Forearm Amputation

Anatomy and Physiology

Forearm amputations require a deep understanding of the local musculoskeletal and neurovascular structures and a thorough knowledge of regional soft tissue to allow flaps, muscle, and tendon transfer to achieve the best functional outcome. In this article, we will focus on local structures.

The goal of trans-radial amputation is to preserve as much length as possible, as this directly correlates with the amount of pronation-supination that can occur. This is a crucial feature in maintaining the functional ability of the limbs and prostheses. It ranges from 120 for wrist disarticulations, down to 0 for very short stump lengths.[5]

The forearm skeleton has the radius which rotates around the axis of the ulna. Arising from these are a total of 20 muscles divided into the anterior (flexor/pronator) and posterior (extensor/supinator) compartments. The two flexors of the upper arm – biceps brachii and brachialis both attach onto the radius and ulna, respectively. These are vital considerations, as tendon transfer of the biceps tendon from the radial tuberosity to the ulna in short amputations provides increased function.[5]

Neurovascularly, there are three primary nerves – the median, ulna, and radial nerves. The median nerve provides primary innervation for the flexors directly and indirectly via the anterior interosseous branch, which supplied flexor pollicis longus and the lateral half of flexor digitorum profundus. The ulna nerve supplies the flexor carpi ulnaris and medial half of flexor digitorum profundus. The radial nerve is the primary nerve for the entire extensor compartment and branches into the posterior interosseous nerve, which supplies the extensors, abductor pollicis longus, and supinator muscles.

Primarily the skeletal considerations are paramount for functional outcomes, however soft tissue coverage can prove challenging. Depending on the cause, the consideration for tissue transfers or flaps may be required.

Indications

Forearm amputations are not a frequent occurrence, but their requirement can be broadly split into three categories: trauma, disease process such as vascular, infection or malignancy, and congenital. Tissue destruction, vascular compromise, and malignancy are the most prevalent, in contrast to the lower limb, where the peripheral vascular disease is the cause in nearly 80% of cases.[2][6]

 Trauma is by far the most common indication at 80 to 90%, and particularly crush injuries in the industry.[2][6] The forearm has the second-highest incidence of compartment syndrome due to this mechanism. Those causing trauma beyond repair requires amputation. Additionally, any injury to vascular supply that cannot be repaired requires amputation. And finally, both burns and thermal/electrical injury and frostbite can necessitate amputation.[7][8][9]

Disease processes, both acute and chronic, can necessitate amputation. Infection is a significant cause, and in the upper limb, the reasons are principally aggressive infection such as necrotizing fasciitis, rather than chronic variants in the lower limb such as osteomyelitis. Not only has the part been rendered useless, but it is also a threat to the life of the patient because the toxic products of tissue destruction are disseminated systemically.

No injury severity score exists to guide severe upper extremity trauma. The decision making is left to the surgeon's judgment. Similarly, in patients with systemic sepsis, amputations are necessary to control the rampant infection. And vascular complications, either from peripheral vascular disease or diabetes, can require amputation in their end stages.

An indication for amputation after nerve injury is the development of uncontrolled trophic ulcers in an upper anesthetic limb. Amputation is usually not indicated in persons with quadriplegia.

Amputations in the upper limb are also indicated for persons with malignant tumors without evidence of metastasis.[10]

Finally, less commonly, there may be a requirement for amputation in congenital deformities or other cases such as severe contractures.

Contraindications

There is only one absolute contraindication to amputation that is a spared limb or part of a limb that would be functionally superior to its amputation. Factors regarding the functional potential of a spared limb include tactile and protective sensation, range of motion, pain, and intended purpose of the limb.

Personnel

Persons required to perform forearm amputation include:

• General/orthopedic surgeon
• Vascular surgeon
• Scrub nurse
• Rotating nurse
• OT technician

Preparation

Preparation will be determined by whether this is a traumatic amputation or elective. Of course, in all traumatic situations, one must adhere to the principles of Advanced Trauma Life Support (ATLS) to ensure an A to E approach is used, and life-threatening injuries are seen before limb-threatening. Of course, the injury to the limb may well be life-threatening. Once the patient is stabilized, if the decision is made to amputate, this should be agreed by two consultants/attendings, and appropriate consent taken from the patient. In the acute setting, a better approach is for progressive debridement with definitive delayed closure. The goal is to safely maintain as much length in the limb to better functional outcomes. The injury mechanism may determine this, as will the amount of soft tissue coverage one can make. One must assess the viability of the musculoskeletal structures outlined above and the motor and sensory function of the three major nerves in the forearm and their branches. Fundamentally, an adequate vascular supply will be the priority in the healing of the stump, mainly if any flaps are used. Therefore, assessing the arterial injury level is paramount and will be the most likely parameter in determining the level of amputation. In elective settings, the majority of the above is right. However, a more planned approach can be used, as well as adjunctive measures such as insertion of peripheral stents to improve blood flow or optimizing the patient. Additionally, one must be considerate towards the team required. Surgically, vascular, general, orthopedic, or plastic surgeons can all perform these amputations. Plastic surgeons will be crucial for flap coverage of the stump and are highly recommended to have their early involvement. Non-surgically, patients may require intensive care or high dependency care postoperatively. And the initial participation of psychologists, physiotherapists, and occupational therapists will improve outcomes. Finally, less commonly, there may be a requirement for amputation in congenital deformities or other cases such as severe contractures.

Technique or Treatment

In a sterile operating room, the patient would be placed supine with the arm outstretched on an arm table. The operative arm is prepped and draped in a sterile fashion. Skin incisions are marked, then the procedure may begin. As already mentioned, the goals are to maintain forearm length and preserve the elbow joint.

The stages of the operation would be as follows:

1. Anterior and posterior skin flaps are created equally to provide adequate soft tissue coverage. Do consider the need for free flaps and grafts if there is not sufficient tissue or including length and depth. When the skin flaps are too thin, there is a higher risk of breakdown, particularly in ischemic causes.
2. The radial and ulnar arteries are identified and ligated.
3. The muscle bellies of the 20 forearm muscles are transected.
4. The radial, median, and ulna nerves are also transected. All nerves, if transected, will aim to regenerate, and therefore cause a neuroma. Thus, the goal in amputation is to identify the free nerve endings and resect them to a level where they can be in a healthy tissue bed, as far away as possible from external stimulus, which would cause pain.
5. The ulna and radius are divided while aiming to maintain at least 5cm of the ulna for better elbow flexion. Aim to contour off the bone endings by palpating through the skin, as to improve prosthesis fit.
6. Finally, the deep fascia, subcutaneous tissue, and then the skin is closed.

Post-operatively, early prosthesis fitting and mobilization of the forearm, elbow, and shoulder are paramount. Adjuncts to help this include compressive stockings, the stump, and drains to prevent hematoma/seroma formation.

Complications

Complications in forearm amputations are much lower than those of the lower limb. Common complications pertain to edema, local infection, wound breakdown, and failure of grafts. These are infrequent but must be recognized.

More specifically, phantom limb pain occurs in the majority of upper limb amputees. This is defined as the patient's awareness of the amputated portion of the limb.[11][12]The incidence has been quoted between 40% to 80%. It is a complex condition requiring multiple treatment modalities to overcome.[13]

Hematomas can form postoperatively if bleeding is not controlled appropriately. Meticulous hemostasis and use of drain can reduce the chance of hematoma formation.

Regardless of the technique employed to divide peripheral nerves, a neuroma always forms.

Joint contractures usually are prevented by immediate postoperative active motion. If contractures develop, more aggressive physical therapy is required.

Revision surgery is a common complication, as trauma is the most common indication. A study in Iraq and Afghanistan soldiers showed that 42% of upper extremity amputees required a repeat surgical procedure, and those with forearm amputations were 4.7 times more likely to develop phantom limb pain.[14]

Finally, psychological stress must not be overlooked. Tintle et al. found that upper-limb amputations have far higher rates of post-traumatic stress disorder (PTSD) and disability than those with lower-limb amputations.[14] Tennent et al. outlined the higher rates of disability that occurs in an active population which under upper-limb amputation, including the significant effects of psychological distress.[15]

Clinical Significance

Forearm amputations are a life-changing event, usually caused due to sudden, unexpected trauma. These are often associated with injuries, and systemic issues must first be dealt with. The priority is to maintain life at the expense of a limb, but the goal is to preserve function. It depends on various factors, and one must be considerate of all before embarking on such a procedure. Regardless of the outcome, these procedures cause monumental physical, psychological, and economical to the patient.

Enhancing Healthcare Team Outcomes

Due to the complex procedural nature and unmeasurable morbidity inflicted upon a patient, as outlined above, a multi-specialty approach is vital in ensuring the best outcomes. 

The first port of call would be stabilizing a traumatic patient in the emergency room by a casualty provider. Due to the unpredictable nature of injuries, a variety of surgical specialties can be utilized to offer the best management – be it free flaps from plastics, revascularization of arteries by vascular surgeons, or optimizing musculoskeletal tissue by orthopedic surgeons to ensure best prosthesis fit and function. Therefore, these injuries should be managed at tertiary units with multi-specialty input.

Post-operatively, to minimize patient morbidity, they must be managed holistically. These injuries take months, if not years, to recover. It can only be done through rehabilitation teams, nursing staff, and psychiatric or counseling teams. This interprofessional approach leads to better outcomes and has also been shown to decrease patient stay by 20 days while increasing discharges of patients with a prosthesis by five times and increasing the effectiveness of long-term rehabilitation.[16] [Level 3]