152 - Thin-walled Pressure Vessel Mechanics and Medial Tibial Stress Syndrome: Hoop Stress Elicited in the Crural Fascia During Dorsiflexion as Novel Shin Splint Etiology

Poster Board Number: 152
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Abstract Body : Introduction and Objective: The crural fascia (CF) has attachments directly along the shaft of the tibia throughout the length of the leg, enclosing the anterior, lateral, superficial and deep compartments. Because it encircles the leg in a grossly cylindrical fashion the CF may be subject to the same longitudinal and hoop stresses seen in gas or liquid-filled cylinders. Although there is a consensus that medial tibial stress syndrome (MTSS), aka “shin splints” could be caused by traction on the tibial periosteum by soft tissues such as muscle and fascia, identification of the specific mechanism has been elusive. Prior researchers have not considered the possibility that a measurable strain on the medial tibia could be produced by CF traction during gait and passive stretching, secondary to fluid pressure increases in the fascial compartments of the leg during these activities. Our team, led by a physical therapist/anatomist and biomechanical engineer, sought to explore this novel application of pressure vessel mechanics to this common and not fully understood orthopedic diagnosis. The purpose of the present research was, therefore, to measure hoop strain in the CF of a cadaver donor at the medial tibial border during a heel cord stretch.
Materials and Methods: Micro strain gauges (SG) (VPG Micro-Measurements, Raleigh, NC), were affixed to the CF of a cadaver donor to measure both hoop and longitudinal strain during passive stretch into dorsiflexion. Three horizontally oriented SGs were placed on the distal right leg of a cadaver donor, and a vertically oriented SG was placed in the posterior compartment of the donor’s left leg. SGs were placed in the middle and distal thirds of the leg to coincide with the segments of the tibia where shin splint symptoms are most commonly felt. Measurements were then taken from each of the SGs while a passive stretch into dorsiflexion was applied concurrently to the metatarsal heads by one investigator.
Results: Repeated heel cord stretches with a maximal force of 341 N were applied, resulting in the production of 182.96 x 10-3 mV/V hoop strain at the CF attachment to the medial tibial border in the distal third of the leg; and 138.00 x 10-3 mV/V hoop strain at the medial tibial border in the middle third of the leg. A maximum longitudinal strain in the CF of the superficial posterior compartment of 75.00 x 10-3 mV/V was elicited.
Conclusion: Our results showed that a heel cord stretch applied to a cadaver donor can elicit a measurable hoop strain within the CF attachment to the medial border of the tibia, in a grossly 2:1 manner consistent with the ratio of hoop to longitudinal strain seen with gases and liquids in a closed cylinder.
Significance: This research is significant because it examines a previously unexplored causal mechanism for this common musculoskeletal patient complaint. Understanding the etiology of MTSS will inform selection of appropriate prevention and treatment interventions for these patients. Further research is indicated to replicate these results in multiple post-mortem and living subjects.