February 4, 2015

ASI Technique – The evolution in total hip arthroplasty

Dr. Ioannis Tsarouchas,MD
Orthopaedic Surgeon PHD,
University of Athens Director Of the Large Joints Clinic Athens Medical Center.

The correct function of the joints, irrespective of age, is essential for most everyday activities and, therefore, for a good quality of life.

More specifically, the hip joint, connecting the legs to the trunk, is necessary for all body movements. If it is defective, it may cause severe pain and motion hindrance.

Anatomy of the hip joint

The hip joint is formed by an articulation of two elements:

  • a hemispherical head of the femoral bone and
  • a concave acetabulum of the pelvis.

The rounded head of the femoral bone rotates inside the cup-like surface of the acetabulum. The contact area is covered by a smooth, glossy tissue, called articular cartilage, which prevents friction, and by a small quantity of synovial fluid, which acts as lubricant, so that under normal conditions, the movements of the joint are carried out smoothly, without friction. The joint is stabilised by strong ligaments and its motion is facilitated by strong muscles.

What is osteoarthritis?

Hip osteoarthritis is a chronic, degenerative disease, which causes deterioration of the cartilage and results in joint stiffness and progressively increasing pain in the groin, the anterior surface of the thigh, or sometimes in the knee.

What causes it? How frequent is it?

It may be caused by a variety of factors or conditions:

  • hereditary: congenital dysplasia (malformation), also known as congenital hip dislocation
  • a chronic disease, such as rheumatoid arthritis
  • previous trauma, such as hip fracture, leading to posttraumatic arthritis
  • aseptic necrosis of the femoral head.

Extended studies show that 10% of the population suffer from osteoarthritis.ASI Technique foto1


Major symptoms are pain and joint dysfunction, that is, stiffness and limping gait, which hinder everyday activities.

What is the treatment?

Depending on the particular characteristics of each patient, the doctor recommends appropriate medications. When, however, a point is reached when drugs no longer offer adequate relief, surgical treatment by total hip arthroplasty is the best solution. This possibility of replacing the damaged joint by an artificial one, is among the most important achievements of orthopaedics, as it allows the patient to return to a normal way of life.

The main treatment of hip osteoarthritis is total hip arthroplasty. A major advance in recent years is the use of an anterior approach, with spectacular results.

Techniques of total hip replacement

There are various techniques of performing the operation, which are mainly differentiated by the method of approach, that is the type of incision the surgeon uses to get to the joint. The classical techniques, which use lateral or posterior approach, require long surgical incisions with significant injury to the soft tissues (muscles and tendons). This results in correspondingly large blood loss necessitating transfusion of at least one, but usually two or more units of blood. Postoperatively, the patients may suffer from pain, they have to remain in hospital for several days, but the main problem is, that the trauma to the soft tissues takes about six weeks to heal. During this time the patients have to be very cautious in their movements and to use a walking aid, such as walkers, crutches or canes. These problems also apply to surface arthroplasty, which however, has the advantage of minimal bone loss.

Innovative method: Anterior approach – ASI

ASI Technique foto2The major advantage of ASI (Anterior Supine Intermuscular) is minimal trauma to the soft tissues. The skin incision is anterior, very short, 6 to 7 cm, section of muscles and tendons is avoided and the duration of the operation is approximately one and a half hour. Thus, blood loss is limited and in patients with normal haematocrit, transfusion is practically never needed. Postoperative pain is minimal and the patient can be mobilised immediately. Depending on the patientʼs physical condition, a walking aid may be unnecessary from the very beginning. Hospitalisation is limited to three to four days. A danger of subluxation is practically non-existent, since no muscle is damaged. Rapid mobilisation decreases significantly the danger of serious complications, such as thrombosis and pulmonary embolism. The patient quickly resumes everyday activities and a normal life. Especially important is the fact that ASI is specially indicated in overweight patients, for whom other techniques are associated with significant problems.

In addition to the obvious advantages of the ASI technique as compared to conventional ones, it is also superior to other, older, minimally invasive techniques. These use special mechanisms of traction, which may cause nerve damage, fractures or subluxation of other joints, at the same time impeding intraoperative assessment of limb length. This may result in limb-length discrepancy. The ASI technique leaves the legs free to be moved. The complications of traction are avoided, while in addition, it permits exact intraoperative limb-length equalisation.

In short, total hip arthroplasty with the ASI method gives a rapid, effective, definitive solution to patients with damaged hip joints.