
==== Front
N Am Spine Soc J
N Am Spine Soc J
North American Spine Society Journal
2666-5484
Elsevier

S2666-5484(24)00225-7
10.1016/j.xnsj.2024.100532
100532
Advances in Spinal Regenerative Therapies
Alignment in motion: Fall risk in spine patients and the effect of vision, support surface, and adaptation on the cone of economy
Haddas Ram PhD Ram_Haddas@URMC.Rochester.edu
a⁎
Singh Manjot BS b
Rubery Paul MD a
Rogerson Ashely MD a
Megas Andrew DO a
Molinari Robert MD a
Ramriez Gabriel MS a
Schmidt Tyler DO c
Daniels Alan H. MD b
Diebo Bassel G. MD b
Puvanesarajah Varun MD a
a Department of Orthopedics, University of Rochester Medical Center, Rochester, NY, United States
b Department of Orthopedics, Brown University, Providence, RI, United States
c Department of Neurosurgery, University of Rochester Medical Center, Rochester, NY, United States
⁎ Corresponding author. University of Rochester Medical Center, 601 Elmwood Ave, Box 665, Rochester, NY 14642. Ram_Haddas@URMC.Rochester.edu
27 7 2024
9 2024
27 7 2024
19 10053217 7 2024
22 7 2024
© 2024 The Author(s)
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Background

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.

Methods

Degenerative lumbar spine patients with radiculopathy (LD) and healthy subjects who were 35-70 years old without spine complaints were recruited. Patient reported outcome measures (PROMs) were collected prior to testing. Fall risk assessment was completed using Computer Dynamic Posturography (CDP), a computer-controlled balance machine that allows cone of economy (CoE) and cone of pressure (CoP) measurements. All patients completed Sensory Organization Tests (SOT) which include normal and perturbed stability, both with and without visual cues.

Results

In total, 43 spine patients and 12 healthy controls were included, with mean age 57.8 years, 39.5% females, and mean BMI of 29.3 kg/m2. Nearly all CoE and most CoP dimensions were found to be larger in LD patients compared to controls across nearly all subtests (p<.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<.05).

Conclusions

In this prospective study, body sway was assessed as a function of CoE and CoP using the CDP system and was found to be elevated in spine patients, especially when they experienced increasing levels of visual and vestibular stimulation. The ability to identify the primary drivers of balance disorders is essential in spine patients and may be helpful in the development of a patient-specific treatment plan, which may in the future aid with fall-prevention initiatives.

Keywords

Fall risk
Cone of economy
Center of pressure
Degenerative lumbar spine disease
Visual
Vestibular
Somatosensory
==== Body
pmcIntroduction

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 (“postfall 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 fall risk assessment tools have been developed to estimate a patient's likelihood of sustaining a fall. These tests include the Berg Balance Scale (BBS), Timed Up and Go (TUG), and Performance Oriented Mobility Assessment (POMA) [5]. Selecting the appropriate tool for patients with spine pathologies can be complex, as there is limited literature comparing the accuracy of these diagnostic measures [5,6]. The precision and dependability of these assessment tools is critical in the formation of effective fall prevention strategies for patients with spinal disorders.

In assessing fall risk, accurate measurement of the spine patient's cone of economy (CoE) is important. CoE dimensions are typically measured in a clinical- or laboratory-safe environment with the Romberg test [7,8]. Previous literature suggests that large sway (i.e., larger CoE dimensions) increases the risk of falls [[7], [8], [9]]. However, this is not always representative of an individual patients’ full capacity of balance and consequent fall risk. Recently, an alternative test using Computer Dynamic Posturography (CDP) was introduced to further characterize balance disorders in both stable and experimentally unstable environments. The CDP is a virtual reality computer-controlled balance device that measures contributions to balance from the visual, vestibular, and somatosensory systems. It may be especially useful in patients with lumbar spinal pathology since compression of the nerve roots can cause dysfunction of perceptive position sense, pressure, vibration, fine/light touch, pain, reflex mechanisms, and motor function [10]. The results of this test indicate the root source of fall risk (e.g. visual, vestibular, and somatosensory), which may then be used to develop a patient-specific treatment plan for spine patients. The purpose of this study was to assess the effects of vision, support surface, and adaptation to changing conditions, as measured by the CDP, on the CoE and risk of falls in degenerative lumbar spine patients.

Methods

Study design

This was a prospective, single-center, concurrent cohort study of degenerative lumbar spine patients and healthy subjects. Ethical approval was granted by the University of Rochester's Research Subjects Review Board (Reference: STUDY00008302). Written informed consent was provided by all patients prior to participation in this study.

Patient population

Degenerative lumbar spine patients (LD) who were scheduled for surgery were recruited. In addition, a convenience sample of healthy subjects (H) between the ages of 35 and 70 years old who had no orthopedic- or musculoskeletal-related symptoms or diagnoses was also recruited from the general population. Patients were excluded from this study if they were pregnant or had any prior history of lower extremity, cervical, thoracic, or lumbar spine surgery.

Study procedures

Assessments were conducted 1 week prior to surgery for the LD group and at a convenient time for the H group. Patient-Reported Outcomes Measurement Information System (PROMIS) function, pain interference, and mood, Oswestry Disability Index (ODI), and Tampa Scale for Kinesophobia (TSK) questionnaires were collected prior to testing. Fall risk assessment was completed using CDP, which measures Center of Pressure (CoP) using 2 force plates with the patient's eyes open and closed on a stable and moving surface (Bertec, Columbus, Ohio, USA) (Fig. 1). The CDP system influences the vestibular, visual, and proprioceptive systems using controlled motion of the floor and surroundings. As the patient performs this test, the CDP measures whether the patient is using their ankles or hips to stay balanced, as well as whether their center of gravity is maintained. In addition, patients were also fitted with a set of external reflective markers to measure traditional CoE using human motion capture (Vicon, Denver, Colorado, USA) [7,11]. All tests are performed with patients protected by a safety harness.Fig. 1 Computerized dynamic posturography with sway surround and sway support.

Fig 1

Patient 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. Each subtest, eyes open with fixed support (EOFS), eyes closed with fixed support (ECFS), eyes open sway surround with fixed support (EOSAFS), eyes open with sway support (EOSS), eyes closed with sway support (ECSS), and eyes open sway surround with sway support (EOSASS), was performed for 20 seconds with 3 repetitions (Fig. 2) [12].Fig. 2 Computerized dynamic posturography 6 Sensory Organization Tests.

Fig 2

Data acquisition

CoE kinematics were recorded at 100 Hz using a 6-camera system and were low-pass filtered using a 4th-order Butterworth filter at a 6 Hz cut-off frequency [11]. CoP was collected using 2 force plates. Both CoE and CoP measurements were calculated using a custom software algorithm (MATLAB R2024b, The Math Works, Natick, MA) [7,8,11,13]. CoE dimensions, which included the sagittal and coronal range of sway (RoS), were defined as the difference between minimum and maximum sway for each plane. Balance effort was calculated by the overall length of the head displacement line in all directions [7,8]. Finally, the SOT score was calculated based on individual equilibrium scores for each trial that are closer to zero, thus indicating that the individual's calculated maximum CoP displacement is closer to the theoretical limits of stability. Scores of 100 indicate perfect stability (i.e. zero sway).

Statistical analysis

Mann-Whitney U tests were used to compare between subset conditions, and between spine patients and the healthy control group. Mann-Whitney U was used to address issues of small sample size without any assumptions on the distribution of the measurements. Pearson's Correlation Coefficient (r) was calculated to investigate the correlation between the CoE and CoP outcomes with the patient reported outcome measurements (PROMs). Significance was defined as a p-value <.05 and was also adjusted for multiple comparisons using Bonferroni's Correction. Statistical analysis was done using Stata 16.1 StataCorp, College Station, Texas 77845.

Results

Patient characteristics

In total, 43 spine patients and 12 healthy controls were included in this study. The mean age was 57.8 years, 39.5% were females, and mean body mass index (BMI) was 29.3 kg/m2, with only BMI being significantly different across groups. Primary diagnoses and patient-reported outcomes are provided in Table 1.Table 1 Patient cohort demographics.

Table 1Variable	LD (N=43)	Control (N=12)	
Demographics	
Age (years)	57.81±17.62	52.58±14.36	
Female Sex	17 (39.5)	4 (33.33)	
Height (m)	1.73±0.09	1.75±0.10	
Weight (kg)	88.07±19.34	80.00±15.38	
BMI (kg/m2)	29.34±5.41*	25.28±4.05	
Primary Diagnosis	
Radiculopathy	18 (41.9)	-	
Spinal Stenosis	13 (30.2)	-	
Spondylolisthesis	6 (14.0)	-	
Other	6 (14.0)	-	
PROMs	
PROMIS Function	34.83±4.49	-	
PROMIS Pain Interference	66.67±5.05	-	
PROMIS Mood	50.58±8.90	-	
ODI	42.87±11.98	-	
TSK	41.97±7.50	-	
⁎ p<.05.

†p<0.01.

‡p<0.001 (adjusted for multiple comparisons using Bonferroni's Correction).

Categorical variables are presented as count (frequency) and continuous variables are presented as mean±standard deviation.

LD, lumbar degeneration; BMI, body mass index; PROMs, patient-reported outcome measures; PROMIS, patient-reported outcomes measurement information system; ODI, Oswestry Disability Index; TSK, Tampa Scale for Kinesophobia.

Cone of economy and cone of pressure assessments

CoE dimensions were found to be larger in LD patients compared to controls across all subtests except EOSASS (coronal RoS: LD: 5.40 vs H: 4.00 cm, p>.05) (Table 2, Fig. 3). However, only some of the CoP dimensions were found to be larger in LD patients compared to controls, including EOFS (sagittal RoS: LD: 2.87 vs H: 2.15 cm, p<.05), ECFS (sagittal RoS: LD: 3.63 vs H: 2.62 cm, p<.05; coronal RoS: LD: 1.89 vs H: 1.13 cm, p<.05), EOSS (coronal RoS: LD: 3.22 vs H: 2.28 cm, p<.05), ECSS (coronal RoS: LD: 3.92 vs H: 2.72 cm, p<.05), and EOSASS (sagittal RoS: LD: 11.91 vs H: 8.67 cm; total sway: LD: 34.48 vs H: 28.50 cm, p<.05) (Table 2, Fig. 3). Furthermore, the SOT total score was significantly lower in LD patients compared to control (LD: 65.74 vs H: 75.08, p<.01) (Table 2). In comparison to baseline measurements (EOFS), CoE and CoP dimensions were significantly larger for all subtests with surround and/or support sway across both LD and control patients. The dimension scores also increased in significance with increasing difficulty of subtest, with the exception of CoP total sway for control patients (Table 3).Table 2 Cone of economy and Center of Pressure during the Sensory Organization Tests with comparison between spine patients and healthy control.

Table 2Condition	CoE sagittal range of Sway (cm)	CoE coronal range of Sway (cm)	CoE total Sway (cm)	CoP sagittal Sway (cm)	CoP coronal Sway (cm)	CoP total Sway (cm)	SOT score (%)	
LD		
	
EOFS	5.41±2.90*	2.52±1.42*	22.60±8.74Ϯ	2.87±0.99*	1.56±0.86	25.41±6.99	65.74±
10.77‡	
ECFS	6.15±2.96*	2.73±1.45Ϯ	26.75±10.91Ϯ	3.63±1.40*	1.89±1.00Ϯ	26.72±6.96	
EOSAFS	7.24±3.44*	2.96±1.53Ϯ	27.79±11.82Ϯ	4.14±1.95	1.89±1.13*	27.31±6.87	
EOSS	11.47±4.29*	4.54±2.04*	51.04±21.09*	8.77±2.67	3.22±1.28*	30.33±7.20	
ECSS	16.28±6.55	5.36±2.32*	66.38±28.73Ϯ	11.72±4.11	3.92±1.82*	33.26±7.37	
EOSASS	17.31±7.20‡	5.40±2.52*	61.00±24.46‡	11.91±3.76*	3.66±1.63	34.48±9.21	
	
Control		
	
EOFS	3.58±1.09	1.49±0.81	15.12±4.91	2.15±0.62	1.10±0.53	26.60±4.92	75.08±6.75	
ECFS	4.28±1.16	1.56±0.66	17.50±4.50	2.62±0.73	1.13±0.46	26.06±4.35	
EOSAFS	5.06±1.87	1.64±0.81	18.17±5.42	3.20±1.35	1.25±0.67	26.42±3.68	
EOSS	8.58±2.62	3.21±0.73	37.44±9.93	7.43±1.41	2.28±0.50	27.71±6.31	
ECSS	13.23±3.32	3.61±0.87	46.62±10.48	10.42±2.68	2.72±0.58	31.18±5.59	
EOSASS	9.55±5.40	4.00±1.72	37.52±11.83	8.67±3.32	2.87±1.15	28.50±7.11	
	
p-values		
	
EOFS	.016	.013	.006	.021	.083	.221	.001	
ECFS	.028	.008	.004	.017	.005	.903	
EOSAFS	.048	.003	.009	.179	.042	.935	
EOSS	.026	.034	.026	.087	.022	.596	
ECSS	.212	.015	.005	.429	.044	.560	
EOSASS	.001	.035	.001	.014	.099	.075	
⁎ p<.05.

Ϯ p<.01.

‡ p<.001(adjusted for multiple comparisons using Bonferroni's Correction).

Variables are presented as mean±standard deviation.

CoP, Center of Pressure; SOT, Sensory Organization Test; LD, lumbar degeneration; EOFS, eyes open with fixed support; ECFS, eyes closed with fixed support; EOSAFS, eyes open sway surround with fixed support; EOSS, eyes open with sway support; ECSS, eyes closed with sway support; EOSASS, eyes open sway surround with sway support.

Fig. 3 Cone of economy and center of pressure measurements during the sensory organization tests for lumbar degenerative patients (Colors) and healthy control (Gray) in comparison to the baseline measurement (EOFS, eyes open with fixed support). ρ p<.05, Ϯ p<.01, ά p<.001(adjusted for multiple comparisons using Bonferroni's Correction). EOFS, eyes open with fixed support; ECFS, eyes closed with fixed support; EOSAFS, eyes open sway surround with fixed support; EOSS, eyes open with sway support, ECSS, eyes closed with sway support, EOSASS, eyes open sway surround with sway support.

Fig 3

Table 3 Cone of economy and Center of Pressure Measurements during the Sensory Organization Tests in Comparison to the Baseline (EOFS).

Table 3Condition	CoE sagittal range of Sway (cm)	CoE coronal range of Sway (cm)	CoE total Sway (cm)	CoP sagittal Sway (cm)	CoP coronal Sway (cm)	CoP total Sway (cm)	
LD	
	
ECFS	0.130	0.460	0.086	0.008Ϯ	0.107	0.206	
EOSAFS	0.008Ϯ	0.166	0.051	0.001Ϯ	0.197	0.107	
EOSS	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	
ECSS	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	
EOSASS	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	
	
Control	
	
ECFS	0.083	0.603	0.149	0.106	0.817	0.644	
EOSAFS	0.033*	0.603	0.184	0.028*	0.603	0.954	
EOSS	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	0.386	
ECSS	0.001‡	0.001‡	0.001‡	0.001‡	0.001‡	0.038*	
EOSASS	0.033*	0.001‡	0.001‡	0.001‡	0.001‡	0.273	
⁎ p<.05.

Ϯ p<.01.

‡ p<.001 (adjusted for multiple comparisons using Bonferroni's Correction).

CoP, Center of Pressure; LD, lumbar degeneration; EOFS, eyes open with fixed support; ECFS, eyes closed with fixed support; EOSAFS, eyes open sway surround with fixed support; EOSS, eyes open with sway support; ECSS, eyes closed with sway support; EOSASS, eyes open sway surround with sway support.

Balance efforts and patient outcomes

In spine patients, ODI was negatively correlated with CoE (sagittal RoS: r=−0.16, p<.05; coronal RoS: r=−0.21, p<.01; total sway: r=−0.21, p<.01) and CoP (sagittal RoS: r=−0.18, p<.05; coronal RoS: r=−0.22, p<.01) measurements (Table 4). In addition, PROMIS Physical Function was positively correlated with CoE (coronal RoS: r=0.15, p<.05; total sway: r=0.18, p<.01) while PROMIS Pain Interference was negatively correlated with CoE (total sway: r=−0.22, p<.001) and CoP (total sway: r=−0.17, p<.01) measurements (Table 4).Table 4 Correlation between cone of economy and Center of Pressure during the Sensory Organization Tests and patients reported outcomes measurement combining all conditions (N=43).

Table 4	PROMIS function	PROMIS Pain interference	PROMIS mood	ODI	TSK	
CoE Sagittal
Range of Sway	0.02
(−0.11, 0.15)	−0.09
(−0.22, 0.04)	−0.09
(−0.21, 0.04)	−0.16*
(−0.30, −0.01)	0.05
(−0.10, 0.20)	
CoE Coronal Range of Sway	0.15*
(0.02, 0.27)	−0.10
(−0.22, 0.03)	−0.01
(−0.14, 0.12)	−0.21Ϯ
(−0.35, −0.06)	0.03
(−0.12, 0.18)	
CoE Total Sway	0.18Ϯ
(0.06, 0.30)	−0.22‡
(−0.34, −0.10)	−0.06
(−0.19, 0.07)	−0.21Ϯ
(−0.34, -0.06)	0.05
(−0.10, 0.20)	
CoP Sagittal
Range of Sway	0.06
(−0.06, 0.19)	−0.11
(−0.24, 0.02)	−0.12
(−0.24, 0.01)	−0.18*
(−0.32, −0.03)	0.01
(−0.15, 0.16)	
CoP Coronal Range of Sway	0.12
(0.00, 0.25)	−0.12
(−0.25, 0.01)	−0.04
(−0.17, 0.09)	−0.22Ϯ
(−0.35, −0.07)	0.00
(−0.15, 0.15)	
CoP Total Sway	0.02
(−0.10, 0.15)	−0.17Ϯ
(−0.30, −0.04)	0.04
(−0.09, 0.16)	0.01
(−0.14, 0.16)	0.03
(−0.12, 0.18)	
SOT score	−0.06
(−0.36, 0.26)	0.16
(−0.16, 0.45)	0.23
(−0.09, 0.51)	0.27
(−0.10, 0.57)	−0.23
(−0.55, 0.14)	
⁎ p<.05.

Ϯ p<.01.

‡ p<.001 (adjusted for multiple comparisons using Bonferroni's Correction).

CoP, Center of Pressure; SOT, Sensory Organization Test; PROMIS, Patient-Reported Outcomes Measurement Information System; ODI, Oswestry Disability Index; TSK, Tampa Scale for Kinesophobia.

Discussion

Falls in elderly patients with degenerative lumbar spine disease are a major cause of morbidity and mortality. While several clinical examination tools have been developed to assess the risk of falls, they may not accurately determine risk. In this single-center prospective investigation of spine patients, we utilized the CDP, a computer-controlled balance assessment device, to demonstrate the influence vision, support surface, and adaptation to changing conditions have on spine patients’ fall risk. Specifically, we found that patients with degenerative lumbar spine disease, in comparison to healthy controls, have larger CoE dimension as seeing by greater sagittal, coronal, and total head range of sway, as well as larger CoP ranges. These dimensions tend to worsen with increasing visual and proprioceptive effort, thus highlighting the role of these systems on the risk of falls.

Numerous studies have previously validated the BBS, TUG, and POMA tests in assessing fall risk among geriatric patients [6]. However, there are unique challenges associated with spinal disorders that might not be fully captured by these tools [5,14]. Changes in the patient's balance and altered spinal biomechanics in this population could skew results, potentially leading to inaccuracies in identifying patients who are at risk of falling [15]. Additionally, while balance is maintained through the vestibular, visual, and proprioceptive/somatosensory inputs, broader health metrics that were not controlled in this study including reflex mechanisms, muscle tone, strength, range of motion, and motor skills, are also known to aid in the prevention of falls as well. Unfortunately, these systems degenerate with natural aging and are especially worse in spine patients [16]. CDP, as shown in this study, may prove to be valuable. Utilizing force plates and sensory testing, CDP gauges a person's ability to maintain stability across varying sensory conditions. This technology may equip clinicians with an objective metric to identify spine patients at increased risk of sustaining a fall due to their radiculopathy and/or concomitant subclinical myelopathy, though further studies would be needed to delineate the differences between the 2.

In particular, the CDP provides an assessment of the contributions of the visual, vestibular, and somatosensory systems on balance effort in a controlled environment. The resulting measures of patient CoE and CoP offer a quantitative measure of overall sway, as well as estimating risk of a fall. In this study, spine patients were observed to have higher CoE and CoP dimensions than controls, with the largest dimensions generally observed in the surrounding and support sway testing condition. The effects of vision on standing balance, especially with swaying support surface, have been well-studied. The visual position and velocity of sway by the support surface provides the body with the cues necessary to reduce sway variability and maintain balance [17,18]. Patients with degenerative lumbar spine disease are frequently more reliant on their vision for balance since their underlying spinal pathology often results in spinal cord or nerve root compression, which makes them less stable than age-matched controls [15]. This may explain why the spine patients in this cohort had higher sway even when only exposed to the surround sway testing condition. The CDP system may be useful in identifying and quantifying the contributions of each of the various balance systems to instability and likelihood of falls. Subsequent optimization of these systems in spine patients through vision checks, vestibular gait training, and other modalities may be a source of therapeutic benefit.

Pain and difficulty maintaining balance during walking have previously been identified as the primary drivers limiting ambulation in patients with degenerative lumbar spine disease [19]. Recent studies have specifically shown that reduced function in various balance control domains, especially proprioceptive and visual orientation, may be contributing to self-reported balance problems and, subsequent, walking limitations [20]. The present study further adds that pain, as measured using ODI and PROMIS Pain Interference scores, may be associated with increasing CoE and CoP dimensions. This could potentially limit ambulation and increase the risk of falls in these patients. A quantitative assessment of the extent of their sway using CoE and CoP measurements may hence serve as a reliable indicator of their functional outcomes.

The use of the CDP system extends beyond the degenerative lumbar spine disease patients and may also be highly applicable to spinal deformity patients. Previous literature has highlighted the importance of the visual, vestibular, and somatosensory system on balance in patients with adolescent idiopathic scoliosis [21]. The resulting body sway is maintained or even increased after deformity correction surgery, though it does tend to decrease gradually over longer follow-up [22]. The asymmetric posture of patients may be associated with balance impairments and correction of their long-standing postural problems through surgery may be associated with continued sway due to adaptation. CoE and CoP measurements, in this case, may be of clinical use to evaluate for sway range and improvement in sway range over time, thus mitigating their risk of falls. Future research should thus assess the role of this system in the clinical management of deformity patients.

A comprehensive, multidisciplinary strategy is essential to manage fall risk in spine patients. Currently, implementation of a specialized exercise program designed to help improve patient's strength, balance, and flexibility is recommended [23]. Physical therapists play a vital role in crafting personalized exercise plans that consider the unique needs of each patient. Therapeutic exercise can include aerobic activities, targeted balance exercises, and resistance training, to help the patient fortify their postural stability and diminish fall risk [24]. In addition to these exercise regimens, the utilization of assistive devices plays an essential role in enhancing mobility and safety among patients with spinal disorders. Occupational therapists also recommend various adaptive equipment and home modifications, to further curtail the risk of a fall [25]. Effective implementation of these modalities for spine patients requires an accurate individualized measure of fall risk. Individual CoE and CoP measurements with the CDP machine may be of clinical benefit.

The present study has several potential limitations. First, the CDP device may not provide a complete assessment of fall risk since it primarily provides quantitative estimates of CoE and CoP. Second, fall risk may also depend on muscle bulk and range of motion which were not assessed in this study. Third, there are inherent limitations of the accuracy of CoE and CoP measurements provided by the machine, and the clinically important difference in these measures is incompletely understood. Fourth, the study cohort was comprised of patients with various primary lumbar pathologies. The resultant sample size limitations preclude subanalysis of the effect of specific lumbar pathologies on fall risk. Fifth, inherent demographic differences among the cohorts, such as BMI, could have contributed to the observed differences in CoE and CoP. Finally, PROMs were completed prior to testing but they may have been more representative of their functional limitations had they been measured immediately after the testing.

Conclusions

Quantification of balance capacity and drivers of balance disorders in spine patients is important. 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 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.

Declaration of competing interests

One or more of the authors declare financial or professional relationships on ICMJE-NASSJ disclosure forms.

Funding

N/A.

Sources of Support

N/A.

Acknowledgments

N/A.

IRB

University of Rochester STUDY00008302.

FDA device/drug status: Not applicable.

Author disclosure: RH: Consulting: Medtronic (C) Grants: National Institute of Arthritis and Musculoskeletal and Skin Diseases (D), Scoliosis Research Society (E), Medtronic (F). MS: Nothing to disclose. PR: Nothing to disclose. AR: Nothing to disclose. AM: Nothing to disclose. RM: Nothing to disclose. GR: Nothing to disclose. TS: Nothing to disclose. AHD: Royalties: Stryker (E), Spineart (F), Medtronic (B); Consulting: Medtronic (C); Research Support (Investigator Salary, Staff/Material)^: Medtronic (F), Orthofix (D), Alphatec (F); Fellowship Support: Medtronic (F). BGD: Nothing to disclose. VP: Nothing to disclose.
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