Differences and similarities in muscle architecture of fibularis longus and brevis-An observational descriptive cross-sectional and feasibility study.

BACKGROUND: The fibularis longus (FL) muscle is larger in volume than fibularis brevis (FB) and is therefore claimed to be the stronger evertor of the two. Clinical observation of FL and FB tendon rupture show that injury to the FB has a serious negative effect on hindfoot eversion. This implies that the FB is the stronger and more important evertor. The strength of a muscle is not purely based on its volume, and the observed discrepancy between the FB and FL may be due to differences in muscle architecture. This study compares the muscle architecture of FL with FB. METHODS: Sixteen legs from eight formaldehyde-fixed human specimens, mean age 83 (range 72-89) years, were dissected. The volume, fibre lengths and fibre pennation angles for both muscles were measured and the physiological cross-sectional area (PCSA) was calculated. RESULTS: The FL was always larger than the FB, with an individual difference in volume that varied from 1.4 to 4.6 times larger with a mean difference of 17 ml (95% CI 14-20; p < 0.001). Mean fibre lengths were 9 mm (95% CI 2-16; p = 0.015) longer in FL than in FB. The mean pennation angle was 9.6 degrees in FL and 8.8 degrees in FB, this difference was not significant (p = 0.32). The mean PCSA for FL was 3 cm2 (95% CI 2-4) larger than for FB (p < 0.001). CONCLUSIONS: With our sample set, the hypothesis that the muscle architecture can explain the clinical discrepancy between the FL and FB, was not supported. The difference in hindfoot eversion might instead depend on the different moment arms of FL and FB and the effect forefoot abduction has on hindfoot eversion.

Role of the Middle Lumbar Fascia on Spinal Mechanics: A Human Biomechanical Assessment.

STUDY DESIGN: Biomechanical experiment. OBJECTIVE: The aims of the present study were to test the effect of fascial tension on lumbar segmental axial rotation and lateral flexion and the effect of the angle of fascial attachment. SUMMARY OF BACKGROUND DATA: Tension in the middle layer of lumbar fascia has been demonstrated to affect mechanical properties of lumbar segmental flexion and extension in the neutral zone. The effect of tension on segmental axial rotation and lateral flexion has, however, not been investigated. METHODS: Seven unembalmed lumbar spines were divided into segments and mounted for testing. A 6 degree-of-freedom robotic testing facility was used to displace the segments in each anatomical plane (flexion-extension, lateral bending, and axial rotation) with force and moment data recorded by a load cell positioned beneath the test specimen. Tests were performed with and without a 20 N fascia load and the subsequent forces and moments were compared. In addition, forces and moments were compared when the specimens were held in a set position and the fascia loading angle was varied. RESULTS: A fascial tension of 20 N had no measurable effect on the forces or moments measured when the specimens were displaced in any plane of motion (P > 0.05). When 20 N of fascial load were applied to motion segments in a set position small segmental forces and moments were measured. Changing the angle of the fascial load did not significantly alter these measurements. CONCLUSION: Application of a 20 N fascial load did not produce a measureable effect on the mechanics of a motion segment, even though it did produce small measurable forces and moments on the segments when in a fixed position. Results from the present study are inconsistent with previous studies, suggesting that further investigation using multiple testing protocols and different loading conditions is required to determine the effects of fascial loading on spinal segment behavior. LEVEL OF EVIDENCE: N/A.

Anatomical and mechanical relationship between the proximal attachment of adductor longus and the distal rectus sheath.

The objectives of this study were to investigate the anatomical relationship between the proximal adductor longus (AL) and rectus abdominis muscles and to determine whether unilateral loading of AL results in strain transmission across the anterior pubic symphysis to the contralateral distal rectus sheath. Bilateral dissections were conducted on 10 embalmed cadavers. Strain transfer across the pubic symphysis was examined on seven of these cadavers. An AL contraction was simulated by applying a controlled load in the direction of its proximal tendinous fibers, and the resultant strain in the contralateral distal rectus sheath was measured using a foil-type surface mounted microstrain gage. Adductor longus attached to the antero-inferior aspect of the pubis. In 18 of the 20 limbs, the proximal attachment of AL was tendinous on its superficial surface and muscular on its deep surface. The proximal AL tendon was found in most instances to have secondary communications with structures such as the contralateral distal rectus sheath, pubic symphysis anterior capsule, ilio-inguinal ligament, and contralateral proximal AL tendon. Despite these consistent anatomical observations, strain measured in the contralateral distal rectus sheath upon unilateral loading of the proximal AL varied considerably between cadavers. Measured strain had an average ± 1SD of 0.23 ± 0.43%. The proximal attachment of AL contributes to an anatomical pathway across the anterior pubic symphysis that is likely required to withstand the transmission of large forces during multidirectional athletic activities. This anatomical relationship may be a relevant factor in explaining the apparent vulnerability of the AL and rectus abdominis attachments to injury.

The middle layer of lumbar fascia can transmit tensile forces capable of fracturing the lumbar transverse processes: an experimental study.

BACKGROUND: Transversus abdominis and its aponeurotic attachment to the lumbar transverse processes via the middle layer of lumbar fascia are of proposed clinical and biomechanical importance. Moderate traction on these structures (simulating submaximal contraction of transversus abdominis) is reported to influence segmental motion, but their tensile capacity is unknown and the effects of sudden, maximal traction on these attachments and the transverse processes are uncertain. METHODS: In 15 embalmed cadaver abdomens, the middle layer of lumbar fascia was isolated, gripped and rapid tension applied in either a lateral or posteroanterior direction (simulating forces that may produce avulsion and traumatic fractures). Peak forces prior to tissue failure were recorded and the gross effects of traction documented. FINDINGS: Lumbar transverse process fractures were produced in all specimens; by transverse traction in 50% of tests and posteroanterior force in 80%. In the remainder the middle layer of lumbar fascia was torn. Mean transverse and posteroanterior peak forces reached in the middle layer of lumbar fascia prior to failure were 82 N (range 20-190 N) and 47 N (range 25-70 N), respectively. INTERPRETATION: The middle layer of lumbar fascia can transmit substantial tensile forces to lumbar vertebrae, capable of transverse process fracture under experimental conditions. Tensile capacity is likely to be even greater in-vivo. This suggests transversus abdominis and the middle layer of lumbar fascia can strongly influence vertebral motion, should be incorporated in biomechanical models of the spine and considered as potential contributors to transverse process fractures by avulsion.

The anatomy of the pubic region revisited: implications for the pathogenesis and clinical management of chronic groin pain in athletes.

Chronic groin pain is a common complaint for athletes participating in sports that involve repetitive sprinting, kicking or twisting movements, such as Australian Rules football, soccer and ice hockey. It is frequently a multifactorial condition that presents a considerable challenge for the treating sports medicine practitioner. To better understand the pathogenesis of chronic groin pain in athletes, a precise anatomical knowledge of the pubic symphysis and surrounding soft tissues is required. Several alternative descriptions of pubic region structures have been proposed. Traditionally, chronic groin pain in athletes has been described in terms of discrete pathology requiring specific intervention. While this clinical reasoning may apply in some cases, a review of anatomical findings indicates the possibility of multiple pathologies coexisting in athletes with chronic groin pain. An appreciation of these alternative descriptions may assist sports medicine practitioners with diagnostic and clinical decision-making processes. The purpose of this literature review is to reappraise the anatomy of the pubic region, considering findings from cadaveric dissection and histology studies, as well as those from diagnostic imaging studies in athletes.

The middle layer of lumbar fascia and attachments to lumbar transverse processes: implications for segmental control and fracture.

The anatomy of the middle layer of lumbar fascia (MLF) is of biomechanical interest and potential clinical relevance, yet it has been inconsistently described. Avulsion fractures of the lumbar transverse processes (LxTP's) are traditionally attributed to traction from psoas major or quadratus lumborum (QL), rather than transversus abdominis (TrA) acting via the MLF. This attachment is also absent from many biomechanical models of segmental control. The aims of this study were to document: (1) the morphology and attachments of the MLF and (2) the attachments of psoas and QL to the LxTP's. Eighteen embalmed cadavers were dissected, measuring the thickness, fibre angle and width of the MLF and documenting the attachments of MLF, psoas and QL. The MLF was thicker at the level of the LxTP's than between them (mean 0.62: 0.40 mm). Psoas attached to the anteromedial surface of each process and QL and TrA to its lateral border; QL at its upper and lower corners and TrA (via the MLF) to its tip. In three cadavers, tension applied to the MLF fractured a transverse process. The MLF has a substantial and thickened attachment to the tips of the LxTP's which supports the involvement of TrA in lumbar segmental control and/ or avulsion fracture of the LxTP's.

Effects of tensioning the lumbar fasciae on segmental stiffness during flexion and extension: Young Investigator Award winner.

STUDY DESIGN: Biomechanical study of unembalmed human lumbar segments. OBJECTIVE: To investigate the effects of tensioning the lumbar fasciae (transversus abdominis [TrA]) aponeurosis) on segment stiffness during flexion and extension. SUMMARY OF BACKGROUND DATA: Animal and human studies suggest that TrA may influence intersegmental movement via tension in the middle and posterior layers of lumbar fasciae (MLF, PLF). METHODS: Compressive flexion and extension moments were applied to 17 lumbar segments from 9 unembalmed cadavers with 20 N lateral tension of the TrA aponeurosis during: 1) "static" tests: load was compared when fascial tension was applied during static compressive loads into flexion-extension; 2) "cyclic loading" tests: load, axial displacement, and stiffness were compared during repeated compressive loading cycles into flexion-extension. After testing, the PLF was incised to determine the tension transmitted by each layer. RESULTS: At all segments and loads (<200 N), fascial tension increased resistance to flexion loads by approximately 9.5 N. In 15 of 17, fascial tension decreased resistance to extension by approximately 6.6 N. Fascial tension during cyclic flexion loading decreased axial displacement by 26% at the onset of loading (0-2 N) and 2% at 450 N (13 of 17). During extension loading, fascial tension increased displacement at the onset of loading (10 of 17) by approximately 23% and slightly (1%) decreased displacement at 450 N. Segment stiffness was increased by 6 N/mm in flexion (44% at 25 N) and decreased by 2 N/mm (8% at 25 N) in extension. More than 85% of tension was transmitted through the MLF. CONCLUSIONS: Tension on the lumbar fasciae simulating moderate contraction of TrA affects segmental stiffness, particularly toward the neutral zone.

Regional morphology of the transversus abdominis and obliquus internus and externus abdominis muscles.

BACKGROUND: The mechanisms by which the abdominal muscles move and control the lumbosacral spine are not clearly understood. Descriptions of abdominal morphology are also conflicting and the regional anatomy of these muscles has not been comprehensively examined. The aim of this study was to investigate the morphology of regions of transversus abdominis and obliquus internus and externus abdominis. METHODS: Anterior and posterolateral abdominal walls were dissected bilaterally in 26 embalmed human cadavers. The orientation, thickness and length of the upper, middle and lower fascicles of transversus abdominis and obliquus internus abdominis, and the upper and middle fascicles of obliquus externus abdominis were measured. FINDINGS: Differences in fascicle orientation, thickness and length were documented between the abdominal muscles and between regions of each muscle. The fascicles of transversus abdominis were horizontal in the upper region, with increasing inferomedial orientation in the middle and lower regions. The upper and middle fascicles of obliquus internus abdominis were oriented superomedially and the lower fascicles inferomedially. The mean vertical dimension of transversus abdominis that attaches to the lumbar spine via the thoracolumbar fascia was 5.2 (SD 2.1) cm. Intramuscular septa were observed between regions of transversus abdominis, and obliquus internus abdominis could be separated into two distinct layers in the lower and middle regions. INTERPRETATION: This study provides quantitative data of morphological differences between regions of the abdominal muscles, which suggest variation in function between muscle regions. Precise understanding of abdominal muscle anatomy is required for incorporation of these muscles into biomechanical models. Furthermore, regional variation in their morphology may reflect differences in function.

Tensile transmission across the lumbar fasciae in unembalmed cadavers: effects of tension to various muscular attachments.

STUDY DESIGN: Traction was applied to muscles attaching to the posterior and middle layers of lumbar fascia (PLF, MLF). Effects on fasciae were determined via tensile force measures and movement of markers. OBJECTIVES: To document tensile transmission to the PLF and MLF when traction was applied to latissimus dorsi (LD), gluteus maximus (GM), external and internal oblique (EO, IO), and transversus abdominis (TrA) in unembalmed cadavers. SUMMARY OF BACKGROUND DATA: A previous study on embalmed cadavers applied traction to muscle attachments while monitoring fascial movement but did not test TrA or the MLF. METHODS: The PLF and MLF were dissected then marked on eight unembalmed cadavers. A strain gauge was inserted through fascia at L3; 10N traction was applied to each muscle attachment while photographs and tension measures were taken. Movement of fascial markers was detected photographically. Fascial widths were also measured. RESULTS: Tension was clearly transmitted to fascial vertebral attachments. Tensile forces and fascial areas affected were highest for traction on LD and TrA in the PLF and for TrA in the MLF. Movement of PLF markers from tension on LD and TrA occurred bilaterally between T12 and S1. Effects from other muscles were variably bilateral, with those from GM and IO occurring below L3 and those from EO occurring above L3. Tensile forces were relatively high in the MLF and its width was less than half that of the PLF. CONCLUSIONS: Low levels of tension are effectively transmitted between TrA and the MLF or PLF. Via them, TrA may influence intersegmental movement.