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Compressive and Entrapment Neuropathies of the Upper Extremities


Upper Extremity

Shoulder

Suprascapular Nerve Syndrome

  • Impingement of the suprascapular nerve occurs at the scapular notch or spinoglenoid notch.

  • The suprascapular nerve originates from the brachial plexus, and at the scapular notch it branches into the supraspinatus and infraspinatus nerves ( Fig. 17-1 ).

    FIGURE 17–1, Normal anatomy of the suprascapular nerve. Drawing of the suprascapular nerve (long arrow) as it courses through the suprascapular notch bounded superiorly by the suprascapular ligament (SSL) . The nerve branches into the supraspinatus nerve (short arrow) and infraspinatus nerve (arrowhead). The infraspinatus nerve has to traverse the spinoglenoid notch, formed between the spinoglenoid ligament (SGL) and the scapula.

  • Proximal entrapment at the scapular notch results in compression of the suprascapular nerve and denervation of both the supraspinatus and infraspinatus muscles ( Figs. 17-2 and 17-3 ).

    FIGURE 17–2, Early denervation of the supraspinatus and infraspinatus muscles. Sagittal T2-weighted MR image demonstrates edema of the supraspinatus and infraspinatus muscles (arrows) due to early denervation.

    FIGURE 17–3, Ganglion cyst in the suprascapular notch. Coronal T2-weighted MR image demonstrates a fluid collection occupying the suprascapular notch (arrow) compressing the suprascapular nerve.

  • Distal entrapment at the spinoglenoid notch results in compression of the infraspinatus nerve and denervation of the infraspinatus muscle only.

Etiology

  • Paralabral cysts (most common) ( Fig. 17-4 )

    FIGURE 17–4, Ganglion cyst in the spinoglenoid notch. Sagittal T2-weighted image demonstrates a fluid collection (long arrow) in the spinoglenoid notch (short arrows) , compressing the infraspinatus nerve. Note the lack of edema or atrophy of the muscle.

  • Scapular fractures and callus formations, hematomas, rotator cuff tears

  • Overhead activities (e.g., volleyball and tennis players, weightlifters, painters, electricians)

  • Soft tissue and osseous tumors, vascular malformations

  • Thickened transverse scapular ligament (bridges scapular notch) or spinoglenoid ligament (bridges spinoglenoid notch)

  • Iatrogenic (e.g., during rotator cuff repair)

Clinical Findings

  • Diffuse shoulder pain, diminished abduction and posterior elevation

Magnetic Resonance Imaging Findings

  • Denervation edema (acute, increased T2 and short tau inversion recovery [STIR] signal) or fatty atrophy (chronic) of affected muscles

Differential Diagnosis

  • Rotator cuff injury, Parsonage-Turner syndrome, cervical radiculopathy

Quadrilateral Space Syndrome

  • Also known as lateral axillary hiatus syndrome, it is caused by compression of axillary nerve in the quadrilateral space ( Fig. 17-5 ).

    FIGURE 17–5, Drawing of the quadrilateral space. View from the posterior aspect of the scapula demonstrating the four margins of the space: the teres minor muscle superiorly (Tm) , the teres major muscle inferiorly (TM) , the medial aspect of the humerus laterally, and the triceps muscle medially (TrM) . Note the axillary nerve passing though the quadrilateral space (arrow) and providing branches to the teres minor, triceps, and deltoid muscles.

  • The quadrilateral space is formed by the long head of the triceps brachii muscle medially, the teres minor muscle superiorly, the teres major inferiorly, and the medial aspect of the humerus laterally.

  • The axillary nerve innervates the teres minor and deltoid muscles and the posterolateral cutaneous region of the shoulder and upper arm.

Etiology

  • Proximal humeral head fractures and callus formations

  • Anterior shoulder dislocation resulting in traction and compression

  • Fibrous bands (posttraumatic)

  • Soft tissue and osseous tumors, paralabral cysts

Clinical Findings

  • Shoulder pain, paresthesias, and discrete point tenderness in lateral aspect of quadrilateral space

Magnetic Resonance Imaging Findings

  • Denervation edema (acute, increased T2 and STIR signal and size) or fatty atrophy (chronic) of the teres minor and/or deltoid muscle ( Fig. 17-6 )

    FIGURE 17–6, Teres minor denervation. A, T1-weighted sagittal MR image demonstrates atrophy of the teres minor muscle (arrow) , indicating late stage. B, Sagittal short tau inversion recovery MR image demonstrates early denervation with edema of the teres minor muscle (arrows) .

Differential Diagnosis

  • Anterior dislocation, proximal humeral fracture, brachial neuritis, Parsonage-Turner syndrome

Elbow

Pronator Syndrome

  • Compression of the median nerve occurs at the level of the pronator teres muscle.

  • Potential sites of entrapment include the space between the superficial (humeral) and deep (ulnar) heads of the pronator teres muscle; at the origin of the flexor digitorum superficialis muscle where a fibrous arch exists; at the lacertus fibrosus, also known as the bicipital aponeurosis; and, less commonly, at the supracondylar process of the distal anteromedial humerus (avian spur) ( Figs. 17-7 and 17-8 ).

    FIGURE 17–7, Normal anatomy of the median nerve at the level of the elbow. The median nerve (short arrow) courses distally from the posterior medial aspect of the arm into the region of the elbow and forearm, where it is located anteromedially. If a supracondylar process is present (arrowhead) , the median nerve is located posterior to the process and the adjacent ligament of Struther (long arrow) . More distally, the median nerve courses under the lacertus fibrosus and the pronator teres and flexor muscles.

    FIGURE 17–8, Entrapment of the median nerve at the level of the supracondylar process. Axial T1-weighted ( A ) and axial short tau inversion recovery (STIR) ( B ) MR images demonstrate a supracondylar process (arrows) with the median nerve located dorsal to the process. Note the increased signal intensity of the median nerve on the STIR image.

Etiology

  • Elbow trauma, repetitive elbow flexion, supination and pronation of forearm, or, less commonly, anatomic variants (e.g., accessory bicipital aponeurosis, accessory head of the flexor pollicis longus muscle, palmaris profundus), bicipital bursitis, and soft tissue masses.

  • Closed reduction of elbow dislocation can also result in intraarticular entrapment of the median nerve.

Clinical Findings

  • Chronic pain and paresthesias in the volar aspects of the elbow and forearm and in the hand affecting the first through third digits and lateral half of the ring finger

  • No muscle weakness

  • Pain on palpation of the pronator teres muscle

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