The radiological anatomy of the scaphoid part 1: Osteology

THE RADIOLOGICAL

ANATOMY

OF THE SCAPHOID

Part 1: Osteology J. P. COMPSON,

J. K. WATERMAN

and F. W. HEATLEY

From the Ovthopaedic Academic Unit, Rayne Institute, United Medical and Dental Schools of Guy’s and St Thomas’s, London, UK

A review of the anatomical and clinical literature found that previous descriptions of the scaphoid were not detailed enough to match our present clinical knowledge or the requirements of modern imaging. With this in mind a revised and extended description has been produced following a study of 50 dry cadaver scaphoids. The incidence of the new features described were assessed in 90 pairs of Caucasian scaphoids. Journal of Hand Surgery (British and European Volume, 1994) 19B: 183-187

The practice of surgery is based on three-dimensional anatomy. Unfortunately the anatomical basis of the science does not always match the requirements produced by our advancing clinical knowledge ( McGrouther, 199 1). For the scaphoid, osteological descriptions found in anatomical texts are virtually confined to the articular facets (Testut and Latarjet, 1948; Breathnach, 1965; Williams et al, 1989; White, 1991). In fact the only feature of the scaphoid named in the current “Nomina Anatomica” (International Anatomical Nomenclature Committee, 1989) is the tuberculum ossis scaphoidei or tubercle. Although this is important, it is only a small part of the anatomical knowledge required to treat injuries of this complex bone. The surgeon should also have a clear idea of its three-dimensional shape and variability as well as the position and orientation of the grooves and ridges which run across its surface. These features, rather than the facets, are the key to describing fracture patterns in three-dimensiolns and also how the scaphoid appears radiologically. The latter is especially important since a surgeon’s perception of anatomy is through imaging. At no point in treatment of a fracture, even in the operating theatre, does the surgeon directly see all of the bone. His decisions are therefore based on his ability to interpret these radiological images. The clinical literature is often equally at fault in using anatomical terms loosely. For example the tubercle is often incorrectly called the tuberosity. Furthermore anatomical terms are used without defining their anatomical boundaries. This makes classifications of scaphoid fracture types based on terms like proximal and distal pole imprecise. Anatomical nomenclature is also used to describe radiological appearances, for instance the waist, which do not always correspond to the true anatomy. We believe that to improve the study of this troublesome bone a more precise osteological description, based on surgical requirements, is needed. In particular the features which can be seen radiologically need to be described and named. MATERIALS

were assessed for the presence of consistent anatomical landmarks which could be used in describing the radiological anatomy. From these specimens an osteological description of the scaphoid was produced. A method of describing the complex variability found in the bones was formulated. The incidence of the features described in the first part of the study was assessed in 90 pairs of Caucasian scaphoids from the Spitalfields collection at the Natural History Museum in London. This collection of skeletons, which has been extensively used for osteological surveys, is well documented as to the sex and age of death of the specimens. Osteology

(Fig I)

The scaphoid is unique amongst the carpal bones in that it lies anatomically and functionally as a bridge between the two carpal rows. It has a highly complex three-dimensional geometry. It has six surfaces, four of which are articular facets. The lunate facet is semilunar in shape and faces medially and slightly palmarwards. The capitate facet is larger and concave and faces medially and slightly distally. The dorsal edge of the capitate facet is more concave than the palmar and can contain a notch. The position of the capitate facet varies in its relationship to the proximal end of the scaphoid, which leads to an associated variability in the width of the lunate facet (Fig 2). The radial facet is convex and faces proximally and laterally. The distal surface is a combined facet for the trapezoid and trapezium and faces predominantly distally but also slightly dorsally. Occasionally a ridge in the articular surface marks the boundary between the two articulations. The remaining two surfaces, dorsal and palmar, are non-articular. The dorsal surface is long and thin and, in a neutral position of the wrist, lies transverse to the long axis of the limb and parallel to the distal articular surface of the radius. It has two prominent features, a dorsal sulcus and a dorsal ridge. The dorsal sulcus is the more distal of the two and extends laterally to the tip of the tubercle. It is normally single but can be double. Proximal to the sulcus is a dorsal ridge which marks the distal end of the radial facet. It does not

AND METHODS

50 dry cadaver scaphoids were selected at random. The race and sex of the bones were unknown. The bones 183

184

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DISTAL

6.

;

**

ULNAR

PROXIMAL

Fig 1

(a) Palmar (b) Dorsal (c) Radial and (d) Ulnar views of a left scaphoid.

D.A. = Dorsal apex of the ridge. L.A. = Lateral apex of the ridge. TUB. = Tuber& S.C.=Scapho-capitate joint. S.L. =Scapho-lunate joint. S.R. =Scapho-radial joint. S.T.T. =Scapho-trapezium-trapezoid

joint.

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185

TUBERCLE.

Fig 2

(a and b). Ulnar view of two left scaphoids showing variance in the size of the lunate facet (shaded area) and the ridge which is the origin of the scapho-capitate interosseous ligament (*).

normally extend laterally as far as the sulcus. At its dorso-medial end it has a prominence, the dorsal apex of the ridge. Laterally as it turns palmarwards towards the tubercle there is another prominence, the lateral apex of the ridge, which is best seen in contour. The palmar surface is also non-articular. Proximally it is flat and faces anteriorly. Projecting palmarwards and slightly laterally is the tubercle which is highly variable in size compared to the rest of the bone. The boundaries of the tubercle are difficult to define since the landmarks in this area are inconsistent (Fig 3). However it is roughly pyramidal in shape. One side arises from the palmar surface of the body and faces proximally. Another side faces distally and contains the articular facet of the trapezium and the lateral end of the sulcus. The third side faces medially and slightly palmarwards and sometimes has a groove for flexor carpi radialis. Occasionally its base is marked with a small ridge where the scapho-capitate interosseous ligament inserts (Fig 2). The body of the scaphoid can therefore be defined as the part of the scaphoid which is not the tubercle. The scaphoid has a central narrowing or waist (Fig 4).

Fig 3

Views of a left scaphoid showing the surface markings of the base of the tubercle. A: palmar, B: radial, C: ulnar, D: dorsal.

The surface marking on the bone is a line which runs across the capitate facet from the centre of the dorsal edge to the centre of the palmar edge. It then passes across the palmar surface along the base of the tubercle to a point just distal to the lateral apex of the ridge. It then crosses the dorsal sulcus obliquely to its starting point. Defining the proximal and distal poles is arbitrary, due to the lack of natural boundaries. However the most consistent definition would be to describe the proximal pole as the area proximal to the waist and the distal pole as the area distal to the waist. Though the shape of the scaphoid appears complex, this can be simplified if the body and tubercle are considered as two individual parts. The body is oval in outline, oval in cross-section and concave towards the capitate in two planes. The tubercle, arising from the distal end of the body, projects palmarwards and radially. Although the body has no intrinsic rotation in its long axis, the offset tubercle gives the complete bone a twisted appearance. Because of the variability in the tubercle, both in its relative size and the angle it subtends

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WAIST.

Fig 4

Views of a left scaphoid anatomical waist.

showing

the surface

markings

of the

to the body, the amount of this apparent twist varies considerably.

Fig 5

Scaphoid pleomorphism

Left: Equally developed poles. Middle: Underdeveloped proximal pole. Right: Underdeveloped distal pole. * = Lateral apex of the ridge. ’ = Dorsal apex of the ridge. Shaded area = area of scapho-lunate joint.

On assessment of the shape of the 50 scaphoids it appeared that, although there was significant variation, this could be simplified by describing the shape in terms of development of the two poles. Hence there are three possible morphological types (Fig 5): 1. Equally developed poles 2. Underdeveloped proximal pole 3. Underdeveloped distal pole

Photograph (a) showing radial view and (b) line illustrations showing ulnar and radial views of three right scaphoids illustrating pleomorphism in development of the poles.

Table l-Percentage

DISCUSSION

Evaluation and treatment of injuries to the scaphoid remains one of the most difficult problems in hand

Female

Male L

Incidence of anatomical features

All of the anatomical features described above, when assessed in the 90 pairs of Caucasian scaphoids, were present in most of the bones studied (Table 1).

presence of anatomical landmarks

Tubercle Waist Dorsal sulcus Dorsal ridge Dorsal apex of the ridge Lateral apex of the ridge

R

L

R

n=44

n=44

n=46

n=46

100 100 93 98

100 100 95 98

100 100 93 82

100 100 93 80

100

100

98

98

100

98

98

98

OSTEOLOGY

OF SCAPHOID

surgery. We believe that a major contributing factor is the confusing image produced by the bone radiologically. This is particularly relevant when it has undergone rotation or collapse following fracture. Unfortunately, since many of the clinical decisions made by a surgeon are based on interpreting radiological images into true anatomy, a full understanding of this complex radiographic anatomy is essential for successful treatment. This requires ;a thorough knowledge of the shape of the scaphoid, its surface anatomy and how the shape and anatomical features project on each X-ray view. The shape of the scaphoid is complex and we strongly recommend any surgeon treating scaphoid fractures to study dry cadaver bones. We believe that the shape can be simplified by looking at the body and the tubercle as separate entities, with the body being bean-shaped and the tubercle offset from the distal end by about 45”. This explains the twisted appearance of the overall bone. By visualizing the bone in various planes one can then appreciate the outline one sees on X-ray views. There are other anatomical features which are essential for describing the outline. The previous osteological descriptions were not detailed enough for this purpose and we have (described and named new landmarks, in particular the dorsal ridge and apices. Likewise other features, for instance the dorsal sulcus which, though described by other authors (Lindgren, 1949; Herbert, 1990), needed to be defined in more detail. We have als,o tried to define anatomical parts of the scaphoid, in particular the waist, proximal and distal poles, which are often used in describing the site of scaphoid fractures. Unfortunately many authors use these apparently anatomical terms to describe radiologi-

187

cal images rather than true anatomy. This is particularly true of the apparent waist seen in the outline of the bone on postero-anterior X-ray views. This ‘radiological’ waist is rarely the same as the true anatomical waist due to the foreshortening of the bone which normally lies in flexion. The position of this apparent waist is highly dependent on the angle of the X-ray beam, which changes with carpal alignment. We believe that, to clarify the situation, all terms used to describe the scaphoid should be based on true anatomy. We not only use this extended description of the scaphoid to interpret the radiological anatomy but also to define the fracture patterns found in the bone. Acknowledgements We are grateful for financial support for this project from the Wishbone of the BOA, and the Special Trustees of St Thomas’s Hospital.

Trust

References BREATHNACH, A. S. Frazer’s Anatomy ofthe Human Skeleton, 6th Edn. London, Churchill, 1965: 93. HERBERT, T. J. The Fractured Scaphoid. St Louis, Quality Medical Publishing, 1990: 13. LINDGREN. E. (1949). Some radiological asuects of the carnal scauhoid and its fractures. kcta khirurgica Scanldinavica, 98: 538-548. _ _ McGROUTHER, D. A. (1991). Anatomy, descriptive and surgical. Journal of Hand Surgery, 16B: 3: 240-242. INTERNATIONAL ANATOMICAL NOMENCLATURE COMMITTEE. Nomina Anatomica, 6th Edn. Edinburgh, Churchill Livingstone, 1989: A23. TESTUT, L. and LATARJET, A. Traits! D’Anatomie Humaine, 9th Edn. Paris, Doin, 1948: Vol 1: 340-341. WHITE, T. D. Human Osteology, London, Academic Press, 1991: 193. WILLIAMS, P. L., WARWICK, R., DYSON, M. and BANNISTER, L. H. Gray’s Anatomy, 37th Edn. Edinburgh, Churchill Livingstone, 1989: 417.

Accepted: 14 September 1993 MI J. P. Compson, Orthopaedic Lambeth

Palace

Road,

Q 1994 The Britisb

London

Society

Academic Unit, SE1 7EH. UK.

for Surgery

of the Hand

Rayne

Institute,

St Thomas’s

Hospital,