Diagnostic Criteria for the Painful Swollen Pediatric Knee: Distinguishing Septic Arthritis From Aseptic Effusion in a Non-Lyme Endemic Area

Purpose: The child with a painful swollen knee must be worked-up for possible septic arthritis; the classic clinical prediction algorithms for septic arthritis of the hip may not be the best models to apply to the knee.Materials and methods: This was a retrospective case-control study of 17 years of children presenting to one hospital with a chief complaint of a painful swollen knee, to evaluate the appropriateness of applying a previously described clinical practice algorithm for the hip in differentiating between the septic and aseptic causes of the painful knee effusions. The diagnoses of true septic arthritis, presumed septic arthritis, and aseptic effusion were established, based upon the cultures of synovial fluid, blood cultures, synovial cell counts, and clinical course. Using a logistic regression model, the disease status was regressed on both the demographic and clinical variables.Results: In the study, 122 patients were included: 51 with true septic arthritis, 37 with presumed septic arthritis, and 34 with aseptic knee effusion. After applying a backward elimination, age <5 years and C-reactive protein (CRP) >2.0 mg/dl remained in the model, and predicted probabilities of having septic knee arthritis ranged from 15% for the lowest risk to 95% for the highest risk. Adding a knee aspiration including percent polymorphonucleocytes (%PMN) substantially improved the overall model performance, lowering the lowest risk to 11% while raising the highest risk to 96%.Conclusions: This predictive model suggests that the likelihood of pediatric septic arthritis of the knee is >90% when both “age <5 years” and “CRP > 2.0 mg/dl” are present in a child with a painful swollen knee, though, in the absence of these factors, the risk of septic arthritis remains over 15%. Aspiration of the knee for those patients would be the best next step.

LIMITED INTER-RATER RELIABILITY IN ANTEROLATERAL LIGAMENT DETECTION IN PEDIATRIC KNEE MRIS

Background: Despite the rapidly expanding anterolateral ligament (ALL) literature base, little has focused on the reliability of its detection on MRI. This is especially important in the pediatric population where the scarcity of pediatric cadaveric specimens hinders the accurate estimation of its prevalence. Purpose: The purpose of this study was to assess the visibility of ALL on common MRI pulse sequences and to calculate the inter-rater reliability among multiple expert readers in a cohort of normal pediatric knee MRIs. Methods: A series of 3T pediatric knee MRIs obtained from 8/2018-4/2019 were reviewed to identify patients without significant knee pathology. Knee laterality, age, gender, and regional physeal status were also recorded. One orthopedic surgeon, 1 pediatric musculoskeletal (MSK) radiologist, and 1 adult MSK radiologist, independently reviewed each MRI pulse sequence (T1-weighted, PD-weighted, and PD-weighted fat-suppressed images) separately, to determine the presence or absence of the 3 parts of the ALL (femoral, tibial, and meniscal proper). Inter-rater reliability was calculated using Fleiss’ Kappa (K). Results: Inclusion criteria were met for 75 patient knees with a mean age of 12.7±3.42y (3-19) and a greater proportion of females (57.3%). The distribution of regional physeal status was: Open-48.0%, Closing-29.3%, and Closed-22.7%. Inter-rater reliability was slight to fair (K: 0.141-0.340) for visualizing any specific ALL component on a unique MRI sequence (Table 1). For visualizing a specific attachment on any MRI sequence, there was slight to moderate agreement (K: 0.018-0.411). Visualizing any ALL attachment on any MRI sequence also yielded slight agreement (K: 0.190). Inter-rater reliability between specialities (i.e. Ortho vs. MSK Radiology) did not differ substantially from group findings. No single study sequence demonstrated enhanced reliability for all ALL components. Conclusion: The reliability of ALL detection on MRI across multiple clinicians was slight to moderate for all components in this cohort of normal 3T pediatric knee MRIs. No single sequence was consistently better for ALL detection agreement. This is in contrast with previous work showing substantial agreement among raters and describing PD-weighted imaging as preferable for viewing the ALL. Experience in musculoskeletal imaging did not confer improved agreement. Establishing diagnostic reliability should be a prerequisite for use of an imaging finding in the research or clinical setting. Existing literature drawing conclusions from ALL findings on MRI may need to be interpreted with caution if reliability testing is not described. [Table: see text]

A Pediatric Knee Exoskeleton With Real-Time Adaptive Control for Overground Walking in Ambulatory Individuals With Cerebral Palsy

Gait training via a wearable device in children with cerebral palsy (CP) offers the potential to increase therapy dosage and intensity compared to current approaches. Here, we report the design and characterization of a pediatric knee exoskeleton (P.REX) with a microcontroller based multi-layered closed loop control system to provide individualized control capability. Exoskeleton performance was evaluated through benchtop and human subject testing. Step response tests show the averaged 90% rise was 26 ± 0.2 ms for 5 Nm, 22 ± 0.2 ms for 10 Nm, 32 ± 0.4 ms for 15 Nm. Torque bandwidth of P.REX was 12 Hz and output impedance was less than 1.8 Nm with control on (Zero mode). Three different control strategies can be deployed to apply assistance to knee extension: state-based assistance, impedance-based trajectory tracking, and real-time adaptive control. One participant with typical development (TD) and one participant with crouch gait from CP were recruited to evaluate P.REX in overground walking tests. Data from the participant with TD were used to validate control system performance. Kinematic and kinetic data were collected by motion capture and compared to exoskeleton on-board sensors to evaluate control system performance with results demonstrating that the control system functioned as intended. The data from the participant with CP are part of a larger ongoing study. Results for this participant compare walking with P.REX in two control modes: a state-based approach that provided constant knee extension assistance during early stance, mid-stance and late swing (Est+Mst+Lsw mode) and an Adaptive mode providing knee extension assistance proportional to estimated knee moment during stance. Both were well tolerated and significantly improved knee extension compared to walking without extension assistance (Zero mode). There was less reduction in gait speed during use of the adaptive controller, suggesting that it may be more intuitive than state-based constant assistance for this individual. Future work will investigate the effects of exoskeleton assistance during overground gait training in children with neurological disorders and will aim to identify the optimal individualized control strategy for exoskeleton prescription.