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Motor Branch of Extensor Carpi Radialis Longus: Anatomic Localization

Published:March 28, 2012DOI:https://doi.org/10.1016/j.apmr.2012.03.015

      Abstract

      Genet F, Autret K, Schnitzler A, Lautridou C, Bernuz B, Denormandie P, Allieu Y, Parratte B. Motor branch of extensor carpi radialis longus: anatomic localization.

      Objective

      To identify extensor carpi radialis longus (ECRL) motor nerve coordinates in relation to anatomic surface landmarks.

      Design

      Descriptive study.

      Setting

      Anatomy institute of a school of medicine in Paris, France.

      Cadavers

      Fresh adult cadaver upper limbs (N=20).

      Intervention

      Anatomic dissection of upper limbs.

      Main Outcome Measures

      Three measurements (mm) were taken of the position of the ECRL motor branch: the distance between the lateral epicondyle and the emergence of the ECRL branch along the forearm axis, the branch depth, and the ratio between the distance corresponding to the nerve depth and the intercondylar distance.

      Results

      The radial nerves of 4 men and 6 women (age range 59–80y) were identified between the brachioradialis and the ECRL and traced proximally to the lateral epicondyle. The injection point was between the lateral epicondyle posteriorly and the wrist extensor group anteriorly. Direction was perpendicular to the axis of the forearm. Mean depth was 35.6mm (minimal value: 24.0; maximal value: 58.0; SD=9mm). Ratio between nerve depth and intercondylar distance was .46 (.37; .53±.05).

      Conclusions

      The ECRL motor nerve branch is easy to reach using specified landmarks. Selective motor nerve block of the ECRL branch should be considered in the clinical assessment to test the capacity of the extensor carpi radialis brevis to extend the wrist alone and to assess the command and overactivity of antagonists before surgery.

      Key Words

      List of Abbreviations:

      ECRL (extensor carpi radialis longus), ECRB (extensor carpi radialis brevis)
      THE TECHNIQUE of motor nerve block is to inject a local anesthetic drug close to a motor nerve, thus temporarily inhibiting its conduction.
      • Filipetti P.
      • Decq P.
      Interest of anesthetic blocks for assessment of the spastic patient: a series of 815 motor blocks.
      These blocks are a useful and innocuous technique for the evaluation of muscle function in the case of spasticity due to central nervous system damage. These types of blocks have been used since 1928,
      • Labat G.
      Regional anesthesia: its techniques and clinical application.
      but it was not until 1964 that they were proposed for the prognostic assessment of the effects of alcohol neurolysis.
      • Tardieu G.
      • Hariga J.
      Treatment of muscular rigidity of cerebral origin by infiltration of dilute alcohol: results of 500 injections.
      In 1975, Zancolli
      • Zancolli E.
      Surgery for the quadriplegic hand with active, strong wrist extension preserved: a study of 97 cases.
      described the use of nerve blocks for the assessment of overactivity of antagonist muscles before carrying out spastic hand surgery. More recently, several studies have demonstrated the diagnostic use of motor nerve blocks for all pretreatment assessment of spasticity (botulinum toxin, chemical neurolysis, etc).
      • Filipetti P.
      • Decq P.
      Interest of anesthetic blocks for assessment of the spastic patient: a series of 815 motor blocks.
      • Viel E.J.
      Neurophysiological approach in the peripheral anesthetic blocks as a diagnosis and prognosis tool for spasticity.
      • Viel E.J.
      • Perennou D.
      • Ripart J.
      • Pelissier J.
      • Eledjam J.J.
      Neurolytic blockade of the obturator nerve for intractable spasticity of adductor thigh muscles.
      • Viel E.
      • Pellas F.
      • Ripart J.
      • Pelissier J.
      • Eledjam J.J.
      Peripheral neurolytic blocks and spasticity.
      • Sung D.
      • Bang H.
      Motor branch block of the rectus femoris: its effectiveness in stiff-legged gait in spastic paresis.
      • Deltombe T.
      • et al.
      Selective blocks of the motor nerve branches to the soleus and tibialis posterior muscles in the management of the spastic equinovarus foot.
      • Buffenoir K.
      • Decq P.
      • Lefaucheur J.P.
      Interest of peripheral anesthetic blocks as a diagnosis and prognosis tool in patients with spastic equinus foot: a clinical and electrophysiological study of the effects of block of nerve branches to the triceps surae muscle.
      While the block is effective, it is possible to differentiate between spasticity, muscle retraction, and activity of the antagonist muscles before carrying out surgery. Prior assessment using motor nerve block can avoid surgical overcorrection, which can lead to functional disasters. Motor nerve blocks are particularly useful before tendon transfer to assess the activity of the different agonist muscles.
      • Mendelson L.S.
      • Peckham P.H.
      • Freehafer A.A.
      • Keith M.W.
      Intraoperative assessment of wrist extensor muscle force.
      It is essential to assess the isolated strength of the agonist muscle that will function alone following surgery.
      Since the 1970s, surgery to improve upper-limb function has been developing following central nervous system damage and particularly for the hand in patients with tetraplegia.
      • Zancolli E.
      Surgery for the quadriplegic hand with active, strong wrist extension preserved: a study of 97 cases.
      • Freehafer A.A.
      Flexion and supination deformities of the elbow in tetraplegics.
      • Lamb D.W.
      • Landry R.
      The hand in quadriplegia.
      • Moberg E.
      Surgical treatment for absent single-hand grip and elbow extension in quadriplegia: principles and preliminary experience.
      • Allieu Y.
      • Coulet B.
      • Chammas M.
      Functional surgery of the upper limb in high-level tetraplegia: part I.
      The extensor carpi radialis longus (ECRL) is often used for this purpose.
      • Zancolli E.
      Surgery for the quadriplegic hand with active, strong wrist extension preserved: a study of 97 cases.
      • Mendelson L.S.
      • Peckham P.H.
      • Freehafer A.A.
      • Keith M.W.
      Intraoperative assessment of wrist extensor muscle force.
      • Nayak S.R.
      • Krishnamurthy A.
      • Prabhu L.V.
      • Rai R.
      • Ranade A.V.
      • Madhyastha S.
      Anatomical variation of radial wrist extensor muscles: a study in cadavers.
      It can be transferred to flexor digitorum profundus to gain finger flexion and to flexor pollicis longus to gain thumb flexion.
      • Zancolli E.
      Surgery for the quadriplegic hand with active, strong wrist extension preserved: a study of 97 cases.
      • Mendelson L.S.
      • Peckham P.H.
      • Freehafer A.A.
      • Keith M.W.
      Intraoperative assessment of wrist extensor muscle force.
      • Mohammed K.D.
      • Rothwell A.G.
      • Sinclair S.W.
      • Willems S.M.
      • Bean A.R.
      Upper-limb surgery for tetraplegia.
      Prior to surgery, it is essential to assess whether the strength of extensor carpi radialis brevis (ECRB) is sufficient to extend the wrist following transfer of the ECRL.
      • Zancolli E.
      Surgery for the quadriplegic hand with active, strong wrist extension preserved: a study of 97 cases.
      • Mendelson L.S.
      • Peckham P.H.
      • Freehafer A.A.
      • Keith M.W.
      Intraoperative assessment of wrist extensor muscle force.
      • Allieu Y.
      • Coulet B.
      • Chammas M.
      Functional surgery of the upper limb in high-level tetraplegia: part I.
      • Mohammed K.D.
      • Rothwell A.G.
      • Sinclair S.W.
      • Willems S.M.
      • Bean A.R.
      Upper-limb surgery for tetraplegia.
      • Allieu Y.
      General indications for functional surgery of the hand in tetraplegic patients.
      • Ketchum L.D.
      • Brand P.W.
      • Thompson D.
      • Pocock G.S.
      The determination of moments for extension of the wrist generated by muscles of the forearm.
      • Hentz V.
      • Leclercq C.
      Surgical rehabilitation of the upper limb in tetraplegia.
      The capacity to extend the wrist is very useful for patients who have lost control of finger flexion because it enables them to use the tenodesis effect for prehension of light objects, particularly if the flexor digitorum superficialis and profundus are shortened or overactive.
      • Wilson J.N.
      Providing automatic grasp by flexor tenodesis.
      The assessment of the isolated strength of the ECRB is particularly important when the patient's functional level (as assessed by the Giens International Surgical Classification) is classified as GIENS 2 to 3 (GIENS 2, weak wrist extension with only the ECRL) or strong (GIENS 3, strong wrist extension with the ECRL and the ECRB).
      • Welraeds D.
      • Ismail A.A.
      • Parent A.
      Functional reconstruction of the upper extremity in tetraplegia: application of Moberg's and Allieu's procedures.
      • Mc Dowel C.
      • Moberg E.
      • House J.
      The second international conference on surgical rehabilitation of the upper limb in tetraplegia (quadraplegia).
      Wrist extension may be strong as a result of the combined action of the 2 radial wrist extensors, while the ECRB itself may be weak, thus contraindicating transfer of the ECRL. Accurately evaluating the 2 radial wrist extensors is difficult; thus, one must be cautious before transferring an ECRL.
      • Mohammed K.D.
      • Rothwell A.G.
      • Sinclair S.W.
      • Willems S.M.
      • Bean A.R.
      Upper-limb surgery for tetraplegia.
      • Allieu Y.
      General indications for functional surgery of the hand in tetraplegic patients.
      • Hentz V.
      • Leclercq C.
      Surgical rehabilitation of the upper limb in tetraplegia.
      We suggest that selective motor nerve block of the ECRL branch would give a more precise indication of ECRB strength and is an easy and innocuous technique. There is no anatomic surface landmark published to practice an ECRL selective motor nerve block. The aim of this study was thus to locate this branch and to describe the localization procedure that can be used in vivo to carry out motor blocks of the branch of the ECRL nerve.

      Methods

      Methods of similar studies published have been followed.
      • Sung D.
      • Bang H.
      Motor branch block of the rectus femoris: its effectiveness in stiff-legged gait in spastic paresis.
      • Albert T.
      • Yelnik A.
      • Colle F.
      • Bonan I.
      • Lassau J.P.
      Anatomic motor point localization for partial quadriceps block in spasticity.
      Fresh cadavers were used for the study. Age, sex, and forearm dominance were noted.

      Dissection

      The localization and course of the ECRL nerve branch is well known.
      • Abrams R.A.
      • Ziets R.J.
      • Lieber R.L.
      • Botte M.J.
      Anatomy of the radial nerve motor branches in the forearm.
      The radial nerve is situated between the brachioradialis and ECRL muscles and traced proximally to the lateral epicondyle of the humerus. The forearm was positioned in supination. A midline incision was made along the long axis of the forearm on the anterior surface. Skin flaps were elevated and the superficial muscle groups were exposed. The radial nerve and the ECRL branch were localized. Three measurements were taken, based on anatomic landmarks
      • Abrams R.A.
      • Ziets R.J.
      • Lieber R.L.
      • Botte M.J.
      Anatomy of the radial nerve motor branches in the forearm.
      to localize the motor branch: “d” equals the distance between the lateral epicondyle and the emergence of the ECRL branch along the forearm axis and the ratio between the distance corresponding to the nerve depth (measured on a needle that was inserted transversely in the forearm from the lateral epicondyle until it contacted the nerve [mm]) and the intercondylar distance (mm).

      Results

      Results are shown in Table 1, Table 2 and Fig 1, Fig 2, Fig 3, Fig 4.
      Table 1Nerve Depth by Side
      Nerve Depth (mm)LeftRightTotal
      Mean35.8035.4035.6
      Minimum25.0024.0024.0
      Maximum58.0056.0058.0
      SD9.558.939.0
      Table 2Ratio Depth/Intercondyle Distance by Side
      RatioLeftRightTotal
      Mean.455.457.46
      Minimum.38.37.37
      Maximum.53.53.53
      SD.05.05.05
      Figure thumbnail gr1
      Fig 1Posterolateral view of the forearm (in pronation as it is used to be seen in spastic deformation).
      Figure thumbnail gr2
      Fig 2Anterior view of the right upper limb. An elbow region.
      Figure thumbnail gr3
      Fig 3Location of the morphoanatomic site for the ECRL motor block nerve.
      A total of 20 forearms from 10 fresh cadavers were used for the study (4 men, 6 women; age range 59–80y).
      As has been previously described, the radial nerve was identified between the brachioradialis and ECRL muscles and traced proximally to the lateral epicondyle of the humerus. Following the forearm axis, the distance “d” below the epicondyle was not significant. The needle has to enter the forearm just under and against the lateral epicondyle. The injection point is between the lateral epicondyle posteriorly and the wrist extensor group anteriorly. The needle has to keep a perpendicular direction to the forearm axis. The mean depth was 35.6mm (24; 58±9), and the ratio between the nerve depth and the intercondylar distance was .46 (.37; .53±.05). The dissected side of the arm (left vs right) had no influence.

      Discussion

      Main Results

      According to anatomic landmarks, the injection for a selective motor nerve block of the ECRL is easy to practice: in front of the epicondyle, between the lateral epicondyle posteriorly and the wrist extensor group anteriorly, perpendicularly to the axis of the forearm at about a depth between the third and the half of the intercondylar distance.

      Determining the Anatomic Landmarks

      No particular problems were encountered during the dissections. The motor branch of the ECRL was easily identified. The epicondyle was used as a reference because it is easily palpable for a clinician. Equally, the wrist extensors are easily located, even if they are paralyzed. The depth parameter is also very important for the clinician, but it depends on morphologic parameters (eg, sex, muscle size, dominance). We thus used the ratio between the nerve depth (measured in vivo on the needle) and the forearm width (distance interepicondylar) to account for these variations and to obtain measurements that were independent from the patient's morphology.

      Potential Benefits of Selective Motor Block of the ECRL Nerve

      Several functional and surgical scales have been used to determine the potential benefit of surgery. In the case of tetraplegia, for which ECRL transfer is frequently advocated, the GIENS scale is used to determine transferable muscles depending on the patient's impairment.
      • Welraeds D.
      • Ismail A.A.
      • Parent A.
      Functional reconstruction of the upper extremity in tetraplegia: application of Moberg's and Allieu's procedures.
      • Mc Dowel C.
      • Moberg E.
      • House J.
      The second international conference on surgical rehabilitation of the upper limb in tetraplegia (quadraplegia).
      This classification is more specific than Zancolli's
      • Zancolli E.
      Surgery for the quadriplegic hand with active, strong wrist extension preserved: a study of 97 cases.
      classification, for which the defined groups are too large and include patients with varying levels of muscle strength. The GIENS classification takes level of strength into account, for example, weak (GIENS 2, weak wrist extension with only the ECRL) or strong (GIENS 3, strong wrist extension with the ECRL and the ECRB) wrist extension. However, no scales are able to differentiate between the strength of the 2 wrist extensors. The assessment of the isolated strength of the ECRB is difficult and is particularly important when the patient's functional level is classified as GIENS 2 to 3.
      • Welraeds D.
      • Ismail A.A.
      • Parent A.
      Functional reconstruction of the upper extremity in tetraplegia: application of Moberg's and Allieu's procedures.
      • Mc Dowel C.
      • Moberg E.
      • House J.
      The second international conference on surgical rehabilitation of the upper limb in tetraplegia (quadraplegia).
      For that, several teams use personal indirect assessments to determine whether the ECRL could be transferred.
      • Moberg E.
      Surgical treatment for absent single-hand grip and elbow extension in quadriplegia: principles and preliminary experience.
      • Mohammed K.D.
      • Rothwell A.G.
      • Sinclair S.W.
      • Willems S.M.
      • Bean A.R.
      Upper-limb surgery for tetraplegia.
      • Hentz V.
      • Leclercq C.
      Surgical rehabilitation of the upper limb in tetraplegia.
      • House J.H.
      Reconstruction of the thumb in tetraplegia following spinal cord injury.
      For example, clinical tests such as 10 static repetitions with a regular strength of wrist extension above 4/5 should indicate sufficient strength of the ECRB alone for wrist extension or the observation of a groove between the extensor bellies during the contraction of the wrist extensors is considered to be a sign of sufficient strength of both muscles for the transfer of the ECRL.
      • Mohammed K.D.
      • Rothwell A.G.
      • Sinclair S.W.
      • Willems S.M.
      • Bean A.R.
      Upper-limb surgery for tetraplegia.
      • Hentz V.
      • Leclercq C.
      Surgical rehabilitation of the upper limb in tetraplegia.
      • House J.H.
      Reconstruction of the thumb in tetraplegia following spinal cord injury.
      Thus, the question of differentiating between these 2 subgroups arises frequently, and selective motor block of the ECRL nerve can answer this question.

      Study Limitations

      First, anatomic variations between subjects are often found in the forearm.
      • Nayak S.R.
      • Krishnamurthy A.
      • Prabhu L.V.
      • Rai R.
      • Ranade A.V.
      • Madhyastha S.
      Anatomical variation of radial wrist extensor muscles: a study in cadavers.
      The presence of a third wrist extensor has been found in approximately 10.4% of the cases.

      Recommendations for Further Research

      This technique should be evaluated in a single blind clinical study comparing ECRL motor nerve blocks with the preoperative strategies that are usually used to determine indications for surgery. Particularly, the results of surgery following the different assessment techniques should be compared.

      Conclusions

      Anatomic surface landmarks of the selective motor branch of the ECRL, and direction and depth of the needle, are described in this article. Selective motor nerve block of the ECRL branch should be included in the clinical assessment to test the capacity of the ECRB to extend the wrist alone and to assess the command and overactivity of antagonists before surgery.

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        Neurophysiological approach in the peripheral anesthetic blocks as a diagnosis and prognosis tool for spasticity.
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