A Systemic and Local Comparison of Senescence in an Acute Anterior Cruciate Ligament Injury-A Pilot Case Series.

BACKGROUND: Senescence, a characteristic of cellular aging and inflammation, has been linked to the acceleration of osteoarthritis. The purpose of this study is to prospectively identify, measure, and compare senescent profiles in synovial fluid and peripheral blood in patients with an acute knee injury within 48 h. METHODS: Seven subjects, aged 18-60 years, with an acute ACL tear with effusion were prospectively enrolled. Synovial fluid and peripheral blood samples were collected and analyzed by flow cytometry, using senescent markers C12FDG and CD87. The senescent versus pro-regenerative phenotype was probed at a gene and protein level using qRT-PCR and multiplex immunoassays. RESULTS: C12FDG and CD87 positive senescent cells were detected in the synovial fluid and peripheral blood of all patients. Pro-inflammatory IL-1ß gene expression measured in synovial fluid was significantly higher (p = 0.0156) than systemic/blood expression. Senescent-associated factor MMP-3 and regenerative factor TIMP-2 were significantly higher in synovial fluid compared to blood serum. Senescent-associated factor MMP-9 and regenerative factor TGFß-2 were significantly elevated in serum compared to synovial fluid. Correlation analysis revealed that C12FDG++/CD87++ senescent cells in synovial fluid positively correlated with age-related growth-regulated-oncogene (ρ = 1.00, p < 0.001), IFNγ (ρ = 1.00, p < 0.001), IL-8 (ρ = 0.90, p = 0.0374), and gene marker p16 (ρ = 0.83, p = 0.0416). CONCLUSIONS: There is an abundance of senescent cells locally and systemically after an acute ACL tear without a significant difference between those present in peripheral blood compared to synovial fluid. This preliminary data may have a role in identifying strategies to modify the acute environment within the synovial fluid, either at the time of acute ligament injury or reconstruction surgery.

Biomechanical Evaluation of Posterior Shoulder Instability With a Clinically Relevant Posterior Glenoid Bone Loss Model.

BACKGROUND: Existing biomechanical studies of posterior glenoid bone loss and labral pathology are limited by their use of anterior instability models, which differ in both orientation and morphology and have been performed in only a single, neutral arm position. PURPOSE: To evaluate the biomechanical effectiveness of a posterior labral repair in the setting of a clinically relevant posterior bone loss model in various at-risk arm positions. STUDY DESIGN: Controlled laboratory study. METHODS: Ten fresh-frozen cadaveric shoulders were tested in 7 consecutive states using a 6 degrees of freedom robotic arm: (1) native, (2) posterior labral tear (6-9 o'clock), (3) posterior labral repair, (4) mean posterior glenoid bone loss (7%) with labral tear, (5) mean posterior glenoid bone loss with labral repair, (6) large posterior glenoid bone loss (28%) with labral tear, and (7) large posterior glenoid bone loss with labral repair. Bone loss was created using 3-dimensional printed computed tomography model templates. Biomechanical testing consisted of 75 N of posterior-inferior force and 75 N of compression at 60° and 90° of flexion and scaption. Posterior-inferior translation, lateral translation, and peak dislocation force were measured for each condition. RESULTS: Labral repair significantly increased dislocation force independent of bone loss state between 10.1 and 14.8 N depending on arm position. Dislocation force significantly decreased between no bone loss and small bone loss (11.9-13.5 N), small bone loss and large bone loss (9.4-14.3 N), and no bone loss and large bone loss (21.2-26.5 N). Labral repair significantly decreased posterior-inferior translation compared with labral tear states by a range of 1.0 to 2.3 mm. In the native state, the shoulder was most unstable in 60° of scaption, with 29.9 ± 6.1-mm posterior-inferior translation. CONCLUSION: Posterior labral repair improved stability of the glenohumeral joint, and even in smaller to medium amounts of posterior glenoid bone loss the glenohumeral stability was maintained with labral repair in this cadaveric model. However, a labral repair with large bone loss could not improve stability to the native state. CLINICAL RELEVANCE: This study shows that larger amounts of posterior glenoid bone loss (>25%) may require bony augmentation for adequate stability.

Current State of Platelet-Rich Plasma and Cell-Based Therapies for the Treatment of Osteoarthritis and Tendon and Ligament Injuries.

➤: Orthobiologics encompass numerous substances that are naturally found in the human body including platelet-rich plasma (PRP), isolated growth factors, and cell therapy approaches to theoretically optimize and improve the healing of cartilage, fractures, and injured muscles, tendons, and ligaments. ➤: PRP is an autologous derivative of whole blood generated by centrifugation and is perhaps the most widely used orthobiologic treatment modality. Despite a vast amount of literature on its use in osteoarthritis as well as in tendon and ligament pathology, clinical efficacy results remain mixed, partly as a result of insufficient reporting of experimental details or exact compositions of PRP formulations used. ➤: Mesenchymal stromal cells (MSCs) can be isolated from a variety of tissues, with the most common being bone marrow aspirate concentrate. Similar to PRP, clinical results in orthopaedics with MSCs have been highly variable, with the quality and concentration of MSCs being highly contingent on the site of procurement and the techniques of harvesting and preparation. ➤: Advances in novel orthobiologics, therapeutic targets, and customized orthobiologic therapy will undoubtedly continue to burgeon, with some early promising results from studies targeting fibrosis and senescence.

Commercial 3-dimensional imaging programs are not created equal: version and inclination measurement positions vary among preoperative planning software.

Background: Variability exists between total shoulder arthroplasty preoperative planning software (PPS) systems for glenoid angular measurements. The purpose of this study is to locate the region on the glenoid at which inclination and version are measured on the PPS modalities of Blueprint and VIP. Methods: Preoperative computed tomography scans of 30 consecutive patients undergoing primary arthroplasty were analyzed using two PPS systems (VIP and Blueprint) to independently obtain glenoid version and inclination measurements through their respective protocols. Three-dimensional equivalent images were independently analyzed utilizing open-source OsiriX DICOM software by two board-certified orthopedic sports medicine surgeons measuring glenoid version and inclination along ten equal intervals of the glenoid from superior to inferior and anterior to posterior. Manual version and inclination measurements were compared to both the VIP and the Blueprint measurements, and variances were analyzed by calculating root mean square error (RMSE). The closest interval (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) to the VIP and Blueprint measurement was identified for both version and inclination to determine the region of the glenoid both software programs obtained their measurements. Results: Mean glenoid retroversion manually measured using OsiriX was 13.5° compared with 15.1° recorded by Blueprint (P = .516) and 12.2° by VIP (P = .621). Mean inclination using OsiriX was 5.5°, compared with 7.1° (P = .314) and 9.0° (P = .024) recorded by Blueprint and VIP, respectively. RMSE for version between Osirix and VIP was 4.65°, for Osirix and Blueprint was 4.44°, and for VIP and Blueprint was 4.45°. RMSE for inclination between Osirix and VIP was 6.43°, for Osirix and Blueprint was 5.25°, and for VIP and Blueprint was 5.13°. For version, VIP measurements most frequently aligned with the inferior quadrant of the glenoid (n = 13) with a median interval of 7, while Blueprint aligned with the superior quadrant of the glenoid (n = 13) with a median interval of 4. Inclination measurements aligned with the posterior quadrant of the glenoid for both VIP (n = 19) and Blueprint (n = 15) with a median interval of 8. Conclusion: PPS systems for shoulder arthroplasty vary in the region of the glenoid for which version and inclination are measured, which may affect the absolute values generated. Location of version measurement was different among the two commercial software programs, with VIP corresponding closest to the most inferior region of the glenoid, while Blueprint to the most superior one. Further research should assist in determining the version and inclination variations among commercial planning software.

Femoroacetabular Impingement in Elite Skiers and Snowboarders: Return to Sports and Outcomes After Hip Arthroscopy.

BACKGROUND: Hip arthroscopy has been shown to be an effective treatment for femoroacetabular impingement (FAI) in high-level athletes; however, limited outcome and return-to-play data exist for hip arthroscopy in skiers and snowboarders. PURPOSES: To determine the return-to-sports rate of elite skiers and snowboarders who have undergone hip arthroscopic surgery for FAI and to assess hip-related outcomes at a minimum 2-year follow-up. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Elite skiers and snowboarders who underwent hip arthroscopy for the treatment of FAI between 2005 and 2018 were identified via a retrospective review of prospectively collected data. Data were obtained from fis-ski.org, usskiandsnowboard.org, xgames.com, and wikipedia.org, including information on each player's career length, participation on a national team, and time between surgery and first competition after surgery. Patient-reported outcomes (PROs) were prospectively collected preoperatively and at minimum 2 years postoperatively. RESULTS: In total, 26 elite skiers and snowboarders (34 hips) were included. The mean ± standard deviation age at surgery was 24.5 ± 6.7 years (range, 18.7-46.8 years). A total of 85% (22/26) returned to elite-level competition at 8.9 months (range, 2.9-23.7 months) with an average career length of 3.6 ± 2.7 years after surgery. Four athletes (5 hips) required revision arthroscopy, with adhesions being the most frequent indication. At a mean follow-up of 7.7 ± 3.2 years, significant improvement in PROs (P < .05) was demonstrated for the Hip Outcome Score (HOS)-Activities of Daily Living (from 76 ± 20 to 95 ± 6), HOS-Sport Specific Subscale (from 63 ± 28 to 92 ± 14), modified Harris Hip Score (from 70 ± 19 to 89 ± 12), and 12-Item Short Form Health Survey Physical Component Summary (from 45 ± 11 to 54 ± 8). Patient satisfaction had a mean of 8 ± 2 (range, 1-10) and median of 10. CONCLUSION: The return-to-competition rate in elite skiers and snowboarders after hip arthroscopy for FAI was 85% at an average of 8.9 months and with a career length of 3.6 years after surgery. Significant improvement in PROs was demonstrated for the HOS-Activities of Daily Living, HOS-Sport Specific Subscale, modified Harris Hip Score, and 12-Item Short Form Health Survey Physical Component Summary, with a median patient satisfaction score of 10. These findings support hip arthroscopy as an effective procedure for the treatment of FAI in elite skiers and snowboarders with symptomatic activity-limiting hip pain, allowing them to return to their previous levels of competition at a high rate.

Arthroscopic Segmental Medial Meniscus Allograft Transplant Using Three Fixation Techniques.

Partial meniscectomy or failed meniscus repair can lead to pain, dysfunction, and cartilage degradation due to increased contact forces. Meniscus transplantation can lead to favorable outcomes and cartilage preservation with careful patient selection. Limited data exist on segmental meniscus allograft transplantation, with promising results using synthetic grafts and early animal and biomechanical studies on segmental allograft transplantation, showing similar results to full meniscus allograft transplantation. This article presents a technique for arthroscopic segmental medial meniscus allograft transplant and a brief review of the literature.

Postoperative Stiffness and Pain After Arthroscopic Labral Stabilization: Consider Anchor Arthropathy.

PURPOSE: To describe the key clinical, imaging, and arthroscopic characteristics of anchor arthropathy after arthroscopic shoulder stabilization procedures and, secondarily, to define risk factors for the development of anchor-induced arthropathy. METHODS: A total of 23 patients who underwent revision arthroscopic shoulder surgery and were diagnosed with glenohumeral arthropathy were retrospectively identified from prospectively collected data registries between January 2000 and May 2018. Data included initial diagnosis and index procedure performed, presenting arthropathy symptoms including duration, and examination findings before revision surgery. Pre-revision imaging was used to assess presence of glenohumeral osteoarthritis and chondromalacia, anchors/sutures, loose bodies, and labral pathology. The same parameters were recorded intraoperatively during revision surgery. Descriptive statistics were performed for demographic data and means with standard deviations were calculated for continuous data. A McNemar-Bowker test was used to analyze marginal homogeneity between preoperative imaging and intraoperative findings. RESULTS: Mean age at presentation was 33.4 ± 11.7 years (range 16-59, 17 male patients; 6 female patients). More than one half (13/23) developed symptoms within 10 months after index arthroscopic procedure (mean 32.2 ± 59.9 months, range <1 to 165.2 months) with 87% presenting with pain and 100% presenting with loss of motion on examination. Plain radiographs demonstrated humeral osteoarthritis in 57% (13/23) of patients, magnetic resonance imaging (MRI) revealed recurrent labral pathology in 19 of 23 (83%) patients, potential proud implants in 12 of 23 (52%), and loose bodies in 12 of 23 (52%). Intraoperatively, all had evidence of osteoarthritis; 22 of 23 (96%) had prominent implants. Humeral head chondromalacia was present in 21 of 23 patients (91%), the majority of which was linear stripe wear, and 6 of 23 (26%) had severe global glenohumeral osteoarthritis. Statistical analysis revealed a 54.5% (95% confidence interval 0.327-0.749) sensitivity of MRI identification of proud implants with a specificity of 100% (95% confidence interval 0.055-1). The ability of MRI to accurately assess chondromalacia of the humeral head (P = .342) or glenoid (P = .685) was not statistically significant. CONCLUSIONS: Anchor arthropathy is characterized by symptoms of pain and stiffness on examination and in many cases develops early after stabilization surgery (<10 months). Implants were implicated in the majority of cases of humeral head chondromalacia. MRI scans may produce false-negative identification of proud implants and can be a poor predictor of the severity of chondromalacia and intra-articular pathology; thus, a high index of clinical suspicion is necessary in patients with motion loss and pain postoperatively. LEVEL OF EVIDENCE: Level IV, case series.

Anchor Arthropathy of the Shoulder Joint After Instability Repair: Outcomes Improve With Revision Surgery.

PURPOSE: To report clinical and patient-reported outcome measures (PROMs) in patients undergoing revision surgery after diagnosis of anchor-induced arthropathy. METHODS: Patients who underwent revision arthroscopic shoulder surgery and were diagnosed with post-instability glenohumeral arthropathy performed from January 2006 to May 2018 were included in the current study. Patients were excluded if they underwent prior open shoulder procedures, if glenoid bone loss was present, or if prerevision imaging and records were incomplete or not available. Data included initial diagnosis and index procedure performed, presenting arthropathy symptoms including duration, exam findings before revision surgery, and surgical intervention. PROMs were prospectively collected before surgery and at minimum 2-year follow-up. RESULTS: Fourteen patients were included with a mean (± standard deviation) age at presentation of 35.2 ± 12.1 years (range 16 to 59). The follow-up rate was 86%, with a mean follow-up of 3.8 years (range 1.1 to 10.6). Mean time to development of arthropathy symptoms was 48.2 months (range <1 month to 13.8 years), all presenting with pain and decreased range of motion on exam. At time of revision surgery, all patients underwent either open or arthroscopic removal of previous implants, including anchors and suture material. Six patients underwent additional revision stabilization procedures, 1 underwent total shoulder arthroplasty, and 7 underwent arthroscopic intraarticular debridement, capsular release, and chondroplasty with or without microfracture. Pain significantly improved in 79% of patients (P = .05). Significant improvements in all PROMs were observed, including 12-item Short Form (43.8 to 54.8, P < .01); Disabilities of the Arm, Shoulder, and Hand, shortened version (31.8 to 8.4, P < .01); Single Assessment Numeric Evaluation (47.0 to 84.5, P < .05); and American Shoulder and Elbow Surgeons (61.6 to 92.1, P < .01). Average external rotation significantly improved, from 31° ± 22° to 52° ± 24° (P = .02). CONCLUSION: Rapid intervention after diagnosis, through either revision arthroscopic or open debridement and stabilization, can lead to significant improvement in range of motion, pain, and overall patient function and satisfaction. LEVEL OF EVIDENCE: IV, retrospective case series.

Generating the American Shoulder and Elbow Surgeons Score Using Multivariable Predictive Models and Computer Adaptive Testing to Reduce Survey Burden.

BACKGROUND: The preferred patient-reported outcome measure for the assessment of shoulder conditions continues to evolve. Previous studies correlating the Patient-Reported Outcomes Measurement Information System (PROMIS) computer adaptive tests (CATs) to the American Shoulder and Elbow Surgeons (ASES) score have focused on a singular domain (pain or physical function) but have not evaluated the combined domains of pain and physical function that compose the ASES score. Additionally, previous studies have not provided a multivariable prediction tool to convert PROMIS scores to more familiar legacy scores. PURPOSE: To establish a valid predictive model of ASES scores using a nonlinear combination of PROMIS domains for physical function and pain. STUDY DESIGN: Cohort study (Diagnosis); Level of evidence, 3. METHODS: The Military Orthopaedics Tracking Injuries and Outcomes Network (MOTION) database is a prospectively collected repository of patient-reported outcomes and intraoperative variables. Patients in MOTION research who underwent shoulder surgery and completed the ASES, PROMIS Physical Function, and PROMIS Pain Interference at varying time points were included in the present analysis. Nonlinear multivariable predictive models were created to establish an ASES index score and then validated using "leave 1 out" techniques and minimal clinically important difference /substantial clinical benefit (MCID/SCB) analysis. RESULTS: A total of 909 patients completed the ASES, PROMIS Physical Function, and PROMIS Pain Interference at presurgery, 6 weeks, 6 months, and 1 year after surgery, providing 1502 complete observations. The PROMIS CAT predictive model was strongly validated to predict the ASES (Pearson coefficient = 0.76-0.78; R2 = 0.57-0.62; root mean square error = 13.3-14.1). The MCID/SCB for the ASES was 21.7, and the best ASES index MCID/SCB was 19.4, suggesting that the derived ASES index is effective and can reliably re-create ASES scores. CONCLUSION: The PROMIS CAT predictive models are able to approximate the ASES score within 13 to 14 points, which is 7 points more accurate than the ASES MCID/SCB derived from the sample. Our ASES index algorithm, which is freely available online (https://osf.io/ctmnd/), has a lower MCID/SCB than the ASES itself. This algorithm can be used to decrease patient survey burden by 11 questions and provide a reliable ASES analog to clinicians.

Risk Factors for Failure of Nonoperative Treatment of Posterior Shoulder Labral Tears on Magnetic Resonance Imaging.

INTRODUCTION: There are no reports in the literature describing risk factors for failure of nonoperative treatment of patients with posterior labral tears on magnetic resonance imaging (MRI). The purpose of this study is to identify risk factors for failure of nonoperative treatment in patients with an isolated posterior glenoid labral tear identified on MRI only. Patients with posterior labral tears on MRI who fail to improve with nonoperative treatment likely share a constellation of clinical history, physical exam, and radiographic findings. METHODS: One hundred and fifty-nine active duty military service members under the age of 40 with a posterior labral tear seen on MRI and who were clinically evaluated by a musculoskeletal trained physician were identified. We retrospectively evaluated their records ensuring a minimum of 2 years follow-up after MRI to identify surgical intervention for the posterior labral tear during this time period. Patients were stratified into two groups, those treated with any combination of nonoperative modalities and those treated with posterior labral repair surgery during the 2 years after the MRI. The electronic medical records were reviewed for clinical presentation and physical exam results. We measured multiple radiographic parameters, including glenoid version, size of the tear, and bone loss on MRI. Qualitative and quantitative data were compared between groups using Fisher's exact test and Student's t-test, respectively. This study was conducted under institutional review board approval. RESULTS: Of the 157 patients' shoulders in our study, 52% (n = 82) of patients with posterior labral tears underwent nonoperative treatment while 48% (n = 75) underwent surgery. The significant risk factors associated with surgery were a history of a specific injury, primary presenting complaint of instability, patient reported history of subluxation, inability to trust their shoulder with overhead activity, decreased strength with weight lifting, positive posterior load/shift exam, positive anterior apprehension, increased osseous glenoid retroversion, increased humeral head subluxation ratio, and anterior labral height (P < 0.05). Patients with a chief complaint of pain were much more likely to succeed with nonoperative treatment while those with instability underwent surgery more often. Ten (12.5%) of the surgical procedures included an anterior and posterior labral repair/stabilization procedure. CONCLUSION: Patients with an MRI confirmed posterior labral tear, which present with subjective complaints and physical exam maneuvers consistent with instability, appear less likely to be treated nonoperatively. Increased glenoid retroversion and posterior humeral head subluxation may also predispose patients toward surgical treatment. Additionally, posterior labral tears may extend into the anterior labrum more frequently than is recognized on MRI.

Validation of varus stress radiographs for anterior cruciate ligament and posterolateral corner knee injuries: A biomechanical study.

PURPOSE: The purpose of this study was to determine the effect of isolated anterior cruciate ligament (ACL) insufficiency on the radiographic varus stress test, and to provide reference data for the increase in lateral compartment opening under varus stress for a combined ACL and PLC injury. METHODS: Ten cadaveric lower extremities were fixed to a jig in 20° of knee flexion. Twelve Newton-meter (Nm) and clinician-applied varus loads were tested, first with intact knee ligaments, followed by sequential sectioning of the ACL, fibular collateral ligament (FCL), popliteus tendon and the popliteofibular ligament (PFL). Lateral compartment opening was measured after each sequential sectioning. RESULTS: Maximum increase in lateral compartment opening for an isolated ACL deficient knee was 1.06mm with mean increase of 0.52mm (p=0.021) for the clinician-applied load. Mean increase in lateral compartment opening in an ACL and FCL deficient knee compared to the intact knee was 1.48mm (p<0.005) and 1.99mm (p<0.005) for the 12-Nm and clinician-applied loads, respectively, increasing to 1.94mm (p<0.005) and 2.68mm (p<0.005) with sectioning of the ACL and all PLC structures. CONCLUSIONS: Anterior cruciate ligament deficiency contributes to lateral compartment opening on varus stress radiographs though not sufficiently to confound previously established standards for lateral ligament knee injuries. We did not demonstrate the same magnitude of lateral compartment opening with sectioning of the PLC structures as previously reported, questioning the reproducibility of varus stress radiographic testing among institutions. Clinicians are cautioned against making surgical decisions based solely on current standards for radiographic stress examinations.

A Radiographic Assessment of Failed Anterior Cruciate Ligament Reconstruction: Can Magnetic Resonance Imaging Predict Graft Integrity?

BACKGROUND: Magnetic resonance imaging (MRI) showing an "intact" anterior cruciate ligament (ACL) graft may not correlate well with examination findings. Reasons for an ACL graft dysfunction may be from malpositioned tunnels, deficiency of secondary stabilizers, repeat injuries, or a combination of factors. PURPOSE: To evaluate the concordance/discordance of an ACL graft assessment between an arthroscopic evaluation, physical examination, and MRI and secondarily to evaluate the contributing variables to discordance. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 50 ACL revisions in 48 patients were retrospectively reviewed. The ACL graft status was recorded separately based on Lachman and pivot-shift test data, arthroscopic findings from operative reports, and MRI evaluation and was categorized into 3 groups: intact, partial tear, or complete tear. Two independent evaluators reviewed all of the preoperative radiographs and MRI scans, and interrater and intrarater reliability were evaluated. Concordance and discordance between a physical examination, arthroscopic evaluation, and MRI evaluation of the ACL graft were calculated. Graft position and type, mechanical axis, collateral ligament injuries, chondral and meniscal injuries, and mechanism of injury were evaluated as possible contributing factors using univariate and multivariate analyses. Sensitivity and specificity of MRI to detect a torn ACL graft and meniscal and chondral injuries on arthroscopic evaluation were calculated. RESULTS: The interobserver and intraobserver reliability for the MRI evaluation of the ACL graft were moderate, with combined κ values of .41 and .49, respectively. The femoral tunnel position was vertical in 88% and anterior in 46%. On MRI, the ACL graft was read as intact in 24%; however, no graft was intact on arthroscopic evaluation or physical examination. The greatest discordance was between the physical examination and MRI, with a rate of 52%. An insidious-onset mechanism of injury was significantly associated with discordance between MRI and arthroscopic evaluation of the ACL (P = .0003) and specifically with an intact ACL graft on MRI (P = .0014). The sensitivity and specificity of MRI to detect an ACL graft tear were 60% and 87%, respectively. CONCLUSION: Caution should be used when evaluating a failed ACL graft with MRI, especially in the absence of an acute mechanism of injury, as it may be unreliable and inconsistent.

Pectoralis major muscle rupture repair: technique using unicortical buttons.

Over the past few decades, there has been increased awareness of pectoralis major muscle injuries necessitating further evaluation of management options and, in particular, surgical repair. Injury typically occurs when an eccentric load is applied to the muscle, such as with bench pressing, and failure usually occurs through the tendon. Although nonoperative management is sometimes appropriate, given the injury's propensity for young, active male patients, surgical intervention is often warranted. Because the injury typically occurs at the muscle-tendon interface, surgery focuses on repair of the avulsed tendon into its anatomic attachment site. We describe the use of a unicortical suture button to repair the ruptured tendon. This technique achieves the goals of strong fixation and anatomic repair of the tendon back into its native footprint.