Association of Muscle Quality and Pain in Adults With Symptomatic Knee Osteoarthritis, Independent of Muscle Strength: Findings From a Cross-Sectional Study.

OBJECTIVE: Knee osteoarthritis (OA) is a leading cause of chronic pain in adults and shows wide interindividual variability, with peripheral and central factors contributing to the pain experience. Periarticular factors, such as muscle quality (eg, echo intensity [EI] and shear wave velocity [SWV]), may contribute to knee OA pain; however, the role of muscle quality in OA symptoms has yet to be fully established. METHODS: Twenty-six adults (age >50 years) meeting clinical criteria for knee OA were included in this cross-sectional study. Quantitative ultrasound imaging was used to quantify EI and SWV in the rectus femoris of the index leg. Pearson correlations followed by multiple linear regression was used to determine associations between muscle quality and pain, controlling for strength, age, sex, and body mass index. RESULTS: EI and SWV were significantly associated with movement-evoked pain (b = 0.452-0.839, P = 0.024-0.029). Clinical pain intensity was significantly associated with SWV (b = 0.45, P = 0.034), as were pressure pain thresholds at the medial (b = -0.41, P = 0.025) and lateral (b = -0.54, P = 0.009) index knee joint line, adjusting for all covariates. Pain interference was significantly associated with knee extension strength (b = -0.51, P = 0.041). CONCLUSION: These preliminary findings suggest that EI and SWV may impact knee OA pain and could serve as malleable treatment targets. Findings also demonstrate that muscle quality is a unique construct, distinct from muscle strength, which may impact pain and treatment outcomes. More research is needed to fully understand the role of muscle quality in knee OA.

Measuring fascicle lengths of extrinsic and intrinsic thumb muscles using extended field-of-view ultrasound.

Complex motion of the human thumb is enabled by the balanced architectural design of the extrinsic and intrinsic thumb muscles. Given that recent imaging advances have not yet been applied to enhance our understanding of the in vivo properties of thumb muscles, the objective of this study was to test the reliability and validity of measuring thumb muscle fascicle lengths using extended field of view ultrasound (EFOV-US). Three muscles (FPL: flexor pollicis longus, APB: abductor pollicis brevis, and ECU: extensor carpi ulnaris) were imaged in eight healthy adults (4 female; age, 21.6 ± 1.3 years; height, 175.9 ± 8.3 cm)[mean ± SD]. Measured fascicle lengths were compared to cadaveric data (all muscles) and ultrasound data (ECU only). Additionally, to evaluate how fascicle lengths scale with anthropometric measurements, height, forearm length, hand length, and hand width were recorded. The EFOV-US method obtained precise fascicle length measurements [mean ± SD] for the FPL (6.2 ± 0.5 cm), APB (5.1 ± 0.3 cm), and ECU (4.0 ± 0.4 cm). However, our EFOV-US measurements were consistently different (p < 0.05) than prior cadaveric data, highlighting the need to better understand differences between in vivo and ex vivo fascicle length measurements. Fascicle length was significantly related to only hand length (r2 = 0.56, p = 0.03) for APB, highlighting that anthropometric scaling may not accurately estimate thumb muscle length. As the first study to apply EFOV-US to measure thumb muscle fascicle lengths, this study expands the utility of this imaging technology within the upper limb.

Linear relationship between electromyography and shear wave elastography measurements persists in deep muscles of the upper extremity.

Recent works have demonstrated a linear relationship between muscle activation and shear modulus in various superficial muscles. As such, it may be possible to overcome limitations of traditional electromyography (EMG) methods by assessing activation using shear wave elastography. However, the relationship has not been wholly validated in deep muscles. This study measured the association between squared shear wave velocity, which is related to shear modulus, and activation within superficial and deep muscles. This relationship was also compared between surface and intramuscular EMG electrodes. We simultaneously recorded EMG and shear wave velocity in one deep (brachialis) and one superficial (brachioradialis) muscle in ten healthy individuals during isometric elbow flexion across a wide range of contraction intensities. Muscle activation and squared shear wave velocity demonstrated good reliability (ICC > 0.75) and showed a linear relationship (P < 0.05) for all muscle/EMG electrode type combinations (study conditions) after down-sampling. Study condition was not a significant within-subject factor to the slope or intercept of the relationship (P > 0.05). This work demonstrates that activation of both superficial and deep muscles can be assessed noninvasively using ultrasound shear wave elastography and is a critical step toward demonstrating elastography's utility as an alternative to EMG.