Morphology and Morphometry of the Distal Articular Surface of Lunate Bone in a Kenyan Population/ Morfologia y Morfometria de la Superficie Articular Distal del Hueso Semilunar en Una Poblacion de Kenia.
According to variations in the distal articular surface of the lunate, the bone has been categorized into Type I and Type II. A Type I lunate has one distal facet for articulation with the capitate while a Type II lunate has an additional facet medially for articulating with the hamate (Viegas et al, 1990; Nakamura et al, 2001; Dharap et al, 2006a). The prevalence of the Type II lunate ranges from 26.7 % to 73.3 % and shows population variation (Viegas et al., 1993, Dharap et al., 2006a).
Type II lunate is more prone to degenerative changes in the hamato-lunate joint (HLJ) that may cause ulnar-sided wrist pain (Burgess, 1990; Viegas et al., 1993; Nakamura et al., 2000; Galley et al., 2007; Haase et al., 2007). In Type II lunates the width of the accessory facet ranges from 1-12 mm (Viegas et al, 1993; Lamas et al, 2007). Proximal pole arthrosis of the hamate occurs not only in the presence of Type II lunates but also if the width of the medial facet (MF) exceeds 3 mm (Nakamura et al., 2001).
Wrists with a Type II lunate are larger in terms of length and width (Sagerman et al., 1995; Dyankova et al., 2007). Correlation of width of wrist with width of MF in type II lunate may allow morphometric estimation of the width of the MF from in vivo measurements of wrist width and hence the likelihood of proximal pole arthrosis as a cause of ulnar-sided wrist pain.
This study aimed at determining the prevalence of type 2 lunates and when present, correlating the width of the MF and the width of the wrist.
MATERIAL AND METHOD
Fifty-six (56) disarticulated hands were obtained from the dissection laboratory at the Department of Human Anatomy, University of Nairobi. Data was collected by a single observer in two sittings. Intra-observer variability was mitigated by taking two measurements and recording the average.
For each hand, measurements were taken using a pair of vernier calipers (SOMETTM CN-25 1234; accurate to 1 mm). The width of the wrist was measured across the mid-carpal joint and recorded. The lunate was identified from the proximal aspect between the scaphoid laterally and the triquetrum medially and incisions made to free it. Fascia and connective tissue were cleaned off and the distal articular surface was exposed by division of the dorsal intercarpal ligaments. Observation of the distal articular surface for the presence of the MF for the HLJ was done. This classified each lunate as either Type I or Type II. The width of the medial facet in Type I lunate was measured and recorded. Representative photographs were taken using a digital camera (Sony Cybershot R, DSC W50, 7.2 Megapixels).
Data Analysis. Recorded observations of lunate types and measurements o wrist width and MF width were tabulated and analysis done using SPSS Versior 17.0 (for Windows[TM] SPSS Inc., Chicago, III). Frequencies and percentages o the prevalence of morphological types of Lunate were calculated. Means, standard Deviations and ranges of the morphometric data were then computed Due to the ratio-type of data collected, the Pearson's correlation test was used to correlate measurements of wrist width with width of MF in type 2 lunates.
Fifty-six (56) human wrists (34 left and 22 right) were analyzed in this study. The morphological types of lunate described by Viegas et al. (1990 were observed.
According to the prevalence of Lunate types, out of the 56 wrists studied 34 (61 %) showed Type II Lunate (Fig. 1A), whereas 19 (34 %) had Type Lunate (Fig. 1B). Lunotriquetral fusion (Fig. 1C) was seen in 3 (5 %) of the specimens. Representative photomacrographs are shown overleaf.
In the comparison of wrist width, the mean width of wrists with type lunate was 41.1 [+ or -] 2.8 mm with a range of 37-46 mm and a median of 41 mm. In Type II wrists, the mean width was 46.1 [+ or -] 4.3 mm with a range of 38-55 mn and a median of 46 mm.
According to the width of medial facet, the average width of the media facet was 4.4 [+ or -] 1.4 mm. The median was 4 mm with a range of 2-7 mm though most (65 %, n= 34) had a width of 4-6mm as shown below in the Figure 2.
The Pearson correlation test was used to carry out the analysis. Then was no correlation between the width of the wrist and the width of the MF (p= 0.226 at 95 % CI.
Observations of the current study revealed that in the Kenyan population, the Type II lunate has a higher prevalence, occurring in 34 (61 %) than type I lunate which occurred in 19 (34 %). Both are within the range reported in literature (Table II). Prevalence of Type II lunate varies in different populations with the highest prevalence of 73 % recorded by Viegas et al. (1990) in Texas (USA) and the lowest of 26.7 % recorded by Dharap et al., (2005) in Malaysia (Table II). These differences may be due to varied ethnicities of the populations studied. Pertinent to this suggestion is an inference by Dharap et al. (2006b) which points to genetics as the reason for these observations.
The presence of a medial distal facet in type II lunate is associated with different movement patterns and ligamentous attachment in the wrist (Galley et al.). More important, it is associated with cartilage erosion and arthrosis at the HLJ which causes ulnar-sided wrist pain (Nakamura et al., 2000; Haase et al.). In a study based on 2D motion analysis of the lunate, Nakamura et al. (2000) suggested that differences in motion, joint loading and injury patterns may contribute to this higher incidence of arthrosis in wrists with Type II lunate. Subsequently, it was also noted that there was a higher incidence of arthrosis at the HLJ if the medial facet was 3 mm or more (Nakamura et al., 2001).
In our population the incidence of Type II lunate is relatively high, (61 %, n= 56) and 71 % of them had a medial facet width of 4-7 mm. This varies from report by Nakamura et al. (2001) in an American population in which 78 % had a medial facet width of 1-3 mm. This suggests that arthrosis at the HLJ may be a significant cause of ulnar-sided wrist pain in the Kenyan population. Clinicians may find this information useful in modifying their approach to management of ulnar-sided wrist pain within this population.
Anthropometric studies have shown statistically significant differences in wrist dimensions depending on lunate type. In a study by Dyankova, the basic anthropometric characteristics (length, width and height) of wrists with lunate Type II were larger than those with lunate Type I. In our study the average width of wrists with lunate Type I was 41.1 [+ or -] 2.8 mm with a range of 37-46 mm. In Type II wrists, the mean width was 46.1 [+ or -] 4.3 mm with a range of 38-55 mm, thus supporting reports that wrists with Type II lunate are larger than wrists with Type I lunate.
The use of x-rays to determine lunate morphology has limited predictive value and may therefore be inaccurate in examinations done to determine the cause of ulnar-sided wrist pain (Sagerman et al.). We had postulated that a correlation between the width of the wrist and the width of the medial lunate facet in lunate Type II may provide a better way of determining lunate morphology. Using a Pearson's correlation test we found that there was no correlation between the two parameters (p= 0.226 at 95 % CI) and thus wrist width cannot be used to determine lunate morphology.
In this study, an interesting finding was that in 5 % (n= 56) of wrists there was Lunotriquetral fusion of the complete type according to the classification of Devilliers Minnaar (1952). This is consistent with literature reports of 9 % among blacks (Szaboky et al., 1969). Carpal bone coalition may be congenital or acquired. Congenital coalitions are due to a failure of segmentation and cavitation at a site of future joint space within the carpus (Gam et al., 1976). Acquired coalitions can occur secondary to arthritis, trauma or as a metaplastic conversion of intra-articular structures to bone. It may also be a result of surgery done for joint stabilization (Poznanski & Holt, 1971).
Such coalition may present symptoms such as carpal tunnel syndrome, ulnar nerve neuropathy and pain under exhausting conditions such as repeated prehensile movements, playing musical instruments and strenuous sporting activities (Singh et al., 2003). This suggests that in cases of these conditions, coalition of carpal bones should be considered as a differential diagnosis.
As limitations, it was not possible to determine the gender of specimens thus variations according to gender were not studied. Further studies are needed so as to document the handedness of the individuals and the prevalence of carpal bone coalition. There was a shortage of data on the incidence and management of wrist pain in our local setup and we propose that clinical studies be carried out to provide a basis for better management of this clinical entity in our population.
In this study, incidence of Type II lunate was higher than Type I and this may point to proximal pole arthrosis as a cause of ulnar-sided wrist pain in our setup. There was no correlation between the width of the wrist and the width of the medial facet of the lunate. Carpal bone coalition is present in our population.
Burgess, R. C. Anatomic variations of the midcarpal joint. J. Hand Surg. Am., 15(1):129-131, 1990.
Devilliers Minnaar, A. B. Congenital fusion of the lunate and triquetral bones in the South African Bantu. J. Bone Joint Surg. Br., 34-B(1):45-8, 1952.
Dharap, A. S.; Al-Hashimi, H.; Kassab, S. & Abu-Hijleh, M. F. The hamate facet of the lunate: a radiographic study in an Arab population from Bahrain. Surg. Radiol. Anat., 28(2):1858, 2006a.
Dharap, A. S.; Lutfi, I. & Abu-Hijleh, M. F. Population variation in the incidence of the medial (hamate) facet of the carpal bone lunate. Anthropol. Anz., 64(1):59-65, 2006b.
Dyankova, S. Anthropometric characteristics of wrists joint surfaces depending on lunate types. Surg. Radiol. Anat., 29(7):551-9, 2007.
Galley, I.; Bain, G. I. & McLean, J. M. Influence of lunate type on scaphoid kinematics. J. Hand Surg. Am., 32(61:842-7, 2007.
Garn, S. M.; Burdi, A. R. & Babler, W. J. Prenatal origins of carpal fusions. Am. J. Phys. Anthropol., 45(21:203-8, 1976.
Haase, S. C.; Berger, R. A. & Shin, A. Y. Association between lunate morphology and carpal collapse patterns in scaphoid nonunions. J. HandSurg. Am., 32(7):1009-12, 2007.
Lamas, C.; Carrera, A.; Proubasta, I.; Llusa, M.; Majo, J. & Mir, X. The anatomy and vascularity of the lunate: considerations applied to Kienbock's disease. Chir.Main, 26(1):13-20,2007.
Nakamura, K.; Beppu, M.; Patterson, R. M.; Hanson, C. A.; Hume, P. J. & Viegas, S. F. Motion analysis in two dimensions of radial-ulnar deviation of type I versus type II lunates. J. Hand Surg. Am, 25(5):877-88, 2000.
Nakamura, K.; Patterson, R. M.; Moritomo, H. & Viegas, S. F. Type I versus type II lunates: Ligament anatomy and presence of arthrosis. J. Hand Surg. Am., 26(3) :428-36, 2001.
Poznanski, A. K. & Holt, J. F. The carpals in congenital malformation syndromes. Am. J. Roentgenol. Radium Ther Nucl. Med, 112(3):443-59, 1971.
Sagerman, S. D.; Hauck, R. M. & Palmer, A. K. Lunate morphology: can it be predicted with routine x-ray films? J. Hand Surg. Am., 20(1):38-41, 1995.
Singh, P.; Tuli, A.; Choudhry, R. & Mangal, A. Intercarpal fusion --A review. J. Anat. Soc. India, 52(2): 183-8, 2003.
Szaboky, G. T.; Muller, J.; Melnick, J. & Tamburro, R. Anomalous fusion between the lunate and triquetrum. J. Bone Joint Surg. Am., 51(5):1001-4, 1969.
Viegas, S. F.; Patterson, R. M.; Hokanson, J. A. & Davis, J. Wrist anatomy: incidence, distribution, and correlation of anatomic variations, tears, and arthrosis. J. Hand Surg. Am., 18(3):46375, 1993.
Viegas, S. F.; Wagner, K.; Patterson, R. & Peterson, P. Medial (hamate) facet of the lunate. J. Hand Surg. Am., 15(4):56471, 1990.
J. M. Muthoka
Department of Human Anatomy
University of Nairobi
P.O Box 30197,00100
Johnstone M. Muthoka *, Wycliff O. Kaisha *, Gachambira Gikenye *, Julius A. Ogengo *
Caption: Fig. 1. Photomacrographs showing distal articular surfaces of lunate types. A) Type II lunate in which the distal articular surface has two facets; one (FC) for the capitate and a medial facet (MF) for the hamate (HT). Note the scaphoid (SC) and the triquetrum (TM). B) Type I lunate in which the distal articular surface (LN) has a single facet for articulation with the capitate (CP). Note the hamate (HT) and the triquetrum (TM). C) Lunotriquetral fusion (LTF) in which a fused lunate and triquetrum articulates with the hamate (HT) and capitate (CP).
Caption: Fig. 2. Bar graph showing relative distribution of medial facet width.
Table I. Showing morphometric parameters of wrists according to lunate type. Type of lunate Mean wrist Width Range (mm) Median (mm) [+ or -] SD (mm) I 41.1 [+ or -] 2.8 37-46 41 II 46.1 [+ or -] 4.3 38-55 46 Table II. Showing the prevalence of lunate types in different countries. * = 5% had Lunotriquetral fusion. Author Year Country Number Incidence % Type 1 Type 2 Viegas et al. (1993) USA 393 27 73 Arai et al. (1993) Japan 127 42.5 57.5 Aufauvre et al. (1999) France 100 44 56 Nakamura et al. (2001) USA 170 29 71 Dharap et al. (2005) Malaysia 90 73.3 26.7 Dharap et al. (2006) Bahrain 381 61.2 38.8 Current study * (2016) Kenya 56 34 61