Oral Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

PARASPINAL MUSCLE FIBRE STRUCTURAL AND CONTRACTILE CHARACTERISTICS DEMONSTRATE DISTINCT IRREGULARITIES IN SPINAL DEGENERATION AND DEFORMITY PATIENTS (#MP-5c)

Alex M. Noonan 1 , Masoud Malakoutian 2 , Iraj Dehghan-Hamani 2 , Stephen Lewis 3 , John Street 2 , Thomas R. Oxland 2 , Stephen H.M. Brown 1
  1. University of Guelph, Guelph, Ontario, Canada
  2. University of British Columbia, Vancouver, BC, Canada
  3. University of Toronto, Toronto, ON, Canada

INTRODUCTION: Aging of the spine results in a progressive kyphotic deformity and sagittal imbalance in 20-40% of the adult population [1]. Paraspinal and spinopelvic muscular dysfunction are often hypothesized to be a significant causative factor for spinal degeneration and deformity [2]; however, our fundamental understanding of paraspinal muscle (dys)function is poorly understood. Our objective was to measure and compare the intrinsic structural and contractile properties of muscle fibres from degenerative spine patients who are either sagittally balanced or imbalanced as well as to compare to healthy age-matched literature norms from a commonly studied lower limb muscle (vastus lateralis).

METHODS: Twelve degenerative surgical spine patients were recruited and categorized into group DEG (four patients) with no sagittal imbalance and no usage of compensatory mechanisms; group DEG-COMP (four patients) with no sagittal imbalance through use of compensatory mechanisms; and group DEG-COMP-UNBAL (four patients) with sagittal imbalance despite use of compensatory mechanisms. From each patient, eight biopsies were collected from right and left multifidus (MULT) and longissimus (LONG) for single fibre contractile and structural measurements.

RESULTS: Eight of 48 (17%) collected biopsies did not exhibit any contractile properties; in other words, the muscle tissue was completely dysfunctional. From the remaining biopsies, a total of 175 fibres were tested and statistically analyzed. Muscle fibre specific force (measure of intrinsic muscle force generating capability) was not different between groups for the MULT (p=0.47) but was greater in group DEG compared to group DEG-COMP-UNBAL for the LONG (p=0.02) (Figure 1). Values for both muscles in all three groups were generally lower than mean age- and fibre type-matched literature norms for vastus lateralis. Muscle fibre unloaded shortening velocity (measure of the maximum speed of contraction) was also greater in group DEG compared to group DEG-COMP-UNBAL for the LONG (p<0.05) but not the MULT. Values for both muscles in all three groups were in the same range as mean age- and fibre type-matched literature norms for vastus lateralis. Force sarcomere-length properties for both muscles were unusually variable both within and amongst patients across the groups. Thin filament (actin) lengths were in general shorter and more variable than published norms for human muscle.

DISCUSSION: This study is the first to show a heightened intrinsic contractile muscle disorder in degenerative patients who are sagittally imbalanced (compared to degenerative sagittally balanced patients); this was most apparent in the LONG muscle. Additionally, there are clear indications that degenerative spine patients (all groups) have intrinsic force sarcomere-length properties that are dysregulated. This provides important insight into the pathophysiology of muscle weakness in spinal degenerative and deformity patients.

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  1. [1] Kado DM, Prenovost K, Crandall C (2007) Narrative review: hyperkyphosis in older persons. Ann Intern Med 147:330–338.
  2. [2] Roghani T, Zavieh MK, Manshadi FD, King N, Katzman W (2016) Age-related hyperkyphosis: update of its potential causes and clinical impacts - narrative review. Aging Clin Exp Res 1-11.