Below Knee Amputation
Edited by Ken Hunt, MD
The loss of part of a limb is a difficult event for anyone. However, there are times either after an acute injury or following a complex chronic problem, (ex. Diabetic foot infection, ulcers due to poor blood supply, bone infections, etc) where a below-the-knee amputation is not only warranted, but offers the patient the best chance for a more functional, more timely, and often less painful extremity. Patients with a well-fitted below-the-knee prosthesis may be able to function at a high level, often without a noticeable limp. However, mobility and function following successful surgery and rehabilitation is often limited by the patient’s pre-surgery level of function. Those that had limited function prior to surgery may also be limited post-surgery. Recovery from a below knee amputation involves wound healing, rehabilitation, and emotional support.
There are a variety of indications for a below knee amputation including:
- An uncontrolled infection of the foot (ex. a severe diabetic foot infection)
- A traumatic injury to the foot or lower leg that cannot be salvaged
- Loss of blood supply to the foot either from trauma or vascular disease
- A chronic foot or ankle injury or deformity that can not be salvaged or reconstructed in a functional way
- Birth defects
- Malignant bone tumors
Pre-operative planning is typically performed to determine the surgical incisions, residual limb length, etc. The procedure is performed in order to preserve the function of the knee joint, so the remaining stump must be long enough to fit a prosthesis, and to provide adequate soft-tissue padding over what would otherwise be a prominent stump of bone. The amputation is typically performed in the middle of the lower leg. However, it should be done at a level that removes all the damaged tissue and allows closure of the skin layer with sufficient soft tissue, which may require a shorter stump in some cases. The skin incision and dissection is typically made significantly longer in the back (posteriorly) of the leg than in the front (anteriorly). This allows the calf muscle to be brought forward, providing padding over the bony stump. The major veins and arteries are identified, tied off and then cut. Nerves are cut short to minimize the risk of painful nerve remnant (neuroma). The major nerves are identified and both the larger bone (tibia) and smaller bone (fibula) of the lower leg are cut with a saw and smoothed. The fibula is usually cut shorter than the tibia and at a 45 degree inward angle to avoid a prominent bone edge. The front of the cut tibia is also cut at a slant (beveled) to avoid a sharp ridge of bone at the front of the leg. The amputation is then closed by suturing the layers of tissue together, including often suturing a remnant of what was part of the Achilles tendon to the front of the tibia, to improve stability of the stump. After surgery, most patients spend 1-2 days in the hospital.
Healing Phase (0 thru 6-12 weeks)
During the healing phase, the wound of the amputation stump is healing. Sutures are removed when the incision is healed, between 2-6 weeks post-surgery, typically on the longer end of this in patients with diabetes and/or peripheral neuropathy. Swelling is very common following a below knee amputation, and can last several months. Often, a stump shrinker (a sock that provides even pressure to the healing stump) is applied once the sutures have been removed. It is important to keep the knee functioning as normally as possible (including the ability to fully straighten) during the healing phase. It is not uncommon for patients to fall during this phase, as they may momentarily “forget” that they have had their leg amputated.
Prosthetic Fitting (8+ weeks)
Prosthetic fitting is started once the wound and soft-tissues have healed adequately. A prosthetist is a trained expert who coordinates the prosthetic fitting. This individual needs to work closely with the patient over a number of months to ensure that the prosthesis fits optimally. Initially, a preparatory prosthesis is molded and fit. Patients are encouraged to slowly start walking with support and often begin physical therapy at this time. Initially, patients can only wear the prosthesis for short periods of time, but gradually this time period increases. Over time, the amputation stump shrinks from a combination of less swelling and atrophy of the muscles. As this occurs, more and more stump shrinkers need to be added and the socket of the prosthesis needs to be adjusted. When the stump has reached a stable size, usually 6-9 months following the amputation, a “permanent” prosthesis is made.
Learning to walk with the prosthesis, rehabilitating muscles and joints that often have not been used normally for many months is critical for a successful result, following a below-knee amputation. Regular physical therapy is essential. Starting with a lot of support (i.e. a walker) and gradually progressing to improve strength, balance, and endurance will help optimize the results. This can be a long and difficult process and there can be setbacks, so patients should seek a strong support network and try to avoid becoming discouraged when these occur. There are many support groups online and within local health systems.
Often the amputation stump will become irritated in localized areas, requiring the patient to decrease their activities for a period of time. Alterations in the liner and socket of the prosthesis are usually required, so regular visits to the prosthetist are common. Occasionally, minor surgical procedures might be required to eliminate prominent areas, excise neuromas, and repair non-healing wounds.
There are a variety of potential complications that can occur following a below knee amputation. These include general post surgical complications, as well as more specific complications such as:
- Wound healing problems
- Phantom limb pain
- Knee contracture
- Bone spur formation at the amputation site (heterotopic ossification)
- Difficult with prosthetic fitting
- Decreased function (increased energy expenditure)
- Blood Clot (DVT)
- Pulmonary embolism
By removing unhealthy tissue and creating a leg that is more functional and less painful, a below knee amputation can improve quality of life in many patients. It is important to work closely with a doctor and medical team to ensure resources and education are in place to optimize recovery.
Edited January 19, 2018
Previously Edited by Daniel Cuttica, DO