Overview of Sural Nerve Graft
Peripheral nerve injuries often happen due to accidents, and can be caused by various factors like cuts, bruises, stretching, pressure, or even due to a medical procedure. Such injuries are generally not life-threatening but can have a big impact on a person’s day-to-day activities and general quality of life. By repairing the damaged nerve, the function of the nerve can be restored and thereby improve a patient’s life.
The most preferred method for repairing a severed peripheral nerve is a method known as primary end-to-end neurorrhaphy. But, sometimes this method can’t be used because the nerve ends are too far apart due a cut or disease or due to the occurrence of scarring or nerve tissue destruction. This can create gaps that are difficult to bridge with the existing tissue or it could cause too much pressure on the repaired nerve, leading to an unsatisfactory result. In these cases, a part of another nerve, typically the sural nerve, can be transplanted into the gap. This method was traditionally done using an open surgical technique, but recently, advances in medical technology have enabled doctors to use minimally invasive techniques.
The goal of reconstructing a peripheral nerve using a nerve graft is to allow new nerve fibers to grow towards the end of the damaged nerve to restore its function. The graft also brings with it specialized cells, known as Schwann cells, that aid in nerve regeneration. A careful linking of the nerve graft to the nerve stumps without any tension, along with suitable alignment and orientation are crucial for a successful outcome. Under ideal conditions, the regrowing nerve can advance at a speed of approximately 1 to 1.5 millimeters per day.
Even though nerve repair surgery can potentially improve the functioning of the damaged nerve, complete recovery is not always guaranteed. Many factors such as location of the nerve injury, the exact timing of the surgery, the length of the nerve gap, patient’s age, smoking habits and others can influence the final result. As there are many variables affecting the outcome of nerve reconstruction, complete recovery of nerve function after such a surgery is not always the norm but rather an exception.
Anatomy and Physiology of Sural Nerve Graft
The sural nerve is a nerve that is purely for feelings and sensations. It’s made up of fibers from parts of the spine known as L4-S1. The sural nerve usually comes from the joining of two nerves, the lateral and medial sural cutaneous nerves. These are parts of the common peroneal and posterior tibial nerves.
The medial sural cutaneous nerve goes down in between the two parts of the gastrocnemius muscle in your leg, beneath a vein called the lesser saphenous vein. It then comes up beneath the fascia (a layer of fibrous tissue in the body) where it joins with the lateral sural cutaneous nerve to form the sural nerve. This usually happens at the middle or lower part of the leg.
The sural nerve then goes at an angle towards the back of the lateral malleolus (the bony bit on the outside of the ankle), where it curves forward. Near the end, the nerve has one side branch approximately 6 cm from the lateral malleolus: the lateral calcaneal branch. The sural nerve ends 2 cm below the lateral malleolus; with one part going to the top side of the foot to join the superficial peroneal nerve, and the other part goes to the outer edge of the foot.
Along the route of the nerve, the superficial sural artery and lesser saphenous vein are usually just beneath and just behind the nerve. Recent studies suggest that the structure of the sural nerve can vary considerably from person to person, with a significant number of sural nerves consisting of differing combinations of nerve fibers.
Why do People Need Sural Nerve Graft
A surgeon might use a sural nerve graft (a piece of nerve tissue taken from the lower leg) in situations similar to when other nerve grafts would be used. This particular nerve grafting method might be favored because it can offer some benefits over other options, especially for longer nerve repairs.
The use of nerve grafts is common when there is a gap or loss in a motor or sensory nerve that is greater than about 1/2 to 1 inch in length. This is because careful rearrangement of the nerve ends might be able to make smaller gaps disappear, while ‘bridges’ or ‘channels’ for nerve growth might be effective only for gaps smaller than 1/5 of an inch.
For a nerve graft to work, or even to repair a nerve injury directly (without a graft), you need two healthy nerve ends – the ‘upstream’ and ‘downstream’ ends if you will. Sometimes, there may not be a healthy ‘upstream’ nerve end – say, in case of injuries near the base of the skull. In such situations, a different method called ‘nerve transfer’ to the ‘downstream’ nerve end may be a better way.
In facial reanimation or recovery, the sural nerve graft can be used because it can run from the healthy facial nerve on one side of the face to the nerve end on the paralyzed side. Also, it has been used successfully to lengthen the nerve in certain types of injuries to the brachial plexus, a complex of nerves that sends signals from your spine to your shoulder, arm and hand.
More recently, sural nerve grafts have been used to treat a disorder of the eye called ‘neurotrophic keratitis’, caused by lack of feeling or numbness in the cornea (the outer transparent part of the eye). This can cause a loss of the blinking reflex and tear production, leading to ulcers and scarring on the cornea that might make it clouded. Here, sural nerve grafting along with ‘great auricular nerve’ grafting (the ‘great auricular’ nerve is from near the ear) can be used to restore feeling to the cornea, with these ‘functional’ sensory nerves sending their long ‘axon’ fibers towards the affected cornea.
When a Person Should Avoid Sural Nerve Graft
There are certain situations where nerve grafts can’t be used to help restore movement and functionality to a part of the body. For example, if the muscle at the end of the nerve has been without nerve connection for too long (usually over 12-18 months) it may shrink and harden, losing its ability to move even if a nerve connection is restored later. Hence, doctors prefer to perform nerve graft surgeries as quickly as possible to avoid this situation.
However, restoring a nerve connection is not an instant fix – nerves slowly regenerate at a rate around 1 to 1.5 millimeters per day. This means the muscle might not start responding immediately after the surgery and it may take some time before the benefits are seen.
In some cases, if the nerve gap is too wide (longer than 6 cm), or if there’s significant loss of surrounding soft tissue or if radiation treatment is required, a different type of nerve graft may be preferred. This special type is called a ‘free vascularized nerve graft’, which has its own blood supply enabling better survival and integration.
This unique type of nerve graft may also be considered if the area where the nerve is going to be grafted has a lot of scars or bad blood circulation. Also, if past surgery or injury has affected the outer and back side of the leg, the doctor may choose a different nerve to replace the damaged one. They will of course ensure that the nerve they are harvesting (or taking from another area) is functioning well, especially in patients with nerve diseases which are known as peripheral neuropathies.
Equipment used for Sural Nerve Graft
When a doctor needs to get a graft from your sural nerve using a tool called a tendon stripper, they typically use several instruments. These include small retractors (a tool used to hold tissue out of the way), forceps (medical tweezers), a scalpel (a surgical knife) for cutting, and an electrocautery forceps (a tool used to stop bleeding by heating the tissue). They also might use scissors, a needle holder, vessel loops (used to control bleeding), and a tendon stripper (a tool used to remove a piece of the sural nerve).
After getting the graft, the next step is to insert the graft. They will use a set of really tiny instruments, a microscope, and stitches. Sometimes, the doctor might also use a biological glue to help seal the graft, or a conduit (a type of cover) to wrap around the graft. This set of steps is known as the graft inset.
Note: Sometimes, instead of doing this procedure with an open cut, the doctor might use an endoscope which is a long tube with a light and camera on the end. This way, the whole procedure can be performed through just one small cut on your leg. Carbon dioxide is used to inflate the area so that the doctor can see better. Usually, for an endoscopic procedure, the same instruments used to get vein grafts can be used to get the nerve graft.[3]
Who is needed to perform Sural Nerve Graft?
A team of healthcare professionals is involved in any surgery. The main person is the surgeon, who is a special type of doctor trained in performing operations. A surgical first assist, who is a person that helps the surgeon, is also usually present on the team.
Then we have the anesthesia provider, whose job it is to make sure you’re not in pain during the surgery. They might put you to sleep or just numb an area of your body, depending on the operation.
The operating room circulating nurse ensures the smooth operation of the surgery by making sure all rules and safety measures are followed. Lastly, the surgical technologist helps the surgeon, first assist, and nurse by making sure the right tools and equipment are available and in good condition.
Combined, this team of experts works together to take care of you before, during, and after your operation.
Preparing for Sural Nerve Graft
Before the procedure, the doctor will first give the patient an in-depth understanding of the process. This includes discussing the risks associated with the procedure’s ‘donor site’ (the area from which tissue or organs are taken for transplantation). For instance, the patient might feel numbness on the side of the calf or the top of the foot after the procedure. Furthermore, it’s important for patients to understand that there may be visible scars on the leg, particularly if an ‘open harvesting technique’ (a procedure where the surgeon makes a large incision to access the organ or tissue) is used. All these details must be fully discussed with the patient before the procedure takes place.
How is Sural Nerve Graft performed
Sural nerve grafting is a medical procedure that doctors performs under general anesthesia. In simpler terms, the patient is put to sleep for the procedure. The patient lies flat on their back for the procedure. To avoid excessive bleeding, doctors can use a technique where blood flow is temporarily blocked. They may also use optical magnification, like special glasses, to see the area better.
Next, the doctor cleans the area where the operation will be held using a 10% povidone-iodine solution. This cleaning is applied from foot to knee level on the leg that will be operated on, also known as the donor leg. Surgical drapes are positioned to ensure the operation area on the leg is accessible and can be moved as needed during operation. The knee is bent and supported by a rolled surgical towel.
A small 2 cm cut is made a little behind and above the lateral malleolus, which is the small bony bump on your ankle. The doctor will slowly work their way through the fat layers. There, one often finds the lesser saphenous vein, a major blood vessel, and the sural nerve, which is the target of our operation. The surgical team isolates these structures to avoid confusion between the two. The vein often gets marked and moved to improve visibility of the nerve.
Once the nerve is found, it’s carefully isolated and moved further up the leg to prepare for grafting. It’s okay if additional nerve is removed, as longer grafts do not affect sensitivity. Smaller “stair-step” incisions about 5 to 10 cm apart may be used to reduce damage to the nerve and improve the operation outcome. However, this method requires extra effort.
Once the nerve graft of the required length is dissected, it’s cut out and taken out from the surgical area. This nerve is then marked to ensure it’s inserted properly, as reversing the direction may cause axonal loss.
After the nerve graft has been harvested, the incisions are closed using stitches. Applying an antibiotic ointment and wrapping the leg completes the surgical process.
There are variations to this main technique as well. Some involve making zig-zag cuts, but these do not improve the operation results and can leave bigger scars. Another method involves using an endoscope to reduce incision sizes and improve the scar appearance. This method, however, takes longer.
Whether using an endoscope or not, the nerve is prepared and collected in the same way. If an endoscope is not available, a nerve or tendon stripper can be used to quickly dissect the nerve. However, an extra step is required to prevent the nerve from getting tangled and cut too early.
Possible Complications of Sural Nerve Graft
Harvesting a sural nerve graft, a type of nerve taken from the leg, can sometimes have problems, just like any surgery. These might include the wound not healing well or forming thick, raised scars. In some cases, there might be a buildup of blood, known as a hematoma, near the surgery site. Very rarely, a painful lump called a neuroma can develop, which might limit the patient’s activities due to discomfort.
After the surgery, patient might feel numbness on the top and side of the foot. But this is a normal side effect rather than a problem. Over time, this sensation often gets better as other nearby nerves grow and accommodate for the harvested nerve. This improvement can take around one to two years.
What Else Should I Know About Sural Nerve Graft?
Injuries to the nerves in our limbs and face are often treated by professionals like plastic surgeons or orthopedic surgeons. Sometimes, these injuries can be repaired directly, but other times, if the damage is larger, they’ll need to be fixed using what we call autografts. One example of an autograft is the sural nerve, which is a nerve from your leg that can be used to fix other nerves.
The doctor will determine the best approach to treat the nerve damage based on several factors. Understanding what the injury requires, the suitable and unsuitable scenarios for each operation, the anatomy of the nerve, and the best way to perform the surgery, will allow the doctor to safely collect the nerve for the graft. This minimizes further injury to the graft and also maximizes the chances of a good recovery after the operation.
