[The popliteal fossa: an unrecognized junction].

The popliteal fossa is located at an important place of the osteo-articular system near the knee of course but also in strong relationship with the neighboured vascular, muscular and nervous structures. The symptomatology of the Baker's cyst is well known but its physiopathology is less obvious. It is important to remain aware of some unusual conditions that must prompt a differential diagnosis reaching from functional articular conditions over vascular and nervous problems to major tumoral problems. The patient's history and a rigorous clinical examination must remain the main stone of the medical evaluation; however, most situations require complementary diagnostic procedures among which the ultrasonography and/or the MRI represent nowadays the gold standards. It belongs to the physician's skill to use these tools in an efficient way according to the clinical condition. Actually, the Baker's cyst is in most cases secondary to a mechanical or inflammatory intraarticular knee problem; the treatment of this condition will cure the cyst that usually doesn't require any own treatment.