- Developmental dysplasia encompasses a wide spectrum of hip pathology ranging from a shallow acetabulum to a completely dislocated 'high-riding' hip. It is a common cause of secondary osteoarthritis in young adults and is the underlying diagnosis in up to 48% of patients requiring THA for coxarthrosis.
- The additive anomalies of the dysplastic hip concentrate high forces (increased body weight lever arm due to relative hip center of rotation (COR) lateralization) over smaller contact areas (due to poor coverage of the femoral head). Abnormally high stresses may lead to premature joint destruction.
- Treatment principles are aimed at:
i) prolonging longevity of the joint (osteotomy)
ii) replacement for advanced arthritis (arthroplasty)
- Shallow and hypoplastic with deficient bone anteriorly and laterally
- Often oval shaped with relatively narrow AP diameter
- Increased anteversion
- Lateralized center of rotation
- High riding hips; the true acetabulum may be thin and soft
- Hypoplastic femur with a straight, narrow canal and loss of metaphyseal flare
- Narrower M/L than A/P
- Increased proximal femoral anteversion
- Shortened, valgus neck
- Posteriorly displaced greater trochanter
- Femoral head may be small and aspherical
- Thickened capsule
- Contracted muscles - iliopsoas, rectus, adductors and hamstrings
- Shortened sciatic nerve
- Horizontal abductors
Imaging and Diagnostic Studies
- AP Pelvis
- Assess for degenerative changes, version, joint congruency, and dysplasia on both the femoral and acetabular side
- False Profile View (Faux Profil)
- Assess the anterior center-edge angle
- Abduction view (leg in neutral rotation)
- Assess joint congruency, coverage improvement offered
Radiographic Measurements of Dysplasia
Acetabular Angle (of Sharp)
Anterior Center-Edge Angle (of Lequesne)
Lateral Center-Edge Angle (of Wiberg)
Tonnis Angle (aka Acetabular Index)
Anterior Center-Edge Angle (of Lequesne)
- measures anterior dysplasia on the false profile view (represents a true lateral of the socket and allows assessment of the degree of femoral head anterior (un)coverage.)
- Angle formed by intersection of a vertical line through the center of the femoral head and a line extending through the center of the femoral head to the anterior sourcil
- Normal: 25 - 50 degrees; <20 is diagnostic of DDH
Acetabular Angle (of Sharp)
- measures acetabular inclination or opening
- Angle formed between a horizontal line and a line from the teardrop to lateral acetabulum
- Normal: 33 - 38 degrees
Tonnis Angle (aka Acetabular Index of the Weightbearing Zone, aka the Horizontal toit externe (HTE) angle)
- measures angle of the weight-bearing surface or sourcil
- Angle formed between a horizontal and a line extending from the medial to lateral edges of the sourcil
- Normal: ~ 10 degrees
Lateral Center-Edge Angle (of Wiberg)
- Measures femoral head lateralization an AP view of pelvis
- Angle formed by intersection of a vertical line through the center of the femoral head and a line extending through the center of the femoral head to the lateral sourcil
- Normal: 25 - 45 degrees; <20 is diagnostic of DDH
- based on the extent of proximal migration of the femoral head
- I: less than 50% subluxation
- II: 50 - 75%
- III: 75 - 100%
- IV: greater than 100% subluxation
- To calculate, first measure the height of the femoral head
- When the head is deformed, take 20% of the total pelvic vertical height as the estimation of femoral head height.
- Next, measure the vertical distance from the inter-teardrop line to the inferomedial head-neck junction
- Then, divide that distance by the femoral head height
- Example: If the head is 40 mm and it has migrated 20 mm proximally (20/40), then the head has migrated 50%.
Tönnis Classification of Osteoarthritis by Radiographic Changes
Grade 0: No signs of OA
Grade 1: Increased sclerosis, slight joint space narrowing, no or slight loss of head sphericity
Grade 2: Small cysts, moderate joint space narrowing, moderate loss of head sphericity
Grade 3: Large cysts, severe joint space narrowing, severe deformity of the head
Treatment - Arthroscopy
- Rule out acetabular version problems
- Minimal dysplasia
- Mechanical symptoms
- Loose bodies, labral tears
- Incompletely studied, few patients meet strict criteria
Treatment - Osteotomy
The goal of osteotomy on the pelvic or femoral side is to reestablish normal hip biomechanics and preserve longevity of the hip.
In adults with hip dysplasia, the anatomic abnormality is usually greatest on the acetabular side. Increasing experience and improved techniques have made pelvic osteotomies more common.
Femoral vs. Pelvic Osteotomy:
- Correction of the anatomic abnormality is performed on the side of the joint that has the greatest deformity.
- A rotational pelvic (periacetabular) osteotomy is usually required to correct the acetabular deformity
- Varus ± extension intertrochanteric osteotomy is indicated in patients where the major deformity is on the femoral side (coxa valga) and minimal acetabular deformity
- If major deformity exists on both sides of the joint, osteotomies may be required on both the pelvic and femoral sides.
- Acetabular dysplasia or Coxa Valga
- Young patient (symptomatic)
- Minimal arthritis
- Good range of motion
- Skeletally mature (periacetabular osteotomy)
- AP pelvis, true lateral
- Abduction in internal rotational
- better assessment of neck-shaft angle
- False profile view (assess anterior coverage)
- Periacetabular (Bernese) Osteotomy
- Provides powerful correction of anterior and lateral deficiency, allows medialization of acetabulum
- Indicated in skeletally mature patients
- Five cuts through one exposure (infracotyloid, pubis, ilium, quadrilateral surface, ischium)
- Anterior arthrotomy if labral symptoms
- Posterior column remains intact allowing for improved rehabilitation
- Goal Correction:
- Medialize head to within 5-15mm of ilioischial line
- Tönnis angle < 15 degrees
- Anterior and lateral CEA greater than 20 degrees
- Anteverted socket (Avoid retroversion of acetabulum)
- Chiari Osteotomy
- A capsular interposition arthroplasty
- Consider only in cases in which other reconstructions are impossible:
- femoral head cannot be centered in acetabulum
- painfully subluxated hips with early degenerative changes
- Shelf Procedures
- The acetabular roof is extended laterally, posteriorly or anteriorly, either by a graft or by turning the acetabular roof and a portion of the lateral ilium distally over the femoral head.
- Use only in cases in which no other procedure will restore acceptable joint congruity
- Concerns regarding osteonecrosis of osteotomized fragment
- Limited ability to medialize hip and/or provide anterior coverage
- Salter single innominate osteotomy
- Beneficial in children
- Difficult in adults due to non-compliant pubis symphysis
- Double/Triple Osteotomy
- Soft tissue attachments to pelvis and size of fragments limit coverage improvement
- Triple osteotomies lead to significant pelvic deformities if significant corrections are made.
Less often the primary site of deformity. The ideal candidate has a spherical, congruent head; a valgus neck-shaft angle; and minimal acetabular involvement. Look closely for poor anterior coverage on the false profile view, as minimal correction can be achieved through extension on the femoral side.
- Varus osteotomy
- Single cut - avoids additional shortening
- Upper third of lesser trochanter
- If no pelvic osteotomy consider extension (femoral head rotated posteriorly with apex anterior) for increased anterior coverage
- If excessive internal rotation, consider derotation osteotomy
- Limit correction to no more than 20 - 25 degrees due to concomitant limb shortening and abductor weakness.
- Valgus-producing osteotomy
- Indicated in patients with large, elliptical heads and large inferomedial osteophytes known as "capital drop" osteophytes (Bombelli). Must have improved congruency demonstrated on adduction views.
Dependent on severity of arthritis: more arthritis - poorer result
Periacetabular osteotomy - steep learning curve, potential for complications
Treatment - Arthroplasty
- Patients not suitable for osteotomy
- Advanced arthritis
- Older patient
- Surgeon's choice for Crowe I and II
- Trochanteric osteotomy or trochanteric slide for Crowe III and IV
- May consider a 'subtrochanteric' approach if performing a subtroch osteotomy (requires considerable soft tissue stripping)
- Restore anatomical hip center when possible
- May require anterolateral femoral head autograft
- Reserve high hip center for patients in whom majority of cup would rest on graft
- Uncemented hemispherical cup when possible (may require extra small cup with 22mm ID liner for sufficient poly thickness)
- Avoid excessive medialization for coverage (controversial)
- Requires prosthesis with narrow metaphyseal flare
- Beware of excessive anteversion - may need to place stem in a more 'retroverted' position relative to neck, or may require a derotation osteotomy.
- Cemented or uncemented depending on bone quality, age, anatomy, and surgeon philosophy
- Uncemented cylindrical prosthesis with diaphyseal fixation or modular implant that allows adjustment of version may be helpful
- May require shortening for Crowe III or IV if normal center of rotation restored.
- May shorten proximally or through subtrochanteric region
- Soft tissues
- May require releases (psoas, adductors, gluteus max insertion)
- Avoid excessive lengthening (2 - 4 cm)
- Assess sciatic nerve tension intraoperatively
- Consider intraoperative nerve monitoring / wake up test
Treatment Guidelines (These are, of course, very broad recommendations not applicable to every case!)
- Crowe I Hips
- Acetabulum: True hip center
- Femur: Component, fixation of choice
- Approach: Surgeon preference
- Crowe IV Hips
- Acetabulum: True hip center, small component
- Femur: Shortening subtrochanteric osteotomy from a posterior approach; or, transtrochanteric osteotomy with sequential proximal femoral shortening and GT reattachment
- Crowe II - III Hips
- Based on femoral morphology and patient
- Commonly, lateral acetabular bone deficiency is present secondary to wearing on a subluxed femoral head. The resulting superior bone stock deficiency makes acetabular reconstruction difficult.
- Reaming to medial wall near the true hip center may provide sufficient coverage in some cases. If not, three alternative techniques are available:
- Medialize into the pelvis (acetabuloplasty)
- Structural femoral head autograft
- High hip center
- Approach: Variable, based on planned reconstruction and need for femoral shortening
- Increased incidence of:
- Nerve palsy (3 - 15%)
- Dislocation (5-11%)
- Trochanteric nonunion (10-29%)
- Cemented stems have outperformed cemented sockets in patients with DDH.
- Placement of the socket outside of the true hip center has been shown to result in higher failure rates of both cemented sockets and stems. The use of autograft femoral head does appear to provide initial implant support and lasting restoration of bone stock, particularly when paired with uncemented implants
Treatment - Other
- If not a candidate for osteotomy or THA
- Contra-indicated in: morbid obesity, systemic arthritis, contralateral hip disease, LS spine disease, or ipsilateral knee problems (arthritis, instability, deformity).
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