The Diagnostic Utility of Cervical Spine Proprioception for Adolescent Concussion.

OBJECTIVE: Cervical spine proprioception may be impaired after concussion. Our objective was to determine the diagnostic utility of cervical spine proprioception for adolescent concussion. DESIGN: Cross-sectional. SETTING: Research laboratory. PARTICIPANTS: Adolescents ≤18 days of concussion and uninjured controls. INTERVENTIONS: N/A. MAIN OUTCOMES: Head repositioning accuracy (HRA) testing, a measure of cervical spine proprioception. The HRA test involved patients relocating their head back to a neutral starting position with eyes closed after maximal cervical spine flexion, extension, and right and left rotations. The overall HRA error score was the mean error (distance from the starting point to self-reported return to neutral) across 12 trials: 3 trials in each direction. We used t-tests to compare group means and logistic regression (outcome = group, predictor = HRA, covariates) to calculate odds ratios. We used a receiver operator characteristic curve to evaluate area under the curve (AUC) and calculate the optimal HRA cutpoint to distinguish concussion from controls. RESULTS: We enrolled and tested 46 participants with concussion (age = 15.8 ± 1.3 years, 59% female, mean = 11.3 ± 3.3 days postconcussion) and 83 uninjured controls (age = 16.1 ± 1.4 years, 88% female). The concussion group had significantly worse HRA than controls (4.3 ± 1.6 vs 2.9 ± 0.7 degrees, P < 0.001, Cohen d = 1.19). The univariable HRA model AUC was 0.81 (95% CI = 0.73, 0.90). After adjusting for age, sex, and concussion history, the multivariable model AUC improved to 0.85 (95% CI = 0.77, 0.92). The model correctly classified 80% of participants as concussion/control at a 3.5-degree cutpoint. CONCLUSIONS: Adolescents with concussion demonstrated worse cervical spine proprioception than uninjured controls. Head repositioning accuracy may offer diagnostic utility for subacute concussion.

Playing Surface and Sport Contact Status Modulate Time to Lower Extremity Musculoskeletal Injury at a Greater Level than Concussion History Among Collegiate Student-Athletes.

OBJECTIVES: While previous investigations have demonstrated a positive correlation between previous concussion and risk of subsequent lower extremity musculoskeletal injury (LEMSKI), the effect of sport- and patient-specific factors on time to injury has not been thoroughly described. This study's main objective was to evaluate the relationship between prior concussion and time to LEMSKI among a population of collegiate student-athletes. Secondary objectives were to evaluate the relationship between playing surface, sport contact status, and biologic sex on time to LEMSKI. We hypothesized that those with previous concussion, those competing on synthetic surfaces, and those competing in collision sports would experience decreased latency to LEMSKI overall. METHODS: A retrospective observational analysis of National Collegiate Athletic Association (NCAA) Division I student-athletes was conducted utilizing a mixed linear model analysis with contrasts. Inclusion criteria included participation in the Pac-12 Health Analytics Program with a documented LEMSKI between 2017 and 2020. Exclusion criteria included concurrent concussion and LEMSKI, injury resulting in serious morbidity or mortality, and incomplete medical record. Participants were classified by whether they sustained a concussion prior to LEMSKI in each athletic season. RESULTS: Of 1179 athletes included, 1140 had no previous concussion and 37 had a previous concussion. There was no observed effect of previous concussion (F=0.038; p=0.846) on time to LEMSKI overall. Student-athletes competing on constructed surfaces sustained a subsequent LEMSKI 14.5 days sooner (SE=5.255; p=0.045), and those competing on organic surfaces sustained a subsequent LEMSKI 23.5 days sooner (SE=4.018; p<0.001) in the season than those competing on synthetic surfaces. Contact sport student-athletes sustained a subsequent LEMSKI 52.1 days sooner than collision sport student-athletes (SE=5.248; p<0.001), and limited contact sport student-athletes sustained a subsequent LEMSKI 42.29 days sooner than collision sport student-athletes (SE=4.463; p<0.001). There was no observed effect of biologic sex (F=0.602; p=0.438) on time to LEMSKI overall. CONCLUSION: There was no observed impact of concussion on time to LEMSKI overall in this collegiate athletic population. Contact sports were associated with decreased time to LEMSK, while synthetic surfaces were associated with increased time to LEMSKI in this population. There was no observed impact of biologic sex on time to LEMSKI. LEVEL OF EVIDENCE: Case-control, level of evidence III.

Decay-Accelerating Factor Differentially Associates With Complement-Mediated Damage in Synovium After Meniscus Tear as Compared to Anterior Cruciate Ligament Injury.

We have reported that anterior cruciate ligament (ACL) injury leads to the differential dysregulation of the complement system in the synovium as compared to meniscus tear (MT) and proposed this as a mechanism for a greater post-injury prevalence of post traumatic osteoarthritis (PTOA). To explore additional roles of complement proteins and regulators, we determined the presence of decay-accelerating factor (DAF), C5b, and membrane attack complexes (MACs, C5b-9) in discarded surgical synovial tissue (DSST) collected during arthroscopic ACL reconstructive surgery, MT-related meniscectomy, osteoarthritis (OA)-related knee replacement surgery and normal controls. Multiplexed immunohistochemistry was used to detect and quantify complement proteins. To explore the involvement of body mass index (BMI), after these 2 injuries, we examined correlations among DAF, C5b, MAC and BMI. Using these approaches, we found that synovial cells after ACL injury expressed a significantly lower level of DAF as compared to MT (p<0.049). In contrast, C5b staining synovial cells were significantly higher after ACL injury (p<0.0009) and in OA DSST (p<0.039) compared to MT. Interestingly, there were significantly positive correlations between DAF & C5b (r=0.75, p<0.018) and DAF & C5b (r=0.64 p<0.022) after ACL injury and MT, respectively. The data support that DAF, which should normally dampen C5b deposition due to its regulatory activities on C3/C5 convertases, does not appear to exhibit that function in inflamed synovia following either ACL injury or MT. Ineffective DAF regulation may be an additional mechanism by which relatively uncontrolled complement activation damages tissue in these injury states.

The Everted Acetabular Labrum: Outcomes of Surgical Management.

BACKGROUND: An everted acetabular labrum (EL) is a pathologic variant in which the labrum is flipped to the capsular side of the acetabular rim. An iatrogenic EL is a known complication of a poorly executed labral repair, and a recent study described the native acetabular EL. PURPOSE: To analyze surgical outcomes after advancement or reconstruction of an EL in a native hip. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: This was a multicenter retrospective review of prospectively collected data on primary hip arthroscopic surgeries performed between 2013 and 2023. An EL was identified arthroscopically as a labrum-femoral head gap while off traction in the native hip. All patients with EL who were analyzed in this study underwent arthroscopic labral repair and advancement or labral augmentation or reconstruction. Patients with hip dysplasia also underwent periacetabular osteotomy with or without a derotational femoral osteotomy. Patient-reported outcomes (PROs) were assessed using the 12-item International Hip Outcome Tool (iHOT-12) and the Nonarthritic Hip Score. PROs were obtained preoperatively and up to 24 months after surgery. PROs were compared with those of a case-matched control cohort in a 1:2 ratio. Only patients with PROs available at ≥1 year postoperatively were included in the outcome analysis. RESULTS: A total of 111 patients (129 hips) with EL during the study period were identified, with PROs available in 96 hips. The mean age of patients with EL was 30.5 years, and women made up 87% of the cohort. Of the 129 hips with an EL, an isolated diagnosis of an EL was present in 11.6% of hips. Deficient acetabular coverage (lateral center-edge angle <25°) was seen in 40.6% of EL hips. No difference was seen in iHOT-12 scores between EL and control groups at 12- or 24-month follow-up (P = .18 and .94, respectively). Patients with EL reported a significant improvement of PROs at latest follow-up (P < .001 for iHOT-12 and Nonarthritic Hip Score). CONCLUSION: Surgical management of a native EL with restoration of the labral seal on the femoral head and correction of concomitant pathologies resulted in significant clinical improvement, with postoperative outcome scores comparable to those of patients without an EL. These findings provide evidence supporting surgical intervention for a native EL.

Insufficient Evidence for Anterior Cruciate Ligament Reconstruction Utilizing Suture Tape Augmentation: A Systematic Review of Clinical Outcomes at Minimum 1-Year Follow-up.

PURPOSE: To perform a systematic review of clinical studies to directly compare clinical outcomes of patients undergoing anterior cruciate ligament reconstruction (ACLR) with versus without suture tape (ST) augmentation. METHODS: A systematic review was performed by searching PubMed, the Cochrane Library, and Embase to identify comparative studies directly comparing outcomes of ACLR with versus without ST augmentation with a minimum follow-up of 12 months. The search terms used were anterior cruciate ligament suture tape. Patients were evaluated based on graft failure rates, return to sport (RTS), anteroposterior (AP) laxity, and patient-reported outcomes (PROs). RESULTS: Five studies (all Level III) met inclusion criteria, including a total of 246 patients undergoing ACLR with ST augmentation (SA group) and 282 patients undergoing ACLR without augmentation (control group). Patient age ranged from 14.9 to 29.7 years. The mean follow-up time ranged from 24.0 to 48.6 months. The mean body mass index ranged from 25.3 to 26.3 kg/m2 and the overall percentage of males ranged from 43.4% to 69.0%. Overall, the graft failure rate ranged from 1.0% to 25.0% in the SA group and 8.0% to 20.0% in the control group. Among the studies that reported RTS rates, the rate ranged from 69.2% to 88.9% in the SA group and 51.5% to 87.5% in the control group. Among all PROs, 2 studies found a significant difference in the Tegner score favoring the SA group. Otherwise, no significant differences were found between groups in terms of PROs. No significant differences in AP laxity were found between groups within any particular study. There was heterogeneity between studies regarding surgical techniques, postoperative rehabilitation protocols, and reported PROs. CONCLUSIONS: There is insufficient evidence to suggest that patients undergoing ACLR with ST augmentation may experience favorable clinical outcomes compared with ACLR alone. LEVEL OF EVIDENCE: Level III, systematic review of Level III studies.

Microfracture of Acetabular Chondral Lesions Is Not Superior to Other Cartilage Repair Techniques in Patients With Femoroacetabular Impingement Syndrome: A Systematic Review.

PURPOSE: To perform a systematic review to compare clinical outcomes of hip arthroscopy patients undergoing microfracture (MFx) versus other cartilage repair procedures for chondral lesions of the acetabulum. METHODS: A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines by searching PubMed, the Cochrane Library, and Embase to identify comparative studies that directly compared outcomes between MFx and other cartilage repair procedures for full-thickness chondral lesions of the acetabulum identified during hip arthroscopy. The search phrase used was: hip AND arthroscopy AND microfracture. Patients were evaluated based on reoperation rates and patient-reported outcomes. RESULTS: Six studies (all Level III evidence) met inclusion criteria, including a total of 202 patients undergoing microfracture (group A) and 327 patients undergoing another cartilage repair procedure (group B). Mean patient age ranged from 35.0 to 45.0 years. Mean follow-up time ranged from 12.0 to 72.0 months. Significantly better patient-reported outcomes (PROs) were found in patients undergoing treatment with bone marrow aspirate concentrate, microfragmented adipose tissue concentrate, autologous matrix-induced chondrogenesis, and a combination of autologous matrix-induced chondrogenesis and bone marrow aspirate concentrate compared with MFx. No studies found significantly better postoperative PROs in group A. The reoperation rate ranged from 0% to 34.6% in group A and 0% to 15.9% in group B. Three of 5 studies reporting on reoperation rate found a significantly greater reoperation rate in group A, with no difference in the other 2 studies. CONCLUSIONS: The literature on MFx of acetabular chondral lesions is limited and heterogeneous. Based on the available data, MFx alone results in a greater or equivalent reoperation rate and inferior or equivalent PROs compared with other cartilage repair procedures for acetabular chondral lesions in patients with femoroacetabular impingement syndrome. LEVEL OF EVIDENCE: Level III, systematic review of level III studies.

Rotator Cuff Repair With Patch Augmentation Is Associated With Lower Retear Rates for Large Tears: A Systematic Review of Randomized Controlled Trials.

PURPOSE: To perform a systematic review of randomized controlled trials comparing clinical outcomes of rotator cuff repair with and without patch augmentation. METHODS: A systematic review was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines by searching PubMed, the Cochrane Library, and Embase to identify randomized controlled trials that directly compared outcomes between rotator cuff repair (RCR) with versus without patch augmentation. Patients were evaluated based on retear rate, histological outcomes, radiological outcomes, and patient-reported outcomes (Constant score; American Shoulder and Elbow Surgeons [ASES] score; University of California-Los Angeles shoulder scale; Simple Shoulder Test; EuroQol-visual analog scale; Disabilities of the Arm, Shoulder and Hand score; and PENN shoulder score questionnaire). RESULTS: Six studies (1 level I, 5 level II) met inclusion criteria, including 188 patients undergoing RCR alone (Control) and 193 patients undergoing RCR with patch augmentation (Patch). Patient age ranged from 56.0 to 68.0 years. The mean follow-up time ranged from 14.0 to 68.4 months. The average body mass index ranged from 24.4 to 29.4, and the overall percentage of males ranged from 32.5% to 82.3%. Three studies found significantly decreased retear rates with patch augmentation. The retear rate ranged from 34.0% to 65.4% in the Control group and 9.1% to 52.9% in the Patch group. One study found a significant difference for the Constant score favoring the Patch group. Two studies found a significant difference for the ASES score favoring the Patch group. One study found significantly better results with patch augmentation in terms of repaired tendon thickness and footprint coverage, based on magnetic resonance imaging. CONCLUSIONS: Patch augmentation of rotator cuff repairs may be associated with lower retear rates for large tears. There is limited evidence to suggest that patch augmentation is associated with improved patient-reported outcomes. LEVEL OF EVIDENCE: Level II, systematic review of level I and II studies.

During Postless Hip Arthroscopy, Male Patients, High Body Mass Index, Low Beighton Scores, and Limited Range of Motion Require High Traction Force.

PURPOSE: To determine the effects of demographic and anatomic factors on traction force required during postless hip arthroscopy. METHODS: A prospectively collected database was retrospectively analyzed on patients undergoing hip arthroscopy by the senior author, including patient sex, age, body mass index (BMI), Beighton Hypermobility Score, hip range of motion in clinic and under anesthesia, hip dysplasia, acetabular version, and femoral version. All patients underwent postless hip arthroscopy under general anesthesia. At the initiation of hip arthroscopy, the traction force required to distract the hip joint was measured before and following interportal capsulotomy. Multiple regression analysis was performed to determine the effects of demographic and anatomic factors on measured distraction force. RESULTS: In total, 352 hips (114 male, 238 female) were included with a mean age of 32.6 years and a mean BMI of 24.1 kg/m2. Mean initial traction force was 109 lbs and decreased to 94.3 lbs following capsulotomy (P < .0001). The starting traction force was significantly greater in male patients (P < .001), patients with a lack of hypermobility (Beighton Hypermobility Score of 0-2) (P = .026), and in patients with lower abduction (P < .001), lower internal rotation (P = .002), and lower external rotation (P = .012) on multiple regression analysis. When performing a subanalysis divided by sex, male patients with elevated BMI required significantly greater starting traction force (P = .014). Lateral center edge angle, sourcil angle, and the presence of hip dysplasia did not demonstrate a significant correlation with traction force. CONCLUSIONS: Male patients, patients with reduced preoperative hip range of motion, patients with a lack of joint hypermobility, and male patients with an elevated BMI require greater initial traction force during postless hip arthroscopy. LEVEL OF EVIDENCE: Level IV, retrospective case series.

Screw Fixation for the Latarjet Procedure May Reduce Risk of Recurrent Instability but Increases Reoperation Rate Compared to Suture-Button Fixation: A Systematic Review.

PURPOSE: To perform a systematic review to compare clinical outcomes, complications, and reoperation rates of patients undergoing the Latarjet procedure with screw vs suture-button fixation. METHODS: A systematic review was performed by searching PubMed, the Cochrane Library, and Embase to identify clinical studies directly comparing screw vs suture-button fixation for the Latarjet procedure. The search terms used were shoulder screw suture button. Patients were evaluated based on reoperation rate, complication rate, recurrent instability, radiologic outcomes, and patient-reported outcomes. Graft and screw position were assessed via computed tomography. RESULTS: Seven studies (1 Level II, 6 Level III) met inclusion criteria, with 845 patients undergoing the Latarjet procedure with screw fixation (screw group) and 279 patients with suture-button fixation (suture-button group). Mean patient age ranged from 21.2 to 29.6 years. Mean follow-up time ranged from 6.0 to 40.8 months. The recurrent instability rate ranged from 0% to 2.5% in the screw group and 0% to 8.3% in the suture-button group. The reoperation rate ranged from 0% to 7.7% in the screw group compared to 0% to 1.9% in the suture-button group. One study reported significantly lower visual analog scale pain scores in the suture-button group compared with the screw group (1.5 vs 1.2, P = .003). No other studies reported significant differences in any patient-reported outcomes. There was no significant difference in horizontal or vertical graft position, graft union rate, or complication rate between groups in any study. CONCLUSIONS: The Latarjet procedure with screw fixation may result in a lower risk of recurrent instability compared to suture-button fixation, although screw fixation may also have a higher reoperation rate due to hardware-related complications. LEVEL OF EVIDENCE: Level III, systematic review of Level II to III studies.

Association of Grit With Postoperative Knee Outcomes and Physical Function After ACL Reconstruction in Adolescent Athletes.

BACKGROUND: Grit is the disposition to strive for long-term goals despite setbacks and challenges. Given the lengthy, arduous process of rehabilitation after anterior cruciate ligament reconstruction (ACLR), an athlete's grit may predict postoperative outcomes across time. PURPOSE/HYPOTHESIS: The primary aim of the study was to evaluate the relationships between baseline (preoperative) grit and postoperative knee outcomes across the year after ACLR among adolescents. We hypothesized that athletes with more grit would achieve better postoperative outcomes over time than less gritty athletes. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: All participants completed the Short Grit Scale, the Pediatric International Knee Documentation Committee (Pedi-IKDC) Scale, the Lysholm Knee Scoring Scale, the Patient-Reported Outcomes Measurement Information System (PROMIS) pediatric scale for pain interference and mobility, the Hospital for Special Surgery Pediatric Functional Activity Brief Scale (HSS Pedi-FABS), and the Quality of Life in Neurological Disorders (NeuroQoL) Lower Extremity Function Short Form at a preoperative appointment and then again at approximately 3, 6, and 12 months after ACLR. We constructed linear mixed models to assess the relationships between baseline grit, time, age, sex, and postoperative outcome measures (statistical significance of α = .05). RESULTS: We included 137 participants (mean age 15.8 ± 2.74 years, 70% female) from a prospective registry of athletes undergoing ACLR by 1 surgeon at a single institution. There were no statistically significant changes in grit over time or differences in grit between age and sex. Higher baseline grit was significantly associated with greater postoperative HSS Pedi-FABS scores (ß = 3.72 ± 1.46; P = .01; 95% CI, 0.85-6.59) and NeuroQoL scores across time (ß = 3.37 ± 0.93; P < .001; 95% CI, 1.55-5.20). There were no significant associations between baseline grit and Pedi-IKDC, Lysholm, and PROMIS pain interference or mobility scores. CONCLUSION: Athletes with higher baseline grit reported superior postoperative physical function and activity level over the course of 1 year after ACLR compared with less gritty athletes. Grit may be a useful measure in predicting success in regaining physical function across time after ACLR in adolescent athletes.

Propensity scores as a novel method to guide sample allocation and minimize batch effects during the design of high throughput experiments.

BACKGROUND: We developed a novel approach to minimize batch effects when assigning samples to batches. Our algorithm selects a batch allocation, among all possible ways of assigning samples to batches, that minimizes differences in average propensity score between batches. This strategy was compared to randomization and stratified randomization in a case-control study (30 per group) with a covariate (case vs control, represented as ß1, set to be null) and two biologically relevant confounding variables (age, represented as ß2, and hemoglobin A1c (HbA1c), represented as ß3). Gene expression values were obtained from a publicly available dataset of expression data obtained from pancreas islet cells. Batch effects were simulated as twice the median biological variation across the gene expression dataset and were added to the publicly available dataset to simulate a batch effect condition. Bias was calculated as the absolute difference between observed betas under the batch allocation strategies and the true beta (no batch effects). Bias was also evaluated after adjustment for batch effects using ComBat as well as a linear regression model. In order to understand performance of our optimal allocation strategy under the alternative hypothesis, we also evaluated bias at a single gene associated with both age and HbA1c levels in the 'true' dataset (CAPN13 gene). RESULTS: Pre-batch correction, under the null hypothesis (ß1), maximum absolute bias and root mean square (RMS) of maximum absolute bias, were minimized using the optimal allocation strategy. Under the alternative hypothesis (ß2 and ß3 for the CAPN13 gene), maximum absolute bias and RMS of maximum absolute bias were also consistently lower using the optimal allocation strategy. ComBat and the regression batch adjustment methods performed well as the bias estimates moved towards the true values in all conditions under both the null and alternative hypotheses. Although the differences between methods were less pronounced following batch correction, estimates of bias (average and RMS) were consistently lower using the optimal allocation strategy under both the null and alternative hypotheses. CONCLUSIONS: Our algorithm provides an extremely flexible and effective method for assigning samples to batches by exploiting knowledge of covariates prior to sample allocation.

Patients With Knee Osteoarthritis Who Receive Platelet-Rich Plasma or Bone Marrow Aspirate Concentrate Injections Have Better Outcomes Than Patients Who Receive Hyaluronic Acid: Systematic Review and Meta-analysis.

PURPOSE: To systematically review the literature to compare the efficacy and safety of platelet-rich plasma (PRP), bone marrow aspirate concentrate (BMAC), and hyaluronic acid (HA) injections for the treatment of knee osteoarthritis (OA). METHODS: A systematic review was performed by searching PubMed, the Cochrane Library, and Embase to identify Level I studies that compared the clinical efficacy of at least 2 of the following 3 injection therapies: PRP, BMAC, and HA for knee OA. The search phrase used was knee AND osteoarthritis AND randomized AND ("platelet rich plasma" OR "bone marrow aspirate" OR "hyaluronic acid"). Patients were primarily assessed based on patient-reported outcome scores (PROs) including the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), visual analog scale (VAS) for pain, and Subjective International Knee Documentation Committee (IKDC) score. RESULTS: Twenty-seven studies (all Level I) met inclusion criteria, including 1,042 patients undergoing intra-articular injection(s) with PRP (mean age 57.7 years, mean follow-up 13.5 months), 226 patients with BMAC (mean age 57.0 years, mean follow-up 17.5 months), and 1,128 patients with HA (mean age 59.0 years, mean follow-up 14.4 months). Nonnetwork meta-analyses demonstrated significantly better postinjection WOMAC (P < .001), VAS (P < .01), and Subjective IKDC scores (P < .001) in patients who received PRP compared with patients who received HA. Similarly, network meta-analyses demonstrated significantly better postinjection WOMAC (P < .001), VAS (P = .03), and Subjective IKDC (P < .001) scores in patients who received BMAC compared with patients who received HA. There were no significant differences in postinjection outcome scores when comparing PRP with BMAC. CONCLUSIONS: Patients undergoing treatment for knee OA with PRP or BMAC can be expected to experience improved clinical outcomes when compared with patients who receive HA. LEVEL OF EVIDENCE: Level I, meta-analysis of Level I studies.

Effects of a 14-Day Hydration Intervention on Individuals with Habitually Low Fluid Intake.

BACKGROUND: Debate continues over whether or not individuals with low total water intake (TWI) are in a chronic fluid deficit (i.e., low total body water) [1]. When women with habitually low TWI (1.6 ± 0.5 L/day) increased their fluid intake (3.5 ± 0.1 L/day) for 4 days 24-h urine osmolality decreased, but there was no change in body weight, a proxy for total body water (TBW) [2]. In a small (n = 5) study of adult men, there were no observable changes in TBW, as measured by bioelectrical impedance, after increasing TWI for 4 weeks [3]. However, body weight increased and salivary osmolality decreased indicating that the study may have been underpowered to detect changes in TBW. Further, no studies to date have measured changes in blood volume (BV) when TWI is increased. OBJECTIVES: Therefore, the purpose of this study was to identify individuals with habitually low fluid intake and determine if increasing TWI, for 14 days, resulted in changes in TBW or BV. METHODS: In order to identify individuals with low TWI, 889 healthy adults were screened. Participants with a self-reported TWI less than 1.8 L/day (men) or 1.2 L/day (women), and a 24-h urine osmolality greater than 800 mOsm were included in the intervention phase of the study. For the intervention phase, 15 participants were assigned to the experimental group and 8 participants were assigned to the control group. The intervention period lasted for 14 days and consisted of 2 visits to our laboratory: one before the intervention (baseline) and 14 days into the intervention (14-day follow-up). At these visits, BV was measured using a CO-rebreathe procedure and deuterium oxide (D2O) was administered to measure TBW. Urine samples were collected immediately prior, and 3-8 h after the D2O dose to allow for equilibration. Prior to each visit, participants collected 24-h urine to measure 24-h hydration status. After the baseline visit, the experimental group increased their TWI to 3.7 L for males and 2.7 L for females in order to meet the current Institute of Medicine recommendations for TWI. RESULTS: Twenty-four-hour urine osmolality decreased (-438.7 ± 362.1 mOsm; p < 0.001) and urine volume increased (1,526 ± 869 mL; p < 0.001) in the experimental group from baseline, while there were no differences in osmolality (-74.7 ± 572 mOsm; p = 0.45), or urine volume (-32 ± 1,376 mL; p = 0.89) in the control group. However, there were no changes in BV (Fig. 1a) or changes in TBW (Fig. 1b) in either group. CONCLUSIONS: Increasing fluid intake in individuals with habitually low TWI increases 24-h urine volume and decreases urine osmolality but does not result in changes in TBW or BV. These findings are in agreement with previous work indicating that TWI interventions lasting 3 days [2] to 4 weeks [3] do not result in changes in TBW. Current evidence would suggest that the benefits of increasing TWI are not related changes in TBW.