Background/Purpose: While musculoskeletal ultrasound (MSUS) use in pediatric rheumatology is becoming more common, the majority of pediatric MSUS literature continues to focus on ultrasound findings in healthy children and juvenile idiopathic arthritis with little discussion of other musculoskeletal problems that may mimic arthritis such as joint hypermobility. Chronic joint pain related to hypermobility is a common referral to pediatric rheumatology clinics. Our aim is to describe the MSUS characteristics of the knee in a population with joint hypermobility and pain in comparison to hypermobile children without pain and children without hypermobility or pain.

Methods: Patients were recruited and assigned into three groups for a case-control study. Inclusion criteria for the case group were patient age ≥ 14 years, >10 degrees of knee hyperextension on goniometer measurement, and pain score ≥ 1 (out of 10) in the knee over the past month. Control patients were matched by age and gender. One control group had knee hypermobility without pain symptoms (pain score = 0). Another control group had no knee hypermobility (≤10 degrees of knee hyperextension) and no pain symptoms. Patients could not have a current diagnosis associated with arthritis, history of previous knee surgery, or history of knee trauma within the month prior to evaluation. Demographic and clinical information including Beighton score were collected. A rheumatology fellow obtained B-mode and Doppler MSUS of each knee. A blinded rheumatologist scored the images according to a recently published protocol for synovial effusion, synovial hypertrophy, hyperemia, and tendon abnormalities. Descriptive statistics are used for demographic variables, medication use, laboratory parameters and MSUS findings. Poisson regression with robust standard errors is used to evaluate risk of synovial effusion and synovial effusion/hypertrophy quantitative score.

Results: To date, 80 knees were evaluated with ultrasound. MSUS abnormalities are seen in 65 of 80 (81%) of all ultrasounds with abnormalities in 31 of 32 (97%) knees in the case group, 15 of 22 (68%) knees in the hypermobility/no pain group, and 19 of 26 (73%) knees in the no hypermobility/no pain group. The most frequent finding was synovial effusion in 21 of 32 (66%) knees of the case group. The finding was also frequent in the control groups in 10 of 22 (45%) knees in the hypermobility/no pain group and 13 of 26 (50%) knees in the no hypermobility/no pain group. Only two of 80 total knees (2%) had positive Doppler signal in the synovium. There were no significant differences between the groups for the risk of effusion or increased synovial effusion/hypertrophy quantitative score.

Conclusion: A high frequency of abnormalities is seen in all knee ultrasounds obtained in this study. Many knees in all groups had synovial effusion which suggests this finding may be physiologic rather than an association with joint hypermobility or pain symptoms. Few knees had positive Doppler signal which may be helpful to differentiate patients with abnormalities related to hypermobility or physiologic changes versus inflammatory arthritis. Further study is needed to assess if any abnormal findings are associated with reported pain symptoms.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/musculoskeletal-ultrasound-assessment-in-pediatric-knee-hypermobility/