Pickleball Primer: An Overview of Common Injuries, Treatment, and Optimization Strategies in Pickleball Athlete.

Pickleball is one of the fastest growing sports in the United States with millions of players nationwide. It is a relatively appealing sport because of its ease of access, low impact, and highly social atmosphere, allowing players of all ages to participate. As the number of players continues its dramatic increase, player injuries are certain to increase in turn. There is little to no orthopaedic research on pickleball-related injuries and a paucity of data regarding treatment and prevention strategies. This summary was designed to familiarize orthopaedic surgeons with the basics of the sport and highlight potential pickleball-related injuries they may encounter in practice.

Similar incidence of postoperative sciatic nerve palsy in direct anterior and posterior approach total hip arthroplasty.

BACKGROUND: Sciatic nerve palsy is a rare but devastating complication following total hip arthroplasty (THA). While the use of the direct anterior approach is increasing, limited data exist regarding sciatic nerve palsy and surgical approach. The purpose of this study was to determine the factors and outcomes associated with sciatic nerve palsy (SNP) after THA. METHODS: A retrospective analysis was performed at a single institution of 7 SNP that occurred in 4045 THA via direct anterior approach and 10 SNP in 8854 THA via posterior approach, being operated between 01 January 2017 and 12 December 2021. SNP patients were matched 1:5 to patients without SNP. Medical records were reviewed for demographics including age, gender, body mass index (BMI), comorbidities, and preoperative indication. Additional workup of SNP patients including advanced imaging and reoperation were documented. Recovery grades were assigned to all SNP patients at most recent clinical follow-up. RESULTS: 5 of the SNP were complete and 12 partial. They occurred as frequently with the direct anterior (0.17%) and posterior approach (0.11%, p = 0.5). The presence of femur cables and reoperations were associated with SNP (p = 0.04 and p = 0.002, respecitvely). Age, gender, BMI, comorbidities, and surgical indication had no effect on SNP. 4 of the 17 affected patients had almost complete recovery at latest follow-up. CONCLUSIONS: The incidence of SNP was similar in direct anterior and posterior approach. Surgeons should counsel patients regarding the risks of SNP regardless of the used approach.

Binding Affinity, Selectivity, and Pharmacokinetics of the Oxytocin Receptor Antagonist L-368,899 in the Coyote (Canis latrans).

L-368,899 is a selective small-molecule oxytocin receptor (OXTR) antagonist originally developed in the 1990s to prevent preterm labor. Although its utility for that purpose was limited, L-368,899 is now one of the most commonly used drugs in animal research for the selective blockade of neural OXTR after peripheral delivery. A growing number of rodent and primate studies have used L-368,899 to evaluate whether certain behaviors are oxytocin dependent. These studies have improved our understanding of oxytocin's function in the brains of rodents and monkeys, but very little work has been done in other mammals, and only a single paper in macaques has provided any evidence that L-368,899 can be detected in the CNS after peripheral delivery. The current study sought to extend those findings in a novel species: coyotes ( Canis latrans ). Coyotes are ubiquitous North American canids that form long-term monogamous pair-bonds. Although monogamy is rare in rodents and primates, all wild canid species studied to date exhibit social monogamy. Coyotes are therefore an excellent model organism for the study of oxytocin and social bonds. Our goal was to determine whether L-368,899 is a viable candidate for future use in behavioral studies in coyotes. We used captive coyotes at the USDA National Wildlife Research Center's Predator Research Facility to evaluate the pharmacokinetics of L-368,899 in blood and CSF during a 90-min time course after intramuscular injection. We then characterized the binding affinity and selectivity of L-368,899 to coyote OXTR and the structurally similar vasopressin 1a receptor. We found that L-368,899 peaked in CSF at 15 to 30 min after intramuscular injection and slowly accumulated in blood. L-368,899 was 40 times more selective for OXTR than vasopressin 1a receptors and bound to the coyote OXTR with an affinity of 12 nM. These features of L-368,899 support its utility in future studies to probe the oxytocin system of coyotes.

Disparities in Demographics in Hip Arthroplasty Between U.S. Active Duty Military and the ACS-NSQIP Clinical Registry.

INTRODUCTION: Patient demographics, such as sex and age, are known risk factors for undergoing revision following primary total hip arthroplasty (THA). The military population is unique because of the increased rates of primary and secondary osteoarthritis of the hip. Treatment options are limited for returning patients to their line of duty; however, THA has been shown to be an effective option. The primary purpose of this study was to evaluate and contrast the demographic differences of patients undergoing primary THA between the U.S. active duty military population and the general population. The secondary goal was to identify the proportion of primary THA performed at the MTF within the military health system (MHS). METHODS: This was an exempt study determined by the local institutional review board. A retrospective analysis of the MHS Data Repository (MDR) and the National Surgical Quality Improvement Program (NSQIP) was performed. The databases were used to identify the patients who underwent THA from January 1, 2015 to December 31, 2020. The MDR was used to identify demographics such as sex, age, setting of surgery, geographic location, previous military deployments, history of deployment-related injuries, branch of service, and rank. The NSQIP database was queried for sex and age. The median age of the population was compared using the Mann-Whitney U test and gender was compared using the Chi-square test. RESULTS: The MDR was used to evaluate 2,734 patients, whereas the NSQIP database was used to evaluate 223,832 patients. In the military population, patients who underwent THA were 87.7% male with an average age of 45 years, whereas in the general population as measured via the NSQIP database, 45.2% patients were male with an average age of 66.0 years. Comparing the two groups, we demonstrated that the military patients were significantly more likely to be younger (P < .001) and males (P < .001). Only 29.6% of primary THAs were performed within the MTF. CONCLUSIONS: Patients in the MHS are undergoing THA at a younger age and are more likely to be male compared to the general population. A significant portion of primary THAs in the MHS are also being performed at civilian institutions. These demographics may result in increased risk of revision; however, long-term studies are warranted to evaluate survivorship in this unique population.

Detection of Traumatic Ankle Arthrotomies: Computed Tomography Scan Versus Saline Load Test.

OBJECTIVE: Periarticular wounds present a common diagnostic dilemma for emergency providers and orthopedic surgeons because traumatic arthrotomies (TA) often necessitate different management from superficial soft tissue wounds. Historically, TA have been diagnosed with the saline load test (SLT). Computed tomography (CT) scan has been studied as an alternative to SLT in diagnosing TA in several joints, but there are limited data specifically pertaining to the ankle. This study aimed to compare the ability of a CT scan to identify an ankle TA versus a traditional SLT. The hypothesis was that there would be no significant difference between a CT scan and SLT in diagnosing ankle TA in a cadaveric model. METHODS: This cadaveric study used 10 thawed fresh-frozen cadaveric ankles. A baseline CT scan was performed to ensure no intra-articular air existed before simulated TA. After the baseline CT, a 1 cm TA was created in the anterolateral arthroscopy portal site location. The ankles then underwent a postarthrotomy CT scan to evaluate for the presence of intra-articular air. After the CT scan, a 30 mL SLT was performed using the anteromedial portal site location. RESULTS: After arthrotomy, intra-articular air was visualized in 7 of 10 cadavers in the postarthrotomy CT scan. All the ankles had fluid extravasation during the SLT with <10 mL of saline. The sensitivity of the SLT for TA was 100% versus 70% for the CT scan. CONCLUSIONS: The SLT was more sensitive in diagnosing 1-cm ankle TA than a CT scan in a cadaveric model.

Correlation of Patient-Reported Preoperative Narcotic Use and Postoperative Requirements in Total Joint Arthroplasty.

Preoperative narcotic use is associated with diminished outcomes and increased complications in patients undergoing primary total joint arthroplasty (TJA). The goal of this study was to compare self-reported and state database identified preoperative narcotic use and correlate it with perioperative narcotic requirements in patients undergoing primary arthroplasty. A total of 788 patients undergoing unilateral TJA from a single institution were examined using self-reported preoperative narcotic use questionnaires and were verified using the Massachusetts Prescriber Awareness Tool (MassPAT). Demographic data, perioperative morphine milligram equivalents, and postdischarge refills were recorded and analyzed. Of the total population, 16.4% of patients undergoing TJA had verified MassPAT narcotics prescriptions preoperatively. Of these patients, 55% accurately reported use to their surgeon. Patients with verified MassPAT narcotic prescriptions required more morphine milligram equivalents than patients without MassPAT prescriptions, regardless of their preoperative self-report at all time points in the study. Patients who accurately reported use required more narcotics than those who did not. Patients with MassPAT prescriptions required more postdischarge refills than patients without MassPAT prescriptions. These data suggest that state-run narcotics databases may be more useful than self-reports for identifying which patients may require more opioids both immediately postoperatively and after hospital discharge. [Orthopedics. 2024;47(1):34-39.].

A Lack of Generalizability-Total Knee Demographics in the Active Duty Population.

INTRODUCTION: Age and sex are known demographic risk factors for requiring revision surgery following primary total knee arthroplasty (TKA). Military service members are a unique population with barriers to long-term follow up after surgery. This study aims to compare demographic data between active duty military personnel and a nationwide sample to identify differences that may impact clinical and economic outcomes. METHODS: A retrospective observational analysis was performed using the Military Health System Data Repository (MDR) and the National Surgical Quality Improvement Program (NSQIP). Databases were queried for patients undergoing primary TKA between January 1, 2015 and December 31, 2020. The MDR was queried for demographic data including age, sex, duty status, facility type, geographic region, history of prior military deployment, history of deployment-related health condition, branch of military service, and military rank. National Surgical Quality Improvement Program was queried for age and sex. Median age between populations was compared with the Mann-Whitney U test, and gender was compared with a chi-squared test. RESULTS: During the study period, 2,094 primary TKA patients were identified from the MDR, and 357,865 TKA patients were identified from the NSQIP database. Military TKA patients were 79.4% male with a median age of 49.0, and NSQIP TKA patients were 38.9% were male, with a median age of 67. Military TKA patients were significantly more likely to be male (P < .001) and younger (P < .001). CONCLUSION: Patients undergoing TKA in the military are younger and more likely to be male compared to national trends. Current evidence suggests these factors may place them at a significant revision risk in the future. The application of quality metrics based on nationwide demographics may not be applicable to military members within the Military Health System.

The Cost of Stiffness After Total Knee Arthroplasty.

BACKGROUND: Stiffness after primary total knee arthroplasty (TKA) is debilitating and poorly understood. A heterogenous approach to the treatment is often utilized, including both nonoperative and operative treatment modalities. The purpose of this study was to examine the prevalence of treatments used between stiff and non-stiff TKA groups and their financial impact. METHODS: An observational cohort study was conducted using a large database. A total of 12,942 patients who underwent unilateral primary TKA from January 1, 2017, to December 31, 2017, were included. Stiffness after TKA was defined as manipulation under anesthesia and a diagnosis code of stiffness or ankylosis, and subsequent diagnosis and procedure codes were used to identify the prevalence and financial impact of multiple common treatment options. RESULTS: The prevalence of stiffness after TKA was 6.1%. Stiff patients were more likely to undergo physical therapy, medication, bracing, alternative treatment, clinic visits, and reoperation. Revision surgery was the most common reoperation in the stiff TKA group (7.6%). The incidence of both arthroscopy and revision surgery were higher in the stiff TKA population. Dual component revisions were costlier for patients who had stiff TKAs ($65,771 versus $48,287; P < .05). On average, patients who had stiffness after TKA endured costs from 1.5 to 7.5 times higher than the cost of their non-stiff counterparts during the 2 years following index TKA. CONCLUSION: Patients who have stiffness after primary TKA face significantly higher treatment costs for both operative and nonoperative treatments than patients who do not have stiffness.

A history of shoulder instability is more common in young patients undergoing total shoulder arthroplasty.

BACKGROUND: Previous studies have shown an association between shoulder instability and the development of glenohumeral arthritis leading to total shoulder arthroplasty (TSA). The primary goal of this study was to evaluate if a history of shoulder instability was more common in patients aged <50 years undergoing TSA. The secondary objective was to determine if a history of prior surgical stabilization is more common in patients aged <50 years undergoing TSA. METHODS: Using the military health system data repository (MDR) and the Military Analysis and Reporting Tool (M2), we identified 489 patients undergoing primary TSA from October 1, 2013, to May 1, 2020, within the Military Health System (MHS). Patients aged <50 years were matched 1:2 with patients aged ≥50 years based on sex, race, and military status, with the final study population comprising 240 patients who underwent primary TSA during the study period. Electronic medical records were examined, and factors showing univariate association (P < .2) were included in a binary logistic regression analysis to determine associations between demographic or clinical factors and TSA prior to age 50 years. RESULTS: The groups differed significantly in shoulder arthritis subtype, with the older group having significantly more primary osteoarthritis (78% vs. 51%, P < .001). The younger group had significantly more patients with a history of shoulder instability (48% vs. 12%, P < .001), prior ipsilateral shoulder surgery of any type (74% vs. 34%, P < .001), and prior ipsilateral shoulder stabilization surgery (31% vs. 5%, P < .001). In the resultant logistic regression model, a history of shoulder instability (OR 5.0, P < .001) and a history of any prior ipsilateral shoulder surgery (OR 3.5, P < .001) were associated with TSA prior to the age of 50 years. CONCLUSIONS: Shoulder instability is a risk factor for TSA before age 50 years. It is unclear how surgical stabilization influences the development of secondary glenohumeral arthritis in shoulder instability. Patients should be counseled that recurrent instability could lead to earlier TSA, regardless of whether surgical stabilization is performed.

Validation of a novel large animal intra-articular tibial plafond fracture model.

BACKGROUND: Large animal fracture models that allow for anatomic fracture fixation are currently lacking. It was hypothesized that a compressed air impaction system can generate a reproducible tibial plafond fracture and be adjustable to create fractures consistent with high and low energy fractures seen in humans. METHODS: Pilot testing of the impaction system was done by impacting polyurethane foam blocks at varying compressed air pressures. A guillotine impaction test was performed on the same foam blocks to create an energy conversion. A total of 12 porcine hindlimb hindlimbs were subjected to low-energy (42.2 J) and high-energy (73.9 J) impact to create tibial plafond fractures. FINDINGS: Guillotine impaction test demonstrated strong correlations between potential energy and foam block impaction depth (R2 = 0.99). Compressed air impaction system test strongly correlated with foam block impaction depth (R2 = 0.99). All six porcine hindlimbs in the low-energy group developed simple coronal split tibial plafond fractures. All six porcine hindlimbs in the high-energy group developed complex, multi-fragmentary tibial plafond fractures. INTERPRETATION: This porcine fracture model created tibial plafond fracture patterns with similar fracture morphology as human patients without violation of the soft tissue structures or adjacent joints. This model would allow for anatomic fixation, the study of post-traumatic osteoarthritis, or the delivery of locally targeted therapeutics to the ankle joint.

Articular fragment restoration is critical to mitigate post-traumatic osteoarthritis in a porcine pilon fracture model.

Objective: During articular fracture reconstruction, orthopedic surgeons are frequently faced with the dilemma of retaining small articular fragments versus discarding these fragments. The purpose of this study was to compare post-traumatic osteoarthritis (PTOA) development between tibial plafond fractures and plafond fractures with a missing articular fragment (MF) in a porcine model. Design: High-energy tibial plafond fractures in skeletally mature Yucatan mini pigs (n â€‹= â€‹12) were created. During surgery, a 3 â€‹× â€‹3 mm section of the articular surface was removed in six animals (MF group). Ankle synovial fluid was analyzed for IL-1ß, IL-1Ra, IL-6, IL-8, and IL-10 concentrations obtained at initial surgery and 12 weeks post-surgery. Plafond and talus sections were evaluated for subchondral bone porosity and stained with Sanderson's Rapid Bone Stain and blindly evaluated to determine the Osteoarthritis Research Society International (OARSI) grade and vascular invasion. Results: Fractured ankles had greater concentrations of IL-1ß, IL-1Ra, IL-6, IL-8, and IL-10 compared to control ankles. There was no difference in cytokine concentrations between fractured and fractured â€‹+ â€‹MF ankles. Fractured ankles had significantly greater bone porosity, vascular invasion, and OARSI grade as compared to the control group. In comparing tibial plafonds, the MF group had significantly more bone porosity, more vascular invasion, and a higher average OARSI grade than the anatomically reconstructed group. In comparing the talus, the MF group had higher average OARSI grade and similar bone porosity. Conclusions: Articular fractures with a MF had worse PTOA development as measured by bone porosity, vascular invasion, and OARSI grade than the anatomically reconstructed fractures.

Royal knifefish generate powerful suction feeding through large neurocranial elevation and high epaxial muscle power.

Suction feeding in ray-finned fishes involves powerful buccal cavity expansion to accelerate water and food into the mouth. Previous XROMM studies in largemouth bass (Micropterus salmoides), bluegill sunfish (Lepomis macrochirus) and channel catfish (Ictalurus punctatus) have shown that more than 90% of suction power in high performance strikes comes from the axial musculature. Thus, the shape of the axial muscles and skeleton may affect suction feeding mechanics. Royal knifefish (Chitala blanci) have an unusual postcranial morphology, with a ventrally flexed vertebral column and relatively large mass of epaxial muscle. Based on their body shape, we hypothesized that royal knifefish would generate high power strikes by utilizing large neurocranial elevation, vertebral column extension and epaxial shortening. As predicted, C. blanci generated high suction expansion power compared with the other three species studied to date (up to 160 W), which was achieved by increasing both the rate of volume change and the intraoral subambient pressure. The large epaxial muscle (25% of body mass) shortened at high velocities to produce large neurocranial elevation and vertebral extension (up to 41 deg, combined), as well as high muscle mass-specific power (up to 800 W kg-1). For the highest power strikes, axial muscles generated 95% of the power, and 64% of the axial muscle mass consisted of the epaxial muscles. The epaxial-dominated suction expansion of royal knifefish supports our hypothesis that postcranial morphology may be a strong predictor of suction feeding biomechanics.

The Avian Diet Database as a source of quantitative information on bird diets.

This data paper describes a compilation of 73,075 quantitative diet data records for 759 primarily North American bird species, providing standardized information not just on the diet itself, but on the context for that diet information including the year, season, location, and habitat type of each study. The methods used for collecting and cleaning these data are described, and we present tools for summarizing and visualizing diet information by bird species or prey.

Implementation and Evaluation of Gradient Strip Antimicrobial Susceptibility Testing in US Public Health Laboratories to Respond to Resistant Gonorrhea.

BACKGROUND: Gradient strip antimicrobial susceptibility testing using Etest is conducted by local public health jurisdictions participating in the Strengthening the US Response to Resistant Gonorrhea (SURRG) program to inform public health responses to resistant gonorrhea. Proficiency testing results across the participating laboratories were analyzed and a comparison of Etest with the agar dilution method was conducted. METHODS: Laboratories participating in SURRG performed Etest for azithromycin (AZM), cefixime (CFX), and ceftriaxone (CRO). Concurrence between minimum inhibitory concentrations (MICs) obtained with Etest versus the agar dilution method using corresponding isolates was defined as ±1 double dilution. Specific levels of reduced susceptibility were termed "alerts" and included isolates with the following MICs: ≥2.0 µg/mL (AZM), ≥0.25 µg/mL (CFX), and ≥0.125 µg/mL (CRO). Categorical (alert/nonalert) agreement was calculated for MICs determined using Etest and agar dilution methods. RESULTS: Strengthening the US Response to Resistant Gonorrhea laboratories had high proficiency testing scores (≥98%) and low levels of interlaboratory variations in MICs. The overall concurrence of MICs (essential agreement) determined using agar dilution, and Etest was 96% (CRO), 96% (CFX), and 95% (AZM). Depending on the antibiotic tested, between 27% and 66% of isolates with alert MICs determined by Etest also had alert MICs using the reference agar dilution methodology; however, most of these alert MICs were detected at threshold levels. CONCLUSIONS: This study demonstrates that MICs produced by SURRG laboratories using Etest have a high level of concurrence with agar dilution. Although confirmation of specific alert MICs varied, Etest facilities rapid detection and response to emerging resistant gonorrhea.

Use, Safety Assessment, and Implementation of Two Point-of-Care Tests for COVID-19 Testing.

OBJECTIVES: The Abbot ID NOW COVID-19 assay and Quidel Sofia 2 SARS Antigen FIA are point-of-care assays that offer rapid testing for severe acute respiratory syndrome coronavirus 2 viral RNA and nucleocapsid protein, respectively. Given the utility of these devices in the field, we investigated the feasibility and safety of using the ID NOW and Sofia assays in the public health response to the coronavirus disease 2019 pandemic and in future public health emergencies. METHODS: A combination of utilization and contamination testing in addition to a review of instrument workflows was conducted. RESULTS: Utilization testing demonstrated that both tests are intuitive, associated with high user test success (85%) in our study, and could be implemented by staff after minimal training. Contamination tests revealed potential biosafety concerns due to the open design of the ID NOW instrument and the transfer mechanisms with the Sofia. When comparing the workflow of the ID NOW and the Sofia, we found that the ID NOW was more user-friendly and that the transfer technology reduces the chance of contamination. CONCLUSIONS: The ID NOW, Sofia, and other emerging point-of-care tests should be used only after careful consideration of testing workflow, biosafety risk mitigations, and appropriate staff training.

Estimating reef fish size distributions with a mini remotely operated vehicle-integrated stereo camera system.

We tested the efficacy of a stereo camera (SC) system adapted for use with a remotely operated vehicle (ROV) to estimate fish length distributions at reef sites in the northern Gulf of Mexico. A pool experiment was conducted to test the effect of distance (1, 2, 3 or 5 m), angle of incidence (AOI; 0° to 40° at 5° increments), and SC baseline distance (BD; BD1 = 406, BD2 = 610, and BD3 = 762 mm camera separation) on the accuracy and precision of fish model length (288, 552, or 890 mm fork length) estimates compared to a red laser scaler (RLS). A field experiment was then conducted at 20 reef sites with SCs positioned at BD1 to compare fish length distribution estimates between the SC and RLS systems under in situ conditions. In the pool experiment, mean percent errors were consistently within the a priori selected threshold of ±5% at AOIs ≤10° at all distances with all four systems. However, SCs produced accurate estimates at AOIs up to 30° at all distances tested; 2-3 m was optimal. During reef site surveys, SCs collected 10.4 times as many length estimates from 4.3 times as many species compared to the RLS. Study results demonstrate that, compared to laser scalers, ROV-based SC systems can substantially increase the number of available fish length estimates by producing accurate length estimates at a wider range of target orientations while also enabling measurements from a greater portion of the cameras' field of view.

Atypical Mutation in Neisseria gonorrhoeae 23S rRNA Associated with High-Level Azithromycin Resistance.

A2059G mutation in the 23S rRNA gene is the only reported mechanism conferring high-level azithromycin resistance (HL-AZMR) in Neisseria gonorrhoeae Through U.S. gonococcal antimicrobial resistance surveillance projects, we identified four HL-AZMR gonococcal isolates lacking this mutational genotype. Genetic analysis revealed an A2058G mutation of 23S rRNA alleles in all four isolates. In vitro selected gonococcal strains with homozygous A2058G recapitulated the HL-AZMR phenotype. Taken together, we postulate that the A2058G mutation confers HL-AZMR in N. gonorrhoeae.

Fishes can use axial muscles as anchors or motors for powerful suction feeding.

Some fishes rely on large regions of the dorsal (epaxial) and ventral (hypaxial) body muscles to power suction feeding. Epaxial and hypaxial muscles are known to act as motors, powering rapid mouth expansion by shortening to elevate the neurocranium and retract the pectoral girdle, respectively. However, some species, like catfishes, use little cranial elevation. Are these fishes instead using the epaxial muscles to forcefully anchor the head, and if so, are they limited to lower-power strikes? We used X-ray imaging to measure epaxial and hypaxial length dynamics (fluoromicrometry) and associated skeletal motions (XROMM) during 24 suction feeding strikes from three channel catfish (Ictalurus punctatus). We also estimated the power required for suction feeding from oral pressure and dynamic endocast volume measurements. Cranial elevation relative to the body was small (<5 deg) and the epaxial muscles did not shorten during peak expansion power. In contrast, the hypaxial muscles consistently shortened by 4-8% to rotate the pectoral girdle 6-11 deg relative to the body. Despite only the hypaxial muscles generating power, catfish strikes were similar in power to those of other species, such as largemouth bass (Micropterus salmoides), that use epaxial and hypaxial muscles to power mouth expansion. These results show that the epaxial muscles are not used as motors in catfish, but suggest they position and stabilize the cranium while the hypaxial muscles power mouth expansion ventrally. Thus, axial muscles can serve fundamentally different mechanical roles in generating and controlling cranial motion during suction feeding in fishes.

Pectoral fin kinematics and motor patterns are shaped by fin ray mechanosensation during steady swimming in Scarus quoyi.

For many fish species, rhythmic movement of the pectoral fins, or forelimbs, drives locomotion. In terrestrial vertebrates, normal limb-based rhythmic gaits require ongoing modulation with limb mechanosensors. Given the complexity of the fluid environment and dexterity of fish swimming through it, we hypothesize that mechanosensory modulation is also critical to normal fin-based swimming. Here, we examined the role of sensory feedback from the pectoral fin rays and membrane on the neuromuscular control and kinematics of pectoral fin-based locomotion. Pectoral fin kinematics and electromyograms of the six major fin muscles of the parrotfish, Scarus quoyi, a high-performance pectoral fin swimmer, were recorded during steady swimming before and after bilateral transection of the sensory nerves extending into the rays and surrounding membrane. Alternating activity of antagonistic muscles was observed and drove the fin in a figure-of-eight fin stroke trajectory before and after nerve transection. After bilateral transections, pectoral fin rhythmicity remained the same or increased. Differences in fin kinematics with the loss of sensory feedback also included fin kinematics with a significantly more inclined stroke plane angle, an increased angular velocity and fin beat frequency, and a transition to the body-caudal fin gait at lower speeds. After transection, muscles were active over a larger proportion of the fin stroke, with overlapping activation of antagonistic muscles rarely observed in the trials of intact fish. The increased overlap of antagonistic muscle activity might stiffen the fin system in order to enhance control and stability in the absence of sensory feedback from the fin rays. These results indicate that fin ray sensation is not necessary to generate the underlying rhythm of fin movement, but contributes to the specification of pectoral fin motor pattern and movement during rhythmic swimming.

A mobility-based classification of closed kinematic chains in biomechanics and implications for motor control.

Closed kinematic chains (CKCs), links connected to form one or more closed loops, are used as simple models of musculoskeletal systems (e.g. the four-bar linkage). Previous applications of CKCs have primarily focused on biomechanical systems with rigid links and permanently closed chains, which results in constant mobility (the total degrees of freedom of a system). However, systems with non-rigid elements (e.g. ligaments and muscles) and that alternate between open and closed chains (e.g. standing on one foot versus two) can also be treated as CKCs with changing mobility. Given that, in general, systems that have fewer degrees of freedom are easier to control, what implications might such dynamic changes in mobility have for motor control? Here, I propose a CKC classification to explain the different ways in which mobility of musculoskeletal systems can change dynamically during behavior. This classification is based on the mobility formula, taking into account the number of loops in the CKC and the nature of the constituent joint mobilities. I apply this mobility-based classification to five biomechanical systems: the human lower limbs, the operculum-lower jaw mechanism of fishes, the upper beak rotation mechanism of birds, antagonistic muscles at the human ankle joint and the human jaw processing a food item. I discuss the implications of this classification, including that mobility itself may be dynamically manipulated to simplify motor control. The principal aim of this Commentary is to provide a framework for quantifying mobility across diverse musculoskeletal systems to evaluate its potentially key role in motor control.