A preliminary report of a simple rig to aid study of the functional anatomy of the cadaver human knee joint

The Instant Centre Pathway as a Parameter of Joint Motion — An Experimental Investigation of a Method of Assessment of Knee Ligament Injury and Repair

Movement under load is the most demanding function required of a diarthrodial joint. This presentation will illustrate, pertinent to the context of this meeting, the effects on a parameter of movement of certain types of knee ligament injury which are supposed to occur in real life, and the assessment of the capacity of different methods of repair to restore the movement to normal.

Evaluation of total knee mechanics using a crouching simulator with a synthetic knee substitute

Mechanical evaluation of total knees is frequently required for aspects such as wear, strength, kinematics, contact areas, and force transmission. In order to carry out such tests, we developed a crouching simulator, based on the Oxford-type machine, with novel features including a synthetic knee including ligaments. The instrumentation and data processing methods enabled the determination of contact area locations and interface forces and moments, for a full flexion-extension cycle. To demonstrate the use of the simulator, we carried out a comparison of two different total knee designs, cruciate retaining and substituting. The first part of the study describes the simulator design and the methodology for testing the knees without requiring cadaveric knee specimens. The degrees of freedom of the anatomic hip and ankle joints were reproduced. Flexion-extension was obtained by changing quadriceps length, while variable hamstring forces were applied using springs. The knee joint was represented by three-dimensional printed blocks on to which the total knee components were fixed. Pretensioned elastomeric bands of realistic stiffnesses passed through holes in the block at anatomical locations to represent ligaments. Motion capture of the knees during flexion, together with laser scanning and computer modeling, was used to reconstruct contact areas on the bearing surfaces. A method was also developed for measuring tibial component interface forces and moments as a comparative assessment of fixation. The method involved interposing Tekscan pads at locations on the interface. Overall, the crouching machine and the methodology could be used for many different mechanical measurements of total knee designs, adapted especially for comparative or parametric studies.

EOS orthopaedic imaging system to study patellofemoral kinematics: assessment of uncertainty

BACKGROUND

Accurate knowledge of knee joint kinematics, especially patellofemoral joint kinematics,is essential for prosthetic evaluation so as to further improve total knee arthroplasty performances. Improving the evaluation of the functioning of the extensor apparatus appears,in this respect, particularly important in this optimization effort.

OBJECTIVES

The aim of this study was to propose a new experimental setup for the analysis of knee joint kinematics and to validate its relevance in terms of accuracy and uncertainty.The technique developed herein combines 3D reconstruction imaging with the use of a motion capture system.

MATERIAL AND METHODS

Eight pairs of fresh-frozen cadaver specimens with no evidence of previous knee surgery were studied using a new test rig where the femur remains fixed and the tibia is free to rotate. The flexion-extension cycles were executed using computer-controlled traction of the quadriceps tendon combined with an antagonist force applied to the distal part of the tibia. Knee joint kinematics were tracked using an optoelectronic motion capture system after a preliminary stage of data acquisition of bone geometry and markers position. This stage was carried out using a new digital stereophotogrammetric system, EOS, combined with specific 3D reconstruction software that also determined the coordinate system used in the kinematic analysis. The resulting uncertainty was assessed as was its impact on the estimated kinematics.

RESULTS

Test results on eight knees validated the setup designed for the analysis of knee joint kinematics during the flexion-extension cycle. More specifically, the statistical results show that measurement uncertainty for rotations and translations remains below 0.4 and 1.8 mm,respectively, for the tibia and 0.4 and 1.2 mm for the patella (+/- 2 S.D. for all four measurements).

DISCUSSION

The combination of 3D imaging and motion capture enables the proposed method to track the real-time motion of any bone segment during knee flexion-extension cycle. In particular,the new test rig introduced in this paper allows in vitro measurements of the patello femoral and tibiofemoral kinematics with a good level of accuracy. Moreover, this personalized experimental analysis can provide a more objective approach to the evaluation of knee implants as well as the validation of the finite-elements-based models of the patellofemoral joint.

The effects of removal and reconstruction of the anterior cruciate ligament on patellofemoral kinematics

Patellofemoral pain may be associated with anterior cruciate ligament deficiency or may occur after anterior cruciate ligament reconstruction. We investigated the effects of the removal and reconstruction of the anterior cruciate ligament on the kinematics of the tibiofemoral and patellofemoral joints during physiologic levels of quadriceps muscle loads in seven cadaveric knees. A bone-patellar tendon-bone graft was used for intraarticular reconstruction of the anterior cruciate ligament. The spatial positions of the tibiofemoral and patellofemoral joints were measured between 0 degrees and 90 degrees of knee flexion in 15 degrees increments with a six degree-of-freedom digitizing system. Excision of the anterior cruciate ligament resulted in statistically significant increases in anterior tibial translation between 0 degrees and 90 degrees and valgus tibial rotation between 30 degrees and 90 degrees; intraarticular reconstruction returned these to levels not significantly different from those of the intact knee. Excision of the anterior cruciate ligament resulted in significant increases in lateral patellar tilt, ranging from 6.3 degrees to 9.0 degrees between full extension and 90 degrees of knee flexion, and in lateral patellar shift, ranging from 2.9 mm at 15 degrees of knee flexion to 5.9 mm at 90 degrees; intraarticular reconstruction returned these to levels not significantly different from those of the intact knee. Neither removal nor reconstruction of the anterior cruciate ligament significantly affected tibial internal-external rotation, patellar flexion, patellar mediolateral rotation, patellar anteroposterior translation, or patellar proximodistal translation.

Strategies for attachment site locations and twist of the intraarticular anterior cruciate ligament graft

We modeled an intraarticular anterior cruciate ligament graft and investigated the effects of attachment orientation and twist of the graft on its isometry during quadriceps muscle loading. Physiologic levels of quadriceps muscle loads were applied to 15 intact cadaveric knees. We measured the changes in distance between points on the tibia and femur for knee flexion angles between 0 degree and 120 degrees using a three-dimensional digitizer. Selected points on the tibia and femur, representing graft attachment sites, allowed us to model the graft as a broad band. Distance was used to approximate graft fiber length. A 180 degrees twist in the graft significantly reduced the maximal range of changes in distance when the graft was attached in the anteroposterior direction. Range is defined as the difference between the largest and smallest changes in distance among the fibers of the graft for a given angle of flexion. This reduction enhanced isometry among the fibers of the graft. Enhanced isometry would be expected to enhance load sharing among these fibers, thereby increasing the overall strength of the graft. For a graft 10 mm wide and 4 mm thick, the dimensions of a typical patellar tendon graft, the best overall isometry was found when the breadth of the graft was attached to the tibia in the mediolateral direction, to the femur along the most isometric line, and with a 180 degrees twist in the graft.

Iliotibial band tenodesis: a new strategy for attachment

We investigated the changes in distance between Gerdy's tubercle on the tibia and points on the posterior two thirds of the lateral surface of the lateral femoral condyle and adjacent lateral femoral shaft in 15 cadaveric knees. A three-dimensional digitizer was used to quantify motion of the knee during flexion ranging from full extension to 120 degrees of flexion. Four load states were applied: internal, external, and neutral rotation, and quadriceps muscles loads based on one third of values in the literature for maximal isometric quadriceps muscles moments. The femoral location most isometric to Gerdy's tubercle was found to be strongly influenced by the load state. A 1.0 cm wide iliotibial band tenodesis was modelled by five straight lines arising from Gerdy's tubercle and attaching to a simulated washer at the junction of the lateral femoral condyle and shaft. Using this model and the motion data obtained from the cadavers, we investigated the effects of quadriceps muscles loading and external rotation of the knee on changes in the distances between these tibial and femoral attachments for each of the five lines. A 180 degrees twist modelled into the tenodesis significantly reduced the range of changes in distance (difference between the largest and smallest changes in distance among the lines for a given angle of flexion) for both of these load states. Therefore, a 180 degrees twist in the tenodesis can enhance isometry among the fibers of the tenodesis. This implies that a 180 degrees twist can enhance load sharing among the fibers of the tenodesis and, therefore, enhance the overall strength of the tenodesis.

Kinematics of successful knee prostheses during weight-bearing: three-dimensional movements and positions of screw axes in the Tricon-M and Miller-Galante designs

Using roentgen stereophotogrammetric analysis we recorded the three-dimensional movements in six knees with implanted Tricon-M prostheses and ten knees with Miller-Galante prostheses as the patients ascended a platform. Fourteen patients with normal knees were used as controls. The two prosthetic designs displayed decreased internal tibial rotation and the Tricon-M increased valgus rotation. A central point on the tibial articular surface had a more lateral position in the Tricon-M design and a more distal one in the Miller-Galante design compared to normal knees. Increased posterior displacement with increasing flexion was observed in both designs. When the normal knees were extended at full weight-bearing the helical axes mainly shifted inclination in the frontal plane. In the prosthetic knees there was a tendency to anterior-posterior displacement of the axes as extension proceeded, especially in the Miller-Galante design. Translations along the helical axes were larger than normal in the Miller-Galante and smaller in the Tricon-M knees, reflecting differences in constraint of the two designs.

Relation between knee motion and ligament length patterns

Fifteen knee specimens were tested in a 6°-of-freedom test machine using quadriceps force to drive continuous flexion-extension motion. Ten of the knees were again tested following isolated transaction of the anterior cruciate ligament. From transducer outputs, three-dimensional motion was determined. Using biplanar radiography and bone sectioning, ligament insertion coordinates and joint surface geometry were determined and used to calculate ligament length ratios as a function of knee flexion. Consistent motion patterns were seen in all knees. The prominent aspects of motion were a 15° internal rotation and an 8.6 mm anterior displacement of the tibia with flexion from 0 to 120°. Anterior cruciate transaction resulted in abnormal and excessive anterior-posterior displacement in early flexion, but a return to normal in late flexion. The results indicated that under our test conditions the boundaries of anterior-posterior motion were determined primarily by the cruciate ligaments, but tibial rotation was not guided by the cruciate ligaments.

Length and moment arm of human leg muscles as a function of knee and hip-joint angles

Lengths of muscle tendon complexes of the quadriceps femoris muscle and some of its heads, biceps femoris and gastrocnemius muscles, were measured for six limbs of human cadavers as a function of knee and hip-joint angles. Length-angle curves were fitted using second degree polynomials. Using these polynomials the relationships between knee and hip-joint angles and moment arms were calculated. The effect of changing the hip angle on the biceps femoris muscle length is much larger than that of changing the knee angle. For the rectus femoris muscle the reverse was found. The moment arm of the biceps femoris muscle was found to remain constant throughout the whole range of knee flexion as was the case for the medial part of the vastus medialis muscle. Changes in the length of the lateral part of the vastus medialis muscle as well as the medial part of the vastus lateralis muscle are very similar to those of vastus intermedius muscle to which they are adjacent, while those changes in the length of the medial part of the vastus medialis muscle and the lateral part of the vastus lateralis muscle, which are similar to each other, differ substantially from those of the vastus intermedius muscle. Application of the results to jumping showed that bi-articular rectus femoris and biceps femoris muscles, which are antagonists, both contract eccentrically early in the push off phase and concentrically in last part of this phase.

Helical axes of passive knee joint motions

The purpose of this study was to determine finite helical axes for passive knee joint motions in vitro and to evaluate the descriptive value of the finite helical axes for step-by-step flexion motions, with respect to consistency and reproducibility. An accurate Roentgenstereophotogrammetric system was used for motion measurements. Four knees were tested in a motion and loading rig with one and the same experimental protocol. A fifth specimen was used to study the effects of some of the experimental conditions on the axis parameters. On the basis of earlier reported motion characteristics in terms of Euler rotations and translations, two motion pathways were chosen to be reported here: a flexion motion with an internal torque of 3 Nm and one with an external torque of 3 Nm on the tibia. The positions and orientations of the axes were described relative to the insertions of the four major ligaments and the geometry of the articular surfaces of the femur, and also as intersections with a medial and a lateral sagittal plane. The three-dimensional patterns of the helical axes of the four knee specimens were found to be highly reproducible and consistent for each of the two motion pathways. The axis patterns were not unique, but reflected the particular combination of flexion and axial rotation for each particular motion pathway. Although small, the helical translations indicated medial motions of the tibia relative to the femur. This medial helical translation was more pronounced for the internal pathway compared with the external pathway. Above 70 degrees flexion, the axes move posteriorly relative to the femur.

The geometry of the knee in the sagittal plane

A geometric model of the tibio-femoral joint in the sagittal plane has been developed which demonstrates the relationship between the geometry of the cruciate ligaments and the geometry of the articular surfaces. The cruciate ligaments are represented as two inextensible fibres which, with the femur and the tibia, are analysed as a crossed four-bar linkage. The directions of the ligaments at each position of flexion are calculated. The instant centre, where the flexion axis crosses the parasagittal plane through the joint, lies at the intersection of the cruciates. It moves relative to each of the bones during flexion and extension. The successive positions of the flexion axis relative to a fixed femur and to a fixed tibia are deduced. The shapes of articular surfaces which would allow the bones to flex and extend while maintaining the ligaments each at constant length are calculated and are found to agree closely with the shapes of the natural articular surfaces. The calculated movements of the contact point between the femur and the tibia during flexion also agree well with measurements made on cadaver specimens. The outcome is a geometric simulation of the tibio-femoral joint in the sagittal plane which illustrates the central role played by the cruciate ligaments in the kinematics of the knee and which can be used for the analysis of ligament and contact forces.

Interaction between intrinsic knee mechanics and the knee extensor mechanism

The ability of the quadriceps muscles to extend the knee was studied relative to the intrinsic mechanical features of the knee joint. The quadriceps mechanical efficiency changed by nearly 50% between 0 and 90 degrees of knee flexion. The peak efficiency occurred at approximately 20 degrees of knee flexion. The mechanical efficiency of the quadriceps was dependent on the movement of the net anteroposterior (AP) tibiofemoral contact center of pressure, the change in patellar ligament angle, and the change in the quadriceps-to-ligament force transfer ratio. The average net AP tibiofemoral contact center of pressure moved posteriorly on the tibial plateau as the knee flexed from 0 to 90 degrees. The excision of both cruciate ligaments reversed the posteriorly directed movement of the net AP tibiofemoral contact center of pressure at flexion angles from 60 to 90 degrees, resulting in a reduction in extension moment.

Effects of total knee replacement design on femoral-tibial contact conditions

Ten fresh knee specimens with prosthetic components inserted were tested in a loading rig. Compressive and shear force were applied to the femur with the tibia held fixed. The location of the femoral-tibial contact points was measured. The contact reaction forces, the shear forces, and the rocking moments transmitted to the tibial component were calculated. The variations in the test conditions were: high and low compressive force, flexion angles of 0 degree, 45 degrees, and 90 degrees, three curvatures of tibial plastic inserts, and the posterior cruciate retained or resected. When the posterior cruciate was retained, the contact points were close to the center of the component; for cruciate resection, the contacts were close to the anterior of the component. The shear forces and rocking moments were higher for cruciate resection, but the contact reaction forces were lower. There is a wide variety of knee prosthesis designs, but the amount of inherent stability between the femoral and tibial surfaces, and whether the posterior cruciate ligament is retained or sacrificed, are two of the most important design variables. This study shows that cruciate resection increases the shear forces and the rocking moments to the tibial components and that additional fixation means may be necessary to compensate. On the other hand, cruciate retention with low conformity gives higher contact forces, which may lead to more wear in the long term. Cruciate sacrificing designs with intercondylar guiding surfaces are a separate category of design and were not considered in this study.

Geometry and motion of the knee for implant and orthotic design

By analysing sections of distal femurs in the computer, and by making direct measurements, the posterior femoral condyles were shown to closely fit spherical surfaces. The center of the spheres were then used as reference points and used to define reference axes in a motion study. In flexing from 0 to 120 degrees the medial femoral condyle moved little, the lateral moved posteriorly by 17 mm, and there was an axial rotation of 20 degrees. The data were applied to implant and orthotic design and evaluation.

One parameter model for error in instantaneous centre of rotation measurements

Many statistical distributions have a single parameter which describes its spread. In the kinematic study of the instantaneous centre of rotation, error in data cause a non-symmetrical distribution for the centre. As an aid in describing its spread, the analytical form of the probability density function was reduced to a single-parameter model. This results in a convenient way of analysing experimental data through the use of an 'ICR Error Chart'.

Errors in kinematic parameters of a planar joint: guidelines for optimal experimental design

Kinematic characteristics of a body joint performing planar motion are precisely defined by the centers and angles of rotation as the joint undergoes its full range of physiological movement. These potentially (clinically) useful non-invasive kinematic parameters are, however, highly sensitive to input coordinate measurement errors and the experimental design. This paper compares results of an experimental study and a statistically based mathematical model of the errors in the centers and angles of rotation. Guidelines are provided to design optimal kinematic experiments so that, for given measurement equipment, the highest possible precision may be achieved in the results.