Microstructural damage in arterial tissue exposed to repeated tensile strains

Vertebral artery (VA) damage has been anecdotally linked to high-speed, low-amplitude spinal manipulative treatments (SMTs) of the neck. Apart from a single study quantifying the maximum stresses and strains imposed on the VA during cervical SMT, there are no data on the mechanics of the VA for this treatment modality, and there is no information on the possible long-term effects of repeat exposure to cervical SMT. The purpose of this study was to quantify microstructural damage in arterial tissue exposed to repeat strain loading of a magnitude similar to the maximum strains measured in the VA during high-speed, low-amplitude cervical SMT.

Twenty-four test specimens from cadaveric rabbit ascending aorta were divided into 2 control groups (n = 12) and 2 experimental groups (n = 6 each). Specimens were exposed to 1000 strain cycles of 0.06 and 0.30 of their in situ length. A pathologist, blinded to the experimental groups, assessed microstructural changes in the arteries using quantitative histology. Pearson chi(2) analysis (alpha = .05) was used to assess differences in tissue microstructure between groups.

Control and 0.06 strain tissues were statistically the same (P = .406), whereas the 0.30 strain group showed microstructural damage beyond that seen in the control group (P = .024).

We conclude that cadaveric rabbit arterial tissue similar in size and mechanical properties of that of the human VA can withstand repeat strains of magnitudes and rates similar to those measured in the cadaveric VA during cervical SMT without incurring microstructural damage beyond control levels.