The Journal of Bone and Joint Surgery, Vol 74, Issue 6 839-848, Copyright © 1992 by Journal of Bone and Joint Surgery, Inc
The effect of femoral stem geometry on interface motion in uncemented porous-coated total hip prostheses. Comparison of straight-stem and curved-stem designs
JJ Callaghan, CS Fulghum, RR Glisson and SK Stranne
Orthopaedic Research Laboratory, Duke University Medical Center, Durham, North Carolina 27710.
We compared the magnitudes of motion between the prosthesis and bone during
axial and torsional loading in seven matched pairs of fresh-frozen femora
of cadavera in which an uncemented, collarless, isthmus-filling,
straight-stem (Harris-Galante) prosthesis had been placed in one femur and
an uncemented, collarless, proximal-filling, curved-stem (anatomic)
prosthesis had been placed in the other femur. The comparison was performed
in order to determine the effect of the geometry of the stem on the
magnitude of motion. Single-limb-stance loads and combined axial and
torsional loads were applied to the implanted femoral prostheses with the
use of a jig that simulated acetabular and trochanteric loading.
Extensometers were used to measure motion at the prosthesis-bone interface.
The prostheses were then removed and were reinserted, with cement applied
to the proximal porous coating to simulate ingrowth of bone. The
single-limb-stance and combined axial and torsional loads were reapplied
and the magnitude of motion was recorded again. No significant differences
in the magnitudes of the motion were found between the femora in which the
straight stem had been implanted and the femora in which the curved stem
had been implanted, during either simulated single-limb-stance or
low-intensity torsional loading. When large torsional moments (twenty-two
newton-meters) were applied, significantly less motion occurred at the
bone-prosthesis interface, both proximally (p = 0.019) and distally (p =
0.0013), in the femora with the curved-stem implant than in the femora with
the straight-stem implant. When cement had been applied proximally,
proximal and distal motion between the prosthesis and the femur was
decreased during simulated single-limb-stance and during torsional loading
in the femora with the straight stem and the femora with the curved stem.