Patterns of Load-to-Strength Ratios Along the Spine in a Population-Based Cohort to Evaluate the Contribution of Spinal Loading to Vertebral Fractures

Abstract

Vertebral fractures (VFx) are common among older adults. Epidemiological studies report high occurrence of VFx at mid‐thoracic and thoracolumbar regions of the spine; however, reasons for this observation remain poorly understood. Prior reports of high ratios of spinal loading to vertebral strength in the thoracolumbar region suggest a possible biomechanical explanation. However, no studies have evaluated load‐to‐strength ratios (LSRs) throughout the spine for a large number of activities in a sizeable cohort. Thus, we performed a cross‐sectional study in a sample of adult men and women from a population‐based cohort to: 1) determine which activities cause the largest vertebral LSRs, and 2) examine patterns of LSRs along the spine for these high‐load activities. We used subject‐specific musculoskeletal models of the trunk to determine vertebral compressive loads for 109 activities in 250 individuals (aged 41 to 90 years, 50% women) from the Framingham Heart Study. Vertebral compressive strengths from T4 to L4 were calculated from computed tomography–based vertebral size and bone density measurements. We determined which activities caused maximum LSRs at each of these spinal levels. We identified nine activities that accounted for >95% of the maximum LSRs overall and at least 89.6% at each spinal level. The activity with the highest LSR varied by spinal level, and three distinct spinal regions could be identified by the activity producing maximum LSRs: lateral bending with a weight in one hand (upper thoracic), holding weights with elbows flexed (lower thoracic), and forward flexion with weight (lumbar). This study highlights the need to consider a range of lifting, holding, and non‐symmetric activities when evaluating vertebral LSRs. Moreover, we identified key activities that produce higher loading in multiple regions of the spine. These results provide the first guidance on what activities to consider when evaluating vertebral load‐to‐strength ratios in future studies, including those examining dynamic motions and the biomechanics of VFx. © 2020 American Society for Bone and Mineral Research (ASBMR).

Electromyographic Comparison of an Abdominal Rise on a Ball with a Traditional Crunch

“…The neutral position of the spine allows for the transmission of compressive forces to the entire surface of the vertebrae or intervertebral discs, significantly reducing localized pressure, which is one of the main causes of spinal injury. This is especially important for people who already have problems with the intervertebral discs and for people with osteoporosis [21,45]. Although the activation of ES is much lower when performing a TC than an ARB, a TC may be a risky exercise for patients with osteoporosis because of the high local load on the intervertebral discs and vertebrae.…”

“…The neutral posture of the spine distributes the load evenly among the vertebrae and intervertebral discs, reducing the risk of high local pressure [2] and injury [6]. The latter may be of particular interest in osteoporosis patients to prevent anterior collapse of the vertebrae [21].…”

Evaluation of Load-To-Strength Ratios in Metastatic Vertebrae and Comparison With Age- and Sex-Matched Healthy Individuals

“…Similarly, higher LSRs predict incident OVF (Wang et al, 2012;Kopperdahl et al, 2014). We have previously reported that holding a weight in flexed and upright postures produces high LSRs in the thoracolumbar region of the spine (Bruno et al, 2017a;Mokhtarzadeh et al, 2021), where OVF occurs most frequently, suggesting that the pattern of spinal loading is an important consideration in OVF (Wang et al, 2012;Kopperdahl et al, 2014). As a metastatic lesion is specific to a vertebral level and can degrade bone integrity far more rapidly than osteoporosis, PVF risk prediction requires a level-and activityspecific approach to evaluate spinal loading.…”

“…To eliminate negative BMD values due to air bubbles within the degassed vertebrae, CT values < 0 indicating air were set to a value of 0. Vertebral strength (Vs) was estimated in all specimens at all levels included in the CT scan using a previously developed regression equation (Mokhtarzadeh et al, 2021), Eq. 1:…”

“…Due to the difficulty of performing spinal loading measurements in vivo, in silico biomechanical models have been created to predict spinal loading throughout the thoracolumbar spine (Han et al, 2012;Bruno et al, 2017a;Bruno et al, 2017b). A recent study by Mokhtarzadeh et al (2021) employing a biomechanical modeling approach identified several activities that commonly cause large loads in the spine, highlighting that these activities create differing loads in different spinal regions. As metastases and PVF may occur throughout the spine, a better understanding of the pattern of vertebral loading at each specific level for common daily tasks is useful in algorithms for predicting fracture risk.…”