Comparison of the acoustic windows for the thoracic paramedian epidural approach after shoulder rotation: The lateral decubitus versus the sitting position.

BACKGROUND: The aim of this study was to compare the mean lengths of the posterior longitudinal ligament (PLL) as the acoustic window during the thoracic paramedian epidural approach after shoulder rotation, while subjects were in the lateral decubitus or in the sitting position. METHODS: Thirty-two adult male volunteers were placed in the right decubitus position or sitting position on a horizontal operating table. To obtain an optimal ultrasound view for the PLL on the right side, thoracic spinal ultrasonography was performed at the T6/7 interspace using the paramedian oblique sagittal plane. PLL length was measured on the ultrasound image before and after right shoulder rotation. RESULTS: Before shoulder rotation, the difference in mean PLL length between the sitting (11.1±1.3mm) and lateral decubitus (10.7±1.2mm) positions was not statistically significant (P=0.05). Within-position, the before and after comparison revealed that after shoulder rotation, PLL length was significantly increased to 12.2±1.4mm (P<0.001) and 12.0±1.5mm (P<0.001) in the sitting and lateral decubitus positions, respectively. However, after shoulder rotation the between-position difference in mean PLL length was not statistically significant (P=0.50) CONCLUSIONS: Shoulder rotation did not result in a statistically significant difference in the dimension of the acoustic target window for paramedian thoracic epidural access in the sitting compared to the lateral decubitus position.

Unión cráneo-cervical - anatomía normal y correlación con imágenes / Cranio Cervical Junction - Anatomy and Imaging Correlation

La solicitud de estudios de imagen en pacientes con trauma cervical es muy frecuente en la práctica diaria. Esa patología es causa relativamente frecuente de discapacidad en pacientes jóvenes junto con el trauma encéfalo craneano. En un porcentaje no despreciable de los casos, las lesiones traumáticas comprometen la unión cráneo- cervical y en esos pacientes, la morbi-mortalidad es más significativa. La transición entre el cráneo y el raquis se basa en un conjunto de estructuras óseas relacionadas por articulaciones muy móviles y estabilizadas por un grupo de ligamentos y músculos que le brindan al mismo tiempo gran solidez. Para una correcta interpretación de los estudios de imagen de uso corriente en la clínica, es fundamental un sólido conocimiento anatómico de la unión cráneo-cervical y sus componentes. Es el objetivo de esta revisión, sistematizar la anatomía de la unión cráneo-cervical con especial énfasis en sus ligamentos, analizar la fisiología de sus movimientos y el concepto de estabilidad para luego realizar una correlación con tomografía computada multi-detector y resonancia magnética.

The request of imaging techniques in patients with cervical spine trauma is very common in clinical practice. Cervical trauma is a relatively common cause of disability in young patients. In a significant percentage of cases traumatic injuries compromise the cranio-cervical junction with more important morbidity and mortality in this group of patients. The transition between the skull and the spine is based on a set of bony structures, high mobility joints, and stabilization mechanism formed by a group of ligaments and muscles. A solid anatomical knowledge of the cranio-cervical junction and its components is essential for a correct interpretation of current high resolution imaging studies. The goal of this review is highlight the anatomy of the cranio-cervical junction with special emphasis on the ligaments, analyze the biomechanics of their movements and the concept of stability. At last but not leastwe will establish a correlation with multidetector computed tomography and high-resolutionmagnetic resonance imaging.

Morphometric study of the posterior longitudinal ligament at the lumbar spine.

PURPOSE: There are only two descriptions of posterior longitudinal ligament (PLL) at the lumbar spine level but its morphologic characteristics are different to cervical and thoracic levels. METHOD: Spine explantation (from Th12 to L5) followed by resection of the neural arch and the dural sheath in 13 fresh cadavers was performed. The PLL was isolated from other epidural structures and its width was measured and compared to the vertebral body width at each vertebral levels. It was conducted at a microanatomic study concerning the PLL and the posterior outer annulus fibrosus. RESULTS: The PLL width was reduced craniocaudaly significantly, becoming thin from L4. The average width of PLL was 7.8 mm at L1 and 1.9 mm at L5. The width decreased gradually from L1 to L5 or abruptly from L4. The ratio of PLL width compared to the vertebral body width was 21% at L1 and 3% at L5. Microanatomic study confirmed that the PLL is less thick at its annulus fibrosus adhesion at L4-L5 and L5-S1. The relationship between the PLL and other epidural structures are discussed. CONCLUSIONS: The presence and function of the ilio-lumbar ligaments and the articular process orientation of L5-S1 may be explanations for PLL width decrease at L4-L5 and L5-S1. Furthermore, this aspect may be considered as one factor contributing to the occurrence of disc herniations at these levels, which levels are more frequently involved in this pathology.

First sacral nerve and anterior longitudinal ligament anatomy: clinical applications during sacrocolpopexy.

BACKGROUND: The recommended location of graft attachment during sacrocolpopexy is at or below the sacral promontory on the anterior surface of the first sacral vertebra. Graft fixation below the sacral promontory may potentially involve the first sacral nerve. OBJECTIVE: The objectives of this study were to examine the anatomy of the right first sacral nerve relative to the midpoint of the sacral promontory and to evaluate the thickness and ultrastructural composition of the anterior longitudinal ligament at the sacral promontory level. STUDY DESIGN: Anatomic relationships were examined in 18 female cadavers (8 unembalmed and 10 embalmed). The midpoint of the sacral promontory was used as reference for all measurements. The most medial and superior point on the ventral surface of the first sacral foramen was used as a marker for the closest point at which the first sacral nerve could emerge. Distances from midpoint of sacral promontory and the midsacrum to the most medial and superior point of the first sacral foramen were recorded. The right first sacral nerve was dissected and its relationship to the presacral space was noted. The anterior longitudinal ligament thickness was examined at the sacral promontory level in the midsagittal plane. The ultrastructural composition of the ligament was evaluated using transmission electron microscopy. Height of fifth lumbar to first sacral disc was also recorded. Descriptive statistics were used for data analyses. RESULTS: Median age of specimens was 78 years and median body mass index was 20.1 kg/m2. Median vertical distance from midpoint of sacral promontory to the level of the most medial and superior point of the first sacral foramen was 26 (range 22-37) mm. Median horizontal distance from the midsacrum to the first sacral foramen was 19 (range 13-23) mm. In all specimens, the first sacral nerve was located just behind the layer of parietal fascia covering the piriformis muscle, and thus, outside the presacral space. Median anterior longitudinal ligament thickness at the sacral promontory level was 1.9 (range 1.2-2.5) mm. Median fifth lumbar to first sacral disc height was 16 (8.3-17) mm. CONCLUSION: Awareness of the first sacral nerve position, approximately 2.5 cm below the midpoint of the sacral promontory and 2 cm to the right of midline, should help anticipate and avoid somatic nerve injury during sacrocolpopexy. Knowledge of the approximate 2-mm thickness of the anterior longitudinal ligament should help reduce risk of discitis and osteomyelitis, especially when graft is affixed above the level of the sacral promontory.

The Effects of Shoulder Rotation on the Acoustic Window for Thoracic Paramedian Epidural Approach in the Lateral Decubitus Position.

BACKGROUND AND OBJECTIVES: The aim of this study was to examine whether shoulder rotation increases the length of the posterior longitudinal ligament (PLL) in the lateral decubitus position. METHODS: Thirty-four adult male volunteers were placed in the right or left lateral decubitus and flexion position on a horizontal operating table. Thoracic spinal ultrasonography was performed using the paramedian oblique sagittal plane to obtain the optimal ultrasound view for the PLL on the dependent side. The lengths of the PLL were measured at the T6/7 and T9/10 interspaces before and after ipsilateral 30-degree shoulder rotation. RESULTS: In the right lateral decubitus position, the ipsilateral shoulder rotation increased the mean (SD) of the PLL from 7.4 (2.8) to 8.4 (2.6) mm (P = 0.006) at the T6/7 level and from 8.4 (2.9) to 10.6 (2.8) mm (P < 0.0001) at the T9/10 level. Similarly, in the left lateral decubitus position, the ipsilateral shoulder rotation increased the mean (SD) of the PLL from 8.0 (2.6) to 9.1 (2.6) mm (P = 0.001) at the T6/7 level and from 9.3 (2.8) to 11.8 (3.1) mm (P < 0.0001) at the T9/10 level. CONCLUSIONS: Shoulder rotation significantly increased the dimension of the acoustic target window for paramedian thoracic epidural access in the lateral decubitus position at both T6/7 and T9/10 levels. Further clinical studies are needed to investigate the effect of shoulder rotation on thoracic epidural access.

Critical Anatomy Relative to the Sacral Suture: A Postoperative Imaging Study After Robotic Sacrocolpopexy.

OBJECTIVE: This study aimed to characterize pertinent anatomy relative to the sacral suture placed at time of robotic sacrocolpopexy using postoperative computed tomography and magnetic resonance imaging. METHODS: A vascular clip was placed at the base of the sacral suture at the time of robotic sacrocolpopexy. Six weeks postoperatively, subjects returned for a computed tomography scan and magnetic resonance imaging. RESULTS: Ten subjects completed the study. The middle sacral artery and vein coursed midline or to the left of midline in all the subjects. The left common iliac vein was an average of 26 mm from the sacral suture. To the right of the suture, the right common iliac artery was 18 mm away. Following the right common iliac artery to its bifurcation, the right internal iliac was on average 10 mm from the suture. The bifurcations of the inferior vena cava and the aorta were 33 mm and 54 mm further cephalad, respectively.The right ureter, on average, was 18 mm from the suture. The thickness of the anterior longitudinal ligament was 2 mm.The mean angle of descent of the sacrum was 70 degrees. Lastly, we found that 70% of the time, a vertebral body was directly below the suture; the disc was noted in 30%. CONCLUSIONS: We describe critical anatomy surrounding the sacral suture placed during robotic sacrocolpopexy. Proximity of both vascular and urologic structures within 10 to 18 mm, as well as anterior ligament thickness of only 2 mm highlights the importance of adequate exposure, careful dissection, and surgeon expertise.

Bone-formers and bone-losers in an archaeological population.

OBJECTIVES: Recent biomedical research suggests that, in modern human populations, individuals may vary in their inherent tendency toward bone formation at skeletal and extra-skeletal locations. However, the nature of this phenomenon is incompletely understood, and the extent to which it might apply to past populations is unclear. It is hypothesized that if there is inter-individual variation in some overall tendency toward bone formation in skeletal and extra-skeletal sites then there should be a positive relationship between ligamentous ossification and thickness of cortical bone. This work is a test of this hypothesis in an archaeological population. MATERIALS AND METHODS: The study material comprises adult skeletons (N = 137 individuals) of documented age at death from 18th to 19th century London. It examines the relationship between bone deposition in the anterior longitudinal ligament (ALL) in the thoracic spine and cortical index (CI) at the metacarpal measured by radiogrammetry. RESULTS: Controlling for the potential confounders age, sex, skeletal completeness, occupation (males) and parity (females), there was a positive association between ossification into the ALL and CI. This reflects lesser medullary cavity width in those showing ALL ossification. DISCUSSION: Ligamentous ossification in the axial skeleton and peripheral cortical bone status are linked, individuals with ALL ossification showing lesser resorption of cortical bone at the endosteal surface. This is consistent with the idea of inter-individual variation in some general bone-forming/bone-losing tendency in this 200 year old study population, but there was no evidence of a link between ALL ossification and increased skeletal subperiosteal bone deposition.

A comprehensive review of the sub-axial ligaments of the vertebral column: part I anatomy and function.

BACKGROUND: As important as the vertebral ligaments are in maintaining the integrity of the spinal column and protecting the contents of the spinal canal, a single detailed review of their anatomy and function is missing in the literature. METHODS: A literature search using online search engines was conducted. RESULTS: Single comprehensive reviews of the spinal ligaments are not found in the extant medical literature. CONCLUSIONS: This review will be useful to those who treat patients with pathology of the spine or who interpret imaging or investigate the anatomy of the ligaments of the vertebral column.

Basic aspects in MR imaging of degenerative lumbar disk disease.

Degenerative disease may lead to spinal canal stenosis and long-lasting pain. It is among the leading cause of disability that may affect the ability to work. It has become more common in an increasingly aging population. MRI is the most comprehensive imaging modality and provides detailed morphologic information. A standardized terminology facilitates communication with referring physicians. Yet imaging findings need careful interpretation in conjunction with the results of clinical tests and symptoms to truly help guide therapeutic decision making. This review summarizes aspects of normal anatomy of the intervertebral disk, pathologic mechanisms, terminology, and examples of the imaging spectrum of disk degeneration and herniation.

Implementation and validation of probabilistic models of the anterior longitudinal ligament and posterior longitudinal ligament of the cervical spine.

The objective of this investigation was to develop probabilistic finite element (FE) models of the anterior longitudinal ligament (ALL) and posterior longitudinal ligament (PLL) of the cervical spine that incorporate the natural variability of biological specimens. In addition to the model development, a rigorous validation methodology was developed to quantify model performance. Experimental data for the geometry and dynamic properties of the ALL and PLL were used to create probabilistic FE models capable of predicting not only the mean dynamic relaxation response but also the observed experimental variation of that response. The probabilistic FE model uses a quasilinear viscoelastic material constitutive model to capture the time-dependent behaviour of the ligaments. The probabilistic analysis approach yields a statistical distribution for the model-predicted response at each time point rather than a single deterministic quantity (e.g. ligament force) and that response can be statistically compared to experimental data for validation. A quantitative metric that compares the cumulative distribution functions of the experimental data and model response is computed for both the ALL and PLL throughout the time histories and is used to quantify model performance.

Lowest colpopexy sacral fixation point alters vaginal axis and cul-de-sac depth.

OBJECTIVE: To determine the variation in vaginal axis and posterior cul-de-sac depth when the lowest suture used to attach the sacrocolpopexy mesh to the anterior longitudinal ligament is anchored at different levels. STUDY DESIGN: At five lumbosacral mesh attachment sites, the anterior vaginal wall axis angle was measured relative to a line between the lowest border of the pubic symphysis and fourth sacral (S4) foramen in 9 unembalmed cadavers. The vertical distance from S4 to the posterior mesh was measured as a surrogate of cul-de-sac depth. RESULTS: From a mesh fixation point at the lower border of S2 to a point at the lower border of L5, there was a 3-fold increase in both vaginal axis angle (13.04 ± 3.19 vs 42.88 ± 4.16 cm) and distance from S4 to the posterior mesh (2.50 ± 0.61 vs 7.38 ± 1.30 cm) between these points. CONCLUSION: During sacrocolpopexy, progressively cephalad sacral attachment increases vaginal axis angle and cul-de-sac depth.

The long posterior sacroiliac ligament: a histological study of morphological relations in the posterior sacroiliac region.

OBJECTIVES: To investigate the morphology of the long posterior sacroiliac ligament (LPSL) and its potential relationship to adjacent structures in the posterior sacroiliac region, and to consider any possible functional anatomical implications that may arise. METHODS: Four large cadaveric tissue blocks of the posterior sacroiliac region were utilised in this qualitative histological study. The blocks underwent demineralisation in ethyl-diamine-tetra-acetic acid (EDTA). The end-point was determined radiographically. The demineralised tissue blocks were subsequently processed and a base sledge microtome used to section the blocks. Sequential sections were stained with Harris haematoxylin and alcoholic eosin (H&E) and mounted on glass slides prior to viewing under a light microscope. RESULTS: The LPSL was observed to have proximal and distal regions of osseous attachment. Between these regions of attachment the middle LPSL was observed as a confluence of three layers: the erectores spinae aponeurosis, the 'deep fascial layer' and the gluteal aponeurosis. Deep to the 'deep fascial layer' a layer of adipose and loose connective tissue was observed. Lateral branches of the dorsal sacral rami were identified within this layer. CONCLUSIONS: The middle long posterior ligament appears to provide a pathway for the lateral branches of the dorsal sacral rami between the posterior sacral region and the gluteal region. This histological study provides a morphological basis for the proposal that putative sacroiliac joint pain may be due to an entrapment neuropathy of the lateral branches of the dorsal sacral rami at the long posterior sacroiliac ligament.

[Basic and clinical studies on lumbar vertebral canal expansion with preservation of posterior ligaments complex].

OBJECTIVE: To investigate the clinical application and efficacy of lumbar vertebral canal expansion with preservation of posterior ligaments complex, and to study its biomechanical properties. METHODS: Eight fresh lumbosacral cadaveric samples were divided into 3 groups. In group A, 8 intact lumbosacral cadaveric samples were used for biomechanical test. In group B, L3-5 laminectomy were, after the test in group A, performed and the posterior ligaments complex was preserved. In group C, the posterior ligaments complex was excised after the test in group B. In all 3 groups, the axial compression test, three-point bending test and torsional test were conducted. From June 2000 to June 2006, 309 patients (152 males and 157 females, aged 20-80 years with the average of 57.2 ) with lumbar canal stenosis received operation of the lumbar vertebral canal expansion with preservation of posterior ligaments complex. The course of disease was 3 months to 41 years. There were 55 patients suffering from pure lumbar canal stenosis, and 254 from lumbar canal stenosis combined with lumbar disc herniation, among which 105 were at L4,5 level, 56 at L4-S1 level, 86 at L5, S1 level, and 7 at L2,3 level. The therapeutic effect was assessed based on the JOA low back pain scoring system, the satisfaction degree of patient and radiographical observation. RESULTS: The axial compression test was performed. In the position of forward bending, stress, strain and axial displacement were smaller in groups A, B than those in group C, and axial stiffness in groups A, B was higher than those in group C, and the difference was significant (P < 0.01). In the position of backward extension, there was no significant difference among 3 groups (P > 0.05). Concerning the three-point bending test, under the same bending moment, there was a significant difference in deflection, dip and bending rigidity between group A and group C, and also between group B and group C (P < 0.01), but no significant difference between group A and group B (P> 0.05). In the torsional test, under the same torsional angle, the torque in group B was bigger than that in group C (P < 0.01). Under the same torque, the torsional angle in group B was smaller than that in group C (P < 0.01), and the torsional stiffness in group B was higher than that in group C (P < 0.01). The complications included 7 cases of distraction of nerve root, 5 leakage of cerebrospinal fluid and 4 wound infection. All complications were treated and restored completely. All patients were followed up for 1-7 years. According to the JOA low back pain scoring system, the improvement rate averaged 86.0%. Of all the 309 cases, 163 were excellent, 112 good, 34 fair, and the choiceness rate was 89%. The satisfaction rate of patient was 87%. There was no radiographic vertebral instability postoperatively. CONCLUSION: The lumbar vertebral canal expansion with preservation of posterior ligaments complex is conducive to maintaining the stability of lumbar spine and have good clinical outcomes.

[Optimization of capsulotomy of enhanced posterior soft tissue repair in total hip arthroplasty].

OBJECTIVE: To investigate the anatomic feature of the posterior hip joint capsule and its distributional difference of collagen fibers and to probe the optimization of the capsulotomy which can reserve the best strength part. METHODS: Ten adult cadaver pelvises (6 males and 4 females, aged 28-64 years) fixed with formalin were used. Ten right hips were used for anatomical experiment of hip joint capsule. The posterior hip joint capsules were divided into 3 sectors (I-III sectors) and 9 parts (I(A-C), II(D-F), III(G-I). The average thickness of each part was measured and the ischiofemorale ligaments were observed. Five capsules selected from ten left hips were used for histological experiment. The content of collagen fibers in sector I and sector II was analyzed by Masson's staining. Two fresh frozen specimens which were voluntary contributions were contrasted with the fixed specimens. The optimal incision line of the posterior capsule was designed and used. RESULTS: The thickness in the posterior hip joint capsule [I(A) (2.30 +/- 0.40), I(B) (4.68 +/- 0.81), I(C) (2.83 +/- 0.69), II(D) (2.80 +/- 0.79), II(E) (4.22 +/- 1.33), II(F) (2.50 +/- 0.54), III(G) (1.57 +/- 0.40), III(H) (2.60 +/- 0.63), III(I) (1.31 +/- 0.28) mm] had no uniformity (P < 0.01). The III(G) part and the III(I) part were thinner than the I(B) part and the II(E) part (P < 0.01). Two weaker parts located at obturator externus sector (sector III), the ischiofemorale ligament trunk went through two thicker parts (I(B) and II(E)). The distribution of the collagen fibers in sector I and sector II(I(A) 20.34% +/- 5.14%, I(B) 48.79% +/- 12.67%, I(C) 19.87% +/- 5.21%, II(D) 17.57% +/- 3.56%, II(E) 46.76% +/- 11.47%, II(F) 28.65% +/- 15.79%) had no uniformity (P < 0.01). The content of collagen fibers in I(B) part and II(E) part were more than that of other parts (P < 0.01). There were no statistically significant difference in the distribution feature of the thickness and the ischiofemorale ligaments between the fresh frozen specimens and the fixed specimens. The optimal incision line C-A-B-D-E of the posterior capsule was designed and put into clinical application. The remaining capsular flap comprise the most of the ischiofemorale ligament trunk and the part of gluteus minimus. CONCLUSION: Although enhanced posterior soft tissue repair in total hip arthroplasty was investigated deeply and obtained great development, but the postoperative dislocation rate was not eliminated. It is significant for optimizing the capsulotomy to reserve the best strength part of the posterior capsule and to bring into full play the function of the ischiofemorale ligaments.

Morphometric studies of the ligamentum flavum: a correlative microanatomical and MRI study of the lumbar spine.

BACKGROUND: Foraminal degenerative lumbar stenosis is traditionally considered a result of bony narrowing due to osteophytic appositions on the superior articular process. Clinical experience reveals that significant additional compression of the neural structures is due to degenerative hypertrophy of the adjacent ligamentum flavum. Therefore, microanatomical and neuroradiological investigations were performed to determine the microtopography of this ligament, especially with respect to its lateral extension. METHODS: Lumbar spine specimens of eight mid-aged human cadavers (mean age 34.5 years) were collected, and MRI studies with T1-weighted images were performed. The specially embedded specimens were sectioned horizontally at the level of the spinal ganglion (slice thickness: 2 mm). Anatomical morphometric data were correlated with identical measurements based on neuroradiological imaging and were analyzed statistically. RESULTS: The distance between midline and extraforaminal extension of the ligamentum flavum showed a mean value of 17 mm. The distance increased to 19 mm when the lateral insertion was correlated to the origin of the ligamentum flavum at the anterior margin of the lamina. The farthest lateral segment of the ligamentum flavum was determined in each case; it covered the synovial cavity of the lumbar facet joint in the direction of the extraforaminal segment of the intervertebral canal. CONCLUSIONS: Measurements from mid-aged cadavers show the extent of the ligamentum flavum including its intra- and extraforaminal parts. Due to this anatomical situation a hypertrophic ligamentum flavum may contribute significantly to nerve root compression at the level of the lateral spinal recess. This has to be kept in mind during surgical decompression, which might be incomplete unless these hypertrophied parts are completely removed.

The temperature-dependent viscoelasticity of porcine lumbar spine ligaments.

STUDY DESIGN: A uniaxial tensile loading study of 13 lumbar porcine ligaments under varying environmental temperature conditions. OBJECTIVES: To investigate a possible temperature dependence of the material behavior of porcine lumbar anterior longitudinal ligaments. SUMMARY OF BACKGROUND DATA: Temperature dependence of the mechanical material properties of ligament has not been conclusively established. METHODS: The anterior longitudinal ligaments (ALLs) from domestic pigs (n = 5) were loaded in tension to 20% strain using a protocol that included fast ramp/hold and sinusoidal tests. These ligaments were tested at temperatures of 37.8 degrees C, 29.4 degrees C, 21.1 degrees C, 12.8 degrees C, and 4.4 degrees C. The temperatures were controlled to within 0.6 degrees C, and ligament hydration was maintained with a humidifier inside the test chamber and by spraying 0.9% saline onto the ligament. A viscoelastic model was used to characterize the force response of the ligaments. RESULTS: The testing indicated that the ALL has strong temperature dependence. As temperature decreased, the peak forces increased for similar input peak strains and strain rates. The relaxation of the ligaments was similar at each temperature and showed only weak temperature dependence. Predicted behavior using the viscoelastic model compared well with the actual data (R2 values ranging from 0.89 to 0.99). A regression analysis performed on the viscoelastic model coefficients confirmed that relaxation coefficients were only weakly temperature dependent while the instantaneous elastic function coefficients were strongly temperature dependent. CONCLUSIONS: The experiment demonstrated that the viscoelastic mechanical response of the porcine ligament is dependent on the temperature at which it is tested; the force response of the ligament increased as the temperature decreased. This conclusion also applies to human ligaments owing to material and structural similarity. This result settles a controversy on the temperature dependence of ligament in the available literature. The ligament viscoelastic model shows a significant temperature dependence on the material properties; instantaneous elastic force was clearly temperature dependent while the relaxation response was only weakly temperature dependent. This result suggests that temperature dependence should be considered when testing ligaments and developing material models for in vivo force response, and further suggests that previously published material property values derived from room temperature testing may not adequately represent in vivo response. These findings have clinical relevance in the increased susceptibility of ligamentous injury in the cold and in assessing the mechanical behavior of cold extremities and extremities with limited vascular perfusion such as those of the elderly.

Biomechanical analysis of rotational motions after disc arthroplasty: implications for patients with adult deformities.

STUDY DESIGN: An anatomic and biomechanical bench-top basic scientific comparative analysis to determine the appropriateness of total disc replacement (TDR) in a lumbar spine with scoliotic tendencies. OBJECTIVES: Only limited data are currently available studying the application of disc replacement adjacent to scoliosis fusions. Theoretically, motion preservation should help delay the continuum of lumbar degeneration adjacent to scoliosis fusions and rotationally unstable lumbar segments. SUMMARY OF BACKGROUND DATA: As a tertiary referral center for failed TDR, we noticed an alarming number of lumbar spinal rotational iatrogenic instability patterns but none occurring in the cervical spine. It is appropriate to analyze the bench-top rotational stability of disc replacement to predict whether this new technology is feasible for a larger prospective clinical study in the treatment of degenerative scoliosis. METHODS: Measurements were taken from 60 human specimens from the Hamann-Todd Osteological Collection: 1) to determine the rotational arc of influence (AOI) = the angle formed from the center of axial rotation to the outermost extent of the facet joints; and 2) to determine the relative anatomic size discrepancy between the left and right facets proportionately with the cross-sectional area of the intervertebral disc = facet/endplate ratio (FER). Biomechanical testing was performed using fresh frozen human cadaveric spines with the following conditions to determine the rotational stability: 1) intact; 2) resection of ALL, anulus, disc, and PLL simulating the preparation for a TDR; 3) a more radical anular resection; 4) entire 360 degrees anular resection; and 4) insertion of the respective unconstrained-type disc replacement. Using a 6 degrees of freedom spine simulator, unconstrained pure moments of +/-8.0 Nm (lumbar) and +/-3.0 Nm (cervical) were used for axial rotation with quantification of the operative level range of motion and neutral zone, with data normalized to the intact spine condition. RESULTS: There were anatomic limitations in the lumbar spine that make it less desirable to apply uncon-strained disc replacements; indeed, the spine was at risk for iatrogenic lumbar scoliosis. The anulus fibrosis, anterior longitudinal ligament, and the posterior longitudinal ligament are critical structures in preventing iatrogenic scoliosis. The lumbar facet joints are more posteriorly located and are smaller relative to the intervertebral disc, compared with this association in the cervical spine. Because the facet capsular ligaments are mechanically less effective with lower tensile strength in the lumbar spine, multiple-level arthroplasty tends to accentuate scoliotic tendencies; this is independent of prosthetic design and surgical technique. DISCUSSION: Implantation of the lumbar TDR never restored the motion segment back to the rotational stability of the intact segment achieving a range of 120% to 140% rotational range of motion compared with the intact condition. This rotational instability proved to be additive as a two-level lumbar TDR resulted in between 240% and 260% increase in rotational instability compared with the intact condition. CONCLUSION: The neutral zone of the intact cervical spine was restored even using an unconstrained cervical TDR. The greater inherent rotational constraints of the cervical spine make it more amenable to stable multilevel arthroplasty compared with the lumbar spine.

Calculation of dynamic spinal ligament deformation.

OBJECTIVE: Previous methods to determine spinal ligament deformation have included either custom-designed transducers or computational methods using rigid body transformation of kinematic data. Goals of the present study were to describe a computational methodology to determine dynamic deformations of an arbitrarily oriented ligament in a spine specimen and its associated errors. METHODS: Calculation of ligament deformation in a spinal segment with vertebral motion tracking flags utilized digital stereophotography, lateral neutral posture radiograph, and detailed quantitative anatomy to develop geometrical relationships between flag markers and ligament attachment points. A custom jig, consisting of two flags each with four markers, was constructed to quantify errors associated with computed ligament deformation, flag marker translation, and flag rotation. RESULTS: Average error in ligament deformation was dependent upon motion direction and ranged between 0.03 mm (SD 0.45 mm) and 0.28 mm (SD 0.18 mm). Average error for flag marker translation ranged between 0.02 mm (SD 0.14 mm) and 0.11 mm (SD 0.39 mm), and for flag rotation ranged between -0.06 degrees (SD 0.17 degrees ) and 0.07 degrees (SD 0.12 degrees ). CONCLUSIONS: Accuracy of the present technique was equivalent to or greater than that of previous methods. The present technique utilized relatively cost-effective digital stereophotography, and may be used to calculate strain in ligaments not readily accessible for transducer application. The methodology has wide-spread applicability for analyses of dynamic or static spinal or other ligament strains, and may be used to determine spinal canal and intervertebral foramen narrowing and area reduction.

The posterior longitudinal ligament and peridural (epidural) membrane.

The posterior longitudinal ligament (PLL) is described as having deep and superficial layers, though recent studies have suggested that there may be three layers. Additional membranous structures have been reported, although there is no consensus as to their presence or morphology. The vertebral canal and dural sac were opened and the spinal nerve roots and spinal cord removed. The anterior dural ligaments were sectioned at their attachment to the PLL and the dura mater freed from the posterior surface of the vertebral bodies. The borders of the PLL were identified and the superficial and deep layers separated. The PLL is a wide band in the cervical region becoming more denticulate inferiorly, the widest parts being attached to the intervertebral discs (IVD) and adjacent vertebral body where the superficial and deep layers could not be separated. A continuous well developed peridural membrane attaching to the pedicles was present anterior to the deep PLL as well as a separate, thin, incomplete layer in 6 of 18 cadavers, covering the posterior surface of the superficial PLL.