The human posterior cruciate ligament complex: an interdisciplinary study. Ligament morphology and biomechanical evaluation.

To study the structural and functional properties of the human posterior cruciate ligament complex, we measured the cross-sectional shape and area of the anterior cruciate, posterior cruciate, and meniscofemoral ligaments in eight cadaveric knees. The posterior cruciate ligament increased in cross-sectional area from tibia to femur, and the anterior cruciate ligament area decreased from tibia to femur. The meniscofemoral ligaments did not change shape in their course from the lateral meniscus to their femoral insertions. The posterior cruciate ligament cross-sectional area was approximately 50% and 20% greater than that of the anterior cruciate ligament at the femur and tibia, respectively. The meniscofemoral ligaments averaged approximately 22% of the entire cross-sectional area of the posterior cruciate ligament. The insertion sites of the anterior and posterior cruciate ligaments were evaluated. The insertion sites of the anterior and posterior cruciate ligaments were 300% to 500% larger than the cross-section of their respective midsubstances. We determined, through transmission electron microscopy, fibril size within the anterior and posterior cruciate ligament complex from the femur to the tibia. The posterior cruciate ligament becomes increasingly larger from the tibial to the femoral insertions, and the anterior cruciate ligament becomes smaller toward the femoral insertion. We evaluated the biomechanical properties of the femur-posterior cruciate ligament-tibia complex using 14 additional human cadaveric knees. The posterior cruciate ligament was divided into two functional components: the anterolateral, which is taut in knee flexion, and the posteromedial, which is taut in knee extension. The anterolateral component had a significantly greater linear stiffness and ultimate load than both the posteromedial component and meniscofemoral ligaments. The anterolateral component and the meniscofemoral ligaments displayed similar elastic moduli, which were both significantly greater than that of the posteromedial component.

Obesity and symptomatic osteoarthritis of the knee.

Given the growing prevalence of obesity around the world and its association with osteoarthritis of the knee, orthopaedic surgeons need to be familiar with the management of the obese patient with degenerative knee pain. The precise mechanism by which obesity leads to osteoarthritis remains unknown, but is likely to be due to a combination of mechanical, humoral and genetic factors. Weight loss has clear medical benefits for the obese patient and seems to be a logical way of relieving joint pain associated with degenerative arthritis. There are a variety of ways in which this may be done including diet and exercise, and treatment with drugs and bariatric surgery. Whether substantial weight loss can delay or even reverse the symptoms associated with osteoarthritis remains to be seen. Surgery for osteoarthritis in the obese patient can be technically more challenging and carries a risk of additional complications. Substantial weight loss before undertaking total knee replacement is advisable. More prospective studies that evaluate the effect of significant weight loss on the evolution of symptomatic osteoarthritis of the knee are needed so that orthopaedic surgeons can treat this patient group appropriately.

Biomechanical function of the human anterior cruciate ligament.

Knowledge about the biomechanical function of the anterior cruciate ligament (ACL) is very important in the treatment of the ACL deficient knee. This article presents an overview of the biomechanical function of the ACL, including its structural and mechanical properties as well as its role in knee stabilization and normal kinematics. Tensile properties of the prospective biological grafts and future directions in ACL research are also discussed.

Anatomical and biomechanical characteristics of human meniscofemoral ligaments.

The meniscofemoral ligaments (MFL) of 26 human cadaver knees were studied to determine their structural importance. The incidence of at least one MFL in each of the specimens studied was 100%, and 46% of the specimens had both MFL ligaments (Humphry and Wrisberg). Another 23% had a single Humphry ligament, and the remaining 31% had a single Wrisberg ligament. A laser micrometer system was used to measure cross-sectional shape and area. The average cross-sectional areas of the Humphry and Wrisberg ligaments were 7.8 +/- 4.7 mm2 and 6.7 +/- 4.1 mm2, respectively. In specimens with both a Humphry and Wrisberg ligament, the larger ligament area was on average 100% greater than the smaller ligament area. The average ratios of the cross sectional areas of Wrisberg and Humphry to that for the PCL within the same knee were 12.0% +/- 7.7% and 11.9% +/- 5.7%, respectively. The structural properties of the MFL bone-ligament-meniscus complex and the mechanical properties of the MFL midsubstance were determined by uniaxial tensile testing. The average stiffness, ultimate load, and energy absorbed at failure were, respectively, 49.0 +/- 18.4 N/mm, 297.4 +/- 141.4 N and 1125.4 +/- 735.8 N/mm. The tangent modulus between 4% and 7% strain was 355.1 +/- 234.0 MPa. Our findings suggest that the MFL is a significant biomechanical structure in the knee because of its size, stiffness, and strength.

Effect of knee flexion on the in situ force distribution in the human anterior cruciate ligament.

This study was conducted to evaluate the effect of applied load on the magnitude, direction, and point of tibial intersection of the in situ forces of the anteromedial (AM) and posterolateral (PL) bands of the human anterior cruciate ligament (ACL) at 30 degrees and 90 degrees of knee flexion. An Instron was used to apply a 100 N anterior shear force to 11 human cadaver knees, 6 at 30 degrees of knee flexion and 5 at 90 degrees of knee flexion. A Universal Force Sensor (UFS) recorded the resultant 6 degree-of freedom (DOF) forces/moments. Each specimen then underwent serial removal of the AM and PL bands. With the knee limited to 1 DOF (anteroposterior), tests were performed before and after each structure was removed. Because the path was identical in each test, the principle of superposition was applied. Thus, the difference between the resultant forces could be attributed to the force carried by the structure just removed. The magnitudes of force in the ACL at 30 degrees and 90 degrees of knee flexion were 114.1 +/- 7.4 N and 90.8 +/- 8.3 N, respectively (P < 0.05). At 30 degrees, the AM and PL bundles carried 95% and 4% of the total ACL force, respectively. At 90 degrees, the AM and PL bands carried 85% and 13%, respectively (P < 0.05). The direction of the in situ force in the whole ACL as well as its two bands correlated with the anatomic orientation of the ligament.(ABSTRACT TRUNCATED AT 250 WORDS)

A functional comparison of animal anterior cruciate ligament models to the human anterior cruciate ligament.

Many investigators have used animal models to clarify the role of the human anterior cruciate ligament (ACL). Because none of these models are anatomically and biomechanically identical to the human ACL, there exists a need for an objective comparison of these models. To do this, we used a universal force-moment sensor to measure and compare the in situ forces, including magnitude and direction, of the ACL and the anteromedial (AM) and posterolateral (PL) bundles of human, pig, goat, and sheep knees. An Instron was used to apply 50 and 100 N anterior tibial loads at 90 degrees of knee flexion, while a universal force-moment sensor was used to measure the forces applied by the ACL to the tibia, the in situ force of the ACL. We found significant differences between the magnitude of force experienced by the goat and sheep ACL and AM and PL bundles when compared with the human ACL and AM and PL bundles. Also, the direction of the in situ force in the ACL and AM bundles of the goat and sheep were different from the human. The pig knee differed from the human only in the magnitude and direction of the in situ force in the PL bundle in response under anterior tibial loading. A tally of the significant differences between the animal models and the human knees indicates that goat and sheep knees may have limitations in modeling the human ACL, while the pig knee may be the preferred model for experimental studies.