Abstract
- Above and below the knee amputations require basic anatomy knowledge of the muscle compartments, nerves, and arteries of the lower extremity.
- The thigh has three compartments: anterior, posterior, and medial. The calf has four compartments: the anterior, lateral, or peroneal in addition to the deep and superficial posterior ones.
- The lower extremity is perfused by the superficial and deep femoral artery. The superficial femoral artery continues as the popliteal artery after exiting the Hunter’s canal. The popliteal artery bifurcates into tibialis anterior artery and the tibioperoneal trunk. The tibioperoneal trunk gives the fibular artery and continues as the posterior tibial artery. The femoral and sciatic nerves provide innervation to the lower extremity.
Surgical Anatomy
Above and below the knee amputations require basic anatomy knowledge of the muscle compartments, nerves, and arteries of the lower extremity.
The thigh has three compartments: anterior, posterior, and medial. The calf has four compartments: the anterior, lateral, or peroneal in addition to the deep and superficial posterior ones.
The lower extremity is perfused by the superficial and deep femoral artery. The superficial femoral artery continues as the popliteal artery after exiting the Hunter’s canal. The popliteal artery bifurcates into tibialis anterior artery and the tibioperoneal trunk. The tibioperoneal trunk gives the fibular artery and continues as the posterior tibial artery. The femoral and sciatic nerves provide innervation to the lower extremity.
General Principles
The goal with amputation surgery is a functional extremity with a residual limb that successfully interacts with the patient’s future prosthetic and external environment.
The rule of preserving as much length as possible is not always applicable in the lower leg. Long leg stumps often do not heal well because of poor blood supply and do not tolerate prosthesis well.
A short below-knee stump is preferable to knee dislocation, but a stump shorter than 6 cm may not be functional.
Optimal above the knee amputation level is between 12 and 18 cm below the trochanter major.
Use tourniquets to minimize blood loss. The cuff should not be placed directly over bony prominences, such as the head of the fibula or malleoli, to avoid the risk of direct nerve compression and damage. Elevation of the leg to empty the venous blood and reduce blood loss should be done before inflation of the tourniquet cuff. This process may be facilitated with the use of bandage or tourniquet exsanguinators. The inflation pressure is usually set at about 250 mm Hg in adults or about 100 mmHg above the systolic pressure.
All nonviable or contaminated tissue must be removed and there must be sufficient arterial perfusion to allow healing.
Sufficient soft tissues should be preserved to cover the end of the bone without tension. However, excessive amount of soft tissues may interfere with prosthesis fitting.
The scars of weight-bearing stumps should preferably be posteriorly to the edge of the stump.
Nerves are divided as high as possible and allowed to retract. They should be divided sharply and ligated with non-absorbable sutures to reduce the risk of formation of potentially painful neuromas. The ends of the nerves should be away from areas of pressure.
Bone edges should be filed to remove any sharp edges.
In closing the wound, always keep a myofascial layer between the bone and the skin.
Wounds should be closed without tension and suture lines should be placed away from weight-bearing surfaces when possible.
Drains can be used to reduce dead space and to drain residual bleeding.
Special Surgical Instruments
Pneumatic tourniquet and bandage or tourniquet exsanguinator.
Power saw or Gigli saw the division of the bone.
Bone files or rasps are essential to smooth out bone edges.
Compression wraps for post-operative dressings are helpful to decrease edema and to shape the stump for early fittings of prosthetics.
Patient Positioning
The patient is placed in the standard supine trauma position with both arms at 90° to allow anesthesia access to the upper extremities.
The leg should be prepped circumferentially and pneumatic tourniquet applied proximal to the injury to minimize blood loss during the procedure. Padding or surgical towels can be placed under the thigh to allow for elevation of the extremity.
The surgeon stands on the inner side of the leg for better view of the vessels and nerves.
Above-Knee Amputation
The femur can be divided at any length necessary; most commonly this is at the junction of the middle and distal third of the femur shaft for the optimal functional interaction with prosthetic limb (12–18 cm below the trochanter major).
Start with applying a pneumatic tourniquet if there is enough femur length.
Mark with skin pen a transversely oriented fish-mouth incision. The anterior and posterior tissue flaps may be equal or the anterior flap may be longer. The skin incision should be about 15 cm below the planned division of the bone.
The skin and subcutaneous tissue should be divided circumferentially. The saphenous vein is identified in the medial aspect of the thigh and ligated,
Figure 43.3
(a) The anterior thigh compartment muscles are sharply divided to the bone.
(b) The anterior thigh compartment muscles are reflected proximally to expose the femur. The level of division of the femur is marked.
The anterior thigh compartment muscles are sharply divided to the bone about 3–5 cm distal to the planned femoral osteotomy. The divided muscles are reflected proximally.
The femoral artery and vein are identified deep to sartorius muscle and individually ligated and divided.
The transverse osteotomy is performed with a Gigli or power saw and sharp edges should be filed down with the bone rasp
The posterior thigh compartment muscles are sharply divided about 3 cm distal to the femoral osteotomy site. The deep femoral artery is ligated when encountered depending on the level of the amputation. The sciatic nerve is identified, divided sharply and ligated as high as possible.
Periosteal elevator is utilized to separate periosteum from the bone.
