Int J Clin Exp Med 2019;12(12):13981-13992www.ijcem.com /ISSN:1940-5901/IJCEM0103951

Original ArticleAnatomical localization of nerve entry points and centers of intramuscular nerve dense region in quadriceps femoris and its significance in blocking muscle spasticity

Yanrong Li1, Fei Chen1, Jie Wang1, Guoming Zhang2, Yanfei Liu3, Shengbo Yang1

1Department of Anatomy, Zunyi Medical University, Zunyi, People’s Republic of China; 2Department of Radiology, 3Key Laboratory of Cell Engineering of Guizhou Province, The First Affiliated Hospital of Zunyi Medical University, Zunyi, People’s Republic of China

Received September 7, 2019; Accepted November 11, 2019; Epub December 15, 2019; Published December 30, 2019

Abstract: This study aimed to determine the body surface locations and depths of the nerve entry points (NEPs) and the centers of the intramuscular nerve dense region (CINDRs) of the quadriceps femoris. Twelve adult cadavers were dissected. The curves connecting the greater trochanter with the pubic tubercle and with the lateral femoral epicondyle were designated as the horizontal (H) and longitudinal (L) reference lines, respectively. NEP was ana-tomically exposed. Sihler’s staining, barium sulfate, and computed tomography (to determine projection points (P) on the body surface) were employed. The intersection of the longitudinal line through P point and the H line and the horizontal line through P point and the L line were recorded as PH and PL, respectively. The projection of NEP or CIN-DR in the opposite direction across the transverse plane was P’. Percentage positions of PH and PL on lines H and L and NEP and CINDR depths were determined under the Syngo system. Two NEPs were identified in each muscle. For the rectus femoris, vastus intermedius, vastus lateralis, and vastus medialis, their PH were located at 56.79% and 65.90%, 56.90% and 57.89%, 42.51% and 43.81%, and 77.67% and 81.74% of line H; PL were at 5.92%, 16.64%, 6.50%, 8.99%, 16.68%, 34.89%, 42.84%, and 48.28% of line L; depths were at 14.00%, 14.70%, 18.96%, 19.73%, 21.53%, 25.76%, 21.70%, and 17.18% of line PP’, respectively; and they had two, one, one, and one intramuscular nerve dense region, respectively. PH of CINDRs were located at 60.63%, 63.39%, 59.95%, 45.30%, and 78.97% of line H; PL were at 20.95%, 57.59%, 42.45%, 49.14%, and 61.63% of line L; and depths were at 12.16%, 11.73%, 26.31%, 34.46%, and 19.28% of line PP’, respectively. Awareness of these positions and depths can improve the localization efficiency and efficacy of blocking targets for quadriceps femoris spasticity.

Keywords: Quadriceps femoris, spasticity, nerve entry point, intramuscular nerve dense region, target localization

Introduction

The quadriceps femoris includes the rectus femoris, vastus intermedius, vastus lateralis, and vastus medialis, which can extend the knee joint, bend the hip joint, and help in stabi-lizing the knee joint, slowing down the speed at which the calcaneus contacts the ground, and reducing the collision between the knee arti- cular surfaces during normal walking [1, 2]. However, muscle spasticity may occur with stroke, traumatic brain or spinal cord injury, or lateral sclerosis of the spinal cord [3-7]. Sp- asticity of the quadriceps femoris will lead to

difficulties in knee joint stability, knee bending, stepping, etc., which will seriously affect the daily life of patients [8].

At present, many methods are used to treat quadriceps muscle spasticity, such as oral medications [9, 10], partial tendon detachment or extension by surgery [11], selective neurec-tomy [12-14], extramuscular neurolysis by in- jecting phenol or ethanol into the extramuscu-lar nerve trunk or nerve branch, and chemical nerve block by injecting botulinum toxin A (BTX-A) intramuscularly [15, 16]. The latter two meth-ods are especially effective and commonly

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used. However, the precondition of applying these two methods to achieve therapeutic effect lies in the accurate localization of the blocking targets. Although clinicians can rough-ly inject drugs to the target site by palpation, electromyography, ultrasonography, and elec-trical stimulator, etc., they still experience diffi-culties in accurately identifying the location of the blocking target [17-19], avoiding pain caused by exploratory puncture, and grasping the puncture depth, thereby generating some undesirable complications, such as muscle fibrosis, contracture, and antibody formation [15]. Therefore, accurate localization of block-ing targets becomes the key factor for the suc-cessful implementation of these two treatment methods.

Studies have shown that neurolysis by injecting phenol or ethanol into the extramuscular nerve trunk can lead to non-spastic muscle involve-ment and paresthesia [17, 20]. The nerve entry point (NEP) is relatively close to the motor end-plate, so injection at this point is more favor-able for nerve regeneration to the motor end-plate area [4]. BTX-A relieves muscle spasticity by inhibiting acetylcholine release from the pre-synaptic membrane at the motor endplate [21-23]. However, staining of motor endplates re- quires fresh specimens. Since the quadriceps femoris is the largest muscle in the body, this may be the reason why staining the motor end-plate band of the quadriceps femoris has not been studied. Fortunately, some studies have reported that the location of the intramuscular nerve dense region (INDR) is consistent with that of the motor endplate band [24-26] and can be used as a substitute target for the motor endplate band.

Given the aforementioned gap in research, this study aimed to accurately determine the body surface puncture locations and depths of the NEPs and the centers of the intramuscular nerve dense region (CINDRs) of the quadriceps femoris to improve the efficiency and efficacy of blocking target localization for quadriceps fem-oris spasticity. We hoped to achieve this by using barium sulfate, spiral computed tomogra-phy (CT), and three-dimensional reconstruc-tion, and by accurately localizing the body sur-face positions and depths of NEP and CINDR of the quadriceps femoris under the Syngo sys- tem.

Materials and methods

Specimens and ethics

In this study, 12 formaldehyde-fixed cadavers (six men and six women) aged 35-75 years and without histories of neuromuscular diseases and deformities in the lower extremities were examined. Cause of death for donors included: cancer, cardiovascular disease, and traffic acci-dents. None of the cadaver donors belonged to any vulnerable groups, and all donors or their immediate family members had provided free written informed consent. The protocol of this study was approved in advance by the Ethics Committee of our university (Approval No.: #2016-1-006).

Gross anatomy observation, measurement, and reference line design

Oblique (from the anterior superior iliac spine to the pubic tubercle), horizontal (at the level of the tibial tuberosity), and longitudinal (from the anterior superior iliac spine to the fibular head through the greater trochanter) incisions were made. The skin and subcutaneous layer were cut as one layer and turned inward to the poste-rior femoral region. The origin and insertion points of the muscle were exposed. The arr- angement of muscle fibers, source of nerve muscle branches, and presence of blood ves-sels at the NEP were observed. Muscle length, width, and thickness were measured using a Vernier caliper. The greater trochanter (a), pubic tubercle (b), and lateral femoral epicondyle (c) were selected as body surface markers. To con-veniently describe the superior-inferior and me- dial-lateral relationships between the NEP and CINDR of the quadriceps femoris and body sur-face markers, the curve between the greater trochanter and the pubic tubercle closed to the skin was designed as a horizontal (H) reference line, and the curve between the greater tro-chanter and the lateral femoral epicondyle was designed as a longitudinal (L) reference line.

Sihler’s intramuscular nerve staining

Twelve quadriceps femoris (six on the left and six on the right) were removed by cutting closely to the muscle origin and insertion, and Sihler’s staining process was carried out. For depig-mentation, 3% potassium hydroxide and 0.2%

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hydrogen peroxide solution were used for 4-5 weeks until the muscle mass was transparent or translucent. For decalcification, Sihler I solu-tion (one portion of glacial acetic acid + two portions of glycerol + 12 portions of 1% chloral hydrate) was applied for 4-5 weeks; the solu-tion was changed once a week until the retract-ed muscle mass was stretched again. For stain-ing, the specimens were immersed in Sihler II staining solution (one portion of Ehrlich’s hema-toxylin solution + two portions of glycerol + 12 portions of 1% chloral hydrate) for 4 weeks, which was changed once during the staining period. For the decolorization process, Sihler I solution was used for 4-20 h, ideally until the muscle turned lavender and the nerve branch-es were black. For neutralization, 0.05% lithium carbonate solution was used for 2 h and stirred. Prior to the above steps, specimens were wa- shed with running water for 30 min. For trans-parency, the specimens were placed in glycerol for 1 week with a stepwise gradient increment (i.e., 40%, 60%, 80%, and 100%). The intra-muscular nerve distribution pattern was ob-served under X-ray reading lamp. The percent-age positions of the CINDRs on the muscle length and muscle width were measured with a Vernier caliper. Photographs were taken, and the pattern was plotted. The pattern plot was restored to the corresponding position of the human skeleton according to its corresponding proportion.

Spiral CT localization of NEP and CINDR

The right quadriceps femoris and NEPs of six cadavers, left quadriceps femoris, and NEPs of the other six cadavers were anatomically exposed. Muscle length, width, and thickness were measured. By combining the results of Sihler’s staining process, the corresponding position of the CINDR was found, NEP and CINDR were labeled with barium sulfate (1 ml of glue: 4 g of medical barium sulfate powder), mixed with 801 glue (Wenzhou 801 Glue Company, China), dried by heat, and sutured layer by layer in situ. A needle was inserted at each of the body surface markers a, b, and c. A barium sulfate-soaked silk thread was sutured on the skin between ab and ac to represent lines H and L, respectively. Three-dimensional reconstruction was conducted by 16-row spiral CT (Siemens, Germany) with a collimation of 64 mm, a layer thickness of 1 mm, a pitch of 1:1, automatic tube milliampere current, and a voltage of 120 kV. Under the Syngo system

(Siemens, Germany), on the transverse section, the first white point, i.e., barium sulfate-labeled NEP or CINDR, was searched for from the distal end to the proximal end of the lower limb.

According to the results, each of the four heads of the quadriceps femoris had two NEPs. In this study, the NEPs of the rectus femoris, vastus intermedius, vastus lateralis, and vastus medi-alis were labeled NEP1a, NEP1b, NEP2a, NEP2b, NE- P3a, NEP3b, NEP4a, and NEP4b, respectively. Th- ere were two CINDRs in the rectus femoris and one in each of the other three heads, so CINDRs were named CINDR1a, CINDR1b, CINDR2, CINDR3, and CINDR4, respectively. Under the same bed indicator light, the projection points (P) of a NEP or CINDR on the body surface were localized by CT and percutaneous needle puncture perpen-dicular to the coronal plane, and the puncture points were P1a, P1b, P2a, P2b, P3a, P3b, P4a, and P4b or P1a, P1b, P2, P3, and P4. CT was performed ag- ain for three-dimensional reconstruction, and lengths of lines H and L were measured using curve measuring tools along the skin surface on the transverse and coronal sections. The intersection point of the longitudinal line th- rough point P and line H was denoted as PH, the intersection point of the horizontal line through point P and line L was denoted as PL, the length of the curve between point a and PH was denot-ed as H’, and the length of the curve between point a and PL was denoted as L’. H’/H×100% and L’/L×100% were calculated, and the per-centage positions of a NEP or CINDR on the body surface were determined. On the trans-verse section, the point where P was projected onto the skin of the opposite direction after passing through a NEP or CINDR was defined as P’, the lengths of P-NEP or P-CINDR and PP’ were measured by a straight line tool, and P-NEP (P-CINDR)/PP’ ×100% was calculated to determine the percentage puncture depth. After localization, the quadriceps femoris was removed, and Sihler’s staining of intramuscular nerves was performed to verify whether the morphology and position of the INDR were con-sistent with those on the contralateral side and whether barium sulfate labeling was accurate and to exclude individual variants.

Statistical processing

Measured data are expressed as percentage (n%) to eliminate the influence of individual dif-

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ferences. SPSS17.0 (SPSS Inc., Chicago, IL, USA) was used to process the data. The paired t-test was used for comparison between the left and right sides, and the independent sam-ple t-test was used for comparison between male and female cadavers. The significance level was α=0.05.

Results

Gross anatomy findings

The muscle fibers in the four heads of the quad-riceps femoris are arranged in pennate shapes, and their innervation originates from the femo-ral nerve. The femoral nerve enters the thigh from the deep surface medial to the midpoint of the inguinal ligament and travels for 3-5 cm to form broom-like branches. Among them, usually, two muscular nerve branches domi-nate each head of the quadriceps femoris, named as the upper branch and the lower branch, i.e., each head has two NEPs. The NEPs of the rectus femoris are located on the deep surface on the lateral side of the mid-upper part of the muscle. The NEPs of the vastus intermedius are located on the superficial sur-face on the lateral and medial sides of the upper part of the muscle. The NEPs of the vas-tus lateralis are located on the superficial sur-face on the lateral side of the mid-upper part of the muscle. The NEPs of the vastus medialis are located on the superficial surface of the upper end of the muscle and the superficial surface on the medial side of the middle part of the muscle. Each NEP has accompanying blood vessels (Figure 1).

Spiral CT and NEP localization

Barium sulfate-labeled NEPs, reference lines, and bone landmarks are shown as white color in CT images. The puncture positions of the injection needles were the positions where the NEPs were projected on the skin. The lengths of lines H and H’ as well as lines L and L’ can be measured using curve measuring tools in the two-dimensional images of the transverse and coronal sections, respectively, and the lengths of P-NEP and PP’ can be measured with straight

Figure 1. Nerve entry point (NEP) of the right quad-riceps femoris shown by gross anatomy. RF, rectus

femoris; VL, vastus lateralis; VI, vastus intermedius; VM, vastus medialis. Blue, red, green, and white dots represent the NEPs of the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis, respectively.

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found between the left and right sides or between male and female cadavers (P>0.05).

Distribution pattern of intra-muscular nerves in the quadri-ceps femoris

Rectus femoris: After the supe-rior nerve branch innervating this muscle enters the rectus femoris, it is usually divided into two primary nerve branch-es, which travel obliquely in the inferolateral direction and be- gin to project arborized bran- ches at approximately 15.08% of the muscle length. After entering the muscle, the inferi-or nerve branch is usually divided into three primary nerve branches, among which the first primary branch travels in the lateral direction and then travels in the inferolateral direction to 48.41% of the muscle length. The branches of the primary branch along the way are anastomosed with the branches of the superior nerve branch to form INDR1a; the second and third primary branches descend on the medial side of the muscle parenchyma and are densely branched at 63.10%-79.37% of the muscle length, anasto-mosing with each other to form INDR1b. The area of these two nerve dense regions and the positions of the central points on muscle length and muscle width are shown in Figure 3 and Table 2.

Vastus intermedius: After the superior and infe-rior nerve branches enter the muscle, they descend to 34.85%-55.37% level of the muscle length and send out abundant arborized branches oblique to both sides, forming INDR2 (Figure 4).

Vastus lateralis: After the superior and inferior nerve branches enter the muscle, the nerve branches at all levels travel toward the infero-

Figure 2. CT localization image of the nerve entry point of the right quad-riceps femoris (e.g., NEP4b). A: Spiral CT three-dimensional reconstruction image shows the projection positions of NEPs on the body surface and the designed reference lines. B: Lengths of lines L and L4b’ measured on the coronal section cutting through line ac. C: Lengths of lines H and H4b’ mea-sured on the transverse section cutting through line H. D: Depth of N4b mea-sured on the transverse section passing through P4b. NEP, nerve entry point.

line tools on the transverse section. The local-ization of NEPs of the nerve branches in the vastus medialis was used as representative for explanation in this study (Figure 2A-D).

Table 1 shows the percentage positions of pro-jection points (P) on the body surface of the NEPs of each head of the quadriceps femoris projected on lines H and L and the percentage depth of NEP. No statistical difference was

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quadriceps femoris, the largest muscle in the whole body. By using barium sulfate to mark NEPs and CINDRs, spiral CT, three-dimensional reconstruction, and designing reference lines with bone landmarks, NEPs and CINDRs were more accurately localized on the body surface, and the puncture depths were obtained.

Muscle spasticity is one of the common clinical manifestations of many patients with central nervous system injury [27, 28]. Patients with muscular spasticity often have hypermyotonia of the upper limb flexors and lower limb exten-sors [22, 28]. The quadriceps femoris is a pow-erful extensor of the knee joint. Quadriceps femoris spasticity causes knee joint hyperex-tension, resulting in difficulties in knee bending and stepping and the “knee lock” phenomenon, with a circle-drawing gait and a tendency to fall, which affects walking [11, 29]. Therefore, one of the important problems that rehabilitation doctors need to solve urgently at present is to effectively relieve spasticity as soon as possi-ble and allow patients to have isolated move-ment, thus alleviating pain and restoring daily life of patients. However, in the clinical process of blocking muscle spasticity by drug injection, accurate localization of the blocking target is not yet possible.

With regard to blocking of an extramuscular nerve motor point for muscle spasticity, some researchers anatomically exposed the nerve branches of the rectus femoris, used as refer-ences lines the connection line from the inter-section point of the femoral nerve and the deep surface of the inguinal ligament to the midpoint of the superior edge of the patella as well as the connection line from the anterior superior iliac spine to the medial femoral condyle, and localized the positional relationship between the NEP and the two reference lines [30]. A study described the positional relationship between the nerve motor point of the vastus intermedius and the line connecting the inter-section point of the femoral nerve and the deep surface of the inguinal ligament with the mid-point of the superior edge of the patella [31]. Page et al. described the positional relationship between the nerve motor points of the four heads of the quadriceps femoris and the line connecting the intersection point of the femo-ral nerve and the deep surface of the inguinal ligament with the midpoint of the superior edge

lateral direction, perpendicular to the oblique arrangement of muscle fibers, and anastomose to form INDR3 at 25.73%-72.64% of the muscle length (Figure 4).

Vastus medialis: The superior nerve branch is relatively thin and branches after it enters the muscle, which mainly dominates the muscle fibers at the upper part of this head. Meanwhile, the inferior nerve branch is relatively thick and branches after it enters the muscle, which mainly shuttles among muscle bundles and forms INDR4 at the middle and lower parts of the muscle length (31.92%-80.13%) (Figure 4). The area of these three INDRs and the posi-tions of the CINDRs on the muscle length and muscle width are shown in Figure 4 and Table 2.

Spiral CT localization of CINDRs

Spiral CT localization images of CINDRs of the rectus femoris, vastus intermedius, vastus late-ralis, and vastus medialis are shown in Figure 5. In this study, the CINDR1a localization of the rectus femoris is taken as a representative for explanation (Figure 5). Table 3 shows the per-centage position of the projection point (P) on the body surface of the CINDR of each head of the quadriceps femoris projected on lines H and L and the percentage depth of CINDR. No statistical difference was noted between the left and right sides or between male and female cadavers (P>0.05).

Discussion

This study successfully demonstrated the in- tramuscular nerve distribution pattern of the

Table 1. Location of PH and PL of NEP on lines H and L, respectively, and depth of NEP (%)NEPs L’/L H’/H P-NEP/PP’NEP1a 5.92±0.19 56.79±1.40 14.00±0.72NEP1b 16.64±0.71 65.90±1.43 14.70±0.78NEP2a 6.50±0.29 56.90±1.43 18.96±0.61NEP2b 8.99±0.45 57.89±1.65 19.73±0.55NEP3a 16.68±0.86 42.51±1.21 21.53±0.80NEP3b 34.89±1.11 43.81±1.28 25.76±0.79NEP4a 42.84±1.13 77.67±1.81 21.70±0.66NEP4b 48.28±1.17 81.74±2.30 17.18±0.64NEP, nerve entry points.

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of the patella [32]. Although these anatomical studies provide useful information on the local-ization of blocking targets for extramuscular neurolysis by phenol or ethanol injection, the first two studies only described one of the four heads, and the medial-lateral relationship

between the motor points and body surface markers was expressed as an absolute value rather than as a percentage, the influence of individual differences could not be eliminated, and only one motor point was described. Page et al. considered localization of the motor

Figure 3. Intramuscular nerve distribution pattern of the right rectus femoris and positions of INDRs in the muscle. (A) Sihler staining process. Ruler: cm. (B) Schematic drawing of (A) and the positions of INDRs and CINDRs in the muscle. The red boxes represent INDRs, and the red dots represent CINDRs. CINDR, centers of the intramuscular nerve dense region.

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Table 2. Area of INDR in each head of the quadriceps femoris and percentage position of CINDR on muscle length and widthINDRs area (cm2) CINDR on muscle length (%) CINDR on muscle width (%)INDR1a 25.80±4.62 33.01±0.98 62.01±1.40INDR1b 12.06±2.73 70.90±1.40 35.38±1.04INDR2 31.89±5.29 45.37±1.07 42.21±1.16INDR3 75.30±12.56 48.93±1.10 75.46±1.46INDR4 63.17±11.85 55.36±1.11 18.92±0.59CINDR, centers of the intramuscular nerve dense region.

Figure 4. Intramuscular nerve distribution pattern of the right vastus intermedius, vastus lateralis, and vastus me-dialis, and positions of INDRs in the muscle. (A) Sihler’s staining process. Ruler: cm. (B) Schematic drawing of (A) and the positions of INDRs and CINDRs in the muscle. The red boxes represent INDRs, and the red dots represent CINDRs. CINDR, centers of the intramuscular nerve dense region.

points of the four heads at the same time and found that both the rectus femoris and vastus lateralis have two nerve motor points. However, Page’s study did not clarify the medial-lateral relationship between the motor points and body surface markers, on the contrary, it was inconsistent with the results of present study that each of the four heads had two nerve motor points. In addition, these studies failed to localize the motor points on the body sur-face, so the operability was not high.

In blocking intramuscular nerve motor points for muscle spasticity, Gallina described the absolute value of the positional relationship between the innervation zone of the vastus medialis and the line connecting the anterior superior iliac spine with the midpoint of the superior edge of the patella [33]. Kaymak defined the innervation area of the quadriceps femoris and the injection site of BTX-A through anatomy, cholinesterase staining, and electro-myography, taking the connection line between

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Table 3. Location of PH and PL of the CINDR on lines H and L, respectively, and depth of CINDR (%)CINDR L’/L H’/H P-CINDR/PP’CINDR1a 20.95±1.01 60.63±1.63 12.16±0.52CINDR1b 57.59±1.35 63.39±1.68 11.73±0.31CINDR2 42.45±1.33 59.95±1.38 26.31±0.78CINDR3 49.14±1.20 45.30±1.46 34.46±1.12CINDR4 61.63±1.56 78.97±1.71 19.28±0.86CINDR, centers of the intramuscular nerve dense region.

the anterior superior iliac spine and the patella of the patient as the reference line under ultra-

sound guidance. The results showed that the injection points of the rectus femoris are at 40% and 60% of the connection line, those of the vastus intermedius are at 50% and 65%, those of the vastus medialis are at 75% and 85% of medial to the connection line, and those of the vastus lateralis are at 50% and 65% of lateral to the connection line [29]. The positions of these targets are completely differ-ent from those described in the present study, which should be caused by the differ-ent reference lines.

BTX-A blocking of muscle spas-ticity is a dose-dependent chemical denervation in the action site of the motor end-plate [26], and its efficacy de- pends on the distance bet- ween the injection needle and the motor endplate. Upon BTX-A injection into the mus-cle, BTX-A immediately spread within a few centimeters near the needle tip [34]. If the posi-tion of the BTX-A injection point deviates from the motor end-plate by 1 cm, the anti-spasm effect will be directly reduced by 50% [23]. Therefore, CINDRs were used as targets in this experiment. Studies have sh- own that 1 U of BTX-A can infil-trate 1.5-3 cm, and 2.5-5 U can infiltrate 4.5 cm [35]. Currently, the clinical dosage

of BTX-A injected for quadriceps femoris spas-ticity is 100-200 U [8, 36-38].

The results of the present study show that the areas of the five INDRs in the quadriceps femo-ris are 25.80±4.62 cm2, 12.06±2.73 cm2, 31.89±5.29 cm2, 75.30±12.56 cm2, and 63.17±11.85 cm2, respectively. This means that as long as the injection location is accu-rate, only 7-15 U of BTX-A needs to be injected into the rectus femoris, the vastus intermedius needs 6-12 U, the vastus lateralis needs 15-30 U, and the vastus medialis needs 13-25 U to achieve relatively good efficacy. This will greatly save the dosage and cost of drugs.

Figure 5. CT image of the center of intramuscular nerve dense region of the left quadriceps femoris (e.g., CINDR1a). A: Spiral CT three-dimensional reconstruction image shows the projection positions of the CINDR on the body surface and the designed reference lines. B: Lengths of lines L and L1a’ measured on the coronal section through line ac. C: Lengths of lines H and H1a’ measured on the transverse section through line H. D: Depth of CINDR1a measured on the transverse section through P1a. CINDR, centers of the intramuscular nerve dense region; CT, computed tomography.

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The results of this experiment suggest that when clinicians need to perform extramuscular neurolysis and intramuscular chemical nerve blocking, the NEP and CINDR localization results in this paper can be used as reference, respectively. During localization, the length of the curve from the greater trochanter to the femoral epicondyle can be measured with a tape ruler against the skin, and a horizontal line can be drawn at the corresponding percentage position. Then, the curve length is measured from the greater trochanter to the pubic tu- bercle, and a longitudinal line is drawn at its corresponding percentage position. The inter-section of the two lines on the skin is the punc-ture point (point P) on the body surface. Then, the length of line PP’ perpendicular to coronal plane through point P is measured using a pel-vis measuring instrument, and the correspond-ing percentages were multiplied to obtain th- eir puncture depths. Notably, when injecting drugs for extramuscular neurolysis, the syringe plunger needs to be pumped back to prevent drugs from straying into accompanying blood vessels.

In this study, during data measurement, curve measurement close to the skin was adopted, and the results were expressed as percentages in the same individual. The results obtained are accurate and have strong operability, which provide a scientific basis for improving the effi-ciency and efficacy of treatment for quadriceps femoris spasticity. However, we still suggest auxiliary localization in clinical application in combination with electrical stimulator, ultra- sonography, or electromyography to further re- duce the pain caused by exploratory puncture and to improve the efficacy and efficiency. Nevertheless, the generalization of our results is limited by the relatively small sample size, and it has not yet revealed whether there are differences among different races. The efficacy and efficiency still need clinical application for confirmation.

In conclusion, the definition of NEPs, CINDRs, and depths can improve the localization effi-ciency and efficacy of blocking targets for quad-riceps femoris spasticity. Moreover, patients with quadriceps femoris spasticity may benefit from extramuscular neurolysis and chemical nerve block by intramuscular BTX-A injection when the defined points are used as reference guides.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 31660294, 31540031).

Disclosure of conflict of interest

None.

Address correspondence to: Dr. Shengbo Yang, Department of Anatomy, Zunyi Medical University, 6 University West Road, Xinpu New Developing Area, Zunyi 563099, People’s Republic of China. Tel: +86-15885627077; Fax: +86-0851-28609666; E-mail: yangshengbo8205486@163.com

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