The management of chronic knee pain secondary to neuromata continues to be optimized. Chronic neuromatous knee pain can be a sequela of total knee arthroplasty or trauma, and it occurs infrequently. Conservative management includes analgesics and physical therapy. These methods are often effective; however, approximately 1% of patients will not obtain pain relief and will be classified as intractable. Therefore, alternative surgical strategies for pain management have evolved.
The concept of denervation for intractable pain was introduced by Wilhelm 1 in 1958. Initial trials with total denervation for chronic upper extremity pain had mixed results. 2 Although there was marked improvement in the pain, the untoward consequences were debilitating and unacceptable. With the introduction of selective denervation, these untoward sequelae have been averted. 3–6 As a result of the success obtained for chronic wrist pain, the principles of selective denervation have been applied to the knee joint with equal success. 7–9 This study reviews the indications, patient selection criteria, and outcome after selective denervation for intractable neuromatous knee pain.
Materials and Methods
At the initial consultation, a thorough history, physical examination, and radiological evaluation (plain films, computed tomography, magnetic resonance imaging) are completed to rule out nonneuromatous sources of pain. These include arthritis and mechanical sources in the nonprosthetic knee; malalignment, aseptic loosening, and polyethylene wear in the prosthetic knee; and radiculopathy and referred pain from hip pathology or pelvic tumors. Once these are ruled out, the patient is evaluated for neuromata.
Evaluation for neuromata requires determining the characteristics of the pain such as the nature, location, duration, and intensity. Neuromatous pain is often sharp and well localized, whereas pain of nonneuromatous origin is often diffuse and poorly localized. Neuromatous pain can be deep (involving the joint capsule) or superficial (involving the skin), whereas pain of nonneuromatous origin is most often deep. The severity of the pain is graded on a visual analog scale (VAS) ranging from 0 to 10 points. The pain may be exacerbated by certain activities such as knee flexion or extension, weight bearing, and climbing stairs. The duration of the pain is variable and may be intermittent or constant.
On physical examination, relevant findings include the location of pain, presence of scars, range of knee motion, and gait assessment. The most important finding for neuromata is the presence of a Tinel’s sign. Our technique is to allow the patient to delineate the territory that is painful. The Tinel points are marked, pain severity on the VAS is assessed, and nerve blockade with 1% lidocaine is performed. After 10 minutes the pain is reassessed. At least a 5-point reduction in pain severity is recommended for consideration for selective denervation. Prior experience with patients experiencing less than a 5-point reduction indicates an increase in the chance of a suboptimal outcome. Observation of gait can assist in ruling out pain of mechanical, neuromatous, and nonneuromatous origin.
After completion of the evaluation stage, recommendations for treatment are made. Candidates for selective denervation must meet the following criteria: presence of pain for a minimum of 1 year, failure to achieve pain relief after conservative management, localization of pain at a Tinel’s point, and reduction of pain severity by at least 5 points on the VAS after nerve blockade. Noncandidates for selective denervation include patients with knee pain of nonneuromatous origin, chronic knee pain of less than a 1-year duration, no previous conservative management, diffuse and nonlocalized pain without a Tinel’s point, and a less than 5-point reduction on the VAS after nerve blockade.
There are seven surgically identifiable nerves that provide sensation to structures around the knee (Fig 1). These nerves are susceptible to injury after operative procedures or trauma. An excellent anatomic description of these nerves has been described previously. 10 There are five nerves that provide sensation to the cutaneous territory around thknee: the anterior, medial, and lateral femoral cutaneous nerves as well as the infrapatellar branch of the saphenous nerve and the tibiofibular branch of the peroneal nerve. There are two nerves that provide sensation to the deep structures around the knee: the medial and lateral retinacular nerves.
The anatomic pathways and location of these nerves are generally constant; however, variability may be encountered, especially in the presence of scars and prior surgery. The superficial nerves around the knee lie within the subcutaneous fat. The deep nerves lie deep to the medial and lateral retinaculum just distal to the medial and lateral vastus lateralis muscle respectively.
Technique of Selective Denervation
A detailed description of the surgical technique has been reported previously. 9 Before induction of anesthesia, the Tinel points are marked, and the bony and retinacular landmarks as well as the usual course of the nerve are delineated. This facilitates location of the neuroma and allows for accurate incision placement. After administration of spinal or general anesthesia, a proximal thigh tourniquet is applied and inflated to 250 mmHg.
Neuromata of the anterior, medial, and lateral femoral cutaneous nerves as well as the infrapatellar branch of the saphenous nerve can be excised through a skin excision 1 to 2 cm away from the Tinel’s point along the usual course of the nerve. Once the nerve is identified, traction is applied to the isolated segment to observe skin retraction at the Tinel’s point. This maneuver confirms that the correct nerve has been isolated. The nerve is divided and the proximal stump is buried in adjacent muscle to prevent recurrence.
Neuromata of the tibiofibular joint are approached by first exposing and releasing the common peroneal nerve. The articular branches to the tibiofibular joint are isolated and divided. A nerve stimulator is necessary to ensure that motor nerves to the peroneus longus muscle are not divided.
Neuromata of the medial and lateral retinacular nerves are approached by first delineating the distal aspect of the vastus medialis and lateralis muscle insertions. A transverse skin incision just distal to the muscle insertion and posterior to the patella is made. The medial retinaculum is incised between the patella and the medial condyle of the femur. The lateral retinaculum is incised between the patella and the iliotibial tract. The nerve, which is located under the retinaculum, is excised.
A prospective evaluation of 43 patients with intractable knee pain who presented from July 1995 to July 1999 was completed. This included 21 men and 22 women with a mean age of 49.6 years (age range, 19–80 years). After the history, physical examination, and response to lidocaine nerve blockade, patients were categorized as having met or not met the established criteria for selective denervation.
Thirty patients met the criteria for selective denervation and included 15 men and 15 women with a mean age of 50.3 years (age range, 31–76 years;Table 1). Etiology included trauma in 19 patients and total knee arthroplasty in 11 patients. Pain intensity was graded as sharp or burning in all patients. The pain was described as constant in 21 patients and intermittent in 9 patients. Mean pain duration was 6.3 years (range, 1–24 years). Mean number of operations on the knee was 4.5 (range, 1–20 operations). Of the 30 patients who met the criteria for selective denervation, 5 patients decided against surgery and 25 were in favor of surgery. Of the 25 patients who underwent selective denervation, 9 patients had single nerve involvement and 16 knees had multiple nerve involvement. A total of 62 nerves were excised and are listed in Figure 2. Reoperation for persistent pain was necessary in 4 patients, and included two operations in 3 patients and three operations in 1 patient. Mean follow-up was 1.7 years (range, 1–3 years).
Thirteen patients evaluated for neuromatous knee pain did not meet the criteria for selective denervation (Table 2). The mean age of this group was 48.6 years (age range, 19–80 years). The etiology of the pain included trauma in nine knees, total knee arthroplasty in three knees, and osteoarthritis in one knee. Pain intensity was graded as sharp in seven knees and dull in six knees. The pain was described as constant in eight knees and intermittent in five knees. Mean duration of pain was 4.5 years (range, 1–18 years). The mean number of prior operations on the knee was 3.4 operations (range, 0–11 operations).
Postoperative assessment was based on the VAS score and subjective evaluation. Patient response was categorized as excellent, good, and poor. An excellent response is defined as complete elimination of pain with a VAS score of 0 to 1 point. A good response is defined as partial relief of pain with at least a 4-point reduction in the VAS score. A poor response is defined as no notable change in pain.
Patients who met the criteria for selective denervation demonstrated a more than 5-point reduction in VAS score after nerve blockade with 1% lidocaine (see Table 1). The mean VAS score before lidocaine administration was 8.4 points (range, 5–10 points) and the mean VAS score after lidocaine administration was 0.7 point (range 0–3 points).
Patients who did not meet the criteria for selective denervation all demonstrated a less than 5-point reduction on the VAS (see Table 2). The mean VAS score before lidocaine injection was 6 points (range, 3–8 points) and the mean VAS score after lidocaine injection was 3.3 points (range, 0–5 points). One patient with a VAS score of 10 points refused lidocaine injection and was therefore not a candidate for selective denervation. One patient with a VAS score of 5 points experienced permanent relief of pain after lidocaine injection and did not desire further treatment. Diffuse pain with poor localization to a Tinel’s point was present in nine knees.
An excellent outcome resulting in complete pain relief was obtained in 11 patients (44%) after selective denervation. The specific nerves excised for each patient are listed in Table 1. This outcome was obtained after a single operation in 9 patients. A second operation was required in 2 patients with partial pain relief. Within this group of 11 patients, the mean pain severity according to VAS score before lidocaine injection was 8.5 points (range, 5–10 points). After lidocaine injection the mean VAS score was 0.4 point (range, 0–1 point) and postoperatively the mean VAS score was 0.5 point (range, 0–2 points). Preoperative pain was isolated to the medial side of the knee in 9 patients (82%), and to the medial and lateral sides in 2 patients (18%). The infrapatellar branch of the saphenous nerve was the most commonly involved nerve and was excised in 10 patients. More than one nerve was excised in 9 patients. Follow-up ranged from 1 to 2.5 years in this group.
A good outcome was reported in 10 patients (40%) after selective denervation. In 2 patients additional denervation procedures were attempted to improve outcome; however, notable improvement was not obtained (see Table 1). Within this group of 10 patients, the mean pain severity according to VAS score before lidocaine injection was 8.6 points (range, 6–10 points). After lidocaine nerve block the mean VAS score was 0.5 point (range, 0–2 points) and the postoperative VAS score was 3.3 points (range 0–5 points). Preoperatively, the pain was isolated to the medial aspect of the knee in 5 patients (50%), and to the medial and lateral aspect of the knee in 5 patients (50%). This outcome was the result of a variety of factors, including new pain or migration of pain in four knees and persistent, deep pain in six knees. Underlying factors that predisposed these patients to this outcome include a history of fracture about the knee or joint replacement in seven knees, arthroscopy for ligamentous injury in two knees, and soft-tissue trauma in one knee.
A poor outcome or no pain relief was reported in 4 patients (16%) after selective denervation. Pain severity according to VAS score before lidocaine nerve blockade was 8.3 points (range, 7–10 points). After lidocaine nerve blockage the VAS score was 1.5 points (range, 0–2 points) and postoperatively the VAS score was 6.8 points (range, 5–9 points). Preoperatively, the pain was isolated to the medial aspect of the knee in 2 patients, and to the medial and lateral aspect of the knee in 2 patients. Underlying factors that possibly predisposed these patients to this outcome include bone or joint surgery in two knees and arthroscopy secondary to ligamentous injury in two knees. The presence of nerve tissue was confirmed histologically in all patients. All patients reported persistent, deep joint pain. No patient was made worse after selective denervation. Follow-up for this group was 2 years.
A 49 year-old-man with a history of traumatic arthritis of the right knee had a total knee replacement in 1994. After the operation, a sharp and intermittent pain in the distribution of the infrapatellar branch of the saphenous nerve and tibiofibular branch of the peroneal nerve was described, in addition to numbness in the distribution of the peroneal nerve (Figs 3A and B). Conservative management was not helpful. Pain severity was graded as 9 points on the VAS. On physical examination, a well-healed midline knee incision was present. A Tinel’s sign was elicited in the medial and lateral infrapatellar regions. Nerve blockade with 1% lidocaine reduced the pain to 1 point on the VAS. Operative excision of the neuromata and release of the peroneal nerve completely eliminated the pain to 0 point on the VAS (Fig 3C). This outcome was graded as excellent, with a 3-year follow-up.
Chronic knee pain after trauma or total knee arthroplasty is a debilitating and often difficult condition to manage. Patients are severely limited in their activities of daily living and are often depressed. A variety of management strategies have evolved—including physical therapy, electrical stimulation, and hydrotherapy—that are frequently successful. However, when unsuccessful, selective denervation can be considered. This technique has been demonstrated by the current and previous studies to be beneficial in select patients with neuromatous knee pain. 7–9
Previous studies using selective denervation for neuromatous knee pain have been encouraging. The initial and subsequent reports by Dellon and colleagues, 7,8 who used this technique in 70 patients, demonstrated good to excellent relief of pain in 60 of 70 knees (86%) at 24 months of follow-up. Our preliminary experience with 13 patients demonstrated good to excellent pain relief in 10 of 13 knees (77%) at a minimum 2-year follow-up. 9 Based on these results of two independent surgeons, further clinical work has continued.
One of the most important elements of selective denervation is determining which patients are candidates for the procedure. This requires a thorough history, physical examination by an orthopedic surgeon and a plastic surgeon, radiographic evaluation, and diagnostic assessment. The purpose of this complex initial evaluation is to differentiate between mechanical knee pain and neuromatous knee pain. This technique is not advocated for mechanical knee pain.
Despite meeting the criteria for selective denervation, not all patients benefit from this procedure. In the current study, 44% of the patients had an excellent outcome, 40% had a good outcome, and 16% had a poor outcome. Comparative analysis of the three groups of patients does not provide an obvious explanation. Preoperatively, there were no substantial differences in the severity and duration of the pain or the response to lidocaine nerve block. Intraoperatively, there was no variation in technique, and the presence of nerve was confirmed histologically. Therefore, other factors were considered. All patients experienced at least partial relief of pain immediately after selective denervation. However, 2 to 6 weeks later the pain intensity increased in four knees. Possible explanations include secondary neuroma formation in the previously painful territory, persistent pain resulting from an unrecognized neuroma, or persistent pain of nonneuromatous origin. The proximal stump of nerve after excision of the neuroma is buried in adjacent muscle for all nerves except the medial and lateral retinacular nerves. Poor excursion of these nerves does not permit mobilization and burial. All patients reporting a poor outcome had persistence of deep pain. Another explanation is overlapping nerve territories. A good response to nerve blockade for one territory may mask a pain signal from another nerve supplying the same territory because of the local effect of the lidocaine. In addition, the presence of multiple neuromas may increase the possibility of neural connections that may complicate excision of the painful neuroma. Finally, the pain may be secondary to a nonneuromatous etiology. These patients can be difficult to manage because the workup of the pain suggests a neuromatous origin. Possible explanations include unrecognized problems with knee hardware, bone pain resulting from early arthritis, and secondary psychosocial factors by the patient.
In conclusion, selective denervation for intractable neuromatous knee pain is a safe and beneficial procedure for select patients. Proper patient selection is critical to achieve a good to excellent result. Predicting a good to excellent outcome is difficult but is enhanced by adherence to criteria that includes presence of pain for a minimum of 1 year, failure to achieve pain relief after conservative management, localization of pain at a Tinel’s point, and reduction of pain severity by at least 5 points on a VAS after nerve blockade. Avoid operating on patients with knee pain of nonneuromatous origin, chronic knee pain of less than 1 year, diffuse and nonlocalized pain without a Tinel’s point, and a less than 5-point reduction on a VAS after nerve blockade.
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© 2001 Lippincott Williams & Wilkins, Inc.
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