Medial-lateral Plane Research Articles

Stabilization of 2-Column Thoracolumbar Fractures With Orthoses

A gross anatomic and motion analysis study in cadavers. Assess spinal motion in a cadaveric spinal fracture model and investigate the ability of external orthoses to control this motion. External orthoses are frequently prescribed for patients who have experienced burst fracture of the thoracolumbar spine. Despite the substantial expense involved, there is little data confirming their value. A T12 burst fracture model was created in 5 lightly embalmed cadavers by resecting the anterior and middle columns of the T12 vertebra through a thoracolumbar anterior approach to the spine. An electromagnetic motion tracking and analysis system was used to track angular and linear displacement at the fracture during routine patient maneuvers. Several commonly used orthoses, including an extension brace and both an "off-the-shelf" and custom-molded thoracic-lumbar-sacral orthosis (TLSO), were applied to the cadavers and the affect on fracture site motion was assessed. Application of all 3 styles of brace resulted in angular motion of 8° to 12° in flexion-extension, 11° to 20° in axial rotation, and 8° to 10° of lateral bending. Brace application resulted in linear displacement of 29 to 46 mm in the medial-lateral plane, 21 to 23 mm in the axial plane, and 21 to 37 mm in the anterior-posterior plane. During logrolling maneuvers, TLSO style braces diminished angular motion, although residual motion in the range of 5° remained. TLSO style braces had little effect on linear translation. When placed in a seated position in bed, TLSO style braces diminished flexion and extension modestly, but did not influence lateral bending or linear translation. Extension style braces had no effect on fracture motion during any activity tested. In a cadaver model of a burst fracture, there is surprising angular and linear motion at the fracture during common hospital activities. TLSO orthoses can decrease angular motion but do not effect translation at the fracture. An extension orthosis had no effect on motion at the spinal fracture site.

Effects of Proprioceptive Training Program on Core Stability and Center of Gravity Control in Sprinters

The purpose of this study was to determinate the effect of a 6-week specific-sprinter proprioceptive training program on core stability and gravity center control in sprinters. Thirty-three athletes (age = 21.82 ± 4.84 years, height = 1.76 ± 0.07 m, weight = 67.82 ± 08.04 kg, body mass index = 21.89 ± 2.37 kg · m(-2)) from sprint disciplines were divided into a control (n = 17) and experimental (n = 16) groups. A 30-minute proprioceptive training program was included in the experimental group training sessions, and it was performed for 6 weeks, 3 times each week. This program included 5 exercises with the BOSU and Swiss ball as unstable training tools that were designed to reproduce different moments of the technique of a sprint race. Stability with eyes open (EO) and eyes closed, postural stability, and gravity center control were assessed before and after the training program. Analyses of covariance (α = 0.05) revealed significant differences in stability in the medial-lateral plane with EO, gravity center control in the right direction and gravity center control in the back direction after the exercise intervention in the experimental athletes. Nevertheless, no other significant differences were demonstrated. A sprinter-specific proprioceptive training program provided postural stability with EO and gravity center control measures improvements, although it is not clear if the effect of training would transfer to the general population.

Comparison of 4 Airway Devices on Cervical Spine Alignment in a Cadaver Model With Global Ligamentous Instability at C5–C6

Human cadaveric study using various intubation devices in a cervical spine instability model. We sought to evaluate various intubation techniques and determine which device results in the least cervical motion in the setting of a global ligamentous instability model. Many patients presenting with a cervical spine injury have other injuries that may require rapid airway management with endotracheal intubation. Secondary neurologic injuries may occur in these patients because of further displacement at the level of injury, vascular insult, or systemic decrease in oxygen delivery. The most appropriate technique for achieving endotracheal intubation in the patient with a cervical spine injury remains controversial. A global ligamentous instability at the C5-C6 vertebral level was created in lightly embalmed cadavers. An electromagnetic motion analysis device (Liberty; Polhemus, Colchester, VT) was used to assess the amount of angular and linear translation in 3 planes during intubation trials with each of 4 devices (Airtraq laryngoscope, lighted stylet, intubating LMA, and Macintosh laryngoscope). The angular motions measured were flexion-extension, axial rotation, and lateral bending. Linear translation was measured in the medial-lateral (ML), axial, and anteroposterior planes. Intubation was performed by either an emergency medical technician or by a board-certified attending anesthesiologist. Both time to intubate as well as failure to intubate (after 3 attempts) were recorded. There was no significant difference shown with regards to time to successfully intubate using the various devices. It was shown that the highest failure-to-intubate rate occurred with use of the intubating LMA (ILMA) (23%) versus 0% for the others. In flexion/extension, we were able to demonstrate that the Lightwand (P = 0.005) and Airtraq (P = 0.019) resulted in significantly less angular motion than the Macintosh blade. In anterior/posterior translation, the Lightwand (P = 0.005), Airtraq (P = 0.024), and ILMA (P = 0.021) all caused significantly less linear motion than the Macintosh blade. In axial rotation, the Lightwand (P = 0.017) and Airtraq (P = 0.022) resulted in significantly less angular motion than the Macintosh blade. In axial translation (P = 0.037) and lateral bending (P = 0.003), the Lightwand caused significantly less motion than the Macintosh blade. In a cadaver model of C5-C6 instability, the greatest amount of motion was caused by the most commonly used intubation device, the Macintosh blade. Intubation with the Lightwand resulted in significantly less motion in all tested parameters (other than ML translation) as compared with the Macintosh blade. It should also be noted that the Airtraq caused less motion than the Macintoshblade in 3 of the 6 tested planes. There were no significant differences in failure rate or the amount of time it took to successfully intubate in comparing these techniques. We therefore recommend the use of the Lightwand, followed by the Airtraq, in the setting of a presumed unstable cervical spine injury over the Macintosh laryngoscope.

Evaluation of Indirect Decompression of the Lumbar Spinal Canal Following Minimally Invasive Lateral Transpsoas Interbody Fusion: Radiographic and Outcome Analysis

The surgical treatment of lumbar stenosis traditionally includes laminectomy for direct decompression of the spinal canal. Selected patients with spinal stenosis may also require lumbar fusion. Minimally invasive lateral transpsoas interbody fusion has the ability of placing a large interbody cage that can increase disc height and distract the spinal level. The purpose of this study was to examine the concept of indirect decompression of the spinal canal in patients with co-existing lumbar spinal stenosis undergoing lateral transpsoas interbody fusion. We reviewed 25 consecutive spinal stenosis patients with instability undergoing lateral transpsoas interbody fusion without laminectomy. All patients had relevant symptoms of back pain, leg pain, and/or spinal claudication and met standard criteria for lumbar fusion. Patients were evaluated by outcome analysis scales (VAS scores, Oswestry disability index and treatment intensity scale). Postoperative MRI scans, when available, were evaluated for change in canal dimensions. Statistical significance was assessed by paired t-test, which compares the mean change. There were 25 patients in the study (mean age 61 years). 15 patients had grade I spondylolisthesis. VAS for back pain intensity improved from 7.74 to 2.07 and for frequency from 7.91 to 2.22. VAS for leg pain intensity improved from 7.24 to 1.87 and frequency from 7.41 to 2.35. All improvements were statistically significant (P<0.0001). The Oswestry disability index improved from 55.1 to 16.4 (P<0.0001), and treatment intensity scale improved from 14.6 to 3.7 (P<0.0001). Radiographic evaluation in 20 treated levels (15 patients) found an increase in dural sac dimension of 54% in the anterior-posterior plane and 48% in the medial-lateral plane (P<0.0001). The calculated area of the dural sac increased an average of 143% (range of - 10.4% to + 495%). Indirect decompression of spinal stenosis can be achieved with lateral transpsoas interbody fusion with improved clinical outcomes. Pre-op and post-op MRI scans showed a significant increase in dural sac dimensions. The mechanism for this indirect decompression may relate to stretching and unbuckling of the spinal ligaments and a decrease in intervertebral disc bulging. Further studies are needed to determine which stenosis patients undergoing this surgery are most appropriate for indirect decompression alone over laminectomy.

Management of postural sensory conflict and dynamic balance control in late-stage Parkinson's disease

Parkinson's disease (PD) is known to affect postural control, especially in situations needing a change in balance strategy or when a concurrent task is simultaneously performed. However, few studies assessing postural control in patients with PD included homogeneous population in late stage of the disease. Thus, this study aimed to analyse postural control and strategies in a homogeneous population of patients with idiopathic advanced (late-stage) PD, and to determine the contribution of peripheral inputs in simple and more complex postural tasks, such as sensory conflicting and dynamic tasks. Twenty-four subjects with advanced PD (duration: median (M)=11.0 years, interquartile range (IQR)=4.3 years; Unified Parkinson's Disease Rating Scale (UPDRS): M "on-dopa"=13.5, IQR=7.8; UPDRS: M "off-dopa"=48.5, IQR=16.8; Hoehn and Yahr stage IV in all patients) and 48 age-matched healthy controls underwent static (SPT) and dynamic posturographic (DPT) tests and a sensory organization test (SOT). In SPT, patients with PD showed reduced postural control precision with increased oscillations in both anterior-posterior and medial-lateral planes. In SOT, patients with PD displayed reduced postural performances especially in situations in which visual and vestibular cues became predominant to organize balance control, as was the ability to manage balance in situations for which visual or proprioceptive inputs are disrupted. In DPT, postural restabilization strategies were often inefficient to maintain equilibrium resulting in falls. Postural strategies were often precarious, postural regulation involving more hip joint than ankle joint in patients with advanced PD than in controls. Difficulties in managing complex postural situations, such as sensory conflicting and dynamic situations might reflect an inadequate sensory organization suggesting impairment in central information processing.

Comparison of Remnant Preserved versus Conventional Anterior Cruciate Ligament Reconstruction

PURPOSE: Surgical reconstruction of the anterior cruciate ligament (ACL) may reduces knee instability. It has been suggested that the lack of full recovery of knee function following ACL reconstruction is partially the result of a sensory deficit. The remnant preserving technique was developed to preserve the prorioception and to enhance the revasularzation of the reconstructed ACL. Therefore, the purpose of this study was to analyze the clinical results of comparing the remnant preserving technique with the conventional ACL reconstruction. METHODS: We have tested 40 patients ACL reconstruction by auto graft-hamstring tendon, by dividing the subjects into 2 different groups; Trial group (preservation of remnant, Group 1) and control group (no remnant, Group 2). We measured concentric peak torque measurements of the knee extensors and flexors at 60°/sec and 180°/sec on an Isokinetic dynamometry. Proprioceptive functions has been assessed using Joint position sense (JPS) and threshold to detection of passive motion (TDPM). Dynamic postural stability was measured as a stability index in the anterior-posterior and medial-lateral planes with the Biodex Stability System. All tests were measured postoperative 1year. For statistical analysis, we used an independent-sample t test and Pearson correlation and found the results to be statistically significant at p<.05. RESULTS: A significant difference was detected in proprioception. we found significant difference between the group 1 and group 2 for Joint position sense (1.79±0.63° vs 3.14±0.95°. p=0.012) and threshold to detect passive motion (1.73±0.68° vs 2.73±1.15°. p=0.007). In dynamic postural stability test, group 1 showed a significantly improved instability of 10.7±8.5% whereas group 2 resulted that of 17.5±8.8%(p=0.037). But, we found no significant difference between the groups for the test results of knee strength. CONCLUSIONS: We thought that the presence of the proprioceptive nerve fibers in the remnant of the ACL may provide a source for the reinnervation of the graft and restoration of normal proprioception. Therefore, preservation of the remnant ACL reconstruction is helpful in preserving the proprioception and function to stabilize the knee.

Attention demand and postural control in children with hearing deficit

To elucidate the mechanisms responsible for deteriorated postural control in children with hearing deficit (CwHD), we measured center-of-pressure (COP) variability, mean velocity and entropy in bipedal quiet stance (feet together) with or without the concurrent cognitive task (reaction to visual stimulus) on hard or foam surface in 29 CwHD and a control group of 29 typically developing children (CON). The CwHD displayed an overall decreased postural performance as compared to the CON in the medial–lateral plane ( p < 0.05). Standing on foam pad revealed slower simple reaction time in the CwHD ( p < 0.05) while the results on hard surface were not different. The CwHD decreased ( p < 0.05) the amount of attention invested in posture during dual task which accounted for the need of more cognitive resources to handle two tasks simultaneously than controls. It was unmistakable that the intergroup differences emerged when the tasks performed were relatively novel and untrained: feet together, foam pad, and reaction time. All these tasks, while being very easy for the CON, made the CwHD deteriorate postural or cognitive performance. These results unravel the difficulty in reaching the consecutive developmental stages in the CwHD and call for specific therapeutic modalities that might facilitate this development.

Proprioceptive and Strength Comparison of Remnant Preserved versus Conventional Anterior Cruciate Ligament Reconstruction

Reconstruction of the anterior cruciate ligament (ACL) restores knee stability. The remnant preserving technique was developed to preserve mechanoreceptor function, promote revasularzation and facilitate ligamentation. The purpose of this study was to analyze the clinical results of ACL reconstruction with remnant preserving. Between October in 2008 and September in 2009, 40 patients underwent ACL reconstruction using auto graft-hamstring tendon. On the basis of the ACL’s condition patients were divided into 2 groups. In the trial group (preserved remnant group, PRG; n=20), there were 20 males with an average age of 26.2 years. In the control group (no remnant group, NRG; n=20) were 20 males with an average of age 27.1 years. We measured concentric peak torque of the knee extensors and flexors at 60/s and 180/s on an Isokinetic dynamometry. Proprioceptive functions have been assessed using Joint position sense and threshold to detection of passive motion. Dynamic postural stability was measured as a stability index in the anterior-posterior and medial-lateral planes with the Biodex Stability System. All tests were measured post-operative 1year. We found significant difference between the PRG and NRG for Joint position sense at 15 (2.40±1.00 vs. 3.36±0.95; p=0.0145) and threshold to detect passive motion at 45 (2.02±0.59 vs. 3.12±0.94; p=0.0213). But, we found no significant difference between the groups for the test results of the dynamic postural stability and knee strength. Therefore, preservation of the remnant ACL reconstruction is helpful in preserving the proprioception and function to stabilize the knee.

Postural control in 13-year-old soccer players

To evaluate the effect of early systematic soccer training on postural control we measured center-of-pressure (COP) variability, range, mean velocity and frequency in bipedal quiet stance with eyes open (EO) and closed (EC) in 44 boys aged 13 (25 boys who practiced soccer for 5–6 years and 19 healthy boys who did not practice sports). The soccer players had better stability, particularly in the medial–lateral plane (M/L); their COP variability and range were lower than in controls in both EO (p < 0.05) and EC (p < 0.0005) condition indicating that the athletes were less dependent on vision than non-athletes. Improved stability of athletes was accompanied by a decrease in COP frequency (p < 0.001 in EO, and p < 0.04 in EC) which accounted for lower regulatory activity of balance system in soccer players. The athletes had lower COP mean velocity than controls (p < 0.0001 in both visual condition), with larger difference in the M/L than A/P plane (p < 0.00001 and p < 0.05, respectively). Postural behavior was more variable within the non-athletes than soccer players, mainly in the EC stances (p < 0.005 for all COP parameters). We conclude that: (1) soccer training described was efficient in improving the M/L postural control in young boys; (2) athletes developed specific postural strategies characterized by decreased COP frequency and lower reliance on vision.

Balance control in quiet upright standing in patients with panic disorder

The postural stability of 30 panic disorder (PD) patients and 30 sex- and age-matched healthy control subjects (age range 27-40 years) was investigated by static posturographic tests of quiet standing on stable and foam surfaces with open and closed eyes. Postural stability was evaluated by sway velocity (SV) and power density of relative power spectrum (RPS) in five frequency ranges. There were no differences of SV between two groups during stance with open eyes on both surfaces. The SV of the PD patients standing with closed eyes was significantly higher compared to controls for the stance on the stable surface (anterior-posterior plane) and on the foam surface (both anterior-posterior and medial-lateral planes). The stance on foam surface did not cause any significant changes in power density of postural sways of healthy subjects, while this parameter was significantly higher for PD patients, especially in closed eyes condition when a sensory conflict may exist. The higher value of SV and RPS (0.5-1.0 Hz) in patients compared to controls suggests that the visual information has more important role in the postural balance when sensory conflict exists during stance on foam surface. We proposed that the altered information from the visual and proprioceptive inputs may induce anxiety and panic symptoms in PD patients, which enhances the sensory conflict, leads to abnormal work of the vestibular system and disturbs the standing balance.

MRI of symptomatic and asymptomatic full-thickness rotator cuff tears

Background and purpose Why some full-thickness rotator cuff tears are symptomatic and others are asymptomatic is not understood. By comparing MRI findings in symptomatic and asymptomatic tears, we wanted to identify any tear characteristics that differed between groups.Patients and methods 50 subjects with asymptomatic and 50 subjects with symptomatic full-thickness tears were examined by MRI. Tear characteristics including tear size, tear location, the condition of the long head of the biceps, atrophy, and fatty degeneration of the muscles were compared between groups.Results Single factor logistic regression analysis showed that there were statistically significant associations between symptoms and tear size exceeding 3 cm in the medial-lateral plane, positive tangent sign, and fatty degeneration exceeding grade 1 of the supraspinatus and infraspinatus muscles.Interpretation We found associations between the symptomatic status of a rotator cuff tear and MRI-derived tear characteristics. The causal relationships are unclear.

Characteristic gait patterns in older adults with obesity—Results from the Baltimore Longitudinal Study of Aging

Obesity in older adults is a growing public health problem. Excess weight causes biomechanical burden to lower extremity joints and contribute to joint pathology. The aim of this study was to identify specific characteristics of gait associated with body mass index (BMI). Preferred and maximum speed walking and related gait characteristics were examined in 164 (50–84 years) participants from Baltimore Longitudinal Study of Aging (BLSA) able to walk unassisted. Participants were divided into three groups based on their BMI: normal weight (19≤BMI<25 kg/m 2), overweight (25≤BMI<30 kg/m 2) and obese (BMI 30≤BMI<40 kg/m 2). Total ankle generative mechanical work expenditure (MWE) in the anterior–posterior (AP) plane was progressively and significantly lower with increase in BMI for both preferred ( p=0.026) and maximum speed walking ( p<0.001). In the medial–lateral (ML) plane, total knee generative MWE was higher in obese participants in the preferred speed task ( p=0.002), and total hip absorptive MWE was higher in obese in both preferred speed ( p<0.001) and maximum speed ( p=0.002) walking task compared to the normal weight participants. Older adults with obesity show spatiotemporal gait patterns that may help in reducing contact impacts. In addition, in obese persons mechanical energy usages tend to be lower in the AP plane and higher in the ML plane. Since forward progression forces are mainly implicated in normal walking, this pattern found in obese participants is suggestive of lower energetic efficiency.

Somatotopic organization in the internal segment of the globus pallidus in Parkinson's disease

Ablation or deep brain stimulation in the internal segment of the globus pallidus (GPi) is an effective therapy for the treatment of Parkinson's disease (PD). Yet many patients receive only partial benefit, including varying levels of improvement across different body regions, which may relate to a differential effect of GPi surgery on the different body regions. Unfortunately, our understanding of the somatotopic organization of human GPi is based on a small number of studies with limited sample sizes, including several based upon only a single recording track or plane. To fully address the three-dimensional somatotopic organization of GPi, we examined the receptive field properties of pallidal neurons in a large cohort of patients undergoing stereotactic surgery. The response of neurons to active and passive movements of the limbs and orofacial structures was determined, using a minimum of three tracks across at least two medial-lateral planes. Neurons (3183) were evaluated from 299 patients, of which 1972 (62%) were modulated by sensorimotor manipulation. Of these, 1767 responded to a single, contralateral body region, with the remaining 205 responding to multiple and/or ipsilateral body regions. Leg-related neurons were found dorsal, medial and anterior to arm-related neurons, while arm-related neurons were dorsal and lateral to orofacial-related neurons. This study provides a more detailed map of individual body regions as well as specific joints within each region and provides a potential explanation for the differential effect of lesions or DBS of the GPi on different body parts in patients undergoing surgical treatment of movement disorders.

Deep brain stimulation of the subcallosal cingulate gyrus for depression: anatomical location of active contacts in clinical responders and a suggested guideline for targeting

Deep brain stimulation (DBS) of the subcallosal cingulate gyrus (SCG), including Brodmann area 25, is currently being investigated for the treatment of major depressive disorder (MDD). As a potential emerging therapy, optimal target selection within the SCG has still to be determined. The authors compared the location of the electrode contacts in responders and nonresponders to DBS of the SCG and correlated the results with clinical outcome to help in identifying the optimal target within the region. Based on the location of the active contacts used for long-term stimulation in responders, the authors suggest a standardized method of targeting the SCG in patients with MDD. Postoperative MR imaging studies of 20 patients with MDD treated with DBS of the SCG were analyzed. The authors assessed the location of the active contacts relative to the midcommissural point and in relation to anatomical landmarks within the medial aspect of the frontal lobe. For this, a grid with 2 main lines was designed, with 1 line in the anterior-posterior and 1 line in the dorsal-ventral axis. Each of these lines was divided into 100 units, and data were converted into percentages. The anterior-posterior line extended from the anterior commissure (AC) to the projection of the anterior aspect of the corpus callosum (CCa). The dorsal-ventral line extended from the inferior portion of the CC (CCi) to the most ventral aspect of the frontal lobe (abbreviated "Fr" for the formula). Because the surgical technique did not vary across patients, differences in stereotactic coordinates between responders and nonresponders did not exceed 1.5 mm in any axis (x, y, or z). In patients who responded to the procedure, contacts used for long-term stimulation were in close approximation within the SCG. In the anterior-posterior line, these contacts were located within a 73.2 +/- 7.7 percentile distance from the AC (with the AC center being 0% and the line crossing the CCa being 100%). In the dorsal-ventral line, active contacts in responders were located within a 26.2 +/- 13.8 percentile distance from the CCi (with the CCi edge being 0% and the Fr inferior limit being 100%). In the medial-lateral plane, most electrode tips were in the transition between the gray and white matter of SCG. Active contacts in patients who responded to DBS were relatively clustered within the SCG. Because of the anatomical variability in the size and shape of the SCG, the authors developed a method to standardize the targeting of this region.

Bowel Displacement for CT-Guided Tumor Radiofrequency Ablation: Techniques and Anatomic Considerations

To describe safety and efficacy of bowel displacement techniques and determine lesion characteristics that are likely to necessitate bowel displacement. A retrospective review of patients who underwent CT-guided renal tumor radiofrequency ablation (RFA) (January 2006-August 2008) was conducted. Techniques included hydrodissection, additional manual torquing of the RFA probe, and additional angioplasty balloon interposition. The goal was to displace bowel from the probe by at least 10 to 20 mm. Air-filled balloon interposition was intended as a thermal barrier. Pre- and postbowel displacement distances were measured by CT. Saline volumes were recorded. Multivariate stepwise regression analysis was used to determine the influence of laterality, renal location, and morphology of renal lesions on their proximity to the colon and use of bowel displacement techniques. RFA was performed on 57 consecutive patients. Eleven (19%) patients had bowel displacement attempts. Median pre-RFA lesion edge to colon distance for nondisplaced vs displaced was 43 mm (range 10-100 mm) vs 6 mm (range 0-16 mm), respectively (P < 0.05). Two variables were significant for bowel displacement (F-ratio = 4.681, P = 0.006): Tumor position within the kidney in the craniocaudal plane (P = 0.014) and anterior-posterior plane (P = 0.007). Lower pole and posterior lesions tended to be closer to the colon and more likely to necessitate bowel displacement. Orientation in the medial-lateral plane (P = 0.77) and exophytic nature of the lesion (P = 0.83) were not significant features. Hydrostatic bowel displacement was always the first-line technique and was completely and partly successful in 8 (73%) and 1 (9%) attempts, respectively. Partial success was augmented by probe torquing (distance increased from 1 mm to 16 mm and then to 23 mm with torquing). Mean saline injection: 105 mL (range 55-440 mL). There were two complete failures (18%) in which bowel was displaced only by 0 to 2 mm despite injection of 280 to 440 mL. Balloon interposition was attempted in these two cases. Five minor complications occurred in the nondisplaced cohort. No complications occurred in the bowel displacement cohort. Lower pole, posterior renal lesions are more likely to necessitate bowel displacement. Bowel displacement techniques are effective and safe in displacing bowel.

Anatomic Determination of Optimal Entry Point and Direction For C1 Lateral Mass Screw Placement

Anatomic study of C1 osteology using computerized tomography. To define the anatomy of the C1 lateral mass and make recommendations for optimal entry point and screw placement at C1. C1 lateral mass screw fixation is a reliable biomechanical technique that gives equivalent stability to that of Magerl transarticular screw fixation combined with posterior wiring for C1-C2 fusion. Use of a lateral mass screw allows alternative stabilization constructs to the transarticular technique when C2 vertebral artery anatomy is unfavorable. Because the vertebral artery travels lateral to the lateral mass, then crosses medially over the C1 neural arch, it is at risk during instrumentation. Medially, the cord and canal contents are at risk. While the anatomy of the C1 vertebra and lateral mass is well known, specific definition of ideal entry points, screw pathway direction, and dimensions of screws requires further clarification to enable a clinically safe surgical technique. Fifty consecutive patients underwent computerized tomography scans of their cervical spine. Using calibrated scans, measurements were taken to give the average dimensions of the C1 vertebra with a view for insertion of lateral mass screws beneath the posterior arch. The range of anatomic dimensions was examined to assess risk of vertebral artery damage in this population. The average length of screw within the lateral mass is 17.9 mm with 21.5 mm of screw posterior to the lateral mass, necessary to allow rod placement posteriorly. The safest entry point was directly beneath the medial edge of the posterior arch/lamina where it joins the lateral mass. The ideal direction of screw angulation in the sagittal plane was parallel to the posterior arch of C1. In the medial lateral plane, direct anterior placement could be used, but the lateral mass will tolerate 20 degrees of medial angulation from this starting point. The average distance between the vertebral artery foramen laterally and the screw pathway was 8.8 mm using these landmarks, and 5.8 mm from the medial aspect of the lateral mass. The range of anatomic variation was such that 9 lateral masses had a vertebral artery foramen to screw distance of only 3 mm. The vertebral artery was not at risk when these anatomic landmarks were used. C1 lateral mass screws are best placed beneath the posterior arch, parallel with the arch in the sagittal plan. The entry point is the medial border of the neural arch at its junction with the lateral mass. Straight ahead screw direction is safe in the axial plane, but up to 20 degrees of medial angulation will increase the safety margin from the vertebral artery foramen, and this technique avoids vertebral artery damage and optimizes lateral mass screw purchase. We suggest that this is the preferred method of entry into the lateral mass of C1.

KINEMATIC TRAJECTORIES WHILE WALKING WITHIN THE LOKOMAT ROBOTIC GAIT-ORTHOSIS

Purpose/Hypothesis: To compare the kinematic patterns of subjects walking in the Lokomat robotic gait-orthosis with those demonstrated during treadmill walking, and to quantify the amount of relative movement inside the device. The field of neurorehabilitation has been adopting robotic devices to help deliver mass-practice therapy to individuals with various types of neurological disorders (Hidler et al, 2005 for review). The Lokomat (Hocoma AG, Volketswil Switzerland) is the most widely adopted robotic system used for gait training. Previous studies have quantified changes in muscle activation pattern when subjects walk in the Lokomat to those on a treadmill (Hidler and Wall, 2005). No studies to date have tracked the kinematic patterns of the legs inside the Lokomat. Number of Subjects: 6 healthy subjects (4 male, 2 female) participated in the study. Materials/Methods: A Codamotion (Charnwood Dynamics, UK) motion analysis system was used to track the kinematic patterns of the subject's pelvis and legs, and the robotic limbs of the Lokomat. Marker clusters were placed on each limb segment and tracked at 100 Hz. Subjects walked on the treadmill with and without the Lokomat at four randomly selected walking speeds (2.0, 2.4, 2.8, 3.2 km/hr). For all trials, subject and Lokomat marker positions and ground reaction forces were recorded for 30-second step sequences. A number of kinematic metrics were compared between the two modalities using a one sample t-test (alpha = 0.05), including ankle, knee, and hip range of motion, maximum and minimum joint flexion and extension angles, and the point in the gait cycle each occurred. The relative knee and hip movement between the subject's and Lokomat's joint centers in both the frontal and sagittal planes were quantified. Results: While some subjects experienced slight differences in kinematic patterns, there were no significant differences in any of the metrics computed for all subjects across walking modalities. Despite there being no differences in sagittal joint angular patterns, the side to side motion of the hip in the medial-lateral plane was significantly less in the Lokomat than on the treadmill, sometimes restricted by as much as 75%. The relative movement of subjects' legs inside the Lokomat was substantial, where the variability in the knee joint center in the sagittal plane was approximately 1 cm while deviations exceeded 2 cm for the hip joint. Conclusions: With proper setup, the Lokomat gait patterns mimic those utilized during treadmill ambulation. Differences in the amount of medial-lateral hip motion can be attributed to the reduced degrees of freedom the Lokomat places on the subject. Clinical Relevance: The finding that there is significant movement of the subject's legs inside the Lokomat is important clinically, as a variable step pattern has been shown to be a more effective gait training strategy than one which forces the same kinematic pattern across successive steps (Cai et al., 2005).

Strategies used by older adults to change travel direction

Introduction A distinct body reorientation strategy during steering tasks has been reported in young adults. As challenges to whole-body stability in older adults occur when navigating complex environments, this study was designed to examine control strategies used by older adults to initiate a voluntary change in travel direction. Methods Thirteen older adults, recruited from an independent living division of a local retirement residence, were instrumented with reflective markers and whole-body kinematic data were monitored using a video camera (30 Hz). Participants executed self-paced walking trials 3-m along a straight path and were instructed prior to the trial to continue either straight ahead or randomly turn 40° left or right and continue walking for an additional 2-m. Timing of changes with respect to when the trunk crossed the turning point were calculated for deviations in head and trunk position and foot rotation in the medial-lateral plane. Results Older adults reoriented themselves into the new travel direction in a top-down, segmental sequence, beginning with head reorientation followed by trunk reorientation, foot rotation and foot displacement into the new travel direction. These changes were initiated over two or more steps 69% of the time and over one step 31% of the time. A significant relationship between turning strategy used and balance confidence was observed; the frequency of using a turning strategy involving two or more steps to initiate a change in travel direction increased as balance confidence decreased. Discussion and conclusion Older adults made segmental changes to voluntarily reorient themselves in a new travel direction in a similar sequence to that observed in young adults. Older adults chose primarily to initiate these changes two or more steps prior to the turn; the selection of this strategy was related to balance confidence.

Gender differences in balance performance at the time of retirement

Background. Impairments in balance performance are a commonly accepted risk factor for falling in older people. Since there is a higher reported incidence of falling in women, it is of interest to test whether this correlates with poorer balance performance in women than men at the time of retirement in order to plan health promotional strategies. The purpose of this study was to investigate whether any gender differences exist in balance performance in people approaching retirement age. Methods. Ninety-seven healthy volunteers (44 males, 53 females) planning to retire shortly were enrolled in the study (age range 50–67 years). Balance assessments during quiet standing were performed under various conditions; feet together eyes open, feet together eyes closed and single limb stance eyes open. The range of centre of pressure displacement in both the anterior–posterior and medial–lateral planes was collected for each task using a force platform. Findings. For several of the balance tasks the men exhibited a statistically significant larger range of centre of pressure displacement than the women ( P < 0.01). However, after normalising the data for height, no gender differences were seen. Over half of the group failed to complete all three single limb stance trials on both limbs. Interpretation. When the data was normalised for height, no differences were found in static balance performance between men and women of retirement age. A number of participants demonstrated balance impairments whilst performing the single limb stance likely to affect functional activities. Health promotional messages should be targeted equally at men and women.

Measuring Functional Ankle Instability

1148 Functional ankle instability (FAI) is a common chronic condition in which an individual's ankle “gives way” and rolls with activity but is not due to joint laxity. PURPOSE: To compare passive joint position sense (JPS), time to stabilization (TTS), and electromyography (EMG) of ankle musculature in recreational athletes with and without FAI. METHODS: 20 recreational athletes aged 18–25 years were placed into functionally stable (n = 10) or unstable ankle groups (n = 10). We measured unilateral range of motion and passive angle reproduction in plantarflexion, dorsiflexion, inversion, and eversion. Unilateral TTS and mean EMG amplitude of the tibialis anterior, peroneals, lateral gastrocnemius, and soleus muscles for a single leg jump-landing were measured. TTS is the point in time after impact when vertical, anterior-posterior, and medial-lateral jump landing ground reaction forces (GRF) resemble static stance. Unstable ankle subjects landed on the unstable ankle and stable subjects landed on the ankle matched for limb dominance. EMG was measured from 200ms prior to 1000 ms after ground contact. Bivariate Pearson correlations were performed for exploratory analysis. RESULTS: Independent samples t-tests showed no significant group differences in range of motion, JPS error scores in any direction, or TTS measures in the medial-lateral plane. No significant group differences were revealed on peak vertical GRF normalized to body mass. The unstable ankle group had significantly longer anterior-posterior TTS (P < .05). Eight repeated-measures t-tests were used to compare the EMG of the four muscles before and after landing in the two groups. The stable ankle group had significantly higher mean soleus EMG amplitude after landing (P< .05). No other significant differences were found for mean EMG amplitudes before or after landing. Pearson bivariate correlations demonstrated significant positive relationships between plantarflexion-dorsiflexion (r = 0.45;P < .05) and plantarflexion-eversion JPS error scores (r = 0.54;P < .05). Negative relationships were found between post-landing EMG mean amplitudes and JPS error scores (r = −0.45;P< .05) CONCLUSIONS: Subjects with FAI demonstrated deficits in landing stability and soleus muscle activity during landing that may represent chronic adaptive changes following injury. The unstable ankle group may undergo decreased closed kinetic chain ankle dorsiflexion upon landing, resulting in decreased eccentric loading of the soleus.