Isolated fractures of the teardrop of the acetabulum.

INTRODUCTION

Fractures of the teardrop are very rare. We would like to present two patients with a fracture of the teardrop. The teardrop is a radiological entity, also known as the U figure. It can be seen on the antero-posterior as well as on the obturator oblique radiographs of the pelvis. It is one of the six fundamental radiographic reference lines corresponding to anatomical landmarks, which Letournel introduced for the evaluation of acetabular fractures. Injuries of the hip joint may include pure hip dislocations, dislocations with fracture of the femoral head, dislocations with fracture of the acetabulum, or both. The position of the femoral head in relation to the acetabulum and the vector of the force at the time of impact determine the type of injury produced. Dislocation of the hip can be classified as posterior, anterior, obturator, or central. Anterior dislocations of the hip are uncommon and constitute 10-15% of traumatic hip dislocations. Anterior dislocations are classified according to the position assumed by the femoral head: pubic, obturator, or perineal. In obturator dislocations, the femoral head can cause a fracture of the infero-medial margin of the acetabulum-the teardrop.

METHODS

Two patients are presented with a fracture of the teardrop. Both had a different type of trauma mechanism. The first patient had an obturator hip dislocation combined with a fracture of the teardrop and a fracture of the femoral head. In this case, the intra-articular fragments had to be removed. The second patient had an isolated fracture of the infero-medial margin of the acetabulum probably due to an anterior subluxation and spontaneous relocation of the femoral head. This fracture was treated non-operatively.

RESULTS

At 12 and 24 months post-operatively, functional outcome scores were normal, with a normal range of motion and a pain-free hip joint. At 24 months, the radiographs of both patients showed a normal containment of the femoral head inside the joint, no narrowing of the joint space, and no signs of posttraumatic arthritis.

CONCLUSIONS AND SIGNIFICANCE

An isolated fracture of the teardrop is very rare. The typical injury mechanism consists in an anterior subluxation or luxation of the femoral head needing hip reduction on an emergency basis. The fracture of the teardrop itself can be treated non-operatively with a perfect functional result, because the infero-medial localization of the fracture does not impair the containment or congruity of the hip joint. In case of a painful or displaced fragment of the teardrop interfering with hip joint mobility, fragment removal may be indicated. In case of an associated supero-lateral femoral head fracture, the fragment can either be internally fixed or debrided depending on its size and fragmentation.