Cerebral palsy (CP) is a neurological disorder of development affecting more than 750,000 people in the US (1). A common source of morbidity in this condition is gait disorders, with crouch gait being one of the most common forms (3). Crouch is a fatiguing gait (4-5), characterized by excessive knee flexion during stance (6-7), that often requires surgical correction to allow patients to continue to ambulate as they mature (8). Distal femoral extension osteotomy coupled with patellar tendon advancement (DFEO + PTA) is a promising surgical approach for reducing crouch and restoring quadriceps strength in these children (2, 9). While short term outcomes are generally good, little is known about the why the coupled procedures are better than either procedure alone, and which surgical parameters are most efficacious. Perhaps more importantly, the long term implications of the procedures on skeletal growth and cartilage health are unclear (10). This project aims to use musculoskeletal modeling, dynamic magnetic resonance imaging (MRI), and gait analysis techniques to investigate the influence of DFEO + PTA on knee extensor mechanics. Surgical simulations will be performed on computer models of the musculoskeletal system to gain insights into how the degree of osteotomy and patellar advancement affects muscle moment arms, muscle operating lengths, and knee extensor strength post-surgery. A novel dynamic MRI technique (11) will then be used to discover changes in kinematics and cartilage contact that can result from the substantial surgical corrections. Finally, gait analysis will be coupled with computational models to relate surgically induced changes in joint mechanics to functional gait performance. The anticipated outcome is a scientific understanding of the surgical effects on the musculoskeletal system, which can be used to mitigate the potential for adverse outcomes in both the short- and long-term. Through the completion of this project as part of this fellowship, Rachel Lenhart will be exposed to many areas of experimental and computational biomechanics research. Her training plan also includes coursework in mechanical and biomedical engineering to develop her technical skills to compliment her formal medical training. Given that her end goal is to be a successful physician scientist, development of clinical and communication skills will also be a focus. Through consistent participation in the clinic, continual practice and feedback on writing and presentation abilities, and regular meetings with her sponsors and advisory team, Rachel will be poised for success both as a pediatric orthopedic surgeon and as an independent biomechanics researcher.

Public Health Relevance

This study proposes to study changes in musculoskeletal mechanics that result from orthopedic surgical procedures used to correct gait disorders in children. In particular, computer modeling, dynamic MRI, and gait analysis will investigate surgically-induced changes at the knee after correction of crouch gait. This will provide scientifi evidence for optimizing surgical variables, helping to enhance patient-specific outcomes.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Individual Predoctoral NRSA for M.D./Ph.D. Fellowships (ADAMHA) (F30)
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Special Emphasis Panel (ZRG1)
Program Officer
Panagis, James S
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University of Wisconsin Madison
Engineering (All Types)
Biomed Engr/Col Engr/Engr Sta
United States
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Brandon, Scott C E; Thelen, Darryl G; Smith, Colin R et al. (2018) The coupled effects of crouch gait and patella alta on tibiofemoral and patellofemoral cartilage loading in children. Gait Posture 60:181-187
Bittmann, Moria F; Lenhart, Rachel L; Schwartz, Michael H et al. (2018) How does patellar tendon advancement alter the knee extensor mechanism in children treated for crouch gait? Gait Posture 64:248-254
Lenhart, Rachel L; Youlo, Sylvester; Schroth, Mary K et al. (2017) Radiographic and Respiratory Effects of Growing Rods in Children With Spinal Muscular Atrophy. J Pediatr Orthop 37:e500-e504
Lenhart, R L; Smith, C R; Schwartz, M H et al. (2017) The effect of distal femoral extension osteotomy on muscle lengths after surgery. J Child Orthop 11:472-478
Lenhart, Rachel L; Brandon, Scott C E; Smith, Colin R et al. (2017) Influence of patellar position on the knee extensor mechanism in normal and crouched walking. J Biomech 51:1-7
Smith, Colin R; Vignos, Michael F; Lenhart, Rachel L et al. (2016) The Influence of Component Alignment and Ligament Properties on Tibiofemoral Contact Forces in Total Knee Replacement. J Biomech Eng 138:021017
Smith, Colin R; Lenhart, Rachel L; Kaiser, Jarred et al. (2016) Influence of Ligament Properties on Tibiofemoral Mechanics in Walking. J Knee Surg 29:99-106
Lenhart, Rachel L; Smith, Colin R; Vignos, Michael F et al. (2015) Influence of step rate and quadriceps load distribution on patellofemoral cartilage contact pressures during running. J Biomech 48:2871-8
Lenhart, Rachel L; Kaiser, Jarred; Smith, Colin R et al. (2015) Prediction and Validation of Load-Dependent Behavior of the Tibiofemoral and Patellofemoral Joints During Movement. Ann Biomed Eng 43:2675-85