Introduction: Dubousset first introduced the concept of the cone of economy (CoE) as a reference to the area of standing posture that minimizes energy expenditure. Two decades later, Haddas et al. developed a method to quantify the CoE. This concept has been quickly adopted and has made a significant impact on our understanding of concepts such as sagittal balance and restoration of alignment to decrease the physiologic burden of gait and balance. As imbalance increases, the patient deviates from the center of the cone, resulting in a larger CoE. The resources currently required to collect CoE data are substantial as it requires a full array of motion capture sensors in a gait lab run with highly-trained staff. This is a significant hurdle to the widespread clinical use of CoE measurements. Haddas et al established a cheaper way, although still limited to a lab or clinical setting, to quantify the CoE using a force platform. Therefore, there will be a need for simple, objective measures to summarize the complexity of modern motion tracking data sets to simple, clinically meaningful, and interpretable terms. Therefore, the purpose of this study was to compare CoE between spine patients and controls in their home-based environment.

Methods: Twelves Lumbar Degenerative surgical candidates (LD; Age: 59.6, Height: 1.68 m, Weight: 71.5 kg) and 12 healthy controls (C; Age: 46.1, Height: 1.74 m, Weight: 80.1 kg) wore a small sensor (30 x 44 x 8mm, weight: 12 grams) with a patch on T1 for 24 hours. The sensor detected trunk sway and range of motion (RoM) for different types of activities during the day and also captured the patient’s level of activity in the patient’s home.   

Results: Balance effort and CoE dimensions were found to be significantly greater in degenerative lumbar spinal pathologies patients compared to controls. Standing and walking Range of Sway (RoS) found to be significantly larger in both sagittal (Standing: LD: 7.9° vs C: 5.8°, p<0.050) and coronal (Standing: LD: 7.2° vs C: 3.2°, p<0.050; Walking: LD: 18.4° vs C: 13.1°, p<0.001) planes in spine patients in comparison to controls (Figure 1). Moreover, patients with degenerative lumbar spinal pathologies presented with a lower level of activity (Walking:4.7%, Standing: 11.6%, Sitting: 25.3%) in comparison to controls (Walking:7.9%, Standing: 21.7%, Sitting: 17.1%).

Discussion: The overall goal of this study was achieved by providing surgeons with a practical method for producing home-based objective global balance data via CoE measurements from a wearable device. Several benefits are anticipated from this quantitative tool to assist with preoperative planning for patient-specific alignment objectives and also prognostic information, recovery monitoring, and treatment data. More physicians may consider incorporating this technology into their clinical practice as wearable devices are relatively affordable, portable, and straightforward to use. Moreover, using this data with the Haddas’ CoE classification system will help to identify patients that may benefit from surgery and guide their postoperative prognosis.