Biomedical subjects

Guoan Li

Publications and source records attributed to Guoan Li.

44 records · Page 3Linked to original sources

PubMed2003

The kinematics of fixed- and mobile-bearing total knee arthroplasty.

The success of any total knee arthroplasty (TKA) is influenced by a complex interaction between component geometry and the surrounding soft tissues. The objective of this study was to investigate posterior femoral translation and tibial rotation in a single design posterior-stabilized TKA offering fixed- and mobile-bearing tibial components. Specifically, we examined whether mobile-bearing TKA restores normal knee translation and rotation better than fixed-bearing TKA design. Eleven human knee specimens retrieved postmortem were tested using a robotic system. The translation and rotation of the intact and reconstructed knees were compared. The data indicate that for all knees, posterior femoral translation occurs along the passive path and under muscle loading conditions. Furthermore, increasing flexion angle corresponded with increased internal tibial rotation. Femoral translation and tibial rotation for fixed- and mobile-bearing posterior-stabilized TKAs were similar despite component design variations. However, both arthroplasties only partially restored intact knee translation and rotation. The data presented here may serve as an aid in the development of a rationale for additional improvement in surgical techniques and prosthesis design, so that normal knee function may be restored.

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PubMed2003

Determination of optimal graft lengths for posterior cruciate ligament reconstruction--a theoretical analysis.

Various graft materials have been used in posterior cruciate ligament (PCL) reconstruction. However, it is unclear if these grafts can reproduce the structural behavior of the PCL. This paper analyzed the effect of graft length on the structural behavior of the graft using a minimal deformation energy method. An analytical solution was obtained to determine the optimal effective graft length that can best reproduce the structural behavior of the PCL. This optimal graft length was determined as a function of the axial rigidity of the graft. Two typical grafts, bone-patella tendon-bone (BPTB) and Achilles tendon, were analyzed. The data demonstrated that in order to reproduce the PCL behavior, the effective length of a BPTB graft (10 mm width) should be 34 mm, while the Achilles tendon graft (with a cross sectional area of 55 mn2) needs to be 48 mm in length. Longer grafts result in less resistance and shorter graft increased the graft resistance. An initial graft tension cannot help recreate the overall structural behavior of the PCL. These results suggest that graft length is an important surgical variable in PCL reconstruction. An optimal reconstruction of the PCL should reproduce the structural properties of the PCL by using a graft with an optimal length.

Achilles Tendon↗

PubMed2002

Biomechanical consequences of PCL deficiency in the knee under simulated muscle loads--an in vitro experimental study.

The mechanism of chronic degeneration of the knee after posterior cruciate ligament (PCL) injury is still not clearly understood. While numerous biomechanical studies have been conducted to investigate the function of the PCL with regard to antero-posterior stability of the knee, little has been reported on its effect on the rotational stability of the knee. In this study, eight cadaveric human knee specimens were tested on a robotic testing system from full extension to 120 degrees of flexion with the PCL intact and with the PCL resected. The antero-posterior tibial translation and the internal-external tibial rotation were measured when the knee was subjected to various simulated muscle loads. Under a quadriceps load (400 N) and a combined quadriceps/hamstring load (400/200 N), the tibia moved anteriorly at low flexion angles (below 60 degrees). Resection of the PCL did not significantly alter anterior tibial translation. At high flexion angles (beyond 60 degrees), the tibia moved posteriorly and rotated externally under the muscle loads. PCL deficiency significantly increased the posterior tibial translation and external tibial rotation. The results of this study indicate that PCL deficiency not only changed tibial translation, but also tibial rotation. Therefore, only evaluating the tibial translation in the anteroposterior direction may not completely describe the effect of PCL deficiency on knee joint function. Furthermore, the increased external tibial rotations were further hypothesized to cause elevated patello-femoral joint contact pressures. These data may help explain the biomechanical factors causing long-term degenerative changes of the knee after PCL injury. By fully understanding the etiology of these changes, it may be possible to develop an optimal surgical treatment for PCL injury that is aimed at minimizing the long-term arthritic changes in the knee joint.

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PubMed2002

The effect of axial tibial torque on the function of the anterior cruciate ligament: a biomechanical study of a simulated pivot shift test.

PURPOSE: Various techniques are used to produce the pivot shift phenomenon after anterior cruciate ligament (ACL) injury. In particular, the amount of applied axial tibial torque varies among examiners. Thus, the objective of this study was to determine the effect of the magnitude and direction of axial tibial torque in combination with valgus torque on the resulting knee kinematics during such a simulated pivot shift test. TYPE OF STUDY: This was a biomechanical study that used cadaveric knees with the intact knee of the same specimen serving as a control. METHODS: On 19 human cadaveric knees (age, 26 to 69 years), a constant 10-Nm valgus torque was applied at 15 degrees of knee flexion. Then, internal and external tibial torque was applied incrementally from 0 to 10 Nm and the resulting kinematics of the ACL-intact and ACL-deficient knee, as well as the in situ force in the ACL, were measured using a robotic/universal force-moment sensor testing system. RESULTS: In response to isolated valgus torque, the coupled anterior tibial translation for the ACL-intact and ACL-deficient knee was 1.6 +/- 2.4 mm and 8.5 +/- 4.7 mm, respectively; therefore the difference between the ACL-intact and ACL-deficient knee was 6.9 +/- 3.4 mm. With an external tibial torque greater than 5 Nm, the tibia translated up to 4 mm posteriorly for both the ACL-intact and ACL-deficient knee. Whereas, internal tibial torque greater than 1.6 Nm caused a rapid increase in coupled anterior tibial translation up to 10.2 mm in the ACL-deficient knee, while causing only a gradual increase for the ACL-intact knee. With excessive internal torque of 10 Nm, the difference in coupled anterior tibial translation was only 4.4 +/- 2.2 mm, suggesting a decrease in the sensitivity of the test. Correspondingly, the in situ force in the ACL under 10 Nm valgus tibial torque was 43 +/- 17 N, and increased up to 87 +/- 32 N as a 10-Nm internal torque was added. By applying a 3.3-Nm external tibial torque in addition to the 10-Nm valgus torque, the in situ force decreased to 21 +/- 14 N. CONCLUSIONS: This study showed that a minimal amount of internal torque in combination with valgus torque may be a suitable way to elicit a pivot shift from an ACL-deficient knee.

Adult↗

PubMed2002

Biomechanics of posterior-substituting total knee arthroplasty: an in vitro study.

The cam-spine system in posterior-substituting total knee arthroplasty was designed to improve posterior stability and to increase posterior femoral translation (rollback). Little is known on its effectiveness in the restoration of femoral rollback under functional loads. In the current study, the effect of cam-spine engagement on knee motion under simulated muscle loads was investigated using knees from cadavers. The translations of the lateral and medial femoral condyles of the knee before and after total knee arthroplasty were compared from 0 degrees to 120 degrees flexion. Cam-spine contact forces were measured under the same muscle loads. The posterior translations of both femoral condyles in the total knee arthroplasty were significantly lower than that of the native knee beyond full extension. Cam-spine engagement occurred between 60 degrees and 90 degrees flexion followed by an increase in posterior translation of both femoral condyles. However, the resultant femoral translation of the total knee arthroplasty was still lower than that of the native knee from 90 degrees to 120 degrees flexion. Knee motion after cam-spine engagement was independent of muscle loads, indicating the importance of the cam-spine mechanism at high flexion angles. Decreased posterior translation of both femoral condyles after total knee arthroplasty may be a limiting factor at high flexion.

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PubMed2002

The effect of anterior cruciate ligament injury on knee joint function under a simulated muscle load: a three-dimensional computational simulation.

Understanding the biomechanical effect of various factors on knee behavior after anterior cruciate ligament (ACL) injury or reconstruction is instrumental for the development of an optimal surgical treatment of ACL injury that can better restore normal knee function. This paper presents the application of a three-dimensional (3D) computational knee model for parametric studies of knee kinematics in response to simulated muscle loads. The knee model was constructed using the magnetic resonance images and biomechanical experimental data of the same cadaveric human knee specimen. The kinematics of the knee predicted by the computational model was compared with that measured from different specimens in a wide range of loading conditions and flexion angles. In general, the model predictions were within the range of experimental data. The model was then used to predict knee motion, ligament forces, and contact pressure in response to a simulated quadriceps force when the knee was ACL deficient. Partial ACL injury was simulated by reducing the stiffness of the ACL in the model. The results demonstrated that even with a reduction of 75% of the ACL stiffness, the ACL still carried a significant amount of the load (more than 58%) carried by an intact ACL. The kinematics (both tibial translation and rotation) varied less than 20% compared to that of the knee with intact ACL. The 3D computational model can be a powerful tool to simulate different variables that would influence knee function after ACL reconstruction, such as the initial tension of the ACL graft, the insertion sites of the graft, multibundle grafts, graft materials, and various physiological loading conditions.

Anterior Cruciate Ligament↗

PubMedDate not supplied

The effect of posterior cruciate ligament reconstruction on patellofemoral contact pressures in the knee joint under simulated muscle loads.

BACKGROUND: The mechanism of cartilage degeneration in the patellofemoral joint (PFJ) and medial compartment of the knee following posterior cruciate ligament (PCL) injury remains unclear. PCL reconstruction has been recommended to restore kinematics and prevent long-term degeneration. The effect of current reconstruction techniques on PFJ contact pressures is unknown. PURPOSE: To measure PFJ contact pressures after PCL deficiency and reconstruction. METHOD: Eight cadaveric knees were tested with the PCL intact, deficient, and reconstructed. Contact pressures were measured at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under simulated muscle loads. Knee kinematics were measured by a robotic testing system, and the PFJ contact pressures were measured using a thin film transducer. A single bundle achilles tendon allograft was used in the reconstruction. RESULTS: PCL deficiency significantly increased the peak contact pressures measured in the PFJ relative to the intact knee under both an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Reconstruction did not significantly reduce the increased contact pressures observed in the PCL-deficient knee. CONCLUSION: The elevated contact pressures observed in the PCL-deficient knee and reconstructed knee might contribute to the long-term degeneration observed in both the non-operatively treated and PCL-reconstructed knees.

Aged↗

PubMedDate not supplied

The biomechanical effect of posterior cruciate ligament reconstruction on knee joint function. Kinematic response to simulated muscle loads.

BACKGROUND: The effectiveness of posterior cruciate ligament reconstruction in restoring normal kinematics under physiologic loading is unknown. HYPOTHESIS: Posterior cruciate ligament reconstruction does not restore normal knee kinematics under muscle loading. STUDY DESIGN: In vitro biomechanical study. METHODS: Kinematics of knees with an intact, resected, and reconstructed posterior cruciate ligament were measured by a robotic testing system under simulated muscle loads. Anteroposterior tibial translation and internal-external tibial rotation were measured at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under posterior drawer loading, quadriceps muscle loading, and combined quadriceps and hamstring muscle loading. RESULTS: Reconstruction reduced the additional posterior tibial translation caused by ligament deficiency at all flexion angles tested under posterior drawer loading. Ligament deficiency increased external rotation and posterior translation at angles higher than 60 degrees of flexion when simulated muscle loading was applied. Posterior cruciate ligament reconstruction reduced the posterior translation and external rotation observed in posterior cruciate ligament-deficient knees at higher flexion angles, but differences were not significant. CONCLUSION: Under physiologic loading conditions, posterior cruciate ligament reconstruction does not restore six degree of freedom knee kinematics. CLINICAL RELEVANCE: Abnormal knee kinematics may lead to development of long-term knee arthrosis.

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