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increased by 29% (~7.5-8.0 Xbody weight); it
increased by up to 37% with a displacement
of 37 mm. This compared with a joint reaction
force of 1.5 to 2.0 X body weight at the normal
hip center. There was no increase in the joint
reaction force with superior hip placement
alone. Vertical placement of the acetabulum
has been shown to have higher polyethylene
wear rates as well.14,15 These factors may
infl uence the rate of mechanical failure in
metallic reinforcement devices. Udomkiat
et al16 reported clinical and radiographic
short-term results of 3 different metallic
reconstruction devices (Burch–Schneider,
Ganz, and Muller) for primarily type II and III
defects. The overall mechanical failure rate,
at an average of 4.6 years, was 17%. The
Burch–Schneider cage had less favorable
biomechanical characteristics than the other
devices—abduction angles of 70.7 +12.6 and
elevated hip centers of 16.6 +12.5 mm. Hip
center lateralization was not documented,
which could show an even more unfavorable
biomechanical environment. The Ganz ring,
with an inferior hook, had abduction angles
of 61.9 +10.5 and elevated hip centers of
12.6 +15.2 mm. No statistical analysis was
documented on these parameters; however,
there was no difference in the mechanical
failure rate between the 3 devices. Their
conclusions were that structural allograft, in
contrast to particulate allograft, should be
used in the superior portion of the acetabulum
to prevent early failure. However, there
was no consideration of the unfavorable
biomechanical environment around the graft
itself, which most likely contributed to early
failure. In general, the surgical technique,
particularly with the Burch–Schneider cage,
focused on stabilizing the implant on host
bone. This would lead, particularly with large
defi ciencies, to superior and lateral hip center
placement, which would explain a higher
mechanical failure rate. In contrast, Kerboull
et al7 reported a 10-year follow-up survivorship
rate of 92.1 +5% for on type III and IV
defi ciencies. The biomechanical parameters
were more favorable, with a device abduc-
tion angle of 38.7 +7.6. This device and the
surgical technique focus on normal hip center
orientation with an inferior crimping hook,
similar to the Restoration GAP cup.
However, the need to use structural allografts
with gages does not provide immediate stability
of the construct and relies on a favorable
integration of the graft to the host bone which
is not 100% predictable. Consequently, the
introduction of new metals such as tantalum
offer immediate stability of the implant and
avoids premature failure of structural allografts18.
References
1. Lewallen DG, Berry DJ: Acetabular revision:
Techniques and results, in Morrey
BF (ed): Joint Replacement Arthroplasty.
Philadelphia, Churchill Livingstone, 2003,
pp 824-843.
2. Paprosky WG, Perona PG, Lawrence JM:
Acetabular defect classifi cation and surgical
reconstruction in revision arthroplasty.
J Arthroplasty 9:33-44, 1994
3. D’Antonio JA, Capello WN, Borden LS,
et al: Classifi cation and management of
acetabular abnormalities in total hip arthroplasty.
Clin Orthop 243:126-137, 1989
4. Muller ME: Acetabular revision, in Salvati
EA (ed): Proceedings of the Open Scientifi
c Meeting of The Hip Society. St Louis,
Mosby, 1981, pp 46-56
5. Rosson J, Schatzker J: The use of reinforcement
rings to reconstruct defi cient
acetabula. J Bone Joint Surg 74B:716-
720, 1992
6. Berry DJ, Muller ME: Revision Arthroplasty
using an anti-protrusio cage for massive
acetabular bone defi ciency. J Bone Joint
Surg 74B: 711-715, 1992
7. Gill TJ, Siebenrock KA, Oberholzer R, et
al: Acetabular reconstruction in develop-