Anterior cruciate ligament anatomy

ACL is attached to a depression on the posteromedial surface of the lateral condyle of femur. On the tibia it inserts into a fossa that is anterior and lateral to the anterior tibial spine. The tibial attachment is known to be stronger than the femoral attachment.

The ACL is intracapsular but is extrasynovial. Its course is anterior, medial, and distal from the femur to the tibia. Close your eyes and imagine this course. It will help you understand the mechanism of injury.

The Anterior Cruciate Ligament has 2 bands - the anteromedial band and the posterolateral band. During flexion when the back of the leg comes closer to the back of the thigh, the anterior band is taught. When the leg is straightened posterolateral band is tight.

Breast cancer, HER2 receptors and Monoclonal antibodies

One thirds of all breast malignancies have amplification of the HER2 gene. HER2 stands for human epidermal receptor type 2. HER2 receptor is a transmembrane tyrosine kinase receptor whose stimulation leads to a number of molecular pathways associated with tumor growth and progression.

Cancers that express HER2 have poorer prognosis.

Trastuzumab also known as Herceptin is a recombinant monoclonal antibody specifically directed against the HER2 receptor and it has been shown to be improve the response rate in breast cancer patients. This antibody is used in combination with chemotherapy including doxorubicin, cyclophosphamide and paclitaxel.
 
Another antibody named Lapatinib (a.k.a. Tykerb) which is a 4-anililoquinazoline kinase that inhibits the tyrosine kinase domains of HER2 receptor is also being studied.

National Comprehensive Cancer Network recommends use of these agents in addition to chemotherapy for patients with HER2-positive breast cancers that are larger than 1 cm and have spread to lymphnodes.

***This topic is hot for the USMLE***

Anterior interosseous syndrome

Anatomy: Few inches distal to the cubital fossa, the median nerve gives a branch named anterior interosseous nerve, which travels on the interosseous membrane and supplies the flexor pollicis longus (flexor of the thumb), the flexor digitorum profundus to the radial 2 digits, and the pronator quadratus at its termination. The nerve innervates the pronator teres, flexor capri radialis, the flexor digitorum sublimis, and the 2 radial flexor digitorum profundus tendons.

Symptoms: include pain in the proximal forearm and weakness of the thumb and index finger. Affected persons cannot form a circle by pinching their thumb and index finger (ie, hyperextension of index distal interphalangeal joint and thumb interphalangeal joint).

Treatment: Medical treatment includes rest, NSAIDs (Non Steroidal Anti Inflammatory Drugs), and splints. Surgical treatment includes exploration and release.

Vibrio cholera

This organism can not survive in acidic pH. Hence any condition that causes decrease stomach acidity will cause it to proliferate.

Botulism

Botulism is caused by a gram positive rod Clostridium botulinum. The toxin released by this bacteria binds irreversibly to the presynaptic membranes of peripheral neuromuscular and autonomic nerve junctions. This binding inhibits acetylcholine release, causing weakness and flaccid paralysis. The paralysis persists until the nerve endings regenerate.

The 3 types of botulism are as follows:

Infant botulism is caused by ingested spores of the bacteria which germinate in the gut releasing toxin inside the body.

Wound botulism results from contamination of a wound with toxin-producing clostridia.

Foodborne botulism occurs after consumption of contaminated food for e.g. canned vegetables.

Key points for USMLE:
-The binding of toxin is irreversible
-Infant botulism is associated with consumption of honey

Differential diagnosis of botulism:

* Guillain-Barré syndrome
* Myasthenia gravis
* Lambert-Eaton myastheic syndrome
* Polio
* Tick paralysis
* Stroke
* Diphtheric paralysis
* Congenital neuropathy or myopathy
* Snake bite (Cobra)