The hip joint is a ball and socket joint. The ball is called the femoral head and the socket is called the acetabulum. The ball glides smoothly in the socket and is capable of movement in all directions due to a covering of articular cartilage. The hip joint can be affected in a variety of ways producing pain, stiffness and lack of mobility. The femoral head itself can lose its blood supply (termed avascular necrosis) leading to softening and collapse of the ball or the cartilage could wear out resulting in direct contact of the bony surfaces. These are some of the disorders that result in a need for replacement of the ball and socket joint.

There are so many varieties of artificial joints on the market that it would not be wrong to say that there are as many prostheses as there are orthopaedic surgeons. There are also various different materials that these joints are made from. The companies that make these joints all claim that their product or material is the best. Is it better to have metal on metal or ceramic on ceramic or metal on polyethylene? Is it better to go fully uncemented or fully cemented? A lot of the time these decisions are taken based on availability, cost and a personal surgical preference. What is the science? Is one better than the other?

When you choose your daily attire, what factors govern your decision? Perhaps you perspire a lot and require a breathable outfit or maybe you are planning to spend the day cooking and require a material that is unlikely to catch fire. If you were faced with a situation where you could only pick one to wear everyday for the rest of your life, what would it be?

In the past, joint replacement was principally carried out to relieve pain. Now, we perform surgery on increasingly younger people. The aim today is to give the patient their life back and at the same time ensure that the prosthesis stands up to the test of time. Our modern patients would like a hip as good as their own, to enjoy absolutely all the activities they previously could and to get back to their usual work routine.

The main factors that govern a surgeon’s decision are therefore:

• The quality of bone and the reason the joint wore out in the first place.

• The age of the patient

• Co-existing factors – weak musculature, obesity, neurological disorders, etc

• Occupation / Activity

In a young patient with worn cartilage but healthy bone, there is no need to completely sacrifice the ball (femoral head). Such an individual could have a hip resurfacing where a metal cap is impacted onto the strong femoral head and moves within a metal liner fitted onto the socket. If in a young patient the ball was weak due to a reduction in blood supply, an uncemented ceramic on ceramic total hip replacement could be carried out. Ceramic on ceramic bearing surfaces have the least coefficient of friction. They produce the least amount of debris. Debris is produced in all joint replacements owing to movement between the ball and the socket. These particles affect the bond between the implant and the bone and produce loosening. This greatly reduces the longevity of artificial joints.

In an older person, suffering from Parkinsonism or obesity or a fractured neck of femur requiring total hip replacement, (conditions where there is a high chance of dislocation – the ball popping out of the socket) it is ideal to use a big head (36mm or higher) to reduce the risk of dislocation.

In the elderly, where one encounters weak bone, it may be necessary to use bone cement to ensure proper stability and fit. As they may also have weak musculature, a cemented component could be combined with a big head to reduce the chance of dislocation.

It is logical therefore that one has to choose carefully from an array of products to ensure each patient gets the best suited hip. But there is more. The angles in which the prostheses are placed affect their longevity and function. A badly placed prosthesis could result in a huge restriction in mobility, prove to be unstable and and dislocate easily or even wear out quickly. Careful pre-operative planning using radiographic images ensures that leg leg inequality is corrected and post operatively the limbs are the same length. This results in a normal gait pattern being quickly established.

The surgical approach plays an important role too. Minimally invasive surgery involves virtually no muscle cutting. The need for blood transfusion is nil and faster mobility and early discharge reduce the chance of deep vein thrombosis and shorten hospital stay. All this translates to a great saving in cost for the patient. Less muscle damage also reduces the risk of dislocation.

The ideal hip inserted via an ideal approach results in the ideal result:
A joint for life.
This is the MIOT promise.