Intercarpal Fusion A Review

Transcription

1 183 J Anat. Soc. India 52(2) (2003) A Review Singh, P., Tuli, A., Choudhry, R., Mangal, A. Department of Anatomy, Lady Hardinge Medical College, New Delhi, INDIA Abstract. Coalition among the various carpal bones is seen in any possible combination occuring either as an indepedent entity or in association with syndromes and metabolic disorders. An absence of joint cavitation in the embryo and chondrification of the joint interzone leads to this phenomenon of carpal synostosis. A wide geographic variation in the incidence of carpal fusion is seen underlining the involvement of genetic factors, the trait being transmitted as Mandelian dominant factor (not sex linked). Among the different population groups observed the highest incidence is seen in people of African descent with a greater predeliction of female to male (2:1). Though mostly asymptomatic and thus usually a chance finding discovered on radiographs taken for unrelated reasons these may be associated with symptoms due to loss of movement between the fused bones. Stretching of the surrounding soft tissues leads to sprain causing pain, fractures are common and at times carpal bossing may also occur. Anthropological significance of this fusion anomaly can not be ignored which may be considered a step towards specialization of hand or an attempt to stabilize the postaxial border of hand. Key words : Carpus, Congenital anomaly, Carpal fusion, Arthrodesis Introduction : Synostosis of carpal bones, usually a chance finding discovered on radiographs obtained for unrelated reasons, is a congenital or acquired anomaly seen in otherwise normal people. The former is present commonly as an isolated entity but may occur as part of syndrome or may be associated with metabolic disorders. Generally isolated carpal fusions involve two bones of the same row, while the syndrome associated fusions are quite often multiple (Knezevich & Gottesman, 1990). Acquired fusion can occur secondary to arthritis, trauma or as a metaplastic conversion of intra-articular structures such as fibrous tissue, ligaments or cartilage to bone (all being mesodermal derivatives). It may be a result of surgery done for joint stabilization (Poznanski & Holt, 1971). Carpal fusion is mostly an asymptomatic condition. It may present symptoms by virtue of alteration of the normal biomechanics of the wrist thus predisposing the contributing joints and the surrounding soft tissues to abnormal stress. There may be discomfort or pain under exhausting conditions such as repeated prehensile movements, playing musical instruments, strenuous sporting activities etc. Though carpal fusion usually occurs in two or more adjacent bones the former is more commonly found in almost any combination i.e. lunatetriquetral (most common), capitate-hamate, trapezium-trapezoid, scaphoid-trapezium, scaphoidlunate, pisiform-hamate, triquetral-pisiform and trapezoid-capitate (rare). Multiple bone fusion may involve any number of carpals or all carpals appearing as a single mass. It is a common feature present in syndrome associated fusions such as Ellis van Creveld syndrome, arthrogryposis, symphalangia, diastrophic dwarfism, Turner s syndrome. Fusions may be complete when actual union occurs with no joint space present or less commonly may be incomplete with narrowing of joint space between the two bones without adjacent sclerosis or osteophytosis (Resnik et al, 1986). Any two ossific centers lying adjacent may exhibit fusion (O Rahilly, 1953), those on the ulnar side and occupying the same row are more commonly involved (Garn et al, 1971). Fusion of carpal bones is hereditary and the trait is transmitted as Mandelian dominant factor which is not sex linked (Henry, 1945). Vast and unwieldy literature is available and a need was felt for a comprehensive account to underline the embryological, roentgenological and clinical aspects of this apparently straight forward condition. Classification : Though categorizations of fusion have been presented earlier. (Smitham, 1948; Minaar, 1952 and Cockshott, 1963) they do not encompass all possibilities of intercarpal synostosis hence many types of presentations are left out. Based on

2 184 morphology and architecture of the resultant fused bones we find it imperative to propose a new classification. COMPREHENSIVE CLASSIFICATION OF CARPAL FUSION Type I Shape of Fused Bones (a) Retaining Shape (b) Distorted Shape Type II Site of Fusion (a) Palmar Fusion (b) Dorsal Fusion (c) Central Fusion (d) Proximal Fusion (e) Distal Fusion (f) Intermediate Fusion (g) Complete Fusion Type III Apparent Fusion Type IV Non-Osseous Fusion These may be seen as separate features or as a combination of any of the above. Type I Shape of Fused Bones These have been categorized into two subtypes (according to their shape after coalition) depending on whether the original shape of the bones taking part in synostosis are maintained (I, a) (Hughes & Tanner, 1966; Knezevich & Gottesman, 1990 and Choudhry et al, 1998) or distorted (I, b) (Kosowicz, 1965 and Poznanski & Holt, 1971). Type II Site of Fusion Fusion where union commences either on palmar surface (groove dorsally) (II a) or conversely the process is restricted to the dorsal aspect, groove on the palmar aspect (II b) or combination of both may be observed. Bony bridge in the last mentioned pattern is observed in the centre with trench on both the palmar and dorsal aspects (II c) (Choudhry et al, 1998). Clefts are reported either distally, proximally or at both ends. Proximal fusion (II d) (Smitham, 1948 and Cockshott, 1963) in which only the proximal part unites and a groove of varying depth can be seen distally or conversely union is present distally leaving a gap proximally (II e) described and illustrated by Minaar (1952), Dean & Jones (1959) and Pfitzner (1900). Fusion is possible in which synostosis begins in the middle and does not reach either the proximal or distal end thus leaving proximal and distal clefts (II f) as observed by Smitham (1948). A combination of dorsal and distal fusion with groove on proximal and palmar aspect has been mentioned by Pfitzner (1900). In complete fusion (II g) actual bony union occurs between the articular surface of bones without any notching illustrated by Butterworth & Daner (1946), Hammond (1947), Caffey (1952), Silverman (1955), Hughes & Tanner (1966) and Wahab et al (1993). Type III Apparent Fusion Two bones in this type of synostosis seem to be completely fused all along but actually have a central cavity between them visualized radiologically representing normal joint formation (Resnik et al, 1986). Type IV Non-Osseous Fusion A cartilaginous bridge of variable length stretches across the bones thus uniting them. This is due to incomplete or aborted differentiation of the joint and may be associated with degenerative findings similar to Class I of Minaar (1952) and illustrated by Simmons and McKenzie (1985). Narrowing of apparent joint space with filling defect is seen on arthrography (Resnik et al, 1986). Incidence of Various Combinations of Carpal Fusion : Lunate-Triquetral Fusion This is the most common fusion anomaly of the carpus which was first described in anatomy text in the late eighteenth century by Sandifort (1779) but the earliest clinical case was reported approximately hundred and twenty years later in early twentieth century by Corson (1908). This bone anomaly is mostly bilateral but more common on the left side when unilaterally present (Hammond, 1947; Cockshott, 1969; Simmons & Mckenzie, 1985 and Choudhry et al, 1998). Among the various population groups studied the highest incidence is seen in people of African descent with a greater predeliction of female to male (2;1) and strong familial tendency (Hammond, 1947; Garn et al, 1971 and Simmons & McKenzie, 1985). In the African continent the maximum incidence is on the West coast, particularly Nigeria and the figure diminishes as one crosses the continent eastward so that at Nairobi in

3 Singh, P. et al Kenya and Dar-es-Salaam in Tanzania the condition is virtually not seen (Cockshott, 1963). In the American population the estimated incidence falls between 0.08% 0.13% (Szaboky et al, 1969). The lowest in frequency chart are the Caucasians and Whites ( %) followed by Black Americans (1.6%), next in the line are East Africans (1-2%) and the hgihest being West Africans: Nigeria & Ghana ( %). Thus the incidence is times more in blacks than the Whites (Cockshott, 1963; Hughes & Tanner, 1966 and Simmons & Mckenzie, 1985). Capitate-Hamate Fusion The second familiar pattern of coalition of carpal bones is os capitato-hamate first reported in two cases by Dwight in Later, a number of other workers also outlined this fusion anomaly (Bogart, 1932; Hudson, 1943; White, 1944; Butterworth & Daner, 1946; Smitham, 1948; Cockshott, 1963; Hughes & Tanner, 1966 and Garn et al, 1976). Its occurrence is far more freuquent in Negroes and is more freuquently bilateral (White, 1944 and Smitham, 1949) though it may be present unilateral also (Cockshott, 1963). Amongst the various racial groups studied the lowest incidence is seen in East Africans (0.14%) followed by Whites ( %) and finally West Africans ( %) Capitate-Trapezoid Fusion An uncommon occurrence as only a few cases have been recorded (Dwight, 1907; Cave, 1926; Bogart, 1932; Garn et al, 1976; Geutjens, 1994 and Choudhry et al, 1998). In one study the incidence was reproted to be 0.1% (Hughes & Tanner, 1966). Pisiform-Hamate Fusion This rare anomaly is seen due to metaplastic conversion of ligament into bone and not due to failure of formation of articular interzones. It has been reported in Nigerians usually as a bilateral presentation (Cockshott, 1963, 1969). Other carpal fusions have been reported (Fig. 1) but their incidence has not been studied. Age of Establishment of Fusion : The age at which the ossific centres fuse shows a wide spectrum. Capitato-Hamate fusion has early union of bony centres as their ossific centres are the first to appear. Normally fusion is established and obvious before the age of 2 years (Cockshott, ). However in another study fusion was reported at an older age of 8 years (Hughes & Tanner, 1966). Lunato-Triquetral fusion however occurs between 6 to 15 years (Cockshott, 1963 and Hughes & Tanner, 1966). Capitato-Trapezoid fusion is a rarity and not many authors have commented on this entity with only one study where compelete fusion is docuented at 14 years (Hughes & Tanner, 1966). No literatue about the maturity of other fusions is available. Radiological Appearance : Radiography serves as an important tool for physical anthropology and can be used for mass screening for detecting such an anomaly. At birth human hand is almost cartilagenous in nature and errors in segmentation cannot be detected radiologically as centres have either not appeared or not spread to the outermost zone of carpal bone (Orlin & Alpert, 1967) thus necessitating multiple radiographic projections. Radiogaphic appearances of carpal fusion is present in diverse forms such as bones may be completely united or partially so with notch present or there may be narowing of joint space (Resnik et al, 1986) and many other indicated in the classification (Fig. 2). Carpal Fusion in Various Syndromes : Ellis-van Creveld Syndrome This syndrome also known as chondroectodermal dysplasia was first recognized and named by Ellis & Van Creveld in The most common associated anomaly is capitate-hamate fusion (mostly bilateral), or fusion may be massive involving multiple carpals (Ellis & Van Creveld, 1940 and Caffey, 1952). Symphalangism This is a hereditary condition manifested by partial or total absence of interphalangeal joints together with carpal and tarsal fusions. Diverse pattern of carpal fusion such as capitate-hamate, capitate-trapezium, lunatetriquetral, scaphoid-trapezium are seen but most frequent occurrence is triquetral-hamate (Harle & Stevenson, 1967 and Geelhoed et al, 1969). Arthrogryposis Multiplex Congenita This symptom complex consists of an array of skeletal abnormalities besides carpal and less common tarsal synostosis. The fusions are variable, first

4 186 involving the proximal row and and as the process proceeded extensive coalition occurs which may be manifested bilaterally (Orlin & Alpert, 1967 and Poznanski & La Rowe, 1970). It is more often acquired than congenital evidenced by presence of some remnant joint space seen in dissected specimens (Newcombe et al, 1969). Osteochondritis Dissecans It is characterized by numerous developmental anomalies including striking facial appearance, ptosis, pectus excavatum, cryptorchidism, short little fingers and fifth toes. Capitate-trapezoid fusion has been reported to occur (Hanley et al, 1967). Gonadal Dysgenesis (Turner s syndrome) This chromosomal abberation is a multisystem disease also presenting with coalition of carpals (Finby & Archibald, 1963). Typical anomaly is abnormally shaped bones of proximal carpal row with positive carpal sign and coarse trabecular pattern. Madelung s deformity associated with os lunato-triquetral has been reported (Kosowicz, 1965). Nievergelt s Syndrome This condition has a genetic basis presenting as massive bilateral carpal coalition in conjunction with bilateral tarsal coalition and radial head dislocation (Pearlman et al, 1964). Foetal Alcohol Syndrome A consistent pattern of malformation is recognised in the offspring of alcoholic mothers being characterized by low intelligence, low birth weight, microcephaly, blepharophimosis, absent nasolabial folds and narrow upper lip. Skeletal manifestations in addition to radio-ulnar synostosis include coalition of capitate and hamate present either unilaterally or bilaterallly (Jaffer et al, 1981). Holt-Oram Syndrome It is an autosomal dominant trait associated with abnormally shaped scaphoid fused to other carpals. Narrowing of joint space between trapezium and scaphoid is observed along with presence of accessory carpal bone (Poznanski & Holt, 1971). Hand-Foot-Uterus Syndrome Individuals with this syndrome have very small feet with short great toes along with duplication of genital tract in females. Deformity of schapoid along with scaphoid trapezium fusion is evident (Poznanski & Holt, 1971). Oto-Palato Digital Syndrome Abnormalities of ear and cleft palate along with associated anomalies of shape and position of carpals (comma shaped trapezoid and transverse position of capitate) is observed more commonly in males. Fusion of scaphoid with other carpal bones or various others forms of intercarpal union may be present (Langer, 1967 and Poznanski & Holt, 1971). Diastrophic Dwarfism Carpal bones may be deformed and precocious in their appearance Narrowing of joint space with carpal fusion is commonly seen especially in older individuals (Poznanski & Holt, 1971). Etiology of Carpal Fusion : Embryogenesis Congenital fusion is defined as failure of differentiation in embryo resulting in union of two or more structures normally separate from one another (McCredie, 1975). Carpal bones usually follow a definite plan of development. The morphogenesis is initiated in a two month old human embryo in whom location of normal carpal joint spaces are already established by the presence of an interarticular zone with richly cellular mesenchyme between precartilage analge of carpal bone (Weatherman, 1952). In the third month of intrauterine life the precartilage centres are converted to cartilage. By fourth month the intermediate zone cavitates and the remaining cells help to form joint cartilage, joint capsule and ligaments. Lack of cavitation at the site of future joint space with subsequent chondrification and ossification rather than union of separate carpal bones leads to carpal coalition. A wave of centrifugal ossification, the ossification gradient is not affected by the cartilaginous segmentation implying that the fused bones still retain their shape and independent origin from a centre (Hughes & Tanner, 1966). Teratogens (as well as genes) may bring about such abnormalities by preventing programmed cellular death (Garn et al, 1976). It has been interestingly worded that future joint interfaces are demarcated during developmental period and failure of orderly demarcation results in coalition which are therefore more properly termed failures of differentiation (Knezevish & Gottesman, 1990). The term fusion is thus a misnomer as the basic fault is

5 Singh, P. et al a failure of separation (Cockshott, 1963) or a segmentation error (Silverman, 1955). Trauma Associated Fusion These can be categorized into either those occuring due to injury or induced surgically (arthrodesis) to improve the hand condition. Traumatic conditions cause rupture in the ligament or lead to chronic periostitis which eventually result in bony union at the affected joints. Conditions warranting intercarpal arthrodesis include degenerative disease, subluxation, dislocation, fracture, nonunion, avascular necrosis etc. to relieve pain or dysfunction. Bridging and packing of joint space with bone pegs is done thus maintaining stability and preserving partial motion at the joint (Peterson & Lipscomb, 1967). Syndrome Related Fusion The syndromes in which carpal synostosis has been described include Ellis-van Creveld syndrome, Turner s syndrome, Holt-Oram syndrome, Arthrogryposis among others. Carpal fusion occurring as part of congenital syndrome may be massive and may also be associated with tarsal coalition. Such cases result from failure of segmentation of the developing cartilaginous canals, and lack of joint formation. Drug Induced Fusion Drug intake by the mother especially during early months of pregnancy can be deleterious to varying degrees to the developing foetus. Congenital multiple carpal fusion is a recurrent feature of thalidomide embryopathy. Maternal alcoholism can lead to Foetal alcohol syndrome characterized by os capitato-trapezoid and radio-ulnar synostosis. In all such cases cartilaginous model formed at 5 weeks is abnormal due to destructive arthritis thus leading to abnormal ossification at 8 weeks. Internal trabeculation at the site of joint is normally undisturbed suggesting absence of joint space dividing the bones leading to fusion of carpals and other bones (McCredie, 1975). A genetic predisposition in terms of inherent metabolic pathways for alcohol is of importance in the pathogenesis of Foetal alcohol syndrome (Jaffer et al, 1981). Inflammation Linked Fusion Many arthropathies including rheumatoid arthritis, juvenile chronic arthritis, psoriatic arthritis, Reiter s syndrome, osteoarthritis etc. show a distinct pattern 187 of intra-articular osseous fusion occurring mostly bilaterally and commonly involving mid carpal joints. The causative factor is the stimulus to cells lining the synovial membrane. In such cases lysosomal enzymes are formed in increased amount which destroy collagen producing focal erosion and subsequent bony fusion. Fusion due to Metaplasia Ligament, cartilage and bone are all mesodermal derivatives and metaplastic conversion of one into another can occur thus leading to bony fusion. Union of pisiform with triquetral or hamate is by this process. Clinical and Anthropological Significance : Complete or incomplete coalition of the carpus normally does not interfere with the external appearance or function of wrist (Curr, 1946; Hammon, 1947; Minaar, 1952 and Szaboky et al, 1969). However, these may at times become symptomatic leading to pain and discomfort. With movement lost between the fused bones, compensatory increase in motion at surrounding joints along with stretching of soft tissue restraints predisposes to recurrent sprains causing pain under stressful conditions (Knezevich & Gottesman 1990). Occasionally this may also result in carpal bossing an overgrowth of bone in response to stress (Geutjens, 1994). A fused bone is also more exposed to the risk of fracture with subsequent cyst formation and pseudoarthrosis (Cockshott, 1963). Persistence of grooves, notches and cavities at the site of fusion appears to be a factor contributing towards fracture. Since this coalition is always an incidental finding it may have anthropologic significance representing an advance towards specialization of hand or may be an attempt to stabilize the postaxial border of hand. It is commonly found that the fusion is between Lunate & Triquetral and Capitate & Hamate (Fig. 1) which supports the above premise. It is also considered to be a primitive adaptation that has persisted (Minaar, 1952) Roentgenography can serve as a useful ancillary method in physical anthropology for the tracing of past population movements and ethnic relationships of various population groups.

6 188 Referenes : 1. Bogart, F.B. (1932); Variations of bones of the wrist. American Journal of Roentgenology and Radium Therapy. 28: Butterworth, R.D. and Daner, W.E. (1946): A bilateral anomaly of the wrist. Journal of Bone and Joint Surgery. 28(2): Cave, A.J.E. (1926): Fusion of carpal elements. Journal of Anatomy. 60: Caffey, J. (1952): Chondroectodermal dysplasia (Ellis-van Creveld disease). American Journal of Roentgenology, Radium Therapy and Nuclear Medicine. 68(6): Chouhdry, R., Tuli, A., Chimmalgi, M. and Anand, M. (1998): Os capitatotrapezoid: a case report. Surgical Radiological Anatomy. 20: Cockshott, W.P. (1963): Carpal fusions. American Journal of Roentgenology. 89(6): Cockshott, W.P. (1969): Pisiform hamate fusion. Journal of Bone and Joint Surgery. 51(A): Corson, E.R. (1908): Fusion of the semilunar and cuneiform bones (os lunatum and os triquetrum) in both wrists of an adult male Negro- shown by the x-ray, Anatomical Record 2: Curr, J.F. (1946); Congenital fusion of lunate and triquetrum. British Journal of Surgery. 34: Dean, R.F.A. and Jones, P.R.M. (1959): Fusion of triquetral and lunate bones shown in serial radiographs. American Journal of Physical Anthropology. 17: Dwight, T. Variations of Bones of Hands and Feet. A Clinical Atlas, J.B. Lippincott, Philadelphia (1907) 12. Ellis, R.W.B. and Van Creveld, S. (1940): Syndrome characterized by ectodermal dysplasia, polydactyly, chondrodysplasia and congenital morbus cordis; report of three cases. Archieves of Diseases of Childhood. 15: Finby, N. and Archibald, R.M. (1963). Skeletal abnormalities associated with gonadal dysgenesis. American Journal of Roentgenology, Radium Therapy and Nuclear medicine. 89: Garn, S.M., Frisancho, R., Poznanski, A.K. Schweitzer, J. and McCann, M.B. (1971) Analysis of Triquetral-Lunate fusion. American Journal of Physical Anthropology. 34: Garn, S.M., Burdi, A.R. and Babler, W.J. (1976): Prenatal origins of carpal fusions. American Journal of Physical Anthropology. 45: Geelhoed, G., Neel, J.V. and Davidson, R.T. (1969); Symphalangism and tarsal coalitions: hereditary syndromes; report on two families. Journal of Bone and Joint Surgery. 51(B); Geutjens, G. (1994): Carpal bossing with capitate trapezoid fusion. Acta Orthopedica Scandinavia 65(1): Hammond, G. (1947): Unilateral congenital synostosis of lunate and triangular bones. Surgery. 22: Hanley, W.B., McKusic, V.A and Baranco, F.T. (1967): Osteochondritis dissecans with associated malformations in two brothers. Journal of Bone and Joint Surgery. 49(A): Harle, T.S. and Stevenson, J.R. (1967): Hereditary symphalangism associated with carpal and tarsal fusions Radiology 89; Henry, M.B. (1945); Anomalous fusion of the scaphoid and the greater multangular bone Archieves of Surgery. 50: Hudson, E. (1943): Unusual carpal abnormality. Radiography. 9: Hughes, P.C.R. and Tanner, J.M. (1966): The development of carpal bone fusion as seen in serial radiographs. British Journal of Radiology. 39: Jaffer, Z., Nelson, M. and Beighton, P. (1981): Bone fusion in foetal alcohol syndrome Journal of Bone and Joint Surgery. 63(B) : Kosowicz, J. (1965): The roentgen appearance of hand and wrist in gonadal dysgenesis. American Journal of Roentgenology. 93 : Knezevich, S. and Gottesman, M. (1990): Symptomatic scapholunatotriquetral carpal coalition with fusion of the capitometacarpal joint. Clinical Orthopedics. 251: Langer, L.O. (1967): Roentgenographic features of Oto- Palato-Digital syndrome. American Journal of Roentgenology, Radium Therapy and Nuclear Medicine. 100: McCredie, J. (1975): Congenital fusion of bones: Radiology, Embryology and Pathogenesis Clinical Radiology. 26: Minaar, A.B.deV. (1952): Congenital fusion of lunate and triquetral in South African Bantu. Journal of Bone and Joint Surgery 34 (B): Newcombe, D.S., Abbott, J.L., Munsie, W.J. and Keats, T.E. (1969): Arthrogryposis multiplex congenital and spontaneous carpal fusion. Arthrology & Rheumatology. 12: O Rahilly, R. (1953): A survey of carpal and tarsal anomalies. Journal of Bone and Joint Surgery. 35A: Orlin, H. and Alpert, M. (1967): Carpal coalition in arthrogryposis multiplex congenita British Journal of Radiology 40: Pearlman, H.S., Edkin, RE. and Warren, R.F. (1964) : Journal of Bone and Joint Surgery 46(A): 585. Cited by Orlin and Alpert Peterson, H.A. and Lipscomb, P.R. (1967): Intercarpal arthrodesis. Archieves of Surgery. 95: Pfitzner, W. (1900): Die morphologischen Elemente des menschlichen Handskelets. Zeitschr. Morphol. u. Anthropol. 2: ; Poznanski, A.K. and La Rowe, P.C. (1970): Radiographic manifestations of arthrogryposis syndrome Radiology. 95: Poznanski, A.K. and Holt, J.F. (1971): The carpals in congenital malformation syndromes. American Journal of Roentgenology. 112: Resnik, C.S., Grizzard, J.D., Simmons, B.P. and Yaghmai, I. (1986): Incomplete carpal coalition. American Journal of Roentgenology. 147: Sandifort, E. (1779): Observationum anatomico pathoiogicarum. Batavia 3: Silverman, F.N. (1955): Note on os lunatotriquetrum. American Journal of Physical Anthropology. 13: Simmons, B.P. and McKenzie W.D. (1985) : Symptomatic carpal coalition. The Journal of Hand Surgery. 10A: Smitham, J.H. (1948): Some observations on certain congenital abnormalities of the hand in African natives. British Journal of Radiology XXI(250): Szaboky, G.T., Muller, J., Melnick, J. and Tamburro, R. (1969): Journal of Bone and Joint Surgery [Am]. 51: Wahab K.H.A., Woolf V.J. and Mulnier J.J.H. (1993): Case report: Bilateral carpal and tarsal synostosis. British Journal of Radiology. 66-(788): Weathermann, A. (1952); Die Entwicklungsstorungen der Extremitaten in Handbuch der Spez. Pathology Anatomy Histology 9(6): 319 (Springer Verlag, Berlin). Cited by Orlin and Alper White, E.H. (1944): Bilateral congenital fusion of carpal capitate and hamate. American Journal of Roentgenology and Radium Therapy. 52:

7 Opp. 184 Fig. 1 : Diagram (left hand) depicting carpal fusions. Dark links show the two commonest fusion anomalies. II (a) Palmar Fusion II (b) Dorsal Fusion II (c) Central Fusion II (d) Proximal Fusion II (e) Distal Fusion II (f) Intermediate Fusion II (g) Complete Fusion III Apparent Fusion IV Non-osseous Fusion Fig. 2 : Diagrammatic representation of proposed classification of carpal fusion (fused Trapezoid and Capitate taken as an example). Type II (a), (b), (c) viewed from distal and Type II (d), (e) (f), (g), Type III, Type IV viewed from palmar aspect.