To the Editor:

>Drs. Mader and colleagues raise a valid point about the need to use identical materials in tests such as those in our study. The intramedullary rod and humeral blade plate used in our study were both titanium, but we did not specify the material of the humeral blade plate in the paper. The Synthes blade plate was titanium, and thus our data were obtained using identical materials.

>In the study by Mann et al., one posterior-anterior screw was compared with one lateral-medial screw in terms of rotational stiffness only. They did not test the constructs under dorsiflexion, and there was no control for osteopenia. Further, these investigators used one screw distally as opposed to the standard clinical protocol of two screws in tibiocalcaneal arthrodesis and three screws in tibiotalocalcaneal arthrodesis. Our study looked at rotation, dorsiflexion, and, for the first time, fatigue loading using a true tibiotalocalcaneal fusion model with a full complement of screws and an evaluation of bone density. We followed the clinical protocol for intramedullary rod insertion with a first generation nail, which reflected the standard protocol at the time of the study.

>We agree that use of the supplementary screw may have influenced the results in favor of the blade plate. We used this construct because that was our clinical technique. This screw is easier to insert with a blade and more difficult with a rod, and thus we have not used the supplementary screw with the rod clinically. We didn't consider this appropriate to test because it is not practical clinically, and we don't know of any surgeon using this technique. We are currently investigating posterior-anterior versus lateral-medial screw fixation with an intramedullary rod and other variations of technique such as use of a supplementary screw.

>Drs. Mader et al. have done a clinical study on results using an intramedullary rod with posterior to anterior screw fixation. Further comparative clinical studies like theirs will be helpful in further illuminating the differences among available techniques.

To the Editor:

We read with great interest the biomechanical investigation by Chiodo et al. The authors concluded that a blade-plate with a supplemental screw in the sagittal plane provides a stiffer construct than does intramedullary fixation. We think that two issues are problematic in the experimental technique and may have influenced the results of the investigation in favour of the blade- plate.

The intramedullary rod (DePuy/ACE, Warsaw, Indiana) is made of titanium, while the humeral blade-plate (Synthes, Paoli, Pennsylvania) is a stainless steel implant. The use of two different implant materials with different metallurgic compositions and differing biomechanical load and fatigue characteristics may influence the loading stiffness in the experimental setup. This potential error could have been easily avoided by using implants of identical material.

The inferior fatigue resistance of titanium was demonstrated clearly by Vallittu and and Kokkonen(1). Banovetz et al. have shown in a clinical setting that titanium implants have a higher rate of implant failure than those made of stainless steel because of titanium's lower fatigue strength. (2)

In this study, locking of the intramedullary implant was performed with two interlocking bolts placed from medial to lateral in the os calcis and talus. Mann et al. have demonstrated in a biomechanical study that a posterior-to-anterior (PA) calcaneal interlocking screw increases the stiffness of a retrograde arthrodesis nail used for tibiotalocalcaneal fusion when compared with the standard lateral-to-medial (transverse) screw(3). In accordance with these biomechanical results a retrograde arthrodesis nail with PA locking in talus, os calcis and tibia was prospectively studied clinically with a high union rate and no implant failure occured (4). In the blade-plate group, a supplementary screw was inserted in the sagital plane. This supplementary screw might have significantly influenced the results in favour of the afore- mentioned implant. >P>We would therefore recommend that a study be performed that uses identical implant materials and locking of the intramedullary nail in a PA direction in order to elucidate the fatigue characteristics of the implants when tested in an experimental setup with optimum biomechanical prerequisites. A recommendation to use a blade-plate construct can not be made from the data presented in this article.

K. Mader, MD T. Gausepohl, MD D. Pennig, MD, PhD Department of Trauma Surgery, Hand And Reconstructive Surgery St. Vinzenz- Hospital, Cologne Germany k.mader@ndh.net

References 1. Vallittu PK, Kokkonen M. Deflection fatigue of cobalt-chromium, titanium, and gold alloy cast denture clasp. J Prosthet Dent. 1995 Oct;74(4):412-9. 2. Banovetz JM, Sharp R, Probe RA, Anglen JO. Titanium plate fixation: a review of implant failures. J Orth Trauma 1996; 10: 389-394. 3. Mann MR, Parks BG, Pak SS, Miller SD. Tibiotalocalcaneal arthrodesis: A biomechanical analysis of the rotational stability of the Biomet ankle arthrodesis nail. Foot Ankle 2001;22:731-3. 4. Mader K, Pennig D, Gausepohl T, Patsalis T. Calcaneotalotibial arthrodesis with a retrograde posterior-to-anterior locked nail as a salvage procedure for severe ankle pathology. J Bone Joint Surg Am. 2003 (Suppl. 4):123-8.

We appreciate the correspondence from Dr. Miller in response to our article.

The results of Dr. Miller’s study had not yet been published at the time our study was initiated, and the results with the “second-generation” nail he mentions were not yet available to us. However, we are not certain such data would have led us to change our design for this study because many surgeons were using so-called “first-generation” nails at the time of our study and many continue to use these nails today.

As Dr. Miller points out, he compared rod fixation with anterior- posterior distal screws against rod fixation with medial-lateral distal screws only with regard to rotational strength. A study comparing dorsiflexion and plantarflexion strength with these two screw orientations is currently under way in our laboratory.

Alhough this point is not related to our study, we believe that the use of supplemental posterior-to-anterior screws placed outside of a nail cannot be recommended in the clinical setting. With an appropriately sized rod, we find that there is insufficient room for use of such screws. Future studies by others may establish more data on this topic.

Sincerely,

Lew C. Schon, M.D.

December 19, 2003

To the Editor:

I was confused by the article “Intramedullary Rod Fixation Compared with Blade-Plate-and-Screw Fixation for Tibiotalocalcaneal Arthrodesis: A Biomechanical Investigation” (2003;85:2425-2428) by Chiodo et al. While the study was well done and the analysis excellent, the editorial reviewers certainly should have questioned the basic parameters of the experimental design. Why did the investigators choose a first-generation intramedullary nail for testing, when the same lab previously demonstrated that the second-generation design, with a posterior-anterior distal locking screw instead of a lateral to medial screw, was 40% stronger in rotational strength (1)

The other difficult element of this testing was the addition of a posterior-to-anterior screw for augmentation of ankle fusion for the blade plate. Dr. Myerson has advocated this screw for augmentation of intramedullary nail fixation as well (personal communication). Why didn't the investigators add a similar screw to the intramedullary nail construct and measure the increase in fixation?

I have used one screw to augment my intramedullary nail arthrodesis and have even managed two screws from the calcaneus into the distal tibia to further augment fixation. In the bench-testing situation where the joint surfaces are not debrided and prepared, I would assume that the screw plays an even more important role in stabilizing the joint.

My concerns are noted here because readers might assume that the blade plate is stronger than the intramedullary nail on the basis of this experiment which was limited to the blade-plate-and-screw construct versus an early design of intramedullary nail. A modern nail design and the addition of a calcaneal- tibial screw might make the intramedullary-nail-and-screw fixation comparable to the blade-plate-and-screw fixation.

Sincerely,

Stuart D. Miller, M.D. Foot and Ankle Service Department of Orthopaedic Surgery Union Memorial Hospital Baltimore, Maryland 21218

Note: Dr. Miller is one of the designers and developers of the Biomet Ankle Arthrodesis Nail and receives royalties from its sale references 1.Mann, M.R., Parks, B.G., Pak, S.S., and Miller, S.D., “Tibiocalcaneal Arthrodesis: A Biomechanical Analysis of the Rotational Stability of the Biomet Ankle Arthrodesis Nail” Foot and Ankle International, 22(9): 731-733, 2001.)