To The Editor:
The article "The Load Applied to the Foot in a Patellar Ligament-Bearing
Cast," by Aita et al. (80-A: 1597-1602, Nov. 1998), was interesting. The
attempt to measure the pressure difference between the foot-cast
and cast-floor interfaces was particularly worthy of appreciation.
However, all of the tests were carried out on normal volunteers
and not on people with tibial fractures. This gives rise to the
following doubts.
First, in an intact tibia, smooth, uninterrupted weight transmission
can occur along the entire bone. This is not the situation in a
fractured bone, where discontinuity in the osseous trabeculae alters
the mechanics of transmission.
Second, Sarmiento (according to the authors) speaks of telescoping
of bone ends at the fracture site. This leads to an expansion of
tissues against the rigid cast walls, decreasing load at the fracture
site. Further, this vertical movement of bone within the cast brings
the medial tibial condylar flare to bear against the molded surface of
the cast, transferring part of the weight to it. As no such telescoping
occurs in normal bone, an important mechanism for loading the cast (and
off-loading the fracture) is lost.
Third, it is important to remember that the purpose of a patellar
tendon-bearing cast is twofold: to off-load the fracture to permit
comfortable walking, and to allow axial loading sufficient to stimulate
healing. This means that too much weight through the fracture would
make walking uncomfortable while too little would not stimulate
healing. The clinical success of the patellar tendon-bearing cast
over the years is probably because it permits loading within this
ideal window. One wonders whether the other cast-and-brace combinations
used in the current study can provide this.
Thus, for a true conclusion to be drawn about the efficacy of
the patellar tendon-bearing cast, it seems only right to analyze
it in actual clinical settings - that is, in patients with fractures
rather than in normal individuals.
T. M. Sunil, M.S.(Orth), D.N.B.(Orth)
Department of Orthopaedic Surgery
P.O. Box 5425
M. S. Ramaiah Medical College
Bangalore 560 054, India
A. Bhave and J. E. Herzenberg reply:
We concur with Dr. Sunil's argument regarding the efficacy of
the patellar tendon-bearing cast for managing tibial fractures.
In our article, we do not question its use for managing tibial fractures
but question extending its role for managing conditions such as
neuropathic feet and calcaneal fractures. As documented by several studies,
the PTB cast is an effective method for managing tibial fractures
conservatively. When its use is extended to obtain unloading of
the foot, however, one must start questioning its efficacy.
The purpose of our study was to assess whether unloading of the
foot occurs when the patellar tendon-bearing cast is used. Our results
show that if the goal of treatment is to reduce the load on the
foot, then it is best to apply a knee brace in maximum extension.
Lastly, Dr. Sunil raises two questions about off-loading the fracture
and allowing axial loading of the fracture. Our study shows that
a large load reduction (30 percent) is obtained by using a combination
of the patellar tendon-bearing cast and a knee-extension brace. Although
not studied, in theory the combination method is more likely to
produce true axial loading because the knee joint is locked.
We appreciate the feedback from Dr. Sunil and the opportunity
to address the concerns raised.
Anil Bhave, P.T.
John E. Herzenberg, M.D., F.R.C.S.(C)
Corresponding author: John E. Herzenberg, M.D., F.R.C.S.(C)
Maryland Center for Limb Lengthening and Reconstruction
The James Lawrence Kernan Hospital
2200 Kernan Drive
Baltimore, Maryland 21207