A Preliminary Report on a New Design of a Spinal Orthosis for Spondylotic Patients: Review of the Literature and Initiation for Future Study of a New Design.

Keith M. Smith

ABSTRACT

Currently, there exist two accepted treatment protocols for spondylolytic patients-the Williams Flexion Orthosis and a polymer LSO, such as the Boston Overlap Orthosis. Literature ranging from the late fifties through the present are reviewed to determine the biomechanics and effectiveness of these protocols.

A prototype was made that combined the two orthoses and radiographs were taken to determine its effectiveness. The anterior section was adapted from Williams and the posterior section from the polymer, and it was molded to a positive cast of the patient. Radiographs were also taken showing the difference in the lumbar spine alignment between the two orthoses used on our patient.

This article explains the importance of maintaining a posterior pelvic tilt and emphasizes the importance of sagittal flexion through the use of a new design.

Key Words: Spondylolysis; Spondylolisthesis; Williams Flexion Orthosis; Boston Overlap Orthosis; Lordosis; Flexion.

Introduction

It is currently accepted protocol to treat patients with Grades I and II spondylolisthesis, as well as spondylolytic patients, through observation and orthotic treatment, or, in some cases, surgical fusion. There has been success with each treatment choice. The confusion lies in determining what is the best method for the conservative approach. Teitz and colleagues cite that 6% of the general population can be diagnosed with spondylolysis (1). Wiltse and colleagues cite five types of spondylolisthesis and spondylolysis: dysplastic (elongation of the pars), isthmic (fracture of the pars); degenerative (degradation from time); traumatic (fractures other than in the pars); and pathological (bone disease) (2). By classification, the author is able to link each condition more specifically and learn more about each etiology as a separate entity. Since the author is working with treatment modalities in adolescents, this report concentrates heavily on the isthmic etiology, which is a stress fracture of the pars interarticularis and the dysplastic types.

Some authors have stated that there are hereditary implications (3-5), while other studies indicate that spondylolisthesis is rarely seen to progress past skeletal maturity (1,6). Eisenstein showed that there is no significant variation to be seen between the sexes or races leaving it to mechanical stresses (7).

Over the years, there has been confusion as to the exact mechanism of injury, but by looking at successes from treatment protocols and observing certain groups prone to the defects, it is the general consensus that it is more likely a stress injury from an increase in lordosis or sudden loading of the posterior elements (1,3,6,8,9). Troup cites studies that suggest flexion as a mechanical etiology, but he goes on to show that because there is little muscular activity in a lordotic position there is no prestress to the neural arch, thereby allowing anterior shear to result when jerking motions are applied to the loaded spine (10). Spratt and colleagues found in their studies of patients with lower back pain that extension protocol gave more favorable results than flexion for spondylolytic patients as well (9). Unfortunately, they could not explain their findings and recognized that it went against current trends in spondylolytic research.

Several authors conducting spondylolytic research have compared man to apes and found that the lytic symptoms are unique to man (11,12,14). Apes carry themselves in a flexed lumbar position, whereas man has developed a secondary curve pattern-an extended lumbar position. Further, it should be noted that spondylolysis is not present at birth, but appears when we assume an upright posture (4,13). It has been shown by numerous studies that there is a higher incidence of lytic conditions in gymnasts, football linemen, or anyone who participates in activities that require forced hyperextension of the lumbar spine (6,8,10,14-17).

In discussing principles of load sharing in the spinal column, Bridwell points out that the weight-bearing line falls behind the lumbar vertebrae and just behind or through the lumbosacral joint (18). His theory presents the posterior column, as described by Denis, as being the weight-bearing or principle structural support for the lumbar spine (19). According to Bridwell's theory, the anterior and posterior columns are the chief supporters. When one is damaged, the other column will be left to bear the weight.

Morita and colleagues found that when treating an early lytic defect, 73% had healed from lumbosacral support (20). These statistics alone exemplify the importance of research and development in this area. Muscik's study of 86 young athletes with a spondylolysis or spondylolisthesis condition showed that there was no need to end athletic participation (13). Maintaining good muscular strength was of benefit to healing. Others have shown that limiting activity is more beneficial (1, 3,6,14,21).

The review of the literature indicated that flexion was beneficial to healing with or without the orthosis and in combination with a posterior pelvic tilt provided for a biomechanical advantage (15,16,22,23). Michelli, Hall, and Miller had excellent results in eight of twelve patients studied with spondylolytic back pain and four with good results using the Boston system (15). From the Mayo Clinic that same year, Sinaki and colleagues studied two patient populations-one doing flexion exercises and one doing extension exercises. They found that 82% of the flexion group said they had less pain while only 37% of the extension group stated similar feelings (12). Sinaki and colleagues in a three-year follow up study studied two patient populations again-one doing flexion exercises and one doing extension exercises. After three months and exercises, 73% of the flexion group expressed mild or no pain whereas only 33% of the extension group expressed mild or no pain. After three years, the numbers went to 81% for flexion group and remained unchanged for the extension group (24).

Another study in 1984 (four years later than original Boston article) again showed excellent results for the Boston system. Of the patient population in Steiner and Michelli's study, 78% showed excellent or good results(16). We must keep in mind that for the majority of studies, excellent results meant pain-free, not necessarily bony union. Their paper even cited Sinaki's findings that flexion exercises were beneficial but failed to address the fact that the Boston system limited this beneficial lumbar flexion. Bell and colleagues also studied patients with a spondylolytic spine using a rigid thoracolumbar orthosis and found that after 25 months, all patients were pain-free (22). This study also failed to address what the results would have been in an antilordotic orthosis that allowed flexion of the lumbar spine. They also failed to follow up with the patients to compare their degrees of lordosis before and after orthotic treatment. Magora found that intra-abdominal pressure from a corset caused the back and abdominal muscles to weaken (21). Again, this represents a situation in which post-orthotic posture has been sacrificed for an attempt at healing.

As an orthotist, I am constantly asked the question of positioning techniques concerning lumbosacral spine instabilities, especially spondylolytic patients. My interest was sparked in particular by the debate between lordotic versus antilordotic positioning as well as free flexion versus limited flexion. Recently, I encountered patients who had been treated with orthoses that maintained lordosis and who all expressed continued pain and, in confirmation with the physician, also a lack of healing. By simply reducing the lordosis, every patient expressed relief of pain symptoms and went on to more of their activities of daily living. This caused some of the more active adolescents to inquire on follow-ups if there was anything that could be done to allow for even more flexibility. They all had felt limited by their existing polymer orthoses, which put a hold on the sagittal plane. I thought of the Williams Flexion Orthosis and immediately began to research the design. It is constructed of thoracic, pelvic, lateral, and oblique (for structure) bands made of malleable aluminum with an anterior elastic corset front and nonelastic pelvic strap. Its design allows for flexion in the sagittal plane while maintaining a posterior pelvic tilt.

The Boston Overlap Orthosis, on the other hand, is a full polymer LSO limiting flexion anteriorly in the sagittal plane. According to Steiner and Micheli, it is a total contact orthosis compressing all soft tissues, including the abdominal muscles (16). The Boston orthosis attempts to put a hold on the sagittal plane, (preventing flexion and extension in the lumbosacral region), despite the fact that Dr. Paul Williams showed in his studies that it was beneficial to treatment to allow free flexion with only a stop on extension in the sagittal plane (11). The literature supports Williams' views on the importance of the antilordotic position (15,16,22,23). Williams stressed the importance of maintaining a posterior pelvic tilt , but he also emphasized the importance of adapting the body to hold this position postorthotic treatment (11).

By increasing intra-abdominal pressure, the abdomen becomes weak. Keeping in mind that the abdominal muscles are posterior pelvic tiltors, it is obvious to conclude that postorthotic treatment, the patient will assume a more lordotic position than preorthotic treatment. This modality of treatment is not considering postorthotic treatment, for as the abdominals become weak, there is no longer a lever assisting the hip extensors to pull the lumbar spine into flexion. Williams emphasized the importance of strengthening the lumbar spine flexors or posterior pelvic tiltors while at the same time stretching the extensors or anterior pelvic tiltors. By strengthening the lumbar spine flexors, an opposing force is maximized to combat any tight extensor tendons. Williams' orthosis fell short due to the lever arm posteriorly ending too inferior, but to this day stands next to the Boston system as protocol for spondylolysis as well as Grades I and II spondylolisthesis patients.

According to Williams' article, the posterior section's height was determined by measuring from C7 inferiorly to the sacrococcygeal junction and then subtracting three inches and dividing by two. The Williams Flexion Orthosis has developed into a stock item in which control of height has been lost. Manufacturers across the nation dispense the Williams with uniform posterior sections. Because the lever arm usually ends up being too inferior, patients are still able to override the orthosis and accomplish extension in the lumbar spine.

Since Williams' research, the field of orthotics has been revolutionized by the introduction of thermoplastic systems and custom-molded orthoses. With these technologies and Williams' expertise, we can hypothesize that orthotically we should implement the antilordotic position with the custom thermoplastic posterior section where we can control the lever arm and also allow free flexion anteriorly.

New Research

To initiate research the author plans to implement a program of orthotic treatment as well as postural strengthening and stretching. The orthosis will put a stop on extension and allow free flexion in the sagittal plane while maintaining a posterior pelvic tilt. The patients included in the study will be limited to adolescents with a pars fracture or spondylolisthesis of grades I or II.

Materials and Methods. A prototype was made to determine the ability of the new orthosis to maintain a posterior pelvic tilt and allow flexion radiographically. The prototype used was a molded posterior rigid copolymer system with the Williams type elastic anterior panel and nonelastic pelvic strap to maintain the posterior pelvic tilt (Figure 1) . A zipper was used as closure to allow for ease in donning and doffing. The system is a custom-molded orthosis that makes use of positioning techniques in the impression as key.
Impression Technique. The prototype was constructed by taking an impression in which the plaster was circumferentially wrapped from the inferior angle of the scapula inferiorly to the gluteal fold. The patient was then seated in a position in which the knee joints were superior to the hip joints looking through the coronal plane. This position was adapted from Williams' notion that when sitting, if the knees are higher than the hips, then the lumbar spine is in a flexed position and vice versa. The impression was then poured and the positive mold was modified. The posterior section was simply smoothed, indentions between the last rib and iliac crest were made bilateral to prevent migration of the orthosis, and the anterior section was left untouched. A polymer was pulled for the lateral and posterior aspects and trimmed posteriorly from the 24 mm inferior to the most inferior angle of the scapula, inferiorly past the sacrococcygeal junction. The middle section has a window for air because biomechanically it is not needed. It is important to note that inferiorly, on each lateral side, the orthosis must be trimmed to prevent the orthosis from migrating when sitting, then the elastic panel must be added. The nonelastic strap should lie inferior to or on the ASIS levels to insure a posterior pelvic tilt, but not low enough to cause impingement on the quadriceps.
Results. Radiographs were taken of the patient without the orthosis, wearing the orthosis, standing and wearing the orthosis, flexing. Figure 2 and Table A show the results where the prototype reduced the lordosis, and the lumbosacral angle, and allowed flexion in the lumbar spine to 5 degrees of kyphosis.

Case Study

Our first patient is an active 13-year-old who was originally seen by his orthopedic surgeon for anterior knee pain, at which time radiographs of the knee were taken and no noticeable defects revealed. At a 1-month follow-up, tight hamstrings were observed by the physician, at which time he began to suspect involvement of the lower lumbar spine. Oblique radiographs revealed nonunion of the L5 right pars interarticularis and an evolving defect on the left. A polymer LSO was constructed for the patient, but on follow-up in the next few months the patient still expressed pain at the L5-S1 site with oblique bending and extension. He was also diagnosed with Grade I spondylolisthesis.

After four months of wearing the LSO, the patient discontinued wearing it due to increased pain. His gait was now slow with the knees in flexion and the lumbar spine in kyphosis. He had pain radiating into the left buttocks region and the slip had increased from 2 mm to 6 mm. At this time, a pad was added to the inferior half of the posterior section of the orthosis in an attempt to reduce further extension into the lumbar spine.

One month later, the patient was ambulating better, the pain had slightly decreased, and there was no progression of slip. There was still evidence of hamstring tightness and he was referred to me for a second orthotist opinion. After reviewing the patient's history and observing that his current orthosis was indeed holding the lumbar spine in an extended position, I agreed with the orthopedic surgeon's recommendation that the patient's lordosis needed to be further reduced. We decided to implement the new design as described in this article and three months later, the patient is pain free. A lateral radiograph showed that the alignment of L5-S1 improved back to normal. Lateral radiographs were also taken of the patient in the polymer LSO after the pad was added to help reduce extension, and also of the patient in the new orthosis design described in this article. By looking at Figure 3 , we can see qualitatively that the new design (B) reduced the slippage observable in (A) back to normal alignment.

Discussion

The scope of this paper can be illustrated by a statement made by Pettine and colleagues in their case study, when they said, "To our knowledge, this is the only report that gives any data on the ability of bracing... to heal a spondylolysis (17)." They were citing Steiner and Michelli's article on the Boston Orthosis. Each study reports that more studies should be done concerning treatment. The initiation of a study on spondylolytic patients treated with an antilordotic orthosis which allowed flexion would give us a standard to compare the excellent results of the Boston system against. This would also answer the question of whether or not intraabdominal pressure is needed. With the observation noted that patients healed without orthotic treatment, allowed to continue participation in sports, and with Williams' theory we are also left to ask whether a full polymer system with a hold on the sagittal plane in the lumbar spine could be considered overmanagement. Due to the fact that there is not always pain initially with a spondylolytic fracture, sometimes the potential for bony union is substantially decreased and in some cases ruled out. For this study, we plan to adapt good results as meaning absence of pain. These are questions that could be answered by future studies implementing the designs described here and comparing them to accepted protocol. Of the sixteen patients currently in this new study, each (except for one due to noncompliance) has expressed relief from pain and all are implementing flexion exercise regimens in the orthosis.

Acknowledgements

Special thanks to Dr. Anderson and Dr. Otis of Mid-County Orthopedics in St. Louis, Missouri for radiographic assistance, introduction of patients into the study, and informative expertise.

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