How to perform a below-knee amputation

Skin Incision and Advancing to Fascia

1. Following the planned transverse incision, the skin and subcutaneous tissue are incised with a scalpel to the fascia surface level.

2. The lateral longitudinal incision is made with the same technique, advancing through the skin and subcutis following the traced plan. The fascia should be visible throughout the full incision length.

3. The medial longitudinal incision is made similarly. Care is taken to identify and preserve the great saphenous vein and saphenous nerve, which run along the medial aspect of the leg.

4. The great saphenous vein is identified in the subcutaneous tissue along the medial incision.

5. The vein is clamped distally and proximally, and then divided. Both ends of the vessel are ligated.

6. The saphenous nerve is identified near the great saphenous vein.

7. The nerve is isolated and sharply transected proximally to allow retraction away from the surgical site.

8. With the fascia exposed along all incision lines, the underlying muscle compartments are now accessible.

Dividing the Anterior Compartment

To expose the tibia and fibula for transection, both the anterior and lateral compartments are divided with their neurovascular structures managed. The anterior compartment is addressed first, with its anterior tibial vessels and deep peroneal nerve handled.

1. The fascia of the anterior compartment is incised at the planned amputation level.

2. The anterior compartment muscles are first separated from the lateral compartment along the anterior intermuscular septum, then freed from the tibia medially.

3. The muscles are then bluntly encircled while carefully excluding the neurovascular bundle at the base of the compartment, just anterior to the interosseous membrane.

4. The encircled muscles are divided sharply at the amputation level. With the tourniquet in use, bleeding from the muscle is minimal.

5. The neurovascular bundle of the anterior compartment is identified at the base of the compartment. This bundle contains the anterior tibial artery, the anterior tibial veins, and the deep peroneal nerve.

6. The deep peroneal nerve is identified, separated from the vessels, and divided sharply at proximal level.

7. The anterior tibial artery is isolated, clamped proximally and distally, and then divided. The artery and its accompanying veins should be ligated separately to prevent arteriovenous fistula formation.

8. To ensure secure ligation and prevent the ligature from slipping off, a transfixion suture is placed through and around the proximal end of the artery. A second ligature can be placed proximally to this for additional security.

9. The distal end of the artery is ligated with a simple suture.

10. Complete division of the anterior compartment is confirmed by visualization of the interosseous membrane at the compartment floor.

Dividing the Lateral Compartment

The lateral compartment along the fibula contains the superficial peroneal nerve requiring transection, but not the peroneal artery, which lies in the deep posterior compartment and will be managed after the bone cuts.

1. The compartment is encircled with a finger.

2. The muscles are divided sharply at the amputation level until the superficial peroneal nerve appears.

3. The nerve is identified, isolated, and sharply transected proximally to allow retraction away from the stump. Anesthetic will be applied later.

4. The remaining lateral compartment muscles are divided completely.

5. With the anterior and lateral compartments divided, both the tibia and fibula are now visible and ready to be prepared for cutting.

Bone Transection

To achieve the planned limb length, the tibia is cut at the determined level and the fibula slightly more proximally. To enable safe transection, the tibia and fibula are first encircled and freed from surrounding tissues.

1. The interosseous membrane connecting the tibia and fibula is identified at the bottom of the anterior compartment.

2. The membrane is incised with a scalpel at the planned amputation level to allow the tibia to be encircled and cut.
   The deep posterior compartment behind the membrane, containing the major vessels and tibial nerve, is not accessed now but will be addressed after the distal leg has been separated.

3. The tibia is encircled with Crile forceps along the bone surface, passed both laterally and medially, to separate the bone from adjacent tissues and enable retractor placement.

4. The anterior periosteum is freed from the tibia for a few centimeters proximally; this area will be beveled later.

5. The fibula cut level is planned approximately 1 to 2 centimeters proximal to the tibial cut level. This prevents the fibula from creating a prominent distal point that could cause pressure issues with the prosthesis.

6. Using the same technique as for the tibia, Crile forceps encircle the fibula and the periosteum is elevated at the cut site.

7. Retractors are placed to protect the adjacent soft tissues during bone cutting.

8. A final assessment confirms that this cut level will position the anterior closure line appropriately on the stump.

9. The tibia is cut transversely with an oscillating saw at the planned level.

10. The fibula is cut with the same technique at the more proximal level. Similarly, retractors are positioned to protect the soft tissues.

11. With the bones cut at appropriate levels, the posterior structures can be addressed next to complete the amputation.

Posterior Flap Detachment and Distal Limb Removal

The objective is to detach the posterior soft tissues from the bones and remove the distal leg, leaving an initial posterior flap of adequate length for bone coverage.

1. The fascia is opened along the lateral and medial vertical incisions to allow the distal bones to be mobilized.

2. The distal tibia and fibula are lifted and reflected forward.

3. The posterior muscles are sharply detached from the posterior aspects of the bones, staying directly on the bone surface to avoid injuring the major posterior arteries. Small perforating vessels between compartments are clamped as needed, and any major venous bleeding is ligated.

4. The dissection continues distally posterior to the bones down to the level defined by the skin incisions.

5. The posterior flap length is assessed to ensure adequate coverage for the tibial bone end without tension. The flap will be thinned and shaped more later.

6. At this point, the posterior flap includes both superficial and deep posterior compartment muscles. With tourniquet control, the flap can be transected sharply with the vascular structures in the deep compartment ligated afterward. Alternatively, the major arteries could be controlled and ligated before transection.

7. As the posterior flap is transected at the determined level, the distal leg is separated, leaving adequate length of the posterior tissue for tension-free bone coverage.

Managing Neurovasculars and Dividing the Deep Posterior Compartment

The next step is to manage the nerves and vessels of the flap to achieve reliable hemostasis while maintaining flap viability and to create a pain-free stump. The deep posterior compartment contains the tibialis posterior and toe flexor muscles. Between the toe flexor muscles lie the major neurovascular structures: the tibial nerve and the posterior tibial vessels, along with the peroneal vessels.

1. The tibial nerve is located in the deep posterior compartment. Being the thickest nerve in the lower leg, identification is typically straightforward.

2. The nerve is carefully exposed without excessive tension.

3. Sharp transection of the nerve is done at an appropriate proximal level to allow the nerve ending to retract away from the weight-bearing surface of the stump. Anesthetic can be applied at the time of transection, or pain control managed later.

4. Then the plane separating the deep posterior compartment from the superficial posterior compartment is identified.

5. The compartments are separated along this avascular plane.

6. The deep compartment muscles are removed to reduce the bulk of the stump by transecting them at the amputation level.

7. The superficial posterior compartment contains the gastrocnemius and soleus muscles, with the gastrocnemius forming the majority of the flap and receiving its blood supply from the popliteal artery above the amputation level, ensuring continued flap viability.

8. The posterior tibial and peroneal vessels are identified in the deep compartment, running surprisingly close to each other.

9. Crile forceps are applied for temporary control.

10. Both main arterial trunks are secured with transfixion suture ligatures to prevent slippage and delayed bleeding. Double ligation can be performed on the arteries. The veins can be ligated separately to prevent arteriovenous fistula formation.

Bone End Beveling and Preparation

The bone ends are prepared to prevent irritation of the overlying soft tissues.

1. The fibula is confirmed to be cut 1 to 2 centimeters more proximally than the tibia to prevent skin irritation from the longer bone end.

2. The anterior edge of the tibia is beveled with the saw to create an oblique surface. The soft tissues are protected with retractors during sawing.

3. Any sharp edges are filed smooth to create a rounded bone surface suitable for weight-bearing.

4. The medullary canal can be evacuated and bone wax applied if bleeding is significant.

Posterior Flap Trimming and Shaping

The goal of this step is to achieve optimal muscle coverage of the bone stump to ensure adequate healing. Excessive bulk would interfere with prosthesis fitting, while closure under tension would compromise wound healing. It is important to note that the stump should not be thinned to an optimal-looking result at this point but should appear somewhat bulky, since muscle will atrophy significantly postoperatively.

1. The posterior flap is fitted over the bone stump to assess how much soft tissue is required for closure and to determine the appropriate flap length without tension.

2. Before transecting the muscle layer, the sural nerve is identified posteriorly and divided sharply. The accompanying small saphenous vein is ligated if not already done at this stage.

3. The posterior flap is then transected at the determined length.

4. Small intramuscular vessels should be cauterized to reduce bleeding when the tourniquet is released. However, excessive cauterization should be avoided to preserve tissue viability.

5. The corners of the flap are trimmed and rounded to improve the fit and shape.

6. Then the challenging work of determining the optimal muscle volume begins. Muscle is removed gradually with evaluation after each trimming.
   The muscle volume achieved here affects bone coverage, stump shape for prosthesis use, and wound healing success. The muscle tissue must look vital with healthy appearance and bleeding surface to heal properly. Any non-viable tissue must be removed.

7. While reducing muscle volume, the subcutaneous tissue and skin length must be evaluated to ensure adequate length for tension-free closure.

8. In this case, there is an adequate amount of soft tissue to cover the stump without tension.
   The stump appears slightly mushroom-shaped initially, but it will slim considerably with atrophy and the help of compressive bandages. If made too neat now, it becomes tapered and too thin later.

9. To further facilitate closure, the posterior fascia can be dissected slightly from the posterior subcutaneous flap. The dissection should not be so extensive that the skin flap becomes devascularized, but enough to allow better muscle fitting.

10. The flap now fits well over the bone stump with vital muscle tissue and minimal tension, providing adequate coverage without overly excessive bulk.

If excess subcutaneous tissue and skin remain at this point, they can be trimmed later.

Anesthesia and Hemostasis

1. The locations of the nerve trunks are confirmed and, if not already applied at the time of transection, anesthetic is administered at the nerve transection sites.

2. A pain catheter can be inserted along the tibial nerve trunk for continued postoperative pain control.

3. The tourniquet is then released, and complete hemostasis is ensured. Remaining bleeders are cauterized or ligated as needed. Some diffuse muscle oozing is acceptable, as it typically stops when the muscles are approximated, avoiding excessive cauterization that could impair healing.

4. Drain placement is controversial. It prevents hematoma when hemostasis is suboptimal but may interfere with pain catheter function. If no drain is used, bone wax can seal the medullary canal to prevent deep hematoma.

Muscle and Fascial Closure

The goal is to secure the posterior muscle flap over the bone stump by suturing the posterior fascia to the anterior fascia edge, ensuring secure coverage without excessive tension that might compromise tissue perfusion.

1. Interrupted sutures are placed using size 0 or 1 absorbable suture. The bites are taken from the posterior fascia to the thick, sturdy anterior fascia edge.

2. The sutures are first placed sparsely to evaluate stump formation and tissue alignment.
   If the closure appears too tight, the tissues are misaligned, or the flap does not settle properly over the bone stump, individual sutures can be removed and repositioned.

3. Here, the flap conforms nicely to the bone stump without tension and the overall appearance and alignment are acceptable.

4. Additional sutures can be placed to approximate any gaping areas.

5. When the posterior and anterior fascial layers are securely opposed throughout the length of the wound without gaps or excessive tension, subcutaneous and skin closure can proceed.

Subcutaneous Closure

1. Depending on the thickness of the subcutaneous layer, few sutures can be applied to shape the tissue and set up for optimal skin approximation. A watertight subcutaneous closure should be avoided, as this could compromise flap perfusion and cause ischemia.

2. In this case, few interrupted sutures using inverted mattress technique with size 2-0 absorbable suture are placed.

3. If needed, excess subcutaneous tissue and skin can be removed at this stage, generally from the posterior flap, which is mobile, rather than the anterior side, which is fixed to the compartment and tibia.

4. Subcutaneous closure is adequate when the skin edges can be approximated without tension, no apparent dog ears will form, and no further deep adjustments are required.

Skin Closure

1. Skin closure starts with first placing few interrupted nylon sutures sparsely to align the anterior and posterior flap. This prevents misalignment that could occur if stapling proceeds from one end to the other. Excess skin could still be trimmed at this stage if dog ears would form.

2. Once it seems that the flaps will align nicely, rapid closure with staples can be done.

3. The staples are applied at intervals of approximately 1 centimeter or a bit less, balancing secure closure with preservation of wound edge perfusion.

4. Initially, the appearance of the stump often remains slightly bulky and mushroom-shaped, which is appropriate. If thinned excessively at this point, the stump will become atrophic as muscle atrophies significantly after surgery.

5. To mold the stump into adequate shape for prosthesis fitting, compressive dressing is essential for the next weeks. The dressing also takes the pressure off the suture line.