Spine and Spinal Cord Surgery

Spring 2001
Volume 12, Number 1

The physical therapy field has shown many promising advances in back care in the past few years. The most exciting advancements have been in the field of stabilization of the lumbar spine. Conventional therapy has dictated the use of larger global musculature in an attempt to stabilize the spine. The purpose of this paper is to introduce recent research that suggests the use of a more specific segmental rehabilitation program.

Introduction. The muscular system can be divided into 3 classifications: 1) Local stabilizers, 2) Global stabilizers, and 3) Global mobilizers.2 Local stabilizers are defined as muscles that control the joint neutral position. They usually cross over only one spinal segment. They work at low load and do not produce movement. They also attach directly to the lumbar spine. Activity of the local stability system is independent of direction of movement. Examples of local stabilizers in the lumbar spine, are transverse abdominis, deep lumbar multifidus, and posterior fasciculus of psoas. Dysfunction of the local systems results in motor control deficit associated with delayed timing, or recruitment deficiency. These muscles react to pain and pathology with inhibited firing patterns.3 This delay in recruitment results in decreased muscle stiffness and poor spinal segmental control. The ability to control a joint neutral position is also diminished.

The global muscle system is comprised of the larger torque producing muscles.2 They contract concentrically and eccentrically to produce or control range of movement. Their activity is direction dependent and they activate to control and transfer load. Contraction of these muscles can produce rigidity if the load is great enough or to protect pathology. When rigidity is produced in the lumbar spine, there is evidence to suggest an increase in spinal compression.4 When these muscles are in dysfunction, it is usually a reaction to pain and a painful spasm is produced. Examples of global muscles are oblique abdominis, rectus abdominis, spinalis, iliocostalis, gluteus maximus, and hamstrings. The global system consists of the muscles that are traditionally strengthened in people with low back pain. Evidence would suggest that training of the global system may not be the optimal starting point for people who have low back pain.

Retraining of the local stability system in people with low back pain is a concept that has made its way into the physical therapy setting within the last 4 to 5 years. Retraining the local stability system is not altogether a new concept. The vastus medialis oblique (VMO) is a local stability muscle. Therapists have known for a long time that performing knee rehabilitation without first training the VMO can lead to patellofemoral problems. With the research being conducted at the University of Queensland, by Paul Hodges, PT, PhD, Julie Hides, PT, PhD, Carolyn Richardson, PT, PhD, and Gwen Jull, PT, PhD, the same concept is being used on patients with low back pain. The concept is to create stiffness in the spine before load is placed on the spine, thus controlling mid range or neutral zone. Control of this mid range helps reduce shear force and compression during movement and spinal loading. When working properly, the local intrinsic musculature fires before the actual motion of an extremity or of the trunk occurs.5 The pre-contraction of the intrinsic musculature can become delayed or inhibited in the presence of pain or pathology. This delay, or inhibition of the stability system, decreases a patient’s ability to control a joint neutral position during movement or under load. This can also be described as spinal instability.6 In 1992, Panjabi developed a model to describe spinal instability. This model is based on the belief that most low back pain is caused by mechanical derangement of the spine or “clinical spinal instability.” Panjabi relates this mechanical derangement to the clinical signs and symptoms. He theorizes that spinal stability is dependent on 3 sub-systems; 1) The Passive System comprised of osseous and connective tissue structures, 2) The Active System consisting of the musculotendinous unit and is concerned with dynamic force generation, 3) The Control System relating to the nervous system. The nervous system receives sensory information “proprioceptive afferent feedback” and activates the active subsystem (motor control and recruitment). Each sub-system reacts to and influences the others.7

Panjabi defines the neutral zone as the range of intervertebral motion within which the spinal motion is produced with minimal internal resistance. He goes on to define clinical instability as a significant decrease in the ability of the stability system to maintain this intervertebral neutral zone within physiological limits, which results in pain and disability.7

The muscles best suited to control the neutral zone in the lumbar spine are transverse abdominis, deep lumbar multifidus, and the posterior fasciculus of psoas.

The transverse abdominis is the only abdominal muscle that attaches to the lumbar spine directly. It does so via the lumbodorsal fascia. Transverse abdominis generates spinal stiffness in a number of ways; 1) an extensor moment: the transverse abdominis generates an extensor moment on the lumbar spine via the thoracolumbar fascia, 2) Intra-abdominal pressure: by stabilizing the abdominal contents during respiration, the transverse abdominis creates pressure on the anterior aspect of the lumbar spine, thus counteracting the extension moment created by the lumbodorsal fascia, 3) Rigid cylinder: transverse abdominis’ circumferential orientation creates a rigid cylinder to absorb load.

Deep lumbar multifidus attaches directly to each segment of the lumbar spine. Multifidus contributes to segmental stiffness as a hydraulic amplifier. It also contributes to the control of joint neutral position and increased spinal stiffness.8 Multifidus dysfunction has been shown post surgically and in both chronic and acute low back pain. Post surgically, muscle atrophy and Type I fiber pathology have been shown. Muscle biopsy studies were performed 5 years post disc herniation surgery. Type I fiber pathology was indicated with muscle biopsy. Patients who showed multifidus muscle pathology were also the majority of the patients who had poor outcomes from surgery. Consequently, patients not showing multifidus pathology had the better outcomes.9 In patients with chronic low back pain, the multifidus showed an increased propensity to fatigue compared to patients without low back pain. There was a definite loss of segmental motor control in acute first episode unilateral low back pain patients.10 These and other works suggest deep lumbar multifidus is directly effected in patients who have low back pain.8 This combination, with the muscle’s role in controlling joint neutral position, provides a basis for retraining of the deep lumbar multifidus.

A muscle that is being looked at closely is psoas. The work on psoas is just beginning to shed some light on its role with spinal stability. Psoas has been described as a phasic hip flexor. Recent unpublished studies have suggested that psoas cannot perform effectively as a prime mover of the hip. Anatomical dissection has revealed psoas as having short pennate fibers with attachments to individual lumbar vertebrae. These short pennate fibers form a common tendon which blend to the anterior fasciculus and iliacus. Due to the muscle’s short fiber orientation, as well as its short contractile length, it seems unlikely that psoas could generate enough torque to flex the hip. In recent published studies, segmental attachment of psoas has been shown to decrease in cross-sectional area at the level of confirmed disc herniation by MRI.11 Psoas’ prime fiber orientation on the anterior aspect of the lumbar vertebrae, make it a very good segmental stabilizer. Further studies are being conducted to confirm psoas’ function on the lumbar spine.

There are many different ways to evaluate the deep intrinsic musculature for function. The most common evaluation procedure is palpation. Muscles are palpated through different rehab strategies to ensure proper firing patterns without substitution of the phasic system. A pressure biofeedback cuff can also be used to evaluate a patient’s ability to fire the correct muscles as well as assessing the maintenance of the holding patterns. The most recent evaluation tool used by physical therapists is diagnostic ultrasound. This is a way to measure firing patterns, endurance times, view the consistency of the muscles, as well as measuring cross-sectional area.12 Diagnostic ultrasound is also used to educate patients, giving them a visual feedback mechanism that helps speed up the rehabilitation process.

It is interesting to note that even though the research on the intrinsic systems has evolved within the past 5 years there are other systems that possibly effect the intrinsic system as well. These exercise systems include Feldenkrais, Aston Patterning, and Alexander Technique. All employ smaller controlled movements that simulate intrinsic re-education. They emphasize motor control, not strength, which is the basis for intrinsic retraining. These are excellent programs for graduating patients after their course of physical therapy. Pilates is another system that utilizes more motor control strategy, although it does emphasize the use of the global phasic system. Pre-setting of musculature is also taught preceding the loading of the extremities. Yoga and Tai-Chi have also been identified as programs that patients can use to encourage and maintain intrinsic stability.

Conclusion. Looking at the future of exercise rehabilitation in the low back pain patient, the training of the intrinsic system is a major paradigm shift. Conventional therapy has dictated that strength is synonymous with stability and that more is better. This is not to say that strength training is not appropriate. When a patient requires rigidity under load, they must be trained to function under those conditions, but the vast majority of patients who experience low back pain need an intrinsic retraining program first to ensure control of the joint neutral position.13-15 Although this intrinsic system can be more time consuming and difficult to teach at first, the system cannot be ignored any longer as the future in exercise rehabilitation.
 

Address comments and questions to:

Pete Emerson, PT, MMTC
Back and Sports Injury Physical Therapy
1550 S. Pearl Street, Suite 101
Denver, CO 80210