Deformation behavior of the iliotibial tract under different states of fixation

Abstract 

Background and objective

The iliotibial tract (tract) is an important structure for the biomechanics of both the hip and knee joint. While a detailed characterization of its mechanical properties might help to better understand its specific role in the load transfer from the pelvis to femur and tibia, determination of those properties is complicated by its particular structure of thin fibers in the fresh state. Moreover, although the tracts mechanical properties are often derived from cadaveric material chemically fixed with either ethanol or formaldehyde, the influence of such fixation methods remains to be elucidated. Aim of this study was to determine Young's modulus (tensile modulus, YM) of the tract. We hypothesized that either ethanol or formaldehyde fixation would significantly increase the YM compared to the tracts condition in a fresh state.

Material and methods

13 specimens of tract were gained from donators. The ends of the probes were plastinated with resin creating a sharp interface between the clamp and the probe to prevent material slippage. The specimens were measured in their fresh state, under ethanol- and formaldehyde-fixed conditions and re-measured after rinsing with tap water.

Results

The YM of the fresh probes averaged 397.3N/mm² with a standard deviation (SD) of 151.5N/mm². The YM of the ethanol-fixed specimens was significantly higher (673.2N/mm², SD 328.5N/mm², p<0.05). After rinsing with tap water, the YM decreased to 95% of the fresh condition value (377.4N/mm², SD 144.5N/mm², non-significant change from fresh). After formaldehyde fixation, the YM reached 490.3N/mm² (SD 143.0N/mm², p<0.05). When the formaldehyde-fixed specimens were rinsed, the YM was 114% of the value of the fresh condition (452.6N/mm², SD 115.1N/mm², non-significant change from fresh).

Conclusions

This study found a significant influence of the chemical fixation method on the YM of the IT tract. If such fixation is required, our results suggest using a treatment with ethanol and subsequent rinsing that results in minimal changes to the tracts YM. Furthermore, plastination of the ends of the specimens could be crucial to allow in vitro determination of valid YM of ligaments data that can then be integrated with confidence in further finite element analyses.

Keywords: Biomechanics, Fixation, Formaldehyde, Finite elements, Iliotibial tract, Ligament, Lower extremity, Pelvis, Young's modulus