Hip Arthroscopy in Staging Avascular Necrosis of the Femoral Head

Disclosures

J South Orthop Assoc. 2000;9(4) 

In This Article

Abstract and Introduction

The purposes of this study were to evaluate how accurately current imaging modalities predict the quality of the articular surface in avascular necrosis (AVN) of the femoral head and to provide arthroscopic correlation to current staging modalities. An arthroscopic classification system, derived from the work of Marcus et al, was used to prospectively stage the articular surface in 23 hips with AVN using plain radiographs, magnetic resonance imaging (MRI), and arthroscopy. There was little correlation between all three diagnostic modalities. These findings were not statistically significant. Patients with stage IV disease had the widest variation in the appearance of the articular surface. This study shows poor correlation in the staging of AVN using current imaging techniques. Magnetic resonance imaging has been shown to be inadequate at assessing the articular cartilage. Therefore, either arthroscopy or direct visualization is required for accurate evaluation and staging, especially in stage IV disease.

The ideal management of avascular necrosis (AVN) of the femoral head continues to be controversial. Proposed surgical approaches have included core decompression with and without bone grafting, implantable bone stimulators, rotational and angular osteotomies, vascularized and nonvascularized bone grafts, and resurfacing and total hip arthroplasty.[1,2,3,4,5,6,7,8,9,10,11,12,13] Success rates after these procedures are variable, and few conclusions may be drawn regarding the superiority of one technique over another.[12]

Inability to accurately determine the stage of the disease process when intervention is initiated may contribute to wide variation in success rates reported for these procedures. In AVN, the softened necrotic cancellous bone is unable to withstand physiologic forces and collapses, usually signaling the onset of symptoms. A cleavage plane occurs between the articular surface, which is nourished by the joint fluid, and the necrotic bone beneath it.[14] At this time, the avascular fragment will "ballote" with compression, much like a tennis ball will compress and then resume its shape (Fig 1).

(click image to zoom) Diagram of infarct in femoral head (left). Instrument depresses osteochondral fragment into cleavage plane (center). After release, segment "springs" back out to resume its previous shape (right).

Collapse of the articular surface is visible when the fragment no longer assumes its original shape, and the head appears flattened. Later, the articular surface becomes disassociated from cancellous bone and cleaves off as a large fragment. This process of cleavage, which is called "delamination," is the end stage of the disease process and initiates frank arthrosis of the joint (Fig 2).[14]

Delamination of osteochondral fragment with softened necrotic trabecular bone underneath.

Once the articular surface has collapsed, salvage of a congruent hip apparently is impossible.[1] Therefore, to draw any valid conclusions regarding the efficacy of treatment, it is imperative to know the shape and quality of the femoral articular cartilage before initiating that therapy. We hypothesize that current imaging modalities do not allow adequate visualization of the articular surface of the femoral head. The goals of this study were to evaluate how accurately current imaging modalities predict the quality of the articular surface and to provide arthroscopic correlation to current staging modalities.

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