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Increased reflectivity and loss in bulk of the pronator quadratus muscle does not always indicate anterior interosseous neuropathy on ultrasound
European Journal of Radiology 82 (2013) 526–529
Contents lists available at SciVerse ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Increased reflectivity and loss in bulk of the pronator quadratus muscle does not always indicate anterior interosseous neuropathy on ultrasound Alberto Tagliafico a,∗ , Maribel Miguel Perez f , Luca Padua b,c , Andrea Klauser d , Antonio Zicca a , Carlo Martinoli e,1 a
Department of Human Anatomy, DIMES, Università di Genova, Largo Rosanna Benzi 8, 16138 Genoa, Italy Department of Neuroscience, Institute of Neurology, Catholic University, Largo Francesco Vito 1, Rome, Italy c Department of Neuroscience, Don Gnocchi Foundation, Rome, Italy d Department of Diagnostic Radiology, Medical University Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria e Radiology Department, DISC, Università di Genova, Largo Rosanna Benzi 8, 16138 Genoa, Italy f Unit of Human Anatomy and Embryology, Department of Pathology and Experimental Therapy, Faculty of Medicine (C Bellvitge), University of Barcelona, Barcelona, Spain b
a r t i c l e
i n f o
Article history: Received 12 March 2012 Received in revised form 17 May 2012 Accepted 28 September 2012 Keywords: Pronator quadratus Ultrasound Atrophy Anterior interosseous nerve Kiloh–Nevin
a b s t r a c t Purpose: To assess if isolated atrophy of the pronator quadratus muscle indicates anterior interosseous neuropathy on ultrasound. Materials and methods: IRB approval and written informed from every patient were obtained. A prospective study including 100 consecutive wrist and hand ultrasound studies in 77 patients (46 females and 31 males; 23 patients had bilateral studies) with a mean age of 45 years (range, 21–86 years) was performed between March 2010 and January 2012. The patients were chosen irrespective of age, sex, and body mass index. The studies were performed for several reasons, the most common being wrist pain (n = 56), followed by ganglion cyst (n = 11) and soft-tissue masses (n = 10). Clinical histories, previous imaging studies and US examinations were evaluated to rule out anterior interosseous nerve neuropathy. US examinations were performed with a commercially available equipment. Pronator quadratus was checked for atrophy using flexor pollicis longus, flexor digitorum superficialis and profundus for comparison. Descriptive statistic was used. Results: US signs of pronator quadratus atrophy were present in 7/100 (7%) of patients. None of the patients had a bilateral atrophy of the pronator quadratus. In the patients with atrophy of the pronator quadratus, adjacent flexor muscles were normal. There was no significant difference between males and females (3 females vs 4 males) (p = 0.506). Conclusion: Increased reflectivity and loss in bulk of the pronator quadratus muscle does not always indicate anterior interosseous neuropathy on ultrasound. © 2012 Published by Elsevier Ireland Ltd.
1. Introduction The entrapment of the anterior interosseous nerve in the forearm, a condition also known as the Kiloh–Nevin syndrome [1], may be present in different conditions, such as fibrous bands, anomalous muscles (Gantzer muscle) and accessory tendons from the flexor digitorum superficialis [2,3]. Isolated anterior interosseous neuropathy leads to pain in the volar forearm and difficulty in performing pinching movements with the digits (inability to do “ok”
∗ Corresponding author. Tel.: +39 0103537882; fax: +39 0103537885. E-mail address: albertotagliafi[email protected] (A. Tagliafico). 1 Tel.: +39 0105555248; fax: +39 0105556288. 0720-048X/$ – see front matter © 2012 Published by Elsevier Ireland Ltd. http://dx.doi.org/10.1016/j.ejrad.2012.09.028
with the fingers) and handwriting. US diagnosis of an overt anterior interosseous neuropathy may be suggested by loss in bulk and increased reflectivity of the innervated muscles: the flexor pollicis longus, the flexor digitorum profundus and the pronator quadratus [4–6]. However, using magnetic resonance imaging (MRI), increased signal intensity of the pronator quadratus muscle has been described on fluid-sensitive images in patients without anterior interosseous nerve syndrome [7–9]. Similarly, we noted that on wrist ultrasonographic examinations it is possible to find loss in bulk and increased reflectivity at the pronator quadratus muscle in patients without symptoms related to anterior interosseous neuropathy. Therefore, the purpose of this study was to assess the prevalence of denervation-like signs (loss in bulk and increased reflectivity) in the pronator quadratus in patients without anterior
A. Tagliafico et al. / European Journal of Radiology 82 (2013) 526–529
527
interosseous neuropathy. Knowledge of this feature will be useful to avoid this potential pitfall.
2. Materials and methods 2.1. Anatomical correlation The anatomical correlation portion of this project was approved by the Anatomic Donations Department. The anatomy of the pronator quadratus was at first examined on three cadaveric arms (males: 56, 66, and 81 years old) dissected by an anatomist with 20 years of experience in dissection from the shoulder to the forearm. The specimens were deep-frozen at −40 ◦ C. Concomitant osseous pathology at the level of the wrist was excluded. No evidence of previous surgery around the wrist was observed. The specimens were prepared to demonstrate the anatomy of the pronator quadratus and its innervation. Visual inspection was also performed by a musculoskeletal radiologist with 7 years of experience in musculoskeletal imaging.
2.2. Patients IRB approval and written informed consent were obtained A prospective study including 100 consecutive wrist and hand ultrasound studies in 77 patients (46 females and 31 males; 23 patients had bilateral studies) with a mean age of 45 years (range, 21–86 years) was performed between March 2010 and January 2012. The patients were chosen irrespective of age, sex, and body mass index. The studies were performed for several reasons, the most common being wrist pain (n = 56), followed by ganglion cyst (n = 11) and soft-tissue masses (n = 10). Available clinical data, imaging studies and actual clinical findings were investigated for abnormal findings that would raise the possibility of an anterior interosseous nerve neuropathy or of a cause that may damage the anterior interosseous nerve. Wrist ultrasound was performed following the guidelines proposed by the European Society of Skeletal Radiology [8]. Patients were placed with the dorsal wrist facing the examination table. After placing the probe over the palm on axial planes the transducer was moved cranially to fully identify the pronator quadratus. Probe orientation was adjusted accordingly to avoid muscular anisotropy artifacts. Tilting movements of the probe optimized depiction of pronator quadratus echotexture. Flexor digiturum superficialis, profundus and flexor pollicis longus muscles were considered for comparison. The examination was conducted form the elbow to the wrist visualizing the interosseous membrane and artery (which is the landmark for the anterior interosseous nerve). This maneuver was done to rule out potential soft-tissue masses compressing the anterior interosseous nerve. Every US examination was performed with commercially available equipment (iU22, Philips, the Nederlands) and 12-7 MHz and 17-5 MHz transducers. Pronator quadratus muscle fatty infiltration was assessed by evaluating its echogenicity and echostructure. The echogenicity and echostructure of the pronator quadratus muscle was evaluated as normal or atrophic (homogeneously hyperechoic and loss in bulk). Pronator quadratus muscles with slight loss of normal pattern with very poor fatty streaks were included in the normal group. Two radiologists, one with 7 years of musculoskeletal radiology experience and one with 2 years of musculoskeletal radiology experience, performed the studies independently. Each radiologist noted, subjectively, whether there was atrophy within the pronator quadratus. Quantitative evaluation of fatty atrophy was also performed using a software (MedDensity 1.0® ) previously used for other muscular fatty infiltration evaluation [10]. Results were analyzed with descriptive statistic.
Fig. 1. Cadaveric view of the pronator quadratus and interosseous membrane with the flexor digitorum profundus and flexor pollicis longus moved upward (a). In (b) the nerve branch of the anterior interosseous nerve reaching the pronator quadratus is visible (yellow mark). Red mark: artery.
3. Results 3.1. Anatomical correlation Dissection showed that the distal part of the anterior interosseous nerve enters the pronator quadratus muscle and may have some variable branches reaching the connective tissue and the interosseous membrane (Fig. 1). 3.2. Patients Ultrasonographic signs of pronator quadratus atrophy were present in 7/100 (7%) of patients examined (Fig. 2). None of the patients had a bilateral atrophy of the pronator quadratus muscle. Both radiologists were concordant with these findings. In the patients with echogenicity of the pronator quadratus classified as atrophic (homogeneously hyperechoic), adjacent flexor muscles resulted normal. There was no significant difference between males and females (3 females vs 4 males) (p = 0.506). Quantitative evaluation (Fig. 3) showed that the difference in fatty infiltration between normal muscles and atrophic muscles was approximately 35% (p = 0.05). 4. Discussion US diagnosis of anterior interosseous neuropathy, the so called Kiloh–Nevin syndrome, may be suggested by loss in bulk and increased reflectivity of the innervated muscles: the flexor pollicis longus, the flexor digitorum profundus and the pronator quadratus
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A. Tagliafico et al. / European Journal of Radiology 82 (2013) 526–529
Fig. 2. (a–d) axial (a) and longitudinal (b) US image of a normal pronator quadratus. Axial (c) and longitudinal (d) US image of an atrophic pronator quadratus.
[4]. These findings may be present both in primary or secondary syndromes. On MRI, anterior interosseous neuropathy is evident when on T2-weighted fat-suppressed or STIR images increased signal intensity in the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus muscles is visible [9]. However, it has been demonstrated that on MRI increased signal intensity of the pronator quadratus muscle is a frequent normal finding of unclear etiology and not related to disease [7]. On MRI it has been estimated that the signal intensity of the pronator quadratus was greater than that of an adjacent flexor muscle in 79 of 100 MRI examinations [7]. Intramuscular increased signal intensity on fluid-sensitive sequences is one of the MRI features of muscular denervation. In anterior interosseous nerve injury, denervationrelated alterations are evident at the pronator quadratus, flexor pollicis longus, or radial aspect of the flexor digitorum profundus muscles. In concordance with MRI findings, our study reveals that, on US, asymptomatic denervation-like alterations such increased reflectivity and loss in bulk of the pronator quadratus muscle may be isolated and not related to anterior interosseous neuropathy.
The criteria to define pronator quadratus atrophy on ultrasound were kept compatible with the current clinical practice: only visible atrophic muscles were included. On the base of our study, it is not possible to identify or suppose a definite reason for this phenomenon. Clarification of the etiology of pronator quadratus atrophy in patients without anterior interosseous neuropathy was beyond the purpose of our study. Some hypothesis, however, should be made: the first is that the pronator quadratus plays only a minor role in pronation. The main muscle that guarantees the pronation of the forearm is the pronator teres and the pronator quadratus play a minor role. Animals that live and travel in trees displayed a well-developed pronator quadratus to support travel and maintain balance on trees [11]. It is possible that in non-active individuals this muscle loses bulk so that it becomes atrophic due to poor utilization. Moreover, genetic, occupational factors and anatomical variants in the innervation may also be responsible of this phenomenon. The anatomical oblique disposition of pronator quadratus muscular fibers respect to other flexor tendons may have influenced the
Fig. 3. Screen shot showing the software interface (MedDensity 1.0, 3TC Engineering) used to make quantitative assessment of intramuscular fat in pronator quadratus muscle.
A. Tagliafico et al. / European Journal of Radiology 82 (2013) 526–529
echogenicity of the muscle but it is not responsible of muscle loss in bulk. Neuropathy of the branch of the anterior interosseous nerve directed to the pronator quadratus muscle is another possible, although unlikely, explanation. However, every patient involved had a negative neurological examination. We believe that the reason for this finding is still unknown. The pronator quadratus is an important reference structure for measuring the dimensions of the median nerve, therefore care should be taken in case of atrophy. This study has limitations. First, only a-symptomatic patients were included and no patients with Kiloh–Nevin syndrome were included. Second, no surgical correlate was obtained for obvious reasons. In conclusion, we found that atrophy of the pronator quadratus may be present in patients with no anterior interosseous nerve syndrome and may be not related to any pathological condition known today. References [1] Kiloh LG, Nevin S. Isolated neuritis of the anterior interosseous nerve. British Medical Journal 1952;1:850–1.
529
[2] Tagliafico A, Rubino M, Autuori A, Bianchi S, Martinoli C. Wrist and hand ultrasound. Seminars in Musculoskeletal Radiology 2007;11(2):95–104. [3] Martinoli C, Perez MM, Padua L, et al. Muscle variants of the upper and lower limb (with anatomical correlation). Seminars in Musculoskeletal Radiology 2010;14(2):106–21. [4] Grainger AJ, Campbell RSD, Stothard J. Anterior interosseous nerve syndrome: appearance at MR imaging in three cases. Radiology 1998;208:381–4. [5] Hide IG, Grainger AJ, Naisby GP, et al. Sonographic findings in the anterior interosseous nerve syndrome. Journal of Clinical Ultrasound 1999;27:459–64. [6] Martinoli C, Bianchi S, Pugliese F, et al. Sonography of entrapment neuropathies in the upper limb (wrist excluded). Journal of Clinical Ultrasound 2004;32:438–50. [7] Gyftopoulos S, Rosenberg ZS, Petchprapa C. Increased MR signal intensity in the pronator quadratus muscle: does it always indicate anterior interosseous neuropathy? AJR: American Journal of Roentgenology 2010;194(2):490–3. [8] Martinoli C. Musculoskeletal ultrasound: technical guidelines. Insight into Imaging 2010;1(3):99–141. [9] Andreisek G, Crook DW, Burg D, Marincek B, Weishaupt D. Peripheral neuropathies of the median, radial, and ulnar nerves: MR imaging features. Radiographics 2006;26(5):1267–87. [10] Tagliafico AS, Ameri P, Bovio M, et al. Relationship between fatty degeneration of thigh muscles and vitamin D status in the elderly: a preliminary MRI study. AJR: American Journal of Roentgenology 2010;194(3):728–34. [11] Larson SG, Stern Jr JT. Maintenance of above-branch balance during primate arboreal quadrupedalism: coordinated use of forearm rotators and tail motion. American Journal of Physical Anthropology 2006;129(1):71–81.
Contents lists available at SciVerse ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Increased reflectivity and loss in bulk of the pronator quadratus muscle does not always indicate anterior interosseous neuropathy on ultrasound Alberto Tagliafico a,∗ , Maribel Miguel Perez f , Luca Padua b,c , Andrea Klauser d , Antonio Zicca a , Carlo Martinoli e,1 a
Department of Human Anatomy, DIMES, Università di Genova, Largo Rosanna Benzi 8, 16138 Genoa, Italy Department of Neuroscience, Institute of Neurology, Catholic University, Largo Francesco Vito 1, Rome, Italy c Department of Neuroscience, Don Gnocchi Foundation, Rome, Italy d Department of Diagnostic Radiology, Medical University Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria e Radiology Department, DISC, Università di Genova, Largo Rosanna Benzi 8, 16138 Genoa, Italy f Unit of Human Anatomy and Embryology, Department of Pathology and Experimental Therapy, Faculty of Medicine (C Bellvitge), University of Barcelona, Barcelona, Spain b
a r t i c l e
i n f o
Article history: Received 12 March 2012 Received in revised form 17 May 2012 Accepted 28 September 2012 Keywords: Pronator quadratus Ultrasound Atrophy Anterior interosseous nerve Kiloh–Nevin
a b s t r a c t Purpose: To assess if isolated atrophy of the pronator quadratus muscle indicates anterior interosseous neuropathy on ultrasound. Materials and methods: IRB approval and written informed from every patient were obtained. A prospective study including 100 consecutive wrist and hand ultrasound studies in 77 patients (46 females and 31 males; 23 patients had bilateral studies) with a mean age of 45 years (range, 21–86 years) was performed between March 2010 and January 2012. The patients were chosen irrespective of age, sex, and body mass index. The studies were performed for several reasons, the most common being wrist pain (n = 56), followed by ganglion cyst (n = 11) and soft-tissue masses (n = 10). Clinical histories, previous imaging studies and US examinations were evaluated to rule out anterior interosseous nerve neuropathy. US examinations were performed with a commercially available equipment. Pronator quadratus was checked for atrophy using flexor pollicis longus, flexor digitorum superficialis and profundus for comparison. Descriptive statistic was used. Results: US signs of pronator quadratus atrophy were present in 7/100 (7%) of patients. None of the patients had a bilateral atrophy of the pronator quadratus. In the patients with atrophy of the pronator quadratus, adjacent flexor muscles were normal. There was no significant difference between males and females (3 females vs 4 males) (p = 0.506). Conclusion: Increased reflectivity and loss in bulk of the pronator quadratus muscle does not always indicate anterior interosseous neuropathy on ultrasound. © 2012 Published by Elsevier Ireland Ltd.
1. Introduction The entrapment of the anterior interosseous nerve in the forearm, a condition also known as the Kiloh–Nevin syndrome [1], may be present in different conditions, such as fibrous bands, anomalous muscles (Gantzer muscle) and accessory tendons from the flexor digitorum superficialis [2,3]. Isolated anterior interosseous neuropathy leads to pain in the volar forearm and difficulty in performing pinching movements with the digits (inability to do “ok”
∗ Corresponding author. Tel.: +39 0103537882; fax: +39 0103537885. E-mail address: albertotagliafi[email protected] (A. Tagliafico). 1 Tel.: +39 0105555248; fax: +39 0105556288. 0720-048X/$ – see front matter © 2012 Published by Elsevier Ireland Ltd. http://dx.doi.org/10.1016/j.ejrad.2012.09.028
with the fingers) and handwriting. US diagnosis of an overt anterior interosseous neuropathy may be suggested by loss in bulk and increased reflectivity of the innervated muscles: the flexor pollicis longus, the flexor digitorum profundus and the pronator quadratus [4–6]. However, using magnetic resonance imaging (MRI), increased signal intensity of the pronator quadratus muscle has been described on fluid-sensitive images in patients without anterior interosseous nerve syndrome [7–9]. Similarly, we noted that on wrist ultrasonographic examinations it is possible to find loss in bulk and increased reflectivity at the pronator quadratus muscle in patients without symptoms related to anterior interosseous neuropathy. Therefore, the purpose of this study was to assess the prevalence of denervation-like signs (loss in bulk and increased reflectivity) in the pronator quadratus in patients without anterior
A. Tagliafico et al. / European Journal of Radiology 82 (2013) 526–529
527
interosseous neuropathy. Knowledge of this feature will be useful to avoid this potential pitfall.
2. Materials and methods 2.1. Anatomical correlation The anatomical correlation portion of this project was approved by the Anatomic Donations Department. The anatomy of the pronator quadratus was at first examined on three cadaveric arms (males: 56, 66, and 81 years old) dissected by an anatomist with 20 years of experience in dissection from the shoulder to the forearm. The specimens were deep-frozen at −40 ◦ C. Concomitant osseous pathology at the level of the wrist was excluded. No evidence of previous surgery around the wrist was observed. The specimens were prepared to demonstrate the anatomy of the pronator quadratus and its innervation. Visual inspection was also performed by a musculoskeletal radiologist with 7 years of experience in musculoskeletal imaging.
2.2. Patients IRB approval and written informed consent were obtained A prospective study including 100 consecutive wrist and hand ultrasound studies in 77 patients (46 females and 31 males; 23 patients had bilateral studies) with a mean age of 45 years (range, 21–86 years) was performed between March 2010 and January 2012. The patients were chosen irrespective of age, sex, and body mass index. The studies were performed for several reasons, the most common being wrist pain (n = 56), followed by ganglion cyst (n = 11) and soft-tissue masses (n = 10). Available clinical data, imaging studies and actual clinical findings were investigated for abnormal findings that would raise the possibility of an anterior interosseous nerve neuropathy or of a cause that may damage the anterior interosseous nerve. Wrist ultrasound was performed following the guidelines proposed by the European Society of Skeletal Radiology [8]. Patients were placed with the dorsal wrist facing the examination table. After placing the probe over the palm on axial planes the transducer was moved cranially to fully identify the pronator quadratus. Probe orientation was adjusted accordingly to avoid muscular anisotropy artifacts. Tilting movements of the probe optimized depiction of pronator quadratus echotexture. Flexor digiturum superficialis, profundus and flexor pollicis longus muscles were considered for comparison. The examination was conducted form the elbow to the wrist visualizing the interosseous membrane and artery (which is the landmark for the anterior interosseous nerve). This maneuver was done to rule out potential soft-tissue masses compressing the anterior interosseous nerve. Every US examination was performed with commercially available equipment (iU22, Philips, the Nederlands) and 12-7 MHz and 17-5 MHz transducers. Pronator quadratus muscle fatty infiltration was assessed by evaluating its echogenicity and echostructure. The echogenicity and echostructure of the pronator quadratus muscle was evaluated as normal or atrophic (homogeneously hyperechoic and loss in bulk). Pronator quadratus muscles with slight loss of normal pattern with very poor fatty streaks were included in the normal group. Two radiologists, one with 7 years of musculoskeletal radiology experience and one with 2 years of musculoskeletal radiology experience, performed the studies independently. Each radiologist noted, subjectively, whether there was atrophy within the pronator quadratus. Quantitative evaluation of fatty atrophy was also performed using a software (MedDensity 1.0® ) previously used for other muscular fatty infiltration evaluation [10]. Results were analyzed with descriptive statistic.
Fig. 1. Cadaveric view of the pronator quadratus and interosseous membrane with the flexor digitorum profundus and flexor pollicis longus moved upward (a). In (b) the nerve branch of the anterior interosseous nerve reaching the pronator quadratus is visible (yellow mark). Red mark: artery.
3. Results 3.1. Anatomical correlation Dissection showed that the distal part of the anterior interosseous nerve enters the pronator quadratus muscle and may have some variable branches reaching the connective tissue and the interosseous membrane (Fig. 1). 3.2. Patients Ultrasonographic signs of pronator quadratus atrophy were present in 7/100 (7%) of patients examined (Fig. 2). None of the patients had a bilateral atrophy of the pronator quadratus muscle. Both radiologists were concordant with these findings. In the patients with echogenicity of the pronator quadratus classified as atrophic (homogeneously hyperechoic), adjacent flexor muscles resulted normal. There was no significant difference between males and females (3 females vs 4 males) (p = 0.506). Quantitative evaluation (Fig. 3) showed that the difference in fatty infiltration between normal muscles and atrophic muscles was approximately 35% (p = 0.05). 4. Discussion US diagnosis of anterior interosseous neuropathy, the so called Kiloh–Nevin syndrome, may be suggested by loss in bulk and increased reflectivity of the innervated muscles: the flexor pollicis longus, the flexor digitorum profundus and the pronator quadratus
528
A. Tagliafico et al. / European Journal of Radiology 82 (2013) 526–529
Fig. 2. (a–d) axial (a) and longitudinal (b) US image of a normal pronator quadratus. Axial (c) and longitudinal (d) US image of an atrophic pronator quadratus.
[4]. These findings may be present both in primary or secondary syndromes. On MRI, anterior interosseous neuropathy is evident when on T2-weighted fat-suppressed or STIR images increased signal intensity in the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus muscles is visible [9]. However, it has been demonstrated that on MRI increased signal intensity of the pronator quadratus muscle is a frequent normal finding of unclear etiology and not related to disease [7]. On MRI it has been estimated that the signal intensity of the pronator quadratus was greater than that of an adjacent flexor muscle in 79 of 100 MRI examinations [7]. Intramuscular increased signal intensity on fluid-sensitive sequences is one of the MRI features of muscular denervation. In anterior interosseous nerve injury, denervationrelated alterations are evident at the pronator quadratus, flexor pollicis longus, or radial aspect of the flexor digitorum profundus muscles. In concordance with MRI findings, our study reveals that, on US, asymptomatic denervation-like alterations such increased reflectivity and loss in bulk of the pronator quadratus muscle may be isolated and not related to anterior interosseous neuropathy.
The criteria to define pronator quadratus atrophy on ultrasound were kept compatible with the current clinical practice: only visible atrophic muscles were included. On the base of our study, it is not possible to identify or suppose a definite reason for this phenomenon. Clarification of the etiology of pronator quadratus atrophy in patients without anterior interosseous neuropathy was beyond the purpose of our study. Some hypothesis, however, should be made: the first is that the pronator quadratus plays only a minor role in pronation. The main muscle that guarantees the pronation of the forearm is the pronator teres and the pronator quadratus play a minor role. Animals that live and travel in trees displayed a well-developed pronator quadratus to support travel and maintain balance on trees [11]. It is possible that in non-active individuals this muscle loses bulk so that it becomes atrophic due to poor utilization. Moreover, genetic, occupational factors and anatomical variants in the innervation may also be responsible of this phenomenon. The anatomical oblique disposition of pronator quadratus muscular fibers respect to other flexor tendons may have influenced the
Fig. 3. Screen shot showing the software interface (MedDensity 1.0, 3TC Engineering) used to make quantitative assessment of intramuscular fat in pronator quadratus muscle.
A. Tagliafico et al. / European Journal of Radiology 82 (2013) 526–529
echogenicity of the muscle but it is not responsible of muscle loss in bulk. Neuropathy of the branch of the anterior interosseous nerve directed to the pronator quadratus muscle is another possible, although unlikely, explanation. However, every patient involved had a negative neurological examination. We believe that the reason for this finding is still unknown. The pronator quadratus is an important reference structure for measuring the dimensions of the median nerve, therefore care should be taken in case of atrophy. This study has limitations. First, only a-symptomatic patients were included and no patients with Kiloh–Nevin syndrome were included. Second, no surgical correlate was obtained for obvious reasons. In conclusion, we found that atrophy of the pronator quadratus may be present in patients with no anterior interosseous nerve syndrome and may be not related to any pathological condition known today. References [1] Kiloh LG, Nevin S. Isolated neuritis of the anterior interosseous nerve. British Medical Journal 1952;1:850–1.
529
[2] Tagliafico A, Rubino M, Autuori A, Bianchi S, Martinoli C. Wrist and hand ultrasound. Seminars in Musculoskeletal Radiology 2007;11(2):95–104. [3] Martinoli C, Perez MM, Padua L, et al. Muscle variants of the upper and lower limb (with anatomical correlation). Seminars in Musculoskeletal Radiology 2010;14(2):106–21. [4] Grainger AJ, Campbell RSD, Stothard J. Anterior interosseous nerve syndrome: appearance at MR imaging in three cases. Radiology 1998;208:381–4. [5] Hide IG, Grainger AJ, Naisby GP, et al. Sonographic findings in the anterior interosseous nerve syndrome. Journal of Clinical Ultrasound 1999;27:459–64. [6] Martinoli C, Bianchi S, Pugliese F, et al. Sonography of entrapment neuropathies in the upper limb (wrist excluded). Journal of Clinical Ultrasound 2004;32:438–50. [7] Gyftopoulos S, Rosenberg ZS, Petchprapa C. Increased MR signal intensity in the pronator quadratus muscle: does it always indicate anterior interosseous neuropathy? AJR: American Journal of Roentgenology 2010;194(2):490–3. [8] Martinoli C. Musculoskeletal ultrasound: technical guidelines. Insight into Imaging 2010;1(3):99–141. [9] Andreisek G, Crook DW, Burg D, Marincek B, Weishaupt D. Peripheral neuropathies of the median, radial, and ulnar nerves: MR imaging features. Radiographics 2006;26(5):1267–87. [10] Tagliafico AS, Ameri P, Bovio M, et al. Relationship between fatty degeneration of thigh muscles and vitamin D status in the elderly: a preliminary MRI study. AJR: American Journal of Roentgenology 2010;194(3):728–34. [11] Larson SG, Stern Jr JT. Maintenance of above-branch balance during primate arboreal quadrupedalism: coordinated use of forearm rotators and tail motion. American Journal of Physical Anthropology 2006;129(1):71–81.