FREQUENTLY ASKED QUESTION

Q? What is arthritis and what causes it?

Ans. Arthritis is a complete term for a number of disease entities due to which joints become inflamed and the cartilage that lines the bones deteriorates. Eventually, bone on bone wear occurs, pain and inflammation. One or more joints may be affected. Rheumatoid arthritis (and other forms of inflammatory arthritis) affects the entire system and multiple joints. It is also an autoimmune disorder in which the body perceives the cartilage to be a foreign substance and attacks it.

Q? If I have arthritis in one hip, will I get it in the other?

Ans. Only patients with rheumatoid arthritis often develop problems in both hips.

Q? Can I have joint replacement on both hips at the same time?

Ans. Yes, healthy patients younger than 75 years old, without any cardiopulmonary disease, may be candidates for such surgery. Your orthopedic surgeon can tell you more about this.

Q? What is a prosthetic hip made of?

Ans. You may refer to our detailed discussion of materials on the prosthetic implant section.

Q? Will my new hip set off the metal detector at the airport?

Ans. While hip implants generally do not set off metal detectors, more sensitive machines may register the presence of the implant. You may ask for patients cards to be shown at the airport that explain a hip implant containing metal.

Q? How soon after surgery can I resume driving?

Ans. Most patients can resume driving at six weeks after surgery.

Q? How long will the replacement last?

Ans. Current studies indicated that about 80% of prostheses function well for 20 years. If your prosthesis wears out you may be a candidate for a second hip replacement. Your surgeon will be able to guide you on that.

Introduction

Conventionally, primary total hip replacement is a durable operation in the majority of patients. A hip replacement surgery involves parts that are assembled before and during the operation, referred to as a “ball and socket.” After surgery, the prosthetic ball and socket help restore movement in the hip during the life-span of the prosthesis.

Figure 1: An x-ray of a total hip replacement prosthesis with all details.

As with any other mechanical device, a total hip replacement can be subject to risks of various mechanical or biological failure. Some of which may require a re-operation of the hip replacement to address the cause of failure and its consequences. This is called a “revision.”

Why consider a hip revision?

The majority of elderly patients who receive a hip replacement retain the prosthesis for 15 to 20 years, and sometimes for life. If in case the initial hip replacement surgery is performed at a young age and the patient chooses to have a very active physical lifestyle; there is a need for revision.

Pre-operative investigations in patients who need revision surgery are more extensive than those required in patients scheduled for a primary surgery itself. Special radiographic (x-ray) projections, CT scan, or MRI of the hip may be necessary to determine position and fixation of the replacement parts (components), and the extent of bone loss around the failed implant. A preoperative aspiration (fluid sample) and/or special blood work may be needed as well if the surgeon suspects an infection in the failed hip.

Reasons for hip revision

Revision hip replacement is a relatively infrequent operation. However it is needed when-

  1. There is a repetitive dislocation of a hip replacement
  2. Mechanical failure of the implant (implant wear and tear – loosening – breakage)
  3. Infections seen.

Repetitive (recurrent) hip dislocation:

For a hip replacement to function well, the ball has to be inside the socket at all times. The factors keeping the ball inside the socket are the alignment and fit of the ball and the socket combined with the forces generated by the strong muscles and ligaments around the hip joint. A hip replacement is usually designed to have a large range of motion. However, some hip positions or extreme trauma can force the hip ball out of the socket, a condition commonly referred to as dislocation.

An x-ray of dislocated total hip replacement prosthesis -ball forced out of the socket.

Dislocations are relatively infrequent, in healthy patients however some elderly, debilitated patients, or those who get a hip replacement after a hip fracture or after multiple hip surgeries are an exception.

Patients with a hip dislocation are predisposed to additional dislocations such as a dislocated ball disrupts the important muscles and ligaments around the hip. Multiple dislocations are rare but those who have suffered multiple hip dislocations, the hip replacement orthopedic surgeon may recommend revision surgery.

After the required imaging studies are obtained to determine the exact position and orientation of the different parts of the replacement; one or more parts may need to be re-oriented or completely exchanged. It is important to remember that proper healing of the soft tissues around a revised hip is most important for the success of the operation. Therefore, the surgeon may recommend wearing a brace for a few weeks after surgery.

In certain instances, the surgeon may use a device that “captures” the ball inside the socket (called a constrained socket). The proper healing of the soft tissues around a revised hip is most important for the success of the operation. Therefore, the surgeon may recommend wearing a brace for a few weeks after surgery. After surgery, it is important to follow the surgeon’s advice and to refrain from moving the hip into positions that can generate a new dislocation.

Mechanical wear, implant loosening, and breakage-

The younger and the more physically active the patient is, the faster the wear; where in there are very small particles from constant, repetitive movement of parts during the use of the hip is generated. Depending on the type of hip replacement surgery, the particles will be that of plastic, cement, ceramic, or metal.

The patient’s immune system recognises those particles as foreign and generates an immune response (like an allergic reaction). A strong reaction results in a condition called osteolysis which affects the bone. If bone destruction is severe enough, the components of the replaced hip may therefore become loose (Figure 3).

 An x-ray of a loose total hip replacement prosthesis showing separation of the stem from the bone (as detailed by arrows).

A loose component can move against the surrounding bone, compounding the bone loss. If the bone loss is severe enough, a spontaneous bone fracture or a pathologic fracture occurs.

Mechanical wear and tear leading to loosening of the prosthesis (implant) is one of the most frequent forms of mechanical failure. However, other forms of mechanical failure are also possible, like breakage of the prosthesis.

 An x-ray with details of a broken stem section of a total hip replacement prosthesis.

During any revision surgery the surgeon will assess the amount of bone loss, and remove parts of needed and implant new components. A cadaveric bone from tested donors may also be necessary to rebuild the bone content of the hip lost during the process of prosthetic failure. In the case where there is a large amount of bone graft utilized, or if patient’s bone stock is poor, the surgeon may ask the patient not to bear full weight in the operated leg for a period of time post the surgery.

The risk of infection is higher in close proximity to surgery (i.e. the first six weeks). However, after that, there is a low risk of “late” infections. Sometimes bacteria can also seed and infect a hip replacement, causing hip pain and fever via the blood.

In the case of a prosthetic infection, the surgeon attempts to identify the organism causing the infection and recommend a hip aspiration. The liquid thus aspirated from the hip is sent to the laboratory for the required tests post which several treatment options are suggested.

The most common treatment options for this include-

  1. A thorough surgical cleaning of the hip replacement generally recommended when the infection is discovered very early (within a few hours or days). Patients require six weeks of intravenous antibiotics and, frequently, a low dose of oral antibiotics for a long period of time (sometimes for life).
  2. A complete exchange of a hip replacement done in two stages: A first stage where there is complete removal of the hip replacement, cleaning of the bone, and implantation of a temporary cement spacer that will allow some hip motion and deliver antibiotics to the hip area. This is generally followed by a six week course of intravenous antibiotics. The second stage consists of the re-implantation of a definitive hip replacement (generally 6 to 8 weeks after the initial operation).
  3. A complete exchange of a hip replacement done as a single operation, the infected prosthesis is removed, bone is cleaned, and a new prosthesis is implanted. Patients require 6 weeks of intravenous antibiotics, a low dose of oral antibiotics for a long period of time (or for life).

Preventing the need for revision hip surgery

  • Dislocations can be prevented by following the hip replacement surgeon’s instructions clearly
  • Some forms of hip infection can be prevented by prompt treatment of other bodily infections.
  • It is very important that the patient has his/her hip replacement regularly checked. A simple physical examination and radiographs are necessary at the intervals designated by the surgeon.
  • The results of revision surgery are not as predictable as those of the primary surgery. Complications are more frequent- You may consult your orthopedic surgeon with respect to the same.

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