From the international space station to the clinic: how prolonged unloading may disrupt lumbar spine stability.

BACKGROUND CONTEXT: Prolonged microgravity exposure is associated with localized low back pain and an elevated risk of post-flight disc herniation. Although the mechanisms by which microgravity impairs the spine are unclear, they should be foundational for developing in-flight countermeasures for maintaining astronaut spine health. Because human spine anatomy has adapted to upright posture on Earth, observations of how spaceflight affects the spine should also provide new and potentially important information on spine biomechanics that benefit the general population. PURPOSE: This study compares quantitative measures of lumbar spine anatomy, health, and biomechanics in astronauts before and after 6 months of microgravity exposure on board the International Space Station (ISS). STUDY DESIGN: This is a prospective longitudinal study. SAMPLE: Six astronaut crewmember volunteers from the National Aeronautics and Space Administration (NASA) with 6-month missions aboard the ISS comprised our study sample. OUTCOME MEASURES: For multifidus and erector spinae at L3-L4, measures include cross-sectional area (CSA), functional cross-sectional area (FCSA), and FCSA/CSA. Other measures include supine lumbar lordosis (L1-S1), active (standing) and passive (lying) flexion-extension range of motion (FE ROM) for each lumbar disc segment, disc water content from T2-weighted intensity, Pfirrmann grade, vertebral end plate pathology, and subject-reported incidence of chronic low back pain or disc injuries at 1-year follow-up. METHODS: 3T magnetic resonance imaging and dynamic fluoroscopy of the lumbar spine were collected for each subject at two time points: approximately 30 days before launch (pre-flight) and 1 day following 6 months spaceflight on the ISS (post-flight). Outcome measures were compared between time points using paired t tests and regression analyses. RESULTS: Supine lumbar lordosis decreased (flattened) by an average of 11% (p=.019). Active FE ROM decreased for the middle three lumbar discs (L2-L3: -22.1%, p=.049; L3-L4: -17.3%, p=.016; L4-L5: -30.3%, p=.004). By contrast, no significant passive FE ROM changes in these discs were observed (p>.05). Disc water content did not differ systematically from pre- to post-flight. Multifidus and erector spinae changed variably between subjects, with five of six subjects experiencing an average decrease 20% for FCSA and 8%-9% for CSA in both muscles. For all subjects, changes in multifidus FCSA strongly correlated with changes in lordosis (r2=0.86, p=.008) and active FE ROM at L4-L5 (r2=0.94, p=.007). Additionally, changes in multifidus FCSA/CSA correlated with changes in lordosis (r2=0.69, p=.03). Although multifidus-associated changes in lordosis and ROM were present among all subjects, only those with severe, pre-flight end plate irregularities (two of six subjects) had post-flight lumbar symptoms (including chronic low back pain or disc herniation). CONCLUSIONS: We observed that multifidus atrophy, rather than intervertebral disc swelling, associated strongly with lumbar flattening and increased stiffness. Because these changes have been previously linked with detrimental spine biomechanics and pain in terrestrial populations, when combined with evidence of pre-flight vertebral end plate insufficiency, they may elevate injury risk for astronauts upon return to gravity loading. Our results also have implications for deconditioned spines on Earth. We anticipate that our results will inform new astronaut countermeasures that target the multifidus muscles, and research on the role of muscular stability in relation to chronic low back pain and disc injury.

Lumbar Spine Paraspinal Muscle and Intervertebral Disc Height Changes in Astronauts After Long-Duration Spaceflight on the International Space Station.

STUDY DESIGN: Prospective case series. OBJECTIVE: Evaluate lumbar paraspinal muscle (PSM) cross-sectional area and intervertebral disc (IVD) height changes induced by a 6-month space mission on the International Space Station. The long-term objective of this project is to promote spine health and prevent spinal injury during space missions and here on Earth. SUMMARY OF BACKGROUND DATA: National Aeronautics and Space Administration (NASA) crewmembers have a 4.3 times higher risk of herniated IVDs, compared with the general and military aviator populations. The highest risk occurs during the first year after a mission. Microgravity exposure during long-duration spaceflights results in approximately 5 cm lengthening of body height, spinal pain, and skeletal deconditioning. How the PSMs and IVDs respond during spaceflight is not well described. METHODS: Six NASA crewmembers were imaged supine with a 3 Tesla magnetic resonance imaging. Imaging was conducted preflight, immediately postflight, and then 33 to 67 days after landing. Functional cross-sectional area (FCSA) measurements of the PSMs were performed at the L3-4 level. FCSA was measured by grayscale thresholding within the posterior lumbar extensors to isolate lean muscle on T2-weighted scans. IVD heights were measured at the anterior, middle, and posterior sections of all lumbar levels. Repeated measures analysis of variance was used to determine significance at P < 0.05, followed by post-hoc testing. RESULTS: Paraspinal lean muscle mass, as indicated by the FCSA, decreased from 86% of the total PSM cross-sectional area down to 72%, immediately after the mission. Recovery of 68% of the postflight loss occurred during the next 6 weeks, still leaving a significantly lower lean muscle fractional content compared with preflight values. In contrast, lumbar IVD heights were not appreciably different at any time point. CONCLUSION: The data reveal lumbar spine PSM atrophy after long-duration spaceflight. Some FCSA recovery was seen with 46 days postflight in a terrestrial environment, but it remained incomplete compared with preflight levels. LEVEL OF EVIDENCE: 4.

Pulsed electromagnetic field (PEMF) treatment reduces expression of genes associated with disc degeneration in human intervertebral disc cells.

BACKGROUND CONTEXT: Pulsed electromagnetic field (PEMF) therapies have been applied to stimulate bone healing and to reduce the symptoms of arthritis, but the effects of PEMF on intervertebral disc (IVD) biology is unknown. PURPOSE: The purpose of this study was to determine how PEMF affects gene expression of IVD cells in normal and inflammatory environments. STUDY DESIGN/SETTING: This was an in vitro human cell culture and microarray gene expression study. METHODS: Human annulus fibrosus (AF) and nucleus pulposus (NP) cells were separately encapsulated in alginate beads and exposed to interleukin 1α (IL-1α) (10 ng/mL) to stimulate the inflammatory environment associated with IVD degeneration and/or stimulated by PEMF for 4 hours daily for up to 7 days. RNA was isolated from each treatment group and analyzed via microarray to assess IL-1α- and PEMF-induced changes in gene expression. RESULTS: Although PEMF treatment did not completely inhibit the effects of IL-1α, PEMF treatment lessened the IL-1α-induced upregulation of genes expressed in degenerated IVDs. Consistent with our previous results, after 4 days, PEMF tended to reduce IL-1α-associated gene expression of IL-6 (25%, p=.07) in NP cells and MMP13 (26%, p=.10) in AF cells. Additionally, PEMF treatment significantly diminished IL-1α-induced gene expression of IL-17A (33%, p=.01) and MMP2 (24%, p=.006) in NP cells and NFκB (11%, p=.04) in AF cells. CONCLUSIONS: These results demonstrate that IVD cells are responsive to PEMF and motivate future studies to determine whether PEMF may be helpful for patients with IVD degeneration.

Tibiofemoral contact pressures in radial tears of the meniscus treated with all-inside repair, inside-out repair and partial meniscectomy.

BACKGROUND: To test contact pressures in the knee after treatment of a radial meniscus tear with an all-inside meniscal repair technique and compare the results with inside-out repair and partial meniscectomy. METHODS: Six non-paired cadaveric knees were analyzed with intra-compartment pressures measured at loads of 250 N, 500 N and 1000 N at 0°, eight degrees, 15°, and 30° of knee flexion. Compartmental contact pressures were measured for the intact medial meniscus, radial tear in the posterior horn, all-inside repair using the NovoStitch suture passer device (Ceterix Orthopaedics Inc., Menlo Park, CA), inside-out repair method, and partial meniscectomy. One-way ANOVA was used for statistical analysis. RESULTS: The greatest differences in peak pressures between treatments were observed under 1000 N load at 30° flexion (0.8± (SD) 0.1 MPa (intact meniscus), 0.8± (SD) 0.1 MPa (all-inside), 0.9± (SD) 0.1 MPa (inside-out) and 1.6± (SD) 0.2 MPa (partial meniscectomy)). Treatment with partial meniscectomy resulted in the highest peak pressures compared to all other states (p<0.0001 at each angle). Repair of the radial tear using the all-inside technique as well as the inside-out technique resulted in significantly decreased compartment pressures compared to partial meniscectomies (p<0.0001 at each angle). There were no significant differences between peak pressures in the intact state and after repair with the all-inside or inside-out techniques. CONCLUSION: An all-inside repair technique using the NovoStitch suture passer can decrease contact pressures for a radial meniscus tear similarly to the inside-out repair technique when compared to partial meniscectomy. CLINICAL RELEVANCE: This novel arthroscopic suture passer warrants further analysis in the clinical setting as it may be a reliable method for repair of radial meniscal tears through an arthroscopic all-inside technique.

Alterations in intervertebral disc composition, matrix homeostasis and biomechanical behavior in the UCD-T2DM rat model of type 2 diabetes.

Type 2 diabetes (T2D) adversely affects many tissues, and the greater incidence of discogenic low back pain among diabetic patients suggests that the intervertebral disc is affected too. Using a rat model of polygenic obese T2D, we demonstrate that diabetes compromises several aspects of disc composition, matrix homeostasis, and biomechanical behavior. Coccygeal motion segments were harvested from 6-month-old lean Sprague-Dawley rats, obese Sprague-Dawley rats, and diabetic obese UCD-T2DM rats (diabetic for 69 ± 7 days). Findings indicated that diabetes but not obesity reduced disc glycosaminoglycan and water contents, and these degenerative changes correlated with increased vertebral endplate thickness and decreased endplate porosity, and with higher levels of the advanced glycation end-product (AGE) pentosidine. Consistent with their diminished glycosaminoglycan and water contents and their higher AGE levels, discs from diabetic rats were stiffer and exhibited less creep when compressed. At the matrix level, elevated expression of hypoxia-inducible genes and catabolic markers in the discs from diabetic rats coincided with increased oxidative stress and greater interactions between AGEs and one of their receptors (RAGE). Taken together, these findings indicate that endplate sclerosis, increased oxidative stress, and AGE/RAGE-mediated interactions could be important factors for explaining the greater incidence of disc pathology in T2D.

Dynamic evaluation of pivot-shift kinematics in physeal-sparing pediatric anterior cruciate ligament reconstruction techniques.

BACKGROUND: Conventional transphyseal anterior cruciate ligament (ACL) reconstruction techniques in skeletally immature patients have been questioned because of potential physeal injuries. Consequently, multiple alternative reconstruction options have been described to restore stability while sparing the physes in the skeletally immature patient. HYPOTHESIS: All pediatric reconstruction techniques will restore knee stability to intact levels, and the knee stability index (KSI) will discriminate stability patterns between reconstruction techniques. STUDY DESIGN: Controlled laboratory study. METHODS: A novel mechanical pivot-shift device (MPSD) that consistently applies dynamic loads to cadaveric knees was used to study the effect of different physeal-sparing ACL reconstruction techniques on knee stability. Six adult cadaveric fresh-frozen knees were used. All knees were tested with 3 physeal-sparing reconstruction techniques: all epiphyseal (AE), transtibial over the top (TT), and iliotibial band (ITB). The MPSD was used to consistently perform a simulated pivot-shift maneuver. Tibial anterior displacement (AD), internal rotation (IR), posterior translational velocity (PTV), and external rotational velocity (ERV) were recorded using an Optotrak navigation system. The KSI (score range, 0-100; 0 = intact knee) was quantified using a regression analysis of AD, IR, PTV, and ERV. Repeated-measures analysis of variance and logistic regression were used for comparison of kinematics and derivation of KSI coefficients, respectively. RESULTS: ACL deficiency resulted in an increase of 20% to 115% in all primary stability measures tested compared with the ACL-intact state. All reconstructions resulted in a decrease in ADmax and IRmax as well as PTVmax and ERVmax to within intact ranges, indicating that all reconstructions do improve stability compared with the ACL-deficient state. The ITB reconstruction overconstrained AD and IR by 38% and 52%, respectively. The mean (±SD) KSI for the ACL-deficient state was 61.7 ± 22.2 (range, 47-100), while the ITB reconstruction had a mean KSI of 0.82 ± 24.0 (range, -24 to 35), the TT reconstruction had a mean KSI of 13.3 ± 8.9 (range, 0.3-23), and the AE reconstruction had a mean KSI of -4.0 ± 15.2 (range, -24 to 14). The KSI was not significantly different between reconstructions, and all were significantly lower than the ACL-deficient state (P < .0001). CONCLUSION: Although all reconstruction techniques tested were able to partially stabilize an ACL-deficient knee, the AE reconstruction was most effective in restoring native knee kinematics under dynamic loading conditions that mimic the pivot-shift test. CLINICAL RELEVANCE: This study provides orthopaedic surgeons with objective dynamic rotational data on the ability of physeal-sparing ACL reconstructions to better determine the ideal technique for ACL construction in skeletally immature patients.

Direct lateral approach to lumbar fusion is a biomechanically equivalent alternative to the anterior approach: an in vitro study.

STUDY DESIGN: A human cadaveric biomechanical study of lumbar mobility before and after fusion and with or without supplemental instrumentation for 5 instrumentation configurations. OBJECTIVE: To determine the biomechanical differences between anterior lumbar interbody fusion (ALIF) and direct lateral interbody fusion (DLIF) with and without supplementary instrumentation. SUMMARY OF BACKGROUND DATA: Some prior studies have compared various surgical approaches using the same interbody device whereas others have investigated the stabilizing effect of supplemental instrumentation. No published studies have performed a side-by-side comparison of standard and minimally invasive techniques with and without supplemental instrumentation. METHODS: Eight human lumbosacral specimens (16 motion segments) were tested in each of the 5 following configurations: (1) intact, (2) with ALIF or DLIF cage, (3) with cage plus stabilizing plate, (4) with cage plus unilateral pedicle screw fixation (PSF), and (5) with cage plus bilateral PSF. Pure moments were applied to induce specimen flexion, extension, lateral bending, and axial rotation. Three-dimensional kinematic responses were measured and used to calculate range of motion, stiffness, and neutral zone. RESULTS: Compared to the intact state, DLIF significantly reduced range of motion in flexion, extension, and lateral bending (P = 0.0117, P = 0.0015, P = 0.0031). Supplemental instrumentation significantly increased fused-specimen stiffness for both DLIF and ALIF groups. For the ALIF group, bilateral PSF increased stiffness relative to stand-alone cage by 455% in flexion and 317% in lateral bending (P = 0.0009 and P < 0.0001). The plate increased ALIF group stiffness by 211% in extension and 256% in axial rotation (P = 0.0467 and P = 0.0303). For the DLIF group, bilateral PSF increased stiffness by 350% in flexion and 222% in extension (P < 0.0001 and P = 0.0008). No differences were observed between ALIF and DLIF groups supplemented with bilateral PSF. CONCLUSION: Our data support that the direct lateral approach, when supplemented with bilateral PSF, is a minimally invasive and biomechanically stable alternative to the open, anterior approach to lumbar spine fusion.

Biomechanical evaluation of pediatric anterior cruciate ligament reconstruction techniques.

BACKGROUND: Anterior cruciate ligament (ACL) reconstruction rates in skeletally immature patients have risen recently because of increased injury frequency combined with growing awareness of the importance of treating them in an acute setting. Concerns over potential growth disturbances caused by traditional tunnel placement have prompted the description of several partial and complete physeal-sparing techniques. HYPOTHESIS: Native knee kinematics will most closely be restored by the all-epiphyseal technique because it best re-creates the intra-articular ACL anatomy. STUDY DESIGN: Controlled laboratory study. METHODS: Six cadaveric knees were subjected to static anteroposterior, varus, and internal rotation forces at 0°,15°, 30°, 45°, 60°, and 90° of flexion. Displacement and rotation of the tibia with respect to the femur were measured in the intact knee, after ACL disruption, and again after ACL reconstruction using all-epiphyseal, transtibial over-the-top, and iliotibial band physeal-sparing techniques. RESULTS: Peak anteroposterior translation in the ACL intact and deficient states was 2.8 ± 1.4 mm and 7.2 ± 2.7 mm, respectively, at 30°. The all-epiphyseal reconstruction had a peak translation of 5.1 ± 2.3 mm at 30°, and the transtibial over-the-top reconstruction had a peak of 4.8 ± 1.8 mm at 30°, both significantly greater than the ACL intact state. The iliotibial band technique had a peak anteroposterior translation of 1.7 ± 1.1 mm at 45°, which was significantly less than the ACL-deficient state. Internal rotation was significantly increased in the all-epiphyseal reconstruction compared with the ACL intact state and significantly decreased at all flexion angles except 0° in the iliotibial band reconstruction. The only technique to affect varus rotation was the iliotibial band reconstruction, which significantly decreased varus rotation from the ACL-deficient state at flexion angles greater than 30°. CONCLUSION: All physeal-sparing reconstruction techniques restored some stability to the knee. The iliotibial band reconstruction best restored anteroposterior stability and rotational control, although it appeared to overconstrain the knee to rotational forces at some flexion angles. CLINICAL RELEVANCE: This study provides orthopaedic surgeons with objective knee kinematic data to help guide them in making more informed decisions on the optimal technique for ACL reconstruction in skeletally immature patients.