Machine Learning Methods for Predicting Patient-Level Emergency Department Workload.

BACKGROUND: Work Relative Value Units (wRVUs) are a component of many compensation models, and a proxy for the effort required to care for a patient. Accurate prediction of wRVUs generated per patient at triage could facilitate real-time load balancing between physicians and provide many practical operational and clinical benefits. OBJECTIVE: We examined whether deep-learning approaches could predict the wRVUs generated by a patient's visit using data commonly available at triage. METHODS: Adult patients presenting to an urban, academic emergency department from July 1, 2016-March 1, 2020 were included. Deidentified triage information included structured data (age, sex, vital signs, Emergency Severity Index score, language, race, standardized chief complaint) and unstructured data (free-text chief complaint) with wRVUs as outcome. Five models were examined: average wRVUs per chief complaint, linear regression, neural network and gradient-boosted tree on structured data, and neural network on unstructured textual data. Models were evaluated using mean absolute error. RESULTS: We analyzed 204,064 visits between July 1, 2016 and March 1, 2020. The median wRVUs were 3.80 (interquartile range 2.56-4.21), with significant effects of age, gender, and race. Models demonstrated lower error as complexity increased. Predictions using averages from chief complaints alone demonstrated a mean error of 2.17 predicted wRVUs per visit (95% confidence interval [CI] 2.07-2.27), the linear regression model: 1.00 wRVUs (95% CI 0.97-1.04), gradient-boosted tree: 0.85 wRVUs (95% CI 0.84-0.86), neural network with structured data: 0.86 wRVUs (95% CI 0.85-0.87), and neural network with unstructured data: 0.78 wRVUs (95% CI 0.76-0.80). CONCLUSIONS: Chief complaints are a poor predictor of the effort needed to evaluate a patient; however, deep-learning techniques show promise. These algorithms have the potential to provide many practical applications, including balancing workloads and compensation between emergency physicians, quantify crowding and mobilizing resources, and reducing bias in the triage process.

Association of resident characteristics with patterns of patient self-assignment.

OBJECTIVE: We hypothesized that resident characteristics impact patterns of patient self-assignment in the emergency department (ED). Our goal was to determine if male residents would be less likely than their female colleagues to see patients with sensitive (e.g. breast-related or gynecologic) chief complaints (CCs). We also investigated whether resident specialty was associated with preferentially choosing patients with more familiar chief complaints. METHODS: We performed a retrospective cross-sectional study at a tertiary academic medical center using data from all adult patients presenting to the ED between 2010 and 2019 with one of six CC categories (vaginal bleeding, breast-related concerns, male genitourinary [GU] concerns, gastrointestinal bleeding, epistaxis, and laceration). These CCs were chosen as they each require either an invasive medical exam or procedure, and cannot easily be evaluated with an exam in a hallway bed. We used logistic regression to assess the likelihood of being treated by a male resident compared to a female resident for each CC, adjusting for candidate variables of patient age, race, primary language, ESI score, bed location, time of day, day of week, calendar month, and resident specialty. We also similarly analyzed patterns of patient self-assignment according to resident specialty. RESULTS: Male residents were significantly less likely than female residents to treat patients with breast-related CCs (adjusted OR 0.67, 95% CI 0.54-0.83, p < 0.001) or vaginal bleeding (adjusted OR 0.73, 95% CI 0.63-0.84, p < 0.001, reference group: epistaxis). Off-service residents were more likely to assign themselves to familiar chief complaints, for example surgery residents were more likely to see patients with lacerations (adjusted OR 2.11, 95% CI 1.71-2.61, p < 0.001) and OB/GYN residents were less likely to see patients with male GU concerns (adjusted OR 0.21, 95% CI 0.05-0.85, p = 0.029), compared to emergency medicine residents. CONCLUSION: In a single facility, resident characteristics were associated with preferential patient self-assignment. Further work is necessary to determine the underlying reasons for patient avoidance, and to create work environments in which preferentially choosing patients is discouraged.

Early, awake proning in emergency department patients with COVID-19.

OBJECTIVE: Proning has been shown to improve oxygenation and mortality in certain populations of intubated patients with acute respiratory distress syndrome. Small observational analyses of COVID-19 patients suggest awake proning may lead to clinical improvement. Data on safety and efficacy is lacking. We sought to describe the effect of proning on oxygenation in nonintubated COVID-19 patients. We also evaluated feasibility, safety, and other physiological and clinical outcomes associated with this intervention. METHODS: We conducted a prospective, observational cohort study of nonintubated patients with COVID-19 who underwent proning per an Emergency Department (ED) clinical protocol. Patients with mild to moderate respiratory distress were included. We calculated change in oxygenation by comparing the oxygen saturation to fraction of inspired oxygen ratio (SpO2:FiO2) during the five minutes prior to proning and first 30 min of proning. We also captured data on respiratory rate, duration of proning, need for intubation, intensive care unit admission, survival to discharge. RESULTS: Fifty-two patients were enrolled. Thirty were excluded for not meeting protocol inclusion criteria or missing baseline oxygenation data, leaving 22 for analysis. The SpO2:FiO2 ratio increased by a median of 5 (IQR: 0-15) in the post-proning period compared to the pre-proning period (median: 298 (IQR: 263-352) vs 295 (IQR: 276-350), p = 0.01). Respiratory rate did not change significantly between time periods. No immediate adverse events occurred during proning. Five patients (23%) were intubated within 48 h of admission. CONCLUSION: Early, awake proning may be feasible in select COVID-19 patients and was associated with improved oxygenation.

Does the number of pages received per hour affect resident productivity?

Background: Workflow interruptions are common for emergency physicians and are shown to have downstream consequences such as patient dissatisfaction, delay in clinical response, and increase in medical error. However, the impact of passive interruptions on physician productivity is unclear and has not been well studied. We sought to evaluate if the number of pages received per hour significantly affects the number of patients seen per hour. Methods: Retrospective data was collected on resident physician (RP) emergency department shifts from July 1st, 2021 to June 30th, 2022 at an academic medical center with an annual census of 55,000 patients. A total of 2865 RP shifts were collected among the 26 postgraduate year (PGY) 1 and PGY2 residents. For each RP shift, we identified the number of pages received per hour and the number of new patients seen per hour. Pages consist of any transmitted message that was sent to the RP's personal pager, which includes both automatic (eg, bed assignments, abnormal lab values) and personalized pages from other healthcare practicioners (eg, nursing, consultants). Data were analyzed using Poisson regression controlling for clustering at the physician level to determine if the number of patients seen per hour is significantly affected by the number of pages (divided into quartiles) received. Results: We found the number of pages received per hour did not decrease the number of patients seen per hour. Contrary to our hypothesis, there was a strong positive relationship between the number of pages received per hour and the number of patients seen by RPs in that hour and subsequent hours. During the middle of a shift (hours 3, 4, and 5), RPs receiving pages in the third and fourth quartile (top 50% of pages) saw significantly more patients during that same hour and the next hour (p <0.001). Conclusion: The number of pages received by RPs per hour did not decrease the number of patients seen per hour. When RPs receive a higher number of pages, there is a positive association with the number of patients they see in that hour and subsequent hours. Further studies will be needed to determine whether the content of pages affects resident productivity.

Impact of a Mandatory Prescription Drug Monitoring Program Check on Emergency Department Opioid Prescribing Rates.

BACKGROUND: Prescription drug monitoring programs (PDMPs) exist in 49 states to guide opioid prescribing. In 40 states, clinicians must check the PDMP prior to prescribing an opioid. Data on mandated PDMP checks show mixed results on opioid prescribing. OBJECTIVES: This study sought to examine the impact of the Massachusetts mandatory PDMP check on opioid prescribing for discharges from an urban tertiary emergency department (ED). METHODS: This was a retrospective cohort study of discharges from one ED from 7/1/2010-10/15/2018. The primary outcome was the monthly percentage of patients discharged from the ED with an opioid prescription. The intervention was Massachusetts mandating a PDMP check for all opioid prescriptions. Prescribing was compared pre- and post-mandate. Interrupted time series (ITS) analysis accounted for known declining trends in opioid prescribing. RESULTS: Of 273,512 ED discharges, 35,050 (12.8%) received opioid prescriptions. Mean monthly opioid prescribing decreased post-intervention from 15.1% (SD ± 3.5%) to 5.1% (SD ± 0.9%; p < 0.001). ITS showed equal pre and post-intervention slopes (-0.002, p = 0.819). A small immediate decrease occurred in prescribing around the mandated check: a 3-month level effect decrease of 0.018 (p = 0.039), 6-month level effect 0.019 (p = 0.023), and a 12-month level effect of 0.020 (p = 0.019). The 24-month level effect was not decreased. CONCLUSION: Prior to the mandated PDMP check, ED opioid prescribing was declining. The mandate did not change the rate of decline but was associated with a non-sustained drop in opioid prescribing immediately following enactment.

Conformational changes in the carpus during finger trap distraction.

PURPOSE: Wrist distraction is a common treatment maneuver used clinically for the reduction of distal radial fractures and midcarpal dislocations. Wrist distraction is also required during wrist arthroscopy to access the radiocarpal joint and has been used as a test for scapholunate ligament injury. However, the effect of a distraction load on the normal wrist has not been well studied. The purpose of this study was to measure the three-dimensional conformational changes of the carpal bones in the normal wrist as a result of a static distractive load. METHODS: Using computed tomography, the dominant wrists of 14 healthy volunteers were scanned at rest and during application of 98 N of distraction. Load was applied using finger traps, and volunteers were encouraged to relax their forearm muscles and to allow distraction of the wrist. The motions of the bones in the wrist were tracked between the unloaded and loaded trial using markerless bone registration. The average displacement vector of each bone relative to the radius was calculated, as were the interbone distances for 20 bone-bone interactions. Joint separation was estimated at the radiocarpal, midcarpal, and carpometacarpal joints in the direction of loading using the radius, lunate, capitate, and third metacarpal. RESULTS: With loading, the distance between the radius and third metacarpal increased an average of 3.3 mm +/- 3.1 in the direction of loading. This separation was primarily in the axial direction at the radiocarpal (1.0 mm +/- 1.0) and midcarpal (2.0 mm +/- 1.7) joints. There were minimal changes in the transverse direction within the distal row, although the proximal row narrowed by 0.98 mm +/- 0.7. Distraction between the radius and scaphoid (2.5 mm +/- 2.2) was 2.4 times greater than that between the radius and lunate (1.0 mm +/- 1.0). CONCLUSIONS: Carpal distraction has a significant (p < .01) effect on the conformation of the carpus, especially at the radiocarpal and midcarpal joints. In the normal wrist, external traction causes twice as much distraction at the lunocapitate joint than at the radiolunate joint.

Carpal and forearm kinematics during a simulated hammering task.

PURPOSE: Hammering is a functional task in which the wrist generally follows a path of motion from a position of combined radial deviation and extension to combined ulnar deviation and flexion, colloquially referred to as a dart thrower's motion. The purpose of this study was to measure wrist and forearm motion and scaphoid and lunate kinematics during a simulated hammering task. We hypothesized that the wrist follows an oblique path from radial extension to ulnar flexion and that there would be minimal radiocarpal motion during the hammering task. METHODS: Thirteen healthy volunteers consented to have their wrist and distal forearm imaged with computed tomography at 5 positions while performing a simulated hammering task. The kinematics of the carpus and distal radioulnar joint were calculated using established markerless bone registration methods. The path of wrist motion was described relative to the sagittal plane. Forearm rotation and radioscaphoid and radiolunate motion were computed as a function of wrist position. RESULTS: All volunteers performed the simulated hammering task using a path of wrist motion from radial extension to ulnar flexion that was oriented an average of 41 degrees +/- 3 degrees from the sagittal plane. These paths did not pass through the anatomic neutral wrist position; rather, they passed through a neutral hammering position, which was offset by 36 degrees +/- 8 degrees in extension. Rotations of the scaphoid and lunate were not minimal but averaged 40% and 41%, respectively, of total wrist motion. The range of forearm pronation-supination during the task averaged 12 degrees +/- 8 degrees . CONCLUSIONS: The simulated hammering task was performed using a wrist motion that followed a coupled path of motion, from extension and radial deviation to flexion and ulnar deviation. Scaphoid and lunate rotations were greatly reduced, but not minimized, compared with rotations during pure wrist flexion/extension. This is likely because an extended wrist position was maintained throughout the entire task studied.

Information Management in the Emergency Department.

Information management in the emergency department (ED) is a challenge for all providers. The volume of information required to care for each patient and to keep the ED functioning is immense. It must be managed through varying means of communication and in connection with ED information systems. Management of information in the ED is imperfect; different modes and methods of identification, interpretation, action, and communication can be beneficial or harmful to providers, patients, and departmental flow. This article reviews the state of information management in the ED and proposes recommendations to improve the management of information in the future.

Deep-learning approaches to identify critically Ill patients at emergency department triage using limited information.

STUDY OBJECTIVE: Triage quickly identifies critically ill patients, facilitating timely interventions. Many emergency departments (EDs) use emergency severity index (ESI) or abnormal vital sign triggers to guide triage. However, both use fixed thresholds, and false activations are costly. Prior approaches using machinelearning have relied on information that is often unavailable during the triage process. We examined whether deep-learning approaches could identify critically ill patients only using data immediately available at triage. METHODS: We conducted a retrospective, cross-sectional study at an urban tertiary care center, from January 1, 2012-January 1, 2020. De-identified triage information included structured (age, sex, initial vital signs) and textual (chief complaint) data, with critical illness (mortality or ICU admission within 24 hours) as the outcome. Four progressively complex deep-learning models were trained and applied to triage information from all patients. We compared the accuracy of the models against ESI as the standard diagnostic test, using area under the receiver-operator curve (AUC). RESULTS: A total of 445,925 patients were included, with 60,901 (13.7%) critically ill. Vital sign thresholds identified critically ill patients with AUC 0.521 (95% confidence interval [CI] = 0.519-0.522), and ESI <3 demonstrated AUC 0.672 (95% CI = 0.671-0.674), logistic regression classified patients with AUC 0.803 (95% CI = 0.802-0.804), 2-layer neural network with structured data with AUC 0.811 (95% CI = 0.807-0.815), gradient tree boosting with AUC 0.820 (95% CI = 0.818-0.821), and the neural network model with textual data with AUC 0.851 (95% CI = 0.849-0.852). All successive increases in AUC were statistically significant. CONCLUSION: Deep-learning techniques represent a promising method of augmenting triage, even with limited information. Further research is needed to determine if improved predictions yield clinical and operational benefits.

A computational approach to the "optimal" screw axis location and orientation in the scaphoid bone.

PURPOSE: The development of small cannulated screws permitted minimally invasive percutaneous fixation of acute scaphoid fractures. There are known mechanical advantages to increased screw length and central screw placement, as well as documented deleterious effects of screw malposition, including articular protrusion, proximal pole fracture, and nonunion. The purpose of this study was to compare 2 methods of calculating a screw axis accessible via a volar surgical approach. METHODS: To prevent screw protrusion through the surface of the scaphoid, we required the central screw axis to be contained completely within a "safe zone," defined as a 3-dimensional region located a fixed distance from the inner cortical surface. Safe zones were calculated based on computed tomography-generated models of the right scaphoid from 10 healthy subjects. Two methods for screw axis calculation were compared: (1) maximum screw length (MSL) within the safe zone and (2) a cylinder best-fit (CYL) to the safe zone. The volar approach was defined as percutaneous screw placement through the scaphoid tubercle without violation of the trapezium. Resultant screw axes were compared between the 2 methods for volar accessibility, screw length, and location of the screw axis. RESULTS: The MSL axes were completely accessible without violating the trapezium in all but 2 subjects. The average MSL axes were 11% longer than the CYL axes and passed significantly closer to the scaphoid tubercle than did the CYL axes (1.8 mm vs 6.4 mm). The MSL axes passed significantly farther (1.6 mm) from the bone centroid than did the CYL axes (0.4 mm). All 10 MSL axes were located in the central one-third of the proximal pole. CONCLUSIONS: Without violation of the trapezium, MSL axis can be attained via the volar percutaneous approach to the scaphoid. Using this approach, the ideal starting point for maximal screw length was located 1.7 mm dorsal and 0.2 mm radial to the apex of the scaphoid tubercle.

Variations in Opioid Prescribing Behavior by Physician Training.

INTRODUCTION: Opioid abuse has reached epidemic proportions in the United States. Patients often present to the emergency department (ED) with painful conditions seeking analgesic relief. While there is known variability in the prescribing behaviors of emergency physicians, it is unknown if there are differences in these behaviors based on training level or by resident specialty. METHODS: This is a retrospective chart review of ED visits from a single, tertiary-care academic hospital over a single academic year (2014-2015), examining the amount of opioid pain medication prescribed. We compared morphine milligram equivalents (MME) between provider specialty and level of training (emergency medicine [EM] attending physicians, EM residents in training, and non-EM residents in training). RESULTS: We reviewed 55,999 total ED visits, of which 4,431 (7.9%) resulted in discharge with a prescription opioid medication. Residents in a non-EM training program prescribed higher amounts of opioid medication (108 MME, interquartile ratio [IQR] 75-150) than EM attendings (90 MME, lQR 75-120), who prescribed more than residents in an EM training program (75 MME, IQR 60-113) (p<0.01). CONCLUSION: In an ED setting, variability exists in prescribing patterns with non-EM residents prescribing larger amounts of opioids in the acute setting. EM attendings should closely monitor for both over- and under-prescribing of analgesic medications.

Assessment of Unintentional Duplicate Orders by Emergency Department Clinicians Before and After Implementation of a Visual Aid in the Electronic Health Record Ordering System.

Importance: Electronic health records allow teams of clinicians to simultaneously care for patients, but an unintended consequence is the potential for duplicate orders of tests and medications. Objective: To determine whether a simple visual aid is associated with a reduction in duplicate ordering of tests and medications. Design, Setting, and Participants: This cohort study used an interrupted time series model to analyze 184 694 consecutive patients who visited the emergency department (ED) of an academic hospital with 55 000 ED visits annually. Patient visits occurred 1 year before and after each intervention, as follows: for laboratory orders, from August 13, 2012, to August 13, 2014; for medication orders, from February 3, 2013, to February 3, 2015; and for radiology orders, from December 12, 2013, to December 12, 2015. Data were analyzed from April to September 2019. Exposure: If an order had previously been placed during the ED visit, a red highlight appeared around the checkbox of that order in the computerized provider order entry system. Main Outcomes and Measures: Number of unintentional duplicate laboratory, medication, and radiology orders. Results: A total of 184 694 patients (mean [SD] age, 51.6 [20.8] years; age range, 0-113.0 years; 99 735 [54.0%] women) who visited the ED were analyzed over the 3 overlapping study periods. After deployment of a noninterruptive nudge in electronic health records, there was an associated 49% decrease in the rate of unintentional duplicate orders for laboratory tests (incidence rate ratio, 0.51; 95% CI, 0.45-0.59), from 4485 to 2731 orders, and an associated 40% decrease in unintentional duplicate orders of radiology tests (incidence rate ratio, 0.60; 95% CI, 0.44-0.82), from 956 to 782 orders. There was not a statistically significant change in unintentional duplicate orders of medications (incidence rate ratio, 1.17; 95% CI, 0.52-2.61), which increased from 225 to 287 orders. The nudge eliminated an estimated 17 936 clicks in our electronic health record. Conclusions and Relevance: In this interrupted time series cohort study, passive visual cues that provided just-in-time decision support were associated with reductions in unintentional duplicate orders for laboratory and radiology tests but not in unintentional duplicate medication orders.

Interfragmentary motion in patients with scaphoid nonunion.

PURPOSE: Scaphoid nonunions are a common complication of scaphoid fractures and frequently progress to degenerative arthritis. This study evaluated the effect of scaphoid nonunion on the in vivo kinematics of the radioscaphocapitate articulation. METHODS: Computed tomography with a markerless registration technique was used to quantify motion of the scaphoid, lunate, and capitate in vivo, in 6 patients with unilateral scaphoid nonunion. The 3-dimensional helical axis of motion rotations of each bone were measured as a function of wrist flexion-extension and compared with those of the uninjured contralateral wrist. Mixed linear modeling was used to compare flexion-extension of the injured scaphoid fragments with those of the uninjured scaphoid, and the lunate of the injured wrist with the lunate of the uninjured wrist. Interfragmentary motion in the injured scaphoid was assessed by calculating rotation of the distal fragment relative to the proximal fragment, as well as the linear displacement between the 2 fragments at the fracture site. RESULTS: Flexion and extension of the distal scaphoid fragment was similar to that of the uninjured scaphoid. Extension of the proximal fragment was significantly decreased by 38%, compared with the uninjured scaphoid. Similarly, extension of the lunate in the injured wrist was significantly decreased, by 40%. Interfragmentary rotation was 33% of wrist motion in flexion and 35% of wrist motion in extension. Maximum interfragmentary displacement was on the order of 1 mm. CONCLUSIONS: Scaphoid nonunions have a dramatic impact on carpal kinematics, partially uncoupling the proximal and distal carpal rows. Although the results of this in vivo study differ from past in vitro studies, the increase in lunocapitate motion we identified is consistent with the current theory that the scaphoid acts as a fundamental link between the proximal and distal carpal rows.

A digital database of wrist bone anatomy and carpal kinematics.

The skeletal wrist consists of eight small, intricately shaped carpal bones. The motion of these bones is complex, occurs in three dimensions, and remains incompletely defined. Our previous efforts have been focused on determining the in vivo three-dimensional (3-D) kinematics of the normal and abnormal carpus. In so doing we have developed an extensive database of carpal bone anatomy and kinematics from a large number of healthy subjects. The purpose of this paper is to describe that database and to make it available to other researchers. CT volume images of both wrists from 30 healthy volunteers (15 males and 15 females) were acquired in multiple wrist positions throughout the normal range of wrist motion. The outer cortical surfaces of the carpal bones, radius and ulna, and proximal metacarpals were segmented and the 3-D motion of each bone was calculated for each wrist position. The database was constructed to include high-resolution surface models, measures of bone volume and shape, and the 3-D kinematics of each segmented bone. The database does not include soft tissues of the wrist. While there are numerous digital anatomical databases, this one is unique in that it includes a large number of subjects and it contains in vivo kinematic data as well as the bony anatomy.

Studying primate carpal kinematics in three dimensions using a computed-tomography-based markerless registration method.

The functional morphology of the wrist pertains to a number of important questions in primate evolutionary biology, including that of hominins. Reconstructing locomotor and manipulative capabilities of the wrist in extinct species requires a detailed understanding of wrist biomechanics in extant primates and the relationship between carpal form and function. The kinematics of carpal movement, and the role individual joints play in providing mobility and stability of the wrist, is central to such efforts. However, there have been few detailed biomechanical studies of the nonhuman primate wrist. This is largely because of the complexity of wrist morphology and the considerable technical challenges involved in tracking the movements of the many small bones that compose the carpus. The purpose of this article is to introduce and outline a method adapted from human clinical studies of three-dimensional (3D) carpal kinematics for use in a comparative context. The method employs computed tomography of primate cadaver forelimbs in increments throughout the wrist's range of motion, coupled with markerless registration of 3D polygon models based on inertial properties of each bone. The 3D kinematic principles involved in extracting motion axis parameters that describe bone movement are reviewed. In addition, a set of anatomically based coordinate systems embedded in the radius, capitate, hamate, lunate, and scaphoid is presented for the benefit of other primate functional morphologists interested in studying carpal kinematics. Finally, a brief demonstration of how the application of these methods can elucidate the mechanics of the wrist in primates illustrates the closer-packing of carpals in chimpanzees than in orangutans, which may help to stabilize the midcarpus and produce a more rigid wrist beneficial for efficient hand posturing during knuckle-walking locomotion.

Automatic determination of anatomical coordinate systems for three-dimensional bone models of the isolated human knee.

The combination of three-dimensional (3-D) models with dual fluoroscopy is increasingly popular for evaluating joint function in vivo. Applying these modalities to study knee motion with high accuracy requires reliable anatomical coordinate systems (ACSs) for the femur and tibia. Therefore, a robust method for creating ACSs from 3-D models of the femur and tibia is required. We present and evaluate an automated method for constructing ACSs for the distal femur and proximal tibia based solely on 3-D bone models. The algorithm requires no observer interactions and uses model cross-sectional area, center of mass, principal axes of inertia, and cylindrical surface fitting to construct the ACSs. The algorithm was applied to the femur and tibia of 10 (unpaired) human cadaveric knees. Due to the automated nature of the algorithm, the within specimen variability is zero for a given bone model. The algorithm's repeatability was evaluated by calculating variability in ACS location and orientation across specimens. Differences in ACS location and orientation between specimens were low (<1.5mm and <2.5 degrees). Variability arose primarily from natural anatomical and morphological differences between specimens. The presented algorithm provides an alternative method for automatically determining subject-specific ACSs from the distal femur and proximal tibia.

Simulated radioscapholunate fusion alters carpal kinematics while preserving dart-thrower's motion.

PURPOSE: Midcarpal degeneration is well documented after radioscapholunate fusion. This study tested the hypothesis that radioscapholunate fusion alters the kinematic behavior of the remaining lunotriquetral and midcarpal joints, with specific focus on the dart-thrower's motion. METHODS: Simulated radioscapholunate fusions were performed on 6 cadaveric wrists in an anatomically neutral posture. Two 0.060-in. carbon fiber pins were placed from proximal to distal across the radiolunate and radioscaphoid joints, respectively. The wrists were passively positioned in a custom jig toward a full range of motion along the orthogonal axes as well as oblique motions, with additional intermediate positions along the dart-thrower's path. Using a computed tomography-based markerless bone registration technique, each carpal bone's three-dimensional rotation was defined as a function of wrist flexion/extension from the pinned neutral position. Kinematic data was analyzed against data collected on the same wrist prior to fixation using hierarchical linear regression analysis and paired Student's t-tests. RESULTS: After simulated fusion, wrist motion was restricted to an average flexion-extension arc of 48 degrees , reduced from 77 degrees , and radial-ulnar deviation arc of 19 degrees , reduced from 33 degrees . The remaining motion was maximally preserved along the dart-thrower's path from radial-extension toward ulnar-flexion. The simulated fusion significantly increased rotation through the scaphotrapezial joint, scaphocapitate joint, triquetrohamate joint, and lunotriquetral joint. For example, in the pinned wrist, the rotation of the hamate relative to the triquetrum increased 85%. Therefore, during every 10 degrees of total wrist motion, the hamate rotated an average of nearly 8 degrees relative to the triquetrum after pinning versus 4 degrees in the normal state. CONCLUSIONS: Simulated radioscapholunate fusion altered midcarpal and lunotriquetral kinematics. The increased rotations across these remaining joints provide one potential explanation for midcarpal degeneration after radioscapholunate fusion. Additionally, this fusion model confirms the dart-thrower's hypothesis, as wrist motion after simulated radioscapholunate fusion was primarily preserved from radial-extension toward ulnar-flexion.