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Association Between Lunate Morphology and Carpal Collapse in Cases of Scapholunate Dissociation
SCIENTIFIC ARTICLE
Association Between Lunate Morphology and Carpal Collapse in Cases of Scapholunate Dissociation Peter C. Rhee, DO, Steven L. Moran, MD, Alexander Y. Shin, MD
Purpose Type II lunate morphology has recently been shown to decrease the incidence of dorsal intercalated segment instability (DISI) deformity in patients with scaphoid nonunions. A similar association has been suggested for scapholunate dissociation, but a formal comparison has yet to be performed. The purpose of this study was to determine if an association exists between lunate morphology and DISI in cases of scapholunate dissociation. Methods A retrospective review was performed on 58 patients with the diagnosis of scapholunate dissociation as determined by use of radiographs, magnetic resonance imaging, arthrotomy, and arthroscopy. Posteroanterior radiographs were used to assess the presence of a medial facet on the lunate and to determine the distance between the capitate and the triquetrum. A DISI deformity was defined as a radiolunate angle ⬎15°, and scapholunate instability was defined as a scapholunate angle ⬎60° using the tangential method. Statistical analysis was performed with a chi-squared test and kappa test. Results Twenty-five patients had a type I lunate, and 33 patients had a type II lunate. A total of 15 patients had DISI deformity on preoperative radiographs; of these, 10 patients with a type I lunate and 5 patients with a type II lunate had DISI deformity. This difference was found to be significant. Conclusions In cases of scapholunate dissociation, type II lunates were associated with a significantly lower incidence of DISI despite having radiographic or arthroscopic evidence of a complete scapholunate interosseous ligament tear. Osseous morphology may play a role in the development of a radiographic DISI deformity. Further research is required to assess the clinical importance of this finding and the biomechanical cause of this phenomenon. (J Hand Surg 2009;34A:1633–1639. © 2009 Published by Elsevier Inc. on behalf of the American Society for Surgery of the Hand.) Type of study/level of evidence Prognostic II. Key words Carpal bones, dorsal intercalated segmental instability, lunate morphology, scapholunate dissociation. UNATE MORPHOLOGY VARIES within the human wrist. Lunate morphology has been linked to the development of midcarpal arthritis, as well as the development of Kienböck’s disease.1– 4 Two major types of lunate morphology have been described in the
L
From the Division of Plastic Surgery, Mayo Clinic, Rochester, MN; and the Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN. Received for publication August 28, 2008; accepted in revised form June 16, 2009. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Correspondingauthor:StevenL.Moran,MD,200FirstStreetSW,Rochester,MN55905;e-mail: [email protected]. 0363-5023/09/34A09-0007$36.00/0 doi:10.1016/j.jhsa.2009.06.017
literature, and these are the type I and type II lunate. This categorization is based on the absence (type I) or presence (type II) of a medial facet articulation with the hamate.5–7 The incidence of a type II lunate in the general population has been reported to be between 27% and 73%.1,8,9 The biomechanical importance of this facet has been the source of some debate within the literature; however, presence of the facet in a type II lunate increases the incidence of proximal hamate arthritis, suggesting that the facet has some biomechanical consequences within the midcarpal joint.1–3 Further evidence for the importance of lunate morphology was recently presented by Haase and colleagues. The authors found that a type II lunate was
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TABLE 1.
INFLUENCE OF LUNATE MORPHOLOGY ON DISI
Etiology of Wrist Pain Etiology
Number of Patients
Hyperextension (fall on outstretched hand)
17
Traumatic Motor vehicle accident
7
Crush/blunt injury
5
Work related
3
Sports related
3
Laceration
1
Degenerative (or absence of specific traumatic event)
22
Total
58
Note: The majority of cases of wrist pain could be linked to a specific traumatic event. Twenty-two patients could not recall a specific event leading to their wrist pain.
associated with a decreased incidence of dorsal intercalated segment instability (DISI) deformity in patients with scaphoid nonunions.8 DISI deformity refers to an abnormally extended position of the lunate in the sagittal plane, best seen on lateral projections.10 Dorsal rotation of the lunate about a transverse axis is attributed to an uncoupling of the flexion moment of the scaphoid combined with the extension moment of the lunate, via the lunotriquetral ligament. Such uncoupling has been reported to occur by disruption of the scapholunate ligament, otherwise known as scapholunate dissociation, or by unstable fractures of the scaphoid.11 Within Haase’s publication, the authors theorized that the added lunohamate articulation was protective against abnormal extension of the lunate, providing an additional bony constraint to lunate extension in the absence of an intact scaphoid.8 These findings suggest that the lunohamate articulation may also provide a constraint to lunate extension in cases of scapholunate ligament injury; however, such a study has yet to be performed. The purpose of this study was to determine if an association exists between lunate morphology and DISI in cases of scapholunate dissociation. We hypothesize that the lunohamate articulation of type II lunates will decrease the incidence of DISI deformation in cases of scapholunate dissociation. MATERIALS AND METHODS After institutional review board approval was received, a retrospective review of the surgical records was performed for patients with a pre-procedure diagnosis of
FIGURE 1: Patients were initially screened for ICD-9 codes for the diagnosis of wrist instability. Subsequently, these patients were then cross-matched against a surgical index to select patients who had a surgical procedure for wrist instability. After the initial screening, there were 213 wrists involved in 206 patients with a diagnosis of “wrist instability” who had a procedure. The diagnosis of scapholunate dissociation was then confirmed in 150 wrists by either MRI, arthrotomy, or arthroscopy. Thirty-nine wrists were then excluded because of exclusion criteria, and an additional 48 wrists were excluded for inadequate preoperative xrays. Finally, 5 patients refused to participate in the study leaving 58 wrists for analysis. All patients had a procedure that included surgical repair, reconstruction, or arthroscopy.
“scapholunate dissociation/disruption/tear,” “wrist instability,” or “dorsal wrist pain” from the years 2000 through 2007. The search was limited to patients treated by the two senior authors (S.L.M. and A.Y.S.). All patients had originally presented to their physician with wrist pain. The etiology of wrist pain was variable but was due to a specific traumatic event in 36 of the 58 patients (Table 1). Twenty-two patients could not recall a specific traumatic event leading to their wrist pain, and their wrist pain was classified as degenerative as opposed to traumatic etiology. Table 1 lists the specific mechanism of injury for each patient. Figure 1 provides a flowchart for the inclusion process and means used to obtain the final cohort. All chart and radiographic review was performed by one ob-
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server (P.C.R.). Additionally, age, gender, and hand dominance were observed for each patient. Inclusion criteria were confirmed scapholunate dissociation due to scapholunate ligament disruption and age 12 to 80 years. Scapholunate dissociation was defined as a complete tear noted on magnetic resonance imaging (MRI), arthrotomy, arthroscopy, or scapholunate advanced collapse arthritis on radiographs. Exclusion criteria were a history of scaphoid fracture, previous wrist surgery, congenital wrist abnormalities, history of inflammatory arthritis, and/or multiligamentous wrist injuries. Patients were also excluded if their preoperative radiographs were inadequate for obtaining a true measurement of the scapholunate and radiolunate angles. Surgical reports revealed 150 cases with a confirmed diagnosis of scapholunate dissociation as diagnosed by use of MRI, arthrotomy, or arthroscopy. Of these 150 cases, 39 wrists were excluded due to the above exclusion criteria, and an additional 48 wrists were excluded due to inadequate preoperative radiographs. Finally, 5 patients refused to participate in the study. A total of 58 cases remained for evaluation. Lunate morphology was determined with use of posteroanterior (PA) radiographs.1 Radiographs were examined for the absence (type I) or presence (type II) of a medial hamate facet on the lunate. Capitate-totriquetrum distance was also evaluated in these patients according to the method of Galley et al.12 Galley’s method measures the shortest distance between the capitate and triquetrum and then defines lunate morphology based on this value. Using this method, we define type 1 lunate as a capitate-to-triquetrum distance of ⱕ2 mm, a type II lunate as a capitate-to-triquetrum distance of ⱖ4 mm, and an intermediate lunate as a capitate-totriquetrum distance of ⱖ2.1 mm or ⱕ3.9 mm. Dorsal intercalated segment instability was present if the radiolunate angle on true lateral radiographs was found to be ⬎15°. Radiographic scapholunate instability was defined as a scapholunate angle ⬎60°. The tangential method was used for measurements.13,14 The correlation between an increased scapholunate angle and a DISI deformity was also investigated. Carpal angles were recorded from true lateral wrist radiographs. The tangential method as described by Larsen et al. was used.15 Standardization of lateral wrist radiographs was accomplished by excluding radiographs with a radius-to-long finger metacarpal angle greater than 20° from neutral to limit spurious extension or flexion of the carpal bones.16,17 In addition, lateral radiographs with inadequate distal radioulnar overlap or scaphopisocapitate relationships were excluded.18 A ra-
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dioscaphoid angle of 45° was used as a reference position of the scaphoid and indicates palmar flexion of the scaphoid.19 Comparisons with the contralateral wrist in each patient were not made because these radiographs were not consistently available. We are aware of the controversy regarding the definition of carpal instability among experts.20 For the purpose of this study, we adopted the definition of carpal instability as proposed by the International Wrist Investigators’ Workshop. The radiographic definition of DISI as defined by this committee is as follows: “on a lateral radiograph centered on the wrist, with the wrist in neutral flexion/ extension and prono-supination, the lunate is dorsiflexed with regard to the long axis of the radius, by 15° or more.”21 Carpal angles flexed to the palmar side with respect to the axis of the radius were recorded as positive angles and those extended toward the dorsal side defined as negative angles.22 Thus, a finding of DISI was defined as a radiolunate angle of –15°.16,23 Statistical analysis was performed using the chisquared test to determine if a statistically significant difference existed between the variables. Statistical significance was set at p ⬍ .05. The agreement between the methods used to assess lunate morphology and DISI deformity were performed using kappa statistic. A slight (0.01– 0.20), fair (0.21– 0.40), moderate (0.61– 0.80), substantial (0.61– 0.80), and almost perfect (0.81– 0.99) agreement was noted for the corresponding kappa values. This examination was performed to judge the validity of assessing lunate morphology with the Galley method in the presence of a scapholunate gap, as one would expect the capitate-to-triquetrum distance to increase with increasing scapholunate diastasis.12 Groups were compared to identify differences in age, gender, and hand dominance using a 2-sample t-test, Wilcoxon rank sum test, or a Fisher’s exact test. RESULTS Of the 58 patients, there were 29 men and 29 women. The average age of patients was 39 years, ranging from 12 to 80 years (Table 2). Based on the PA x-ray for the presence of a medial facet, type I lunates existed in 25 patients and type II lunates in 33 patients. When assessing lunate type by capitate-to-triquetrum distance, there were 7 type I lunates, 33 type II lunates, and 18 intermediate lunates. Use of the Galley method provided only a fair agreement ( ⫽ .3924) with the more established PA radiographic analysis of lunate morphology.2,5,8 Because of this fair agreement (Table 3), statistical analysis between groups was performed based on the PA radiographic technique of determining lunate
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TABLE 2.
Patient Demographics
Characteristic Years of age, mean ⫾ SD Years of age, median (min, max)
Overall (N ⫽ 58)
Type I (n ⫽ 25)
Type II (n ⫽ 33)
p Value
39 ⫾ 18
41 ⫾ 17
38 ⫾ 20
.60*
40 (12, 80)
43 (13, 75)
34 (12, 80)
.40†
Gender, n (%)
.79‡
Women
29 (50)
13 (52)
16 (48)
Men
29 (50)
12 (48)
17 (52)
4 (7)
1 (4)
3 (9)
Hand dominance, n (%) Left NA Right
.70‡ 8 (14)
3 (12)
5 (15)
46 (79)
21 (84)
25 (76)
Note: There were no significant differences noted between groups with regard to age, gender, or hand dominance. NA, not applicable. *Two-sample t-test performed. †Wilcoxon rank sum test performed. ‡Chi-square test/Fisher’s exact test performed.
TABLE 3.
Number of Lunate Type Based on PA X-ray and Capitate-to-Triquetrum Distance PA X-ray Type I
Intermediate
Type II
Total Number
7
0
0
7 (12%)
14
0
4
18 (31%)
Capitate-to-triquetrum distance Type I Intermediate Type II Total number
4
0
29
33 (57%)
25 (43%)
0 (0%)
33 (57%)
58 (100%)
type. No differences were noted in either group with regard to gender, age, or hand dominance (Table 2). Based on the radiolunate angle, DISI was present in 10 of 25 patients with type I lunates and 5 of 33 patients with type II lunates (p ⫽ .04). Examination of the scapholunate angle identified 14 of 25 in type I lunates as having scapholunate instability (scapholunate angle ⬎60°) and only 12 of 33 type II lunates showing a scapholunate angle ⬎60° (p ⫽ .14) (Table 4). A discrepancy existed in 4 of 25 type I and 8 of 33 (24%) type II lunates (p ⫽ .44) in which a normal radiolunate angle (x ⬍ 15°) was present with an increased scapholunate angle (x ⬎ 60°). There was a moderate agreement ( ⫽ .5282) between the incidence of DISI and midcarpal instability. DISCUSSION The lunate has been described as the keystone of the wrist.24 Alterations in the radiographic position of the lunate result in the development of the carpal instability
TABLE 4. Presence of DISI and Scapholunate Instability Type I, No. (%) (n ⫽ 25)
Type II, No. (%) (n ⫽ 33)
Radiolunate angle ⱕ15°
15 (60%)
28 (85%)
Radiolunate angle ⬎15°
10 (40%)
5 (15%)
DISI
p Value .04
Scapholunate instability
.14
Scapholunate angle ⱕ60°
11 (44%)
21 (64%)
Scapholunate angle ⬎60°
14 (56%)
12 (36%)
dissociative patterns of DISI or volar intercalated segment instability. DISI is commonly known to occur after a scaphoid nonunion or disruption of the scapholunate ligament. This study found that in the presence of scapholunate injury, the incidence of a DISI deformity
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FIGURE 2: Radiograph (PA view) of type II lunate with medial (hamate) facet.
was significantly lower in type II lunates when compared with that in patients with type I lunates. A previous study showed that the incidence of DISI in scaphoid nonunions was markedly lower in type II lunates. It was theorized that the added lunohamate articulation may serve as a bony restraint restricting lunate hyperextension.8 In that study, a DISI deformity was present in 71% of type I lunates and in 17% of type II lunates.25 This percentage is similar to the 15% (5 of 33) of type II lunates noted to be in a DISI posture in our study. The incidence of type II lunates has been reported to be from 27% to 73%.1,8,9 The wide variation on the incidence of type II lunates is thought to be due to differences in research methods, angle measurement, and differences in populations studied.24 For example, Dharap et al. found that the incidence of type II lunates was 39% in Arab subjects from Bahrain, whereas type II lunates existed in 66% of Bulgarian subjects in another study.9,26 Lunate type has been classified by one of two methods in the literature. One method is to determine the absence or presence of the medial (hamate) facet of the lunate on neutral PA wrist radiographs (Fig. 2). The ability to accurately identify type II lunate has been reported at 64% to 72% in one study.2 Dyankova and Marinov attest that identifying type II lunates with a medial facet of less than 3 mm is “very difficult or impossible” in 15% of plain radiographs.27 Direct visualization of the medial lunate facet, either arthroscopically or at the time of arthrotomy, would provide the most accurate means of classifying lunate morphology; unfortunately in this retrospective study, a description of lunate morphology was not present in all
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FIGURE 3: PA view of radiograph of type I lunate with increased capitate-to-triquetrum distance, which has resulted from a widened scapholunate interval.
of the surgical reports; therefore radiographic classification was required. The other method of lunate classification is based on the shortest distance between the capitate and the triquetrum on PA radiographs. This was based on the observation by Viegas and colleagues that small medial facets could be missed on x-ray.1,5,6,28 Dyankova and Marinov stated that medial (hamate) facets of less than 3 mm could be classified as type I lunates erroneously.27 An increase in the capitate-to-triquetrum distance was noted to be present in addition to a radiographic medial facet.29 Galley et al. used the capitate-totriquetrum distance to classify type I lunate, type II lunate, and an intermediate group, formed by a mixture of both types, in healthy volunteers without wrist pathology.12 However, we found that in cases of scapholunate dissociation, a false type II lunate could exist based on an increased capitate-to-triquetrum distance. This was seen specifically in patients presenting with a wide scapholunate diastasis on PA radiographs and proximal migration of the capitate. In this situation, the capitate pushes the lunate in the ulnar direction and consequently moves the triquetrum farther away from the capitate (Fig. 3). When comparing the capitate-totriquetrum distance method to the standard, only a fair agreement was noted. Although both methods of lunate morphology classification can be inaccurate using PA radiographs, we used the first method to classify lunate type and suggest use of the former method in cases of scapholunate ligament disruption. A more definitive means of lunate classification is necessary, and future prospective studies should include direct arthroscopic
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verification of lunate type with measurements of the facet size; unfortunately, such documentation was not found consistently during chart review in all cases within this study. In our study, we also attempted to correlate midcarpal instability, as defined by a radiolunate angle ⬎15°, and scapholunate instability, as defined by a scapholunate angle ⬎60°. Both measurements were obtained using the tangential method.13,14 We observed 4 of 25 type I lunates and 8 of 33 type II lunates with normal radiolunate angles but abnormal scapholunate angles. We believe that the added lunohamate articulation may prevent extension of the lunate, despite disruption of the scapholunate interosseous ligament. The added lunohamate articulation, with the additional changes noted in midcarpal ligament position with type II lunates, may stabilize lunate position despite unchecked pull of the lunotriquetral ligament in some cases of scapholunate injury. Such speculation must be validated in future biomechanical studies. In many cases, early scapholunate injuries are difficult to appreciate radiographically. So-called “dynamic” scapholunate injury patterns are not identifiable on standard radiographs but may be perceived with stress view radiographs. Previous biomechanical studies have shown that isolated division of the scapholunate interosseus ligament may not always produce instability appreciable on plain radiographs.30 Berger et al. demonstrated few kinematic changes after scapholunate interosseus ligament sectioning.31 Meade et al. also noted that division of the palmar and dorsal portions of the scapholunate interosseus ligament resulted in only a modest increase in the scapholunate gap, to 2.6 mm.32 Other investigators have noted that radiographic signs of scapholunate instability become visible on plain radiographs once other extrinsic ligaments are sectioned.33–38 It is now thought that repetitive motion after scapholunate interosseous ligament injuries will produce attritional changes in these secondary stabilizers, resulting potentially in their eventual failure over time. Our study suggests that lunate morphology may also play a role in stabilizing lunate position after scapholunate injury. Further support for this theory has also been provided by Galley et al., who found that wrists with a type I lunate displayed “row” mechanics and those with type II lunates exhibited “column” mechanics.12 Future studies will have to be performed to confirm the influence of lunate type and associated wrist kinematics on long-term outcome. Limitations of this study are the low number of lunates for investigation, although this study was pow-
ered to detect large differences. In addition, because of the retrospective nature of the study, we found that lunate morphology was not consistently noted within the surgical reports; thus, radiographic identification of lunate type was required. We acknowledge that with use of our lunate identification method, we may have missed some type II lunates with small medial facets; however, it should be noted that the incidence of type II lunates in our study compares favorably with the reported range in the literature. More so, our 57% (33) incidence of type II lunates in cases of scapholunate dissociation is very similar to the 53% incidence of type II lunates in cases of scaphoid nonunions from the same institution.8 One reviewer classified each lunate and recorded each radiographic marker. Therefore, the observations were reviewer dependent. However, interobserver variability was excluded. Finally, this cohort was limited to patients with symptomatic scapholunate injuries; thus, the findings of this study may not be applicable to asymptomatic patients or to patients with wrist instability due to other causes such as adaptive carpal instability or nondissociative carpal instability. REFERENCES 1. Viegas SF, Patterson RM, Hokanson JA, Davis J. Wrist anatomy: incidence, distribution, and correlation of anatomic variations, tears, and arthrosis. J Hand Surg 1993;18A:463– 475. 2. Sagerman SD, Hauck RM, Palmer AK. Lunate morphology: can it be predicted with routine x-ray films? J Hand Surg 2000;25A:877– 888. 3. Nakamura K, Patterson RM, Morimoto H, Viegas SF. Type I versus type II lunates: ligament anatomy and presence of arthrosis. J Hand Surg 2001;26A:428 – 436. 4. Amadio PC, Moran SL. Fractures of the carpal bones. In: Green DP, Hotchkiss RN, Pederson WC, Wolfe S, eds. Green’s operative hand surgery, 5th ed. Philadelphia: Elsevier Churchill Livingston, 2005: 711–768. 5. Viegas SF, Wagner K, Patterson R, Peterson P. Medial (hamate) facet of the lunate. J Hand Surg 1990;15A:564 –571. 6. Viegas SF. The lunatohamate articulation of the midcarpal joint. Arthroscopy 1990;6:5–10. 7. Burgess RC. Anatomic variations of the midcarpal joint. J Hand Surg 1990;15A:129 –131. 8. Haase SC, Berger RA, Shin AY. Association between lunate morphology and carpal collapse patterns in scaphoid nonunions. J Hand Surg 2007;32A:1009 –1012. 9. Dyankova S. Anthropometric characteristics of wrists joint surfaces depending on lunate types. Surg Radiol Anat 2007;29:551–559. 10. Linscheid RL, Boyns JH, Beabout JW, Bryan RS. Traumatic instability of the wrist. Diagnosis, classification, and pathomechanics. J Bone Joint Surg 1972;54A:1612–1632. 11. Smith DK, Gilula LA, Amadio PC. Dorsal lunate tilt (DISI configuration): sign of scaphoid waist displacement. Radiology 1990;176: 497– 499. 12. Galley I, Bain G, McLean J. Influence of lunate type on scaphoid kinematics. J Hand Surg 2007;32A:842– 847. 13. Sarafian SK, Melamed JL, Goshgarian GM. Study of wrist motion in flexion and extension. Clin Orthop 1977;126:153–159. 14. Gilula LA, Weeks PM. Post-traumatic ligamentous instabilities of the wrist. Radiology 1978;129:641– 651. 15. Larsen CF, Mathiesen FK, Lindequist S. Measurements of carpal bone angles on lateral wrist radiographs. J Hand Surg 1991;16A:888–893.
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16. Nakamura R, Hori M, Imamura T, Horii E, Miura T. Method for measurement and evaluation of carpal bone angles. J Hand Surg 1989;14A:412– 416. 17. Tay SC, Moran SL, Shin AY, Linscheid RL. The clinical implications of scaphotrapezium-trapezoidal arthritis with associated carpal instability. J Hand Surg 2007;32A:47–54. 18. Yang Z, Mann FA, Gilula LA, Haerr C, Larsen CF. Scaphopisocapitate alignment: criterion to establish a neutral lateral view of the wrist. Radiology 1997;205:865– 869. 19. Linscheid RL, Dobyns JH, Beckenbaugh RD, Cooney WP III, Wood MB. Instability patterns of the wrist. J Hand Surg 1983;8:682– 686. 20. The Anatomy and Biomechanics Committee of the International Federation of Societies for Surgery of the Hand. Definition of carpal instability. J Hand Surg 1999;24A:866 – 867. 21. Gilula LA, Mann FA, Dobyns JH, Yin Y, the members of the IWIW (International Wrist Investigators’ Workshop Terminology Committee). Wrist terminology as defined by The International Wrist Investigators’ Workshop (IWIW). J Bone Joint Surg 2002;84A:S1–S66. 22. Yasuda M, Kusunoki M, Kazuki K, Yamano Y. Correction of dorsi-flexed intercalated segment instability after restoration of scaphoid height in a cadaver model of scaphoid non-union. J Hand Surg 1995;20B:596 – 602. 23. Linscheid RL. Kinematic considerations of the wrist. Clin Orthop 1986;202:27–39. 24. Sennwald G, Segmuller G. Base anatomique d’un nouveau concept de stabilite du carpe. [Anatomic basis of a new concept of stability of the carpus.] Int Orthop 1986;10:25–30. 25. Craigen MA, Stanley JK. Wrist kinematics. Row, column or both? J Hand Surg 1995;20B:165–170. 26. Dharap AS, Al-Hashimi H, Kassab S. The hamate facet of the lunate: a radiographic study in an Arab population from Bahrain. Surg Radiol Anat 2006;28:185–188. 27. Dyankova S, Marinov G. Comments about “The hamate facet of the lunate: a radiographic study in an Arab population from Bahrain.” Surg Radiol Anat 2007;29:181.
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28. Nakamura K, Beppu M, Patterson RM, Hanson CA, Hume PJ, Viegas SF. Motion analysis in two dimensions of radial-ulnar deviation of type I versus type II lunates. J Hand Surg 2000;25A:877– 888. 29. Nakamura K, Beppu M, Matushita K, Arai T, Ide T. Biomechanical analysis of the stress force on midcarpal joint in Kienbock’s disease. Hand Surg 1997;2:101–115. 30. Crisco JJ, Pike S, Hulsizer-Galvin DL, Akelman E, Weiss AP, Wolfe SW. Carpal bone posture and motions are abnormal in both wrists of patients with unilateral scapholunate interosseous ligament tears. J Hand Surg 2003;28A:926 –937. 31. Berger RA, Blair WF, Crowninshield RD, Flatt AE. The scapholunate ligament. J Hand Surg 1982;7:87–91. 32. Meade TD, Schneider LH, Cherry K. Radiographic analysis of selective ligament sectioning at the carpal scaphoid: a cadaver study. J Hand Surg 1990;15A:855– 862. 33. Short WH, Werner FW, Green JK, Masaoka S. Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate: part II. J Hand Surg 2005;30A:24 –34. 34. Short WH, Werner FW, Green JK, Masaoka S. Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate. J Hand Surg 2002;27A:991–1002. 35. Short WH, Werner FW, Green JK, Weiner MM, Masaoka S. The effects of sectioning the dorsal radiocarpal ligament and insertion of a pressor sensor into the radiocarpal joint on scaphoid and lunate kinematics. J Hand Surg 2002;27A:68 –76. 36. Ruch DS, Smith BP. Arthroscpoic and open management of dynamic scaphoid instability. Orthop Clin North Am 2001;32:233–240. 37. Patterson RM, Moritomo H, Yamaguchi S, Mitsuyasu H, Shah MA, Buford WL, Viegas SF. Scaphoid anatomy and mechanics: update and review. Atlas Hand Clin 2004;9:129 –140. 38. Mitsuyasu H, Patterson RM, Shah MA, Buford WL, Iwamoto Y, Viegas SF. The role of the dorsal intercarpal ligament in dynamic and static scapholunate instability. J Hand Surg 2004;29A:279 –288.
JHS 䉬 Vol A, November
Association Between Lunate Morphology and Carpal Collapse in Cases of Scapholunate Dissociation Peter C. Rhee, DO, Steven L. Moran, MD, Alexander Y. Shin, MD
Purpose Type II lunate morphology has recently been shown to decrease the incidence of dorsal intercalated segment instability (DISI) deformity in patients with scaphoid nonunions. A similar association has been suggested for scapholunate dissociation, but a formal comparison has yet to be performed. The purpose of this study was to determine if an association exists between lunate morphology and DISI in cases of scapholunate dissociation. Methods A retrospective review was performed on 58 patients with the diagnosis of scapholunate dissociation as determined by use of radiographs, magnetic resonance imaging, arthrotomy, and arthroscopy. Posteroanterior radiographs were used to assess the presence of a medial facet on the lunate and to determine the distance between the capitate and the triquetrum. A DISI deformity was defined as a radiolunate angle ⬎15°, and scapholunate instability was defined as a scapholunate angle ⬎60° using the tangential method. Statistical analysis was performed with a chi-squared test and kappa test. Results Twenty-five patients had a type I lunate, and 33 patients had a type II lunate. A total of 15 patients had DISI deformity on preoperative radiographs; of these, 10 patients with a type I lunate and 5 patients with a type II lunate had DISI deformity. This difference was found to be significant. Conclusions In cases of scapholunate dissociation, type II lunates were associated with a significantly lower incidence of DISI despite having radiographic or arthroscopic evidence of a complete scapholunate interosseous ligament tear. Osseous morphology may play a role in the development of a radiographic DISI deformity. Further research is required to assess the clinical importance of this finding and the biomechanical cause of this phenomenon. (J Hand Surg 2009;34A:1633–1639. © 2009 Published by Elsevier Inc. on behalf of the American Society for Surgery of the Hand.) Type of study/level of evidence Prognostic II. Key words Carpal bones, dorsal intercalated segmental instability, lunate morphology, scapholunate dissociation. UNATE MORPHOLOGY VARIES within the human wrist. Lunate morphology has been linked to the development of midcarpal arthritis, as well as the development of Kienböck’s disease.1– 4 Two major types of lunate morphology have been described in the
L
From the Division of Plastic Surgery, Mayo Clinic, Rochester, MN; and the Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN. Received for publication August 28, 2008; accepted in revised form June 16, 2009. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Correspondingauthor:StevenL.Moran,MD,200FirstStreetSW,Rochester,MN55905;e-mail: [email protected]. 0363-5023/09/34A09-0007$36.00/0 doi:10.1016/j.jhsa.2009.06.017
literature, and these are the type I and type II lunate. This categorization is based on the absence (type I) or presence (type II) of a medial facet articulation with the hamate.5–7 The incidence of a type II lunate in the general population has been reported to be between 27% and 73%.1,8,9 The biomechanical importance of this facet has been the source of some debate within the literature; however, presence of the facet in a type II lunate increases the incidence of proximal hamate arthritis, suggesting that the facet has some biomechanical consequences within the midcarpal joint.1–3 Further evidence for the importance of lunate morphology was recently presented by Haase and colleagues. The authors found that a type II lunate was
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TABLE 1.
INFLUENCE OF LUNATE MORPHOLOGY ON DISI
Etiology of Wrist Pain Etiology
Number of Patients
Hyperextension (fall on outstretched hand)
17
Traumatic Motor vehicle accident
7
Crush/blunt injury
5
Work related
3
Sports related
3
Laceration
1
Degenerative (or absence of specific traumatic event)
22
Total
58
Note: The majority of cases of wrist pain could be linked to a specific traumatic event. Twenty-two patients could not recall a specific event leading to their wrist pain.
associated with a decreased incidence of dorsal intercalated segment instability (DISI) deformity in patients with scaphoid nonunions.8 DISI deformity refers to an abnormally extended position of the lunate in the sagittal plane, best seen on lateral projections.10 Dorsal rotation of the lunate about a transverse axis is attributed to an uncoupling of the flexion moment of the scaphoid combined with the extension moment of the lunate, via the lunotriquetral ligament. Such uncoupling has been reported to occur by disruption of the scapholunate ligament, otherwise known as scapholunate dissociation, or by unstable fractures of the scaphoid.11 Within Haase’s publication, the authors theorized that the added lunohamate articulation was protective against abnormal extension of the lunate, providing an additional bony constraint to lunate extension in the absence of an intact scaphoid.8 These findings suggest that the lunohamate articulation may also provide a constraint to lunate extension in cases of scapholunate ligament injury; however, such a study has yet to be performed. The purpose of this study was to determine if an association exists between lunate morphology and DISI in cases of scapholunate dissociation. We hypothesize that the lunohamate articulation of type II lunates will decrease the incidence of DISI deformation in cases of scapholunate dissociation. MATERIALS AND METHODS After institutional review board approval was received, a retrospective review of the surgical records was performed for patients with a pre-procedure diagnosis of
FIGURE 1: Patients were initially screened for ICD-9 codes for the diagnosis of wrist instability. Subsequently, these patients were then cross-matched against a surgical index to select patients who had a surgical procedure for wrist instability. After the initial screening, there were 213 wrists involved in 206 patients with a diagnosis of “wrist instability” who had a procedure. The diagnosis of scapholunate dissociation was then confirmed in 150 wrists by either MRI, arthrotomy, or arthroscopy. Thirty-nine wrists were then excluded because of exclusion criteria, and an additional 48 wrists were excluded for inadequate preoperative xrays. Finally, 5 patients refused to participate in the study leaving 58 wrists for analysis. All patients had a procedure that included surgical repair, reconstruction, or arthroscopy.
“scapholunate dissociation/disruption/tear,” “wrist instability,” or “dorsal wrist pain” from the years 2000 through 2007. The search was limited to patients treated by the two senior authors (S.L.M. and A.Y.S.). All patients had originally presented to their physician with wrist pain. The etiology of wrist pain was variable but was due to a specific traumatic event in 36 of the 58 patients (Table 1). Twenty-two patients could not recall a specific traumatic event leading to their wrist pain, and their wrist pain was classified as degenerative as opposed to traumatic etiology. Table 1 lists the specific mechanism of injury for each patient. Figure 1 provides a flowchart for the inclusion process and means used to obtain the final cohort. All chart and radiographic review was performed by one ob-
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server (P.C.R.). Additionally, age, gender, and hand dominance were observed for each patient. Inclusion criteria were confirmed scapholunate dissociation due to scapholunate ligament disruption and age 12 to 80 years. Scapholunate dissociation was defined as a complete tear noted on magnetic resonance imaging (MRI), arthrotomy, arthroscopy, or scapholunate advanced collapse arthritis on radiographs. Exclusion criteria were a history of scaphoid fracture, previous wrist surgery, congenital wrist abnormalities, history of inflammatory arthritis, and/or multiligamentous wrist injuries. Patients were also excluded if their preoperative radiographs were inadequate for obtaining a true measurement of the scapholunate and radiolunate angles. Surgical reports revealed 150 cases with a confirmed diagnosis of scapholunate dissociation as diagnosed by use of MRI, arthrotomy, or arthroscopy. Of these 150 cases, 39 wrists were excluded due to the above exclusion criteria, and an additional 48 wrists were excluded due to inadequate preoperative radiographs. Finally, 5 patients refused to participate in the study. A total of 58 cases remained for evaluation. Lunate morphology was determined with use of posteroanterior (PA) radiographs.1 Radiographs were examined for the absence (type I) or presence (type II) of a medial hamate facet on the lunate. Capitate-totriquetrum distance was also evaluated in these patients according to the method of Galley et al.12 Galley’s method measures the shortest distance between the capitate and triquetrum and then defines lunate morphology based on this value. Using this method, we define type 1 lunate as a capitate-to-triquetrum distance of ⱕ2 mm, a type II lunate as a capitate-to-triquetrum distance of ⱖ4 mm, and an intermediate lunate as a capitate-totriquetrum distance of ⱖ2.1 mm or ⱕ3.9 mm. Dorsal intercalated segment instability was present if the radiolunate angle on true lateral radiographs was found to be ⬎15°. Radiographic scapholunate instability was defined as a scapholunate angle ⬎60°. The tangential method was used for measurements.13,14 The correlation between an increased scapholunate angle and a DISI deformity was also investigated. Carpal angles were recorded from true lateral wrist radiographs. The tangential method as described by Larsen et al. was used.15 Standardization of lateral wrist radiographs was accomplished by excluding radiographs with a radius-to-long finger metacarpal angle greater than 20° from neutral to limit spurious extension or flexion of the carpal bones.16,17 In addition, lateral radiographs with inadequate distal radioulnar overlap or scaphopisocapitate relationships were excluded.18 A ra-
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dioscaphoid angle of 45° was used as a reference position of the scaphoid and indicates palmar flexion of the scaphoid.19 Comparisons with the contralateral wrist in each patient were not made because these radiographs were not consistently available. We are aware of the controversy regarding the definition of carpal instability among experts.20 For the purpose of this study, we adopted the definition of carpal instability as proposed by the International Wrist Investigators’ Workshop. The radiographic definition of DISI as defined by this committee is as follows: “on a lateral radiograph centered on the wrist, with the wrist in neutral flexion/ extension and prono-supination, the lunate is dorsiflexed with regard to the long axis of the radius, by 15° or more.”21 Carpal angles flexed to the palmar side with respect to the axis of the radius were recorded as positive angles and those extended toward the dorsal side defined as negative angles.22 Thus, a finding of DISI was defined as a radiolunate angle of –15°.16,23 Statistical analysis was performed using the chisquared test to determine if a statistically significant difference existed between the variables. Statistical significance was set at p ⬍ .05. The agreement between the methods used to assess lunate morphology and DISI deformity were performed using kappa statistic. A slight (0.01– 0.20), fair (0.21– 0.40), moderate (0.61– 0.80), substantial (0.61– 0.80), and almost perfect (0.81– 0.99) agreement was noted for the corresponding kappa values. This examination was performed to judge the validity of assessing lunate morphology with the Galley method in the presence of a scapholunate gap, as one would expect the capitate-to-triquetrum distance to increase with increasing scapholunate diastasis.12 Groups were compared to identify differences in age, gender, and hand dominance using a 2-sample t-test, Wilcoxon rank sum test, or a Fisher’s exact test. RESULTS Of the 58 patients, there were 29 men and 29 women. The average age of patients was 39 years, ranging from 12 to 80 years (Table 2). Based on the PA x-ray for the presence of a medial facet, type I lunates existed in 25 patients and type II lunates in 33 patients. When assessing lunate type by capitate-to-triquetrum distance, there were 7 type I lunates, 33 type II lunates, and 18 intermediate lunates. Use of the Galley method provided only a fair agreement ( ⫽ .3924) with the more established PA radiographic analysis of lunate morphology.2,5,8 Because of this fair agreement (Table 3), statistical analysis between groups was performed based on the PA radiographic technique of determining lunate
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TABLE 2.
Patient Demographics
Characteristic Years of age, mean ⫾ SD Years of age, median (min, max)
Overall (N ⫽ 58)
Type I (n ⫽ 25)
Type II (n ⫽ 33)
p Value
39 ⫾ 18
41 ⫾ 17
38 ⫾ 20
.60*
40 (12, 80)
43 (13, 75)
34 (12, 80)
.40†
Gender, n (%)
.79‡
Women
29 (50)
13 (52)
16 (48)
Men
29 (50)
12 (48)
17 (52)
4 (7)
1 (4)
3 (9)
Hand dominance, n (%) Left NA Right
.70‡ 8 (14)
3 (12)
5 (15)
46 (79)
21 (84)
25 (76)
Note: There were no significant differences noted between groups with regard to age, gender, or hand dominance. NA, not applicable. *Two-sample t-test performed. †Wilcoxon rank sum test performed. ‡Chi-square test/Fisher’s exact test performed.
TABLE 3.
Number of Lunate Type Based on PA X-ray and Capitate-to-Triquetrum Distance PA X-ray Type I
Intermediate
Type II
Total Number
7
0
0
7 (12%)
14
0
4
18 (31%)
Capitate-to-triquetrum distance Type I Intermediate Type II Total number
4
0
29
33 (57%)
25 (43%)
0 (0%)
33 (57%)
58 (100%)
type. No differences were noted in either group with regard to gender, age, or hand dominance (Table 2). Based on the radiolunate angle, DISI was present in 10 of 25 patients with type I lunates and 5 of 33 patients with type II lunates (p ⫽ .04). Examination of the scapholunate angle identified 14 of 25 in type I lunates as having scapholunate instability (scapholunate angle ⬎60°) and only 12 of 33 type II lunates showing a scapholunate angle ⬎60° (p ⫽ .14) (Table 4). A discrepancy existed in 4 of 25 type I and 8 of 33 (24%) type II lunates (p ⫽ .44) in which a normal radiolunate angle (x ⬍ 15°) was present with an increased scapholunate angle (x ⬎ 60°). There was a moderate agreement ( ⫽ .5282) between the incidence of DISI and midcarpal instability. DISCUSSION The lunate has been described as the keystone of the wrist.24 Alterations in the radiographic position of the lunate result in the development of the carpal instability
TABLE 4. Presence of DISI and Scapholunate Instability Type I, No. (%) (n ⫽ 25)
Type II, No. (%) (n ⫽ 33)
Radiolunate angle ⱕ15°
15 (60%)
28 (85%)
Radiolunate angle ⬎15°
10 (40%)
5 (15%)
DISI
p Value .04
Scapholunate instability
.14
Scapholunate angle ⱕ60°
11 (44%)
21 (64%)
Scapholunate angle ⬎60°
14 (56%)
12 (36%)
dissociative patterns of DISI or volar intercalated segment instability. DISI is commonly known to occur after a scaphoid nonunion or disruption of the scapholunate ligament. This study found that in the presence of scapholunate injury, the incidence of a DISI deformity
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FIGURE 2: Radiograph (PA view) of type II lunate with medial (hamate) facet.
was significantly lower in type II lunates when compared with that in patients with type I lunates. A previous study showed that the incidence of DISI in scaphoid nonunions was markedly lower in type II lunates. It was theorized that the added lunohamate articulation may serve as a bony restraint restricting lunate hyperextension.8 In that study, a DISI deformity was present in 71% of type I lunates and in 17% of type II lunates.25 This percentage is similar to the 15% (5 of 33) of type II lunates noted to be in a DISI posture in our study. The incidence of type II lunates has been reported to be from 27% to 73%.1,8,9 The wide variation on the incidence of type II lunates is thought to be due to differences in research methods, angle measurement, and differences in populations studied.24 For example, Dharap et al. found that the incidence of type II lunates was 39% in Arab subjects from Bahrain, whereas type II lunates existed in 66% of Bulgarian subjects in another study.9,26 Lunate type has been classified by one of two methods in the literature. One method is to determine the absence or presence of the medial (hamate) facet of the lunate on neutral PA wrist radiographs (Fig. 2). The ability to accurately identify type II lunate has been reported at 64% to 72% in one study.2 Dyankova and Marinov attest that identifying type II lunates with a medial facet of less than 3 mm is “very difficult or impossible” in 15% of plain radiographs.27 Direct visualization of the medial lunate facet, either arthroscopically or at the time of arthrotomy, would provide the most accurate means of classifying lunate morphology; unfortunately in this retrospective study, a description of lunate morphology was not present in all
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FIGURE 3: PA view of radiograph of type I lunate with increased capitate-to-triquetrum distance, which has resulted from a widened scapholunate interval.
of the surgical reports; therefore radiographic classification was required. The other method of lunate classification is based on the shortest distance between the capitate and the triquetrum on PA radiographs. This was based on the observation by Viegas and colleagues that small medial facets could be missed on x-ray.1,5,6,28 Dyankova and Marinov stated that medial (hamate) facets of less than 3 mm could be classified as type I lunates erroneously.27 An increase in the capitate-to-triquetrum distance was noted to be present in addition to a radiographic medial facet.29 Galley et al. used the capitate-totriquetrum distance to classify type I lunate, type II lunate, and an intermediate group, formed by a mixture of both types, in healthy volunteers without wrist pathology.12 However, we found that in cases of scapholunate dissociation, a false type II lunate could exist based on an increased capitate-to-triquetrum distance. This was seen specifically in patients presenting with a wide scapholunate diastasis on PA radiographs and proximal migration of the capitate. In this situation, the capitate pushes the lunate in the ulnar direction and consequently moves the triquetrum farther away from the capitate (Fig. 3). When comparing the capitate-totriquetrum distance method to the standard, only a fair agreement was noted. Although both methods of lunate morphology classification can be inaccurate using PA radiographs, we used the first method to classify lunate type and suggest use of the former method in cases of scapholunate ligament disruption. A more definitive means of lunate classification is necessary, and future prospective studies should include direct arthroscopic
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verification of lunate type with measurements of the facet size; unfortunately, such documentation was not found consistently during chart review in all cases within this study. In our study, we also attempted to correlate midcarpal instability, as defined by a radiolunate angle ⬎15°, and scapholunate instability, as defined by a scapholunate angle ⬎60°. Both measurements were obtained using the tangential method.13,14 We observed 4 of 25 type I lunates and 8 of 33 type II lunates with normal radiolunate angles but abnormal scapholunate angles. We believe that the added lunohamate articulation may prevent extension of the lunate, despite disruption of the scapholunate interosseous ligament. The added lunohamate articulation, with the additional changes noted in midcarpal ligament position with type II lunates, may stabilize lunate position despite unchecked pull of the lunotriquetral ligament in some cases of scapholunate injury. Such speculation must be validated in future biomechanical studies. In many cases, early scapholunate injuries are difficult to appreciate radiographically. So-called “dynamic” scapholunate injury patterns are not identifiable on standard radiographs but may be perceived with stress view radiographs. Previous biomechanical studies have shown that isolated division of the scapholunate interosseus ligament may not always produce instability appreciable on plain radiographs.30 Berger et al. demonstrated few kinematic changes after scapholunate interosseus ligament sectioning.31 Meade et al. also noted that division of the palmar and dorsal portions of the scapholunate interosseus ligament resulted in only a modest increase in the scapholunate gap, to 2.6 mm.32 Other investigators have noted that radiographic signs of scapholunate instability become visible on plain radiographs once other extrinsic ligaments are sectioned.33–38 It is now thought that repetitive motion after scapholunate interosseous ligament injuries will produce attritional changes in these secondary stabilizers, resulting potentially in their eventual failure over time. Our study suggests that lunate morphology may also play a role in stabilizing lunate position after scapholunate injury. Further support for this theory has also been provided by Galley et al., who found that wrists with a type I lunate displayed “row” mechanics and those with type II lunates exhibited “column” mechanics.12 Future studies will have to be performed to confirm the influence of lunate type and associated wrist kinematics on long-term outcome. Limitations of this study are the low number of lunates for investigation, although this study was pow-
ered to detect large differences. In addition, because of the retrospective nature of the study, we found that lunate morphology was not consistently noted within the surgical reports; thus, radiographic identification of lunate type was required. We acknowledge that with use of our lunate identification method, we may have missed some type II lunates with small medial facets; however, it should be noted that the incidence of type II lunates in our study compares favorably with the reported range in the literature. More so, our 57% (33) incidence of type II lunates in cases of scapholunate dissociation is very similar to the 53% incidence of type II lunates in cases of scaphoid nonunions from the same institution.8 One reviewer classified each lunate and recorded each radiographic marker. Therefore, the observations were reviewer dependent. However, interobserver variability was excluded. Finally, this cohort was limited to patients with symptomatic scapholunate injuries; thus, the findings of this study may not be applicable to asymptomatic patients or to patients with wrist instability due to other causes such as adaptive carpal instability or nondissociative carpal instability. REFERENCES 1. Viegas SF, Patterson RM, Hokanson JA, Davis J. Wrist anatomy: incidence, distribution, and correlation of anatomic variations, tears, and arthrosis. J Hand Surg 1993;18A:463– 475. 2. Sagerman SD, Hauck RM, Palmer AK. Lunate morphology: can it be predicted with routine x-ray films? J Hand Surg 2000;25A:877– 888. 3. Nakamura K, Patterson RM, Morimoto H, Viegas SF. Type I versus type II lunates: ligament anatomy and presence of arthrosis. J Hand Surg 2001;26A:428 – 436. 4. Amadio PC, Moran SL. Fractures of the carpal bones. In: Green DP, Hotchkiss RN, Pederson WC, Wolfe S, eds. Green’s operative hand surgery, 5th ed. Philadelphia: Elsevier Churchill Livingston, 2005: 711–768. 5. Viegas SF, Wagner K, Patterson R, Peterson P. Medial (hamate) facet of the lunate. J Hand Surg 1990;15A:564 –571. 6. Viegas SF. The lunatohamate articulation of the midcarpal joint. Arthroscopy 1990;6:5–10. 7. Burgess RC. Anatomic variations of the midcarpal joint. J Hand Surg 1990;15A:129 –131. 8. Haase SC, Berger RA, Shin AY. Association between lunate morphology and carpal collapse patterns in scaphoid nonunions. J Hand Surg 2007;32A:1009 –1012. 9. Dyankova S. Anthropometric characteristics of wrists joint surfaces depending on lunate types. Surg Radiol Anat 2007;29:551–559. 10. Linscheid RL, Boyns JH, Beabout JW, Bryan RS. Traumatic instability of the wrist. Diagnosis, classification, and pathomechanics. J Bone Joint Surg 1972;54A:1612–1632. 11. Smith DK, Gilula LA, Amadio PC. Dorsal lunate tilt (DISI configuration): sign of scaphoid waist displacement. Radiology 1990;176: 497– 499. 12. Galley I, Bain G, McLean J. Influence of lunate type on scaphoid kinematics. J Hand Surg 2007;32A:842– 847. 13. Sarafian SK, Melamed JL, Goshgarian GM. Study of wrist motion in flexion and extension. Clin Orthop 1977;126:153–159. 14. Gilula LA, Weeks PM. Post-traumatic ligamentous instabilities of the wrist. Radiology 1978;129:641– 651. 15. Larsen CF, Mathiesen FK, Lindequist S. Measurements of carpal bone angles on lateral wrist radiographs. J Hand Surg 1991;16A:888–893.
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16. Nakamura R, Hori M, Imamura T, Horii E, Miura T. Method for measurement and evaluation of carpal bone angles. J Hand Surg 1989;14A:412– 416. 17. Tay SC, Moran SL, Shin AY, Linscheid RL. The clinical implications of scaphotrapezium-trapezoidal arthritis with associated carpal instability. J Hand Surg 2007;32A:47–54. 18. Yang Z, Mann FA, Gilula LA, Haerr C, Larsen CF. Scaphopisocapitate alignment: criterion to establish a neutral lateral view of the wrist. Radiology 1997;205:865– 869. 19. Linscheid RL, Dobyns JH, Beckenbaugh RD, Cooney WP III, Wood MB. Instability patterns of the wrist. J Hand Surg 1983;8:682– 686. 20. The Anatomy and Biomechanics Committee of the International Federation of Societies for Surgery of the Hand. Definition of carpal instability. J Hand Surg 1999;24A:866 – 867. 21. Gilula LA, Mann FA, Dobyns JH, Yin Y, the members of the IWIW (International Wrist Investigators’ Workshop Terminology Committee). Wrist terminology as defined by The International Wrist Investigators’ Workshop (IWIW). J Bone Joint Surg 2002;84A:S1–S66. 22. Yasuda M, Kusunoki M, Kazuki K, Yamano Y. Correction of dorsi-flexed intercalated segment instability after restoration of scaphoid height in a cadaver model of scaphoid non-union. J Hand Surg 1995;20B:596 – 602. 23. Linscheid RL. Kinematic considerations of the wrist. Clin Orthop 1986;202:27–39. 24. Sennwald G, Segmuller G. Base anatomique d’un nouveau concept de stabilite du carpe. [Anatomic basis of a new concept of stability of the carpus.] Int Orthop 1986;10:25–30. 25. Craigen MA, Stanley JK. Wrist kinematics. Row, column or both? J Hand Surg 1995;20B:165–170. 26. Dharap AS, Al-Hashimi H, Kassab S. The hamate facet of the lunate: a radiographic study in an Arab population from Bahrain. Surg Radiol Anat 2006;28:185–188. 27. Dyankova S, Marinov G. Comments about “The hamate facet of the lunate: a radiographic study in an Arab population from Bahrain.” Surg Radiol Anat 2007;29:181.
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28. Nakamura K, Beppu M, Patterson RM, Hanson CA, Hume PJ, Viegas SF. Motion analysis in two dimensions of radial-ulnar deviation of type I versus type II lunates. J Hand Surg 2000;25A:877– 888. 29. Nakamura K, Beppu M, Matushita K, Arai T, Ide T. Biomechanical analysis of the stress force on midcarpal joint in Kienbock’s disease. Hand Surg 1997;2:101–115. 30. Crisco JJ, Pike S, Hulsizer-Galvin DL, Akelman E, Weiss AP, Wolfe SW. Carpal bone posture and motions are abnormal in both wrists of patients with unilateral scapholunate interosseous ligament tears. J Hand Surg 2003;28A:926 –937. 31. Berger RA, Blair WF, Crowninshield RD, Flatt AE. The scapholunate ligament. J Hand Surg 1982;7:87–91. 32. Meade TD, Schneider LH, Cherry K. Radiographic analysis of selective ligament sectioning at the carpal scaphoid: a cadaver study. J Hand Surg 1990;15A:855– 862. 33. Short WH, Werner FW, Green JK, Masaoka S. Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate: part II. J Hand Surg 2005;30A:24 –34. 34. Short WH, Werner FW, Green JK, Masaoka S. Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate. J Hand Surg 2002;27A:991–1002. 35. Short WH, Werner FW, Green JK, Weiner MM, Masaoka S. The effects of sectioning the dorsal radiocarpal ligament and insertion of a pressor sensor into the radiocarpal joint on scaphoid and lunate kinematics. J Hand Surg 2002;27A:68 –76. 36. Ruch DS, Smith BP. Arthroscpoic and open management of dynamic scaphoid instability. Orthop Clin North Am 2001;32:233–240. 37. Patterson RM, Moritomo H, Yamaguchi S, Mitsuyasu H, Shah MA, Buford WL, Viegas SF. Scaphoid anatomy and mechanics: update and review. Atlas Hand Clin 2004;9:129 –140. 38. Mitsuyasu H, Patterson RM, Shah MA, Buford WL, Iwamoto Y, Viegas SF. The role of the dorsal intercarpal ligament in dynamic and static scapholunate instability. J Hand Surg 2004;29A:279 –288.
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