Age-sensitivity of time-related in vivo deformability of human lumbar motion segments and discs in pure centric tension.

The goal of this study was to document the effect of aging, sex and disc level on time-dependent in vivo tensile deformability of human lumbar-lumbosacral motion segments and discs in pure centric tension, when the contracting effect of muscles can be neglected. Elongations of segments L3-L4, L4-L5 and L5-S1 were measured during the usual suspension hydrotraction therapy of patients, by using a subaqual ultrasound measuring method reported in (Kurutz et al., 2002a, 2003). Patients were suspended cervically in lukewarm water for 20 min, loaded by 20-20 N lead weights on ankles. The mean initial elastic elongations (strains) of segments or discs were about 0.8 mm (10%) for patients under 40 years; 0.5 mm (6%) between 40-60 years; and 0.2 mm (3%) over 60 years. The mean final viscoelastic elongations were 1.5 mm (18%) under 40 years; 1.2 mm (15%) between 40-60 years; and 0.6 mm (7%) over 60 years. In the beginning/end of the treatment, patients of extended segments were on average 6/8 years younger than those with unextended ones. Based on the in vivo measured elongations, initial tensile stiffness was obtained in terms of aging, sex and disc level. For the above age-classes, the approximate mean tensile stiffness of less/more degenerated lumbar FSUs or discs were about 600/800, 800/1000 and 1800/2800 N/mm, respectively. A new terminology, the so-called age-sensitivity has been introduced as a value of 0.01-0.04 mm/year elongation capacity decrease per a year of aging, after the age of 35. No significant difference was found between sexes regarding age-dependence in tension.