Anatomical Reasons Simplified and Illustrated with Diagrams

By Dr Smita Sudarshana

 This book focuses on the important topic of anatomical reasons in detail,  written with a view to fulfill the long felt genuine need of the students who has to depend on long and lengthy text books to find the reasons of a  common anatomical scenario which is indeed a very tiring, tedious and time-consuming process. 

 

It is written in very simple words in question-and-answer format, is easy to understand, and illustrated with diagrams to enhance the learning. It is arranged system-wise, comprehensively contains almost all clinically relevant topics, and includes previous 20 years (theory and viva) questions asked in various universities of India. Every effort is made to provide accurate, reliable, and updated information about the topic. Every answer is clinically correlated so that students remain motivated and focused while reading this book.

• Language: English
• Publisher: Blue Rose Publishers
• Release date: Nov 9, 2022

Book preview

CHAPTER-1

Anatomical reasons related to Upper Limb.

Anatomical reasons

Give reasons of the following

Question1. What is the anatomical basis of ‘Erb's paralysis’?

Answer - Erb’s paralysis results from the damage of the upper trunk of brachial plexus at Erb’s point.

Neurologically, the Erb’s point is a site at the upper trunk of the brachial plexus located about 2-3 cm above the clavicle formed by the convergence of six nerves.

C5 and C6 nerve roots converge at the upper trunk, which branches off suprascapular nerve and the nerve to the subclavius. The merged nerves divide into the anterior and posterior division of C5 and C6 as shown in figure 1(B).

Erb’s paralysis usually occurs due to the increase in angle between neck and shoulder, leading to stretching or avulsion of the upper trunk of brachial plexus, when a baby’s head has to be moved to one side in order to make more room for delivery of their shoulders in the case of a difficult vaginal delivery, as shown in figure 1(A) or even during cesarean section. It can also occur in adults after traffic accidents involving motorcycles.

Affected nerves are suprascapular, axillary, and musculocutaneous, which can be abbreviated with the mnemonic – SAM

S = Suprascapular nerve that supply supraspinatus and infraspinatus muscle

A = Axillary nerve which supply teres minor and deltoid muscle

M = Musculocutaneous nerve which supies biceps, brachialis and coracobrachialis.

The classical sign of Erb’s palsy or paralysis is called waiter’s tip deformity or policeman’s tip deformity due to loss of lateral rotators of the shoulder joint (supraspinatus, infraspinatus and teres minor), arm flexors (biceps, brachialis and coracobrachialis), flexors of elbow joint (biceps brachii and brachialis), arm abductor (deltoid) and forearm supinator (biceps).

Under such conditions, the position of the upper limb is characterized by:

the arm hanging by side and rotated medially (due to paralysis of lateral rotators), arm adducted (due to paralysis of abductor of arm), forearm extended and pronated ( due to paralysis of flexors of elbow joint and supinator) as shown in figure 1(C).

In addition to this, there is loss of sensation in the lateral aspect of forearm due to involvement of lateral cutaneous nerve of forearm (branch of musculocutaneous nerve), upper lateral part of arm as well as skin over deltoid muscle due to involvement of axillary nerve .

Question 2. Why are anterior dislocations of the shoulder joint more common than other dislocations of shoulder?

Answer - The shoulder joint is the most unstable joint of the body due to shallow glenoid cavity that articulates with only 25 % of the humeral head, making it more prone to dislocation than any other joint in the body.

Out of these, anterior dislocations account for 97% of dislocations.

Anterior dislocation of shoulder are more common due to the following reasons:

1. Mode of injury: - anterior dislocation commonly occur with a blow to an abducted and externally rotated arm with extended extremity as shown in figure 2.

It may also occur because of posterior humerus force or falling on an outstretched arm.

In a position of excessive amount of abduction and external rotation, the inferior glenohumeral ligament joint complex works as the main restraint