Evaluating the Subtalar Joint in Tibiotalocalcaneal Nail

Abstract

Category: Hindfoot Introduction/Purpose: In tibiotalocalcaneal nails for arthrodesis, the path of the nail through the subtalar joint has not been well documented. Ideally, the defect caused by reaming and the nail does not pass through the joint surface so that the amount of bony contact between the talus and calcaneus is maintained in order to optimize fusion. Our hypothesis is that the TTC nail does not destroy a significant amount contact area between the talus and calcaneus. However, using larger diameter nails (which are inherently stronger) will have more of an effect on the contact surface. Methods: Five cadaveric below the knee specimens were obtained. The ankle was disarticulated on each specimen. Subsequently, a guidepin was drilled from the central dome of the talus down to the calcaneus. The 11 mm reamer was then passed over the guidepin through the calcaneus to simulate retrograde reaming of a TTC nail. Then, the subtalar joint was dissected open and the articular surface was documented in comparison with the area that was reamed out. Measurements were then made, using software that calculated two dimensional surface area to determine the percentage of actual subtalar joint area that was reamed out. The mean percentage of articular area that was removed with the reamer was then calculated. Results: Among the five specimens, in the calcaneus, the mean total articular area was 599mm2±113 and the mean drilled articular area was 21mm2±16. The percentage of the calcaneal articular surface that was removed with the reamer was 3.4%±1.9. In the talus, the mean total articular area was 782mm2±130 and the mean drilled articular area was 39mm2±18. The percentage of the talar articular surface that was removed with the reamer was 5.0%±2.3. Additionally, an 11 mm reamer makes a circular surface area of 95mm2, and the statistics above indicate that a significant portion of the reamed area is nonarticular, within the calcaneal sulcus or the talar sulcus. Conclusion: In a tibiotalocalcaneal nail the subtalar joint is typically incompletely visualized, however this anatomic study demonstrates that the 11 mm reamer eliminates about 3.4% of the calcaneal articular surface and about 5% of the talar articular surface. Therefore, the majority of the articular surface is left intact, which is ideal in optimizing arthrodesis outcomes. Furthermore, this study could extrapolate the effects of a larger nail on the availability of joint surface. It could also be used to argue for cartilage stripping of the affected joint surfaces in arthrodesis preparation, because the majority of the articular surface is, in fact, left intact.