Hip Morphology and Related Pathology

J.W. Thomas Byrd MD

Key Points

Development dysplasia of the hip (DDH) is a morphological condition that makes the hip vulnerable to an intra-articular lesion that may then cause pain.
Dysplasia is an etiologic factor in the development of various painful intra-articular lesions, which may be amenable to arthroscopic intervention.
Patients must be assessed for the presence of dysplastic disease of the hip. Whereas arthroscopic debridement may result in significant symptomatic improvement, it may not seriously influence the long-term outlook.
Radiographic evidence of dysplasia is not a contraindication to arthroscopy or necessarily an indicator of poor outcome. Results are more dictated by pathology.
Femoroacetabular impingement (FAI) occurs in the native hip and is believed to be a precursor to the development of osteoarthritis. It has been grouped into pincer type and cam type. Pincer type is attributed to a bony lip of the anterior acetabulum. Cam type is associated with bony abnormalities of the anterior and lateral femoral head/neck junction.

In the past sports-related injuries of the hip joint have gone mostly unrecognized and untreated. Arthroscopy has been instrumental in identifying the nature and extent of numerous intra-articular lesions. In a study of athletes undergoing arthroscopy, in 60% of the cases, the hip was not recognized as the source of symptoms at the time of initial treatment and were managed for an average of 7 months, before the hip was considered as a potential contributing source. Most commonly, these were erroneously diagnosed as a musculotendinous strain.

The arthroscopic anatomy has been defined including normally occurring anatomic variations. Numerous pathological lesions have been identified with efforts at both grading and staging the pathology. Armed with a preliminary understanding of this intra-articular pathology, efforts have focused on interpreting the causative pathomechanics. An appreciation for these pathomechanics is essential to reliably altering the natural history of these processes and perhaps advocating early intervention as a preventative measure.

The correlation of hip morphology and hip disease is not a recent concept. Congenital dislocation of the hip (CDH) more recently referenced as dysplastic disease of the hip (DDH), left untreated, and has long been known to result in early joint deterioration and disability. Femoroacetabular impingement (FAI) is a more recent concept felt to be a causative factor in many cases of osteoarthritis. Osteoarthritis is not so much a specific diagnosis, but simply a common final pathway for a variety of conditions culminating in the osteoarthritic process. In general, dysplasia and impingement are considered to exist on two ends of a spectrum: dysplasia associated with a shallow acetabulum and instability, and impingement associated with over coverage of the acetabulum or insufficient clearance for the proximal femur. However, it is also recognized that in some cases dysplasia and impingement may coexist in the same joint.

Dysplasia

Developmental DDH is not a cause of hip pain. It is simply a morphological condition that makes the hip vulnerable to an intra-articular lesion that may then become symptomatic.
The three most likely structures to be involved include the acetabular labrum, articular surface, and ligamentum teres.

Accompanying a shallow bony acetabulum, the labrum may be enlarged assuming a more important role as a weight-bearing surface as well as added responsibility for joint stability. This hypertrophic labrum is thus exposed to greater joint reaction forces and may be at increased risk for developing symptomatic tearing (1,2,3). Inversion of the acetabular labrum is also known to occur in association with dysplasia, being entrapped within the joint and again being a source of painful tearing (4,5).

The reduced area of the acetabular articular surface results in increased contact forces (6,7). This can result in early development of degenerative wear and may make the articular cartilage more vulnerable to acute fragmentation (8,9,10,11).

Lastly, elongation or hypertrophy of the ligamentum teres accompanies lateral subluxation of the femoral head within the acetabulum (12,13). Entrapment of this ligament can be a source of significant mechanical hip pain, whether from its redundant nature or partial degenerate rupture.

Thus, dysplasia is well recognized as an etiologic factor in the development of various painful intra-articular lesions, which may be amenable to arthroscopic intervention. In fact, in a study by this author, which is the only published report on outcomes of arthroscopy in a dysplastic population, the results were comparable to those previously published in a general population (14). However, there are several caveats, which need to be fully appreciated.

It is important to assess patients carefully for the presence of dysplastic disease of the hip. While arthroscopic debridement may result in significant symptomatic improvement, it may not seriously influence the long-term outlook. Especially for young individuals, arthroscopy should not be used solely for symptomatic improvement when long-term issues need to be addressed. Specifically, patients who are candidates for osteotomy to improve the joint mechanics and weight distribution must be carefully assessed.

As noted, the enlarged labrum accompanying a shallow acetabulum may carry greater weight-bearing responsibility as well as provide a buttress to superolateral subluxation of the femoral head. It is unlikely that simple debridement of the deteriorated portion of the labrum will accentuate this subluxation potential, but great care must be taken in the debridement procedure, especially avoiding an overly zealous resection.

Similarly, indiscriminate debridement of the ligamentum teres should be avoided. The vessel of the ligamentum teres remains patent and contributes to the blood supply of the femoral head in a significant percentage of adults. Arbitrary debridement could unnecessarily place the femoral head at risk for avascular necrosis. However, it seems unlikely that debridement of the ruptured portion should present a problem, and has produced very gratifying symptomatic results.

In summary, radiographic evidence of dysplasia is not a contraindication to arthroscopy, nor is it necessarily an indicator of poor outcome. Results are more dictated by the nature of the pathology. Nonetheless, it is prudent to view arthroscopy as but one tool in the complement of resources necessary in the assessment and management of patients with developmental DDH.

Case Examples

Case 1

A 14 year old female was referred with a 4 month history of painful locking and catching of her right hip. This first occurred while simply raising her leg to step over a railing. Her symptoms had since been unremitting. Her history was remarkable for dysplastic disease of both hips since birth. These were initially treated with closed reduction, but she had subsequently undergone multiple osteotomies of the proximal femur and pelvis. Most recently, she was being evaluated for an acetabular procedure to improve the coverage of her femoral head, when she developed incapacitating mechanical right hip symptoms. Radiographs revealed changes consistent with her underlying disease and previous surgical procedures as well as slight lateral joint space loss on the right compared to the left (Fig 28-1A).

Based on her symptoms and exam findings, arthroscopy was recommended as a method to assess the extent of intraarticular damage that may be contributing to her symptoms and to see if this could be addressed. She was found to have an unstable inverted labrum (Fig 28-1B). This was debrided in a cautious fashion (Fig 28-1C). Care was taken to excise the entrapped portion contributing to her symptoms, while preserving as much of the remaining labrum as possible, to avoid potentially destabilizing the joint. Additionally, there was grade IV articular loss of the acetabulum. The unstable fragments were debrided, creating a stable edge of surrounding cartilage (Fig 28-1D). Microfracture of the lesion was performed to stimulate a fibrocartilaginous healing response (Fig 28-1E). Occluding the inflow, confirmed vascular access through the perforations (Fig 28-1F). Postoperatively, she was maintained on a strict protected weight-bearing status for 2 months emphasizing range of motion. She was then able to resume normal light daily activities with resolution of her mechanical hip pain.

Case 2

A 16 year old male presented with a 9 month history of pain and locking of his left hip. This first occurred while playing football as a freshman in high school. He had received no previous specific treatment, but was known to have a developmental abnormality of his hip since early childhood. Radiographs revealed evidence of a separate bone fragment within the femoral head (Fig 28-2A), which was further substantiated by a computed tomography (CT) scan (Fig 28-2B).

With his mechanical symptoms and imaging evidence of a loose fragment, arthroscopy was recommended. The fragment was actually found to be fixed within the femoral head, but there was a grade IV unstable articular fragment over this area, which was debrided (Fig 28-2C,D and E). Postoperatively, he had resolution of his mechanical pain and catching.

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