Hip-preserving surgery: understanding complex pathomorphology.

Introduction Recent evidence suggests that abnormal hip morphology may be the primary cause of osteoarthritis of the hip in young adults. Hip pathomorphology is manifested as acetabular deficiency or malorientation, or as femoral deformity or malorientation, and most commonly as a combination of these problems. Contemporary surgical intervention for hip preservation has been directed toward correction of these malformations and associated chondrolabral injuries and has shown promise as a way of alleviating hip pain and possibly retarding the progression of osteoarthritis. With the increasing number of available surgical methodologies (e.g., surgical dislocation, osteochondroplasty, hip arthroscopy, and redirectional acetabular osteotomy) that are directed at hip preservation, the importance of understanding the pathologic process that results in a painful hip has become paramount. In an effort to augment the basic information obtained from clinical examination, two-dimensional plain radiography, and magnetic resonance arthrography, we have utilized a validated three-dimensional modeling protocol to serve as a diagnostic and surgical planning tool for hip-preservation surgery. Threedimensional modeling has helped to emphasize the complex pathomorphology that is evident in patients with hip dysplasia and femoroacetabular impingement and may have a future role in the classification and treatment of hip maladies in young adults. The goals of this study were to describe the typical presentation of the young adult with a painful hip and to offer corresponding case examples of the common morphologic abnormalities of the femur and acetabulum. The case examples illustrate the value of a comprehensive imaging protocol to facilitate diagnosis and management of patients who have complex femoroacetabular impingement and dysplasia. In addition, we describe our experience with three-dimensional computational model development as a function of a subset of work focused on the biomechanics of the dysplastic hip, and we outline future streams of work based on three-dimensional imaging. Clinical Presentation and Two-Dimensional Imaging Clinical Presentation Patients with dysplasia or hip impingement will typically present at some time between their late teenage years and their middle or late forties. In our practice, the age range for these patients is fifteen to forty-nine years, with a mean age of twenty-eight years. Patients with classic acetabular dysplasia are more likely to be women and within the age range of fourteen to thirty-five years, whereas patients with femoroacetabular impingement are equally divided in terms of sex and are more likely to be within the age range of twenty years old to the late forties. Patients typically present with a chief complaint of groin pain, which is usually exacerbated by activities. The groin pain is associated with catching, clicking, or popping in as many as 80% of the patients. The onset of pain is associated with a traumatic event approximately one-third of the time, although the underlying morphologic abnormality of the hip has usually been present for a longer period of time. Additionally, it is common for patients who are involved in high-demand activities (e.g., dance, gymnastics, and soccer) to have similar symptoms in the absence of gross anatomic abnormalities because supraphysiologic motion can produce similar joint injury. Most patients describe exacerbation of the pain with sitting, squatting, or activities that involve hip flexion. The duration of pain can range frommonths to years, with an average duration of sixteen months. Most patients have seen multiple prior health-care providers before an appropriate diagnosis is made, and as many as 15% of the patients have undergone prior surgery for hip pain. The physical examination involves assessment of gait, palpation of the hip and the area surrounding the hip, evaluation of the range of motion of the hip, and provocative testing. The gait pattern of patients with dysplasia and femoroacetabular impingement is nonspecific: a normal gait or slight antalgia are the most common observations. Palpation of the hip and the surrounding area usually results in unremarkable findings. Limitation of internal rotation with the hip positioned in 90 of flexion is the most common physical