Michael Skutek
Steven J. Macdonald
Developmental dysplasia of the hip (DDH) is one of the most common neonatal orthopaedic problems, and it has variable morphologic patterns. The term refers to an abnormal relationship between the femoral head and the acetabulum and includes the fetal, neonatal, and infantile periods. It results in anatomic abnormalities leading to increased contact pressure in the joint and, eventually, coxarthrosis. Abnormal mechanical forces on the head of the femur may contribute to DDH; however, the primary cause is still unknown. The pathomorphologic appearance commonly includes an increased femoral neck/shaft angle, increased anteversion of the proximal femur and a shallow acetabulum. In untreated or unsuccessfully treated cases, pain and disability commonly necessitate reconstructive surgery or hip replacement at some time during adult life. However, many patients with hip dysplasia become symptomatic before the development of severe degenerative changes because of abnormal hip biomechanics, hip instability, impingement, or associated labral pathology. Several nonarthroplasty treatment options are available. The primary deformity is most commonly acetabular; therefore, for many patients; a reconstructive osteotomy that restores more nearly normal pelvic anatomy is often considered. Total hip arthroplasty for the treatment of DDH can be complex with technical challenges on both the acetabular and femoral sides.
Pathogenesis
Etiology
There are many theories as to the primary cause and pathogenesis of DDH. During embryonic development the hip joint, both femoral head and acetabulum, develop from the same primitive mesenchymal cells, and after 11 weeks the hip joint is fully formed. At birth the femoral head is deeply seated in the acetabulum and is difficult to dislocate. In a dysplastic hip, however, the femoral head can easily be subluxated or dislocated. Several theories regarding the cause of congenital dysplasia have been proposed, including mechanical factors, hormone-induced joint laxity, primary acetabular dysplasia, and genetic inheritance. Breech delivery, with the mechanical forces of abnormal flexion of the hips, can be seen as a cause of dislocation of the femoral head. It has been observed that in boys, DDH often occurs in association with concomitant deformities and oligohydramnios, whereas in girls it has been attributed to hormone-induced laxity of the hip capsule.
Although most dislocations occur during the first 2 weeks after birth, occasionally a dislocation will occur up to 1 year of age in patients documented to be normal previously. This is particularly true among infants with either a positive family history of DDH, breech presentation, or a persistent hip click on clinical examination. Hence, it is important to screen for DDH even after the newborn period.
Epidemiology
The prevalence of DDH varies considerably depending on genetic factors, habits, and cultural practices of different populations. The historical incidence was between 0.5 and 1.5 cases per 1,000 live births. By current clinical testing almost 10 to 20 newborns per 1,000 are considered to have abnormal hips and therefore normally receive some type of treatment. DDH is approximately five to eight times more common in girls than in boys with the ratio of reported prevalences ranging from 2.4:1 to 9.2:1. Breech deliveries make up approximately 3% to 4% of all deliveries, and the incidence of congenital dysplasia of the hip is increased in this patient population. A family history of DDH of the hip increases the likelihood of this condition to approximately 10%. The risk of a genetic influence was noted by Ortolani, who reported a 70% incidence of a positive family history in children with congenital dysplasia of the hip. Infants treated in a neonatal intensive care unit are also at higher risk. The incidence of DDH is as high as 50 per 1,000 births in Lapps and North American Indians; however, it is almost nonexistent among Chinese and those of African descent. In general, it is more common in white children than in black children. An increased incidence of congenital dysplasia of the hip has been reported in cultures that place infants in swaddling clothes with the hip in constant extension.
P.33
Pathophysiology
There is evidence that the presence of a spherical femoral head, concentrically reduced in the acetabulum, is a very important stimulus for the normal growth of the triradiate cartilage and the three ossification centers of the acetabular portion of the pubis, ilium, and ischium to form a concave acetabulum. The altered growth and bony deformities characteristically include increased neck/shaft and anteversion angles in the proximal femur. The femoral head is usually small, the neck may be short, the greater trochanter is displaced posteriorly, and the femoral canal is narrow. On the pelvic side, the true acetabulum is typically shallow, lateralized, anteverted, and deficient anteriorly and superiorly. Occasionally the whole hemipelvis is underdeveloped. Retrotorsion problems of the acetabulum and/or femur are also seen rarely and may lead to anterior impingement. In combination, these abnormalities lead to a decreased contact area between the femoral head and acetabulum and to lateralization of the center of hip rotation, which increases the body-weight lever arm.
The natural history of untreated DDH is variable; however, the longer DDH goes undetected, the greater is the developmental impairment of both the femoral head and the acetabulum. In adults, the natural history of untreated complete dislocation depends on the presence or absence of a well-developed false acetabulum as well as bilaterality. Back pain eventually occurs in patients with bilateral dislocations. This is thought to be secondary to associated hyperlordosis of the lumbar spine. In unilateral hip dislocations, secondary problems of limb-length inequality, deformity of the hip, ipsilateral knee pain, scoliosis, and gait disturbances are common.
Classification
The degree of hip joint pathology varies from capsular laxity to severe acetabular, femoral head, and femoral neck dysplasia. The anatomical definition of dysplasia refers to inadequate development of the acetabulum, the femoral head, or both. Anatomical classification is performed using the system of Severin (Table 5-1). It has been shown that this classification, a simultaneous evaluation of acetabular dysplasia, femoral head deformity and subluxation, correlates well with long-term radiographic, clinical, and functional outcome.
|
TABLE 5-1 Severin Classification for Radiographic Results |
||||||||||||||
|
||||||||||||||
|
TABLE 5-2 Classification of HIP Dysplasia by Hartofilakidis |
||||||||||||||
|
The classification of Crowe is a method to categorize the degree of dysplasia, i.e., the grade of subluxation. It is calculated using an anteroposterior radiograph by measuring the vertical distance between the interteardrop line and the junction between the femoral head and the medial edge of the neck. The amount of subluxation is the ratio between this distance and the vertical diameter of the undeformed head. When the femoral head is deformed, the predicted vertical diameter of the femoral head has been found to be 20% of the height of the pelvis as measured from the highest point on the iliac crest to the inferior margin of the ischial tuberosity. It is graded as grade I (<50% subluxation), grade II (50% to 75% subluxation), grade III (75% to 100% subluxation), or grade IV (>100% subluxation). An alternate classification by Hartofilakidis (Table 5-2) has also been suggested. 1
Diagnosis
Physical Examination and History
Patients with DDH should be followed carefully and regularly to detect early signs of coxarthrosis following the increased contact pressure in the joint secondary to the anatomic abnormalities. Growth disturbance of the proximal femur, which may be associated with femoral head avascular necrosis, may be a problem after treatment of DDH. History should be taken, and differential diagnosis that includes inflammatory disease, neuromuscular disease, traumatic epiphyseal slip, congenital coxa vara, and abnormal joint laxity should be considered. Incomplete femoral head coverage can also be observed in various conditions other than DDH (cerebral palsy, pelvic tilt). The natural history of dysplasia should be discussed with the patients and radiographs evaluated periodically to monitor the joint for development of arthritis.
The physical examination of the skeletally mature will have distinct features from that of the child. A careful documentation of the leg length and evaluation of impingement signs should be performed. A thorough examination is essential in eliciting signs that confirm clinical suspicions. Clinical examination begins with inspection of the lower
P.34
extremity and includes assessment of gait, limb lengths, muscle power, range of motion, and special tests.
On initial inspection of the leg, any muscle wasting should be noted. Quadriceps atrophy can be indicative of severe or chronic hip problems. The position that the leg spontaneously takes should be carefully observed. This is true not only for abduction and adduction but also for rotation, as for example a leg maintained in internal rotation can be associated with femoroacetabular impingement. Range of hip motion is commonly normal in early hip dysplasia and will begin to decrease as the degree of secondary coxarthrosis increases. A fixed adduction contracture or very limited abduction that reproduces hip pain and may produce a palpable clunk is a sign of hinge abduction present in residual Perthes disease deformity.
Macnicol 2 has described the “gear stick” sign, which will help differentiate trochanteric overgrowth from other sources of decreased hip abduction. With this test hip abduction is full in flexion but is limited in extension by impingement of the greater trochanter on the ilium or posterior wall of the acetabulum.
The external rotators of the hip are examined with the patient prone, the knee flexed, and the hip undergoing rotation. The piriformis and the posterior border of the gluteus medius may be tender on direct palpation, and occasionally this tenderness may extend to the lateral border of the sacrum. In patients with coxa vara with decreased femoral anteversion, tight external rotators as well as hamstrings may be demonstrated. Tight external rotators can also be seen in patients with acetabular retroversion because they maintain their leg in external rotation to minimize anterior impingement and can subsequently develop contractures.
Hip pain exacerbated by hip extension alone, or by external rotation in full extension, is seen in femoroacetabular impingement of various causes. If there is already a lack of full extension, the extension maneuver may force the hip into internal rotation to avoid posteroinferior contact between the acetabulum and the femoral head. If there is an osteophyte present on the posterior aspect of the femoral head, then full extension may become possible only with hip abduction.
Special Tests
The impingement test is used to delineate the acetabular rim syndrome. The hip is internally rotated as it is flexed 90 degrees and adducted 15 degrees (Fig. 5-1). This combination of movement brings the proximal and anterior part of the femoral neck into contact with the anterior rim of the acetabulum, which is the usual location for labral disease. This will elicit sharp pain from a mobile os acetabuli or a torn, degenerative, or ossified anterior acetabular labrum. An uncommon cause for a positive impingement test is acetabular retroversion or decreased femoral neck anteversion, as both of these anatomic variants result in early acetabular-femoral neck impingement with internal rotation.
The apprehension test is used to demonstrate anterior instability. The patient lies supine and the hip is adducted and externally rotated, producing discomfort and a sense of instability as the femoral head experiences deficient anterior acetabular coverage (Fig. 5-2). In a very thin patient this external rotation in extension can produce a mass in the inguinal region referred to as a “lump sign,” which represents the femoral head pushing against the anterior hip capsule.
Abductor fatigue is tested by having the patient examined in the lateral position with the affected hip up and a bicycle pedaling maneuver performed as the lateral and posterior margins of the trochanter are palpated. Provocation of this maneuver can be performed by increasing the load on the pedaling foot, which may exacerbate the pain (Fig. 5-3).
Tenderness is most commonly palpable along the posterior border of the gluteus medius. Under direct palpation, often a crepitation may be felt over the trochanteric bursa, which the patient may have previously described as a sensation of “sand in the joint.''
A true hip click or clunk has been described by some authors as a sign of labral disease. Our experience, however, has demonstrated that in dysplastic hips with deficient anterior coverage, or in other causes of anterior femoral head prominence such as increased femoral neck anteversion, if the extremity is actively flexed and externally rotated and then brought back slowly toward extension and neutral rotation, at between 40 degrees and 50 degrees of external rotation, the iliopsoas tendon snaps over the uncovered femoral head. With the same maneuver in neutral or internal rotation, this click is eliminated.
Clinical Features
Activity-related groin pain is a common sign in patients with DDH. It is often reported with hyperextension and external rotation of the hip and thought to be secondary to subluxation of the femoral head. Locking, giving way symptoms, and catching may indicate associated labral or chondral pathology. Patients with subluxated hips usually have symptom onset at a younger age than those with complete dislocations. Invariably, radiographic subluxation leads to degenerative joint disease. The rate of deterioration is related directly to the severity of the subluxation and the age of the patient. Patients with the most severe subluxations usually develop symptoms during the second decade of life. Those with moderate subluxation often present at 30 to 40 years of age, and those with minimal subluxations experience symptoms usually in their 40s or 50s. Patients with complete dislocations and high-riding hips often will not develop problems until the fifth or sixth decades of life. It is rare to see radiographic changes of degenerative joint disease such as joint space narrowing, osteophyte formation, or subchondral cysts at symptom onset. The only radiographic signs may be subchondral sclerosis in the weight-bearing area. After clinical symptoms and radiographic signs of degenerative joint disease appear, progression is rapid.
Diagnostic Workup Algorithm
The diagnostic workup consists of the history and clinical examination already described and the radiographic imaging as described below. DDH-related problems such as back pain, secondary problems of limb-length inequality,
P.35
deformity of the hip, ipsilateral knee pain, scoliosis, and gait disturbances need to be considered.
|
Figure 5-1 Impingement test. |
Radiologic Features
Selection of appropriate imaging techniques in patients with DDH depends on age and differs for diagnostic versus management situations. Plain radiographs, including an anteroposterior view of the pelvis and lateral view of the hip, are the first steps in imaging evaluation.
Patients with severe degenerative changes in which an arthroplasty is indicated will not routinely require additional imaging. However, occasionally with complex cases a three-dimensional CT scan with reconstructions may give additional information. Further imaging is required in patients in whom joint salvage procedures are being considered. A false profile image, which is a standing lateral hip image, will give valuable information on anterior femoral head coverage and aids in preoperative planning. Abduction and adduction views should also be obtained to assess joint congruency and containment. Labral pathology is best evaluated with MR/MR arthrogram. It is normally indicated in the rare patient presenting with labral pathology with minimal dysplasia in whom arthroscopy alone may be given consideration. MRI can also be helpful in the evaluation of loose bodies, chondral defects, and synovial disease.
|
Figure 5-2 Apprehension test. |
The anteroposterior radiograph should be evaluated by the assessment of the Shenton line, the Tonnis angle, the center edge (CE) angle, and the extrusion index. The Shenton line is drawn between the medial border of the neck of the femur and the superior border of the obturator foramen. In the normal hip this line is an even, continuous arc, whereas in a dislocated hip with proximal displacement of the femoral head, it is broken and interrupted.
A standard anteroposterior pelvic radiograph may not demonstrate the full degree of hip dysplasia that is clearly present on a false profile view. The false profile image should be evaluated with regard to the ventral center edge angle.
The Severin anatomical classification is a simultaneous evaluation of acetabular dysplasia, femoral head deformity, and subluxation (Table 5-1). It has been shown to correlate well with long-term radiographic, clinical, and functional outcomes. Degenerative changes are classified according to Tonnis on a scale from absent (grade 0) to severe (grade III).
P.36
Treatment
There is great variability in the presentation of dysplastic patients with regard to age, severity of radiographic changes, symptoms, and patient expectations. Treatment alternatives vary with each of these factors.
Nonoperative Options
Nonsteroidal anti-inflammatory agents can be used, and high-impact activities should be avoided. Although controversy does exist, most would agree that the surgical alternatives should be reserved for symptomatic patients with severe limitation of their daily activities.
Surgical Options
The nonarthroplasty surgical procedures include arthroscopic surgery, pelvic osteotomy, femoral osteotomy, arthrodesis, and resection arthroplasty. The main goal of these procedures is to decrease pain. Arthroscopy can be beneficial when symptoms seem to be related only to labral tears or lose bodies in the absence of severe structural abnormalities about the hip. Fusion and resection arthroplasty are rarely, if ever, indicated given current treatment alternatives. The operative treatment of residual dysplasia of the hip after skeletal maturity is based on the assumption that the dysplasia, if left untreated, will lead to secondary osteoarthritis of the hip.
Many surgical procedures on the pelvis have been described for late salvage in cases of persistent acetabular maldevelopment and instability (Table 5-3). The common goals of such interventions are the provision of improved acetabular coverage, enhanced femoral head–acetabular congruence and containment, and improved joint biomechanics. Some osteotomies are also expected to slow down progression of degenerative changes by better distributing forces applied through the hip joint, and they may provide better distribution of bone stock that might facilitate further reconstructive surgery if required in the future. In the presence of severe degenerative changes, total joint arthroplasty gives the most predictable outcomes.
|
Figure 5-3 Abductor fatigue test (bicycle test). |
Arthroscopic Surgery
Hip arthroscopy may be considered for selected, mildly dysplastic hips with mechanical symptoms related to either loose bodies or labral tears. Retrotorsion problems of the acetabulum and femur should be ruled out before offering this procedure. Arthroscopic debridement and lavage in the presence of degenerative changes is a less predictive procedure. Arthroscopy alone has limited applications in the dysplastic hip because the underlying bony deformities cannot be addressed.
Osteotomy
Procedures to reorient the articulating surfaces of the hip joint are attractive in the patient with hip dysplasia. Increased joint congruity after reorientation of the osteotomized fragment allows load transmission through a broader area, which can reduce articular surface pressure. In general, osteotomies should be offered to young patients who have symptomatic hip dysplasia without excessive proximal migration of the center of rotation, reasonably well-preserved range of motion, and no more than mild degenerative changes on the articular surface (Fig. 5-4, Table 5-3). The Salter single innominate osteotomy is beneficial in children, but often is insufficient in adults because it allows limited correction (approximately 10-degree change in Tonnis angle) owing to the decreased flexibility of the symphysis pubis. It also lateralizes the hip joint, which is undesirable in dysplastic hips. So-called salvage procedures such as the Chiari iliac osteotomy and shelf procedures still may be indicated in some severely dysplastic hips that cannot be rendered congruent by a reconstructive osteotomy because of the discrepancy in sizes and shapes between the femoral head and the acetabulum.
P.37
|
TABLE 5-3 Osteotomies for Developmental Dysplasia of the HIP (DDH) in Adults |
||||||||||||||||
|
Bernese-Ganz Osteotomy
This osteotomy is currently the acetabular procedure preferred by many reconstructive surgeons. The procedure is indicated in patients with a closed triradiate cartilage. It requires only one incision and is performed with a series of straight, relatively reproducible extra-articular cuts. 3 It allows large corrections of the osteotomized acetabular fragment in all directions. The osteotomy includes a partial osteotomy of the ischium, a complete osteotomy of the superior pubic ramus, an incomplete osteotomy of the ilium, and a final cut connecting the ileal cut to the ischial cut. The posterior column of the hemipelvis remains intact, allowing early ambulation. The periacetabular fragment is mobilized once the osteotomies are completed.
Correction is considered satisfactory when the acetabular sourcil is horizontal, the femoral head is congruous, appropriate version has been obtained, the femoral head is medialized to within 5 to 15 mm of the ilioischial line, and the Shenton line is near normal. The joint may be opened and evaluated for labral lesions.
The periacetabular osteotomy has proven to be an effective technique for surgical correction of a severely dysplastic acetabulum in adolescents and young adults (Fig. 5-5). The early clinical results have been reported in several series, including a series by Clohisy et al. 4in which results were reported as very good at an average of 4.2 years postoperatively. If a total hip arthroplasty is necessary at a later stage, this can be done safely in patients with a previous periacetabular osteotomy and should provide excellent results. 5 The Bernese periacetabular osteotomy can also be used successfully to treat neurogenic acetabular dysplasian skeletally mature patients. 6
Chiari Osteotomy
The Chiari osteotomy is a capsular interposition arthroplasty and should be considered only in those instances in which other reconstructions are impossible: when the femoral head cannot be centered adequately in the acetabulum or in painfully subluxated hips with early signs of osteoarthritis. This procedure deepens the deficient acetabulum by medial displacement of the distal pelvic fragment and improves superolateral femoral coverage. The Chiari procedure is an operation that places the femoral head beneath a surface of joint capsule and cancellous bone with the capacity for regeneration and corrects the lateral pathologic displacement of the femur. The biomechanical effect of medial weight-bearing transfer is to unload the femoral head and reduce the demands on the abductor musculature. The angle of osteotomy is 10 to 20 degrees relative to the plane of the upper acetabular margin, and the lower segment is displaced medially by approximately half its width. The superior fragment of the osteotomy then becomes a shelf, and the capsule is interposed between it and the femoral head.
Shelf Operations
Shelf procedures are useful for subluxations and dislocations that have been reduced and in which no other osteotomy will establish a congruous joint with apposition of the articular cartilage of the acetabulum to the femoral head. In a classic shelf operation, the acetabular roof is extended laterally, posteriorly, or anteriorly, either by a graft or by turning the acetabular roof and part of the lateral cortex of the ilium distally over the femoral head.
Femoral Osteotomy
An intertrochanteric osteotomy is indicated when the femur is the primary site of deformity or when a pelvic osteotomy alone does not provide sufficient correction. Several requirements must be fulfilled before proposing an isolated femoral osteotomy. First, the osteotomy must be able to provide satisfactory correction of the deformity. Second, the preoperative range of motion
P.38
should be sufficient to allow a functional arc of hip motion after correction. Third, the joint should be congruent in the proposed position of correction. Most patients with hip dysplasia who are candidates for isolated femoral osteotomy have coxa valga with mild acetabular deformity.
|
Figure 5-4 Osteotomy options. |
Arthroplasty
Total Hip Replacement.
In patients with symptomatic end-stage coxarthritis secondary to hip dysplasia, total hip arthroplasty (THA) is the procedure of choice. As described elsewhere in the text, there are specific challenges on both the acetabular and femoral sides of the reconstruction. Based on the severity of subluxation, a number of different options are available for acetabular/femoral reconstruction (Table 5-4).
|
TABLE 5-4 Total HIP Arthroplasty Reconstruction Options Based on Severity of HIP Dysplasia (Crowe Classification) |
||||||||||||||||||||
|
||||||||||||||||||||
Surgical Technique.
The goal of acetabular reconstruction is to place the acetabular component in the true acetabulum. There may be bone stock deficiency superiorly depending on the degree of dysplasia and additionally the true acetabulum may have increased, or rarely decreased,
P.39
version, which has to be assessed at the time of component placement. Occasionally the patient's femoral head may be used as an autograft if the component is excessively uncovered (>25%) superolaterally. Cementless acetabulum components with screw fixation are preferred. When choosing the optimal location of acetabular component placement, the advantages of a normal anatomic location must be balanced with the need to provide sufficient acetabular implant coverage. Whenever possible, the acetabular reconstruction should seek normalization of the hip center. Extra-small acetabular implant sizes often are required. Small femoral head sizes to preserve adequate polyethylene thickness may be needed. Because most of these patients are younger, an alternate bearing such as highly cross-linked polyethylene, ceramic on polyethylene, ceramic on ceramic, or metal on metal may be considered.
|
Figure 5-5 Preoperative anteroposterior and false views demonstrating acetabular dysplasia. Postoperative images 6 years following corrective Bernese pelvic osteotomy with preservation of joint space. |
P.40
The femoral anatomy may demonstrate excessive femoral neck anteversion, a valgus neck/shaft angle, metaphyseal-diaphyseal mismatch (with a very narrow medullary canal) and prominent greater trochanter in cases of high dislocation. A shortening femoral osteotomy may have to be performed to minimize injury to the sciatic nerve owing to leg lengthening. Often a modular cementless femoral component is ideally suited to address the host bone abnormalities.
THA has proven to be a reliable procedure, even in patients younger than 30 years of age, especially when other alternatives such as arthrodesis or resection arthroplasty are considered. Pain relief in patients with hip dysplasia after total hip arthroplasty parallels the excellent results of total hip arthroplasty in the general population. Long-term survivorship remains a challenge in this often younger patient population; however, with the advent of alternate bearings with improved wear characteristics this may improve in the future.
Conclusion
Developmental dysplasia in the adult presents as a varied and complex clinical scenario to the adult reconstruction surgeon. A thorough knowledge of the natural history, the physical and radiographic evaluation, and the various treatment alternatives is required to manage these challenging cases.
Reference