Ultrasound for Rectus Femoris Measurement

Overview

Postoperative protocols for orthopedic procedures on the lower limb often require a period of immobilization to protect the surgical site. The consequence of this immobilization is muscle atrophy which can be severe, delaying a patient's return to activity and predisposing them to recovery complications or subsequent injury (1)(2). The current standard methods to assess lower limb muscle atrophy all have their respective limitations. Thigh circumference or isokinetic strength values are indirect measures of atrophy and can be inaccurate. Magnetic resonance imaging (MRI) of muscle cross-sectional area (CSA) is time-consuming and expensive. Computed tomography imaging of muscle CSA is expensive and exposes the patient to radiation (3). For these reasons, none of the current methods are ideal for regular use in the clinic. Musculoskeletal ultrasound is a promising measurement tool to assess muscle atrophy in postoperative patients. Ultrasound is non-invasive, cost-effective, does not involve radiation, and can give direct images of muscle size (4). Musculoskeletal ultrasound requires further research on its potential as an evaluation tool for postoperative lower limb orthopedic patients-specifically, whether ultrasound is a reliable and valid tool for quadriceps size measurements.

Lower limb surgeries, particularly knee surgeries, are prevalent procedures in US orthopedic departments. Many of these procedures require a postoperative period of immobilization, which may be lengthy for surgeries involving ligament reconstruction, fractures, meniscal repairs, or cartilage transplantation. This leg immobilization results in rapid and significant loss of skeletal muscle mass. Even for shorter periods of immobilization, atrophy occurs within as little as 5 days of immobilization in healthy subjects, and the largest extent of post-operative atrophy takes place during the first two weeks of being immobilized (1)(2). Muscle atrophy can prolong recovery times and directly impact the safety of a patient's return to activity progression. Providers need a reliable, valid method of assessing postoperative muscle atrophy which is cost-effective, safe, and simple to implement in a clinical setting (4). The aim of this study is to demonstrate that ultrasounds are reliable and valid tools for measuring large lower limb stabilizers such as the rectus femoris. Upon proving reliability and validity, we aim to use the ultrasound to track and characterize rectus femoris atrophy after a common lower limb surgical procedure; anterior cruciate ligament (ACL) reconstruction. Success of this validation study would support the use of ultrasound to monitor large muscle atrophy after lower limb orthopedic surgical procedures, and to evaluate the impact of muscle health interventions. Our ultimate research aim is to develop a reliable, valid ultrasound measurement technique to evaluate promising perioperative interventions for attenuation of muscle atrophy following surgical procedures of the knee. Patients and Methods: Part I: Ultrasound measurements of the rectus femoris will be obtained in approximately 50 healthy volunteers. Thigh circumference measurements will be taken as well. The ultrasound (US) images will be de-identified with research identifier (ID) only and transferred from the US unit to a secured folder on a research drive, and associated only with basic demographic information such as age, gender, height, and weight. Ultrasounds currently in use at the UIHC Sports Medicine Clinic will be used. Measurements will be made at a point mid-way between the anterior superior iliac spine and the superior border of the patella. Part II: Following validation in healthy controls, approximately 100 ACL reconstruction patients will be enrolled for a longitudinal study which utilizes the same ultrasound methods and equipment to track their rectus femoris size at a preoperative visit, and during the 6 week, 3 month, and 6 month standard postoperative follow-up visits. Thigh circumference measurements will be taken as well. The ultrasound images will be de-identified with research ID only and transferred from the US unit to a secured folder on a research drive, and associated only with basic demographic information such as age, gender, height, and weight; along with basic survey data on physical therapy adherence. The patients will not incur any cost from the ultrasound testing, and the ultrasound testing will occur at the same clinical location (UIHC Sports Medicine Clinic) as their follow-up visits. Aim 1: Assess the inter-rater and intra-rater reliability of ultrasound for measuring skeletal size using a commercially available ultrasound unit. Hypothesis 1: We hypothesize that ultrasound measures of rectus femoris will demonstrate both high intrarater and interrater reliability. Aim 2: Assess the validity of ultrasound in measuring muscle size when utilized by a novice user as compared to a professional sonographer. Hypothesis 2. The ultrasound will demonstrate high validity and ease of use when comparing novice and professionally obtained images. Aim 3: Assess the accuracy of ultrasound in measuring muscle size compared to the literature standard measurement technique of thigh circumference. Hypothesis 3: Ultrasound measurements will be equally or more accurate than thigh circumference measurements at detecting rectus femoris size differences between subjects, and ultrasound measurements will have less interrater and intrarater variability. Aim 4: Develop a descriptive characterization of rectus femoris size parameters among a healthy young adult population. Aim 5: Track and characterize rectus femoris atrophy in ACL reconstruction patients using the validated ultrasound methodology. Hypothesis 4: Patients will show a statistically significant degree of rectus femoris atrophy between their preoperative visit measurement and their 6 week and 3 month follow up measurements. Hypothesis 5: Patients will show a statistically significant degree of improvement in rectus femoris atrophy when comparing their 6 month visit measurements with their 6 week and 3 month visit measurements. Hypothesis 6: There will not be a significant difference between the preoperative and 6 month postoperative rectus femoris measurements. Hypothesis 7: Ultrasounds measurements will be equally or more sensitive at detecting significant rectus femoris atrophy in anterior cruciate ligament reconstruction (ACLR) patients compared to thigh circumference measurements. Aim 6: Analyze how external factors impact rectus femoris atrophy in ACL reconstruction patients using the validated ultrasound methodology Hypothesis 8: Graft choice will impact rectus femoris atrophy and recovery. Hypothesis 9: Fewer physical therapy office visits will impact rectus femoris atrophy and recovery.