Sensory Motor Performance Program

Biodynamics Lab

Mechanisms of ACL Injuries
Mechanisms of noncontact ACL injuries are still not clearly understood. It is hypothesized that ACL can be injured by direct stretch during tibial internal rotation, and for knees with certain 3-D shapes of the intercondylar notch, ACL can be injured by impingement against the lateral notch wall during tibial external rotation/abduction in flexed knees. In general, ACL could also impinge the notch roof at hyperextension. Mechanisms of noncontact ACL injuries during various 3-D tobiofemoral movements were evaluated in cadaver knee specimens using multiple methods, including direct measurement of the ACL strain and its impingement against the intercondylar notch using ultra-microminiature (UM-DVRT) strain sensor and paper-thin force sensor, respectively, arthroscopy with the impingement measured dynamically by a Tekscan pressure sensor, and fluoroscopy.

 

Modeling of ACL Impingement
The femur and tibia are digitized using a laser scanner. A combination of rotary and planar scans performed by the laser scanner generated an accurate 3-D model of the bines represented as a point cloud. A 3-D geometric reconstruction of the knee specimen is generated based on the digitized data points. A 3-D ACL impingement model can then be implemented using data from an individual cadaveric knee with representative ACL impingement, which is loaded passively to induce ACL impingement with the impingement force and 6-DOF tibiofemoral kinematics measured. Thedigitized intercodylar notch surfaces are surface-fitted using bicubic splines with continuity up to the second derivative. The model detects ACL impingement during tibiofemoral movement and uses a "crawling" algorithm to determine the deformed geometry of the impinging ACL.

 

Compensatory Mechanisms for ACL Injury and New Rehabilitation Protocols
Compensation for ACL injuries have been studied from several aspects: 1) EMG signals from multiple muscles during locomotion are analyzed, which shows that ACL injured patients tend to have stronger lateral hamstring and weaker medial hamstring contraction during certain phases of locomotion (Hypothesis: to externally rotate the tibia on the femur to unload the ACL and avoid unstable knee positions). Six degrees-of-freedom knee kinematics during locomotion are obtained and compared between injured and uninjured populations, which corroborates the above EMG finding. Furthermore, individual hamstrings are activated selectively through electrical stimulation and the resulting six-axis forces/moments show that the medial and lateral hamstrings generate significant internal and external rotation torque, respectively. Finally, it has been found that chronic ACL injured patients developed significantly higher strength ratio of external rotation over internal rotation, indicating the gradually developed compensation. Along the same line of thinking, we are developing a new rehabilitation protocol for ACL injured patients to selectively and differentially strengthen those muscles which help protect and unload the ACL

 Fig. 1. The six-degrees of freedom goniometer used to measure the tibial movement relative to the femur in three-dimensional space. The femoral and tibial segments of the goniometer were strapped to the thigh and leg, respectively. Six precision potentiometers with bearings were used to measure the six-degrees of freedom movement. A suction cup was aligned with and pressed against the lateral epicondyle.

ACL Strain During "Locomotion"
Need for the compensatory mechanism depends on whether the ACL is loaded during free-speed walking. Fresh-frozen cadaver knees were used to evaluate the ACL strain during simulated free-speed walking. The cadaver knees was moved following the average knee flexion pattern of the 30 normal subjects using a computer-controlled servomotor, and the ACL strain was measured with a differential variable reluctance transducer (MicroStrain, Burlington, Vermont). The "free-speed walking" was repeated with the tibia placed at different axial rotation and anteroposterior translation positions.


(Click the figure for a video clip)
ACL strain during simulated "free-speed walking" using a cadaver model. Top plot: Knee flexion as a function of stride %; Bottom plot: ACL strain during simulated "free-speed walking", averaged over 48 strides. From top to bottom, the five curves represent the ACL strain with the tibia positioned at internal rotation (7º) plus anterior translation (10 mm), internal rotation (7º), neutral, external rotation (7º), and external rotation (7º) plus posterior translation (10 mm), respectively.

The results showed that the ACL strain varied with knee flexion systematically and the ACL was loaded considerably during "free-speed walking", especially at full knee extension. Furthermore, ACL strain increased substantially with tibial internal rotation and anterior translation and decreased markedly with tibia external rotation and posterior translation. Considering that the tibia was positioned more anteriorly during locomotion in ACL-deficient knees, it made it more likely that the ACL of the patients would be loaded (or getting into the "ACL-loading positions") in locomotion, which made the compensatory mechanism based on tibial external rotation useful.

Relevant Publications
Fung, D. T., R. W. Hendrix, J. L. Koh and L.-Q. Zhang (2005). Modeling ACL Impingement Based on Individual Patients' MRI Data. 51st Annual Meeting of the Orthopaedic Research Socienty, Washington, DC

Park, H.-S., C. Ahn and L.-Q. Zhang (2005). Passive Knee Joint Properties in Tibial Rotation in Men and Women. XXth Congress of the International Society of Biomechanics and 29th Annual Meeting of the American Society of Biomechanics, Cleveland, OH.

Fung, D. T., R. W. Hendrix, J. L. Koh and L.-Q. Zhang (2005). Modeling ACL Impingement Based on Individual Patients' MRI Data. 51st Annual Meeting of the Orthopaedic Research Society, Washington, DC.

Fung, D. T. and Zhang, L.-Q. (2003) Modeling of ACL impingement against the intercondylar notch wall. Clinical Biomechanics, Vol. 18, 933-941.

Li-Qun Zhang, Gordon Nuber, Mark Bowen, Jason Koh, and Jesse Butler, "Multi-Axis Muscle Strength in Anterior Cruciate Ligament Injured Knees - Compensatory Mechanism, Med. Sci. Sport Exerc., Vol. 34, 2-8, 2002.

L.-Q. Zhang, R. G. Shiavi, T. Limbird, J. M. Minorik, “Three-Dimensional Kinematics of ACL Deficient Knees During Locomotion: Compensatory Mechanism,” Gait & Posture, Vol. 17, 34-42, 2003.

Li-Qun Zhang and Guangzhi Wang, "Dynamic and Static Control of the Human Knee Joint in Abduction-Adduction", J. Biomech., Vol. 34, 1107-1115, 2001.

Li-Qun Zhang, Dali Xu, Guangzhi Wang, and Ronald W. Hendrix, "Muscle Strength in Knee Varus and Valgus", Med. Sci. Sport Exerc., Vol. 33, No. 7, 1194-1199, 2001.

Fung, D., and Zhang, L.-Q. (2002) Mathematical modeling of ACL impingement against the intercondylar notch wall. In Proceedings of 4th World Congress of Biomechanics, Calgary, Alberta.

Zhang L-Q, Minorik J M, Lin F, Koh J L, Makhsous M, and Bai Z. ACL strain during simulated free-speed walking. 25th Ann. Meeting Am. Soc. Biomech., San Diego, CA, 2001.

Makhsous, M., Lin, F., and Zhang, L.-Q. (2004) Stabilization functions of passive and active structures crossing the glenohumeral joint. Clinical Biomechanics. 19: 107-114.

Koh, J. L., K. Wirsing, E. Lautenschlager and L.-Q. Zhang, "The Effect of Graft Height Mismatch on Contact Pressure Following Osteochondral Grafting: A Biomechanical Study." American Journal of Sports Medicine, 32(2): 317-320, 2004.

Nam, E., Makhsous, M., Koh, J., Bowen, M. K., Nuber, G. W., and Zhang, L.-Q. Biomechanical and Histological Evaluation of Osteochondral Transplantation in a Rabbit Model, American Journal of Sports Medicine: Vol. 32, 308-316, 2004.

G. Nuber, L.-Q. Zhang, M. Bowen, H. Huang, and W. Z. Rymer, “Patellar Tendon Reflex of ACL Injured and Reconstructed Knees,” Trans. 44th Ann. Meet. Orthop. Res. Soc., New Orleans, 389, March 16-19, 1998.

L.-Q. Zhang, S. Dobson, R. G. Shiavi, S. Peterson, and T. Limbird, “Changes in Knee Kinematics Caused by ACL Deficiency During Fast Walking,” Proc. 3rd Ann. Gait and Clin. Movement Analysis Meeting, San Diego, April 15-18, 1998.

L. Zhang and R. G. Shiavi, “Analysis of Six Degrees of Freedom Knee Kinematics of ACL Injured and Uninjured Knees During Locomotion”, Proc. 10th Int. Soc. Electrophysiol. Kinesiol., Charleston, pp. 128-129, 1994.

L. Zhang, R. Shiavi, M. Hunt, and J. J. Chen, “Clustering analysis and Pattern Discrimination of EMG Linear Envelopes”, IEEE Trans. Biomed. Eng., Vol. 38, pp. 777-784, 1991.

R. Shiavi, L. Zhang, T. Limbird, and M. A. Edmondstone, “Pattern Analysis of Electromyographic Linear Envelopes Exhibited by Subjects with Uninjured and Injured Knees During Free and Fast Speed Walking”, J. Orthopaedic Research, Vol. 10, pp. 226-236, 1992.

Lennie Kahn, Li-Qun Zhang, and Gregory Portland, “Mechanical actions of individual muscles at the knee joint with varus/valgus malalignment.” In Proceedings of BMES-EMBS 1st Joint Meeting., Atlanta, Oct., 1999.

Zhang, L.-Q., Butler, J., Wang, G., Nuber, G., Zeng, K., and Rymer, W. Z., 1997, "Mechanical Actions of Individual Muscles at the Human Knee Joint," Proc. 15th Conf. Am Soc. Biomech., Clemson, SC, pp. 290-291.