Travis H. Matheney and Brian Snyder
DEFINITION
The Chiari osteotomy is primarily a “salvage” osteotomy for acetabular dysplasia in the painful, unstable hip.
It is generally reserved for hips where a congruous reduction is not possible because of arthrosis or femoral head asphericity that prevents use of one of the more standard rotational osteotomies.1,4,5
It is a single pericapsular osteotomy through the iliac (innominate) bone of the pelvis with medialization of the acetabulum and hip joint to improve posterior and lateral coverage. The ilium forms a shelf over the dysplastic, subluxated hip (FIG 1).
The goals are improved femoral head coverage, a stable articulation, and metaplastic transformation of the hip capsule to fibrocartilage to create a stable, pain-free hip.
Contraindications include severe arthrosis, age greater than 45 (relative, where arthroplasty may be a better option), and significant proximal migration of the femoral head (may prevent adequate coverage by thinner proximal ilium).5
ANATOMY
Developmental acetabular dysplasia most commonly involves deficiency of the anterior and anterolateral acetabulum.
In cases of spastic hip dysplasia, the lateral and posterolateral acetabulum is most often deficient.
The location of acetabular deficiency must be considered when planning the shape and orientation of the osteotomy and positioning of the iliac shelf over the hip joint.
Femoral head deformity may include coxa breva, coxa magna, or coxa plana.
In cases of trochanteric overgrowth, simultaneous advancement of the greater trochanter may provide improved abductor mechanics (although the risk of heterotopic ossification may be slightly increased).
This osteotomy may not provide adequate coverage in cases of high dislocation and in the pelvis in patients with advanced neurologic conditions (eg, myelomeningocele, where the ilium is very thin above the acetabulum). Therefore, careful consideration of the available periacetabular bone stock should be made before considering the Chiari osteotomy.
FIG 1 • Concept and steps of the Chiari osteotomy. A. The view required to properly perform the osteotomy. B. The proper placement of the osteotomy in the coronal plane is at the superior border of the acetabulum, just above the capsule and angled upward 10 to 15 degrees. C. The acetabular fragment is displaced medially, hinging on the symphysis pubis. D. The proposed osteotomy (dotted line) as seen from the lateral projection. E. The line of the osteotomy as seen from the inside view of the pelvis. It is above the triradiate cartilage.
The need for additional bone graft to supplement posterior, lateral, and (especially) anterior coverage is common.
This procedure does not require concentric reduction of the femoral head into the acetabulum.
It has the advantage of medializing the femoral head and decreasing the force across the hip joint by increasing the surface area of coverage.
Lateralizing the ilium to form a shelf causes obligatory shortening of the gluteal muscle length and abductor moment arm that weakens the muscle and contributes to postoperative Trendelenburg limp. However, advancing the greater trochanter can restore the resting length of the gluteus medius. Delp et al3 found that decreasing the obliquity of the supra-acetabular osteotomy may decrease the effect on the abductor lever arm.
PATHOGENESIS
The causes of advanced hip disease requiring salvage surgery are many and include late diagnosis of developmental dysplasia of the hip (DDH), spastic or neuromuscular hip dysplasia, failed prior hip procedures (reduction, periacetabular osteotomy), and acetabular trauma.
Femoral head conditions that can lead to incomplete or incongruous femoral head coverage include primary malformation, secondary avascular necrosis, slipped capital femoral epiphysis, epiphyseal–metaphyseal dysplasia, and secondary malformation from longstanding subluxation or impingement.
NATURAL HISTORY
Because this osteotomy is used as a salvage procedure for many hip diseases, it can be used to treat any of the several conditions that result in progressive, painful arthrosis and instability.
The threshold of acetabular dysplasia required to induce arthrosis is incompletely understood. However, when assessing lateral uncovering, Murphy6 found that a lateral center–edge angle less than 16 degrees on an anteroposterior (AP) view of the pelvis correlated with a significantly increased risk of requiring arthroplasty by age 65.
Spastic hip dysplasia can lead to progressive subluxation and painful dislocation in 30% to 50% of cases. It is more common in nonambulatory patients.
PATIENT HISTORY AND PHYSICAL FINDINGS
Key portions of the history include:
Personal or family history of or treatment for DDH
History of other hip disorders, including Legg-Calvé-Perthes disease
Trauma
Skeletal dysplasias
History of cerebral palsy
Birth order and weight
Description of pain and mechanical symptoms, including location, duration, activity limitation, giving way, clicking, catching, and popping
The physical examination should include gait, limb length, assistive devices, and strength.
Specific hip tests include the following:
Trendelenburg test: Demonstrates weakness in abductors
Anterior apprehension test with extension and external rotation of the hip: A positive result is a subjective noting of “apprehension” or instability by the patient.
Gluteus medius and maximus strength
Anterior impingement test (pain with passive hip flexion, adduction, and internal rotation): Test of anterior labral pathology, not just a tear
“Bicycle test” for abductor fatigability of the hip while lying in the contralateral decubitus position
Range of motion: It is important to test internal and external rotation at multiple degrees of flexion as femoral head and acetabular deformities vary. This can often aid in determining where the pathologic articulation is located.
Galeazzi sign: Demonstrates hip subluxation or dislocation
The Chiari osteotomy can increase abduction. It does not always significantly improve range of motion in other planes, and therefore preoperative flexion to 90 degrees, full (or near full) extension, and at least 10 to 20 degrees of adduction are requirements.
Gait is assessed preoperatively. It is important to discern whether any limp is antalgic, due to abductor weakness or instability. The Chiari osteotomy classically can improve antalgia and instability. However, the patient should understand that abductor weakness may not be improved.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Radiography should include weight-bearing anteroposterior (AP) views of bilateral hips, false profile of hips, and AP of hips in maximal abduction and internal rotation (FIG 2). These studies allow assessment of lateral and anterior coverage of the femoral head as well as congruency of the hip joint. Also noted will be the presence of hinge abduction.
FIG 2 • A. AP radiograph of bilateral hips and pelvis of patient with right hip with Legg-Calvé-Perthes disease. B. Frog-leg lateral radiograph of left hip with Legg-Calvé-Perthes disease.
Computed tomography (CT) scan with three-dimensional reconstruction may help in preoperatively assessing the amount and direction of acetabular deficiency.
Magnetic resonance imaging (MRI) of involved hips with radial sequences centered at the femoral head can also help with preoperative assessment of articular and labral cartilage.
DIFFERENTIAL DIAGNOSIS
DDH
Spastic hip dysplasia
Legg-Calvé-Perthes disease, avascular necrosis
Multiple or spondyloepiphyseal dysplasia
Posttraumatic hip or femoral dysplasia
NONOPERATIVE MANAGEMENT
The patient being considered for Chiari osteotomy usually presents with pain and arthrosis.
Activity and job modification and weight loss may be of benefit in delaying or mitigating the onset of arthritic symptoms.
Physical therapy may be of some benefit in increasing range of motion and strength. To date, there are no data to suggest that a specific physical therapy regimen can stop the onset of arthritis in the dysplastic hip.
SURGICAL MANAGEMENT
Hip adductor tenotomy, lengthening, or Botox can be used in an attempt to delay the onset of spastic hip dysplasia (if performed before age 4 to 6) and if hip abduction is less than 45 degrees with hips flexed and extended.
This is especially important if a varus intertrochanteric osteotomy is being performed simultaneously.
Painful, unstable, moderate to severe dysplasia with incongruent articulation with or without femoral head deformity often requires surgical correction.
Additional options to Chiari include arthrodesis, shelf procedures, and arthroplasty.
Preoperative Planning
A complete physical examination is performed and radiographs are obtained.
In the case of marked proximal migration, preoperative traction for 2 to 3 weeks may improve the position of the femoral head relative to the acetabulum, thereby increasing proximal ilial fragment coverage after osteotomy.
Positioning
The patient is placed supine on a radiolucent table with a rolled blanket bump under the operative hip.
All other bony prominences are carefully padded.
A Foley catheter is placed and prophylactic antibiotics are administered.
The use of epidural anesthesia depends on patient and surgeon preferences.
The extremity is prepared free proximally to the costophrenic margin, including the groin and buttock regions.
Approach
The ilioinguinal approach begins along the iliac crest and continues medially for about 10 cm.
The iliofemoral approach is less cosmetic but can aid in visualization in larger patients and can allow combined pelvic and femoral procedures to be done through one incision.
TECHNIQUES
EXPOSURE
The skin incision begins laterally 1 to 1.5 cm below the iliac crest, extending distally to 1.5 cm below the anterior superior iliac spine and then posteriorly over the lateral thigh or medially across the groin to 1.5 to 2 cm medial to the anterior superior iliac spine (ilioinguinal approach; fragment is interposed between the hip capsule and the TECH FIG 1A).
The tensor fascia lata (TFL) compartment is entered just lateral to its intermuscular septum with the sartorius muscle, which is retracted medially.
The TFL muscle belly is bluntly dissected off the intermuscular septum and dissection is carried proximally to the ilium. This allows visualization of the anterior ilium and easy continuation of subperiosteal exposure of the ilium (TECH FIG 1B).
Although the lateral femoral cutaneous nerve is not routinely visualized or isolated, it may be encountered underneath the fascia in the interval between the sartorius and the TFL. Therefore, care should be taken when retracting the medial structures during this dissection, the procedure, and closure of the interval.
The iliac apophysis is split (in younger patients) or subperiosteally dissected (in skeletally mature patients) to allow subperiosteal exposure of the inner and outer tables of the ilium. A moist sponge is packed along the inner table to provide retraction and hemostasis.
The outer table of the ilium is subperiosteally cleared of abductor musculature. This is carried out until a firm endpoint is reached, usually indicating that the surgeon has reached the indirect head of the rectus femoris.
Expose the anterior and superior aspects of the hip joint capsule. Identify the rectus femoris, release the indirect head at its bifurcation from the direct head, and follow it posteriorly. Incise the periosteum of the outer ilium along the border of the indirect head of the rectus and carefully dissect it off the hip capsule. This will allow you to strip the abductor minimus capsular insertion from medial to lateral off the superior capsule.
TECH FIG 1 • A. Planned incisions for both the ilioinguinal approach and the direct lateral approach to the proximal femur for additional intertrochanteric osteotomy. B. Ilioinguinal approach. Shown are the iliac crest and the direct head of the rectus femoris (arrow) deep to the tensor fascia lata compartment (tensor fascia lata retracted posteriorly). C. The outer table of the ilium is exposed. A Lane bone lever placed subperiosteally into the greater sciatic notch allows excellent visualization of the acetabular rim (arrow) all the way to the ischial spine.
A pseudoacetabulum may be present; it can feel like the capsular edge during the initial approach. Intraoperative fluoroscopy will help to discern when you have reached the edge of the true acetabulum if there is any question.
While Chiari originally described a semi-blind osteotomy, it is important to have excellent visualization of the superior hip capsule from the anterior ilium to the greater sciatic notch and along the posterior wall of the acetabulum to the ischial spine. Placement of the osteotomy must be at the capsular edge of the acetabulum (TECH FIG 1C).
OSTEOTOMY
Once the exposure is complete, a variety of methods may be used to create the osteotomy.
The supra-acetabular osteotomy is a curvilinear cut from the anterior ilium, along the capsular edge of the acetabulum, and posterior to the greater sciatic notch. We use a modification advocated by Hall that simply makes a concerted effort to create a dome osteotomy by curving the osteotomy distally when aiming for the notch to maximize the posterior coverage.
The osteotomy starts at the capsular margin and is aimed proximal and medial at an angle of about 10 to 15 degrees (see Fig 1A). This facilitates “sliding down” of the ilium over the hip joint capsule. When properly completed, the cut surface of the ilium will lie in direct contact with the hip capsule and will be in continuity with the lateral bony edge of the acetabulum.
TECH FIG 2 • A–C. Bone models demonstrate the planned supra-acetabular osteotomy using a combination of curved and dome-shaped osteotomes. D. Scoring the inner table of the ilium along the projected course of the osteotomy minimizes splintering. E. AP fluoroscopic view of the right hip during osteotomy. The osteotome enters at the edge of the acetabulum and is directed upward at an angle of about 10 to 15 degrees. F. The completed supra-acetabular osteotomy (arrow). G. Bone model representation of the posterior aspect of the osteotomy. Note the attempt to continue the osteotomy posterior to just above the ischial spine.
Chiari Conventional Method
A Gigli saw is passed through the greater sciatic notch while protecting its contents and is used in a posteriorto-anterior direction.
We find that as the starting point is crucial, it is helpful to notch the posterior column in the sciatic notch and the outer table of the ilium to create a track for the Gigli.
Authors' Preferred Method
We prefer a combination of curved and dome-shaped osteotomes used under fluoroscopic guidance to create the osteotomy.
It is often helpful to score the inner table of the ilium along the projected course of the osteotomy to minimize splintering of the inner table (TECH FIG 2A–F).
To maximize the amount of posterior coverage, an attempt is made to continue the osteotomy at the acetabular rim as far distal and posterior as possible.
This is carried out only to a level just above the ischial spine (TECH FIG 2G).
ACETABULAR DISPLACEMENT
The hip is abducted and pushed medially to displace the distal fragment (TECH FIG 3A,B).
The amount of displacement required is somewhat dependent on the amount of coverage required. One hundred percent displacement is possible and often necessary. In particular, when posterior coverage is required, the ilium is displaced posteriorly over the sciatic notch; take care to prevent compression or entrapment of the sciatic nerve (TECH FIG 3C). Displaced ilium
TECH FIG 3 • Osteotomy displacement. A. The leg is abducted and axial pressure applied to cause the acetabular fragment to displace medially underneath the ilium. B. A view looking down from above assessing the amount of superior coverage provided by the ilium. This also illustrates why augmentation with additional iliac graft may be required anteriorly. The leg is abducted and axial pressure applied to cause the acetabular fragment to displace medially underneath the ilium. C. Sawbones model demonstrating the amount of superior and posterior coverage attained with 100% displacement.
OSTEOTOMY FIXATION
The osteotomy is fixed in place with 3.5 or 4.5-mm cortical screws placed either along the iliac crest or along the outer table of the ilium under fluoroscopic guidance directed into the posterior column of the ischium (TECH FIG 4A,B).
If additional coverage is required (especially anterior), a corticocancellous graft is excised from the inner table of the ilium using a saw or osteotome (TECH FIG 4C). This fragment is interposed between the hip capsule and the transposed ilium now forming part of the roof of the acetabulum (TECH FIG 4D).
TECH FIG 4 • A,B. AP and frog-leg lateral views of the right hip after fixation of the osteotomy and completion of additional intertrochanteric osteotomy. C. Inner table of the ilium is taken for additional anterior-coverage autograft (arrow). D. Final position of osteotomy fragments, iliac crest graft between ilium and hip capsule, and additional cancellous graft placed above.
Bone graft may also be placed medially over the distal acetabular fragment to facilitate bony healing.
Stable reduction through range of motion is confirmed by fluoroscopy before wound closure.
It is important to verify in multiple planes of projection that no screw impinges on the hip joint.
WOUND CLOSURE
Drains can be used at the surgeon's discretion.
The iliac apophysis is closed with heavy, absorbable, interrupted sutures.
The remainder of the wound is closed in layers.
POSTOPERATIVE CARE
Patients are kept toe-touch weight bearing for 6 weeks.
Range of motion is allowed from full extension to 70 degrees of flexion.
Therapy is allowed for gentle passive range of motion within these limits for 6 weeks.
Weight bearing is advanced with evidence of radiographic healing.
If trochanteric advancement was performed, active abduction is limited for 6 weeks.
Patients who have a neuromuscular condition with spasticity or underwent tendon lengthenings in the same surgery are placed in either bilateral long-leg casts held in abduction by a connector bar or knee immobilizers and abduction foam pillow.
Neuromuscular patients will stay in the immobilization for 3 weeks. After 3 weeks patients come out of immobilization for gentle passive range of motion and bathing for an additional 3 weeks.
OUTCOMES
In general, reported outcomes with follow-up from 11 to 34 years are good to excellent for pain relief.1,2,4,5,7,8
Outcomes are better for younger patients with mobile hips (at least 90 degrees of flexion) and adequate corrected coverage.
COMPLICATIONS
Sciatic neuropraxia from sciatic nerve entrapment or injury during osteotomy or neuropraxia of the lateral femoral cutaneous nerve
Incomplete correction and resubluxation
Heterotopic ossification
Infection
REFERENCES
· Bailey TE, Hall JE. Chiari medial displacement osteotomy. J Pediatr Orthop 1985;5:635–641.
· Debnath UK, Guha AR, Karlakki S, et al. Combined femoral and Chiari osteotomies for reconstruction of the painful subluxation or dislocation of the hip in cerebral palsy: a long-term outcome study. J Bone Joint Surg Br 2006;88B:1373–1378.
· Delp SL, Bleck EB, Zajac FE, et al. Biomechanical analysis of the Chiari pelvic osteotomy. Clin Orthop Relat Res 1990;254: 189–198.
· Ito H, Matsuno T, Minami A. Chiari pelvic osteotomy for advanced osteoarthritis in patients with hip dysplasia. J Bone Joint Surg Am 2004;86A:1439–1445.
· Migaud H, Chantelot C, Giraud F, et al. Long-term survivorship of hip shelf arthroplasty and Chiari osteotomy in adults. Clin Orthop Relat Res 2004;418:81–86.
· Murphy SB, Ganz R, Müller M. The prognosis in untreated dysplasia of the hip. J Bone Joint Surg 1995;77A:985–989.
· Ohashi H, Hirohashi K, Yamano Y. Factors influencing the outcome of Chiari pelvic osteotomy: a long-term follow-up. J Bone Joint Surg Br 2000;82B:517–525.
· Windager R, Pongracz N, Schonecker W, et al. Chiari osteotomy for congenital dislocation and subluxation of the hip: results after 20 to 34 years follow-up. J Bone Joint Surg Br 1991;73B:890–895.