Cross-sectional area measurement of soft tissue. A new casting method

The Development of a Gracilis and Quadriceps Tendons Calibration Device for Uniaxial Tensile Tests

To determine the biomechanical properties of the distal tendon of the gracilis muscle and the upper third of the quadriceps femoris muscle used for reconstruction of the medial patellofemoral ligament (MPFL), it is necessary to develop a calibration device for specimen preparation for uniaxial tensile tests. The need to develop this device also stems from the fact that there is currently no suitable regulatory or accurate protocol by which soft tissues such as tendons should be tested. In recent studies, various methods have been used to prepare test specimens, such as the use of different ratios of gauge lengths, different gripping techniques, etc., with the aim of obtaining measurable and comparable biomechanical tissue properties. Since tendons, as anisotropic materials, have viscoelastic properties, the guideline for manufacturing calibrator devices was the ISO 527-1:1993 standard, used for testing polymers, since they also have viscoelastic behaviour. The functionality of a calibrator device was investigated by preparing gracilis and quadriceps tendon samples. Fused deposition modeling (FDM) technology was used for the manufacturing of parts with complex geometry. The proposed calibrator could operate in two positions, horizontal and vertical. The maximum gauge length to be achieved was 60 mm, with the maximum tendon length of 120 mm. The average preparation time was 3 min per tendon. It was experimentally proven that it is possible to use a calibrator to prepare tendons for tensile tests. This research can help in the further development of soft tissue testing devices and also in the establishment of standards and exact protocols for their testing.

Cross-Sectional Area Measurement Techniques of Soft Tissue: A Literature Review

Evaluation of the biomechanical properties of soft tissues by measuring the stress-strain relationships has been the focus of numerous investigations. The accuracy of stress depends, in part, upon the determination of the cross-sectional area (CSA). However, the complex geometry and pliability of soft tissues, especially ligaments and tendons, make it difficult to obtain accurate CSA, and the development of CSA measurement methods of soft tissues continues. Early attempts to determine the CSA of soft tissues include gravimetric method, geometric approximation technique, area micrometer method, and microtomy technique. Since 1990, a series of new methods have emerged, including medical imaging techniques (e.g. magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging (USI)), laser techniques (e.g. the laser micrometer method, the linear laser scanner (LLS) technique, and the laser reflection system (LRS) method), molding techniques, and three-dimensional (3D) scanning techniques.

A novel alginate localization molding technique for cross-sectional area measurement of human tendon to access biomechanical properties

Accurate determination of the biomedical properties of connective tissue such as tendons and ligaments is dependent on the accurate measurement of their cross-sectional area (CSA). To date, techniques for determining cross-sectional areas of ligaments and tendons have been less than ideal due to their complex geometries and their deformations under external load. A novel non-destructive technique has been developed for determining the cross-sectional area of tendon by locating the tendon rupture, in which aqueous rapid curing alginate dental molding materials, digital photography and computerized image analysis are utilized. This technique marks tendons and alginate molds at 1 cm interval and then tendons are taken out for tensile test. Real-time video is recorded to locate the position of tendon rupture. The corresponding alginate slice is found and then analysis through computer image processing software to obtain a more accurate CSA at tendon rupture, which can be used to calculate the stress and young's modulus of tendon. The accuracy of this technique has been investigated and comparisons have been made with the alginate un-localization molding technique and ellipse estimation technique. Results show this technique can provide accurate CSA values (within 2%) and great reproducibility (coefficient of variation = 0.8%). The technique is non-destructive, can obtain morphological information of soft tissue and can detect cavities.

Reliability and Validity of Measurement Tools for Residual Limb Volume in People With Limb Amputations: A Systematic Review

BACKGROUND

Measurements of residual limb volume often guide decisions on the type and timing of prosthetic prescription. To help inform these decisions, it is important that clinicians use measurement tools that are reliable and valid.

PURPOSE

The aim of this systematic review was to investigate the reliability and validity of measurement tools for residual limb volume in people with limb amputations.

DATA SOURCES

A comprehensive search on MEDLINE, EMBASE, CINAHL, Scopus, and Web of Science was performed on July 11, 2016.

STUDY SELECTION

Studies were included if they examined the reliability or validity of measurement tools for residual limb volume, were conducted on humans, and were published in English.

DATA EXTRACTION

Data were extracted from 11 reliability and 4 validity studies and included study characteristics, volumetric estimates, and reliability and validity estimates. The quality of the studies was also rated.

DATA SYNTHESIS

Data from 2 studies (38 participants) indicated good to excellent intrarater (intraclass correlation coefficient [ICC] ≥0.88) and interrater (ICC ≥0.88) reliability and high between-session reliability (coefficient of variation [CV] = 10%) for water displacement volumetry. One study (28 participants) reported excellent intrarater and interrater reliability (ICC ≥0.93) for the circumferential method, and data from 2 studies (19 participants) indicated high between-session reliability for the optical surface scanner (CV ≤9.8%). Three studies (26 participants) indicated good to excellent between-session reliability results for computed tomography (CV = 9.2%-10.9%). One study (7 participants) showed moderate within-session reliability (CV = 50%). Using water displacement volumetry as the gold standard, 2 studies (79 participants) indicated excellent validity for the circumferential method ( r ≥0.92; ICC ≥0.92). All studies reporting measures of reliability or validity were performed with people who had transtibial amputations.

LIMITATIONS

Only studies published in English and in which water displacement volumetry was used as the gold standard were included in this review. The reliability and validity of the quality rating scale used in this review have not been tested.

CONCLUSIONS

On the basis of a limited number of moderate- to high-quality studies with small sample sizes, circumferential and water displacement methods were found to be reliable, and the circumferential method was found to be valid in people with transtibial amputations. There are inadequate data for drawing conclusions about volume measurement methods in people with other types of limb amputations.

A review of methods to measure tendon dimensions

Tendons are soft tissues of the musculoskeletal system that are designed to facilitate joint movement. Tendons exhibit a wide range of mechanical properties matched to their functions and, as a result, have been of interest to researchers for many decades. Dimensions are an important aspect of tendon properties.

Change in the dimensions of tissues is often seen as a sign of injury and degeneration, as it may suggest inflammation or general disorder of the tissue. Dimensions are also important for determining the mechanical properties and behaviours of materials, particularly the stress, strain, and elastic modulus. This makes the dimensions significant in the context of a mechanical study of degenerated tendons. Additionally, tendon dimensions are useful in planning harvesting for tendon transfer and joint reconstruction purposes.

Historically, many methods have been used in an attempt to accurately measure the dimensions of soft tissue, since improper measurement can lead to large errors in the calculated properties. These methods can be categorised as destructive (by approximation), contact, and non-contact and can be considered in terms of in vivo and ex vivo.

White-Tailed Deer as an Ex Vivo Knee Model: Joint Morphometry and ACL Rupture Strength

Animal joints are valuable proxies for those of humans in biomechanical studies, however commonly used quadruped knees differ greatly from human knees in scale and morphometry. To test the suitability of the cervine stifle joint (deer knee) as a laboratory model, gross morphometry, ACL cross section, and ACL rupture strength were measured and compared to values previously reported for the knees of humans and commonly studied animals. Twelve knee joints from wild white-tailed deer were tested. Several morphometry parameters, including bicondylar width (53.5 ± 3.0 mm) and notch width (14.7 ± 2.5 mm), showed a high degree of similarity to those of the human knee, while both medial (16.7 ± 2.1°) and lateral (17.6 ± 4.7°) tibial slopes were steeper than in humans but less steep than other quadrupeds. The median ACL rupture force (2054 N, 95% CI 2017-2256 N), mean stiffness (260 ± 166 N/mm), mean length (33 ± 7 mm), and mean cross sectional area (44.8 ± 18.3 mm²) were also comparable to previously reported values for human knees. In our limited sample size, no significant sexual dimorphism in strength or morphometry was observed (p ≥ 0.05 for all parameters), though female specimens generally had steeper tibial slopes (lateral: p = 0.52, medial: p = 0.07). Our results suggest that the deer knee may be a suitable model for ex vivo studies of ACL rupture and repair.

Structured white light scanning of rabbit Achilles tendon

BACKGROUND

The cross-sectional area (CSA) of a material is used to calculate stress under load. The mechanical behaviour of soft tissue is of clinical interest in the management of injury; however, measuring CSA of soft tissue is challenging as samples are geometrically irregular and may deform during measurement. This study presents a simple method, using structured light scanning (SLS), to acquire a 3D model of rabbit Achilles tendon in vitro for measuring CSA of a tendon.

METHOD

The Artec Spider™ 3D scanner uses structured light and stereophotogrammetry technologies to acquire shape data and reconstruct a 3D model of an object. In this study, the 3D scanner was integrated with a custom mechanical rig, permitting 360-degree acquisition of the morphology of six New Zealand White rabbit Achilles tendons. The reconstructed 3D model was then used to measure CSA of the tendon. SLS, together with callipers and micro-CT, was used to measure CSA of objects with a regular or complex shape, such as a drill flute and human cervical vertebra, for validating the accuracy and repeatability of the technique.

RESULTS

CSA of six tendons was measured with a coefficient of variation of less than 2%. The mean CSA was 9.9±1.0mm², comparable with those reported by other researchers. Scanning of phantoms demonstrated similar results to μCT.

CONCLUSION

The technique developed in this study offers a simple and accurate method for effectively measuring CSA of soft tissue such as tendons. This allows for localised calculation of stress along the length, assisting in the understanding of the function, injury mechanisms and rehabilitation of tissue.

Tensile mechanical properties of human forearm tendons

Previous studies of the mechanical properties of tendons in the upper limb have used embalmed specimens or sub-optimal methods of measurement. The aim of this study was to determine the biomechanical properties of all tendons from five fresh frozen cadaveric forearms using updated methodology. The cross-sectional area of tendons was accurately measured using a laser reflectance system. Tensile testing was done in a precision servo-hydraulic device with cryo-clamp fixation. We determined that the cross-sectional area of some tendons is variable and directly influences the calculated material properties; visual estimation of this is unreliable. Data trends illustrate that digital extensor tendons possess the greatest tensile strength and a higher Young's modulus than other tendon types.

Evaluation of ACL mid-substance cross-sectional area for reconstructed autograft selection

PURPOSE

The purpose of this study was to compare the size of the native ACL mid-substance cross-sectional area and the size of commonly used autografts. Hypothesis of this study was that the reconstructed graft size with autografts would be smaller than the native ACL size.

METHODS

Twelve non-paired human cadaver knees were used. The ACL was carefully dissected, and the mid-substance of the ACL was cross-sectioned parallel to the articular surface of the femoral posterior condyles at 90 degrees of knee flexion. The size of the cross-sectional area of the ACL, and the femoral and tibial footprints were measured using Image J software (National Institute of Health). The semitendinosus tendon (ST) and the gracilis (G) tendon were harvested and prepared for ACL grafts. Simulating an ST graft, the ST was cut in half. The bigger half was regarded as the antero-medial (AM) bundle, and the remaining half was regarded as the postero-lateral (PL) bundle. Simulating an ST-G graft, the bigger half of the ST and G were regarded as the AM bundle, and the smaller half of the ST was regarded as the PL bundle. Each graft diameter was measured, and the graft area was calculated. Simulating a rectangular bone-patella tendon-bone (BPTB) graft, a 10-mm-wide BPTB graft was harvested and the area calculated.

RESULTS

The sizes of the ACL mid-substance cross-sectional area, femoral and tibial ACL footprint were 46.9 ± 18.3, 60.1 ± 16.9 and 123.5 ± 12.5 mm(2), respectively. The average areas of the ST, ST-G, and BPTB grafts were 52.0 ± 3.8, 64.4 ± 6.2, and 40.8 ± 6.7 mm(2), respectively. The ST and BPTB grafts showed no significant difference in graft size when compared with the ACL cross-sectional area.

CONCLUSION

ST and BPTB autografts were able to reproduce the native size of the ACL mid-substance cross-sectional area. The ST-G graft was significantly larger than the ACL cross-sectional area. For clinical relevance, ST and BPTB grafts are recommended in order to reproduce the native size of the ACL in anatomical ACL reconstruction with autograft.

Accuracy of MRI technique in measuring tendon cross-sectional area

Magnetic resonance imaging (MRI) has commonly been applied to determine tendon cross-sectional area (CSA) and length either to measure structural changes or to normalize mechanical measurements to stress and strain. The ability to reproduce CSA measurements on MRI images has been reported, but the accuracy in relation to actual tendon dimensions has never been investigated. The purpose of this study was to compare tendon CSA measured by MRI with that measured in vitro with the mould casting technique. The knee of a horse was MRI-scanned with 1.5 and 3 tesla, and two examiners measured the patellar tendon CSA. Thereafter, the patellar tendon of the horse was completely dissected and embedded in an alginate cast. The CSA of the embedded tendon was measured directly by optical imaging of the cast impression. 1.5 tesla grey tendon CSA and 3 tesla grey tendon CSA were 16.5% and 13.2% lower than the mould tendon CSA, respectively. Also, 3 tesla tendon CSA, based on the red-green border on the National Institute of Health (NIH) colour scale, was lower than the mould tendon CSA by 2.8%. The typical error between examiners was below 2% for all the measured CSA. The typical error between examiners was below 2% for all the measured CSA. These data show that measuring tendon CSA on the grey-scale MRI images is associated with an underestimation, but by optimizing the measurement using a 3 tesla MRI and the appropriate NIH colour scale, this underestimation could be reduced to 2.8% compared with the direct measurements on the mould.

Microstructural stress relaxation mechanics in functionally different tendons

Tendons experience widely varying loading conditions in vivo. They may be categorised by their function as either positional tendons, which are used for intricate movements and experience lower stress, or as energy storage tendons which act as highly stressed springs during locomotion. Structural and compositional differences between tendons are thought to enable an optimisation of their properties to suit their functional environment. However, little is known about structure-function relationships in tendon. This study adopts porcine flexor and extensor tendon fascicles as examples of high stress and low stress tendons, comparing their mechanical behaviour at the micro-level in order to understand their stress relaxation response. Stress-relaxation was shown to occur predominantly through sliding between collagen fibres. However, in the more highly stressed flexor tendon fascicles, more fibre reorganisation was evident when the tissue was exposed to low strains. By contrast, the low load extensor tendon fascicles appears to have less capacity for fibre reorganisation or shearing than the energy storage tendon, relying more heavily on fibril level relaxation. The extensor fascicles were also unable to sustain loads without rapid and complete stress relaxation. These findings highlight the need to optimise tendon repair solutions for specific tendons, and match tendon properties when using grafts in tendon repairs.

Impact of measurement errors on the determination of the linear modulus of human meniscal attachments

For the development of meniscal substitutes and related finite element models it is necessary to know the mechanical properties of the meniscus and its attachments. Measurement errors can falsify the determination of material properties. Therefore the impact of metrological and geometrical measurement errors on the determination of the linear modulus of human meniscal attachments was investigated. After total differentiation the error of the force (+0.10%), attachment deformation (-0.16%), and fibre length (+0.11%) measurements almost annulled each other. The error of the cross-sectional area determination ranged from 0.00%, gathered from histological slides, up to 14.22%, obtained from digital calliper measurements. Hence, total measurement error ranged from +0.05% to -14.17%, predominantly affected by the cross-sectional area determination error. Further investigations revealed that the entire cross-section was significantly larger compared to the load-carrying collagen fibre area. This overestimation of the cross-section area led to an underestimation of the linear modulus of up to -36.7%. Additionally, the cross-sections of the collagen-fibre area of the attachments significantly varied up to +90% along their longitudinal axis. The resultant ratio between the collagen fibre area and the histologically determined cross-sectional area ranged between 0.61 for the posterolateral and 0.69 for the posteromedial ligament. The linear modulus of human meniscal attachments can be significantly underestimated due to the use of different methods and locations of cross-sectional area determination. Hence, it is suggested to assess the load carrying collagen fibre area histologically, or, alternatively, to use the correction factors proposed in this study.

CROSS-SECTIONAL AREA MEASUREMENT OF SOFT TISSUES IN VITRO: A NON-CONTACT LASER SCAN METHOD

Measurements of cross-sectional areas (CSAs) of soft tissues such as tendons and ligaments allow for the evaluation of the biomechanical properties of the tissue. Underlying in vitro techniques are data reduction approaches for determining the average thickness of the tissue and the assumption of the geometry of the cross-section, i.e. circular or elliptical. However, tissue distortions, sagging, and concavities could affect the reliability of these techniques, since these features may not be accounted for adequately. To address some of the concerns faced by these techniques, a non-contact (non-destructive) laser scan technique has been developed. In this technique, a laser scans along the axis of the tissue, a coordinate measuring machine simultaneously locates the corresponding point on the tissue based on the detection of reflected (attenuated) intensity, and, finally, computerized image analysis reconstructs the morphology of the tissue. This technique was applied to patellar tendons (PTs) from New Zealand rabbits. The scanning time for each PT was less than 2 minutes. Reconstructed three-dimensional surface plots revealed microconcavities consistent with images seen under optical microscopy. CSAs of these PTs were determined for repeatability and precision; results from a conventional approach which estimated the corresponding CSAs based on the average thickness and the assumption of ellipsoidal cross-sectional geometry were also determined for the purpose of comparison. Based on the standard cuboid model, the error between the laser technique and the conventional approach was within 0.4%; the reproducibility of the laser technique was within 2%.

A linear laser scanner to measure cross-sectional shape and area of biological specimens during mechanical testing

Measure of the cross-sectional area (CSA) of biological specimens is a primary concern for many biomechanical tests. Different procedures are presented in literature but besides the fact that noncontact techniques are required during mechanical testing, most of these procedures lack accuracy or speed. Moreover, they often require a precise positioning of the specimen, which is not always feasible, and do not enable the measure of the same section during tension. The objective of this study was to design a noncontact, fast, and accurate device capable of acquiring CSA of specimens mounted on a testing machine. A system based on the horizontal linear displacement of two charge-coupled device reflectance laser devices next to the specimen, one for each side, was chosen. The whole measuring block is mounted on a vertical linear guide to allow following the measured zone during sample tension (or compression). The device was validated by measuring the CSA of metallic rods machined with geometrical shapes (circular, hexagonal, semicircular, and triangular) as well as an equine superficial digital flexor tendon (SDFT) in static condition. We also performed measurements during mechanical testing of three SDFTs, obtaining the CSA variations until tendon rupture. The system was revealed to be very fast with acquisition times in the order of 0.1 s and interacquisition time of about 1.5 s. Measurements of the geometrical shapes yielded mean errors lower than 1.4% (n=20 for each shape) while the tendon CSA at rest was 90.29 ± 1.69 mm(2) (n=20). As for the tendons that underwent tension, a mean of 60 measures were performed for each test, which lasted about 2 min until rupture (at 20 mm/min), finding CSA variations linear with stress (R(2)>0.85). The proposed device was revealed to be accurate and repeatable. It is easy to assemble and operate and capable of moving to follow a defined zone on the specimen during testing. The system does not need precise centering of the sample and can perform noncontact measures during mechanical testing; therefore, it can be used to measure variations of the specimen CSA during a tension (or compression) test in order to determine, for instance, the true stress and transverse deformations.

Quantifying ligament cross-sectional area via molding and casting

Ligament cross-sectional areas are difficult to determine because ligaments are soft tissues, can be very short, and may be deep between bones. However, accurate measurements are required for determining the material properties from mechanical testing. Many techniques have been tried, but most suffer from one or more of the following: tissue deformation, tissue destruction, submersion of the tissue in saline, the need for a clear line of site, the inability to detect concavities, or poorly defined cross-sectional perimeters. Molding techniques have been used but have been limited by material issues such as large shrinkages, the inability to capture small detail, or the need to destroy the mold to remove the ligament. In this study, we developed a suitable molding and casting technique without systematic shrinkage that could accurately capture the odd shapes and concavities of foot and ankle ligaments with small clearances between bones. Metal rods of 1.62 mm, 2.90 mm, 3.18 mm, and 9.43 mm in diameter were molded using a liquid silicone rubber and cast with polyurethane. The effect of cutting the mold for specimen removal was investigated, and similar tests were done in the presence of saline. Image analysis software was used to determine the cross-sectional areas from photographs of cut castings. In addition, four different ligaments (each n=5) were dissected, molded, and cast. The cross-sectional area of each ligament was obtained. The maximum difference in area for all cases was 2.00%, with the majority being less than 1.00%; the overall root mean square error was 0.334 mm(2) or 0.97%. Neither cutting the mold for specimen removal nor the presence of saline affected the cross-sectional area of the castings. Various representative foot and ankle ligaments were also molded and cast to capture fine detail of the ligament midsubstance including concavities. We have developed a method of measuring ligament cross-sectional area that can overcome the limitations of other area measurement techniques, while accounting for the complicated anatomy of the bones of the foot. The method was validated using metal rods of known diameters, and a representative set foot ligaments (N=20) was analyzed.

Fascicle-scale loading and failure behavior of the Achilles tendon

Although the overall bulk properties of the Achilles tendon have been measured, there is little information detailing the properties of individual fascicles or their interactions. The knowledge of biomechanical properties at the fascicle-scale is critical in understanding the biomechanical behavior of tendons and for the construction of accurate and detailed computational models. Seven tissue samples (approximately 15x4x1 mm(3)) harvested from four freshly thawed human (all male) tendons, each sample having four to six fascicles, were tested in uniaxial tension. A sequential sectioning protocol was used to isolate interaction effects between adjacent fascicles and to obtain the loading response for a single fascicle. The specimen deformation was measured directly using a novel polarized light imaging system with digital image correlation (DIC) for marker-free deformation measurement. The modulus of the single fascicle was significantly higher compared with the intact fascicle group (single: 226 MPa (SD 179), group: 68 MPa (SD 33)). The interaction effect between the adjacent fascicles was less than 10% of the applied load and evidence of sub- and postfailure fascicle sliding was clearly visible. The DIC direct deformation measurements revealed that the modulus of single fascicles could be as much as three to four times the intact specimen. The consistently higher moduli values of the single (strongest) fascicle indicate that the overall response of the tendon may be dominated by a subset of "strongest" fascicles. Also, fascicle-to-fascicle interactions were small, which was <10% of the overall response. This knowledge is useful for developing computational models representing single fascicle and/or fascicle group mechanical behavior and provides valuable insights into fascicle-scale Achilles tendon material properties.

Geometry, time-dependent and failure properties of human meniscal attachments

Meniscectomies have been shown to lead to osteoarthritis and the success of meniscal replacements remains questionable. It has been suggested that the success of a meniscal replacement is dependent on several factors, one of which is the secure fixation and firm attachment of the replacement to the tibial plateau at the horn locations. To aid in the development of meniscal replacements, the objectives of the current study were to determine the time-dependent and failure properties of human meniscal attachments. In contrast to the time-dependent tests, during uniaxial failure testing a charge-coupled video camera was used to document the local strain and linear modulus distribution across the surface of the attachments. The lateral attachments were statistically smaller in cross-sectional area and longer than the medial attachments. The anterior attachments were statistically longer and had a smaller cross-sectional area than the posterior attachments. From the stress relaxation tests, the load and stress relaxation rates of the medial anterior attachment were statistically greater than the medial posterior attachment. There were no significant differences in the creep, structural properties or the ultimate stress between the different attachments. Ultimate strain varied between attachments, as well as along the length of the attachment. Ultimate strain in the meniscus region (10.4+/-6.9%) and mid-substance region (12.7+/-16.4%) was smaller than the bony insertion region (32.2+/-21.5%). The lateral and anterior attachments were also found to have statistically greater strain than the medial and posterior attachments, respectively. The linear modulus was statistically weaker in the bony insertion region (69.7+/-33.7MPa) compared to the meniscus region (153+/-123MPa) and mid-substance region (195+/-121MPa). Overall the anterior attachments (169+/-130MPa) were also found to be statistically stronger than the posterior attachments (90.8+/-64.9MPa). These results can be used to help design tissue-engineered replacement menisci and their insertions and show the differences in material properties between attachments, as well as within an attachment.

Comparative anatomy of the meniscofemoral ligament in humans and some domestic mammals

The purpose of this study was to investigate the presence, position and relative sizes of the meniscofemoral ligaments (MFL) in three quadrupeds and humans and relate these to the caudal slope of the lateral tibial plateau. Canine, ovine and equine stifles and human knees were dissected to identify the presence of MFLs, their obliquity in relation to the caudal cruciate ligaments (CCL), the relative size and shape of the MFLs compared with the CCL, the points of femoral attachment of the MFLs and CCL, and the distance between the MFLs and CCL at their midpoints. The lateral tibial condyle was divided sagittally with a handsaw and the caudal slope was measured. An MFL was present in all quadrupeds. It was caudal to the CCL, being analogous to the human posterior MFL. There was no structure analogous to the human anterior MFL, a structure that has a different femoral attachment from the human posterior MFL and MFLs in other species examined. The meniscotibial attachments were of varying sizes. The size ratio between the MFL and CCL was greater in all three quadrupeds than it was in the human knee. The MFL lies more obliquely than the CCL in all species examined. The caudal tibial slope was steeper in the quadrupeds. In the stifle joints of quadrupeds, the MFL is a substantial structure and appears to be related to the caudal tibial slope. It is known to resist caudal translation of the tibia in conjunction with the lateral meniscus. This must be borne in mind when considering its function in the human knee.

The Pathomechanics of Plantar Fasciitis

Plantar fasciitis is a musculoskeletal disorder primarily affecting the fascial enthesis. Although poorly understood, the development of plantar fasciitis is thought to have a mechanical origin. In particular, pes planus foot types and lower-limb biomechanics that result in a lowered medial longitudinal arch are thought to create excessive tensile strain within the fascia, producing microscopic tears and chronic inflammation. However, contrary to clinical doctrine, histological evidence does not support this concept, with inflammation rarely observed in chronic plantar fasciitis. Similarly, scientific support for the role of arch mechanics in the development of plantar fasciitis is equivocal, despite an abundance of anecdotal evidence indicating a causal link between arch function and heel pain. This may, in part, reflect the difficulty in measuring arch mechanics in vivo. However, it may also indicate that tensile failure is not a predominant feature in the pathomechanics of plantar fasciitis. Alternative mechanisms including 'stress-shielding', vascular and metabolic disturbances, the formation of free radicals, hyperthermia and genetic factors have also been linked to degenerative change in connective tissues. Further research is needed to ascertain the importance of such factors in the development of plantar fasciitis.

An alternative method of anthropometry of anterior cruciate ligament through 3-D digital image reconstruction

Accurate and flexible measurements of length, area, and volume are important in evaluation of the mechanical properties of soft tissue. Although a number of contact-based and non-contact techniques have been reported in the literature, due to a variety of reasons such as cost, complexity, and low accuracy, the research community has not adopted a standardized technique. In this paper, an alternative method of measuring the geometric parameters of cadaver anterior cruciate ligament (ACL) is presented. In this method, a 3-D scan of the ACL is constructed using a simple, commercially available, scanning system. The 3-D scan is then analyzed using the 3-D Doctor Software to extract important information regarding the length, cross-sectional area, and volume of the ACL. The accuracy and repeatability of measurements obtained by this method are acceptable and comparable to existing non-contact methods. The limitation of the method is that surface concavities cannot be detected. However, the non-contact optical method, described here, has inherent advantages over the existing methods: (1) it is inexpensive; (2) it allows the determination of area at any distance along the length of the tissue of interest; (3) all relevant information including minimum area is extracted from one single application of the method; (4) the volume can be calculated with a simple additional step of length measurement although, for accurate results, condylar blockage must be minimized by coring the ACL out. The entire process of scanning takes less than 30 min. This technique has the potential to become a standard method in anthropometry of soft tissue.

Cross sectional area measurement of tendon and ligament in vitro: a simple, rapid, non-destructive technique

The structural properties of tendons and ligaments are integral to their ability to function effectively in vivo and are determined from both the geometrical form and material properties. Many studies of tendon and ligament include a mechanical assessment of the structure in vitro. However, to determine the material properties of the constituent tissues it is necessary to measure cross-sectional area (CSA). Problems associated with this include damage to the structure, inaccurate values for non-uniform shapes, labour intensive techniques or requirement of expensive equipment. We describe a non-destructive technique for measurement of tendon and ligament CSA based on that of Race and Amis (J. Biomech. 29 (1996) 1207). The modified technique uses aqueous rapid curing alginate dental impression paste, digital photography and computerised image analysis. This technique is quick and simple to carry out and provides accurate values (within 0.8%) for CSA which are reproducible (coefficient of variation = 1.42%). The technique is non-destructive and can be used on specimens with an irregular shape.

Quantitative assessment of thinning of the subscapularis tendon in recurrent anterior dislocation of the shoulder by use of magnetic resonance imaging

It is known that thinning and lengthening of the subscapularis tendon occur in shoulders with recurrent anterior dislocation. However, no studies have been performed to quantify the morphologic changes of the subscapularis tendon under such conditions. We retrospectively measured the thickness and cross-sectional area of the subscapularis tendon by use of magnetic resonance imaging in 22 shoulders in 11 patients with unilateral recurrent anterior dislocation of the shoulder. The contralateral shoulder in each patient served as a control. The thickness and cross-sectional area of the subscapularis on the affected side were smaller than those on the normal side (6.5 +/- 1.7 mm vs 8.0 +/- 1.9 mm, P = .001, and 388.6 +/- 120.0 mm 2 vs 547.9 +/- 128.5 mm 2 , P = .0001, respectively). We conclude that the subscapularis tendon undergoes an 18.7% decrease in thickness and a 29.1% decrease in cross-sectional area in shoulders with recurrent anterior dislocation.

Metabolism and composition of the canine anterior cruciate ligament relate to differences in knee joint mechanics and predisposition to ligament rupture

PURPOSE

The objective of this study was to determine whether differences in the composition and metabolism of the extracellular matrix (ECM) in canine anterior cruciate ligaments (ACLs) might relate to mechanical properties of the canine knee. Variations in ACL biochemistry and knee mechanics could account for divergent predispositions to ligament rupture.

METHODS

Eleven knee joints were obtained from both cadaveric Labrador Retrievers (rupture predisposed) and ex-racing Greyhounds (non-rupture predisposed). Anterioposterior laxity and tensile testing determined mechanical properties of the knee joints and ACL samples respectively. The thermal properties of the collagenous matrix were determined by differential scanning calorimetry (DSC) and the biochemical properties by measuring collagen content, collagen cross-links, glycosaminoglycan (GAG) levels, matrix metalloproteinase-2 (MMP-2), tissue inhibitors of metalloproteinase (TIMP).

RESULTS

The anterioposterior laxity was significantly greater (p = 0.04) in the Labrador Retriever knee joints, and their ACLs tended to be weaker (p = 0.06). Greater collagen turnover was demonstrated by significantly higher (p = 0.02) concentrations of pro-MMP-2, and lower enthalpy of denaturation (p = 0.05) in Labrador Retriever ACLs.

CONCLUSIONS

The different metabolism of the collagenous matrix in the ACLs of dogs predisposed to rupture was related to greater knee joint laxity and lower ligament material properties (ultimate tensile stress). This may be suggestive of a link between ligament rupture and eventual knee osteoarthritis in both dogs and humans.

Cross-Sectional Profiles and Volume Reconstructions of Soft Tissues Using Laser Beam Measurements

Precise geometric reconstruction is a valuable tool in the study of soft tissues biomechanics. Optical methods have been developed to determine the tissue cross section without mechanical contact with the specimen. An adaptation of the laser micrometer developed by Lee and Woo [ASME J. Biomech. Eng., 110 (2), pp. 110–114]. is proposed in which the laser-collimated beam rotates around and moves along a fixed specimen to reconstruct its cross sections and volume. Beam motion is computer controlled to accelerate data acquisition and improve beam positioning accuracy. It minimizes time-dependent shape modifications and increases global reconstruction precision. The technique is also competent for the measurement of immersed collagen matrices.

Mechanical properties of regenerated coracoacromial ligament after subacromial decompression

Recent publications suggest that the coracoacromial ligament regenerates after it has been partially excised during subacromial decompression or acromioplasty. This observation may aid the understanding of the successes and failures of this very commonly performed surgical procedure. This study determines the mechanical properties of the apparently regenerated ligament. Eight regenerated coracoacromial ligaments were excised during revision surgery after subacromial decompression and were taken for mechanical testing. It appears that the ligament does have the ability to re-form relatively quickly after subacromial decompression or acromioplasty but takes time to regain strength. The results indicate that the ligament may possibly regain normal mechanical properties after regeneration times in excess of 3 years.

Stiffness of the healing medial collateral ligament of the mouse

The knee joints of mice can serve as a model for studying knee ligament properties. The goal of our study was to measure the structural stiffness of the medial collateral ligament (MCL) of the murine knee. A tensile test was developed for this purpose. First 84 femur-MCL-tibia complexes of 11-week-old C57Black6 mice were tested. Of four groups (n = 14 per group) the right MCL was ruptured. The mice were sacrificed at 1.5, 3, 6, and 9 weeks after the operation. The other two groups served as controls at 0 and 9 weeks after the operation. Absolute values of the structural stiffness of the healed MCLs at 1.5 weeks were initially significantly lower than their unoperated controls, but were not different from normal values at three, six, and nine weeks of healing. The structural stiffness of the unoperated controls increased by 11% at 20 weeks compared to 11 weeks of age.

Are the material properties and matrix composition of equine flexor and extensor tendons determined by their functions?

REASONS FOR PERFORMING STUDY

Injury to the superficial digital flexor tendon (SDFT) is common in competition horses. The SDFT contributes to locomotory efficiency by storing energy; such tendons have low safety margins. Tendons which merely position the limb, including the opposing common digital extensor tendon (CDET), are rarely injured. The current failure of strategies to prevent or effectively treat injury to the SDFT indicates the importance of understanding how it differs from tendons which are not injury-prone.

HYPOTHESIS

That the structural and material properties and matrix composition of the SDFT and CDET differ, reflecting their specific functional requirements in vivo.

METHODS

Forelimb tendons were harvested from 26 mature horses and loaded to failure prior to matrix composition analysis of specimens.

RESULTS

The SDFT had a significantly higher cross-sectional area, structural stiffness, failure load and failure strain and a lower elastic modulus than the CDET (P < 0.0001).

CONCLUSIONS

The SDFT has conflicting requirements for strength and elasticity; although as a whole it is a stiffer structure than the CDET, differences in the matrix molecular composition including water and total sulphated glycosaminoglycan contents allow it to remain more elastic as a material.

POTENTIAL RELEVANCE

Further information on how the two tendons attain these different properties may be of use in the development of prevention and treatment strategies for SDFT rupture.

A review of the function and biomechanics of the meniscofemoral ligaments

PURPOSE

The goal of this study was to review current knowledge on the anatomy, biomechanics, and functions of the meniscofemoral ligaments.

TYPE OF STUDY

Literature review.

METHODS

A systematic search of the literature spanning the past 2 centuries was performed. This revealed several anatomic and biomechanical studies, which were analyzed for the presence, incidence, function, and biomechanics of the meniscofemoral ligaments.

RESULTS

An analysis of 16 anatomic studies revealed that from 1,022 cadaveric knees examined, 931 (91.1%) had at least 1 meniscofemoral ligament; an anterior meniscofemoral ligament was present in 390 (48.2%) of specimens, and a posterior meniscofemoral ligament was present in 569 (70.4%). The 2 ligaments coexisted in 257 knees (31.8%). This high incidence might imply a functional role for these structures. Early theories on the function of these ligaments focused on their role as secondary restraints supplementing the posterior cruciate ligament. More recent hypotheses have concentrated on a role in guiding the motion of the lateral meniscus.

CONCLUSIONS

The contribution of the meniscofemoral ligaments in the prognosis and management of posterior cruciate ligament and meniscal injuries remains undetermined. An examination of the structure, properties, and function of the meniscofemoral ligaments reveals that more biomechanical and imaging research is required, together with clinical observations, on the consequences of rupture of these ligaments.

Meniscofemoral ligaments--structural and material properties

The meniscofemoral ligaments (MFLs) of 28 human cadaveric knees were studied to determine their incidence, structural and material properties. Using the Race-Amis casting method for measurement, the mean cross-sectional area for the anterior MFL (aMFL) was 14.7 mm(2) (+/-14.8mm(2)) whilst that of the posterior MFL (pMFL) was 20.9 mm(2) (+/-11.6mm(2)). The ligaments were isolated and tensile tested in a materials testing machine. The mean loads to failure were 300.5 N (+/-155.0 N) for the aMFL and 302.5 N (+/-157.9 N) for the pMFL, with elastic moduli of 281 (+/-239 MPa) and 227 MPa (+/-128 MPa), respectively. These significant anatomical and material properties suggest a function for the MFL in the biomechanics of the knee, and should be borne in mind when considering hypotheses on MFL function. Such hypotheses include roles for the ligaments in knee stability and guiding meniscal motion.

Patellar tendon fiber strains: their differential responses to quadriceps tension

This study tested the hypothesis that the posterior fibers of the patellar tendon are subjected to higher tensile strains than the anterior fibers in response to quadriceps tension. The quadriceps tendon was loaded to 1 kN in 10 human cadaver knees and the tensile strain was measured in the anterior and posterior fibers of the patellar tendon. The central third patellar tendon was divided into anterior and posterior halves which were tensile tested to failure. The mean strain at 1 kN load was 1.7% (90 degrees flexion), 2.7% (60 degrees ), and 3.9% (10 degrees ) anteriorly, and 3.2% (90 degrees ) 4.6% (60 degrees ), and 4.9% (10 degrees ) posteriorly. Quadriceps loading caused significantly greater strains in the posterior fascicles between 60 degrees and 90 degrees knee flexion. The material properties in the anterior and posterior regions were similar, except that failure strain was significantly higher posteriorly. Thus the posterior fascicles are adapted to sustain significantly greater tensile strains before failing. This suggests that the higher overall levels of tensile strain in the posterior fibers are not sufficient to explain the clinical pattern of patellar tendonitis.

Comparison of the biomechanical properties of rottweiler and racing greyhound cranial cruciate ligaments

An in vitro study of rottweiler and racing greyhound cranial cruciate ligaments revealed that the rottweiler ligaments had a significantly greater cross-sectional area at their distal attachments. Mechanical testing showed that the ultimate load related to body mass was significantly higher in the extended racing greyhound stifle during cranial tibial loading to failure, as were linear stiffness, tensile strength and tangent modulus. During ligament axis loading to failure, the only significant difference in structural and mechanical properties recorded between the two breeds was a greater ultimate strain for the greyhound ligament with the stifle joint flexed. Energy absorbed by the ligament complex at failure during cranial tibial loading was twice that for ligament axis loading for both breeds. The clinical significance is that the rottweiler cranial cruciate ligament is more vulnerable to damage as it requires half the load per unit body mass that the greyhound requires to cause a rupture.