Technique of Popliteal Node Dissection for Extremity Melanoma

Background

Malignant melanoma of the foot and leg usually metastasizes to the inguinal nodes. Regional lymph nodal involvement is one of the most important prognostic factors in malignant melanoma [1]. Rarely do they metastasize to the popliteal nodes. With the evolution of lymphoscintigraphy studies, nodes in the popliteal region are being increasingly identified during sentinel node biopsies. The involvement of popliteal nodes in malignant melanomas of the foot and leg is less than 10% [2]. Drainage to the popliteal nodes does not follow anatomical predictions. Lesions not in the pathway of the short saphenous vein can also metastasize to the popliteal nodes [3]. There is lack of consensus in considering the popliteal nodes as interval nodes or as regional nodes. With available literature, it may be right to consider the popliteal nodes as regional nodes and do a complete clearance of the popliteal group of nodes when involved [4].

Anatomy

There are 2 levels of nodes in the popliteal fossa, the subfascial nodes and the superficial nodes. The subfascial nodes (nodes around and deep to the popliteal vessels) are considered regional because they are constant in location whereas the superficial nodes being inconsistent in location are considered as interval nodes. There are 2 to 8 nodes in the popliteal fossa [3]. One lymph node is present at the terminal part of the short saphenous vein and one lymph node between the popliteal artery and knee joint. The biceps femoris and the lateral head of the gastrocnemius constitute the lateral boundary, whereas the semimembranosus, the semitendinosus, and the medial head of the gastrocnemius form the medial boundary (Fig. 1). The proximal apex is formed by crossing of the biceps femoris and semimembranosus muscles, and the distal apex by the merging of the two heads of the gastrocnemius.

Fig. 1.

Boundaries of the popliteal fossa

Indications of Popliteal Lymph Node Dissection

• 1. Disease identified in popliteal lymph node (either on FNAC or sentinel lymph node biopsy)

Surgical Consideration

Imaging of the region with CT or MRI should have been done. The technique of popliteal lymph node dissection was first reported by Karakousis [5]. The procedure is done with the patient in prone decubitus position, with the knee slightly flexed. We prefer a lazy S incision over the Z-plasty incision to prevent contracture of the knee (Fig. 2). With skin hooks and traction, lateral and medial flaps are raised superficial to the membranous layer of the superficial fascia. The extent of dissection is up to the borders of the popliteal fossa. The short saphenous vein and sural nerve are preserved. On either end of the coronal plane of dissection, the deep fascia is incised to expose the muscles. The common peroneal nerve and its branches are identified and preserved along the lateral border of the fossa and traced up to its origin from the sciatic nerve usually in the proximal apex of the fossa. The tibial nerve and its branches, the most superficial subfascial structure, are identified, looped, and retracted laterally along with the CPN. The popliteal vein and artery are cleared of all the fibrofatty and lymphatic tissue and the short saphenous vein is preserved. The artery is the deepest structure and lies medial to the vein (Fig. 3). The geniculate vessels are ligated. Care is taken to clear nodes and fatty tissue anterior to the vessels and posterior to the knee without injuring the knee joint capsule. The specimen is usually removed en bloc. Diligent inspection and palpation at the end of the procedure cannot be overemphasized to look for nodes that might have been missed. Hemostasis is achieved and wound is closed over a drain in a single layer using 2–0 ethilon.

Fig. 2.

Lazy S-shaped skin incision; the proximal extent is medial whereas the distal extent is encasing the biopsy tract laterally (trucut biopsy scar, biopsy done elsewhere)

Fig. 3.

Contents of the popliteal fossa (The common peroneal nerve was going through the tumor, hence sacrificed, cut end marked by an asterisk symbol)

Postoperative Care

Wound is managed similar to any other clean surgical wound. The patient’s knee is kept in extension using a long knee brace until wound is completely healed to avoid the contraction of scar leading to decrease in the range of motion of the knee. Isometric exercises for maintaining the strength of quadriceps are advised. Drain is removed once output is less than 15 ml/day and non-hemorrhagic.

Complications

1. Intraoperative complications

   1. Injury to the popliteal vessels.
   2. Neurapraxia or injury to the common peroneal nerve or posterior tibial nerve.
   3. Injury to the posterior joint capsule of the knee.
2. Postoperative complications

   1. Flap necrosis, surgical site infection.
   2. Prolonged drain output.
   3. Contraction of scar leading to the decreased range of motion of the knee.

Conclusion

It is imperative to look for popliteal node metastasis in MM of the foot and leg. When involved and indicated, a complete lymphadenectomy should be performed. The surgeon should be aware of the anatomy and preserve the neurovascular structures while performing this uncommon surgery.

Declarations

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008 (5).

Informed consent was obtained from all patients being included in the study.

Financial Disclosure

No potential competing interest was reported by the authors.

Conflicts of Interest

The authors declare that they have no conflict of interest.