Soft Tissue Coverage

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Introduction

Successful outcomes after total knee arthroplasty (TKA) depend on rapid and uncomplicated wound healing. Problems in achieving this milestone may result, at a minimum, in delayed rehabilitation and in other cases may contribute to failure of the TKA. Whereas up to 20% of patients experience some type of wound problem, the rate of serious problems that require reoperation is less than 0.5%. Factors that may be associated with poor wound healing were reviewed in Chapter 36 . Even if all efforts are made before, during, and after the TKA to reduce the risk of soft tissue problems, situations will occasionally occur that require additional soft tissue procedures.

Whether these circumstances arise intraoperatively or postoperatively, soft tissue transfer procedures that are performed either concomitant with the TKA or days to weeks later are considered salvage procedures. In distinction, soft tissue transfers that are performed weeks to months before the knee surgery are considered prophylactic procedures. Recent work has suggested that these prophylactic procedures are associated with better results, most likely because of a reduction in the risk of infection, the provision of a pliable soft tissue envelope, and minimal impact on rehabilitation after the knee surgery. When a flap that was transferred prophylactically is mobilized at the time of TKA, postoperative range of motion (ROM) and physical therapy may need no or only minimal changes compared with standard rehabilitation protocols. On the other hand, when a salvage flap is required, prolonged periods of bed rest or immobilization may be needed and can seriously affect the functional results of the TKA. In this chapter, soft tissue transfers that may be used either prophylactically or in the salvage setting are reviewed.

Indications and Contraindications

Prophylactic soft tissue transfer may be required in patients with substantial risk factors for wound healing problems. In particular, patients with multiple prior longitudinal incisions about the knee, failed prior soft tissue expansion, or adherent or poor subcutaneous tissues around the knee resulting from prior simple skin grafts onto fascia, radiation treatment, or burns may be at increased risk of wound healing problems. In these cases, options for prophylactic soft tissue transfer include rotational or free fasciocutaneous perforator flaps, such as the anterolateral (ATL) thigh flap; local rotational muscle flaps (with or without the skin and subcutaneous tissue), such as the medial gastrocnemius flap; and free muscle flaps, such as a latissimus dorsi or rectus abdominis muscle flap (with or without the skin and subcutaneous tissues). In general, local rotational fasciocutaneous perforator flaps are best used in the presence of smaller areas of skin involvement without infection, whereas local rotational muscle flaps and free flaps are better suited for larger areas of involvement.

There are no absolute indications to guide the orthopedic surgeon about when a prophylactic procedure should be used; instead, this decision is based on an educated assessment of all the risk factors that are present, including systemic conditions that may further complicate the wound healing potential. Some patients who undergo prophylactic soft tissue procedures might have been able to heal adequately after TKA without them, but considering the potentially devastating complications that can occur if wound problems develop, some degree of overutilization of preemptive soft tissue procedures seems preferable. Fasciocutaneous perforator flaps are particularly well suited for use in the prophylactic setting. The advantages of these perforator flaps in comparison to local muscle flaps include minimal functional deficits (because no muscle is transposed) and better cosmetic results at the recipient site (because they tend to be less bulky and can be easier to revise from a cosmetic standpoint).

Relative contraindications to prophylactic transfer include active soft tissue infection about the knee and deep periprosthetic infection. In these cases, removal of implants or débridement in the setting of acute infection with a simultaneous soft tissue procedure should be considered. Another relative contraindication to the use of soft tissue transfers is an elderly patient with medical comorbidities such as advanced chronic obstructive pulmonary disease, coronary artery disease, or severe cardiac valve stenosis that could contribute to a high risk for perioperative complications during the long operations. Absolute contraindications for prophylactic free muscle flaps include advanced peripheral vascular disease or prior damage to the arterial inflow to the lower leg, where there is no potential for reconstruction of the vessels. In some circumstances, a vascular surgery consultation with Doppler ultrasound imaging or a computed tomographic (CT) angiogram of the legs should be obtained to help define what vascular reconstructive options exist. Another absolute contraindication is multiple prior failed rotational muscle flaps, or free flaps where no viable soft tissue transfer options remain, especially when the soft tissue defect is large.

In the salvage setting, local rotational fasciocutaneous flaps may be used, but in our experience they may not provide adequate coverage; furthermore, use of fasciocutaneous perforator flaps in the setting of deep periprosthetic infection is controversial. In these circumstances, the medial gastrocnemius muscle flap remains the primary means of restoring adequate soft tissue coverage, especially if the wound breakdown occurs over the proximal medial tibia. In some circumstances, the lateral gastrocnemius is also an excellent option. If the medial gastrocnemius has been used previously, or if the compromised soft tissue extends proximally above the level of the tibial tubercle or over the patellar tendon, a free muscle flap or alternative should be considered. Therefore, in most salvage settings we encounter, either medial gastrocnemius muscle flaps or free muscle flaps are most commonly used for gaining adequate soft tissue coverage about the knee.

Relative and absolute contraindications for salvage soft tissue transfers include the same concerns as for prophylactic flaps. However additional contraindications may exist. In the complex clinical settings in which salvage flaps are often required, patients may have numerous associated life-threatening medical comorbidities such as sepsis or hemodynamic instability. In these circumstances, even when the soft tissue defect is ultimately reconstructable, a decision must sometimes be made whether local débridement followed by delayed reconstruction or immediate life-saving amputation is the best choice.