Evaluation of Sarcopenia and Muscle Biomechanics in Older Adults After Lumbar Fusion Surgery

Abstract Background: Lumbar fusion (LF) surgery successfully restores the mechanical stability of the spine; however, postoperative kinesiophobia and complications can trigger secondary sarcopenia. Conventional diagnostic algorithms focus on muscle mass and active strength, leading to the neglect of passive viscoelastic alterations in muscle tissue. This study aimed to investigate the prevalence of secondary sarcopenia and changes in in vivo muscle biomechanics in patients undergoing LF surgery, using ultrasonography and digital myotonometry methods. Methods: This single-center, prospective, comparative, cross-sectional study included 56 older patients with lumbar spinal stenosis. It comprised 31 patients with a history of lumbar fusion (LF) surgery and a control group of 25 patients undergoing conservative treatment, matched for age and body mass index. Sarcopenia staging was performed using ISarcoPRM and EWGSOP2 diagnostic criteria. Appendicular muscle mass was measured via the ultrasound-based "Sonographic Thigh Adjustment Ratio" (STAR). The passive viscoelastic properties of the rectus femoris (RF), tibialis anterior, medial gastrocnemius, and lumbar extensor muscles were assessed using a handheld digital myotonometer.