In: NAVC Proceedings 2006, North American Veterinary Conference (Eds).

The Psoas Muscle Group as a Source of Performance Problems
K.J. Ridgway

Certified Veterinary Acupuncturist, Equisport: Equine Therapeutic Options, Aiken, SC, USA.

In spite of what would seem to be excellently and “appropriately” applied allopathic and complementary therapies, some horses are afflicted with recurrent “back soreness” and may exhibit subclinical lameness and suffer significant performance deficits as a result. Not infrequently, the practitioner will encounter cases where joint stiffness and reduced joint mobility has been “correctly” addressed through musculo-skeletal manipulation or acupuncture, only to have pain, stiffness and gait aberration recur within a week or two. In this practitioner’s hands, neither acupuncture nor manipulation, while very helpful, had provided consistent long term relief in these cases. Something has been missed. The treatment has not been complete.

When examined or re-examined it is often noted that these horses are quite painful bilaterally in the Sacroiliac joints. The lumbo-sacral junction is frequently very tender and “splinted.” Pain is frequently found when pressure is applied in a ventral direction to the sacral base, or to the sacral apex. Lateral traction of the sacral apex can cause an expression of marked pain. It will also be noted that as one applies pressure directly downward at the costal arch over the last two or three ribs, a pain response is elicited. Some patients, as part of the syndrome, exhibit pain in the hamstring group of muscles (biceps femoris, semitendinosus, and the semimembranosus). Tension in the cervical vertebrae and associated muscles may be noted.

I have come to realize that the Psoas group of muscles is often the culprit behind the short duration of relief that the practitioner has achieved. Alleviation of the hypertonicity of this muscle group is the key to longer term success. Correction lies in appropriate acupuncture, appropriate musculoskeletal manipulation but also requires appropriate “yoga” like approach to solving the problem. To accomplish our goal it is necessary to review the fundamentals of the anatomy and biomechanics of the sacropelvic articulations and other structures affected by Psoas hypertonicity.

The Psoas Muscle Group includes the Psoas Major, the Psoas Minor, and the Iliacus muscles. Hypertonicity of this entire group of muscles can be visualized by observing the way many farriers chronically stoop. When hypertonicity exists, it results in an inability to stand up straight. When we get a back spasm, we tend to blame the muscles on the posterior aspect (in human) (dorsal in the horse) portion of the spine. Whereas, in fact, it is often the muscles on the ventral side of the horse’s spine or on the anterior side in the human terminology, that are being maintained in a state of hypertonicity. The largest muscle group on the “underside” is the Psoas group. {vieownly=special}

SACROPELVIC MYOLOGY AND THE BIOMECHANICS OF THE SACRUM AND PELVIS
The sacropelvic muscles provide stability to the pelvis. These muscles are subject to exceedingly strong stressors, such as speed (as in racing), strength (as in pulling), isometric contraction (as in dressage), fatigue from too many contractions (as in endurance), as well as trauma and other pathologies such as the exertional myopathies, or splinting to protect injuries to lower limbs.

These stressors adversely alter the biomechanical function. The resulting stress maintains the muscles in an excess state of hypertonicity. The shortened fibers exhibit decreased contractile power. Hypertonicity alters proprioceptive input and creates a lack of coordination and increased resistance to free movement. The associated fatigue of the muscles further decreases their ability to handle stress. This cycle then leads to further stress and strain and predisposes to fiber damage and “breakdowns” of the ligaments of the pelvis/sacrum or tendons and ligaments of the lower limb.

When the muscles can no longer provide an adequate level of support, the lumbar vertebrae and sacro-pelvic articulations are strained and taxed beyond physiologic parameters. Potentially, these can lead to fracture(s) of the pelvis, or of the limb and stress fractures in the lower lumbar vertebrae.

The strain and lack of stability tends to create more spasms that result in additional muscle imbalance. This imbalance may be signaled by careful palpation. The muscles exhibit tight and tender fibers and a general hypertonicity. Involved muscles are attempting to reposition the vertebrae and lumbo-sacral and sacropelvic articulations based on faulty proprioceptive information. The purpose of the chiropractic or osteopathic type of adjustment is to initiate the appropriate proprioceptive changes in the muscle. Appropriate adjustment creates the proprioceptive changes necessary to maintain the adjustment. Acupuncture is also very helpful in reprogramming and releasing hypertonicity of the muscles and is a key part of therapy.

In order to better understand the effect on the articulations, it is necessary to review the lumbar and sacropelvic osteology.

SACROPELVIC JOINTS
The sacropelvic joints include the zygopophyseal joints of the last lumbar facets and the cranial facets of S-1 (forming the lumbosacral joint). The zygopophyseal joint planes lie vertically in a sagital plane and exhibit a quite spacious joint capsule. Subluxations involving the lumbosacral joints cause significant pain and performance deficit as the capsules are very rich in pain fibers (C-polymodal fibers).

Lumbosacral articulations also include the intertransverse joints. Unique to the horse, these are true synovial joints formed by articulation of the posterior edge of the last lumbar transverse process with the wing of the sacrum. These intertransverse joints stabilize the region and prevent dorsal subluxation. The biomechanics of both the zygopophyseal joints and the intertransverse joints are primarily to accommodate extension - flexion at the lumbosacral area.

The spinous processes of last lumbar vertebrae angles cranially and sacral tubercles/spines angle caudally. The Supraspinous ligament is lacking in this area. The joint can also undergo some axial rotation and some lateral bending thanks to the action of the disc functioning as a joint at the lumbosacral intersection.

The sacroiliac joint: is a synarthrodial as well as synovial joint.

The synarthrodial joint is partially moveable and limited by a very tight joint capsule. It is supported by both a dorsal sacroiliac ligament and a major ligament on the ventral surface - the ventral sacroiliac ligament.

The pubic symphysis is a mid-line cartilaginous joint that ossifies at about 5 years of age. This joint is subject to stress from the sacroiliac joint and the acetabulum. Stress on these structures tends to open the symphysis. Early stress, as from the sudden acceleration from the starting gate, can severely affect and damage this joint. It can lead to permanent deformation of pelvic conformation and can change the biomechanics of the pelvis.

As a critical support and stabilizing system of the pelvis, integrity of the Sacrotuberous Ligament (a very extensive ligament on the lateral pelvic wall) is important. The ligament extends between the sacral apex, the coccygeal transverse processes and the ischial tuberosity. Many of the strong muscles of propulsion originate from the sacrotuberous ligament. These include the Biceps femoris, Middle Gluteal, Superficial Gluteal, Longissimus, Semimembranosus, and the Abductor Cruris Caudalis.

The Iliolumbar ligament is a dense triangular ligament that attaches the lumbar transverse processes to the ventral surface of the ilium. It also provides critical stability but is prone to injury from trauma, such as sudden turns in barrel racing, cutting and stock horsework.

VENTRAL MUSCLES OF THE SPINE AND PELVIS THAT AFFECT THE BIOMECHANICS OF THE PELVIS AND SACRUM
Psoas Major Muscle
This very important muscle originates from the ventral transverse processes of the lumbar vertebrae and from the last two ribs. By its insertion onto the minor trochanter, it flexes the hip and rotates the thigh laterally. With bilateral contraction, it functions to flex the vertebral column and to create a fixation of the vertebral column. Unilaterally contracted, it creates rotation and lateral flexion of the lumbar spine. Normal tone maintains posture and helps prevent a lordotic curve to the back. Innervation is provided by the lumbar spinal nerves and the femoral nerve. The psoas major has a key function of supporting the sacroiliac joint. Hypertonicity of the psoas major leads to ongoing pain and performance deficit.

The Psoas Minor muscle acts in concert with the psoas major to create a powerful flexion of the lumbosacral joint and acts strongly on the sacroiliac joints. It commences on the ventral aspect of the 16th thoracic through the 5th lumbar. Its insertion onto the cervical tuberosity of the ilium makes it such a powerful flexor.

The Iliacus muscle has the function of flexing the hip joint and rotating the thigh laterally. It accomplishes this by its origin on the ilium and on the sacral wing as well as the ventral side of the sacroiliac ligament. It inserts on the lesser trochanter of the femur. The psoas major and the iliacus are intimately united and insert on the lesser trochanter (medial side of femur) by common tendon. The two are often considered as a single muscle known as the Iliopsoas muscle

The Longissimus dorsi muscle as the central portion of the erector spinae has numerous origins including the ilium, the first three sacral tubercles, the thoracic and lumbar spinous processes and the supraspinous ligament. It also has fibers that insert on the thoracic and lumbar spinous processes, as well as the last four cervical spinous processes and on the lateral portion of the ribs. It is a main supporting muscle for the back. This muscle is the major extensor of the back and consequently exhibits many problems when it is hypertonic and not in balance with the abdominal muscles. Many subluxations found at most levels of the back are associated with the longissimus hypertonicity.

Middle Gluteal muscle: Originates from aponeurosis of Longissimus dorsi, from the Gluteal surface of the ilium and from the Sacrotuberous Ligament. It then inserts on the greater trochanter of the femur. These attachments allow the middle gluteal to extend and abduct the limb. The middle gluteal muscle would be active in rearing, kicking and forward propulsion. Innervation is provided by the cranial and caudal gluteal nerves coming from L6, and the first two sacral. There is a reflex connection with the tonic neck extensor muscles.

The Superficial Gluteal muscle originates from the tuber coxae and like the middle gluteal muscle, it inserts on the greater trochanter. So, it also has similar actions in abducting the hip and extending the hip. Also like the middle gluteal, it is supplied by the cranial and caudal gluteal nerves, the sixth lumbar and the first two sacral nerves

The Deep Gluteal muscle originates from the Ischiatic Spine and the body of the Ilium. Like the preceding two gluteal muscles, it inserts on the greater trochanter, but in addition to abducting the limb it rotates the thigh medially. Its innervation is the cranial gluteal nerve.

The Piriformis muscle supports and assists the actions of the Gluteals in that it extends the hip and abducts the leg and is innervated by the cranial gluteal nerve. The piriformis originates from the Sacrotuberous Ligament and from the last sacral vertebra. It inserts lower on the femur than the gluteal muscles. The piriformis inserts instead on the third trochanter instead of onto the greater trochanter.

EXTREMITY MUSCLES AFECTING SACRO-PELVIC BIOMECHANICS
The Biceps Femoris originates from the Ischial tuberosity and the Sacrotuberous ligament. Its three parts insert onto the Femur, the Patella and onto the Tibia. Its action then, is to stabilize the pelvis, extend the hind limb and to abduct the limb. At the spinal level, the innervation is provided by L5, L6, S1, and S2. Therefore, subluxations in these segments are critical to proper movement

The Semitendinosus muscle lies between the Semimembranosus and the caudal most belly of the Biceps Femoris. It, too, extends the hip and hock, but also flexes the stifle because of its insertion on the tibial crest, the crual fascia and the tuber calcis. The semitendinosus, like the semimembranosus is innervated by L-5, L-6, S-1 and S-2

The Semimembranosus muscle is a key muscle in providing extension of the hip as well as to adduct the hind leg. It accomplishes this through having origin on the Sacrotuberous ligament and the ischium and its insertion on the medial epicondyle of the femur. It innervation, like the Biceps femoris, is from L-5, L-6, S1 and S-2.

The Tensor fascia lata muscle, in contrast to the Semitendinosus, extends the stifle and flexes the hip. Thus it serves as an antagonist to the Semitendinosus. It accomplishes its biomechanical action by extending from origin on the Coxal tuber to insertion on the patella, the tibia and the fascia lata. Innervating nerve segments involve L6-, S-1.

The deeper lying Sartorius muscle, another of the flexors of the hip and stifle, has its origin on the crest of the ilium, the thoracolumbar fascia and the coxal tuber (actually on the tendon of the psoas minor). Its insertion is on the medial patellar ligament and the tibial tuberosity. Innervation is provided to the sartorius via the femoral nerve.

BIOMECHANICAL PATHOLOGY OF THE SACRUM AND PELVIS ASSOCIATED WITH TENSION IN PSOAS MAJOR, MINOR AND ILIOSPOAS
Having now reviewed the biomechanics and myology, the immense impact of this muscle group has in stabilization of the pelvis becomes clear. It also makes one aware how these muscles create so many of the movements that are critical to a horse’s performance.

There is a marked impact on the lumbosacral joints. An alternating unilateral contraction of the two paired Psoas major muscles create flexion and external rotation of the femur. It is a major key to forward locomotion. Bilaterally, it provides powerful flexion of the lumbosacral articulations.

By virtue of its origin/insertion, the Psoas Minor also has a powerful action on the flexion of the lumbo-sacral junction. In a pathological state of hypertonicity, it locks the lumbo-sacral articulations and does not allow movement. Between the Psoas major and minor they exert a strong positive or negative influence on the Sacro-iliac joints. If the hypertonicity is uneven, it affects the positioning of the sacrum and may be the source of a sacral apex to the left, or right, or with a base dorsal, or an apex dorsal.

The author has recognized some diagnostic aids in determining whether the psoas group of muscles is involved and in a state of hypertonicity. Because of the origin of the Psoas Major on the ventral sides of the transverse processes of the last two or three lumbars, and from the last two ribs, pressure applied in a ventral direction over the costal arch of the 16th, 17th and 18th ribs typically evokes a pain response.

Additionally, close observation of the area lateral to the last two or three thoracic vertebrae may reveal a slightly depressed area, or “hollow” in the musculature when the examiner causes the horse to do a “belly lift.” One may note that the last two or three ribs appear to be depressed and pulled ventrally.

Pressure applied ventrally over the last two or three thoracic vertebrae, and motioning of the vertebrae with contact over the dorsal spinous processes, will often evoke a response of tenderness and pain. These responses may be more closely related to a hypertonicity of the Psoas Minor and may serve to help distinguish it from the Psoas Major. Subluxations certainly co-exist, though they may be a secondary result. It is also common not to be able to relieve the hypertonicity until reduction of the subluxations and correction of the faulty proprioceptive input has occurred. With reference to “back injections, they seldom correct the problem, although relief may be engendered by the systemic effects of the injected steroid. It takes about a 5 inch needle to reach the Psoas major or minor, so it is difficult to place back injections accurately.

Correction consists of appropriate acupuncture therapy, a reevaluation of the chiropractic findings. For those practitioners of acupuncture it is note worthy that, many if not all, chiropractic “subluxations” can be ameliorated with only the acupuncture and hind limb “releases.” It is also, however, very important to note that some cases will not resolve without very careful evaluation of cervical joint motion and release of cervical dysfunction through manipulation, acupuncture, or a combination of both before resolution of the syndrome can be established. Myofascial connections likely account for the connection between cervical and psoas hypertonicity.

A STRETCHING SYSTEM TO RELEASE THE PSOAS GROUP
For the horse, the author has simply adapted limb manipulation used in physical therapy for the human patient with hypertonic psoas muscles. The goal of the manipulation of the hind limbs is to be able to bring the hind limb forward and bring it dorsally to activate the Spindle cells in the muscle belly of the Psoas thus allowing a relaxation effect. The “release” result is actually a relaxation of the Psoas group. The limb is circled so that gentle release occurs both in abduction and adduction. Typically the stretches are done in a series of three positions performing one to three repetitions on each one of the three release positions.

For the first release, the hind limb is simply picked up to a height of about six inches and maintained in alignment with the other hind limb. The limb is then gently circled in both directions, pausing for release if restrictions are felt. This is done for about 45 seconds and repeated if the horse has difficulty with the procedure. The second release movement requires that the limb be brought to a height of about 12 - 14 inches and brought forward to a position about midway between the front and hind limbs. The procedure is the same - gently rotating the entire limb in gentle circles both ways and, if tolerated, carrying the limb across the midline while circling. An assistant on the other side of the horse can be very helpful. Again, continue the release for approximately 45 seconds. Repeat if necessary. The third phase brings the limb to as much height as can be achieved and as far forward as the patient readily tolerates. Again hold the release pose for about 45 seconds. It is important to do the stretches bilaterally

Several repetitions may be required in order to achieve release. The stretches should be performed daily or even twice daily for a week to ten days. Often after the first few days, the first position stretch can be eliminated and proceed directly to the stage two release. After a week, do the stretches twice a week for two weeks, then once a week for another two weeks.

These stretches can be very hard on the operator’s back. The value of good body mechanics cannot be over-emphasized. It is important, for a successful resolution, to instruct the owner/trainer or groom to do follow-up stretches.

When hypertonicity is relieved, one may carefully add hind limb stretching in the caudal direction. Rearward stretches tend to activate the Golgi bodies at the musculo-tendonous attachments and have a net effect of increasing tension in the psoas group. Applying traction to a muscle already in severe tension/shortening state tends to only increase the tension. The proprioceptive response from the Golgi bodies “informs the central nervous system” that there is too much tension. So the efferent signal back to the muscles indicates that the muscles should tense against the strain.

When horses have hypertonicity in the psoas group, they often resist having a hind limb picked up for trimming and shoeing. Often this resistance can be ameliorated by asking the farrier to first bring the hindlimb forward, hold it for a few moments then “walk” the leg around in an abducted position to the final shoeing position. It may also be helpful if the farrier can work on the leg without too much elevation.

There is no doubt in my mind about the significance of this muscle group. However, there is significant doubt that I have achieved the ideal way to effect release of these muscles. The ideas or experience that others have for accomplishing the goal are more than welcomed by this practitioner. This includes the ideal acupuncture points for release of the various muscles involved.

When dealing with chronic and recurrent pain, as well as when trying to correct the performance deficits that these horses incur, it is most important to realize how the results of soft tissue work can markedly enhance the success of allopathic treatment, musculo-skeletal manipulation, and acupuncture treatment.