- Anatomy of Acetabulum
- Pathophysiology of Acetabular Dysplasia
- Types of Pelvic Osteotomies
- Reconstructive Procedures
- Indications for Pelvic Osteotomies
- Clinical Evaluation
- How to Choose an Osteotomy for a Patient
- Gain Knowledge - Stay Healthy
Pelvic osteotomies are done to stabilize the hip and prevent early osteoarthritis in cases of acetabular dysplasia [Altered congruency of the acetabulum resulting from its maldevelopment]. The acetabulum is the large cup-shaped cavity on the anterolateral aspect of the pelvis that articulates with the femoral head to form the hip joint.
Persistent acetabular dysplasia can lead to early degenerative joint disease whereas early recognition and treatment of persistent acetabular dysplasia can prevent that. Pelvic osteotomies realign the dysplastic acetabulum and provide a biomechanically sound hip joint. Moreover, these help to preserve the natural bone and obviate the need for hip joint arthroplasty at a young age.
Anatomy of Acetabulum
The ilium, ischium, and pubis together contribute to form the acetabulum. The three bones are initially separated by a Y-shaped triradiate cartilage that begins to fuse after puberty. The fusion is complete between 20 and 25 years of age.
An acetabular cartilage complex is a unit that is triradiate medially and cup-shaped laterally and is interposed between the ilium, ischium, and pubis. It is composed of epiphyseal growth-plate cartilage and adjacent articular cartilage.
Interstitial growth within the triradiate part of the cartilage complex causes the hip socket to expand during growth. The depth of the acetabulum increases as the result of interstitial growth in the acetabular cartilage, of appositional growth at the periphery of this cartilage, and of periosteal new-bone formation at the acetabular margin.
A spherical concavity of the acetabulum develops in response to the presence of the spherical femoral head.
Any abnormality in the position of the femoral head with respect to the acetabulum during the growth period can produce an abnormal acetabulum.
For hip osteotomies, posterior ligament anatomy is important to know and understand. These are
- Sacrotuberous ligament
- Sacrospinous ligament
Different ischial cuts have been devised around these ligaments and their mobility is important in pelvic osteotomies.
The acetabulum is supplied primarily by the periosteal arteries, with contributions from numerous local arteries.
Read more about acetabulum and hip anatomy.
Pathophysiology of Acetabular Dysplasia
Acetabular dysplasia increases the stress across the hip joint due to
- Decreased acetabular weight-bearing zone
- Increased joint reaction forces due to the lateral displacement of the center of rotation of the hip
The symptoms of acetabular dysplasia are directly related to its severity. Patients with mild acetabular dysplasia may remain pain-free for 4-5 decades of life or have vague discomfort only. Abductor lurch or a limp is may be present.
Patients with severe acetabular dysplasia have pain in the second decade of life or even earlier.
Patients activity level also affect the symptoms with severe dysplasias being less painful in nonambulatory and mild dysplasia more painful with a high level of activity.
Types of Pelvic Osteotomies
Pelvic osteotomies can be divided into two groups- reconstructive procedures and salvage procedures. These are discussed further under separate headings.
These aim to realign the joint surface and produce more normal loading and to delay or prevent the development of osteoarthritis.
These are indicated in hips with
- Normal joint congruency
- No cartilage damage
- Reduce concentrically on an abduction-internal rotation
Reconstructive procedures are further of two types
- Reshaping osteotomies
- Redierctional Osteotomies
An open triradiate cartilage is a prerequisite for both types of procedures.
- Change the shape and size of the acetabulum
- Done only when the triradiate cartilage is open
- Provide anterior or lateral coverage.
Additional fixation is usually not necessary, though external immobilization is often performed.
Pemberton (pericapsular) osteotomy
The Pemberton osteotomy is used for anteriorly and laterally deficient acetabula in patients older than 18 months who still have an open triradiate cartilage.
The outer iliac cortex is osteotomized, with the cut started just above the anterior inferior iliac spine and carried out posteriorly and parallel to the capsule in the direction of the triradiate cartilage.
The inner table is osteotomized if anterior coverage is necessary.
The osteotomy is opened sufficiently to bring down the anterior and lateral edges of the acetabulum.
A wedge graft is place between the fragments to maintain correction, and a spica cast is applied for 6-8 weeks.
Redislocation, sciatic nerve palsy, and femoral head osteonecrosis are known complications.
Dega osteotomy is similar to that of the Pemberton osteotomy but the Dega osteotomy involves cutting only the lateral aspect of the ilium and thus provides posterolateral coverage. It is commonly used in dysplastic acetabula of cerebral palsy patients where it is often combined with a proximal femoral osteotomy.
These change the orientation of the acetabulum without changing the shape or dimensions. In these osteotomies, the innominate bone is completely transected, and the acetabulum is shifted as a whole into a better position.
Single innominate osteotomy (Salter)
The Salter innominate osteotomy is used to cover the anterolaterally exposed femoral head in a child over 18 months of age.
The existing acetabulum redirect and rotated through the pubic symphysis and the sacroiliac joint. The hip should be concentrically reducible and preferred age is < 6 years.
In older patients, the symphysis pubis does not remain pliable enough to allow rotation.
The osteotomy does not change the configuration of the acetabulum.
The osteotomy starts just proximal to the anterior inferior iliac spine and should exit just above the anterior inferior iliac spine.
The distal fragment is then pulled caudally and anteriorly to obtain more anterolateral coverage. A wedge-shaped graft is then inserted into the opening and fixed by 2 threaded K-wires. A single hip spica immobilization is needed.
In an unstable patient >older than 18 months, a Salter osteotomy is indicated along with an open reduction.
Kalamchi modification of the Salter osteotomy involves resecting a triangular wedge of bone from the posterior aspect of the proximal segment of the iliac bone without disturbing its far-end cortex. This provides extra stability, decreases the displacement of the distal fragment, and decreases the intra-articular pressure.
Double Innominate Osteotomy
After age 6-7 years because the stiffness of the symphysis pubis limits the mobility of the acetabulum and single innominate osteotomy is not able to serve the purpose. Here, a double innominate osteotomy is done to provide adequate coverage.
The iliac osteotomy is similar to that in the Salter procedure. A second osteotomy is performed at the medial aspect of the acetabulum through the thin isthmus between the acetabulum and the pubis. The osteotomy is subsequently fixed with 1 or 2 Kirschner wires, and a hip spica cast is applied for 6 weeks
The first cut is similar to the Salter osteotomy, and the second cut is made just lateral to the symphysis pubis. This osteotomy offers the advantage of some medialization of the hip joint and minimizes the risk of injuring the growing triradiate cartilage. An additional transverse suprapubic incision is needed though.
Triple innominate osteotomy
This osteotomy involves three cuts to further promote acetabular mobility in older children or where greater correction is necessary.
Triple innominate osteotomy include Salter osteotomy, osteotomies are made in the pubis and ischium. Different cuts are devised by different people
The ischium is divided at the tuberosity through a posteroinferior approach.
The ilium and pubis are then divided through an anterior approach.
This osteotomy is recommended after the closure of the ischial epiphysis.
It is not suitable for hip dysplasia secondary to neuromuscular conditions.
Because the cut in the Steel osteotomy is below the sacrotuberous and sacrospinous ligaments and these ligaments limit the mobility of the acetabulum, it can be used in mild to moderate acetabular dysplasia only.
The difference is in the location of the ischial cut. The ischium is accessed through a posterior approach directly over the ischial tuberosity, and the ischial osteotomy is begun proximal to the sacrotuberous ligament and directed proximally so that it exits proximal to the sacrospinous ligament.
This provides improved mobility of the acetabular fragment as the restrain of the ligaments is removed [compare with Steel].
In this variant, the ischial cut starts just below the acetabulum and runs horizontally in between the sacrospinous and sacrotuberous ligaments.
Periacetabular osteotomy of Ganz (Bernese)
This procedure osteotomizes the three pelvic bones close to the acetabulum and provides maximal freedom of rotation and tilt of the acetabular fragment in the desired position.
The osteotomy is suitable to be done in adolescents and young adults [after the closure of triradiate cartilage]
The osteotomy, by virtue of its increased mobility, allows the surgeon to reorient the acetabulum in the sagittal and coronal planes while medializing the hip joint center, thus improving the biomechanics of the hip joint.
As the posterior column of the pelvis remains intact, immediate postoperative mobilization of the patient is possible. This procedure also maintains pelvic diameter and thus does not affect normal child delivery in female patients.
For the osteotomy, 4 cuts are made under fluoroscopy.
- Distal to the acetabulum posteriorly toward the ischial spine
- In the superior ramus just medial to the iliopectineal eminence, an oblique cut to assist in translating the joint medially.
- Supra-acetabular cut is begun just distal to the anterior superior iliac spine.
- Down the posterior column of the pelvis.
Definitive fixation is achieved with 3 or 4 threaded cortical screws
Salvage procedures are indicated for relieving pain, delaying the inevitable arthroplasty and improving function in an incongruently reduced hip joint or a painful joint where redirection or reshaping osteotomies cannot be done.
These are usually done for an adolescent or adult patient with a painful, subluxated hip or for a patient with failed previous surgery.
Salvage osteotomies mainly rely on the metaplasia of the capsule to provide an extension of the articulating surface.
With increased success of Bernese periacetabular osteotomy of Ganz, the salvage surgeries may be used less commonly now.
The Chiari osteotomy involves osteotomy and lateral displacement of ilium that supports the femoral head with the interposed capsule.
The procedure brings the hip joint medially, in addition to expanding the contact area of the femoral head. Femoral head coverage is dependent on the width of the ilium.
The ilium is osteotomized between the capsule and the reflected head of the rectus. The osteotomy follows the capsular insertion in a curved line to the sciatic notch posteriorly and the inferior iliac spine anteriorly. The acetabulum is displaced medially by forced abduction with rotation through the pubic symphysis.
Osteotomy is fixed with threaded pins, supplemented with a hip spica cast for approximately 6 weeks. An additional shelf procedure is sometimes needed to provide adequate coverage.
Increased patient age and higher degrees of joint degeneration worsen the prognosis.
Shelf osteotomy or shelf acetabuloplasty provides an extra-articular buttress to prevent the subluxation of the femoral head and to expand the load-bearing area of the hip joint.
- Anterior approach, outer wall exposure only
- Identify superior acetabular edge
- Create slot 1cm deep along the edge, angled cephalad
- Remove 1 cm cortical strips from the outer table
- Insert into the slot, cutting at the desired lateral overhang
- Use remaining to fill in above slot edge
- Hold in place with reflected fascia and adductors
- Check the range of motion of the hip joint to confirm no impingement by either the femoral neck or the greater trochanter.
Indications for Pelvic Osteotomies
An abnormally shallow acetabulum can result from several causes
- Developmental Diseases of the hip
- Developmental dysplasia of the hip
- Slipped capital femoral epiphysis
- Legg-Calves-Perthes disease
- Neuromuscular conditions
- Cerebral palsy
- Charcot-Marie-Tooth disease
- Ehlers-Danlos syndrome
- Larson syndrome
Any condition that interferes with the relation between the femoral head and the acetabulum during the growth period can lead to acetabular dysplasia.
In general, the reduction of a unilateral hip dislocation is recommended up to 6-8 years of age. Bilateral affected hips tend to have better function without symptoms into adulthood.
- Clinical history
- Physical assessment
- Abductor lurch should be documented.
- Trendelenburg test
- Muscle wasting
- Limb-length discrepancy
- Range of motion
- Joint contracture
- Lumbar spine evaluation
- Pelvic obliquity
- Impingement test – Hip flexion followed by adduction and internal rotation to assess the abnormal femoral head-neck offset or labral damage.
AP view of the Pelvis with both hips in weight-bearing position
Following elements are visualized
A continuous arc extending from the proximal medial femoral metaphysis onto the superior border of the obturator foramen. Any disruption in the continuity of this line indicates that the femoral head is proximally and laterally subluxated or dislocated.
It is a dense layer of subchondral bone that normally appears as a smooth curve of uniform thickness and indicates the location of loading of the hip joint. Any side-to-side asymmetry in the thickness of the sourcil indicates abnormal focal loading.
Acetabular index of the weight-bearing zone
It quantitates the steepness of the acetabular wall or the severity of the acetabular dysplasia.
Lateral center-edge angle of Wiberg
Indicates the amount of femoral head covered by the acetabular roof.
The frog-leg lateral view gives a true lateral view of the proximal femur. The abnormal abutment of acetabular rim to the proximal femur may be noted.
Abduction-internal rotation views of both hips
It is essential for demonstrating a concentric reduction before the performance of a reorientation procedure.
False-profile view of the affected hip.
It is a true lateral view of the acetabulum and is done by rotating pelvis 25° towards the x-ray beam. The view indicates the anterior extent of the acetabulum covering the femoral head.
Arthrography is a dynamic hip study that is performed by injecting contrast medium into the hip joint and then examining the hip directly under the image intensifier. It provides a better understanding of the cartilaginous profile and a more accurate assessment of hip joint stability.
CT and MRI
Computed tomography provides a precise understanding of the pathoanatomy of acetabular dysplasia.
MRI and magnetic resonance arthrography are indicated when associated with labral pathology or cartilage damage is suspected.
How to Choose an Osteotomy for a Patient
Symptomatic medical therapy, muscle-strengthening exercises, and weight-relieving exercises can be provided initially until the execution of the pelvic osteotomy.
Selection of a particular pelvic osteotomy depends on
- Severity of the acetabular dysplasia
- Congruency of hip reduction
- Age of the patient
- In a child aged 2-10 years who has a well-reduced hip with anterolateral acetabular deficiency of a moderate degree
- Salter or a Pemberton procedure
- Shallow, capacious, or wandering type of acetabulum
- In an older child
- Open triradiate cartilage – Triple innominate osteotomy.
- Closed triradiate cartilage – periacetabular osteotomy of Ganz
- Patients with an incongruent hip joint
- If sufficient remodeling potential is present – a Salter or Pemberton
- No remodeling potential is left – Shelf or Chiari osteotomy [If not suited for periacetabular oseotomy]
- Injury to sciatic or femoral nerves
- Intra-articular extension of the osteotomy
- Osteonecrosis of the acetabular fragment
- Nonunion of the pubic osteotomy
- Heterotopic ossification
- Transient lateral cutaneous nerve palsy
- Painful ischial tuberosities
- Obstetric difficulties