Interposition Nerve Grafts

What Are Interposition Nerve Grafts?

Interposition nerve grafts are a microsurgical reconstruction technique used to restore nerve conduction when a nerve is interrupted due to trauma, tumor surgery, or severe tissue loss. In this technique, when the gap created by the damaged or removed nerve segment is too large to be repaired end-to-end, a healthy nerve segment taken from another part of the body is used as a graft. This nerve tissue acts as a bridge between the two ends of the damaged nerve, allowing nerve fibers (axons) to regrow along the graft and reach the target muscles or sensory areas. The procedure is usually performed using microsurgical techniques that require high precision, and the nerve ends are joined with very fine sutures. As a result, nerve transmission can be reestablished, and over time, muscle or sensory functions may be partially or completely restored.

When Is Interposition Nerve Grafting Performed?

There are specific situations in which interposition nerve grafting is performed. These situations are as follows:

• Traumatic nerve injuries: It can be performed to bridge the gap between nerve ends when a section of the nerve is lost or severely damaged as a result of cutting or piercing trauma.
• When a nerve defect occurs after tumor surgery: The interposition nerve graft method can be used when part of the nerve needs to be removed during the removal of skull base tumors, parotid gland tumors, or other tumors surrounding the nerve.
• In facial nerve injuries: It may be preferred to restore nerve conduction in cases of nerve transection causing facial paralysis or nerve loss during surgery.
• When nerve ends cannot be directly joined: When the distance between nerve ends is too great to allow tension-free end-to-end repair, bridging with a nerve graft may be necessary.
• In peripheral nerve reconstructions: It can be applied to reestablish nerve conduction pathways in cases of segmental losses in the arm, leg, or other peripheral nerves.
• In nerve losses following previous surgeries: It can be used to restore nerve function after nerve damage or resections that occurred during previous surgical procedures.

How is Interposition Nerve Graft Surgery Performed?

During interposition nerve graft surgery, the two ends of the damaged nerve are first carefully exposed and cleaned up to healthy nerve tissue. Then, the length of the defect between the nerve ends is measured, and a nerve graft of the appropriate length is planned. In this context, donor nerves such as the sural nerve, great auricular nerve, or medial antebrachial cutaneous nerve, taken from the patient's own body, are usually preferred as grafts. The taken nerve piece is placed between the two ends of the damaged nerve and carefully sutured to both nerve ends using very fine sutures and microsurgical techniques. Thus, after the surgery is completed, nerve fibers (axons) grow along the graft over time, attempting to reach the target muscles or sensory areas. As a result, this process can take months, and gradual functional improvement can be observed in the patient as nerve regeneration progresses.

Advantages of Interposition Nerve Graft Surgery

Interposition nerve graft surgery offers psychological and physical advantages to the patient. To elaborate on these advantages:

• The biggest obstacle to nerve healing is tension. The use of grafts fills the gap between the cut ends, reducing mechanical pressure in the sutured area to zero. This increases the chance for new nerve fibers (axons) to cross over to the other side.
• Even if the transplanted nerve segment has been cleared of dead cells, it provides a natural tunnel structure called “endonatal tubes.” These tubes act as a biological guide for the regenerated axons, allowing them to grow toward their target.
• When an autograft (nerve taken from the patient's own body) is used, the body does not recognize this tissue as a foreign substance. This allows for faster and smoother healing compared to synthetic tubes or grafts taken from cadavers.
• When the distance between nerve ends is more than 2 cm, end-to-end suturing becomes impossible. Interposition grafts allow for the functional repair of even large nerve losses of up to 10-15 cm.
• Especially in hand surgery and facial nerve repair, it has much higher success rates than synthetic methods in restoring sensory and motor functions.
• Since the patient's own tissue is used, immunosuppressive drugs are not required. When the donor site (usually the sural nerve at the back of the leg) is carefully selected, sensory loss in that area remains minimal.
• Live grafts contain growth factors that promote nerve growth and Schwann cells. These cells accelerate the process of covering new nerve fibers with a myelin sheath, thereby increasing nerve conduction velocity.
• The surgeon can select a graft appropriate for the diameter of the damaged nerve. If the main nerve is very thick, several thin grafts can be placed side by side using the “cable graft” technique to achieve a perfect fit.

Interposition Nerve Grafting Sonrası İyileşme Süreci

The recovery process following interposition nerve grafting is gradual and time-consuming, due to the nature of nerve regeneration. During this process, nerve fibers (axons) regrow along the graft, attempting to reach target muscles or sensory areas. This growth typically occurs at an average rate of 1 mm per day; therefore, functional recovery may take several months and, in some cases, the process may exceed one year. In this context, protecting the surgical site, controlling edema, and preventing the risk of infection are of great importance in the early postoperative period.

In the later period, physical therapy, muscle exercises, and rehabilitation programs may be applied as needed to support the recovery of nerve function. The patient's recovery process may vary depending on many factors, such as the degree of nerve damage, the length of the graft, the timing of the surgery, and the individual's capacity for recovery. Therefore, regular clinical follow-up is crucial for evaluating nerve regeneration and guiding the treatment process correctly.

Preoperative Considerations for Interposition Nerve Graft Surgery

Since interposition nerve graft surgery is an intervention that requires microsurgical techniques and a recovery process that requires patience, there are many points to consider before the operation. These points are as follows:

• Management of Blood-Thinning Medications: Bleeding control is critical in microsurgical procedures. Blood-thinning substances such as aspirin, warfarin, or certain herbal supplements should generally be discontinued 7-10 days prior to surgery, with the surgeon's knowledge.
• Quitting Smoking and Tobacco Products: Nicotine causes blood vessels to constrict (vasoconstriction). New blood vessel formation is essential for the nerve graft to “take.” Smoking impairs the graft's nutrition, significantly increasing the risk of failure.
• Maintaining Joint Flexibility: If nerve damage limits joint movement, physical therapy should be used before surgery to prevent joint stiffness (contracture). A stiff joint negatively affects nerve healing after surgery.
• Controlling Chronic Diseases: Diabetes directly affects nerve healing. Stabilizing blood sugar levels before surgery increases the growth potential of nerve fibers (axons).
• Understanding Donor Site Loss: It should be remembered that there will be permanent numbness in the area where the graft is taken (e.g., the outside of the ankle or part of the arm). It is important for the patient to accept this “loss of sensation” before surgery for psychological preparation.
• Nutrition and Vitamin Support: The body needs protein and B vitamins (especially B12) for nerve regeneration. A healthy diet before surgery has a positive effect on the speed of recovery.
• Planning Postoperative Restrictions: After surgery, the relevant area may need to be immobilized with a cast or splint for a period of time to prevent the graft from stretching. The patient should organize their daily activities and work life in advance according to these restrictions.

Precautions to Take After Interposition Nerve Graft Surgery

Just as there are precautions to take before interposition nerve graft surgery, there are also precautions to take after interposition nerve graft surgery. These precautions are listed below:

• Immobilization Period: The operated area is usually immobilized with a splint or cast for the first 2-3 weeks to prevent tension at the graft suture sites. During this period, avoiding sudden movements is vital to prevent the graft, which acts as a “bridge,” from shifting out of place.
• Swelling Control and Positioning: Keeping the operated area (arm or leg) above heart level reduces pressure on the suture line and speeds up healing. Excessive swelling can disrupt blood flow (microcirculation) to the nerve.
• Complete Avoidance of Smoking and Nicotine: Nicotine constricts blood vessels, hindering graft nourishment (revascularization). Smoking is the factor that most increases the risk of nerve graft failure (non-take).
• Sensory and Motor Monitoring: Nerve healing is very slow (approximately 1 mm per day). Tingling, electric shock-like sensations, or a feeling of “pins and needles” (Tinel's sign) in areas far from the surgical site indicate that healing is progressing well.
• Donor (Recipient) Site Care: Permanent numbness in the area where the graft was taken (usually the sural nerve line in the leg) is normal. The stitches in this area must be kept clean and protected from infection.
• Physical Therapy and Rehabilitation: After the cast is removed, passive movements should be started to prevent the joints from stiffening. However, these movements should be within the limits specified by the surgeon and should be controlled. Electrical stimulation therapy may be recommended to prevent muscle wasting (atrophy).
• Vitamin B and Nutritional Support: A protein-rich diet and vitamin B1, B6, and B12 supplements, as recommended by the surgeon, can support the process of nerve tissue repair.
• Protection from Extreme Heat and Cold: Since there will be a loss of sensation in the affected area until nerve transmission is fully restored, burns or frostbite may occur unknowingly. Bath water temperature should be controlled, and hot/cold compresses should be avoided.
• Neuropathic Pain Management: During the healing process, burning or stabbing pains may occur due to stimulation of the nerve endings. This is a sign of “recovery,” but if the pain is severe, neuropathic painkillers prescribed by a doctor should be used.

Differences Between Direct Nerve Repair and Interposition Nerve Grafting

There are fundamental differences between direct nerve repair and interposition nerve grafting. To examine these differences in depth, they are as follows:

Direct Nerve Repair (End-to-End Anastomosis)

• Basic Requirement: It is preferred when there is no gap between the nerve ends or when the ends can be joined without tension, in a way that does not restrict joint movement.
• Surgical Technique: The two ends of the damaged nerve are cleaned and directly sutured to each other using microsurgical sutures.
• Regeneration Process: Nerve fibers pass through a single suture line to reach the target organ. Since no foreign tissue is introduced, the healing process is faster and of higher quality.
• Donor Site Effect: No additional donor site or nerve graft is required; therefore, there is no loss of sensation in another part of the body.
• Expectations for Success: It is an ideal repair method, and the functional recovery rate is significantly higher than that of graft surgery.

Interposition Nerve Graft (Intermediate Nerve Graft)

• Basic Requirement: When the gap between nerve ends is greater than 2 cm or the nerve ends cannot be joined without tension, bridging (grafting) is performed to fill the gap.
• Surgical Technique: A piece of nerve taken from another part of the body (usually the sural nerve) is placed between the two main ends and secured with micro sutures on both sides.
• Regeneration Process: Nerve fibers must pass through two separate connection points (proximal and distal suture lines). This makes it difficult for nerve fibers to reach their target and prolongs the process.
• Donor Site Effect: Temporary or permanent sensory loss inevitably occurs in the area where the graft is taken (donor site).
• Technical Risks: There is a risk that the graft will not nourish itself and “take” (revasculation failure); this risk is almost never seen in direct repair.
• Cellular Support: The natural “endonatal tubes” and Schwann cells within the graft act as a scaffold and guide for axons to grow toward their target.