Protrusio acetabuli is an uncommon defect of the acetabulum, the socket that receives the femoral head to make the hip joint. The hip bone of the pelvic bone/girdle is composed of three bones, the ilium, the ischium and the pubis. In protrusio deformity, there is medial displacement of the femoral head in that the medial aspect of the femoral cortex is medial to the ilioischial line. The socket is too deep and may protrude into the pelvis. Signs and symptoms
Protrusio acetabuli may be asymptomatic. Limitation of joint range of movement is the earliest sign, along with pain. Classification
Protrusio acetabuli is divided into two types, primary and secondary. Primary protrusio acetabuli are characterized by progressive protrusio in middle aged women, and may be associated with osteoarthritis. They may be familial. Secondary protrusio acetabulis causes include femoral head prosthesis, cup arthroplasty, septic arthritis, central fracture dislocation, or total hip replacement surgeryProtrusio acetabuli may also be thought of as unilateral or bilateral. Unilateral protrusio acetabuli may be caused by tuberculous arthritis, trauma, or fibrous dysplasia. Bilateral protrusio acetabuli may be caused by rheumatoid arthritis, Pagets disease, osteomalacia, Marfan syndrome, and ankylosing spondylitis. Prognosis
The protrusio may progress until the femoral neck impinges against the pelvis. Treatment
Arthroscopic surgery (or open joint surgery) is an effective treatment. Joint replacement surgery may be necessary in the case of severe pain or substantial joint restriction. References
External links

McBride MT, Muldoon MP, Santore RF, Trousdale RT, Wenger DR (2001). "Protrusio acetabuli: diagnosis and treatment". J Am Acad Orthop Surg. 9 (2): 79–88. doi:10.5435/00124635-200103000-00002. PMID 11281632.
Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that reflect cyanosis are usually in locations where the skin is thinner, including the mucous membranes, lips, nail beds, and ear lobes. Some medications containing amiodarone or silver, Mongolian spots, large birth marks, and the consumption of food products with blue or purple dyes can also result in the bluish skin tissue discoloration and may be mistaken for cyanosis.Cyanosis is further classified into central cyanosis vs. peripheral cyanosis. Pathophysiology
The mechanism behind cyanosis is different depending on whether it is central or peripheral. Central cyanosis
Central cyanosis is caused by a decrease in arterial oxygen saturation (SaO2) and begins to show once the concentration of deoxyhemoglobin in the blood reaches a concentration of ≥ 5.0 g/dL (≥ 3.1 mmol/L or oxygen saturation of ≤ 85 %). Causes of central cyanosis are discussed below. Peripheral cyanosis
Peripheral cyanosis happens when there is increased concentration of deoxyhemoglobin on the venous side of the peripheral circulation. In other words, cyanosis is dependent on the concentration of deoxyhemoglobin. Patients with severe anemia may appear normal despite higher than normal concentrations of deoxyhemoglobin. On the other hand, patients with increased amounts of red blood cells (e.g. polycythemia vera) can appear cyanotic even with lower concentrations of deoxyhemoglobin.