Total knee arthroplasty (TKA) is known to lead
to a reduction in periprosthetic bone mineral density (BMD). In theory,
this may lead to migration, instability and aseptic loosening of
the prosthetic components. Bisphosphonates inhibit bone resorption
and may reduce this loss in BMD. We hypothesised that treatment
with bisphosphonates and calcium would lead to improved BMD and
clinical outcomes compared with treatment with calcium supplementation
alone following TKA. A total of 26 patients, (nine male and 17 female,
mean age 67 years) were prospectively randomised into two study
groups: alendronate and calcium (bisphosphonate group, n = 14) or calcium
only (control group, n = 12). Dual energy X-ray absorptiometry (DEXA)
measurements were performed post-operatively, and at three months,
six months, one, two, four, and seven years post-operatively. Mean femoral metaphyseal BMD was significantly higher in the
bisphosphonate group compared with controls, up to four years following
surgery in some areas of the femur (p = 0.045). BMD was observed
to increase in the lateral tibial metaphysis in the bisphosphonate
group until seven years (p = 0.002), and was significantly higher than
that observed in the control group throughout (p = 0.024). There
were no significant differences between the groups in the central
femoral metaphyseal, tibial medial metaphyseal or diaphyseal regions
of interest (ROI) of either the femur or tibia. Bisphosphonate treatment after TKA may be of benefit for patients
with poor bone quality. However, further studies with a larger number
of patients are necessary to assess whether this is clinically beneficial. Cite this article:
The relationship between post-operative bone
density and subsequent failure of total knee replacement (TKR) is
not known. This retrospective study aimed to determine the relationship
between bone density and failure, both overall and according to
failure mechanism. All 54 aseptic failures occurring in 50 patients
from 7760 consecutive primary cemented TKRs between 1983 and 2004
were matched with non-failing TKRs, and 47 failures in 44 patients
involved tibial failures with the matching characteristics of age
(65.1 for failed and 69.8 for non-failed), gender (70.2% female), diagnosis
(93.6% OA), date of operation, bilaterality, pre-operative alignment
(0.4 and 0.3 respectively), and body mass index (30.2 and 30.0 respectively).
In each case, the density of bone beneath the tibial component was assessed
at each follow-up interval using standardised, calibrated radiographs.
Failing knees were compared with controls both overall and, as a
subgroup analysis, by failure mechanism. Knees were compared with
controls using univariable linear regression. Significant and continuous elevation in tibial density was found
in knees that eventually failed by medial collapse (p <
0.001)
and progressive radiolucency (p <
0.001) compared with controls,
particularly in the medial region of the tibia. Knees failing due
to ligamentous instability demonstrated an initial decline in density
(p = 0.0152) followed by a non-decreasing density over time (p =
0.034 for equivalence). Non-failing knees reported a decline in
density similar to that reported previously using dual-energy x-ray
absorptiometry (DEXA). Differences between failing and non-failing
knees were observable as early as two months following surgery.
This tool may be used to identify patients at risk of failure following
TKR, but more validation work is needed. Cite this article:
