A comparative evaluation of the mechanical properties of the rabbit medial collateral and anterior cruciate ligaments

The biomechanical properties of the medial collateral and anterior cruciate ligaments from 30 New Zealand White rabbits were measured. Because of its complex geometry, the ACL was divided into two portions (medial and lateral) to provide uniform loading. This allowed an examination of the intra-ligamentous properties. A laser micrometer system was used to measure the cross-sectional area for tensile stress and a video dimension analyzer was used to measure the strain. The mechanical properties (stress-strain curves) of the MCL and ACL were different, with the modulus (determined between 4 and 7% strain) in the MCL (1120 +/- 153 MPa) more than twice that of either portion of the ACL (516 +/- 64 and 516 +/- 69 MPa for the medial and lateral portions, respectively). This higher modulus correlated with the more uniform and dense appearance of the collagen fibrils examined with scanning electron microscopy (SEM).

Characterization of two missense mutations in human galactose-1-phosphate uridyltransferase: Different molecular mechanisms for galactosemia

We report the molecular characterization of two novel galactosemia mutations that exhibit different molecular phenotypes. Both are of the missense type with low or no residual enzyme activity. The R148W mutation results in an unstable protein, although messenger RNA is still produced. In contrast, the L195P mutation produces stable but inactive immunoreactive protein. The R148W mutation alters an amino acid that is not evolutionarily conserved, while the L195P mutation affects a well-conserved residue nine amino acids down-stream from the putative active site nucleophile. These mutations provide evidence that different mechanisms can result in galactosemia: destabilizing mutations in any given area of the protein and missense mutations in conserved domains of the enzyme resulting in low or no activity. These two mutant alleles represent the fifth and sixth galactosemia mutations and confirm the hypothesis that galactosemia results from a multiplicity of mutations at the molecular level.

Rib perichondrial autografts in full-thickness articular cartilage defects in rabbits

This study investigated the resurfacing of full-thickness articular defects in the adult rabbit medial femoral condyle using a rib perichondrial graft. The graft was secured to a 4-mm-diameter bone core removed from the femoral condyle. Two postoperative treatment protocols were studied: one group had ad libitum cage activity (CAGE; n = 95) and the other group received two weeks of passive motion (PM; n = 73; eight hours per day, five days per week) followed by cage activity. Animals in both groups were killed at six, 12, 26, and 52 weeks. Repair tissue resembling hyaline cartilage formed in a majority of animals at all time periods and in both postoperative treatment groups. The overall success rates in which repair tissue formed were 58% in the CAGE group and 56% in the PM group. However, over time, a maturation of the neocartilage into nearly normal hyaline articular cartilage was noted with the percentage of Type II collagen increasing from 55% at six weeks to 82% at one year. The complex shear modulus of the repair tissue for both groups became similar to normal cartilage with increased healing time. There was no statistical difference in shear moduli between the two treatment modalities. These results show that cartilage repair tissue derived from rib perichondrium could mature into hyaline articular cartilage over time and would not degrade by one year after repair.

The effect of storage on the biomechanical behavior of articular cartilage--a large strain study

The transplantation of stored shell osteochondral allografts is a potentially useful alternative to total joint replacements for the treatment of joint ailments. The maintenance of normal cartilage properties of the osteochondral allografts during storage is important for the allograft to function properly and survive in the host joint. Since articular cartilage is normally under large physiological stresses, this study was conducted to investigate the biomechanical behavior under large strain conditions of cartilage tissue stored for various time periods (i.e., 3, 7, 28, and 60 days) in tissue culture media. A biphasic large strain theory developed for soft hydrated connective tissues was used to describe and determine the biomechanical properties of the stored cartilage. It was found that articular cartilage stored for up to 60 days maintained the ability to sustain large compressive strains of up to 40 percent or more, like normal articular cartilage. Moreover, the equilibrium stress-strain behavior and compressive modulus of the stored articular cartilage were unchanged after up to 60 days of storage.

Reconstitution of enzymatic activity in hepatocytes of phenylalanine hydroxylase-deficient mice

Phenylketonuria (PKU) is a metabolic disorder secondary to a deficiency of the hepatic enzyme phenylalanine hydroxylase (PAH). The recent creation of a mouse strain for PAH deficiency has provided an excellent model system to explore the possibility of its phenotypic correction by hepatic gene therapy. A recombinant retrovirus containing the mouse PAH cDNA under the transcriptional control of the human CMV promoter was constructed and used to transduce hepatocytes isolated from PAH-deficient mice. Viral-transduced hepatocytes produced dramatically higher levels of mouse PAH mRNA as compared to control mock-infected hepatocytes. The PAH mRNA was translated efficiently into PAH protein that is capable of converting phenylalanine to tyrosine in vitro. These results demonstrate that the PAH-deficient mouse hepatocytes can be readily reconstituted by retroviral-mediated gene transduction, which is a crucial step towards somatic gene therapy for PKU.

Molecular basis of phenylketonuria and related hyperphenylalaninemias: mutations and polymorphisms in the human phenylalanine hydroxylase gene

Mutations in the human phenylalanine hydroxylase gene producing phenylketonuria or hyperphenylalaninemia have now been identified in many patients from various ethnic groups. These mutations all exhibit a high degree of association with specific restriction fragment-length polymorphism haplotypes at the PAH locus. About 50 of these mutations are single-base substitutions, including six nonsense mutations and eight splicing mutations, with the remainder being missense mutations. One splicing mutation results in a 3 amino acid in-frame insertion. Two or 3 large deletions, 2 single codon deletions, and 2 single base deletions have been found. Twelve of the missense mutations apparently result from the methylation and subsequent deamination of highly mutagenic CpG dinucleotides. Recurrent mutation has been observed at several of these sites, producing associations with different haplotypes in different populations. About half of all missense mutations have been examined by in vitro expression analysis, and a significant correlation has been observed between residual PAH activity and disease phenotype. Since continuing advances in molecular methodologies have dramatically accelerated the rate in which new mutations are being identified and characterized, this register of mutations will be updated periodically.

A defective splice site at the phenylalanine hydroxylase gene in phenylketonuria and benign hyperphenylalaninemia among Palestinian Arabs

Phenylketonuria (PKU) and benign hyperphenylalaninemia (HPA) result from different combinations of mutations at the locus for phenylalanine hydroxylase (PAH). While some of these mutations show widespread ethnic distribution, others are unique to specific communities. We report here the first point mutation common among Palestinian Arabs. The mutation (IVS2nt1) involves a dinucleotide substitution (Gg-->Aa) at the donor splice site of intron 2 of the PAH gene and abolishes a recognition site of the restriction enzyme MnlI. IVS2nt1 is associated with two PAH polymorphic haplotypes, 7 and 42. Homozygotes for this mutation are affected with severe, classical PKU. Compound heterozygotes carrying the IVS2nt1 allele and one of several other yet unknown mutations show different degrees of benign HPA.

Ultrastructural morphometry of anterior cruciate and medial collateral ligaments: an experimental study in rabbits

This study presents morphometric analyses of collagen subfascicle area fraction and collagen fibril diameter distributions for the anterior cruciate (ACL) and medial collateral (MCL) knee ligaments from transmission electron micrographs of ligament cross sections of five mature, female New Zealand White rabbits. Statistically significant differences in subfascicular area fractions were found between the ACL and MCL (0.89 +/- 0.02, 0.97 +/- 0.01, respectively; p less than 0.001). Mean fibril diameters for the ACL and MCL were also significantly different (0.059 +/- 0.005, 0.085 +/- 0.011 microns, respectively; p less than 0.025). Fibril eccentricity (a measure of parallel alignment of collagen fibrils within the ligaments, defined as the ratio of minor to major axes of elliptical fibril outlines) was 0.89 +/- 0.03 and 0.85 +/- 0.08, respectively, for the ACL and MCL; these data were not significantly different (p greater than 0.1). The relative amount of variation in the pooled fibril diameter data due to variation between animals, ligaments, locations within ligaments, and among fibrils at individual locations are reported. The variation of fibril diameter distributions between the ACL and MCL was substantially greater than the variation between different locations within each ligament cross section as well as between different animals. The structural differences reported may help explain known differences in the biomechanical properties of the ACL and MCL.

Two missense mutations causing mild hyperphenylalaninemia associated with DNA haplotype 12

The genetic defects responsible for most phenylketonuria (PKU) and hyperphenylalaninemia (HPA) cases are located in the phenylalanine hydroxylase (PAH) gene. Approximately 50-60 mutations have been reported in Caucasians and are reflected in a wide range of clinical severities. Most mutations are linked to specific haplotypes, as defined by eight polymorphic restriction sites in the PAH gene. We hypothesized that there is at least one mild mutation linked to haplotype 12 in the Swedish PKU/HPA population, since 7 of 8 patients carrying haplotype 12 had mild HPA. Sequence analysis revealed a C-to-G transversion at the second base of codon 322, resulting in a substitution of glycine for alanine, in four mutant haplotype 12 genes, and a G-to-A transition at the second base of codon 408, resulting in a substitution of glutamine for arginine, in another three mutant haplotype 12 genes. These mutations segregated with mutant haplotype 12 alleles in nuclear families but were not present on normal or other mutant alleles. Both mutations were tested in a eukaryotic expression system in which enzyme activities of different mutant PAH enzymes reflect the relative severities of the mutations, although these in vitro activities cannot be translated directly into in vivo hepatic activities. The A322G mutant PAH had about 75% and the R408Q mutant PAH about 55% of the wild-type PAH enzyme activity. These in vitro activities are the highest reported for mutant PAH enzymes produced in the same expression system.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatocellular transplantation in acute hepatic failure and targeting genetic markers to hepatic cells

Orthotopic liver transplantation (OLT) represents the only therapeutic option for many patients with end-stage liver disease as well as many inborn genetic errors of hepatic metabolism. Despite dramatic progress in methods for OLT, the utilization of this procedure is limited by its considerable morbidity and mortality, by a chronic shortage of organs for transplant, and by difficulty arranging funding for many patients. Many children with fulminant hepatic failure do not receive OLT because this technology is unavailable or unaffordable. Hepatocellular transplantation (HCT), in which isolated, heterologous hepatocytes from a donor liver would be infused into the diseased organ in order to provide essential hepatic functions, could provide a much needed therapeutic alternative to OLT in the treatment of some causes of hepatic insufficiency. Experiments in animals have demonstrated that several genetic deficiencies of hepatic metabolism as well as experimental induced hepatic failure in animals can be reversed by HCT. Despite this experience, HCT has never been attempted in human subjects. This protocol represents the first proposed clinical trial of HCT. We are proposing a clinical trial in which HCT would be attempted as a therapeutic intervention in children with acute hepatic failure who have no other medical or surgical options. This proposal is intended to establish surgical methods for HCT and to evaluate the feasibility of this procedure for treating hepatic disease in humans. It is our expectation that HCT may provide short-term support for patients awaiting organ availability, a "bridge to recovery" allowing patients with fulminant hepatic failure to recover, or a long-term repopulation of the patient's liver with healthy donor cells. One of the major limitations of many animal studies in HCT is that, since the donor hepatocytes are often indistinguishable from those of the host, it has often been difficult to demonstrate a clear correlation between engraftment and the therapeutic effect. In order to verify engraftment independent of the therapeutic response, we propose to "mark" the donor hepatocytes by transducing these cells with a recombinant retroviral vector (LNL6) carrying a marker gene (NEO-R, neomycin phosphoribosyl transferase). The presence of this marker will enhance the ability to identify transplanted cells in the host using assays for the NEO-R gene or transcribed NEO-R mRNA. The LNL6 vector has been approved for human use and has been used as a marker gene for transplanted cells in human subjects without any reported adverse effects. We would like to emphasize that this is a proposal with therapeutic intent.(ABSTRACT TRUNCATED AT 400 WORDS)

Application of the u-p finite element method to the study of articular cartilage

The finite element method using the principle of virtual work was applied to the biphasic theory to establish a numerical routine for analyses of articular cartilage behavior. The matrix equations that resulted contained displacements of the solid matrix (mu) and true fluid pressure (p) as the unknown variables at the element nodes. Both small and large strain conditions were considered. The algorithms and computer code for the analysis of two-dimensional plane strain, plane stress, and axially symmetric cases were developed. The u-p finite element numerical procedure demonstrated excellent agreement with available closed-form and numerical solutions for the configurations of confined compression and unconfined compression under small strains, and for confined compression under large strains. The model was also used to examine the behavior of a repaired articular surface. The differences in material properties between the repair tissue and normal cartilage resulted in significant deformation gradients across the repair interface as well as increased fluid efflux from the tissue.

Ultrastructural differences between the cells of the medical collateral and the anterior cruciate ligaments

The anterior cruciate ligament (ACL) does not heal after an interstitial tear, in contrast to the medial collateral ligament (MCL), whose interstitial tears heal readily. The light microscopic and ultrastructural differences between the cells of the two ligaments were studied in rabbit knees to observe the healing characteristics of the two ligaments. A rabbit knee was chosen because the rabbit ACL, like that of humans, does not heal following interstitial injury. The cells populating the MCL have the characteristics of fibroblasts. The cells of the ACL resemble fibrocartilage cells. The phenotypic differences in the cells of the two ligaments may be important determinants of the differences in healing.

Molecular characterization of two galactosemia mutations: correlation of mutations with highly conserved domains in galactose-1-phosphate uridyl transferase

Galactosemia is an autosomal recessive disorder of human galactose metabolism caused by deficiency of the enzyme galactose-1-phosphate uridyl transferase (GALT). The molecular basis of this disorder is at present not well understood. We report here two missense mutations which result in low or undetectable enzymatic activity. First, we identified at nucleotide 591 a transition which substitutes glutamine 188 by arginine. The mutated glutamine is not only highly conserved in evolution (conserved also in Escherichia coli and Saccharomyces cerevisiae), but is also two amino acid residues downstream from the active site histidine-proline-histidine triad and results in about 10% of normal enzymatic activity. The arginine 188 mutation is the most common galactosemia mutation characterized to date. It accounts for one-fourth of the galactosemia alleles studied. Second, we report the substitution of arginine 333 by tryptophan, caused by a transition at nucleotide 1025. The area surrounding this missense mutation is the most highly conserved domain in the homologous enzymes from E. coli, yeast, and humans, and this mutation results in undetectable enzymatic activity, suggesting that this is a severe mutation. This second mutation appears to be rare, since it was found only in the patient we sequenced. Our data provide further evidence for the heterogeneity of galactosemia at the molecular level, heterogeneity which might be related to the variable clinical outcome observed in this disorder.

The effects of frequency and duration of controlled passive mobilization on tendon healing

This study was designed to determine the effects of frequency and duration of controlled passive motion on the healing flexor tendon following primary repair. Adult mongrel dogs were divided into two groups based on frequency of controlled passive motion. In one group, motion was applied manually at a frequency of 12 cycles/min for 5 min/day; in the other group, a continuous passive motion machine was used to apply motion at a lower frequency of 1 cycle/min for 60 min/day, making the number of cycles each day for both groups identical. Gliding function and tensile properties of repaired tendons were evaluated biomechanically at 3 and 6 weeks postoperatively. Results showed that gliding function in both groups was similar, but tensile properties, as represented by linear slope, ultimate load, and energy absorption, were significantly improved in the higher frequency group. It was concluded that frequency of controlled passive motion rehabilitation is a significant factor in accelerating the healing response following tendon repair, and higher frequency-controlled passive motion has a beneficial effect.

Finite element analyses of repaired articular surfaces

The response to a compressive load of a repaired cartilage surface, consisting of full-thickness repair tissue adjacent to normal cartilage, was predicted by the u-p finite element method and compared to that of a normal cartilage surface under the same loading conditions. By individually varying the aggregate modulus, permeability and Poisson's ratio for the repair tissue, analyses were performed to assess the contributions of each to the changes in mechanical behaviour. In comparing the repaired to normal surfaces, the presence of a softer repair tissue resulted in increased axial and decreased radial deformations at any given time point, while a repaired surface with an increased permeability compressed more easily due to the increased fluid flow and caused equilibrium to occur sooner. For smaller Poisson's ratio, the axial deformation was not different from normal if the aggregate modulus was the same as normal; however, the radial expansion was reduced as the repair tissue experienced a larger volume change. These results indicate that the presence of repair tissue in a joint surface can have a strong influence on the mechanical behaviour of the surface.

Stress relaxation of a peripheral nerve

This study determines the change in tension after an acute nerve lengthening, as would occur in peripheral nerve repair. Stress relaxation, a viscoelastic property, was studied with the use of 24 rabbit tibial nerves. The nerves were divided into three groups and were stretched 6%, 9%, or 12% beyond their original resting length. The mean 1-hour stress relaxations for the three groups were 48%, 34%, and 34%, respectively. Nerve stress relaxation was significantly greater at 6% strain than at 9% or 12% strain. These biomechanical findings have important clinical implications for nerve-stretch injury and for nerve repair.

Compound heterozygosity in nonphenylketonuria hyperphenylalanemia: the contribution of mutations for classical phenylketonuria

Hyperphenylalaninemia (HPA) results from defective hydroxylation of phenylalanine in the liver, in most cases because of defective phenylalanine hydroxylase. HPA is highly variable, ranging from moderate elevation of plasma phenylalanine with no clinical consequences to a severe disease, classical phenylketonuria (PKU). Non-PKU HPA was found in excess of PKU in Israel, while the opposite is true in Europe. To study the genetic basis of non-PKU HPA, we performed haplotype analysis at the phenylalanine hydroxylase locus in 27 families with non-PKU HPA. All individuals with this condition were compound heterozygotes. In six of these families, in which both PKU and non-PKU HPA were segregating, haplotype analysis showed that non-PKU HPA resulted from compound heterozygosity for a PKU mutation and a second mutation, with milder effect, which is probably expressed only when it interacts with the severe mutation. The involvement of PKU mutations in non-PKU HPA was further demonstrated in Jewish Yemenite families with non-PKU HPA, in which the individuals with this condition were carriers of the single PKU allele which exists in this community. In addition, two previously known PKU point mutations (R261Q and R408W) were found in individuals with non-PKU HPA. These mutations are associated, in our population, with the same haplotypes as those with which it is associated in Europe. Based on the above-mentioned genetic model for non-PKU HPA, successful prenatal diagnosis of this condition was performed in one family.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a new injury model to study medial collateral ligament healing: primary repair versus nonoperative treatment

The medial collateral ligament (MCL) of the rabbit left hindlimb was ruptured by a rod placed beneath it, resulting in a "mop-end" tear of the ligament substance with simultaneous injury to the insertion sites. Using this model, we compared primary ligament repair and nonoperative treatment using biomechanical and histologic techniques at time zero, 10 days, and 6 and 12 weeks postoperatively. Biomechanical evaluation included measurement of varus-valgus (V-V) knee rotation, in situ load on the MCL, and tensile testing of the femur-MCL-tibia complex (FMTC). The V-V rotation of all experimental knees decreased over time. At 12 weeks, V-V rotation of experimental knees was still 1.3 times larger than that of controls. Primary repair initially decreased V-V rotation, but at 6 and 12 weeks there was no statistical difference between operated and nonoperated knees. The in situ load on the MCL followed the same trends. There was no significant effect of MCL repair on any of the tensile properties. However, postoperative healing time significantly improved the FMTC structural properties in both experimental groups. Failure modes of the FMTCs and histologic sections of the ligament insertion sites indicated that after injury the ligament insertion to bone recovered more slowly than the ligament substance. Tensile testing of the FMTC showed that even at 12 weeks postoperatively the mechanical properties of the healed ligament material remained significantly different from those of the controls.

Viscoelastic shear properties of the equine medial meniscus

Recent studies have shown that the meniscus is highly anisotropic in tension and that its compressive creep behavior can be modeled using biphasic theory. In this study, an alternative approach is used, where viscoelastic shear properties of the meniscal fibrocartilage are measured to determine the anisotropy and inhomogeneity of this tissue with respect to specimen location and fiber orientation. Medial menisci were obtained from eight skeletally-mature horses. Nine test specimens were taken from the circumferential midsubstance of each meniscus, at three circumferential and three axial positions. The magnitude of the complex shear modulus and the phase angle were determined for each specimen from 100-800 Hz, in 100 Hz increments. Data were gathered shearing parallel and perpendicular to the circumferentially-oriented fibers. The magnitude of the shear modulus and the phase angle were both found to be frequency dependent, anisotropic, and inhomogeneous. The magnitude of the shear modulus increased with frequency, and was greatest in specimens from the posterior superior region, shearing parallel to the fibers. The phase angle decreased slightly with frequency and was lowest in specimens from the midsubstance of the anterior region, shearing perpendicular to the fibers. Our data demonstrated that collagen fibers substantially stiffen the meniscus in the direction of its fibers and that the solid matrix of the meniscus, like articular cartilage, behaves largely as an elastic material.

The effects of increased tension on healing medical collateral ligaments

The effects of motion and increased levels of stress on the biomechanical, biochemical, and morphological properties of healing medial collateral ligaments were assessed in a rabbit model. In one group, the medial collateral ligament of the left hindlimb was transected and allowed to heal with cage activity for either 6 or 12 weeks. In another group, the transected ligaments were permitted to heal for 4 weeks and then were placed under increased stress by inserting a stainless steel pin perpendicularly underneath the healing medial collateral ligament. The animals were allowed cage activity for an additional 2 or 8 weeks. The varus-valgus joint laxity and the stress-strain properties of the medical collateral ligament substance were obtained. Further, the quantity of total collagen, amount and ratio of the collagen cross-links, dihydroxylysinonorleucine and hydroxylysinonorleucine, and the histologic appearance of the healing medical collateral ligaments were evaluated for all groups. At 6 weeks, knees with a transected medial collateral ligament were twice as lax as the controls. However, joints with the stainless steel tension pin had varus-valgus values approximately 1.5 times those of the controls. At 12 weeks, joints with increased stress were not statistically different from the controls. The group that had healing with increased stress for 12 weeks produced the highest stress for a given strain compared to any other group. Also, the total collagen levels and the ratio of dihydroxylysinonorleucine/hydroxylysinonorleucine were the closest to normal of any transected group. Finally, qualitative histologic improvements were seen, including a more longitudinal arrangement of collagen fibers and decreased cellularity.

Missense mutations prevalent in Orientals with phenylketonuria: molecular characterization and clinical implications

Two missense mutations in the phenylalanine hydroxylase (PAH) genes of Orientals with phenylketonuria (PKU) have been identified. A G-to-A transition in exon 7 of the gene results in the substitution of Gln243 for Arg243 (R243Q) and accounts for 18% of all PKU chromosomes among Chinese. An A-to-G transition in exon 6 of the gene results in the substitution of Cys204 for Tyr204 (Y204C) and identifies about 13 and 5% of all PKU chromosomes in the Chinese and Japanese populations, respectively. The R243Q construct produced less than 10% of normal PAH activity in in vitro expression analysis in a eukaryotic cell system, and patients homozygous for this substitution exhibit a severe clinical phenotype. These results are consistent with previous findings in this expression system. The Y204C construct, however, produced near normal levels of PAH enzyme activity and immunoreactivity in this in vitro expression system. Because this substitution is present only on PKU chromosomes, it is a valuable marker for identifying the corresponding mutant allele for carrier screening of PKU. With the characterization of these two substitutions, about 60% of PKU alleles in China can now be identified. The continuing search for additional PKU mutations will permit effective carrier screening and prenatal gene diagnosis of PKU in East Asia.

Tensile properties of the human femur-anterior cruciate ligament-tibia complex. The effects of specimen age and orientation

The structural properties of 27 pairs of human cadaver knees were evaluated. Specimens were equally divided into three groups of nine pairs each based on age: younger (22 to 35 years), middle (40 to 50 years), and older (60 to 97 years). Anterior-posterior displacement tests with the intact knee at 30 degrees and 90 degrees of flexion revealed a significant effect of knee flexion angle, but not of specimen age. Tensile tests of the femur-ACL-tibia complex were performed at 30 degrees of knee flexion with the ACL aligned vertically along the direction of applied tensile load. One knee from each pair was oriented anatomically (anatomical orientation), and the contralateral knee was oriented with the tibia aligned vertically (tibial orientation). Structural properties of the femur-ACL-tibia complex, as represented by the linear stiffness, ultimate load, and energy absorbed, were found to decrease significantly with specimen age and were also found to have higher values in specimens tested in the anatomical orientation. In the younger specimens, linear stiffness (242 +/- 28 N/mm) and ultimate load (2160 +/- 157 N) values found when the femur-ACL-tibia complex was tested in the anatomical orientation were higher than those reported previously in the literature. These values provide new baseline data for the design and selection of grafts for ACL replacement in an attempt to reproduce normal knee kinematics.

The effects of knee motion and external loading on the length of the anterior cruciate ligament (ACL): a kinematic study

A six-degrees-of-freedom mechanical linkage device was designed and used to study the unconstrained motion of ten intact human cadaver knees. The knees were subjected to externally applied varus and valgus (V-V) moments up to 14 N-m as well as anterior and posterior (A-P) loads up to 100 N. Tests were done at four knee flexion angles; 0, 30, 45, and 90 deg. Significant coupled axial tibial rotation was found, up to 21.0 deg for V-V loading (at 90 deg of flexion) and 14.2 deg for A-P loading (at 45 deg of flexion). Subsequently, the knees were dissected and the locations of the insertion sites to the femur and tibia for the anteromedial (AM), posterolateral (PL), and intermediate (IM) portions of the ACL were identified. The distances between the insertion sites for all external loading conditions were calculated. In the case when the external load was zero, the AM portion of the ACL lengthened with knee flexion, while the PL portion shortened and the intermediate (IM) portion did not change in length. With the application of 14 N-m valgus moment, the PL and IM portions of the ACL lengthened significantly more than the AM portion (p less than 0.001). With the application of 100 N anterior load, the AM portion lengthened slightly less than the PL portion, which lengthened slightly less than the IM portion (p less than 0.005). In general, the amount of lengthening of the three portions of the ACL during valgus and anterior loading was observed to increase with knee flexion angle (p less than 0.001).