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DOI: 10.1016/J.JHSB.2004.02.006
The Morphological and Morphometric Features of the ScaphoidFrom the Departments of Anatomy and Orthopaedics, Dokuz Eylul University, Izmir, Turkey Correspondence: Dr Izge Gunal, MD, Egitmen sok No: 32/1, Balcova, 35330 Izmir, Turkey. Tel.: + 90-232-2790329; Fax: + 90-232-2775211; E-mail: izge.gunal{at}deu.edu.tr
This cadaveric study used 200 scaphoid bones (100 left and 100 right) to assess 24 morphological and 11 morphometric parameters. At least one morphometric feature was absent in all scaphoids, though the tubercle and the dorsal sulcus were present in all instances. There were significant differences in the circumferences of the waist and the base of the tubercle, the width of the main sulcus and the secondary height of the tubercle between left and right scaphoids. Detailed knowledge of anatomy and correlations between the anatomical features may help better understanding of clinical problems.
Key Words: scaphoid • morphology • morphometry
There is limited data on the morphology and morphometry of the scaphoid bone. Osteological descriptions in anatomical texts are virtually entirely confined to the articular facets (McMinn, 1990; Williams et al., 1995), though a surgeon needs a clear idea of the scaphoid’s three-dimensional shape and variability, and these features are vital when describing fracture patterns (Compson et al., 1994). Similarly, surgical reconstruction of a scaphoid non-union aims to restore the bone’s normal shape, but there is no definition of the "normal scaphoid" or its normal variation. Compson et al. (1994) described six morphological landmarks of the scaphoid and others have made morphometric measurements indirectly from radiographs (Smith, 1993; Smith et al., 1989). This study describes the morphological and morphometric features of the scaphoid using more landmarks and direct measurement of morphometric variables.
Two hundred dry cadaver scaphoid bones (100 left and 100 right) from cadavers of unknown age and sex were used in the study. If a previous fracture was suspected, only the anatomical features in the other parts of the scaphoid were recorded. Twenty-four morphological and 11 morphometric parameters were assessed. At the beginning of the study, ten randomly selected scaphoids were assessed independently by two examiners with regard to 35 parameters. A week later, the same measurements were repeated and inter- and intra-observer reliability were assessed. All measurements were performed with a device with 0.1 mm of sensitivity. Circumferences were measured by placing a thread around them and then measuring its length.
Morphological features
The dorsal sulcus was assessed according to five parameters including its shape, and the number and location of the foramina in the main and secondary sulci. The presence of other foramina, away from the sulcus in the proximal and waist regions, was also recorded. Scaphoid pleomorphism was classed as equally developed poles or underdeveloped proximal or distal poles (Compson et al., 1994). The shape of the distal joint surface of the scaphoid was classified as "wide dorsoulnar width with a tapered radiopalmar aspect" (Type A), "wide dorsoulnar width with a round radiopalmar aspect" (Type B) and "narrow dorsoulnar width with a round radiopalmar aspect" (Type C) as described by Moritomo et al. (2000) (Fig 2). The interfacet ridge of the distal scaphoid was also classified according to its development: grade 1, not visible or palpable; grade2, not visible but palpable; grade 3, clearly visible and palpable. (Moritomo et al., 2000).
The shape of the scapholunate joint surface and the presence of an interfacet ridge were also assessed.
Morphometric measurements The narrowest circumference of the waist and the base of the tubercle were also measured. The primary height of the tubercle was defined as the distance between the most prominent point of the tubercle and the intersection of the anterior and superior ridges of the scaphocapitate articular surface, and the secondary height as the distance between the most prominent point of the tubercle and the deepest point of the waist (Fig 1). The length and width of the main dorsal sulcus were also recorded (Fig 1). Statistical analysis was performed using Spearman’s correlation analysis, Pearson’s analysis, the chi-square test or the t-test. Each variable was investigated with special reference to side and correlation among the variables.
There was no inter- and intra-observer difference in regard to morphological parameters. For morphometric parameters, mean intra-observer reliability was within 1.3 mm and inter-observer reliability was within 1.8 mm. Because of previous fractures in some scaphoids, not all of the parameters were examined in all specimens. Thus each parameter was assessed on a range of 188 to 200 scaphoids.
Morphologic parameters
The shape of the tubercle could not be defined in three bones. In the other 197 scaphoids the tubercle was conical in 142 (72%) and pyramidal in 55 (27%). Most of the scaphoids (57%) had a main dorsal sulcus, 28% had two sulci and 11% had a Y-shaped sulcus (Fig 4). In eight of the scaphoids (4%), the proximal portion of the main sulcus was absent, but the secondary sulcus was present in this region (Fig 4).
All of the scaphoids had at least one foramen in the dorsal main sulcus and 88% had more than five foramen. There was at least one foramen in the distal part of the sulcus in all bones, while18% had no foramen in the proximal region. Similarly, all scaphoids had a foramen in the secondary sulcus, with only 6% having no foramen in its proximal part. When the presence of foramina away from the sulcus was examined, 100%, 80% and 55% of scaphoids had them in the distal, waist and proximal regions respectively. Only six scaphoids had no foramen in any part of the proximal region. Fifty-eight per cent of the scaphoid bones had equally developed proximal and distal poles, while the proximal and distal poles were underdeveloped in 19% and 23% of specimens respectively. The shape of the distal articular surface was type A in 33%, type B in 47% and type C in 20%. The interfacet ridge of the distal articular surface was grade1 in 35%, grade 2 in 41% and grade 3 in 24%. The scapholunate articular surface had the shape of a halfmoon and crescent in 86% and 14% of the scaphoids examined, and 62% had an interfacet ridge. When the morphological parameters were compared between sides, there was no statistically significant difference (P>0.05). There was a very strong positive correlation between the presence of a dorsal ridge and dorsal apex (r=0.523, P<0.001), and the presence of a ridge for the origin of the scaphocapitate interosseous ligament and sulcus of the flexor carpi radialis (r=0.818, P<0.001).
Morphometric parameters
Significant correlations between morphological and morphometric features are displayed in Table 3.
The scaphoid has a highly complex three-dimensional geometry and our knowledge of this bone is insufficient for clinical practice (Compson et al., 1994). Further knowledge and awareness of variations in skeletal morphological features allows better understanding of injury patterns and carpal kinematics (Viegas, 2001). In the present study, all scaphoids had a tubercle and a dorsal sulcus (Table 1). However the sulcus for flexor carpi radialis was absent in about 25% of specimens, which may be releated to scaphoid fractures and carpal instabilities. Interestingly, we could not identify a waist in five scaphoids (Fig 3) which has not been reported before. As we do not know whether these scaphoids came from relatives or were paired scaphoids from the same person, we cannot state whether such a shape is an abnormality or a variant. Although we found a tubercle in all scaphoids, its shape was either conical or pyramidal, and its height strongly correlated with the circumference of its base. This may explain the relatively low incidence of the fractures of the tubercle which provides an insertion for the flexor retinaculum and sometimes for the origin of a few fibres of the abductor pollicis brevis muscle (Clemente, 1985). The force exerted by this muscle may explain the conical or pyramidal shape of the tubercle. The circumferences of the waist and the base of the tubercle of the left-sided scaphoids were significantly lower than those of the right scaphoids which may indicate greater force transmission on the dominant side according to Wolfe’s law. The foramina in the dorsal sulcus are thought to be related to the vascular supply of the scaphoid, and an absence of foramina in the proximal third of the scaphoid may explain the occurrence of non-union and avascular necrosis after proximal fractures (Obletz and Halbstein, 1938). However, these authors did not mention the secondary sulcus or foramina away from the dorsal sulcus. The present study demonstrated more foramina in the proximal region, with only six out of 200 scaphoids having no foramina in any part of the proximal pole. Another clinically important region of the scaphoid is its distal articular surface which it is the second most common site of degenerative change in the wrist. (Moritomo et al. (2000), found degenerative changes occurred most commonly with type B and grade 2 distal articular surfaces. Our study revealed that type B and grade 2 joints were the most common which may explain Moritomo et al.’s (2000) findings. The weak point of the present study is that dry bone specimens were used and that the age and sex of the cadavers are unknown. Thus we have no idea whether all the scaphoids which were examined were normal. Thus, some of our findings may be pathological rather than normal variants, for example the scaphoids without a waist. If so, then the high prevalence of pathological changes is worthy of attention.
Received for publication September 9, 2003. Accepted for publication January 3, 2004.
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Abstract
INTRODUCTION
