Musculoskeletal anatomy fill in the blanks

A fracture of the places the axillary nerve at risk of injury. This nerve passes through the , the lateral border of which is the . This nerve innervates the and the . The clinical features of injury to this nerve include weakness of shoulder and sensory loss in the .

Laceration of the might occur if one suffers a midshaft fracture of the humerus. This artery accompanies the in the of the humerus. A may lacerate the , which accompanies the axillary nerve through the quadrangular space.

Weakness of of the arm may result from a lesion to the of the brachial plexus and one or more of the subscapular nerves, or injury to the lateral or medial pectoral nerves. The major of the arm at the shoulder are the , innervated by the upper subscapular nerve and lower subscapular nerve, the , innervated by the middle subscapular nerve, , innervated by the lower subscapular nerve, and the , innervated by the lateral and medial pectoral nerves.

Weakness in the ability to may result from a lesion of the ; this nerve may be lacerated by a wound to the lateral neck, but not by a humeral fracture. This nerve innervates the trapezius muscle.

Winging of the scapula results from an injury to the , which innervates the . This presents as protrusion of the of the scapula when the patient against a wall. There will be no deficits. The nerve is subject to injury during axillary surgery, such as axillary node dissection for breast cancer.

This patient has weakness of the anterior compartment muscles (loss of ) and lateral compartment muscles ( unopposed ) of the leg. These muscles are innervated by the and , respectively. Both of these nerves are branches of the .

Also, the and provide sensory innervation to the of the foot. The provides sensory innervation to most of the of the foot. The deep peroneal nerve provides sensory innervation to the webspace between the .

The is superficially located at the neck of the fibula. The patient likely compressed this nerve by lying on her or supine with the right leg for long periods of time.

The innervates the muscles and the skin of the anterior thigh. Weakness of these muscles would cause weakness of .

The innervates the muscles of the medial thigh and the skin in this region. Weakness of these muscles would cause weakness of .

The sciatic nerve divides to become the and the . The innervates the muscles of the calf and the skin of the s The calf muscles are responsible for and sensation on the .

The is susceptible to compression injury due to its superficial location at the . Deficits include weakness of anterior compartment muscles () and weakness of lateral compartment muscles (). Loss of sensation on the may also be present.

The is the small bone in the distal row of carpal bones in the wrist that sits directly proximal to the little and ring fingers (5th and 4th digits). It has a bony protrusion, the , which is very vulnerable to trauma of the palm, particularly in the settings of a person hitting the ground forcibly with a stick (including a golf club) or falling on an . An x-ray or CT scan of the wrist can confirm the diagnosis. Therapy involves or .

The crosses the wrist immediately lateral to the hook of the hamate and can be injured in such a fracture. If that occurs, there will be sensory symptoms on the side of the hand on both the dorsal and palmar surfaces of the hand and there could be motor loss in many of the of the hand (not including the or the ).

Because the and have their origins on the hook of the hamate, of the fifth digit against resistance causes pain at the fracture site.

Carpal tunnel syndrome results from compression of the within the . It results in sensory disturbance of the palmar surface of the and weakness of the . It is often the result of swelling of the of the within the carpal tunnel.

Cubital tunnel syndrome causes paresthesias and numbness on the side of the hand due to compression of the at the .

Lunate dislocation is an displacement of the lunate with respect to the rest of the carpals. It can occur in severe trauma of the hand and is usually accompanied by compression of the , with resulting pain and numbness on the aspect of the hand.

Scapholunate ligament rupture causes pain in the and can result from a fall onto an .

The is a wedge-shaped carpal bone with a hooklike process on its . It is located in the carpal row on the side. The may be fractured when a person falls on an outstretched hand, or hits the ground with a stick (i.e., a golf club) in the hand.

Clawing of the ring and little fingers is characteristic of an lesion. lesions can also produce wasting of the eminence and muscles. The latter causes "" between the extensor tendons on the back of the hand. The muscles abduct digits 2-5 and the muscles adduct digits 2-5. lesions also cause loss of sensation to the side of the hand (both palm and dorsal surface) and both the palmar and dorsal surfaces of the finger and the medial half of the finger.

Sensation on the back of the thumb is provided by the

Sensation on the palmar side of the forefinger is provided by the

Wasting of the thenar eminence is associated with lesions of the

"Wrist drop" is associated with lesions of the .

Ulnar nerve lesions can produce:
1. of the and digits
2. of the eminence and muscles
3. Loss of to the side of the hand (both palm and dorsal surface) and both the palmar and dorsal surfaces of the digit and the of the digit.

Loss of elbow flexion indicates denervation to the . Herniation of the C5 intervertebral disc occurs secondary to the tough, covering of the intervertebral disc becoming compromised, allowing the to bulge out and the spinal nerve. This characteristically produces the radiating symptoms that we see in this patient.

As shown in the figure of the brachial plexus below, the C5 nerve root significantly contributes to the , which in turn contributes to the and cords for the and division nerve fibers, respectively. Only certain nerves branching from these cords receive input directly from C5, and typically these nerves innervate more proximal muscles.

Specifically, C5 makes contributions to the s, m, a, l, u, l, l, and part of the p.

The nerve provides innervation to major flexors of the elbow including the and . Loss of sensation in the is in the region of the C5 dermatome. C5 contributions to the axillary nerve are responsible for sensation in this region.