Biomechanical investigation of potential prophylactic scoliosis treatments following various sizes of chest wall resection

BackgroundA well-known problematic sequela of chest wall resections is development of scoliosis. Despite the seriousness and frequency of scoliosis following chest well resection, the etiology and biomechanical information needed to understand this progression aren't well-known.MethodsRange of motion of six specimen (C7–L2) was captured using a custom-built six degrees-of-freedom machine in each of three physiological rotation axes. Left posterior ribs were sequentially resected 7cm from the rib head, starting at the 5^th rib and continuing until the 10^th rib. Injured specimen were instrumented with unilateral anterior rod fixation and then with additional unilateral posterior fixation, each starting at T4 and then extended distally as ribs were resected. Relative motion between the constructs' proximal and distal ends was measured in all three axes for the intact, injured, unilateral anterior, and unilateral anterior with unilateral posterior constructs.FindingsRaw motion of the injured specimen increased in a stepwise manner as ribs were resected. Averaged across all injury sizes, the unilateral anterior construct significantly reduced motion by 47.0±13.4% in lateral bending (P=.001). The combined anterior-posterior construct significantly reduced motion by 57.6±15.9% in flexion/extension (P<.001), 70.3±12.2% in lateral bending (P<.001), and 51.1±14.5% in axial rotation (P<.001). Combined anterior-posterior fixation was significantly more stable than anterior-only fixation in flexion/extension (P=.002).InterpretationRegardless of injury size, posterior rib resection did not create significant immediate instability of the thoracic spine. Concurrent spinal stabilization was shown to maintain thoracic spine stability. Combined anterior-posterior fixation proved to be significantly more rigid than an anterior-only construct.     

In vitro comparison of personalized 3D printed versus standard expandable titanium vertebral body replacement implants in the mid-thoracic spine using entire rib cage specimens

BackgroundExpandable titanium implants have proven their suitability as vertebral body replacement device in several clinical and biomechanical studies. Potential stabilizing features of personalized 3D printed titanium devices, however, have never been explored. This in vitro study aimed to prove their equivalence regarding primary stability and three-dimensional motion behavior in the mid-thoracic spine including the entire rib cage.MethodsSix fresh frozen human thoracic spine specimens with intact rib cages were loaded with pure moments of 5 Nm while performing optical motion tracking of all vertebrae. Following testing in intact condition (1), the specimens were tested after inserting personalized 3D printed titanium vertebral body replacement implants (2) and the two standard expandable titanium implants Obelisc™ (3) and Synex™ (4), each at T6 level combined with posterior pedicle screw-rod fixation from T4 to T8.FindingsNo significant differences (P < .05) in primary and secondary T1-T12 ranges of motion were found between the three implant types. Compared to the intact condition, slight decreases of the range of motion were found, which were significant for Synex™ in primary flexion/extension (−17%), specifically at T3-T4 level (−46%), primary lateral bending (−18%), and secondary lateral bending during primary axial rotation (−53%). Range of motion solely increased at T8-T9 level, while being significant only for Obelisc™ (+35%).InterpretationPersonalized 3D printed vertebral body replacement implants provide a promising alternative to standard expandable devices regarding primary stability and three-dimensional motion behavior in the mid-thoracic spine due to the stabilizing effect of the rib cage.     

Subject Index

Abstract

Shoulder pain is a common orthopedic condition seen by physical therapists, with many potential contributing factors and proposed treatments. Although manual physical therapy interventions for the cervicothoracic spine and ribs have been investigated for this patient population, the specific effects of these treatments have not been reported. The purpose of this investigational study is to report the immediate effects of thoracic spine and rib manipulation in patients with primary complaints of shoulder pain. Using a test-retest design, 21 subjects with shoulder pain were treated during a single treatment session with high-velocity thrust manipulation to the thoracic spine or upper ribs. Post-treatment effects demonstrated a 51% (32mm) reduction in shoulder pain, a corresponding increase in shoulder range of motion (30°-38°), and a mean patient-perceived global rating of change of 4.2 (median 5). These immediate post-treatment results suggest that thoracic and rib manipulative therapy is associated with improved shoulder pain and motion in patients with shoulder pain, and further these interventions support the concept of a regional interdependence between the thoracic spine, upper ribs, and shoulder.     

A model for evaluating the biomechanics of rib fracture fixation

IntroductionHigh rates of morbidity and mortality following flail chest rib fractures are well publicized. Standard of care has been supportive mechanical ventilation, but serious complications have been reported. Internal rib fixation has shown improvements in pulmonary function, clinical outcomes, and decreased mortality. The goal of this study was to provide a model defining the biomechanical benefits of internal rib fixation.MethodsOne human cadaver was prepared with an actuator providing anteroposterior forces to the thorax and rib motion sensors to define interfragmentary motion. Cadaveric model was validated using a prior study which defined costovertebral motion to create a protocol using similar technology and procedure. Ribs 4–6 were fixed with motion sensors anteriorly, laterally and posteriorly. Motion was recorded with ribs intact before osteotomizing each rib anteriorly and laterally. Flail chest motion was record with fractures subsequently plated and analyzed. Motion was recorded in the sagittal, coronal and transverse axes.FindingsCompared to the intact rib model, the flail chest model demonstrated an 11.3 times increase in sagittal plane motion, which was reduced to 2.1 times the intact model with rib plating. Coronal and sagittal plane models also saw increases of 9.7 and 5.1 times, respectively, with regards to flail chest motion. Both were reduced to 1.2 times the intact model after rib plating.InterpretationThis study allows quantification of altered ribcage biomechanics after flail chest injuries and suggests rib plating is useful in restoring biomechanics as well as contributing to improving pulmonary function and clinical outcomes.     

Impact of anchor type on porcine lumbar biomechanics: Finite element modelling and in-vitro validation

BackgroundRigid posterior implants used for spinal stabilization can be anchored to the vertebrae using pedicle screws or screws combined with transverse process hooks. In the present study, a finite element model of a porcine lumbar spine instrumented with screws and hooks is presented and validated.MethodsThe porcine lumbar spine model was validated using in-vitro measurements on six porcine specimens. Validation metrics included intervertebral rotations (L1 to L6) and nucleus pressure in the topmost cranial instrumented disc. The model was used to compare the biomechanical effect of anchor types.FindingsGood agreement was observed between the model and validation experiments. For upper transverse hooks construct, intervertebral rotations increased at the upper instrumented vertebra and decreased at the adjacent level. Additionally, nucleus pressures and stress on the annulus decreased in the adjacent disc and increased in the upper instrumented disc. The pull-out forces predicted for both anchor configurations were significantly lower than the pull-out strength found in the literature.InterpretationThese numerical observations suggest that upper transverse process hooks constructs reduce the mobility gradient and cause less stress in the adjacent disc, which could potentially reduce adjacent segment disease and proximal junction kyphosis incidence without increasing the risk of fixation failure. Future work needs to assess the long-term effect of such constructs on clinical and functional outcomes.     

Effects of surgical joint destabilization on load sharing between ligamentous structures in the thoracic spine: a finite element investigation

Background

In vitro investigations have demonstrated the importance of the ribcage in stabilizing the thoracic spine. Surgical alterations of the ribcage may change load-sharing patterns in the thoracic spine. Computer models are used in this study to explore the effect of surgical disruption of the rib–vertebrae connections on ligament load-sharing in the thoracic spine.

Methods

A finite element model of a T7–8 motion segment, including the T8 rib, was developed using CT-derived spinal anatomy for the Visible Woman. Both the intact motion segment and the motion segment with four successive stages of destabilization (discectomy and removal of right costovertebral joint, right costotransverse joint and left costovertebral joint) were analyzed for a 2000 Nmm moment in flexion/extension, lateral bending and axial rotation. Joint rotational moments were compared with existing in vitro data and a detailed investigation of the load sharing between the posterior ligaments carried out.

Findings

The simulated motion segment demonstrated acceptable agreement with in vitro data at all stages of destabilization. Under lateral bending and axial rotation, the costovertebral joints were of critical importance in resisting applied moments. In comparison to the intact joint, anterior destabilization increases the total moment contributed by the posterior ligaments.

Interpretation

Surgical removal of the costovertebral joints may lead to excessive rotational motion in a spinal joint, increasing the risk of overload and damage to the remaining ligaments. The findings of this study are particularly relevant for surgical procedures involving rib head resection, such as some techniques for scoliosis deformity correction.     

Biomechanical evaluation of anterior lumbar interbody fusion with various fixation options: Finite element analysis of static and vibration conditions

BackgroundAnterior lumbar interbody fusion combined with supplementary fixation has been widely used to treat lumbar diseases. However, few studies have investigated the influence of fixation options on facet joint force and cage subsidence. The aim of this study was to explore the biomechanical performance of anterior lumbar interbody fusion with various fixation options under both static and vertical vibration loading conditions.MethodsA previously validated finite element model of the intact L1–5 lumbar spine was employed to compare five conditions: (1) Intact; (2) Fusion alone; (3) Fusion combined with anterior lumbar plate; (4) Fusion combined with Coflex-F fixation; (5) Fusion combined with bilateral pedicle screw fixation. The models were analyzed under static and vertical vibration loading conditions respectively.FindingsBilateral pedicle screws provided highest stability at surgical level. Applying supplementary fixation diminished the dynamic responses of lumbar spine. Compared with anterior lumbar plate and Coflex-F device, bilateral pedicle screws decreased the stress responses of the endplates and cage under both static and vibration conditions, while increased the facet joint force at adjacent levels. As for comparison between Coflex-F device and anterior lumbar plate, results showed a similarity in biomechanical performance under static loading, and a slightly higher dynamic response of the latter under vertical vibration.InterpretationThe biomechanical performance of lumbar spine was significantly influenced by the variation of fixations under both static and vibration conditions. Bilateral pedicle screws showed advantages in stabilizing surgical segment and relieving cage subsidence, but may increase the facet joint force at adjacent levels.     

A comparative biomechanical study of a novel integrated plate spacer for stabilization of cervical spine: an in vitro human cadaveric model

Background

Integrated plate-spacer may provide adequate construct stability while potentially lowering operative time, decreasing complications, and providing less mechanical obstruction. The purpose of the current study was to compare the biomechanical stability of an anatomically profiled 2-screw integrated plate-spacer to a traditional spacer only and to a spacer and anterior cervical plate construct. In addition, the biomechanical stability of 2-screw integrated plate-spacer was compared to a commercially available 4-screw integrated plate-spacer.

Methods

Two groups, each of nine cervical cadaver spines (C2–C7), were tested under pure moments of 1.5 Nm. Range of motion was recorded at C5–C6 in all loading conditions (flexion, extension, lateral bending, and axial rotation) for the following constructs: 1) Intact; 2) 2-screw or 4-screw integrated plate-spacer; 3) spacer and anterior cervical plate; and 4) spacer only.

Findings

All fusion constructs significantly reduced motion compared to the intact condition. Within the instrumented constructs, spacer and anterior cervical plate, 2-screw and 4-screw integrated plate-spacer resulted in reduced motion compared to the spacer only construct. No significant differences were found in motion between any of the instrumented conditions in any of the loading conditions.

Interpretation

The application of integrated plate-spacer for anterior cervical discectomy and fusion is based on several factors including surgical ease-of-use, biomechanical characteristics, and surgeon preference. The study suggests that integrated plate-spacer provide biomechanical stability comparable to traditional spacer and plate constructs in the cervical spine. Clinical studies on integrated plate spacer devices are necessary to understand the performance of these devices in vivo.     

Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study

BackgroundCervical vertebral body fractures generally are treated through an anterior-posterior approach. Cervical pedicle screws offer an alternative to circumferential fixation. This biomechanical study quantifies whether cervical pedicle screws alone can restore the stability of a three-column vertebral body fracture, making standard 360° reconstruction unnecessary.MethodsRange of motion (2.0 Nm) in flexion-extension, lateral bending, and axial rotation was tested on 10 cadaveric specimens (five/group) at C2–T1 with a spine kinematics simulator. Specimens were tested for flexibility of intact when a fatigue protocol with instrumentation was used to evaluate construct longevity. For a C4–6 fracture, spines were instrumented with 360° reconstruction (corpectomy spacer + plate + lateral mass screws) (Group 1) or cervical pedicle screw reconstruction (C3 and C7 only) (Group 2).FindingsResults are expressed as percentage of intact (100%). In Group 1, 360° reconstruction resulted in decreased motion during flexion-extension, lateral bending, and axial rotation, to 21.5%, 14.1%, and 48.6%, respectively, following 18,000 cycles of flexion-extension testing. In Group 2, cervical pedicle screw reconstruction led to reduced motion after cyclic flexion-extension testing, to 38.4%, 12.3%, and 51.1% during flexion-extension, lateral bending, and axial rotation, respectively.InterpretationThe 360° stabilization procedure provided the greatest initial stability. Cervical pedicle screw reconstruction resulted in less change in motion following cyclic loading with less variation from specimen to specimen, possibly caused by loosening of the shorter lateral mass screws. Cervical pedicle screw stabilization may be a viable alternative to 360° reconstruction for restoring multilevel vertebral body fracture.     

Three-dimensional ultrasound findings of spondylocostal dysostosis in the second trimester of pregnancy.

Spondylocostal dysostosis (SCD) is a rare congenital disorder that is characterized by vertebral segmentation and formation defects, and asymmetrical rib anomalies. We describe a case diagnosed during the second trimester of pregnancy with the sonographic features of abnormal alignment of the spine, hemivertebrae in the thoracic spine and kyphoscoliosis. Three-dimensional ultrasound demonstrated a 'fan-like' rib cage with fusion of the ribs. The postmortem findings confirmed the ultrasound findings and were consistent with SCD.     

高频超声观察T7~8椎旁间隙及其毗邻结构

目的 探讨T7~8椎旁间隙及其毗邻结构的高频超检查方法和声像图特征。方法 采用彩色多普勒超声诊断仪、线阵探头（频率3~12 MHz）,以肩胛骨、肋骨、胸椎棘突及横突等作为解剖标志,检查30名正常成人共60侧T7~8椎旁间隙,观察T7~8椎旁间隙及其毗邻结构的声像图特征。结果 T7~8胸椎旁间隙声像图表现类似三角形,其内部为实性均质性低回声;T7~8椎旁间隙毗邻肌肉从浅至深依次为斜方肌、背阔肌、棘肌、半棘肌、多裂肌、回旋肌、肋间肌;彩色多普勒或能量多普勒血流成像可显示位于胸椎旁间隙内肋间后动脉。结论 高频超声可清晰显示T7~8椎旁间隙及其毗邻结构,可为临床诊治胸椎旁间隙及其毗邻结构病变提供影像学依据。     

How does a novel knitted titanium nucleus prosthesis change the kinematics of a cervical spine segment? A biomechanical cadaveric study

BackgroundTotal disc replacement is a possible treatment alternative for patients with degenerative disc disease, especially in the cervical spine. The aim is to restore the physiological flexibility and biomechanical behavior. A new approach based on these requirements is the novel nucleus prosthesis made of knitted titanium wires.MethodsThe biomechanical functionalities of eight human cervical (C4-C7) spine segments were investigated. The range of motion was quantified using an ultra-sound based motion analysis system. Moreover, X-rays in full flexion and extension of the segment were taken to define the center of rotation before and after implantation of the nucleus prosthesis as well as during and after complex cyclic loading.FindingsThe mean range of motion of the index segment (C5/6) in flexion/extension showed a significant reduction of range of motion from 9.7° (SD 4.33) to 6.0° (SD 3.97) after implantation (P = 0.037). Lateral bending and axial rotation were not significantly reduced after implanting and during cyclic loading in our testing. During cyclic loading the mean range of motion for flexion/extension increased to 7.2° (SD 3.67). The center of rotation remained physiological in the ap-plane and moved cranially in the cc-plane (−27% to −5% in cc height) during the testing.InterpretationThe biomechanical behavior of the nucleus implant might lower the risk for adjacent joint disorders and restore native function of the index segment. Further in vivo research is needed for other factors, like long-term effects and patient's satisfaction.     

Mechanical properties of a thoracic spine mannequin with variable stiffness control*

ObjectiveTo test the posterior-to-anterior stiffness (PAS) of a new thoracic spine training simulator under different conditions of “fixation.”MethodsWe constructed a thoracic spine model using plastic bones and ribs mounted in a wooden box, with skin and soft tissue simulated by layers of silicone and foam. The spine segment could be stiffened with tension applied to cords running through the vertebrae and ribs. We tested PAS at 2 tension levels using a custom-built device to apply repetitive loads at the T6 spinous process (SP) and over adjacent soft tissue (TP) while measuring load and displacement. Stiffness was the slope of the force-displacement curve from 55 to 75 N.ResultsStiffness in the unconstrained (zero tension) condition over the SP averaged 11.98 N/mm and 6.72 N/mm over the TP. With tension applied, SP stiffness increased to 14.56 N/mm, and TP decreased to 6.15 N/mm.ConclusionThoracic model compliance was similar to that reported for humans. The tension control system increased stiffness by 21.3% only over the SP. Stiffness over the TP was dominated by the lower stiffness of the thicker foam layer and did not change. The mannequin with these properties may be suitable for use in manual training of adjusting or PAS testing skills.     

Influence of posture,sex, and age on breathing pattern and chest wall motion in healthy subjects

ObjectiveWe evaluated the effects of posture, sex, and age on breathing pattern and chest wall motion during quiet breathing in healthy participants.MethodsEighty-three participants aged 42.72 (SD = 21.74) years presenting normal pulmonary function were evaluated by optoelectronic plethysmography in the seated, inclined (with 45° of trunk inclination), and supine positions. This method allowed to assess the chest wall in a three dimensional way considering the chest wall as three compartments: pulmonary rib cage, abdominal rib cage and abdomen.ResultsPosture influenced all variables of breathing pattern and chest wall motion, except respiratory rate and duty cycle. Chest wall tidal volume and minute ventilation were reduced (p < 0.05) in both sexes from seated to inclined and from seated to supine positions, mainly in males. Moreover, moving from seated to supine position significantly increased the percentage contribution of the abdomen to the tidal volume in both sexes (p < 0.0001). Regarding sex, women showed higher contribution of thoracic compartment compared to men (p = 0.008). Aging provided reductions on rib cage contributions to tidal volume that were compensated by increases of abdomen contributions (p < 0.0001). In addition, increases in end-inspiratory and end-expiratory volumes over the years were observed.ConclusionThe degree of contribution of chest wall compartments is dependent on posture, sex, and age. Therefore, verticalization increases expansion of pulmonary rib cage as well as horizontalization increases abdominal displacement. Women presented higher thoracic contribution to tidal volume than men. Aging reduces rib cage contributions to tidal volume that were compensated by increases of abdomen contributions.     

Mechanics of intercostal space and actions of external and internal intercostal muscles.

It is conventionally considered that because of their fiber orientations, the external intercostal muscles elevate the ribs, whereas the internal interosseous intercostals lower the ribs. The mechanical action of the intercostal muscles, however, has never been studied directly, and the electromyographic observations supporting this conventional thinking must be interpreted with caution. In the present studies, the external and internal interosseous intercostal muscles have been separately stimulated in different interspaces at, above, and below end-expiratory rib cage volume in anesthetized dogs. The axial (cephalo-caudal) displacements of the ribs were measured using linear displacement transducers. The results indicate that when contracting in a single interspace and other muscles are relaxed, both the external and internal intercostals have a net rib elevating action at end-expiratory rib cage volume. This action increases as rib cage volume decreases, but it progressively decreases as rib cage volume increases such that at high rib cage volumes, both the external and internal intercostals lower the ribs. Stimulating the intercostal muscles in three adjacent intercostal spaces simultaneously produced similar directional rib motion results. We conclude that (a) in contrast with the conventional thinking, the external and internal interosseous intercostals acting alone have by and large a similar effect on the ribs into which they insert; (b) this effect is very much dependent on rib cage (lung) volume; and (c) intercostal muscle action is primarily determined by the resistance of the upper ribs to caudad displacement relative to the resistance of the lower ribs to cephalad displacement. The lateral intercostals, however, might be more involved in postural movements than in respiration. Their primary involvement in rotations of the trunk might account for the presence of two differently oriented muscle layers between the ribs.     

The Immediate Effects of Thoracic Spine and Rib Manipulation on Subjects with Primary Complaints of Shoulder Pain

Shoulder pain is a common orthopedic condition seen by physical therapists, with many potential contributing factors and proposed treatments. Although manual physical therapy interventions for the cervicothoracic spine and ribs have been investigated for this patient population, the specific effects of these treatments have not been reported. The purpose of this investigational study is to report the immediate effects of thoracic spine and rib manipulation in patients with primary complaints of shoulder pain. Using a test-retest design, 21 subjects with shoulder pain were treated during a single treatment session with high-velocity thrust manipulation to the thoracic spine or upper ribs. Post-treatment effects demonstrated a 51% (32mm) reduction in shoulder pain, a corresponding increase in shoulder range of motion (30°-38°), and a mean patient-perceived global rating of change of 4.2 (median 5). These immediate post-treatment results suggest that thoracic and rib manipulative therapy is associated with improved shoulder pain and motion in patients with shoulder pain, and further these interventions support the concept of a regional interdependence between the thoracic spine, upper ribs, and shoulder.KEYWORDS: Manipulation, Manual Therapy, Shoulder Pain, Thoracic SpineRegional interdependence, as described by Wainner and col-leagues^1,2, “refers to the concept that seemingly unrelated impairments in a remote anatomical region may contribute to, or be associated with, the patient''s primary complaint”. This model suggests that many musculoskeletal disorders may respond more favorably to a regional examination and treatment approach that, in addition to localized treatment, encourages physical therapists to examine and treat distant dysfunctions that may be influencing the patient''s symptoms. Although the specific mechanism (whether neurophysiologic, biomechanical, or other) has yet to be elucidated, several high-quality clinical trials have demonstrated the effective use of this regional examination and treatment approach in achieving positive functional outcomes for patients with a variety of musculoskeletal disorders^3–10.Three of these studies^3–5 have investigated the effects of including cervicothoracic spine and rib manual physical therapy into an overall treatment approach for patients with shoulder pain. Winters et al⁵ found that manipulative therapy applied throughout the shoulder girdle was more effective than physiotherapy in reducing the duration of shoulder pain in a subgroup of 58 patients whose shoulder pain was attributed to dysfunctions within the cervical spine, upper thoracic spine, or upper ribs. Bang and Deyle³ reported improved outcomes in strength, function, and pain when manual physical therapy techniques for the shoulder, cervical spine, and thoracic spine were added to an exercise program for patients with shoulder impingement syndrome. In a more recent clinical trial, Bergman et al⁴ assessed the added benefit of applying cervicothoracic and rib manipulations and mobilizations to a standardized treatment regimen of anti-inflammatory and analgesic medications, corticosteroid injections, and physical therapy (exercises, massage, and modalities) for patients with shoulder pain and dysfunction. The addition of manipulative therapy to this usual medical care resulted in significant improvements in short- and long-term recovery rates and symptom severity for these subjects.Although the overall treatment effect of manual physical therapy has been demonstrated in these studies, the relative contribution of specific manipulative techniques applied to the cervical spine, thoracic spine, and/or ribs towards the improvement in functional outcomes for patients with shoulder pain cannot be determined. The purpose of this preliminary study is to report the immediate effects of thoracic and rib manipulation on subjects with primary complaints of shoulder pain. Exploratory studies of this nature are needed to help define the potential interdependence between anatomic regions such as the thoracic spine, upper ribs, and shoulder.     

Comparative studies of cervical spine anterior stabilization systems - Finite element analysis

BackgroundThe object of the study was to assess the impact of one-level stabilization of the cervical spine for both anterior static and dynamic plates. Segments C2–C6 of the cervical spine, were investigated, from which was determined the stress and strain fields in the region of implantation and adjacent motion segments. The purpose was the comparison of changes that affect the individual stabilizers.MethodsFor testing we used finite element analysis. The cervical spine model takes into account local spondylodesis. The study includes both an intact anatomical model and a model with implant stabilization.FindingsThe analysis covered the model loaded with a moment of force for 1 Nm in the sagittal plane during movement. We compared both the modeled response of the whole fragment C2–C6 and the response of individual motion segments. The largest limitation of range of motion occurred after implantation with static plates. The study also showed that the introduction of the one-level stabilization resulted in an increase in stress in intervertebral disc endplates of adjacent segments.InterpretationThe results indicate that the increase in stress caused by stiffening may result in disorders in remodeling of bone structures. The use of dynamic plates showed improved continuity strains in the tested spine, thereby causing remodeling most similar to the physiological state and reducing the stresses in adjacent segments     

Biomechanical evaluation of different surgical procedures in single-level transforaminal lumbar interbody fusion in vitro

BackgroundsA variety of improved surgical methods were adopted in the transforaminal lumbar interbody fusion. A mechanical stability provides an ideal environment for the formation of a fusion mass and is the basis of their good outcomes. The object of this study is to evaluate the initial similarities and differences of four commonly-used posterior surgical procedures biomechanically.MethodsBiomechanical testing was performed at L3–4 motion segment in 6 fresh-frozen human cadaveric lumbar spines (L2–L5), including the following sequentially tested configurations: 1) intact motion segment; 2) bilateral pedicle screw fixation; 3) unilateral pedicle screw fixation; 4) unilateral pedicle screw plus contralateral translaminar facet joint screw fixation according to the Magerl technique; and 5) bilateral pedicle screw fixation with bilateral facetectomies. The range of motion, neutral zone and stiffness of each method and intact segment were collected and compared.FindingsAll of four methods reduce the range of motion significantly in flexion and extension and lateral bending but not in axial torsion compared with the native segment. There is no significant difference among four procedures about the range of motion in all loading modes. All of methods increase the stiffness of segmental motion compared with intact segment in all loading modes, but only bilateral pedicle screw fixation showed significant increases in stiffness in flexion and extension(p = 0.02) and lateral bending(p = 0.023). The stiffness offered by instrumented constructs in different methods showed no significant difference in all loading modes.InterpretationThe stiffness offered by four different posterior fixations in single segmental transforaminal lumbar interbody fusion is not significantly different.     

Knowledge-Based Practice

Abstract

Rib injuries are common in collegiate rowing. The purpose of this case report is to provide insight into examination, evaluation, and treatment of persistent costochondritis in an elite athlete as well as propose an explanation for chronic dysfunction. The case involved a 21 year old female collegiate rower with multiple episodes of costochondritis over a 1-year period of time. Symptoms were localized to the left third costosternal junction and bilaterally at the fourth costosternal junction with moderate swelling. Initial interventions were directed at the costosternal joint, but only mild, temporary relief of symptoms was attained. Reexamination findings included hypomobility of the upper thoracic spine, costovertebral joints, and lateral ribs. Interventions included postural exercises and manual therapies directed at the lateral and posterior rib structures to improve rib and thoracic spine mobility. Over a 3-week time period pain experienced throughout the day had subsided (visual analog scale – VAS 0/10). She was able to resume running and elliptical aerobic training with minimal discomfort (VAS 2/10) and began to reintegrate into collegiate rowing. Examination of the lateral ribs, cervical and thoracic spine should be part of the comprehensive evaluation of costochondritis. Addressing posterior hypomobility may have allowed for a more thorough recovery in this case study.     

Upper and lower adjacent segment range of motion after fixation of different lumbar spine segments in the goat: an in vitro experiment

ObjectivesThe purpose of this study was to examine the biomechanical effects of fixation on range of motion (ROM) in the upper and lower adjacent segments of different lumbar spine segments in a goat spine model.MethodsFifteen goat spine specimens (vertebrae T12–S1) were randomly divided into three groups: A (single-segment fixation), B (double-segment fixation), and C (triple-segment fixation). Motion in different directions was tested using a spinal motion simulation test system with five external loading forces. Transverse, forward–backward, and vertical displacement of the upper and lower adjacent segments were measured.ResultsAs the external load increased, the upper and lower adjacent segment ROM increased. A significantly greater ROM in group C compared with group A was found when the applied external force was greater than 75 N. The upper adjacent segment showed a significantly greater ROM than the lower adjacent segment ROM within each group.ConclusionsAdjacent segment ROM increased with an increasing number of fixed lumbar segments. The upper adjacent segment ROM was greater than that of the lower adjacent segments. Adjacent segment stability after lumbar internal fixation worsened with an increasing number of fixed segments.