Posture Analysis and Center of Gravity Assessment: A Preliminary Review of Adult Volunteers and Adult Scoliosis Patients

• (a - SOFCOT, France; MSD)

Introduction: The global balance of the spine is usually assessed by a set of clinical and radiological parameters. However radiological parameters do not represent the true gravity line of the patient. The goals of this project are to assess the relationship between the commonly employed C7 plumbline and the true center of gravity (COG) in a set of volunteers and adult patients suffering from Scoliosis.

Materials and Methods: This is a prospective study including adult volunteers and patients (age >20 years old). The asymptomatic group included 27 subjects (mean age 50 y.o., range 22-84) and the scoliosis patient group included 41subjects (mean age 59 y.o., range 20-88). A simultaneous assessment of the radiological spinal posture and the floor projection of the COG on a force plate (Zebris(r)) were performed. The X-rays were obtained in a freestanding on the force plate (its center was positioned with regard to the center of the film holder), fingers on the collar bones, elbows flexed at 45º. The force plate was positioned on a manually powered rotating platform (anterior posterior and lateral X-rays films were obtained without modifying subject position). All films were digitized and computerized measurement (Spineview2(r) software) was performed. The location of the COG (obtained from force plate data) was projected on the full spine X-rays and correlated to the C7 Plumbline position. The Wilcoxon(r) signed rank test was applied to determine if two pairs of samples were significantly different (level of significance alpha= 0,050).

Results: The plumbline from C7 did not correlate consistently with the true COG; we found a discrepancy between the positioning of the C7 plumbline (PLC7) and the COG line (GL) in both planes (P-value: 0.000). The frontal discrepancy (Ap (GL-PLC7)), for the volunteer group, min -8 mm (GL on a left position comparing to the PLC7), mean: +31mm, max: +66mm (GL on a right position comparing to PLC7), standard deviation 15mm, for the scoliosis group, min:-72mm, mean: +30mm, max: +69mm, SD: 25mm. The sagittal discrepancy (Lat (GLPLC7)), for the volunteers group, min:-130mm (GL on a forward position comparing to PLC7), mean:-58mm, max: +31mm (GL on a backward position comparing to PLC7), SD: 34mm, for the scoliosis group min:-90mm, mean:- 41mm, max: +57 mm, SD: 35mm. The discrepancy between the C7 plumbline and the true COG (in the frontal plane) was consistently larger in the scoliosis group when compared to the volunteer group.

Conclusions: This study has demonstrated that the commonly applied C7 Plumbline is not an accurate reflection of global spine balance. Significant discrepancy in volunteer adults and more so in Scoliosis patients is noted between PLC7 and COG. Further study in this area is warranted and may reveal a more reproducible and reliable assessment of spinal balance.

• If noted, the author indicates something of value received. The codes are identified as: a-research or institutional support; b-miscellaneous funding; c-stock or stock options; d-royalties; e-other financial or material support.