr)
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MECHANISM Mechanical Debonding of the stem from the cement and
cement fracture. Development of a fibrous membrane between the
cement and the bone is a biological response to debris generated
from the mechanical initiating factors.
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MECHANISM
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PISTONING
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MEDIAL STEM PIVOT
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CALCAR PIVOT
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CANTILEVER BENDING
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TECHNICAL PROBLEMS RELATED TO STEM LOOSENING Failure to remove
the soft cancellous bone from the medial surface of the femoral
neck; consequently, the column of cement does not rest on dense
cancellous or cortical bone and support the stem. The cement is
subjected to greater tensile forces and fractures more easily.
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PROBLEMS Failure to provide a cement mantle of adequate
thickness around the entire stem; a thin column cracks easily. The
tip of the stem should be supported by a plug of cement because
this part of the stem is subjected to axial loading.
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PROBLEMS Removal of all trabecular bone from the canal, leaving
a smooth surface with no capacity for cement intrusion or failure
to roughen areas of smooth neocortex that surrounded previous
implants. Inadequate quantity of cement and failure to keep the
bolus of cement intact to avoid lamination.
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PROBLEMS Failure to pressurize the cement, resulting in
inadequate flow of cement into the interstices of the bone. Failure
to prevent stem motion while the cement is hardening. Failure to
position the component in a neutral alignment or centralized within
the femoral canal.
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PROBLEMS The presence of voids in the cement as a result of
poor mixing or injecting technique or allowing blood or fragments
of bone to be mixed in the cement.
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Grading system for the femoral component cement mantle Grade A
- Complete filling of the medullary canal without radiolucencies
(white-out)
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Barrack, Mulroy and Harris Grading Grade B Slight radiolucency
at bone cement interface ( < 50%) Grade C Radiolucency
surrounding 50-90% or any cement mantle defect. Grade D - Complete
lucency on any projection or a defect of the mantle at the tip of
the stem
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CEMENTLESS FEMORAL COMPONENTS Engh and Bobyn proposed a simple
classification system for implant fixation. Classified as 1) Bone
ingrowth 2) Stable fibrous fixation 3) unstable
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BONE INGROWTH Defined as an implant with no subsidence and
minimal or no radiopaque line formation around the stem. Appears
stable Cortical hypertrophy Stress shielding
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STABLE FIBROUS FIXATION No progressive migration occurs but an
extensive radiopaque line forms around the stem. Lines are parallel
and space of upto 1 mm. No local hypertrophy.
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UNSTABLE Progressive subsidence or migration within the canal
and is at least partially surrounded by divergent radiopaque lines
that are more widely separated from the stem at its extremities.
Inc cortical density and thickenning.
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ACETABULAR LOOSENING Cemented Acetabular components List of
radiologic findings suggesting loosening. Absorption of bone from
around part or all of the cement mantle and an increase in the
width of the area of absorption, which is especially significant if
more than 2 mm wide and progressive 6 months or more after
surgery.
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ACETABULAR LOOSENING Superior or medial migration and
protrusion of the cement mantle and cup into the pelvis; also,
fracture of the medial cortex of the acetabulum. Change in the
angle of inclination or the degree of anteversion of the cup,
indicating component migration. Wear of the cup, as indicated by a
decrease in the distance between the surface of the head and the
periphery of the cup.
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ACETABULAR LOOSENING Fracture of the cup and cement (both
rare). A radiolucency 2 mm wide with or without a surrounding fine
line of density, which may develop in one or more of the three
zones around the cement mass in the pelvis.
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TECHNICAL PROBLEMS CAUSING CUP LOOSENING Inadequate support of
the cup by the surrounding bone and cement. Failure to remove all
of the cartilage, loose bone fragments, fibrous tissue, and blood,
and failure to make a sufficient number of holes in the acetabulum
so that the surface will be irregular enough to secure a good
cement-bone bond.
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CUP LOOSENING Failure to pressurize the cement adequately to
obtain an optimal cement-bone bond. Failure to distribute the
cement about the entire outer surface of the cup. Movement of the
cup or cement mantle while the cement is hardening. Movement of a
relatively small cup while it is held in a large cement mantle in a
large acetabulum.
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CEMENTLESS ACETABULAR COMPONENTS Uncommon finding with
follow-up of up to 10 years. It must be remembered that loosening
of cemented acetabular components begins to escalate at
approximately 10 years.
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OSTEOLYSIS Particles of metal, cement, and polyethylene all can
produce periprosthetic osteolysis. Mechanism of production of
osteolysis 1) the generation of wear particles. 2) the access of
these particles to the periprosthetic bone. 3) the cellular
response to the particulate debris.
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MECHANISM
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HISTOLOGY OF OSTEOLYSIS A synovial-like membrane surrounding
loose total hip components. Membrane contains macrophages and had
the capacity to produce large amounts of collagenase and
prostaglandin E2. High levels of IL-1, IL-6 AND TNF.
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PATTERNS OF OSTEOLYSIS LINEAR Expand around the periphery of
the whole prosthesis. loose prosthesis Expansile Begins at a small
spot and expands into the bskeleton away from the prosthesis. ( not
loose)
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Mx OF SILENT OSTEOLYSIS ROUTINE CT SCAN FOR ALL AFTER 6-7 YRS
negative positive Follow with regular xrays. Rpt CT in one yr.
MODERATE EXTENSION THEN RPT CT IN ONE YR. AND START DRUGS. SEVERE
EXTENSION THEN REVISION OPERATION
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MATERIALS AND METHODS OF REVISION OPERATIONS. Shafts are longer
and bulkier. Metal backed cups with plates and screws for better
anchorage.
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BONE TRANSPLANTAION IN REVISIONS. IMPACTION BONE GRAFTING
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Wear- volumetric analysis
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DECREASING THE GENERATION OF WEAR DEBRIS. Passivation One of
the most imp ways of decreasing the chances of loosening. Methods
include passivation and ion implantation of the implants. Corrosion
resistant oxide layer formed over metal alloy in passivation.
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ION IMPLANTATION Ion implantation is a process, performed in a
vacuum, of hardening the surface that uses energized ions blasted
into the surface of the metal alloy.
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REFERENCES CAMPBELLS OPERATIVE ORTHOPEDICS 10 TH AND 11 TH
EDITIONS. Sensitivity to metal as a possible cause of sterile
loosening after cobalt-chromium total hip- replacement
arthroplasty. - J Bone Joint Surg Am. 1977;59:164-168. Aseptic
loosening in total hip arthroplasty secondary to osteolysis induced
by wear debris from titanium-alloy modular femoral heads.- J Bone
Joint Surg Am. 1989;71:1337-1342.