Distribution of Scaphoid Nutrient Foramina
Patricia Quinn Owira, James Kigera, Hassan Saidi
School of Medicine, University of Nairobi
Correspondence to: Dr. James Kigera, P.O Box 30196-00100 Nairobi.
Introduction: Avascular necrosis (AVN) is a frequent complication of scaphoid fractures especially those involving the proximal segment of the bone. This has been attributed to its precarious blood supply which is further compromised by the fracture and surgery. Knowledge of the distribution of scaphoid nutrient foramina, which show variation across populations, is thus important in estimating the risk of vascular damage during surgical approaches and hence the likelihood of AVN. It may also be useful in determining techniques to mitigate this risk. The purpose of this study was to describe the distribution of scaphoid nutrient foramina in adult Kenyans. Methods: One hundred and four human scaphoids were studied. Each was divided into 3 segments: proximal, middle and distal, and the nutrient foramina in each segment counted and categorized into type I (no foramina), type II (1-2 foramina) and type III (>2 foramina). The number of nutrient foramina on the dorsal and volar aspects of the bone was also compared. Results: Type I nutrient foramina were most common (54%) in the proximal segment of the bone while the middle and distal segments had predominantly type III and type II foramina respectively. More foramina were present on the dorsal aspect with a dorsal-volar ratio of 4.23:1. Conclusion: The dorsal approach may result in more damage to nutrient foramina heightening the risk of avascular necrosis. Non-unions in the proximal segment may require vascularized bone grafts.
Keywords: Scaphoid, Nutrient Foramina, Non Union, Avascular Necrosis
Ann Afr Surg. 2016;13(2): 49-51.
Scaphoid fractures are common injuries representing about 60-70% of all carpal fractures with approximately 20% of them occurring at the proximal pole (1-3). These injuries have an increased risk of delayed union and avascular necrosis (AVN) (4, 5). AVN has been reported to occur in 13 to 50% of scaphoid fractures, with an even higher incidence in those involving the proximal segment of the bone (4, 6). This has been attributed to the precarious blood supply of this region. The blood supply to the scaphoid comes mainly from the radial artery and the proximal pole has been shown to have limited interosseous supply (7, 8). Alternative blood supply comes from the dorsal, laterovolar and distal groups of extraossoeus blood vessels that enter the bone via foramina on the surface of the bone (7). Studying these foraminal pattern can inform on the vascularization of the bone (9). The types of foramina have been previously classified by Dubey et al (9). Knowing the distribution of vascular foramina may aid in evaluating the vascularity of the different segments of the bone. This may be useful in explaining the risk of AVN and in determining the role of vascularised grafts in the management of delayed and non union (9-11). Although the surgical approach to this bone depends on many factors, knowledge of the pattern of blood supply to the volar and dorsal surfaces of the bone may indicate the degree of vascular damage likely to be caused by the chosen surgical approach(12). While some studies have been conducted on vascular foramina, few describe the vascularity per segment and none have been conducted in the African region. This descriptive cross-sectional study therefore sought to describe the distribution of nutrient foramina in the bone in a Kenyan population.
One hundred and four dry adult human scaphoids were obtained from the Department of Osteology, National Museums of Kenya, Nairobi. Broken scaphoids and those that showed obvious gross malformations were excluded from the study. The scaphoid was divided and demarcated into 3 equal portions: the proximal, middle and distal segments. The number of foramina per segment was then counted on both volar and dorsal surfaces of the bone with the aid of a magnifying lens. The average of two counts was taken to minimize errors. We modified the classification initially proposed by Dubey et al (9). The specimen were categorized into type I (no foramina), type II (1-2 foramina) and type III (>2 foramina).
There were fifty two pairs of bones; 21 being male, 16 female and 15 of unknown sex. In the proximal segment, type I nutrient foramina were the most common (54%) with type III nutrient foramina being prevalent in the middle segment (51%). The distal segment showed a dominance of type II nutrient foramina (52%) (Table 1). No type I nutrient foramina was observed at the middle and distal segments. The average number of nutrient foramina in the proximal segment was 1 while that in the middle and distal segments was 4 and 3 respectively. There were more nutrient foramina in the dorsal aspect with a dorsal-volar ratio of 4.23:1.
*Each bone is counted twice, once for the dorsal side and once for the volar side
The proximal segment had a more precarious blood supply evidenced by the high frequency of type I nutrient foramina and the lower number of nutrient foramina in the proximal segment. This may explain the increased occurrence of AVN and non union in this segment (4). This is somewhat consistent with the findings by Purushothama et al. that showed 15% of scaphoids had no nutrient foramina in the proximal segment and also by Ceri et al. that showed that 18% of scaphoids had no nutrient foramina in the proximal segment (13, 14). There is however conflicting data on the vascularity of the bone from other authors who conten