Management of Hip Dysplasia

Courtesy: Dr Ajay Malvya, PhD, FRCS Tr and Orth, Northumbria Healthcare

 

Hip Dysplasia in Young Adults: Assessment and Periacetabular Osteotomy

Introduction

Developmental dysplasia of the hip may persist into adulthood as a spectrum ranging from mild acetabular undercoverage to substantial instability and subluxation.

In young adults, the important clinical question is not simply whether radiographic dysplasia is present, but whether the morphology is responsible for symptoms and whether joint-preserving treatment can alter the mechanical environment of the hip.

The principal goals of treatment are:

• Improve femoral-head coverage.
• Increase the functional weight-bearing surface.
• Reduce excessive contact stress.
• Improve hip stability.
• Preserve the labrum and articular cartilage.
• Delay or prevent progression to secondary osteoarthritis.
• Preserve the native hip for as long as possible.

Periacetabular osteotomy is the principal joint-preserving osteotomy for symptomatic acetabular dysplasia in a skeletally mature patient with a congruent hip and preserved cartilage.

Epidemiology

Radiographic acetabular undercoverage is relatively common in the general population. Depending on the radiographic definition and population studied, approximately 5–12% of asymptomatic individuals may demonstrate features of dysplasia.

Radiographic dysplasia does not necessarily mean symptomatic disease.

This distinction is important:

Morphological dysplasia – symptomatic hip dysplasia.

Symptoms develop through an interaction between bony morphology, soft-tissue stabilizers, activity, muscular control, pelvic alignment and individual loading patterns.

Why Does Dysplasia Become Symptomatic-

1. Reduced acetabular coverage

A shallow acetabulum provides less containment of the femoral head.

This produces:

• Increased load transmission to a smaller area.
• Higher local contact stress.
• Increased shear forces.
• Greater dependence on the labrum and capsule for stability.

2. Labral hypertrophy and injury

The labrum may become hypertrophic as a compensatory stabilizer in an undercovered hip.

Over time, repetitive loading can result in:

• Labral hypertrophy.
• Labral tearing.
• Chondrolabral separation.
• Paralabral cyst formation.
• Secondary cartilage damage.

A labral tear in a dysplastic hip should therefore prompt the clinician to ask:

Why did the labrum fail?

Simply treating the labrum without correcting significant structural instability may not address the underlying pathology.

3. Increased activity

Young adults increasingly participate in:

• Running.
• Competitive sports.
• Marathon training.
• Gym-based activities.
• Repetitive high-impact exercise.

A hip that was asymptomatic during lower activity levels may become symptomatic when subjected to greater repetitive loading.

4. Spinopelvic and muscular factors

Hip mechanics are influenced by:

• Lumbar spine alignment.
• Pelvic tilt.
• Abdominal and paraspinal muscles.
• Iliopsoas.
• Hamstrings.
• Gluteal muscles.
• Tensor fasciae latae.

Alteration of pelvic orientation can change functional acetabular coverage and hip stability.

Natural History

The dysplastic hip is subjected to abnormal load distribution.

A reduction in lateral femoral-head coverage is associated with increased risk of degenerative change. However, the relationship is not determined by a single radiographic measurement.

Important factors include:

• Severity of undercoverage.
• Anterior and posterior coverage.
• Acetabular orientation.
• Femoral morphology.
• Femoral version.
• Joint congruency.
• Labral status.
• Cartilage status.
• Age.
• Activity level.

The lateral center-edge angle is an important measurement, but modern assessment should not depend on this measurement alone. Borderline dysplasia is particularly challenging and requires assessment of several additional parameters.

Clinical Presentation

Patients rarely present saying that they have hip dysplasia.

Typical complaints include:

Pain

• Groin pain — most common.
• Lateral hip pain.
• Buttock discomfort.
• Activity-related pain.
• Pain after prolonged walking or running.

Mechanical symptoms

• Clicking.
• Catching.
• Snapping.
• Sense of giving way.

Instability

True subjective instability is less common than pain.

Abductor symptoms

Patients may develop:

• Abductor fatigue.
• Lateral hip pain.
• Greater trochanteric tenderness.
• Abductor tendinopathy.

This may occur because the abductors are working under an altered mechanical environment.

Clinical Examination

A complete examination should assess the hip, pelvis and spine rather than focusing solely on the acetabulum.

1. Gait

Assess:

• Limp.
• Trendelenburg gait.
• Pelvic tilt.
• Dynamic abductor function.
• Limb-length discrepancy.

2. Hip range of motion

Assess:

• Flexion.
• Extension.
• Abduction.
• Adduction.
• Internal rotation.
• External rotation.

Global restriction of movement, particularly in association with radiographic joint-space loss, should raise concern for established osteoarthritis and poor suitability for joint-preserving surgery.

3. Instability testing

The apprehension test is performed with:

• Hip extension.
• Abduction.
• External rotation.

Reproduction of apprehension or pain may suggest anterior instability.

The test should be interpreted together with the imaging and the remainder of the examination.

4. Rotational profile

Measure hip rotation:

• In extension.
• At 90° flexion.

Markedly increased internal rotation may suggest increased femoral anteversion.

The clinical rotational profile is useful but does not replace imaging when precise femoral version is important for surgical planning.

5. Generalized ligamentous laxity

The Beighton score may be recorded when generalized hypermobility is suspected.

It includes assessment of:

• Fifth-finger hyperextension.
• Thumb-to-forearm apposition.
• Elbow hyperextension.
• Knee hyperextension.
• Forward flexion of the trunk.

Generalized hypermobility may influence hip stability and should be incorporated into treatment planning.

Imaging

1. Plain Radiographs

Plain radiography remains the foundation of assessment.

Useful views include:

• Anteroposterior pelvis.
• Dunn lateral.
• False-profile view.
• Additional views when required.

Assess:

• Femoral-head coverage.
• Acetabular inclination.
• Acetabular version.
• Joint-space width.
• Femoral-head sphericity.
• Shenton line.
• Femoral neck morphology.
• Signs of osteoarthritis.
• Anterior and posterior acetabular walls.

Lateral Center-Edge Angle

The lateral center-edge angle assesses lateral femoral-head coverage.

It is measured between:

1. A vertical line through the center of the femoral head.
2. A line from the center of the femoral head to the lateral edge of the acetabular sourcil.

Traditionally:

• <20° – dysplasia.
• 20–25° – borderline range.
• 25–40° – generally adequate lateral coverage.

However, these are not absolute surgical thresholds. Current consensus supports using the lateral center-edge angle together with other measurements and clinical findings.

Tönnis Acetabular Index

The Tönnis angle evaluates the inclination of the acetabular weight-bearing surface.

Typical interpretation:

• Approximately 0–10° – generally normal.
• >10° – suggests increased acetabular inclination and possible dysplasia.

A high Tönnis angle indicates a more oblique weight-bearing surface and can contribute to instability.

Additional Radiographic Parameters

A comprehensive evaluation may include:

• Anterior center-edge angle.
• Anterior wall index.
• Posterior wall index.
• Femoral head extrusion.
• Femoral neck-shaft angle.
• Alpha angle.
• Shenton line.
• Femoral head sphericity.
• Acetabular version.
• Femoral version.
• Femoro-epiphyseal acetabular roof index.

These measurements are particularly important in borderline dysplasia, where a lateral center-edge angle alone may not accurately describe hip stability.

Anterior and Posterior Acetabular Coverage

The anterior and posterior walls should be carefully evaluated.

Two hips with a similar lateral center-edge angle can have very different three-dimensional morphology.

Assessment should therefore determine whether there is:

• Anterior undercoverage.
• Posterior undercoverage.
• Global undercoverage.
• Acetabular retroversion.
• Excessive anterior coverage.

Three-dimensional computed tomography can be particularly useful when plain radiographs do not adequately explain the morphology.

Computed Tomography

Computed tomography is particularly valuable for surgical planning.

It can demonstrate:

• Three-dimensional acetabular morphology.
• Anterior coverage.
• Posterior coverage.
• Acetabular version.
• Femoral version.
• Femoral-head morphology.
• Global versus focal dysplasia.
• Associated proximal femoral deformity.

Three-dimensional reconstruction can provide an excellent visual representation of the deformity.

Acetabular Version

Acetabular version should be measured at a reproducible anatomical level.

Version varies from the acetabular rim toward the center of the joint, so the precise level of measurement matters.

The transcript emphasizes evaluating the central portion of the acetabulum rather than relying on an arbitrarily selected axial slice.

This is clinically important because apparent focal retroversion may coexist with global undercoverage.

Femoral Version

Femoral version is equally important.

A dysplastic hip may have:

• Normal femoral version.
• Increased femoral anteversion.
• Reduced anteversion.
• Femoral retroversion.

An increased femoral version can contribute to instability and may need consideration during hip-preservation planning.

Conversely, reduced femoral version can compensate for increased acetabular anteversion.

Therefore:

Do not evaluate the acetabulum and femur independently. Assess the entire hip as a three-dimensional mechanical unit.

McKibbin Index

The McKibbin index represents the combined rotational relationship of:

Acetabular version + femoral version

It is useful for identifying combined rotational abnormalities.

Contemporary literature commonly considers approximately 20–50° as a normal combined range, although values vary according to the measurement technique. Higher values may indicate an unstable rotational profile, while low values may indicate an impingement-oriented profile.

It should therefore be regarded as a complementary planning parameter, not an isolated diagnostic threshold.

Magnetic Resonance Imaging

Magnetic resonance imaging is useful for assessing:

• Labral pathology.
• Cartilage damage.
• Subchondral changes.
• Synovial pathology.
• Muscle and soft-tissue abnormalities.

Magnetic resonance imaging becomes particularly useful when there is concern regarding cartilage quality or early degenerative disease that is not adequately characterized on radiographs.

Magnetic resonance arthrography or specialized magnetic resonance protocols may be used when detailed labral or cartilage assessment is required.

Routine magnetic resonance imaging is not necessarily required in every young adult with straightforward radiographic dysplasia.

Patient Selection for Joint Preservation

Before considering osteotomy, answer five questions:

1. Is the patient symptomatic?

Asymptomatic radiographic dysplasia is generally not an indication for corrective osteotomy.

2. Is the hip congruent?

A congruent, concentrically reduced hip is much more suitable for reorientation than a severely subluxated or high-riding femoral head.

3. Is the cartilage reasonably preserved?

Advanced osteoarthritis markedly worsens the prognosis.

4. Is the deformity correctable?

The acetabular and femoral components of the deformity must be understood.

5. Is the patient an appropriate age and activity level?

Younger patients with preserved cartilage generally have the best opportunity for long-term native-hip survival.

Age alone should not be treated as an absolute contraindication; cartilage status, osteoarthritis, morphology and overall patient selection are more important. Long-term evidence consistently identifies advanced age and preoperative osteoarthritis as important negative prognostic factors.

Treatment Options

Management depends on:

• Symptoms.
• Severity of dysplasia.
• Hip congruency.
• Cartilage status.
• Femoral morphology.
• Acetabular morphology.
• Patient age.
• Activity requirements.

Options include:

1. Observation.
2. Activity modification.
3. Physiotherapy.
4. Analgesic treatment.
5. Hip arthroscopy in carefully selected borderline cases.
6. Periacetabular osteotomy.
7. Femoral osteotomy when indicated.
8. Combined acetabular and femoral correction.
9. Arthroplasty for advanced degenerative disease.

Nonoperative Treatment

Asymptomatic dysplasia does not require prophylactic surgery.

For symptomatic patients without an immediate surgical indication:

• Activity modification.
• Hip and trunk strengthening.
• Abductor conditioning.
• Movement retraining.
• Core strengthening.
• Management of generalized hypermobility.
• Appropriate analgesia.
• Weight and load management.

The objective is to reduce symptoms and optimize dynamic hip stability.

Hip Arthroscopy in Dysplasia

A labral tear does not automatically mean that hip arthroscopy is the appropriate treatment.

The underlying structural problem must first be identified.

Important principle

Repairing the labrum does not correct acetabular undercoverage.

In substantial dysplasia, arthroscopic capsular violation can potentially worsen instability.

Borderline dysplasia

Patients with lateral center-edge angles approximately 20–25° represent a heterogeneous group.

Treatment requires assessment of:

• Instability.
• Femoral morphology.
• Acetabular version.
• Anterior coverage.
• Posterior coverage.
• Labral pathology.
• Capsular laxity.
• Femoral version.
• Patient symptoms.

Selected borderline hips may benefit from arthroscopy incorporating labral preservation or repair and appropriate capsular management, whereas others may be better treated with periacetabular osteotomy. There is no single lateral center-edge angle that determines the correct operation for every patient.

Periacetabular Osteotomy

Principle

The objective is to reorient the acetabulum while preserving the patient’s own joint.

By improving coverage:

Undercoverage – increased focal stress – reorientation – increased contact area – reduced stress – improved mechanics

The operation aims to:

• Increase femoral-head coverage.
• Improve load distribution.
• Reduce shear forces.
• Improve stability.
• Preserve the labrum and cartilage.
• Reduce the risk of progressive osteoarthritis.

Bernese Periacetabular Osteotomy

The Bernese periacetabular osteotomy, developed by Ganz and colleagues, is the most widely established form of periacetabular osteotomy.

Its major anatomical advantage is preservation of the posterior column.

This provides:

• A stable acetabular fragment.
• Large freedom for acetabular reorientation.
• Preservation of pelvic-ring continuity.
• Reduced disruption of the posterior pelvic column.
• Early mobilization compared with some traditional pelvic osteotomies.

The original technique remains the foundation of modern periacetabular osteotomy.

PAO Osteotomy Sequence

The classic Bernese procedure uses several controlled osteotomies around the acetabulum.

The principal cuts involve:

1. Ischium.
2. Pubis.
3. Anterior portion of the acetabulum.
4. Posterior column/ischial component.

The acetabular fragment is then mobilized and reoriented.

After satisfactory correction:

• The fragment is fixed with screws.
• Fluoroscopy confirms position.
• The osteotomies are allowed to unite.

Surgical Anatomy

This is a technically demanding procedure because major neurovascular structures lie close to the osteotomy sites.

Important structures include:

• Sciatic nerve.
• Femoral neurovascular bundle.
• Obturator structures.
• Lateral femoral cutaneous nerve.
• Rectus femoris.
• Sartorius.
• Iliopsoas.
• Short external rotators.

Detailed knowledge of three-dimensional pelvic anatomy is essential.

Intraoperative fluoroscopy is an important safety and accuracy tool.

Minimally Invasive PAO

Modern modifications have reduced the size of the incision and extent of soft-tissue dissection.

Potential advantages include:

• Less soft-tissue trauma.
• Reduced blood loss.
• Lower postoperative pain.
• Shorter hospital stay.
• Faster mobilization.
• Improved cosmesis.

However, minimally invasive PAO remains a technically demanding operation and should not be regarded as a simple procedure merely because the incision is smaller.

PAO Versus Triple Pelvic Osteotomy

Feature	Bernese PAO	Triple Pelvic Osteotomy
Posterior column	Preserved	Interrupted
Acetabular mobility	High	High but constrained by pelvic anatomy
Incisions	Usually single approach	May require additional exposure
Neurovascular exposure	Important	Important
Adult application	Established	More limited
Contemporary use	Widely used	Selected centers
Technical demand	High	High

A major advantage of PAO is preservation of the posterior column, allowing substantial acetabular reorientation while maintaining pelvic-ring stability.

Intraoperative Goals

The acetabular fragment should be positioned to provide:

• Adequate lateral coverage.
• Adequate anterior coverage.
• Appropriate posterior coverage.
• Correction of excessive acetabular inclination.
• Preservation of joint congruency.
• Avoidance of excessive lateralization.
• Avoidance of iatrogenic impingement.

Both undercorrection and overcorrection are undesirable.

Undercorrection

May result in:

• Persistent instability.
• Continued excessive contact stress.
• Persistent symptoms.

Overcorrection

May cause:

• Pincer-type impingement.
• Reduced hip motion.
• Excessive anterior coverage.
• Iatrogenic retroversion.
• Secondary joint overload.

Therefore:

The goal is optimal reorientation, not maximal coverage.

Femoral Osteotomy

Acetabular dysplasia may coexist with significant proximal femoral deformity.

Examples include:

• Excessive femoral anteversion.
• Femoral retroversion.
• Coxa valga.
• Residual deformity following childhood hip disease.

A femoral osteotomy may therefore be required in selected patients.

However:

A femoral osteotomy should not be used as a substitute for correcting significant acetabular undercoverage.

The entire femoral-acetabular relationship must be assessed.

Postoperative Rehabilitation

Rehabilitation depends on:

• Osteotomy stability.
• Fixation.
• Bone quality.
• Extent of correction.
• Associated procedures.

Typical principles include:

Early phase

• Protected weight-bearing.
• Pain control.
• Thromboprophylaxis.
• Early controlled range of motion.
• Prevention of stiffness.

Intermediate phase

• Progressive weight-bearing after adequate healing.
• Restoration of hip strength.
• Abductor strengthening.
• Gait retraining.

Later phase

• Progressive strengthening.
• Functional conditioning.
• Gradual return to sporting activities.

Radiographic evidence of osteotomy healing guides progression.

Complications

PAO is a major pelvic osteotomy and complications must be anticipated.

Neurological

• Lateral femoral cutaneous nerve dysesthesia.
• Sciatic nerve injury.
• Femoral nerve injury.
• Obturator nerve injury.

Vascular

• Arterial injury.
• Venous injury.
• Thromboembolic events.

Osteotomy-related

• Posterior column fracture.
• Stress fracture.
• Delayed union.
• Nonunion.
• Loss of correction.
• Intra-articular osteotomy.
• Excessive lateralization.

Wound-related

• Infection.
• Hematoma.
• Soft-tissue problems.

Other

• Heterotopic ossification.
• Persistent pain.
• Residual dysplasia.
• Iatrogenic impingement.
• Need for hardware removal.
• Conversion to total hip arthroplasty.

A systematic review of 24 studies involving 3,471 patients and 3,655 hips reported an overall complication rate of approximately 23.5%, although this included minor complications. Transient lateral femoral cutaneous nerve symptoms and stress fractures were among the more frequent reported complications.

Learning Curve

PAO has a substantial learning curve.

Important components of safe training include:

• Cadaveric anatomy.
• Observing experienced surgeons.
• Fellowship training.
• Stepwise supervised operating.
• Fluoroscopic familiarity.
• Understanding three-dimensional pelvic anatomy.
• Careful patient selection during the early learning period.

Technical complications are well recognized during the learning curve, particularly involving osteotomy position, fragment correction and fixation.

Outcomes

PAO can provide substantial and durable improvement in appropriately selected young adults.

Long-term outcome is influenced strongly by:

• Age.
• Preoperative osteoarthritis.
• Cartilage status.
• Degree of correction.
• Femoral-head sphericity.
• Residual dysplasia.
• Labral pathology.
• Overall hip morphology.

A systematic review and meta-analysis involving 3,655 hips found that conversion to total hip arthroplasty occurred in approximately 6% overall, although reported survivorship varied considerably with follow-up duration and patient selection. Advanced age and preoperative Tönnis grade 2 or greater osteoarthritis were important negative prognostic factors.

Historical long-term series have demonstrated good native-hip preservation when patients are carefully selected, particularly when the hip has preserved cartilage and appropriate correction is achieved.

Factors Associated With Poor Outcome

Important adverse factors include:

• Advanced osteoarthritis.
• Poor cartilage quality.
• Older age.
• Inadequate correction.
• Residual dysplasia.
• Severe femoral-head deformity.
• Poor hip congruency.
• Persistent instability.
• Significant pre-existing degenerative change.

The presence of moderate or severe preoperative osteoarthritis is particularly unfavorable.

Practical Decision-Making Algorithm

Young adult with hip pain

Clinical assessment

• Groin/lateral pain
• Instability symptoms
• Range of motion
• Apprehension
• Gait
• Rotational profile
• Generalized laxity

Standing pelvic radiographs

• Lateral center-edge angle
• Tönnis angle
• Anterior coverage
• Posterior coverage
• Joint space
• Osteoarthritis
• Femoral morphology

Three-dimensional assessment when required

• Computed tomography
• Acetabular version
• Femoral version
• Three-dimensional coverage
• Combined rotational profile

Assess cartilage and labrum when clinically indicated

• Magnetic resonance imaging
• Magnetic resonance arthrography
• Specialized cartilage assessment where available

Asymptomatic dysplasia

Observation and education

Mild/borderline dysplasia

Individualized assessment

-Physiotherapy
-Arthroscopy in selected instability-negative morphology

-Periacetabular osteotomy in appropriate instability-dominant cases

Definite symptomatic dysplasia

Periacetabular osteotomy

± femoral correction
± treatment of associated intra-articular pathology

Advanced osteoarthritis

Consider arthroplasty rather than joint-preserving osteotomy

Key Principles

1. Radiographic dysplasia is not synonymous with symptomatic disease.
2. Do not treat a labral tear without identifying the underlying mechanical cause.
3. The lateral center-edge angle is important but should never be interpreted in isolation.
4. Tönnis angle provides information about acetabular inclination.
5. Anterior and posterior coverage must also be assessed.
6. Femoral version can significantly influence hip stability and treatment planning.
7. The McKibbin index provides useful information about the combined rotational profile.
8. Computed tomography is particularly valuable for three-dimensional bony assessment.
9. Magnetic resonance imaging is valuable for cartilage and labral assessment when clinically indicated.
10. Bernese periacetabular osteotomy preserves the posterior column.
11. Optimal correction is more important than maximal correction.
12. Advanced osteoarthritis is a major negative prognostic factor.
13. Patient selection is central to successful hip preservation.
14. PAO is technically demanding and has a substantial learning curve.
15. The ultimate goal is preservation of the native hip by restoring normal or near-normal biomechanics.

Conclusion

Symptomatic acetabular dysplasia in the young adult should be approached as a three-dimensional mechanical disorder rather than simply as a low lateral center-edge angle.

A successful hip-preservation strategy requires assessment of acetabular coverage, acetabular version, femoral morphology, femoral version, cartilage, labrum, joint congruency and clinical instability.

For appropriately selected symptomatic patients with a congruent hip and preserved cartilage, Bernese periacetabular osteotomy remains the principal reconstructive procedure. Its success depends on accurate diagnosis, appropriate patient selection, precise acetabular reorientation and careful management of associated femoral abnormalities.

The central principle is simple: preserve the joint by correcting the mechanical problem before irreversible cartilage damage develops.