Classic degenerative disc disease is a serious health problem worldwide, whose etiological basis-mechanical stimulus, biochemical changes, or natural aging-is poorly understood. Animal models are critical to the study of degenerative disc disease initiation and progression and for attempts to regulate, ameliorate, or eliminate it. The macaque represents a primate model with natural disc degeneration that might serve to advance the field; we aimed to provide radiographic (morphologic) and biomechanical evidence of natural disc degeneration in this model. A factorial study design was used to examine the relationship between the radiographic appearance of disc degeneration and its biomechanical consequences. Eighteen macaques of advanced age (22.3 AE 0.9 years) had radiographs taken to assess the degree of thoracolumbar intervertebral disc degeneration using a standard atlas method. Each spine was harvested and dynamic biomechanical tests were performed. Advancing disc degeneration (degree of disc space narrowing and osteophytosis) was associated with increased stiffness, decreased energy absorption, and increased natural frequency of the intervertebral disc. These associations linking the dynamics of the intervertebral disc and its degree of degeneration are similar to those found in humans. Our results indicate the macaque model with morphologic and biomechanical efficacy could aid in understanding the progression of disc degeneration and in developing therapeutic strategies to prevent or inhibit its course. Keywords: intervertebral disc; disc degeneration; Macaca fascicularis; disc dynamics; biomechanics Lumbar intervertebral discs change morphologically, biochemically, and biomechanically with advancing age, 1-10 changes that are characterized as disc degeneration and are implicated as the origin of low back pain. Unfortunately, the initiating and perpetuating factors of disc degeneration are unknown, so despite the pain, disability, and economic loss associated with disc degeneration, intervention and mitigation strategies cannot effectively proceed. Morphologically, dehydration and diminished cellularity of the nucleus pulposus and disorganization and lesions of the annulus fibrosus demarcate disc degeneration. These changes manifest as decreased disc height, increased radial bulging, and osteophyte formation. 11,12 Morphologic changes are intrinsically tied to the biochemistry and biomechanics of the system, and visible and radiographic changes are used to define gradations of disc degeneration. [13][14][15][16] The altered biomechanical response of degenerate disc tissues have been measured. [2][3][4][17][18][19][20][21][22][23][24] Disc stiffness decreases with low-grade degeneration and increases with the most severe degeneration, while energy absorption decreases throughout degeneration. Further, spinal segment range of motion and neutral zone increase with advancing degeneration up to the most severely degenerated discs, where these properties reverse course with increasing stiffness. Unfortun...