Larger terminal branch of the posterior cord of the brachial plexus, receiving fibres from C5-T1.
Exits the axillary fossa posterior to axillary artery; passes posterior to humerus in the radial groove with the deep brachial artery between the lateral and medial heads of the triceps; perforated the lateral intermuscular septum and enters the cubital fossa, dividing into the superficial (cutaneous) and deep (motor) radial nerves.
Because of its close relation to the humerus, any fracture of the humerus, partial or complete (especially at the humeral neck) has the potential to damage the radial nerve. The resulting syndrome is weakness in extending the elbow, wrist and fingers, with an associated sensory deficit (see below).
All the muscles of the posterior compartment of the arm (triceps and anconius) and forearm (brachioradialis and extensor carpi radialis longus). NB the rest of muscles in the posterior compartment of the forearm are supplied by the posterior interosseus nerve, a continuation of the radial nerve.
Skin of posterior and inferolateral arm, posterior forearm and dorsum of the hand lateral to the axial line of digit 4.
It is important to note that the radial nerve does not have an autonomous skin zone. However, complete nerve lesion commonly results in loss of sensation on the radiodorsal aspect of the forearm and the dorsum of thumb (the anatomical snuff box). There is loss of ﬁnger extension at the metacarpophalangeal joints, loss of thumb extension, and wrist drop (loss of wrist extension).
The Brachial plexus is a group of somatic nerves that innervate and receive sensory input from the majority of the upper limb.
There are 5 roots involved in the brachial plexus:C5, C6, C7, C8 and T1. There are several points of interest relating to the nerve roots.
- Firstly, C5-C7 all leave the spinal cord above the level of corresponding vertebrae. Spinal nerve C8 exits below vertebra C7 (there is no C8 vertebra), and from then on (including T1 for the purpose of the brachial plexus) spinal nerves exit at below the corresponding vertebral level.
- Secondly, T1 commonly splits into two. The larger branch enters the brachial plexus (C5-8 do not encounter ribs) while the small becomes the first intercostal nerve (to innervate the muscles of inspiration)
- C5-8 pass between the gap between the anterior and middle scalene muscles, with the subclavian artery inferiorly. The subclavian commonly lies in front of (and covers) T1 before it joins the plexus.
The brachial trunks are formed shortly after the roots exit the intervertebral foramina in the inferior part of the neck.
- Superior (upper)trunk- the union of C5 and C6
- Middle trunk– a continuation of C7
- Inferior (lower) trunk– the union of C8 and T1
NB Injury to these can occur.
- Erb’s Palsy is a paralysis of the arm- specifically due to damage to the superior trunk, most commonly seen in babies who have had a difficult delivery (usually very large babies) for which forceps or other assistive measures have been required. The baby doesn’t move the affected arm, reflexes (including the Moro response) are absent or abnormal and the baby may have an associated Horner’s syndrome or respiratory problems. This is usually self-limiting and will resolve in several weeks.
- Klumpke’s palsyis caused in similar circumstances but the damage is to the lower trunk. This causes a claw hand, loss of grip reflex and weakness of the hand muscles. There also can be associated Horner’s/respiratory problems.
Each trunk then divides into an anterior and posterior division as the plexus passes through the cervicoaxillary canal posterior to the clavicle.
- Anterior divisions will go on to supply the anterior compartments of the arm (flexor group)
- Posterior divisions will go on to supply the posterior compartments of the arm (extensor groups)
The cords pass over the 1st rib close to the dome of the lung and continue under the clavicle, and surround the axillary artery (they are named in relation to this artery.
- Lateral cord– made up of the anterior divisions of the superior and middle trunks
- Medial cord– continuation of the anterio division of the inferior trunk
- Posterior cord- made up of the posterior divisions of all three trunks.
NB NOT ALL nerves arise from the cords of the brachial plexus- some originate at the root, trunk and division level.
Broadly speaking, the nerves arising from the brachial plexus can be split into supraclavicular branches and infraclavicular branches depending on whether they arise above or below the clavicle (respectively).
- Supraclavicular branches
- Dorsal Scapular
- Long Thoracic
- Subclavian nerve (nerve to subclavius)
- Infrascapular branches
- Lateral pectoral
- Middle Pectoral
- Medial cutaneous nerve of arm
- Median cutaneous nerve of forearm
- Upper and lower subscapulars
An astigmatism is essential an uneven curvature of the cornea.
It is usually a congenital condition although rarely can be caused by mechanical damage to the cornea e.g from a large meibomian cyst or from cataract surgery.
The patient will have reduced visual acuity. As a result, patients may get headaches in trying to accommodate for the astigmatism.
On examination, the corneal reflection may not be smooth or symmetrical.
Corneal topography will show the degree of astigmatism.
Special lenses can be used to correct the refractive error caused by an astigmatism. It may also be possible to correct the eye’s shape by using a hard contact lens, although this will not always be the case.
Patients with hypermetropia can see distant things clearly, but have trouble focusing on close things.
The problem can be either:
- the eye is too small
- the refractive power of the lens is too weak
This results in the image focusing behind the retina.
To tackle this problem, convex lenses (i.e. positive prescription e.g. +1 Diopters) are used for things like reading to bend light inwards and project the image as if it were a distance. HOWEVER, hypermetropic patients often can accommodate for their long-sightedness by relaxing (and thus thickening) the lens. Common, hypermetropic patients will present much later (than myopic patients who typically present in childhood) with the need for reading glasses. In later life, they may require glasses for both reading and distance vision as the power of the lens weakens with age even more.
Patients with severe hypermetropia are at risk of closed angle glaucoma due to their short eyes.
Patients with myopia can see close things clearly, but have trouble focusing on things in the distance.
The problem can be either:
- the eye is too long
- the refractive power of the lens is too great
This results in the image focusing in front of the retina.
To tackle this problem, concave lenses (i.e. negative prescription e.g. -1 Diopters for mild to -10 diopters for severe) are used for looking into the distance to bend light outwards and project the image as if it were near.
Patients with severe myopia are at risk of retinal detachment, macular degeneration and primary open angle glaucoma, but usually don’t require reading glasses later in life.
This is when the retina detaches from the underlying retinal pigement epithelium (RPE).
Risk factors and epidemiology
Patients with a high myopia (short-sightedness- larger than average eye) are at risk of retinal detachment due to the thinly spread retina. Retinal detachment is also a post-operative risk of cataract surgery (1-2%). Proliferative diabetic retinopathy can cause a tractional RD.
Although RD is not that common, it is an emergency, since once the macula is involved, the outcome for sight is much poorer.
Types of detachment
- Rhegmatogenous (most common type)- occurs due to a retinal break/tear/hole that allows fluid from the vitreous cavity between the retina and RPE.
- Tractional- occurs when fibrous/fibrovascular tissue (usually formed secondary to injury/inflammation/neovascularisation) attaches to the vitreous and pulls the retina from the RPE. Most commonly due to diabetic retinopathy.
- Exudative (serous) – detachment due to a build up of fluid underneathe the retina without tear/hole/break. Usually due to an inflammatory condition, but can also be secondary to hypertension, central retinal vein occlusion (haemorrhage), papilloedema or a retinal tumour.
The 4 F’s:
- Flashes- due to mechanical traction/trauma to the sensory retina. This is the differentiating symptom between PVD and a retinal tear. If they are present, the patient has a retinal tear until proven otherwise.
- Floaters- usually occur when the vitreous, too, has detached and is casting a shadow onto the retina.
- Field defects- patients usually report a shadow in their peripheral fields. This spreads as the retina detaches further. NB a superior field defect indicates pathology in the inferior retina and vice versa (likewise for left and right). Commonly this presents in a ‘theatre curtain-like’ fashion, descending from above
- The patient may have an RAPD
- check visual fields to try and isolate the location of the tear
- there may be a characteristic appearance on fundoscopy showing a pale streak across the fundus, superior to which is choroidal tissue- although this may be difficult to focus on
- there may also be some vitreous haemorrhage on fundoscopy
- Fall in acuity- this is a bad sign as it is likely that the macula +/- foveal region is detaching. If the patient loses all acuity, it is likely that this has already happened and the chances of a successful surgical repair are significantly reduced.
USS may be helpful but commonly this is a clinical diagnosis. It is more useful in exudative forms of retinal detachment, where it can detect the presence of tumours and oedema. Fundus photography can also help but should not be able to add much more than ophthalmoscopy.
There are a number of ways to fix the tear in the retina- e.g. cryotherapy, retinopexy (gas), laser treatment, scleral buckle surgery etc, depending on the size of the tear/hole and the location.