cadera / hip - Active Congress.......

MIÉRCOLES / WEDNESDAY
118
because of the thin polyethylene acetabular
component. The large diameter metal heads
coupled with polyethylene cups resulted in increased
volumetric wear compared to 28mm
diameter femoral heads articulating with
polyethylene. The increased wear with subsequent
osteolysis led to implant loosening.
Since there was no centering femoral stem,
unsatisfactory femoral positioning was more
prevalent. The development of improved
manufacturing methods and metal-on-metal
articulations have provided an opportunity
to once again explore resurfacing hip arthroplasty
as a treatment approach to the younger
arthritic patient. Metal-on-metal surfaces now
are manufactured with tighter tolerances, better
surface fi nishes and improved clearances
that make it a useful articulation for SRA. A
greater range of sizes with 2mm increments
for better matching the patients anatomy
has enhanced the opportunity for improved
outcomes.
Although the early results of these new
designs of metal-on-metal surface replacements
are generally excellent, a number
of signifi cant problems still remain. These
complications include: femoral neck fracture
and femoral loosening, and the long-term issue
of metal ion release from the surface of
the metal-on-metal articulation. Early data
focusing on the metal ion problem, indicate
that there is a signifi cantly increased blood
and tissue level of both cobalt and chromium,
however, the clinical implications of these
elevated metal ion levels has yet to be delineated.
Patient selection still remains controversial.
The ideal patient for a hip resurfacing
procedure is usually a young, active patient
with osteoarthritis without major deformities
and excellent proximal femoral bone quality.
Contraindications include elderly patients with
poor femoral bone, metal hypersensitivity and
impaired renal function. The role of surface
replacement arthroplasty in inflammatory
arthritis remains controversial. Large areas
of avascular necrosis or large cysts in the
femoral head may preclude the application
of SRA.
Our early experience with SRA of the hip is
with the Conserve Plus Prosthesis® (Wright
Medical Technologies), performed in seventy-eight
consecutive patients. Seventy-eight
replacements were performed and followed
six to fi fty-two months (mean 30 months).
The procedure was approved by the hospital
institutional review board. The indications for
the procedure included a younger age group
with a high level of activity. All patients were
Charnley Class A. All of the patients except
one with avascular necrosis had a diagnosis
of osteoarthritis. There were 57 males and
21 females between the age of 29 and 65.
The Conserve Plus® acetabular shell is
170 degrees and nearly hemispherical. It is
manufactured from a high carbon cast cobalt
chromium molybdenum steel conforming to
ASTM F75 standards. The exterior surface
of the acetabular component has sintered
beads ranging from 50-150 microns in diameter
for cementless fi xation. The one piece
acetabular shell is available in a 3.5mm
thin shell and 5mm thick shell. The femoral
component is greater then a hemisphere
(208 degrees) which enables coverage of
all the reamed bone by the component and
maintains the length of the femoral head and
neck. The surface fi nish is approximately
0.008 micrometers. The component has
a short metaphyseal stem and permits a
cement mantle with an average thickness
of 1.25mm around the femoral head. The
components are available in 2mm increments
(the acetabular sizes are 46 to 64 mm, the
femoral head sizes 36 to 54 mm).
The surgical technique has been previously
described and uses a posterior approach. All
patients were managed with adjusted lowdose
Warafi n® for 3 weeks and prophylactic
antibiotics (Kefzol®). Crutches with partial
weight bearing were used for 6 weeks and
a cane thereafter, until the patients did not
have a signifi cant limp. Sports usually were
permitted at four months post-operatively.