All-Suture Suspensory Button Has Similar Biomechanical Performance to Metal Suspensory Button for Onlay Subpectoral Biceps Tenodesis.

Purpose: To evaluate the maximal load at failure, cyclic displacement, and stiffness of onlay subpectoral biceps tenodesis (BT) with an intramedullary unicortical metal button (MB) versus a unicortical all-suture button (ASB). Methods: Eighteen matched paired human cadaveric proximal humeri were randomly allocated for subpectoral BT with either ASB or MB using a high-strength suture. Specimens were tested on a servohydraulic mechanical testing apparatus under cyclic load for 1,000 cycles and then loaded to failure. The clamp was then adjusted to isolate the suture-anchor point interface and loaded to failure. Maximal load to failure, displacement, and stiffness were compared. Results: There was no significant difference between groups in stiffness, displacement, or yield load. The maximal load to failure for the MB was greater than the ASB (347.6 ± 74.1N vs 266.5 ± 69.3N, P = .047). Eight specimens in each group failed by suture pull-through on the tendon. When the suture-anchor point interface was isolated, there was no significant difference in maximal load at failure (MB 586.5 ± 215.8N vs ASB 579.6 ± 255.9N, P = .957). Conclusions: This study demonstrates that the MB and ASB have similar biomechanical performance when used in subpectoral BT. Although the MB showed statistically significant greater maximal load to failure, there was no difference between the MB and ASB when the suture-tendon interface was eliminated. Suture pull-through was the most common mode of failure for both implants, underscoring the importance of the suture-tendon interface. Clinical Relevance: Fixation techniques for the treatment of long head of the biceps brachii tenodesis continue to evolve. The use of an all-suture suspensory button has advantages, but it is important to understand if this implant is a biomechanically suitable alternative to a metal suspensory button.

Differences in Outcomes between Patellar Dislocations Managed in Emergent versus Non-Emergent Care Settings.

Patellar dislocations occur at a much higher rate in military than civilian populations. Past population-level studies have shown that surgical management is as good as or superior to conservative care and may reduce future reoccurrences. Although in acute cases and in civilian clinics, patellar dislocations are usually managed first in an emergent care setting, previous work suggests this can lead to increased costs. This study compared differences in downstream care type and intensity of services based on whether initial care occurred in emergent or non-emergent care settings. In our sample of 1,523 Military Health System (MHS) beneficiaries with patellar dislocation and 2-year follow-up, we found non-significant differences in costs, intensity of services, and rates of surgical repair regardless of whether the patient was initially seen in an emergent versus non-emergent care setting. Although we found significant increases in the use of imaging, patellar dislocation-related medical visits, and frequency of closed treatment approaches in emergent care settings, these values were very small and likely not clinically significant. These findings, which included all the patellar dislocations reported across the entire MHS in a 24-month period, suggest that neither emergent nor non-emergent care settings are likely to influence the long-term care received by the individual.

Epidemiology of Meniscus Injuries in the Military Health System and Predictive Factors for Arthroscopic Surgery.

Meniscus injuries occur at a higher rate in the military than the general population. Appropriate management and rehabilitation of meniscus injuries is important for maintaining readiness. The purpose of this study was to describe the health burden of meniscus injuries in the Military Health System (MHS) to identify the surgical intervention rate for meniscus injuries, and to determine which injury characteristics and demographic variables were associated with the likelihood of surgery after injury. The U.S. Department of Defense Management Analysis and Reporting Tool, a database of health care encounters by military personnel and dependents, was queried for encounters associated with a meniscal injury diagnosis between January 1, 2010, and December 31, 2011. Meniscus injuries were categorized into (1) isolated medial, (2) isolated lateral, (3) combined medial and lateral, and (4) unspecified cohorts. Patients under 18 and over 51 years were excluded, as well as patients without records at least 1 year prior to diagnosis or 2 years after. Relevant surgical procedures were identified with the Current Procedural Terminology (CPT) codes for arthroscopic surgery of the knee, meniscus repair, meniscectomy, and anterior cruciate ligament (ACL) reconstruction. There were 2,969 meniscus injuries meeting inclusion criteria during the study period. There were 1,547 (52.1%) isolated medial meniscus injuries, 530 (17.9%) isolated lateral meniscus injuries, 452 (15.3%) involved both menisci, and 435 (14.7%) were unspecified. The mean age was 35.5 years (standard deviation [SD] = 9.3). An adjacent ligamentous injury occurred in 901 patients (30.3%). The treatment course led to arthroscopic surgery in 52.8% (n = 1,568) of all meniscus injuries. Eighty-five percent (n = 385) of combined medial and lateral tears, 54.9% of medial tears, and 51.6% of lateral tears underwent surgery. Partial meniscectomy was the most common procedure performed while 47.2% (n = 1,401) of tears were not treated surgically. Bilateral meniscus injuries had 4.57 greater odds of undergoing knee arthroscopy (95% confidence interval [CI]: 3.46, 6.04), 2.42 times odds of undergoing a meniscus repair, and 4.59 times odds for undergoing a meniscus debridement (95% CI: 3.62, 5.82). The closed nature of the MHS allows reliable capture of surgical rates for meniscus injuries within the military population. Meniscus injuries are common in the military and impose a significant burden on the MHS. Appropriate management and rehabilitation of this injury is important for maintaining readiness.

Patellar Stress Fracture After Suture Anchor Patellar Tendon Repair in an Active Duty Military Member: A Case Report.

CASE: A 31-year-old US service member presented with a patellar tendon tear that was repaired acutely with 2 biocomposite suture anchors. He presented more than 2 years later with a stress fracture through a suture anchor drill hole and was treated with partially threaded screw fixation. CONCLUSION: Stress fracture through a suture anchor drill hole after patellar tendon repair is a previously unreported complication. Surgeons should have a high index of suspicion and low threshold to obtain advanced imaging in cases of unexplained pain after patellar tendon repair.

Nonoperative Care Including Rehabilitation Should Be Considered and Clearly Defined Prior to Elective Orthopaedic Surgery to Maximize Optimal Outcomes.

Orthopaedic surgery has revolutionized the expectations for restoration of physical function after musculoskeletal injury and, along with physical therapy, has transformed the limits of recovery. Many orthopaedic procedures have a high success rate for improving quality of life and patient-reported outcomes, yet these procedures carry some level of risk, including postoperative complications. The stepped-care model of health care delivery, when applied to musculoskeletal care, recommends implementing less-intense and lower-risk treatments with known efficacy, such as promotion and education of self-management strategies and physical therapy, before more-invasive and higher-risk treatments such as surgery. This model of managing musculoskeletal disability can improve efficiency of care delivery and reduce medical costs at the health system level. Unfortunately, there is a documented lack of implementing an appropriate course of conservative care, especially physical therapy, prior to surgery across multiple orthopaedic disciplines including sports, spine, and trauma medicine and joint arthroplasty. Failure to respond to nonsurgical treatment has been suggested as a requisite component of the surgical appropriateness criteria, yet practical application can be elusive. Multiple barriers to adequate utilization of conservative treatment exist, including U.S. payment models that increase out-of-pocket expense for patients, negative patient perception of therapy, unreasonable patient expectations from therapy versus surgery, and communication barriers between patient, surgeon, and therapist. Surgeons should ensure that high-quality guideline-appropriate care is delivered early and adequately to their patients. Rehabilitation professionals have a responsibility to deliver high-value care, properly documenting the type and extent of treatment to improve surgical decision-making between surgeons and patients. Criteria to determine appropriateness for surgery should include a standardized and extensive assessment of failed therapies prior to certain elective surgeries. Improved collaboration between surgeons and rehabilitation professionals can result in improved outcomes for patients with musculoskeletal disorders. LEVEL OF EVIDENCE: V, expert opinion.

A High-Sensitivity International Knee Documentation Committee Survey Index From the PROMIS System: The Next-Generation Patient-Reported Outcome for a Knee Injury Population.

BACKGROUND: Patient-reported outcomes (PROs) measure progression and quality of care. While legacy PROs such as the International Knee Documentation Committee (IKDC) survey are well-validated, a lengthy PRO creates a time burden on patients, decreasing adherence. In recent years, PROs such as the Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function and Pain Interference surveys were developed as computer adaptive tests, reducing time to completion. Previous studies have examined correlation between legacy PROs and PROMIS; however, no studies have developed effective prediction models utilizing PROMIS to create an IKDC index. While the IKDC is the standard knee PRO, computer adaptive PROs offer numerous practical advantages. PURPOSE: To develop a nonlinear predictive model utilizing PROMIS Physical Function and Pain Interference to estimate IKDC survey scores and examine algorithm sensitivity and validity. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: The MOTION (Military Orthopaedics Tracking Injuries and Outcomes Network) database is a prospectively collected repository of PROs and intraoperative variables. Patients undergoing knee surgery completed the IKDC and PROMIS surveys at varying time points. Nonlinear multivariable predictive models using Gaussian and beta distributions were created to establish an IKDC index score, which was then validated using leave-one-out techniques and minimal clinically important difference analysis. RESULTS: A total of 1011 patients completed the IKDC and PROMIS Physical Function and Pain Interference, providing 1618 complete observations. The algorithms for the Gaussian and beta distribution were validated to predict the IKDC (Pearson = 0.84-0.86; R2 = 0.71-0.74; root mean square error = 9.3-10.0). CONCLUSION: The publicly available predictive models can approximate the IKDC score. The results can be used to compare PROMIS Physical Function and Pain Interference against historical IKDC scores by creating an IKDC index score. Serial use of the IKDC index allows for a lower minimal clinically important difference than the conventional IKDC. PROMIS can be substituted to reduce patient burden, increase completion rates, and produce orthopaedic-specific survey analogs.

Effect of Surfactant Concentration and Hydrophobicity on the Ordering of Water at a Silica Surface.

The performance of nonionic surfactants is mediated by the interfacial interactions at the solid-liquid interface. Here we applied sum frequency generation (SFG) vibrational spectroscopy to probe the molecular structure of the silica-nonionic surfactant solution interface in situ, supplemented by quartz crystal microbalance with dissipation monitoring (QCM-D) and molecular dynamics (MD) simulations. The combined studies elucidated the effects of nonionic surfactant solution concentration, surfactant composition, and rinsing on the silica-surfactant solution interfacial structure. The nonionic surfactants studied include ethylene-oxide (EO) and butylene oxide (BO) components with different ratios. It was found that the CH groups of the surfactants at the silica-surfactant solution interfaces are disordered, but the interfacial water molecules are ordered, generating strong SFG OH signals. Solutions with higher concentrations of surfactant lead to a slightly higher amount of adsorbed surfactant at the silica interface, resulting in more water molecules being ordered at the interface, or a higher ordering of water molecules at the interface, or both. MD simulation results indicated that the nonionic surface molecules preferentially adsorb onto silanol sites on silica. A surfactant with a higher EO/BO ratio leads to more water molecules being ordered and a higher degree of ordering of water molecules at the silica-surfactant solution interface, exhibiting stronger SFG OH signal, although less material is adsorbed according to the QCM-D data. A thin layer of surfactants remained on the silica surface after multiple water rinses. To the best of our knowledge, this is the first time the combined approaches of SFG, QCM-D and MD simulation techniques have been applied to study nonionic surfactants at the silica-solution interface, which enhances our understanding on the interfacial interactions between nonionic surfactants, water and silica. The knowledge obtained from this study can be helpful to design the optimal surfactant concentration and composition for future applications.

The Pericapsular Nerve Group Block for Perioperative Pain Management for Hip Arthroscopy.

Perioperative pain control for hip arthroscopy procedures represents a significant challenge for both surgeons and anesthetists. In light of the opioid crisis, greater emphasis has been placed on multimodal pain control techniques. There is considerable debate regarding regional nerve blockade for hip arthroscopy. Although regional anesthesia has a significant role in perioperative pain management strategies, many of the most common techniques present their own risks and limitations. In particular, the less desirable effects of postoperative weakness in the lower extremity and difficulty with ambulation are commonly produced with standard regional blockades. We present a technique for performing a targeted, sensory nerve block that can be done efficiently and safely in the immediate preoperative period. This block can potentially lower the intraoperative and postoperative opioid requirements without the risks of muscle blockade and falls from other regional anesthesia modalities.

Nonionic Surfactant Properties of Amphiphilic Hyperbranched Polyglycerols.

The surfactant properties of amphiphilic hyperbranched polyglycerols (HPGs) were investigated. The HPGs were prepared by ring-opening multibranching polymerization of glycidol using hydrophobic initiators of varying size and structure. The cloud points for all HPG surfactants were found to be >80 °C in deionized water with >1 wt % NaCl. The HPG surfactants with hydrophilic-lipophilic balance values between 16 and 18 were found to form stable octanol/water (o/w) emulsions within a 24 h period. Several surface properties, including critical micelle concentration (CMC), efficiency of surface tension reduction (pC20), effectiveness of surface tension reduction (γCMC), surface excess concentration at the CMC (Γmax), minimum area/molecule at the interface (Amin), and the CMC/C20 ratio of the HPG surfactants were measured in deionized water at 22.6 °C. In general, increasing HPG size was marked by an increase in minimum surface area per molecule (Amin) at the aqueous liquid/air interface. This increase in size also led to lower CMC and greater pC20 values of HPG surfactants prepared with Tergitol 15-S-7 initiator (HPG 5a-5d), a commercially available ethylene glycol oligomer with a branched hydrophobic tail.

Subpectoral Biceps Tenodesis of the Shoulder: Indications and Technique Options.

Subpectoral biceps tenodesis of the shoulder may be a useful tool that can address a wide range of disorders in the setting of pathology of the long head of the biceps tendon. Primary indications include (1) zone 2 or zone 3 tendon pathology and (2) failed previous proximal tendon tenodesis. Secondary indications include (1) an overhead athlete or thrower, (2) chronic tendinopathy, and (3) surgeon preference. A subpectoral technique allows tendon fixation directly posterior (deep) to the pectoralis tendon high in the bicipital fossa or in the mid fossa or fixation low in the fossa inferior to the pectoralis tendon (infrapectoral). Fixation technique options include an onlay suture anchor, onlay unicortical button, inlay bicortical button, or inlay interference screw. Potential surgical complications include humeral fracture, loss of fixation, tendon pullout or rupture, and neurovascular injury. Regardless of the specific location or technique used, subpectoral tenodesis is a valuable tool for the treatment of proximal biceps tendon pathology.

Functional Outcomes After Isolated and Combined Posterior Cruciate Ligament Reconstruction in a Military Population.

BACKGROUND: The rates of return to full activity, persistent disability, complications, and surgical revisions after operative management of posterior cruciate ligament (PCL) tears in a physically active population have not been reported. PURPOSE: To evaluate the clinical outcomes of active military patients with symptomatic PCL tears who underwent surgical reconstruction and compare outcomes between isolated PCL and multiligament injuries. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Individuals undergoing surgical reconstruction of the PCL (Current Procedural Terminology code 29889) were isolated from the Military Health System Management Analysis and Reporting Tool between fiscal years 2005 and 2010. Demographic variables and rates of postoperative complications, activity limitations, rates of revision surgery, physical disability ratings, and ultimate medical discharge were recorded from the electronic medical record and US Army Physical Disability Agency database. RESULTS: A total of 182 patients underwent 193 surgeries, including 118 isolated PCL reconstructions and 75 multiligament knee reconstructions, with an average follow-up of 19.5 months. There were 174 primary procedures and 19 revision reconstructions. The mean ± SD patient age was 28.4 ± 7.2 years, with males comprising 96.2% of patients. The overall surgical complication rate was 12.4%, with a significantly higher rate in multiligament knee reconstructions compared with isolated PCL reconstructions (18.7% vs 8.5%; P = .045). Overall, 35.1% of patients were discharged from military service due to disability. Rates of discharge were significantly higher in those undergoing surgery at lower volume institutions (those that performed <2 PCL reconstructions per year during the study period) than those at higher volume institutions (41.1% vs 26%; P = .040). The overall revision rate was 10.9%, with no significant difference between the isolated PCL and multiligament knee reconstructions. Of the 103 patients with primary isolated PCL reconstructions, 35% underwent medical discharge for persistent knee complaints, and 12.6% required revision PCL reconstruction. The overall failure rate for primary isolated PCL reconstructions, which includes both revision surgery and knee-related medical discharge from military service, was 42.7%. CONCLUSION: In a physically active, military population, nearly one-third of patients were unable to return to previous level of military function, and 12.6% required revision at short-term follow-up due to persistent instability. Perioperative complication rates were significantly higher among patients with multiligament knee reconstructions.

Effect of Ethylcellulose on the Rheology and Mechanical Heterogeneity of Asphaltene Films at the Oil-Water Interface.

Asphaltenes are surface-active molecules that exist naturally in crude oil. They adsorb at the water-oil interface and form viscoelastic interfacial films that stabilize emulsion droplets, making water-oil separation extremely challenging. There is, thus, a need for chemical demulsifiers to disrupt the interfacial asphaltene films, and, thereby, facilitate water-oil separation. Here, we examine ethylcellulose (EC) as a model demulsifier and measure its impact on the interfacial properties of asphaltene films using interfacial shear microrheology. When EC is mixed with an oil and asphaltene solution, it retards the interfacial stiffening that occurs between the oil phase in contact with a water phase. Moreover, EC introduces relatively weak regions within the film. When EC is introduced to a pre-existing asphaltene film, the stiffness of the films decreases abruptly and significantly. Direct visualization of interfacial dynamics further reveals that EC acts inhomogeneously, and that relatively soft regions in the initial film are seen to expand. This mechanism likely impacts emulsion destabilization and provides new insight to the process of demulsification.

The Conservative Treatment of Osteoarthritis of the Knee.

Osteoarthritis has one of the highest associations for all-cause mortality in the United States. Comorbidities are common in patients with end-stage disease. In most cases, it is critical to exhaust conservative modalities of care before resorting to surgical intervention. This article discusses common conservative approaches focusing on injectable treatments that can be employed prior to total knee replacement. [Orthopedics. 2018; 41(5):256-260.].

Single Versus Double-Bundle PCL Reconstruction: Scientific Rationale and Clinical Evidence.

PURPOSE OF REVIEW: The goal of this paper is to review the biomechanical and clinical rationale for single-bundle versus double-bundle posterior cruciate ligament (PCL) reconstruction. The primary question is whether there has been demonstrated any clear biomechanical or clinical superiority of a double-bundle reconstruction over a single-bundle reconstruction. RECENT FINDINGS: There is some recent evidence demonstrating biomechanical superiority of double-bundle versus single-bundle reconstruction; however, this is not definitive. Clinical superiority has not been clearly demonstrated as of yet. The primary question which served as the basis of this review remains unanswered. There is recent biomechanical data to suggest a potential benefit of double-bundle versus single-bundle reconstruction, but not all studies are in agreement. Furthermore, the possible biomechanical advantages have not yet been borne out in clinical studies. At this point, we cannot clearly recommend one technique versus another and the decision should be left to the treating surgeon.

Stress radiographs for evaluating acromioclavicular joint separations in an active-duty patient population: What have we learned?

INTRODUCTION: Acromioclavicular (AC) joint separation is a common entity in athletic patient populations. The surgical treatment of these injuries varies based upon extent of injury, with numerous imaging modalities recommended to differentiate injury severity and treatment options. The use of weighted stress radiographs is controversial in the diagnostic evaluation of AC separation with previous consensus recommending against their use. No study to date has investigated the clinical utilization of diagnostic studies in the evaluation of AC joint separations in a military surgeon population. METHODS: Thirty-eight shoulder or sports medicine sub-specialty certified orthopaedic surgeons on active service in the Army, Air Force, and Navy were surveyed on their evaluation and treatment protocols for AC joint injuries. Specifically analyzed were imaging choice including the use of weighted stress radiographs as well as treatment recommendations based upon Rockwood grade. Responses were recorded in addition to surgeon descriptive data. Responses were analyzed with descriptive statistics. RESULTS: Thirty-seven of the identified thirty eight surgeons responded to the survey, for a 97% response rate. Of the group, 70% of surgeons were within 10 years of completing fellowship with an estimated average of 15 AC joint separations treated annually. Plain radiographic examination was relied upon by 48% of surgeons for treatment of AC joint separation with 13% using weighted stress radiographs. Overall, 10% of surgeon stated that their treatment plan would vary based upon results from a weighted stress view. 51% of surgeons included magnetic resonance imaging in their diagnostic approach of these injuries. Treatment recommendation varied according to injury severity with 78% preferring nonoperative treatment for acute Grade III injuries with 86% waiting a minimum of 3 months before proceeding with operative treatment. For Grade V injuries, 81% of surgeon preferred operative treatment, with 59% incorporating a soft-tissue graft in their repair or reconstructive procedure. DISCUSSION: This study identified substantial practice variation amongst military surgeons treating a relatively homogenous population with AC joint separations, reflective of a lack of definitive evidence to guide diagnosis and treatment. Overall, nonoperative management is the preferred initial approach for Type III injuries and operative treatment is the preferred initial approach for Type V injuries. The diagnostic evaluation varied across the surgeon cohort, but 87% elected against the use of weighted stress radiographs for the evaluation of AC joint separations, with only 10% relying upon them to dictate their recommended treatment. Future research identifying optimal diagnosis and treatment of AC joint separations is needed.

Report of the 2017 Arthroscopy Association of North America Traveling Fellowship-A Fellowship Odyssey.

It was an honor to be selected to participate in the 2017 Arthroscopy Association of North America Advanced Arthroscopy Traveling Fellowship. This year's group included Michael J. Alaia, M.D., Assistant Professor and Associate Sports Medicine Fellowship Director at NYU Hospital for Joint Diseases; Nathan K. Endres, M.D., Associate Professor at the University of Vermont; LCDR Patrick W. Joyner, M.D., Assistant Professor at Naval Medical Center Portsmouth, and Head Physician East Coast Navy Seals; and LTC Christopher J. Tucker, M.D., Assistant Professor at the Uniformed Services University and Chief of Sports Service at Fort Belvoir Community Hospital. This year, we were honored to have a true pioneer in sports medicine and arthroscopic surgery, Dr. Jack M. Bert, Past President of Arthroscopy Association of North America and Adjunct Clinical Professor at the University of Minnesota, serve as our Godfather.

Comparison of the Suture Anchor and Transosseous Techniques for Patellar Tendon Repair: A Biomechanical Study.

BACKGROUND: Minimizing gap formation and maximizing the strength of patellar tendon repairs are 2 critical factors for successful healing of these injuries. PURPOSE/HYPOTHESIS: The purpose of this study was to compare transosseous and screw-in anchor repair techniques to determine if there is a difference in gap formation and load to failure of the 2 constructs. The research hypotheses were that the anchor construct would have significantly less gap formation and would also have significantly greater load-to-failure strength. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 24 porcine specimens were randomly assigned into transosseous and 4.75-mm polyetheretherketone (PEEK) screw-in anchor repair groups. The repairs were then completed using 2 No. 2 FiberWire sutures, and each specimen was cyclically loaded on a tensile test machine to 250 N for a total of 1000 cycles. Gap formation was measured at 1, 10, 250, 500, and 1000 cycles. Each specimen was loaded to failure after 1000 cycles. Independent t tests were conducted. RESULTS: Statistically significant gap formation and load-to-failure differences were found between the 2 repair techniques. The mean gap in the anchor group (2.16 ± 1.81 mm) was significantly less than that seen in the transosseous group (5.71 ± 1.58 mm) (P < .001). The mean load to failure of the anchor group (669.9 ± 91.8 N) was significantly higher than that of the transosseous group (582.8 ± 92.6 N) (P = .03). CONCLUSION: The results support the 2 study hypotheses. These findings suggest that the 4.75-mm PEEK screw-in anchor construct may be superior to the transosseous technique for minimizing gap formation and improving load-to-failure strength after surgical repair of the patellar tendon. CLINICAL RELEVANCE: The use of the suture anchor technique in patellar tendon repair may support early load-bearing rehabilitation.

Shoulder impingement in the United States military.

BACKGROUND: Little is known about the incidence and characteristics of primary, or external, shoulder impingement in an occupationally and physically active population. A longitudinal, prospective epidemiologic database was used to determine the incidence and risk factors for shoulder subacromial impingement in the United States (U.S.) military. Our hypothesis was that shoulder impingement is influenced by age, sex, race, military rank, and branch of service. METHODS: The Defense Medical Epidemiology Database was queried for all shoulder impingement injuries using International Classification of Disease, Ninth Addition, Clinical Modification code 726.10 within a 10-year period from 1999 through 2008. An overall injury incidence was calculated, and a multivariate analysis performed among demographic groups. RESULTS: In an at-risk population of 13,768,534 person-years, we identified 106,940 cases of shoulder impingement resulting in an incidence of 7.77/1000 person-years in the U.S. military. The incidence of shoulder impingement increased with age and was highest in the group aged ≥40 years (incidence rate ratio [IRR], 4.90; 95% confidence interval [CI], 4.61-5.21), was 9.5% higher among men (IRR, 1.10, 95% CI, 1.06-1.13), and compared with service members in the Navy, those in the Air Force, Army, and Marine Corps were associated with higher rates of shoulder impingement (IRR, 1.46 [95% CI, 1.42-1.50], 1.42 [95% CI, 1.39-1.46], and 1.31 [95% CI, 1.26-1.36], respectively). CONCLUSIONS: The incidence of shoulder impingement among U.S. military personnel is 7.77/1000 person-years. An age of ≥40 years was a significant independent risk factor for injury.

Surface shear inviscidity of soluble surfactants.

Foam and emulsion stability has long been believed to correlate with the surface shear viscosity of the surfactant used to stabilize them. Many subtleties arise in interpreting surface shear viscosity measurements, however, and correlations do not necessarily indicate causation. Using a sensitive technique designed to excite purely surface shear deformations, we make the most sensitive and precise measurements to date of the surface shear viscosity of a variety of soluble surfactants, focusing on SDS in particular. Our measurements reveal the surface shear viscosity of SDS to be below the sensitivity limit of our technique, giving an upper bound of order 0.01 µN·s/m. This conflicts directly with almost all previous studies, which reported values up to 10(3)-10(4) times higher. Multiple control and complementary measurements confirm this result, including direct visualization of monolayer deformation, for SDS and a wide variety of soluble polymeric, ionic, and nonionic surfactants of high- and low-foaming character. No soluble, small-molecule surfactant was found to have a measurable surface shear viscosity, which seriously undermines most support for any correlation between foam stability and surface shear rheology of soluble surfactants.