Ultimate stress and age-dependent deformation characteristics of the iliotibial tract

Donor age has no relevant role in biomechanical properties of allografts used in anterior cruciate ligament (ACL) reconstruction: A systematic review

PURPOSE

Surgeons generally consider the donor age as a factor that negatively influences the quality of allograft used in anterior cruciate ligament (ACL) reconstruction, however, the available evidence does not clearly support this statement. The purpose of the study was to investigate if donor age influences the biomechanical properties of allografts used in ACL reconstruction.

METHODS

A comprehensive literature search was conducted for all relevant articles using MEDLINE (PubMed), Scopus, and Cochrane Collaboration Library, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis. Studies including the analysis of the correlation between biomechanical properties of the allografts and donor age were selected. The role of donor age was labelled as 'none' if absent, 'higher' or 'lower' if the properties were higher or lower in older specimens with respect to younger. The correlation was defined as 'weak' or 'strong' according to each study definition.

RESULTS

No conflicting role of donor age was reported for modulus of elasticity, load to failure, strain, stiffness and displacement. The only parameters where the significant results were consistent were the tensile strength and the stress (low or moderate correlations). When considering the tested samples with a donor's age <65 years, a significant role of age was reported in only four out of 13 groups of graft tested (patellar tendon, fascia lata, anterior tibialis tendon and posterior tibialis tendon).

CONCLUSION

The current literature did not allow to state that the donor age negatively influences the biomechanical properties of allografts, making it impossible to identify a clear age cut-off value to exclude them from ACL reconstruction procedures.

LEVEL OF EVIDENCE

Level IV, systematic review.

Can lateral tenodesis improve the rotational stability of the ACL reconstruction? A finite element analysis

One of the most common knee injuries is the Anterior Cruciate Ligament (ACL) rupture with severe implications on knee stability. The usual treatment is the ACL Reconstruction (ACLR) surgery where the surgeon replaces the torn ligament with a graft in an effort to restore knee kinematics. In case of excessive rotatory instability, Lateral Extra-Articular Tenodesis (LET) can be performed in combination with ACLR. Additionally, LET appears to reduce ACLR graft forces minimizing graft failure chances. However, there are concerns about overconstraining physiological rotation. To gain insight in this controversial topic, we developed an automatic, open-source tool to create a series of Finite Element (FE) models attempting to investigate the interactions of ACLR and LET through simulation. We started by creating a validated model of the healthy knee joint that served as reference for subsequent FE simulations. Then, we created FE models of standalone ACLR and combined ACLR-LET. Each model was assessed by applying a loading profile that resembles the reduction phase of the Pivot-Shift clinical exam. We measured the External Tibia Rotation (ETR), the Posterior Tibia Translation (PTT) of the lateral tibial compartment, and the ACLR graft stress developed around the femoral tunnel insertion site. We observed the following: a) LET reduces ETR and PTT compared to isolated ACLR, b) combined ACLR-LET is more sensitive to LET graft pretension with lower values showcasing performance closer to the healthy joint, c) LET reduces ACLR graft forces for the same pretension values, d) LET exhibits significant overconstraint for higher pretension values. In general, these findings are in agreement with relevant clinical studies and accentuate the potential of the developed framework as a tool that can assist orthopaedists during surgery planning. We provide open access for the FE models of this study to enhance research transparency, reproducibility and extensibility.

Shear wave elastography demonstrates different material properties between the medial collateral ligament and anterolateral ligament

BACKGROUND

Anterolateral ligament and medial collateral ligament injuries could happen concomitantly with anterior cruciate ligament ruptures. The anterolateral ligament is injured more often than the medial collateral ligament during concomitant anterior cruciate ligament ruptures although it offers less restraint to knee movement. Comparing the material properties of the medial collateral ligament and anterolateral ligament helps improve our understanding of their structure-function relationship and injury risk before the onset of injury.

METHODS

Eight cadaveric lower extremity specimens were prepared and mechanically tested to failure in a laboratory setting using a hydraulic platform. Measurements of surface strains of superficial surface of each medial collateral ligament and anterolateral ligament specimen were found using three-dimensional digital image correlation. Ligament stiffness was found using ultrasound shear-wave elastography. t-tests were used to assess for significant differences in strain, stress, Young's modulus, and stiffness in the two ligaments.

FINDINGS

The medial collateral ligament exhibited greater ultimate failure strain along its longitudinal axis (p = 0.03) and Young's modulus (p < 0.0018) than the anterolateral ligament. Conversely, the anterolateral ligament exhibited greater ultimate failure stress than the medial collateral ligament (p < 0.0001). Medial collateral ligament failure occurred mostly in the proximal aspect of the ligament, while most anterolateral ligament failure occurred in the distal or midsubstance aspect (P = 0.04).

INTERPRETATION

Despite both being ligamentous structures, the medial collateral ligament and anterolateral ligament exhibited separate material properties during ultimate failure testing. The weaker material properties of the anterolateral ligament likely contribute to higher rates of concomitant injury with anterior cruciate ligament ruptures.

Characterizing the viscoelastic properties of the anterolateral ligament and grafts commonly used in its reconstruction

BACKGROUND

Current anatomic anterolateral ligament reconstruction is typically performed using either a gracilis tendon or an iliotibial band graft based on their quasi-static behavior. However, there is limited knowledge about their viscoelastic behaviors. This study aimed to characterize the viscoelastic properties of the anterolateral ligament, distal iliotibial band, distal gracilis tendon and proximal gracilis tendon for graft material choice in anterolateral ligament reconstruction.

METHODS

All the tissues were harvested from thirteen fresh-frozen cadaveric knees and subjected to preconditioning (3-6 MPa), sinusoidal cycle (1.2-12 MPa), dwell at constant load (12 MPa), and load to failure (3%/s). The quasi-static and viscoelastic properties of the soft tissues were computed and compared using a linear mixed model (p < 0.05).

FINDINGS

The hysteresis of anterolateral ligament (mean:0.4 Nm) was comparable with gracilis halves (p > 0.85) but iliotibial band (6 Nm) was significantly higher (p < 0.001,ES = 6.5). In contrast, the dynamic creep of anterolateral ligament (0.5 mm) was similar to iliotibial band (0.7 mm, p > 0.82) whereas both gracilis halves were significantly lower (p < 0.007,ES > 1.4). The elastic modulus of anterolateral ligament (181.4 MPa, p < 0.001,ES > 2.1) was the lowest compared to the grafts materials (distal gracilis tendon:835 MPa, distal gracilis tendon:726 MPa, iliotibial band:910 MPa). Additionally, the failure load of the anterolateral ligament (124.5 N, p < 0.001,ES > 2.9) was also the lowest.

INTERPRETATION

The mechanical properties of the gracilis halves and iliotibial band were significantly different from anterolateral ligament, except for hysteresis and dynamic creep, respectively. Our findings showed that the gracilis halves may be a more appropriate graft choice for anterolateral ligament reconstruction due to its low energy dissipation and permanent deformation under dynamic loads.

Mechanical Characterization of Human Fascia Lata: Uniaxial Tensile Tests from Fresh-Frozen Cadaver Samples and Constitutive Modelling

Human Fascia Lata (FL) is a connective tissue with a multilayered organization also known as aponeurotic fascia. FL biomechanics is influenced by its composite structure formed by fibrous layers (usually two) separated by loose connective tissue. In each layer, most of the collagen fibers run parallel in a distinct direction (with an interlayer angle that usually ranges from 75-80°), mirroring the fascia's ability to adapt and withstand specific tensile loads. Although FL is a key structure in several musculoskeletal dysfunctions and in tissue engineering, literature still lacks the evidence that proves tissue anisotropy according to predominant collagen fiber directions. For this purpose, this work aims to analyze the biomechanical properties of ex-vivo FL (collected from fresh-frozen human donors) by performing uniaxial tensile tests in order to highlight any differences with respect to loading directions. The experimental outcomes showed a strong anisotropic behavior in accordance with principal collagen fibers directions, which characterize the composite structure. These findings have been implemented to propose a first constitutive model able to mimic the intra- and interlayer interactions. Both approaches could potentially support surgeons in daily practices (such as graft preparation and placement), engineers during in silico simulation, and physiotherapists during musculoskeletal rehabilitation, to customize a medical intervention based on each specific patient and clinical condition.

Comparing the accuracy of ultrasound-based measurements of the cervical vagus nerve

Vagus nerve stimulation (VNS) has become a promising therapy especially for drug resistant epilepsy and other pathologies. Side effects or missing therapeutic success are observed due to cuff electrodes that are too narrow or too wide. Preoperative high-resolution ultrasound is used to evaluate the size of the cervical vagus nerve (CVN) to estimate the size of cuff electrodes for VNS. It remains unclear how precise ultrasound reflects the CVN dimensions, which has been the objective of this study. CVN cross-sections and diameters were investigated in 23 sides from 12 bodies, using ultrasound, histology, and CVN casting in situ as a reference. Morphometric data were obtained including fascicle count and nerve composition in histology. CVN yielded significant side-, age-, and BMI-related differences. CVN cross-sections were smaller in ultrasound when compared to casting and histology (1.5 ± 0.4 vs. 3.1 ± 0.9 vs. 2.3 ± 0.7 mm²). With the given setting in ultrasound, CVN cross-sections were consistently underestimated when compared to casting. Ultrasound-based cross-section measurements are related to a biased estimation of CVN size. A factor to correct for method related differences may help to adjust for accurate cuff electrode sizes for patient needs and to reduce undesired effects and potentially material consumption.

Fatigue Testing of Human Flexor Tendons Using a Customized 3D-Printed Clamping System

Improved surgical procedures and implant developments for ligament or tendon repair require an in-depth understanding of tissue load-deformation and fatigue properties. Cyclic testing will provide crucial information on the behavior of these materials under reoccurring loads and on fatigue strength. Sparse data are available describing soft tissue behavior under cyclic loading. To examine fatigue strength, a new technology was trialed deploying 3D-printing to facilitate and standardize cyclic tests aiming to determine tendon fatigue behavior. Cadaveric flexor digitorum tendons were harvested and mounted for tensile testing with no tapering being made, using 3D-printed clamps and holder arms, while ensuring a consistent testing length. Loads ranging between 200 to 510 N were applied at a frequency of 4 Hz, and cycles to failure ranged between 8 and >260,000. S–N curves (Woehler curves) were generated based on the peak stresses and cycles to failure. Power regression yielded a combined coefficient of determination of stress and cycles to failure of R2 = 0.65, while the individual coefficients for tissues of single donors ranged between R2 = 0.54 and R2 = 0.88. The here-presented results demonstrate that S–N curves of human tendons can be obtained using a standardized setting deploying 3D-printing technology.

The Iliotibial Band: A Complex Structure with Versatile Functions

The development of a pronounced iliotibial band (ITB) is an anatomically distinct evolution of humans. The mechanical behaviour of this “new” structure is still poorly understood and hotly debated in current literature. Iliotibial band syndrome (ITBS) is one of the leading causes of lateral knee pain injuries in runners. We currently lack a comprehensive understanding of the healthy behaviour of the ITB, and this is necessary prior to further investigating the aetiology of pathologies like ITBS. Therefore, the purpose of this narrative review was to collate the anatomical, biomechanical and clinical literature to understand how the mechanical function of the ITB is influenced by anatomical variation, posture and muscle activation. The complexity of understanding the mechanical function of the ITB is due, in part, to the presence of its two in-series muscles: gluteus maximus (GMAX) and tensor fascia latae (TFL). At present, we lack a fundamental understanding of how GMAX and TFL transmit force through the ITB and what mechanical role the ITB plays for movements like walking or running. While there is a range of proposed ITBS treatment strategies, robust evidence for effective treatments is still lacking. Interventions that directly target the running biomechanics suspected to increase either ITB strain or compression of lateral knee structures may have promise, but clinical randomised controlled trials are still required.

Influence of transducer orientation on shear wave velocity measurements of the iliotibial band

Tissue anisotropy influences estimation of mechanical properties of connective tissues, such as the iliotibial band (ITB). This study investigated the influence of ultrasound transducer rotation and tilt on shear wave velocity (SWV, an index of stiffness) measurements of the ITB and the intra-rater repeatability of SWV measurements in the longitudinal direction. SWV was measured unilaterally (dominant limb) using ultrasound shear wave elastography in the middle region of the ITB in supine at rest (20-25° knee flexion) in ten healthy volunteers (4 females). A 3-dimensional video system provided real-time feedback of probe orientation with respect to the thigh. Measurements were made at 10° increments of probe rotation, from longitudinal to transverse alignment relative to the approximate direction of ITB fibres, and 5-10° tilts about the longitudinal and sideways axes of the transducer. One-way repeated measures ANOVA compared SWV between angles and tilts. Intraclass correlation coefficients (ICCs) and standard error of measurement (SEM) were used to calculate repeatability for two to five (longitudinal only) repetitions. SWV was greatest when the transducer was aligned to ITB fibres (longitudinal: 10.5 ± 1.7 m/s) and lowest when perpendicular (transverse: 5.8 ± 2.4 m/s). Compared to longitudinal alignment, SWV decreased significantly (p < 0.01) when the transducer was rotated 20° or more. Tilted measurements did not differ between angles. Intra-rater repeatability was excellent with the average of two measurements (ICC = 0.99, 95% CI 0.95, 0.99; SEM = 0.31 m/s). These findings show that SWV changes with orientation relative to fibre direction. Transducer orientation requires careful control to ensure comparable measures.

Surface coating and speckling of the human iliotibial tract does not affect its load-deformation properties

Stochastic surface patterns form an important requirement to facilitate digital image correlation and to subsequently quantify material properties of various tissues when loaded and deformed without artefacts arising from material slippage. Depending on the samples' natural colour, a surface pattern is created by speckling with colour or dye only, or it requires combined surface coating and speckling before to enhance the contrast, to facilitate high-quality data recording for mechanical evaluation. However, it is unclear to date if the colours deployed for coating and speckling do significantly alter the biomechanical properties of soft tissues. The given study investigated the biomechanical properties of 168 human iliotibial tract samples as a model for collagen-rich soft tissues, separated into four groups: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling following a standardized approach of application and data acquisition. The results reveal that elastic modulus, ultimate tensile strength and strain at maximum force of all groups were similar and statistically non-different (p ≥ 0.69). Qualitatively, the speckle patterns revealed increasing contrast differences in the following order: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling. Conclusively, both coating by water- and solvent-based paints, as well as exclusive graphite speckling, did not significantly influence the load-deformation parameters of the here used human iliotibial tract as a model for collagen-rich soft tissues. In consequence, water- and solvent-based coating paints seem equally suitable to coat collagen-rich soft tissues for digital image correlation, resulting in suitable speckle patterns and unbiased data acquisition.

What is Considered a Variation of Biomechanical Parameters in Tensile Tests of Collagen-Rich Human Soft Tissues? - Critical Considerations Using the Human Cranial Dura Mater as a Representative Morpho-Mechanic Model

Background and Objectives: Profound knowledge on the load-dependent behavior of human soft tissues is required for the development of suitable replacements as well as for realistic computer simulations. Regarding the former, e.g., the anisotropy of a particular biological tissue has to be represented with site- and direction-dependent particular mechanical values. Contrary to this concept of consistent mechanical properties of a defined soft tissue, mechanical parameters of soft tissues scatter considerably when being determined in tensile tests. In spite of numerous measures taken to standardize the mechanical testing of soft tissues, several setup- and tissue-related factors remain to influence the mechanical parameters of human soft tissues to a yet unknown extent. It is to date unclear if measurement extremes should be considered a variation or whether these data have to be deemed incorrect measurement outliers. This given study aimed to determine mechanical parameters of the human cranial dura mater as a model for human soft tissues using a highly standardized protocol and based on this, critically evaluate the definition for the term mechanical "variation" of human soft tissue. Materials and Methods: A total of 124 human dura mater samples with an age range of 3 weeks to 94 years were uniformly retrieved, osmotically adapted and mechanically tested using customized 3D-printed equipment in a quasi-static tensile testing setup. Scanning electron microscopy of 14 samples was conducted to relate the mechanical parameters to morphological features of the dura mater. Results: The here obtained mechanical parameters were scattered (elastic modulus = 46.06 MPa, interquartile range = 33.78 MPa; ultimate tensile strength = 5.56 MPa, interquartile range = 4.09 MPa; strain at maximum force = 16.58%, interquartile range = 4.81%). Scanning electron microscopy revealed a multi-layered nature of the dura mater with varying fiber directions between its outer and inner surface. Conclusions: It is concluded that mechanical parameters of soft tissues such as human dura mater are highly variable even if a highly standardized testing setup is involved. The tissue structure and composition appeared to be the main contributor to the scatter of the mechanical parameters. In consequence, mechanical variation of soft tissues can be defined as the extremes of a biomechanical parameter due to an uncontrollable change in tissue structure and/or the respective testing setup.

The influence of different sample preparation on mechanical properties of human iliotibial tract

In the run-up to biomechanical testing, fresh human tissue samples are often frozen in order to inhibit initial decomposition processes and to achieve a temporal independence of tissue acquisition from biomechanical testing. The aim of this study was to compare the mechanical properties of fresh tissue samples of the human iliotibial tract (IT) to fresh-frozen samples taken from the same IT and those modified with different concentrations of Dimethylsulfoxide (DMSO) prior to freezing. All samples were partial plastinated and destructive tensile tests were conducted with a uniaxial tensile test setup. A plastination technique already established in the laboratory was modified to improve the clamping behaviour of the samples. Material failure was caused by a gradual rupture of the load-bearing collagen fibre bundles. Contrary to our expectations, no significant difference was found between the tensile strength of fresh and fresh frozen specimens. The addition of 1 wt% DMSO did not increase the tensile strength compared to fresh-frozen samples; an addition of 10 wt% DMSO even resulted in a decrease. Based on our findings, the use of simple fresh-frozen specimens to determine the tensile strength is viable; however fresh specimens should be used to generate a complete property profile.

Strain Assessment of Deep Fascia of the Thigh During Leg Movement: An in situ Study

Fascia is a fibrous connective tissue present all over the body. At the lower limb level, the deep fascia that is overlying muscles of the outer thigh and sheathing them (fascia lata) is involved in various pathologies. However, the understanding and quantification of the mechanisms involved in these sheathing effects are still unclear. The aim of this study is to observe and quantify the strain field of the fascia lata, including the iliotibial tract (ITT), during a passive movement of the knee. Three fresh postmortem human subjects were studied. To measure hip and knee angles during knee flexion-extension, passive movements from 0° to around 120° were recorded with a motion analysis system and strain fields of the fascia were acquired using digital image correlation. Strains were computed for three areas of the fascia lata: anterior fascia, lateral fascia, and ITT. Mean principal strains showed different strain mechanisms depending on location on the fascia and knee angle. For the ITT, two strain mechanisms were observed depending on knee movement: compression is observed when the knee is extended relative to the reference position of 47°, however, tension and pure shear can be observed when the knee is flexed. For the anterior and lateral fascia, in most cases, minor strain is higher than major strain in absolute value, suggesting high tissue compression probably due to microstructural fiber rearrangements. This in situ study is the first attempt to quantify the superficial strain field of fascia lata during passive leg movement. The study presents some limitations but provides a step in understanding strain mechanism of the fascia lata during passive knee movement.

Water-content related alterations in macro and micro scale tendon biomechanics

Though it is known that the water content of biological soft tissues alters mechanical properties, little attempt has been made to adjust the tissue water content prior to biomechanical testing as part of standardization procedures. The objective of this study was to examine the effects of altered water content on the macro and micro scale mechanical tissues properties. Human iliotibial band samples were obtained during autopsies to osmotically adapt their water content. Macro mechanical tensile testing of the samples was conducted with digital image correlation, and micro mechanical tests using atomic force microscopy. Analyses were conducted for elastic moduli, tensile strength, and strain at maximum force, and correlations for water content, anthropometric data, and post-mortem interval. Different mechanical properties exist at different water concentrations. Correlations to anthropometric data are more likely to be found at water concentrations close to the native state. These data underline the need for adapting the water content of soft tissues for macro and micro biomechanical experiments to optimize their validity. The osmotic stress protocol provides a feasible and reliable standardization approach to adjust for water content-related differences induced by age at death, post-mortem interval and tissue processing time with known impact on the stress-strain properties.

Do We Need a Separate Classification for Fragility Fractures of the Pelvis?

Fragility fractures of the pelvis are occurring with increasing frequency. These fractures, occurring in the geriatric patient population, are low-energy injuries and are dissimilar in many ways from those caused by high-energy trauma. For example, the mechanism of injury is different and emergency treatment is usually not necessary. Having diminished bone strength, fragility fracture lines follow areas of low bone mineral density and loss of pelvic stability may increase over time. Based on our clinical experience, we propose a comprehensive classification of pelvic fragility fractures separate from the existing pelvic ring injury classification to provide a framework for distinguishing the different fragility fracture types and their recommended treatment. This classification is derived first from the degree of fracture instability, followed by the location of the fracture. Anterior pelvic fractures are differentiated from posterior pelvic ring fractures, nondisplaced fractures from displaced, and unilateral from bilateral. It is our belief that this new in-depth analysis of these lesions will assist the clinician in identifying the specific patterns of fragility fracture instability and selecting the appropriate choice of treatment. Further investigation is required to determine the ultimate value of this proposed pelvic fragility fracture classification system. LEVEL OF EVIDENCE:: Diagnostic Level V.

Acute Surgical Injury Alters the Tensile Properties of Thoracolumbar Fascia in a Porcine Model

Recent work utilizing ultrasound imaging demonstrated that individuals with low back pain (LBP) have increased thickness and decreased mobility of the thoracolumbar fascia (TLF), an indication that the TLF may play a role in LBP. This study used a porcine injury model (microsurgically induced local injury)-shown to produce similar results to those observed in humans with LBP-to test the hypothesis that TLF mechanical properties may also be altered in patients with LBP. Perimuscular TLF tissue was harvested from the noninjured side of vertebral level L3-4 in pigs randomized into either control (n = 5) or injured (n = 5) groups. All samples were tested with a displacement-controlled biaxial testing system using the following protocol: cyclic loading/unloading and stress relaxation tests at 25%, 35%, and then 45% of their resting length. Tissue anisotropy was also explored by comparing responses to loading in longitudinal and transverse orientations. Tissues from injured pigs were found to have greater stretch-stretch ratio moduli (measure of tissue stiffness), less energy dissipation, and less stress decay compared to tissues from control pigs. Responses across these variables also depended on loading orientation.

CLINICAL SIGNIFICANCE

these findings suggest that a focal TLF injury can produce impairments in tissue mechanical properties away from the injured area itself. This could contribute to some of the functional abnormalities observed in human LBP.

Utilization of 3D printing technology to facilitate and standardize soft tissue testing

Three-dimensional (3D) printing has become broadly available and can be utilized to customize clamping mechanisms in biomechanical experiments. This report will describe our experience using 3D printed clamps to mount soft tissues from different anatomical regions. The feasibility and potential limitations of the technology will be discussed. Tissues were sourced in a fresh condition, including human skin, ligaments and tendons. Standardized clamps and fixtures were 3D printed and used to mount specimens. In quasi-static tensile tests combined with digital image correlation and fatigue trials we characterized the applicability of the clamping technique. Scanning electron microscopy was utilized to evaluate the specimens to assess the integrity of the extracellular matrix following the mechanical tests. 3D printed clamps showed no signs of clamping-related failure during the quasi-static tests, and intact extracellular matrix was found in the clamping area, at the transition clamping area and the central area from where the strain data was obtained. In the fatigue tests, material slippage was low, allowing for cyclic tests beyond 10⁵ cycles. Comparison to other clamping techniques yields that 3D printed clamps ease and expedite specimen handling, are highly adaptable to specimen geometries and ideal for high-standardization and high-throughput experiments in soft tissue biomechanics.

Cervical vagus nerve morphometry and vascularity in the context of nerve stimulation - A cadaveric study

Vagus nerve stimulation (VNS) has become a well-established therapy for epilepsy and depression, and is emerging to treat inflammatory disease, with the cervical vagus nerve (CVN) as major stimulation site. CVN morphometries are missing for VNS, considering its variability. Morphometric data were obtained from CVNs in 27 cadavers, including branching patterns and histology. Cross-sectional area, greater and lesser diameters averaged 7.2 ± 3.1 mm², 5.1 ± 1.5 and 4.1 ± 1.3 mm, and were ≤11.0 mm², ≤7.0 and ≤5.8 mm in 90% of the specimens, respectively. Midline distance (position lateral to the laryngeal eminence) and skin distance (anterior-posterior from skin) averaged 34.5 ± 6.2 and 36.2 ± 9.4 mm, ≤49.0 and ≤41.0 mm in 90%, respectively. Nerve dimensions and surface topography correlated closely, but without gender-, side- or branching-dependent differences. The nerve fascicle number averaged 5.2 ± 3.5. Vagal arteries were observed in 49% of the cases. Negative correlations were found for age and cross-sectional area, as well as subperineural vessel count. Detailed anatomical data on the CVN and its vascularity are given, forming the morphometric basis for VNS refinement, filling an evident gap in light of the CVN being a structure with variable positions and branching. A 35 × 35-mm rule may apply for the CVN position, irrespective of branching or positional variation.

An anatomic study of trifurcate iliotibial bands for correcting valgus knee deformity

BACKGROUND

The iliotibial band (ITB) trifurcates into the anterior, central and posterior branches at the knee level, and sometimes the branches must be selectively released to correct the valgus knee deformity during total knee arthroplasty. However, the anatomical morphology of the trifurcate ITBs has not been investigated.

METHODS

Fifty-two knees from 26 embalmed cadavers were dissected to observe and record the relationship of the three branches given off from the ITB trifurcation. Fourteen parameters with regard to the length, width, thickness, and trifurcate angle of each branch were measured. These parameters were compared between sex and sides (left or right). Meanwhile, the correlations between parameters and subject age, weight and height were assessed.

RESULTS

The longest, widest and thickest branches of the ITB were the posterior band (59.82±5.14mm), anterior band (39.56±4.17mm) and central band (2.61±0.36mm), respectively. The length and thickness of ITB were significantly larger in males than in females (P<0.05). No significant differences were found between sides (P>0.05). The ITB thickness showed a negative correlation with subject age, while the length and width of the ITB were positively correlated with subject height and weight, respectively.

CONCLUSIONS

This study provided an anatomical reference of trifurcate ITBs to help the release of ITB in valgus knees. The anatomical variations regarding the subject's sex, age, height and weight should be considered in the selective release of ITB.

Mechanical Analysis of Extra-Articular Knee Ligaments. Part One: Native knee ligaments

BACKGROUND

The aim of this study was to provide a characterization of the tensile properties of the medial collateral ligament (MCL), lateral collateral ligament (LCL), anterolateral ligament (ALL) and medial patellofemoral ligament (MPFL). Our hypothesis was that extra-articular knee ligaments are heterogeneous in nature and possess distinct material properties.

METHODS

MCL (n=12), LCL (n=11), MPFL (n=12) and ALL (n=19) samples from fresh frozen human cadaveric knees were subjected to uniaxial tensile testing to failure and analyzed for their material properties. The elastic modulus (slope of the linear portion of the stress/strain curve), ultimate stress (stress at failure), ultimate strain (strain at failure) and strain energy density (area under the stress/strain curve) were calculated.

RESULTS

The MCL had the highest elastic modulus (441.8±117.2MPa) and was significantly greater than the MPFL (294.6±190.4MPa) and LCL (289.0±159.7MPa) (P<0.05) as well as the ALL (173.7±91.8MPa) (P<0.001). The ultimate stress was significantly higher (P<0.05) for the LCL (83.6±38.1MPa) and MCL (72.4±20.7MPa), relative to the MPFL (49.1±31.0MPa) and ALL (46.4±20.1MPa). The ultimate strain of the LCL (41.0±9.9%) and ALL (37.8±7.9%) were significantly higher (P<0.05) compared to the MCL (22.9±2.5%) and MPFL (22.2±5.6%). The strain energy density of the LCL (15.2±6.4MPa) was significantly greater (P<0.05) than all other ligaments (ALL 7.8±3.1MPa, MCL 7.5±2.9MPa and MPFL 5.0±2.9MPa).

CONCLUSIONS

Extra-articular knee ligaments are a heterogeneous group with respect to material characteristics. Each ligament has tensile properties that are significantly different from others and treatment strategies should take these findings into account.

Mechanical Analysis of Extra-Articular Knee Ligaments. Part two: Tendon grafts used for knee ligament reconstruction

OBJECTIVES

The aim of this study was to provide information about the mechanical properties of grafts used for knee ligament reconstructions and to compare those results with the mechanical properties of native knee ligaments.

METHODS

Eleven cadaveric knees were dissected for the semitendinosus, gracilis, iliotibial band (ITB), quadriceps and patellar tendon. Uniaxial testing to failure was performed using a standardized method and mechanical properties (elastic modulus, ultimate stress, ultimate strain, strain energy density) were determined.

RESULTS

The elastic modulus of the gracilis tendon (1458±476MPa) (P<0.001) and the semitendinosus tendon (1036±312MPa) (P<0.05) was significantly higher than the ITB (610±171MPa), quadriceps tendon (568±194MPa), and patellar tendon (417±107MPa). In addition, the ultimate stress of the hamstring tendons (gracilis 155.0±30.7MPa and semitendinosus 120.1±30.0MPa) was significantly higher (P<0.001, respectively P<0.05), relative to the ITB (75.0±11.8MPa), quadriceps tendon (81.0±27.6MPa), and patellar tendon (76.2±25.1MPa). A significant difference (P<0.05) could be noticed between the ultimate strain of the patellar tendon (24.6±5.9%) and the hamstrings (gracilis 14.5±3.1% and semitendinosus 17.0±4.0%). No significant difference in strain energy density between the grafts was observed.

CONCLUSIONS

Material properties of common grafts used for knee ligament reconstructions often differ significantly from the original knee ligament which the graft is supposed to emulate.

The Anterolateral Ligament Has Similar Biomechanical and Histologic Properties to the Inferior Glenohumeral Ligament

PURPOSE

To characterize the tensile and histologic properties of the anterolateral ligament (ALL), inferior glenohumeral ligament (IGHL), and knee capsule.

METHODS

Standardized samples of the ALL (n = 19), anterolateral knee capsule (n = 15), and IGHL (n = 13) were isolated from fresh-frozen human cadavers for uniaxial tensile testing to failure. An additional 6 samples of the ALL, capsule, and IGHL were procured for histologic analysis and determination of elastin content.

RESULTS

All investigated mechanical properties were significantly greater for both the ALL and IGHL when compared with capsular tissue. In contrast, no significant differences between the ALL and IGHL were found for any property. The elastic modulus of ALL and IGHL samples was 174 ± 92 MPa and 139 ± 60 MPa, respectively, compared with 62 ± 30 MPa for the capsule (P = .001). Ultimate stress was significantly lower (P < .001) for the capsule, at 13.4 ± 7.7 MPa, relative to the ALL and IGHL, at 46.4 ± 20.1 MPa and 38.7 ± 16.3 MPa, respectively. The ultimate strain at failure was 37.8% ± 7.9% for the ALL and 39.5% ± 9.4% for the IGHL; this was significantly greater (P = .041 and P = .02, respectively) for both relative to the capsule, at 32.6% ± 8.4%. The strain energy density was 7.8 ± 3.1 MPa for the ALL, 2.1 ± 1.3 MPa for the capsule, and 7.1 ± 3.1 MPa for the IGHL (P < .001). The ALL and IGHL consisted of collagen bundles aligned in a parallel manner, containing elastin bundles, which was in contrast to the random collagen architecture noted in capsule samples.

CONCLUSIONS

The ALL has similar tensile and histologic properties to the IGHL. The tensile properties of the ALL are significantly greater than those observed in the knee capsule. CLINICAL RELEVANCE: The ALL is not just a thickening of capsular tissue and should be considered a distinct ligamentous structure comparable to the IGHL in the shoulder. The tensile behavior of the ALL is similar to the IGHL, and treatment strategies should take this into account.

The Stress-Strain Data of the Hip Capsule Ligaments Are Gender and Side Independent Suggesting a Smaller Contribution to Passive Stiffness

Background

The ligaments in coherence with the capsule of the hip joint are known to contribute to hip stability. Nevertheless, the contribution of the mechanical properties of the ligaments and gender- or side-specific differences are still not completely clear. To date, comparisons of the hip capsule ligaments to other tissues stabilizing the pelvis and hip joint, e.g. the iliotibial tract, were not performed.

Materials & Methods

Hip capsule ligaments were obtained from 17 human cadavers (9 females, 7 males, 13 left and 8 right sides, mean age 83.65 ± 10.54 years). 18 iliofemoral, 9 ischiofemoral and 17 pubofemoral ligaments were prepared. Uniaxial stress-strain properties were obtained from the load-deformation curves before the secant elastic modulus was computed. Strain, elastic modulus and cross sections were compared.

Results

Strain and elastic modulus revealed no significant differences between the iliofemoral (strain 129.8 ± 11.1%, elastic modulus 48.8 ± 21.4 N/mm²), ischiofemoral (strain 128.7 ± 13.7%, elastic modulus 37.5 ± 20.4 N/mm²) and pubofemoral (strain 133.2 ± 23.7%, elastic modulus 49.0 ± 32.1 N/mm²) ligaments. The iliofemoral ligament (53.5 ± 15.1 mm²) yielded a significantly higher cross section compared to the ischiofemoral (19.2 ± 13.2 mm²) and pubofemoral (15.2 ± 7.2 mm²) ligament. No significant gender- or side-specific differences were determined. A comparison to the published data on the iliotibial tract revealed lower elasticity and less variation in the ligaments of the hip joint.

Conclusion

Comparison of the mechanical data of the hip joint ligaments indicates that their role may likely exceed a function as a mechanical stabilizer. Uniaxial testing of interwoven collagen fibers might lead to a misinterpretation of the mechanical properties of the hip capsule ligaments in the given setup, concealing its uniaxial properties. This underlines the need for a polyaxial test setup using fresh and non-embalmed tissues.

Tensile properties of the hip joint ligaments are largely variable and age-dependent - An in-vitro analysis in an age range of 14-93 years

INTRODUCTION

Hip joint stability is maintained by the surrounding ligaments, muscles, and the atmospheric pressure exerted via these structures. It is unclear whether the ligaments are capable of preventing dislocation solely due to their tensile properties, and to what extent they undergo age-related changes. This study aimed to obtain stress-strain data of the hip ligaments over a large age range.

METHODS

Stress-strain data of the iliofemoral (IL), ischiofemoral (IS) and pubofemoral ligament (PF) were obtained from cadavers ranging between 14 and 93 years using a highly standardized setting. Maximum strains were compared to the distances required for dislocation.

RESULTS

Elastic modulus was 24.4 (IL), 22.4 (IS) and 24.9N/mm² (PF) respectively. Maximum strain was 84.5%, 86.1%, 72.4% and ultimate stress 10.0, 7.7 and 6.5N/mm² for the IL, IS and PF respectively. None of these values varied significantly between ligaments or sides. The IS' elastic modulus was higher and maximum strain lower in males. Lower elastic moduli of the PF and higher maximum strains for the IS and PF were revealed in the ≥55 compared to the <55 population. Maximum strain exceeded the dislocation distance of the IS without external hip joint rotation in females, and of the IS and cranial IL under external rotation in both genders.

DISCUSSION

Tensile and failure load properties of the hip joint ligaments are largely variable. The IS and PF change age-dependently. Though the hip ligaments contribute to hip stability, the IS and cranial IL may not prevent dislocation due to their elasticity.

Load and failure behavior of human muscle samples in the context of proximal femur replacement

BACKGROUND

To ensure adequate function after orthopedic tumor reconstruction, it is important to reattach the remaining soft tissue to the implant. This study aimed at obtaining mechanical properties of textile muscle-implant and muscle-bone connections in a preliminary test.

METHODS

Two groups of soft-tissue attachment were mechanically tested and compared: Native bone-muscle samples obtained from human femora and muscles attached to a prosthetic implant by means of Trevira® attachment tubes. Additionally, muscle samples were tested with muscle fibers aligned parallel and perpendicular to the tension load. A uniaxial load was exerted upon all samples.

RESULTS

Failure loads of 26.7 ± 8.8 N were observed for the native bone-muscle group and of 18.1 ± 9.9 N for the Trevira® group. Elongations of 94.8 ± 36.2 % were observed for the native bone-muscle group and 79.3 ± 51.8 % for the Trevira® group. The location of failure was mainly observed in the central area of the muscle fibers. Muscle fibers with parallel fiber orientation (47.6 ± 11.5 N) yielded higher tensile strength than those with perpendicular fiber orientation (14.8 ± 4.1 N).

CONCLUSIONS

Our experiments showed that higher forces were transmitted in the origin and insertion areas than in areas of flat soft tissue reconstruction using attachment tubes. The data indicate that the tested material allows reattaching muscles, but without reinforcing the insertion site. Therefore, attachment tubes with region-dependent and potentially anisotropic material behavior might be advantageous to optimize muscle-bone load transmission after surgery, which may allow lower complication rates and shorter physical recovery.

Acellularization-Induced Changes in Tensile Properties Are Organ Specific - An In-Vitro Mechanical and Structural Analysis of Porcine Soft Tissues

Introduction

Though xenogeneic acellular scaffolds are frequently used for surgical reconstruction, knowledge of their mechanical properties is lacking. This study compared the mechanical, histological and ultrastructural properties of various native and acellular specimens.

Materials and Methods

Porcine esophagi, ureters and skin were tested mechanically in a native or acellular condition, focusing on the elastic modulus, ultimate tensile stress and maximum strain. The testing protocol for soft tissues was standardized, including the adaption of the tissue’s water content and partial plastination to minimize material slippage as well as templates for normed sample dimensions and precise cross-section measurements. The native and acellular tissues were compared at the microscopic and ultrastructural level with a focus on type I collagens.

Results

Increased elastic modulus and ultimate tensile stress values were quantified in acellular esophagi and ureters compared to the native condition. In contrast, these values were strongly decreased in the skin after acellularization. Acellularization-related decreases in maximum strain were found in all tissues. Type I collagens were well-preserved in these samples; however, clotting and a loss of cross-linking type I collagens was observed ultrastructurally. Elastins and fibronectins were preserved in the esophagi and ureters. A loss of the epidermal layer and decreased fibronectin content was present in the skin.

Discussion

Acellularization induces changes in the tensile properties of soft tissues. Some of these changes appear to be organ specific. Loss of cross-linking type I collagen may indicate increased mechanical strength due to decreasing transverse forces acting upon the scaffolds, whereas fibronectin loss may be related to decreased load-bearing capacity. Potentially, the alterations in tissue mechanics are linked to organ function and to the interplay of cells and the extracellular matrix, which is different in hollow organs when compared to skin.

A preliminary technical study on sodium dodecyl sulfate-induced changes of the nano-structural and macro-mechanical properties in human iliotibial tract specimens

INTRODUCTION

Acellular scaffolds are frequently used for the surgical repair of ligaments and tendons. Even though data on the macro-mechanical properties related to the acellularization process exist, corresponding data on the nano-structural properties are still lacking. Such data would help identify target proteins of the formed extracellular matrix that are chemically altered by the acellularization. In this study we examined the altered structure by comparing molecular properties of collagens from native and acellular iliotibial tract samples to the macroscopic stress-strain behavior of tract samples.

MATERIAL AND METHODS

Matched pairs of five human iliotibial tract samples were obtained from five donors (mean age 28.2±4.7 years). One of each pair was acellularized using 1vol% sodium dodecyl sulfate (SDS) for 7 days. (13)C magic angle spinning nuclear magnetic resonance spectroscopy ((13)C CP MAS NMR) was utilized to compare the collagen overall secondary structure and internal dynamics of collagen-typical amino acid proteins. The resulting data was compared to age-matched stress-strain data of tract samples obtained in an uniaxial tensile setup and histologically.

RESULTS

Typical and nearly identical collagen (13)C CP MAS NMR spectra were found in the tract samples before and after acellularization with SDS. The characteristic collagen backbone remained intact in the native and acellular samples. Collagen molecular composition was largely unaltered in both conditions. Furthermore, a similar dynamic behavior was found for the amino acids Hyp γ, Pro α/Hyp α, Ala α, Gly α and Ala β. These minute alterations in the collagens' molecular properties related to acellularization with SDS were in line with the similarly minute changes in the macro-mechanical tensile behavior, such as the elastic modulus and ultimate stress. Histology showed intact type I collagens, minute amounts of elastins before and after acellularization and evidence for acellularization-induced reductions of proteoglycans.

DISCUSSION

Nano-structural properties of collagens are minutely affected by SDS treatment for acellularization, indicated by the molecular composition and dynamics. The lacking acellularization-related changes in the molecular structure properties of collagens in iliotibial tract samples are in line with the small alterations in their macro-mechanical tensile behavior. Though the given setup approaches soft tissue mechanics from both scaling extremes of mechanical testing, further structural analyzes are needed in a larger sample size to substantiate these findings.

The human iliotibial band is specialized for elastic energy storage compared with the chimp fascia lata

This study examines whether the human iliotibial band (ITB) is specialized for elastic energy storage relative to the chimpanzee fascia lata (FL). To quantify the energy storage potential of these structures, we created computer models of human and chimpanzee lower limbs based on detailed anatomical dissections. We characterized the geometry and force-length properties of the FL, tensor fascia lata (TFL) and gluteus maximus (GMax) in four chimpanzee cadavers based on measurements of muscle architecture and moment arms about the hip and knee. We used the chimp model to estimate the forces and corresponding strains in the chimp FL during bipedal walking, and compared these data with analogous estimates from a model of the human ITB, accounting for differences in body mass and lower extremity posture. We estimate that the human ITB stores 15- to 20-times more elastic energy per unit body mass and stride than the chimp FL during bipedal walking. Because chimps walk with persistent hip flexion, the TFL and portions of GMax that insert on the FL undergo smaller excursions (origin to insertion) than muscles that insert on the human ITB. Also, because a smaller fraction of GMax inserts on the chimp FL than on the human ITB, and thus its mass-normalized physiological cross-sectional area is about three times less in chimps, the chimp FL probably transmits smaller muscle forces. These data provide new evidence that the human ITB is anatomically derived compared with the chimp FL and potentially contributes to locomotor economy during bipedal locomotion.

Human vagus nerve branching in the cervical region

BACKGROUND

Vagus nerve stimulation is increasingly applied to treat epilepsy, psychiatric conditions and potentially chronic heart failure. After implanting vagus nerve electrodes to the cervical vagus nerve, side effects such as voice alterations and dyspnea or missing therapeutic effects are observed at different frequencies. Cervical vagus nerve branching might partly be responsible for these effects. However, vagus nerve branching has not yet been described in the context of vagus nerve stimulation.

MATERIALS AND METHODS

Branching of the cervical vagus nerve was investigated macroscopically in 35 body donors (66 cervical sides) in the carotid sheath. After X-ray imaging for determining the vertebral levels of cervical vagus nerve branching, samples were removed to confirm histologically the nerve and to calculate cervical vagus nerve diameters and cross-sections.

RESULTS

Cervical vagus nerve branching was observed in 29% of all cases (26% unilaterally, 3% bilaterally) and proven histologically in all cases. Right-sided branching (22%) was more common than left-sided branching (12%) and occurred on the level of the fourth and fifth vertebra on the left and on the level of the second to fifth vertebra on the right side. Vagus nerves without branching were significantly larger than vagus nerves with branches, concerning their diameters (4.79 mm vs. 3.78 mm) and cross-sections (7.24 mm2 vs. 5.28 mm2).

DISCUSSION

Cervical vagus nerve branching is considerably more frequent than described previously. The side-dependent differences of vagus nerve branching may be linked to the asymmetric effects of the vagus nerve. Cervical vagus nerve branching should be taken into account when identifying main trunk of the vagus nerve for implanting electrodes to minimize potential side effects or lacking therapeutic benefits of vagus nerve stimulation.

Do cells contribute to tendon and ligament biomechanics?

INTRODUCTION

Acellular scaffolds are increasingly used for the surgical repair of tendon injury and ligament tears. Despite this increased use, very little data exist directly comparing acellular scaffolds and their native counterparts. Such a comparison would help establish the effectiveness of the acellularization procedure of human tissues. Furthermore, such a comparison would help estimate the influence of cells in ligament and tendon stability and give insight into the effects of acellularization on collagen.

MATERIAL AND METHODS

Eighteen human iliotibial tract samples were obtained from nine body donors. Nine samples were acellularized with sodium dodecyl sulphate (SDS), while nine counterparts from the same donors remained in the native condition. The ends of all samples were plastinated to minimize material slippage. Their water content was adjusted to 69%, using the osmotic stress technique to exclude water content-related alterations of the mechanical properties. Uniaxial tensile testing was performed to obtain the elastic modulus, ultimate stress and maximum strain. The effectiveness of the acellularization procedure was histologically verified by means of a DNA assay.

RESULTS

The histology samples showed a complete removal of the cells, an extensive, yet incomplete removal of the DNA content and alterations to the extracellular collagen. Tensile properties of the tract samples such as elastic modulus and ultimate stress were unaffected by acellularization with the exception of maximum strain.

DISCUSSION

The data indicate that cells influence the mechanical properties of ligaments and tendons in vitro to a negligible extent. Moreover, acellularization with SDS alters material properties to a minor extent, indicating that this method provides a biomechanical match in ligament and tendon reconstruction. However, the given protocol insufficiently removes DNA. This may increase the potential for transplant rejection when acellular tract scaffolds are used in soft tissue repair. Further research will help optimize the SDS-protocol for clinical application.

The extent of ligament injury and its influence on pelvic stability following type II anteroposterior compression pelvic injuries--A computer study to gain insight into open book trauma

Surgical stabilization of the pelvis following type II anteroposterior compression pelvic injuries (APCII) is based on the assumption that the anterior sacroiliac, sacrospinous, and sacrotuberous ligaments disrupt simultaneously. Recent data on the ligaments contradict this concept. We aimed at determining the mechanisms of ligament failure in APCII computationally. In an individual osteoligamentous computer model of the pelvis, ligament load, and strain were observed for the two-leg stance, APCII with 100-mm symphyseal widening and for two-leg stance with APCII-related ligament failure, and validated with body donors. The anterior sacroiliac and sacrotuberous ligaments had the greatest load with 80% and 17% of the total load, respectively. APCII causes partial failure of the anterior sacroiliac ligament and the pelvis to become horizontally instable. The other ligaments remained intact. The sacrospinous ligament was negligibly loaded but stabilized the pelvis vertically. The interosseous sacroiliac and sacrotuberous ligaments are likely responsible for reducing the symphysis and might serve as an indicator of vertical stability. The sacrospinous ligament appears to be of minor significance in APCII but plays an important role in vertical stabilization. Further research is necessary to determine the influence of alterations in ligament and bone material properties.