Unilateral Spondylolysis and the Presence of Facet Joint Tropism

Abstract

Retrospective review of the CT scans performed in a group of patients examined for a possible spondylolysis. To investigate whether there is an association between unilateral spondylolysis and facet joint tropism. Spondylolysis is a fatigue fracture of the pars interarticularis of great importance in sports injury. The demonstration of a unilateral spondylolysis is important because there is a potential for full healing if the athletic activity is modified, whereas bilateral spondylolysis frequently leads to established nonunion. Coronally orientated facet joints are known to predispose to spondylolysis by increasing the point loading of the pars interarticularis. The importance of this finding has not been investigated in unilateral spondylolysis. A review of patients with low back pain and a possible diagnosis of spondylolysis who were investigated with multislice CT was performed. The coronal orientation of the facet joints at L4/5 and L5/S1 was measured and comparison was done between those with and without a spondylolysis. The coronal angle of 140 facet joints in 35 patients was recorded. Of 35 patients, 23 had a spondylolysis which was unilateral in 12 patients. The facet joint angle was significantly more coronally orientated in the presence of a spondylolysis when compared with an intact pars (means, 53° and 43°, respectively; P < 0.01). In the presence of a unilateral spondylolysis, the facet joint was significantly more coronally orientated on the side of the spondylolysis (means, 52° and 45°, respectively; P < 0.01). CONCLUSION.: This study is the first investigation of facet joint anatomy in unilateral spondylolysis. Asymmetric facet joints do increase the force through one side of the spine, with a unilateral spondylolysis occurring on the side of the more coronally orientated facet joint.