DEVELOPMENTAL DYSPLASIA OF THE HIP

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DEVELOPMENTAL DYSPLASIA OF THE HIP

The term developmental dysplasia of the hip (DDH) is necessarily general and encompasses the many facets of the condition. DDH is variable at presentation and is defined as an abnormal formation of the hip joint occurring between organogenesis and maturity as a result of instability. It is intentionally non-specific to include the entire spectrum of the disorder both in time and severity. This spectrum does not include hip abnormalities caused by other diseases, such as cerebral palsy or myelodysplasia. As in many other conditions delay in detection leads to more severe consequences for treatment and prognosis. However, not all individuals at the same age of presentation have the same degree of abnormality. Therefore the concept of DDH as a spectrum in time and severity should be useful in organising one's understanding of this rather enigmatic problem.

CASE REPORT

NS., a two and a half year old girl, born full term, via spontaneous vaginal delivery with a birth weight of 2.7kg. She was the second child in the family. Once she started to walk at the age of one and a half years old, her parents noticed that she was walking with a limping gait. Clinically, she was a healthy child and walked with a Trendelenberg gait. The left lower limb was shortened. There was limited abduction and marked internal rotation of the left hip. Plain radiographs showed that the left hip joint dislocated superiorly and the acetabulum was dysplastic.

Left adductors release, open reduction of the left hip and left femoral derotation osteotomy was performed. Anterior(Smith-Paterson) approach was used. The findings were the adductors were tight, the left hip had dislocated superiorly, the capsule was markedly thickened with hourglass constriction, the labrum was thickened and inverted, the transverse acetabular ligament was also thickened, the acetabulum was filled with pulvinar and the femoral head anteverted by about 60 degrees. One third tubular plate was used to hold the osteotomy site. Postoperatively hip spice was applied.

Patient discharged well. The hip spica was changed twice, that was 3 weeks and 6 weeks after the operation. When she was reviewed four months postoperatively in the clinic, the left hip was stable with full flexion and there was slight left lower limb shortening. The surgical wound healed well. The plate over the left femur was removed eleven months postoperatively. The osteotommy site had united with no fracture gap seen.

DISCUSSION

DDH was formally known as congenital dislocation of the hip. The disease did not change but there are some very good reasons to adapt the new terminology. The change from congenital to developmental is crucial because clear evidence has shown that not all cases are diagnosable at birth. Hips that are found to be normal at birth (and even in the first few months of life) can subsequently be found to be abnormal later. In addition, this terminology acknowledges that with the passage of time changes occur.

In general the incidence in white neonates is 1% for dysplasia and 0.1% for dislocated hips. Incidence varies with race. There is four-fold increase likelihood in females and the left side is involved in 60% of cases (right 20%, bilateral 20%). Associated birth factors include breech presentation, torticolis, talipes equinovarus, metatarsus adductus and being first born. These factors are believed to be "packaging" issues. Although 2-3% of all babies are breech presentations, 16-25% of the DDH patients are born breech. Risk is relative to intrauterine position with cephalic 0.7%, footling breech 2% and frank breech 20%.

Three theories have been postulated to account for the disease process of DDH, (i) mechanical, (ii) primary acetabular dysplasia and (iii) ligamentous laxity. The mechanical theory helps to explain the increase incidence in first born and breech position as well as the association with the other packaging problems. It implies abnormal intrauterine positioning as a cause. The theory of primary acetabular dysplasia has two main proponents, Faber and Wynne-Davis. They believe that there is a primary acetabular dysplasia that predisposes to dislocation and an increased rate of acetabular dysplasia in biologic parents of patients with late DDH. Howorth and Massie support the theory of ligamentous laxity. The hormonal effects of relaxin on the collagenous structures of the infant are similar of those to the mother. Novacheck (1996) believes that combination of ligamentous laxity with mechanical factors from malpositioning can cause the femoral head to move out of the confines of the acetabulum. The changes that occur in the acetabulum are secondary to these primary problems and are the result rather than the cause of the dysplasia.

The pathologic changes in patients with DDH are the basis for understanding DDH as a spectrum in time and severity. Changes begin in the hip joint capsule. Laxity of the structure allows the femoral head to begin to migrate out of the acetabulum. Redundancy is present superolaterally. The labrum is a cartilaginous structure that normally enlarges the capacity of the bony acetabulum. With subluxation the labrum everts, and the ligamentum teres elongates. At this point the femoral head is subluxated or subluxatable. With further laxity, the femoral head dislocates and the labrum inverts. At this point, the intraarticular structures, including the ligamentum teres and the pulvinar (fibrofatty tissue in the floor of the acetabulum) may begin to hypertrophy. The labrum become pathologic in size and shape is then referred to as the limbus. With these changes, the femoral head can no longer be relocated because of the obstruction to reduction caused by the soft tissues. The psoas tendon coursing across the front of the joint capsule courses a narrowing at the isthmus. The transverse acetabular ligament, capsule, limbus, pulvinar and ligamentum teres all may have a role in preventing relocation of the femoral head and at this point the dislocation is fixed. With the passage of time, contractures can develop in the iliopsoas and hip adductors, further prohibiting positioning of the leg and efforts to reduce the hip. Ultimately, because the growth forces have been abnormal, the cartilage models of the proximal femur and acetabulum deform with several possible consequences, including flattening of the femoral head, valgus neck-shaft angle, excessive femoral anteversion, and acetabular dysplasia.

Because of the differences in severity of the dysplasia and the progressive changes that occur over time, presentation and the method of confirming the diagnosis are variable. Before walking age, the diagnosis is based on physical examination. Initially, the examination in the new-born nursery is the critical screening tool to detect loose, dislocatable, and dislocated hips. Detection up until approximately 4 to 6 months of age still depends primarily on the Barlow and Ortolani manoeuvres as part of routine well-baby examinations. At approximately 6 months of age, the family may notice a difference in the range of motion with some difficulty diapering. Occasionally the family may notice or the examination may indicate a leg length difference or an asymmetric appearance of the two legs (asymmetric skinfolds). The importance of frequent, routine screening hip examinations until walking age by an experienced examiner cannot be overemphasised. With the onset of walking, gait asymmetry (generally related to leg discrepancy) is the hallmark for identifying an abnormal hip. Occasionally, asymmetric intoeing or outtoeing is the clue. If the hip abnormality remains undiagnosed, it will likely be the onset of pain or more noticeable gait asymmetry that draws attention to the hip as the child becomes older, larger, and more well developed. (Novacheck, 1996)

Physiologic flexion, abduction and external rotation contractures are normal findings in neonatal hip examinations. Knee flexion contractures are also typical. These of course are related to normal intrauterine positioning. An asymmetric examination may be a subtle clue to the presence of hip dysplasia. Barlow provocative tests and Ortolani reduction manoeuvre is the mainstay screening examination. A helpful trick to remember is that the "O" in Ortolani stands for the hip is "out". The examination is a reduction manoeuvre to place it back to a normal position. The Barlow's provocative test then detects the subluxatable or dislocatable hip. The key to detection is not a "click" but rather a "clunk". One tries to detect abnormal movements between the femoral head and the acetabulum. Novacheck (1996) recommends minimisation of movements of abduction and adduction and to emphasis the push of the Barlow's test to try to move the femoral head posteriorly and the pull of the Ortolani reduction manoeuvre to draw the femoral head anteriorly back into place. The child should be at rest and not struggling against the examiner. The presence of asymmetric skinfolds is a sensitive but non-specific indicator of abnormality. If the folds are symmetric than it would be very unlikely that the hips are abnormal. Asymmetric is common and is present in 30% of all infants. It can be used as an indicator to raise one's index of suspicion, As time passes and secondary soft tissue contractures develop the Barow and Ortolani manoeuvres become less dependable as the hip becomes fixed in its normal position. Limited abduction, skinfold asymmetry, and the Galeazzi sign (relative shortening of the femoral segment) become more important. Bilateral hip disease is especially difficult to identify because no asymmetry is present. Findings on examination include widening of the perineum, symmetric limited abduction (less than 45o) and the appearance of abnormally short thigh segments for the child's overall size. After walking age hyperlordosis and a waddling gait are the classic findings.

Radiographs before 4 months of age can be fraught with problems and may provide a false sense of security if they seem normal. Because the secondary centre of ossification of the femoral head has not yet developed, an abnormal relationship between the upper end of the femur and the acetabulum may not be apparent. In addition, unless the femoral head lies in an abnormal position at rest, the radiograph may provide false-negative information. Therefore, the only way that the radiograph can be useful is if it is abnormal. A normal radiograph before 4 months of age cannot rule out pathology.

Figure 1. Radiographic signs of subluxation and dysplasia on an AP view. The proximal femoral ossification center has been drawn but may be absent before age 6 months (H, Hilgenreiner's line; P, Perkins' line; S, Shenton's line (broken on left); AI, acetabular index). Note the subluxation in the left hip.

( i ) The acetabular index (AI). It is an indicator of the slope of the acetabulum. The upper limit of normal values is 30o (up to 1 year), 25o (1-3 years) and 20o (3 years to adult).

( ii ) The vertical line of Perkin's (P) is an extremely valuable determinant because it can identify with considerable accuracy the relationship of the proximal femur to the acetabulum. It consists of a vertical line drawn through the outermost tip of the ossified acetabular roof and perpendicular to the horizontal Y-line of Hilgenreiner. If the proximal metaphysis of the femur lies lateral to this line, it is considered to be dysplastic or subluxated (or even dislocated) hip.

( iii ) Shenton's line (S). This is a line drawn between the medial border of the femoral neck and the superior border of the obturator foramen. A normal hip reveals a continuous line while a dislocated hip reveals a disrupted line.

( iv ) Centre-edge (CE) angle of Wiberg is also useful in assessment of the future of the joint. This is measured from the centre of the head to the superolateal edge of the acetabulum. Any angle less than 20o indicates lateral subluxation of the hip.

( v ) Von-Rosen's view - Von Rosen's lines; with the hips adducted 45o and in internal rotation, the femoral shaft should point into the acetabulum.

Ultrasonography is usually used whether as the first imaging study for infants in whom physical examination of the hip is abnormal or as a screening examination for infants who have an increased risk of dislocation of the hip. Compared with x-rays of the pelvis, ultrasound examination has several advantages -

( i ) it is a sensitive indicator of malposition, instability and lack of acetabular development;

( ii ) it is more accurate than a radiograph in defining abnormality of the hip because it shows the cartilaginous components of the acetabulum and the proximal part of the femur, which are not visualised on routine radiographs;

( iii ) with dynamic techniques, it accurately describes stability and can show subluxation with or without dislocability; in dislocated hips, examination by ultrasound assesses reducibility;

( iv ) with ultrasound, the child is not exposed to ionising radiation.

Ultrasound is invaluable in managing a child undergoing treatment particularly in the first few months of life (Benson, 1998). Taylor (1997) in his study concluded that ultrasound monitoring has led to an acceptably low level of intervention, a high reduction and minimal iatrogenic complications. Mosert et al. (2000) in their study on the results of Pavlik harness treatment for neonatal hip dislocation as related to Graf's sonographic classification, concluded that this method has become an indispensable tool in guiding their treatment policy in dislocated hips in children younger than 26 weeks of age.

An important issue is whether the sensitivity of ultrasonography leads to unnecessary treatment. Harcke et al. (1991) in their experience have indicated that, in infants who are younger than 30 days, and in whom laxity of the hip is seen on ultrasound examination but the results of clinical examination are normal, the hip almost always becomes normal without treatment.

The routine use of ultrasound screening of all newborn infants has become a controversial issue. Clarke et al. (1989) showed that the screening of all infants who had risk factors (for example, breech delivery, positive family history, deformity of the foot or torticolis) and of all infants who had abnormality on physical examination did not reduce the prevalence of late cases in the practice. Paton et al. (1999) from their study results also suggest that selective screening of infants with "at-risk" factors in isolation is of little value in reducing the incidence of late dislocation. However, they found that screening clinically unstable hips alone or associated with "at-risk" factors has a high rate of detection.

The essential, basic goals of treatment are the same regardless of the age at diagnosis. The treatment necessary to achieve those goals varies and depends on the age at diagnosis and the degree of abnormality. The goals are hierarchic and are as follows-

1. The hip must be concentrically reduced. The cartilage of the surface of the femoral head must lie directly on the cartilage of the floor of the acetabulum. There can be no intervening space or soft tissue between them.

2. When step 1 is achieved, stability must be obtained so that when the leg is allowed to move freely without support, it does not move away from the socket floor (subluxate) or dislocate.

3. All of the dysplastic features of bone and cartilage must resolve. These are the most long-lasting changes and the slowest to correct. For resolution to occur, the femoral head must be stable and located in the acetabulum. These dysplastic features include flattening of the femoral head, a misshapen acetabulum, and abnormal shape of the proximal femur (excessive femoral anteversion and increased neck-shaft angle).

All of these steps must be accomplished while avoiding complications. The two most important complications are failure to achieve all of these goals and aseptic necrosis (loss of the blood supply to the femoral head). Aseptic necrosis may be common, and its outcome can be worse than the initial problem. Failure to achieve the three goals also leads to a poor long-term outcome. Because of the progressive changes that occur over time, treatment options are frequently divided into age categories, but treatment pertinent to the case would be discussed.

Persistent Dislocation: 18 months to the Age Limit

In this age group, closed reduction is less likely to succeed; most orthopaedist would proceed straight to arthrography and open reduction.

Before the procedure of arthrography and open reduction, a period of traction will help loosen the tissue and bring the femoral head down opposite the acetabulum. However, some researchers have advocated femoral shortening rather than preoperative skeletal traction, as the later has been associated with high incidence of avascular necrosis, redislocation and poor results. Schoenecker et al. (1984) in their study of 39 hips using the method of femoral diaphyseal shortening, first described by Ombredane on 1923, reported no significant avascular necrosis or resultant deformity, low rate of redislocation (8%) and less stiffness in the hip joint. They clearly demonstrated that femoral diaphyseal shortening was preferable to traction as an aid in the operative reduction of a DDH in children who were more than 3 years old. Galpin et al. (1989) concluded that in the child who is 2 years or older, the treatment of DDH with one stage femoral shortening, open reduction, capsulorraphy, and if necessary pelvic osteotomy can produce reliable results and without an increase in the risk of avascular necrosis. The limb-length discrepancy that is produced by the shortening does not appear to cause a clinical problem.

In arthrography, a diluted radio-opaque contrast is injected into the unanaesthesised child's hip. The arthrogram will clarify the anatomy of the hip. It may demonstrate an obstruction to reduction. Typically, this is an enfolded limbus; however, a tight inferior transverse ligament and capsular constriction, secondary to encroaching iliopsoas, may be involved.

The major indications of open reduction are -

( i ) An older age. The likelihood of concentric reduction of an untreated dislocation, without interposition of soft tissue, decreases and the prevalence of avascular necrosis increases with closed treatment after a child has begun to walk. Therefore, attempts at closed reduction should be limited to children who are less than 3 years old.

( ii ) The failure of closed treatment to achieve or maintain a concentric reduction at any age.

( iii ) The failure of previous open reduction.

There are a wide variety of operative approaches used in open reduction of DDH and are found to be successful. These include medial and anterior approaches. They may be combined with femoral shortening (as mentioned above), femoral derotation and pelvic osteotomy.

There are two ways to approach the hip form the medial side: anteromedially and posteromedially. The difference is the direction that the dissection takes with respect to the adductor brevis muscle. The anteromedial approach proceeds anterior to the adductor brevis muscle and either anterior or posterior to the pectinus, to expose the iliopsoas and hip capsule. Typically a branch of the medial circumflex artery must be ligated during the anteromedial approach. The posteromedial approach develops in the interval between the adductor brevis and adductor magnus muscles directly to the hip capsule.

The advantages of medial approach are -

( i ) Simple, minimum dissection, bloodless access to the medial and inferior aspects of the hip joint.

( ii ) Direct approach to the common obstacles to reduction before the child has begun to walk, which are the psoas tendon, capsular constriction and transverse acetabular ligament.

The disadvantages are -

( i ) Poor access to the acetabulum and its internal structures, such as the neolimbus, ligamentum teres and pulvinar.

( ii ) In ability to plicate the capsule (capsular repair).

( iii ) Reconstructive procedure on the pelvis or femur cannot be accomplished.

This approach is not used in children who have begun to walk and when a dislocated femoral head has migrated proximally.

The anterior approach (Smith-Patterson approach) is a popular, comprehensive approach to the hip joint that provides superior exposure of the acetabulum, access to intraarticular structures, ability to plicate the capsule, and access to the pelvis if pelvic osteotomy is to be performed concurrently.

Dissection proceeds between the sartorius and tensor fascia late muscles, with release of the sartorius form the anterior superior iliac spine and of the straight head of the rectus from the inferior spine, to gain access to the hip capsule. This approach is appropriate for any child of any age. The disadvantages are -

( i ) Increased amounts of dissection and blood loss.

( ii ) More difficult in obtaining access to the iliopsoas and in exposure of the transverse acetabular ligament.

After open reduction, the affected hip is immobilised in a cast for a period of 3 months or so. The affected hip is usually maintained in 90o of flexion and 30o of abduction. A degree of internal rotation is usually required for congruous reduction.

During open reduction if excessive femoral anteversion (> 50o) mandates substantial internal rotation (typically more than 20-30o) to maintain the femoral had in the stable zone, proximal femoral osteotomy may be performed. The procedure may be combined with femoral shortening in children who are less than 3 years old. Derotation osteotomy is virtually always combined with femoral shortening in older children. Klisic et al. (1988) described this proceed in the study of long-term results of open reduction combined with femoral shortening, iliac osteotomy, reorientation of upper femur and medial iliopsoas transfer in older children (ranging from 7-15 years). They reported good results in two third of their patients. This procedure is not advised after the appearance of pubertal signs.

Concomitant pelvic osteotomy to redirect the acetabulum in children who are older than 18 months has been advocated. This procedure will increase the stable zone particularly in patients who have substantial acetabular dysplasia. Pelvic osteotomy combined with open reduction is an accepted practice and the major indication is the need to increase the stable zone of the hip and accelerate the development of the acetabulum towards normal.

Reduction of dislocation above the "age limit" (age where reduction of dislocation is unwise as the risk of avascular necrosis is greatly increased) in unilateral dislocation is about 10 years. The untreated hip is mobile, the patient limps but has little pain until mid life (late third or early fourth decade). With bilateral dislocation, the deformity and the waddling gait is symmetrical and therefore not so noticeable, thus the risk of operative intervention is greater because failure on one side turns this into asymmetrical deformity. So the "age limit" in this group is about 6 years. The untreated patient as reported by Crawford et al. (1999) achieved a better quality of life then many patients of similar age who have undergone surgical treatments aimed at reducing such late presenting hip dislocations.

In conclusion, DDH represents a spectrum in time and severity, which helps to explain the disease process and improve one's ability to properly screen for hip abnormalities. Regardless of age and diagnosis the goals of treatment remain the same: the femoral head must be reduced, it must be stable in the reduced position, and all dysplastic features of bone and cartilage must resolve (while complications are avoided). Early detection is important because these goals are easier to achieve at younger ages with less intervention and a lower likelihood of complications.

REFERENCES

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4. Galpin RD, Roach JW, Wenger DR, et al. One-Stage Treatment of Congenital Dislocation of the Hip in Older Children, Including Femoral Shortening. J. Bone Joint Surg. 1989;71-A:734-41

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9. Quinn RH, Renshaw TS & DeLuca PA. Preliminary Traction in the Treatment of Developmental Dislocation of the Hip. J. Pediatr. Orthop. 1994;14:636-42

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