Modern joint replacement surgery and the prostheses used in these surgeries are a mature technology, with many advancements over the past several decades. However, despite the wide success and excellent outcomes, nearly all artificial joints can be expected to wear out after enough time and wear. Joint replacement surgery is analogous to repairing the moving parts of a car, then sealing the engine compartment and achieving decades of 16+ hours of daily use without lifting the hood again!
Interestingly, many of the revision surgeries that we perform today are not so much because the implant failed, but rather because the bone surrounding the implant failed and no longer provides adequate support. The prostheses gradually may become loose.
There can be a number of reasons why joint replacements need to be revised. Trauma and periprosthetic fractures (fractures that occur around the replacement) often result from the same types of accidents that routine broken bones occur in, such as falling or being involved in a motor vehicle accident. Mechanical (aseptic) loosening is another common cause, as the prosthesis becomes loose from the surrounding bone; this often is an indirect result from a slow inflammatory reaction from worn away plastic material (osteolysis). Infection is another cause for revision surgery. Other potential causes include instability or recurrent dislocations, or mechanical failure, such as breakage of the artificial joint parts, although this has become a very uncommon reason in recent years when compared to those listed above.
Regardless of the reason, revision surgery is a complex and demanding surgery, with a wide variation in complexity depending on the diagnosis and underlying problem, scar tissue, potential damage to nerves or blood vessels (again, often because of scar tissue or calcified tissue called heterotopic bone), and longer surgical time and increased blood loss because of the need to remove the old components.
Revision joint replacements are among the most complex procedures in modern orthopaedics, and in contrast to routine primary (first time) joint replacement surgeries, relatively few surgeons and centers perform revision surgeries. For that reason, many of our patients undergoing revision surgery have been referred from other centers or surgeons.
Trauma and Periprosthetic Fractures
When a patient with an artificial hip or knee is involved in a fall or trauma, most often it is the surrounding bone that breaks before the metal prosthesis fails. As a result, the bone surrounding and anchoring the artificial joint may fracture, requiring that the joint replacement be revised as part of the surgery to treat the broken bones.
This often is a significantly more complex procedure than simply treating the fracture alone, as the old prosthesis may be loose but still attached in places to some bone fragments or cement. Old cement usually has to be completely removed from the bone, a time-consuming process that leads to extended operating time and increased blood loss. Scar tissue around the area leads to an increased incidence of nerve injury and bleeding. Once the hip or knee replacement has been reconstructed with the surrounding fracture stabilized with fixation (often wires, plates, screws, and/or bone graft), it is common that a prolonged period of limited weightbearing is needed in order to allow the fractured bone surrounding the prosthesis to heal.
Mechanical (Aseptic) Loosening and Osteolysis
Another relatively common reason for failure of an artificial hip or knee is loosening of the bone surrounding the implant that occurs without any known infection. Over time, a patient's bone may simply re-absorb in the area that previously held the prosthesis with bony ingrowth or cement, leading to the gradual onset of pain as the prosthesis loosens.
A bone scan (not to be confused with a bone density scan, which checks for osteoporosis) is often helpful for diagnosing early loosening of a prosthesis that cannot yet be seen on regular x-rays. When loosening has been progressing for some time, advanced loosening changes become visible on regular x-rays without the need for a bone scan.
This patient presented with severe knee pain 20 years
after his knee replacement surgery. The metal plate in
the tibia is worn and cracked.
A common reason for accelerated loosening is a process known as osteolysis. This term simply refers to the resorption of bone, but it usually is indirectly related to a slow inflammatory reaction caused by plastic wear. If an artificial joint contains a metal or ceramic surface that rubs against a plastic (polyethylene) surface, over a period of years millions of microscopic plastic particles are generated from the wear. White blood cells try to digest these plastic particles, and when they cannot be digested, the cells burst and release the enzymes that they normally use to digest bacteria and foreign bodies. As a result of this process being repeated millions of times, some of the bone that anchors the prosthesis in place is reabsorbed, leading to loosening.
As more has become known about this process, engineering efforts in the past decade have focused intensely on solving this problem. As a result, ceramic on ceramic or metal on metal joints have come into widespread use (especially for younger patients) that generate less wear by eliminating the plastic components.
This is the same patient after revision of his knee
This x-ray shows the knee from the
side in order to better
show the long stems used
to reconstruct the knee
after removing the
old broken prosthesis.
In replacements that still need a plastic component, the plastic (polyethylene) has been improved markedly with materials engineering improvements, such as highly crosslinked polyethylene. These newer materials are thought to produce far less wear than previous generations of hip and knee replacements. Additionally, a sterilization process using gamma radiation in the 1990’s was responsible for early wear of many of the plastic components within 10 years or less, but engineering advances in the past 15 years have largely made this a historical issue. The plastic components used today are expected to last many years based on simulator studies and retrieval studies.
Many modern hip and knee replacement designs allow for a limited revision surgery called a liner exchange.
When the plastic liner in the hip socket or the plastic bushing between the metal parts of a knee replacement begins to wear out, often a limited surgery can be performed to simply replace the plastic component only.
In this way, the metal parts that are grown in or cemented to the surrounding bone do not need to be revised, and the limited revision has a fairly quick recovery and takes significantly less time than a surgery that revises the parts fixed to the bones.
Artificial joints do not often become infected, but when they do, surgery is usually required. Infections can either occur in the weeks or months after surgery or can occur because of hematogenous spread (spread of an infection through the bloodstream to the joint replacement). For this reason, patients with joint replacements are urged to seek medical treatment whenever they become ill with fevers or have a prolonged infection in another part of the body (such as a urinary tract infection or a diabetic ulcer on a leg that does not heal). There is a risk of a prolonged infection at one of these sites spreading through the bloodstream and causing the previously healthy joint replacement to become infected.
If an infection has only been present for a short period of time (a few days), it may be possible to simply “wash out” the joint. This is often referred to as “irrigation and debridement.” This surgery usually involves cleaning the joint out, removing any infected appearing tissue, and washing a large amount of saline and antibiotics through the wound. Some infections may be treated with an arthroscopic washout, meaning that small incisions and an arthroscope may be used for the procedure.
When bacteria multiply and adhere to an artificial surface, it is difficult for the body's immune system to remove the bacteria. The most virulent types of bacteria multiply on the artificial joint surface and build a wall, called a glycocalyx, that prevents the immune system from getting at them. As a result, if an infection has been present for a while (more than a few days or couple of weeks), it may be necessary to remove the artificial joint entirely, treat the patient with antibiotics, and then re-implant the joint replacement weeks or months later when the infection appears resolved.
Often a cement spacer that is impregnated with high-power antibiotics is placed within a hip or knee joint after removing a prosthesis. This keeps the space for the replacement from filling in and also delivers antibiotics into the joint for weeks. The spacer is removed when the joint replacement is reimplanted.
It is not uncommon for an infection of any type (not just joint replacements) to require an open wound in order to heal. Infections that are closed over tend to not resolve as well as those that are left open, allowing the wound to drain.The body then fills in the infected space from the bottom up, with healing tissue called granulation tissue.
The classic treatment has employed frequent dressing changes to pack the wound as it heals, although recent advances have included wound vacs that have greatly improved the process.sponge is placed into the open wound and covered with a plastic dressing, and a vacuum pump is attached through a small hole in the dressing. This draws out any fluid but also pulls the edges of the wound close together, A surgical helping it to heal significantly faster. The vacuum pumps are small enough now that they may be worn on the patient's hip in a small holster, allowing the patient to get out and about while the vacuum pump heals the wound. The sponge and dressing typically only has to be changed two or three times per week in most cases, which has greatly facilitated the treatment of such wounds.
Instability or Dislocations
Sometimes a joint replacement becomes unstable, with the artificial joint dislocating or subsiding (sinking into the underlying bone that anchors it). Hip replacements can be particularly problematic if the ball keeps popping out of the socket (dislocating), which requires a trip to the hospital to pop the joint back into place under quick anesthesia. If it happens just once or twice, often as the result of some careless or risky activity, no further treatment may be necessary and the patient goes on to enjoy their joint replacement without difficulty.
This patient presented to our practice having gone
many years since she saw her surgeon (she had
moved here from another city). At this point, this
hip replacement is dislocated, chronically infected,
and broken. This will require extensive surgery
to fix, but most patients seek help years before
reaching this point.
At other times, however, the dislocations can become recurrent and problematic. Repeated dislocations (or problems with instability in general, as can occur with a knee replacement) may lead to the need to revise the joint replacement to make it more difficult to dislocate. For example, with a hip replacement that develops recurrent dislocations, possible treatments might include changing the ball to a larger diameter ball, using a liner in the socket that has a lip to add more stability (at a cost of decreased range of motion), changing the angle of the components if they are not optimal, or changing the length of the femoral neck to increase tension in the joint and hold it in place (with a trade-off of making the leg longer). Sometimes the underlying problem may be more complex, possibly including multiple causes, and extensive revision surgery may be recommended.
Outcomes From Revision Joint Replacement Surgery
As technology and surgical techniques have
progressed, revision surgery has much better outcomes
than it did twenty to thirty years ago. However, as
noted at the beginning of this chapter, revision
arthroplasty often is still one of the most complex
procedures in modern orthopaedic surgery.
Complication rates are higher among revision surgeries,
particularly the more complex revisions that require
extensive reconstruction or in older patients.
Not all revision surgery is necessarily complex;
some revisions are limited and may only require
exchanging a liner or other part. Still other surgeries
may represent major undertakings to remove broken
parts and cement, reconstruct portions of the pelvis,
femur, or tibia, and augment with bone graft. There is
a wide variation depending on exactly what is needed.
Please remember the information on this site is for educational purposes only and should not be used to make a decision on a condition or a procedure. All decisions should be made in conjunction with your surgeon and your primary care provider.