To The Editor:
I am writing with regard to the article entitled "Load-Sharing at the
Wrist Following Radial Head Replacement with a Metal Implant. A Cadaveric
Study" (2004;86:1023-30),
by Markolf et al. The conclusion of Markolf and colleagues to "insert
the thickest radial head implant possible" is, in my view, incorrect.
Metallic radial head implants are currently in wide use and are effective for
stabilizing the elbow and forearm after fracture-dislocation. However, the
main drawbacks of metallic radial head implants include capitellar wear,
lateral gapping of the ulnohumeral joint, and synovitis (see the case report
by Van Riet et al.1 in the same issue of The Journal).
These are usually only a problem when the radial head implant is too
large.
The issue of whether radial head resection affects function of the wrist or
distal radioulnar joint in the absence of injury to the interosseous ligament
has been a traditional source of interest but not a major source of clinical
problems. So-called "over-stuffing" of the radiocapitellar joint
is a recognized problem and is the major pitfall of the use of a metallic
radial head prosthesis.
Clearly, one should aim to restore the radius to its original length if
possible, and our results support this. Clinically, a surgeon may utilize
radiographic measurements of the contralateral radial length as a guide or may
examine the relative lengths of the radius and ulna at the time of surgery
with different implant sizes until an appropriate length and distal radioulnar
joint congruency are achieved.
This biomechanical study focused on the effects on load transmitted through
the distal part of the ulna when changing the radial implant thickness. We
found that when the reconstructed radius was too short, distal ulnar force was
increased, thereby negating the desired objective of the operation. We
concluded that if it is not possible to measure or estimate the original
radial length, it is better from a biomechanical perspective to insert an
implant that is slightly too thick, rather than too thin, although certainly
within a relatively narrow range of radial head implant thicknesses to avoid
"overstuffing" of the joint.
By stating that the surgeon should insert the thickest implant possible, we
did not mean to imply that the joint should always be
"overstuffed." Forcing an implant into a space that is too small
could increase contact stresses at the cartilage interface and possibly
produce wear. Rather, we meant to state that if the choice of trial implants
comes down to one that is slightly too thick or one that is slightly too thin,
the thicker one should be selected. In the Discussion section of our
manuscript, we noted that an implant that was thicker than normal would
increase proximal radial load, which in turn could have adverse clinical
consequences such as "increased cartilage wear at the interface, implant
loosening, elbow arthritis, pain, and loss of motion."
The anecdotal case report by Van Riet et
al.1 described
extreme wear of the cartilage and underlying bone in a patient who had
undergone radial head replacement forty-four months after initial resection of
the radial head. Disuse osteoporosis was cited as a major contributing factor
in this highly unusual case of extreme wear of cartilage and bone.
"Overstuffing" of the radiohumeral joint was also mentioned as a
possibility, although there were no indications that the authors attempted to
estimate the original radial length by radiographic measurements of the
contralateral forearm.
The prevalence and severity of capitellar wear in conjunction with metallic
radial head replacements is an interesting topic that deserves further
clinical study.
Van Riet RP, Van Glabbeek F, Verborgt
O, Gielen J. Capitellar erosion caused by a metal radial head prosthesis.
A case report. J Bone Joint Surg Am.2004;86:
1061-4.861061
2004
[PubMed]