Orthopedics Commons^™

Characteristics Of Clinical Shoulder Research Over The Last Decade: A Review Of Shoulder Articles In The Journal Of Bone & Joint Surgery From 2004 To 2014, Gary M. Gartsman, Brent J. Morris, R. Zackary Unger, Mitzi S. Laughlin, Hussein A. Elkousy, T. Bradley Edwards

Orthopaedic Surgery and Sports Medicine Faculty Publications

Background: The purpose of this study was to determine characteristics and trends in published shoulder research over the last decade in a leading orthopaedic journal.

Methods: We examined all clinical shoulder articles published in The Journal of Bone & Joint Surgery from 2004 to 2014. The number of citations, authorship, academic degrees of the authors, country and institution of origin, topic, level of evidence, positive or nonpositive outcome, and inclusion of validated patient-reported outcome measures were assessed for each article.

Results: Shoulder articles that included an author with an advanced research degree (MD [Doctor of Medicine] with a PhD …

Multiple Epidural Steroid Injections And Body Mass Index Linked With Occurrence Of Epidural Lipomatosis: A Case Series., Rafael Jaimes, Angelo G. Rocco

Orthopaedic Surgery Faculty Publications

BACKGROUND:

Epidural lipomatosis (EL) is an increase of adipose tissue, normally occurring in the epidural space, sufficient to distort the thecal sac and compress neural elements. There is a lack of knowledge of risk factors, impact on patient's symptoms, and its possible association with epidural steroid injections.

METHODS:

History, physical examination, patient chart, and MRI were analyzed from 856 outpatients referred for epidural steroid injections. Seventy patients with signs of EL on MRI comprised the study group. Thirty-four randomly selected patients comprised the control group. The severity of EL was determined by the MRI assessment. The impact of EL was …

Periprosthetic Joint Infection Increases The Risk Of One-Year Mortality., Benjamin Zmistowski, Joseph A. Karam, M.D., Joel B Durinka, David S Casper, Md, Javad Parvizi Md

Rothman Institute Papers

BACKGROUND: Periprosthetic joint infection continues to potentially complicate an otherwise successful joint replacement. The treatment of this infection often requires multiple surgical procedures associated with increased complications and morbidity. This study examined the relationship between periprosthetic joint infection and mortality and aimed to determine the effect of periprosthetic joint infection on mortality and any predictors of mortality in patients with periprosthetic joint infection.

METHODS: Four hundred and thirty-six patients with at least one surgical intervention secondary to confirmed periprosthetic joint infection were compared with 2342 patients undergoing revision arthroplasty for aseptic failure. The incidence of mortality at thirty days, ninety …

Predictors Of Perioperative Blood Loss In Total Joint Arthroplasty., Jai Hyung Park, Mohammad R Rasouli, S M Javad Mortazavi, Anthony T Tokarski, Mitchell G Maltenfort, Javad Parvizi

Rothman Institute Papers

UNLABELLED: UPDATE The print version of this article has errors that have been corrected in the online version of this article. In the Materials and Methods section, the sentence that reads as "During the study period, our institution offered preoperative autologous blood donation to all patients who were scheduling for total joint arthroplasty with a hemoglobin level of no less than 11 mg/dL or a hematocrit level of at least 33%." in the print version now reads as "During the study period, our institution offered preoperative autologous blood donation to all patients who were scheduling for total joint arthroplasty with …

Patients With Atrial Fibrillation Undergoing Total Joint Arthroplasty Increase Hospital Burden., Vinay K Aggarwal, Eric H Tischler, Zachary D Post, Ian Kane, Fabio R Orozco, Alvin Ong

Rothman Institute Papers

BACKGROUND: More than 3 million people in the United States have atrial fibrillation, most of whom are being managed with anticoagulation therapy for life. The goal of the present study was to examine the effect of chronic anticoagulation therapy on patients with atrial fibrillation who undergo total joint arthroplasty.

METHODS: We retrospectively reviewed all patients undergoing aseptic primary or revision total joint arthroplasty at our facility from March 2007 to August 2011. One hundred and sixty-one patients with atrial fibrillation (Group A) were compared with 161 matched controls (Group B). A total of 112 hips and 210 knees underwent 239 …

The Effect Of Malnutrition On Patients Undergoing Elective Joint Arthroplasty., Ronald Huang, Md, Max Greenky, Bs, Glenn J. Kerr, Md, Mathew S. Austin, Md, Javad Parvizi, Md, Frcs

Rothman Institute Papers

Malnutrition has been linked to serious complications in patients undergoing elective total joint arthroplasty (TJA). This study prospectively evaluated 2,161 patients undergoing elective TJA for malnutrition as defined by either an abnormal serum albumin or transferrin. The overall incidence of malnutrition was 8.5% (184 of 2,161) and the rate of overall complications in the malnourished group was 12% as compared to 2.9% in patients with normal parameters (P55years-old undergoing TJA and is associated with a significant increase in post-operative complications.

Spinal Anesthesia: Should Everyone Receive A Urinary Catheter?: A Randomized, Prospective Study Of Patients Undergoing Total Hip Arthroplasty., Adam G Miller, Md, James Mckenzie, Bs, Max Greenky, Ba, Erica Shaw, Rnp, Kishor Gandhi, Md, William J Hozack, Md, Javad Parvizi, Md, Frcs

Rothman Institute Papers

BACKGROUND: The objective of this randomized prospective study was to determine whether a urinary catheter is necessary for all patients undergoing total hip arthroplasty under spinal anesthesia.

METHODS: Consecutive patients undergoing total hip arthroplasty under spinal anesthesia were randomized to treatment with or without insertion of an indwelling urinary catheter. All patients received spinal anesthesia with 15 to 30 mg of 0.5% bupivacaine. The catheter group was subjected to a standard postoperative protocol, with removal of the indwelling catheter within forty-eight hours postoperatively. The experimental group was monitored for urinary retention and, if necessary, had straight catheterization up to two …

Common Peroneal Nerve Palsy Following Total Hip Arthroplasty: Prognostic Factors For Recovery., Jai Hyung Park, Bryan Hozack, Peter Kim, Robert Norton, Steven Mandel, Camilo Restrepo, Javad Parvizi

Rothman Institute Papers

BACKGROUND: Common peroneal nerve palsy, although rare, is a serious complication of total hip arthroplasty. Although several publications have dealt with the risk factors for peroneal nerve palsy, there is little literature regarding the time it takes for the nerve to recover and the factors that influence its recovery. The purpose of this study was to elucidate the clinical course of this injury and identify prognostic factors for recovery.

METHODS: From January 2000 to December 2007, 7969 primary and 1601 revision total hip arthroplasties were performed at our institution. Common peroneal nerve palsy developed following thirty-one (0.32%) of these procedures. …

Functional And Quality-Of-Life Outcomes In Geriatric Patients With Type-Ii Dens Fracture., Alexander R Vaccaro, Christopher K Kepler, Branko Kopjar, Jens Chapman, Christopher Shaffrey, Paul Arnold, Ziya Gokaslan, Darrel Brodke, John France, Mark Dekutoski, Rick Sasso, S Tim Yoon, Christopher Bono, James Harrop, Michael G Fehlings

Rothman Institute Papers

BACKGROUND: Dens fractures are relatively common in the elderly. The treatment of Type-II dens fractures remains controversial. The aim of this multicenter prospective cohort study was to compare outcomes (assessed with use of validated clinical measures) and complications of nonsurgical and surgical treatment of Type-II dens fractures in patients sixty-five years of age or older.

METHODS: One hundred and fifty-nine patients with a Type-II dens fracture were enrolled in a multicenter prospective study. Subjects were treated either surgically (n = 101) or nonsurgically (n = 58) as determined by the treatment preferences of the treating physicians and the patients. The …

Kerlan-Jobe Orthopaedic Clinic Overhead Athlete Scores In Asymptomatic Professional Baseball Pitchers., Matthew J Kraeutler, Michael G Ciccotti, Christopher C Dodson, Robert W Frederick, Brian Cammarota, Steven B. Cohen

Rothman Institute Papers

BACKGROUND: The Kerlan-Jobe Orthopaedic Clinic (KJOC) Shoulder and Elbow score is a subjective questionnaire that has been validated and been shown to be more specific in overhead athletes than the American Shoulder and Elbow Surgeons scale. The purpose of this study was to determine a mean KJOC score and reasonable range of KJOC scores within which a healthy asymptomatic professional baseball pitcher will fall. It was hypothesized that healthy professional baseball pitchers would have very high KJOC scores.

MATERIALS AND METHODS: KJOC questionnaires were given to all healthy pitchers before the start of the season at all levels in 1 …

What's New In Adult Reconstructive Knee Surgery., Carl A Deirmengian, Jess H Lonner

Rothman Institute Papers

No abstract provided.

Acetabular Components In Total Hip Arthroplasty: Is There Evidence That Cementless Fixation Is Better?, Nader Toossi, Bahar Adeli, Andrew J Timperley, Fares S Haddad, Mitchell Maltenfort, Javad Parvizi

Department of Orthopaedic Surgery Faculty Papers

BACKGROUND: The use of cementless acetabular components in total hip arthroplasty has gained popularity over the past decade. Most total hip arthroplasties being performed in North America currently use cementless acetabular components. The objective of this systematic review and meta-analysis was to compare the survivorship and revision rate of cemented and cementless acetabular components utilized in total hip arthroplasty.

METHODS: A primary literature search in PubMed identified 3488 articles, of which 3407 did not meet the inclusion criteria and were excluded. Only English-language articles on either the survivorship or revision rate of primary total hip arthroplasty at a minimum of …

Acetabular Components In Total Hip Arthroplasty: Is There Evidence That Cementless Fixation Is Better?, Nader Toossi, Bahar Adeli, Andrew J Timperley, Fares S Haddad, Mitchell Maltenfort, Javad Parvizi

Rothman Institute Papers

BACKGROUND: The use of cementless acetabular components in total hip arthroplasty has gained popularity over the past decade. Most total hip arthroplasties being performed in North America currently use cementless acetabular components. The objective of this systematic review and meta-analysis was to compare the survivorship and revision rate of cemented and cementless acetabular components utilized in total hip arthroplasty.

METHODS: A primary literature search in PubMed identified 3488 articles, of which 3407 did not meet the inclusion criteria and were excluded. Only English-language articles on either the survivorship or revision rate of primary total hip arthroplasty at a minimum of …

The Influence Of Obesity On The Outcome Of Treatment Of Lumbar Disc Herniation: Analysis Of The Spine Patient Outcomes Research Trial (Sport)., Jeffrey A Rihn, Mark Kurd, Alan S Hilibrand, Jon Lurie, Wenyan Zhao, Todd Albert, James Weinstein

Rothman Institute Papers

BACKGROUND: Questions remain as to the effect that obesity has on patients managed for symptomatic lumbar disc herniation. The purpose of this study was to determine if obesity affects outcomes following the treatment of symptomatic lumbar disc herniation.

METHODS: An as-treated analysis was performed on patients enrolled in the Spine Patient Outcomes Research Trial for the treatment of lumbar disc herniation. A comparison was made between patients with a body mass index of/m² (nonobese) (n = 854) and those with a body mass index of ≥30 kg/m² (obese) (n = 336). Baseline patient demographic and clinical characteristics were documented. Primary …

Successful Identification Of Pathogens By Polymerase Chain Reaction (Pcr)-Based Electron Spray Ionization Time-Of-Flight Mass Spectrometry (Esi-Tof-Ms) In Culture-Negative Periprosthetic Joint Infection., Christina L Jacovides, Rachael Kreft, Bahar Adeli, Bryan Hozack, Garth D Ehrlich, Javad Parvizi

Rothman Institute Papers

BACKGROUND: The diagnosis of periprosthetic joint infection poses many challenges, one of which is the difficulty of isolating the infecting organism. Recently, a sophisticated modality (the Ibis Biosciences T5000 biosensor system) has been introduced that uses pan-domain primers in a series of polymerase chain reactions (PCRs) to identify and speciate essentially all bacteria and fungi as well as to identify key antibiotic resistance genes. We investigated the role of the Ibis in identifying infecting organisms in cases of known and suspected periprosthetic joint infection.

METHODS: Synovial fluid specimens were collected prospectively from eighty-two patients undergoing eighty-seven arthroplasty procedures (sixty-five knee …

Risk Factors For Wound Complications After Ankle Fracture Surgery., Adam G Miller, Andrew Margules, Steven M Raikin

Department of Orthopaedic Surgery Faculty Papers

BACKGROUND: The overall rate of complications after ankle fracture fixation varies between 5% and 40% depending on the population investigated, and wound complications have been reported to occur in 1.4% to 18.8% of patients. Large studies have focused on complications in terms of readmission, but few studies have examined risk factors for wound-related issues in the outpatient setting in a large number of patients. A review was performed to identify risk factors for wound complications tracked in the hospital and outpatient setting.

METHODS: Four hundred and seventy-eight patients underwent open reduction and internal fixation of an ankle fracture between 2003 …

Low Rate Of Infection Control In Enterococcal Periprosthetic Joint Infections., Mohammad R Rasouli, Mohan S Tripathi, Robert Kenyon, Nathan Wetters, Craig J Della Valle, Javad Parvizi

Department of Orthopaedic Surgery Faculty Papers

BACKGROUND: Enterococcal periprosthetic joint infections (PJIs) are rare after joint arthroplasty. These cases are usually reported in series of PJIs caused by other pathogens. Because few studies have focused only on enterococcal PJIs, management and control of infection of these cases have not yet been well defined.

QUESTIONS/PURPOSES: We asked (1) what is the proportion of enterococcal PJI in our institutes; and (2) what is the rate of infection control in these cases?

METHODS: We respectively identified 22 and 14 joints with monomicrobial and polymicrobial PJI, respectively, caused by enterococcus. The diagnosis of PJI was made based on the presence …

The Effect Of Iliac Crest Autograft On The Outcome Of Fusion In The Setting Of Degenerative Spondylolisthesis: A Subgroup Analysis Of The Spine Patient Outcomes Research Trial (Sport)., Kristen Radcliff, Raymond Hwang, Alan Hilibrand, Harvey E Smith, Jordan Gruskay, Jon D Lurie, Wenyan Zhao, Todd Albert, James Weinstein

Rothman Institute Papers

BACKGROUND: There is considerable controversy about the long-term morbidity associated with the use of posterior autologous iliac crest bone graft for lumbar spine fusion procedures compared with the use of bone-graft substitutes. The hypothesis of this study was that there is no long-term difference in outcome for patients who had posterior lumbar fusion with or without iliac crest autograft.

METHODS: The study population includes patients enrolled in the degenerative spondylolisthesis cohort of the Spine Patient Outcomes Research Trial who underwent lumbar spinal fusion. Patients were divided according to whether they had or had not received posterior autologous iliac crest bone …

Functional Results And Outcomes After Repair Of Proximal Hamstring Avulsions., Steven B Cohen, Ashwin Rangavajjula, Dharmesh Vyas, James P Bradley

Rothman Institute Papers

BACKGROUND: The purpose of this study was to assess postsurgical outcomes in active patients after primary repair of acute and chronic proximal hamstring tears.

HYPOTHESIS: Surgical treatment of both acute and chronic proximal hamstring avulsion injuries would result in improved patient outcomes using validated outcome scores and a hamstring-specific questionnaire, and operative repair of these injuries results in excellent outcomes with a high level of patient satisfaction, pain relief, and return to function.

STUDY DESIGN: Case series; Level of evidence, 4.

METHODS: Fifty-two patients who underwent proximal hamstring repair (26 male and 26 female; average age, 47.7 years) completed the …

A Prospective Analysis Of Glove Perforation In Primary And Revision Total Hip And Total Knee Arthroplasty., Aaron H Carter, Md, David S Casper, Md, Javad Parvizi, Md, Mathew Austin, Md

Department of Orthopaedic Surgery Faculty Papers

Literature in regard to glove perforation rates in revision total joint arthroplasty (TJA) is scarce. Our purpose was to determine the incidence of perforation in revision TJA. Gloves from all scrubbed personnel were tested based on the American Society for Testing and Materials. A total of 3863 gloves were collected from 58 primary and 36 revision arthroplasty cases. Surgeons had a 3.7% outer-glove perforation rate in primary TJA compared with 8.9% in revision TJA. When both gloves were perforated, the outer-glove perforation was recognized intraoperatively 100% of the time, and the inner-glove perforation was noted only 19% of the time. …

Management Of Periprosthetic Joint Infection: The Current Knowledge: Aaos Exhibit Selection., Javad Parvizi, Bahar Adeli, Benjamin Zmistowski, Camilo Restrepo, Alan Seth Greenwald

Rothman Institute Papers

Periprosthetic joint infection continues to frustrate the medical community. Although the demand for total joint arthroplasty is increasing, the burden of such infections is increasing even more rapidly, and they pose a unique challenge because their accurate diagnosis and eradication can prove elusive. This review describes the current knowledge regarding diagnosis and treatment of periprosthetic joint infection. A number of tools are available to aid in establishing a diagnosis of periprosthetic joint infection. These include the erythrocyte sedimentation rate, serum C-reactive protein concentration, synovial white blood-cell count and differential, imaging studies, tissue specimen culturing, and histological analysis. Multiple definitions of …

What's New In Spine Surgery., Keith H Bridwell, Paul A Anderson, Scott D Boden, Alexander R Vaccaro, Jeffrey C Wang

Rothman Institute Papers

No abstract provided.

Does The Load-Sharing Classification Predict Ligamentous Injury, Neurological Injury, And The Need For Surgery In Patients With Thoracolumbar Burst Fractures?: Clinical Article., Kristen Radcliff, Christopher K Kepler, Todd A Rubin, Motasem Maaieh, Alan S Hilibrand, James Harrop, Jeffrey A Rihn, Todd J Albert, Alexander R Vaccaro

Department of Orthopaedic Surgery Faculty Papers

OBJECT: The load-sharing score (LSS) of vertebral body comminution is predictive of results after short-segment posterior instrumentation of thoracolumbar burst fractures. Some authors have posited that an LSS > 6 is predictive of neurological injury, ligamentous injury, and the need for surgical intervention. However, the authors of the present study hypothesized that the LSS does not predict ligamentous or neurological injury.

METHODS: The prospectively collected spinal cord injury database from a single institution was queried for thoracolumbar burst fractures. Study inclusion criteria were acute (< 24 hours) burst fractures between T-10 and L-2 with preoperative CT and MRI. Flexion-distraction injuries and pathological fractures were excluded. Four experienced spine surgeons determined the LSS and posterior ligamentous complex (PLC) integrity. Neurological status was assessed from a review of the medical records.

RESULTS: Forty-four patients were included in the study. There were 4 patients for whom all observers …

Does International Normalized Ratio Level Predict Pulmonary Embolism?, Patricia Hansen, Benjamin Zmistowski, Camilo Restrepo, Javad Parvizi, Richard H Rothman

Rothman Institute Papers

BACKGROUND: Preventing pulmonary embolism is a priority after major musculoskeletal surgery. The literature contains discrepant data regarding the influence of anticoagulation on the incidence of pulmonary embolism after joint arthroplasty. The American College of Chest Physicians guidelines recommend administration of oral anticoagulants (warfarin), aiming for an international normalized ratio (INR) level between 2 and 3. However, recent studies show aggressive anticoagulation (INR > 2) can lead to hematoma formation and increased risk of subsequent infection.

QUESTIONS/PURPOSES: We asked whether an INR greater than 2 protects against pulmonary embolism.

PATIENTS AND METHODS: We identified 9112 patients with 10,122 admissions for joint arthroplasty …

Early Versus Delayed Decompression For Traumatic Cervical Spinal Cord Injury: Results Of The Surgical Timing In Acute Spinal Cord Injury Study (Stascis)., Michael G Fehlings, Alex R. Vaccaro, Jefferson R Wilson, Anoushka Singh, David W Cadotte, James Harrop, Bizhan Aarabi, Christopher Shaffrey, Marcel Dvorak, Charles Fisher, Paul Arnold, Eric M Massicotte, Stephen Lewis, Raja Rampersaud

Department of Orthopaedic Surgery Faculty Papers

BACKGROUND: There is convincing preclinical evidence that early decompression in the setting of spinal cord injury (SCI) improves neurologic outcomes. However, the effect of early surgical decompression in patients with acute SCI remains uncertain. Our objective was to evaluate the relative effectiveness of early (injury) versus late (≥ 24 hours after injury) decompressive surgery after traumatic cervical SCI.

METHODS: We performed a multicenter, international, prospective cohort study (Surgical Timing In Acute Spinal Cord Injury Study: STASCIS) in adults aged 16-80 with cervical SCI. Enrolment occurred between 2002 and 2009 at 6 North American centers. The primary outcome was ordinal change …

Duration Of Symptoms Resulting From Lumbar Disc Herniation: Effect On Treatment Outcomes: Analysis Of The Spine Patient Outcomes Research Trial (Sport)., Jeffrey A Rihn, Alan Hilibrand, Kristen Radcliff, Mark Kurd, Jon Lurie, Emily Blood, Todd J Albert, James N Weinstein

Rothman Institute Papers

BACKGROUND: The purpose of the present study was to determine if the duration of symptoms affects outcomes following the treatment of intervertebral lumbar disc herniation.

METHODS: An as-treated analysis was performed on patients enrolled in the Spine Patient Outcomes Research Trial (SPORT) for the treatment of intervertebral lumbar disc herniation. Randomized and observational cohorts were combined. A comparison was made between patients who had had symptoms for six months or less (n = 927) and those who had had symptoms for more than six months (n = 265). Primary and secondary outcomes were measured at baseline and at regular follow-up …

Duration Of Symptoms Resulting From Lumbar Disc Herniation: Effect On Treatment Outcomes: Analysis Of The Spine Patient Outcomes Research Trial (Sport)., Jeffrey A Rihn, Alan S Hilibrand, Kristen Radcliff, Mark Kurd, Jon Lurie, Emily Blood, Todd J Albert, James N Weinstein

Department of Orthopaedic Surgery Faculty Papers

BACKGROUND: The purpose of the present study was to determine if the duration of symptoms affects outcomes following the treatment of intervertebral lumbar disc herniation.

METHODS: An as-treated analysis was performed on patients enrolled in the Spine Patient Outcomes Research Trial (SPORT) for the treatment of intervertebral lumbar disc herniation. Randomized and observational cohorts were combined. A comparison was made between patients who had had symptoms for six months or less (n = 927) and those who had had symptoms for more than six months (n = 265). Primary and secondary outcomes were measured at baseline and at regular follow-up …

Burden Of Traumatic Spine Fractures In Tehran, Iran., Maziar Moradi-Lakeh, Mohammad R Rasouli, Alexander Vaccaro, Soheil Saadat, Mohammad R Zarei, Vafa Rahimi-Movaghar

Rothman Institute Papers

UNLABELLED: ABSTRACT:

BACKGROUND: The Disability-Adjusted Life Year (DALY) was designed by the World Health Organization (WHO) to measure, compare, and analyze the burden of various diseases. To the best of our knowledge, this is the first study on the assessment of burden of traumatic spinal fracture (TSF) in an Iranian community. We estimated burden of TSF includes both isolated (iTSF) and associated injuries related to traumatic spinal fractures (aTSF) in Tehran, the capital of Iran, for the year 2006-2007 using DALYs.

METHODS: Burden of TSF was estimated based on information provided by the national data on Iranian trauma, data from …

Classification And Treatment Of Proximal Humerus Fractures: Inter-Observer Reliability And Agreement Across Imaging Modalities And Experience., Abtin Foroohar, Rick Tosti, John M Richmond, John P Gaughan, Asif M Ilyas

Rothman Institute Papers

SUMMARY: Proximal humerus fractures (PHF) are common injuries, but previous studies have documented poor inter-observer reliability in fracture classification. This disparity has been attributed to multiple variables including poor imaging studies and inadequate surgeon experience. The purpose of this study is to evaluate whether inter-observer agreement can be improved with the application of multiple imaging modalities including X-ray, CT, and 3D CT reconstructions, stratified by physician experience, for both classification and treatment of PHFs.

METHODS: Inter-observer agreement was measured for classification and treatment of PHFs. A total of sixteen fractures were imaged by plain X-ray (scapular AP and lateral), CT …

Potent Inhibition Of Heterotopic Ossification By Nuclear Retinoic Acid Receptor-Γ Agonists., Kengo Shimono, Wei-En Tung, Christine Macolino, Amber Hsu-Tsai Chi, Johanna H Didizian, Christina Mundy, Roshantha A Chandraratna, Yuji Mishina, Motomi Enomoto-Iwamoto, Maurizio Pacifici, Masahiro Iwamoto

Department of Orthopaedic Surgery Faculty Papers

Heterotopic ossification consists of ectopic bone formation within soft tissues after surgery or trauma. It can have debilitating consequences, but there is no definitive cure. Here we show that heterotopic ossification was essentially prevented in mice receiving a nuclear retinoic acid receptor-γ (RAR-γ) agonist. Side effects were minimal, and there was no significant rebound effect. To uncover the mechanisms of these responses, we treated mouse mesenchymal stem cells with an RAR-γ agonist and transplanted them into nude mice. Whereas control cells formed ectopic bone masses, cells that had been pretreated with the RAR-γ agonist did not, suggesting that they had …