Introduction
Tapered uncemented femoral stems are popular implants in total hip arthroplasty
(THA). They are easy to use and excellent long-term results have been reported for
patients with primary osteoarthritis of the hip (OA).
The disadvantages of these devices include post-operative periprosthetic bone
loss, the clinical importance of which is still uncertain, and an increased risk
of early periprosthetic fractures. These stems rely on initial primary stability to
achieve biological fixation to bone. Poor bone quality, such as in patients with
previous surgery of the hip or osteoporosis, is therefore generally considered to
be a contraindication.
Hypotheses
We hypothesized that (1) femoral periprosthetic bone loss occurs after implantation
of these devices and is related to the stem size used as well as the pre-operative
bone mineral density (BMD) of the hip, (2) that femoral hip revision surgery using
these implants is a reliable procedure with predictable mid-term results despite
compromised proximal femoral bone stock prior to revision, (3) that a bisphosphonate
will reduce the femoral periprosthetic bone loss and finally (4) that a
tapered, uncemented, hydroxyapatite-(HA) coated femoral stem can provide
durable fixation and good clinical outcome in elderly patients with osteoporotic
fractures of the femoral neck.
Materials and methods
Two similar tapered uncemented HA-coated femoral stems were used in the
studies. Bone mineral density (BMD) was measured using Dual-energy X-ray Absorptiometry
(DXA), migration was assessed using radiostereometry (RSA) and
Einzel-Bild-Röntgen-Analyse (EBRA). Clinical outcome was evaluated using the
Harris hip score (HHS) and health related quality of life (EQ-5D) Results
Study I
In a retrospective study, a single cohort of 138 patients with a unilateral THA
was examined 3 years after surgery with DXA. It was found that periprosthetic
proximal bone loss was related to stem size. Patients with the larger stem sizes lost
more bone than patients with smaller stems.
Study II
In a retrospective analysis of 60 patients, who were examined 6 years after uncemented
femoral stem revision surgery due to aseptic loosening, we found a 95%
survival rate of the stem and no cases of aseptic loosening. We also noted that
all stems were stable according to radiological parameters and that the clinical
outcome was acceptable.
Study II
In a randomized, double-blind, placebo-controlled trial of 73 patients with hip
OA, risedronate was given once weekly for 6 months following THA surgery.
Risedronate reduced the proximal femoral bone loss by 7% up to 12 months postoperatively.
In both groups, patients with a low pre-operative BMD lost significantly
more bone than patients whose initial BMD was high.
Study IV
In a prospective single-cohort study of 50 cognitively intact elderly patients operated
with a new HA-coated stem due to a displaced FNF, we found stable stems
after 3 months. We also found a continuous decrease in BMD around the stems
up to 2 years after surgery. Patients with osteoporosis lost more bone than patients
with a normal BMD.
Conclusions
Periprosthetic bone loss after THA can be reduced with bisphosphonate treatment.
Future studies on prevention of bone loss after THA should focus on patients
who have a low pre-operative BMD of the hip.
An uncemented, tapered HA-coated stem can be used successfully for elderly
patients with osteoporotic fractures of the femoral neck. Further studies are
needed to ascertain whether uncemented femoral stems are superior, equivalent
or inferior to cemented stems in the treatment of FNFs in the elderly