Anterior Hip Subluxation due to Lumbar Degenerative Kyphosis and Posterior Pelvic Tilt

Nontraumatic anterior subluxation and dislocation of the hip joint are extremely rare. A 58-year-old woman presented to our outpatient clinic with left hip pain with a duration of 15 years. There was no history of trauma or other diseases. Her hip pain usually occurred only on walking and not at rest. Physical examinations demonstrated no tenderness in the hip joint. The range of motion of both hip joints was almost normal. Laxity of other joints was not observed. The bone mineral density of the lumbar spine and proximal femur confirmed a diagnosis of osteoporosis. A plain radiograph showed osteoarthritic changes of the hip joints, severe posterior pelvic tilt, and superior displacement of both femoral heads, especially in a standing position. Three-dimensional computed tomography (3DCT) revealed anterior subluxation of both femoral heads. Seven years after the initial visit, both hip joints showed progression to severe osteoarthritis. Although the exact cause remains unclear, lumbar kyphosis, posterior pelvic tilt, and a decrease in acetabular coverage may have influenced the current case. We should be aware of these factors when we examine patients with hip osteoarthritis. 1. Introduction Subluxation and dislocation of the hip joint are generally high-impact injuries, and nontraumatic anterior subluxation and dislocation are extremely rare. We describe herein a case of bilateral hip anterior subluxation possibly related to lumbar degenerative kyphosis and posterior pelvic tilt. 2. Case Presentation A 58-year-old woman presented to our outpatient clinic with left hip pain with a duration of 15 years. There was no history of trauma or other diseases. Her hip pain usually occurred only on walking and not at rest. Physical examination demonstrated no tenderness in the hip joint, and Patrick’s fabere test was negative. The range of motion of both hip joints was almost normal: flexion was 140/140 degrees (right/left), abduction was 35/35 degrees, and adduction was 10/10 degrees. Laxity of other joints was not observed. There was no abnormal value on laboratory examinations. The bone mineral density of the lumbar spine (L2–4, 0.643？g/cm2, -score: ？3.41？S.D.) and proximal femur (0.760？g/cm2, -score: ？1.99？S.D.) confirmed a diagnosis of osteoporosis. Plain radiography of the pelvis in supine (Figure 1(a)) and standing (Figure 1(b)) positions showed osteoarthritic changes of the hip joints and severe posterior pelvic tilt on visualizing superior displacement of both femoral heads. Lumbosacral angles (LSA) on lying and standing were 27 and 6 degrees,