Josh R Baxter, PhD

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Assistant Professor of Orthopaedic Surgery
Director, Human Motion Laboratory, Hospital of the University Of Pennsylvania
Department: Orthopaedic Surgery

Contact information
3450 Hamilton Walk
372A Stemmler Hall
Philadelphia, PA 19104
Office: 215-898-7395
BS (Exercise Science)
Central Washington University, 2007.
MS (Nutrition and Exercise Science)
Oregon State University, 2009.
PhD (Kinesiology - Biomechanics)
Pennsylvania State University, 2012.
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Description of Research Expertise

My research is focused on improving rehabilitation loading protocols to treat musculoskeletal injuries. In orthopaedics, we leverage mechanical loads as a way to treat musculoskeletal injuries. For example, following a tendon rupture, an orthopaedic surgeon will repair the tendon using suture to restore the mechanical integrity of the tissue to bare mechanical loads. While these treatments stabilize the tissue while biologic healing restores tissue function, our understanding of the post-operative loading environment that promotes healing is less understood. My research is exploring the rehabilitation period following musculoskeletal injury and surgical treatment to safely promote tissue healing and improve patient outcomes.

My group uses preclinical and clinical models to identify what loads are therapuetic for tissue healing and what loads are injurious. This is critical because it works within the current reimbursement structure of musculoskeletal care. Once we identify therapuetic loading profiles, we will be able to deliver precision rehabilatiton through reimbursable physical therapy pathways to maximize healing and patient outcomes.

My group is currently performing 5 funded projects:
1 - Modifying muscle remodeling following Achilles tendon ruptures funded by the NIH/NIAMS K01-AR075877. The goal of this study is for the PI to receive mentoring and training in small animal models, imaging, and muscle physiology to develop clinically viable treatment paradigms for Achilles tendon ruptures.
2 - Tendon loading profiles that promote healing in Achilles tendinopathy funded by the NIH/NIAMS R01-AR078898. The goal of this study is to determine rehabilitation loading profiles and ultrasound imaging biomarkers that explain tendon healing and functional outcomes in patients with mid-substance Achilles tendinopathy.
3 - Linking structural changes and functional outcomes following Achilles tendon rupture funded by the American Orthopaedic Foot and Ankle Society. The goal of this study is to link tendon loading throughout healing with muscle-tendon structure and functional outcomes in patients who undergo surgical repair for acute Achilles tendon ruptures.
4 - Precision rehabilitation to restore plantar flexor function following Achilles tendon rupture repair funded by the NIH/NIAMS R21-AR081497. The goal of this study is to identify therapeutic loads that can be translated to the clinic and guide precision rehabilitation using a small animal model.
5 - Defining the neuromechanical mechanisms of Achilles tendinopathy funded by the NIH/NIAMS R01-AR081062. The goal of this study is to measure plantar flexor neuromechanics using our innovative high-density surface electromyography sensors custom developed at Penn to determine how rehabilitation exercises can be optimized to guide treatment and improve outcomes in patients with Achilles tendinopathy.

Selected Publications

Cone SG, Martin JA, Knurr KA, Baxter JR, Thelen DG: Longitudinal Tracking of Achilles Tendon Morphology and Function in the Near-Term After Rupture and Repair. Annual Meeting of the Orthopaedic Research Society Feb 2022 Notes: poster presentation.

Lil Z, Leel SH, Kim DH, Mondal S, Nimmer E, Hederick L, Tran R, Baxter JR, Bae Y, Burdick J, Mauck R, Heo SJ: Development of an Extracellular Matrix-Based Multiphasic Scaffold System for Rotator Cuff Repair. Annual Meeting of the Orthopaedic Research Society Feb 2022 Notes: poster presentation.

My My Tang, Natalie Fogarty, Courtney A. Nuss, Todd J. Hullfish, Tejvir Khurana, and Josh R. Baxter: Surgically repairing Achilles tendon ruptures restores plantar flexor function better than non-surgical treatment in a rat model. American Orthopaedic Foot and Ankle Society - Annual Meeting 2022 Notes: J. Leanard Goldner Award Finalist Podium presentation.

Ke Song, Stephanie G. Cone, Jennifer A. Zellers, Darryl G. Thelen, and Josh R. Baxter : Tracking Day-To-Day Achilles Tendon Loading Progression During Rupture Recovery: A Case Study. American Orthopaedic Foot and Ankle Society - Annual Meeting 2022 Notes: Audio Poster Presentation.

Todd J. Hullfish, Daniel C. Farber, Casey J. Humbyrd, Josh R. Baxter: Achilles tendon loading in an immobilizing boot is dependent on immobilization style and boot construction American Orthopaedic Foot and Ankle Society - Annual Meeting 2022 Notes: Podium presentation.

My M. Tang, Courtney A. Nuss, Natalie Fogarty, Josh R. Baxter: Plantar flexor deficits following Achilles tendon rupture: a novel small animal dynamometer and detailed instructions. bioRxiv [preprint] 2022 Notes: doi:

Hullfish TJ, Drazan JF, Baxter JR: Experimental recommendations for estimating lower extremity loading based on joint and activity. Journal of Biomechanics 127: 110688, October 2021.

Drazan JF, Phillips WT, Seethpathi N, Hullfish TJ, Baxter JR: Moving outside the lab: markerless motion capture accurately quantifies sagittal plane kinematics during the vertical jump. Journal of Biomechanics 125: 110547, August 2021.

Stoeckl BD, Zlotnick HM, Farrell MJ, Fryhofer GW, Hast MW, Miller LM, Sennett ML, Baxter JR, Schaer TP, Mauck RL,teinberg DR: The Porcine Accessory Carpal Bone as a Model for Biologic Joint Replacement for Trapeziometacarpal Osteoarthritis. Acta Biomaterialia 15(129): 159-168, July 2021.

Zellers JA, Baxter Jr, Gravare-Silbernagel K: Functional ankle range of motion but not peak Achilles tendon force diminished with heel-rise and jumping tasks after Achilles tendon repair. American Journal of Sports Medicine 49(9): 2439-2446, July 2021.

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Last updated: 03/20/2023
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