BKA is the common medical abbreviation for Below-Knee Amputation, a major surgical procedure involving the removal of the lower limb between the ankle and the knee joint. This procedure is also known as a transtibial amputation because the cut is made across the tibia and fibula bones. The primary goal of a BKA is to remove diseased or damaged tissue while preserving the knee joint. Preserving the knee significantly improves the patient’s potential for mobility and functional outcomes compared to an above-knee amputation. This surgery is undertaken when other options for limb preservation have been exhausted or when the limb poses a threat to the patient’s life.
Indications for Below-Knee Amputation
The primary reason for performing a Below-Knee Amputation is to address conditions where the lower leg tissue is no longer viable or poses a severe risk of infection. The most frequent cause, accounting for over 50% of cases, is poor circulation stemming from peripheral arterial disease (PAD), often linked to diabetes. Diabetes can lead to non-healing ulcers and foot infections that progress to gangrene due to compromised blood flow and nerve damage.
Chronic limb-threatening ischemia (CLTI), a severe form of PAD, causes insufficient oxygen delivery to the tissues, resulting in rest pain, non-healing wounds, or tissue death. When revascularization procedures, such as bypass surgery, have failed or are not possible, amputation becomes necessary. This prevents the spread of necrosis and systemic infection.
Other significant causes include severe trauma, such as crush injuries or non-reconstructible damage, where the limb cannot be saved. Uncontrolled, necrotizing infections, like rapidly spreading gangrene, may necessitate an urgent BKA to prevent sepsis. Malignant tumors of the bone or soft tissue that cannot be fully removed through limb-sparing surgery are also an indication for this procedure.
The Surgical Procedure and Immediate Post-Operative Care
The BKA surgery is carefully planned to create a residual limb, often called a stump, that is optimally shaped for fitting a prosthetic. The surgeon preserves as much of the tibia and fibula as possible, aiming for an ideal bone length to maximize leverage and function. The tibia is typically beveled or rounded at the end to eliminate sharp edges that could cause skin breakdown under the pressure of a prosthetic socket.
Special attention is given to creating a soft tissue flap, usually with a longer posterior flap containing the calf muscles, to cover the bone end with durable tissue. The major nerves are carefully cut and allowed to retract to minimize the formation of painful nerve endings, known as neuromas. A drain is often placed in the wound to prevent fluid accumulation, and the wound is closed, dressed, and placed into a rigid dressing or knee immobilizer.
Immediate post-operative care focuses on managing pain, monitoring the surgical site, and preventing joint contractures. Multimodal analgesia, including nerve blocks and oral pain medication, is used to control post-surgical discomfort. The limb is elevated to reduce swelling, and the wound is checked frequently for signs of infection or necrosis of the skin edges. Physical therapy is often initiated within 24 to 48 hours to begin exercises and positioning the limb to prevent the knee from developing a permanent bent position, which would complicate prosthetic fitting.
Rehabilitation and Prosthetic Adaptation
The journey toward full recovery begins with a structured rehabilitation program, often starting a few weeks after surgery once the wound has healed. Physical therapy (PT) is central to this phase, focusing on strengthening the hip and core muscles to compensate for the lost lower leg muscles. Therapists also work on range of motion exercises to maintain flexibility in the knee and hip joints, which is necessary for a smooth gait.
The residual limb must be shaped and conditioned for the prosthetic socket using compression therapy, such as elastic bandages or shrinker socks. This compression helps reduce swelling and molds the limb into a cylindrical shape for a secure prosthetic fit. Once the swelling has subsided and the wound is fully healed (typically four to six weeks), the patient is evaluated by a prosthetist.
The prosthetist creates a custom-fitted prosthesis, often starting with a temporary test socket to allow for adjustments as the limb changes shape. Once the definitive prosthesis is fitted, the physical therapist begins gait training. This training teaches the patient how to walk efficiently, manage uneven surfaces, and navigate obstacles like stairs. Occupational therapy (OT) helps the patient adapt daily living skills and make necessary modifications to their environment, supporting long-term independence.