The precise knowledge of the evolution of the anatomy of the radius is essential to understand the main points of the treatment decision and the surgical principles.
General anatomy of the distal radius subdivides it in a diaphysis, metaphysis, and epiphysis. Each surface of different shape is covered by a different structure, mostly tendoninous. The angulations of the ulnar and the radial columns are different. The watershed line is the most distal limit that a standard osteosynthesis plate must not exceed.
The “radiographic check list” of the distal radius include:
radial inclination (frontal plain)
dorsal rim line
Importance of the Problem
A distal radius fracture (DRF) is a very frequent pathology, involving 15% of women after age of 50 years, in relation with decrease of bone mineral density (85% low BMD, 51% osteoporosis). Development and innovation of not only the anatomy’s comprehension, but also of the implants and approaches have considerably improved the function of these patients.
Advanced knowledge of basic anatomy and individual variations are deemed mandatory for the anatomic reduction of distal radius fractures (mainly in case of comminution) as well as to obtain fracture fixation while “staying out of trouble,” hence avoiding iatrogenic tendinous/ligamentous injuries when anatomic principles are violated.
Finding the Evidence
Cochrane search: Distal Radius Fracture
Pubmed (Medline): distal radius fracture*[tiab] AND anatom*[tiab]
Bibliography of eligible articles
Articles that were not in the English or French language were excluded.
Quality of the Evidence
For purposes of this chapter, the authors assembled the full bibliography of articles published by our unit since 2004 on the current subject. Furthermore, we included the most recent metaanalyses, reviews, and international expert
A 63-year-old woman fell on her left upper limb 10 days ago and was immobilized in a sugar tong splint ( Fig. 1 ). What radio-anatomic aspects of the radius are important to improve in this patient?
Distal radius anatomy: general aspects ( Fig. 2 )
Anatomic features of distal radius include four surfaces (anterior, lateral, posterior, and medial), the styloid process and the dorsal tubercle.
The three concave articular surfaces are the scaphoid fossa, the lunate fossa, and the sigmoid notch.
The anterior surface is concaved, palmary directed and covered by the pronator quadratus ( Fig. 2 A). The surface is rough for the attachment of the palmar radiocarpal ligaments extending radially form the radial styloid ulnarly to the TFCC. The lateral surface extends along the lateral margin to form the styloid process ( Fig. 2 B). The styloid process is conical and projects 10–12 mm distal to the articular surface for the proximal scaphoid and lunate. The radial styloid area may have a flat groove for the tendon of the first dorsal compartment (abductor pollicis longus and extensor pollicis brevis tendons).
The dorsal surface of the distal radius is irregular, convex, and acts as a fulcrum for extensor tendon function ( Fig. 2 C).
The prominent dorsal tubercle (Lister’s tubercle) lies from 5 to 10 mm from the distal joint surface. On the medial aspect of the dorsal tubercle is a smooth groove for passage of the extensor pollicis longus tendon. Ulnar to the dorsal tubercle, are grooves for passage of the extensor indicis which passes deeper than the extensor digitorum communis. The posterior interosseous nerve courses along the dorsal margin and adjacent to the cortex.
The medial surface of the distal radius consists of the ulnar notch and the articular surface for the ulnar head ( Fig. 2 D). The distal radius rotates about the ulnar head via the sigmoid notch which is concave, with a well-defined dorsal, palmar, and distal margin but variation in the depth of the articulation with the ulnar head.
The height of the ulna in respect to the radius varies with pronation and supination. There are various degrees of positive or negative ulna variance which affect the amount of force transmitted to the distal radius and to the triangular fibrocartilage complex (TFCC). Between the distal radioulnar joint and the radiocarpal joint there is a ridge, located in the ulnar notch, which provides the radial attachment for the triangular fibrocartilage. In various degrees of radio-ulnar deviation there is greater or lesser contact with the TFCC.
Fresh Look at Anatomy of the Distal Radius
Few studies of the anatomy of radial epiphysis have been published in the past 15 years. However, with the availability of new implants (intra- or extramedullary) and the recent rash of avoidable iatrogenic injuries, there is an increased need for a more detailed description of the metaphysis-epiphysis region in the distal radius. Studies on this topic are scarce and its clinical applications may be difficult to interpret.
The review by Herzberg et al. performed in 1998 on regional and bony anatomy is one of those examples. They found the anterior cortex to be thicker than the posterior cortex and the tendons and nerves to run along the dorsal side.
In 2005, Nelson characterized the most distal edge of the epiphysis and described the watershed and pronator quadratus lines ( Fig. 3 ).
The pronator quadratus line marks the highest part of the epiphysis and helps the surgeon visualize the patient-specific radius curvature. If an implant goes beyond this line when viewed on lateral radiographs, there is a potential for impingement with the thumb and finger flexor tendons. The watershed line marks the most distal edge of the epiphysis; sometimes it is as high as the pronator quadratus line, sometimes it is higher. A small 3–5 mm thick strip of bone separates these two lines. If you go past the watershed line, you will be in the joint!
Imatani et al. studied the volar aspect of the distal radius macroscopically and histologically in 20 distal forearms of 10 cadavers. The watershed line might not be a distinct line, corresponding to the distal margin of the pronator fossa in the lateral half of the volar radius and to a hypothetical line between the distal and proximal lines in the medial half.
Windish et al. defined the protuberance as the radial part of the radial epiphysis. The geometry of this protuberance varies greatly. Two recent studies from the same team provide an even better description of the distal radius. Pichler et al. found large variability in the measurements about the Lister tubercle and the extensor pollicis longus groove (cadaver study with 30 forearms) and also found a difference between the radial and ulnar slopes (cadaver study with 100 radiuses).
Buzzell et al. evaluated eight distal radius volar plates and found that the area between the plate and distal radius is very thin and varies by 3%–6%. Gasse et al. have shown in their anatomic study that the ulnar column had an average angle of 155.3 degrees and the intermediate column 144.9 degrees.
Based on this data, it seems logical to imagine using a plate of varying curvature for optimal fit on the wrist. However, because the radial epiphysis actually has two slopes (due to its two columns), it is more difficult to develop anatomical plates.
Plates that are currently available on the market have a slope of approximately 155 degrees. However, their slope is constant and does not change over the width of the radius. Four generations of plates are now available on the market. The last generation with polyaxial screw and special design of the plate in order to apply it on the ulnar column which is further forward than the radial column ( Fig. 4 ).