Systematic Quantification of Stabilizing Effects of Subtalar Joint Soft-Tissue Constraints in a Novel Cadaveric Model

SLR - November 2017 Garrett A. Melick

Reference: Pellegrini MJ, Glisson RR, Wurm M, Ousema PH, Romash MM, Nunley JA, Easley ME. Systematic Quantification of Stabilizing Effects of Subtalar Joint Soft-Tissue Constraints in a Novel Cadaveric Model. J Bone Joint Surg Am. 2016 May 18;98-A (10), 842–848.

Scientific Literature Review

 

Reviewed By: Garrett A. Melick, DPM

Residency Program: Cambridge Health Alliance, Cambridge, MA

Podiatric Relevance: With inversion injuries, attention is immediately drawn to assessment of anterior talofibular (ATFL) injury, but concomitant STJ instability is often overlooked. This article delineates the importance of certain ligamentous and retinacular constraints with regard to STJ instability, and via a thorough construct design, describes a systematic approach to proper clinical diagnosis. 

Methods: Level IV Diagnostic Cadaveric Study. Sixteen cadaveric leg specimens were used with a metal tube placed surrounding the tibial shaft and the fibula isolated from the apparatus. To anchor the construct, screws were inserted into the calcaneus. Cables, pulleys, levers and weights were employed to simulate motion in all planes. Calcaneal motion was measured with the ankle 10 degrees dorsiflexed, neutral, 10 degrees plantarflexed and 20 degrees plantarflexed. To test motions attributable to the STJ only, a monorail and Steinmann pin were placed across the ankle joint. Following removal of this construct, any extra motion was attributable to the ankle joint. Calcaneal motion was further observed after release of the inferior extensor retinaculum (IER) and sequential release of the CFL followed by CL and then ITCL (Group 1) or sequential release of CL, ITCL and CFL (Group 2). Repeated-measures ANOVA were employed for both groups.

Results:

  • IER release produced no significant change in calcaneal motion.
  • Calcaneal motion was only significantly altered for inversion or external rotation in both groups.
  • Group 1
    • Inversion
      • After CFL transection, increase noted with ankle dorsiflexed 10 degrees.
      • After CL transection, increase noted with ankle dorsiflexed 10 degrees and with the ankle neutral.
      • After ITCL transection, increase noted at all ankle conditions.
    • External Rotation
      • After CFL transection, increase noted with ankle dorsiflexed 10 degrees and plantarflexed 10 degrees.
      • After CL transection, increase noted with the ankle dorsiflexed 10 degrees, neutral, and plantarflexed 10 degrees.
      • After ITCL transection, no increase was noted at all static ankle conditions.
  • Group 2
    • Inversion: No significant change until final transection of the CFL, at which point inversion was significantly increased in all static ankle conditions.
    • External rotation: No significant increase.

Conclusions: This study demonstrates that the CFL is the most important static stabilizing structure of the STJ. Its insufficiency is most accurately assessed with the ankle in 10 degrees of passive dorsiflexion while applying an external rotation and varus force to the calcaneus. If this test produces increased inversion compared to the contralateral foot, advanced imaging should be considered to confirm the diagnosis and plan for CFL repair or reconstruction. Of course, the modified Broström technique provides great correction in the setting of both lateral ankle and STJ instability, but I have seen personally that primary ATFL repair is sometimes performed without giving proper attention to the CFL. Although not addressed in this paper, the dynamic nature of the STJ warrants testing for peroneal tendon subluxation in conjunction with testing for CFL insufficiency, as overinversion of the STJ causes the CFL to push the peroneal tendons against the superior peroneal retinaculum.