The widened teardrop distance: a plain film indicator of hip joint effusion in adults

The teardrop distance is defined as the distance from the lateral margin of the pelvic teardrop to the most medial aspect of the femoral head as seen on anteroposterior pelvic radiographs. The structure responsible for the teardrop is the anteroinferior portion of the acetabular fossa with contributions from the ischium and from the superior pubic ramus. Anteroposterior pelvic radiographs of 10 patients with documented cases of unilateral hip effusion were retrospectively evaluated for teardrop distance widening on the affected side. Proof of the presence of hip effusion was based on the results of percutaneous hip joint aspirations as described in the patient's medical records. A teardrop distance widening of 1 mm or more was always consistent with hip joint fluid. In addition, radiographs from 20 patients with no known hip abnormalities were reviewed as a control population. These showed side-to-side symmetry in 16 cases (80%) and widening of less than 1 mm in the remaining four cases (20%). Thus, hip joint effusion in adults can be accurately diagnosed from plain radiographs in the presence of a teardrop asymmetry of 1 mm or more and in the absence of degenerative joint disease.