(I-351) Muscle Oxygen Saturation as a Digital Biomarker to Guide Orthopedic and Cardiac Rehabilitation

Introduction:: Wearable devices and digital health technologies, broadly speaking, have become increasingly utilized in clinical trials to quantify patient reported outcome measures to complement subjective assessments. The ability to monitor continuous, internal digital biomarkers enables real-time measures related to patient compliance, medication tolerability and rehabilitation status. Recently, near infrared spectroscopy-based wearable devices have emerged as a means to measure blood-based biomarkers with specificity and sensitivity required for clinical decision making. One such biomarker of interest is muscle oxygen saturation (SmO₂), which is the ratio of oxygenated hemoglobin to total hemoglobin. From an exercise physiology standpoint, a decrease in SmO₂ is indicative of greater muscle exertion, higher energy output, and greater oxygen consumption. In the context of sports medicine, wearable technology serves as an objective and continuous means to complement athlete ratings of perceived exertion and has been used in orthopedic rehabilitation following anterior cruciate ligament reconstruction as an example. From a cardiac rehabilitation standpoint, measurement of muscle oxygen saturation has emerging utility as a predictive marker for recovery in heart failure patients presenting with sarcopenia. This presentation will highlight on-going efforts on the use of a NIR sensor to measure muscle oxygen saturation as a complementary digital biomarker to guide rehabilitation following anterior cruciate ligament reconstruction. Furthermore, this presentation will highlight emerging efforts on the use of muscle oxygen saturation for cardiac rehabilitation in patients with congestive heart failure presenting with sarcopenia.


Materials and Methods:: On the orthopedic front, currently ongoing is a multi-arm IRB approved study (20191389) assessing muscle oxygen saturation levels in the legs of healthy subjects (arm 1, n=50) and patients after anterior cruciate ligament reconstruction (arm 2, n=50). Inclusion criteria involved participants being 14- 22 years of age, have no history of prior anterior cruciate ligament reconstruction, knee arthroscopic surgery, or hip arthroscopic surgery, and not pregnant. A standardized workout was created for testing at 6-, 9-, and 12 -months post reconstruction. Sensors are placed on the vastus medialis (VMO) bilaterally using medical grade adhesives to record muscle oxygen saturation levels. Healthy patients undergo testing once, while surgical patients undergo the testing at 6-, 9-, and 12-months postoperatively. All testing occurs under the supervision of a physical therapist at high volume physical therapy center.

Results, Conclusions, and Discussions:: Thus far, data has been collected on 47 out of 50 healthy subjects and 24 out of 50 patients following anterior cruciate ligament reconstruction. Results demonstrate convergence in muscle oxygen saturation levels during the 6, 9, and 12 month rehabilitation timepoints, with an improvement in oxygen utilization occurring in the surgical leg thereby suggestive of improved vascularization of the neoligament following surgery. The change in muscle oxygen saturation for patients following anterior cruciate ligament reconstruction is likely due to a combination of altered hemoglobin-oxygen unbinding, altered blood delivery, detraining, and muscle atrophy. These changes in muscle oxygen saturation correlate with improvement in other return to play testing. Muscle oxygen saturation data offers complementary, internal, and objective data in RTP criteria. Future work will enable the development of an integrative algorithm that physicians and physical therapists can employ to gauge athlete readiness following ACLR with broader implications to other musculoskeletal injuries. Sports medicine offers the opportune environment for assessing wearable technologies. While patients with heart failure represent the other end of the patient spectrum, lessons learned on the orthopedic rehabilitation front enables the measurement of muscle oxygen saturation as a digital biomarker and objective means to quantify rehabilitation in heart failure patients with sarcopenia.

Acknowledgements (Optional): : The project described was supported by a grant (#2022PM2) from the American Orthopaedic Society for Sports Medicine. The content is solely the responsibility of the authors and does not necessarily represent the official views of the American Orthopaedic Society for Sports Medicine.


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