Biomedical Engineering Reference
In-Depth Information
type III: posteromedial wall defect involving the lesser trochanter
type IV: total proximal circumferential bone loss at various distances
below the lesser trochanter
The transfemoral approach used involves diaphyseal osteotomy of the
femur by an “open book” procedure. This technique allows easy removal
of the prosthesis and all the residual cement. After resection, following the
direction of the fibers, the gluteus maximus and fascia lata, the greater tro-
chanter, and the vastus lateralis are exposed and then the femoral osteotomy
can be performed. The length of the osteotomy corresponds to the primary
prosthesis and is delimited by Steinmann nails to evaluate the distance
between the osteotomy and the greater trochanter. The osteotomy is per-
formed with a chisel and an oscillating saw which allows the “topic open-
ing” of the femur, saving the proximal insertion of the vastus lateralis.
Once the bone is open and the prosthesis exposed, the cement and granu-
lation tissue can be accurately removed until femoral bone bleeding occurs.
The shortest stem that ensures sufficient biomechanical stability is implanted
in the conically reamed osseous bed until stable stem anchoring is achieved.
Subjects were instructed to avoid weight bearing for the first 30 days after
the operation; then, partial weight bearing was allowed and, finally, full load
bearing was permitted at 90 days after the operation.
8.5.2
Clinical and Densitometric Evaluation
The evaluation conducted by Dallari et al. was as follows [56]. First, subjects
were evaluated at the preoperative exam and at the final follow-up (90 days
after surgery) using the Merle D'Aubigné scale, modified by Charley. This
scoring method includes the evaluation of pain, the ability to walk, and
mobility, with each parameter scored on a scale from 1 (pain: severe, also at
rest; walking: impossible; mobility: flexion < 15°) to 6 (pain: absent; walking:
normal; mobility: flexion > 90°, abduction ≥ 15°).
For densitometric measurement, subjects underwent dual-energy x-ray
absorptiometry (DXA) postoperatively, within 10 days, and at 90 days after
surgery. DXA was performed using an Eclipse (Norland, Fort Atkinson,
Wisconsin) [56]. The subjects were positioned with the limb to be investi-
gated extended and in neutral rotation, using a specific device for limb
immobilization. On the DXA image, five regions of interest were identified
(see Figure 8.8): two corresponding to the lateral diaphyseal osteotomy from
the apex of the greater trochanter, one at the distal osteotomy area, and two
at the medial periprosthetic cortex. Region 1 was from the tip of the greater
trochanter to a point on the lateral cortex one-third of the distance to the tip
of the prosthesis; regions 2 and 3 were immediately distal to region 1 on the
lateral aspect of the femur. Region 5 had the same dimension as region 3, but
on the medial side, and region 6 was between region 5 and the lower edge of
the lesser trochanter.
