Early MRI and intraoperative findings in rapidly destructive osteoarthritis of the hip: A case report

Abstract

Introduction: The pathophysiology of rapidly destructive hip osteoarthritis (OA) of the hip is still unclear. Also, there have been only few reports on the initial stage of the disease. We report a case of an initial-stage rapidly destructive hip OA, documented by magnetic resonance imaging and intraoperative findings.

Presentation of case: A 77-year-old woman reported left hip pain without any antecedent trauma. Initial radiographs showed no obvious abnormality. After 4 months of conservative therapy, radiographs showed progressive joint-space narrowing and T1-weighted magnetic resonance images revealed a bone-marrow edema pattern not only on the femoral head but also on the lateral side of the acetabulum. Then during total hip arthroplasty, we found extensive inversion of the anterosuperior portion of the acetabular labrum, and the location was mostly consistent with the bone-marrow edema lesions in the femoral head and acetabulum.

Discussion: Several theories for the etiology of rapidly destructive hip OA have been proposed, including idiopathic chondrolysis, abnormal immunoreaction, intra-articular deposition of hydroxyapatite crystals, and subchondral insufficiency fracture. One of the reasons rapidly destructive hip OA is still considered idiopathic is the lack of reports regarding the initial stage of the disease. Our report is the first to demonstrate magnetic resonance imaging for initial-stage disease with intraoperative findings before collapse of the femoral head.

Conclusion: Inversion of the acetabular labrum may be a mechanism of rapidly destructive hip OA.

Keywords: Bone marrow edema; Early findings; Inverted acetabular labrum; Rapidly destructive hip osteoarthritis.

Fig. 1

(A) Anteroposterior radiograph of the left hip at 3 weeks after the onset of pain. (B) In this radiograph obtained at 4 months after the onset of pain, it is apparent that joint-space narrowing of the superolateral portion of the femoral head had progressed rapidly.

Fig. 2

Magnetic resonance images obtained 4 months after the onset of hip pain show joint effusion and a pattern of bone-marrow edema from the upper portion of the femoral head to the intertrochanteric region, with diffuse low intensity on a T₁-weighted image (A) and high intensity on the short τ inversion recovery (STIR) sequence (B). In addition, a small low-intensity band paralleling the articular surface in the femoral head is apparent on the T₁-weighted image that indicates subchondral insufficiency fracture (white arrow).

Fig. 3

Tomosynthesis (A) and multiplanar reconstruction of computed tomography (B) evaluation for subchondral fracture were performed. No obvious subchondral fracture was found in either image.

Fig. 4

(A) The labrum at the anterosuperior portion (arrowheads) was obviously inverted and widely covered the lunate surface of the acetabulum. The asterisk indicates the fossa acetabuli. ANT = anterior; POST = posterior. (B) Intraoperative photograph showing a defect of the acetabular cartilage just under the inverted labrum after resection of the labrum. (C) Intraoperative photograph showing an anterosuperior cartilage defect of the femoral head. (D) Photomicrograph obtained from the inverted labrum included lots of fragments of articular cartilage.

Fig. 5

(A) A hemipelvis with a tilt within the normal range. (B) A hemipelvis with posterior tilting. The distance between the free margin of the acetabular labrum to the femoral head–neck junction (arrows) is longer than that in a normal pelvis (i.e., distance B > distance A). (C) The free margin of the acetabular labrum is more likely to be trapped by the femoral head into the intra-articular space in a posteriorly tilted pelvis than in a normal pelvis because in the tilted pelvis, the distance where the free margin of the acetabular labrum runs across the surface of the femoral head is longer when the hip joint bends. (D) Abnormal stress caused by inversion of the acetabular labrum to the superolateral portion of the femoral head and lateral part of the acetabulum.