Knee Reconstruction, Soft Tissue Treatment & Management

Updated: Sep 04, 2015
  • Author: Steven L Bernard, MD; Chief Editor: Jorge I de la Torre, MD, FACS  more...
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Treatment

Medical Therapy

Infected total knee prostheses require removal and treatment with long-term targeted antibiotic therapy. The author’s routine as supported by recent literature [3] is to stage the procedure by removing the total joint, placing an antibiotic (tobramycin)–impregnated methyl methacrylate spacer of the same approximate size and covering that spacer with a muscle flap (see following for technique). The patient is then treating with at least 6 weeks of antibiotics followed by a new TKA procedure.

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Surgical Therapy

Repairing a deep soft tissue defect around the knee is a difficult clinical problem. [4] Revision of the wound with secondary suturing is ineffective. Moving local muscles over most defects is required to adequately close deep wounds with exposed prostheses. Less extensive wounds may be amenable to simpler fasciocutaneous skin flaps, while more complex wounds require microsurgery to move tissue not adjacent to the knee down over the wound with free tissue transfer for knee salvage.

The first procedure to perform is an excision (debridement) of the wound to clinically viable tissue. Complete debridement is crucial and should, if possible, include removal of scarred or irradiated tissue. If the joint is entered during the debridement or is already exposed, thoroughly irrigate it with antibiotic solution. In the event of insufficient debridement, initial healing may be followed by a secondary fistula, ultimately leading to the loss of the implant.

When treating tumors around the knee, one should create the wound coverage flaps at the time of resection to avoid complications of wound healing and to reduce delays in chemotherapy.

The size of the resultant defect after wound debridement or tumor resection affects the decision for reconstruction. Typically, muscle flaps are preferred to skin-muscle (myocutaneous) flaps because they conform to the defect better than composite skin-muscle flaps, thereby eliminating dead space or improving coverage of a prosthesis.

The types of muscle and myocutaneous flaps available for reconstruction include gastrocnemius, vastus medialis, vastus lateralis, and sartorius flaps; however, these flaps are sometimes too bulky for reconstruction and result in varying degrees of functional loss. Another relative disadvantage of the myocutaneous flap is the degraded appearance of the calf after tissue donation.

To mitigate these disadvantages, local fasciocutaneous flaps can be effective if the underlying repaired joint capsule is intact. Fasciocutaneous flaps such as those described by Ponten are useful when the gastrocnemius muscle cannot be used or dehiscence is not extensive. [5]

Fasciocutaneous flaps do not further compromise an already crippled extremity, are simple and durable, and leave no muscle deficit. In addition, skin flaps do not preclude concurrent or future use of muscle flaps, require shorter procedural time, and ultimately result in less donor site morbidity. The cross-leg flap remains an option as well but is mainly of historical interest since the advent of free tissue transfer. The cross-leg flap involves significant additional morbidity resulting from fixing the legs together for a prolonged time, and this technique would be a last choice.

Finally, if the above options are inadequate or local tissue is of poor quality, the only option for knee salvage is free tissue transfer. The use of undamaged muscle or composite tissue from another area of the body can salvage an otherwise impossible situation. The main disadvantages of free tissue transfer remain donor morbidity and the need for microsurgical expertise.

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Muscle Flaps

Gastrocnemius flap

The gastrocnemius muscle flap is the workhorse of all muscle flaps for soft tissue coverage around the knee. The unique vascular anatomy of the gastrocnemius muscle (one pedicle at the level of the knee joint situated close to its origin), the size of the muscle belly, the fact that it is situated in the dissection field, and the fact that its transfer does not affect the function of the spared limb too adversely make it ideally suited to coverage of wounds in the knee region. [6]

The gastrocnemius muscles are the most superficial muscles of the posterior compartment of the leg. The medial gastrocnemius origin is the rough area of the popliteal surface of the femur immediately above the medial femoral condyle. The lateral gastrocnemius origin is on the upper posterior part of the lateral surface of the lateral supracondylar line of the femur. The anterior edge of the medial head lies along the medial border of the tibia, while that of the lateral head is separated from the tibia by the muscles of the anterior and lateral compartments.

Posteriorly, the muscle bellies converge in the midline of the calf, intermingling and running together inferiorly. Extending downward for approximately two thirds of the length of the muscles, aponeurotic bands cover the outer margins and posterior surfaces of the muscle subunits and provide further attachment for the muscle fibers. The tendon of the gastrocnemius joins with that of the soleus to form the Achilles tendon. These muscles act in concert to plantar-flex the foot. Because it crosses the knee, the gastrocnemius also contributes to the flexion of that joint.

In the popliteal fossa, nerves lie superficially and laterally to the vascular structures. The popliteal artery is the deepest and most medial structure. The medial and lateral sural arteries provide independent blood supply to the 2 heads of the gastrocnemius muscle. These vessels arise from the popliteal artery above the level of the knee joint. Each courses a few centimeters with its venae comitantes before entering the anterior aspect of the proximal muscle belly with the innervating branches of the tibial nerve. The vessels then pass down the longitudinal axis of the muscle bellies. The vascular arrangement is constant and effectively constitutes the sole supply of the muscle. The independent neurovascular supply of the 2 muscle bellies allows them to be used as separate muscle and musculocutaneous flaps.

Dissection can be performed under tourniquet control. A vertical incision located 2 cm medial to the anterior edge of the tibialis and overlying the pulse of the popliteal artery is used to visualize the medial gastrocnemius and soleus. To make the dissection easier, the patient should be in the prone or lateral position and the incision should be taken to a level above the knee joint in the midline.

The muscle flap is based proximally on the sural artery. Medially, the saphenous vein and nerve are located subcutaneously; avoid these. The sural nerve is identified and preserved at the deep lateral border at the intermuscular raphe midline as the nerve traverses the surface of the soleus muscle. The distal musculotendinous portion of the flap is transected, preserving the fine areolar tissue over the triceps surae and Achilles tendon, and then folded back on itself. The lateral gastrocnemius is elevated in a similar fashion, with preservation of the superficial peroneal nerve. The flap is then passed under a skin bridge, inset, and sutured in place. A split-thickness skin graft is applied, and the donor site is closed primarily.

When the neurovascular bundle is too short and jeopardizes the flap, dissection of the popliteal artery up to the Hunter canal and down to the trifurcation adds extra length to the vessels. Division of the origin of the medial head from the medial condyle of the femur releases the muscle and extends the arc of rotation by 5-8 cm, permitting more effective coverage of the knee and distal thigh. When the muscle is freed from its proximal and distal insertions, the only attachment left is its neurovascular bundle. Also, the dense fascia on the anterior aspect of the muscle may be incised, and the muscle can be tunneled under the semimembranosus and tendinosis with a flexed knee to gain length.

The skin paddles of the medial and lateral gastrocnemius muscles extend to within 5 cm of the medial malleolus and within 8 cm of the lateral malleolus, respectively. The arc of rotation and area of potential wound closure are greater for the myocutaneous flap than for the muscle flap alone. The proximal reach is 15-17 cm above the knee joint. Although myocutaneous flaps can cover a greater area than muscle flaps alone, the donor defect is extensive, leading to less satisfactory results.

The gastrocnemius muscle can be used to cover large soft tissue defects, described in one series as large as 60 cm2 and covering both the distal one third of the thigh and proximal one third of the calf with minimal aesthetic donor deformity. The decision whether to use the medial or lateral head of the gastrocnemius or the entire muscle unit depends on the size of the defect and its location. The medial segment of the muscle is used more often than the lateral segment because of its greater size and length as well as its easier mobilization.

This is particularly significant for long musculotendinous flaps providing vascularized replacement of the patella or quadriceps tendons. In patients with a partial defect of the tendon or loss of tendon thickness, the thick aponeurosis from the deeper aspect of the gastrocnemius can be dissected and transferred as a pedicled tendon flap to reconstruct the tendon defect. In patients with a complete defect of the tendon, the superficial layer of the Achilles tendon together with the deep aponeurotic layer of the gastrocnemius muscle can be used to reconstruct the tendon.

Postoperatively, the knee is immobilized for 7-14 days, and then the leg may be actively ranged. The gastrocnemius contributes significantly to ankle plantar flexion and is important in power push off, but removal of one head does not result in significant loss for most patients when compared to alternate treatments. Those with musculocutaneous flaps may report sensory loss in the distribution of the saphenous nerve, and peripheral edema is observed more often than with the simple muscle flap. Edema probably develops because the saphenous vein and adjacent lymphatics have been severed.

Muscle flaps with residual innervation demonstrate more secondary wound breakdown and more contraction pain due to spasms; therefore, consider denervation when using the gastrocnemius muscle. If the muscle is used to cover a defect left from the removal of a prosthesis, the interval between flap coverage of the knee and reimplantation of the prosthesis ranges from 35 days to 1 year in various reports, and orthopedic surgeons often place antibiotic impregnated methylmethacrylate as a spacer while awaiting reimplantation.

Gracilis flap

A study by Mitsala et al reported that a distally based, pedicled gracilis muscle flap can be used for complex soft tissue defects associated with an exposed knee joint, patella, or proximal knee or an exposed knee prosthesis, if a pedicled gastrocnemius muscle flap would be insufficient (ie, if the defect is in the superolateral area of the proximal knee) and a free flap is not an option. The study involved nine patients, with the pedicled gracilis muscle flap providing successful knee salvage in eight of them. [7]

Vastus lateralis flap

Vascular injuries in the popliteal region or below-the-knee amputations (BKAs) also occasionally preclude the use of a gastrocnemius flap. The vastus lateralis can be an option for soft tissue coverage because it is adequately sized, sufficiently long, and not too thick. The vastus lateralis muscle is 1 of the 4 parts of the quadriceps and is the largest of the quadriceps muscle group, extending from the proximal femur to the patella. The muscle is located between the vastus intermedius and the biceps femoris muscles and beneath the tensor fascia lata. It originates from the greater trochanter, intertrochanteric line, gluteal tuberosity, and lateral intermuscular septum and inserts into the patella.

The vastus lateralis is a type II flap and may be based on its distally located minor pedicle and rotated to the knee with an arc of rotation of approximately 19 cm. The flap is designed using only the mid muscle belly. If based on the distal 2 branches, the muscle flap can reach to the proximal one third of the tibia. Use of the entire muscle based distally may require microvascular anastomosis of the dominant pedicle to suitable receptor vessels at the defect site. The flap is ideally suited for use in the popliteal fossa posteriorly and in the inferior portion of the knee anteriorly. This muscle is a strong leg extensor muscle, but it is expendable because of the remaining 3 muscles of the quadriceps extensor group. The functional defects are of little importance.

The dominant pedicle is the descending branch of the lateral circumflex femoral artery and venae comitantes. It is located in the superior one third of muscle extending inferiorly along the medial border of the muscle belly. The pedicle enters the medial deep aspect of the muscle approximately 10-15 cm below the anterior superior iliac spine.

It also has 3 additional minor pedicles. The transverse branch of the lateral circumflex femoral artery and venae comitantes enter the muscle in its superior one-fourth deep surface. The posterior branch from the profunda femoris artery is located at the inferior half of the posterior muscle at the lateral intermuscular septum. Third, the superficial branch of the lateral superior genicular artery and venae comitantes courses around and superior to the lateral condyle of the knee deep to the biceps femoris and provides a superficial branch to the distal muscle, entering the lateral posterior aspect of the vastus lateralis muscle. Unlike the medial thigh, which has a segmental blood supply from branches of the superficial femoral artery (SFA), the vastus lateralis is devoid of significant vascular contributions in its mid portion.

The muscle extends between the gluteal tuberosity and greater trochanter of the femur to the patella in the anterior lateral thigh. The anterior portion of the tensor fascia lata is divided through a midlateral thigh incision, exposing the vastus lateralis muscle. The muscle is exposed through a lateral thigh incision from a point 10 cm below the anterior superior iliac spine at the level of the greater trochanter to the lateral condyle of the femur. The incision is carried through the deep fascia at the medial edge of the tensor fascia lata muscle in the proximal one fourth of the leg and the iliotibial tract distally. The border between the vastus lateralis and medialis is identified and separated.

In the distally based flap based on the minor pedicle, isolating and preserving a segment of the descending branch of the lateral circumflex femoral artery and associated venae comitantes is preferable. If the muscle circulation appears inadequate at the time of transposition, performing a microvascular anastomosis between the dominant pedicle and a suitable receptor vessel in the superior portion of the lower leg may be helpful. The distally based muscle flap may not be reliable and is recommended as an alternative flap. The donor site is closed primarily.

Vastus medialis flap

The vastus medialis muscle flap has been used as a rotation flap or advancement flap for small defects. It allows muscle coverage of the anterior knee to approximately 10 cm below the patella. The vastus medialis is a large muscle on the medial aspect of the thigh, deep to the sartorius and medial to the rectus femoris. It is a muscle and musculocutaneous flap with a type II pattern of circulation. It has one dominant pedicle, which is the branch of the SFA and venae comitantes. It enters the muscle at the junction of the middle and upper thirds accompanied by the motor nerve. Another branch of the SFA and venae comitantes and the musculoarticular branches of the descending genicular artery and venae comitantes are 2 additional minor pedicles.

The arc of rotation of the distal portion of the muscle may be elevated based on its distal minor pedicles. This muscle has a short arc of rotation useful for covering upper knee defects. It also may be designed as a V-Y advancement flap that covers the knee. The distal muscle is most useful for transposition as a flap based on the minor pedicles from the SFA. A skin island overlying that portion of the muscle also may be included with the flap for transposition. However, the most common application of this flap has been as a muscle flap covered with a skin graft. A composite vastus medialis musculocutaneous flap can be elevated for patellar tendon repair.

The patella, the medial condyle, and the anterior superior iliac spine are the major landmarks. The skin territory of this muscle lies between the skin territory of the rectus femoris and gracilis. The incision is made along the sartorius. The vastus medialis is identified under the sartorius, lying between the sartorius and the medial border of the rectus femoris. The muscle is divided from its insertion into the quadriceps tendon and is then separated from the other quadriceps muscles. Care must be taken to preserve the femoral neurovascular bundle, which lies just medial and deep to the vastus medialis. This muscle has a relatively small arc of rotation that covers only the upper parts of an exposed knee.

A V-Y advancement musculocutaneous flap is designed with the skin island apex extending medially toward the upper thigh and the base located at the knee. Flap elevation proceeds with the skin incision and elevation of the vastus medialis from the adjacent muscle. The flap is then advanced distally, and the donor area is closed as a V-Y flap. Further modification may include portions of the quadriceps tendon.

Sartorius flap

The delayed total sartorius flap provides a durable and somewhat reliable alternative for reconstruction of the knee in circumstances in which other reconstructive options are not available. The sartorius muscle is a long, thin, flat, superficial muscle extending from the anterior superior iliac spine diagonally across the thigh to the medial tibial condyle. The sartorius has a segmental vascular supply but receives its proximal and principal vascular pedicle from the profunda femoris vessels. At the level of the Hunter canal, small vessels that are branches of the femoral vessels form the inferior pedicle of the sartorius. Six to seven branches from the SFA provide blood flow to the sartorius muscle. The segmental vessels enter the muscle on the deep or medial surface. The greater saphenous vein, owing to its easy dissection, must be included in the superior proximal pedicle of the sartorius muscle.

The arc of rotation is limited by the segmental type IV blood supply. The muscle insertion may be transposed for coverage of small knee defects following division of the most distal 1 or 2 pedicles. Small islands of skin may be elevated with the underlying muscle. When the muscle is divided, suture the ends of the skin to the overlying fat. This helps prevent shearing stress to the small perforating blood vessels passing through the muscle into the skin.

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Fasciocutaneous Flaps

V-Y retroposition fasciocutaneous flap

Fasciocutaneous flaps can be simple and durable, while leaving no muscle deficit. Their use does not preclude concurrent or future use of muscle flaps and may be less likely to further compromise an already-disabled extremity. If the amount of soft tissue is in question at the outset of a TKA, these flaps can be performed concurrently with the knee replacement.

First, the deficit is debrided and incorporated in the proximal aspect of one limb of the V incision, with the point of the V pointed toward the foot. The incision is carried down to muscle. On the medial aspect, flap elevation necessitates sacrifice of the greater saphenous nerve and vein. Care must be taken when elevating the medial flap at the attachment of the tendons of the sartorius, gracilis, and semitendinous muscles. This medial flap is based on the saphenous artery and vein. If a similar flap is elevated laterally, be careful to avoid injury to the common peroneal nerve, which is superficial at the proximal fibula. A suction drain is placed deep to the flap and brought out through a separate stab incision.

Postoperatively, the patient is kept at bed rest with splinting of the involved knee for 2 weeks. Following the period of bed rest, ambulation is allowed in a graduated manner, and weight bearing is allowed as recommended by the orthopedic surgeon treating the patient. Knee ranging is begun 3 weeks postoperatively.

Saphenous flap

The saphenous flap was first described in 1981 as a free flap. [5] The saphenous flap is a reliable local flap for soft tissue coverage of the knee. It is a simple 1-stage operation. The saphenous flap is based on the saphenous artery originating from the descending genicular artery. It covers defects on both the anterior and posterior surfaces of the leg, including the popliteal fossa and knee joint. The flap has also been described as a reversed-flow saphenous island flap based on the medial inferior genicular artery and, rarely, a venous saphenous flap based solely on the saphenous vein.

The saphenous artery flap is located on the medial aspect of the knee and upper leg. The typical size of the flap is approximately 7 by 20 cm, but flaps up to 29 by 8 cm and 15 by 11 cm have been reported. It is a fasciocutaneous flap with type A circulation. The dominant pedicle, measuring 5-15 cm, is the saphenous artery branch of the descending genicular artery, a branch of the SFA, and venae comitantes. Occasionally, it arises directly from the popliteal artery. The descending genicular artery originates from the SFA 14-15 cm above the medial joint line of the knee. It then runs distally for 0.5-2 cm, dividing into 2-3 branches that include the saphenous artery, osteoarticular branch, and muscular branch.

The origin of the saphenous artery is approximately 13 cm superior to the medial joint line. The saphenous artery pierces the sheath of the adductor canal and then joins the saphenous nerve and passes deep to the sartorius muscle between the sartorius and gracilis muscles to supply the inferior medial aspect of the leg. At the level of the joint line, the sartorius muscle becomes tendinous, and the saphenous artery runs out from beneath the tendon.

At this level, several branches emerge and fan out over the capsule of the knee joint to anastomose with the medial inferior genicular artery and other branches of the patellar arterial plexus. Retrograde flow through the saphenous artery is supplied by anastomoses with the medial inferior genicular artery in a distally based flap.

The saphenous artery then continues distally in an epifascial plane and supplies another large area of skin on the anterior and medial aspects of the leg below the knee. Venous drainage consists of paired venae comitantes running along with the artery. The greater saphenous vein runs superficially 1-2 cm behind the artery.

Some prefer to perform angiographic studies before surgery to check for anatomic variations. Mapping of the subcutaneous perforators using Doppler ultrasound is also important for design. Typically, this flap has less subcutaneous fat than other flaps, facilitating easy detection of the perforators with Doppler imaging. Angiography is more necessary in patients with a history of trauma, surgery, or arteriosclerosis.

In designing the flap, a line is first drawn from the anterior superior iliac spine to the medial condyle of the tibia, outlining the course of the sartorius muscle. The skin island is centered over the distal portion of the sartorius, with the upper border as much as 10-15 cm above the knee joint. The incision is made in the medial thigh over the sartorius muscle along the line from the anterior superior iliac spine to the medial tibial condyle and continues down to the deep fascia of the sartorius. Blunt dissection of the anterior border of the sartorius muscle exposes the septocutaneous branches of the saphenous artery.

The deep fascia is divided anterior to the sartorius muscle, and the saphenous artery is visualized between the sartorius and vastus medialis. The pedicle courses deep to the sartorius muscle several centimeters superior to the skin island, with perforating vessels coursing on either side of the muscle supplying the skin. The medial femoral cutaneous nerve and saphenous vein run along the posterior border of the sartorius muscle. The distal saphenous artery is identified next. The skin and deep fascia are then divided cautiously up to within 6 cm of the knee joint while searching carefully for the arterial branching pattern.

Next, identify which cutaneous vessels predominate. If the perforators emerging anterior to the sartorius are predominant, the skin island is placed anterior to the muscle. If the perforators emerging posterior to the sartorius are predominant, the skin island is placed posterior to the sartorius. If the anterior and posterior vessels are equal in size, the skin island is centered on the sartorius and a portion of muscle is included within the flap. Dividing or including portions of the sartorius with the flap may be necessary to preserve the cutaneous branches. Distally, the saphenous vein is divided at the distal flap margin for inclusion proximally to enhance venous outflow. The flap is dissected from below upward.

The arc of rotation can be based on its dominant pedicle and transposed to the knee. The saphenous flap can also be based on a reverse flow based on collateral vessels around the knee that can communicate with the terminal branches of the saphenous artery. The skin island for the reverse flap is usually located higher than for the standard flap. The saphenous vein and artery are identified and divided at the proximal flap border. This modification covers upper portions of the leg and is useful for amputation stump coverage. The saphenous vein flap can be used, but it is not the first line of defense for this location and can be expected to have a relatively high complication rate. Early reports of the unipedicled venous flaps postulated a to-and-fro flow pattern in the vein, seemingly supported by experimental and mathematical models. The survival of unipedicled type 1 venous flaps has now been attributed to either a perivenous or perineural capillary network.

The large venous flap is a modification of the saphenous flap in which the entire skin island is elevated to include the saphenous vein. The skin island is centered over the course of the saphenous vein in the inferior medial thigh. The saphenous vein is identified at the distal flap border and divided. The flap is then elevated and transposed, including the saphenous vein. The distal vein may be anastomosed to a suitable receptor artery if an arterialized venous flap is planned.

Extending the length of the pedicle is possible by dissecting the saphenous artery proximally and the descending genicular artery to the level of the SFA. Its length may be extended to approximately 15 cm. For the venous flap, the saphenous vein can be dissected approximately up to the level of the groin, creating a pedicle up to 30 cm long. For flaps no wider than 6-7 cm, the donor site may be closed directly. This leaves an obvious scar, and a skin graft may be needed for larger flaps. Tight closures necessitate splinting the knee in extension for 2 weeks to avoid wound dehiscence.

The donor site has been reported to cause problems at times, including sensory disturbance of the medial leg and the stretched donor scar around the joint. Sacrifice of the saphenous nerve leads to a bothersome area of anesthesia at the anteromedial leg. Therefore, when not required, attempt to safely dissect the nerve from the saphenous artery. Otherwise, the saphenous flap is very useful because it has a dependable vascular supply, is a 1-step procedure, and can be performed with the patient in the supine position.

Sural fasciocutaneous flap

While the gastrocnemius has been the mainstay muscle flap for coverage of the knee and upper tibia, the sural fasciocutaneous flap offers several distinct advantages over the gastrocnemius. It has a longer arc of rotation than the gastrocnemius and is capable of resurfacing defects proximal to the patella, which is difficult with a gastrocnemius flap. This flap is located between the popliteal fossa and the mid portion of the leg, centered over the midline raphe between the medial and lateral heads of the gastrocnemius muscle.

The sural fasciocutaneous flap can be used as a pedicled island or free flap. [8] Islanding significantly augments the distance the flap is able to traverse. For pedicled transfer, this flap has some advantages. Elevation is simple, the flap is thin and endowed with numerous sensory nerves, and the flap size can be readily modified to suit the demands of reconstruction. The flap covers large defects (the largest in one study being 17 by 8 cm) and reaches defects in the popliteal fossa and upper one third of the leg. Tissue expansion can further increase the flap dimension prior to flap elevation.

The descending cutaneous branches of the popliteal artery typically supply the sural artery fasciocutaneous flap. Three vessels in the posterior calf supply blood flow to the skin. These are the lateral, median, and medial vessels. These vessels have variable origins, whether from the popliteal artery directly or from one of the 2 sural arteries supplying the gastrocnemius muscle. The medial sural cutaneous nerve, a branch of the tibial nerve within the popliteal fossa, courses with the lesser saphenous vein and cutaneous artery. The nerve and vascular pedicle enter the skin at the midposterior leg.

The dominant pedicle, either the medial or a lateral superficial sural artery with its venae comitantes, is located in the popliteal fossa entering the deep fascia between the medial and lateral heads of the gastrocnemius muscle. The pedicle generally courses slightly lateral to the posterior midline over the lateral gastrocnemius muscle. The median cutaneous artery arises from the popliteal artery in 48%, lateral sural artery in 39%, and inferior geniculate vessels in 13%. In cadaver studies, the midline vessel accompanies the sural nerve, and a smaller one accompanies the lateral sural nerve. However, the dominant posterior axial vessel has been demonstrated to usually course posterolaterally, intimately associated with the lateral sural nerve. In summary, these vessels take a variable origin from either the popliteal artery directly or one of the 2 sural arteries supplying the gastrocnemius, and one must carefully determine if the medial or lateral sural cutaneous artery is dominant.

The venous drainage typically consists of paired venae comitantes emptying into the popliteal or sural veins. The flap is innervated in the superior calf by the posterior cutaneous nerve of the thigh and in the middle and inferior calf by the posterior branch of the medial cutaneous nerve of the thigh and the lateral sural cutaneous branch of the common peroneal nerve.

Preoperatively, the superficial sural artery is first detected with a Doppler flow meter. The operation can be performed with the patient in any position, but the prone position is usually best. The flap territory extends from the superior flexion crease of the calf at the popliteal fossa to the junction of the middle and inferior thirds of the posterior calf. The flap is designed in the calf and includes a line representing the course of the superficial sural artery either in the center or in the lateral part of the calf. Medially and laterally, the midaxial lines serve as the anterior limits. After marking the flap boundaries according to the above guidelines, elevate the flap distally with an incision through the skin, subcutaneous tissues, and deep fascia. [9]

The flap is elevated subfascially to avoid damaging the vessels. When incising both sides and exposing the pedicle, take care to prevent injury to the common peroneal nerve and the pedicle of the flap, preserving both medial and lateral superficial sural arteries until both are observed. Furthermore, both fasciocutaneous vessels may unite before their junction with the popliteal artery and vein. Once clearly defined, the larger vessel is included in the mid axis of the flap. Proximal superficial draining veins are also preserved to enhance venous drainage in standard flap transposition or for use in microvascular composite tissue transplantation.

Deep to the fascia, the distal lesser saphenous vein is identified, divided, and included with the flap. The sural nerve, which runs in close proximity to the arterial supply, is also transected distally and included. Dissection of the sural nerve from the vascular pedicle places the artery and its venae comitantes at undue risk of injury.

As the dissection proceeds superiorly, gastrocnemius perforators must be divided. In elevating the flap, musculocutaneous perforators that anastomose with the sural cutaneous artery may be encountered. Ligation of these can result in poor perfusion to the flap, and sequentially ligating or performing a trial occlusion may be safer.

Reportedly, after ligating most of these perforators, it became apparent that the axial vessel was not enough to sustain the flap, and the flap was replaced and the medial gastrocnemius flap was used to reconstruct the soft tissue defect. This illustrated the point of an inverse relationship between the superficial and deep systems. Small sural cutaneous arteries are often found concurrently with large perforators, and sacrifice of these perforators may compromise the flap. Only after the vascular pedicle has been identified on the deep surface of the flap may the superior skin margin be incised safely. If the venous congestion, which is uniformly noted after initial flap elevation, is irreversible or the venae comitantes prove to be exceedingly small, then a subcutaneous vein should be included with the flap proximally to serve as an additional source of venous outflow.

After cleaning the recipient site, the flap is transferred to the skin defect. It can be transposed as a peninsular fasciocutaneous flap or isolated on its vascular pedicle alone for transposition as an island flap. The rotation point of the pedicle is usually located at the popliteal fossa. Tension and kinking or twisting of the pedicle must be avoided. Drains are placed under the flap. Primary closure of the donor site is possible with a flap having a width of 6 cm or less, but larger flaps require a skin graft of the donor site. Inevitably, the sural nerve is divided; consequently, the outer aspect of the foot is rendered numb. The transection of this nerve also carries the risk of neuroma formation in the transferred flap.

Popliteal-based posterior thigh fasciocutaneous flap

Several fasciocutaneous flaps have been described involving the lower posterior and lateral thigh and deriving inflow from branches arising from the knee region. The popliteal-posterior thigh fasciocutaneous island flap covers the knee and reaches to the upper and middle thirds of the calf. A direct ascending branch of the popliteal artery arising 7-11 cm above the knee supplies the popliteal-posterior thigh fasciocutaneous flap. The vessel emerges between the semimembranous and biceps femoris muscles at the level of the popliteal fossa. The posterior femoral nerve can potentially provide sensation to the flap.

The flap is designed using Doppler images and may include the vessel origin inferiorly and can extend superiorly to the gluteal crease. Laterally, it lies over the hamstring musculature. The incision is carried down through the subcutaneous tissue and deep fascia of the thigh. The distal incision is made, and the distal end of the flap is gently turned upward. The intermuscular septum between the hamstring muscles is divided between the muscles. The fascial septum is included to augment the circulation, but do not rely on the fasciocutaneous branches along the fascial septum. Local rotation on its vascular pedicle has allowed coverage about the knee. A 10-cm defect can be closed primarily.

Lateral genicular artery fasciocutaneous flap

This flap features a 1-stage reconstruction of defects around the knee and provides excellent contour of the recipient site. Even though the origin of the artery may vary, its cutaneous perforator is located in the small triangular area formed by the superior margin of the lateral femoral condyle, the posterior margin of the vastus lateralis, and the anterior margin of the short head of the biceps femoris. [10]

The lateral genicular fasciocutaneous flap is supplied by the superior lateral genicular artery (SLGA). This originates from the popliteal artery or the sural artery approximately 4 cm above the knee. It courses in a superolateral direction, giving off branches to the vastus lateralis, biceps femoris, and the knee joint. After traveling the intermuscular space between the vastus lateralis and the short head of the biceps femoris, the SLGA penetrates the deep fascia just proximal to the lateral condyle of the femur. The point at which the cutaneous perforator of the SLGA penetrates the deep fascia ranges from 3-8 cm from the knee joint.

The cutaneous perforator of the SLGA terminates in small cutaneous branches following a radial pattern. These cutaneous branches anastomose freely with the rete patellae, the lateral perforator of the profunda femoris artery, the musculocutaneous perforators from the popliteal artery, and the musculocutaneous or septocutaneous perforators from the descending branch of the lateral circumflex femoral artery.

The flap is designed on the lateral aspect of the lower thigh and includes the triangle containing the vascular pedicle formed by the vastus lateralis anteriorly, the biceps femoris posteriorly, and the lateral femoral condyle inferiorly. The proximal end of the flap can be extended safely to the midpoint between the greater trochanter and the lateral condyle of the femur. Because of the subcutaneous communication between the SLGA and the lateral perforators of the profunda femoris artery, the lateral genicular artery flap can be extended safely to the midpoint between the greater trochanter and the lateral condyle of the femur, the point at which the cutaneous branch of the third perforating artery can usually be found. The incision is started from the proximal apex of the flap, and the plane of dissection is maintained on the loose areolar layer over the deep fascia.

Distal to the point 10 cm above the knee joint, the dissection should be carried down to the iliotibial tract for the safe dissection of the intermuscular septum between the vastus lateralis and the short head of the biceps femoris. Dividing the vastus lateralis and the short head of the biceps femoris, the vascular pedicle can be identified just above the lateral condyle of the femur. The islanded lateral genicular artery flap is then elevated and transferred to the defect. The rotation arc of the flap reaches the distal one third of the thigh, the knee, and the popliteal fossa and the proximal one third of the lower leg, with the exception of the medial aspects of these regions. A 10-cm wide donor defect can be closed primarily. Otherwise, a skin graft is applied to the donor site.

Anterolateral thigh flap

Anterolateral thigh flaps have increased in popularity over recent years because of their versatility. The donor site can often be closed primarily and the harvest results in little or no functional loss. [11] When based on a distal perforator, the flap can often be rotated to cover the knee. Care must be taken during harvest of the flap to avoid congestion, and Erba et al recommend both preoperative angiography and maintaining a subcutaneous strip to the knee where the take-off of the superior genicular artery supplies the flap. [12]

Medial thigh adipofascial flap

An adipofascial flap, which is related to fasciocutaneous flaps but in a separate category, is a low-morbidity option to consider. Adipofascial flaps are derived from the fascia and fat overlying muscle and contain a blood supply that normally feeds the skin overlying the flap itself.

An adipofascial flap is shown below.

This is an illustration of the adipofascial flap. This is an illustration of the adipofascial flap. The drawing shows the flap elevated and ready to be flipped on itself for inset over the wound of the knee.

Useful only for anterior or medial wounds, the blood supply of the medial thigh adipofascial flap is from perforators of the medial geniculate artery. The midline axis of the flap is designed along a line from the midpoint of the inguinal ligament to the medial femoral condyle. The length of the flap is determined by the size of the defect and follows the basic formula of a pedicle equal in size to the defect itself and centered on an operable perforator. The length then needs to be approximately 2 times the size of the pedicle with the vascular supply of the distal portion of the flap random in nature. For example, for a defect 8 cm in diameter, an adjacent base pedicle approximately 8 by 8 cm is designed, and the entire flap length is 24 cm. The distal 16 cm are detached from the underlying muscle and used to cover the wound.

The flap is elevated by first making an incision along the axis as described above and taking it down into the superficial subcutaneous tissue (just subdermal). The incision has to be longer than the flap to allow sufficient room for undermining. The skin is elevated off of the flap in the subdermal plane over the entire flap, and then the flap is elevated from distal to proximal (in this case, from the proximal part of the medial thigh toward the knee). The plane of elevation is the fascia of the underlying muscle. The dissection is stopped at the edge of the base pedicle, with great care used to maintain the proximal perforator. The flap is then flipped on itself and inset into the defect. The flap is then skin-grafted in either an immediate or delayed fashion.

Flap harvest is technically easy, and overall morbidity is low because of the lack of removing donor muscle, but the usefulness of this flap is limited by several potential problems. The overlying skin can have wound healing problems. The blood supply is not as robust as either muscle or even fasciocutaneous flaps, and this flap should not be used in patients with comorbidities such as diabetes or patients who smoke. It is also a poor choice in obese patients, but in patients of normal weight, it provides thin pliable tissue and excellent contour over the anterior medial knee.

Foot-to-knee island flap

A specialized area of knee coverage is required for patients whose injuries to the lower leg are so severe that amputation is necessary. In young patients with injuries severe enough to require an amputation, a below-knee amputation (BKA) allows for near-normal function. The same cannot be said for AKAs. AKAs, especially in older patients, usually result in the patient being wheelchair-bound. In light of this, preservation of the amputation at the below-knee level is critical. Unfortunately, many patients with injuries so severe that they require amputation also have fractures that involve the proximal tibia above a level at which a BKA prosthesis can be used (approximately 10 cm below the anterior tibial tuberosity).

To increase the length of the remaining leg and close the wound below the knee, one available option is to use the remaining foot on the posterior tibial neurovascular bundle. The bundle is dissected under loupe magnification for its entire length down to the foot and carefully oriented in a gentle loop in its new position. This option is possible because the foot is often spared from injury, even with severe open fractures of the tibia.

By removing the distal bones of the foot (tarsal, phalanges, metatarsals) in a subperiosteal fashion, the remaining soft tissue is preserved, and the calcaneus bone can be rotated 180° and plated to the proximal tibia. Using the foot as an island flap adds both 6 cm of length of bone and provides sensate, thick skin that does not shear on the underlying subcutaneous tissue and that is far superior to other free cutaneous or myocutaneous flaps, which tend to wobble. The resulting neurovascular pedicle island flap gives substantial 360° coverage of the open wound up to the knee. Consider this filet of foot option every time the foot is in good shape but the lower leg is not salvageable at a BKA level.

Free flap coverage of the knee

In reconstruction around the knee, the use of a free flap plays a critical role in patients with extensive defects or those for whom local flaps are unavailable, when only free flaps can provide a chance to salvage the legs. Most defects can be managed with local muscle flaps as described above. However, if needed, a free muscle flap with an overlying skin graft provides reliable, durable, and pliable coverage around the knee joint, without functional limitation.

Free flaps used for coverage of the knee vary depending on the size of the defect. One may choose a latissimus dorsi, serratus anterior, rectus abdominus, or free fasciocutaneous flap such as a parascapular flap. The most difficult hurdles to manage are choosing the recipient vessels for the free flap and the possible need for a vein graft. Selection of recipient vessels depends on the location of the wound, size of the defect, and size of the flap. At times, vein grafts may be necessary. Recipient arteries used include the distal superficial femoral artery (SFA; most common), saphenous artery, sural arteries, the descending branch of the lateral circumflex femoral artery, popliteal artery, anterior tibial artery, and the superior medial genicular artery (SMGA). The use of small arteries and venae comitantes as recipient vessels has increased the effective reach of free flaps and decreased the need for vein grafts.

The saphenous artery can be readily identified at the adductor canal through an anterior incision extending medial to the sartorius muscle. Its origin, the descending geniculate artery, can also be used. The descending geniculate artery originates from the femoral artery just before passing through the adductor hiatus. The saphenous artery has been used in defects of the entire knee, anterior knee, and lateral knee.

For suprapatellar and lateral knee defects, the descending branch of the lateral circumflex artery can be used. This artery descends inferiorly, lying either along the anterior edge of the vastus lateralis (10%) or within the muscle (90%).

The popliteal vessels should be used with care in free tissue transfer to the anterior surface of the knee, and an end-to-side anastomosis to the popliteal artery may pose a potential danger to the popliteal artery. For similar reasons, the sural vessels are difficult to use in a free tissue transfer to the region proximal to the knee.

The distal SFA has been used as a recipient vessel in patients in whom the defect was over the entire knee or medial aspect of the knee but, at its most superficial point in the thigh, was located a significant distance from the knee.

The superior medial genicular vessels can be used in defects located posterior to the knee, and the descending genicular vessels can be used in defects anterior to the knee. The SMGA branches off the popliteal artery at approximately the level of the femoral condyle and runs deep to the semimembranous muscle and the semitendinous muscle to reach the lowermost fibers of the vastus medialis muscle. It then emerges between the sartorius and vastus medialis to branch off to the capsule of the knee joint and skin superior and medial to the patella. The descending geniculate artery arises from the femoral artery, immediately proximal to the adductor hiatus. It then pierces the fascia between the vastus medialis muscle and the adductor magnus muscle. The deep branch then continues downward between the 2 muscles, and the superior branch descends distally and branches off to an infrapatellar branch.

To identify the artery in the posterior region, first identify the popliteal artery. Gentle retraction of the semimembranosus muscle exposes the SMGA and the accompanying venae comitantes at the level of the upper edge of the femoral condyle. At the anterior surface, a vertical incision is made between the vastus medialis muscle and the sartorius muscle in the medial aspect of the distal thigh. The sartorius is retracted medially, and descending geniculate vessels are typically found immediately posterior to the vastus medialis muscle.

Advantages to using the superior medial geniculate vessels and the descending geniculate vessels are (1) they are protected from crushing injuries of the knee or popliteal region because they are deep in the muscle, (2) they are an excellent size match for an end-to-end anastomosis, and (3) the location is relatively constant. The drawback is that they are deeply seated between muscle, which may make the anastomosis challenging.

Postoperatively, the lower extremity rehabilitation with range-of-motion exercises can be started after the fourth week. In one series, all patients regained ambulatory status with functional ability expected for their injuries and preexisting conditions.

A study by Seo et al indicated that with the use of supermicrosurgery, peroneal perforator free flaps can effectively be used in the reconstruction of small to medium-sized defects of the knee and the proximal and middle lower leg. The study, which involved 22 patients with these defects, reported that the procedure required just a short time to harvest the flap and secure the recipient vessel, avoided damage to a main artery, and provided a flap that was thin and pliable enough to avoid contour deformity. [13]

Many flaps have been described. The rationale for choosing a particular flap depends on the reconstructive needs of the patient, the size of the defect, and the surgeon's experience.

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Intraoperative Details

See Surgical therapy for details on the use of specific flaps.

Relevant images are shown below.

This photograph shows a complex degloving wound of This photograph shows a complex degloving wound of the left knee.
With the skin retracted, open fracture and fixatio With the skin retracted, open fracture and fixation hardware is evident in the wound.
The medial (top) and lateral (bottom) gastrocnemiu The medial (top) and lateral (bottom) gastrocnemius muscles are elevated and ready for inset and wound coverage. Access to the muscles was through a midline posterior incision (the incision is not seen in this photograph, which is of the anterior leg).
The medial and lateral muscles are sutured to each The medial and lateral muscles are sutured to each other and inset over the wound.
The knee wound is healed. The knee wound is healed.
This is an illustration of the adipofascial flap. This is an illustration of the adipofascial flap. The drawing shows the flap elevated and ready to be flipped on itself for inset over the wound of the knee.
This photograph shows a leg that cannot be salvage This photograph shows a leg that cannot be salvaged, even with a standard below-the-knee amputation, because of the extent of damage to both the knee and calf. The foot, however, is in good shape and can be used for a filet of foot flap.
The foot has been isolated on the posterior tibial The foot has been isolated on the posterior tibial vessels and tibial nerve. The phalanges and metatarsal bone have all been removed. Of the tarsal bones, only the calcaneus is saved. The intervening tibia and fibula have been removed, as well.
The foot is now rotated 180 degrees and rigidly fi The foot is now rotated 180 degrees and rigidly fixed to the remaining stump of the tibia.
As can be seen in this photograph, the end of the As can be seen in this photograph, the end of the amputation stump now has the excellent and tough coverage of the sole of the foot and heel.
Mobility is preserved in the knee. Mobility is preserved in the knee.
The good coverage allows for prosthesis fitting. The good coverage allows for prosthesis fitting.
The salvage of the knee in this patient allows for The salvage of the knee in this patient allows for greatly improved function over an above-the-knee amputation.
Large wound with extensive damage to the femur and Large wound with extensive damage to the femur and tibia and exposed hardware.
Radiograph of the leg. Radiograph of the leg.
Latissimus dorsi muscle free flap is inset into th Latissimus dorsi muscle free flap is inset into the wound and covered with a split-thickness skin graft.
Healed wound of the knee. Healed wound of the knee.
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Outcome and Prognosis

Conclusion

Knee exposure, whether from postarthroplasty dehiscence, trauma, or tumor excision, is a challenge for both plastic and orthopedic surgeons. Furthermore, prior to any surgery on or around the knee, identifying those at risk for wound complications is important. In planning surgery, considering whether the patient was on long-term steroids for arthritis, has medical conditions such as diabetes, and has had other prior surgical procedures in the area is important. Once faced with the task of providing soft tissue coverage over or around the knee, identifying whether the knee is infected versus contaminated is also important. This determines whether an implant may be salvageable.

The first stage is the excision of nonviable tissue and the obliteration of dead space with an appropriate flap cover. A well-vascularized flap provides fresh blood supply, which can deliver antibiotics and humoral defense factors to the wound. After thoroughly evaluating the extent of the wound and, if applicable, the zone of injury, consider a flap with the least amount of morbidity and risk to the patient. If the wound is small and a local fasciocutaneous flap is not in the zone of injury, it should be the first option of closure. If no fasciocutaneous flap is available or the wound is too extensive, the next line of defense is a myocutaneous or muscle rotation flap such as the gastrocnemius flap.

Local muscle flaps are more advantageous than free flaps because they require less operative time, can be performed under epidural anesthesia, and have minimal donor site morbidity. If no local rotation flap is available, a free tissue transfer flap, such as a latissimus dorsi flap, is an option. Depending on the location of the wound, size of the defect, and the size of the flap, vein grafts may be needed.

Ultimately, a study revealed that approximately 75% of exposed knee arthroplasties can be saved with flap coverage, but once exposed, these result in a worse functional outcome than those that healed primarily. The outcome is still superior to amputation or arthrodesis. Results are also better after early, noninfected breakdown in osteoarthritic patients versus delayed breakdown, suggesting chronic infection. Finally, if amputation is necessary, flap coverage can assist in preserving a below-knee level when otherwise-insufficient soft tissue dictates a highly morbid AKA. Therefore, the patient benefits from the functional advantage of a below-knee prosthetic device and a functional knee joint.

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