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Ebopras > Wrist Kinematics > Flashcards

Wrist Kinematics Flashcards

1
Q

What is the carpal height ratio?

A

It is the distance defined from the base of the third metacarpal to the distal subchondral bone of the radius divided
by the length of the third metacarpal. The normal ratio is 0.54±0.03.

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2
Q

What are the main muscles primarily responsible for wrist motion?

A

They include the flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis longus and brevis, and extensor carpi ulnaris (ECU).

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3
Q

What is the only muscle that inserts into the carpus?

A

Flexor carpi ulnaris attaches into the pisiform.

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4
Q

How many degrees of freedom are their pertaining to wrist range of motion?

A

There are 6 degrees of freedom: flexion, extension, radial deviation, ulnar deviation, pronation, and supination.

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5
Q

What is the intercalated segment within the wrist?

A

The proximal row (scaphoid, lunate, and triquetrum) is the intercalated segment within the wrist. The bones of the proximal row are less tightly bound together than the distal row and there is approximately three times more motion between the scaphoid and lunate compared to the lunotriquetral joint.

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6
Q

How does the position of the proximal row change with wrist range of motion?

A

During wrist flexion, the bones of the proximal row go into flexion and ulnar deviation whereas with wrist extension, they go into extension and radial deviation. Similar motion is noted within the distal carpal row albeit with less radial and ulnar deviation as noted with the proximal carpal row during wrist extension and flexion, respectively.

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7
Q

What are the different regions within the scapholunate ligament called?

A

There are three regions that comprise the scapholunate ligament: the dorsal, the membranous or proximal, and
palmar regions. In cadaveric studies, disruption of the dorsal scapholunate ligament resulted in a significant change
in the spatial relationship between the scaphoid and lunate.

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8
Q

What position does the scaphoid assume with disruption of the scapholunate ligament?

A

The scaphoid flexes and pronates with respect to the radius whereas the lunate assumes an extended position. This
is termed dorsal intercalated segment instability (DISI) of the lunate

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9
Q

What structures need to be disturbed for the lunate to assume a volar-intercalated segment instability (VISI)
position?

A

Disruption of the dorsal and palmar regions of the lunotriquetral ligament does not manifest with VISI static
instability. For VISI to be noted, disruption of the dorsal radiotriquetral or dorsal scaphotriquetral must also occur.

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10
Q

What is the normal force transmission through the wrist?

A

In neutral position and neutral ulnar variance, approximately 80% to 85% of axial load is transmitted through the
radiocarpal joint and 15% to 20% through the ulnocarpal joint.

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11
Q

What are the components of the triangular fibrocartilaginous complex (TFCC)?

A

The TFCC comprises an articular disc, superficial and deep dorsal and palmar radioulnar ligaments, ulnotriquetral,
ulnolunate, ulnocapitate ligaments, and the ECU within its subsheath.

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12
Q

What is the function of the TFCC?

A

The primary responsibility of the TFCC is to maintain stability of the distal radioulnar joint (DRUJ). In addition,
it plays an important role in force transmission across the wrist with studies showing that removal of two-thirds or
more of complex having an effect on force transmission

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12
Q

What are the dynamic and static stabilizers of the DRUJ?

A

The dynamic stabilizers of the DRUJ include the ECU and pronator quadratus whereas the static restraints include
the DRUJ capsule, ulnotriquetral and ulnolunate ligaments, interosseous membrane, and TFCC. In terms of the
latter, the primary stabilizers of the DRUJ are the palmar and dorsal radioulnar ligaments. They originate from the
distal margins of the DRUJ and appear as thickenings at the junction of the TFCC, DRUJ, and ulnocarpal capsule.
The cartilaginous disc is located centrally between these ligaments. As the radioulnar ligaments pass toward the
ulna, they divide into a superficial limb, which inserts into the ulna styloid, and a deep limb that attaches to the
fovea. They remain in a relaxed position until terminal pronation and supination, thereby permitting palmar and
dorsal translation of the ulna head over several millimeters

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13
Q

What is the stable bone of the DRUJ?

A

The ulnar is the fixed bone of the DRUJ around which the radius rotates.

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14
Q

What is the name of the articular surface of the radius that articulates with the ulnar?

A

The sigmoid notch. The sigmoid notch has a radius of curvature that is greater than that of the ulnar head.
Increased stability to this articulation is provided by the DRUJ ligaments and palmar/dorsal fibrocartilaginous
projections from the sigmoid notch.

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15
Q

What changes are seen in relation of the ulnar head to sigmoid notch of the radius during pronation and
supination?

A

In full pronation, the ulnar head rests against the dorsal lip of the sigmoid notch. In supination, the ulnar head rests
against the palmar surface of the sigmoid notch.

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16
Q

What position of the forearm reduces dorsal dislocation of the ulnar with respect to the radius?

A

These dislocations are reduced with the forearm in a supinated position

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17
Q

What is the eponym commonly given to ipsilateral radial head fractures and concomitant DRUJ injuries?

A

Essex Lopresti lesions represent ligament injury at the distal DRUJ combined with elements of attenuation or
disruption of the interosseous membrane. Its importance is related to the observation that the radius can migrate
proximally if the radial head is excised and not replaced given disruption of its distal tether at the wrist.

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18
Q

What happens to force transmission across the wrist with changes in ulnar length?

A

In patients with a short ulnar (ulnar negative variance), as often seen in Kienbock disease, there is a decrease in force
transmission across the ulnar with corresponding increase across the radiocarpal joint

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19
Q

What is the blood supply to the proximal pole of the scaphoid?

A

The main blood supply is from the radial artery and enters through small foramina in the dorsal ridge. Fractures
proximal to this area may result in avascular necrosis of the proximal pole.

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20
Q

Which extrinsic wrist ligament is felt to be the strongest support in the wrist?

A

The radioscaphocapitate ligament is felt to be the most important ligament for wrist support.

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21
Q

As the wrist moves from ulnar deviation to radial deviation, what happens to the scaphoid?

A

The scaphoid moves from an extended position into a palmar flexed position

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22
Q

What are the major extrinsic ligaments of the dorsal wrist?

A

The dorsal radiocarpal ligament and the dorsal intercarpal ligament are the major dorsal extrinsic wrist ligaments.

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23
Q

What does DISI stand for?

A

DISI stands for dorsal intercalary segment instability and is related to tears of the scapholunate ligament.

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24
Q

What is the Terry Thomas sign?

A

The Terry Thomas sign is an abnormal gap between the scaphoid and lunate that occurs in scapholunate ligament
tears. It is named after the gap-toothed British comedian.

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25
Q

The spilled tea-cup sign is seen in which carpal instability pattern?

A

The spilled tea-cup sign is seen in Volar Intercalary Segment Instability (VISI).

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26
Q

What is meant by “progressive perilunate instability”?

A

Progressive perilunate instability is a progression of injury, beginning at the scapholunate joint and progressing in
severity to total perilunate injury.

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27
Q

What is Stage I perilunate instability?

A

Stage I perilunate instability is scaphoid fracture or a scapholunate interosseous ligament tear.

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28
Q

What is Stage II perilunate instability?

A

Stage II perilunate instability is a scapholunate ligament injury with lunocapitate dislocation and a tear through the
space of Poirie

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29
Q

What is Stage III perilunate instability?

A

Stage III perilunate instability is associated with a lunotriquetral ligament tear or triquetrum fracture

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30
Q

What is Stage IV perilunate instability?

A

Stage IV perilunate instability is a lunate dislocation

31
Q

How does one differentiate a perilunate dislocation from a lunate dislocation?

A

In a perilunate dislocation, the lunate remains seated in the lunate fossa of the radius and all other carpal bones are
sitting dorsal to their typical position. In a lunate dislocation the lunate is dislocated palmarly into the carpal tunnel
and the other carpal bones are in their typical location

32
Q

What is the most common fracture in carpal bones?

A

The scaphoid is the most commonly fractured carpal bone.

33
Q

What differentiates a perilunate dislocation and a trans-scaphoid perilunate dislocation?

A

In a trans-scaphoid perilunate dislocation, the scaphoid bone is fractured and the scapholunate interosseous
ligament remains intact.

34
Q

What radiographic lines in the wrist are used to help determine normal anatomy from certain pathologic
states including lunate and perilunate dislocations?

A

Gilula lines show continuity of the radiocarpal and midcarpal joints

35
Q

What is the scaphoid shift test?

A

The scaphoid shift test is a test looking for scapholunate ligament injury. With the wrist held in ulnar deviation,
and the examiner’s thumb holding pressure on the scaphoid tubercle, the wrist is passively brought into radial
deviation. In patients with scapholunate dissociation, the scaphoid, being held extended by the thumb, shifts
dorsally causing pain and a clunk as the scaphoid moves back into the scaphoid fossa.

36
Q

What is the current treatment for the acute static scapholunate dissociation?

A

Most surgeons are currently performing scapholunate ligament repair, supplemented by some form of dorsal wrist
capsulodesis.

37
Q

What is the current treatment for lunate and perilunate dislocations?

A

The recommended treatment is ORIF with both volar capsular repair and dorsal ligament repair.

38
Q

What is the current recommendation for proximal pole fractures of the scaphoid?

A

Owing to the high rate of nonunion ORIF with screw fixation, using a dorsal approach is recommended.

39
Q

What is ulnar translocation of carpus?

A

In individuals where there is tearing of the radioscaphocapitate and long radiolunate ligaments, the carpus will
sometimes migrate ulnarly and volarly following the slope of the radius. Translocation can also occur in certain
rheumatologic conditions of the wrist.

40
Q

Which fractures of the radius are frequently associated with scapholunate ligament tears?

A

Intra-articular fractures of the radius that are in the vicinity of the scapholunate ligament are frequently associated
with scapholunate ligament tears.

41
Q

What is the appropriate initial treatment for an individual who after a fall onto an outstretched hand has
pain in the snuffbox and negative radiographs?

A

The appropriate initial treatment is short arm thumb spica splinting or casting with follow-up in 2 weeks.
Continued pain in the snuff box in the absence of x-ray findings required additional studies to rule out scaphoid
fracture (bone scan/MRI/CT scan)

42
Q

Scaphoid fractures in which location have the best prognosis?

A

Fractures of the distal pole of the scaphoid have the best prognosis. These fractures can be managed by short arm
thumb spica splint or short arm thumb spica cast.

43
Q

What is the second most commonly fractured carpal bone?

A

The triquetrum is the second most commonly fractured carpal bone. Most triquetral fractures are dorsal marginal
fractures.

44
Q

What is the most common mechanism for fractures of the hook of the hamate?

A

Most fractures of the hook of the hamate occur as the result of a direct blow.

45
Q

If one suspects a hook of the hamate fracture clinically, what is the best confirmatory study?

A

The best confirmatory for hook of hamate fractures study is a CT scan.

46
Q

In a patient with a hook of hamate nonunion, what is the best treatment?

A

The best treatment for a hook of hamate nonunion is excision of the hook of the hamate

47
Q

What imaging modality is used to stage Kienbock disease?

A

Plain radiographs are used to stage Kienbock disease. MRI is helpful in diagnosing Kienbock disease

48
Q

What are the X-ray findings in Stage I Kienbock disease?

A

X-rays are either normal or you may see linear fractures in the lunate

49
Q

What are the X-ray findings in Stage II Kienbock disease?

A

The lunate shows increased density in Stage II Kienbock disease.

50
Q

What are the X-ray findings in Stage III Kienbock disease?

A

The lunate shows collapse and/or fragmentation in Stage III Kienbock disease.

51
Q

What are the X-ray findings in Stage IV Kienbock disease?

A

Arthritis is present in Stage IV Kienbock disease.

52
Q

What X-ray finding of the bones of the forearm is associated with Kienbock disease?

A

Ulnar negative variance has been associated with Kienbock disease.

53
Q

What are the measurements of carpal height used for?

A

Measurements of carpal height are used as a means of diagnosing scapholunate dissociation. The normal ratio is
0.54. Smaller ratios are indicative of the carpal collapse seen in scapholunate dissociation

54
Q

What does the term SLAC wrist refer to?

A

The term SLAC refers to scapholunate advanced collapse.

55
Q

What is the SLAC procedure and what must be normal to consider this procedure?

A

The SLAC procedure is a four-corner (C-L-H-T) fusion with excision of the scaphoid and radial styloidectomy.
The lunate fossa and proximal articular surface of the lunate must be intact to consider this procedure.

56
Q

What radiographic findings are usually present in patients with a lunatotriquetral ligament tear?

A

Plain radiographs are usually normal in patients with isolated lunatotriquetral ligament tears. VISI deformities can
be seen in more complex LT ligament injuries.

57
Q

What are the components of the triangular fibrocartilage complex?

A

The components are the TFC proper, the ulnar collateral ligament, the ECU subsheath, the meniscus homologue,
the ulnolunate and ulnotriquetral ligaments, and the dorsal and palmar radioulnar ligaments

58
Q

What parts of the scapholunate ligament are responsible for the biomechanical behavior of the joint?

A

The thick dorsal and volar portions of the ligament are 3 mm thick and give strength and integrity to the joint.

59
Q

What is a Geisler Stage 1 scapholunate (SL) instability?

A

This is where attenuation or hemorrhage of the SL ligament can be seen from the radiocarpal joint. The SL joint
appears to be congruent when viewed from the midcarpal portal.

60
Q

What is a Geisler Stage 2 scapholunate instability?

A

Similar findings are noted within the radiocarpal joint as seen with Geisler Stage 1. The SL joint appears to be
incongruent when viewed from the midcarpal portal and a gap less than the width of a probe may be present
between the scaphoid and lunate

61
Q

What is a Geisler Stage 3 instability?

A

Incongruency/step off between the scaphoid and lunate can be seen from both the radiocarpal and midcarpal spaces
and the probe can be passed between the carpal bones.

62
Q

What is a Geisler Stage 4 instability?

A

A Geisler Stage 4 instability occurs when the arthroscope (2.7 mm) can be passed through the midcarpal joint to
the radiocarpal joint. This is also known as the drive-through sign.

63
Q

What percent of arthrograms will show a scapholunate ligament tear in an asymptomatic patient?

A

27% of arthrograms will show an SL tear in asymptomatic patients.

64
Q

What is the reported accuracy of MR arthrogram for determining SL ligament tears?

A

The reported accuracy of MR arthrography is 95%

65
Q

What is the definitive diagnostic test for intercarpal pathology?

A

Wrist arthroscopy is the definitive test for intercarpal pathology

66
Q

What is the average radial inclination of the distal radius?

A

22◦

67
Q

What is the average volar tilt of the distal radius?

A

11◦

68
Q

How many millimeters of intra-articular displacement within a distal radius fracture is considered to be
acceptable with nonoperative management?

A

Up to 1 mm of displacement.

69
Q

What is a “Colles” fracture?

A

This is a distal radius fracture with dorsal angulation, dorsal comminution, dorsal displacement, and radial
shortening.

70
Q

What is a “Smith” fracture?

A

This is a distal radius fracture with apex dorsal angulation with volar subluxation of the carpus (this is opposite to a
Colles fracture that has apex volar angulation with dorsal displacement of the carpus). This is an important
recognition as the mold placed within the cast for each fracture differs.

71
Q

What is a “Barton” fracture?

A

This is an intra-articular distal radius fractur

72
Q

Why is the assessment of median nerve function important in the examination of patients with a distal
radius fracture?

A

Patients with acute distal radius fractures can experience paresthesias within the median nerve distribution
secondary to an acute carpal tunnel syndrome. After fracture reduction, these symptoms should improve and nerve
compression can be treated with observation alone. Should they progress, an emergent release of the carpal tunnel is
indicated.

73
Q

What is the most common tendon susceptible to spontaneous rupture in undisplaced distal radius fracture?

A

The EPL tendon is susceptible to rupture and is more likely in undisplaced compared to displaced distal radius
fractures. Postulated theories for the etiology include tendon attrition and impaired blood supply to the tendon

74
Q

What is the most common tendon rupture seen with volar plating of distal radius fracture?

A

The FPL tendon is susceptible to rupture as it runs over the volar lip of the distal radius. For this reason, it is of vital
importance that the plate NOT be placed to distal.

Ebopras (32 decks)

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