ENTRAPMENT OF THE SUPERFICIAL PERONEAL NERVE

Transcription

1 ENTRAPMENT OF THE SUPERFICIAL PERONEAL NERVE DIAGNOSIS AND RESULTS OF DECOMPRESSION JORMA STYF From Gothenburg University, Sweden Entrapment of the superficial peroneal nerve was treated in 24 legs of 21 patients by fasciotomy and neurolysis; 19 of the patients were reviewed after a mean period of 37 months. Nine were satisfied with the result, another six were improved but not satisfied because of residual limitation of athletic activity, three were unchanged and one was worse. Conduction velocity in the superficial peroneal nerve had increased after operation, but the change was not significant. In five patients the nerve had an anomalous course and in 1 1 there were fascial defects over the lateral compartment. Chronic lateral compartment is an unusual cause of nerve entrapment. Operative decompression produces cure or improvement in three-quarters of the cases, but is less effective in athletes. Entrapment of the superficial peroneal nerve was first described by Henry in The symptoms are pain and sometimes sensory abnormality in the distribution of the nerve over the dorsum of the foot. Only a few cases have been reported, but several possible causes for compression have been described. These include : lipoma (Banerjee and Koons 1981), ankle sprain (Kernohan, Levack and Wilson 1985), muscle herniation (Garfin, Mubarak and Owen 1977; McAuliffe, Fiddian and Browett 1985), a peroneal tunnel (Lowdon 1985) and after fasciotomy for chronic anterior compartment (Styf and K#{246}rner 1986b). The incidence of superficial peroneal nerve entrapment as a cause of anterolateral leg pain is probably higher than is suggested by the literature (Styf 1988). This study aimed to determine the effects of operation on both the symptoms and the nerve conduction velocity in 21 patients with superficial peroneal nerve entrapment. MATERIALS AND METHODS From 1981 to 1986, a prospective study was made of 21 patients with entrapment of the superficial peroneal nerve. Two patients were excluded because they did not want an operation, so 19 patients were reviewed. There were 10 male and 1 1 female patients with a mean age of J. Styf, MD, PhD, Senior Registrar Department of Orthopaedics, Gothenburg University, East Hospital, Gothenburg, Sweden. Correspondence should be sent to Dr Styf British Editorial Society of Bone and Joint Surgery X/89/1014 $2.00 J Bone Joint Surg [Br] 1989:71-B: years (range 1 5 to 79 years). Three patients had bilateral symptoms. Clinical details and the results of pre-operative and postoperative tests for nerve conduction velocity are given in Table I. Questionnaire. Each patient was asked a number of questions about symptoms and physical limitations both before entering the study, and again at an average of 37 months (range 10 to 56 months) after operation. The patients also indicated on three drawings ofthe leg where they felt pain or sensory abnormality, and reported whether the operation had a satisfactory result. Examination. Each patient was examined to record the range ofmovement ofall legjoints, stability ofthe ankle, and the presence of fascial herniae. Three provocation tests were used : in the first, pressure is applied where the nerve emerges from the deep fascia, while the patient actively dorsiflexes and everts the foot against resistance (Styf 1988); in the second test, the foot is passively plantar flexed and inverted without local pressure over the nerve; finally, maintaining passive stretch, gentle percussion is applied over the course of the nerve (Tinel 1915). Pain or paraesthesia caused by any of these tests suggested compression of the peroneal nerve and was taken as an indication for neurophysiological investigation. Anteroposterior, lateral and oblique radiographs of the leg were taken to exclude stress fracture and bone tumour. Electrophysiology. Conduction velocities in the superficial peroneal nerve were determined using surface electrodes, and electromyograms of both peroneal muscles and the anterior tibial muscles were recorded from needle electrodes (Jabre 1981 ; Ma and Liveson 1983). VOL. 71-B, No. 1, JANUARY

2 I 32 J. STYF Conduction velocities were obtained before operation and between six and 1 2 weeks afterwards. Conduction velocities below 44 m/sec were considered abnormal (Jabre 1981), though there is a relationship to the age of the patient. Usually, the symptom-free leg could be used as a control. Compartment pressure. This was recorded bilaterally in the lateral compartment in all patients and in the anterior compartment also in 1 5 of the 2 1 patients. Two patients with chronic lateral compartment (Cases 6 and 20) had recordings six months after decompression. Recordings were made with the patient supine, wearing shoes which were attached to an ergometer to ensure that the work was equal in both legs. For the peroneal muscles, eversion and dorsiflexion was repeated against a load of 4 to 6 kg about once every second until pain or weakness forced the patient to stop. Intramuscular pressure was measured by microcapillary infusion technique (Styfand K#{246}rner1986a) using an infusion rate of 1.5 ml/hour, a teflon catheter and an electromagnetic transducer. Diagnostic criteria. Entrapment of the nerve was diagnosed when there was decreased sensibility and pain over the dorsum of the foot at rest or during an exercise test and at least one of the three provocation tests was positive. A nerve conduction velocity of less than 44 m/sec or a fascial defect where the nerve emerges from the lateral compartment provided confirmation. Chronic lateral compartment was diagnosed when muscle relaxation pressure exceeded Table I. Details of all 21 patients with results in 19 Nerve conduction Operative findings velocity (m/sec) Age Duration Post- Peroneus Fascial Case and Athletic of pain Follow-up Pre-op Post-op stenotic tunnel defect number sex Possible cause activity Side yr/mth yr/mth L/R L/R Result Waist swelling (cm) (mm) Other I 32 F Contusion L 4/10 3/1 48/54 NS 2 20 F Anterior fasciotomy Tennis L/R 2/0 3/2 0/0 52/51 S 3 22 M Fractured tibia Running R 4/5 2/2 61/37 - S F Sprained ankle R 1/0 4/ /49 NS x F Muscle herniation Running R 3/2 2/9 59/56 S x M Anterior and lateral fasciotomies Football R 0/8 4/8 48/22 51/50 NS* Scar 7 22 M Anterior fasciotomy Running R 0/8 3/8 54/44 52/50 NS* x15 8 5SF 9 67 M Anterior compartment R 7/0 0/10 50/48 L 4/3 2/8 33/45 38/41 NS + I 5 x 50 Impingement M Muscle herniation F Muscle herniation 12 20M M Anterior compartment F Anterior fasciotomy L/R 1/6 2/8 28/49 43/46 NS R 2/0 2/0 50/0 45/39 S + Football L 2/0 2/7 21/50 45/46 NS5 Running R 1/0 0/10 46/39 L 1/0 3/11 11/46 12/52 S + + 3/3 20 x 20 Impingement IS x x F Varicose veins R 3/0 2/10 - S + 15 x 15 Impingement M Muscle herniation R 5/0 4/2 0/0 0/0 NS* + 20 x 20 Scar F Running L 1/ F Anterior fasciotomy Running L 0/9 4/0 54/55 51/51 NS + 3/9 29/47 57/53 S M Varicose veins Running R 3/0 3/10 lsxls Impingement M Lateral compartment L/R 7/0 4/2 26/42 46/51 S 3/ F Varicose veins L 2/6 3/9 32/33 - NS + 15 x I 5 Impingement S improved NS not satisfied: S satisfied THE JOURNAL OF BONE AND JOINT SURGERY

3 ENTRAPMENT OF THE SUPERFICIAL PERONEAL NERVE 133 d Superficial peroneal nerve 30 mmhg during exercise (Styf and K#{246}rner 1987), intramuscular pressure exceeded 30 mmhg at rest after exercise (Mubarak and Hargens 1981) and it took more than 10 minutes for pressure to return to normal Fascia (Reneman 1975). Fig. Diagram of the superficial peroneal nerve showing findings at operation and some possible sites of entrapment: a, the peroneus tunnel : h, impingement at the exit from the tunnel : c, compression by herniating muscle producing a waist on the nerve tissue: d, poststenotic swelling. I Operation. The site of nerve compression is identified and marked pre-operatively and decompression is performed under general anaesthesia with a tourniquet. A 7 to 10 cm skin incision is made over the middle and distal thirds of the lateral compartment, 1 cm posterior to the site ofcompression. The nerve is located and released by local fasciectomy and, in addition, a subcutaneous fascial release is performed from the level of the head of the fibula to the anterior retinaculum. The epimysium of the muscle is protected during the fasciotomy. In five patients with an anomalous course of the nerve, a local fasciectomy of the anterior intermuscular septum and fasciotomy of the anterior compartment was performed. Statistics. Pressures and conduction velocities are given as the mean with one standard deviation. Significance was tested, using Student s t-test. RESULTS Fig. 2 About 5 mm ofthe peroneus tunnel has been incised. Impingement and flattening is seen, with some post-stenotic swelling (large arrow). Table II. Summary of the patients opinions at six months and 37 months (s.d. 12) after decompression Time since operation Six months 37 months n=2l n=19 Satisfied No symptoms 3 S Few symptoms 5 4 Not satisfied Improved 6 6 Unchanged S 3 Worse 2 I Physical activity Unlimited 4 6 Increased 6 7 Unchanged 11 6 Decreased 0 0 The clinical results are shown in Table II. At a mean of 37 months, nine patients were satisfied and 10 were not. Physical ability was unlimited or increased in 13 and unchanged in six. Four of those with improvement were athletes (Cases 6, 7, 12 and 17), but they remained unsatisfied because they could not attain the desired level ofcompetitive activity. One patient (Case 4) had another operation, at which the nerve was found to be trapped in scar tissue. Except after known fractures, radiographs were normal. Electrophysiology. Pre-operative conduction velocities were 28 m/sec (s.d. 18.5) in the symptomatic legs and 49.8 m/sec (s.d. 6.7) in symptom-free legs. After operation, this increased to 40.3 m/sec (s.d. 17.1) in the operated legs and it was unchanged on the normal side. This increase of conduction velocity was not significant. All electromyographic studies were normal. Findings at operation. Details are given in Table I and are shown in Figure 1. Clearly visible waisting of the nerve was seen in 1 2 legs, and was associated with a poststenotic swelling in five (Fig. 2). When the nerve was found to be compressed and flattened very locally between the fascial edge and herniating muscle, this was termed impingement (Fig. 2) and was found in six legs. A peroneus tunnel of up to 3 cm was accepted as normal, and a short tunnel was found in most legs. However, the tunnel was between 3 and 1 1 cm in 10 legs, and in several of these the nerve was noticeably thinner within the tunnel. Two patients with long tunnels (Cases 10 and 19) also had impingement. VOL. 71-B, No. I. JANUARY 1989

4 134 J. STYF In six legs of five patients the course of the nerves was anomalous. These nerves entered the anterior compartment of the leg through a fascial opening in the anterior intermuscular septum at 1 2 to 16 cm proximal to the ankle, and emerged through the fascia ofthe anterior compartment between 6 and 10 cm above the ankle. In one patient (Case 1 1 ), only the medial dorsal cutaneous branch was anomalous, the intermediate dorsal cutaneous branch emerging through a fascial defect over the lateral compartment. Fascial openings over the lateral compartment exceeding 1 5 mm in diameter were considered abnormal (Fig. 3), and muscle herniation through such a fascial defect where the nerve emerged was found in 12 legs. patients (Cases 1, 8 and 1 7), two of whom were found to have an anomalous nerve. Normally the nerve runs in a short fibrous tunnel in the corner between the anterior intermuscular septum and the fascia over the lateral compartment. In nine patients, the tunnel was fibrotic, of low compliance and more than 3 cm in length; it is speculated that, in such a tunnel, oedema after trauma may lead to a mini compartment. Compartment pressure. Chronic lateral compartment was diagnosed in two patients (Cases 6 and 20) with increased muscle relaxation pressure, and pressure at rest after exercise of 32 to 40 mmhg in the anterior and lateral compartments. Pressure did not return to normal within 20 minutes. Six months after decompressive fasciotomy of the lateral compartment, pressures were normal. DISCUSSION Only nine of the 19 patients were completely satisfied, though I 3 had unlimited or increased physical ability after 37 months, and the mean conductive velocity of the nerve had increased. Entrapment of the superficial peroneal nerve has many causes. A history of local trauma has been reported in about 25% of patients with nerve compression (Kopell and Thompson 1963; Stack, Bianco and MacCarty 1965); this is in line with the findings of the present study. Five of the patients had had an operation for chronic anterior compartment (Table I); the mechanism by which compression of the nerve may follow fasciotomy of the anterior compartment has been discussed previously (Styf 1988). Only two patients had chronic lateral compartment. This agrees with other reports that this is an unusual cause of anterolateral pain (Styf and K#{246}rner 1987; Styf 1988). Nerve compression in patients with fascial defects is explained by the normal increase in muscle relaxation pressure and intramuscular pressure at rest during and after exercise (Styf and K#{246}rner 1986). This increase is sufficient to herniate muscle tissue and impinge upon or compress the nerve (Fig. 3). The exercise test, followed by clinical examination, was useful in the diagnosis. During this test all patients had local pain and many developed diminished sensation to light touch over the dorsum of the foot. Electrophysiological studies helped the diagnosis, especially in patients who had pain after an anterior fasciotomy. Normal conduction velocity at rest does not exclude compression of the superficial peroneal nerve, as was shown in three Fig. 3 Operative view of an abnormal fascial opening. The arrow shows where the nerve has been displaced by muscle herniation. The patients who were not satisfied with their result, were unable to increase their athletic activity to the desired level, but old trauma and previous surgery to the leg may have contributed, while too cautious postoperative mobilisation may have allowed oedema formation. Complete fasciotomy of the lateral compartment does give some minor discomfort over the proximal third of the compartment, and it is considered that an operation including only incision of the peroneus tunnel and local fasciectomy may be preferable in appropriate patients and help avoid the edge effect of fascia on the normal swelling of muscle. It is concluded that entrapment of the superficial peroneal nerve is an unusual reason for pain in the lower leg but the diagnosis can be made from local tenderness and sensory abnormality, and confirmed by an exercise test. Nerve conduction studies were complementary in the diagnosis and follow-up. Decompression of the nerve relieves pain and sensory abnormality in half of the patients, and produces improvement in another quarter ofthem, but it is less effective in athletes because of their levels of physical activity. No benefits in any form have been received or will he received from a commercial party related directly or indirectly to the subject of this article. THE JOURNAL OF BONE AND JOINT SURGERY

5 ENTRAPMENT OF THE SUPERFICIAL PERONEAL NERVE 135 REFERENCES Banerjee T, Koons DD. Superficial peroneal nerve entrapment : report oftwo cases. J Neurosurg 1981:55: Garfin S, Mubarak SJ, Owen CA. Exertional anterolateral-compartment : case report with fascial defect, muscle herniation, and superficial peroneal-nerve entrapment. J Bone Joint Surg [Am] 1977:59-A : Henry AK. Extensile exposure. Edinburgh etc : E & S Livingstone, Jabre JF. The superficial peroneal sensory nerve revisited. Arch Neuro/ 1981:38: Kernohan J, Levack B, Wilson JN. Entrapment of the superficial peroneal nerve: three case reports. J Bone Joint Surg [Br] l985:67-b:60-l. Kopell HP, Thompson WAL. Peripheral entrapment neuropathies. Baltimore: Williams and Wilkins, Lowdon IMR. Superficial peroneal nerve entrapment: a case report. J Bone Joint Surg [Br] 1985:67-B:58-9. Ma D, Liveson JA. Nen e conduction handbook. Philadelphia, F.A. Davis Co Mubarak SJ, Hargens AR. Compartment s and Vo/kmanns contracture. Saunders Monographs in Clinical Orthopaedics 3. Philadelphia etc: WB Saunders, McAuliffe TB, Fiddian NJ, Browett JP. Entrapment neuropathy of the superficial peroneal nerve : a bilateral case. J Bone Joint Surg [Br] 1985 :67-B :62-3. Reneman RS. The anterior and lateral compartmental of the leg due to intensive use of muscles. C/in Orthop 1975 :1 13: Stack RE, Bianco AJ Jr, MacCarty CS. Compression of the common peroneal nerve by ganglion cysts : report of nine cases. J Bone Joint Surg [Am] 1965;4-A: Styf J, K#{246}rnerL. Microcapillary infusion technique for measurement of intramuscular pressure during exercise. C/in Ort hop 1986a ;207 : Styf JR, K#{246}rnerLM. Chronic anterior-compartment of the leg : results of treatment by fasciotomy. J Bone Joint Surg [AmJ 1986b;68-A : StyfJ, K#{246}rnerL. Diagnosis ofchronic anterior compartment of the lower leg. Acta Orthop Scand 1987:58: Styf J. Diagnosis of exercised-induced pain in the lower leg. Am J Sports Med 1988;l6: Tinel J. Le signe du foumillement dans lesions des nerfs p#{233}riph#{233}riques. Presse Med Par 1915,23: VOL. 71-B, No. I. JANUARY 1989