PT  - JOURNAL ARTICLE
AU  - Sawa, Anna G. U.
AU  - de Andrada Pereira, Bernardo
AU  - Rodriguez-Martinez, Nestor G.
AU  - Reyes, Phillip M.
AU  - Kelly, Brian P.
AU  - Crawford, Neil R.
TI  - In Vitro Biomechanics of Human Cadaveric Cervical Spines With Mature Fusion
AID  - 10.14444/8114
DP  - 2021 Sep 24
TA  - International Journal of Spine Surgery
PG  - 8114
4099  - https://www.ijssurgery.com/content/early/2021/09/20/8114.short
4100  - https://www.ijssurgery.com/content/early/2021/09/20/8114.full
AB  - Background This study sought to compare index and adjacent-level biomechanics of cadaveric specimens with mature fusion versus normal spines in intact and acutely fused conditions.Methods Eight human cadaveric cervical spines with mature fusion across 1 to 3 levels were studied. Intervertebral angular range of motion (ROM) was determined at fused and adjacent levels during pure moments inducing flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Mature fusion data were compared to data from normal spine specimens tested intact and then with a 1-level anterior plate/graft (fresh fixation). Bone qualities were compared using dual-energy x-ray absorptiometry.Results Mean bone mineral density was significantly greater in mature fusion spines (0.632 ± 0.239 g/cm2) than in normal spines (0.489 ± 0.195 g/cm2) (P < .001). Mean ROM for levels with mature fusion was 42% (FE), 42% (LB), and 29% (AR) of the mean same-level ROM in freshly fixated specimens (P ≤ .045). The mean adjacent-level ROM in spines with mature fusion was less than in normal spines (matched levels) in all directions, with the greatest difference 1 level below fusion (FE: −38%, P < .001; LB: −42%, P < .001; AR: −49%, P = .001), followed by 1 level above fusion (FE: −23%, P = .04; LB: −22%, P = .07; AR: −28%, P = .02) and 2 levels above fusion (FE: −20%, P = .08; LB: −18%, P = .11; AR: −31%, P = .009). Mature fusion reduced the magnitude of coupled LB during AR at C6-7 and C7-T1 (P ≤ .03).Conclusion Cervical spine segments with mature fusion have higher bone mass, are less flexible than freshly fixed spines, and have reduced mobility at adjacent levels.