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Yo-yo on a string sign - Stener lesion

The yo-yo on a string sign denotes the characteristic appearance of the torn, proximally retracted and superficially displaced ulnar collateral ligament (UCL) due to a Stener lesion. Mechanism The sign occurs as a consequence of the tear of the ulnar collateral ligament of the thumb (gamekeepe...

Yunis-Varón syndrome

Yunis Varón syndrome is a rare skeletal dysplasia. It is thought to be autosomal recessive. Radiographic features severe neurologic impairment include small cerebellar vermis and dandy walker malformation cleidocranial dysplasia absent clavicles macrocrania diastasis of sutures micrognath...

Z deformity

The Z deformity is one of the musculoskeletal manifestations of rheumatoid arthritis in hand: radial deviation at the wrist ulnar deviation of the digits, and often palmar subluxation of the proximal phalanges This should be differentiated from the Z-thumb deformity, also known as the hitchi...

Z deformity (mnemonic)

A mnemonic to remember the features of Z deformity of the hand in rheumatoid arthritis is: WRD UPP Mnemonic Consider mnemonic to be pronounced "word up" to help remember it. WR: wrist radial deviation  DU: digits ulnar deviation PP: proximal phalanges palmar subluxation See also Z deform...

Zebra stripe sign (bones)

The zebra stripe sign occurs where children with osteogenesis imperfecta have been treated with cyclical bisphosphonate therapy, e.g. pamidronate. When the drug is delivered in cycles, dense bone is formed while treatment is being given. This results in dense stripes across the metaphyses of bon...

Zimmerman-Laband syndrome

Zimmerman-Laband syndrome is a rare congenital syndrome, characterized primarily by gingival hypertrophy and skeletal abnormalities.  Pathology The molecular basis of the syndrome is currently unknown. An autosomal dominant mutation with a high mutation rate and rare instances of germinal mosa...

Zona orbicularis

The zona orbicularis are circular fibers of the hip joint capsule and form a collar around the femoral neck. Though partly blended with the pubofemoral and ischiofemoral ligaments, these fibers are not directly attached to bone. 

Zone classification of flexor tendon injury

The zone classification of flexor tendon injuries divides injuries into five zones based on anatomical location. It is the most widely used flexor tendon injury classification system (c. 2007) 1. Classification Flexor tendon injuries were classified into five zones by Kleinart and Verdan in 19...


Z-scores are a way to translate individual data points into terms of a standard deviation.  Z = (X - Xbar) / σ X: individual data point Xbar: the arithmetic mean σ: the standard deviation The purpose of the Z-score is to allow comparison between values in different normal distributions. Two...


The zygoma (also known as zygomatic bone or malar bone) is an important facial bone which forms the prominence of the cheek. It is roughly quadrangular in shape. Gross anatomy Zygoma has three surfaces, five borders, and two processes. Surfaces anterolateral surface is convex, pierced at its...

Zygomaticus major muscle

The zygomaticus major muscle is a member of the buccolabial muscle group of the upper lip, a subset of the facial muscles 1. It joins with the muscle fibers of levator anguli oris, orbicularis oris and the more deeply placed muscular bands to move the side of the mouth upwards and sideways durin...

Zygomaticus minor muscle

The zygomaticus minor muscle is a member of the buccolabial muscle group of the facial muscles. Together with the levator labii superioris alaeque nasi and levator labii superioris muscles it is one of the main elevators of the lip, exposing the maxillary teeth 1. Along with its other action of ...

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