How to Screen for Lumbar Spine Stiffness in Patients Awaiting Total Hip Arthroplasty.

BACKGROUND: This study aimed to (1) define the prevalence of spinopelvic abnormalities among patients who have hip osteoarthritis (OA) and controls (asymptomatic volunteers) and (2) identify factors that reliably predict the presence of lumbar spine stiffness. METHODS: This is a prospective, cross-sectional, case-cohort study of patients who have end-stage primary hip OA, who underwent primary total hip arthroplasty (THA). Patients were compared with a cohort of asymptomatic volunteers, matched for age, sex, and body mass index (BMI), serving as a control group. Spinopelvic pathologies were defined as: lumbar spine flatback deformity (difference of 10 or more degrees for pelvic incidence minus lumbar lordosis angle), a standing sagittal pelvic tilt of 19° or more and lumbar spine stiffness (lumbar flexion of less than 20° between both postures). RESULTS: The prevalence of spinopelvic pathologies was similar between patients and controls (flatback deformity: 16% versus 10%, P = .209; standing pelvic tilt >19°: 17% versus 24%, P = .218; lumbar spine stiffness: 6% versus 5%, P = .827). Age over 65 years-old and standing lumbar lordosis angle less than 45° were associated with high sensitivity and specificity for identifying lumbar spine stiffness (age >65 years: 82% and 66%; standing lumbar lordosis angle <45°: 85% and 73%). CONCLUSION: The presence of end-stage hip osteoarthritis was not associated with increased prevalence of adverse spinopelvic characteristics compared to matched, asymptomatic volunteers. Age and LLstanding are the strongest predictors of lumbar spine flexion and can guide clinical practice on when to obtain additional radiographs for patients who have hip OA before arthroplasty to identify at-risk patients. LEVEL OF EVIDENCE: II (prospective, cohort study).

The Current Proposed Total Hip Arthroplasty Surgical Planning Guidelines Based on Classification of Spine Stiffness May be Flawed Due to Incorrect Assumptions.

BACKGROUND: The available classifications and preoperative planning tools for total hip arthroplasty assume that: 1) there is no variation in the sagittal pelvic tilt (SPT) if the radiographs are repeated, and 2) there is no significant change in the postoperative SPT postoperatively. We hypothesized that there would be significant differences in postoperative SPT tilt as measured by the sacral slope, thus rendering the current classifications and tools flawed. METHODS: This study was a multicenter, retrospective analysis of preoperative and postoperative (1.5-6 months) full-body imaging of 237 primary total hip arthroplasty (standing and sitting positions). Patients were categorized as 1) stiff spine (standing sacral slope sitting sacral slope < 10°) and 2) normal spine (standing sacral slope-sitting sacral slope ≥ 10°). Results were compared using the paired t-test. The posthoc power analysis showed a power of 0.99. RESULTS: The difference in mean standing and sitting sacral slope between the preoperative and postoperative measurements was 1°. However, in standing position, this difference was more than 10° in 14.4% of patients. In the sitting position, this difference was more than 10° in 34.2% of patients and more than 20° in 9.8% of patients. Postoperatively, 32.5% of patients switched groups based on the classification, which rendered the preoperative planning suggested by the current classifications flawed. CONCLUSION: Current preoperative planning and classifications are based on a single acquisition of preoperative radiographs without the incorporation of possible postoperative changes in SPT. Validated classifications and planning tools should incorporate repeated measurements to determine the mean and variance in SPT and consider the significant postoperative changes in SPT.

Current Concepts in Diagnosis and Management of Patients Undergoing Total Hip Replacement with Concurrent Disorders of Spinopelvic Anatomy: A Narrative Review.

Despite the high success rate of primary total hip replacement (THR), a significant early revision rate remains, which is largely attributed to instability and dislocations. Despite the implants being placed according to the safe zone philosophy of Lewinnek, occurrence of THR dislocation is not an uncommon complication. Large diagnostic and computational model studies have shown variability in patients' mobility based on the individual anatomic and functional relationship of the hip-pelvis-spine complex. The absolute and relative position of hip replacement components changes throughout motion of the patient's body. In the case of spinopelvic pathology such as spine stiffness, the system reaches abnormal positional states, as shown with computerized models. The clinical result of such pathologic hip positioning is edge loading, implant impingement, or even joint dislocation. To prevent such complications, surgeons must change the dogma of single correct implant positioning and take into account patients' individualized anatomy and function. It is essential to broaden the standard diagnostics and their anatomical interpretation, and correct the pre-operative surgical planning. The need for correct and personalized implant placement pushes forward the development and adaptation of novel technologies in THR, such as robotics. In this current concepts narrative review, we simplify the spinopelvic biomechanics and pathoanatomy, the relevant anatomical terminology, and the diagnosis and management algorithms most commonly used today.

The Effects of Isometric Fatigue on Trunk Muscle Stiffness: Implications for Shear-Wave Elastography Measurements.

Muscle stiffness has been implicated as a possible factor in low back pain risk. There are few studies on the effects of isometric fatigue on the shear modulus of trunk muscles. This study aimed to investigate the effects of trunk isometric fatigue on the passive and active (during low and high-level contractions) shear moduli of the erector spinae (ES) and superficial and deep multifidus (MF) muscles. We assessed passive and active shear modulus using shear-wave elastography in healthy young participants (n = 22; 11 males, 11 females), before and after an isometric trunk extension fatigue protocol. Maximal voluntary force decreased from 771.2 ± 249.8 N before fatigue to 707.3 ± 204.1 N after fatigue (-8.64%; p = 0.003). Passive shear modulus was significantly decreased after fatigue in the MF muscle (p = 0.006-0.022; Cohen's d = 0.40-46), but not the ES muscle (p = 0.867). Active shear modulus during low-level contraction was not affected by fatigue (p = 0.697-0.701), while it was decreased during high-level contraction for both muscles (p = 0.011; d = 0.29-0.34). Sex-specific analysis indicated the decrease in ES shear modulus was significant in males (p = 0.015; d = 0.31), but not in females (p = 0.140). Conversely, the shear modulus in superficial MF had a statistically significant decrease in females (p = 0.002; d = 0.74) but not in males (p = 0.368). These results have important implications for further investigations of the mechanistic interaction between physical workloads, sex, muscle stiffness (and other variables affecting trunk stability and neuromuscular control), and the development/persistence of low back pain.

The effect of age on in-vivo spine stiffness, postures and discomfort responses during prolonged sitting exposures.

Many industrialised working populations are ageing and prolonged sitting exposures are prevalent across occupational sectors. The purpose of this work was to determine the effect of age and sex on passive spine stiffness, postures and discomfort in response to seated work. A total of 34 participants were recruited, with 17 older adults with an average age of (standard deviation) 63.7 (±3.9) years and 17 younger adults aged 23.8 (±5.0) years. Participants were asked to sit continuously for 90 min while typing. Baseline passive spine stiffness was higher in older adults at 40% flexion compared to younger adults (p = .0233). Older adults sat in less normalised flexion, at 33.4% (±16.4) compared to 60.9% (±20.2) in the younger group (p = .0003). Discomfort was higher among older adults in the neck, right shoulder and middle back regions (p < .0086). An understanding of age-specific responses to workplace exposures is essential to determine whether age-specific interventions are warranted.   Practitioner summary: Older adults had higher passive spine stiffness and sat with less flexion during prolonged sitting. Discomfort was higher among older adults and occurred earlier in the simulation compared to younger participants, indicating that interventions, such as walking breaks may need to be implemented earlier during sitting for aged workers.

Stiffness and axial pain are associated with the progression of calcification in a mouse model of diffuse idiopathic skeletal hyperostosis.

BACKGROUND: Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by progressive calcification of spinal tissues; however, the impact of calcification on pain and function is poorly understood. This study examined the association between progressive ectopic spine calcification in mice lacking equilibrative nucleoside transporter 1 (ENT1-/-), a preclinical model of DISH, and behavioral indicators of pain. METHODS: A longitudinal study design was used to assess radiating pain, axial discomfort, and physical function in wild-type and ENT1-/- mice at 2, 4, and 6 months. At endpoint, spinal cords were isolated for immunohistochemical analysis of astrocytes (GFAP), microglia (IBA1), and nociceptive innervation (CGRP). RESULTS: Increased spine calcification in ENT1-/- mice was associated with reductions in flexmaze exploration, vertical activity in an open field, and self-supporting behavior in tail suspension, suggesting flexion-induced discomfort or stiffness. Grip force during the axial stretch was also reduced in ENT1-/- mice at 6 months of age. Increased CGRP immunoreactivity was detected in the spinal cords of female and male ENT1-/- mice compared to wild-type. GFAP- and IBA1-immunoreactivity were increased in female ENT1-/- mice compared to wild-type, suggesting an increase in nociceptive innervation. CONCLUSION: These data suggest that ENT1-/- mice experience axial discomfort and/or stiffness and importantly that these features are detected during the early stages of spine calcification.

Spinopelvic Mobility Pattern and Acetabular Anteversion in Stiff Hips With Ankylosing Spondylitis After Total Hip Arthroplasty.

Background: Fused hips with spine stiffness in ankylosing spondylitis (AS) reduce spinopelvic mobility. We aimed to assess spinopelvic mobility pattern and acetabular anteversion in AS after total hip arthroplasty (THA). Material and methods: Ninety-four stiff hips in 58 AS individuals (mean age: 37.05) who underwent THA between 2012 and 2018 with a modified lateral approach were included. Twenty-three hips were fused, and 71 hips had mean flexion of 37.67°. Pelvic tilt, pelvic inclination, sacral slope (SS), and lumbar lordosis were correlated with THA, and functional outcomes were assessed at 34.6-month mean follow-up. Results: Thirty-seven had a stuck sitting pattern with stuck standing seen in 4 individuals. SS standing before and after THA were 25.08° and 27.30°. SS sitting was 8.99° compared to 16.80°. SS from sitting to standing was reduced (17.7°) in 17 individuals. Spine stiffness in extension was seen in 4 out of 37. Mean acetabular inclination after THA was 42.67°, and acetabular anteversion was 17.48°. Flexion after THA improved to mean 98.47°. Changes in SS from sitting to standing were correlated with THA (r-value: 0.93, P-value: .0001). The Harris Hip Score improved from 25.31 to 82.39 (P-value <.05), and the mean 12-item Short Form Survey at review was 52.18 and 59.55 (physical and mental components). The mean Western Ontario and Mc Master Universities Arthritis Index score was 17.56. Conclusions: Spinopelvic mobility change was <10° after THA in AS, stuck sitting was seen in 37 of 58 (63.8%), and stuck standing was seen in 4 of 58 (6.9%), including spine stiffness in flexion or extension. Acetabular anteversion assessed was 17.48° (standard deviation: 4.41), with significant functional improvement. Level of Evidence: Level 4.

Younger Patients Are Differentially Affected by Stiffness-Related Disability Following Adult Spinal Deformity Surgery.

OBJECTIVE: The Lumbar Stiffness Disability Index (LSDI) assesses impact of lumbar stiffness on activities of daily living. We hypothesized that patients <60 years old would perceive greater lumbar stiffness-related functional limitation following fusion for adult spinal deformity. METHODS: Patients completed the LSDI and Scoliosis Research Society 22 Questionnaire, Revised (SRS-22r) preoperatively and at 2 years postoperatively. The primary independent variable was patient age <60 versus ≥60. Multivariable regression analyses were used. RESULTS: Analysis included 267 patients. Patients <60 years old (51.3%) and ≥60 years old (48.7%) were evenly represented. In bivariable analysis, patients age <60 exhibited lower LSDI at baseline versus patients age ≥60 (25.7 vs. 35.5, ß -9.8, P < 0.0001), but a directionally smaller difference at 2 years (26.4 vs. 32.3, ß -5.8, P = 0.0147). LSDI was associated with lower SRS-22r total score among both age groups at baseline and 2 years (all P < 0.0001); the association was stronger among patients age <60 versus ≥60 at 2 years. LSDI was associated with SRS-22r satisfaction scores at 2 years among patients age <60 (P < 0.0001), but not patients age ≥60 (P = 0.2250). The difference in SRS-22r satisfaction per unit LSDI between patients <60 years old and ≥60 years old was significant (P = 0.0021). CONCLUSIONS: Among patients with adult spinal deformity managed operatively, higher LSDI was associated with inferior SRS-22r total score and satisfaction at 2 years postoperatively. The association between increased LSDI and worse patient-reported outcome measures was greater among patients age <60 versus ≥60. Preoperative counseling is needed for patients age <60 undergoing adult spinal deformity surgery regarding effects that lumbar stiffness may have on postoperative function and satisfaction.

Kinematic alignment versus conventional techniques for total hip arthroplasty: A retrospective case control study.

BACKGROUND: Residual complications of conventionally implanted hip components have only been partially reduced by improved implant design and higher surgical precision, and their occurrence is poorly predicted by the radiographic standing/supine cup orientation. This has raised awareness that conventional techniques may not aim for the correct component orientation target, and the lumbo-pelvic kinematics, which influences the functional acetabular orientation, may be of interest to further improve THA clinical outcomes. This has led to the development of the Lumbo-Pelvic kinematic alignment (KA) technique for THA that aims to anatomically position and kinematically align hip implants (acetabular and femoral, total and resurfacing components), in order to optimise prosthetic hip biomechanics and hopefully improve prosthetic function, patient satisfaction, and components' lifespan. Therefore, we conducted a case control investigation to assess the early-term safety and efficacy of this new technique by answering the following questions: does the KA technique for THA: (1) better restore the native hip anatomy, (2) generate a different radiographic supine cup position, and (3) improve clinical outcomes in comparison to the conventional mechanical alignment technique? HYPOTHESES: Using KA technique allows there is no statistically significant difference between the pre to postoperative differential for acetabular medial and vertical offsets, femoral offset, and leg length. METHODS: We led a case control retrospective study with prospectively collected clinical data. Forty-one consecutive unselected KA-THAs performed with manual instrumentation were paired with 41 mechanically aligned THAs. The 1-year clinical outcomes and radiographical measurements were compared. RESULTS: Compared to the mechanical alignment technique, the KA technique resulted in a more anatomical restoration of the prosthetic hip centre of rotation with a lower delta pre- to post-operative horizontal acetabular offset (1.47mm for KA versus -5.1mm for MA, p=0.001), and with 74% of KA versus 50% of MA cups (p=0.044) being within 15% of native anatomy for the horizontal acetabular offset. In addition, the KA technique resulted in a higher cup anteversion (22°±7° vs 15°±8°, p<0.001) but similar cup inclination (41°±6° vs. 42°±7°, p=0.25), a similar proportion of cups within the Lewinnek zone (65% vs. 70%, p=0.8), similar excellent functional outcomes (delta Oxford score pre- to follow-up of 24.3 and 23.5 points for KA and MA groups, respectively, p=0.88), similar patient satisfaction scores of 95.4/100 and 89.5/100 for KA and MA groups, respectively, and the same absence of aseptic complications. CONCLUSION: The KA technique for THA has been demonstrated to be safe, efficacious, and not inferior to the conventional MA technique at early-term. As the concept of the KA technique for THA is only at an early stage, its influence on mid to long-term clinical outcomes remains to be determined and further refinements of the concept are yet to be made. LEVEL OF EVIDENCE: III; case-control retrospective study.

Examining the validity and reliability of a portable sleep posture assessment protocol, using infrared cameras, under a variety of light and bed cover situations in the home environment.

BACKGROUND: Spinal symptoms of pain and stiffness on waking have been linked to sleep posture. Sleep posture is commonly classified as supine, side lying and prone. It is clinically postulated that sleeping postures with sustained end of range rotation and extension may influence pain sensitive spinal tissues. However, the lack of a valid and reliable method of assessing sleep posture, means clinicians are unable to provide corrective advice based upon evidenced based research. OBJECTIVE: To determine the validity and reliability of a sleep posture recording protocol in the home environment. METHOD: Twenty health professionals viewed a pre-recorded video recording of randomised sleep postures under natural and infrared light situations, with a variety of bed coverings, to represent the habitual environment. Sleep postures were classified into six categories including two intermediate postures (supported side lying and provocative side lying). Viewing was repeated after two days. RESULTS: Intra-and inter-rater reliability were excellent; Cohen's Kappa = .93 (95% CI 0.80 to 1.0) and Fleiss Kappa = 0.83 (95% CI 0.82 to 0.84) respectively. Validity, determined as concordance between the health professionals' classifications and the known postures, was also excellent Cohen's Kappa = .91 (95% CI 0.77 to 1.0). CONCLUSIONS: Reliable and valid assessment of sleep posture, including intermediate postures, could be achieved using low cost, portable, infrared video recording equipment, under a variety of lighting conditions and a variety of bed cover situations typical of the home environment.

A new method to approximate load-displacement relationships of spinal motion segments for patient-specific multi-body models of scoliotic spine.

Load-displacement relationships of spinal motion segments are crucial factors in characterizing the stiffness of scoliotic spine models to mimic the spine responses to loads. Although nonlinear approach to approximation of the relationships can be superior to linear ones, little mention has been made to deriving personalized nonlinear load-displacement relationships in previous studies. A method is developed for nonlinear approximation of load-displacement relationships of spinal motion segments to assist characterizing in vivo the stiffness of spine models. We propose approximation by tangent functions and focus on rotational displacements in lateral direction. The tangent functions are characterized using lateral bending test. A multi-body model was characterized to 18 patients and utilized to simulate four spine positions; right bending, left bending, neutral, and traction. The same was done using linear functions to assess the performance of the proposed tangent function in comparison with the linear function. Root-mean-square error (RMSE) of the displacements estimated by the tangent functions was 44 % smaller than the linear functions. This shows the ability of our tangent function in approximation of the relationships for a range of infinitesimal to large displacements involved in the spine movement to the four positions. In addition, the models based on the tangent functions yielded 67, 55, and 39 % smaller RMSEs of Ferguson angles, locations of vertebrae, and orientations of vertebrae, respectively, implying better estimates of spine responses to loads. Overall, it can be concluded that our method for approximating load-displacement relationships of spinal motion segments can offer good estimates of scoliotic spine stiffness.