Biplanar  Fluoroscopic  Measurement  of  Transverse  Tarsal  Kinematics  In  Static  Cadaveric  Simulated  Gait  +1Blankenhorn, BD; 1Schwarz, J; 1Dawson, M; 1Bariteau J; 1Moore, D; 1DiGiovanni, CW  +1The Warren Alpert School of Medicine at Brown University and Rhode Island Hospital  

blankenhorn@gmail.com

 INTRODUCTION: The transverse tarsal joint, or Chopart, joint, is formed from the combination of the calcaneocuboid and talonavicular joints. The motion of the transverse tarsal joint has been historically described by Elftman1 to lock with inversion of the subtalar joint. It has been postulated that during the later portion of the stance phase of gait, the subtalar joint inverts and “locks” the midfoot. This transverse tarsal locking mechanism creates a rigid midfoot allowing for an efficient transfer of force from the hindfoot to the forefoot. This mechanism has not been completely elucidated, but previous studies have attempted to clarify the transverse tarsal joint locking mechanism.2 However, this study did not measure the motion of the transverse tarsal joint while it was subjected to axial or muscular forces. We hypothesize that when subjected to axial and muscular forces, the transverse tarsal joint motion will decrease (lock) later in the stance phase of gait with calcaneal inversion. This study utilized a biplanar fluoroscopic system to measure the motion of the transverse tarsal joint motion during static simulated gait in a cadaveric model with the objective of testing the above hypothesis. METHODS: Seven cadaver right lower extremities (2M, 5F, 70 ± 7 yrs.) were prepared for use with a simple static gait simulator modeling the stance phase of gait. Specimen preparation involved the dissection of the 9 extrinsic foot tendons (Achilles, tibialis posterior, flexor digitorum longus, flexor hallicus longus, combined peroneus longus and brevis, tibilias anterior, and combined extensor digitorum longus and extensor hallicus longus), and implanting 4 tantalum marker beads (1.0 mm diam.) into each of the tibia, fibula, calcaneus, talus, navicular, cuboid, medial cuneiform, and first, third, and fifth metatarsals. The proximal tibia and fibula of specimens were then potted and secured in a fixture simulating fibular head height 34 cm above the lateral malleolus. The gait simulator secured the fixture along an adjustable track, modeling fibular head location in 9 evenly distributed positions (with time) from heel contact to 90% of   stance phase of gait (Figure 1).

Figure 1. Testing apparatus within the biplane fluoroscopy system with

simulated axial and extrinsic muscular loads. Specimens were positioned in 0° ankle dorsi/plantar flexion and 0° subtalar inversion/eversion at the beginning of mid-stance, and loaded with approximately 35 kg in compression (roughly 50% body weight) as measured by F-Scan (Tekscan, South Boston, MA). This magnitude was chosen to provide a reasonable amount of loading given the confines of the system [2]. Specimens were then imaged in each of the 9 positions in a bi-planar videofluoroscopy system, with prepared tendons loaded using a low-friction cable assembly and dead-weights varied at each position based on EMG data. Bead markers were tracked and rigid body transforms were calculated between simulated positions using custom written Matlab code. Digital models of the beaded bones were generated from clinical CT acquired at a voxel resolution of ~0.6 × ~0.6 × 0.625 mm. Kinematic analysis was performed within a talus-based coordinate system constructed from the neutral foot position. The helical axis of motion, centroid motion, and vertical ground reaction force were calculated for the talus, cuboid and navicular at each position. All motion was referenced to a talar anatomic coordinate system.

RESULTS: The motion of the centroid of the cuboid and navicular occurred primarily between heel strike and foot flat. There was minimal motion of the centroid relative to the talus for the remainder of the stance phase of gait. From heel strike to foot flat the centroid of the cuboid and navicular translated 20.9+8.5 mm and 9.3+3.8 mm in the frontal plane, respectively. In contrast, for the remainder of the stance phase of gait, the cuboid and navicular translated 2.1+1.6 mm and 1.2+0.8 mm, respectively. This finding was consistent for the motion of the centroid of the cuboid and navicular in the coronal and sagittal planes, and suggests that there is little motion through the transverse tarsal joint from foot flat to toe off. The mean difference in orientation of the helical axes of motion for the cuboid and navicular from heel strike to foot flat was 1.8°+2.0° (Figure 2). The helical axes of motion for these two bones is similar in orientation, and this finding suggests that the cuboid and navicular are moving together from heel strike to foot flat.

Figure 2: Helical axis of motion the cuboid and navicular relative to the talus between heel strike and foot flat. The navicular and cuboid appear

to moving as a unit. DISCUSSION: The goal of this study was to elucidate the transverse tarsal joint locking mechanism in a cadaveric static gait simulator with simulated muscular and axial forces. Our findings of minimal relative motion between the cuboid and navicular suggest that the bones function as a unit. We also found that there is little motion in the transverse tarsal joint after foot flat, suggesting that it is essentially “locked” earlier in the stance phase of gait than predicted from previously published data. We did not see eversion of the subtalar joint during the mid-portion of the stance phase of gait that has been seen in previously published data. Our findings must be interpreted within the context of our study design. While our set-up was able to produce a reasonable simulation of gait, a static cadaveric study probably does not represent the subtlety and variability of human gait. Our reduced loading profile (50% of physiologic forces) may have minimized eversion of the subtalar joint and earlier locking of the transverse tarsal joint. Despite these limitations, our findings provide useful initial insight into the motion of the transverse tarsal joint, and suggest that the motion at this joint is likely more complex than originally described by Elftman1. SIGNIFIGANCE: Locking of the transverse tarsal joint creates a rigid foot and allows for efficient gait, and understanding how this mechanism works can effect the counseling and treatment of patients. This study uses a static cadaveric model of gait combined with biplanar fluoroscopy to elucidate the kinematics of the transverse tarsal joint. ACKNOWLEDGEMENTS: This study was funded with a grant from the AOFAS, Rhode Island Hospital Orthopaedic Foundation, and the Department of Orthopaedics. REFERENCES: 1. Elftman H. The Transverse Tarsal Joint and Its Control. Clin

Orthop, 1960; 16: 41-46. 2. Blackwood CB, Yuen TJ, Sangeorzan BJ, Ledoux WR. The

Midtarsal Joint Locking Mechanism. Foot Ankle Int, 2005; 26(12): 1074-1080.

Poster No. 0907 • ORS 2012 Annual Meeting