Anesthesia-Related Closed Claims in Free-Standing Ambulatory Surgery Centers.

BACKGROUND: As higher acuity procedures continue to move from hospital-based operating rooms (HORs) to free-standing ambulatory surgery centers (ASCs), concerns for patient safety remain high. We conducted a contemporary, descriptive analysis of anesthesia-related liability closed claims to understand risks to patient safety in the free-standing ASC setting, compared to HORs. METHODS: Free-standing ASC and HOR closed claims between 2015 and 2022 from The Doctors Company that involved an anesthesia provider responsible for the claim were included. We compared the coded data of 212 free-standing ASC claims with 268 HOR claims in terms of severity of injury, major injuries, allegations, comorbidities, contributing factors, and financial value of the claim. RESULTS: Free-standing ASC claims accounted for almost half of all anesthesia-related cases (44%, 212 of 480). Claims with high severity of injury were less frequent in free-standing ASCs (22%) compared to HORs (34%; P = .004). The most common types of injuries in both free-standing ASCs and HORs were dental injury (17% vs 17%) and nerve damage (14% vs 11%). No difference in frequency was noted for types of injuries between claims from free-standing ASCs versus HORs--except that burns appeared more frequently in free-standing ASC claims than in HORs (6% vs 2%; P = .015). Claims with alleged improper management of anesthesia occurred less frequently among free-standing ASC claims than HOR claims (17% vs 29%; P = .01), as well as positioning-related injury (3% vs 8%; P = .025). No difference was seen in frequency of claims regarding alleged improper performance of anesthesia procedures between free-standing ASCs and HORs (25% vs 19%; P = .072). Technical performance of procedures (ie, intubation and nerve block) was the most common contributing factor among free-standing ASC (74%) and HOR (74%) claims. Free-standing ASC claims also had a higher frequency of communication issues between provider and patient/family versus HOR claims (20% vs 10%; P = .004). Most claims were not associated with major comorbidities; however, cardiovascular disease was less prevalent in free-standing ASC claims versus HOR claims (3% vs 11%; P = .002). The mean ± standard deviation total of expenses and payments was lower among free-standing ASC claims ($167,000 ± $295,000) than HOR claims ($332,000 ± $775,000; P = .002). CONCLUSIONS: This analysis of medical malpractice claims may indicate higher-than-expected patient and procedural complexity in free-standing ASCs, presenting patient safety concerns and opportunities for improvement. Ambulatory anesthesia practices should consider improving safety culture and communication with families while ensuring that providers have up-to-date training and resources to safely perform routine anesthesia procedures.

A Contemporary Analysis of Closed Claims Related to Wrong-Site Surgery.

BACKGROUND: Wrong-site surgeries are considered "never events" and continue to occur despite the implementation of the Universal Protocol by The Joint Commission in 2003. METHODS: The authors reviewed closed claims data on wrong-site surgery between 2013 and 2020 from a medical malpractice company. The claims were classified by allegations made by claimants, the responsible services, the types of procedures, the injuries, and contributing factors. Researchers performed a descriptive analysis of the available variables and reviewed the clinical summary of each case. RESULTS: Between 2013 and 2020, there were 68 wrong-site closed claims cases. The mean age of the patients was 55.7 (standard deviation 16.21) years, and 51.5% were female. The services most frequently responsible for these were Orthopedic (35.3%), Neurosurgery (22.1%), and Urology (8.8%). The most common types of procedures were spine and intervertebral disc surgery (22.1%), arthroscopy (14.7%), and surgery on muscles/tendons (11.8%). The severity of claims was higher in the inpatient setting compared to the ambulatory setting. The most common alleged injuries included the need for additional surgery (45.6%), pain (33.8%), mobility dysfunction (10.3%), worsened injury (8.8%), death (7.4%), and total loss (7.4%). The top contributing factors to wrong-site surgery were failure to follow policy/protocol (83.8%) and failure to review the medical records (41.2%). The mean closed claim value was $136,452.84, and 60.3% of cases were settled. CONCLUSION: The risk of wrong-site surgeries is increased with spine surgeries, likely due to unique technical challenges. Further research is required to identify effective methods of prevention of these events.

Determination of Ethnic Variation in Infant Nasolabial Anthropometry Using 3D Photographs: Implications for Bilateral Cleft Lip Nasal Correction.

OBJECTIVE: We aimed to assess significant ethnic variabilities in infants' nasolabial anthropometry to motivate variations in surgical correction of a synchronous bilateral cleft lip/nasal anomaly, specifically whether a long columella is a European feature, therefore accepting a short columella and/or delayed columellar lengthening suitable for reconstruction in ethnic patients. METHODS: Thirty-three infants without craniofacial pathology (10 African American [AA], 7 Hispanic [H], and 16 of European descent [C]), ages 3 to 8 months, presenting to the Johns Hopkins All Children's general pediatric clinic were recruited. Four separate 3D photographs (2 submental and frontal views each) were taken using the Vectra H1 handheld camera (Canfield Imaging). Eighteen linear facial distances were measured using Mirror 3D analysis (Canfield Imaging Systems). Difference between ethnicities was measured using analysis of variance with the Bonferroni/Dunn post hoc comparisons. Pearson correlation was employed for interrater reliability. All statistical analyses were carried out using SPSS version 21.0 (IBM Corp), with statistical significance set at P < .05. RESULTS: Nasal projection (sn-prn) and columella length (sn-c) did not differ significantly between groups (P = .9). Significant differences were seen between ethnic groups in nasal width (sbal-sbal [C-AA; P = .02]; ac-ac [C-AA; P = .00; H-AA; P = .04]; al-al [C-AA; P = .00; H-AA; P = .001]) and labial length (sn-ls [C-AA; P = .041]; sn-sto [C-AA; P = .005]; Cphs-Cphi L [C-AA; P = .013]; Cphs-Cphi R [C-AA; P = .015]). Interrater reliability was good to excellent and significantly correlated for all measures. CONCLUSIONS: African American infants exhibited wider noses and longer lips. No difference was noted in nasal projection or columella length, indicating that these structures should be corrected during the primary cleft lip and nasal repair for all patients and should not be deferred to secondary correction.

Right-sided heart failure is also associated with transverse tubule remodeling in the left ventricle.

Right-sided heart failure is a common consequence of pulmonary arterial hypertension. Overloading the right ventricle results in right ventricular hypertrophy, which progresses to failure in a process characterized by impaired Ca2+ dynamics and force production that is linked with transverse (t)-tubule remodeling. This also unloads the left ventricle, which consequently atrophies. Experimental left-ventricular unloading can result in t-tubule remodeling, but it is currently unclear if this occurs in right-sided heart failure. In this work, we used a model of monocrotaline (MCT)-induced right heart failure in male rats, using confocal microscopy to investigate cellular remodeling of t-tubules, junctophilin-2 (JPH2), and ryanodine receptor-2 (RyR2). We examined remodeling across tissue anatomical regions of both ventricles: in trabeculae, papillary muscles, and free walls. Our analyses revealed that MCT hearts demonstrated a significant loss of t-tubule periodicity, disruption of the normal sarcomere striated pattern with JPH2 labeling, and also a disorganized striated pattern of RyR2, a feature not previously reported in right heart failure. Remodeling of JPH2 and RyR2 in the MCT heart was more pronounced in papillary muscles and trabeculae compared with free walls, particularly in the left ventricle. We find that these structures, commonly used as ex vivo muscle preparations, are more sensitive to the disease process.NEW & NOTEWORTHY In this work, we demonstrate that t-tubule remodeling occurs in the atrophied left ventricle as well as the overloaded right ventricle after right-side heart failure. Moreover, we identify that t-tubule remodeling in both ventricles is linked to sarcoplasmic reticulum remodeling as indicated by decreased labeling periodicity of both the Ca2+ release channel, RyR2, and the cardiac junction-forming protein, JPH2, that forms a link between the sarcoplasmic reticulum and sarcolemma. Studies developing treatments for right-sided heart failure should consider effects on both the right and left ventricle.

Positive airway pressure for sleep-disordered breathing in acute quadriplegia: a randomised controlled trial.

RATIONALE: Highly prevalent and severe sleep-disordered breathing caused by acute cervical spinal cord injury (quadriplegia) is associated with neurocognitive dysfunction and sleepiness and is likely to impair rehabilitation. OBJECTIVE: To determine whether 3 months of autotitrating CPAP would improve neurocognitive function, sleepiness, quality of life, anxiety and depression more than usual care in acute quadriplegia. METHODS AND MEASUREMENTS: Multinational, randomised controlled trial (11 centres) from July 2009 to October 2015. The primary outcome was neurocognitive (attention and information processing as measure with the Paced Auditory Serial Addition Task). Daytime sleepiness (Karolinska Sleepiness Scale) was a priori identified as the most important secondary outcome. MAIN RESULTS: 1810 incident cases were screened. 332 underwent full, portable polysomnography, 273 of whom had an apnoea hypopnoea index greater than 10. 160 tolerated at least 4 hours of CPAP during a 3-day run-in and were randomised. 149 participants (134 men, age 46±34 years, 81±57 days postinjury) completed the trial. CPAP use averaged 2.9±2.3 hours per night with 21% fully 'adherent' (at least 4 hours use on 5 days per week). Intention-to-treat analyses revealed no significant differences between groups in the Paced Auditory Serial Addition Task (mean improvement of 2.28, 95% CI -7.09 to 11.6; p=0.63). Controlling for premorbid intelligence, age and obstructive sleep apnoea severity (group effect -1.15, 95% CI -10 to 7.7) did not alter this finding. Sleepiness was significantly improved by CPAP on intention-to-treat analysis (mean difference -1.26, 95% CI -2.2 to -0.32; p=0.01). CONCLUSION: CPAP did not improve Paced Auditory Serial Addition Task scores but significantly reduced sleepiness after acute quadriplegia. TRIAL REGISTRATION NUMBER: ACTRN12605000799651.

Outcomes of patients with spinal cord injury before and after introduction of an interdisciplinary tracheostomy team.

OBJECTIVES: To assess outcomes in patients with spinal cord injury (SCI) and a tracheostomy tube (TT), before and after the introduction of a tracheostomy review and management service (TRAMS) for ward-based patients. DESIGN: Matched-pairs design with two cohorts, before and after the intervention. SETTING: 900-bed tertiary hospital in Melbourne, Victoria. PARTICIPANTS: SCI patients with a TT that was removed: 34 patients in the post-TRAMS period (September 2003 to September 2006) were matched to 34 from the pre-TRAMS period (September 1999 to December 2001). INTERVENTION: TRAMS was introduced as a consultative team of specialist physicians, clinical nurse consultants, physiotherapists and speech pathologists. The team coordinated tracheostomy care, conducted twice-weekly rounds, and provided policy, education, and support. MAIN OUTCOME MEASURES: Comparison of length of stay (LOS), duration of cannulation (DOC), improved communication through use of a one-way valve, number of adverse events and related costs. RESULTS: Median patient LOS decreased from 60 days (interquartile range [IQR], 38-106) to 41.5 days (IQR, 29- 62) (P = 0.03). The pre-TRAMS median DOC decreased from 22.5 days (IQR, 17-58) to 16.5 days (IQR, 12-25) (P = 0.08). Speaking-valve use increased from 35% (12/34) to 82% (28/34) (P < 0.01). Median time to a valve trial decreased from 22 days (IQR, 13-44) to 6 days (IQR, 4-10) after TT insertion (P < 0.01). There were two tracheostomy-related medical emergency calls pre-TRAMS and none post-TRAMS. There were no tracheostomy-related deaths in either group. The annual cost savings from implementing TRAMS were about eight times greater than the cost of service provision. CONCLUSION: Implementing a tracheostomy review and management service improved outcomes for SCI patients: they left acute care sooner, spoke sooner, and the TT was removed earlier, with associated cost savings.

High-throughput quantification of Alzheimer's disease pathological markers in the post-mortem human brain.

Quantitative analysis of amyloid plaques and neurofibrillary tangles is central to many Alzheimer's disease studies. A novel approach for quantitative immunohistochemistry of plaques and tangles has arisen from the need to account for the heterogeneous expression pattern of these markers in the human brain. This approach aims to overcome the human bias inherent to many sampling strategies, to account for the effects of tissue shrinkage resulting from antigen-retrieval procedures, and to accelerate the analysis of large sample sets by using a high-throughput quantification system. The procedure entailed three coordinated steps: acquisition of montaged images of entire tissue sections, randomised sampling across the cortex, and automated quantification of the selected samples with morphometric image analysis software. Two-dimensional estimates of plaque and tangle densities were obtained from the superior temporal gyrus and middle temporal gyrus of Alzheimer's disease and normal human brains. Results showed a robust correlation between the numbers of plaques and tangles quantified by automated image analysis and those acquired by manual counting. Correction for antigen-retrieval tissue shrinkage ensured that density measurements were not over-estimated. The value and applicability of this assay was demonstrated by the statistically significant differences observed between the averaged densities of plaques and tangles within different investigational groups. We report an accurate and objective approach to the quantification of plaques and tangles in human brain tissue. Implementation of a randomised sampling strategy coupled with a reproducible automated quantification system will facilitate more rigorous comparison of quantitative data derived from different immunohistochemical studies.

Immunohistochemical study of monocyte chemoattractant protein-1 in the pancreas of NOD mice following cyclophosphamide administration and during spontaneous diabetes.

In type 1 diabetes mellitus (T1DM), the processes which control the recruitment of immune cells into pancreatic islets are poorly defined. Complex interactions involving adhesion molecules, chemokines and chemokine receptors may facilitate this process. The chemokine, monocyte chemoattractant protein-1 (MCP-1), previously shown to be important in leukocyte trafficking in other disease systems, may be a key participant in the early influx of blood-borne immune cells into islets during T1DM. In the non-obese diabetic (NOD) mouse, the expression of MCP-1 protein has not been demonstrated. We employed dual-label immunohistochemistry to examine the intra-islet expression, distribution and cellular source of MCP-1 in the NOD mouse following cyclophosphamide administration. NOD mice were treated with cyclophosphamide at day 72-73 and MCP-1 expression studied at days 0, 4, 7, 11 and 14 after treatment and comparisons were made between age-matched NOD mice treated with diluent and non-diabetes-prone CD-1 mice. Pancreatic expression of MCP-1 was also examined in NOD mice at various stages of spontaneous diabetes. In the cyclophosphamide group at day 0, MCP-1 immunolabelling was present in selective peri-islet macrophages but declined at day 4. It increased slightly at day 7 but was more marked from day 11, irrespective of diabetes development. The pattern of MCP-1 expression in macrophages was different over time in both the cyclophosphamide and control groups. In the cyclophosphamide group, there was a change over time with an increase at day 11. In the control group, there was little evidence of change over time. There was no significant difference in the mean percentage of MCP-1 positive macrophages between the cyclophosphamide-treated diabetic and non-diabetic mice. During spontaneous diabetes in the NOD mouse, only a few peri-islet MCP-1 cells appeared at day 45. These became more numerous from day 65 but were absent at diabetes onset. We speculate that a proportion of early islet-infiltrating macrophages which express MCP-1 may attract additional lymphocytes and macrophages into the early inflamed islets and intensify the process of insulitis.

ASPAN's [corrected] EBP conceptual model: framework for perianesthesia practice and research.

The American Society of PeriAnesthesia Nurses (ASPAN) highly regards evidence-based practice (EBP) as a guide to promoting "Best Practices" and improving patient outcomes. EBP is now considered the "gold standard" in improving patient care through the use of the best available evidence. EBP models provide the health care provider with a rigorous systematic method of rating and appraising the evidence that includes, but is not limited to, randomized controlled trials, descriptive studies, qualitative studies, national guidelines, and expert opinion. ASPAN's EBP Team was charged with the development of an EBP Conceptual Model to provide the framework for future perianesthesia practice, education, and research. This article describes how ASPAN's EBP model may be used as a framework for practice and research.

Histopathological changes in insulin, glucagon and somatostatin cells in the islets of NOD mice during cyclophosphamide-accelerated diabetes: a combined immunohistochemical and histochemical study.

The cyclophosphamide model of accelerated diabetes in the NOD mouse is a useful model of insulin-dependent diabetes mellitus (IDDM). Knowledge on the progressive destruction of beta cells and the fate of other islet endocrine cell-types in this model is sparse. We employed immunohistochemistry and histochemistry, to study temporal changes in islet cell populations, insulitis and glucose transporter-2 expression during cyclophosphamide administration. Cyclophosphamide was administered to day 95 female NOD mice and the pancreas studied at days 0 ( = day 95), 4, 7, 11 and 14 after treatment and in age-matched control mice. At day 0, a majority of the endocrine cells were insulin-positive. Glucagon and somatostatin cells were mostly in the islet periphery and also internally. In the cyclophosphamide group, insulitis was moderate at day 0, declined at day 4 but increased progressively from day 7. The extent of insulitis in treated mice which were diabetes-free at day 14 was comparable to age-matched control mice. From day 11, the marked increase in insulitis correlated with a reciprocal decline in the extent of insulin immunostained islet area. At day 14, the mean insulin area per islet was markedly less in diabetic mice than in age-matched non-diabetic treated and controls. At diabetes, some islets showed co-expression of glucagon and insulin. Our studies suggest that the mean number of glucagon or somatostatin cells per islet does not vary during the study. Glucose transporter-2 immunolabelling was restricted to beta cells but declined in those adjacent to immune cells. We conclude that in the cyclophosphamide model, there is specific and augmented destruction of beta cells immediately prior to diabetes onset. We speculate that the selective loss of glucose transporter-2 shown in this study suggests the existence of a deleterious gradient close to the immune cell and beta cell surface boundary.

Vagal innervation of the air sacs in a songbird, Taenopygia guttata.

The air sacs of birds are thin-walled chambers connected to the lung that act as bellows in the ventilatory mechanism. Physiological evidence exists to suggest that they may contain receptors that are innervated by the vagus nerve, but no morphological study has examined the vagal innervation of these putative structures. To do this, we injected the cervical vagus nerve with choleragenoid and examined the innervation of the air sacs using light and confocal microscopy. We identified vagally innervated structures in the air sac wall that resemble the neuroepithelial bodies (NEBs) described in the airways of many vertebrates. Although NEBs have been proposed to have a dual chemoreceptive and mechanoreceptive role, their specific function in the air sacs of birds remains unclear.

Fas and Fas ligand immunoexpression in pancreatic islets of NOD mice during spontaneous and cyclophosphamide-accelerated diabetes.

During insulin-dependent diabetes mellitus, beta cell destruction may involve activation of the Fas-Fas ligand (Fas-FasL) system. Here, we employed dual-label immunohistochemistry to examine the intra-islet expression, distribution, and cellular sources of Fas and FasL in the NOD mouse. Pancreatic tissues were studied during spontaneous diabetes (days 21, 40, and 90) and following acceleration of diabetes with cyclophosphamide (days 0, 4, 7, 11, and 14 after cyclophosphamide administration). Our results show that FasL was expressed constitutively in most beta cells of NOD mice and in nondiabetes-prone mice, but not in glucagon or somatostatin cells or in islet inflammatory cells. It paralleled the loss of insulin immunolabeling with advancing disease. Immunolabeling for Fas was first observed in extra-islet macrophages and those close to the islet in NOD and nondiabetes-prone mice. During spontaneous and cyclophosphamide diabetes, it was observed in a higher proportion of islet infiltrating macrophages than in CD4 and CD8 cells. In the cyclophosphamide group, Fas expression in intra-islet CD4 and CD8 cells showed an increase close to the onset of diabetes. At days 11 and 14, several intra-islet macrophages with immunolabeling for Fas also coexpressed interleukin-1beta and inducible nitric oxide synthase. Fas was not detected in beta cells and other endocrine cells during spontaneous and cyclophosphamide diabetes. We show constitutive expression of FasL in beta cells in the NOD mouse and predominant expression of Fas in intra-islet macrophages and to a lesser extent in T cells prior to diabetes onset. The role of Fas-FasL in beta cell destruction in the NOD mouse requires further clarification.

Immunolocalization of caspase-3 in pancreatic islets of NOD mice during cyclophosphamide-accelerated diabetes.

Apoptosis may be a major mechanism of beta cell loss during insulin-dependent diabetes mellitus. Caspase-3 is a key enzyme involved in the terminal steps of this death process. Here, the intra-islet expression of caspase-3 in the NOD mouse was examined immunohistochemically following acceleration of the disease with cyclophosphamide. Female NOD mice were treated at day 95 with cyclophosphamide, and caspase-3 expression in pancreatic sections was studied at days 0, 4, 7, 11, and 14 and compared with age-matched control tissue. In the treated group at day 0, caspase-3 labeling was seen in several peri-islet macrophages and only extremely rarely in beta cells. At day 4, only a few beta cells weakly expressed the enzyme. From day 7, caspase-3 expression began to increase in intra-islet macrophages and reached a peak at days 11 and 14, when a small number of CD4 and CD8 T cells also showed positive labeling. Beta cell expression of caspase-3 at days 11 and 14 was rare. At this stage, several intra-islet immune cells with positive labeling for the enzyme coexpressed either Fas or interleukin-1beta. Only a small proportion of intra-islet caspase-3 cells showed apoptotic nuclei judged by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). We conclude that, during cyclophosphamide-accelerated diabetes, the predominant caspase-3 immunolabeling in intra- and extra-islet macrophages suggests that apoptosis of macrophages may be an important mechanism for their elimination. The virtual absence of caspase-3 immunolabeling in most beta cells even during the height of beta cell loss supports the need for developing other markers of early beta cell apoptosis in the NOD mouse.

Immunohistochemical study of caspase-3-expressing cells within the pancreas of non-obese diabetic mice during cyclophosphamide-accelerated diabetes.

During insulin-dependent diabetes mellitus, immune cells infiltrate pancreatic islets progressively and mediate beta cell destruction over a prolonged asymptomatic prediabetic period. Apoptosis may be a major mechanism of beta cell loss during the disease. This process involves a proteolytic cascade in which upstream procaspases are activated which themselves activate downstream caspases, including caspase-3, a key enzyme involved in the terminal apoptotic cascade. Here dual-label immunohistochemistry was employed to examine the intra-islet expression, distribution and cellular sources of active caspase-3 in the non-obese diabetic (NOD) mouse given cyclophosphamide to accelerate diabetes. NOD mice were treated at day 95 and caspase-3 expression was studied at days 0, 4, 7, 11 and 14. Its expression was also correlated with advancing disease and compared with age-matched NOD mice treated with diluent alone. At day 0 (=day 95), caspase-3 immunolabelling was observed in several peri-islet and intra-islet macrophages, but not in CD4 and CD8 cells and only extremely rarely in beta cells. At day 4, only a few beta cells weakly expressed the enzyme, in the absence of significant insulitis. At day 7, caspase-3 expression was observed in a small proportion of intra-islet macrophages. At day 11, there was a marked increase in the number of intra-islet macrophages positive for caspase-3 while only a few CD4 cells expressed the enzyme. At day 14, caspase-3 labelling became prominent in a significant proportion of macrophages. Only a few CD4 and CD8 cells expressed the enzyme. Capase-3 labelling was also present in a proportion of macrophages in perivascular and exocrine regions. Surprisingly, beta cell labelling of caspase-3 at days 11 and 14 was rare. At this stage of heightened beta cell loss, a proportion of intra-islet interleukin-1beta-positive cells coexpressed the enzyme. Caspase-3 was also observed in numerous Fas-positive cells in heavily infiltrated islets. During this late stage, only a proportion of caspase-3-positive cells contained apoptotic nuclei, as judged by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL). We conclude that during cyclophosphamide-accelerated diabetes in the NOD mouse, the predominant immunolabelling of caspase-3 in intra-islet macrophages suggests that apoptosis of macrophages may be an important mechanism for its elimination. The virtual absence of caspase-3 immunolabelling in most beta cells even during heightened beta cell loss supports their rapid clearance following their death during insulin-dependent diabetes mellitus.

Distribution of newly synthesized aggrecan in explant cultures of bovine cartilage treated with retinoic acid.

This paper describes temporal changes in the metabolism and distribution of newly synthesized aggrecan and the organization of the extracellular matrix when explant cultures of articular cartilage maintained in the presence of fetal calf serum were exposed to retinoic acid for varying periods of time. Explant cultures of articular cartilage were incubated with radiolabeled sulfate prior to exposure to retinoic acid. The radiolabeled and chemical aggrecan present in the tissue and appearing in the culture medium was studied kinetically. Changes in the localization of radiolabeled aggrecan within the extracellular matrix were monitored by autoradiography in relation to type VI collagen distribution in the extracellular matrix. In control cultures where tissue levels of aggrecan remain constant the newly synthesized aggrecan remained closely associated with the territorial matrix surrounding the chondrocytes. Exposure of cultures to retinoic acid for the duration of the experiment, resulted in the extensive loss of aggrecan from the tissue and the redistribution of the remaining radiolabeled aggrecan from the chondron and territorial matrix into the inter-territorial matrix. These changes preceded alterations in the organization of type VI collagen in the extracellular matrix that involved the remodeling of the chondron and the appearance of type VI collagen in the inter-territorial matrix; there was also evidence of chondrocyte proliferation and clustering. In cartilage explant cultures exposed to retinoic acid for 24 h there was no loss of aggrecan from the matrix but there was an extensive redistribution of the radiolabeled aggrecan into the inter-territorial matrix. This work shows that maintenance of the structure and organization of the extracellular matrix that comprises the chondron and pericellular microenvironment of chondrocytes in articular cartilage is important for the regulation of the distribution of newly synthesized aggrecan monomers within the tissue.