To The Editor:
I read with great interest "Superior Compressive Strength of
a Calcaneal Fracture Construct Augmented with Remodelable Cancellous
Bone Cement" (81-A: 239-246, Feb. 1999), by Thordarson et al. I
agree with the treatment concept that displaced intraarticular fractures
of the calcaneus should be rigidly fixed and augmented with bone-cement-like
materials, which could lead to more rapid rehabilitation and a shorter
period of disability. I performed a similar procedure3, with use
of conventional polymethylmethacrylate bone cement, for the treatment
of displaced intra-articular fractures of the calcaneus in two elderly
patients with poor-quality bone. Both patients could walk smoothly two
weeks after surgery. Cortical union was obtained within six weeks,
and a good clinical outcome was obtained for six years. However,
a sign of stress-shielding (bone atrophy around the cement) was
found six years after surgery. I hope that my study will be consulted
by other researchers performing clinical investigations on the use
of Norian SRS (Skeletal Repair System) cement for the treatment
of displaced intra-articular fractures of the calcaneus.
Norian SRS is an absorbable material but does not lead to acute
inflammation by macrophages1. As long as normal bone-remodeling
continues, Norian SRS is promising for the treatment of fractures
in patients with poor-quality bone.
Yoshiro Kiyoshige, M.D., Ph.D.
Department of Orthopaedic Surgery
Saiseikai Yamagata Hospital
79-1 Oki-machi
Yamagata 990-8545, Japan
D. B. Thordarson, T. P. Hedman, D. N. Yetkinler, E. Eskandar,
T. N. Lawrence, and R. D. Poser reply:
We thank Dr. Kiyoshige for his interest in our manuscript and
apologize for not having noted his experience with polymethylmethacrylate
cement in augmenting fracture reconstructions in osteoporotic patients
who have had operative treatment of a calcaneal fracture3. His findings are
quite interesting as they support the concept of more rapid rehabilitation
with a shorter period of disability, which we are now seeing clinically.
There has been much debate about whether the mechanism of bone loss
that results in the clinical phenomenon of stress-shielding is mechanical
(moduli mismatch) or biological (decreased vascularity). The remodelability
of the cement addresses both issues. The dynamic change from a solid
mass of cement to a composite of trabecular bone, marrow space,
and cement was documented by Frankenburg et al.1. Such a composite
has compressive strength in a physiologically normal range and enhances
the vascularity of the region. The amount of hardware currently
used for the treatment of depressed calcaneal fractures far outweighs
the effect that the cement would likely have on stress-shielding.
Decreasing the amount of hardware and making the remodelable cement
implant accountable for the stability of the fracture construct
may further minimize a stress-shielding phenomenon because there
will be less residual hardware.
SRS bone cement is clearly different than conventional polymethylmethacrylate
cement. Furthermore, Frankenburg et al., in a canine study, reported
no adverse remodeling of the adjacent host bone after 4.5 years
of follow-up2.
We certainly will continue to follow our patients for the signs
of stress-shielding observed by Dr. Kiyoshige.
David B. Thordarson, M.D.
Thomas P. Hedman, Ph.D.
Duran N. Yetkinler, M.D., Ph.D.
Enass Eskandar, M.D.
T. N. Lawrence, B.S.
Robert D. Poser, D.V.M.
Corresponding author: David B. Thordarson, M.D.
Department of Orthopaedic Surgery
University of Southern California School of Medicine
2025 Zonal Avenue
GNH 3900
Los Angeles, California 90033