Peri Prosthetic Loosening: Facts, figures and numbers

A joint is formed by the ends of two or more bones that are connected by thick tissues. The bone ends of a joint are covered with a smooth layer of articular cartilage, and normal cartilage allows nearly frictionless and pain-free movement. When the cartilage is damaged or diseased by arthritis, the joint become stiff and painful, and does often lead to total incapacitation of the affected patient.

The procedure of removing a damaged or arthritic joint and replacing it with an artificial joint is called Total Joint Replacement. The goal of this procedure is to relieve pain and restore the joints function. Although weight bearing joints such as hip and knee are the most common joint to be replaced, this surgery can be conducted on other joints, including the ankle, foot, shoulder, elbow and fingers.

The most common diagnosis necessitating total joint arthroplasty is osteoarthritis, although the diagnostic cause is age dependent, and the age of the patient has a strong influence on the diagnosis. In young patients, as expected, there is a much higher incidence of patients with a diagnosis of avascular necrosis and hip dysplasia compared to the more elderly cohort of patients.

Focusing on the hip joint, a prosthesis is composed of a metal or polyethylene acetabular cup that is cemented or made to perfect fit the pelvic bone and a metal femoral stem that is inserted into the femoral bone. The femoral stem is equipped with a metal, ceramic or polyethylene femoral head that fits the acetabular cup. Alternatively only the femoral head is replaced, leaving most of the femur intact.

There exist a vast number of different types and manufacturers of artificial joints. UK numbers from 2012 states that 146 brands of femoral stem, 101 brands of acetabular cup and eight brands of resurfacing cup were used. In terms of bearing combinations the use of metal-on-polyethylene remains the most common selection in just under 60% of cases followed by a ceramic-on-ceramic articulation.

The surgical procedure of joint arthroplasty is successful in 9 of 10 patients, although complications such as nerve injury or blood clots may occur. The most usual post-operative complication is infection in the site of surgery and non-infectious inflammatory processes in the joint, leading to loosening of the prosthesis and necessitating replacement surgery and insertion of a new prosthesis. Over time, the most common complication is inflammation mediated osteolysis around the prosthesis, causing the prosthesis to become loose. This process is termed Periprosthetic Loosening, as it is the tissue around (peri) the prosthesis that degrades and thereby causes the prosthesis to become loose.

In general, prosthetic loosening is a common process, and the life expectancy of a hip prosthesis is 10-20 years. In 2012 a total of 86,488 hip procedures were recorded in the UK. Of these 10,040 were revision procedures where the prosthesis is replaced. The ‘revision’ burden now stands at 12%, which is well in line with numbers from other parts of the world. Causing 40% of the revision procedures, aseptic loosening was the single most common reason for revisions.

Germany is the European country that conducts most hip replacement procedures per capita, and numbers from OECD gives that 240,000 total joint arthroplasties was conducted in Germany alone in 2009. Looking towards the US, in 2009 719,00 knee replacement and 332,000 hip replacement procedures was conducted. The 2012 numbers from Norway show that 9,085 total joint arthroplasties of the hip was conducted this year, of where 1,299 (14,3%) was revision procedures. The yearly numbers of total joint arthroplasties has increased steadily since registration started in 1987

The global number of total joint arthroplasties and revision procedures are expected to increase significantly in the next years and decades.