Biomedical subjects

L Blankevoort

Publications and source records attributed to L Blankevoort.

At least 19 recordsLinked to original sources

PubMed2006

Interventions for treating chronic ankle instability.

BACKGROUND: Chronic lateral ankle instability occurs in 10% to 20% of people after an acute ankle sprain. The initial form of treatment is conservative but if this fails and ligament laxity is present, surgical intervention is considered. OBJECTIVES: To compare different treatments, both conservative and surgical, for chronic lateral ankle instability. SEARCH STRATEGY: We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialized Register (to July 2005), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2005, Issue 3), and MEDLINE (1966 to April 2006), EMBASE (1980 to April 2006), CINAHL (1982 to April 2006) and reference lists of articles. SELECTION CRITERIA: All randomised and quasi-randomised controlled trials of interventions for chronic lateral ankle instability were included. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed methodological quality and extracted data. Where appropriate, results of comparable studies were pooled. MAIN RESULTS: Seven randomised trials were included and divided into three groups: surgical interventions; rehabilitation programs after surgical interventions; and conservative interventions. None of the studies were methodologically flawless. Only one study described an adequate randomisation procedure. Only two studies, both about rehabilitation programs after surgery, had a moderate risk of bias; all other studies had a high risk of bias. Due to clinical and methodological diversity, extensive pooling of the data was not possible. Surgical interventions (four studies): one study showed more complications after the Chrisman-Snook procedure compared to an anatomical reconstruction, whereas another study showed greater mean talar tilt after an anatomical reconstruction. Subjective instability and hindfoot inversion was greater after a dynamic than after a static tenodesis in a third study. The fourth study showed that the operating time for anatomical reconstructions was shorter for the reinsertion technique than for the imbrication method. Rehabilitation after surgical interventions (two studies): both studies provided evidence that early functional mobilization leads to an earlier return to work and sports than immobilisation. Conservative interventions: the only study in this group showed better proprioception and functional outcome with the bi-directional than with the uni-directional pedal technique on a cyclo-ergometer. AUTHORS' CONCLUSIONS: In view of the low quality methodology of almost all the studies, this review does not provide sufficient evidence to support any specific surgical or conservative intervention for chronic ankle instability. However, after surgical reconstruction, early functional rehabilitation was shown to be superior to six weeks immobilisation regarding time to return to work and sports.

Ankle Joint↗

PubMed2005

Dermal connective tissue development in mice: an essential role for tenascin-X.

Deficiency of the extracellular matrix protein tenascin-X (TNX) causes a recessive form of Ehlers-Danlos syndrome (EDS) characterized by hyperextensible skin and hypermobile joints. It is not known whether the observed alterations of dermal collagen fibrils and elastic fibers in these patients are caused by disturbed assembly and deposition or by altered stability and turnover. We used biophysical measurements and immunofluorescence to study connective tissue properties in TNX knockout and wild-type mice. We found that TNX knockout mice, even at a young age, have greatly disturbed biomechanical properties of the skin. No joint abnormalities were noted at any age. The spatio-temporal expression of TNX during normal mouse skin development, during embryonic days 13-19 (E13-E19), was distinct from tropoelastin and the dermal fibrillar collagens type I, III, and V. Our data show that TNX is not involved in the earliest phase (E10-E14) of the deposition of collagen fibrils and elastic fibers during fetal development. From E15 to E19, TNX starts partially to colocalize with the dermal collagens and elastin, and in adult mice, TNX is present in the entire dermis. In adult TNX knockout mice, we observed an apparent increase of elastin. We conclude that TNX knockout mice only partially recapitulate the phenotype of TNX-deficient EDS patients, and that TNX could potentially be involved in maturation and/or maintenance of the dermal collagen and elastin network.

Animals↗

PubMed2005

A measurement device for anterior laxity of the ankle joint complex.

BACKGROUND: Evaluation of anterior ankle joint laxity remains an intriguing clinical problem. Manual examination is of subjective nature. The aim of the present in-vitro and in-vivo study was to develop a tester for quantitative measurement of anterior ankle joint laxity. METHODS: The tester was evaluated on 7 cadaver specimens and on 24 individuals, 14 with prior ligament injury and 10 without. Subsequently, a post hoc analysis was performed on 6 individuals without ligament injury. FINDINGS: In the cadaver tests, mean increase in anterior displacement was 2.0 mm (SD 1.6) with cut anterior talofibular ligament, 2.7 mm (SD 2.7) with cut anterior talofibular and calcaneofibular ligaments and 3.3 mm (SD 3.3) with cut anterior talofibular, calcaneofibular and posterior talofibular ligaments. In the normal subjects, mean displacement was 23 mm (SD 6.6) for left and 25 mm (SD 7.5) for right ankles. In the group of subjects with prior ankle ligament injuries but no instability symptoms, there was no detectable laxity difference between injured and non-injured. The intra-observer reliability for the tester was 0.94. Post-hoc analysis showed a device-related systematic error of < 1mm. INTERPRETATION: The displacement values present the motion between the anterior aspect of the distal tibia and the posterior aspect of the heel, not solely motion in the ankle joint but in the entire ankle joint complex. The test principle has the potential to provide an objective value for anterior displacement values of the ankle joint. The test apparatus in its present form is not suitable for use in clinical practice.

Adult↗

PubMed2005

The insertion geometry of the posterolateral corner of the knee.

We have quantitatively documented the insertion geometry of the main stabilising structures of the posterolateral corner of the knee in 34 human cadavers. The lateral collateral ligament inserted posterior (4.6 mm, sd 2) and proximal (1.3 mm, sd 3.6) to the lateral epicondyle of the femur and posterior (8.1 mm, sd 3.2) to the anterior point of the head of the fibula. On the femur, the popliteus tendon inserted distally (11 mm, sd 0.8) and either anterior or posterior (mean 0.84 mm anterior, sd 4) to the lateral collateral ligament. The popliteofibular ligament inserted distal (1.3 mm, sd 1.2) and anterior (0.5 mm, sd 2.0) to the tip of the styloid process of the fibula. The ligaments had a consistent pattern of insertion and, despite the variation between specimens, the standard deviations were less than the typical size of drill hole used in reconstruction of the posterolateral corner. The data provided in this study can be used in the anatomical repair and reconstruction of this region of the knee.

Aged↗

PubMed2004

Twist and its effect on ACL graft forces.

Graft tension is a controversial topic in anterior cruciate ligament (ACL) surgery. Evidence suggests a narrow range of graft tensions, which allow the graft to remodel to a stable and mature neoligament. In previous cadaver experiments, we showed that twisting the graft could modulate the graft forces. In this study we hypothesized that the same phenomena would be found in patients, and that twisting the graft intraoperatively can reduce peak forces in the graft. The effects of twist on graft forces in bone-patellar tendon-bone grafts were measured during anterior cruciate ligament surgery on 15 consecutive patients using a custom-made tension-measurement device. Variations in surgical procedure that could potentially affect the graft force patterns were quantified. Graft force as a function of knee-flexion angle was measured with the graft in the neutral, untwisted position and repeated with the tibial bone block rotated externally or internally by 180 degrees. In eight of the 15 knees, external twisting of the graft reduced the maximal graft force to 50%. However, in five knees the forces in extension increased by twisting to a maximum of 300%. Of the surgical variables, only the femoral tunnel position appeared to have a consistent effect on the graft force pattern. Due to the unpredictable effect of graft twisting, a general recommendation on whether the graft should be twisted, and if so, in which direction, cannot be given. Intraoperatively, graft twisting may however be considered in every individual knee to modulate the graft force as a function of flexion angle.

Adolescent↗

PubMed2003

Augmentation in anterior cruciate ligament reconstruction-a histological and biomechanical study on goats.

We studied reconstruction of the anterior cruciate ligament (ACL) in skeletally mature goats. In one group, the autogenous tissue was augmented with polydioxanone (PDS), the other group had no augmentation. Histological complete incorporation and remodeling of the transplant was found in both groups. The newly formed connective tissues gradually assumed the microscopic properties of the normal ligament. The augmented group showed a delay in remodeling and maturation of the fiber bundles. Mechanically, the PDS-augmented transplants were stronger than the nonaugmented transplants immediately after surgery. During the first 6 weeks, a rapid decrease in strength of the augmented transplants was found, whereas the strength of the nonaugmented group gradually increased. The results of our experiment do not favor augmentation of autografts in reconstruction of the ACL.

Animals↗

PubMed2003

Effects of twisting of the graft in anterior cruciate ligament reconstruction.

In an in vitro study on six knees from cadavers, the effect of bone-patellar tendon-bone graft twist on anterior knee laxity was measured at different knee flexion angles. A motion and loading rig was used to prescribe the flexion angle, to restrain axial rotation, and to apply 100 N anterior force to the tibia. Roentgen stereophotogrammetric analysis was used to measure the relative anteroposterior position of the tibia and femur. The tibial bone block was cemented in a cylinder that allowed rotation in the bone tunnel. The anterior cruciate ligament was transected and reconstructed with neutral, 90 degrees, and 150 degrees internal twists and 90 degrees and 150 degrees external twists. External and internal graft twists in the reconstruction resulted in significant reductions of anterior laxity, however, at the cost of a more posterior position of the unloaded tibia relative to the femur (anteroposterior-error). The results are explained by the anterior relocation of the graft insertion by twisting the tibial bone block. The inclination angle of the graft in the anteroposterior direction flattens, which could improve the anterior laxity. A consequent side effect is the increase of posterior shift of the tibia relative to the femur.

Aged↗

PubMed2002

Different functional treatment strategies for acute lateral ankle ligament injuries in adults.

BACKGROUND: Acute lateral ankle ligament ruptures are common problems in present health care. Early mobilisation and functional treatment are advocated as a preferable treatment strategy. However, functional treatment comprises a broad spectrum of treatment strategies and as of yet no optimal strategy has been identified. OBJECTIVES: The objective of this review is to assess different functional treatment strategies for acute lateral ankle ligament ruptures in adults. SEARCH STRATEGY: We searched the Cochrane Musculoskeletal Injuries Group specialised register (December 2001), the Cochrane Controlled Trials Register (The Cochrane Library, Issue 4, 2001), MEDLINE (1966 to May 2000), EMBASE (1980 to May 2000), CURRENT CONTENTS (1993 to 1999), BIOSIS (to 1999), reference lists of articles, and contacted organisations and researchers in the field. SELECTION CRITERIA: Randomised clinical trials describing skeletally mature individuals with an acute lateral ankle ligament rupture and comparing different functional treatment strategies were evaluated for inclusion. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed the quality of included trials and extracted relevant data on treatment outcome. Where appropriate, results of comparable studies were pooled. Individual and pooled statistics are reported as relative risks (RR) for dichotomous outcome and (weighted) mean differences (WMD) for continuous outcome measures with 95 per cent confidence intervals (95%CI). Heterogeneity between trials was tested using a standard chi-squared test. MAIN RESULTS: Nine trials involving 892 participants were included. Lace-up ankle support had significantly better results for persistent swelling at short-term follow up when compared with semi-rigid ankle support (RR 4.19, 95% CI 1.26 to 13.98); elastic bandage (RR 5.48; 95% CI 1.69 to 17.76); and to tape (RR 4.07, 95% CI 1.21 to 13.68). Use of a semi-rigid ankle support resulted in a significantly shorter time to return to work when compared with an elastic bandage (WMD (days) 4.24; 95% CI 2.42 to 6.06); one trial found the use of a semi-rigid ankle support saw a significantly quicker return to sport compared with elastic bandage (RR 9.60; 95% CI 6.34 to 12.86) and another trial found fewer patients reported instability at short-term follow-up when treated with a semi-rigid support than with an elastic bandage (RR 8.00; 95% CI 1.03 to 62.07). Tape treatment resulted in significantly more complications, the majority being skin irritations, when compared with treatment with an elastic bandage (RR 0.11; 95% CI 0.01 to 0.86). No other results showed statistically significant differences. REVIEWER'S CONCLUSIONS: The use of an elastic bandage has fewer complications than taping but appears to be associated with a slower return to work and sport, and more reported instability than a semi-rigid ankle support. Lace-up ankle support appears to be effective in reducing swelling in the short-term compared with semi-rigid ankle support, elastic bandage and tape. However, definitive conclusions are hampered by the variety of treatments used, and the inconsistency of reported follow-up times. The most effective treatment, both clinically and in costs, is unclear from currently available randomised trials.

Adult↗

PubMed2002

An instrumented, dynamic test for anterior laxity of the ankle joint complex.

Evaluation of anterior laxity of the ankle joint complex is a difficult clinical problem. Currently, the prime determinant for anterolateral ligament function is the subjective manual examination of anterior laxity of the ankle joint complex. An instrumented dynamic test was developed for objective measurement of anterior laxity of the ankle joint complex. The principle of the test was to apply a force-impulse to the calcaneus, within the muscle reflex time, and to measure anterior-posterior and mediolateral rotation. The test was performed on a cadaver specimen and on 15 volunteers of which five subjects suffered from chronic one-sided lateral ankle ligament instability. In the cadaver test, anterior translation values increased from 5 to 11 mm, after cutting the anterior talofibular ligament and subsequently cutting the calcaneofibular ligament. In the 10 normal subjects, the mean anterior translation value was 6.7 mm (+/-1.9 mm). The relative variation of the test result within a measurement session was 2.5% (+/-1.6%). Between the sessions the relative laxity variation was 2.6% (+/-2.6%). In the ten normal subjects the mean right-left difference was not significantly different from zero. In four out of the five patients it was more than 2mm. As in the cadaver test in all measurements, the mediolateral rotations were small (<2.5 degrees ). The volunteers complained about same pain at the heel after multiple test sessions. In conclusion the dynamic, functional test appears to be capable of objectively measuring a value for anterior laxity of the ankle joint complex reflecting the functional status of the anterolateral ankle ligaments.

Ankle Injuries↗

PubMed2001

Anterior lateral ankle ligament damage and anterior talocrural-joint laxity: an overview of the in vitro reports in literature.

OBJECTIVE: To provide a clear overview of the literature on the relationship between increased lateral ankle ligament damage and anterior talocrural-joint laxity. DESIGN: A systematic review of the literature. BACKGROUND: Diagnostic methods for inversion injuries of the ankle have remained controversial throughout the years. An instrumented test for anterior talocrural-joint laxity could be a diagnostic tool for evaluation of anterior lateral ankle ligament function. METHODS: An advanced electronic database search using MEDLINE and EMBASE was performed to find studies describing the correlation between lateral ankle ligament damage and talocrural-joint laxity. Two reviewers assessed the methodological quality for each study and agreement was noted. Two reviewers extracted all relevant data with respect to methodology, motion constraints and laxity measurement. RESULTS: The quality assessment resulted in 5 studies being scored as high quality and 5 as low quality. Different test devices were used to apply the load and measure the displacement. All in vitro tests applied a load to the calcaneus and subsequently measured the translation of the talus and/or calcaneus relative to the tibial dome. Rotation in the transversal and frontal plane was restricted in 8 tests. After analysis of the results presented by nine different studies, the mean value of anterior talocrural-joint laxity with intact ligaments is 4.2 mm. After sectioning of the anterior talofibular ligament, the mean anterior laxity value is 6.5 mm. The mean anterior laxity value after sectioning of the calcaneofibular ligament increases to 8.4 mm. The mean anterior laxity value with the foot in dorsal flexion (3.1 mm) is less than the mean value with the foot in neutral position (4.5 mm) or in plantar flexion (4.7 mm). The applied load and the anterior laxity values between the different studies vary greatly. CONCLUSIONS: Each ligament section results in significantly increased talocrural-joint laxity. Talocrural-joint laxity can be used as a measure for damage to the anterior talofibular ligament and/or the calcaneofibular ligament. From this review, it is neither possible to give universal recommendations about the optimal flexion angle for testing talocrural-joint laxity as a measure for lateral ankle ligament function, nor to recommend the ideal load for performing the test. RELEVANCE: The development of an instrumented test as a diagnostic tool for anterior talocrural-joint laxity in the clinical setting is near at hand and practicable.

Ankle Injuries↗

PubMed2000

Hamstrings and iliotibial band forces affect knee kinematics and contact pattern.

Many clinical studies have emphasized the role of the hamstrings and the iliotibial band on knee mechanics, although few biomechanical studies have investigated it. This study therefore examined two hypotheses: (a) with loading of the hamstrings, the tibia translates posteriorly and rotates externally and the tibial contact pattern shifts anteriorly; furthermore, the changes in tibial kinematics alter patellar kinematics and contact; and (b) loading the iliotibial band alters the kinematics and contact pattern of the tibiofemoral joint similarly to loading the hamstrings, and loading the iliotibial band laterally translates the patella and its contact location. Five cadaveric knee specimens were tested with a specially designed knee-joint testing machine in an open-chain configuration. At various flexion angles, the knees were tested always with a quadriceps force but with and without a hamstrings force and with and without an iliotibial band force. The results support the first hypothesis. Hence, the hamstrings may be important anterior and rotational stabilizers of the tibia, a role similar to that of the anterior cruciate ligament. The results also support the second hypothesis, although the iliotibial band force had a smaller effect on the tibia than did the hamstrings force. Both forces also changed patellar kinematics and contact, demonstrating that these structures should also be considered during the clinical management of patellar disorders.

Aged↗

PubMed2000

Influence of muscular activity on local mineralization patterns in metatarsals of the embryonic mouse.

This study addressed the theory that local mechanical loading may influence the development of embryonic long bones. Embryonic mouse metatarsal rudiments were cultured as whole organs, and the geometry of the primary ossification center was compared with that of rudiments that had developed in utero. The mineralization front in vivo was found to be nearly straight, whereas in vitro it acquired a more convex shape due to a slower mineralization rate at the periphery of the mineralized cylinder. A poroelastic finite element analysis was performed to calculate the local distributions of distortional strain and fluid pressure at the mineralization front in the metatarsal during loading in vivo as a result of muscle contractions in the embryonic hindlimbs. The distribution of fluid pressure from the finite element analysis could not explain the difference in mineralization shape. The most likely candidate for the difference was the distortional strain, resulting from muscle contraction, which is absent in vitro, because its value at the periphery was significantly higher than in the center of the tissue. Without external loads, the mineralization process may be considered as pre-programmed, starting at the center of the tissue and resulting in a spherical mineralization front. Strain modulates the rate of the mineralization process in vivo, resulting in the straight mineralization front. These results confirm that disturbances in muscle development are likely to produce disturbed mineralization patterns, resulting in a disordered osteogenic process.

Animals↗

PubMed1999

Why does intermittent hydrostatic pressure enhance the mineralization process in fetal cartilage?

The purpose of this study was to determine which factor is the most likely one to have stimulated the mineralization process in the in vitro experiments of Klein-Nulend et al. (Arth. Rheum., 29, 1002-1009, 1986), in which fetal cartilaginous metatarsals were externally loaded with an intermittent hydrostatic pressure, by compressing the gas phase above the culture medium. Analytical calculations excluded the possibility that the tissue was stimulated by changes in dissolved gas concentration, pH or temperature of the culture medium through compression of the gas phase. The organ culture experiments were also mechanically analyzed using a poroelastic finite element (FE) model of a partly mineralized metatarsal with compressible solid and fluid constituents. The results showed that distortional strains occurred in the region where mineralization proceeded. The value of this strain was, however, very sensitive to the value of the intrinsic compressibility modulus of the solid matrix (Ks). For realistic values of Ks the distortional strain was probably too small (about 2 microstrain) to have stimulated the mineralization. If the distortional strain was not the factor to have enhanced the mineralization process, then the only candidate variable left is the hydrostatic pressure itself. We hypothesize that the pressure may have created the physical environment enhancing the mineralization process. When hydrostatic pressure is applied, the balance of the chemical potential of water across cell membranes may be disturbed, and restored again by diffusion of ions until equilibrium is reached again. The diffusion of ions may have contributed to the mineralization process.

Animals↗

PubMed1998

Patellar stabilization: a quantitative evaluation of the vastus medialis obliquus muscle.

Twenty-one cadaveric knees were dissected to analyze the functional anatomy of the vastus medialis complex (VMC), which is composed of the vastus medialis obliquus (VMO) and the vastus medialis longus (VML) muscles. The physiologic cross-sectional area of the VMO for 20 of the knees was 29% of the total physiologic cross-sectional area for the VMC. These values differed in one knee with a dysplastic VMO. The quantitative description of the VMO provided by this study will facilitate future efforts to accurately model the physiologic function of the VMO in cadaveric investigations on patellofemoral mechanics. The effect of simulated pathologies and surgical reconstructions then may be determined with more certainty to improve patient management.

Adult↗

PubMed1997

An inverse dynamics modeling approach to determine the restraining function of human knee ligament bundles.

During knee motion, the fiber bundles of ligaments are nonuniformly loaded in a recruitment pattern which is different for successive knee-joint positions. As a result, the restraining functions of these ligaments are variable. To analyze the relative restraint contributions of the fiber bundles in different knee-joint positions, a new method was developed. Its application was illustrated for the cruciate ligaments of one knee-joint specimen. The methods developed to estimate bundle forces comprise five steps. First, the three-dimensional motions of a knee specimen are measured for anterior-posterior forces, using Röntgen Stereophotogrammetric Analysis. Second, bone-ligament-bone tensile tests are performed to evaluate the mechanical properties of these structures in several relative orientations of the bones. Third, multiple fiber bundles are identified in each ligament, based on the main fiber orientations. Fourth, the nonlinear force-length relationship of each functional bundle, as defined by a stiffness and a recruitment parameter, is determined by combining the multidirectional tensile tests with a multiline-element ligament model. Finally, the information obtained is combined in a whole-joint computer model of the knee, to determine the internal forces in the initial kinematic experiment, using an inverse dynamics approach. The technique appeared to be extremely time consuming and technologically involved. However, it was demonstrated to be useful and effective. The preliminary results reveal that the fiber bundle restraints are extremely sensitive to the knee flexion angle and the restraining forces are highly variable within the ligaments. For both cruciate ligaments, a gradual transition was demonstrated in load transfer from the posterior bundles to the more anteriorly positioned ones during knee flexion. Furthermore, it appeared that relatively high forces were carried by only a few fiber bundles at each flexion angle. Based on these preliminary results, it is concluded that the determination of forces in multiple ligament bundles is important for the understanding of failure mechanisms of ligaments. In particular, alternate loading of different fiber bundles suggests that successful operative reconstruction of the cruciate ligaments may not be achieved simply by a one-bundle preparation.

Algorithms↗

PubMed1997

Error propagation for relative motion determined from marker positions.

In this paper, the error propagation for relative motion reconstructed from noisy marker position data was investigated, particularly the influence of the distance between two rigid bodies was explored. Based on a mathematical derivation, an error propagation model for relative motion was proposed and computer simulations were used to validate the proposed model. The results indicated that the error in the translation components for relative motion between two rigid bodies are proportional to the distance between the rigid bodies. The maximum absolute difference between the model and the simulation is 0.58% which strongly validated the accuracy of the error propagation model.

Computer Simulation↗

PubMed1996

A mechanism for rotation restraints in the knee joint.

Ligament function in restraining axial rotation of the tibia relative to the femur cannot be revealed by analysis of ligament forces alone. The action of the articular surfaces should be taken into account as well. In this study, three-dimensional mathematical models of four human knee joints were used to determine the limits of axial rotation between 0 and 90 degrees of flexion, whereby the forces in the ligaments and articular contact were calculated, together with their contribution to the restraint moment that was required to counterbalance the applied axial moment of 3 Nm. In external rotation, the direct axial restraint was provided by the collateral ligaments. In internal rotation, when the cruciate ligaments and medial collateral ligament were predominantly loaded, the direct restraint moment resulting from the ligament forces was not sufficient to counterbalance the applied moment. The articular contact forces, which resulted from balancing the axial components of the ligament forces, contributed considerably to the restraint of internal rotation. Depending on the flexion angle, the contact forces provided approximately 50-85% of the internal restraint, whereas 95-100% of the external rotation restraint was accounted for by the ligament forces.

Humans↗

PubMed1996

Characterization of the mechanical behavior of human knee ligaments: a numerical-experimental approach.

During knee-joint motions, the fiber bundles of the knee ligaments are nonuniformly loaded in a recruitment pattern, which depends on successive relative orientations of the insertion sites. These fiber bundles vary with respect to length, orientation and mechanical properties. As a result, the stiffness characteristics of the ligaments as a whole are variable during knee-joint motion. The purpose of the present study is to characterize this variable mechanical behavior. It is hypothesized that for this purpose it is essential to consider the ligaments mechanically as multi-bundle structures in which the variability in fiber bundle characteristics is accounted for, rather than as one-dimensional structures. To verify this hypothesis, bone-ligament-bone preparations of the ligaments were subjected to series of unidirectional subfailure tensile tests in which the relative insertion orientations were varied. For each individual test specimen, this series of tensile tests was simulated with a mathematical ligament model. Geometrically, this model consists of multiple line elements, of which the insertions and orientations are anatomically based. In a mathematical optimization process, the unknown stiffness and recruitment parameters of the line elements are identified by fitting the variable stiffness characteristics of the model to those of the test series. Thus, lumped parameters are obtained which describe the mechanical behavior of the ligament as a function of the relative insertion orientation. This method of identification was applied to all four knee ligaments. In all cases, a satisfactory fit between experimental results and computer simulation was obtained, although the residual errors were lower for the cruciate ligaments (1.0-2.4%) than for the collateral ligaments (3.7-8.1%). It was found that models with three or less line elements were very sensitive to geometrical parameters, whereas models with more than 7 line elements suffered from mathematical redundancy. Between 4 and 7 line elements little difference was found. It is concluded that the present ligament models can realistically simulate the variable tensile behavior of human knee ligaments. Hereby the hypothesis is verified that it is essential to consider the ligaments of the knee as multi-bundle structures in order to characterize fully their mechanical behavior.

Aged↗