Acute Surgical Injury Alters the Tensile Properties of Thoracolumbar Fascia in a Porcine Model

Abstract

Recent work utilizing ultrasound imaging demonstrated that individuals with low back pain (LBP) have increased thickness and decreased mobility of the thoracolumbar fascia (TLF), an indication that the TLF may play a role in LBP. This study used a porcine injury model (microsurgically induced local injury)-shown to produce similar results to those observed in humans with LBP-to test the hypothesis that TLF mechanical properties may also be altered in patients with LBP. Perimuscular TLF tissue was harvested from the noninjured side of vertebral level L3-4 in pigs randomized into either control (n = 5) or injured (n = 5) groups. All samples were tested with a displacement-controlled biaxial testing system using the following protocol: cyclic loading/unloading and stress relaxation tests at 25%, 35%, and then 45% of their resting length. Tissue anisotropy was also explored by comparing responses to loading in longitudinal and transverse orientations. Tissues from injured pigs were found to have greater stretch-stretch ratio moduli (measure of tissue stiffness), less energy dissipation, and less stress decay compared to tissues from control pigs. Responses across these variables also depended on loading orientation.

Clinical significance: these findings suggest that a focal TLF injury can produce impairments in tissue mechanical properties away from the injured area itself. This could contribute to some of the functional abnormalities observed in human LBP.

Fig. 1

Samples were extracted from each strip of tissue (a) and labeled according to the region they were taken from for consistency (b)

Fig. 2

TLF samples mounted for testing in the uniaxial longitudinal (a), transverse (b), and biaxial (c) conditions. Once mounted the testing apparatus was enclosed in a temperature and humidity controlled environment to ensure consistent hydration (d).

Fig. 3

Representative data of a control sample undergoing UL tension in (a) cyclic loading (fourth cycle shown) and (b) stress-relaxation. Both tests are depicted for the 35% stretch condition.

Fig. 4

Tensile testing results: (a) SS modulus, (b) strain energy, (c) hysteresis, and (d) stress decay compared between injured and control tissues at each stretch level. Average values depicted for each measure are collapsed across all orientations and loading conditions. Error bars represent the standard error associated with each mean. Significant differences between injured and control values are denoted by “*”.