To The Editor:
I was interested in "Contribution of Monoblock and Bipolar Radial Head Prostheses to Valgus Stability of the Elbow" (2001;83:1829-34), by Pomianowski et al., who analyzed the stability of elbows with a deficient medial collateral ligament after a variety of treatments, including preservation, resection, or replacement of the radial head with different radial head prostheses. This cadaveric study, which proves the mechanical efficiency of radial head replacement and confirms some clinical observations, is a great contribution to the understanding of both the biomechanics and certain pathological conditions of the elbow.
I have just a few methodological questions that pertain to the validity of the results presented by Pomianowski et al. The Judet bipolar prosthesis, which is designed to restore the anatomy of the radial head, has a neck-shaft angle that reproduces the anatomic, so-called supination curvature. This design reproduces the anatomic offset of the intact radial head, and one of the most important technical surgical details is the choice of position for this offset and thus the rotational seating of the intramedullary stem of the implant.
An incorrect position creates a malalignment of the radial head and allows some undesirable tilting of the mobile cup, which results in less valgus stability. In the paper by Pomianowski et al., I could not find any data on the rotational seating of the Judet bipolar prosthesis.
Did the authors follow a reproducible protocol for the rotational seating of this implant? If so, what was the position chosen and what landmarks were used to obtain it?
My current opinion is that incorrect positioning of the prosthesis could explain some of the results observed by the authors.
B.F. Morrey, S. Pomianowski, P.G. Neale, M.J. Park, S.W. O'Driscoll, and K.N. An reply:
Professor Judet's observations are quite relevant. Methodology is extremely important in studies such as ours. Specifically, we did follow a very precise protocol for the rotational seating of the Judet bipolar implant as well as for that of the KPS bipolar and Wright monoblock implants. This protocol was mentioned briefly in the Materials and Methods section: "After implantation, an image intensifier was used to confirm correct alignment and seating of each prosthesis" (page 1832). The answer to the question of what landmarks were used is that the position chosen was a neutral rotation of the forearm, in which the angle of the proximal part of the stem was pointed anteriorly to anatomically replicate the neck-shaft angle. This position was confirmed with use of the image intensifier. So we did make a real effort in this regard since we agree with Professor Judet that proper orientation and rotational seating of the implant is a critical issue.
It is relatively easy to check rotation with use of the image intensifier, so we believe that we were consistent in this matter.
The surgical exposure that we used in this cadaveric study involved osteotomy of the lateral epicondyle and release of the collateral ligament, which provides excellent exposure (better than is often obtained at surgery) that facilitates accurate placement of the implant. In addition, we agree with Professor Judet that the proximal part of the Judet implant reproduces the normal 15°ree; angle of the radial neck. We were aware that the neck angle was an issue with use of the longer stem. In the Discussion, we mentioned that "[the] rotation-dependence of the Judet prosthesis might be due to the angled neck design" (page 1833) in an attempt to address the situation that Professor Judet described in his letter.