Thomas M. Gavin

Effect of compressive follower preload on the flexion–extension response of the human lumbar spine

Traditional experimental methods are unable to study the kinematics of whole lumbar spine specimens under physiologic compressive preloads because the spine without active musculature buckles under just 120 N of vertical load. However, the lumbar spine can support a compressive load of physiologic magnitude (up to 1200 N) without collapsing if the load is applied along a follower load path. This study tested the hypothesis that the load–displacement response of the lumbar spine in flexion–extension is affected by the magnitude of the follower preload and the follower preload path. Twenty‐one fresh human cadaveric lumbar spines were tested in flexion–extension under increasing compressive follower preload applied along two distinctly different optimized preload paths. The first (neutral) preload path was considered optimum if the specimen underwent the least angular change in its lordosis when the full range of preload (0–1200 N) was applied in its neutral posture. The second (flexed) preload path was optimized for an intermediate specimen posture between neutral and full flexion. A twofold increase in flexion stiffness occurred around the neutral posture as the preload was increased from 0 to 1200 N. The preload magnitude (400 N and larger) significantly affected the range of motion (ROM), with a 25% decrease at 1200 N preload applied along the neutral path. When the preload was applied along a path optimized for an intermediate forward‐flexed posture, only a 15% decrease in ROM occurred at 1200 N. The results demonstrate that whole lumbar spine specimens can be subjected to compressive follower preloads of in vivo magnitudes while allowing physiologic mobility under flexion–extension moments. The optimized follower preload provides a method to simulate the resultant vector of the muscles that allow the spine to support physiologic compressive loads induced during flexion–extension activities.

A reliable and accurate method for measuring orthosis wearing time.

Study Design. Compliance monitor measurement of orthosis wearing time during laboratory climate tests and normal volunteer subject tests were compared to normal diaries. Objective. To develop and test the accuracy and reliability of a device designed to measure spinal orthosis wearing time. Summary of Background Data. Orthosis wearing time is an important factor in orthotic treatment for spine disorders. A reliable and objective method for measuring orthosis wearing time currently is lacking. Methods. Four pressure switches and a data logger embedded in each thoracolumbosacral orthosis recorded orthosis wearing time. Orthoses were assumed to be worn when at least two switches were “on.” Laboratory climate tests and normal volunteer tests were conducted to assess the ability of the compliance monitor to measure orthosis wearing time. A manual wearing-event diary was kept during all the tests. The length of each wearing-time interval, the daily wearing time, and the cumulative wearing time were calculated from data recorded by the compliance monitor and the manual diaries. Results. A linear regression was performed on all orthosis wearing-time intervals as recorded by the compliance monitor and by the manual diaries. Climate chamber tests yielded 121 sensor trigger-event intervals (R2 = 0.998; slope = 1.003;P < 0.0001). Normal subject testing yielded 72 orthosis wearing-time intervals (R2 = 0.998; slope = 0.998;P < 0.0001). Conclusion. As indicated by the regression analyses, the compliance monitor accurately quantified the orthosis wearing-time intervals during the laboratory climate tests and the tests with normal volunteers.

Biomechanical analysis of cervical orthoses in flexion and extension: a comparison of cervical collars and cervical thoracic orthoses.

The analysis of current cervical collars (Aspen and Miami J collars) and cervical thoracic orthoses (CTOs) (Aspen 2-post and Aspen 4-post CTOs) in reducing cervical intervertebral and gross range of motion in flexion and extension was performed using 20 normal volunteer subjects. The gross sagittal motion of the head was measured relative to the horizon with the use of an optoelectronic motion measurement system. Simultaneous measurement of cervical intervertebral motion was performed with the use of a video fluoroscopy (VF) machine. Intervertebral motion was described as (1) the angular motion of each vertebra and (2) the translational motion of the vertebral centroid. We used surface electromyographic (EMG) signal data to compare subject efforts between the two collars and between the two CTOs. Each orthosis significantly reduced gross and intervertebral motion in flexion and extension (p < 0.05). No statistically significant differences were found between the Miami J and Aspen collars in reducing gross or intervertebral sagittal motion, except at C5-6. Both CTOs provided significantly more restriction of gross and intervertebral flexion and extension motion as compared to the two collars (p < 0.05). The Aspen 2-post CTO and 4-post CTO performed similarly in flexion, but the Aspen 4-post CTO provided significantly more restriction of extension motion (p < 0.05).

Geometric analysis of coronal decompensation in idiopathic scoliosis

Study Design. Frontal plane geometry of postoperative curves was analyzed using a geometric model to investigate the relationship between coronal decompensation and postoperative apical shifts from the center sacral line for various thoracic and lumbar Cobb angles. Objective. To determine if a balanced spinal configuration is possible when the postoperative lumbar curve is larger than the thoracic curve, and to determine the limits on the postoperative magnitude of the lumbar curve relative to the thoracic curve beyond which a spinal configuration with acceptable balance cannot be achieved. Summary of Background Data. Previous studies have suggested that overcorrection of the primary thoracic curve may be the principal cause of coronal de‐compensation after selective thoracic correction and fusion in King Type II curves. Also, other causative factors, such as inappropriate selection of fusion levels and hook patterns, have been implicated as possible reasons for decompensation after Cotrel‐Dubousset instrumentation for idiopathic scoliosis. Methods. Postoperative thoracic curves of 20°, 25°, and 30° were simulated on a model spine. For each thoracic Cobb angle, three left lumbar curves were simulated with the lumbar curve larger than thoracic by 5°, 10°, and 15°. For each combination of thoracic and lumbar Cobb angles, spinal configurations corresponding to different lateral shifts of the thoracic and lumbar apical vertebrae from the center sacral line were obtained. Results. For a given combination of postoperative thoracic and lumbar Cobb angles, there is an optimal range of postoperative lateral distance between the thoracic and lumbar apices (relative apical distance) that will maintain acceptable balance (decompensation ≤ 10 mm). Smaller values of the relative apical distance will decompensate the spine. For a constant postoperative thoracic Cobb angle, the postoperative distance between the thoracic and lumbar apices needed to maintain a balanced spine increases with increasing postoperative lumbar Cobb angle. Similarly, for a constant difference between the postoperative thoracic and lumbar Cobb angles, the postoperative distance between the thoracic and lumbar apices needed to maintain a balance spine increases with increasing postoperative thoracic Cobb angle. For postoperative thoracic curves of 20°‐30°, acceptable balance can be achieved when the magnitude of the postoperative lumbar curve is up to twice the thoracic curve as long as adequate postoperative relative apical distance can be maintained. Conclusions. Decompensation does not appear to be caused by the relative magnitudes of the postoperative thoracic and lumbar curves, but is a result of inadequate relative distance between the thoracic and lumbar apical vertebrae in the postoperative geometry.

Getting started in prosthetic-orthotic research

The authors discuss getting started in O&P research and provide examples for organizing research projects, including how to identify the basic problem to forming the hypothesis, testing the hypothesis and drawing statistically or clinically significant conclusions. Several common early errors in getting started with a project design are briefly discussed. Being concise, clear and significant are shown to be some of the most important factors in formulating a project. Constraints of time, funding and proper equipment to carry out research investigations should be considered but can be overcome and should not discourage the new researcher. Solving these logistical constraints is also discussed. The impact of O&P research is paramount to the future of our field with the waning physician interest in carrying out O&P projects.

Biomechanical Comparison of the Milwaukee Brace (CTLSO) and the TLSO for Treatment of Idiopathic Scoliosis

The decision to choose between a CTLSO (Milwaukee brace) and a TLSO (such as the Boston system, Wilmington, Miami or Rosenberger orthosis) is affected by several factors including cosmesis, geographical preference and popularity of a given orthosis. Performance usually is a secondary consideration since objective comparisons have been difficult. A finite element model was used to quantify and compare the effects of the CTLSO and TLSO in increasing spinal stability as measured in terms of the critical load of right primary thoracic with left lumbar compensatory and left primary lumbar with right compensatory idiopathic scoliotic curves. While the CTLSO and TLSO were equal in stabilizing lumbar primary curves, the TLSO was 25 percent less effective in stabilizing primary thoracic curves. Pad and counterforce placement were critical factors influencing stability for both the CTLSO and TLSO, demonstrating the importance of proper initial fit and timely growth adjustments to ensure proper pad placement throughout the duration of wear.

The Etiology and Natural History of Scheuermann???s Kyphosis

Postural kyphosis manifests as an increase in thoracic kyphosis while standing. Curve flexibility is seen when the patient stands erect as opposed to when the posture is relaxed. When the patient is prone or supine, the “deformity” resolves spontaneously. This nonprogressive condition is commonly seen in middle-school-aged children, especially girls, and almost always resolves by itself and requires no specific treatment; however, thoracic hyperextension exercises may be helpful.

Methodology???Measurements, Part II: Instrumentation and Apparatus

ABSTRACT Laboratory instrumentation of orthoses and prostheses can be used to objectively assess the functional differences between various componentry designs and to measure the effect of an orthosis or prosthesis on the outcome of treatment. This article describes the electromechanical transducers and instrumentation systems that may be used to accomplish these tasks. The transducers are grouped in the following categories: stress and strain, linear and angular displacement, acceleration, force, pressure, temperature and humidity. Examples of transducer applications, instrumentation selection and integration are described.

Preliminary results of orthotic treatment for chronic low back pain

The use of spinal orthoses for chronic low back pain has traditionally been random and empirical. Frequently, a lumbosacral corset is prescribed and, upon failure of the corset to reduce pain, orthotic treatment is abandoned. In this prospective study, the test instrument of Willner, consisting of a rigid aluminum thoracic lumbosacral orthosis (TLSO) with a sagittal lumbar pad that is adjustable in lumbar flexion or extension, is used to test the hypothesis that a five-day trial in a test orthosis will be a good predictor of the outcome of orthotic treatment for chronic low back pain.

An Alternative Bracing Approach To Scheuermann???s Disease: A Case Study

Scheuermann’s disease manifests itself as a thoracic or thoracolumbar kyphosis classically characterized by anterior wedging of 5 degrees or more of three adjacent thoracic vertebral bodies. Bracing has been shown to be effective in controlling a progressive curve in the adolescent patient. These adolescent patients typically present for medical attention because of pain or cosmetic deformity or both. Early treatment may be limited to observation and exercises, whereas patients who have kyphosis of up to 75 degrees and growth remaining may benefit from bracing. For the more common thoracic form with apices superior to T8, the Milwaukee brace’s effectiveness has been documented and is usually the treatment of choice. This purpose of this article is to document a case for the treatment of the thoracic form of Scheuermann’s disease (apice T6–7) with an underarm thoracolumbosacral orthosis. A custom thoracolumbosacral orthosis was measured and fabricated as an alternative to the Milwaukee brace to treat a 71-degree kyphosis with an apice of T6-T7. Initial in brace correction was 49%. At a fourteen-month follow-up, out-of-brace correction was maintained at 27% of the original kyphosis. These results indicate that a thoracolumbosacral orthosis may be a viable alternative to the Milwaukee brace in treating Scheuermann’s disease with high apices.