What Is Radiofrequency Ablation?
Radiofrequency ablation is a therapy that uses radio waves to create an electrical current. This current delivers heat to targeted nerve tissues, in an attempt to reduce chronic pain symptoms that are associated with various conditions. The way the heat is applied to the nerve tissue impairs or destroys the nerves, resulting in a semi-permanent disturbance of the transmission of pain signals from the spinal column to the brain.Radiofrequency ablation is a non-surgical therapy that was initially discovered to be an effective treatment for the relief of chronic pain in 1931 when it was utilized to treat a patient with trigeminal neuralgia, which is a pain condition that affects facial nerves, resulting in severe jolts of pain. Due to the treatment benefits of this procedure, radiofrequency ablation has become increasingly popular for both physicians and patients over the past 15 years.
Numerous reports have shown that radiofrequency ablation leads to a greater reduction in spinal pain compared to conventional treatment options, due to the disruption of nerve function that occurs with this procedure. Further, the reports have suggested that the pain reduction is sustained for six to 12 months after the procedure is performed. There are additional benefits of this treatment that may also contribute to the appeal of this procedure for physicians and patients. These benefits include being able to perform the procedure in an outpatient environment, needle insertion precision, and being able to repeat the procedure if needed.
Continuous radiofrequency and pulsed radiofrequency are the two basic types of radiofrequency ablation. Both of these methods have been shown to be effective for disrupting pain signal transmission from specific nerves, resulting in a reduction or elimination of chronic pain symptoms. It has been found that the damage that is induced by the heat is primarily responsible for the efficacy of this pain therapy procedure. However, some reports have suggested that the effect that the electrical field has on gene expression within the pain processing neurons may be responsible for relief of pain symptoms.
At the present time, radiofrequency ablation is frequently used to treat lumbar facet joint pain. The facet joints are located within the spine and connect the vertebrae to one another. Within the facet joints are medial branch nerve networks, which are responsible for transmitting pain signals to the brain when there is nerve tissue damage or inflammation. When a patient’s pain becomes persistent, radiofrequency ablation is usually performed to destroy the affected medical branch nerve, which helps to relieve or eliminate the patient’s pain. Additionally, radiofrequency ablation has been used successfully to treat other conditions, including arthritis pain, lumbar spine pain, and cervical facet joint pain.
Radiofrequency Ablation Procedure
The radiofrequency ablation procedure is performed in an outpatient setting and requires minimal pharmacologic intervention. Prior to initiating the procedure, the physician will address any concerns and acknowledge any complications that may occur during the procedure. Patients are discharged within a few hours after the completion of the procedure, making this relatively quick.
Must Watch Video – Radiofrequency Ablation Performed Live!
In an effort to decrease discomfort during a radiofrequency ablation procedure, an anesthetic and possibly a mild sedative are given to the patient via an intravenous line. After the anesthetic has numbed the area sufficiently, the physician inserts a needle into the area of the spinal column where the nerves that are causing the pain are located. Usually, the patient is placed in a prone position for this procedure; however, if the affected nerves are located in areas such as the neck, the patient may lie in a supine position.
Imaging techniques, including X-ray or fluoroscopic guidance, are utilized during radiofrequency ablation to help guide the needle and ensure proper needle insertion. After proper needle insertion is complete, a microelectrode is inserted through the needle. While the microelectrode is positioned, a very small electric current is initiated, which produces a tingling sensation. The patient is asked if they can feel the tingling while the physician observes both motor and sensory stimulation in the patient. This helps to ensure that the microelectrode is positioned properly. It is imperative that the nerve responsible for creating pain is treated during this procedure as opposed to motor nerves. Therefore, mild electrical stimulation is also used to confirm that the large muscle groups are not being stimulated by the treatment. This electrical stimulation may result in undesired effects, such as twitching and throbbing; however, it is necessary as it provides the physician with an indication of areas that they should avoid to prevent damage to motor nerves.
Once ideal needle and electrode placement is established, a high frequency current that generates heat is transmitted through the electrodes directly into affected nerves or into the tissues that surround the affected nerves. The physician applies a numbing agent to the targeted nerves before a higher electrical current is initiated. Occasionally, corticosteroids may be injected to help reduce inflammation that may be present or that may potentially develop from the procedure. The patient should not feel pain or discomfort during the heat application, as they will have received sufficient anesthetic medications as well as other medical agents, such as mild sedatives and corticosteroids.
Nerve function is disrupted as the nerve’s ability to transmit pain signals to the spinal cord is interrupted by the high frequency current that is used during a radiofrequency ablation procedure. The electrical current is transmitted from a generator to the electrode; the current then passes from the electrode to the patient’s body and into a grounding pad. This process establishes an electromagnetic field at the electrode and this creates electro-thermal heat. The heat that is applied to the targeted nerves impairs or destroys the nerves, resulting in a disruption of pain signal transmission, resulting in the relief of chronic pain.
Some patients may experience pain during a radiofrequency ablation procedure, and the physician will frequently inquire if pain is being felt. If the patient is experiencing pain, the needle position may need to be adjusted or additional anesthetic may need to be administered. Patients should be told to immediately inform the treating physician if they begin to experience pain during the procedure as this may signal that nerves that are not treatment targets are being affected by the heat.
Once the radiofrequency ablation procedure is complete, patients are monitored for adverse reactions, including motor deficits, paralysis, muscle weakness, and severe pain. Patients are advised to have someone drive them home after the procedure and to use caution when returning to regular activities because mild soreness and pain may develop during their recovery period. Moreover, it can take up to one month for damaged nerves to lose their functioning completely, and during this time, mild pain may be experienced by the patient. Until the nerve functioning is completely lost, patients may continue to experience symptoms such as muscle weakness. It can therefore be necessary for the physician to prescribe analgesic medication to help the patient manage their pain and discomfort during their recovery period.
After a radiofrequency ablation procedure, there are some restrictions that patients should follow, including:
- Driving or operating heavy machinery should be avoided for a period of 24 hours after the procedure
- Vigorous activity (i.e. weight lifting, etc.) should be avoided for a period of 24 hours after the procedure
- Bathing should be avoided for 24 to 48 hours after the procedure; however, showers may be taken
- Swimming should be avoided for 48 hours after the procedure
- Bandages covering the site may be removed prior to bedtime, but may need to be reapplied upon waking until the injection site has healed completely
- Ensure that the bandage is securely adhered prior to taking a shower to avoid getting the injection site wet, as this will help to avoid infection
If the patient’s pain does not respond adequately, the procedure may be repeated in two to three weeks. Generally, the nerves that are targeted and damaged during a radiofrequency ablation procedure may re-grow after six to 18 months. However, even though the nerves have the ability to regenerate, it does not mean that the patient will experience the same level of pain that was experienced prior to the treatment. Additionally, patients should be informed that by engaging in physical therapy and remaining physically active, they can improve muscle strength and help to keep pain levels to a minimum. If pain returns despite attempts to control it, the radiofrequency ablation procedure can be repeated.
Types Of Radiofrequency Ablation
Continuous radiofrequency and pulsed radiofrequency are the two types of radiofrequency that are used in ablation procedures. Continuous radiofrequency was developed in 1931, and pulsed radiofrequency was developed in the 1970s. The frequency of the current used in continuous radiofrequency is gradually increased until the electrode temperature is between 50° and 80°C (122° and 176° F). This temperature is maintained for 80 to 90 seconds, which is approximately the length of time required for the heat to cause nerve damage.To increase the likelihood of causing the nerve to be completely cut, multiple sites along a nerve are often exposed to the heat. As a result of the heat that is generated by the electrodes, the nerve’s ability to transmit pain signals is reduced. This procedure can take approximately one to two hours, depending on the injection site position as well as the number of nerves that need to be targeted for treatment.
While a pulsed radiofrequency ablation procedure is similar to continuous ablation procedure, it uses brief intervals of high voltage current (20 milliseconds) followed by silent, longer intervals (489 milliseconds). The alternating current produces temperatures ranging from 40° to 42°C (104° to 107.8°F) and the pulsed pattern is maintained for at least two minutes, and for up to eight minutes depending on the number and location of nerves that need to be targeted for treatment.
In between the intervals of high voltage current, the heat is able to disperse and the targeted tissue remains lower than 42°C. Therefore, the degree of tissue damage that is accomplished with continuous radiofrequency ablation procedures is not achieved with the pulsed procedure. The purpose of the pulsed approach to radiofrequency ablation procedures is to stun the targeted nerves as opposed to damaging or cutting them, which is achieved with the continuous method. Clinical studies have revealed that alternating between bursts of heat and silence weakens the membranes of the targeted nerves, but does not cause lesions. Therefore, pulsed radiofrequency ablation results in a temporary inhibition of the nerve’s ability for pain signal transmission from the spine to the brain, without causing serious nerve damage.
Pulsed radiofrequency carries advantages compared to continuous radiofrequency ablation procedures, including a reduced degree of nerve injury and a reduced need for anesthetic medication during the procedure. Furthermore, the pulsed radiofrequency approach results in fewer cases of pain after the procedure, reduced scarring, and it can be utilized for various sites and conditions that would be inappropriate for the continuous radiofrequency approach. An example of this is the treatment of certain neuropathic pain conditions, including trigeminal neuralgia. This condition is the result of nerve injury and therefore using a continuous approach to treatment would result in further nerve damage and potentially worsen the patient’s symptoms. In these cases, it is more advantageous to block the pain signals by stunning the nerves through a pulsed radiofrequency procedure.
Must Watch Video – Cervical Radiofrequency Ablation Performed Live!
The pain relief benefits of continuous radiofrequency ablation are longer lasting compared to pulsed methods; however, the pulsed method was developed in an effort to reduce the prevalence of adverse effects including motor nerve damage, which may result in motor deficits as well as deafferentation pain. Deafferentation pain occurs when nerves that were not targets for treatment become injured or damaged during the radiofrequency ablation procedure, resulting in inflammation and damage that was not intended. Clinical studies have shown that patients receiving pulsed radiofrequency ablation procedures do not report adverse reactions. Furthermore, these studies show that the pulsed method to radiofrequency ablation is more cost effective than the continuous method.
Risk Factors Associated With Radiofrequency Ablation
Radiofrequency ablation procedures are associated with various risks, including permanent nerve damage and infection. If an infection develops, hospitalization and the administration of intravenous (IV) antibiotics, as well as surgery may be necessary.A radiofrequency ablation procedure is not appropriate in patients with active infections (e.g. a cold or sinus infection), or for patient’s with blood clotting issues, or for those who may be pregnant. Further, this procedure is not appropriate for patients weighing more than 250 pounds. Diabetic patients need to have their insulin dose adjusted on the day of the procedure.
Patients who have poorly controlled diabetes or those who have heart conditions and that need to take blood-thinning medication (e.g. aspirin) on a daily basis need to get medical clearance from their physician to stop taking the medication for one week. Additionally, non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, need to be stopped for a minimum of 24 hours, but preferably 72 hours, prior to the procedure. NSAIDs need to be discontinued as they can affect the blood clotting process, which can result in serious bleeding complications. Furthermore, taking corticosteroids, such as prednisone, methylprednisolone, and cortisone, regularly can aggravate and complicate symptoms that are caused by inflammation of nerves.
Side Effects Of Radiofrequency Ablation
Radiofrequency ablation is associated with a number of side effects, including minor bleeding, swelling, skin discoloration, and bruising at the needle insertion site. These side effects generally subside during the first few days after the procedure. Additionally, some patients may experience leg numbness; however, this side effect usually only lasts for a couple of hours and may actually be the result of the anesthetic used during the procedure. If a patient experiences leg numbness, they should receive assistance when they try to walk or move around.During the procedure, the electrode is positioned extremely close to the targeted nerves and this may result in a temporary increase in pain that may extend into the extremities. However, the anesthetic that is administered during this procedure is meant to reduce the amount of discomfort and pain that is experienced as the result of this procedure. Blood vessels and motor nerves that are located near the targeted nerves may also be injured during a radiofrequency ablation procedure. Further, the electrical current that passes through the electrode may result in a burn, however, this rarely occurs.
Very rarely, serious side effects that may occur during a radiofrequency ablation procedure include reactions to the medications used during the procedure (e.g. anesthetic, or sedative); this may lead to respiratory or cardiac problems, as well as seizures.
When the anesthetic wears off, the patient may experience mild back pain around the injection site. This pain usually resolves within 48 to 72 hours and can be treated with over-the-counter pain medication, as well as cold packs on the day of the procedure, and hot packs from the second day onward, until the pain resolves. Some patients may experience slightly increased pain for approximately one to two weeks after the treatment, which should gradually decrease. Patients who undergo a continuous radiofrequency ablation procedure may have pain for up to one month after the procedure as the procedure causes lesions on the nerves but it can take this length of time for the targeted nerves to die. However, the pain that a patient experiences after a radiofrequency ablation procedure should not be as severe as the pain they had prior to the procedure.
Side effects that are experienced by patients after a radiofrequency ablation procedure should be closely monitored, as they may be the first signs of a serious adverse reaction. For example, pain at the site of the injection should not be severe; additionally, if it occurs with swelling, redness, and paralysis or leg weakness, the patient should seek medical attention immediately as more serious complications such as bleeding may be the source of the symptoms. Moreover, a fever of more than 100.4°F, or fluid draining from the injection site may be indicative of a developing infection that requires immediate medical attention.
Although radiofrequency ablation is associated with a number of side effects, it has been proven to be a safe and effective treatment option for chronic pain. Reports have also shown that radiofrequency ablation is well-tolerated by most patients and that complications are rare.
Methods For Diagnosis
Patients suffering from chronic pain symptoms that have not experienced relief from conservative treatment options including physical therapy, non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroid injections, or epidural injections, may need to undergo more invasive treatment procedures. A qualified physician at a pain management clinic will be able to determine if a patient is an ideal candidate for a radiofrequency ablation procedure. Typically, before deciding if a patient is suitable for radiofrequency ablation, the physician will want to know how long they have utilized conservative treatment options for. For example, if a patient’s pain is unresponsive to medications and exercise after six weeks, they will want to know if other conservative treatments, including physical therapy or chiropractic care, were utilized for a minimum of four to six months prior to being referred to a pain clinic.Once the patient is referred to a pain clinic for the treatment of their chronic pain symptoms, they may be treated with corticosteroid injections for a minimum of three months to determine if this form of therapy will provide pain relief. If corticosteroid injections fail to provide pain relief, then medial branch blocks will be performed. A medial branch block is a type of nerve block where a needle is inserted into the area of the spinal column where the affected nerve roots are located. Fluoroscopy or X-ray is used to visualize proper needle placement for the procedure. Once proper needle placement is confirmed, a catheter is inserted through the needle, which delivers the pain medication to the nerves that are believed to be causing the chronic pain. A corticosteroid and anesthetic, or a substance that dissolves nerve tissue, is injected. This treatment method is believed to provide extended pain relief by blocking pain signal transmission. If the patient reports pain relief from a minimum of two diagnostic medical branch blocks, then radiofrequency ablation will be recommended for the management of their pain.
The degree of pain relief that a patient experiences from a medial branch block provides an impression of whether or not radiofrequency ablation, which typically has long-lasting effects compared to medial branch blocks, will be successful for reducing pain. More specifically, when a patient reports increased pain relief with repeated medial branch blocks, they are more likely to have positive outcomes after a radiofrequency ablation procedure. Reports have shown that the pain relief experienced from radiofrequency ablation lasts from six to 12 months, and in some patients, up to 22 months.
Some patients who have received corticosteroid injections prior to being referred to a pain management clinic may have also undergone surgery. However, surgery does not always alleviate chronic pain, especially in patients suffering from chronic back pain. In these cases, radiofrequency ablation may be recommended for pain control. Radiofrequency ablation is minimally invasive, only requiring a local anesthetic and in some instances, a mild sedative. It is therefore often preferred over surgical interventions, as surgery is often associated with a higher incidence of complications due to open procedures and general anesthesia.
Before recommending radiofrequency ablation for the treatment of chronic pain, patients should undergo a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan to assess their spine. If spinal abnormalities are visualized on these scans, a radiofrequency ablation procedure may be deemed as inappropriate because the needle placement can be difficult.
Conditions Related To Radiofrequency Ablation
Initially, empirical studies showed that the benefits associated with radiofrequency ablation were focused on lumbar facet joint pain, in addition to the reduction and removal of bone spurs and tumors. However, throughout the years, radiofrequency ablation treatment has proven to be effective for the management of various other conditions, including:
- Lumbar facet pain
- Cervical facet pain
- Dorsal root ganglion pain caused by a herniated disc
- Lumbar spine pain caused by sacroiliac joint complex
- Trigeminal neuralgia
- Sympathetic ganglia
- Sphenopalatine ganglion pain (headache and atypical facial pain)
- Arthritis pain
Lumbar Facet Pain And Cervical Facet Pain
Lumbar facet and cervical facet pain are common conditions that may result because of nerve damage or arthritis. Research has consistently shown that patients who undergo at least two successful medial branch blocks before undergoing a radiofrequency ablation procedure are likely to experience significant relief of pain from either continuous or pulsed radiofrequency. The medial branch nerve is responsible for the sensation of pain that is felt in the corresponding joints of the neck and lower back. A minimally invasive medial branch block will help to provide an impression of whether the patient will respond positively to radiofrequency ablation treatment.
In regards to lumbar facet pain, continuous radiofrequency ablation has been found to provide a range of pain relief. Patients have reported pain relief lasting from four months to two years, with the range of four to six months being the most common time frame for pain relief after this procedure. Patients have also reported that their physical health and the range of motion in the affected joints significantly improved six months after the procedure. Additionally, reports have indicated that continuous radiofrequency ablation provides similar pain relief benefits for patients suffering with cervical facet pain, with patients typically reporting a reduction in pain symptoms for six to 18 months after the procedure. Conversely, most patients report relief of pain symptoms for a period of four months when pulsed radiofrequency ablation is utilized.
Dorsal Root Ganglion
Inflammation of the dorsal root ganglia may cause neuropathic spinal pain. This condition has been shown to be effectively treated with pulsed radiofrequency ablation at 42°C (104°F) for two minutes. Following treatment with pulsed radiofrequency ablation, patients report significant pain relief at one month, moderate relief of pain at six months, and mild relief of pain at 12 months. The pulsed approach to ablation therapy is more appropriate for dorsal root ganglion pain as it is usually caused by nerve damage and a continuous approach to ablation therapy would result in more nerve damage, and potentially worsen symptoms.
Herniated intervertebral disc and failed back surgery are other common causes of low back pain, with some patients also experiencing lower extremity pain. Clinical studies have found that pulsed radiofrequency ablation, applied to the dorsal root ganglia that is responsible for lower back pain, as well as to ganglia that are responsible for lower extremity pain can lead to significant pain relief one month after the procedure. The pain relief benefits of this treatment lasted for up to one year in most patients. For pain that develops as the result of a herniated intervertebral disc, it is typically due to increased pressure on the nerves, and pain resulting from failed back surgery could mean that the nerves were unintentionally damaged during surgery. In these cases the use of continuous radiofrequency ablation would not be appropriate, as it would cause more damage and potentially result in increased pain symptoms.
Lower Back Pain
Studies have indicated that radiofrequency ablation that is utilized for the treatment of lower back pain is associated with a significant decrease in pain severity that is sustained for one to two years in the majority of patients that undergo this procedure. Moreover, the pain relief reported after radiofrequency ablation treatment is reported to be much more significant and longer lasting compared to corticosteroid injections. Some patients that were treated with spinal surgery also reported more significant pain relief, improved range of motion, improved quality of life, reduced recovery time, and a decreased need for analgesic medication after receiving radiofrequency ablation therapy.
Some patients who had spinal surgery prior to undergoing radiofrequency ablation therapy did not experience the same level of pain relief as patients with low back pain that did not have surgery prior to the ablation treatment. This indicates that spinal surgery may occasionally cause nerve damage that interferes with the effectiveness of radiofrequency ablation. For example, when untargeted nerves become damaged during treatment, such as motor nerves, deafferentation pain may result, and cause a patient’s pain symptoms to worsen. If this occurs, the pain resulting from the spinal surgical procedure will not be improved with ablation therapy.
Trigeminal neuralgia is a painful condition in which the trigeminal nerve, which is responsible for the perception of pain and touch in the mouth, nose, eyes, and face, becomes affected. It is believed that multiple sclerosis or pressure on the nerve resulting from swollen blood vessels or a tumor are the most common causes of this condition. Trigeminal neuralgia is characterized by severe pain that occurs during normal activities such as drinking, chewing, eating, shaving, putting on makeup, or brushing the teeth. Trigeminal neuralgia is usually treated with medications, glycerol injections, or surgery. However, it appears that radiofrequency ablation therapy provides the longest lasting periods of pain relief.
Medications including anti-seizure drugs, antidepressants, and muscle relaxants are often prescribed to patients suffering with trigeminal neuralgia. However, this form of treatment only reduces the occurrence and severity of pain as opposed to permanently relieving the symptoms of the condition. Glycerol injections block the transmission of pain signals by damaging the trigeminal nerve; however, patients have reported pain recurrence, as well as facial numbness and tingling following this treatment. Surgical options for this condition include cutting or destroying a section of the trigeminal nerve. However, surgery poses the risk of motor deficits. Numerous patients suffering from trigeminal neuralgia that have been treated with pulsed radiofrequency ablation report improvement in symptoms, lasting between ten and 22 months.
The results of clinical trials that have been conducted in regards to trigeminal neuralgia have shown that stunning the nerves in the face and disturbing their membranes by way of a pulsed radiofrequency ablation approach is sufficient for providing long-lasting relief of symptoms. Typically the pulsed approach to treatment only provides patients with lumbar or cervical facet pain with four months of pain relief so a continuous approach is preferred in these patients, despite the risks involved. However, damage to facial motor nerves could lead to serious complications so a pulsed approach to radiofrequency ablation is preferred in trigeminal neuralgia patients.
The sphenopalatine ganglion is a cluster of nerves that provide touch and pain sensations to the head and face region. When this cluster of nerves becomes irritated or inflamed, a patient may experience facial pain and chronic headaches. Damage to the sphenopalatine ganglia can result in muscle deficits, and even paralysis. Reports have indicated that pulsed radiofrequency ablation to treat chronic headaches and other conditions that may be causing atypical facial pain, can provide patients with relief of mild to moderate pain for up to one year, and in some patients may provide complete pain relief. In addition to the pain relief benefits, patients have reported a decreased need for opioids, and the elimination of complications such as infection, bleeding, fluid retention around the injection site, swelling, and numbness. The clinical studies that have been conducted suggest that a pulsed method for radiofrequency ablation is more effective for treating nerve pain in sensitive areas such as the face and head as opposed to a continuous approach.
The level of pain relief that patients experience from radiofrequency ablation therapy is dependent upon a number of factors including the location of pain and the number of nerves that need to be treated. Continuous radiofrequency ablation procedures involve cutting or damaging the targeted nerves. Following continuous radiofrequency ablation, moderate to complete relief of pain usually occurs once the targeted nerves have completely lost their function, which can take between two to four weeks to occur. The pain relief benefits from this type of therapy usually last for six to 12 months. Conversely, pulsed radiofrequency ablation procedures stun the targeted nerves and weaken their membranes. Some patients have reported immediate relief of symptoms after this procedure. Some patients report that pain relief lasts for up to two years after a radiofrequency ablation procedure.
Radiofrequency ablation is a non-surgical therapy that is minimally invasive that has been found to be one of the most precise treatments for the management of chronic pain symptoms. The procedure results in the temporary destruction of the nerves that are responsible for pain symptoms through the use of an electrical current that creates heat in the area where the inflamed nerves are located. The heat that is generated causes lesions along the nerve, which leads to a loss of nerve function and the disruption of transmission of pain signals from the spinal cord to the brain. The result is significant pain reduction after the procedure.Radiofrequency ablation therapy is used to treat a wide variety of conditions. In addition to pain relief, patients have also reported reduced recovery times, improvement in quality of life, increased range of motion, and the decreased need to take pain medications when compared to more conservative treatment options such as physical therapy and steroid injections, as well as surgery.
Continuous radiofrequency ablation and pulsed radiofrequency ablation are the two techniques that are used for this procedure. Before determining if radiofrequency ablation therapy should be performed, physicians require that a patient receive a minimum of two successful medial branch blocks. The success of a medial branch block is indicative of how successful a radiofrequency ablation procedure will be. If the physician determines that the patient is an ideal candidate for the procedure, they will determine if a continuous approach or pulsed approach to radiofrequency ablation should be utilized, depending on the location and number of nerves that need to be treated.
At the present time, both the continuous and pulsed approaches are being optimized for the treatment of various conditions. As the procedures are further improved, physicians may be able to utilize this therapy for a variety of other pain conditions.