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Infections associated with implants are the most serious complications in joint replacement surgeries and can jeopardize the functionality of orthopedic implants. Local antimicrobial delivery could enable antibiotics to attain concentrations above the minimum inhibitory concentration (MIC) threshold at the joint replacement site while preventing systemic side effects. Therefore, there is a dire need for the development of improved biomaterial-based delivery systems for local antibiotic administration in prosthetic infections. In this context, this review highlights the latest breakthroughs in the design of biomaterial-based formulations intended for the prophylaxis and treatment of prosthetic infections. Delivery systems for distinct forms of administration (i.e., direct intra-articular administration, loading into bone cements, coating of implant surfaces, or loading into hydrogels) are here comprehensively compiled with a focus on the design of microparticles and nanosystems for local antimicrobial administration and their impact on distinct in vitro and in vivo models of implant infections., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Importance: The field of meniscal root preservation has undergone significant advancement over the past decades; however, the challenge remains to fully understand whether meniscal root repair can ultimately arrest or delay osteoarthritic changes., Objective: To assess longitudinal changes in articular cartilage, subchondral bone, and progression to meniscal extrusion (ME) using high-resolution magnetic resonance imaging (MRI)., Methods: Medial meniscus posterior root tear was surgically induced in 39 New Zealand white rabbits. Animals were randomly assigned into three experimental groups: partial meniscectomy after root tear (PM, n ​= ​13); root tear left in situ (CT, n ​= ​13); and transtibial root repair (RR, n ​= ​13). Contralateral limbs were used as healthy controls. High resolution 4.7 Tesla MRI of the knee joint was performed at baseline, after 2-, and 4-months of post-surgery. Cartilage thickness was calculated in medial and lateral compartments. In addition, the evaluation of ME, subchondral bone edema and healing potential after root repair were assessed too., Results: Progressive cartilage thinning, ME, and subchondral bone edema were evident in all 3 study groups after 4-months of follow-up. The mean cartilage thickness in the PM group was 0.53 ​mm (±0.050), 0.57 ​mm (±0.05) in the CT group, and 0.60 ​mm (±0.08) in the RR group. The PM group exhibited significantly higher cartilage loss when compared to the CT and RR groups (p ​< ​0.001). Moreover, progressive ME and subchondral bone edema were associated with a more severe cartilage loss at the final follow-up., Conclusion: Meniscal root repair did not halt but rather reduced the progression of osteoarthritis (OA). Degenerative changes worsened at a rapid rate in the PM group compared to the RR and CT groups. Early cartilage swelling, persistent subchondral edema, and progressive ME predicted a more severe progression to knee OA in the CT and RR groups., Level of Evidence: II., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: The real degree of constraint of rotating hinge knee and condylar constrained prostheses is a matter of discussion in revision knee arthroplasty. The objective of this study is to compare the tibial rotation between implants in the clinical settings., Methods: An investigator blinded experimental study was designed including 20 patients: in 10 of them a rotating hinge knee prosthesis (Endomodel®, LINK) was implanted and in the remaining 10 a constrained condylar knee prosthesis (LCCK®, Zimmer) was used. A medial parapatellar approach was performed and implantation was performed according to conventional surgical technique. Tibial rotation was measured with two accelerometers in full extension and at 30°, 60° and 90° of flexion. Pre and postoperative Knee Injury and Osteoarthritis Outcome Score was recorded., Findings: Both groups were homogenous in age (73.4 years in rotating hinge knee prosthesis vs 74 years in constrained condylar knee group), sex, laterality and preoperative Knee Injury and Osteoarthritis Outcome Score (p > 0.05). The postoperative Knee Injury and Osteoarthritis Outcome Score was significantly higher in the rotating hinge knee prosthesis group (80.98 vs 76.28). The degrees of tibial rotation measured by inertial sensors in the rotating hinge knee prosthesis group were also significantly higher than those measured in the constrained condylar knee group (5.66° vs 2.1°) with p = 0.001., Interpretation: Rotating hinge knee prosthesis appears to represent a lower rotational constraint degree than constrained condylar knee systems in clinical practice and it may increase the clinical satisfaction. The clinical significance: Rotating hinge knee prosthesis appears to represent a lower constraint degree than constrained condylar knee systems in clinical practice., Competing Interests: Declaration of Competing Interest “Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.”, (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Background: The optimal treatment option for meniscus root tears is still challenging, and whether the meniscus root repair ultimately can arrest or delay osteoarthritic changes is still a concern., Purpose/hypothesis: The purpose of this study was 2-fold: (1) to describe and compare histopathologic findings of 3 different therapeutic options for medial meniscus posterior root tear: nonoperative management, partial meniscectomy, and meniscus root repair; and (2) to test the hypothesis that meniscus root tears treated nonoperatively predispose to a lower risk of osteoarthritic progression compared with partial meniscectomy., Study Design: Controlled laboratory study., Methods: Posteromedial meniscus root tears were carried out in 39 New Zealand White rabbits. Animals were randomly assigned into 3 experimental groups: partial meniscectomy after root tear (PM; n = 13), root tears treated conservatively (CT; n = 13), and transtibial root repair (RR; n = 13). Contralateral limbs were used as healthy controls. The animals were euthanized at 16 weeks postoperatively; tissue samples of femoral and tibial articular cartilage were collected and processed for macro- and microscopic assessment to detect signs of early osteoarthritis (OA). Each sample was histopathologically assessed using the Osteoarthritis Research Society International grading and staging system., Results: Osteoarthritic changes were the hallmark in all 3 experimental groups. The RR group had the lowest scores for cartilage damage (mean, 2.5; range, 2-3), and the PM group exhibited higher and more severe signs of OA (mean, 16; range, 9-16) compared with the CT group (mean, 5; range, 4-6). The between-group comparison revealed significant differences, as the PM group showed a significantly higher rate of macro- and microscopic osteoarthritic changes compared with the RR ( P < .001) and CT ( P < .001) groups. The weightbearing area of the medial femoral condyle was the most severely affected, and tidemark disruption was evident in all tissue samples., Conclusion: Meniscus root repair cannot completely arrest the histopathologic progression of knee OA but leads to significantly less severe degenerative changes than partial meniscectomy and nonoperative treatment. Partial meniscectomy leads to the most severe osteoarthritic progression, while stable radial tears left in situ have lower progression compared with partial meniscectomy., Clinical Relevance: Histologic assessment is an essential tool and metric for guiding and understanding osteoarthritic features, providing insight into the disease development and progression. This study provides histopathologic evidence on osteoarthritic progression after medial meniscus posterior root repair. This knowledge can help to set more realistic expectations and can lead to the future development of augmented techniques.

Introduction: The correct positioning of the implant in revision total hip arthroplasty (rTHA) is critical to obtaining substantial functional outcomes, and to avoiding complications. Current literature supports three-dimensional (3D)-printed models as potentially useful tools for preplanning, as well as the "do it yourself (DIY)" methodology to reduce both the time and costs of this procedure. However, no study has determined the efficacy of both methods combined in a cohort of patients with severe acetabular defects. In the lack of bibliography, we performed rTHA after preoperative planning by DIY-3D-printed models to evaluate its influence in: 1) the surgical time, 2) the functional scores, 3) the intra and postoperative complications, and 4) the reconstruction of the center of rotation (COR) of the hip., Hypothesis: Preoperative planning through 3D-DIY printed models will both improve the accuracy of the implant positioning, and the surgical time, leading the latter to improved functional scores and reduced complications., Materials & Methods: A comparative study of 21 patients with Paprosky IIB to IIIB acetabular defects who underwent rTHA after 3D-printed model preoperative planning by the DIY method between 2016 and 2019 was conducted. A historical cohort of 24 patients served as the comparator. Surgical time, reconstruction of the COR, functional scores, and complications were analyzed., Results: The mean follow-up was 32.4 (range, 12 to 60) months. All the patients showed significant improvement of the Harris hip score (HHS) after the operation (3D group: 26.58±10.73; control group 22.47±15.43 (p=0.00)). In the 3D-printed model preoperative planning group the mean operation time and the intraoperative complications were significantly lower (156.15±43.03min vs 187.5±54.38min (p=0.045); and 19% vs 62.5% (p=0.003), respectively), and the HHS and patient satisfaction score (PSS) were significantly greater (83.74±8.49 vs 75.59±11.46 (p=0.019); and 8.17±0.88 vs 7.36±1.17 (p=0.023), respectively). No differences were found in the postoperative complications, nor in the restoration of the COR as determined from the acetabular index, verticalization or horizontalization, although the acetabular index was closer to the intended one in the 3D-printed model planning group (46.67°±7.63 vs 49.22±8.1 (p=0.284))., Conclusion: Preoperative planning of severe acetabular defects through 3D-printed models shortens the surgical time, leading to a decrease in complications and thus to better functional outcomes and greater patient satisfaction. Moreover, the DIY philosophy could decrease both the time and costs of traditional 3D planning., Level of Evidence: III, retrospective case matched study., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Purpose: To develop a predictable and reproducible model of knee osteoarthritis after medial meniscus posterior root release., Methods: Posteromedial meniscal root tears were created in 12 White New Zealand rabbit knees. The contralateral limbs were used as healthy controls. The animals were euthanized at 16 weeks postoperatively; tissue samples of femoral and tibial articular cartilage were collected and processed for macro and microscopic analyses to detect signs of early degeneration. Clinical evaluation of the weight-bearing status on the affected knee was conducted at 0-, 4-, 8-, and 16-weeks postoperatively., Results: Early and severe osteoarthritic changes were the hallmark and the main findings after 16-weeks post-surgery. Macroscopically, extensive osteoarthritic changes were observed across the femoral condyle and tibial plateau. Microscopic finding included ulcerations, fissures, fibrillations, pitting, and loss of the superficial layer. Cellularity was diminished, the normal pattern of distribution in columns was lost, and subchondral bone exposure was also evident., Conclusions: This study describes a novel model of knee osteoarthritis that may guide the development of tailored interventions to delay or prevent knee osteoarthritis. This knowledge could shift the current treatment paradigm toward more conservative and knee salvageable treatment options and increase surgeons' awareness of this injury pattern. Such considerations may have a positive impact on clinical decision-making and subsequent patient-reported clinical outcomes., Design: Controlled laboratory study., Level of Evidence: II., (© 2022. The Author(s).)

Purpose: The purpose of this study was to compare clinical and radiological outcomes of transtibial pullout technique and partial meniscectomy, and to establish prognostic factors in middle-aged patients with mild knee osteoarthritis., Methods: A comparative case-control analysis was conducted. 65 patients between 40 and 60 years of age were included into two groups: 30 patients who underwent transtibial pullout technique (group 1) and 35 patients who underwent partial meniscectomy (group 2). Mean follow-up was set at 27.2 months. Primary clinical outcomes included Knee injury and Osteoarthritis Outcome Score and Lysholm Knee Questionnare. Preoperative MRI and intraoperative arthroscopic findings were recorded. The correlation between these findings and patient-reported subjective outcome were assessed., Results: The transtibial pullout group exhibited significantly greater improvement in clinical outcomes. A univariate model revealed that the presence of preoperative meniscal extrusion, body mass index (> 30), osteochondral defect, and female gender were predictors of poor clinical outcome. Multivariate regression analysis showed meniscal extrusion and osteochondral defect as significant prognostic factors for both study groups., Conclusion: Medial meniscus root repair leads to significantly improved clinical outcomes compared to partial meniscectomy in middle-aged patients with mild knee osteoarthritis. Presence of meniscal extrusion, osteochondral defect, BMI > 30, and female gender were deemed as predictors of poor postoperative patient-reported outcome., Level of Evidence: III therapeutic case-control study., Competing Interests: Conflict of InterestThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© Indian Orthopaedics Association 2022.)

Purpose: Microencapsulation techniques have allowed the addition of rifampicin to bone cement, but its in vivo efficacy has not been proven. The aim of our study is to determine the superiority of cement containing gentamicin and rifampicin microcapsules in the treatment of PJI versus cement exclusively containing gentamicin., Methods: An S. aureus PJI was induced in 15 NZW rabbits. A week after inoculation, the first stage of replacement was carried out, and the animals were divided into two groups: group R received a spacer containing gentamicin and rifampicin microcapsules, and group C received a spacer containing gentamicin. Intra-articular release curve of rifampicin and infection and toxicity markers were monitored for four weeks post-operatively, when microbiological analysis was performed., Results: The microbiological cultures showed a significantly lower growth of S. aureus in soft tissue (2.3·10 4 vs 0; p = 0.01) and bone (5.7·10 2 vs 0; p = 0.03) in the group with rifampicin microcapsules. No differences were found in systemic toxicity markers. Rifampicin release from the cement spacer showed higher concentrations than the staphylococcal MIC throughout the analysis., Conclusion: The in vivo analyses demonstrated the superiority of cement containing gentamicin and rifampicin microcapsules versus the isolated use of gentamicin in the treatment of PJI in the rabbit model without serious side effects due to the systemic absorption of rifampicin. Given the increasing incidence of staphylococci-related PJI, the development of new strategies for intra-articular administration of rifampicin for its treatment has a high clinical impact., (© 2022. The Author(s).)

Introduction: There is a paucity of comparative clinical data between arthroscopic all-inside end-to-end meniscal root suture and transtibial pullout technique in medial meniscus posterior root tears (MMPRT). Therefore, this study aimed to compare treatment failure, mid-term clinical and radiological outcomes of all-inside meniscus root repair versus the transtibial pullout technique and to analyze prognostic factors of postoperative clinical and radiological outcomes., Material and Methods: Forty-four patients were included in two therapeutic group: arthroscopic all-inside meniscal suture (MS: 13 knees) and transtibial pullout technique (TP: 31 knees).Primary clinical outcomes at a minimum of 27.2 months postoperatively included Knee injury and Osteoarthritis Outcome Score (KOOS) and Lysholm Knee Questionnare (LKQ). Radiographic assessment of the knee was performed to determine osteoarthritis severity using the Kellgren-Lawrence (KL) grading system.In addition, pre and postoperative MRI scans and intraoperative arthroscopic findings were recorded and the correlations between these findings, as outcome predictors and postoperative patients reported subjective outcome were assessed., Results: No significant differences in postoperative KOOS and LKQ scores were found between the MS and TP group (p = 0.38 and 0.17, respectively).During follow-up one patients (7.7%) in the MS group and two (6.5%) in the TP group underwent total knee arthroplasty. The difference did not reach the statistical significance (p = 0.88).No differences were observed in postoperative MRI findings such as meniscal extrusion, osteochondral defect, chondromalacia patella, and bone morrow edema (p = 0.25, 0.97, 0.97, and 0.88, respectively).A univariate model revealed that the presence of postoperative meniscal extrusion; osteochondral defect; chondromalacia patella; increased BMI; age (>40 years) and longer time lapse between clinical onset to surgery (>6 months) were predictors of poor clinical outcome. The presence of meniscal extrusion, osteochondral defect and chondropatia patella portended worst postoperative outcomes in a multiple linear regression model., Conclusions: It can be concluded that both techniques can reach good results when performed properly and if the injury pattern allows meniscal suture may be considered a treatment option for the management of MMPRT in well-selected patients.Patients with increased BMI, preoperative meniscal extrusion, chondromalacia patella, and osteochondral defect were at higher risk of poor clinical outcomes., (© 2021 Professor P K Surendran Memorial Education Foundation. Published by Elsevier B.V. All rights reserved.)

The real degree of constriction of rotating hinge knee (RHK) and condylar constrained prostheses (CCK) is a matter of discussion in revision knee arthroplasty. The objectives of this study are to compare the tibial rotation of both implants and validate the use of inertial sensors with optical tracking system as movement measurement tools. A total of 16 cadaver knees were used. Eight knees were replaced using a RHK (Endomodel LINK), and the remaining eight received a CCK prosthesis (LCCK, Zimmer). Tibial rotation range of motion was measured in full extension and at 30°, 60°, and 90° of flexion, with four continuous waveforms for each measurement. Measurements were made using two inertial sensors with specific software and compared with measurements obtained using the gold standard technique - the motion capture camera. The comparison of the accuracy of both measurement methods showed no statistically significant differences between inertial sensors and motion capture cameras, with p > .1; the mean error for tibial rotation was 0.21°. Tibial rotation in the RHK was significantly greater than in the CCK (5.25° vs. 2.28°, respectively), p < .05. We have shown that RHK permit greater tibial rotation, being closer to physiological values than CCKs. Inertial sensors have been validated as an effective and accurate method of measuring knee movement. The clinical significance: RHK appears to represent a lower constriction degree than CCK systems., (© 2020 Orthopaedic Research Society. Published by Wiley Periodicals LLC.)

Introduction: The management of massive femoral bone defects following prosthetic infection remains a surgical challenge, particularly when the entire femur is affected., Methods: We present the first results of a new biarticular cement spacer with antibiotic technique using a cephalomedullary nail for the treatment of infected hip arthroplasty involving complete femoral bone loss., Results: 5 patients with a minimum follow-up of 1 year were included. In all cases 2-stage replacement due to hip periprosthetic infection was carried out, with the need for a biarticular complete femoral spacer in view of the magnitude of the bone defect. The infection was resolved in all patients, with no complications (spacer fracture or dislocation) associated to spacer use, and the patients were all able to maintain the sitting position with active knee movements between the 2 surgical stages. Improvement with respect to preoperative functional status was observed in all cases, as evidenced by the Harris Hip Score (HHS) (from 24.2 to 73; p  < 0.001) and 12-Item Short-Form Health Survey (SF-12) (from 16.8 to 33.2; p  = 0.001), with a lessened need for walking aids., Discussion: The described technique offers a possible solution to a number of complications observed with the use of spacers in massive defects, affording greater patient comfort and autonomy while waiting to receive total femoral replacement.

Background: Infection after arthroplasty (prosthetic joint infection; PJI) is a devastating complication that can lead to functional loss of the affected limb. The purpose of the present study is to develop an animal model of PJI using a three-dimensional printed species-specific implant, which is a step forward for future research to develop new therapeutic strategies., Methods: Fifteen New Zealand White rabbits were employed to reproduce PJI by intra-articular inoculation of 10 5  cfu/ml of Staphylococcus aureus ATCC® 29213. Three-dimensional printing technology was used to design a species-specific four-millimeter-thick implant maintaining the anatomical irregularities of the tibial-articular surface. Response to bacterial inoculation was monitored by clinical (weight and temperature), hematological (leukocyte, lymphocyte and platelet counts) and biochemical (erythrocyte sedimentation rate) analyses at the time of inoculation and seven days thereafter, when microbiological samples for culture were also taken., Results: All animals recovered from surgery and all displayed full weight-bearing four days postoperatively. Fourteen of the 15 tested animals (93.3%) presented positive microbiological cultures. A statistically significant increase was found in the number of platelets and leukocytes, as well as a significant decrease in the percentage of lymphocytes, with P = 0.0001 in all cases., Conclusions: An experimental model faithfully reproducing the periprosthetic infection environment and achieving a high rate of infection has been designed. The use of three-dimensional printed species-specific implants allows rapid postoperative recovery of animals and the development of a stable biofilm. These characteristics make it an interesting model to study its pathogenesis and possible therapeutic strategies., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to disclose., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: The increase in life expectancy has led to the appearance of a subgroup of hip fracture (HF) patients with special characteristics known as centenarians. The aim of the present study is to analyse the demographic characteristics, complications and mortality rate of this subgroup in order to identify the specific risk factors for mortality in these patients., Methods: Retrospective analysis of 69 patients (58 women and 11 men) aged 100 years or older admitted to a tertiary hospital for HF between 1999 and 2018., Results: The average age was 101.3 years (100-108, median 101). More than half (62.3%) of all patients presented with extracapsular fractures. The most common complications observed were delirium (52.3%) and urinary retention (27.7%). Haematoma (9.2%) was the most common surgical complication. Only 3 patients (7.3%) changed their place of residence after admission. In-hospital, 30-day and 1-year mortality rates were 13.8%, 21.5% and 54.2%, respectively. A high Charlson Comorbidity Index and baseline Functional Ambulation Classification (FAC) <3 were associated with a higher in-hospital mortality rate (OR = 1.95 95% CI [1.03-3.69] and OR = 5.7 95% CI [1.2-26.8]), respectively. The presence of more than 3 comorbidities and baseline FAC <3 were associated with a higher risk of 30-day mortality (OR = 6, 95% CI [1.4-24.7] and OR = 4, 95% CI [1.13-14.2]), respectively. Dementia has been associated with a higher risk of 30-day and 1-year mortality (OR = 4.6, 95% CI [1.2-16.7]) and OR = 5.11, 95% CI [1.6-21]) respectively., Conclusion: FAC score, number of comorbidities, dementia and the Charlson Comorbidity Index have been shown to be risk factors of mortality in centenarians with HF., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Introduction: Periprosthetic infection is considered an increasing incidence pathology whose therapeutic strategies can be defined as unsatisfactory. Currently, animal models are employed to study its physiopathology and strategic therapies, but non-species-specific materials are implanted as foreign bodies. The use of these implants implies intrinsic instability, which hinders the development of a biofilm on their surfaces and complicates the post-operative recovery of the animal. The objective of the present study is the design of a species-specific implant for the New Zealand white (NZW) rabbit by means of 3D printing., Materials and Methods: A CT scan of the knee of a NZW rabbit was performed, and the tibial surface was reconstructed in order to fabricate a species-specific tibial plateau using Horos ® and Autodesk ® Meshmixer™ software. This implant was inserted in fifteen NZW rabbits, and the assessment of its stability was based on the position of the limb at rest and the animal weight-bearing capacity. Biofilm formation on the surface was demonstrated by crystal violet staining., Results: A 1.81 cm × 1 cm × 1.24 cm stainless steel implant was designed. It consisted of a 4-mm-thick tibial plate with a rough surface and an eccentric metaphyseal anchoring. All of the animals exhibited hyperflexion of the operated limb immediately post-operative, and 100% could apply full weight bearing from day 5 after surgery., Conclusions: The species-specific design of implants in experimental surgery encourages rapid recovery of the animal and the development of a biofilm on their surfaces, making them ideal for the study of the physiopathology and for establishing possible therapeutic targets for prosthetic infection.

Introduction: Acetabular revision surgery poses a challenge due to the increased frequency of severe defects and poor quality of the remaining bone. We compare the clinical and radiological outcomes, complications, and survival of two systems commonly used in complex acetabular revisions (AAOS types II, III, and IV): trabecular metal system (TM) and Burch-Schneider antiprotrusion cages (BS)., Methods: Eighty-four patients underwent acetabular revision surgery with TM or BS in our centre between 2008 and 2014. Comparison was made of demographic and clinical characteristics, satisfaction, radiographic parameters, complications, and survival of the implants. A BS was implanted in 30.9% of the patients, while 69.1% received a TM implant. The mean follow-up was 4.77 years., Results: The BS group required a significantly greater number of constrained implants (p = 0.001) and more walking aids (p = 0.04). The mean satisfaction (p = 0.02) and HHS scores at the end of the follow-up were higher in the TM group (p = 0.003). No differences were observed in the incidence of complications, though the only two cases of implant rupture corresponded to the BS group. The overall survival rate was 88.1% after 7.5 years., Conclusion: TM implants afforded better clinical outcomes and greater patient satisfaction than antiprotrusion cages in the treatment of severe acetabular defects.

The echinoderm nervous system is one of the least studied among invertebrates, partly because the tools available to study the neurobiology of this phylum are limited. We have now produced a monoclonal antibody (RN1) that labels a nervous system component of the sea cucumber Holothuria glaberrima. Western blots show that our antibody recognizes a major band of 66 kDa and a minor band of 53 kDa. Immunohistological experiments show that, in H. glaberrima, the antibody distinctly labels most of the known nervous system structures and some components that were previously unknown or little studied. A surprising finding was the labeling of nervous plexi within the connective tissue compartments of all organs studied. Double labeling with holothurian neuropeptides and an echinoderm synaptotagmin showed that RN1 labeled most, if not all, of the fibers labeled by these neuronal markers, but also a larger component of cells and fibers. The presence of a distinct connective tissue plexus in holothurians is highly significant since these organisms possess mutable connective tissues that change viscosity under the control of the nervous system. Therefore, the cells and fibers recognized by our monoclonal antibodies may be involved in controlling tensility changes in echinoderm connective tissue.

The holothuroid echinoderm Holothuria glaberrima can regenerate its intestine after a process of evisceration. Spherule-containing cells, the spherulocytes, appear to be associated with intestinal regeneration. We have used histochemistry and immunocytochemistry to characterize these cells and their role in the regeneration process. Spherulocytes are 10-20 microm in diameter with an acrocentric nucleus and spherule-like structures within their cytoplasm. They are found in the connective tissue of the intestine and mesentery of noneviscerated and regenerating animals. During the second week of regeneration, the number of spherulocytes in the regenerating intestine increases and a dramatic change in their morphology occurs. Together with the morphological change, the immunohistochemical labeling of the cells also changes; the antibodies not only recognize the spherule structures but also label the cellular cytoplasm in a more homogeneous pattern. Moreover, immunohistochemical labeling also appears to be dispersed within the extracellular matrix, suggesting that the cells are liberating their vesicular contents. Spherulocytes are found in other tissues of H. glaberrima, always associated with the connective tissue component. Our data strongly suggest that spherulocytes are involved in intestinal regeneration but their specific role remains undetermined. In summary, our data expand our knowledge of the cellular events associated with regeneration processes in echinoderms and provide for comparisons with similar processes in vertebrates., (Copyright (c) 2006 Wiley-Liss, Inc.)

Among higher metazoans, echinoderms exhibit the most impressive capacity for regeneration. Holothurians, or sea cucumbers, respond to adverse stimuli by autotomizing and ejecting their visceral organs, which are then regenerated. Neuronal fibers and cell bodies are present within the viscera, but previous regeneration studies have not accounted for the nervous component. We used light microscopic immunocytochemistry and ultrastructural studies to describe the regeneration of the enteric nervous system in the sea cucumber Holothuria glaberrima. This study provides evidence that the enteric nervous system of this echinoderm regenerates after evisceration and that in 3-5 weeks the regenerated system is virtually identical to that of noneviscerated animals. The regeneration of the enteric nervous system occurs parallel to the regeneration of other organ components. Nerve fibers and cells are observed within the mesenterial thickenings that give rise to the new intestine and within the internal connective tissue prior to lumen formation. We also used bromodeoxyuridine incorporation to show that proliferation of the neuronal population occurs in the regenerating intestine. The regeneration of the nervous system commands high interest because members of the closely related phylum Chordata either lack or have a very limited capacity to regenerate their nervous system. Thus, holothurians provide a model system to study enteric nervous system regeneration in deuterostomes.

Echinoderms are the deuterostome group with the most striking capacity to regenerate lost body parts. In particular, members of the class Holothuroidea are able to regenerate most of their internal organs following a typical evisceration process. Such formation of new viscera in an adult organism provides a unique model to study the process of organogenesis. We have studied this process in the sea cucumber Holothuria glabberrima by describing the spatial and temporal pattern of cellular events that occur during intestine regeneration following chemically induced evisceration. Regeneration begins as a thickening of the mesenteries that supported the autotomized organs to the body wall. The mesenterial thickening consists of tissues where most of the cellular populations found in the normal intestine are already present. However, the cell numbers differ, particularly those of hemocytes and amoebocytes, suggesting that some of these cells play an important role in the formation of the solid rod of hypertrophic mesentery that characterizes the intestinal primordia. The appearance of the luminal epithelium, together with the formation of the lumen, occurs during the second week of regeneration by proliferation and extensive migration of cells from the esophagus and cloacal ends into the thickenings. At this stage all tissue layers are present, but it takes an additional week for them to exhibit the proportions typical of the normal organ. Cell division, as determined by BrdU labeling, mainly occurs in the coelomic epithelia of the hypertrophic mesentery and in the regenerating luminal epithelium. Our study provides evidence that the process of new organ formation in holothurians can be described as an intermediate process showing characteristics of both epimorphic and morphallactic phenomena.