Sagittal Alignment With Downward Slope of the Lower Lumbar Motion Segment Influences Its Modes of Failure in Direct Compression: A Mechanical and Microstructural Investigation.

Study Design: Microstructural investigation of compression-induced herniation of ovine lumbar discs with and without added component of anterior-inferior slope.

Objective: Does increased shear arising from a simulated component of motion segment slope imitating sacral slope weaken the lateral annulus and increase risk of overt herniation at this same region.

Summary Of Background Data: An increase in sacral slope secondary to lordosis and pelvic incidence increases shear stresses at the lumbosacral junction and has been associated with an increase in spondylolisthetic disorders and back injury.

Protein Levels and Microstructural Changes in Localized Regions of Early Cartilage Degeneration Compared with Adjacent Intact Cartilage.

Objective: It was hypothesized that the respective protein profiles of bovine cartilage from sites of localized mild to moderate (GI to GII) degeneration versus adjacent sites of intact tissue would vary in accordance with the tissue microstructural changes associated with a pre-osteoarthritic state.

Methods: A total of 15 bovine patellae were obtained for this study. Paired samples of tissue were collected from the lateral region of each patella.

New evidence for structural integration across the cartilage-vertebral endplate junction and its relation to herniation.

Background Context: The cartilaginous and bony material that can be present in herniated tissue suggests that failure can involve both cartilaginous and vertebral-endplates. How structural integration is achieved across the junction between these two distinct tissue regions via its fibril and mineral components is clearly relevant to the modes of endplate failure that occur.

Purpose: To understand how structural integration is achieved across the cartilaginous-vertebral endplate junction.

The Influence of Concordant Complex Posture and Loading Rate on Motion Segment Failure: A Mechanical and Microstructural Investigation.

Study Design: Microstructural investigation of compression-induced herniation of a lumbar disc held in a concordant complex posture.

Objective: To explore the significance of loading rate in a highly asymmetric concordant posture, comparing the mechanisms of failure to an earlier study using a nonconcordant complex posture.

Summary Of Background Data: A recent study with a nonconcordant complex posture (turning in the opposite direction to that which the load is applied) demonstrated the vulnerability of the disc to loading that is borne by one set of oblique-counter oblique fiber sets in the alternating lamellae of the annulus, and aggravated by an elevated loading rate.

How a decreased fibrillar interconnectivity influences stiffness and swelling properties during early cartilage degeneration.

Objective: The functional coupling between the fibrillar network and the high-swelling proteoglycans largely determines the mechanical properties of the articular cartilage matrix. The objective of this new study was to show specifically how changes in fibrillar interconnectivity arising from early cartilage degeneration influence transverse stiffness and swelling properties at the tissue level.

Design: Radial zone transverse layers of cartilage matrix were obtained from intact and mildly degenerate bovine patellae.

A more realistic disc herniation model incorporating compression, flexion and facet-constrained shear: a mechanical and microstructural analysis. Part II: high rate or 'surprise' loading.

Purpose: Part I of this study explored mechanisms of disc failure in a complex posture incorporating physiological amounts of flexion and shear at a loading rate considerably lower than likely to occur in a typical in vivo manual handling situation. Given the strain-rate-dependent mechanical properties of the heavily hydrated disc, loading rate will likely influence the mechanisms of disc failure. Part II investigates the mechanisms of failure in healthy discs subjected to surprise-rate compression while held in the same complex posture.

A more realistic disc herniation model incorporating compression, flexion and facet-constrained shear: a mechanical and microstructural analysis. Part I: Low rate loading.

Purpose: To date, the mechanisms of disc failure have been explored at a microstructural level in relatively simple postures. However, in vivo the disc is known to be subjected to complex loading in compression, bending and shear, and the influence of these factors on the mechanisms of disc failure is yet to be described at a microstructural level. The purpose of this study was to provide a microstructural analysis of the mechanisms of failure in healthy discs subjected to compression while held in a complex posture incorporating physiological amounts of flexion and facet-constrained shear.

Does an Annular Puncture Influence the Herniation Path?: An In Vitro Mechanical and Structural Investigation.

Study Design: A study of mechanically induced herniation in punctured ovine discs followed by structural analysis.

Objective: To investigate whether an annular puncture influences the path that herniation takes by providing direct passage for nucleus through the annulus and therefore whether it increases the risk of acute herniation from overload at the site of damage independent of any longer-term degeneration.

Summary Of Background Data: Ten years after treatment with discography both degenerative changes and frequency of herniation have been shown to increase compared to untreated discs.

A Microstructural Investigation of Disc Disruption Induced by Low Frequency Cyclic Loading.

Study Design: Microstructural investigation of low frequency cyclic loading and flexing of the lumbar disc.

Objective: To explore micro-level structural damage in motion segments subjected to low frequency repetitive loading and flexing at sub-acute loads.

Summary Of Background Data: Cumulative exposure to mechanical load has been implicated in low back pain and injury.

Microstructure Variations in the Soft-Hard Tissue Junction of the Human Anterior Cruciate Ligament.

The role of the sub-bundles in the anterior cruciate ligament (ACL) has been defined, such that the anterior-medial bundle directly resists anterior tibial translation while the posterior lateral bundle is involved in rotational stability. With regards to this biomechanical function, much of the previous work on bundle-specific morphology has been carried out on the macroscale, with much less attention given to the micro-to-ultrastructural scalar levels. This is especially true of the enthesis and its microstructure, a biomechanically significant region that has been largely neglected in the published literature dealing with ACL sub-bundle anatomy.

Posterolateral Disc Prolapse in Flexion Initiated by Lateral Inner Annular Failure: An Investigation of the Herniation Pathway.

Study Design: Structural investigation of mechanically induced herniations in ovine lumbar motion segments.

Objective: This new study addresses the question of whether there are regions other than the posterior and posterolateral aspects that are implicated in the initiation of disc disruption and herniation.

Summary Of Background Data: Flexion in combination with compressive loading will induce disc herniations in healthy motion segments in vitro.

The influence of early degenerative changes on the vulnerability of articular cartilage to impact-induced injury.

Background: Recently, the structural changes in a bovine model of early degeneration were validated by our research group to be analogous to that in early human osteoarthritis. The hypothesis of this study was that the structural changes associated with increasing levels of degeneration would lead to higher levels of tissue damage in response to impact induced injury.

Methods: A total of forty bovine patellae were obtained for this study.

How maturity influences annulus-endplate integration in the ovine intervertebral disc: a micro- and ultra-structural study.

The annulus-endplate anchorage system plays a vital role in structurally linking the compliant disc to its adjacent much more rigid vertebrae. Past literature has identified the endplate as a region of weakness, not just in the mature spine but also in the immature spine. The aim of this structural study was to investigate in detail the morphological changes associated with annulus-endplate integration through different stages of maturity.

Staying connected: structural integration at the intervertebral disc-vertebra interface of human lumbar spines.

Purpose: To investigate the microscopic fibrous integration between the intervertebral disc, cartilage endplates and vertebral endplates in human lumbar spines of varying degrees of degeneration using differential interference contrast (DIC) optics. Weakness at these junctions is considered to be an important factor in the aetiology of disc herniations.

Methods: Magnetic resonance images (MRIs) of cadaveric lumbar spines were graded for degeneration and motion segments from a range of degenerative grades isolated and bisected sagittally.

ISSLS Prize Winner: Vibration Really Does Disrupt the Disc: A Microanatomical Investigation.

Study Design: Microstructural investigation of vibration-induced disruption of the flexed lumbar disc.

Objective: The aim of the study was to explore micro-level structural damage in motion segments subjected to vibration at subcritical peak loads.

Summary Of Background Data: Epidemiological evidence suggests that cumulative whole body vibration may damage the disc and thus play an important role in low back pain.

How a radial focal incision influences the internal shear distribution in articular cartilage with respect to its zonally differentiated microanatomy.

Articular surface fibrillation and the loss of both transverse interconnectivity and zonal differentiation are indicators of articular cartilage (AC) degeneration. However, exactly how these structural features affect the load-redistributing properties of cartilage is still poorly understood. This study investigated how a single radial incision made to varying depths with respect to the primary zones of AC influenced its deformation response to compression.

Multi-scalar mechanical testing of the calcified cartilage and subchondral bone comparing healthy vs early degenerative states.

Objective: The calcified cartilage layer is thought to be integral to force transmission between the compliant articular cartilage (AC) above and underlying stiff bone. This study aims to determine how such a stiffness gradient across the calcified cartilage and bone changes with joint degeneration and how different scalar levels of testing are correlated.

Method: Using a bovine model of early osteoarthritis (OA), multiple samples of calcified cartilage on subchondral bone (SB) from sixteen bovine patellae, displaying a range of cartilage states from intact (healthy) to moderately degenerate, were tested using macroscopic three-point bending, microhardness indentation, and nanoindentation.

Derivation of inter-lamellar behaviour of the intervertebral disc annulus.

The inter-lamellar connectivity of the annulus fibrosus in the intervertebral disc has been shown to affect the prediction of the overall disc behaviour in computational models. Using a combined experimental and computational approach, the inter-lamellar mechanical behaviour of the disc annulus was investigated under conditions of radial loading. Twenty-seven specimens of anterior annulus fibrosus were dissected from 12 discs taken from four frozen ovine thoracolumbar spines.

ISSLS Prize Winner: A Detailed Examination of the Elastic Network Leads to a New Understanding of Annulus Fibrosus Organization.

Study Design: Investigation of the elastic network in disc annulus and its function.

Objective: To investigate the involvement of the elastic network in the structural interconnectivity of the annulus and to examine its possible mechanical role.

Summary Of Background Data: The lamellae of the disc are now known to consist of bundles of collagen fibers organized into compartments.

"Surprise" Loading in Flexion Increases the Risk of Disc Herniation Due to Annulus-Endplate Junction Failure: A Mechanical and Microstructural Investigation.

Study Design: Microstructural investigation of compression-induced herniation of the flexed lumbar disc.

Objective: To provide a microstructural analysis of the mechanisms of annular wall failure in healthy discs subjected to flexion and a rate of compression comparable with the maximum rate at which the muscles of the spinal column can generate a force.

Summary Of Background Data: Clinical evidence indicates the involvement of the endplate in herniation.

Crimp morphology in the ovine anterior cruciate ligament.

While the crimp morphology in ligaments and tendons has been described in detail in the literature, its relative distribution within the tissue has not been studied, especially in relation to the complex multi-bundle arrangement as is found in the anterior cruciate ligament (ACL). In this study, the crimp morphology of the ovine ACL was examined topologically and with respect to its double-bundle structure. The crimp morphologies were compared with the knee in three knee positions, namely stance, maximum extension and maximum flexion.

A multiscale structural investigation of the annulus-endplate anchorage system and its mechanisms of failure.

Background Context: The annulus-endplate anchorage system performs a critical role in the disc, creating a strong structural link between the compliant annulus and the rigid vertebrae. Endplate failure is thought to be associated with disc herniation, a recent study indicating that this failure mode occurs more frequently than annular rupture.

Purpose: The aim was to investigate the structural principles governing annulus-endplate anchorage and the basis of its strength and mechanisms of failure.

Microanatomy of the medial collateral ligament enthesis in the bovine knee.

This study applied transmission and differential interference contrast light microscopy imaging methodologies to revisit the microanatomy of the ligament-bone junction of the medial collateral ligament, with the aim of providing new insights into the mechanostructural significance of the enthesis. The data show that the microscale structural features of the enthesis are more complex than the conventional description of "direct versus indirect," or "fibrous versus nonfibrous" insertions. From a materials perspective the enthesis may be viewed as a specialised functionally graded structural continuum whose unique microlevel structural adaptation contributes to maintaining both the local tissue micromechanical environment and joint function at the macrolevel.

A multi-scale structural study of the porcine anterior cruciate ligament tibial enthesis.

Like the human anterior cruciate ligament (ACL), the porcine ACL also has a double bundle structure and several biomechanical studies using this model have been carried out to show the differential effect of these two bundles on macro-level knee joint function. It is hypothesised that if the different bundles of the porcine ACL are mechanically distinct in function, then a multi-scale anatomical characterisation of their individual enthesis will also reveal significant differences in structure between the bundles. Twenty-two porcine knee joints were cleared of their musculature to expose the intact ACL following which ligament-bone samples were obtained.