Short collagen fibers provide control of contraction and permeability in fibroblast-seeded collagen gels.

Tissue engineering may allow for the reconstruction of breast, facial, skin, and other soft tissue defects in the human body. Cell-seeded collagen gels are a logical choice for creating soft tissues because they are biodegradable, mimic the natural tissue, and provide a three-dimensional environment for the cells. The main drawback associated with this approach, however, is the subsequent contraction of the gel by the constituent cells, which severely reduces permeability, initiates apoptosis, and precludes control of the resulting shape and size of the construct. In this study, type I collagen gels were seeded with fibroblasts and cast either with or without the addition of short collagen fibers. Gel contraction was monitored and permeability was assessed after 7 and 14 days in culture. The addition of short collagen fibers both significantly limited contraction and increased permeability of fibroblast-seeded collagen gels. The addition of short collagen fibers had no detrimental effect on cell proliferation, and there were a high number of viable fibroblasts in gels with fibers and gels without fibers. Gels containing short collagen fibers demonstrated permeabilities that were 100 to 1000 times greater than controls and also closely maintained their casting dimensions (never less than 96% of original). By limiting contraction and maintaining permeability, the incorporation of short collagen fibers should enable the creation of larger constructs by allowing for greater nutrient diffusion, and permit the creation of more complicated shapes during gel casting.

The forces in the anterior cruciate ligament and knee kinematics during a simulated pivot shift test: A human cadaveric study using robotic technology.

PURPOSE: Although it is well known that the anterior cruciate ligament (ACL) is a primary restraint of the knee under anterior tibial load, the role of the ACL in resisting internal tibial torque and the pivot shift test is controversial. The objective of this study was to determine the effect of these 2 external loading conditions on the kinematics of the intact and ACL-deficient knee and the in situ force in the ACL. TYPE OF STUDY: This study was a biomechanical study that used cadaveric knees with the intact knee of the specimen serving as a control. MATERIALS AND METHODS: Twelve human cadaveric knees were tested using a robotic/universal force-moment sensor testing system. This system applied (1) a 10-Newton meter (Nm) internal tibial torque and (2) a combined 10-Nm valgus and 10-Nm internal tibial torque (simulated pivot shift test) to the intact and the ACL-deficient knee. RESULTS: In the ACL-deficient knee, the isolated internal tibial torque significantly increased coupled anterior tibial translation over that of the intact knee by 94%, 48%, and 19% at full extension, 15 degrees, and 30 degrees of flexion, respectively (P <.05). In the case of the simulated pivot shift test, there were similar increases in anterior tibial translation, i.e., 103%, 61%, and 32%, respectively (P <.05). Furthermore, the anterior tibial translation under the simulated pivot shift test was significantly greater than under an isolated internal tibial torque (P <.05). Under the simulated pivot shift test, the in situ forces in the ACL were 83 +/- 16 N at full extension and 93 +/- 23 N at 15 degrees of knee flexion. These forces were also significantly higher when compared with those for an isolated internal tibial torque (P <.05). CONCLUSION: Our data indicate that the ACL plays an important role in restraining coupled anterior tibial translation in response to the simulated pivot shift test as well as under an isolated internal tibial torque, especially when the knee is near extension. These findings are also consistent with the clinical observation of anterior tibial subluxation during the pivot shift test with the knee near extension.

Mechanical behavior of two hamstring graft constructs for reconstruction of the anterior cruciate ligament.

We compared the mechanical behavior of two common hamstring graft constructs that are frequently used for reconstruction of the anterior cruciate ligament-Graft A: quadrupled semitendinosus tendon fixed with titanium button/polyester tape and suture/screw post, and Graft B: a double semitendinosus and double gracilis tendon fixed with a cross pin and two screws over washers. The experimental protocol used to evaluate each graft construct included stress relaxation (with and without preconditioning), cyclic loading, and a tensile load-to-failure test. The amount of stress relaxation without preconditioning was 60.6% for Graft A and 53.8% for Graft B. With preconditioning, it significantly decreased (p < 0.05) to 48.7 and 42.3%, respectively. Elongation of the graft construct in response to 100 cycles of loading (20-150 N) was 1.8 and 0.6% of the original length for Grafts A and B, respectively. However, after a series of five cyclic loading tests, the residual permanent elongation for each construct was 3.8 +/- 1.2 and 0.3 +/- 0.2 mm, a significant difference (p < 0.05) between the two graft constructs. Further analysis found more than 90% of the permanent elongation in the proximal and distal regions of Graft A, which consisted of polyester tape tied to a titanium button (proximal) and sutures tied around a screw post (distal). The tensile load-to-failure tests also revealed significant differences (p < 0.05) between the two graft constructs. Linear stiffness was 32 +/- 1 and 119 +/- 19 Nmm and ultimate load was 415 +/- 36 and 658 +/- 128 N for Grafts A and B, respectively. For Graft A, the polyester tape consistently failed; for Graft B, slippage or tearing from the washers was the mode of failure. We conclude that a quadruple-hamstring graft fixed over a cross pin proximally and with metal washers distally (Graft B) has less permanent elongation in response to cyclic loading and has structural properties superior to those of a graft construct that includes suture and tape material (Graft A). The large permanent elongation following repetitive loading of a graft construct with tape and suture material during the early postoperative period is of concern.

Importance of the medial meniscus in the anterior cruciate ligament-deficient knee.

The incidence of meniscal tears in the chronically anterior cruciate ligament-deficient knee is increased, particularly in the medial meniscus because it performs an important function in limiting knee motion. We evaluated the role of the medial meniscus in stabilizing the anterior cruciate ligament-deficient knee and hypothesized that the resultant force in the meniscus is significantly elevated in the anterior cruciate ligament-deficient knee. To test this hypothesis, we employed a robotic/universal force-moment sensor testing system to determine the increase in the resultant force in the human medial meniscus in response to an anterior tibial load following transection of the anterior cruciate ligament. We also measured changes in the kinematics of the knee in multiple degrees of freedom following medial meniscectomy in the anterior cruciate ligament-deficient knee. In response to a 134-N anterior tibial load, the resultant force in the medial meniscus of the anterior cruciate ligament-deficient knee increased significantly compared with that in the meniscus of the intact knee; it increased by a minimum of 10.1 N (52%) at full knee extension to a maximum of 50.2 N (197%) at 60 degrees of flexion. Medial meniscectomy in the anterior cruciate ligament-deficient knee also caused a significant increase in anterior tibial translation in response to the anterior tibial load, ranging from an increase of 2.2 mm at full knee extension to 5.8 mm at 60 degrees of flexion. Conversely, coupled internal tibial rotation in response to the load decreased significantly, ranging from a decrease of 2.5 degrees at 15 degrees of knee flexion to 4.7 degrees at 60 degrees of flexion. Our data confirm the hypothesis that the resultant force in the medial meniscus is significantly greater in the anterior cruciate ligament-deficient knee than in the intact knee when the knee is subjected to anterior tibial loads. This indicates that the demand on the medial meniscus in resisting anterior tibial loads is increased in the anterior cruciate ligament-deficient knee compared with in the intact knee, suggesting a mechanism for the increased incidence of medial meniscal tears observed in chronically anterior cruciate ligament-deficient patients. The large changes in kinematics due to medial meniscectomy in the anterior cruciate ligament-deficient knee confirm the important role of the medial meniscus in controlling knee stability. These findings suggest that the reduction of resultant force in the meniscus may be a further motive for reconstructing the anterior cruciate ligament, with the goal of preserving meniscal integrity.

Hamstring graft motion in the femoral bone tunnel when using titanium button/polyester tape fixation.

The objective of this study was to determine the relative motion of a quadruple hamstring graft within the femoral bone tunnel (graft-tunnel motion) under tensile loading. Six graft constructs were prepared from the semitendinosus and gracilis tendons of human cadavers and were fixed with a titanium button and polyester tape within a bone tunnel in a cadaveric femur. Three different lengths of polyester tape (15, 25, and 35 mm loops) were evaluated. The femur was held stationary and uniaxial tensile loads were applied to the distal end of the graft using a materials testing machine. Each construct was subjected to loading for ten cycles with upper limits of 50 N, 100 N, 200 N and 300 N. Graft-tunnel motion was then determined using the distances between reflective tape markers placed on the hamstring graft and at the entrance to the femoral bone tunnel, which were tracked with a high-resolution video system. Graft-tunnel motion was found to range from 0.7 +/- 0.2 mm to 3.3 +/- 0.2 mm, and significant increases in graft-tunnel motion were observed with increasing tensile loads (P < 0.05). Shorter tape length (15 mm) resulted in significantly less motion when compared to longer tape length (35 mm) (P < 0.05). We conclude that graft-tunnel motion is significant and should be considered when using this fixation technique. Early stress on the graft, as seen in postoperative rehabilitation exercises and athletic activities, may cause large graft-tunnel motion before graft incorporation is complete. A shorter distance between the tendon tissue and the titanium button is recommended to minimize the amount of graft-tunnel motion. Alternative fixation materials to polyester tape, or different fixation techniques, need to be developed such that graft-tunnel motion can be reduced. Further studies are needed to evaluate the effect of graft-tunnel motion on graft incorporation in the bone tunnel.

Injury and reconstruction of the anterior cruciate ligament and knee osteoarthritis.

OBJECTIVE: The objective of this study was to study injury and reconstruction of the anterior cruciate ligament (ACL) and their effects on knee osteoarthritis. DESIGN: This manuscript discusses the function of knee ligaments, including the basic mechanical properties, the structural properties of their respective bone-ligament-bone complexes, as well as their time- and history-dependent viscoelastic characteristics. The in-situ forces in the ACL and its replacement grafts and knee kinematics before and after ACL reconstruction are also examined. RESULTS: A robotic/universal force-moment sensor (UFS) testing system has been developed which offers a unique method in determining the multiple-degree of freedom knee kinematics and in-situ forces in human cadaveric knees. Under a 110 N anterior tibial load we found at flexion angles of 15 degrees or lower, there was a significantly larger in-situ force in the PL bundle (approximately 75 N) of the ACL as compared to the AM bundle (approximately 35 N)(P < 0.05). We also found that a quadruple semitendinosus and gracilis tendon ACL graft may be better at fully restoring in-situ forces for the whole range of knee flexion when compared to a bone-patellar tendon-bone ACL graft. CONCLUSIONS: The robotic/UFS testing system allows us to determine knee kinematics and the in-situ forces in cadaveric knees in a non-invasive, non-contact manner. Additionally, the ability to reproduce kinematics during testing allows us to evaluate ACL and ACL graft function under external and simulated muscle loading conditions. Finally, we can also examine many of the variables of ACL reconstructions that affect knee kinematics and graft forces including graft tensioning, graft type, graft placement and tibial positioning during graft fixation.

Relative contribution of the ACL, MCL, and bony contact to the anterior stability of the knee.

Ligaments and other soft tissues, as well as bony contact, all contribute to anterior stability of the knee joint. This study was designed to measure the in situ force in the medial collateral ligament (MCL), anterior cruciate ligament (ACL), posterolateral structures (PLS), and posterior cruciate ligament (PCL) in response to 110 N anterior tibial loading. The changes in knee kinematics associated with ACL deficiency and combined MCL+ACL deficiency were also evaluated. Utilizing a robotic/universal force-moment sensor system, ten human cadaveric knee joints were tested between 0 degrees and 90 degrees of knee flexion. This unique testing system is designed to determine the in situ forces in structures of interest without making mechanical contact with the tissue. More importantly, data for individual structures can be obtained from the same knee specimen since the robotic manipulator can reproduce the motion of the intact knee. The in situ forces in the ACL under anterior tibial loading to 110 N were highest at 15 degrees flexion, 103 +/- 14 N (mean +/- SD), decreasing to 59.2 +/- 30 N at 90 degrees flexion. For the MCL, these forces were 8.0 +/- 3.5 N and 38.1 +/- 25 N, respectively. Forces due to bony contact were as high as 34.1 +/- 23 N at 30 degrees flexion, while those in the PLS were relatively small at all flexion angles. Combined MCL+ACL deficiency was found to significantly increase anterior tibial translation relative to the ACL-deficient knee only above 60 degrees of knee flexion. These findings confirm the hypothesis that there is significant load sharing between various ligaments and bony contact during anterior tibial loading of the knee. For this reason, the MCL and osteochondral surfaces may also be at significant risk during ACL injury.

Improvement of accuracy in a high-capacity, six degree-of-freedom load cell: application to robotic testing of musculoskeletal joints.

This study investigated a previously unaccounted for source of error in a high-capacity, six degree-of-freedom load cell used in multi-degree-of-freedom robotic testing of musculoskeletal joints, an application requiring a load cell with high accuracy in addition to high load capacity. A method of calibration is presented for reducing the error caused by changes in universal force-moment sensor (UFS) orientation within a gravitational field. Uncorrected, this error can exceed a magnitude of 1% of the full-scale load capacity-the manufacturer-stated accuracy of the UFS. Implementation of the calibration protocol reduced this error by approximately 75% for a variety of loading conditions. This improvement in load cell accuracy (while maintaining full load capacity) should improve both the measurement and control of specimen kinetics by robotic/UFS and other biomechanical testing systems.

The effect of anterior cruciate ligament graft fixation site at the tibia on knee stability: evaluation using a robotic testing system.

Despite its current popularity and relative success, endoscopic reconstruction of the anterior cruciate ligament (ACL) using a bone-patellar tendon-bone (BPTB) graft has not yet been perfected. Using a recently developed robotic/UFS testing system, we assessed the overall stability of porcine knees following ACL reconstruction with different sites of tibial graft fixation--proximal, central, and distal. Testing of the intact knee was performed first to determine the normal anterior-posterior (A-P) displacements and in situ forces of the ACL under 110 N of anterior tibial loading of 30 degrees, 60 degrees, and 90 degrees of knee flexion. The knee was then reconstructed with a BPTB autograft, and the distal end of the graft was fixed sequentially at three different locations in each specimen--proximal, central, distal. A-P testing was repeated for each fixation site, and the resulting knee kinematics and the in situ forces of the grafts were compared to the intact case. The site of tibial fixation was demonstrated to have a significant effect on the resulting anterior displacement and internal rotation of the tibia as well as the in situ forces of the graft. Proximal fixation produced the most stable knee (A-P displacements reduced to 120% of intact at 30 degrees and 170% at 90 degrees), becoming significantly less stable with more distal fixation. These results suggest that proximal graft fixation may provide the most acute stability of the reconstructed knee.

Evaluation of the effect of joint constraints on the in situ force distribution in the anterior cruciate ligament.

The function of the anterior cruciate ligament was investigated for different conditions of kinematic constraint placed on the intact knee using a six-degree-of-freedom robotic manipulator combined with a universal force-moment sensor. To do this, the in situ forces and force distribution within the porcine anterior cruciate ligament during anterior tibial loading up to 100 N were compared at 30, 60, and 90 degrees of flexion under: (a) unconstrained, five-degree-of-freedom knee motion, and (b) constrained, one-degree-of-freedom motion (i.e., anterior translations only). The robotic/universal force-moment sensor testing system was used to both apply the specified external loading to the intact joint and measure the resulting kinematics. After tests of the intact knee were completed, all soft tissues except the anterior cruciate ligament were removed, and these motions were reproduced such that the in situ force and force distribution could be determined. No significant differences in the magnitude of in situ forces in the anterior cruciate ligament were found between the unconstrained and constrained testing conditions. In contrast, the direction of in situ force changed significantly; the force vector in the unconstrained case was more parallel with the direction of the applied tibial load. In addition, the distribution of in situ force between the anteromedial and posterolateral bundles of the ligament was nearly equal for all flexion angles for the unconstrained case, whereas the anteromedial bundle carried higher forces than the posterolateral bundle at both 60 and 90 degrees of flexion for the constrained case. This demonstrates that the constraint conditions placed on the joint have a significant effect on the apparent role of the anterior cruciate ligament. Specifically, constraining joint motion to one degree of freedom significantly alters both the direction and distribution of the in situ force in the ligament from that observed for unconstrained joint motion (five degrees of freedom). Furthermore, the changes observed in the distribution of force between the anteromedial and posterolateral bundles for different constraint conditions may help elucidate mechanisms of injury by providing new insight into the response of the anterior cruciate ligament to different types of external knee loading.

In situ forces in the anterior cruciate ligament and its bundles in response to anterior tibial loads.

The anterior cruciate ligament has a complex fiber anatomy and is not considered to be a uniform structure. Current anterior cruciate ligament reconstructions succeed in stabilizing the knee, but they neither fully restore normal knee kinematics nor reproduce normal ligament function. To improve the outcome of the reconstruction, it may be necessary to reproduce the complex function of the intact anterior cruciate ligament in the replacement graft. We examined the in situ forces in nine human anterior cruciate ligaments as well as the force distribution between the anteromedial and posterolateral bundles of the ligament in response to applied anterior tibial loads ranging from 22 to 110 N at knee flexion angles of 0-90 degrees. The analysis was performed using a robotic manipulator in conjunction with a universal force-moment sensor. The in situ forces were determined with no device attached to the ligament, while the knee was permitted to move freely in response to the applied loads. We found that the in situ forces in the anterior cruciate ligament ranged from 12.8 +/- 7.3 N under 22 N of anterior tibial load applied at 90 degrees of knee flexion to 110.6 +/- 14.8 N under 110 N of applied load at 15 degrees of flexion. The magnitude of the in situ force in the posterolateral bundle was larger than that in the anteromedial bundle at knee flexion angles between 0 and 45 degrees, reaching a maximum of 75.2 +/- 18.3 N at 15 degrees of knee flexion under an anterior tibial load of 110 N. The magnitude of the in situ force in the posterolateral bundle was significantly affected by knee flexion angle and anterior tibial load in a fashion remarkably similar to that seen in the anterior cruciate ligament. The magnitude of the in situ force in the anteromedial bundle, in contrast, remained relatively constant, not changing with flexion angle. Significant differences in the direction of the in situ force between the anteromedial bundle and the posterolateral bundle were found only at flexion angles of 0 and 60 degrees and only under applied anterior tibial loads greater than 66 N. We have demonstrated the nonuniformity of the anterior cruciate ligament under unconstrained anterior tibial loads. Our data further suggest that in order for the anterior cruciate ligament replacement graft to reproduce the in situ forces of the normal anterior cruciate ligament, reconstruction techniques should take into account the role of the posterolateral bundle in addition to that of the anteromedial bundle.

Forces and moments in six-DOF at the human knee joint: mathematical description for control.

A mathematical description of six-degree of freedom (6-DOF) forces and moments with respect to a commonly utilized knee joint coordinate system was performed using a [6 x 6] Jacobian matrix developed in this study. The presented Jacobian allows the proper transformation of the forces and moments measured at a sensor coordinate system (attached to the tibia in this case) into the joint coordinate system and is dependent on the kinematics of the joint itself. Experimental application of the developed mathematics to A-P drawer tests of the intact knee confirmed that it is possible to determine the forces and moments applied to a human knee within the joint coordinate system during joint loading. More importantly, the inverse Jacobian was also determined for implementation in the force-moment control of the joint during testing using a robotic testing system. This approach is demonstrated for the joint coordinate system for the human knee in the current study, although it may be more generally applied to allow determination and control of forces and moments within any description of motions, and for any additional joints in the human body.

A combined robotic/universal force sensor approach to determine in situ forces of knee ligaments.

We developed a system that uses a 6-degree-of-freedom (6-DOF) robotic manipulator combined with a 6-DOF force-moment sensor and a control system. The system is used to find and record the passive knee flexion path for controlling the knee flexion positions. It is also used to strain a knee structure by finding a multiple-DOF path in response to specific joint loading, e.g. anterior-posterior tibial force application. It is additionally used to measure in-situ forces in ligaments by recording differences in forces and moments when repeating a prerecorded path, both before and after removal of the ligament of interest. Example applications are included in the study.

A single integral finite strain viscoelastic model of ligaments and tendons.

A general continuum model for the nonlinear viscoelastic behavior of soft biological tissues was formulated. This single integral finite strain (SIFS) model describes finite deformation of a nonlinearly viscoelastic material within the context of a three-dimensional model. The specific form describing uniaxial extension was obtained, and the idea of conversion from one material to another (at a microscopic level) was then introduced to model the nonlinear behavior of ligaments and tendons. Conversion allowed different constitutive equations to be used for describing a single ligament or tendon at different strain levels. The model was applied to data from uniaxial extension of younger and older human patellar tendons and canine medial collateral ligaments. Model parameters were determined from curve-fitting stress-strain and stress-relaxation data and used to predict the time-dependent stress generated by cyclic extensions.

In-situ forces in the human posterior cruciate ligament in response to posterior tibial loading.

Although some investigators have referred to the human posterior cruciate ligament (PCL) as the center of the knee, it has received less attention than the more frequently injured anterior cruciate ligament (ACL) and medial collateral ligament (MCL). Therefore, our understanding of the function of the PCL is limited. Our laboratory has developed a method of measuring the in-situ forces in a ligament without contacting that ligament by using a universal force-moment sensor (UFS). In this study, we attached a UFS to the tibia and measured in-situ forces of the human PCL as a function of knee flexion in response to tibial loading. At a 50-N posterior tibial load, the force in the PCL increased from 25 +/- 11 N (mean +/- SD) at 30 degrees of knee flexion to 48 +/- 12 N at 90 degrees of knee flexion. At 100 N, the corresponding increases were to 50 +/- 17 N and 95 +/- 17 N, respectively. Of note, at 30 degrees knee flexion, approximately 45% of the resistance to posterior tibial loading was caused by contact between the tibia and the femoral condyles, whereas, at 90 degrees of knee flexion, no resistance was caused by such contact. For direction of the in-situ force, the elevation angle from the tibial plateau was greater at 30 degrees of knee flexion than at 90 degrees of knee flexion. The data gathered on the magnitude and direction of the in-situ force of the PCL should help in our understanding of the dependence of knee flexion angle of the forces within the PCL.

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.

Insertion-site anatomy of the human menisci: gross, arthroscopic, and topographical anatomy as a basis for meniscal transplantation.

A cadaveric study was performed to determine the insertion-site anatomy of the human menisci, their topographical relationships to adjacent intra-articular structures, and which arthroscopic portal provides for optimal visualization of each insertion site. Fifteen fresh-frozen cadaver knees were studied (ages 48 to 63 years). Ten knees underwent arthroscopy using four standard arthroscopic portals. Visualization and placement of an arthroscopic guide over each meniscal horn insertion site was attempted through the four arthroscopic portals. Guide wires were drilled to mark horn insertions followed by a gross dissection to evaluate accuracy of the guide wire gross dissection to evaluate accuracy of the guide wire placement and to isolate meniscal horn insertion sites. Insertion sites were outlined and evaluated for size and topographical relationships to other intra-articular structures. Five additional knees were dissected free of all soft tissues except the tibial insertions of the meniscal roots and anterior cruciate ligament/posterior cruciate ligament. Each tibia was mounted in a jig and a digitizing system was used to record coordinates of points along the outline of each bony meniscal horn insertion site, the ACL tibial insertion, and the articular surface of each tibial plateau. The x, y, z coordinates for each point were calculated and loaded into a computer program allowing for surface area determination and computer-generated topographical maps to assess relative position of each specific insertion site. Placement of the arthroscope in the anterolateral portal allows optimal visualization and guide wire placement for both lateral meniscal horn insertion sites. Medial meniscal anterior and posterior horn insertion sites are best visualized with the arthroscope in the anteromedial and posteromedial portals respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the in situ forces and force distribution within the human anterior cruciate ligament.

The in situ forces and their distribution within the human anterior cruciate ligament (ACL) can clarify this ligament's role in the knee and help to resolve controversies regarding surgical treatment of ACL deficiency. We used a universal force-moment sensor (UFS) to determine the magnitude, direction, and point of application of the in situ forces in the ACL in intact human cadaveric knees. Unlike previous studies, this approach does not require surgical intervention, the attachment of mechanical devices to or near the ACL, or a priori assumptions about the direction of in situ force. Anterior tibial loads were applied to intact knees, which were limited to 1 degree of freedom at 30 degrees flexion. The in situ forces developed in the ACL were lower than the applied force for loads under 80 N, but larger for applied loads of more than 80 N. The direction of the force vector corresponded to that of the anteromedial (AM) portion of the ACL insertion on the tibial plateau. The point of force application was located in the posterior section of the anteromedial portion of the tibial insertion site. The anterior and posterior aspects of the anteromedial portion of the ACL supported 25% and 70% of the in situ force, respectively, with the remainder carried by the posterolateral portion. We believe that the data obtained with this new UFS methodology improves our understanding of the role of the ACL in knee function, and that this methodology can be easily extended to study the function of other ligaments.

Comparative study of the size and shape of human anterior and posterior cruciate ligaments.

As an important step toward determination of the function of cruciate ligaments, the cross-sectional shapes and areas of the anterior cruciate, posterior cruciate, and meniscofemoral ligaments were evaluated in situ within the same knee with use of a laser micrometer system. Measurements were made in eight human cadaveric knees at five levels along the midsubstance of each ligament, with the knee at 0 degree, 30 degrees, 60 degrees, and 90 degrees of flexion. The posterior cruciate ligament was found to be widest in the medial-lateral direction, whereas the anterior cruciate ligament usually was larger in the anterior-posterior direction. The cross-sectional shapes of the anterior cruciate ligament generally were noted to be more circular along the entire midsubstance than were those of the posterior cruciate ligament. In contrast, the cross-sectional shapes of the posterior cruciate ligament were more circular near the tibia, becoming progressively more elongated toward the femur. The meniscofemoral ligaments were more circular than the cruciate ligaments, with an occasional medial-lateral widening similar to that of the posterior cruciate ligament. The cross-sectional area of both the cruciate ligaments changed along the length of the midsubstance, with the anterior cruciate ligament becoming slightly larger distally and the posterior cruciate ligament enlarging proximally. The angle of flexion of the knee was not found to have a significant effect on the cross-sectional areas of the ligaments but was noted to alter the cross-sectional shapes.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of a universal force-moment sensor to determine in-situ forces in ligaments: a new methodology.

Determination of ligament forces is an integral part of understanding their contribution during motion and external loading of an intact joint. While almost all previous investigations have reported only the magnitude of tension, this alone cannot adequately describe the function of a particular ligament. An alternative approach to determine the in-situ forces in ligaments has been developed which utilizes a universal force-moment sensor in conjunction with a force transformation scheme. In addition to providing the magnitude of ligament force, the direction and point of application of this in-situ force can also be determined. Further, the approach does not require mechanical contact with the ligament. Application of this new methodology is demonstrated for the human anterior cruciate ligament in the present study (n = 7) although it may be similarly applied to other ligaments at the knee or in other synovial joints of the human body.