Inter Groove

[Boleslao Drinker]

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Objectives: This study evaluated the danger zone (DZ) in mesial roots of mandibular molars and the correlation between anatomical references of the DZ and some anatomical landmarks including tooth/root length, depth of mesial and distal grooves, and inter-canal orifices distance.

Material and methods: Twenty-eight mesial roots of mandibular molars with 2 independent canals were scanned and divided into 2 groups according to root length. The anatomical landmarks were correlated (Pearson or Spearman coefficients) with root level, thickness, and position of the DZ and also compared (independent samples t or Mann-Whitney tests) between the 2 groups at α = 5%.

Conclusions: The length of tooth/root, the distance of canal orifices, and the depth of mesial/distal grooves of mesial roots of mandibular molars might be predictive factors for the root level, position, and thickness of the DZ.

Clinical relevance: The length, distance of mesial canal orifices, and the depth of mesial and distal grooves of the mesial roots of mandibular molars might be moderate predictive factors for the root level, position, and thickness of the DZ.

The bicipital groove (intertubercular groove, sulcus intertubercularis) is a deep groove on the humerus that separates the greater tubercle from the lesser tubercle. It allows for the long tendon of the biceps brachii muscle to pass.

The bicipital groove separates the greater tubercle from the lesser tubercle.[1] It is usually around 8 cm long and 1 cm wide in adults.[1] It lodges the long tendon of the biceps brachii muscle between the tendon of the pectoralis major muscle on the lateral lip and the tendon of the teres major muscle on the medial lip. It also transmits a branch of the anterior humeral circumflex artery to the shoulder joint.[citation needed]

The bicipital groove (also known as the intertubercular sulcus or sulcus intertubercularis) is the indentation between the greater and lesser tuberosities of the humerus that lodges the biceps tendon.

The tendon of the long head of the biceps muscle runs in this groove and attaches on the supraglenoid tubercle of the scapula. The short head of the biceps muscle on the other hand has its origin on the coracoid process of the scapula.

This changed in the early 1900s when percutaneous access to the brachial plexus was first described. In 1925, July Etienne1 reported the successful block of the brachial plexus by inserting a needle halfway between the lateral border of the sternocleidomastoid muscle and the anterior border of the trapezius muscle at the level of the cricothyroid membrane, making a single injection in the area around the scalene muscles.

More recently, the introduction of ultrasound-guided techniques has allowed for additional refinements and improved block consistency with reduced local anesthetic volumes.(see Ultrasound-Guided Interscalene Brachial Plexus Block)

The plexus is formed by the ventral rami of the fifth to eighth cervical nerves and the greater part of the ventral ramus of the first thoracic nerve (Figure 1). In addition, small contributions may be made by the fourth cervical and the second thoracic nerves. There are multiple complex interconnections between the neural elements of brachial plexus as they course from the interscalene groove to their endpoints in terminal nerves. However, most of what happens to these roots on their way to becoming peripheral nerves is not clinically essential information for the practitioner.

Only three nerves of the brachial plexus innervate the shoulder. The most proximal of these is the upper lateral brachial cutaneous nerve, a branch of the axillary nerve that innervates the lateral side of the shoulder and the skin overlying the deltoid muscle. The upper medial side of the arm is innervated by both the medial brachial cutaneous and the intercostobrachial cutaneous nerves. In the anterior portion of the arm over the biceps muscle, the skin is innervated by the medial antebrachial cutaneous nerve.

Apart from the cutaneous nerve supply to the shoulder, the innervation of the joint deserves special consideration. In general, a nerve crossing a joint gives branches that innervate that joint. Therefore, the nerves supplying the ligaments, capsule, and synovial membrane of the shoulder derive from the axillary, suprascapular, subscapular, and musculocutaneous nerves.

The relative contributions of these nerves are not constant, and the supply from the musculocutaneus nerve may be very small or completely absent. Anteriorly, the axillary nerve and suprascapular nerve provide most of the nerve supply to the capsule and glenohumeral joint (Figure 3). In some instances, the musculocutaneous nerve may innervate the anterosuperior portion of the joint. In addition, the anterior capsule may be supplied by either the subscapular nerves or the posterior cord of the brachial plexus after piercing the subscapularis muscle.

Superiorly, the primary contribution is from two branches of the suprascapular nerve, one branch supplying the acromioclavicular joint and proceeding anteriorly as far as the coracoid process and coracoacromial ligament and the other branch reaching the posterior aspect of the joint. Other nerves contributing to this region of the joint are the axillary nerve and musculocutaneous nerve. Posteriorly, the main nerves are the suprascapular nerve in the upper region and the axillary nerve in the lower region (Figure 4). Inferiorly, the anterior portion is primarily supplied by the axillary nerve, and the posterior portion is supplied by a combination of the axillary nerve and lower ramifications of the suprascapular nerve.

Several approaches to the interscalene brachial plexus block have been described with the use of a nerve stimulator. In this chapter, we describe the classic (Winnie) technique and common modifications, including the low interscalene approach. The posterior (paravertebral) approach and its modifications have been largely abandoned for safety reasons and will be omitted from this volume.

The classic approach of Winnie is performed at the level of the sixth cervical vertebra. Winnie originally used a paresthesia technique; however, most practitioners eventually adopted nerve stimulation.

Reported complications with this technique are total spinal anesthesia, epidural anesthesia, cervical spinal cord injection with resultant paraplegia, as well as injections into the vertebral artery. These complications are more likely to occur with the classic technique than its modifications because the needle is directed perpendicularly towards the spinal cord. Although an infrequent complication, pneumothorax can also occur. This technique is not well suited for the placement of an interscalene catheter because of the perpendicular approach to the trunks.

Some common responses to nerve stimulation and the course of action to obtain the proper response are shown in Table 3. The following motor responses can all be accepted as successful localization of the brachial plexus with a similar success rate:

The continuous interscalene brachial plexus block is an advanced technique. Paradoxically, although the single-shot interscalene block is one of the easiest intermediate techniques to perform and master, placement of the catheter in the interscalene groove is much more challenging. This is partially due to the shallow position of the brachial plexus and difficulties in stabilizing the needle during catheter advancement. This technique provides excellent analgesia in patients after shoulder, arm, and elbow surgery.

Early complications (soon after block administration), such as epidural, spinal, or intravascular injection are primarily related to the approach chosen (see Table 5). Late complications include neuropathy, mechanical plexus injury, and infection.

Nerve injuries are a well-recognized complication of anesthesia, although nerve injury directly attributable to interscalene block is extremely rare.

Factors related to patient position, such as the use of shoulder braces and the head position, malposition of the arms, and sustained neck extension may increase the risk of injury. Little data are available on the rate of complications related to the use of the continuous interscalene catheters. Table 6 lists reported complications of interscalene blocks and suggestions on how to avoid them.

Interscalene nerve block is one of the most clinically applicable nerve block techniques. With proper training, equipment, and monitoring precautions the technique results in a predictable success rate, excellent anesthesia, and superb postoperative analgesia.

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An interscalene nerve block anesthetizes most of the territory innervated by the brachial plexus, sparing the inferior trunk. This block is performed on patients undergoing shoulder, upper arm, or elbow surgery. It is not recommended for hand surgery as the inferior trunk may be spared. This activity reviews the indications, contraindications, and techniques for performing an interscalene nerve block. It highlights the role of the interprofessional team in the care of patients undergoing this procedure.

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