Introduction: Falls are a leading cause of death and disability in elderly patients, with more than 2 million serious injuries and healthcare costs exceeding $20 billion annually.1-2 In addition to physical injury, falls may result in substantial fear and psychological trauma (“post-fall syndrome”), leading to voluntarily diminished mobility for fear of recurrent falls and loss of independence.3 The risk of falls is especially elevated in degenerative lumbar spine patients since these patients frequently have functional deficits and gait abnormalities associated with nerve compression and pain-related disability.4 Several assessment tools have been developed to estimate a patient’s likelihood risk of falling. None of these measures estimate the contributions of the visual, vestibular, and somatosensory systems to fall risk, especially in patients with degenerative lumbar spine disease. Therefore, the purpose of this study was to assess the effects of vision, support surface, and adaptation to changing conditions on the cone of economy (CoE) and risk of falls in degenerative lumbar spine patients.
Methods: Seventy-one lumbar degenerative (LD) surgical candidates, consisting of 35 unilateral radiculopathy (UR) and 36 neurogenic claudication (NC) with bilateral symptoms patients, and 30 healthy controls were enrolled in the study. Patient reported outcome measures were collected prior to testing. Patients were subjected to a mock falling environment and performed a series of Romberg Tests in the CDP system. All patients and control subjects performed the Sensory Organization Tests (SOT) which include normal and perturbed stability, both with and without visual cues for 20 seconds with 3 repetitions (Figure 1).5 Cone of economy (CoE) and center of pressure (CoP) measurements were calculated. Mann-Whitney U tests were used to compare between subset conditions, and between spine patients and the healthy control group.
Results: Nearly all CoE and most CoP dimensions were found to be larger in LD patients compared to controls across nearly all subtests (p<0.05), with the largest dimensions generally observed in the surrounding and support sway testing condition. In LD patients, ODI and PROMIS Pain Interference were negatively correlated with CoE and CoP measurements (p<0.05). CoE dimensions were found to be larger in LD patients compared to controls across all subtests except eyes open sway surround with fixed support (coronal RoS: LD: 5.40 vs H: 4.00 cm, p>0.05). The ODI score was negatively correlated with CoE (sagittal RoS: r=-0.16, p<0.05; coronal RoS: r=-0.21, p<0.01; total sway: r=-0.21, p<0.01) and CoP (sagittal RoS: r=-0.18, p<0.05; coronal RoS: r=-0.22, p<0.01) measurements. Similar trend found with the PROMIS Physical Function and Pain Interference measurements.
Discussion: In this prospective investigation, body sway as a function of CoE and CoP was assessed using the CDP system and was found to be abnormally elevated in lumbar spine patients, especially when they were subjected to both increasing levels of visual and vestibular effort. By allowing patients to replicate motions that may result in a fall in a controlled environment, clinicians and scientists can better understand the cause of balance disorders and provide patients with lumbar degenerative disease individualized therapeutic optimization plans.