Published online Apr 26, 2023.
https://doi.org/10.3988/jcn.2022.0206
Ultrasonographic Evaluation of the Optimal Needle Position in the Supinator Muscle
Abstract
Background and Purpose
Investigating the supinator muscle (SUP) is important for diagnosing radial neuropathy or cervical radiculopathy in needle electromyography (EMG). However, different authors have proposed several locations for needle EMG placement in the SUP. This study aimed to determine the optimal needle insertion position for examining the SUP via needle EMG under ultrasonographic guidance.
Methods
This study included 16 male (32 upper limbs) and 15 females (30 upper limbs). In the supine position, the line connecting the midpoint of the dorsal wrist to the upper margin of the radial head (RH) (RH_WRIST line) was measured while the forearm was pronated. Under ultrasonographic guidance, the thickness of the SUP was measured at 1-cm intervals from the RH to 4 cm along the RH_WRIST line. Moreover, the horizontal distance (HD) from the RH_WRIST line to the posterior interosseous nerve (PIN) and the distance from the RH to the point where the RH_WRIST line and the PIN intersected (VD_PIN_CROSS) were measured.
Results
VD_PIN_CROSS was 51.25±7.0 mm (mean±SD). The muscle was the thickest at 3 cm (5.6±0.8 mm) and 4 cm (5.4±1.0 mm) from the RH. The distances from the PIN to these points were 14.1±3.9 mm and 9.0±4.3 mm, respectively.
Conclusions
Our findings suggest that the optimal needle placement is at 3 cm from the RH.
INTRODUCTION
The brachioradialis or extensor carpi radialis (ECR) longus muscles are often sampled when identifying lesions between the spiral groove of the radius and the arcade of Frohse. However, it may be helpful to examine the supinator muscle (SUP) to determine whether a lesion is present before or after the point where the radial nerve divides into the superficial sensory and deep motor branches. The ECR brevis has many anatomical variations and is not conducive to localization. Therefore, if the ECR longus is normal and the SUP is abnormal, the lesion can be considered to be near to the branching point of the radial nerve.1
However, different authors have proposed several locations for needle placement in electromyography (EMG) in the SUP. Perotto and Delagi2 suggested the radial side of the distal biceps tendon. Lee and DeLisa3 suggested conducting EMG at the gap between the ECR and the extensor digitorum (ED) in the proximal third of the forearm. Chu-Andrews and Johnson proposed a location 3 cm distal from the radial head (RH) along the ED.4
Needle EMG is a relatively safe examination that rarely results in hematoma due to needle injury.5 However, there is one report of hematoma often occurring in the superficial muscles (lumbar paravertebral, ED, and tibialis anterior) when the patient is taking oral anticoagulants.6 The SUP has a higher risk of events such as neurovascular injury or unwanted muscle examination because it is located deep and the posterior interosseous nerve (PIN) and artery pass between the SUP. In particular, in the case of a volar approach such as the method proposed by Delagi, special attention is required because of the short distance between the insertion into the biceps tendon and the superficial radial nerve.7, 8 Additionally, Lee and DeLisa3 suggested that the ED and ECR should be contracted to identify the muscle, and the needle would then be inserted between them. However, it can be difficult to identify the muscle in cases of severe neuropathy and radiculopathy.
Developments in ultrasonography have led to many methods being proposed for visualizing difficult-to-examine muscles.9, 10 Structures such as the SUP and PIN can be accurately identified using ultrasonography. However, needle EMG using ultrasonography is a time-consuming process.
In a previous cadaveric study, the needle was found to be safely inserted without damage to the PIN at a point 3 cm distal to the line connecting the RH and the midpoint of the dorsal wrist.7 In the present study, we aimed to determine whether the location identified in that study could be a safe distance from the PIN in healthy people and whether it provides an appropriate muscle thickness for ultrasonographic examination.
METHODS
Participant recruitment
The study participants comprised 31 adults. There were no abnormal findings in neurological examinations and no medication use among them. Potential participants were excluded if they had a forearm injury, a history of surgery, or a diagnosis of upper-extremity neuropathy. The weight, height, body mass index (BMI), and forearm length of each participant were measured. The study protocol was approved by the Institutional Review Board (IRB No. 2020AS0184), and written informed consent was obtained from all participants.
Ultrasonographic examinations
High-resolution real-time ultrasonography was performed by an expert physiatrist using the Accuvix V20 system (Samsung Medison, Seoul, South Korea) with a 5- to 13-MHz linear-array transducer. Each ultrasonographic examination of the proximal forearm was performed with the subject in the supine position while the forearm was pronated. An imaginary line (RH_WRIST line) was drawn from the upper margin of the RH to the midpoint of the dorsal wrist (midwrist). The thickness of the SUP (T_SUP1 to T_SUP4) and the horizontal distance (HD) to the PIN (HD_PIN1 to HD_PIN4) were measured at 1-cm intervals from the RH at four points (RH_1 to RH_4) along the RH_WRIST line (Figs. 1 and 2). The vertical distance was also measured from the RH to the intersection of the PIN and RH_WRIST lines (VD_PIN_CROSS).
Fig. 1
The ultrasonographic examinations were performed with the proximal forearm in the supine position while the forearm was pronated. The line (RH_WRIST line) connecting the upper margin of the RH and the midpoint of the dorsal wrist (midwrist) was drawn. The thicknesses of the supinator (T_SUP1 to T_SUP4) and the horizontal distances the PIN and the needle (HD_PIN1 to HD_PIN4) to the PIN were measured at 1-cm intervals from the RH at four points (RH_1 to RH_4) along the RH_WRIST line. The distance from the RH to the intersection of the PIN and RH_WRIST lines (VD_PIN_CROSS) was measured. PIN, posterior interosseous nerve; RH, radial head.
Fig. 2
Short-axis ultrasonography view of the SUP and PIN. The needle insertion point and PIN are marked with red and yellow dots, respectively (A and B). The thickness of SUP (T_SUP) were defined as the distance between the superficial and deep muscle layers (A). The horizontal distances between the PIN and the needle (HD_PIN) were measured at four points (RH_1 to RH_4) at 1-cm intervals from the RH (B). PIN, posterior interosseous nerve; RH, radial head; SUP, supinator muscle.
Statistical analysis
The minimum, maximum, and mean±SD were calculated for each variable. To quantify the relationships among weight, height, and lengths of the RH_WRIST line and VD_PIN_CROSS, Pearson product-moment correlation coefficients were calculated. Analysis of variance was performed to determine if the mean SUP thickness (T_SUP1 to T_SUP4) and PIN (HD_PIN1 to HD_PIN4) distance differed significantly among the four groups. Equal variance was determined using Levene’s test, which did not yield any evidence of unequal variances among the groups. Repeated-measures analysis of variance was performed to compare the means among variables, followed by Tukey’s honestly significant difference test and a post-hoc test for individual comparisons. All statistical analysis results were two-tailed, and differences for which p<0.05 were considered significant. All statistical analyses were performed using R software (version 4.0.5, R Project for Statistical Computing, Vienna, Austria).
RESULTS
The measured values are listed in Table 1. The coefficients for the correlations of VD_PIN_CROSS with the length and height of the RH_WRIST line were 0.37 (p<0.05) and 0.34 (p<0.05), respectively (Fig. 3). VD_PIN_CROSS was 51.25±7.0 mm. T_SUP1 to T_SUP4 increased until 3 cm from the RH. T_SUP3 was 5.6±0.8 mm and T_SUP4 was 5.4±1.0 mm. The thickness did not differ significantly between 3 cm and 4 cm from the RH (p>0.05). The distance from the RH_WRIST line to the PIN (HD_PIN) decreased between HD_PIN1 and HD_PIN4. HD_PIN3 and HD_PIN4 were 14.1±3.9 mm and 9.0±4.3 mm, respectively (Fig. 4).
Fig. 3
The coefficient for the correlation between the length of RH_WRIST and VD_PIN_CROSS was 0.37 (p<0.05), which indicated a positive relationship (A). The coefficient for the correlation between height and VD_PIN_CROSS was 0.34 (p<0.05), which indicated a positive relationship (B). RH_WRIST, the line connecting the midpoint of the dorsal wrist to the upper margin of the radial head; VD_PIN_CROSS, the vertical distance from the RH to the intersection of the PIN and RH_WRIST lines.
Fig. 4
SUP thickness on the RH_WRIST line (T_SUP) increased as the distance from the RH increased (RH_1 to RH_4). (A) Using host hoc analysis with the Tukey's test, T_SUP had statistically significant differences among the measurement levels except between RH3 and RH4 (*p<0.001). The horizontal distance (HD_PIN) from the RH_WRIST line to the posterior interosseou nerve decreased as the distance from the RH increased (RH_1 to RH_4). (B) Using host hoc analysis with the Tukey's test, HD_PIN had statistically significant differences among all measurement levels (p<0.001). T_SUP1, T_SUP2, and T_SUP3 each had a statistically significant difference in thickness; T_SUP3 and T_SUP4 did not show significant differences. RH, radial head.
Table 1
Demographic and ultrasonographic parameters of the supinator muscle and posterior interosseous nerve
DISCUSSION
This study confirmed the most-suitable position for examining the SUP among the various previously proposed methods. A point 3–4 cm distal from the RH along the RH_WRIST line was considered a safe location in a previous cadaveric study.7 In another cadaveric study, L_CROSS in the cadaver (corresponding to VD_PIN_CROSS, 51.25±7.0 mm) had a median of 50.95 mm (range=35.5–64.6 mm), and W_PIN_Inj (corresponding to HD_PIN3, 14.1±3.9 mm) had a median of 14.6 mm (range=10.0–20.4 mm). The measurements in the present study did not differ significantly from those in the previous cadaver study.
In the present study, 4 cm was the minimum distance between RH and the intersection of the RH_WRIST line and the PIN (VD_PIN_CROSS). We confirmed that the distance between the RH_WRIST line and the PIN decreased as the distance from the RH increased. The safest location for needle insertion was near the RH. However, EMG is more accurate when the needle is placed in a thicker part of the muscle. The SUP was thickest at 3 cm and 4 cm distal to the RH, and the differences between these points were not significant. The position with the optimal SUP thickness upon securing the distance from the PIN was therefore 3 cm away from the RH.
VD_PIN_CROSS was positively correlated with the length of the RH_WRIST line (Fig. 3). This means that if the forearm is long, VD_PIN_CROSS will be positioned further from the RH. No significant relationship with weight or BMI was noted.
The above results were more similar to those of the Chu-Andrews method4 than to other published methods. The Chu-Andrews method4 involves needle insertion into the tendinous origin of the ED muscle at 3 cm from the RH. However, identifying the ED in patients with severe cervical radiculopathy or radial neuropathy may be difficult when employing this method. This also applies to the Lee and DeLisa3 method, in which the needle is inserted between the ECR and ED; using this method may restrict the ability to identify muscles. However, the muscle was not considered a landmark in our method. This test is possible if the midpoint of the dorsal wrist is identifiable and the RH is palpable, and is therefore even more convenient. This method can ensure sufficient SUP thickness, and its use is safe and valuable for examining the muscle in patients with neuropathy without requiring a muscle landmark.
Study limitations
Our study had several limitations. First, it assumed that the RH is palpable, which may not be the case in patients with obesity. Among the participants in our study, the highest BMI was 28.38 kg/m2 and no problem in palpating the RH was encountered; however, it may not be possible in the case of patients with obesity (BMI >30 kg/m2). Second, since the midpoint of the wrist must be connected, there may be limitations in cases with an amputation or a cast to remediate a forearm injury.
In conclusion, considering HD_PIN and T_SUP, performing the examination at a distance of 3 cm from the RH would be the safest and most efficient method.
Author Contributions:
Conceptualization: Dong Hwee Kim.
Data curation: Hong Bum Park, Ki Hoon Kim.
Formal analysis: Hong Bum Park, Chae Hyeon Ryou.
Methodology: Chae Hyeon Ryou.
Supervision: Dong Hwee Kim.
Validation: Ki Hoon Kim, Dong Hwee Kim.
Writing—original draft: Hong Bum Park, Chae Hyeon Ryou.
Writing—review & editing: Ki Hoon Kim, Dong Hwee Kim.
Conflicts of Interest:The authors have no potential conflicts of interest to disclose.
Funding Statement:This work was supported by the Korea University grants (grant number K2212031).
Availability of Data and Material
The datasets generated or analyzed during the study are not publicly available because they contain personal information of the subjects. But are available from the corresponding author on reasonable request.
References
-
Preston DC, Shapiro BE. In: Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations. 3rd ed. Philadelphia, PA: Elsevier; 2012. pp. 414-440.
-
-
Perotto A, Delagi EF. In: Anatomical guide for the electromyographer: the limbs and trunk. 5th ed. Springfield, IL: Charles C Thomas Publisher; 2011. pp. 93-94.
-
-
Lee HJ, DeLisa JA. In: Manual of nerve conduction study and surface anatomy for needle electromyography. 4th ed. Philadelphia, PA: Lippincott Wilkins & Williams; 2005. pp. 180-181.
-
-
Chu-Andrews J, Johnson RJ. In: Electrodiagnosis: an anatomical and clinical approach. Philadelphia, PA: Lippincott; 1986. pp. 315-320.
-
