Dr. Tornetta responds to the recent letter by Dr. Michelson(ed.)

I thank Dr Michelson for his interest in our work. I fear, however, that he is dismayed for no good reason. I will frame my answers under subheadings.

Issues of clarification:

I thank Dr Michelson for bringing up the following points: The pin in the talus was also in the sagittal plane, just not in the coronal plane, as that would have allowed it to interfere with dorsiflexion. The question of the measured pin angle with respect to talar rotation is not justified. Since Dr Michelson seems to approve of the Needleman article, I will reference that they demonstrated a 1.5° difference in rotation before and after syndesmotic screw placement. This difference would have no bearing on the pin angle or the results of our paper. Dr Michelson also brings up the issue of loading of the joint during examination. A good question, but one without a clear answer. To clarify, the joint was loaded as the board used to push up on the ankle was held both behind and in front of the foot and used to dorsiflex. Loading was necessary to produce this force. We estimate this to be approximately 30 lbs., but it was not controlled for.

Issues of confusion:

I agree that the Needleman paper was very well done. Unfortunately, Dr Michelson needs to revisit it as he misquotes both the methods and results in his letter. Needleman, et al. found a decrease in rotation and drawer after syndesmotic screw placement. There was NO difference demonstrated in dorsiflexion (the p value was .89 at 70 Kg of load) as we correctly quote in our paper. There are several factors that I believe would limit the Needleman study's ability to pick up subtle differences in dorsiflexion. They measured dorsiflexion with the entire foot potted, which does not isolate the tibiotalar joint (as we did), and fixed the rotation of the joint to one axis (which by all accounts is not completely accurate). It is because of these factors that we began our study, feeling that direct measurement of the tibiotalar joint only, without restricting the foot in rotation, would be a more sensitive test. I believe that it was, and that the data is clear…there simply is no difference. Additionally, we did demonstrate this with an appropriate power analysis.

Lastly, I would like to remind him that our conclusions apply only to ankles with a disrupted syndesmosis. Dr Michelson's use of his own paper and that of Harper stating that the distal fibula remains reduced to the talus in its normal rotation, etc by CT scan (which I, too, believe), is not in conflict with our recommendations. I fear that again, the point is missed. When the medial side of the ankle is disrupted, particularly with a deltoid ligament injury, dorsiflexion of the talus with its accompanied external rotation may subluxate the ankle joint, allowing the talus to force the fibula laterally or posteriorly resulting in a malreduction of the syndesmosis. It is this mechanism that concerns me about previous recommendations to dorsiflex the foot. If the fibula remains in its normal position with respect to the talus, then it is more likely to be displaced by the increased external rotation and lateral translation possible in the face of a deltoid injury. I am, of course, assuming one would fix only an unstable joint (not discussed in the Michelson or Harper papers which addressed stable joints).

Finally, I hope that the readers of the manuscript recognize that our conclusion after performing this investigation was that the position of the foot need not be in maximal dorsiflexion during syndesmotic fixation; that whatever position allows for an anatomic reduction of the joint should be chosen as this is what correlates with results. I hope that Dr Michelson has time to re-review the paper of Needleman, Harper and Michelson.

Harper, MC: The short oblique fracture of the distal fibula without medial injury: an assessment of displacement. Foot Ankle Intl. 16:181-186, 1995.

Michelson, JD; Ahn, UM; Helgemo, SL: Ankle motion following simulated supination-external rotation fracture. J Bone Joint Surg (Am). 78:1024- 1031, 1996.

Needleman, JD; Skrade, DA; Stiehl, JB: Effect of the syndesmotic screw on ankle motion. Foot Ankle. 10:17-24, 1989.

Dear Dr. Heckman,

I was dismayed to read the recent paper by Tornetta, et.al. (JBJS 83A:489-492, 2001). There are so many methodological errors in the study that the results are completely uninterpretable. In addition, Dr. Tornetta ignores the large body of literature that has accumulated regarding the mechanics of the ankle.

Perhaps the most obvious issue to address is the choice made by Tornetta, et.al. to assess the ankle range of motion without axial loading. Many researchers 3;6;9;11;12 have clearly demonstrated that the range of motion, and the characteristics of motion are different when the ankle is axially loaded as apposed to the unloaded configuration presented by Tornetta. In particular, the ankle in the unloaded testing configuration can be forced to act like a hinge, since the talus can distally migrate in the mortise. This is particularly important in this study, since any mortise closing that would otherwise limit talar dorsiflexion could easily be compensated for by such a non-physiological migration of the talus. Closely linked to this issue is the existence of coupled motions of the ankle 1;4;6;8, in which sagittal motion of the talus is linked to internal/external rotation and varus/valgus rotation of the talus. This is a physiologic relationship that does not exist when ankle range of motion is tested without axial loading (such as that done by Tornetta).

The relationship between the trapezoidal shape of the talus and dorsiflexion is not as simple as portrayed by Tornetta. The shape of the talus dictates its progressive external rotation as it is brought into dorsiflexion 1;3. If this external rotation is blocked, as by inappropriate medialization of the lateral malleolus by overtightening of the syndesmosis, then either dorsiflexion is limited 8, or very high talo- malleolar pressures will ensue 5. Again, testing for the mechanical derangement induced by over-tightening of the syndesmosis in a model that does not take into account the effect of axial loading will completely miss this critical attribute of ankle kinematics. I would refer readers to the excellent paper by Needleman, et.al.8, in which the effect of syndesmotic overtightening is tested in an axially loaded ankle model. Their results, under more physiologic conditions than that of Tornetta, et.al., clearly demonstrate the dorsiflexion limiting effect of syndesmotic overtightening.

There are additional methodological flaws in this study. The reference pin placed in the tibia was identified as being in the sagittal plane. However, all the radiographic measurements were taken using a “true lateral” of the ankle. Since the “true lateral” is not the sagittal plane of the tibia 10, there is an unknown amount of out-of-plane angular rotation of the reference pin that varies between specimens, and contributes an unknown magnitude of error into the measurements. This is even more true for the talar pin, the plane of which is not even identified in the paper. As earlier noted, the methodology ignores the coupled motions in the trans-axial plane (internal/external rotation). There is no attempt to recognize, let alone measure, the alteration on trans-axial coupled rotation that occurs with over-tightening of the syndesmosis.

Finally, Tornetta, et.al. ignore the recent literature regarding fibular position following ankle fracture. Prospective studies 2;7have conclusively demonstrated that the deformity of the fibula that occurs is not external rotation of the distal fragment, but, rather, internal rotation of the proximal fibular shaft. Consequently, holding the ankle in a dorsiflexed position does not lead to malreduction, because the talo- fibular relationship was never altered to begin with. The only way to reduce the fibular fracture is to manipulate the proximal fragment by external rotating it to match the distal fragment. Consequently, the risk of a malunion lies not with dorsiflexion of the talus that causes distal fibular external rotation, but with failure to reduce the proximal shaft of the fibula to the distal fragment. That maneuver should have been successfully completed by the time the syndesmotic screw is being place, so dorsiflexing the talus cannot cause a fibular malunion.

I look forward to Dr. Tornetta’s response.

Sincerely,

James Michelson, MD

References

1. Close, J. R.: Some applications of the functional anatomy of the ankle joint. J. Bone. Joint. Surg. [Am]. 38:761-781, 1956.

2. Harper, M. C.: The short oblique fracture of the distal fibula without medial injury: an assessment of displacement. Foot Ankle Int. 16:181-186, 1995.

3. McCullough, C. J. and Burge, P. D.: Rotatory stability of the load-bearing ankle. An experimental study. J. Bone. Joint. Surg. [Br]. 62:460-464, 1980.

4. Michelson, J. D., Ahn, U. M., and Helgemo, S. L.: Ankle Motion Following Simulated Supination-External Rotation Fracture. J. Bone. Joint. Surg. [Am]. 78:1024-1031, 1996.

5. Michelson, J. D., Checcone, M., Kuhn, T., and Varner, K.: Intra- articular load distribution in the human ankle joint during motion. Foot Ankle Int. 22:226-233, 2001.

6. Michelson, J. D. and Helgemo, S. L., Jr.: Kinematics of the axially loaded ankle. Foot Ankle Int. 16:577-582, 1995.

7. Michelson, J. D., Magid, D., Ney, D. R., and Fishman, E. K.: Examination of the pathologic anatomy of ankle fractures. J. Trauma. 32:65 -70, 1992.

8. Needleman, R. L., Skrade, D. A., and Stiehl, J. B.: Effect of the syndesmotic screw on ankle motion. Foot Ankle. 10:17-24, 1989.

9. Sammarco, G. J., Burstein, A. H., and Frankel, V. H.: Biomechanics of the ankle: A kinematic study. Orthop. Clin. North. Am. 4:75-96, 1973.

10. Sarrafian, S. K.: Anatomy of the Foot and Ankle. New York, J.B. Lippencott Co., 1983.

11. Stiehl, J. B., Skrade, D. A., Needleman, R. L., and Scheidt, K. B.: Effect of axial load and ankle position on ankle stability. J. Orthop. Trauma. 7:72-77, 1993.

12. Stormont, D. M., Morrey, B. F., An, K. N., and Cass, J. R.: Stability of the loaded ankle. Relation between articular restraint and primary and secondary static restraints. Am. J. Sports. Med. 13:295-300, 1985.