Osteoarthritis and Hip Arthroplasty (Part One)

Osteoarthritis (OA) of the hip (coxofemoral joint) is one of the most common pathologies that orthopedists encounter in their practice. Arthroplasty, or the total replacement of the coxofemoral joint, is the "ultimate solution" for advanced osteoarthritis. The first attempts at total hip replacement date back to around the 1890s. Nowadays, arthroplasty has reached the level of one of the most accomplished surgeries.

We will not dwell long on the factors that influence the development of osteoarthritis. There are many, and we will mention only a few. Trauma is one of the most common causes, which results in damage to the cartilage of the femoral head, the acetabular joint cartilage, the ligament of the femoral head, the acetabular rim, and many other components.

As a result of the damage to the aforementioned elements, over time the joint loses its strength, the density of the bones decreases, which leads to a change in the biomechanics of the hip and muscles. Infection is another factor that can damage the cartilage (chondros). Hemorrhages within the joint are common after bacterial and viral infections. Many researchers give a special role to genetics, making some people more prone to developing osteoarthritis of the hip.

Conservative treatment is one of the solutions for treating osteoarthritis. Some of the medications used are analgesic groups that make it possible to reduce pain. If medications from the "Non-Steroidal Anti-Inflammatory" (NSAID) group are used, they reduce pain and inflammation in the joint.

One of the most effectively used groups of drugs are the isolated “COX-2 inhibitors”. Special importance is given to therapeutic treatment, which significantly increases the quality of life of patients. Science and practice have shown that osteoarthritis is, unfortunately, an incurable condition. Every conservative treatment method has a temporary effect.

In the early stages of osteoarthritis, pain is noticed in the lumbar area, the back of the pelvic area, and the "sitting bones", sometimes even extending down along the lower limb. Often, in more advanced stages, pain is noticed in the inguinal area. As the pathology progresses, the joint becomes stiff over time, and even minimal movements of the limb are painful. Also, a noticeable shortening of the leg occurs, which results in limping during walking.

The types of prostheses used nowadays, the talent of surgeons, minimally invasive implantation methods, and certainly the quality of life outcomes for patients have made arthroplasty one of the most successful operations to date. To achieve a successful surgical intervention and to make it as effective as possible for the patient, I and every other surgeon plan the operation and the steps to be taken.

 

The first necessary thing is the pelvic radiography to clearly show both coxofemoral joints. In addition to the pelvic radiography (fig 1), it is necessary to have a radiography of the joint planned for surgery in anteroposterior and lateral projection in abduction (fig 2). These projections clarify the degree of osteoarthritis. The second step is a detailed anamnesis of the patient. The radiography and anamnesis give the surgeon a clear idea of the type of prosthesis to be implanted.

 

Before we look at the types of hip prostheses that exist, I would like us to take a look at their parts. The prosthesis is divided into 3 components (fig3).

• The first component is the femoral component, also known as the stem of the prosthesis.
• The second component is the acetabular component, which is implanted into the pelvis's acetabulum.
• The third component is the head along with its accessories, which connects the acetabular component with the femoral one.

In modern orthopedics, hundreds of different types of hip prostheses are implanted. We will make a simple classification so that we have a clear idea of how the surgeon chooses the prosthesis for implantation.

They are divided into two major groups (fig5). The first group consists of prostheses in which both the femoral and acetabular components are fixed with cement (fig 5 right). The second group consists of prostheses whose components are fixed without cement in a "press-fit" manner (fig5 left).

The friction forces that occur between the prosthesis head and the acetabular socket make the second classification of prostheses, which is based on the types of friction forces (fig6). The types of friction forces of prostheses we have today are: metal-polyethylene (plastic), metal-metal, ceramic-ceramic, ceramic-polyethylene, ceramic-metal.

Another classification made for the stems of prostheses is based on their shapes and the position they occupy in the femoral canal. The stem of the prosthesis is implanted within the femoral bone canal. Based on the position where the stem will occupy space in the canal and will bear weight, they are divided into stems with proximal fixation (fig7), stems with intermediate fixation, and stems with distal fixation. The stem of the prosthesis in fig 7, compared to the stem of the prosthesis in fig 5, is distinguished by its width and shortness. These two parameters allow it to occupy space at the entrance of the femoral bone canal.