Nerve pain is a common outcome after total knee replacement, but little is known about the causes, impact, and effective management of this pain. This area of research is particularly important as over 1 million TKR’s are performed in the US and Europe each year [1]. Nerve pain is defined as pain radiating along the distribution of a specific nerve and its branches, with or without associated changes in sensation, and can be caused by a variety of mechanisms. For many patients with severe knee arthritis, TKR is a very successful operation that leads to a significant improvement in quality of life. Sadly, about 17% of patients are not satisfied with the result of their TKR, and nerve pain has been identified as one of the potentially reversible causes of dissatisfaction [2, 3]. The specific hypothesis and aims of this study are: To identify the impact of persistent post-operative nerve pain after TKR on patient-perceived satisfaction and quality of life. To characterize the somatosensory symptoms and signs associated with nerve pain in this patient group using quantitative sensory testing (QST) and To identify pre-operative and peri-operative factors that are predictive of the development of post-operative nerve pain. This will be the first study to systematically investigate the impact of knee replacement on a specific group of pain conditions associated with an identifiable anatomical lesion (neuropathic pain). By identifying the factors predictive of post-operative nerve pain, it may be possible to take steps to modify some of those factors and thereby reduce the likelihood of patients developing this type of pain.
Understanding Nerve Pain after Knee Surgery
Nerve pain, also known as neuropathic pain or neuralgia, is a pain that comes from problems with signals from the nerves. It was once believed that damage to the nerves was the cause of pain. However, this belief has changed in the last 20 years. We now know that the damage to the nerves is less of a direct cause and the pain is more of a result of the way the nerves are sending signals. Up until recently it was thought that the pain was due to the regrowth of damaged nerves. We now know this is not the case in many instances. The generated signals are often abnormal and continue to fire for no apparent reason. Nerves are an essential part of our body. They carry the messages that tell our bodies how to work. They transmit information to the brain in the form of electrical signals from the various parts of the body. This information is then interpreted by the brain which then sends a message back to the body part on what to do. For example, if the body part is a leg and the message is to move, the brain sends a signal down the nerves in the leg that cause the specific muscles for moving to contract. This whole process is then reversed if a message is sent to the brain from another body part. For example, if the hand touches something hot, a message is sent to the brain, which then sends a message back down the nerves that tell the hand to move away. This involving the motor nerves which transmit the message, and the sensory nerves which transmit the information about what the body part is doing, is very complicated and any disruption in this process can cause dysfunction of the body part and/or pain.
Importance of Effective Treatment
Although the cause of nerve pain after knee surgery may be understood, current treatments and outcomes often leave patients dissatisfied. Katherine was a 53-year-old woman who had surgery on her right knee to repair osteoarthritis. The surgery was 100% successful in repairing the arthritic damage by removing all debris and floating particles while also healing a partial tear to her patellar tendon. Four months post-surgery, Katherine began to have short bursts of severe burning pain on the medial aspect of her right kneecap. This pain quickly became more severe and constant. It was aggravated by activity and relieved only by strong pain medication and the R.I.C.E method. Any kneeling, squatting, or any slight bump to the knee would provoke a “shock-like” pain radiating to the inner aspect of her lower leg and ankle. Her OS referred her to a neurologist who diagnosed her with damage to the saphenous nerve. At this point, there was still no muscle wasting or weakness, and the neurologist suggested a wait-and-see approach. He explained that the nerve may or may not heal itself and treatments at this point have unpredictable outcomes. This left Katherine confused and anxious for effective treatment. Faced with this complex and unpredictable condition, Katherine decided to use her case to critically examine treatment for nerve pain after knee surgery in hopes to aid herself and others who experience similar problems.
Non-Surgical Treatment Options
Medications could be a helpful tool in treating nerve pain after knee surgery. Unfortunately, there is limited data on the use of medications for post-operative nerve pain. Trials of medications to suppress the signals in the nerve and lessen pain at the spinal cord or brain can be given. Agents like gabapentin, pregabalin, and duloxetine have been shown to be effective in treating chronic pain and neuropathy. Since these medications can have numerous side effects and could potentially react with other post-operative medications, consultation with the patient’s surgeon or primary care physician is recommended.
Physical therapy may be an effective treatment for nerve pain after knee surgery. The aim is to limit aggravation of the nerve and to minimize the nerve’s signaling of pain and unpleasant symptoms to the brain. Traditional modalities such as ice and massage can give temporary relief. Iontophoresis (use of a steroid patch under an electric charge to drive medication into tissues) using dexamethasone may provide pain relief. Medical evaluation for the appropriateness of a home exercise program or supervised rehabilitation is indicated. Exercises should be carefully progressed, as exacerbation of the pain could result in a delayed recovery.
Physical Therapy
The key to any of these exercises is not an aggressive approach, but a gentle one. Overstrain may result in increased pain that could last for days, even making some symptoms worse. This is where a skilled therapist would be important. They could monitor and determine the extent of how much exercise should be done on any given day. They are also crucial in determining what exercises should be done in order to prevent the symptoms from returning. It is important to find a therapist who is creative. Sciatic nerve pain can be very difficult to treat if the therapist is using the same routine on everyone. This is why a therapist with a large arsenal of exercises and the knowledge to use them is a worthy candidate for a good recovery.
Physical therapy involves supervised exercises on a prescribed routine over a period of time for a specific desired outcome. The goal is to decrease pain, improve flexibility, strength, endurance, coordination, and overall functional ability of the patient. Often, a home program is created in order to adhere to the consistencies of the therapy. There are ways to prevent a recurrence of the original symptoms and prevention of further injury or a new one.
Medications
While most pain medication is directed at decreasing inflammation, newer medications are directed at various causes of nerve pain. A short course of anti-inflammatory medications may have some benefit. The possible side effects of anti-inflammatory medications must be weighed against the potential benefits in an older adult, particularly if there is a history of stomach, kidney, or heart problems. These medications may also function as nerve pain pills. Since general narcotics such as Codeine, Vicodin, and Oxycontin are directed at general pain relief they are typically not as effective in relieving nerve pain. Tramadol (Ultram) is a narcotic-like pain medication that has been shown to be more effective for nerve pain than other narcotics and is associated with a lower frequency of abuse. A prescription of a short-term (5-7 day) “burst” of oral steroids might be beneficial. This is the treatment with the highest potential benefit but also the highest potential risk. High-dose steroids can have serious side effects. Newer medications that were originally developed for treatment of epilepsy or depression are also effective for relieving nerve pain. The most widely used group of medications for this are the SSRIs or serotonin-norepinephrine reuptake inhibitors. They have been shown to be effective for nerve pain and have a low frequency of side effects in comparison to other medications. A similar group of medications that are effective nerve pain pills are the anticonvulsants or seizure medications. These medications have a wide effectiveness for different forms of nerve pain and are considered a first-line treatment. Most medications are tried at a low dose and increased as needed to optimize pain relief and minimize side effects. In order to avoid “trial and error” and more effectively relieve pain, both the type of pain and the medication must be matched appropriately, a task that may call for a consultation with a neurologist or pain specialist.
Nerve Blocks
Nerve blocks have been used for years to help control pain. They are most often used in surgery, but they have also been used to help control chronic (long-lasting) pain. A nerve block is an injection of a substance that helps decrease the body’s ability to feel pain signals. A pain management physician or an anesthesiologist is usually the doctor who administers the nerve block. This is sometimes done in the doctor’s office. But some nerve blocks are done at a hospital or an ambulatory surgery unit. Nerve blocks are quite effective, but they are reversible. So, they are not a good option for those with long-term chronic pain from OA, unless it is used to help control pain after joint replacement surgery. This is a consideration for a patient who is contemplating a complete joint replacement down the line, but who wishes to delay the surgery and get pain relief in the interim.
Surgical Treatment Options in Singapore
In Singapore, decompression surgery is the most common surgical procedure used to relieve nerve pain and restore function following nerve compression caused by injury or entrapment. The goal of decompression surgery is to relieve the painful symptoms that are caused by pressure on the nerve. Pressure on a nerve can be caused by injury or other conditions such as nerve entrapment or compression by surrounding tissues. The pain occurs because the nerve is not able to transmit electrical signals in an optimal way. This can be due to damage of the nerve itself or problems with other structures that affect the nerve. Decompression surgery involves removal of tissue that is causing the compression on the nerve. This can include part of a herniated disc or a section of the piriformis muscle. After removing the cause of compression, the surgeon will inspect the area to ensure that the nerve is free of compression and then close the wound. If the nerve has been damaged, a repair surgery may be needed at a later stage to restore function. The success of decompression surgery can be variable and it is not uncommon for a patient’s pain to persist or for new symptoms to develop. An incomplete understanding of the causes of nerve pain and the variability in patients’ symptoms are contributing factors to the lack of consistent successful outcomes for nerve decompression surgeries.
Decompression Surgery
Decompression implies “to get rid of pressure.” Many nerves can get entrapped, causing severe pain. The common peroneal nerve is the nerve affected by a knee injury. It runs just below the knee joint, and when the knee is injured or has undergone surgery, the surrounding muscles and tissues respond by swelling. This then puts pressure on the nerve, and over a period of time, it can become entrapped. Symptoms include burning pain around the knee cap and weakness in lifting the foot and toes. Decompression surgery involves locating the nerve and freeing it of all the surrounding tissues. It is a minimally invasive procedure and has a good success rate in relieving pain. The common peroneal nerve, when entrapped, can cause a condition called “foot drop.” This is because the nerve supplies the muscles that lift the foot and toes, and when it is not functioning properly, the foot does not get lifted off the floor. During one particular type of knee surgery, I was required to be in a straight leg cast for 6 weeks and then a brace for a further 2 weeks. On seeing a specialist for the foot drop, it was found that the nerve was badly entrapped. Surgery was performed to decompress the nerve and was followed by an intensive period of physiotherapy to regain full function.
Nerve Repair Surgery
Nerve repair surgery is based on the neurosensory and motor re-learning (NERVE) program treatment theory of nerve recovery. It recognizes that a badly damaged nerve will regenerate to the muscle tissue at only 1mm per day and will need reinnervation of sensory receptors prior to or during regeneration to ensure the muscle acts under the correct proprioceptive guidance. The key element of this is prevention of muscle imbalance which results if reinnervation is allowed to occur when the muscle has already started to contract under the wrong guidance. This process has been termed “time-sensitive reinnervation” and if achieved, can potentially alter the natural history of nerve recovery, effectively producing better results than the no treatment option. This method hinges on accurate diagnosis and demanding surgery with respect to tissue handling.
Nerve Transfer Surgery
Nerve transfer surgery involves identifying an expendable motor nerve (a nerve that causes muscle contraction) that is still in good condition because muscles to which it is attached are still functioning, and connecting (i.e. transferring) it to the denervated muscle through a nerve graft to provide reinnervation for the new function. This is based on the principle that a denervated muscle will lose its muscle mass and strength (due to loss of nerve supply) over time and will eventually be functionless unless it is reinnervated. This surgery has been highly successful for certain peripheral nerve injuries such as brachial plexus injuries and has recently been applied to restore muscle function after knee arthroplasty. An example of a nerve transfer for a knee surgery patient involves transfer of the distal branch of the healthy functioning tibial nerve innervating the gastrocnemius muscle to the motor point of the soleus muscle, another muscle innervated by the tibial nerve but has become denervated due to nerve damage at a higher site. This procedure can only be performed in certain cases where it is deemed that there is no hope of spontaneous recovery of the nerve injury and there is still potential for functional improvement of the muscle.
Pain Management in the Back of the Knee
The back of the knee is a very sensitive area because it is the location of several large arteries, nerves, and veins. Damage to any of these structures can result in severe complications. The most commonly damaged nerve is the Saphenous nerve, which is found on the inside of your knee. This nerve provides feeling to the skin of the leg as well as the inner portion of the knee joint. Injury to this nerve can result in pain, numbness, or a tingling sensation on the inside of the knee. The cause of the pain is fat pad irritation due to the fact that the Saphenous nerve supplies sensation to the fat pad. Any damage to the nerve by surgery, injection, or direct trauma can result in a condition known as Saphenous neuralgia. This is when the nerve sends abnormal signals to the brain in the absence of any stimulation to the area that the nerve supplies. This abnormal signaling can result in a burning or shooting pain in the inner portion of the knee which can be very difficult to treat.
Causes of Pain in the Back of the Knee
Cause of pain in the back of the knee can vary, and some factors may be related to more than one condition. A number of patients suffer from pain at night as a result of their daytime activities. Certain occupations allow little rest for the knee. Those who work in low seated positions exacerbate mechanical knee problems. For example, post meniscectomy patients who develop a tear of the articular cartilage when the meniscus is no longer present to protect the joint. Teachers, who are required to spend long hours on their feet, frequently aggravate inflammatory conditions. Pain may also be referred from a back problem, since there are many nerve endings in the back which transmit pain to the lower extremities. One study documented that the knee was the source of pain in only 62% of patients with osteoarthritis. Of those with pain from another source, 85% reported significant improvement of their knee pain after rehabilitation of their back or hip problem. A similar theory applies to patients who have a history of injury in the lower leg. If the injury is to a tendon or ligament which has healed in a weakened state, there will likely be chronic problems with pain as a result of instability around the knee joint. Erythema nodosum, a condition primary in women, involves redness and swelling of the shins, it is often associated with systemic inflammation from infection or another underlying disease process. Chronic swelling of the knee with possible effusion and synovitis may cause posterior pain due to impingement of the medial and lateral gastrocnemius on the femoral condyles. This is common in inflammatory arthropathies and may also be present with Baker’s cyst. Finally, the knee may experienced referred pain from a muscle imbalance or malalignment. The popliteal muscle and semimembranosus have been reported to cause medial pain while the biceps femoris may cause lateral pain. Any or all the above may be a causative factor for pain in the back of the knee, a successful diagnosis is important in providing effective treatment.
Non-Invasive Treatment Options
Treatment for pain back of knee and upper calf is a common complaint of patients whose sensory nerves do not recover following surgery. If there are no skin incisions in this area, it is probable that the injury was caused by retractors on the inner side of the knee, and this can occur in any surgery using a supine position and medial knee mediation of the lower extremity. This can also occur in hip surgeries when the knee is rested on a post or lateral decubitus position with the knee flexed. Although there are no controlled studies on nerve injury after knee surgery, neuropraxia in this area from positioning or tourniquet pressure usually completely resolves within a few months. If there is no resolution or only partial improvement to 1-2+ on a Semmes Weinstein monofilament test, the nerve has most likely been injured. In these patients, I have found concentrated sensory nerve testing to elucidate the exact area of neural deficit to be most helpful. This can also be done using sural nerve conduction studies and SFEMG of the medial gastrocnemius and tibialis posterior. SFEMG has been found to be abnormal in most cases of focal nerve injury, and it is important to rule out more proximal nerve compression. Affected patients may gain partial relief with peroneal nerve blocks and AFOs with solid or hinged ankle control help prevent foot drop and reduce the risk of further injury. High drop-out socket designs can provide relief for posterior leg pain, but in most cases, the nerve will not recover until direct surgical intervention is taken to decompress the nerve or it may not recover at all. Previous studies have suggested that anti-inflammatory drugs and therapeutic ultrasound will improve recovery following nerve injury, but I have found no significant results with these treatments.
Invasive Treatment Options
Invasive treatment option consists of an anesthetic or a steroid injection at the place where the nerves were damaged. It was thought that the pain is caused by a neuroma, which is a growth of nerve ending that is usually swollen and painful. Nerves can be viewed with ultrasound and then a small needle inserted to introduce the steroid or anesthetic to the area. An anesthetic will provide a block in nerve conduction and is a test to see if the pain can be stopped if the nerve is removed. Steroids are anti-inflammatory and may reduce swelling and pressure on the nerve and provide long-term pain relief. A steroid injection into the spine is another option and may be used if the nerves that are causing pain can be linked with the nerve in the back, unfortunately this has been shown to be ineffective for knee pain in some studies. If the damage of the nerve is identified and is thought to be the cause of the painful it is possible to surgically remove the neuroma or damaged nerve. This is a risky procedure as the nerve may grow back with greater pain or numbness of the area skin, and it can also disrupt the normal nerve and create a painful phantom neuroma. A spinal cord stimulator system is a surgical implant which delivers electrical signals to the spinal cord in order to control pain. A recent study using a rat model with nerve injury showed that electrical stimulation succeeded in preventing the pain and reversing the changes in the central nervous system. This is another option that may be used to see if nerve pain after knee surgery can be controlled, but may not be effective if the pain is local and not widespread. High intensity focused ultrasound (HIFC) is a non-invasive treatment to destroy tissue with focused ultrasound and is used for treatment of cancers and tumors. An MR guided version of this can be used to treat knee pain nerve lesions and a recent study of rats with a nerve injury model has shown prevention of neuroma formation and long-term reduction in pain behavior. However, today it is a very new technology and is not commonly practiced.
