Purpose: We aimed to identify whether osteoporosis was associated with intervertebral disc degeneration (IVDD), Modic changes, and fatty infiltration in the paraspinal muscles at all lumbar levels and to understand their relationship with each other in the process of proximal junctional disorders.
Methods: Age- and gender-matched osteoporotic and non-osteoporotic subjects with chronic low back pain were evaluated in terms of IVDD, Modic changes, and fatty infiltration in the multifidus, erector spinae, and psoas at all lumbar levels. We tested our findings in a separate, independent sample of subjects operated up to upper lumbar levels.
Results: Patients with osteoporosis at the lumbar spine had lower Pfirrmann scores at L2-L3 level than those without osteoporosis. Patients with osteoporosis at the lumbar spine had fattier psoas muscles at L1-L2, L2-L3, and L5-S1 levels whereas those with osteoporosis at the femoral neck had fattier psoas muscles at only L1-L2 level. In the second part of the study, we observed that patients with fattier psoas muscle at the upper instrumented levels had proximal junctional disorders.
Conclusion: Impaired extension of the upper lumbar spine due to fatty psoas could be the underlying mechanism of proximal junctional disorders following surgery for degenerative spine disorders (DSD) in patients with osteoporosis. We strongly recommend the assessment of paraspinal muscles, particularly the psoas, as an inevitable part of preoperative planning in patients with DSD and osteoporosis.