Postoperative Vitamin D Surveillance and Supplementation in Revision Total Knee Arthroplasty Patients: A Retrospective Cohort Analysis.

This study was a retrospective cohort analysis of 20 patients who underwent 23 revision total knee arthroplasty procedures in a single geographic region of the United States from January 2015 to February 2023. We analyzed their 25-OH vitamin D levels preoperatively and postoperatively at 1 month, 3 months, 6 months, 1 year, and 2 years. We categorized their supplementation regimens by dose: none, low dose (1000 IU and below), medium dose (1001-5000 IU), and high dose (>5000 IU). We found that there was a high incidence of vitamin D deficiency in this patient population.

Racial and Ethnic Minority Patients Have Increased Complication Risks When Undergoing Surgery While Not Meeting Clinical Guidelines.

BACKGROUND: Clinical guidelines for performing total joint arthroplasty (TJA) have not been uniformly adopted in practice because research has suggested that they may foster inequities in surgical access, potentially disadvantaging minority sociodemographic groups. The aim of this study was to assess whether undergoing TJA without meeting clinical guidelines affects complication risk and leads to disparities in postoperative outcomes. METHODS: This retrospective cohort study evaluated the records of 11,611 adult patients who underwent primary TJA from January 1, 2010, to December 31, 2020, at an academic hospital network. Based on self-reported race and ethnicity, 89.5% of patients were White, 3.5% were Black, 2.9% were Hispanic, 1.3% were Asian, and 2.8% were classified as other. Patients met institutional guidelines for undergoing TJA if they had a hemoglobin A1c of <8.0% and a body mass index of <40 kg/m 2 and were not currently smoking. A logistic regression model was utilized to identify factors associated with complications, and a mixed-effects model was utilized to identify factors associated with not meeting guidelines for undergoing TJA. RESULTS: During the study period, 11% (1,274) of the 11,611 adults who underwent primary TJA did not meet clinical guidelines. Compared with the group who met guidelines, the group who did not had higher proportions of Black patients (3.2% versus 6.0%; p < 0.001) and Hispanic patients (2.7% versus 4.6%; p < 0.001). An increased risk of not meeting guidelines at the time of surgery was demonstrated among Black patients (odds ratio [OR], 1.60 [95% confidence interval (CI), 1.22 to 2.10]; p = 0.001) and patients insured by Medicaid (OR, 1.75 [95% CI, 1.26 to 2.44]; p = 0.001) or Medicare (OR, 1.22 [95% CI, 1.06 to 1.41]; p = 0.007). Patients who did not meet guidelines had a higher risk of reoperation than those who met guidelines (7.7% [98] versus 5.9% [615]; p = 0.017), including a higher risk of infection-related reoperation (3.1% [40] versus 1.4% [147]; p < 0.001). CONCLUSIONS: We found that patients who underwent TJA despite not meeting institutional preoperative criteria had a higher risk of postoperative complications. These patients were more likely to be from racial and ethnic minority groups, to have a lower socioeconomic status, and to have Medicare or Medicaid insurance. These findings underscore the need for surgery-related shared decision-making that is informed by evidence-based guidelines in order to reduce complication burden. LEVEL OF EVIDENCE: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Reverse Fragility Index: Comparing Revision Rates Between Direct Anterior and Other Approaches in Total Hip Arthroplasty. A Systematic Review of Randomized Controlled Trials.

BACKGROUND: Despite increasing adoption of the direct anterior (DA) approach in total hip arthroplasty (THA), uncertainty persists regarding its outcomes beyond the 1-year mark in comparison to other approaches. We used the reverse fragility index (RFI) to evaluate the robustness of reported findings in the literature. METHODS: We conducted a systematic review of randomized controlled trials (RCTs) comparing implant revision rates between DA and other approaches in THA, defined as all those different from DA. Our primary outcome was the RFI, which gauges the number of events needed for a nonsignificant result to become significant, in the revision rate between DA and other approaches. We also calculated the reverse fragility quotient by dividing the RFI by each study's sample size. Median values and interquartile ranges (IQRs) were displayed. RESULTS: A total of 10 RCTs with a total of 971 patients were included. The median RFI was 5 (IQR, 4 to 5), indicating the study's results would be statistically significant if the outcomes of 5 patients in 1 treatment arm were reversed. The median reverse fragility quotient was 0.049 (IQR, 0.04 to 0.057), indicating that a change of outcome in 4.9% of patients would render the revision rate significant. The median number of patients lost to follow-up was 4 (IQR, 0 to 7). Of the 10 RCTs, 6 had more patients lost to follow-up than their respective RFI values. CONCLUSIONS: Notable fragility was evidenced in most studies comparing DA to other approaches for THA. Surgeons should not solely rely on the P value to determine clinical significance and instead use multiple metrics. LEVEL OF EVIDENCE: II.

Patients With Significant Medical Comorbidities May Benefit from Unicompartmental Knee Arthroplasty Over Total Knee Arthroplasty.

Many studies have compared outcomes in total knee arthroplasty (TKA) versus unicompartmental knee arthroplasty (UKA); however, to the authors' knowledge, there is no study evaluating complication rates in patients with significant comorbidities. The purpose of this retrospective study was to compare the incidence of postoperative complications, readmission and reoperation rates, length of stay (LOS), and discharge location for patients with significant medical comorbidities undergoing TKA versus UKA. Using the NSQIP database from 2008 to 2018, patients were identified by CPT code (27447 or 27446) and admission diagnostic code of primary osteoarthritis and included in the study if they had an American Society of Anesthesia score greater than or equal to 3. Chi-square test was used to compare categorical variables and t-test for continuous variables. Multivariate regression was used to compare outcomes of interest between groups. A total of 167,054 patients were analyzed with 97.3% undergoing TKA. TKA patients had a greater overall complication rate than those undergoing UKA (p < 0.001). Readmission rates were approximately 1.5 times higher in TKA compared with UKA (p = 0.002), while no statistically significant difference was discovered in reoperation rates (p = 0.868). TKA was also associated with decreased rates of same day discharge, discharge within 24 hours of surgery, and discharge home (p < 0.001, <0.001, and <0.001, respectively). This study found an increase in complication rates, readmission rates, and LOS, along with a lower likelihood of discharge home when undergoing a TKA. These findings suggest that patients with significant medical comorbidities at baseline may benefit from UKA over TKA when anatomically indicated.

Trunnions and Modularity in Total Hip Arthroplasty: A Historical Review With Current Clinical Implications.

Trunnion in total hip arthroplasty refers to the interface between the neck of a femoral stem and the femoral head. Clinical complications arising from damage to this junction, whether it be due to mechanical wear, corrosion, or a combination, are referred to as mechanically assisted crevice corrosion (MACC), also commonly known as trunnionosis. With the use of modular hip prostheses, which help customize offset and leg length to an individual patient's anatomy, the incidence of MACC and revision due to MACC has increased in recent years. Although the cause of MACC is multifactorial, with patient factors and technique factors contributing to this condition, taper design and geometry, metallurgical properties of implants, and size mismatch of the bearing couple are some of the implant factors that have also been implicated in this clinical phenomenon. Understanding the history of taper design and geometry, the track record of older implants, and the rationale behind the development of current prostheses can help surgeons choose the right implants for their patients and accurately assess the pros and cons of new implants being introduced to the market each year.

Assessment of Patient Satisfaction and Outcomes After Outpatient Joint Arthroplasty in Academic Medical Centers.

Background: There is limited literature evaluating patient satisfaction and outcomes after outpatient joint arthroplasty procedures in academic medical centers (AMCs). The aims of this study are to determine: (1) patients' desires to repeat their procedures and be discharged on the same day, (2) patient-reported outcome measures (PROMs), (3) time to discharge, (4) readmission rates, and (5) factors that predict PROMs in patients undergoing outpatient joint arthroplasty in AMCs. Methods: A prospective survey was completed by 66 total hip arthroplasty (THA), 35 total knee arthroplasty (TKA), and 180 unicondylar knee arthroplasty (UKA) outpatients who underwent surgery from May 2018 to December 2020 in 2 AMCs. The survey consisted of questions regarding hip or knee PROMs (Hip Disability and Osteoarthritis Outcome Score for Joint Replacement, and Knee Injury and Osteoarthritis Outcome Score for Joint Replacement), satisfaction with outpatient procedures and discharges, and reasons for readmissions. Linear regression analysis was conducted with statistical significance set at P < .05. Results: 100% of THA, 93.8% of TKA, and 93.0% of UKA outpatients stated that they would re-elect to undergo their respective procedure. Furthermore, 94% of THA, 81% of TKA, and 95% of UKA patients stated they would like same-day discharge again. THA, TKA, and UKA patients reported respective mean PROM scores of 94.7, 89.9, and 86.1. Readmission rates were 1.5%, 0.0%, and 0.5%, for THA, TKA, and UKA, respectively. Conclusions: Patients who underwent outpatient joint arthroplasty procedures at 2 AMCs experienced minimal readmissions and reported a high desire to repeat their outpatient procedures.

Optimizing Spinal Anesthesia in Same-Day Discharge Knee Arthroplasty Patients: Mepivacaine Versus Ropivacaine.

BACKGROUND: Short-acting spinal anesthetics are playing an increasing role in same-day discharge total joint arthroplasty though their direct comparison remains to be studied. Therefore, this study aims to compare two formulations of spinal anesthesia regarding time to discharge following knee arthroplasty surgery. METHODS: A retrospective study was performed on 207 patients who underwent unicompartmental knee arthroplasty (UKA, n = 172) and total knee arthroplasty (TKA, n = 35) from May 2018 to December 2020 at a single institution and were discharged the same day. Two formulations of the spinal anesthetic were routinely administered in this population: 1) mepivacaine 1.5% 3-4 mL (n = 184) and 2) ropivacaine 0.5% 2.3-2.7 mL (n = 23). Discharge times were subsequently compared between mepivacaine and ropivacaine spinal anesthesia for each surgical procedure and between surgical procedures. RESULTS: There was no significant difference in discharge times between patients receiving mepivacaine versus ropivacaine for UKA (202 minutes [range = 54-449] versus 218 minutes [range = 175-385], P = .45) or TKA (193 minutes [range = 68-384] versus 196 minutes [range = 68-412], P = .93). Similarly, no difference was found in discharge times between UKA and TKA patients receiving mepivacaine (P = .68) or ropivacaine (P = .51). CONCLUSION: There was no significant difference in discharge times between anesthetic agents among knee surgery patients. Therefore, either agent may be recommended for same-day discharge.

The Emergence of Collaboration in the Education of Fellows and Residents during COVID-19.

BACKGROUND: COVID-19 has created a void in surgical education. Given social distancing and postponed surgeries, unique educational opportunities have arisen. Attendings from 10 adult reconstruction fellowships led a multi-institution web-based weekly collaborative, the Arthroplasty Consortium (AC), developed to educate trainees through complex arthroplasty case-based discussions. METHODS: We performed an anonymous survey of AC participants and American Association of Hip and Knee Surgeons (AAHKS) adult reconstruction fellows. Participants were polled with regards to educational tools used before and after COVID-19 and their value. Specifically, participation in the AC, AAHKS FOCAL (Fellows Orthopedic Continued AAHKS Learning) lectures, institutional lectures, industry lectures, textbooks, online videos, journal articles, and webinars was assessed. RESULTS: Fifty-seven participants responded with 49 (86%) at the fellow level. There was an increase in the use of web-based learning, including the AC (Not applicable pre, 61% post), AAHKS FOCAL lectures (Not applicable pre, 82% post), industry lectures (53% pre, 86% post), and AAHKS/AAOS webinars (35% pre, 56% post). Usage declined with institutional lectures (89% pre, 80% post), textbooks (68% pre, 49% post), and journal articles (97% pre, 90% post), with minimal change in the use of online surgical videos (84% pre, 82% post). The majority of fellows not involved in the AC would like to see the addition of a multi-institutional case conference added to fellowship education. Of AC participants, the 2 most valuable educational tools were the AC and FOCAL lectures. CONCLUSION: Trainee education has changed post-COVID-19 with a greater focus on web-based learning. Multi-institutional collaborative lectures and case-based discussions have significant perceived value among trainees and should be considered important educational tools post-COVID 19.

Weight loss before total joint arthroplasty using a remote dietitian and mobile app: study protocol for a multicenter randomized, controlled trial.

BACKGROUND: The months prior to elective surgery may present an opportunity for patients to initiate behavior changes that will simultaneously ready them for surgery and improve their overall health status. An upcoming elective total joint arthroplasty (TJA) may serve as motivation for patients with severe obesity (body mass index [BMI]> 40 kg/m2) to lose weight, as it may optimize clinical outcomes following TJA and help them become eligible for TJA since some surgeons use a BMI of 40 kg/m2 as a cut-off for offering surgery in an effort to optimize outcomes. METHODS: The purpose of this multicenter randomized, controlled trial is to assess the feasibility and efficacy of a 12-week remote dietitian (RD) supervised dietary and physical activity weight loss intervention and mobile app for 60 patients with severe obesity prior to undergoing TJA. Intervention participants will receive access to a smartphone app and connect with an RD who will contact these participants weekly or bi-weekly via video calls for up to nine video calls. Together, participants and RDs will set goals for lifestyle modifications, and RDs will check on progress towards achieving these goals using in-app tools such as food logs and text messages between video calls. All patients will be encouraged to lose at least 20 pounds with a goal BMI < 40 kg/m2 after 12 weeks. Individuals randomized to the control group will receive clinical standard of care, such as nutritionist and/or physical therapy referrals. Outcome and demographic data will be collected from blood serology, chart review, mobile app user data, pre- and postintervention surveys, and phone interviews. The primary outcome measure will be weight change from baseline. Secondary outcome measures will include percentage of patients eligible to undergo TJA, number of sessions completed with dietitians, self-reported global health status (PROMIS Global Health scale), self-reported joint-specific pain and function (Knee injury and Osteoarthritis Outcome Score (KOOS) or Hip disability and Osteoarthritis Outcome Score (HOOS)), and serologies such as hemoglobin A1c, total lymphocyte count, albumin, and transferrin. Qualitative responses transcribed from phone interviews about the intervention will also be analyzed. DISCUSSION: This will be the first study to assess pre-operative weight loss in patients with severe obesity anticipating orthopaedic surgery using an RD and mobile app intervention aimed at helping patients become eligible for TJA. TRIAL REGISTRATION: Registered on 1 April 2020 at Clincialtrials.gov. Trial number is NCT04330391 .

Team Approach: Same-Day Discharge of Patients Undergoing Total Joint Arthroplasty.

Same-day-discharge total joint arthroplasty is becoming increasingly feasible because of advances in anesthesia, physical therapy, surgical techniques, and perioperative protocols. In appropriately selected patient populations, same-day-discharge total joint arthroplasty is safe, does not increase readmission rates, and is cost-effective. As the push for value-driven health care continues and the incidence of total joint arthroplasty continues to grow, same-day-discharge arthroplasty will likely become more prevalent and increasingly incentivized. A team-based approach to each phase of care is vital for effective and safe same-day-discharge total joint arthroplasty.

Surgical Treatment of Acute Periprosthetic Knee Infection with Concurrent Presumed COVID-19: A Case Report.

CASE: We report the case of a 64-year-old man who presented with a late onset of acute periprosthetic joint infection after total knee arthroplasty and a positive severe acute respiratory syndrome coronavirus 2 polymerase chain reaction test. We describe our perioperative protocol and challenges for ensuring the safety of healthcare providers while operating on a coronavirus disease 2019 (COVID-19)-positive patient. CONCLUSIONS: Given the incredible spread of COVID-19 globally, hospitals should anticipate perioperative protocols for the surgical management of COVID-19-positive patients with concurrent pathology to ensure safety to healthcare providers.

Efficacy of manipulation under anesthesia beyond three months following total knee arthroplasty.

BACKGROUND: Stiffness after total knee arthroplasty (TKA) is often treated with manipulation under anesthesia (MUA) to improve range of motion (ROM). However, many authors recommend against MUA beyond 3 months after TKA. This study investigates the timing of MUA for stiffness after TKA, focusing on MUA performed at >12 weeks. METHODS: In total, 142 MUAs were retrospectively reviewed. "Early" MUAs were at <12 weeks after TKA; "Late" MUAs were >12 weeks. MUAs were further subdivided into 4 groups: 83 "Group I" cases at <12 weeks, 34 "Group II" between 12 and 26 weeks, 12 "Group III" between 26 and 52 weeks, and 13 "Group IV" at >52 weeks. Gains in ROM were compared between groups. RESULTS: Gains in flexion and overall ROM were statistically equivalent in Early vs Late MUA when controlling for pre-MUA ROM. ROM gains between the early Group I and the later Groups II-IV were also statistically comparable. Overall ROM gain in Group I was 24.1°, 17.9° in Group II, 20.8° in Group III, and 11.1° in Group IV. There were no significant complications. CONCLUSIONS: Early and late MUA resulted in statistically equivalent gains in ROM, regardless of timing after TKA. All groups showed an average improvement in ROM of ≥11°. MUA performed beyond 3 months, and even beyond 1 year, appears to be safe and may improve ROM and allow select patients to avoid revision surgery.

Mixed Reality Meets Pharmaceutical Development.

As science evolves, the need for more efficient and innovative knowledge transfer capabilities becomes evident. Advances in drug discovery and delivery sciences have directly impacted the pharmaceutical industry, though the added complexities have not shortened the development process. These added complexities also make it difficult for scientists to rapidly and effectively transfer knowledge to offset the lengthened drug development timelines. While webcams, camera phones, and iPads have been explored as potential new methods of real-time information sharing, the non-"hands-free" nature and lack of viewer and observer point-of-view render them unsuitable for the R&D laboratory or manufacturing setting. As an alternative solution, the Microsoft HoloLens mixed-reality headset was evaluated as a more efficient, hands-free method of knowledge transfer and information sharing. After completing a traditional method transfer between 3 R&D sites (Rahway, NJ; West Point, PA and Schnachen, Switzerland), a retrospective analysis of efficiency gain was performed through the comparison of a mock method transfer between NJ and PA sites using the HoloLens. The results demonstrated a minimum 10-fold gain in efficiency, weighing in from a savings in time, cost, and the ability to have real-time data analysis and discussion. In addition, other use cases were evaluated involving vendor and contract research/manufacturing organizations.

The Effect of Patellar Thickness on Intraoperative Knee Flexion and Patellar Tracking in Patients With Arthrofibrosis Undergoing Total Knee Arthroplasty.

BACKGROUND: We evaluated the intraoperative effect of patellar thickness on intraoperative passive knee flexion and patellar tracking during total knee arthroplasty (TKA) in patients with preoperative arthrofibrosis and compared them to patients with normal preoperative range of motion (ROM) documented in a prior study. METHODS: Routine posterior cruciate ligament-retaining TKA was performed in a total of 34 knees, 23 with normal ROM and 11 with arthrofibrosis, defined as ≤100° of passive knee flexion against gravity under anesthesia. Once clinical balance and congruent patellar tracking were established, custom trial patellar components thicker than the standard trial by 2-mm increments (2-8 mm) were sequentially placed and trialed. Passive flexion against gravity was recorded using digital photograph goniometry. Gross mechanics of patellofemoral tracking were visually assessed. RESULTS: On average, passive knee flexion decreased 2° for every 2-mm increment of patellar thickness (P < .0001), which was similar to patients with normal preoperative ROM. In addition, increased patellar thickness had no gross effect on patellar subluxation and tilt in patients with arthrofibrosis as well as those with normal ROM. CONCLUSIONS: Patellar thickness had a modest effect on intraoperative passive flexion and no effect on patellar tracking in patients with arthrofibrosis undergoing TKA. There was no marked difference in intraoperative flexion and patellar tracking between patients with arthrofibrosis and patients with normal preoperative ROM.

Incidence and mechanism of late stent malapposition after phosphorus-32 radioactive stent implantation.

Late stent malapposition is a potential complication of intracoronary brachytherapy. The aim of our study was to determine the incidence and mechanism of late stent malapposition after implantation of phosphorus-32 radioactive stents. We analyzed 159 patients for de novo lesions after the implantation of phosphorus-32 radioactive stents. There were 15 late stent malappositions. The incidence of malapposition was higher in patients who received Hot-Ends Isostents. External elastic membrane expansion greater than plaque increase in malapposed segments was observed. Late stent malapposition is caused by a localized increase in external elastic membrane that is greater than the increase in plaque area; this is believed to be a dose-dependent phenomenon because it was more common with Hot-Ends Isostents.

Regional remodeling as the cause of late stent malapposition.

BACKGROUND: Late stent malapposition (LSM) is only detected if intravascular ultrasound (IVUS) is performed at implantation and follow-up. We used a novel "regional" IVUS analysis to assess the mechanism of LSM. METHODS AND RESULTS: Corresponding image slices on postimplantation and follow-up IVUS studies of 11 malapposed stents were identified and electronically rotated until they were aligned. The geometric center of the stent was identified, and the angle of late malapposition measured. Radii were drawn from this center through the transition points between complete apposition and LSM. These two circumferences were divided into equal arcs, and radii were drawn to the external elastic membrane (EEM). Measurements included EEM radius and circumference, plaque and media (P&M=EEM minus stent radius) thickness and area, and stent-intima separation. Mean baseline EEM radius and P&M thickness were similar in apposed and malapposed circumferences. At follow-up, mean EEM radius increase within the malapposed circumference (0.57+/-0.34 mm) was larger than within the apposed circumference (0.16+/-0.18 mm; P=0.0004). DeltaEEM for each malapposed radius was greater than for each apposed radius (P<0.05 for all comparisons). Stent-intima separation correlated with EEM radius increase within the malapposed circumference (r=0.83, P=0.0013). At follow-up, the mean P&M thickness decreased in the malapposed circumference (-0.31+/-0.22 mm; P<0.0001). However, the decrease in P&M thickness in the malapposed circumference occurred because the same P&M area was distributed over a larger circumference (4.1+/-1.6 mm to 5.4+/-3.0 mm; P=0.05), the result of positive remodeling. CONCLUSIONS: The main cause of LSM is a regional increase in EEM (regional positive remodeling).

Background incidence of late malapposition after bare-metal stent implantation.

BACKGROUND: Late stent malapposition has been reported to be an abnormal finding after vascular brachytherapy and, possibly, implantation of drug-eluting stents. It can only be detected if intravascular ultrasound (IVUS) is performed at follow-up. However, the "background" frequency of late stent malapposition after bare-metal stent implantation is not known. METHODS AND RESULTS: We studied 206 patients with native artery lesions who had tubular-slotted bare-metal stent implantation and who had IVUS performed at index and after 6+/-3 months of follow-up. There were 9 patients (4.4%) with late malapposition, which is separation of at least 1 stent strut from the arterial wall intima that does not overlap a side-branch, with evidence of blood flow (speckling) behind the strut, and where the immediate postimplantation IVUS revealed complete apposition of the stent to the vessel wall. The location of late malapposition was the stent edge in 8 of 9 patients. The maximum area, length, volume, and arc of late malapposition measured 3.1+/-2.4 mm(2), 3.3+/-2.2 mm, 21+/-27 mm(3), and 110+/-61 degrees, respectively. There was an increase in external elastic membrane (EEM) area (20.7+/-4.9 to 26.9+/-4.2 mm, P=0.0021) and plaque area (10.1+/-3.7 to 14.8+/-3.6 mm, P=0.0022); however, the increase in EEM was greater than the increase in plaque. The area of late malapposition correlated directly with the increase in EEM area (r=0.75, P=0.0205). CONCLUSION: Late malapposition occurs in 4% to 5% of slotted-tube bare-metal stents, usually at stent edges. The main cause is positive remodeling out of proportion to the increase in peri-stent intimal hyperplasia.

Dose volume histogram assessment of late stent malapposition after intravascular brachytherapy.

PURPOSE: Positive remodeling and decreased neointima proliferation are among the causes for Late Stent Malapposition (LSM). It was our interest to investigate a possible relationship between dose and incidence of LSM. METHODS: Index and follow up IVUS examinations of 238 patients (152 treated with Intravascular Brachytherapy (IVBT), 86 control) enrolled in IVBT trials were reviewed to identify patients with LSM. 7.2% of patients treated with IVBT and 2.3% of patients in the control group were found to have LSM on their 6-month follow-up IVUS. Using the index IVUS study. Dose Volume Histograms (DVH) were constructed for a segment of the adventitia comprising an arc deep to the area where LSM is present at follow up. For control, two areas: an arc deep to complete apposition (Control 1) and a segment within the stent but 5 mm apart from the LSM (Control 2). Volumes were defined by IVUS images that were 1 mm apart and the media-adventitial contour was taken to be 0.5 mm thick from the border. RESULTS: DVH of 90% and 50% adventitial volume of LSM area received a significantly (p < .05) higher dose compared to both controls. Calculated are 12 LSM sites in 9 patients and 9 control sites. At all 12 sites Mean Cross Sectional Area of External Elastic Membrane (EEM CSA) was significantly larger in the LSM group at follow up compared to index (p-.001). CONCLUSIONS: DVH analysis showed a positive correlation between radiation dose to the adventitia and incidence of LSM. The myofibroblasts in the adventitia are known to be the target for irradiation. Proliferation of myofibroblasts leads to neointima formation. LSM may be due to the higher dosages delivered to 50% and 90% of the adventitia volume (LSM area) which may have led to profound neointima suppression. In turn the neointima could not compensate positive remodeling reflected by an increase in EEM CSA.