The presence of physiological stress shielding in the degenerative cycle of musculoskeletal disorders

Augmentation of musculoskeletal soft tissue morphology within low back pain patients may suggest the presence of physiological stress shielding: An in vivo study

INTRODUCTION

The pathomechanism of low back pain (LBP) remains unknown. However, changes to mechanical properties of soft tissues affected by LBP may indicate the presence of stress shielding, which may manifest via tissue remodeling. This study investigates the potential for physiological stress shielding within the lumbar spine by examining differences within lumbar soft tissue morphology between control and LBP subjects.

METHODS

Through MRI, the total and functional cross-sectional area (tCSA, fCSA) and fatty infiltration (FI) of the lumbar multifidus (MF), erector spinae (ES), quadratus lumborum (QL), psoas major (PM), and thoracolumbar fascia (TLF) were measured from the L1/L2 to L5/S1 intervertebral disc levels of 69 subjects (36 LBP and 33 control subjects). Statistical analysis was conducted using Mann-Whitney U. P < 0.05 denoted significance.

RESULTS

Comparison of male LBP patients and male healthy controls yielded an increase in tCSA and fCSA within the L4/L5 PM (p < 0.01), and the L4/L5 ES (p = 0.02) and PM (p < 0.01), respectively, of LBP patients. Female LBP patients' FI compared to female controls increased within the L1/L2 MF (p = 0.03), L3/L4 MF (p = 0.04) and ES (p = 0.02), and L4/L5 QL (p = 0.01). The L3/L4 TLF also demonstrated an 8% increase in LBP subjects.

CONCLUSION

Male patients' results suggest elevated tissue loading during motion yielding hypertrophy in the L4/L5 ES and PM fCSA, and PM tCSA. Female LBP patients' MF, ES, and PM at L3/L4 demonstrating elevated FI coupled with TLF tCSA hypertrophy may suggest irregular stress distributions and lay the foundation for stress shielding within musculoskeletal soft tissues.

Response to Mechanical Properties and Physiological Challenges of Fascia: Diagnosis and Rehabilitative Therapeutic Intervention for Myofascial System Disorders

Damage to the fascia can cause significant performance deficits in high-performance sports and recreational exercise and may contribute to the development of musculoskeletal disorders and persistent potential pain. The fascia is widely distributed from head to toe, encompassing muscles, bones, blood vessels, nerves, and internal organs and comprising various layers of different depths, indicating the complexity of its pathogenesis. It is a connective tissue composed of irregularly arranged collagen fibers, distinctly different from the regularly arranged collagen fibers found in tendons, ligaments, or periosteum, and mechanical changes in the fascia (stiffness or tension) can produce changes in its connective tissue that can cause pain. While these mechanical changes induce inflammation associated with mechanical loading, they are also affected by biochemical influences such as aging, sex hormones, and obesity. Therefore, this paper will review the current state of knowledge on the molecular level response to the mechanical properties of the fascia and its response to other physiological challenges, including mechanical changes, innervation, injury, and aging; imaging techniques available to study the fascial system; and therapeutic interventions targeting fascial tissue in sports medicine. This article aims to summarize contemporary views.

The relationship between clinical examination measures and ultrasound measures of fascia thickness surrounding trunk muscles or lumbar multifidus fatty infiltrations: An exploratory study

Patients with chronic low back pain (CLBP) exhibit remodelling of the lumbar soft tissues such as muscle fatty infiltrations (MFI) and fibrosis of the lumbar multifidus (LuM) muscles, thickness changes of the thoracolumbar fascia (TLF) and perimuscular connective tissues (PMCT) surrounding the abdominal lateral wall muscles. Rehabilitative ultrasound imaging (RUSI) parameters such as thickness and echogenicity are sensitive to this remodelling. This experimental laboratory study aimed to explore whether these RUSI parameters (LuM echogenicity and fascia thicknesses), hereafter called dependent variables (DV) were linked to independent variables (IV) such as (1) other RUSI parameters (trunk muscle thickness and activation) and (2) physical and psychological measures. RUSI measures, as well as a clinical examination comprising physical tests and psychological questionnaires, were collected from 70 participants with LBP. The following RUSI dependent variables (RUSI-DV), measures of passive tissues were performed bilaterally: (1) LuM echogenicity (MFI/fibrosis) at three vertebral levels (L3/L4, L4/L5 and L5/S1); (2) TLF posterior layer thickness, and (3) PMCT thickness of the fasciae between subcutaneous tissue thickness (STT) and external oblique (PMCT_STT/EO ), between external and internal oblique (PMCT_EO/IO ), between IO and transversus abdominis (PMCT_IO/TrA ) and between TrA and intra-abdominal content (PMCT_TrA/IA ). RUSI measures of trunk muscle's function (thickness and activation), also called measures of active muscle tissues, were considered as independent variables (RUSI-IV), along with physical tests related to lumbar stability (n = 6), motor control deficits (n = 7), trunk muscle endurance (n = 4), physical performance (n = 4), lumbar posture (n = 2), and range of motion (ROM) tests (n = 6). Psychosocial measures included pain catastrophizing, fear-avoidance beliefs, psychological distress, illness perceptions and concepts related to adherence to a home-based exercise programme (physical activity level, self-efficacy, social support, outcome expectations). Six multivariate regression models (forward stepwise selection) were generated, using RUSI-DV measures as dependent variables and RUSI-IV/physical/psychosocial measures as independent variables (predictors). The six multivariate models included three to five predictors, explaining 63% of total LuM echogenicity variance, between 41% and 46% of trunk superficial fasciae variance (TLF, PMCT_STT/EO ) and between 28% and 37% of deeper abdominal wall fasciae variance (PMCT_EO/IO , PMCT_IO/TrA and PMCT_TrA/IA ). These variables were from RUSI-IV (LuM thickness at rest, activation of IO and TrA), body composition (percent fat) and clinical physical examination (lumbar and pelvis flexion ROM, aberrant movements, passive and active straight-leg raise, loaded-reach test) from the biological domain, as well as from the lifestyle (physical activity level during sports), psychological (psychological distress-cognitive subscale, fear-avoidance beliefs during physical activities, self-efficacy to exercise) and social (family support to exercise) domains. Biological, psychological, social and lifestyle factors each accounted for substantial variance in RUSI-passive parameters. These findings are in keeping with a conceptual link between tissue remodelling and factors such as local and systemic inflammation. Possible explanations are discussed, in keeping with the hypothesis-generating nature of this study (exploratory). However, to impact clinical practice, further research is needed to determine if the most plausible predictors of trunk fasciae thickness and LuM fatty infiltrations have an effect on these parameters.

Improve biomechanical stability using intramedullary nails with femoral neck protection in femoral shaft fractures

BACKGROUND AND OBJECTIVE

Elderly patients treated for femoral shaft fractures have a higher risk of hip fracture. We hypothesized that intramedullary nails protecting the femoral neck can improve mechanical strength and reduce the risk of subsequent hip fracture. This study aims to analyze the biomechanical stability using intramedullary nails with or without femoral neck protection through finite element analysis.

METHODS

Thirty finite element models (FEMs) were established, including five different conditions of femoral shaft fracture: Fracture healing, Proximal fractures (Transverse and oblique), Distal fractures (Transverse and oblique), and five different fixation methods. Femoral neck protection groups: cephalomedullary nail (CN), reconstruction nail (RN); No femoral neck protection groups: type-1 of antegrade intramedullary nail (AIN-1), type-2 of antegrade intramedullary nail (AIN-2), and retrograde intramedullary nail (RIN). The maximum stress of bone and internal fixation in the femoral neck region for all type of fixation were calculated to evaluate the biomechanical stability.

RESULTS

Maximum equivalent stress values of bone in the femoral neck region for five different conditions of femoral shaft fracture: AIN-2 (77.23 MPa) >RIN (77.15 MPa) > AIN-1 (76.71 MPa) > CN (60.74 MPa) > RN (57.66 MPa) for the fracture healing; RIN (80.05 MPa) > AIN-1 (79.15 MPa) > AIN-2(78.77 MPa) > RN (65.16 MPa) > CN (65.03 MPa) for the proximal transverse fracture; RIN (80.10 MPa) > AIN-2 (79.36 MPa) > AIN-1 (79.18 MPa) > RN (65.09 MPa) > CN (64.96 MPa) for the proximal oblique fracture; RIN (80.24 MPa) > AIN-2 (79.68 MPa) > AIN-1 (79.33 MPa) > CN (65.02 MPa) > RN (64.76 MPa) for the distal transverse fracture; RIN (80.23 MPa) > AIN-2 (79.61 MPa) > AIN-1 (79.35 MPa) > CN (65.06 MPa) > RN (64.76 MPa) for the distal oblique fracture. Maximum equivalent stress of internal fixation in the femoral neck region is greater than the maximum stress of bone and avoids stress concentration of bone for the femoral neck protection groups (CN and RN).

CONCLUSIONS

Intramedullary nails with femoral neck protection in the treatment of femoral shaft fractures improve mechanical strength and prevent secondary hip fractures and decrease the overall risk of reoperation postoperatively.

Age-Related Susceptibility to Muscle Damage Following Mechanotherapy in Rats Recovering From Disuse Atrophy

The inability to fully recover lost muscle mass following periods of disuse atrophy predisposes older adults to lost independence and poor quality of life. We have previously shown that mechanotherapy at a moderate load (4.5 N) enhances muscle mass recovery following atrophy in adult, but not older adult rats. We propose that elevated transverse stiffness in aged muscle inhibits the growth response to mechanotherapy and hypothesize that a higher load (7.6 N) will overcome this resistance to mechanical stimuli. F344/BN adult and older adult male rats underwent 14 days of hindlimb suspension, followed by 7 days of recovery with (RE + M) or without (RE) mechanotherapy at 7.6 N on gastrocnemius muscle. The 7.6 N load was determined by measuring transverse passive stiffness and linearly scaling up from 4.5 N. No differences in protein turnover or mean fiber cross-sectional area were observed between RE and RE + M for older adult rats or adult rats at 7.6 N. However, there was a higher number of small muscle fibers present in older adult, but not adult rats, which was explained by a 16-fold increase in the frequency of small fibers expressing embryonic myosin heavy chain. Elevated central nucleation, satellite cell abundance, and dystrophin-/laminin+ fibers were present in older adult rats only following 7.6 N, while 4.5 N did not induce damage at either age. We conclude that age is an important variable when considering load used during mechanotherapy and age-related transverse stiffness may predispose older adults to damage during the recovery period following disuse atrophy.

The examination of stress shielding in a finite element lumbar spine inclusive of the thoracolumbar fascia

Despite the prevalence of low back pain (LBP) in society, the pathomechanism of LBP continues to elude researchers. LBP patients have demonstrated morphological and material property changes to their lumbar soft tissues, potentially leading to irregular load sharing within the lumbar spine. This study aims to analyze potential stress shielding consequential of augmented soft tissue properties via the comparison of a healthy and LBP finite element models. The models developed in this study include the vertebrae, intervertebral discs and soft tissues from L1-S1. Soft tissue morphology and material properties for the LBP model were augmented to reflect documented clinical findings. Model validation preceded testing and was confirmed through comparison to the available literature. Relative to the healthy model, the LBP model demonstrated an increase in stress by 15.6%, with 99.8% of this stress increase being distributed towards the thoracolumbar fascia. The majority of stress skewed towards the fascia may indicate a potential stress allocation bias whereby the lumbar muscles are unable to receive regular loading, leading to stress shielding. This load allocation bias and subsequent stress shielding may potentially contribute to the progression and pathomechanism of LBP but prospective studies would be required to make that link.

Investigation of physiological stress shielding within lumbar spinal tissue as a contributor to unilateral low back pain: A finite element study

INTRODUCTION

The pathomechanism of low back pain (LBP) remains unknown. Unilateral LBP patients have demonstrated ipsilateral morphological and material property changes within the lumbar soft tissues, potentially leading to asymmetric tissue loading. Through the comparison of healthy and unilateral LBP validated finite element models (FEMs), this study investigates potential stress shielding consequential of spinal tissue property augmentation.

METHODS

Two FEMs of the musculoskeletal system - one demonstrating healthy and unilateral LBP conditions - were developed undergoing 30-degree flexion. FEMs included the vertebrae, intervertebral discs, and soft tissues from L1-S1. Material properties selected for the soft tissues were retrieved from published literature. To reflect unilateral LBP, the paraspinal morphology was atrophied, while the tissue moduli were increased. The symptomatic thoracolumbar fascia (TLF) was uniformly increased. Validation of the models preceded testing.

RESULTS

Model validation in spinal flexion was accomplished through comparison to literature. Compared to the healthy model, the unilateral LBP multifidus (MF), longissimus thoracis (LT), and TLF exhibited average tension changes of +7.9, -5.1, and +9.3%, respectively. Likewise, the symptomatic MF, LT, and TLF exhibited tension changes of +19.0, -10.4, and +16.1% respectively, whereas the asymptomatic MF, LT, and TLF exhibited -4.0, -2.0, and +0.4% changes in tension, respectively.

CONCLUSION

Relative to the healthy tissues, the symptomatic LBP soft tissues demonstrated a 19.5 kPa increase in stress, with 99.8% of this increase distributed towards the TLF, suggesting a load allocation bias within the symptomatic unilateral LBP tissues. Consequentially, symptomatic paraspinal muscles may be unable to withstand loading, leading to stress shielding.

Quantifying the Effects of Aging on Morphological and Cellular Properties of Human Female Pelvic Floor Muscles

Age-related pelvic floor muscle (PFM) dysfunction is a critical defect in the progression to pelvic floor disorders (PFDs). Despite dramatic prevalence of PFDs in older women, the underlying pathophysiology of age-related PFM dysfunction remains poorly understood. Using cadaveric specimens, we quantified aging effects on functionally relevant PFM properties and compared PFMs with the appendicular muscles from the same donors. PFMs, obturator internus, and vastus lateralis were procured from younger (N = 4) and older (N = 11) donors with known obstetrical and medical history. Our findings demonstrate that PFMs undergo degenerative, rather than atrophic, alterations. Importantly, age-related fibrotic degeneration disproportionally impacts PFMs compared to the appendicular muscles. We identified intramuscular lipid accumulation as another contributing factor to the pathological alterations of PFMs with aging. We observed a fourfold decrease in muscle stem cell (MuSC) pool of aged relative to younger PFMs, but the MuSC pool of appendicular muscles from the same older donors was only twofold lower than in younger group, although these differences were not statistically significant. Age-related degeneration appears to disproportionally impact PFMs relative to the appendicular muscles from the same donors. Knowledge of tissue- and cell-level changes in aged PFMs is essential to promote our understanding of the mechanisms governing PFM dysfunction in older women.

Structural remodeling of the lumbar multifidus, thoracolumbar fascia and lateral abdominal wall perimuscular connective tissues: A search for its potential determinants

Recently remodeling of lumbar soft tissues has received increased research attention. However, the major determinants that influence remodeling need to be elucidated in order to understand the impact of different rehabilitation modalities on tissue remodeling. The main aim of this study was to explore the between-subject variance of different measures of lumbar soft tissues quantified with rehabilitative ultrasound imaging (RUSI). RUSI measures (n = 8) were collected from 30 subjects without and 34 patients with LBP: (1) lumbar multifidus (LM) echogenicity (fatty infiltration/fibrosis) at three vertebral levels (L3/L4, L4/L5 and L5/S1) (n = 3); (2) posterior layer thickness of the thoracolumbar fascia (n = 1); and (3) thickness of the fasciae surrounding the external oblique (EO), internal oblique (IO), and transversus abdominis (TrA) (n = 4). Forward stepwise multivariate regression modeling was conducted with these RUSI measures as dependent variables, using the following independent variables as potential determinants: age, sex, the presence of LBP, body size/composition characteristics (height, weight, trunk length, subcutaneous tissue thickness over the abdominal, and LM muscles), trunk muscle function (or activation) as determined with the percent thickness change of LM, EO, IO, and TrA muscles during a standardized effort (RUSI measures), and physical activity level during sport and leisure activities as estimated with a self-report questionnaire. Two or three statistically significant predictors (or determinants) were selected in the regression model of each RUSI measure (n = 8 models), accounting for 26-64% of their total variance. The subcutaneous tissue thickness on the back accounted for 15-30% variance of LM echogenicity measures and thoracolumbar fascia thickness while the subcutaneous tissue thickness over the abdominals accounted for up to 42% variance of the fascia separating the subcutaneous adipose tissues and the EO muscle. The thickness of IO at rest accounted for 13-21% variance of all investigated abdominal fasciae except the fascia separating the subcutaneous adipose tissue and EO. Pain status accounted for 13-18% variance of the anterior and posterior fasciae of the TrA. Age accounted for 11-14% variance of LM echogenicity at all investigated vertebral levels while sex accounted for 15-21% variance of LM echogenicity at L3/L4 and fascia separating subcutaneous adipose tissue and EO muscle. The function (or activation) of EO and LM at L3/L4 accounted for 8-11% variance of the thoracolumbar fascia and fascia separating TrA and intra-abdominal content (TrA posterior fascia), respectively. Finally, the physical activity level during sport activities accounted for 7% variance of the fascia separating the subcutaneous adipose tissues and the EO muscle. These findings suggest that determinants other than body size characteristics may impact the remodeling of lumbar soft tissues, more importantly the subcutaneous adipose tissue deposits (thickness RUSI measures), which are associated with ectopic fat deposition in the LM and in the fasciae that are more closely positioned to the surface. While age, sex, and pain status explain some variability, modifiable factors such as physical activity level as well as trunk muscle thickness and function were involved. Overall, these results suggest that rehabilitation can potentially impact tissue remodeling, particularly in terms of intramuscular and perimuscular adipose tissues.

Blocking substance P signaling reduces musculotendinous and dermal fibrosis and sensorimotor declines in a rat model of overuse injury

Purpose/Aim: Substance P-NK-1R signaling has been implicated in fibrotic tendinopathies and myositis. Blocking this signaling with a neurokinin 1 receptor antagonist (NK1RA) has been proposed as a therapeutic target for their treatment.Materials and Methods: Using a rodent model of overuse injury, we pharmacologically blocked Substance P using a specific NK1RA with the hopes of reducing forelimb tendon, muscle and dermal fibrogenic changes and associated pain-related behaviors. Young adult rats learned to pull at high force levels across a 5-week period, before performing a high repetition high force (HRHF) task for 3 weeks (2 h/day, 3 days/week). HRHF rats were untreated or treated in task weeks 2 and 3 with the NK1RA, i.p. Control rats received vehicle or NK1RA treatments.Results: Grip strength declined in untreated HRHF rats, and mechanical sensitivity and temperature aversion increased compared to controls; these changes were improved by NK1RA treatment (L-732,138). NK1RA treatment also reduced HRHF-induced thickening in flexor digitorum epitendons, and HRHF-induced increases of TGFbeta1, CCN2/CTGF, and collagen type 1 in flexor digitorum muscles. In the forepaw upper dermis, task-induced increases in collagen deposition were reduced by NK1RA treatment.Conclusions: Our findings indicate that Substance P plays a role in the development of fibrogenic responses and subsequent discomfort in forelimb tissues involved in performing a high demand repetitive forceful task.

Blocking CTGF/CCN2 reduces established skeletal muscle fibrosis in a rat model of overuse injury

Tissue fibrosis is a hallmark of overuse musculoskeletal injuries and contributes to functional declines. We tested whether inhibition of CCN2 (cellular communication network factor 2, previously known as connective tissue growth factor, CTGF) using a specific antibody (termed FG‐3019 or pamrevlumab) reduces established overuse‐induced muscle fibrosis in a clinically relevant rodent model of upper extremity overuse injury. Young adult rats performed a high repetition high force (HRHF) reaching and lever‐pulling task for 18 weeks, after first being shaped for 6 weeks to learn this operant task. Rats were then euthanized (HRHF‐Untreated), or rested and treated for 6 weeks with FG‐3019 (HRHF‐Rest/FG‐3019) or a human IgG as a vehicle control (HRHF‐Rest/IgG). HRHF‐Untreated and HRHF‐Rest/IgG rats had higher muscle levels of several fibrosis‐related proteins (TGFβ1, CCN2, collagen types I and III, and FGF2), and higher muscle numbers of alpha SMA and pERK immunopositive cells, compared to control rats. Each of these fibrogenic changes was restored to control levels by the blocking of CCN2 signaling in HRHF‐Rest/FG‐3019 rats, as were HRHF task‐induced increases in serum CCN2 and pro‐collagen I intact N‐terminal protein. Levels of cleaved CCN3, an antifibrotic protein, were lowered in HRHF‐Untreated and HRHF‐Rest/IgG rats, compared to control rats, yet elevated back to control levels in HRHF‐Rest/FG‐3019 rats. Significant grip strength declines observed in HRHF‐Untreated and HRHF‐Rest/IgG rats, were restored to control levels in HRHF‐Rest/FG‐3019 rats. These results are highly encouraging for use of FG‐3019 for therapeutic treatment of persistent skeletal muscle fibrosis, such as those induced with chronic overuse.

Investigation of the inter-dependence between intra-abdominal pressure and spinal stability

INTRODUCTION

Many researchers have explored the link between intra-abdominal pressure and the biomechanical stability of the spine. Children severely affected with cerebral palsy have low engagement of the abdominal region and correspondingly very poor spine stability. Rehabilitation programs often seek to improve such resources, but a link has never been objectively demonstrated in this patient population who may greatly benefit from potential gains. Thus, the purpose is to evaluate the interdependency between intra-abdominal pressure and spinal stability in cerebral palsy patients undergoing a targeted rehabilitation program.

METHODS

A non-randomized prospective cohort treatment study of patients with gross motor function classification system types 4 and 5 over five years old while undergoing a high-frequency rehabilitation program targeting spinal stability. Blinded measures of intra-abdominal pressure and seated spinal stability were acquired. All measures were taken at baseline and bi-annually for 2 years. GMFCS classification were taken at baseline to distinguish the study group. Study directives were approved by independent ethical committees. Non-parametric Wilcoxon tests were utilized to perform data analyses.

FINDINGS

Measures of intra-abdominal pressure, by way of customized indentometer, improved from 3.23 to 4.46 lbs./in. of compression between baseline and 24 months (p < 0.05). Seated spinal stability improved from scores of 2.3 to 3.1 after 24 months (p < 0.05). Results showed a trend of collinearity between intra-abdominal pressure and seated spinal stability.

INTERPRETATION

Results suggest a correlation between intra-abdominal compression and, correspondingly, better seated spinal stability for GMFCS class 4 and 5 patients.

Blocking CCN2 Reduces Progression of Sensorimotor Declines and Fibrosis in a Rat Model of Chronic Repetitive Overuse

Fibrosis may be a key factor in sensorimotor dysfunction in patients with chronic overuse-induced musculoskeletal disorders. Using a clinically relevant rodent model, in which performance of a high demand handle-pulling task induces tissue fibrosis and sensorimotor declines, we pharmacologically blocked cellular communication network factor 2 (CCN2; connective tissue growth factor) with the goal of reducing the progression of these changes. Young adult, female Sprague-Dawley rats were shaped to learn to pull at high force levels (10 min/day, 5 weeks), before performing a high repetition high force (HRHF) task for 3 weeks (2 h/day, 3 days/week). HRHF rats were untreated, or treated in task weeks 2 and 3 with a monoclonal antibody that blocks CCN2 (FG-3019), or a control immunoglobulin G (IgG). Control rats were untreated or received FG-3019, IgG, or vehicle (saline) injections. Mean task reach rate and grasp force were higher in 3-week HRHF + FG-3019 rats, compared with untreated HRHF rats. Grip strength declined while forepaw mechanical sensitivity increased in untreated HRHF rats, compared with controls; changes improved by FG-3019 treatment. The HRHF task increased collagen in multiple tissues (flexor digitorum muscles, nerves, and forepaw dermis), which was reduced with FG-3019 treatment. FG-3019 treatment also reduced HRHF-induced increases in CCN2 and transforming growth factor β in muscles. In tendons, FG-3019 reduced HRHF-induced increases in CCN2, epitendon thickening, and cell proliferation. Our findings indicate that CCN2 is critical to the progression of chronic overuse-induced multi-tissue fibrosis and functional declines. FG-3019 treatment may be a novel therapeutic strategy for overuse-induced musculoskeletal disorders. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2004-2018, 2019.

Diverse Role of Biological Plasticity in Low Back Pain and Its Impact on Sensorimotor Control of the Spine

Pain is complex. It is no longer acceptable to consider pain solely as a peripheral phenomenon involving activation of nociceptive neurons. The contemporary understanding of pain involves consideration of different underlying pain mechanisms and an increasing awareness of plasticity in all of the biological systems. Of note, recent advances in technology and understanding have highlighted the critical importance of neuroimmune interactions, both in the peripheral and central nervous systems, and the interaction between the nervous system and body tissues in the development and maintenance of pain, including low back pain (LBP). Further, the biology of many tissues changes when challenged by pain and injury, as reported in a growing body of literature on the biology of muscle, fat, and connective tissue. These advances in understanding of the complexity of LBP have implications for our understanding of pain and its interaction with the motor system, and may change how we consider motor control in the rehabilitation of LBP. This commentary provides a state-of-the-art overview of plasticity of biology in LBP. The paper is divided into 4 parts that address (1) biology of pain mechanisms, (2) neuroimmune interaction in the central nervous system, (3) neuroimmune interaction in the periphery, and (4) brain and peripheral tissue interaction. Each section considers the implications for clinical management of LBP. J Orthop Sports Phys Ther 2019;49(6):389-401. doi:10.2519/jospt.2019.8716.

Influence of N-acetyl cysteine (NAC) and 2-methylene-1,3-dioxepane (MDO) on the properties of polymethyl methacrylate (PMMA) bone cement

The properties of polymethyl methacrylate (PMMA) bone cement make it a popular bone filling material. However, its disadvantages, such as lack of biodegradability and osteogenesis, restrict its clinical application. Studies have indicated the osteogenic properties of N-acetyl cysteine (NAC) and the biodegradability of 2-methylene-1,3-dioxepane/methyl methacrylate-based (MDO/MMA) copolymers. In this study, we developed bioactive PMMA cements through modification with fixed concentrations of NAC and different proportions of MDO. The purpose of this study was to compare the mechanical properties, morphology, NAC release, biocompatibility, degradability and mineralization capability of modified bone cements with those of conventional cement. The specific-modified specimens (NAC-p (5% MDO-co-MMA)) exhibited a lower bending modulus but had little effect on compressive strength. This material was morphologically compact and nonporous, similar to conventional PMMA bone cement. NAC could be released from NAC-p (5% MDO-co-MMA) continuously and appropriately. NAC-p (5% MDO-co-MMA) was biologically safe and showed satisfactory tissue compatibility. Ester was introduced into the polymer, which reinforced the degradation properties of NAC-p (5% MDO-co-MMA). NAC-p (5% MDO-co-MMA) enhanced the mineralization capability of osteoblastic cells.

The properties of polymethyl methacrylate (PMMA) bone cement make it a popular bone filling material.

Fascial tissue research in sports medicine: from molecules to tissue adaptation, injury and diagnostics: consensus statement

The fascial system builds a three-dimensional continuum of soft, collagen-containing, loose and dense fibrous connective tissue that permeates the body and enables all body systems to operate in an integrated manner. Injuries to the fascial system cause a significant loss of performance in recreational exercise as well as high-performance sports, and could have a potential role in the development and perpetuation of musculoskeletal disorders, including lower back pain. Fascial tissues deserve more detailed attention in the field of sports medicine. A better understanding of their adaptation dynamics to mechanical loading as well as to biochemical conditions promises valuable improvements in terms of injury prevention, athletic performance and sports-related rehabilitation. This consensus statement reflects the state of knowledge regarding the role of fascial tissues in the discipline of sports medicine. It aims to (1) provide an overview of the contemporary state of knowledge regarding the fascial system from the microlevel (molecular and cellular responses) to the macrolevel (mechanical properties), (2) summarise the responses of the fascial system to altered loading (physical exercise), to injury and other physiological challenges including ageing, (3) outline the methods available to study the fascial system, and (4) highlight the contemporary view of interventions that target fascial tissue in sport and exercise medicine. Advancing this field will require a coordinated effort of researchers and clinicians combining mechanobiology, exercise physiology and improved assessment technologies.

The effect of extracapsular injuries on growth and development of the mandible condyle: an experimental study in growing dogs

OBJECTIVE

To investigate the effects of condylar extracapsular injuries on the development of the mandibular condyle and try to find a way to treat condylar hyperplasia by electively using such injuries to restrict the overdeveloped mandibular condyle.

STUDY DESIGN

Sixty 6-month-old beagle puppies were divided randomly into five groups: blank control; unilateral fracture to the condylar neck; unilateral fracture to the condylar neck treated with rigid internal fixation; unilateral periosteum injury; unilateral decortication of the condylar neck. Computed tomography, ^{99 m}Tc single-photon emission computed tomography, and tetracycline-calcein double-labeling were performed after surgery. The puppies were sacrificed 12 and 24 weeks after surgery. Morphologic analyses and examination of growth activity were done.

RESULTS

Unilateral fracture of the condylar neck without fixation caused local morphologic changes during the early postoperative period, but compensatory growth of the condyle altered such changes after healing. The other types of injury failed to inhibit the growth of the condyle and the mandible, whereas functional deviation of the chin was found after unilateral fracture of the condylar neck with or without fixation.

CONCLUSIONS

The four types of extracapsular injury described here failed to inhibit the growth of the mandibular condyle and could not be selected as alternatives to treat condylar hyperplasia.

The Effects of a Home-Based Connective Tissue Targeting Therapy on Hip Development in Children With Cerebral Palsy: Six Case Reports

Hip subluxation in children with Cerebral Palsy (CP) has an incidence of 10-30 %, and children with severe CP having the highest incidence. The condition deteriorates if left untreated. Surgery is the most common method used in managing hip subluxation because standard conservative therapies do not improve it. Surgery may have to be repeated and comes at a biological cost to the child. A new home-based CAM, Advanced Biomechanical Rehabilitation (ABR), has shown encouraging results leading to improved spinal stability and stability in sitting in children with severe CP. This case report examines hip development over time in six children with severe CP in the ABR Program. Changes in their clinical picture and pelvic X-Rays are reported. ABR appeared to help stabilize and improve hip subluxation, resulting in these children not requiring further surgical intervention. These findings warrant further investigation of ABR as a noninvasive therapy for hip subluxation.

Anterior cruciate ligament reconstruction, rehabilitation, and return to play: 2015 update

Anatomical discoveries and a growing appreciation of the knee as a complex organ are driving innovations in patient care decision-making following anterior cruciate ligament (ACL) injury. Surgeons are increasing their efforts to restore combined mechanical-neurosensory ACL function and placing more consideration on when to reconstruct versus repair native anatomical structures. Surgical options now include primary repair with or without reinforcing the injured ACL with suture-based internal bracing, and growing evidence supports biological augmentation using platelet-rich plasma and mesenchymal stem cells to enhance tissue healing. Physical therapists and athletic trainers are increasing their efforts to facilitate greater athlete cognitive engagement during therapeutic exercise performance to better restore nonimpaired neuromuscular control activation amplitude and timing. Knee brace design and use needs to evolve to better match these innovations and their influence on the rehabilitation plan timetable. There is a growing appreciation for the multifaceted characteristics of the rehabilitation process and how they influence neuromuscular, educational, and psychobehavioral treatment goal achievement. Multiple sources may influence the athlete during the return to sports process and clinical outcome measures need to be refined to better evaluate these influences. This update summarizes contemporary ACL surgical, medical, and rehabilitation interventions and future trends.

Manual therapy as an effective treatment for fibrosis in a rat model of upper extremity overuse injury

Key clinical features of carpal tunnel syndrome and other types of cumulative trauma disorders of the hand and wrist include pain and functional disabilities. Mechanistic details remain under investigation but may involve tissue inflammation and/or fibrosis. We examined the effectiveness of modeled manual therapy (MMT) as a treatment for sensorimotor behavior declines and increased fibrogenic processes occurring in forearm tissues of rats performing a high repetition high force (HRHF) reaching and grasping task for 12 weeks. Young adult, female rats were examined: food restricted control rats (FRC, n=12); rats that were trained for 6 weeks before performing the HRHF task for 12 weeks with no treatment (HRHF-CON, n=11); and HRHF task rats received modeled manual therapy (HRHF-MMT, n=5) for 5 days/week for the duration of the 12-week of task. Rats receiving the MMT expressed fewer discomfort-related behaviors, and performed progressively better in the HRHF task. Grip strength, while decreased after training, improved following MMT. Fibrotic nerve and connective tissue changes (increased collagen and TGF-β1 deposition) present in 12-week HRHF-CON rats were significantly decreased in 12-week HRHF-MMT rats. These observations support the investigation of manual therapy as a preventative for repetitive motion disorders.

Influence of Nano-HA Coated Bone Collagen to Acrylic (Polymethylmethacrylate) Bone Cement on Mechanical Properties and Bioactivity

Objective

This research investigated the mechanical properties and bioactivity of polymethylmethacrylate (PMMA) bone cement after addition of the nano-hydroxyapatite(HA) coated bone collagen (mineralized collagen, MC).

Materials & Methods

The MC in different proportions were added to the PMMA bone cement to detect the compressive strength, compression modulus, coagulation properties and biosafety. The MC-PMMA was embedded into rabbits and co-cultured with MG 63 cells to exam bone tissue compatibility and gene expression of osteogenesis.

Results

15.0%(wt) impregnated MC-PMMA significantly lowered compressive modulus while little affected compressive strength and solidification. MC-PMMA bone cement was biologically safe and indicated excellent bone tissue compatibility. The bone-cement interface crosslinking was significantly higher in MC-PMMA than control after 6 months implantation in the femur of rabbits. The genes of osteogenesis exhibited significantly higher expression level in MC-PMMA.

Conclusions

MC-PMMA presented perfect mechanical properties, good biosafety and excellent biocompatibility with bone tissues, which has profoundly clinical values.

Increased CCN2, substance P and tissue fibrosis are associated with sensorimotor declines in a rat model of repetitive overuse injury

Key clinical features of cumulative trauma disorders include pain, muscle weakness, and tissue fibrosis, although the etiology is still under investigation. Here, we characterized the temporal pattern of altered sensorimotor behaviors and inflammatory and fibrogenic processes occurring in forearm muscles and serum of young adult, female rats performing an operant, high repetition high force (HRHF) reaching and grasping task for 6, 12, or 18 weeks. Palmar mechanical sensitivity, cold temperature avoidance and spontaneous behavioral changes increased, while grip strength declined, in 18-week HRHF rats, compared to controls. Flexor digitorum muscles had increased MCP-1 levels after training and increased TNFalpha in 6-week HRHF rats. Serum had increased IL-1beta, IL-10 and IP-10 after training. Yet both muscle and serum inflammation resolved by week 18. In contrast, IFNγ increased at week 18 in both muscle and serum. Given the anti-fibrotic role of IFNγ, and to identify a mechanism for the continued grip strength losses and behavioral sensitivities, we evaluated the fibrogenic proteins CCN2, collagen type I and TGFB1, as well as the nociceptive/fibrogenic peptide substance P. Each increased in and around flexor digitorum muscles and extracellular matrix in the mid-forearm, and in nerves of the forepaw at 18 weeks. CCN2 was also increased in serum at week 18. At a time when inflammation had subsided, increases in fibrogenic proteins correlated with sensorimotor declines. Thus, muscle and nerve fibrosis may be critical components of chronic work-related musculoskeletal disorders. CCN2 and substance P may serve as potential targets for therapeutic intervention, and CCN2 as a serum biomarker of fibrosis progression.

The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders

Background

We examined the relationship of musculoskeletal risk factors underlying force and repetition on tissue responses in an operant rat model of repetitive reaching and pulling, and if force x repetition interactions were present, indicative of a fatigue failure process. We examined exposure-dependent changes in biochemical, morphological and sensorimotor responses occurring with repeated performance of a handle-pulling task for 12 weeks at one of four repetition and force levels: 1) low repetition with low force, 2) high repetition with low force, 3) low repetition with high force, and 4) high repetition with high force (HRHF).

Methods

Rats underwent initial training for 4–6 weeks, and then performed one of the tasks for 12 weeks, 2 hours/day, 3 days/week. Reflexive grip strength and sensitivity to touch were assayed as functional outcomes. Flexor digitorum muscles and tendons, forelimb bones, and serum were assayed using ELISA for indicators of inflammation, tissue stress and repair, and bone turnover. Histomorphometry was used to assay macrophage infiltration of tissues, spinal cord substance P changes, and tissue adaptative or degradative changes. MicroCT was used to assay bones for changes in bone quality.

Results

Several force x repetition interactions were observed for: muscle IL-1alpha and bone IL-1beta; serum TNFalpha, IL-1alpha, and IL-1beta; muscle HSP72, a tissue stress and repair protein; histomorphological evidence of tendon and cartilage degradation; serum biomarkers of bone degradation (CTXI) and bone formation (osteocalcin); and morphological evidence of bone adaptation versus resorption. In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation. Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.

Conclusions

Although not consistent in all tissues, we found several significant interactions between the critical musculoskeletal risk factors of force and repetition, consistent with a fatigue failure process in musculoskeletal tissues. Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.