TREATMENT OF TOTAL  KNEE INFECTIONS

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The more complicated model of total knee prosthesis the greater the risk of postoperative infection (Furnes 2002)

Type of total knee prosthesis	%  of postoperative infections
Unicondylar knee prosthesis	< 0,3%
Total knee without patella replacement	0,3 %
Total knee with  patella replacement	0,7 %

 

The knee joint lies more superficially and it is thus easier to discover a postoperative infection. Due to this the late postoperative infections after total knee replacement make only about 40 % of all postoperative infections.

Once the wound infection gets hold in the tissues around the total knee joint, treatment of postoperative infection with antibiotic only is not effective.

This is so because the infecting bacteria produce quickly a slime envelope that protects them effectively against the action of antibiotics.  The prosthesis and the soft tissues have slime forming bacteria firmly adherent to them. The surgeon must remove the  infected total joint prosthesis with tissues around it   mechanically. First when the  the slime forming bacteria have been removed the antibiotic treatment  will be effective against the few bacteria that remained.

The most often used, and the most often successful method is the   staged exchange of the infected prosthesis. This method uses  two operations to heal the infection.

 

Staged exchange of an infected  total knee prosthesis   Click on the icons for a full size picture A.   The prosthesis bathes in a sea of pus (gray in the picture). The infection has destructed large areas of skeleton around the prosthesis. B.   In the " first stage" operation the surgeon removes the prosthesis and all infected tissues around it. The surgeon then places two large piece of bone cement, formed as the removed  knee prosthesis in the space after the infected total knee joint prosthesis (yellow in this picture). The wound is then closed. The pieces of bone cement are called spacer. They are imbibed with potent antibiotics. The spacer  has two functions: First, it keeps the muscles and other tissues around the knee joint  at right tension. Second, large quantities of antibiotics leak continually from the spacer  in the space after the removed infected prosthesis. If any bacteria remained in this space after the  extraction of the infected prosthesis, it will be now killed by the high concentration of antibiotics. With the spacer in place, the patient can continue to use his/her leg and exercise the muscles. The use of  the spacer is a big progress compared with the older practice, when the patient has had a traction through his leg and was confined to bed. Antibiotic treatment with massive doses of antibiotics continues for several weeks. (Short antibiotic treatment is one of the causes for failure of the staged exchange operation) C.   When laboratory tests show that the infection is eradicated, the surgeon carries out the second stage of this procedure. In a second operation, the surgeon removes the spacer and puts a special new total knee  joint prosthesis in place. The revision total knee prosthesis has long shafts. With these shafts the components can be anchored in the intact parts of the thigh and shin bones. Usually, the surgeon must use a filling material to fill all dead space around the revision prosthesis. The material may be bone cement imbibed with antibiotics, bone grafts, or a mixture of both. (Void space would otherwise collect blood and offer nourishment to new bacteria) Antibiotic treatment continues after the second stage operation. Some patients may need very long, sometimes lifelong, suppressive antibiotic therapy after staged  revision operation, with all risks that such treatment implies.

Results of treatment of PWI after the  knee operations:

The results depend on

• how early the PWI was detected and treated. The PWI detected and treated late have worse results than PWI detected and treated early 

• how widespread was the destruction of bone and soft tissues 

• what kind of bacteria caused the PWI

PWI caused by the so called Gram- positive bacteria are easier to treat than the infections caused by the so called Gram -negative bacteria.

(Gram- positive and Gram-negative bacteria: classification introduced by the Danish bacteriologist H C Gram.)

In general, about 70% of all PWI after the total  hip or knee replacement will heal after the first staged exchange operation, 15 % will need repeated staged exchange operations, and in about 15 % of all PWI, the artificial hip or knee  joint cannot be saved.

.Patient satisfaction after the staged exchange

The results of the staged exchange operations after PWI of  total knees are worse then the results of revision operations for non-infectious loosening of total knee prostheses.

Compared with revisions for  non-infectious loosening of the total knee, the patients with successful staged exchanges have more stiff knee, more often residual pain, and could less often return to the activities of daily living.

In spite of these deficiencies, the patients with successful revision operations of the  infected total knee were equally satisfied with the results as the patients with revisions after the non-infectious loosening. (Barrack  2000)

When the exchange operation fails,

The surgeon has more options how to treat the unstable rests of the knee joint if the exchange operations of the total knee replacement fail.

The fusion operation (arthrodesis) of the rests of the knee joint is much easier and more often successful than the attempts to fuse the failed total hip joint.

Many patients can be fitted with a brace and need not a fusion operation.

There are still (very few) patients where a failed   total knee prosthesis must be treated with an amputation

(Robertsson  1999)

References:

Barrack RL et al.  J Arthroplasty 2000;15: 990-3

Furnes et al.  Acta Orthop Scand 2002; 117-29

Robertsson O et al. Acta Orthop Scand 1999;70:467 -72

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