Knee Reconstruction, Soft Tissue

Soft tissue defects of the knee that require reconstructive surgery occur after trauma or following a surgical procedure. A common procedure that may require reconstructive surgery to achieve adequate soft tissue coverage of the knee is total knee arthroplasty (TKA). Wound breakdown with exposure of the prosthesis is rare and is a challenge for both plastic and orthopedic surgeons. Previously, recommended management has been implant removal followed by arthrodesis and, at times, has required above-knee amputation (AKA). More recently, the goals are to preserve the prosthetic components and the function of the knee. ^[1] Knee coverage to avoid arthrodesis or AKA results in a more normal gait and greatly reduces the energy required for the patient to ambulate. See the image below.

The salvage of the knee in this patient allows for greatly improved function over an above-the-knee amputation.

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Reconstruction must be designed so that the desired functional and aesthetic results can be achieved using the simplest method available and with minimal donor tissue or donor-site morbidity. Early, aseptic closure is of paramount importance to the preservation of the function of the knee joint. Soft tissue reconstruction can reestablish mobility and joint function, provide dynamic stabilization of the joint, provide soft tissue coverage of the prosthesis, and fill the dead space. Good, healthy, well-vascularized soft tissue coverage leads to positive local effects, provides dead space obliteration, and improves the host’s defenses by increasing vascularity, which results in the proper delivery of oxygen, antibiotics, and humeral defense factors to the wound bed.

Another cause of soft tissue deficit results from the release of burn contractures involving the knee. ^[2] In burn injuries of the knee, contractures left untreated for prolonged periods result in permanent shortening of the flexor tendons, nerves, and vessels. Patients with contracted burned extremities also present multiple problems for nurses, one of which is the maintenance of perineal hygiene. Adequate release of these contractures is possible only after lengthening the shortened tendons. Release of the contracture leaves large skin defects and exposes bow-stringed hamstring tendons and major vessels and nerves in the popliteal fossa, requiring soft tissue coverage.

For excellent patient education resources, visit eMedicineHealth's patient education article Knee Joint Replacement.

Frequency

The knee is an anatomical area with little padding and minimal excess skin. As such, relatively minor injuries can lead to joint exposure. As many as 17-20% of patients with arthroplasties have complications that result in healing difficulties, ranging from superficial skin loss to more severe areas of skin and subcutaneous tissue necrosis and implant exposure.

Risks

Penetrating trauma or surgical wounds both put the knee at risk of exposure. Exposure can progress to infection of the joint or prosthesis. Prostheses in the knee are particularly at risk because of their superficial location and the location of the surgical access wounds. The need for early motion may interfere with wound healing, jeopardizing the prosthesis. Often, patients who require a knee replacement have insensate and unstable skin around the knee joint secondary to trauma, post–knee arthroplasty wound breakdown, or persistent synovial fistula following an arthroscopy.

Patients requiring a TKA often have a long history of degenerative joint disease, rheumatoid arthritis, or systemic lupus erythematosus. Most patients with these diseases are female. Subsequently, they may be on long-term steroid therapy, which adversely affects wound healing.

After excision of malignant tumors, some patients receive radiation and chemotherapy, which impairs wound healing. This requires continual surveillance because infection or open wounds can happen early or as many as 1-3 years after surgery. Other factors that negatively affect wound healing include a history of smoking prior to surgery, long-term steroid treatment, diabetes mellitus, hypoproteinemia, and hypothyroidism. Ultimately, the knee may be exposed as a result of impaired healing, poor vascular supply, or simple mechanical erosion.

The most common cause of failure is infection. The knee can become infected by early postoperative cellulitis, abscess, or delayed hematogenous seeding. Wound complications increase the risk of infection and implant loss. Soft tissue defects occur at the central-to-distal third of the incision. True dehiscence is a more severe postoperative complication, is more likely to have bacterial contamination requiring more rapid action, and may have a poorer outcome.

Differentiating wound infection leading to wound breakdown from failed wound healing leading to contamination is important because different clinical outcomes are expected. If contaminated, the knee can be irrigated thoroughly and closed with a flap; however, if it is infected, the prosthesis should be removed, the flap should be closed, and antibiotics should be administered for 6 weeks. Wound contamination occurring outside the United States is mainly by staphylococci; in the United States, pseudomonads are observed. Chronic infections that occur 3 months or more after arthroplasty can also involve staphylococci or pseudomonads.

The knee is composed of 4 bones: the femur, tibia, fibula and patella. All these bones are functional in the knee joint, except for the fibula.

The femur is the longest and strongest bone in the human body. The proximal end forms the head of the femur, which projects anterosuperomedially to articulate with the acetabulum. The distal end is wider and forms a double condyle that articulates with the tibia and patella. The tibia articulates with the distal lateral and medial femoral condyles. The patella articulates anteriorly to the femoral condyles in the region of the intercondylar fossa (trochlear groove).

The tibia lies distal to the femur and medial to the fibula. The proximal end consists of medial and lateral condyles, an intercondylar area, and the tibial tuberosity that articulates with the medial and lateral condyles of the femur. Distally, the tibia articulates with the ankle. The distal and proximal ends of the tibia articulate with the fibula. In addition, the shaft of the tibia and fibula are connected with an interosseous membrane to form a syndesmosis joint.

The fibula does not articulate with the femur or patella. Furthermore, the fibula is not directly involved in weight transmission.

The patella is the largest sesamoid bone in the human body. This bone is flat, proximally curved, and distally tapered; however, the shape can vary. The posterior patella articulates with the femur, but the apex sits proximal to the line of the knee joint. The tendon of the quadriceps femoris completely encompasses the patella.

For more information about the relevant anatomy, see Knee Joint Anatomy and Muscular System Anatomy.

See also Surgical therapy for anatomic details of specific flaps.

Judging the potential for meaningful postsurgical rehabilitation is the first consideration when evaluating a patient in need of soft tissue reconstruction over the knee. Consider whether the patient is reluctant to participate in a complex rehabilitation. Many procedures are performed in conjunction with an orthopedic procedure (eg, TKA, tumor resection) that requires complex rehabilitation. Also consider whether significant neurologic deficit (eg, paralysis, myopathies) will limit the patient's mobility. Moreover, consider whether the knee contracture has significantly limited the range of motion of the knee.

Another issue to consider before surgery is that patients must undergo routine preoperative clearance. Identify characteristics that place patients at higher risk for complications. Cardiac disease (eg, a history of myocardial infarction, angina, hypertension, diabetes, peripheral vascular disease, congestive heart failure) is a risk factor. Another is pulmonary disease (eg, emphysema, chronic obstructive pulmonary disease). Also consider a history of embolus or deep vein thrombosis, obesity, age (>70 y), drug use (eg, ethanol, tobacco), and gastrointestinal reflux disease as pertinent surgical risk factors.

If the patient is deemed a moderate risk to receive general anesthesia, many of the procedures outlined in this article may be performed with the patient under spinal anesthesia.