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Hip Disorders Supplement

How to Choose the Right Patient for Correction of Acetabular Dysplasia After Skeletal Maturity

Matheney, Travis MD

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Journal of Pediatric Orthopaedics: July/August 2013 - Volume 33 - Issue - p S13-S20
doi: 10.1097/BPO.0b013e318293e5d0
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Abstract

The “how to” of surgical correction for symptomatic acetabular dysplasia is well described.1–5 The mid-term to long-term outcomes are good to excellent in the vast majority of properly selected patients.6–15 The selection of the proper candidate for surgical treatment depends on several factors. The first and most important factor is the recognition of dysplasia-related pain versus other etiologies. Once you have made the diagnosis that dysplasia exists, the next biggest concern is whether it should be treated surgically or not.

The purpose of this paper is to provide a brief description of the workup for symptomatic acetabular dysplasia in the skeletally mature patient, current criteria for patient selection, outcomes after surgical correction, and factors predicting poor long-term outcome. I will be focusing on acetabular dysplasia in isolation from other coexisting conditions.

HISTORY

There is little debate over what should be done for hips that are at the “extremes.” With regard to infant and juvenile developmental dysplasia of the hip (DDH), dislocated and subluxated hips are treated without much discussion in an effort to maximize function and prevent “certain” painful arthrosis at a young age. On the other end of the spectrum, “older” patients and hips with advanced arthrosis on radiograph have commonly been deemed not appropriate for hip preservation surgery. In the late teen and adult patient other considerations come into play when deciding whether to correct acetabular dysplasia such as presence of pain, activity level, and are there ways to modify activity to stop the hip from hurting. There are indeed instances where DDH is confirmed on radiographs taken for a purpose other than hip pain. These present a uniquely challenging situation. As we do not truly know the natural history of DDH, it is difficult to make a surgical recommendation in the absence of symptoms. Therefore, a general recommendation is to educate the patient about the warning signs of impending arthrosis and when follow-up imaging would be indicated.

Ultimately, what we and our patients want to know is the natural history of acetabular dysplasia, outcomes after joint-preserving treatment, and whether the patient will have a long-lasting, pain-free result from joint-preserving surgery or would it be better to wait for a joint replacement. Unfortunately, there are few true natural history studies that delineate exactly which hips will go on to end-stage arthritis based upon what we can see at initial evaluation when the patient presents at a young age. Murphy et al16 evaluated hips that underwent arthroplasty and found that no hips with a lateral center-edge angle of >16 degrees or an acetabular index >15 degrees required arthroplasty by the age of 65 years. Outcomes after surgical treatment will be discussed later.

COMMON PRESENTATIONS OF ACETABULAR DYSPLASIA

Assuming the patient has not been followed through their adolescence for previously known hip dysplasia, Nunley et al17 found the average age at presentation of patients with symptoms is 24 to 30 years. That said, an estimated 25% to 30% have had prior treatment for DDH.9,13

Most patients recount moderate-to-severe pain daily. Pain is typically localized to the groin and lateral hip but may also present as referred pain down the anterior thigh, to the buttock, and to the medial knee. The quality of pain can be sharp or dull. Some are inhibited by their discomfort enough to cause significant activity modification as increasing activity causes increased pain. Types of activity that had to be limited not only included running and impact activities but also walking and prolonged sitting. Not uncommonly the true cause of the patient’s pain will go undiagnosed for a prolonged period of time. Delays in diagnosis most commonly arise from failure to recognize the cause of pain as secondary to dysplasia assigning the pain solely to the commonly present labral injury and then treating the labral injury alone. Other etiologies entertained include muscle/soft-tissue strain and overuse injuries. These diagnoses can also lead to referrals to other health care providers including physical therapists, chiropractors, acupuncturists, and orthopaedic surgeons.17

Mechanical symptoms have also been described. These included descriptors such as locking, clicking, catching, popping, and giving out. At least one of these was noted in 80%.17

PHYSICAL EXAMINATION

The physical examination can often tell you a great deal about the presence of intra-articular hip pathology. It is important to determine the location and inciting activities for pain as well as the presence of gait abnormalities. Approximately 50% in Nunley et al17 study presented with a limp and 40% with a Trendelenburg sign. To this point, the abductor muscles can show weakness and/or early fatigue on direct testing. Moreover, the presence of some of these symptoms preoperatively seemed to predict long-term outcome after joint-preserving surgery.9,10 Therefore, as the primary goal of surgical correction is the relief of symptoms, paying close attention to the presence or absence of various symptoms may be of benefit in predicting the success of treatment.

On supine examination, range of motion testing may show maintained “excellent,” almost supraphysiological motion in the early stages with minimal arthritis. However, especially in unilateral cases, when arthritis has begun decreases in range of motion may be present.

Special tests to assess for intra-articular problems include the anterior and posterior impingement tests. As the names imply these 2 tests are meant to look for symptomatic areas of the labrum at the end points of motion between femoral neck and acetabulum along the anterior and posterior aspects of the hip. They are tested by: flexing, adducting, and internally rotating the hip or extending, abducting, and externally rotating the hip, respectively. An important point is that other conditions can mimic intra-articular hip pathology. One example is how a “positive” anterior impingement sign can be elicited in the presence of iliopsoas tendonitis or other soft-tissue compression. This is of particular significance if the patient has previously undergone hip surgery where scar tissue in the area can become or remain symptomatic in the region. Additional examination to differentiate tendonitis from labral pathology includes direct testing of the iliopsoas through strength testing (resisted straight leg raise) and stretch testing. The latter can be accomplished by extending and internally rotating the hip and placing the tendon on stretch. You can test the iliopsoas’ contribution to symptomatic “snapping” by one of several methods. I prefer to start with the leg fully extended then ask the patient to abduct and flex the hip to 90 degrees followed by adduction and extension. During this maneuver I place additional pressure at the anterior iliac brim over the region of the iliopsoas in an attempt to palpate the snapping phenomenon. Either one of these maneuvers can be helpful in discerning whether the groin pain and snapping the patient is experiencing is secondary to an irritated tight iliopsoas or labral pathology.

Iliotibial band tightness and tendonitis can also mimic the lateral pain of intra-articular hip pathology. When irritated it can also cause pain and/or snapping. On physical examination, it is tender directly over the greater trochanter. Special tests include the Ober test which can be performed with the patient lying on the unaffected side, extending the affected hip, and either adducting the hip or allowing the hip and lower leg to externally rotate with gravity (Fig. 1).18 This test is meant to elicit painful stretch of the iliotibial band and the tensor fascia latae.

FIGURE 1
FIGURE 1:
The Ober test. Line drawing illustrating the maneuvers for an Ober test of the tightness in the iliotibial band. Note that the arrows show the practitioner can allow the foot to rotate upward and downward to check tightness.

If question remains as to the true etiology of the patient’s hip pain, either intra-articular or peri-iliopsoas injection can be both diagnostic and therapeutic. These can be performed in the operating room with fluoroscopic guidance and sedation or, if available, in the office with ultrasonographic guidance. The latter has the added benefit of direct patient feedback within minutes of injection and can allow both to be injected in sequence within minutes of one another.

IMAGING

An estimated 90% of hip arthrosis and subsequent arthritis is felt to be secondary to either hip dysplasia or a pathomorphology between femur and acetabulum that creates femoroacetabular impingement (FAI).19,20 Therefore, a thorough understanding of the imaging studies required to fully assess DDH (and FAI) is critical. The imaging that forms the basis for much of the workup includes plain radiographs and magnetic resonance imaging (MRI). Arthrograms are being utilized less with the increased availability of MRI. Computed tomography scans remain a good adjunct in some cases to fully assess 3D nature of combined femoral and acetabular deformity as well as more accurately measure the amount of acetabular version.

Plain Radiographs

The most frequently ordered radiographs of the hip include: an anteroposterior (AP) pelvis in either the standing or supine position and a frog leg lateral of the “hip.” The latter is a great second image to assess the femur. However, it adds little to the assessment of the acetabulum. Therefore, to complete the assessment for DDH it is mandatory to include a false profile image of the acetabulum.21

From the former radiograph one can assess lateral coverage of the femoral head (lateral center-edge angle of Wiberg,22 normal 22 to 35 degrees, Fig. 2), and the acetabular inclination or Tönnis roof angle23 (normal between 0 and 10 degrees, Fig. 2). Additional characteristics of the acetabulum seen on the AP view include: amount of osteoarthrosis (Tönnis grade 0 to 3),23 the ischial spine sign (indicative of acetabular retroversion),24 Shenton line (when broken can be indicative of femoral head subluxation),25 posterior wall sign (positive if posterior wall of the acetabulum is medial to the center of the femoral head indicative of global dysplasia),26 and the cross-over sign (positive when the anterior acetabular wall shadow crosses over the posterior wall shadow indicative of possible anterior overcoverage of the femoral head and/or acetabular retroversion).26

FIGURE 2
FIGURE 2:
AP radiograph of the pelvis. The lines on the left side of the image are indicating the Tönnis acetabular roof angle and the lines on the right indicating the lateral center-edge angle of Wiberg.

As anterior coverage of the femoral head can be deficient alongside or in isolation from lateral undercoverage in DDH it is important to obtain a false profile radiograph. This is a lateral view of the acetabulum and is used to measure the anterior coverage of the femoral head or the anterior center-edge angle (normal, between 22 and 35 degrees, Fig. 3) as well as further appreciate joint space narrowing and/or subluxation that may not be evident on the AP view (Figs. 4A, B).

FIGURE 3
FIGURE 3:
False profile radiograph of the acetabulum. The lines are measuring the anterior center-edge angle of Lequesne and de Sèze.
FIGURE 4
FIGURE 4:
A and B, Supine AP pelvis and standing false profile radiographs of left hip. In the supine radiograph there appears to be mild to moderate dysplasia of the left hip without significant subluxation. The standing false profile of the left hip demonstrates that the majority of the pathology and subluxation for the left hip is primarily seen on the false profile view only and may have been missed if only a supine AP radiograph was obtained.

Additional radiographs include the von Rosen abduction and internal rotation AP of the pelvis (Fig. 5) and the Dunn flexion and abduction AP of the hip (Fig. 6).27,28 The purpose of the von Rosen view is 2-fold. It can illustrate what the relationship between the femoral head and acetabulum will be after surgical correction of the acetabular dysplasia. Joint congruency can be assessed as excellent to poor with poorer preoperative congruency being shown to predict poorer postoperative long-term results.13,29,30 It can also help to provide some insight into whether the weight-bearing cartilage available will be sufficient after surgical correction. One example is the hip with joint space narrowing at the acetabular rim that demonstrates marked improvement in the apparent joint space on von Rosen indicating that the hip may still be a candidate for joint-preserving surgery (Figs. 7A–C). With an increased understanding of the prevalence of FAI morphology, the Dunn lateral can be useful to demonstrate the presence of femoral-sided cam lesions that may need attention at the time of acetabular correction.31

FIGURE 5
FIGURE 5:
von Rosen abduction AP radiograph of the pelvis and hips.
FIGURE 6
FIGURE 6:
Dunn lateral radiograph of the proximal femur with 45 degrees hip flexion. Note cam-type morphology at the anterior femoral neck.
FIGURE 7
FIGURE 7:
A–C, AP radiograph of left hip, preoperative von Rosen radiograph left hip, postoperative AP radiograph left hip. This series of images illustrates 1 potential utility of the von Rosen abduction view which is helping to define the congruency and anticipated radiographic joint space after reorienting acetabular osteotomy. In this case the painful left hip had Tönnis osteoarthrosis grade 2 preoperatively on the AP image but had improvement in appearance of joint space on the von Rosen view. The patient is pain free at 16 years after surgery.

MRI

MRI is an important addition to the imaging workup. They are commonly obtained to assess for labral tears, perilabral cysts, and articular cartilage injury (Figs. 8A, B). Additional cartilage-sensitive imaging techniques and sequences include delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T2 mapping, and T1 ρ.32–36 These have proven beneficial in assessing cartilage “health” and predicting outcome after surgical correction of hip dysplasia.33 Periarticular soft-tissue etiologies of hip pain can also be assessed. In addition to soft-tissue pathologies, the MRI can be utilized to assess acetabular version and femoral neck deformity. A particularly beneficial sequence is the radial sequence MRI centered on the femoral neck, which is helpful in assessing the labrum through multiple cross sections at various positions around the acetabulum.37,38

FIGURE 8
FIGURE 8:
Coronal proton density with fat saturation MRIs of the right and left hip, respectively. A, The classic hypertrophic labrum with degenerative injury. B, More advanced disease on the left hip with labral-chondral separation and subchondral cyst formation.

TYPES OF SURGICAL CORRECTION

Multiple techniques have been described for surgical correction of acetabular dysplasia in the skeletally mature patient. The end goal is the same for all—correction of the biomechanical environment by improving anterolateral femoral head coverage. They range from the innominate osteotomy of Salter to variations of periacetabular osteotomy (PAO) that further improve the ability to maneuver the acetabular fragment into virtually any position necessary to correct the insufficient coverage of the femoral head.1–5 Of these, the Bernese PAO, rotational or spherical acetabular osteotomy, and the triple pelvic osteotomy are the best described. All have been successful at correcting the primarily anterolateral acetabular deficiency. One potential problem with the innominate osteotomy can be creating relative under coverage of the posterior femoral head when correcting severe anterolateral deficiency.

When considering surgical treatment of hip pain in general, the question of whether to treat labral tears in the presence of DDH without treating the underlying acetabular dysplasia has been raised.39,40 Labral tears in the presence of acetabular dysplasia occur, we believe in most cases, as a consequence of the labrum doing a job it is not designed to do—weight bear. When the labral tear is debrided without correction of the underlying mechanical problem, increased acetabular rim overload ensues and progression of arthrosis can be rapid.41,42 It is possible to perform an arthroscopic repair of the labrum in the same operative setting before performing the PAO. That said, a case can be made for treatment of labral tears in the presence of radiographically mild dysplasia, especially in older patients, as the arthroscopic treatment is a much simpler and less invasive procedure that may provide adequate relief.39 Although it has been suggested that labral tears can occur in the absence of bony pathology, these cases should be scrutinized carefully by the treating surgeon as a diagnosis of exclusion and assume a bony etiology until proven otherwise.43

SURVIVORSHIP

As the clinician sits with the patient and their family to describe acetabular dysplasia and how they can correct it surgically, there are inevitably 2 things the patient and physician would like to know: will this surgery be my last and is there any way to predict whether it will last or fail. Mid-term to long-term outcomes after surgical correction of acetabular dysplasia have been published by multiple authors. In addition, several studies evaluating specific subpopulations have been performed.6,7,9,11–14,29,44,45 An abbreviated list can be seen in Table 1. With some variances, approximately 80% of hips are surviving to 10 years and fewer to 20 years. It is important to understand that there is variation in current studies with regard to inclusion and exclusion criteria and the criteria used to declare a hip a “failure.” Many studies evaluate heterogenous groups that include acetabular dysplasia secondary to trauma and in the setting of various neuromuscular conditions. Some reports use conversion to arthroplasty as the primary endpoint for failure, whereas others include this definition along with patients describing significant pain but are not requesting conversion to arthroplasty. Although there are differences in study design, the basic messages derived from all studies are: provided adequate correction is attained virtually all hips had improvement in their pain and function with hips that were younger and with less arthrosis having the best long-term survivorship, regardless of surgical technique and hips that later required arthroplasty did so at an average of 6 to 20 years after osteotomy (Table 1).

TABLE 1
TABLE 1:
Selection of Current Literature Regarding Outcome After Surgical Treatment of DDH

PREDICTORS OF OUTCOME

From the current literature we can now add to the discussion with our patients’ additional information regarding survivorship as well as share some predictors of outcome after osteotomy to correct acetabular dysplasia. A list of these predictors are shown in Table 2. If we think about these in terms of general themes, many are intuitive. Older age is consistently seen as a predictor of poor mid-term to long-term outcome.9,10,13 A mismatch in femoroacetabular congruency also seems to predict poorer outcome.9,13,30 However, scales of femoral head sphericity and congruency can also take into account other aspects of arthrosis including joint space narrowing and osteophytes. Increased joint arthrosis on radiograph and MRI can predict poorer results.33 Finally presence of severe symptoms before surgery such as pain and limping possibly indicative of worse preoperative disease may also predict poorer outcome.9,10 This last predictor may be the most difficult to understand as pain is what generally brings the patient to your office. Hence, although poorer performance on preoperative patient-reported measures are important to know, exactly how bad your hip needs to be working to be considered “too far gone” is left to be determined.

TABLE 2
TABLE 2:
Predictors of Poor Outcome

In an effort to simplify some of these predictors and make them more useful during the clinician-patient surgical conversations, some authors have dichotomized them and/or create prediction rules. From our mid-term to long-term results after Bernese PAO, we created a predictor model to assess the probability of PAO failure with increasing numbers of independent risk factors (Table 3).13 A receiver operator characteristic analysis demonstrated overall good to excellent reliability of these 2 factors (area under the curve, 0.8).

TABLE 3
TABLE 3:
Prediction Model of Probability of PAO Failure

SUMMARY

Ideally, symptomatic hip dysplasia in the skeletally mature patient should be treated based upon known predictors of success and failure. Table 4 shows a summary of selection criteria derived from the previously mentioned works as well as an informal survey of 20 hip joint-preserving surgeons asking “when is the hip too far gone to be considered for joint-preserving surgery?” Although statistically derived predictors can be helpful in estimating outcome, they are still not the final answer to the question of whether a patient’s hip should undergo a hip-preserving surgery. Every study and every practice has patients and hips that “defy the odds.” Whether it be the 39-year-old patient with Tönnis grade 2 to 3 arthrosis, whose x-rays looked better on abduction views that is now 18 years from surgery or the 18-year-old college student that had maybe Tönnis grade 2 arthrosis and a large labral tear, whose hip lasted 2 years before asking for arthroplasty; the general consensus still is that known predictors may help, but ultimately the decision for surgery relies heavily upon: recognition of a problem, accurate assessment of the clinical and radiographic picture, and a clear discussion between the patient and surgeon regarding treatment possibilities.

TABLE 4
TABLE 4:
Summary of Patient Selection

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Keywords:

acetabular dysplasia; periacetabular osteotomy; hip dysplasia; patient selection

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