ENDOCENTER

Stationary operations --> Joint prostheses --> The hip

The hip

The artificial hip-joint
What does the natural hip-joint look like?

The natural hip joint is nearly spherical in shape and consists of a head and a cup whose surfaces are covered by articular cartilage. The cup-shaped part of the pelvic bone is called acetabulum or hip socket. The spherical part of the joint is the femoral head, which is connected via the femoral neck with the thigh bone.

 

hip-joint

Hip radiograph

What is a hip endoprosthesis?

When replacing a hip joint, normally a total hip joint prosthesis is used. A prosthesis is also called an implant. It completely replaces the two bony parts of the worn joint – the femoral head and acetabulum. The head of the prosthesis is anchored with a stem in the femur. Most hip joint prostheses consist of four parts (cup, insert, head and stem). They have a modular design, so that the surgeon can adjust the artificial joint to the original form of the hip.
The most important part of the artificial joint is the so-called tribological pairing, which forms the actual joint and consists of two parts. The head is made of ceramic or metal and is fixed to the stem of the prosthesis. It articulates against in a half-shell insert which is fixed to the cup of the prosthesis. This insert is made of synthetics, ceramic or metal.

hip endoprosthesis

How is a hip prosthesis fixed to the bone?

After acetabulum and femur have been prepared for the operation by reaming and/or rasping, the artificial hip cup and stem are either impacted or fixed with a so-called bone cement. We distinguish three types of prostheses:

• The cementless hip prosthesis: The artificial cup and stem are being pressed in the prepared bone bed (so-called «press-fit» technique) or the cup is screwed in. Additionally, bone screws may be used. The rough surface allows for adhesion or ongrowth of bone. The prerequisite is a good bone quality, which makes this procedure particularly suitable for younger patients.
• The cemented hip prosthesis: The artificial cup which entirely consists of polyethylene and the stem are anchored with a bone cement. Bone cement is a polymer which is interlocked with the trabeculae and therefore securely anchors the artificial joint. An adhesion or ongrowth of the bone is not necessary. That is why this method shows very good long-term results even with elderly patients.
• The hybrid-endoprosthesis: This type of artificial joint combines both methods of fixation. Most often the artificial cup is free of cement, the stem on the other hand is inserted with bone cement. Especially if the bone quality is not good, this method has its advantages on the stem side. The stem has to be fixed similar to a wedge in a cylinder. In contrast, the artificial cup can be safely anchored even without bone cement or when the bone is not of good quality, as in this case no shear forces occur.

What are the experiences with hip replacements?

The artificial hip joint replacement is the most common and most successful orthopaedic surgery of all. Comprehensive register studies show  that patients older than 65 years do have a 90 percent or higher chance to live in comfort and symptom-free and are able to participate in all daily activities. Even 16 years after the surgery the artificial joint of over 80 percent of all patients is still working fine. Because of these excellent results, even younger patients choose this intervention, as they want to stay active and mobile in face of an irreversible damage of the hip.

Which implant is right?

The selection of suitable joint replacements and types of anchorage depends on the cause of the disease, age, gender, bone quality and the individual needs of the patient. Younger patients do have the option of a surface implant of the hip-joint or a short stem prosthesis in contrast to the traditional total hip prosthesis. Depending on the health situation and the expectations of the patient, the most adequate implant is selected together with the surgeon.

Before the operation

What does the optimal surgical preparation look like?

As the operation is performed under general anaesthesia, either the anaesthesiologist or the family doctor respectively an internist has to determine the suitability for anaesthesia. This is done by checking your general health. If necessary, one may have to take several actions, in order to restore the suitability for anaesthesia, such as:

• The discontinuity of blood thinning medication, e.g. Falithrom, warfarin or Aspirin (usually at least 10 days prior to surgery). However, certain drugs for pathological elevated blood sugar (Diabetes mellitus), for example Metformin, should be discontinued 2 days before surgery. On the other hand, the patient is allowed to continue taking blood pressure medications. The ultimate decision of which medications should be discontinued and which not should be reached by the family doctor and the operating hospital.
• The treatment of a cardiac insufficiency
• The setting up of blood pressure in hypertensive
• Existing hyperglycaemia in diabetes mellitus

The clarification of suitablilty for anaesthesia and the general health status are essential for the postoperative prognosis and thus for the entire healing process.
Furthermore, various other measures are taken, which concern and therewith also affect either the intervention itself or the rehabilitation phase.

Below are listed some of these measures

Autologous blood donation:

During a prosthetic surgery, an increased blood loss cannot be excluded. As this surgery is mostly an elective one, the patient has the possibility to donate his own blood in advance. An autologous donation is usually done two to four weeks before the planned intervention takes place. Approximately 500 ml of blood are taken from the patient.

Cellsave:

If the operating hospital uses cellsaver systems, the patient often can dispense with autologous blood donation. These systems clean the patients’ blood which is lost during surgery so that the patient can get it back. In doing so, the loss of blood is minimized and the insertion of allogeneic blood is mostly not necessary.

Physiotherapeutic actions:

If prior to the operation there already exists a strong movement impairment, one should take action of physiotherapy already before the operation. The aims should be the strengthening of the muscles and a better mobility in order to enable a better and faster rehabilitation after the operation.

How does the surgeon prepare the operation?

As part of an ambulatory surgical preparation, the surgeon discusses the most suitable type of prosthesis and the necessary prearrangements. Before the operation, a design draft is created, computer-assisted with a digital radiograph. Afterwards, the components of the prosthesis are determined and tailored to the individual patient. Stem thickness, size of cup and head and the optimal positioning of the prosthesis are determined. Even the correction of certain deformities is possible. The long-lasting operational experience and discernment of the surgeon are essential for the optimal planning.

What can the patient do?

You can also contribute to the success of the operation. You should get as fit and healthy as possible to the hospital. The better your general health, the smoother the operation and recovery. With specific muscle formation you create good preconditions for your new joint. When you have overweight you should consider a diet before the operation. It is absolutely essential that your physician informs you about medications, chronic diseases as diabetes mellitus or cardiovascular diseases. Same applies to existing allergies or acute infections. All important issues should be discussed and answered within a conversation with the surgeon and the anaesthesiologist. Together with them you should come to the decision of general or partial anaesthesia. An autologous blood donation is also possible.

The operation

During the operation the hip has to be exposed that much that the prosthesis can be safely inserted. This can be done in different ways: The surgeon can open the hip joint from the front, back or side. The choice of these “approaches” depends on the patients’ physical characteristics and the surgeon’s experience. Today, so-called minimally invasive approaches are getting more and more popular, as long skin incisions, the separating of musculature and the damage of soft tissue can mostly be avoided. Too small approaches though, may also be difficult as the surgeon hardly sees anything when the patients are very obese or the bony conditions are too complicated. In such cases the surgeon should operate via a conventional approach.

Conventional supply shaft

How is the operation being finished?

At the end of the operation, bandages and drains are created and the remaining blood is eliminated. Afterwards, the first X-ray is done in order to control the surgical outcome and to assess the post-op treatment. When the patient is transferred to the ward, the operated leg is positioned with pillows or in a special brace. According to the individual condition of the patient, the mobilisation (gait training, ascending stairs etc.) usually starts already one day after the operation. Daily tasks such as cleansing, toilet visits or putting on socks, shoes and pants is explicitly allowed and are practiced as well.

After surgery

What happens after the operation?

The early phase after the operation comes along with an optimal pain management. Therefore the latest pain catheters, pain pumps and well tolerated drugs are available. On the day after the surgery, you will stand up for the first time and stress the implant. What does the patient have to be aware of after the operation? Depending on which approach was chosen, you should avoid too much motion in the first four to six weeks, as the hip-joint and the surrounding capsule need to grow back first and if necessary, even disconnected muscles may have to grow back.

It is of high importance to avoid a dislocation of the new artificial joint. In this case the head of the prosthesis would detach from the cup of the prosthesis (the anchoring of the prosthesis in the bone is not involved). Over time the joint is stabilized by the healing process and the muscle formation. Then, a dislocation is very rare and occurs only in the context of accidents. But in the early phase of the after-treatment, certain positions and movements should be avoided. However, a gentle full weight bearing should take place very soon. By the use of crutches, this can be achieved in the first weeks. Sleeping on the operated side is allowed at an early stage, after the wound is healed. Sleeping on the opposite side should be supported in the first four to six weeks with a pillow between the knees.

How does the after-treatment look like?

The muscles at the hip, but even the total leg and back muscles often have changed due to long lasting illness. Usually, a protective attitude has developed, which has brought about an altered interaction of the muscles. To normalize this interaction again or at least achieve the best possible condition is the job of outpatient or inpatient rehabilitation. Thereby the own training of the patient is essential. After one week, most patients are able to climb stairs on crutches. Despite the allowed full weight bearing, you should use the crutches until you reach your old walking safety again.

When can I drive a car again?

You can drive a car again after approximately six weeks. To accompany somebody is possible earlier.

When can I go back to work?

The work ability of course depends on the profession. Many patients with standing or walking jobs return to work after eight to twelve weeks. An earlier come-back is possible with jobs which include less movement.

How long does it take to get used to the implant?

The proprioception phase can last more than one year. In this stadium, some patients report on an easy meteorosensitivity in the new joint. A slight clacking or other sensations from the hip might be recognised.

What sports can be practiced with a hip prosthesis?

In the normal course of operation and successful rehabilitation, sports such as cycling, swimming, golf or walking are possible and even useful in order to train the musculature. Some patients can even play tennis or go skiing again. But generally spoken, this is not recommendable, especially for untrained persons. After four to six weeks, you can start with the following sports and perform them regularly after twelve weeks:

• Cycling
• Hiking
• Jogging
• Swimming
• Playing golf
• Tennis (only with an existing good technique)

Unsuitable, especially for untrained persons, are generally:

• Alpine skiing (if, then after at least half a year)
• Cross-country skiing (because of the risk of falling)
• All competitive sports with direct contact with the opponent, e.g. soccer or handball