What are the Risks of Knee Replacement Surgery?

Studies indicate that 90% to 95% of knee replacements are successful, with most patients pleased with the pain relief and exceptional functional recovery that are common after the procedures. Nonetheless, occasionally complications occur. Typically, these complications are minor and have limited clinical consequence; in rare instances, additional surgery or medical management may be necessary. The list below is a description of some of the complications that may arise. The list is not all-inclusive; some unforeseen problems may occur. Dr. Lonner and the clinical staff at the 3B Orthoapedics and Philadelphia Center for Minimally Invasive Knee Surgery will discuss these risks with you. This section is intended for educational purposes. It is not meant to substitute for the consultation with Dr. Lonner and the professional associates in the practice.

Infection:
The risk of getting an infection after knee replacement surgery nationwide is approximately 1 to 1.5%. A recent analysis at Pennsylvania Hospital found that the risk of infection in Dr. Lonner’s practice is 0.5% or one half of one percent (data from 2008). Precautions are taken to minimize the development of infections, including giving antibiotics before and after surgery, performing surgery in an efficient manner, minimizing soft tissue trauma, and using a specially ventilated surgical room (termed laminar flow) and self-contained exhaust suits. Despite these precautions, infections may occur. If an infection develops, and is diagnosed early, treatment involves washing out the knee replacement. This has a success rate that ranges from 9% to 56% depending on the bacterial organism and duration of infection. Oftentimes when an infection develops, the implant must be removed and the joint thoroughly cleaned and washed out. In those circumstances, a temporary implant coated with cement and a high concentration of antibiotics is inserted in the knee. Typically, after three months with the temporary antibiotic spacer, a revision of the original knee replacement can be performed, with a likelihood of clearing the infection of between 85% and 90%. Occasionally, reimplantation is either unsuccessful or not practical and if so, an attempt is made to fuse the knee (made stiff so that the patient can walk), although some patients find this undesirable since they can’t bend the knee afterwards. In rare instances, because of overwhelming infection or when an infection cannot be cleared, an above knee amputation is necessary. Most knee infections come from other sites in the body, traveling to the knee through the blood stream. That is why you should call your medical doctor immediately if you have a bacterial infection (urinary tract infection, pneumonia, infected toe nail, etc.) or your dentist if you have a tooth abscess- so you can be placed on antibiotics as soon as possible to limit the risk of infection spreading to your knee. If you think your knee may be infected, call us immediately so you can see Dr. Lonner or one of his associates for an evaluation before starting antibiotics.

Blood Clots:
Blood clots occur commonly after knee replacement surgery. Most blood clots cause no symptoms and those which do oftentimes require no treatment. Occasionally, however, blood clots are large or occur in the larger veins of the lower extremities. These blood clots may require treatment, including the use of additional and prolonged blood thinners and occasionally a filter which helps to catch the blood clot if it embolizes (dislodges and travels through the veins). Embolization that travels to the veins in the lungs or brain can cause respiratory difficulty and chest pains or a stroke. There is a very small risk of death, occurring in less than 0.1% of cases. Occasionally blood clots can cause chronic swelling, pain or discoloration of the lower extremity. However, studies have shown that the risk of this condition, known as post-thrombotic syndrome, is low in patients with asymptomatic blood clots. We use blood thinners such as aspirin or coumadin, as well as mechanical pumps, to minimize the risks of phlebitis or blood clots, but they may still occur.

Nerve Injury:
There are several nerves that run by the knee joint that are at risk during or after surgery. These nerves may be at particuilar risk in patients who have had prior knee surgery or in patients with significant knee deformity. For instance, stretching of a nerve called the peroneal nerve can occur when correcting an arthritic knee with a knock-knee deformity. Symptoms of a nerve stretch include numbness and tingling and occasionally partial or complete weakness in the toes, foot and ankle. A stretched nerve will often regain its function and sensitivity over a 6 to 12 month period. Cutting the peroneal nerve is unusual during knee replacement, but has been reported in the literature. Occasionally, particularly in patients who have diabetes or poor blood flow to the leg, numbness, tingling, or weakness may develop in the foot after surgery, because the nerves are sensitive to the use of tourniquets in surgery and to bending as part of the surgery or postoperative rehabilitation. Rarely temporary nerve palsy can occur if the peroneal nerve around your knee gets compressed against the frame of the continuous passive motion (CPM) machine that we often use after knee replacement surgery for rehabilitation. The nurses in the hospital will constantly monitor the position of your limb in the CPM while you are hospitalized.

All patients have numbness next to the scar (on the outside of the knee) because the small nerves that provide sensation to the skin around the knee must be cut during surgery to gain exposure to the knee. While the area of numbness may shrink slightly over several years, it will always be present.

Blood Vessel Injuries:
Numerous blood vessels pass through and around the knee. Most of these are small vessels which cannot be seen or are just large enough to be cauterized (surgically sealed) during the procedure. Occasionally, these vessels can cause a small amount of bleeding into the knee joint after surgery, resulting in swelling, pain, and perhaps even a small amount of drainage, which typically stops with a period of immobilization and compression.

There are several larger arteries in the back of the knee. There are two primary concerns with these arteries (blood vessels) – one is that they can become blocked (clotted) during surgery; the other is that they can be lacerated. Both of these are uncommon complications (well less than 1%), but if they occur, a vascular surgeon will be called upon to assist in your care. Patients with significant peripheral vascular disease (poor circulation), may be asked to see a vascular surgeon before knee replacement surgery to advise us whether a tourniquet could be utilized during surgery (which is the norm) or even whether the vascular surgeons should perform a procedure before surgery (such as an arterial bypass or angioplasty) to improve the circulation.

Loosening:
While some knee replacements will last a lifetime, others will loosen over time and may require additional surgery. Signs of loosening include new onset of swelling or pain with weight bearing that was not present previously. Most cases of loosening will occur after ten years, although early cases of loosening can occur in some patients.

Wear:
The knee replacement is made of both metal and a plastic bearing (polyethylene). Contemporary polyethylene inserts are durable, but they can wear out over time, causing swelling, inflammation and tightness in the knee. Ultimately, wear of polyethylene can lead to loosening of the implant, requiring revision surgery. Early identification of polyethylene wear can occasionally be treated by changing the plastic bearing, other times a complete revision of the entire knee replacement is necessary.

Fracture:
The bones around the knee are at risk for fracturing either during implantation or at any time after surgery. Treatment of fractures can range from protected weight bearing and observation with immobilization of the limb in a brace or cast to surgical intervention or revision of the components. This typically depends on the type and location of the fracture, level of disability associated with the fracture, and whether the implant is loose.

Avascular necrosis of the patella:
One of the risks of putting in an artificial polyethylene button on the patella (which is typically done during total knee, patellofemoral and bicompartmental replacements) is that the remaining bone of the patella may lose its blood supply and develop a condition called avascular necrosis. This condition often causes no symptoms and may require little treatment other than modification of activity and observation. However, it occasionally causes pain in the front of the knee and may make a fracture of the kneecap more likely. In rare instances, surgical intervention may be necessary, although the success of treatment varies.

Persistent Pain:
While pain is either substantially reduced or completely relieved in 95% of patients, occasionally some pain persists after surgery despite a well-fixed and well-aligned and well-functioning knee replacement. Often this is related to soft tissue irritation, which is unpredictable and unavoidable after knee replacement surgery because the soft tissues of the knee such as tendons, joint lining, ligaments and muscles rub on the implant surfaces. Occasionally pain can result from sources such as bursitis, tendonitis, swelling, and other treatable conditions. A condition called reflex sympathetic dystrophy has also been reported to occur and may require neurological intervention. Other times, pain in the knee may result from an arthritic or diseased hip or lower back – this is called “referred pain.”

Stiffness:
While the average knee motion after total knee replacement surgery ranges between 115 to 125 degrees, occasionally patients end up with less motion and stiffness. The knees of patients who had very limited motion prior to surgery and who had poorly controlled pain may remain stiff after surgery. If you have a difficult time gaining flexibility after knee replacement surgery, despite pain management and physical therapy, a manipulation under anesthesia may be recommended to try to restore motion and break-up scar tissue which may have formed. The manipulation is typically performed with epidural anesthesia and requires an overnight hospital stay. In rare instances, changing one or several components of the knee replacement and removal of scar tissue may be recommended in an attempt to improve motion in a stiff knee.

Leg Length Discrepancy:
When a total knee replacement is performed the limb is straightened, degenerated cartilage is replaced, and contracted ligaments are balanced. Each of these steps results in the relative lengthening of the limb. Often, the lengthening is imperceptible, but occasionally patients notice a difference in the limbs length. In these cases, a shoe lift may be necessary. This condition may be more pronounced in patients who also have hip arthritis, a limb deformed from trauma, or scoliosis (curvature of the spine) with a tilted pelvis. Some patients may even have an apparent leg length discrepancy before knee replacement surgery, but it may not be evident to them because they have lived with it for years. Occasionally it does not become noticeable to them until after the knee replacement. This is less likely in the partial knee resurfacing procedures.

Limp:
Occasionally patients limp after knee replacement surgery. This may be because of weakness of the quadriceps (thigh) muscles, pain, leg length discrepancy, or arthritis in other joints of the lower extremities. Depending on the cause of the limp, it may improve after several months as the patient recovers from surgery. A new limp (particularly one that is accompanied by knee pain) that develops after a successful knee replacement could be a sign that there is a problem with the implant (such as loosening, wear, or infection) A patient with these symptoms should seek an immediate consultation with us.

Tendon or Ligament Tear or Rupture:
There are a number of tendons and ligaments around the knee which are protected and preserved during knee replacement and resurfacing. In rare cases, these can be injured during surgery; in other cases, a traumatic injury can damage these structures anytime after the surgery. In either case, they may need to be repaired or reconstructed.

Instability:
Occasionally, the ligaments around the knee may stretch out. Subtle instability may develop making the knee feel unsteady. This may cause pain, swelling, or a sense of buckling. Treatment of this problem may range from bracing and physical therapy, to insertion of a thicker plastic bearing surface, or complete revision of the knee replacement. Unlike hip replacements, which dislocate in approximately 1 to 2% of cases, dislocation of the knee replacement components is unlikely in the absence of trauma. Nonetheless, occasionally, knees can dislocate from traumatic events, requiring surgical repair.

Patella (Knee-cap) Dislocation:
Occasionally, the patella (kneecap) will dislocate after knee replacement. Depending on the cause, treatment may involve bracing, realignment of soft tissues, or even revision of the components. A condition called “patellar clunk” occurs when a nodule of scar tissue develops on the undersurface of the knee-cap and quadriceps tendon. This can cause a grating sensation and a “clunking” sensation as the knee is straightened from a bent position. It can be treated successfully by arthroscopic shaving of the nodule.

Blisters:
Occasionally blisters can develop around the knee, thigh, foot, or ankle, as a result of swelling. The blisters generally heal but occasionally can form large scabs, which may take a while to heal. In rare cases, additional surgery may be necessary to help the healing process.

Problems Unique to Partial Replacements:
The partial knee replacements only resurface one or two of the three compartments of your knee, leaving the non-arthritic compartments with their natural parts. The cartilage in the remaining compartments may develop arthritis, the meniscus (shock absorber) may tear, or the ligaments in the knee may become injured. Those problems may require treatment, such as arthroscopic surgery for a torn meniscus. If you develop arthritis in the portion of your knee that was not resurfaced, it may be necessary for you to undergo either a partial resurfacing of the arthritic compartment or conversion to a total knee replacement. If you develop a problem in another part of your knee after partial knee resurfacing surgery, do not have cortisone (steroid) injected into your knee because it could theoretically put your knee at an increased risk of developing an infection. However, occasionally bursitis (a type of soft tissue inflammation) can develop – this can be treated with a local cortisone injection, medicine, and physical therapy.

Medical Complications:
There are risks of anesthesia and medical complications which can occur during and after surgery. The anesthesiologist assigned to your case will discuss the anesthetic risks. Your medical care will be managed by the consultant medical physician who will monitor your health from a medical perspective while you are hospitalized and afterwards. Potential medical problems may include, but are not limited to, nausea, vomiting, abdominal distention (ileus), intestinal obstruction, constipation, pneumonia, blood clotting, urinary tract infection, urinary retention, kidney infection, kidney failure, stroke, myocardial infarction (heart attack), irregular heartbeat, and even death. The risk of death after knee replacement surgery is less than 0.1% (one tenth of one percent).