Increased Survivorship of Cementless versus Cemented TKA in the Morbidly Obese. A Minimum 5-Year Follow-Up.

BACKGROUND: Total knee arthroplasty (TKA) in the morbidly obese patients can be challenging with an increased risk of complications. Studies have shown increased aseptic failures with well-aligned cemented TKAs in the obese patient. The purpose of this study is to determine if TKA in the morbidly obese (body mass index [BMI] ≥ 40) using cementless implants would demonstrate improved results and survivorship compared to cemented TKA at a minimum 5-year follow-up. METHODS: This is a retrospective study comparing clinical results of cemented vs cementless primary TKA with a posterior stabilized design TKA in morbidly obese (BMI ≥ 40) patients with minimal 5-year follow-up. There were 108 patients in the cementless group with a mean BMI of 45.6. In the cemented cohort, there were 85 cemented TKAs with a mean BMI of 45.0. Demographic, clinical, surgical, and radiographic data along with complications were extracted for all study patients. RESULTS: There were 5 failures requiring revision in the cementless group, including 1 for aseptic tibial loosening (0.9%). In the cemented group, there were 22 failures requiring revision, including 16 implants for aseptic loosening (18.8%; P = .0001). Survivorship with aseptic loosening as the endpoint was 99.1% in the cementless group vs 88.2% in the cemented cohort at 8 years (P = .02). CONCLUSION: Morbidly obese patients (BMI ≥ 40) have a higher failure due to aseptic loosening with cemented TKA with decreasing survivorship over time. The use of cementless TKA in morbidly obese patients with the potential of durable long-term biologic fixation and increased survivorship appears to be a promising alternative to mechanical cement fixation.

Selected Heat-Sensitive Antibiotics Are Not Inactivated During Polymethylmethacrylate Curing and Can Be Used in Cement Spacers for Periprosthetic Joint Infection.

BACKGROUND: Antibiotic use in polymethylmethacrylate (PMMA) spacers has historically been limited to those which are "heat-stable" and thus retain their antimicrobial properties after exposure to the high temperatures which occur during PMMA curing. METHODS: This study examines the requirement of "heat stability" by measuring temperatures of Palacos and Simplex PMMA as they cure inside commercial silicone molds of the distal femur and proximal tibia. Temperature probes attached to thermocouples were placed at various depths inside the molds and temperatures were recorded for 20 minutes after PMMA introduced and a temperature curve for each PMMA product was determined. A "heat-stable" antibiotic, vancomycin, and a "heat-sensitive" antibiotic, ceftazidime, were placed in a programmable thermocycler and exposed to the same profile of PMMA curing temperatures. Antimicrobial activity against Staphylococcus aureus was compared for heat-treated antibiotics vs room temperature controls. RESULTS: Peak PMMA temperatures were significantly higher in tibial (115.2°C) vs femoral (85.1°C; P < .001) spacers. In the hottest spacers, temperatures exceeded 100°C for 3 minutes. Simplex PMMA produced significantly higher temperatures (P < .05) compared with Palacos. Vancomycin bioactivity did not change against S aureus with heat exposure. Ceftazidime bioactivity did not change when exposed to femoral temperature profiles and was reduced only 2-fold with tibial profiles. CONCLUSION: The curing temperatures of PMMA in knee spacers are not high enough or maintained long enough to significantly affect the antimicrobial efficacy of ceftazidime, a known "heat-sensitive" antibiotic. Future studies should investigate if more "heat-sensitive" antibiotics could be used clinically in PMMA spacers.

Cemented vs Cementless Total Knee Arthroplasty in Morbidly Obese Patients.

BACKGROUND: Primary total knee arthroplasty (TKA) in morbidly obese patients has been associated with greater postoperative complications. Cementless TKA has the potential for biologic fixation which may provide more durable long-term stability. METHODS: This was a multicenter review of 298 TKAs in 292 morbidly obese patients (body mass index, >40) undergoing TKA, with 154 TKAs (149 patients) in the cemented and 144 TKAs (143 patients) in the cementless group. RESULTS: There were significantly more revisions in the cemented group (n = 20) than in the cementless group (n = 1; 13.0% vs 0.7%). There was a significantly higher incidence of aseptic loosening in the cemented cohort vs the cementless cohort (9 vs 0 TKAs). All revisions in the cementless cohort were due to infection (0.7%). CONCLUSION: Cementless fixation may be an alternative in the morbidly obese patient undergoing primary TKA.

Improved Patient Satisfaction following Robotic-Assisted Total Knee Arthroplasty.

Approximately 20% of the patients are dissatisfied with their total knee arthroplasty (TKA). Computer technology has been introduced for TKA to provide real time intraoperative information on limb alignment and exact flexion/extension gap measurements. The purpose of this study was to determine if patient satisfaction could be improved with the use of robotic-assisted (RA) technology following primary TKA. A total of 120 consecutive patients undergoing RA-TKA with real time intraoperative alignment and gap balancing information were compared with a prospective cohort of 103 consecutive patients undergoing TKA with manual jig-based instruments during the same time period. There were no differences between groups with age, gender, baseline Knee Society Score (KSS) knee and function scores, follow-up, and ASA scores. TKAs were performed using same technique, implant design, anesthesia, and postoperative treatment protocols. Patient satisfaction survey using KSS and Likert scoring system were obtained at 1-year follow-up. Likert scoring system demonstrated 94% of the patients in the RA group were either very satisfied or satisfied versus 82% in the manual instruments TKA group (p = 0.005). RA-TKA group had better average scores of all five satisfaction questions although not significant. RA-TKA group had a better average overall satisfaction score of 7.1 versus 6.6 in the manual instrument group, p = 0.03. KSS function scores were significantly better at 6 weeks and 1 year postoperatively (p = 0.02, 0.005), and KSS knee scores were significantly better at 1 year postoperatively (p = 0.046). There are multiple reasons for patient dissatisfaction following primary TKA. Using intraoperative computer technology with RA surgery for patients undergoing a primary TKA, a significant improvement in patient satisfaction was demonstrated compared with TKA using conventional manual jig-based instruments. RA surgery provides several advantages in TKA including real time information in millimeters to help obtain balanced gaps, accurate bone cuts, reduced soft tissue injury, and achieve the target alignment which may lead to improved patient satisfaction.

Decreased Opioid Consumption and Length of Stay Using an IPACK and Adductor Canal Nerve Block following Total Knee Arthroplasty.

Peripheral nerve blocks such as a femoral + sciatic block have demonstrated significant pain relief following TKA. However, these nerve blocks have residual motor deficits which prevent immediate postoperative ambulation. The purpose of this study was to compare outcomes in patients undergoing primary TKA with femoral and sciatic (Fem + Sci) motor nerve blocks versus an adductor canal and the interspace between the popliteal artery and the capsule of the posterior knee and adductor canal block (IPACK + ACB) sensory nerve blocks. A total of 100 consecutive patients were reviewed, 50 received Fem + Sci nerve blocks and 50 received IPACK + ACB blocks preoperatively. There were no differences in the two groups with respect to surgical technique, implant type, postoperative pain, and physical therapy protocols. Differences in opioid requirements, length of stay (LOS), distance walked, and common knee scoring systems were analyzed. Among them, 62% IPACK + ACB patients were discharged on postoperative day 1 compared with 14% in the Fem + Sci group (p < 0.0001). The IPACK + ACB patients had a shorter LOS (mean 1.48 days vs. 2.02 days, p < 0.001), ambulated further on postoperative day 0 (mean 21.4 feet vs. 5.3 feet, p < 0.001), and required less narcotics the day after surgery (mean, 15.7 vs. 24.0 morphine equivalents p < 0.0001) and at 2 weeks (mean, 6.2 vs. 9.3 morphine equivalents, p = 0.025). The use of this combination IPACK and ACB demonstrated improved early ambulation with a decrease in opioid use and length of stay compared with a femoral and sciatic motor nerve block in patients undergoing primary TKA.

Distinct host cell proteins incorporated by SIV replicating in CD4+ T cells from natural disease resistant versus non-natural disease susceptible hosts.

BACKGROUND: Enveloped viruses including the simian immunodeficiency virus (SIV) replicating within host cells acquire host proteins upon egress from the host cells. A number of studies have catalogued such host proteins, and a few have documented the potential positive and negative biological functions of such host proteins. The studies conducted herein utilized proteomic analysis to identify differences in the spectrum of host proteins acquired by a single source of SIV replicating within CD4+ T cells from disease resistant sooty mangabeys and disease susceptible rhesus macaques. RESULTS: While a total of 202 host derived proteins were present in viral preparations from CD4+ T cells from both species, there were 4 host-derived proteins that consistently and uniquely associated with SIV replicating within CD4+ T cells from rhesus macaques but not sooty mangabeys; and, similarly, 28 host-derived proteins that uniquely associated with SIV replicating within CD4+ T cells from sooty mangabeys, but not rhesus macaques. Of interest was the finding that of the 4 proteins uniquely present in SIV preparations from rhesus macaques was a 26 S protease subunit 7 (MSS1) that was shown to enhance HIV-1 'tat' mediated transactivation. Among the 28 proteins found in SIV preparations from sooty mangabeys included several molecules associated with immune function such as CD2, CD3ε, TLR4, TLR9 and TNFR and a bioactive form of IL-13. CONCLUSIONS: The finding of 4 host proteins that are uniquely associated with SIV replicating within CD4+ T cells from disease susceptible rhesus macaques and 28 host proteins that are uniquely associated with SIV replicating within CD4+ T cells from disease resistant sooty mangabeys provide the foundation for determining the potential role of each of these unique host-derived proteins in contributing to the polarized clinical outcome in these 2 species of nonhuman primates.

Robotic-assisted total knee arthroplasty demonstrates decreased postoperative pain and opioid usage compared to conventional total knee arthroplasty.

AIMS: Robotic-assisted total knee arthroplasty (RA-TKA) has been introduced to provide accurate bone cuts and help achieve the target knee alignment, along with symmetric gap balancing. The purpose of this study was to determine if any early clinical benefits could be realized following TKA using robotic-assisted technology. METHODS: In all, 140 consecutive patients undergoing RA-TKA and 127 consecutive patients undergoing conventional TKA with minimum six-week follow-up were reviewed. Differences in visual analogue scores (VAS) for pain at rest and with activity, postoperative opiate usage, and length of stay (LOS) between the RA-TKA and conventional TKA groups were compared. RESULTS: Patients undergoing RA-TKA had lower average VAS pain scores at rest (p = 0.001) and with activity (p = 0.03) at two weeks following the index procedure. At the six-week interval, the RA-TKA group had lower VAS pain scores with rest (p = 0.03) and with activity (p = 0.02), and required 3.2 mg less morphine equivalents per day relative to the conventional group (p < 0.001). At six weeks, a significantly greater number of patients in the RA-TKA group were free of opioid use compared to the conventional TKA group; 70.7% vs 57.0% (p = 0.02). Patients in the RA-TKA group had a shorter LOS; 1.9 days versus 2.3 days (p < 0.001), and also had a greater percentage of patient discharged on postoperative day one; 41.3% vs 20.5% (p < 0.001). CONCLUSION: Patients undergoing RA-TKA had lower pain levels at both rest and with activity, required less opioid medication, and had a shorter LOS.

Risk of Reinfection after Irrigation and Debridement of Acute Periprosthetic Joint Infection following TKA.

The purpose of this study was to determine the risk factors associated with reinfection in patients treated with irrigation and debridement (I&D) with liner exchange for an acute (less than 3 months) prosthetic joint infection following the index primary total knee arthroplasty (TKA). Medicare claims database was queried to identify patients with periprosthetic joint infection within 3 months of their index TKA who underwent I&D with tibial polyethylene liner exchange. Exclusion criteria included age < 65 years and < 1 year of claims prior to TKA. A total of 341 patients met our criteria and were analyzed by age, sex, diabetes, obesity, Charlson comorbidity score, and time between TKA and I&D with liner exchange. Average time to I&D with liner exchange following primary TKA was 38.5 ± 21.3 days and multivariate analysis showed a significantly higher risk of reinfection within 1 year in patients > 85 years old (p < 0.001) and diabetes (p < 0.02). The risk of reinfection was lowest for patients treated with I&D with liner exchange within 14 days after TKA (p = 0.028). The incidence of reinfection was 223% greater if I&D with liner exchange was performed 2 to 4 weeks after primary TKA (p < 0.03), and 277% higher if performed > 6 weeks after index procedure compared with those performed within 2 weeks. Patients older than 85 years, diabetics, or treated with I&D with liner exchange > 14 days following the primary TKA had a significantly higher risk of reinfection within 1 year. Patients should be cautioned on the risk of reinfection prior to proceeding with I&D with liner exchange > 2 weeks following the index procedure.

Vancomycin-Loaded Polymethylmethacrylate Spacers Fail to Eradicate Periprosthetic Joint Infection in a Clinically Representative Mouse Model.

BACKGROUND: Periprosthetic joint infection (PJI) remains a devastating complication following total joint arthroplasty. Current animal models of PJI do not effectively recreate the clinical condition and thus provide limited help in understanding why treatments fail. We developed a mouse model of the first-stage surgery of a 2-stage revision for PJI involving a 3-dimensionally printed Ti-6Al-4V implant and a mouse-sized cement spacer that elutes vancomycin. METHODS: Vancomycin was mixed with polymethylmethacrylate (PMMA) cement and inserted into custom-made mouse-sized spacer molds. Twenty C57BL/6 mice received a proximal tibial implant and an intra-articular injection of 3 × 10 colony-forming units of Staphylococcus aureus Xen36. At 2 weeks, 9 mice underwent irrigation and debridement of the leg with revision of the implant to an articulating vancomycin-loaded PMMA spacer. Postoperatively, mice underwent radiography and serum inflammatory-marker measurements. Following euthanasia of the mice at 6 weeks, bone and soft tissues were homogenized to quantify bacteria within periprosthetic tissues. Implants and articulating spacers were either sonicated to quantify adherent bacteria or examined under scanning electron microscopy (SEM) to characterize the biofilm. RESULTS: Vancomycin-loaded PMMA spacers eluted vancomycin for ≤144 hours and retained antimicrobial activity. Control mice had elevated levels of inflammatory markers, radiographic evidence of septic loosening of the implant, and osseous destruction. Mice treated with a vancomycin-loaded PMMA spacer had significantly lower levels of inflammatory markers (p < 0.01), preserved tibial bone, and no intra-articular purulence. Retrieved vancomycin-loaded spacers exhibited significantly lower bacterial counts compared with implants (p < 0.001). However, bacterial counts in periprosthetic tissue did not significantly differ between the groups. SEM identified S. aureus encased within biofilm on control implants, while vancomycin-loaded spacers contained no bacteria. CONCLUSIONS: This animal model is a clinically representative model of PJI treatment. The results suggest that the antimicrobial effects of PMMA spacers are tightly confined to the articular space and must be utilized in conjunction with thorough tissue debridement and systemic antibiotics. CLINICAL RELEVANCE: These data provide what we believe to be the first insight into the effect of antibiotic-loaded cement spacers in a clinically relevant animal model and justify the adjunctive use of intravenous antibiotics when performing a 2-stage revision for PJI.

Propionibacterium acnes Host Inflammatory Response During Periprosthetic Infection Is Joint Specific.

BACKGROUND: Propionibacterium acnes (P. acnes) has become increasingly recognized as a cause of periprosthetic joint infection (PJI). QUESTIONS/PURPOSES: It is not currently known if the clinical presentation of P. acnes varies depending on the joint being infected. METHODS: We retrospectively reviewed patients infected with P. acnes after total hip, knee, and shoulder arthroplasty from two institutions. Patients were classified as having a PJI based on the Musculoskeletal Infection Society criteria and were excluded if they had a polymicrobial culture. Patient demographics, preoperative laboratory values, and microbiology data were analyzed. RESULTS: Eighteen knees, 12 hips, and 35 shoulders with a P. acnes PJI were identified. Median ESR was significantly higher in the knee (38.0 mm/h, IQR 18.0-58.0) and hip (33.5 mm/h, IQR 15.3-60.0) groups compared to the shoulder group (11.0 mm/h, IQR 4.5-30.5). C-reactive protein levels were higher in the knee (2.0 mg/dl, IQR 1.3-8.9) and hip (2.4 mg/dl, IQR 0.8-4.9) groups compared to the shoulder group (0.7 mg/dl, IQR 0.6-1.5). Median synovial fluid WBC was significantly higher in the knee group than shoulder group (19,950 cells/mm3, IQR 482-60,063 vs 750 cells/mm3, IQR 0-2825, respectively). Peripheral blood WBC levels were similar between groups, as was mean time of P. acnes growth in culture. Clindamycin resistance was present in all groups. CONCLUSION: The manner in which a patient with P. acnes PJI presents is joint specific. Inflammatory markers were significantly higher in the knee and hip groups compared to the hip and shoulder groups, and long hold anaerobic cultures up to 14 days are necessary to accurately identify this organism.

Quantification of Peri-Implant Bacterial Load and in Vivo Biofilm Formation in an Innovative, Clinically Representative Mouse Model of Periprosthetic Joint Infection.

BACKGROUND: Periprosthetic joint infection (PJI) is a devastating complication following total joint arthroplasty. Current animal models of PJI are limited because of a lack of quantitative methods and failure to effectively recreate the periprosthetic space. We therefore developed a murine PJI model involving a 3-dimensionally printed Ti-6Al-4V implant capable of bearing weight and permitting quantitative analysis of periprosthetic bacterial load and evaluation of biofilm. METHODS: Twenty-five 12-week-old C57BL/6 mice received a unilateral proximal tibial implant and intra-articular injection of either 3 × 10 colony forming units (CFUs) of Staphylococcus aureus Xen 36 or saline solution. Postoperatively, mice underwent gait analysis, knee radiographs, and serum inflammatory marker measurements. Following euthanasia at 2 or 6 weeks, bone and soft tissues were homogenized to quantify bacteria within periprosthetic tissues. Implants were either sonicated to quantify adherent bacteria or examined under scanning electron microscopy (SEM) to characterize biofilm. RESULTS: All mice survived surgery and were not systemically septic. The control mice immediately tolerated weight-bearing and had normal inflammatory markers and radiographic signs of osseointegration. Infected mice had difficulty walking over time, exhibited radiographic findings of septic implant loosening, and had significantly elevated inflammatory markers. Periprosthetic tissues of the infected animals displayed a mean of 4.46 × 10 CFUs of S. aureus at 2 weeks and 2.53 × 10 CFUs at 6 weeks. Viable S. aureus was quantified on retrieved implant surfaces. SEM demonstrated S. aureus cocci in clusters encased within biofilm. CONCLUSIONS: This animal model is, to our knowledge, the most clinically representative PJI replication to date. It is the first that we know of to produce infection through the same method hypothesized to occur clinically, utilize a weight-bearing implant that can osseointegrate, and provide quantitative data on 8 aspects of PJI, including radiographic features, inflammatory markers, and bacterial loads. CLINICAL RELEVANCE: This novel animal model is, to our knowledge, the first to provide a load-bearing translational representation of clinical PJI that effectively recreates the periprosthetic space.

Wear Analysis of Second-generation Highly Cross-Linked Polyethylene in Primary Total Hip Arthroplasty.

A major limiting factor in the longevity of total hip replacement is the wear rate of the hip bearing. As manufacturing technology has improved during the past several decades, much attention has been focused on developing newer generations of polyethylene that have lower rates of wear while minimizing free radical formation and subsequent osteolysis. The turning point for the manufacture of polyethylene was moving from gamma irradiation in air to irradiation in a low oxygen environment, which reduced free radical formation while increasing the wear resistance. New polyethylene manufacturing methods, including multiple cycles of irradiation and annealing, have resulted in greater wear resistance. Wear analysis studies are essential to determine if these new liners actually show a benefit from prior generations of polyethylene and, more importantly, if they are safe to use. This study involved a single center retrospective review of 60 patients with a mean follow-up of 5.5 years who underwent primary total hip arthroplasty with a second-generation highly cross-linked polyethylene manufactured by 3 cycles of sequential irradiation and annealing. Linear and volumetric wear rates were determined from digitized radiographs using contemporary wear analysis software. The mean linear wear rate for the entire group was 0.025 millimeters per year (mm/y). This value represents a linear wear rate 2.7 times less than that of a first-generation highly cross-linked polyethylene and 4.2 times less than that of a conventional polyethylene. At an average of 5 years, compared with a first-generation highly cross-linked polyethylene, a second-generation highly cross-linked polyethylene appears to show significant improvement regarding wear. [Orthopedics. 2016; 39(6):e1178-e1182.].

Developing a Clinically Representative Model of Periprosthetic Joint Infection.

➤The poor treatment outcomes for periprosthetic joint infection (PJI) reflect the limited understanding that currently exists regarding the pathogenesis of this devastating clinical problem.➤Current animal models of PJI are limited in their translational nature primarily because of their inability to recreate the periprosthetic environment.➤A greater mechanistic understanding of the musculoskeletal and immune systems of small animals, such as mice and rats, provides a more robust platform for modeling and examining the pathogenesis of PJI.➤A clinically representative PJI model must involve an implant that recreates the periprosthetic space and be amenable to methodologies that identify implant biofilm as well as quantify the peri-implant bacterial load.

Intermittent Parathyroid Hormone Enhances Cancellous Osseointegration of a Novel Murine Tibial Implant.

BACKGROUND: Long-term fixation of uncemented joint implants requires early mechanical stability and implant osseointegration. To date, osseointegration has been unreliable and remains a major challenge in cementless total knee arthroplasty. We developed a murine model in which an intra-articular proximal tibial titanium implant with a roughened stem can be loaded through the knee joint. Using this model, we tested the hypothesis that intermittent injection of parathyroid hormone (iPTH) would increase proximal tibial cancellous osseointegration. METHODS: Ten-week-old female C57BL/6 mice received a subcutaneous injection of PTH (40 µg/kg/day) or a vehicle (n = 45 per treatment group) five days per week for six weeks, at which time the baseline group was killed (n = 6 per treatment group) and an implant was inserted into the proximal part of the tibiae of the remaining mice. Injections were continued until the animals were killed at one week (n = 7 per treatment group), two weeks (n = 14 per treatment group), or four weeks (n = 17 per treatment group) after implantation. Outcomes included peri-implant bone morphology as analyzed with micro-computed tomography (microCT), osseointegration percentage and bone area fraction as shown with backscattered electron microscopy, cellular composition as demonstrated by immunohistochemical analysis, and pullout strength as measured with mechanical testing. RESULTS: Preimplantation iPTH increased the epiphyseal bone volume fraction by 31.6%. When the data at post-implantation weeks 1, 2, and 4 were averaged for the iPTH-treated mice, the bone volume fraction was 74.5% higher in the peri-implant region and 168% higher distal to the implant compared with the bone volume fractions in the same regions in the vehicle-treated mice. Additionally, the trabecular number was 84.8% greater in the peri-implant region and 74.3% greater distal to the implant. Metaphyseal osseointegration and bone area fraction were 28.1% and 70.1% higher, respectively, in the iPTH-treated mice than in the vehicle-treated mice, and the maximum implant pullout strength was 30.9% greater. iPTH also increased osteoblast and osteoclast density by 65.2% and 47.0%, respectively, relative to the values in the vehicle group, when the data at post-implantation weeks 1 and 2 were averaged. CONCLUSIONS: iPTH increased osseointegration, cancellous mass, and the strength of the bone-implant interface. CLINICAL RELEVANCE: Our murine model is an excellent platform on which to study biological enhancement of cancellous osseointegration.

Counterregulation of clathrin-mediated endocytosis by the actin and microtubular cytoskeleton in human neutrophils.

We have recently reported that disruption of the actin cytoskeleton enhanced N-formylmethionyl-leucyl-phenylalanine (fMLP)-stimulated granule exocytosis in human neutrophils but decreased plasma membrane expression of complement receptor 1 (CR1), a marker of secretory vesicles. The present study was initiated to determine if reduced CR1 expression was due to fMLP-stimulated endocytosis, to determine the mechanism of this endocytosis, and to examine its impact on neutrophil functional responses. Stimulation of neutrophils with fMLP or ionomycin in the presence of latrunculin A resulted in the uptake of Alexa fluor 488-labeled albumin and transferrin and reduced plasma membrane expression of CR1. These effects were prevented by preincubation of the cells with sucrose, chlorpromazine, or monodansylcadaverine (MDC), inhibitors of clathrin-mediated endocytosis. Sucrose, chlorpromazine, and MDC also significantly inhibited fMLP- and ionomycin-stimulated specific and azurophil granule exocytosis. Disruption of microtubules with nocodazole inhibited endocytosis and azurophil granule exocytosis stimulated by fMLP in the presence of latrunculin A. Pharmacological inhibition of phosphatidylinositol 3-kinase, ERK1/2, and PKC significantly reduced fMLP-stimulated transferrin uptake in the presence of latrunculin A. Blockade of clathrin-mediated endocytosis had no significant effect on fMLP-stimulated phosphorylation of ERK1/2 in neutrophils pretreated with latrunculin A. From these data, we conclude that the actin cytoskeleton functions to limit microtubule-dependent, clathrin-mediated endocytosis in stimulated human neutrophils. The limitation of clathrin-mediated endocytosis by actin regulates the extent of both specific and azurophilic granule exocytosis.