Injuries to the anterior cruciate ligament (ACL) are occurring at epidermic proportions from athletic endeavors. The most common surgical treatment of an ACL deficiency is ACL reconstruction using autogenous grafts. Although reconstructive techniques are commonly employed, graft implantation variables and post-operative rehabilitation programs remain controversial and unknown. Since the goal of an ACL reconstruction is to restore the normal biomechanics of the knee, it is important to understand the strain behavior of the normal ACL. We propose to continue our in vivo investigation of strain in the normal ACL focusing on commonly prescribed rehabilitation activities (Group #1). In addition, we would like to measure the stress and strain in two commonly used autografts (patellar tendon and hamstrings tendon) during ACL reconstructive surgery (Group #2). The group #1 volunteers are patients who are candidates for arthroscopic meniscectomy. After the routine surgical procedure, a Hall effect strain transducer (HEST) will be implanted into the anteromedial band of the normal ACL. Patients will then perform different rehabilitation activities; isotonic contractions, isometric contractions, squatting, biking, and stair climbing. Strain will be determined as a function of flexion angle and compared with analytical predictions of the shear forces at the knee during these activities. The group #2 patients are volunteers who are candidates for arthroscopic reconstruction of the knee. Graft type will be selected randomly. During graft implantation, a tension measuring device (tensiometer) will be used to document graft placement and set initial graft tension. A modified HEST which incorporates a pressure sensor, calibrated to tensile stress, will be attached to the graft. Stress, strain and laxity measurements will be performed to determine the initial tension required to restore normal knee stability. The graft will then be fixed and the surgery completed. The stress-strain biomechanics will then be measured during anteroposterior shear loading and passive flexion-extension of the knee. Stress-strain comparisons will be made between the two graft types and the normal ACL. This will be the first study to determine if the reconstructed ACL restores normal knee biomechanics. By using these experimental methods, the strain biomechanics of the normal ACL will be characterized, the effects of initial graft tension and graft replacement will be evaluated, and the stress-strain biomechanics of different grafts will be determined. The results of the proposed study will assist the clinician in determining the best surgical treatment and post-operative rehabilitation program for patients undergoing reconstructive surgery. These variables determine the long-term success of the grafts and may reduce cartilage degeneration which has been shown to persists after ACL reconstruction.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
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Orthopedics and Musculoskeletal Study Section (ORTH)
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University of Vermont & St Agric College
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United States
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Fleming, Braden C (2003) Biomechanics of the anterior cruciate ligament. J Orthop Sports Phys Ther 33:A13-5
Fleming, B C; Peura, G D; Beynnon, B D (2000) Factors influencing the output of an implantable force transducer. J Biomech 33:889-93
Fleming, B C; Good, L; Peura, G D et al. (1999) Calibration and application of an intra-articular force transducer for the measurement of patellar tendon graft forces: an in situ evaluation. J Biomech Eng 121:393-8
Fleming, B C; Beynnon, B D; Renstrom, P A et al. (1999) The strain behavior of the anterior cruciate ligament during stair climbing: an in vivo study. Arthroscopy 15:185-91
Fleming, B C; Beynnon, B D; Renstrom, P A et al. (1998) The strain behavior of the anterior cruciate ligament during bicycling. An in vivo study. Am J Sports Med 26:109-18
Beynnon, B D; Fleming, B C (1998) Anterior cruciate ligament strain in-vivo: a review of previous work. J Biomech 31:519-25
Beynnon, B D; Johnson, R J; Fleming, B C et al. (1997) The effect of functional knee bracing on the anterior cruciate ligament in the weightbearing and nonweightbearing knee. Am J Sports Med 25:353-9
Beynnon, B D; Johnson, R J; Fleming, B C et al. (1997) The strain behavior of the anterior cruciate ligament during squatting and active flexion-extension. A comparison of an open and a closed kinetic chain exercise. Am J Sports Med 25:823-9
Beynnon, B; Yu, J; Huston, D et al. (1996) A sagittal plane model of the knee and cruciate ligaments with application of a sensitivity analysis. J Biomech Eng 118:227-39
Beynnon, B D; Fleming, B C; Johnson, R J et al. (1995) Anterior cruciate ligament strain behavior during rehabilitation exercises in vivo. Am J Sports Med 23:24-34

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