Which Ligament Prevents Excessive Anterior Rotation Of The Innominate

Interosseus Sacroiliac – forms the major connection between the sacrum and the innominate and is a strong, short ligament deep to the posterior sacroiliac ligament. It resists anterior and inferior movement of the sacrum.

The pathogenesis involves wear and tear on the joint cartilage, which over time, leads to decreased protective joint space. As bones begin to rub on one another, they attempt to make up for the lost cartilage and form bone spurs or osteophytes. Nonsurgical treatments involve lifestyle modifications such as weight loss, or minimizing activates that exacerbate pain. Physical therapies, the use of assistive devices, and medications such as NSAIDs, acetaminophen, and corticosteroids also show evidence of effectiveness. For patients whose pain is still irretraceable, surgical intervention may need to be required. Surgical options include osteotomy, hip resurfacing, and total hip replacement.[10]

Most commonly presents in adults, greater than 40 years old. Symptoms include pain, disability, ambulatory dysfunction, and stiffness/contracture. The patient typically feels pain in the anterior groin, and occasionally involving the buttocks and lateral thigh. Some patients can develop generalized hip referred pain of the knee. It is crucial to consider and/or rule out co-existing lumbar spinous pathology/radiculopathy, and ipsilateral knee conditions.

Also known as developmental dysplasia of the hip, this can arise when there are problems with the development of the hip joint in utero. Risk factors include breech presentation, positive family history, and oligohydramnios. Diagnosis is possible via physical exam with the Barlow and Ortolani maneuvers, which assess joint stability. Additional characteristic findings are leg length asymmetry as well as asymmetric inguinal skin folds.

The DA approach is becoming increasingly popular among THA surgeons. The internervous interval is between the tensor fascia lata (TFL) and sartorius on the superficial end, and the gluteus medius and rectus femoris (RF) on the deep side. DA THA advocates cite the theoretical decreased hip dislocation rates in the postoperative period and the avoidance of the hip abduction musculature.

Patients will typically present with significant pain and inability to bear weight. Approximately 10% of cases may have concurrent damage to the sciatic nerve. Treatment consists of both nonoperative and operative measures. In the acute setting, emergent closed reduction is recommended within six hours of the injury. Following a successful closed reduction, a CT scan can assess and evaluate the extent of associated osseous injuries. Additionally, the presence of incarcerated fragments in the joint is of utmost importance as appreciably large fragments will not only prevent the complete reduction of the native hip joint but these fragments also potentially can cause further intra-articular damage and chondral injuries secondary to mechanical abrasion and pathologic contact/abutment.

The sacroiliac joints form the “key” of the arch between the two pelvic bones; with the symphysis pubis, they help to transfer the weight from the spine to the lower limbs and provide elasticity to the pelvic ring (Figure 10-1). This triad of joints also acts as a buffer to decrease the force of jars and bumps to the spine and upper body caused by contact of the lower limbs with the ground. Because of this shock-absorbing function, the structure of the sacroiliac and symphysis pubis joints is different from that of most joints that are assessed. Assessment of the sacroiliac joints and symphysis pubis should be included in the examination of the lumbar spine and/or hips if there is no direct trauma to either one of these joints.1 Normally, a comprehensive examination of the sacroiliac joints is not made until examination of the lumbar spine and/or hip has been completed. If both of these joints are examined and the problem still appears to be present and remains undiagnosed, an examination of the pelvis should be initiated.

A Publication of Regenerative Medicine Techniques

Which Ligament Prevents Excessive Anterior Rotation Of The Innominate

The pelvis has been a puzzle that has consumed the greater part of my working life. The sacrum is the keystone of the puzzle, but does not function as a keystone. When the sacrum is loaded with the superincumbent weight and the joint is symmetrical, little or no movement has been observed. Measurements of movement have varied widely. The sacrum is a non-weight bearing joint that hangs from the posterior interosseous ligaments with weight loading. Movement of the sacrum on the pelvis occurs with ambulation and is moderately complex, but not incomprehensible. When the pelvis moves into asymmetry the innominate on the side of loading moves the sacrum caudad on that side, but does not move caudad on the sacrum. The innominate on the side of the trailing leg rotates cephalad as the sacrum is unloaded on that side, causing it to flex laterally toward the side of loading, rotating on a mid-sacral axis. Innominate rotation occurs on an axis through the pubic symphysis. A force-dependent oblique axis of rotation is created. The sacrum then rotates on that oblique axis to drive counter rotation of the spine to decrease the forces of loading. Static x-rays in the extreme long straddle position demonstrate the movement of the innominates on the sacrum. An error in method by an early researcher demonstrated only minute motion in the long straddle position, which has impeded further research. Pelvic dynamics has a primary effect on normal gait.

Journal of Prolotherapy. 2011;3(1):561-567.

The purpose of this article is to succinctly describe the normal movement and function of the pelvis; the aim is to dispel the myths that the sacroiliac joint (SIJ) has no important movement or function and that the function of the pelvis is so complex that it is impossible to describe. Salient features of the structure are described and related to movement. When the ligaments of the SIJ are loaded they become balanced and function as force couples. During normal gait, the pelvis moves into asymmetry and functions to drive counter rotation of the trunk to decrease the forces of loading. X-rays demonstrate movement in the extreme long straddle position with counter rotation of the trunk.

The pelvis consists of the sacrum and two innominates. White, et al. and O’Donoghue1, 2 have described the sacrum as functioning as the keystone of an arch, however, the keystone of an arch becomes wedged more tightly as weight is applied from above. The sacrum is actually suspended from the ilia by the dense posterior sacroiliac ligaments and functions as the reverse of a keystone by hanging more deeply between the ilia with increased weight loading3-6 until it reaches its limit of motion. The posterior superior iliac spines (PSIS) approximate and further movement of the sacrum downward between the innominates is blocked.5 Superincumbent weight is transferred from the sacrum through the posterior interosseous ligaments to the ilia. The SIJs are inherently non-weight-bearing joints.

With superincumbent weight loading Weisl6 found that the sacrum descends between the innominate bones when moving from a supine to an erect posture. This movement is in accord with Erhard and Bowling7 who stated that for all practical purposes the only motions permitted are gliding in a ventral and caudal direction and return to the resting position.

Primary loading of the superincumbent weight on the sacrum is on the posterior interosseous ligaments. Vukicevic, et al. found that the joints do not approximate with weight loading as long as the posterior interosseous ligaments are intact.8 When the posterior interosseous ligaments are removed the sacrum can no longer sustain weight bearing.8 The superincumbent weight is transferred from the sacrum to the ilia through the posterior interosseous ligaments.

The sacrum then rotates anteriorly and downward on a transverse sacral loading axis just posterior to the S3 segments.9 (See Figure 1.) Gracovetsky verified this bony transition point.10 This axis is essentially force-dependent and must lie between the ligaments of primary loading and the ligaments of secondary loading. The sacral axis is also forced by the iliac tuberosities, which prevent an axis within the SIJ.11 (See Figure 2.) Simultaneously with the primary loading, the caudal sacrum rotates dorsally and cephalad and causes a secondary loading on the sacrotuberous ligaments with a force in the opposite direction balancing the primary loading force.11, 12 (See Figure 3.)

In the normal standing posture the line of gravity is anterior to the sacral axis and posterior to the transverse acetabular axis. Primary loading will cause an increase in lumbar lordosis and an increase in the lumbosacral angle. The primary sacral loading also causes a primary pelvic loading. The pelvis rotates posteriorly on the acetabular axis, which flattens the lumbar lordosis and decreases the lumbosacral angle. Secondary pelvic loading creates balancing forces on both the posterior interosseous ligaments and the sacrotuberous ligaments. (See Figure 4.)

The balanced ligaments create force couples on each side. (See Figure 5.) These balanced tensile forces result in a tendency to rotate around a transverse axis created by and perpendicular to the force couples. Force couples absorb, balance and redirect various forces such as linear velocity, linear acceleration, angular velocity, angular acceleration, linear momentum, angular momentum, the rate of change of momentum, force and moment of force.11

The pelvis is very stable when it is loaded and symmetrical. In order to extend the length of the stride when walking the pelvis swings horizontally so it is asymmetrical and oblique to the line of travel. When the pelvis moves into asymmetry, the innominate on the side of loading moves the sacrum caudad, while the innominate on the side of the trailing leg rotates cephalad, each rotating on an axis through the pubic symphysis. This innominate rotation causes the sacrum to flex laterally toward the side of loading as it rotates on a force dependent mid-sacral axis in the center of the sacral loading axis. The lateral sacral flexion creates a force-dependent oblique axis from the superior margin of S1 on the side of loading to S3 on the contra lateral side.11

The line of gravity is anterior to this oblique axis and the sacrum is obliquely unstable so it rotates on that oblique axis anteriorly at the S1 segment on the side of the trailing leg and posteriorly at the S3 segment on the side of loading. The sacral rotation on the oblique axis drives counter rotation of the trunk to decrease the forces of loading on the side of loading.9 (See Figure 6.) Gracovetsky termed this a controlled instability.10 The piriformis and the sacral origin of the gluteus maximus function as prime movers of the sacroiliac joint as they work together with the sacrotuberous ligament to pull the sacrum erect so the pelvis is again symmetrical at mid-step.11 (See Figure 7.)

Other factors also help to decelerate the loading side prior to impact. The sacral origin of the gluteus maximus on the contra lateral side undergoes an eccentric contraction from mid-stance until impact. The triceps surae and toe flexors on that side also function to decelerate the side of loading. This action is usually mistaken for a push-off of the trailing leg, but in actuality the function is that of a decelerator.11, 13 Pierrynowski noted that sacral flexion and rotation is repeated each step and causes an oscillation of the sacrum with an increase in lumbar lordosis and the spinal curves from the sacrum cephalad.14 The spinal curves recover when the pelvis is again symmetrical at the single support phase. (See Figure 8.) This rhythmic sacrocranial vertebral oscillation was measured by Thorstensson, et al. in treadmill studies and found to be about 2-2.5 cm at L3 and 1-1.5 cm at C7.15 The spine functions as a decreasing waveform to damp this oscillation in order to keep the head stable while ambulating. It appears to function as a biological stabilizing system.11, 13 The posterior movement of the spine just prior to symmetry at single support then facilitates the hip flexors in the forward propulsion of the trailing leg.


What does the sacrotuberous ligament limit?

The ligament works with the sacrotuberous ligament to prevent rotation of the illum past the sacrum thus preventing excessive twisting of the pelvis, low back pain, and SIJ strain.

What is the purpose of the sacrotuberous ligament?

Anterior rotation of the innominate may also occur as a result of adductor muscle tension shifting the head of the femur forward. As the iliacus attempts to stabilise the hip, it counternutates the SIJ resulting in sacral rotation/torsion to the opposite side and pelvic rotation to the ipsilateral side.

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