Monitoring bone defects of the femur before hip revision and bone growth after hip revision arthroplasty with DEXA, a pilot study

Bone mineral density (BMD) is usually measured with Dual-Energy X-ray
Absorptiometry (DEXA). DEXA can measure BMD in a reproducible, precise and
accurate manner and is also preferred because of the low radiation exposure to
the patient and the low costs [1, 2]. A DEXA scan measures bone mineral content
in grams (BMC) and area (A) in cm2, from which BMD (g/ cm2) is calculated.
Several studies used DEXA to understand the BMD and bone remodelling around
prosthetic implants [1, 3-10]. These studies showed that DEXA scanning is an
accurate and reproducible procedure to determine periprosthetic BMD when
positioning and rotation are strictly controlled. Less is known about revision
hip arthroplasty with bone impaction grafting. Histology of the bone after bone
impaction grafting in hip revision surgery showed that bone remodeling is slow
and that bony healing after hip revision may be less predictable compared to
primairy arthroplasies [11, 12]. Also, a few studies report evaluation of the
results after revision of the hip [13-19], but only Karrholm et al. [19]
included measurements of BMD with DEXA in vivo. Laursen et al. [20] studied
experimental defects around acetabular components in human post mortem pelvis
specimens. They concluded that DEXA scanning provides a sensitive measure of
changes in BMC around cementless hemispherical metal-backed cups.
In hip revision arthroplasty with bone impaction grafting the bone defects are
restored with tightly impacted morselized cancellous bone chips in combination
with a cemented cup, before implantation of the new prosthesis. The allograft
bone will be resorbed and new woven bone will be formed. Remodeling of this
newly formed bone into its characteristic structure will lead to the biological
repair of the defect site in years after the surgery [16]. Absence of balance
between the resorption of the allograft bone and the formation of new bone
could contribute to stem migration [21]. To monitor this balance DEXA might be
a valuable tool after hip revision surgery. Also, to determine bone loss before
undergoing hip revision surgery, DEXA results could be an accurate manner.
One goal of this study is to determine if DEXA is accurate predict bone loss of
the femur before undergoing hip revision arthroplasty. Can a measured
difference in bone loss in the femur be correlated to differences in BMD, BMC
or A and in this way, provide a tool for quantification of bone loss of the
femur before hip revision arthroplasty? Another goal of this study is to
monitor bone remodelling after hip revision surgery.

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Is DEXA accurate to predict bone loss of the femur before undergoing hip
revision arthroplasty and provide a tool for quantification of bone loss of the
femur before hip revision arthroplasty? Can DEXA be used to monitor bone
remodelling after hip revision surgery?

This study is an observational pilot study, comparing the outcomes of DEXA
before and after hip revision arthroplasty for the femoral component. The study
contains two parts, which are both case-control studies.

1: Observational cohort study after hip revision arthroplasty
To monitor bone remodeling after hip revision arthroplasty of the femoral
component, patients will be examined with DEXA and results will be compared to
the results of the contralateral side and the lumbar spine.

Inclusion:
Orthopaedic Department of RdGG Hospital Delft

Procedure
First, all hip revisions with bone impaction grafting performed during last 5
years will be evaluated and patients will be selected. Second, a DEXA scan will
be made of the revised hip and results will be compared to the DEXA results of
the contralateral hip to monitor bone growth at different times after hip
revision arthroplasty. Also, BMD of the lumbar spine will be measured with DEXA
as a control. Oxford Hip Score and Hip disability and Osteoarthritis Outcome
Score (HOOS) will be used to evaluate clinical outcomes.

2: Observational cohort study before and after hip revision arthroplasty
To determine bone defects of the femur before hip revision arthroplasty with
DEXA, results will be compared to results of the contralateral side as well as
to results of the defect scored during surgery. Also, bone remodeling after hip
revision arthroplasty will be examined with DEXA at different times after
surgery.

Inclusion:
Orthopaedic Department of RdGG Hospital Delft

Procedure
Before hip revision arthroplasty, a DEXA scan will be made of both hips and of
the lumbar spine. Results of the contralateral hip and the lumbar spine will be
used as control.
After hip revision arthroplasty, DEXA scans will be made at 4 different moments
after surgery. Totally, at 5 different moments DEXA scans will be made: 2 weeks
after surgery, 3 months, 12 months and at 24 months after surgery.

All DEXA results of the revised hip postoperatively will be compared to each
other to monitor bone growth around the prosthesis. The pre-operative DEXA and
the scans at 3 months and at 12 months will be made twice to determine
repeatability and accuracy of the DEXA results. All scans are made at moments a
control visit was planned at the hospital, except for the 24 month follow up.
Therefore, for each patient, only one extra visit to the hospital has to be
made.
After each DEXA scan, Oxford Hip Score and Hip disability and Osteoarthritis
Outcome Score (HOOS) will be used to evaluate clinical outcomes.
During hip revision arthroplasty, bone loss of the femur will be determined
using the Paprosky classification [22]. The pre-operative DEXA will be used to
see whether the results of the Paprosky classification are comparable to
results of bone loss determined with DEXA.

This study has a low risk for participants since DEXA has a low radiation
exposure. Visits of the hospital for a DEXA scan will be coupled to regular
control visits as much as possible and therefore the burden to participate will
be low.

The potential risks for revision hip surgery in general are:
- infection
- post-operative pain

The potential benefits for the follow-up with DEXA after hip revision surgery
are:
- early detection of complication/loosening of the prosthesis