SECONDARY POSTERIOR INTEROSSEOUS NERVE LESIONS ASSOCIATED WITH HUMERAL FRACTURES CARMEN ERRA, MD,1 PAOLA DE FRANCO, MD,2 GIUSEPPE GRANATA, MD,1 DANIELE CORACI, MD,3 CHIARA BRIANI, MD, PhD,4 ILARIA PAOLASSO, MD,2 and LUCA PADUA, MD, PhD1,2 1
Department of Neurology, Catholic University of Sacred Heart, Largo A. Gemelli 8, 00168, Rome, Italy Don Carlo Gnocchi Foundation, Milan, Italy 3 Department of Orthopedic Science, Board of Physical Medicine and Rehabilitation, Sapienza University, Rome, Italy 4 Department of Neurosciences: Sciences NPSRR, University of Padova, Padova, Italy 2
Accepted 24 June 2015 ABSTRACT: Introduction: Radial nerve lesions associated with humeral shaft fractures are the most common traumatic nerve lesions observed with long bone fractures. Secondary indirect posterior interosseous nerve (PIN) lesions can be associated with traumatic radial nerve palsy. The aim of this study was to identify cases of traumatic double-site radial nerve involvement through ultrasound (US). Methods: Patients with traumatic radial nerve lesions referred to our laboratory from January 2010 to January 2014 were evaluated. Results: Of the 35 patients, 18 had US evidence of a radial nerve lesion at the fracture site associated with secondary PIN involvement at the arcade of Frohse. Conclusions: Multiple-site nerve lesions are difficult to demonstrate through electrodiagnostic tests. In our case series, half of the patients with traumatic radial nerve damage had US evidence of PIN injury. Prospective studies with follow-up are needed to determine the clinical and prognostic relevance of this finding and the best therapeutic approach. Muscle Nerve 53: 375–378, 2016
Radial nerve lesions associated with humeral shaft fractures are the most common traumatic nerve lesions associated with long bone fractures1 and have an estimated prevalence of between 2% and 18%.2 This frequent association is likely due to the anatomical contiguity of the radial nerve to the humerus together with the reduced mobility of the nerve in the passage through the lateral intermuscular septum in the distal third of the arm. Nerve ultrasound (US) is a tool of growing importance for assessment of the peripheral nervous system, especially for evaluation of traumatic nerve lesions, entrapment syndromes, and peripheral nerve tumors. Bodner and colleagues2 showed the usefulness of nerve US in patients with radial nerve palsy associated with humeral fractures. Their multilevel evaluation (X-ray, electromyography, nerve US) of 11 patients with complete or partial radial palsy Abbreviations: CSA, cross-sectional area; MRC, Medical Research Council; PIN, posterior interosseous nerve; SM, supinator muscle; US, ultrasound Key words: double nerve lesion; humeral fracture; nerve ultrasound; posterior interosseous nerve; radial nerve Additional Supporting Information may be found in the online version of this article. Correspondence to: C. Erra; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 25 June 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.24752
Double Traumatic Nerve Lesion
associated with humeral fractures showed that US allows visualization of radial nerve damage that could provide surgeons with useful anatomical information and accelerate the time to surgery. In 2009, we described a 24-year-old patient with radial nerve damage secondary to humeral shaft fracture3 with inhomogeneous involvement of the radial nerve–innervated muscles with more severe involvement of posterior interosseous nerve (PIN)– innervated muscles. US evaluation showed focal enlargement of the radial nerve at the spiral groove associated with PIN enlargement at the arcade of Frohse, and a double-site radial nerve injury diagnosis was made. Because the trauma did not directly involve the forearm, an indirect stretching mechanism was hypothesized as the cause of the PIN involvement. Based on this and subsequent similar observations in daily clinical practice, we decided to evaluate the PIN in all patients with traumatic radial nerve lesions associated with humeral fractures who were referred to our laboratory. Our aim was to assess the frequency of US evidence of PIN involvement in humeral fracture–associated radial nerve lesions. METHODS
We evaluated all patients with traumatic humeral fractures and radial nerve lesions referred to our laboratory from January 2010 to January 2014. Both electrodiagnostic and US evaluations were performed. Electrodiagnostic evaluation included needle examination and radial sensory nerve conduction studies in all patients (using the antidromic technique of stimulating the thumb and recording at the wrist). Motor nerve conduction studies (stimulating the radial nerve at the elbow and above the spiral groove and recording from the extensor digitorum muscle or extensor indicis muscle) were carried out only on a few patients (mainly those with severe muscle weakness, normal radial nerve sensory nerve action potential 10 days after the trauma, and scant needle signs of denervation after 1 month) due to technical difficulties (presence of external fixators, or patients with high body mass index, cutaneous wounds, or edema). MUSCLE & NERVE
March 2016
375
The upper cut-off of the PIN from our laboratory (obtained from 42 healthy subjects assessed bilaterally; mean age 41.5 years, range 19–81 years) is 3 mm2. The upper cut-off of the radial nerve at the spiral grove from our laboratory (obtained from the same 42 healthy subjects) is 8 mm2. Enlarged CSA associated with a hypoechoic appearance and/or loss of fascicular structure was considered a sign of nerve damage.
RESULTS
FIGURE 1. (a) Radial nerve ultrasound (patient 6) of the middle third of the arm in transverse section showing enlargement of radial nerve (arrow) at the spiral groove (CSA 5 10 mm2). (b) PIN ultrasound (patient 6) of the proximal third of the forearm in transverse section showing enlargement of the PIN (arrow) at the arcade of Frohse (CSA 5 5 mm2). H, humerus; S, supinator muscle; R, radius.
US evaluation of the radial nerve was performed with a high-frequency 10–18-MHZ linear transducer (MyLab 70; Esaote). Patients were examined in the supine position. Unless hampered by the presence of external fixators, the preferred scanning position for the radial nerve in the arm was with the elbow flexed at 908 and lying on a surface to access the lateral aspect of the arm. The normal radial nerve appears as a round/ovalshaped fascicular structure with a hyperechoic rim on transverse scan. US nerve evaluation is based on qualitative assessment of nerve echotexture and on quantitative measurement of nerve crosssectional area (CSA). CSA is recorded on the short axis of the nerve with the ellipse method at the spiral groove and at any other point where the nerve appears to be enlarged. The scanning position for the PIN was with the forearm pronated and lying on a surface. Passive rotation of the forearm was used, if necessary, to better visualize the nerve during examination. PIN CSA was recorded at the arcade of Frohse and at any other site where the nerve appeared enlarged. 376
Double Traumatic Nerve Lesion
Thirty-five consecutive patients (24 men and 11 women, mean age 46 years, range 11–92 years) were studied. Electrodiagnostic studies showed axonal damage in the majority of patients; 2 patients had evidence of axonal damage associated with neurapraxic block of the radial nerve at the spiral groove. The latency between trauma and first US examination ranged from 5 days to 12 months. Eighteen patients had US evidence of a radial nerve lesion in the arm (Fig. 1a) associated with PIN involvement characterized by CSA enlargement at the arcade of Frohse (2–5 times larger than the contralateral side; Figs. 1b and 2). At the most distal sites, the nerve appeared normal in all patients (see Tables S1 and S2 in Supplementary Material, available online).
FIGURE 2. PIN ultrasound on transverse section at the proximal third of the forearm. The left column shows the enlarged PIN (arrow) at the arcade of Frohse. The right column shows the normal PIN (arrow) on the contrateral side for each patient. (a, d) Patient 3. (b, e) Patient 4. (c, f) Patient 10. S, supinator muscle; R, radius. MUSCLE & NERVE
March 2016
FIGURE 3. Clinical and sonographic follow-up of patients with double PIN and radial nerve lesion [continuous line 5 cross-sectional area (CSA) of posterior interosseous nerve (PIN), dotted line 5 MRC score of extensor digitorum communis (EDC)].
Seventeen patients had US evidence of a radial nerve lesion (Fig. 1a) with a normal PIN (Tables S3 and S4, available online). We also performed neurophysiological and sonographic follow-up of 7 patients with double radial and PIN lesions. Six patients showed clinical improvement along with reduction in size of PIN (Fig. 3) and radial nerve enlargement; 1 patient (patient 2) showed no clinical improvement, and US evaluation demonstrated neurotmesis of the radial nerve in the distal third of the arm. In 3 more patients we follow-up by telephone, and all 3 reported complete recovery of range of motion of both finger and wrist extension. We also performed clinical and US follow-up of 2 patients with isolated radial nerve lesions; 1 (patient 21) had complete clinical recovery along with normalization of radial nerve US appearance, whereas the second (patient 20) had partial recovery of strength [Medical Research Council (MRC) grade 3 for extensor carpi and extensor digitorum communis] with US evidence of radial nerve abnormality over a humeral metallic plaque. In 7 more patients we followed up by telephone and found that all reported complete recovery of range of motion of both finger and wrist extension. DISCUSSION
The radial nerve divides into 2 terminal branches anterior to the lateral humeral epicondyle, the superficial and deep branches. The deep branch travels in the posterior region of the forearm as the PIN, pierces the supinator muscle (SM) with an arched path at the arcade of Frohse, and then proceeds along the forearm to the wrist. The arcade of Frohse is a point where the PIN has reduced mobility, and can be entrapped.4,5 Double Traumatic Nerve Lesion
The motor component of the radial nerve innervates the triceps brachii, anconeous, brachioradialis, and extensor carpi radialis longus, whereas the PIN innervates the extensor carpi radialis brevis, SM, extensor digitorum, extensor carpi ulnaris, extensor digiti minimi, extensor indicis, abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus. Patients with pure PIN palsy show radial deviation of the wrist during wrist extension (due to impairment of the extensor carpi ulnaris) and finger extension palsy (finger drop). Multiple-site lesions of the same nerve along its course are hard to diagnose. They can sometimes be hypothesized based on clinical examination, but they are rarely demonstrated through electrodiagnostic testing and are often overlooked. After reporting an association between radial nerve and PIN involvement,3 we described a double nerve lesion involving the brachial plexus and the musculocutaneous nerve, where US showed the 2 sites of nerve damage that other diagnostic techniques failed to demonstrate.6 The PIN may be entrapped in the region of the supinator muscle (primary PIN syndrome) or secondary to compression by external masses (lipomas, ganglia, synovial overgrowth of the cubital joint), vessels, trauma, or posttraumatic conditions. In either case, nerve US has been shown to be a useful diagnostic tool that shows increased size (CSA and diameter) and loss of fascicular structure with reduced echogenicity of the PIN.7 Our results show that US found that half of the patients with radial nerve damage at the site of trauma have evidence of PIN involvement. In our opinion this finding is consistent with a second site of pathology, but the clinical relevance, prognostic implications, and possible treatment still need to be clearly assessed. MUSCLE & NERVE
March 2016
377
In this case series, the different patients were evaluated at diverse time-points since the occurrence of the trauma, and therefore we cannot identify the onset of US alterations in the PIN. The patient who was evaluated at the shortest time from the trauma was examined 5 days posttrauma when PIN enlargement was already visible, along with radial nerve enlargement. The exact mechanism of PIN involvement far from the site of trauma is still unknown. The 2 main hypotheses are stretch-induced injury simultaneous to the trauma or delayed double crush syndrome. As PIN US abnormalities have been observed as early as 5 days after the trauma (patient 13), we believe the first hypothesis is the most probable. This finding could also suggest that PIN lesions may in fact develop after the original trauma in many cases. It is not possible to clarify this point without a prospective study carrying out serial examinations over time beginning soon after the injury. The PIN has reduced mobility at the arcade of Frohse, as it is fixed under a fibrous structure (the arch of the supinator). The proximal injury of the radial nerve may cause PIN traction at this site and therefore induce a stretch injury. Although we could perform follow-up in only a few patients (none of whom underwent surgery for a PIN lesion), we observed that all patients with the double lesion who recovered clinically (6 of 7) also showed significant reduction of PIN CSA (Fig. 3), along with radial nerve CSA reduction. The only patient who did not improve had US evidence of radial nerve neurotmesis in the distal third of the arm. It is not clear whether the improvement was due to PIN or radial nerve recovery. Also, almost all patients with isolated radial nerve damage in whom we performed follow-up (8 of 17) showed clinical improvement, with 1 exception (patient
378
Double Traumatic Nerve Lesion
20); in this patient, US showed signs of radial nerve damage over a humeral osteosynthetic metallic plaque. Based on these preliminary data, addition of a PIN lesion does not seem to negatively influence clinical outcome. There are no data on the best therapeutic approach to this type of nerve damage. The progressive spontaneous clinical improvement and CSA reduction observed in the patients we followed up seems to suggest a positive natural evolution of the PIN stretch injury. None of our patients with US evidence of PIN involvement underwent surgery for the PIN lesion, but we cannot exclude that surgical decompression may be useful in very severe patients. Further prospective studies are needed to better define the clinical relevance and natural course of this type of lesion, the prognostic implications, and the possible role of surgical decompression. In conclusion, on the basis of these, we recommend the use of US in cases of humeral fracture with more severe involvement of PIN-innervated muscles, extending assessment to the PIN at the arcade of Frohse. REFERENCES 1. DeFranco MJ, Lawton JN. Radial nerve injuries associated with humeral fractures. J Hand Surg Am 2006;31:655–663. 2. Bodner G, Buchberger W, Schocke M, Bale R, Huber B, Harpf C, et al. Radial nerve palsy associated with humeral shaft fracture: evaluation with US—initial experience. Radiology 2001;219:811–816. 3. Liotta G, Granata G, Librante A, di Pasquale A, Caliandro P, Martinoli C, et al. Atypical double nerve lesion after humeral fracture: diagnosis by ultrasound. Muscle Nerve 2010;41:287–288. 4. Papadopoulos N, Paraschos A, Pelekis P. Anatomical observations on the arcade of Frohse and other structures related to the deep radial nerve. Anatomical interpretation of deep radial nerve entrapment neuropathy. Folia Morphol (Praha) 1989;37:319–327. 5. Knutsen EJ, Calfee RP. Uncommon upper extremity compression neuropathies. Hand Clin 2013;29:443–453. 6. Bianchi ML, Padua L, Granata G, Erra C. Double site nerve lesion: ultrasound diagnosed musculocutaneous involvement in traumatic brachial plexus injury. Clin Neurophysiol 2013;124:629–630. 7. Djurdjevic T, Loizides A, L€ oscher W, Gruber H, Plaikner M, Peer S. High resolution ultrasound in posterior interosseous nerve syndrome. Muscle Nerve 2014;49:35–39.
MUSCLE & NERVE
March 2016
Department of Neurology, Catholic University of Sacred Heart, Largo A. Gemelli 8, 00168, Rome, Italy Don Carlo Gnocchi Foundation, Milan, Italy 3 Department of Orthopedic Science, Board of Physical Medicine and Rehabilitation, Sapienza University, Rome, Italy 4 Department of Neurosciences: Sciences NPSRR, University of Padova, Padova, Italy 2
Accepted 24 June 2015 ABSTRACT: Introduction: Radial nerve lesions associated with humeral shaft fractures are the most common traumatic nerve lesions observed with long bone fractures. Secondary indirect posterior interosseous nerve (PIN) lesions can be associated with traumatic radial nerve palsy. The aim of this study was to identify cases of traumatic double-site radial nerve involvement through ultrasound (US). Methods: Patients with traumatic radial nerve lesions referred to our laboratory from January 2010 to January 2014 were evaluated. Results: Of the 35 patients, 18 had US evidence of a radial nerve lesion at the fracture site associated with secondary PIN involvement at the arcade of Frohse. Conclusions: Multiple-site nerve lesions are difficult to demonstrate through electrodiagnostic tests. In our case series, half of the patients with traumatic radial nerve damage had US evidence of PIN injury. Prospective studies with follow-up are needed to determine the clinical and prognostic relevance of this finding and the best therapeutic approach. Muscle Nerve 53: 375–378, 2016
Radial nerve lesions associated with humeral shaft fractures are the most common traumatic nerve lesions associated with long bone fractures1 and have an estimated prevalence of between 2% and 18%.2 This frequent association is likely due to the anatomical contiguity of the radial nerve to the humerus together with the reduced mobility of the nerve in the passage through the lateral intermuscular septum in the distal third of the arm. Nerve ultrasound (US) is a tool of growing importance for assessment of the peripheral nervous system, especially for evaluation of traumatic nerve lesions, entrapment syndromes, and peripheral nerve tumors. Bodner and colleagues2 showed the usefulness of nerve US in patients with radial nerve palsy associated with humeral fractures. Their multilevel evaluation (X-ray, electromyography, nerve US) of 11 patients with complete or partial radial palsy Abbreviations: CSA, cross-sectional area; MRC, Medical Research Council; PIN, posterior interosseous nerve; SM, supinator muscle; US, ultrasound Key words: double nerve lesion; humeral fracture; nerve ultrasound; posterior interosseous nerve; radial nerve Additional Supporting Information may be found in the online version of this article. Correspondence to: C. Erra; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 25 June 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.24752
Double Traumatic Nerve Lesion
associated with humeral fractures showed that US allows visualization of radial nerve damage that could provide surgeons with useful anatomical information and accelerate the time to surgery. In 2009, we described a 24-year-old patient with radial nerve damage secondary to humeral shaft fracture3 with inhomogeneous involvement of the radial nerve–innervated muscles with more severe involvement of posterior interosseous nerve (PIN)– innervated muscles. US evaluation showed focal enlargement of the radial nerve at the spiral groove associated with PIN enlargement at the arcade of Frohse, and a double-site radial nerve injury diagnosis was made. Because the trauma did not directly involve the forearm, an indirect stretching mechanism was hypothesized as the cause of the PIN involvement. Based on this and subsequent similar observations in daily clinical practice, we decided to evaluate the PIN in all patients with traumatic radial nerve lesions associated with humeral fractures who were referred to our laboratory. Our aim was to assess the frequency of US evidence of PIN involvement in humeral fracture–associated radial nerve lesions. METHODS
We evaluated all patients with traumatic humeral fractures and radial nerve lesions referred to our laboratory from January 2010 to January 2014. Both electrodiagnostic and US evaluations were performed. Electrodiagnostic evaluation included needle examination and radial sensory nerve conduction studies in all patients (using the antidromic technique of stimulating the thumb and recording at the wrist). Motor nerve conduction studies (stimulating the radial nerve at the elbow and above the spiral groove and recording from the extensor digitorum muscle or extensor indicis muscle) were carried out only on a few patients (mainly those with severe muscle weakness, normal radial nerve sensory nerve action potential 10 days after the trauma, and scant needle signs of denervation after 1 month) due to technical difficulties (presence of external fixators, or patients with high body mass index, cutaneous wounds, or edema). MUSCLE & NERVE
March 2016
375
The upper cut-off of the PIN from our laboratory (obtained from 42 healthy subjects assessed bilaterally; mean age 41.5 years, range 19–81 years) is 3 mm2. The upper cut-off of the radial nerve at the spiral grove from our laboratory (obtained from the same 42 healthy subjects) is 8 mm2. Enlarged CSA associated with a hypoechoic appearance and/or loss of fascicular structure was considered a sign of nerve damage.
RESULTS
FIGURE 1. (a) Radial nerve ultrasound (patient 6) of the middle third of the arm in transverse section showing enlargement of radial nerve (arrow) at the spiral groove (CSA 5 10 mm2). (b) PIN ultrasound (patient 6) of the proximal third of the forearm in transverse section showing enlargement of the PIN (arrow) at the arcade of Frohse (CSA 5 5 mm2). H, humerus; S, supinator muscle; R, radius.
US evaluation of the radial nerve was performed with a high-frequency 10–18-MHZ linear transducer (MyLab 70; Esaote). Patients were examined in the supine position. Unless hampered by the presence of external fixators, the preferred scanning position for the radial nerve in the arm was with the elbow flexed at 908 and lying on a surface to access the lateral aspect of the arm. The normal radial nerve appears as a round/ovalshaped fascicular structure with a hyperechoic rim on transverse scan. US nerve evaluation is based on qualitative assessment of nerve echotexture and on quantitative measurement of nerve crosssectional area (CSA). CSA is recorded on the short axis of the nerve with the ellipse method at the spiral groove and at any other point where the nerve appears to be enlarged. The scanning position for the PIN was with the forearm pronated and lying on a surface. Passive rotation of the forearm was used, if necessary, to better visualize the nerve during examination. PIN CSA was recorded at the arcade of Frohse and at any other site where the nerve appeared enlarged. 376
Double Traumatic Nerve Lesion
Thirty-five consecutive patients (24 men and 11 women, mean age 46 years, range 11–92 years) were studied. Electrodiagnostic studies showed axonal damage in the majority of patients; 2 patients had evidence of axonal damage associated with neurapraxic block of the radial nerve at the spiral groove. The latency between trauma and first US examination ranged from 5 days to 12 months. Eighteen patients had US evidence of a radial nerve lesion in the arm (Fig. 1a) associated with PIN involvement characterized by CSA enlargement at the arcade of Frohse (2–5 times larger than the contralateral side; Figs. 1b and 2). At the most distal sites, the nerve appeared normal in all patients (see Tables S1 and S2 in Supplementary Material, available online).
FIGURE 2. PIN ultrasound on transverse section at the proximal third of the forearm. The left column shows the enlarged PIN (arrow) at the arcade of Frohse. The right column shows the normal PIN (arrow) on the contrateral side for each patient. (a, d) Patient 3. (b, e) Patient 4. (c, f) Patient 10. S, supinator muscle; R, radius. MUSCLE & NERVE
March 2016
FIGURE 3. Clinical and sonographic follow-up of patients with double PIN and radial nerve lesion [continuous line 5 cross-sectional area (CSA) of posterior interosseous nerve (PIN), dotted line 5 MRC score of extensor digitorum communis (EDC)].
Seventeen patients had US evidence of a radial nerve lesion (Fig. 1a) with a normal PIN (Tables S3 and S4, available online). We also performed neurophysiological and sonographic follow-up of 7 patients with double radial and PIN lesions. Six patients showed clinical improvement along with reduction in size of PIN (Fig. 3) and radial nerve enlargement; 1 patient (patient 2) showed no clinical improvement, and US evaluation demonstrated neurotmesis of the radial nerve in the distal third of the arm. In 3 more patients we follow-up by telephone, and all 3 reported complete recovery of range of motion of both finger and wrist extension. We also performed clinical and US follow-up of 2 patients with isolated radial nerve lesions; 1 (patient 21) had complete clinical recovery along with normalization of radial nerve US appearance, whereas the second (patient 20) had partial recovery of strength [Medical Research Council (MRC) grade 3 for extensor carpi and extensor digitorum communis] with US evidence of radial nerve abnormality over a humeral metallic plaque. In 7 more patients we followed up by telephone and found that all reported complete recovery of range of motion of both finger and wrist extension. DISCUSSION
The radial nerve divides into 2 terminal branches anterior to the lateral humeral epicondyle, the superficial and deep branches. The deep branch travels in the posterior region of the forearm as the PIN, pierces the supinator muscle (SM) with an arched path at the arcade of Frohse, and then proceeds along the forearm to the wrist. The arcade of Frohse is a point where the PIN has reduced mobility, and can be entrapped.4,5 Double Traumatic Nerve Lesion
The motor component of the radial nerve innervates the triceps brachii, anconeous, brachioradialis, and extensor carpi radialis longus, whereas the PIN innervates the extensor carpi radialis brevis, SM, extensor digitorum, extensor carpi ulnaris, extensor digiti minimi, extensor indicis, abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus. Patients with pure PIN palsy show radial deviation of the wrist during wrist extension (due to impairment of the extensor carpi ulnaris) and finger extension palsy (finger drop). Multiple-site lesions of the same nerve along its course are hard to diagnose. They can sometimes be hypothesized based on clinical examination, but they are rarely demonstrated through electrodiagnostic testing and are often overlooked. After reporting an association between radial nerve and PIN involvement,3 we described a double nerve lesion involving the brachial plexus and the musculocutaneous nerve, where US showed the 2 sites of nerve damage that other diagnostic techniques failed to demonstrate.6 The PIN may be entrapped in the region of the supinator muscle (primary PIN syndrome) or secondary to compression by external masses (lipomas, ganglia, synovial overgrowth of the cubital joint), vessels, trauma, or posttraumatic conditions. In either case, nerve US has been shown to be a useful diagnostic tool that shows increased size (CSA and diameter) and loss of fascicular structure with reduced echogenicity of the PIN.7 Our results show that US found that half of the patients with radial nerve damage at the site of trauma have evidence of PIN involvement. In our opinion this finding is consistent with a second site of pathology, but the clinical relevance, prognostic implications, and possible treatment still need to be clearly assessed. MUSCLE & NERVE
March 2016
377
In this case series, the different patients were evaluated at diverse time-points since the occurrence of the trauma, and therefore we cannot identify the onset of US alterations in the PIN. The patient who was evaluated at the shortest time from the trauma was examined 5 days posttrauma when PIN enlargement was already visible, along with radial nerve enlargement. The exact mechanism of PIN involvement far from the site of trauma is still unknown. The 2 main hypotheses are stretch-induced injury simultaneous to the trauma or delayed double crush syndrome. As PIN US abnormalities have been observed as early as 5 days after the trauma (patient 13), we believe the first hypothesis is the most probable. This finding could also suggest that PIN lesions may in fact develop after the original trauma in many cases. It is not possible to clarify this point without a prospective study carrying out serial examinations over time beginning soon after the injury. The PIN has reduced mobility at the arcade of Frohse, as it is fixed under a fibrous structure (the arch of the supinator). The proximal injury of the radial nerve may cause PIN traction at this site and therefore induce a stretch injury. Although we could perform follow-up in only a few patients (none of whom underwent surgery for a PIN lesion), we observed that all patients with the double lesion who recovered clinically (6 of 7) also showed significant reduction of PIN CSA (Fig. 3), along with radial nerve CSA reduction. The only patient who did not improve had US evidence of radial nerve neurotmesis in the distal third of the arm. It is not clear whether the improvement was due to PIN or radial nerve recovery. Also, almost all patients with isolated radial nerve damage in whom we performed follow-up (8 of 17) showed clinical improvement, with 1 exception (patient
378
Double Traumatic Nerve Lesion
20); in this patient, US showed signs of radial nerve damage over a humeral osteosynthetic metallic plaque. Based on these preliminary data, addition of a PIN lesion does not seem to negatively influence clinical outcome. There are no data on the best therapeutic approach to this type of nerve damage. The progressive spontaneous clinical improvement and CSA reduction observed in the patients we followed up seems to suggest a positive natural evolution of the PIN stretch injury. None of our patients with US evidence of PIN involvement underwent surgery for the PIN lesion, but we cannot exclude that surgical decompression may be useful in very severe patients. Further prospective studies are needed to better define the clinical relevance and natural course of this type of lesion, the prognostic implications, and the possible role of surgical decompression. In conclusion, on the basis of these, we recommend the use of US in cases of humeral fracture with more severe involvement of PIN-innervated muscles, extending assessment to the PIN at the arcade of Frohse. REFERENCES 1. DeFranco MJ, Lawton JN. Radial nerve injuries associated with humeral fractures. J Hand Surg Am 2006;31:655–663. 2. Bodner G, Buchberger W, Schocke M, Bale R, Huber B, Harpf C, et al. Radial nerve palsy associated with humeral shaft fracture: evaluation with US—initial experience. Radiology 2001;219:811–816. 3. Liotta G, Granata G, Librante A, di Pasquale A, Caliandro P, Martinoli C, et al. Atypical double nerve lesion after humeral fracture: diagnosis by ultrasound. Muscle Nerve 2010;41:287–288. 4. Papadopoulos N, Paraschos A, Pelekis P. Anatomical observations on the arcade of Frohse and other structures related to the deep radial nerve. Anatomical interpretation of deep radial nerve entrapment neuropathy. Folia Morphol (Praha) 1989;37:319–327. 5. Knutsen EJ, Calfee RP. Uncommon upper extremity compression neuropathies. Hand Clin 2013;29:443–453. 6. Bianchi ML, Padua L, Granata G, Erra C. Double site nerve lesion: ultrasound diagnosed musculocutaneous involvement in traumatic brachial plexus injury. Clin Neurophysiol 2013;124:629–630. 7. Djurdjevic T, Loizides A, L€ oscher W, Gruber H, Plaikner M, Peer S. High resolution ultrasound in posterior interosseous nerve syndrome. Muscle Nerve 2014;49:35–39.
MUSCLE & NERVE
March 2016
