Wrist joint replacement

Question 1

What are the two types of wrst joint replacement?

Answer 1

Flexible hinge

Total wrist

Question 2

What is the main indication for wrist joint replacement?

Answer 2

Pain associated with RA and OA

Question 3

When is arthrodesis the preferred option in wrist joint pathology?

Answer 3

When only the radiocarpal joint is affected

Especially young patient and for those who through their activities exert large and regular loads on their wrist

Question 4

How many tendons cross the wrist?

Answer 4

24

Question 5

Where are the strong flexor tendons of the wrist found?

Answer 5

Carpal tunnel (formed by the transverse arch arrangement of the carpals)

Question 6

What is the primary function of the distal radioulnar joint?

Answer 6

Pronation and supination

Question 7

How is a diseased distal radioulnar joint treated?

Answer 7

Around 1cm of the distal ulna is excised and the remaining distal ulna is carefully stabilised with soft tissues

Question 8

Where is the overall composite motion of the wrist centred?

Answer 8

Fixed point on the capitate

Question 9

How much flexion and extension does the wrist normally allow?

Answer 9

80-90 degrees flexion

70-80 degrees extension

Question 10

How much abduction and adduction does the wrist allow?

Answer 10

15-20 degrees abduction

35 degrees adduction

Question 11

What range of motion of the wrist is satisfactory for activities of daily living?

Answer 11

10 degrees flexion

35 degrees extension

Question 12

What position is the wrist set at in arthrodesis?

Answer 12

20 to 30 degrees extension

Question 13

What type of joint is the radiocarpal joint?

Answer 13

Condyloid joint

Question 14

How does the shape of the radiocarpal joint affect its stability in different directions?

Answer 14

Greater radius of curvature of abduction-adduction (more stability)

Smaller radius for flexion-extension (less stability but greater arc of motion)

Question 15

How does the carpal tunnel reduce the moment about the wrist joint?

Answer 15

Maintains the strong flexor tendons close to the axis of rotation of the wrist joint

Question 16

What is the basic design of a flexible hinge prosthesis?

Answer 16

Proximal stem inserted into the medullary canal of the distal radius

Distal stem inserted into the 3rd metacarpal through the partially resected capitate

Barrel-shaped midsection

Question 17

Example of flexible hinge prosthesis?

Answer 17

Swanson

Question 18

What is the swanson prosthesis made of?

Answer 18

Silicone elastomer (rubber) - with/without titanium bone liners (grommets)

Question 19

Why were grommets introduced to the flexible hinge prosthesis?

Answer 19

Improve the durability of the implant by protecting it from sharp bone edges (was found that up to 20% tear)

Question 20

Is the flexible hinge prosthesis a total prosthesis?

Answer 20

Nope - it is a resection arthroplasty with interposition of a silicone rubber spacer (the barrel-shaped midsection)

Question 21

What is the purpose of the spacer in a flexible hinge prosthesis?

Answer 21

Helps to maintain adequate joint space and overall wrist alignment

Question 22

What changes happen over time in the flexible hinge prosthesis?

Answer 22

New ccapsulo-ligamentous system develops around the midsection
Steam are not fixed into bone so during wrist motion the implant not only articulates through the flexible midsection but the stems slide in and out of the medullary canals

Question 23

What have results found with the flexible hinge prosthesis?

Answer 23

Good pain relief, maintenance of preop ROM and correction of deformity

But after 5 years
70% show radiographic deterioration
20% have torn on the bone edges of the medullary canal
70% subside into radius, carpus or both

Question 24

Name 2 total wrist prosthese

Answer 24

Voltz

Meuli

Question 25

Describe the Meuli prosthesis

Answer 25

Distal component with eccentric pronds inserted into 2nd and 3rd metacarpals

Twin pronged radial component

Polyethylene ball (fitted on to the radial component and articulates with distal component) - ball is not constrained so permits slight distraction of the prosthesis

Question 26

What is the disadvantage of the ball-and-socket design used in the Meuli prosthesis?

Answer 26

Relies on adequate and proper soft tissue balance to prevent undesirable rotatory motion

Question 27

What are the advantages of the ball-and-ocket design used in the Meuli prosthesis?

Answer 27

Avoids the possibility of rotational failures

Reduces stresses on the anchorage of the distal and radial components - because impingement can occur only at the extremes of motion

Question 28

Describe the Voltz prosthesis

Answer 28

Metacarpal component with single stem inserted into the 3rd metacarpal

Single stem radial component

Polyethylene cup (mounted on radial component and articulates with metacarpal component)

Question 29

Describe the shape of the polyethylene cup used in a Voltz prosthesis

Answer 29

Not a true sphere

Larger radius of curvature for abduction-adduction

Question 30

What is the ROM permitted by the Voltz prosthesis?

Answer 30

90 degrees flexion-extension

50 degrees abduction-adduction

Question 31

What problems were encountered with the original Voltz and Meuli prostheses? Why?

Answer 31

Ulnar deviation - due to increased moment arms of the ulnar wrist tendons - caused by siting of the prosthetic centre of rotation radial to the normal wrist’s centre of rotation

Question 32

What were the follow-up results of the Voltz and Meuli prostheses?

Answer 32

Meuli - Stem loosening and stress shielding of dist radius 50%

Voltz - bone resorption undr radial collar 80% (better results with single stemmed)