FEMORO-ACETABULAR IMPINGEMENT

The aim of this article is to increase the awareness and understanding of therapists in the pathology involved in femoro- acetabular impingement (FAI). FAI is not a cause of hip pain but is a morphological condition that predisposes the hip to intra-articular pathology, which is a precursor of hip osteoarthritis. Over the next few years, due to the inability of the human body to attenuate the forces directed through the hip joint, the number of cases of FAI secondary to trauma, repetitive micro-trauma and instability is likely to increase significantly.

BY DAVID BINNINGSLEY BSC (HONS) MCSP SRP

Consider the following questions: n When diagnosing labral lesions, is this the primary or secondary pathology? n Was it direct trauma that damaged the labrum, which then altered the biomechanics and caused the resulting damage to the bearing surfaces? Or was it a very subtle change in the bony contours at the femoral head–neck junction at a young age that resulted in labral pathology caused by repetitive microtrauma? n Does the amount of sport played by children, especially in professional teams, increase the amount of repetitive trauma in skeletally immature individuals?

INTRODUCTION

Femoro-acetabular impingement (FAI) was first described in the literature in 1990s by Rhienhold Ganz. It is known to result from structurally distinct abnormalities, which include pincer- and cam-type FAI, acetabular retroversion, lack of femoral neck anteversion and coxa profunda, the clinical presentation of which is in common with developmental hip dysplasia (2). FAI is not a cause of hip pain.

Rather, it is a morphological condition that predisposes the hip to intra- articular pathology, which then becomes painful and is a precursor of hip osteoarthritis (OA) (3).

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RELEVANT ANATOMY The labrum is made of dense type II collagen (4), forming a triangular rim attached to the acetabulum. It consists of alternating layers of hyaline cartilage matrix and thick layers of collagen fibres, all oriented in the direction of functional stresses. The integrity of cartilage is maintained by chondrocytes, which are embedded in the extracellular matrix. Cartilage in the superior and posterior regions is considerably thicker, with a higher glycosaminoglycan content, and lower water and collagen content, than in its periphery (5). Aydingoz and Ozturk found a 15% variation in labral shape and 25% size variation, even in asymptomatic individuals (6). Tan et al. found that the labrum increases the surface area of the acetabulum by approximately 28% and deepens it by 21% (7). A double-layered synovial membrane surrounds the joint, the external membrane communicating with the capsule and the internal membrane helping to narrow the acetabulum.

The importance of the labrum

is shown by the contact stresses between the joint surfaces, which creates a sealing effect. Following the removal of the labrum, the frictional force between the femoral and acetabular surfaces is increased by up to 92% (8). The centre of contact

sportEX medicine 2009;40(Apr):10-15