Association of Knee Osteoarthritis and Flexion Contracture With Localized Tibial Articular Cartilage Loss: Data From the Osteoarthritis Initiative.

OBJECTIVE: To evaluate whether a knee flexion contracture (FC) was associated with localized tibial articular cartilage loss over a 1-year period using Osteoarthritis Initiative quantitative data. METHODS: Five hundred seventy-eight participants from a previously established nested case-control study of people with radiographic knee OA with or without progression, based on radiographs and symptoms, had their knee range of extension measured at baseline and received magnetic resonance imaging (MRI) at baseline and 1 year. The tibial articular cartilage of the medial and lateral condyles was segmented into anterior, center, and posterior regions. We tested for associations between knee FC (defined as lack of extension to 0°), and localized changes in tibial articular cartilage thickness or percent of denuded bone (0 mm thickness) after 1 year relative to baseline using ANOVA, controlling for baseline MRI outcomes and clinical factors. RESULTS: Knee FC was associated with denuded bone in the medial condyle center (ß 0.44, 95% CI 0.02-0.86) and preserved cartilage thickness in the medial condyle posterior (ß 0.01, 95% CI 0.002-0.03) regions. CONCLUSION: Knee FC unloading the tibial center region and loading the posterior region was associated with localized articular cartilage loss centrally and preserved articular cartilage posteriorly. These findings are consistent with knee FC negatively affecting unloaded tibial articular cartilage.

Baseline knee extension may be associated with volumetric cartilage loss in the anterolateral tibia: data from the Osteoarthritis Initiative.

OBJECTIVES: Animal studies suggest regional unloading of the knee due to flexion contracture (FC) results in cartilage loss in the anterior tibia. We looked for an association between the range of knee extension and articular cartilage thickness in the tibia of patients with knee OA, using quantitative MRI data from the OA Initiative. METHODS: Baseline knee extension was measured using a goniometer. Cartilage thickness was measured using 3-Tesla coronal MRI images of the knee. The tibia articular cartilage was segmented into medial and lateral regions, then further divided into anterior, central and posterior subregions. We evaluated differences between participants with and without a knee FC and associations between knee extension and cartilage thickness, including percentage denudation of bones (0 mm thickness), using linear models. RESULTS: A total of 596 participants were included. Participants with a knee FC had a larger percentage of denuded bone in the anterolateral tibia vs participants without FC (2.2 ± 0.7% vs 0.4 ± 0.1%; P = 0.006), and knee extension was associated with anterolateral tibia denuded bone (r = 0.16, P < 0.001). After correcting for demographics, knee alignment, and OA severity, presence of FC and lost knee extension were associated with the percentage of denuded bone in the anterolateral tibia [ß = 1.702 (0.634-2.770) and ß = 0.261 (95% CI 0.134, 0.388), respectively]. CONCLUSION: While causation cannot be determined in this study, limitation in knee extension was statistically associated with the percentage of denuded bone in the anterolateral tibia. These novel data support that maintaining range of motion over the entire joint surface may help preserve articular cartilage health.

Characterizing the effect of exposure to microgravity on anemia: more space is worse.

The effects of space travel have renewed importance with space tourism and plans for long-term missions to the moon and Mars. The study of space anemia is limited by the availability of subjects and extreme conditions. An approach using the accumulated data on human space flight may characterize space anemia. A total of 17 336 hemoglobin (Hb) concentration measures from 721 space missions and controls were used to study acute and long-term effects of duration of exposure to space on Hb decrement. Nearly half of astronauts (48%) landing after long duration missions were anemic. Returning to Earth revealed Hb decrements whose magnitude and time to recover were dependent on exposure to space: -0.61 g/dL (4%), -0.82 g/dL (5%) and -1.66 g/dL (11%) of preflight Hb for mean exposure to space of 5.4, 11.5, and 145 days, respectively. Astronauts returning from a mean 5.4 days in space took 24 days to return to preflight Hb while astronauts 11.5 to 145 days in space took 49 days. Negative effects of microgravity on Hb persisted throughout female and male astronauts' terrestrial lives (-0.001 and -0.002 mg/dL Hb respectively) for every day spent in space (both P < .05). The negative effect of exposure to space was not overcome by a statistically significant effect of being an astronaut compared to controls. Exposure to space showed a dose-response relationship with acute and chronic Hb decrements. Space anemia contributes to the deconditioning of astronauts returning to Earth, and needs to be considered for space travel to other planets, space tourism and for the care of bedridden patients who present similar changes as astronauts.

Tendon contains more stem cells than bone at the rotator cuff repair site.

BACKGROUND: The rotator cuff (RC) repair failure rate is high. Tendon and bone represent sources of mesenchymal stem cells (MSCs), but the number of MSCs from each has not been compared. Bone channeling may increase bone-derived MSC numbers participating in enthesis re-formation at the "footprint" repair site. The effect of preoperative channeling on increasing bone MSC numbers has never been reported. We asked (1) whether bone contains more MSCs than tendon at the time of arthroscopic repair and (2) whether bone preoperative channeling at the RC repair site increases the number of bone-derived MSCs at the time of surgery. METHODS: In 23 participants undergoing arthroscopic RC repair, bone was sampled from the footprint and tendon was sampled from the distal supraspinatus. We randomized participants to the channeling or no-channeling group 5 to 7 days before surgery. We enumerated MSCs from both tissues using the colony-forming unit-fibroblast (CFU-F) assay (10 per group). We identified MSC identity using flow cytometry and MSC tri-differentiation capacity (n = 3). RESULTS: Tendon CFU-F per gram exceeded bone CFU-F per gram for both groups (479 ± 173 CFU-F/g vs. 162 ± 54 CFU-F/g for channeling [P = .036] and 1334 ± 393 CFU-F/g vs. 284 ± 88 CFU-F/g for no channeling [P = .009]). Ninety-nine percent of cultured cells satisfied the MSC definition criteria. CONCLUSIONS: The distal supraspinatus tendon contained more MSCs per gram than the humeral footprint. Tendon may represent an important and overlooked MSC source for postoperative enthesis re-formation. Further studies are needed to evaluate the repair role of tendon MSCs and to recommend bone channeling in RC repair.

Imaging of the rabbit supraspinatus enthesis at 7 Tesla: a 4-week time course after repair surgery and effect of channeling.

PURPOSE: To image the supraspinatus enthesis reformation of rabbit shoulders by magnetic resonance at 7 Tesla (T) using T2 mapping after surgical repair and to assess the effects of channeling aimed at enhancing enthesis reformation. MATERIALS AND METHODS: In 112 rabbits, the distal supraspinatus (SSP) tendon was unilaterally detached and reattached after 1 week. At the first surgery, channeling was performed at the footprint in 64 rabbits. At the second surgery, the SSP tendon of all rabbits was re-attached to the greater tuberosity. The shoulders were harvested at 0, 1, 2, or 4 weeks after the repair surgery and were imaged at 7T. Quantitative T2 mapping was performed using multi slice two-dimensional multi-echo spin-echo sequence with fat saturation. Enthesis regions of interests were drawn on three slices at the footprint to measure T2 relaxation times. RESULTS: Tendon repair (F(2, 218) = 44; P < 2.2e-16) and postoperative duration (F(3, 218) = 4.8; P = 0.006) both affected significantly the T2 values while channeling had no significant effect. For the time effect, the only pair with a statistical difference was the 0-week and 4-week for the channeling groups (P = 0.023). CONCLUSION: Enthesis reformation early after surgical repair of the SSP distal tendon was characterized by increasing T2 values. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:461-467.

Temporal gene expression profiling of the rat knee joint capsule during immobilization-induced joint contractures.

BACKGROUND: Contractures of the knee joint cause disability and handicap. Recovering range of motion is recognized by arthritic patients as their preference for improved health outcome secondary only to pain management. Clinical and experimental studies provide evidence that the posterior knee capsule prevents the knee from achieving full extension. This study was undertaken to investigate the dynamic changes of the joint capsule transcriptome during the progression of knee joint contractures induced by immobilization. We performed a microarray analysis of genes expressed in the posterior knee joint capsule following induction of a flexion contracture by rigidly immobilizing the rat knee joint over a time-course of 16 weeks. Fold changes of expression values were measured and co-expressed genes were identified by clustering based on time-series analysis. Genes associated with immobilization were further analyzed to reveal pathways and biological significance and validated by immunohistochemistry on sagittal sections of knee joints. RESULTS: Changes in expression with a minimum of 1.5 fold changes were dominated by a decrease in expression for 7732 probe sets occurring at week 8 while the expression of 2251 probe sets increased. Clusters of genes with similar profiles of expression included a total of 162 genes displaying at least a 2 fold change compared to week 1. Functional analysis revealed ontology categories corresponding to triglyceride metabolism, extracellular matrix and muscle contraction. The altered expression of selected genes involved in the triglyceride biosynthesis pathway; AGPAT-9, and of the genes P4HB and HSP47, both involved in collagen synthesis, was confirmed by immunohistochemistry. CONCLUSIONS: Gene expression in the knee joint capsule was sensitive to joint immobility and provided insights into molecular mechanisms relevant to the pathophysiology of knee flexion contractures. Capsule responses to immobilization was dynamic and characterized by modulation of at least three reaction pathways; down regulation of triglyceride biosynthesis, alteration of extracellular matrix degradation and muscle contraction gene expression. The posterior knee capsule may deploy tissue-specific patterns of mRNA regulatory responses to immobilization. The identification of altered expression of genes and biochemical pathways in the joint capsule provides potential targets for the therapy of knee flexion contractures.

Quantitative analysis of the reversibility of knee flexion contractures with time: an experimental study using the rat model.

BACKGROUND: Knee flexion contractures prevent the full extension of the knee joint and cause disability. The etiology is not well defined. Extended periods of immobilization of joints lead to contractures difficult to completely reverse by rehabilitation treatments. Recovery of the complete range of motion without intervention has not been studied but is of importance to optimize clinical management. This study was designed to quantify the spontaneous reversibility of knee flexion contractures over time. METHODS: Knee flexion contractures of increasing severities were induced by internally fixing one knee of 250 adult male rats for 6 increasing durations. The contractures were followed for four different durations of spontaneous recovery up to 48 weeks (24 groups, target n=10 per group). The angle of knee of extension at a standardized torque was measured. Contralateral knees constituted controls. RESULTS: Full reversibility characterized by knee extension similar to controls was only measured in the lowest severity group where 4 weeks of spontaneous recovery reversed early-onset contractures. Spontaneous recovery of 2, 4 and 8 weeks caused partial gain of knee extension in longer-lasting contractures (P ≤ 0.05; all 4 comparisons). Extending the durations of spontaneous recovery failed to further improve knee extension (P>0.05, all 12 comparisons). No reversal occurred in the highest severity group (32 week; P>0.05). CONCLUSIONS: Reversibility of knee flexion contractures was dependent on their severity. Full spontaneous recovery was limited to the least severe contractures. While contractures initially improved, a plateau was reached beyond which additional durations of spontaneous recovery led to no additional gain of knee extension. These results support our view that without treatment, permanent losses in knee mobility must be anticipated in immobility-induced contractures.

Transcriptomic evidence of erythropoietic adaptation from the International Space Station and from an Earth-based space analog.

Space anemia affects astronauts and the underlying molecular alterations remain unknown. We evaluated the response of erythropoiesis-modulating genes to spaceflight through the analysis of leukocyte transcriptomes from astronauts during long-duration spaceflight and from an Earth model of microgravity. Differential expression analysis identified 50 genes encoding ribosomal proteins with reduced expression at the transition to bed rest and increased during the bed rest phase; a similar trend was observed in astronauts. Additional genes associated with anemia (15 genes), erythrocyte maturation (3 genes), and hemoglobin (6 genes) were down-regulated during bed rest and increased during reambulation. Transcript levels of the erythropoiesis transcription factor GATA1 and nine of most enriched erythrocyte proteins increased at reambulation after bed rest and at return to Earth from space. Dynamic changes of the leukocyte transcriptome composition while in microgravity and during reambulation supported an erythropoietic modulation accompanying the hemolysis of space anemia and of immobility-induced anemia.

The Characteristic Response of the Human Leukocyte Transcriptome to 60 Days of Bed Rest and to Reambulation.

INTRODUCTION: We sought to isolate the microgravity effect of spaceflight from other space stressors by characterizing the leukocytes' transcriptome of participants to a 60-d bed rest study; an Earth model of microgravity. METHODS: Twenty healthy men received a nutritional supplement or not and 10 blood samples were collected throughout three study phases: baseline data collection (BDC) (BDC-12, BDC-11), head-down tilt (HDT) bed rest (HDT1, HDT2, HDT30, HDT60), and reambulation (R1, R2, R12, R30). We measured gene expression through RNA sequencing of leukocytes, applied generalized linear models to assess differential expression followed by enrichment analysis to identify temporal changes (model 1) and to measure the impact of a nutritional supplement (model 2). RESULTS: Baseline transcriptomes included 14,624 protein-coding transcripts and showed both high intraindividual correlations (mean Kendall coefficient, 0.91 ± 0.04) and interindividual homogeneity (0.89 ± 0.03). We identified 2415 differentially expressed protein-coding transcripts grouping into six clusters (C1-C6). At phase transitions, clusters showed either a decrease-then-increase (C3 and C5) or an increase-then-decrease (C1, C2, C6) pattern. All six clusters converged toward average expression at HDT30 and HDT60. Gene ontology terms at baseline related to immune functions while in bed rest and reambulation related to sequestration of ions, immune response, cellular stress, and mineralization. The nutritional intervention had no effect. CONCLUSIONS: The temporal profiles of leukocytes' transcriptomes emphasized the dynamic nature of gene expression occurring during and after bed rest. Enriched biological processes among the differentially expressed genes included immune related and unrelated responses. The convergence toward no differential expression at days 30 and 60 of bed rest suggests a hypometabolic state. Current findings can guide future work on the complex responses and adaptation mechanisms to microgravity.

The transcriptome response of astronaut leukocytes to long missions aboard the International Space Station reveals immune modulation.

Introduction: Spaceflight leads to the deconditioning of multiple body systems including the immune system. We sought to characterize the molecular response involved by capturing changes in leukocyte transcriptomes from astronauts transitioning to and from long-duration spaceflight. Methods: Fourteen male and female astronauts with ~6-month- long missions aboard the International Space Station (ISS) had 10 blood samples collected throughout the three phases of the study: one pre-flight (PF), four in-flight (IF) while onboard the ISS, and five upon return to Earth (R). We measured gene expression through RNA sequencing of leukocytes and applied generalized linear modeling to assess differential expression across all 10 time points followed by the analysis of selected time points and functional enrichment of changing genes to identify shifts in biological processes. Results: Our temporal analysis identified 276 differentially expressed transcripts grouped into two clusters (C) showing opposite profiles of expression with transitions to and from spaceflight: (C1) decrease-then-increase and (C2) increase-then-decrease. Both clusters converged toward average expression between ~2 and ~6 months in space. Further analysis of spaceflight transitions identified the decrease-then-increase pattern with most changes: 112 downregulated genes between PF and early spaceflight and 135 upregulated genes between late IF and R. Interestingly, 100 genes were both downregulated when reaching space and upregulated when landing on Earth. Functional enrichment at the transition to space related to immune suppression increased cell housekeeping functions and reduced cell proliferation. In contrast, egress to Earth is related to immune reactivation. Conclusion: The leukocytes' transcriptome changes describe rapid adaptations in response to entering space followed by opposite changes upon returning to Earth. These results shed light on immune modulation in space and highlight the major adaptive changes in cellular activity engaged to adapt to extreme environments.

Bone marrow adiposity modulation after long duration spaceflight in astronauts.

Space travel requires metabolic adaptations from multiple systems. While vital to bone and blood production, human bone marrow adipose (BMA) tissue modulation in space is unknown. Here we show significant downregulation of the lumbar vertebrae BMA in 14 astronauts, 41 days after landing from six months' missions on the International Space Station. Spectral analyses indicated depletion of marrow adipose reserves. We then demonstrate enhanced erythropoiesis temporally related to low BMA. Next, we demonstrated systemic and then, local lumbar vertebrae bone anabolism temporally related to low BMA. These support the hypothesis that BMA is a preferential local energy source supplying the hypermetabolic bone marrow postflight, leading to its downregulation. A late postflight upregulation abolished the lower BMA of female astronauts and BMA modulation amplitude was higher in younger astronauts. The study design in the extreme environment of space can limit these conclusions. BMA modulation in astronauts can help explain observations on Earth.

Skeletal anatomy of the pectoral fin in mudskipper species from terrestrial and aquatic habitats.

Mudskippers are a group of amphibious fishes in the family Oxudercidae, whose species inhabit a range of habitats from mostly aquatic to mostly terrestrial. Most of our understanding about habitat preference comes from natural history observations, particularly where they are collected (i.e., low intertidal vs. high intertidal regions). Mudskippers have undergone several morphological changes to accommodate a terrestrial life, including major changes to the pectoral and pelvic girdles. These changes result in a novel crutching gait, which mudskippers use to move over land. Though the appendicular morphology and crutching gait of mudskippers have been described in some species, few studies have compared skeletal structures across the family. In our study, we use microcomputed tomography (µCT) scans to compare the skeletal anatomy of 16 species of aquatic and terrestrial mudskippers. Linear discriminant analysis is used to analyze measurements obtained through geometric morphometrics (landmarks). We found bone structures of the pectoral region in the terrestrial group were significantly longer and wider than those in the aquatic group. Furthermore, a significant difference in anatomy is shown between terrestrial and aquatic genera with both axial and appendicular elements contributing to the separation between groups. This work describes the differences in skeletal morphology associated with terrestriality in mudskippers and provides valuable insights into specific anatomical characteristics contributing to their adaptation to novel environments.

Hemolysis contributes to anemia during long-duration space flight.

Anemia in astronauts has been noted since the first space missions, but the mechanisms contributing to anemia in space flight have remained unclear. Here, we show that space flight is associated with persistently increased levels of products of hemoglobin degradation, carbon monoxide in alveolar air and iron in serum, in 14 astronauts throughout their 6-month missions onboard the International Space Station. One year after landing, erythrocytic effects persisted, including increased levels of hemolysis, reticulocytosis and hemoglobin. These findings suggest that the destruction of red blood cells, termed hemolysis, is a primary effect of microgravity in space flight and support the hypothesis that the anemia associated with space flight is a hemolytic condition that should be considered in the screening and monitoring of both astronauts and space tourists.

Effect of rehabilitation on biologic and transcriptomic responses after hospital-acquired deconditioning: a prospective longitudinal feasibility study.

PURPOSE: The objective of this study is to explore the transcriptomic and biologic variables characterizing the longitudinal rehabilitation intervention of patients with hospital-acquired deconditioning (HAD). METHODS: This prospective clinical trial recruited HAD patients (n = 10) who spent ≥3 weeks hospitalized and then received inpatient rehabilitation. Functional improvement was measured using the Functional Independence Measure (FIM). Transcriptomic and biological variables were recorded at rehabilitation admission and 1, 2, 4, and 6 weeks post-admission. RNA sequencing studied the temporal changes of gene expression in leukocytes. Between-subject transcriptome comparisons were performed using principle component analysis. Within-subject changes in gene expression were analyzed using a gene ontology hierarchical clustering to identify common biological terms. Heart rate, weight, albumin, creatinine, and complete blood counts were analyzed. RESULTS: Patients average age was 50.6 ± 7.2, FIM increased during inpatient rehabilitation (p = 0.01), weight increased (p = 0.01), lymphocytes decreased (p = 0.05), neutrophil increased (0.03) and red cell distribution width decreased (p = 0.05). The temporal profiles of gene expression revealed within-patient homogeneity and between-patients heterogeneity. The biological terms "bone morphogenesis" and "muscle cell development" were the most significantly enriched differentially expressed genes. CONCLUSION: Transcriptomic and biologic markers paralleled the functional improvements of HAD patients during inpatient rehabilitation. Transcriptomic analyses were consistent with the cohort heterogeneity. Enrichment of the biological pathways bone morphogenesis and muscle cell development constituted evidence at the gene expression level of the effect of rehabilitation. Larger studies of various rehabilitation patient groups may increase gene expression profile homogeneity. Objective transcriptomic and biologic markers have the potential to improve the rehabilitation of HAD patients.IMPLICATIONS FOR REHABILITATIONNovel gene expression methods are increasingly being integrated into clinical practice and may apply to rehabilitation.Patients with hospital-acquired deconditioning (HAD) enriched gene expression of pathways targeted by inpatient rehabilitation such as bone morphogenesis and muscle cell development.The gene expression paralleled functional improvement of HAD patients.These data demonstrated the feasibility of molecular methods to identify markers of rehabilitation success in HAD patients.

Six degrees head-down tilt bed rest caused low-grade hemolysis: a prospective randomized clinical trial.

This study aimed to measure hemolysis before, during and after 60 days of the ground-based spaceflight analog bed rest and the effect of a nutritional intervention through a prospective randomized clinical trial. Twenty male participants were hospitalized for 88 days comprised of 14 days of ambulatory baseline, 60 days of 6° head-down tilt bed rest and 14 days of reambulation. Ten participants each received a control diet or daily polyphenol associated with omega-3, vitamin E, and selenium supplements. The primary outcome was endogenous carbon monoxide (CO) elimination measured by gas chromatography. Hemolysis was also measured with serial bilirubin, iron, transferrin saturation blood levels and serial 3-day stool collections were used to measure urobilinoid excretion using photometry. Total hemoglobin mass (tHb) was measured using CO-rebreathing. CO elimination increased after 5, 11, 30, and 57 days of bed rest: +289 ppb (95% CI 101-477 ppb; p = 0.004), +253 ppb (78-427 ppb; p = 0.007), +193 ppb (89-298 ppb; p = 0.001) and +858 ppb (670-1046 ppb; p < 0.000), respectively, compared to baseline. Bilirubin increased after 20 and 49 days of bed rest +0.8 mg/l (p = 0.013) and +1.1 mg/l (p = 0.012), respectively; and iron increased after 20 days of bed rest +10.5 µg/dl (p = 0.032). The nutritional intervention did not change CO elimination. THb was lower after 60 days of bed rest -0.9 g/kg (p = 0.001). Bed rest enhanced hemolysis as measured through all three by-products of heme oxygenase. Ongoing enhanced hemolysis over 60 days contributed to a 10% decrease in tHb mass. Modulation of red blood cell control towards increased hemolysis may be an important mechanism causing anemia in astronauts.

Rotator cuff anchor repair: Histological changes associated with the recovering mechanical properties in a rabbit model.

Rotator cuff anchor repair is an increasingly common surgical procedure but the failure rate remains high. In order to improve surgical outcomes, a better understanding of postrepair histological and cellular responses at the tendon-bone attachment site (enthesis) is needed. We examined operated shoulders from 42 New Zealand female white rabbits. The animals underwent unilateral supraspinatus detachment followed by anchor repair a week later. To assess enthesis reformation, fibrocartilage staining area and the number of chondrocytes or nonchondrocytes were quantified at 0, 1, 2, and 4 weeks postrepair. Using linear regression, we correlated these results with the load to failure and stiffness recorded during mechanical testing of the tendons. Fibrocartilage staining and chondrocyte number increased during the first 2 weeks of enthesis formation. Between 2 and 4 weeks, fibrocartilage staining plateaued while chondrocyte number decreased. The presence of nonchondrocytes remained similar between 0- and 1-week postrepair but then decreased abruptly at 2 weeks. There was a linear correlation between fibrocartilage staining area and load to failure as well as stiffness. Nonchondrocyte number negatively correlated with stiffness. Early plateau of fibrocartilage staining and decrease in chondrocytes between 2 and 4 weeks postrepair suggest a blunted enthesis formation response in our animal model.

Bone replaces unloaded articular cartilage during knee immobilization. A longitudinal study in the rat.

BACKGROUND: Joint immobility results in deleterious changes such as capsule shortening, bone loss and articular cartilage damage. Immobilization of rat knees in flexion for 32 weeks resulted in the distinctive feature of well-established replacement of articular cartilage by bone. Determining the time of onset of bone replacement is critical for the prevention of this likely irreversible complication of joint immobilization. OBJECTIVES: To determine the onset and progression of bone replacement in the anterior tibial articular cartilage following knee immobilization in flexion. METHODS: One hundred forty-nine adult male Sprague-Dawley rats were used. The experimental groups had one knee immobilized at 135°of flexion for durations of 2, 4, 8, 16 or 32 weeks and were compared to age-matched controls. The knees were evaluated histologically for the presence and cross-sectional area of bone within the articular cartilage of the tibia. Distance between the anterior aspect of the tibia and intact articular cartilage and cross-sectional bone area of the tibial epiphysis were also measured. RESULT: Bone replacement in the articular cartilage was observed in 14%, 75%, 95%, 100% and 100% of knees after 2, 4, 8, 16 and 32 weeks of immobilization, respectively. No bone replacement was seen in the control knees. The mean area of bone replacement increased from 0.004 ± 0.007 mm2 after 2 weeks to 0.041 ± 0.036 mm2; 0.085 ± 0.077 mm2; 0.092 ± 0.056 mm2 and 0.107 ± 0.051 mm2 after 4, 8, 16 and 32 weeks of immobilization, respectively, (p < 0.001) largely restricted to the anterior tibial articular cartilage. Mean distance to intact articular cartilage increased from 0.89 ± 0.69 mm at 2 weeks to 1.10 ± 0.35 mm; 1.65 ± 0.77 mm; 1.48 ± 0.63 mm; and 1.78 ± 0.58 mm after 4, 8, 16 and 32 weeks of immobilization, respectively (p = 0.001). Epiphyseal bone cross-sectional area was significantly reduced following 4, 8, and 16 weeks of immobilization compare to controls (all 3 p < 0.05). CONCLUSION: Knee immobilization in flexion resulted in bone replacement in the anterior tibial articular cartilage that began after 2 weeks and was prevalent after 4 weeks of immobilization. The bone replacement progressed in an anterior-to-posterior direction and stopped at the area of contact between tibia and femur. These findings stress the importance of mobility to maintain joint health.

Bone Marrow Reconversion With Reambulation: A Prospective Clinical Trial.

METHODS: In a prospective clinical trial, 20 healthy men participated in a 60-day, 6-degree head-down tilt bed rest study. Serial 3-T magnetic resonance (MR) imaging measures of the lumbar spine were performed at baseline, after 57 days of bed rest, and at 30, 360, and 720 days of reambulation (100 MR imaging scans). Proton density with and without fat saturation, 2-point Dixon, and single-voxel MR spectroscopy techniques were used to assess bone marrow composition (300 measures). Erythropoiesis was measured using hematocrit, reticulocyte, and ferritin. Also, participants randomly received either a nutritional intervention composed of polyphenols, omega-3, vitamin E, and selenium or a normal diet. RESULTS: Thirty days of reambulation after 60 days of bed rest caused a marked decrease of the mean lumbar vertebral fat fraction (VFF) (-9.2 ± 1.6 percentage points, -8.0 ± 1.3 percentage points, and -12.7 ± 1.2 percentage points compared with baseline using proton density, Dixon, MR spectroscopy, respectively; all 3, P < 0.05). Reambulation also decreased the fat saturation index (-5.3 ± 1.1 percentage points compared with baseline; P < 0.05). These coincided with lower hematocrit and ferritin and with increased reticulocytes at reambulation day 13 compared with baseline (all 3, P < 0.05). After 57 days of bed rest, the VFF was unchanged from baseline (all 3 MR techniques, P > 0.05); reambulation for 2 years returned the lumbar VFF to baseline values. INTERPRETATION: This longitudinal trial established that 30 days of reambulation after 60 days of bed rest constituted a powerful stimulus for bone marrow reconversion. In this model, the enhanced erythropoiesis coupled with preferential consumption of fatty acids from regulated marrow adipose tissue to supply energy for erythropoiesis and bone anabolism may explain the lumbar vertebrae reconversion. These results will help interpreting bone marrow signal in ambulatory patients after long periods of bed rest.

Preoperative bone marrow stimulation does not improve functional outcomes in arthroscopic cuff repair: a prospective randomized controlled trial.

AIMS: Despite recent advances in arthroscopic rotator cuff repair, re-tear rates remain high. New methods to improve healing rates following rotator cuff repair must be sought. Our primary objective was to determine if adjunctive bone marrow stimulation with channelling five to seven days prior to arthroscopic cuff repair would lead to higher Western Ontario Rotator Cuff (WORC) scores at 24 months postoperatively compared with no channelling. METHODS: A prospective, randomized controlled trial was conducted in patients undergoing arthroscopic rotator cuff repair. Patients were randomized to receive either a percutaneous bone channelling of the rotator cuff footprint or a sham procedure under ultrasound guidance five to seven days prior to index surgery. Outcome measures included the WORC, American Shoulder and Elbow Surgeons (ASES), and Constant scores, strength, ultrasound-determined healing rates, and adverse events. RESULTS: Overall, 94 patients were randomized to either bone channelling or a sham procedure. Statistically significant improvements in all clinical outcome scores occurred in both groups from preoperative to all timepoints (p < 0.001). Intention-to-treat analysis revealed no statistical differences in WORC scores between the two interventions at 24 months postoperatively (p = 0.690). No differences were observed in secondary outcomes at any timepoint and healing rates did not differ between groups (p = 0.186). CONCLUSION: Preoperative bone channelling one week prior to arthroscopic rotator cuff repair was not associated with significant improvements in WORC, ASES, Constant scores, strength, or ultrasound-determined healing rates. Cite this article: Bone Joint J 2021;103-B(1):123-130.