THE
`
`ASSOCIATION
`
`LE
`DEL,_
`M H
`MEDICALE
`
`Volume 98 . Number 20 . May 18,1968
`
`Etiology, Pathogenesis and Possible Prevention of
`Congenital Dislocation of the Hip
`ROBERT B. SALTER, M.D., M.S., F.R.C.S.[C], F.A.C.S.,* Toronto
`AS a seventh-generation Canadian, I feel particu¬
`man has any right to publish unless he has some¬
`larly honoured in Canada's Centennial Year
`thing to say and has done his best to say it aright."
`to have been invited to deliver the Eighth Alex-
`Such high standards of academic excellence repre¬
`sent a challenging goal for all of us.
`ander Gibson Memorial Lecture at the Univer¬
`sity of Manitoba. Having read the many glowing
`In the First Alexander Gibson Lecture, Sir Walter
`tributes to Dr. Alexander Gibson.and having been
`Mercer1 referred to Dr. Gibson's lifelong interest in
`inspired by them.I only regret that, for chronological
`congenital dislocation of the hip among Indian chil¬
`reasons, it was not my privilege to have had the
`dren in northern Canada. In the Fifth Alexander
`opportunity to meet and know this outstanding man
`Gibson Lecture, Professor William Boyd,2 a class-
`whom we all honour this evening.
`mate and close personal friend of Dr. Gibson, dis¬
`cussed what he referred to as "a subject of general
`One of the most inspiring tributes to Dr. Gibson
`interest to every scientist and to every doctor,
`came from the pens of the late Dr. R. I. Harris of
`namely, the relation of cause to effect". It would
`Toronto and Dr. W. B. MacKinnon of Winnipeg;
`seem appropriate, therefore, in the present Alexander
`it reads as follows: "His qualities of integrity and
`Gibson Lecture to include some aspects of both of
`sincerity, his capacity for clear thinking and con-
`these subjects in a discussion of the etiology, patho¬
`vincing speech, his great fund of knowledge accumu-
`genesis and possible prevention of congenital dislo¬
`lated by study and experience, and his strong sense
`cation of the hip.
`of duty made him a great citizen as well as a great
`surgeon."
`Congenital dislocation of the hip represents
`As President of the Canadian Orthopaedic Asso¬
`ciation, Dr. Alexander Gibson designed the official
`one of the most important and most challenging
`crest of the Association. Of this crest, Dr. Gibson
`congenital abnormalities of the musculoskeletal
`himself wrote as follows: "The significance of the
`system. Since its detection at birth requires a
`design is that the maple leaf stands for English-
`specific method of examination, it is
`still not
`speaking Canada, combined with the fleur-de-lys
`being recognized sufficiently early throughout
`representing French-speaking Canada, the stalk of
`the world, and may even escape detection until
`both emblems being in common/'
`after the child has started to walk. Under these
`Of the 77 scientific publications of this truly great
`circumstances, treatment becomes progressively
`scholar, including as they do many original ideas,
`more difficult and the results become progres¬
`it has been written that they "presented uncommon
`sively less satisfactory. Furthermore, congenital
`clarity of mind and lucidity of language which
`dislocation of the hip, unless treated early and
`enabled him to make the complicated simple and
`skilfully, leads inevitably to degenerative arthritis
`the chaotic orderly". It has also been recorded that
`of the hip in adult life (Fig. 1).
`before permitting publication of any material, Dr.
`Gibson applied the following rigid formula: "No
`In most congenital
`of
`the
`abnormalities
`musculoskeletal system, such as clubfoot and
`spina bifida, the anatomical deformity is maximal
`at birth and it is obvious that the abnormality
`has been present from an early stage of intra¬
`uterine development. In congenital dislocation
`of the hip, by contrast, the anatomical deformity
`
`The Eighth Alexander Gibson Memorial Lecture, pre¬
`sented at the University of Manitoba on October 27, 1967.
`*Surgeon-in-Chief, The Hospital for Sick Children; Re¬
`search Associate, Research Institute; and Professor of
`Surgery. University of Toronto, Toronto, Ontario.
`Reprint requests to: Dr. R. B. Salter, Surgeon-in-Chief,
`The Hospital for Sick Children, 555 University Avenue,
`Toronto 2, Ontario.
`
`933
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`934
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`Salter: Congenital Hip Dislocation
`
`Canad. Med. Ass. J.
`May 18, 1968, vol. 98
`
`hypothesis fit the known facts rather than try
`to make the facts fit a preconceived hypothesis.
`Facts About Congenital Dislocation
`of the Hip
`1. Facts Concerning Embryology
`It has been established by Strayer3 that the
`hip joint develops from a single mass of meso-
`dermal tissue in the blastema, or primary limb
`bud. By about the tenth week, a joint space ap¬
`pears in this mass of mesodermal tissue and joint
`movement becomes possible. Therefore, it would
`seem reasonable to assume that the hip joint is
`not dislocated from the beginning of its forma¬
`tion, but that something must happen to it
`postnatal
`late prenatal
`early
`during its
`or
`development that produces a dislocation.
`2. Facts Concerning Anatomy
`The normal hip joint is one of the most stable
`of all synovial joints in the body. Three struc¬
`tural factors contribute to this stability: the
`shape of the opposing bony and cartilaginous
`joint surfaces of this ball and socket joint, the
`action of the muscles controlling hip movement,
`and the integrity of the capsule and ligamentum
`teres. From a clinical and radiographic study,
`congenitally
`arthrography,
`including
`dis¬
`of
`located hips in newborn infants, it is apparent
`that the shape of the joint surfaces is virtually
`normal at birth; furthermore, the shape of the
`joint surfaces becomes progressively abnormal
`only if the hip remains dislocated during sub¬
`sequent growth. Therefore, the shape of the joint
`surface at the time of birth cannot be an etio¬
`logical factor in the initial dislocation. Clinical
`of the hip
`of paralytic dislocations
`studies
`secondary to poliomyelitis and spina bifida reveal
`that while muscle imbalance alone can indeed
`result in dislocation of the hip, it does so only
`gradually and over a relatively long period of
`time. As far as can be determined, in congenital
`dislocation of the hip the surrounding muscles
`are perfectly normal at the time of birth. The
`importance of the fibrous capsule in hip joint
`stability is emphasized by some studies that we
`have conducted in the postmortem room on the
`hip joint of stillborn infants. These anatomical
`studies reveal that the normal hip can be made
`to dislocate only after the capsule and liga¬
`mentum teres have been divided. I will enlarge
`upon these studies subsequently.
`These clinical, radiographic and anatomical
`observations suggest that of the three possible
`structural factors that could account for the
`instability of the congenitally abnormal hip, the
`most significant is an abnormality of the joint
`
`Fig. 1..Radiograph of the hip joints of a 45-year-old
`woman who is disabled by painful bilateral degenerative
`arthritis of the hips as a late result of unsuccessful treat¬
`ment of congenital dislocation of the hips in early child¬
`hood.
`
`is minimal at the time of birth and, if untreated,
`becomes progressively more marked during post¬
`natal growth. This observation raises the possi¬
`bility of prevention of at least the postnatal ac¬
`quired deformities of the hip which are second¬
`ary to the original dislocation. It also raises the
`possibility even of preventing the initial disloca¬
`tion. Thus, a consideration of the etiological
`factors and the sequence of events in the patho¬
`genesis of congenital dislocation of the hip is of
`more than academic interest.
`Unfortunately, the controversial question of
`the etiology of congenital dislocation of the hip
`to a plethora of theoretical
`has giyen rise
`speculations and a paucity of scientific investiga¬
`tions. Each of the many physical phenomena
`associated with congenital dislocation, such as
`acetabular dysplasia, femoral anteversion and
`elongation of the capsule, has at some time been
`considered to be the primary cause of the dis¬
`location.
`In the organization of this lecture, I have
`chosen firstly to discuss many of the proven facts
`about congenital dislocation of the hip as well
`as my interpretation of these facts; secondly, to
`develop a hypothesis concerning the etiological
`factors and the sequence of events in the patho¬
`genesis of this abnormality, and thirdly, on the
`basis of this hypothesis, to suggest what might
`be done to prevent the initial dislocation. It
`should be pointed out that the present discussion
`concerns only the "typical" form of congenital
`dislocation of the hip to the exclusion of the
`"atypical"
`teratologic
`form
`associated
`with
`arthrogryposis and spina bifida.
`What are the known facts about congenital
`dislocation of the hip? Facts, as opposed to
`opinions, are of the utmost importance to us;
`they are the building blocks with which we must
`build the structure of hypothesis, and the more
`facts we can gather, the more complete will be
`our hypothesis. Furthermore, we must make the
`
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`

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`Canad. Med. Ass. J.
`May 18, 1968, vol. 98
`
`capsule and ligamentum teres. Furthermore, the
`most likely abnormality is an undue laxity of
`these structures as demonstrated by Andren,4 as
`well as by Carter and Wilkinson.5
`3. Facts Concerning the Incidence of
`Congenital Dislocation of the Hip
`(a) General incidence..While the general in¬
`cidence of clinically detected congenital disloca¬
`tion of the hip is approximately 1 to 1.5 per 1000
`live births, the incidence of this abnormality.
`unlike the incidence of other equally common
`congenital musculoskeletal abnormalities, such
`as clubfoot.varies widely in different parts of
`the world. This suggests the possibility that post¬
`natal environmental factors may be superim-
`posed upon the original congenital abnormality
`and have an effect, either for better or for worse,
`on the natural course of the condition. It also
`suggests that there may be a racial variation in
`the incidence of any underlying genetic factor.
`(b) Hereditary and familial incidence..In ap¬
`proximately 20% of children with congenital
`dislocation of the hip, a family history of the
`abnormality can be obtained. This means that
`in 80% of the children the abnormality has
`appeared for the first time in the family. Fur¬
`thermore, in a clinical study conducted at The
`Hospital for Sick Children, Toronto, in collabor-
`ation with Mrs. D. Wilson Cox6 of the Depart¬
`ment of Genetics, we found that of 226 children
`.one parent of whom had congenital disloca¬
`tion.only four had the abnormality. This means
`that the other 222 children, each of whom had
`parent, were perfectly normal
`one afflicted
`(Table I). Therefore, the genetic factor alone
`cannot explain the incidence of congenital dis¬
`location of the hip.
`
`TABLE I..Incidence of Congenital Dislocation of
`the Hip in Offspring when One Parent is Afflicted
`Based on a genetic study of 226 offspring, The Hospital
`for Sick Children.1963.
`1 in 112.Incidence of 0.9%
`Sons
`Daughters 3 in 114 (1 in 38).Incidence of 2.6%
`
`Furthermore, studies of identical twins by
`Idelberger7 reveal that of 29 pair of identical
`twins, both twins were afflicted in only 10 of the
`pairs. Thus, in two out of three pair of identical
`twins, one twin was afflicted and the other was
`normal despite an identical genetic composition.
`All of these observations on the hereditary and
`familial incidence indicate that while there is
`definitely a genetic factor in the etiology of con¬
`genital dislocation of the hip, there must be
`other factors as well.
`
`Salter: Congenital Hip Dislocation 935
`
`(c) Sex incidence..The repeated observation
`that 80 to 90% of the children with congenital
`dislocation of the hip are girls is very significant
`in that such a predominantly female incidence is
`not seen in other congenital abnormalities of
`the musculoskeletal system. Furthermore, there
`is the impression, which cannot be documented,
`that the girls with congenital dislocation of the
`hip tend to be more feminine than the average.
`They have a very feminine type of body build
`with wide hips. In addition, they are rather
`coquettish and know how to use their eyes even
`as young girls. Furthermore, the boys who do
`have congenital dislocation of the hip tend to be
`less masculine (or more feminine) than the
`average. These observations suggest the possibil¬
`ity of an endocrine or hormonal factor. Recent
`investigations by Andren and Borglin8 suggest
`that an abnormality of estrogen metabolism in
`afflicted infants may be responsible for the laxity
`of the hip joint capsule associated with congeni¬
`tal dislocation of the hip.
`(d) Age incidence..This may seem to be an
`unusual point to consider in any condition that
`is deemed congenital. However, there is growing
`evidence that the initial dislocation does not al¬
`ways occur at the same chronological age. While
`the atypical or teratologic type of dislocation
`almost certainly occurs long before birth, the
`typical type usually occurs at or shortly after
`birth and in most infants probably within the
`first two weeks. Rarely, however, we see a child
`in whom the initial dislocation does not appear
`until the child begins to stand. In these children
`there is no dysplasia of the acetabulum, which is
`another reason why we believe that dysplasia is
`secondary to the dislocation; that is, that the
`dysplasia is the result rather than the cause.
`(e) Geographical and racial incidence..The
`wide variation in the incidence of congenital
`dislocation of the hip encountered in different
`geographical areas and among different races is
`
`Fig. 2..(a) A Nigerian baby being carried on her
`mother* s back with the hips in flexion and abduction.
`(b) A Chinese baby in Hong Kong being carried in a
`sling on his mother's back with the hips in flexion and
`abduction. (c) A northern Canadian Eskimo baby bemg
`carried in her mother's parka; the baby is in a sitting
`position with the hips in flexion and abduction.
`
`Petitioner Ex. 1029 Page 3
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`

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`936
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`Salter: Congenital Hip Dislocation
`
`Canad. Med. Ass. J.
`May 18,1968, vol. 98
`
`Fig. 3..(a) A reproduction of one of the
`figures of Andrea Della Robia (fourteenth
`century). The infant is swaddled in band-
`ages ("fascia tura"). The original figure
`Hospital,
`Florence,
`the
`Infant's
`is
`in
`(b) A contemporary Italian baby
`Italy.
`living in Toronto, Ontario. The baby is
`swaddled in a blanket with the hips in
`extension and adduction. A somewhat
`similar type of swaddling ("Steckkissen")
`is used in West Germany. (c) A northern
`Indian baby strapped to a
`Canadian
`cradleboard ("tikonagan") with the hips
`in extension and adduction. A somewhat similar type of cradleboard ("komse") is used by Laplanders in Northern
`Scandinavia.
`
`.
`
`not seen in relation to other congenital abnor¬
`malities of the musculoskeletal system. This
`wide variation is undoubtedly due to a combina¬
`tion of genetic factors and environmental influ-
`ences. A study of the geographical and racial
`incidence suggests that one of the environmental
`influences that may be significant in the etiology
`of the initial dislocation is the position in which
`the hips of newborn infants are maintained dur¬
`ing the early months of postnatal growth and
`development. Among those races in which the
`hips of newborn infants are commonly held in
`flexion and abduction, the incidence of congeni¬
`tal dislocation of the hip is remarkably low. Low-
`incidence groups are the Negroes of Central and
`South Africa,9'10 the Chinese of Hong Kong11
`and the Eskimos of Northern Canada (Figs. 2a,
`2b and 2c). The position of flexion and abduc¬
`tion is the very position maintained by various
`types of splints during the treatment of infants
`with congenitally unstable hips.
`By contrast, among those races in whom the
`hips of newborn infants are commonly held in
`extension and adduction by various methods of
`swaddling, the incidence of congenital disloca¬
`tion of the hip is remarkably high. Examples of
`high incidence groups are Northern Italians,12
`North American Indians,13"16 West Germans17
`and Laplanders of Northern Scandinavia18 (Figs.
`3a, 3b and 3c).
`
`These observations suggest that a congenitally
`unstable and dislocatable hip, which has been
`maintained in the position of flexion and abduc¬
`tion during intrauterine life, is "protected" by
`the postnatal position of flexion and abduction
`and made worse by the postnatal position of
`extension and adduction. It would seem that the
`newborn hip joint of the human is not develop-
`mentally prepared for a sudden, complete and
`maintained change from the intrauterine posi¬
`tion of flexion to the erect position of extension
`in the early months of postnatal life, particularly
`if the hip joint is already congenitally unstable
`from some cause such as capsular laxity.
`While it is difficult to separate the genetic
`factors from the environmental influences in
`these observations, a study of Indian children in
`Northern Canada has proved helpful. We found
`that whereas the incidence of congenital disloca¬
`tion of the hip throughout the Indian population
`
`TABLE II..Correlation op the Cradleboard
`(Tikonagan) to the Incidence of Congenital
`Dislocation of the Hip
`Based on a Survey of Canadian Indian Tribes, 1963
`Cradleboard not used.. 17 cases C.D.H. in 1347 live births
`(1.2% incidence)
`Cradleboard used.250 cases C.D.H. in 2032 live births
`(12.3% incidence)
`Incidence of C.D.H. 10 times greater with use of cradle¬
`board.
`
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`

`
`Canad. Med. Ass. J.
`May 18, 1968, vol. 98
`
`Fig. 4..Two views of a newborn infant tightly wrapped
`in a blanket. The hip joints are maintained in extension
`and adduction.
`
`is higher than in the white population of Canada
`(possibly due to consanguinity), the incidence
`in those tribes in which the cradle board (tiko-
`nagan) was used for their children was 10 times
`higher than in those tribes in which it was not
`used (Table II). Studies by Rabin et al.15 as
`well as by Houston and Buhr16 have not, how¬
`ever, shown such a striking relationship between
`the use of the cradleboard and the incidence of
`congenital dislocation of the hip. An extremely
`low incidence, on the other hand, may not be so
`clearly related to postnatal position of the hips.
`Edelstein,9 in an examination of 9000 South
`African Negro newborn infants, found no con¬
`genital instability of the hips.an observation
`that may be due to the absence of predisposing
`genetic factors in this particular racial group.
`Huckstep10 has made similar observations in
`Central Africa.
`Seasonal incidence..Record and Ed-
`(f)
`wards19 in England and others in some of the
`European countries have reported a significantly
`higher incidence of congenital dislocation of the
`hip in children who are born during winter
`months. This has not been noticed in more
`temperate climates or where central heating is
`generally used. This interesting seasonal inci¬
`dence suggests the possibility that, when the
`weather is cold, the newborn babies and young
`infants may be more tightly wrapped in blankets
`
`Salter: Congenital Hip Dislocation 937
`
`which passively extend the hips and limit active
`movement (Fig. 4). The common habit of wrap-
`ping infants tightly in blankets with their hips in
`extension and adduction should be abandoned.
`(g) Incidence in relation to birth presenta¬
`tion..In a combined clinical and genetic study
`of congenital dislocation of the hip at The Hos¬
`pital for Sick Children,20 we found that 23% of
`all children with congenital dislocation of the
`hip had been delivered as a breech presentation,
`whereas in the normal population the incidence
`of breech presentation is below 5%. Further¬
`more, the incidence of congenital dislocation of
`the hip is 10 times higher in children born by
`breech presentation than in those born by vertex
`presentation. Another fascinating aspect of this
`study is that in those children with congenital
`dislocation of the hip who have been born by
`breech presentation, the usually predominant fe¬
`male sex incidence is much less striking.only
`two to one, instead of nine to one. These facts
`suggest that the initial dislocation in a congeni¬
`tally unstable hip might be caused (at least in
`this group of infants) by an iatrogenic factor
`such as forceful passive extension of the hips
`associated with traction on the lower limbs dur¬
`ing delivery.
`4. Facts About Physical Findings in Children
`The physical findings associated with con¬
`genital dislocation of the hip vary with the
`child's age, and this suggests a progression of
`changes in the hip after birth. Within the first
`few days of postnatal life, the most significant
`
`Fig. 5..The Ortolani sign of congenital instability of
`(a) With slight adduction and pressure
`the hip joint.
`along the long axis of the thigh, the hip can be felt to
`dislocate or subluxate posteriorly. (b) With slight abduc¬
`tion and traction on the thigh the hip can be felt to
`relocate.
`
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`938
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`Salter: Congenital Hip Dislocation
`
`Canad. Med. Ass. J.
`May 18, 1968, vol. 98
`
`Fig. 6..Radiographic dysplasia of the acetabulum. (a) A newborn infant; the left hip is
`completely dislocated but there is no evidence of dysplasia of the acetabulum. (b) A 15-month-
`old child with an untreated dislocation of the left hip; the dysplasia of the left acetabulum and
`femoral head is quite marked. (c) A 10-year-old girl with an untreated congenital dislocation
`of the right hip; the dysplasia of the acetabulum is extreme.
`
`and indeed often the only physical sign is in¬
`stability of the involved joint as depicted by the
`Ortolani sign21 (Fig. 5a and 5b). At this stage
`the hip joint is lax and is dislocatable but not
`permanently dislocated and there is usually no
`adduction contracture. Barlow,22 in an examina¬
`tion of over 9000 newborn infants in England,
`found that on the first day of life 1 infant in 60
`had instability of one or both hips. Of these,
`68% became stable within one week, and 88%
`had become stable by the end of the second
`month, leaving only 12% of the original group
`still demonstrating instability.an incidence of
`1.5 per 1000 live births (which is the general
`incidence of congenital dislocation of the hip).
`This suggests that the primary problem in the
`newborn period is congenital laxity of the hip
`joint capsule with resultant instability of the
`joint. It also suggests that there is a tendency for
`the capsular laxity to improve spontaneously,
`provided the hip does not remain dislocated.
`After the first few months of life, if the hip re¬
`mains dislocated, the well-known physical signs
`of adduction contracture, apparent and real
`shortening, telescoping and a Trendelenburg
`sign become progressively more apparent and
`indicate anatomical changes that would seem to
`be the result of the dislocation rather than the
`cause.
`
`5. Facts Concerning Dysplasia of the
`Acetabulum
`In congenital dislocation of the hip, radio¬
`graphic dysplasia of the acetabulum is minimal,
`and indeed often undetectable, on the first day
`of life, but it becomes progressively more severe
`as long as an abnormal relationship exists be¬
`tween the head of the femur and the acetabulum
`(Figs. 6a, 6b and 6c). Furthermore, during at
`least the first year of life, the acetabular dys¬
`plasia is to a large extent reversible, provided a
`
`normal relationship between the femoral head
`and the acetabulum has been restored (Figs. 7a
`and 7b). These observations suggest that dys¬
`plasia is not a primary genetic defect of the
`
`(a) Radiograph of
`Fig. 7..Reversibility of dysplasia.
`the hips of a 4-month-old child with bilateral congenital
`dislocation of the hip. There is a moderate degree of
`dysplasia of the acetabulum on each side. (b) Radiograph
`of the same child one year after bilateral closed reduction;
`both hip joints have developed well, indicating that the
`acetabular dysplasia is reversible in the very young child
`provided a normal relationship between the femoral head
`and acetabulum has been restored and maintained.
`
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`

`
`Canad. Med. Ass. J.
`May 18, 1968, vol. 98
`
`Salter: Congenital Hip Dislocation 939
`
`b
`a
`c
`Fig. 8..Experimental dysplasia of the hip in pigs. (a)
`Newborn pig with the left hip maintained in flexion and
`the right hip in extension. (b) Normal pelvis of a 6-week
`old control pig. Note the direction in which each aceta¬
`bulum faces. (c) Pelvis of a 6-week-old experimental pig.
`The left hip had been maintained in flexion and the aceta¬
`bulum on this side has developed normally. The right hip
`was maintained in extension during the six-week period.
`The right acetabulum is dysplastic: it is not only smaller
`and more shallow but it also faces in a completely ab¬
`normal direction.
`
`acetabulum, but rather that it is secondary to
`displacement.
`Experimental investigations by Smith et al.2Z
`using dogs, by Harrison24 using rats and by
`Langenskiold, Sarpio and Michelsson25 using
`rabbits revealed that dysplasia of the acetabu¬
`lum always followed experimentally produced
`dislocation.
`In an experimental investigation using new¬
`born pigs26 we have shown that maintained
`extension of the hip joint for six weeks consis¬
`tently resulted in dysplasia of the acetabulum,
`whereas maintained flexion of the hip joint led
`
`to normal acetabular development (Figs. 8a, 8b
`and 8c). Furthermore, the most impressive fea¬
`ture of the dysplasia was the abnormal direction
`in which the entire acetabulum faced. In addi¬
`tion, we have shown in another series of pigs
`that the experimentally produced dysplasia was
`reversible when the hip was released and the
`animals were allowed to run free for a period of
`10 weeks (Figs. 9a and 9b).
`The results of these experimental investiga¬
`tions suggest that maintained extension of the
`newborn hip joint has a deleterious effect on its
`subsequent development, whereas maintained
`flexion has a beneficial effect. These experimen¬
`tal results in animals, as well as the clinical
`investigations in children, suggest that in con¬
`genital dislocation of the hip, the dysplasia,
`rather than acting as a cause, is a result of the
`dislocation.
`
`6. Facts Concerning Acetabular Direction
`The direction in which the acetabulum faces
`is difficult to assess by radiographic examination
`limited to two dimensions, and can be deter¬
`mined correctly only by seeing the entire aceta¬
`bulum in three dimensions. At birth, the normal
`acetabulum faces more forward and more later-
`ally than it does in adult life, and it is presumed
`that the change in direction takes place gradu¬
`ally as the position of the hip changes from the
`intrauterine position of flexion and abduction
`to the erect position of extension and adduction.
`However, if the hip dislocates at or shortly after
`birth, there is no longer any corrective force
`being applied to the acetabulum through the
`capsule and, as a result, the acetabulum con-
`tinues to face relatively forward and laterally.
`This residual abnormal direction of the entire
`acetabulum is best appreciated in children over
`the age of 18 months at the time of open reduc¬
`tion for a congenital dislocation, particularly
`
`9..Reversibility of experimental dysplasia.
`Fig.
`(a)
`Radiograph of the hip of a 6-week-old experimental pig.
`The left hip had been maintained in flexion and the
`acetabulum on this side has developed normally. The
`right hip was maintained in extension during the six-
`week period. The right acetabulum is dysplastic. The
`"sloping acetabular roof" is an indication of the ab¬
`(b)
`normal direction in which the acetabulum faces.
`Pelvis of a 16-week-old experimental pig. The left hip
`had been maintained in extension for six weeks and was
`then released so that the animal could run free. Radio¬
`graphic examination at that time revealed dysplasia of
`the left acetabulum. During the ensuing ten weeks the
`dysplasia of the left hip was almost completely reversed.
`
`Innominot*
`oftaotomy
`
`Fig. 10..The principle of innominate osteotomy.re-
`direction of the entire acetabulum as a unit.
`
`Petitioner Ex. 1029 Page 7
`
`

`
`940
`
`Salter: Congenital Hip Dislocation
`
`Canad. Med. Ass. J.
`May 18,1968, vol. 98
`
`Fig. 11..Preoperative and postoperative radiographs of
`(a) Residual acetabular
`the hips of a 4-year-old girl.
`dysplasia and subluxation despite one year of closed
`treatment; there would seem to be "sloping of the aceta¬
`bular roof". This child's left hip was then treated by
`innominate osteotomy. (b) Six weeks after innominate
`osteotomy the left acetabulum appears comparable to the
`right. The only change during the six-week interval had
`been redirection of the entire acetabulum by the opera¬
`tion. Therefore, the correct interpretation of (a)
`is an
`abnormal direction of the entire acetabulum (acetabular
`maldirection) rather than a "sloping of the acetabular
`roof".
`
`when compared with the normal acetabulum of
`a child of comparable age in the postmortem
`room. Therefore, we have come to interpret the
`usually described "sloping of the acetabular
`roof as seen in the radiograph not as a defect
`in the roof, but rather as an abnormal direction
`of the entire acetabulum, i.e. acetabular mal¬
`direction. Indeed, this concept is pivotal in the
`principle of innominate osteotomy (Fig. 10),
`which is re-direction of the entire acetabulum as
`a unit.27 Further evidence of this interpretation
`is provided by a comparison of the preoperative
`radiographs of a child with residual acetabular
`dysplasia and the radiographs following innomi¬
`nate osteotomy (Figs, 11a and 11b).
`7. Facts Concerning Femoral Anteversion
`At birth the average normal femoral antever¬
`sion is approximately 30°, but under normal
`circumstances it gradually decreases with sub¬
`sequent growth to 10° or less. However, if the
`hip dislocates at or shortly after birth, there is
`no longer any corrective force being applied to
`the upper end of the femur and, as a result, the
`femoral anteversion not only persists but may
`even increase. During the year or so following
`complete restoration of the stability of the hip
`in young children, the femoral anteversion cor-
`rects spontaneously with further growth. These
`
`WfifiKSSXR.
`Fig. 12..Experimental investigation of femoral ante¬
`version in growing rabbits with the hips maintained in
`a position of (a) full internal (medial) rotation and (b)
`full external (lateral) rotation. (c) Axial views of femoral
`necks from above; (top) normal femur of control rabbit.
`there is no anteversion; (left) retroversion of the femoral
`neck from a rabbit whose hips had been maintained in
`external (lateral) rotation for six weeks; (right) femoral
`anteversion from a rabbit whose hips had been main¬
`tained in internal (medial) rotation for a period of six
`weeks.
`
`observations suggest that the femoral antever¬
`sion, rather than being a cause of the dislocation,
`is a result of the dislocation. Furthermore, we
`have shown by experimental investigation in
`rabbits that a maintained position of forced
`internal rotation of a growing hip increases
`femoral anteversion during subsequent growth,
`whereas a maintained position of forced external
`rotation results in femoral retroversion (Figs.
`12a, 12b and 12c).
`8. Facts Concerning the Hip Joint Capsule
`Howorth28 has rightly pointed out that the
`most significant anatomical finding in congenital
`dislocation of the hip at the time of birth is
`laxity and elongation of the hip joint capsule
`and the ligamentum teres. Indeed, since the dis¬
`location is intracapsular, the capsule and liga¬
`mentum teres must be elongated, as can be seen
`
`Petitioner Ex. 1029 Page 8
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`

`
`Canad. Med. Ass. J.
`May 18, 1968, vol. 98
`
`Salter: Congenital Hip Dislocation 941
`
`Fig. 13..Arthrogram of a congenitally dislocated right
`hip joint in a 2-year-old child. The dislocation is intra-
`capsular and the capsule has become markedly elongated.
`
`in an arthrogram (Fig. 13) However, the cause
`of the underlying capsular laxity is as yet un-
`known. It is known that children with congenital
`dislocation of the hip tend to show a greater
`degree of generalized congenital laxity of liga-
`ments than those without a dislocation; this has
`been well documented by Carter and Wilkin-
`son5 and by Wilkinson.29 However, there may
`well be an additional factor acting in the new¬
`born period that unduly increases the capsular
`laxity. Andren4 and Andren and Borglin8 have
`demonstrated excessive laxity of the hip joints
`as well as of the pelvic joints in newborn infants
`of the hip and
`with congenital dislocation
`ascribe this phenomenon to the effect of ma¬
`ternal hormones on the fetus. This type of
`further
`investigation
`attention,
`merits
`since
`it would seem that undue laxity of the hip
`joint capsule and ligamentum teres at the time
`of birth is the most important structural abnor¬
`mality that permits the initial dislocation when
`the hip is first extended passively. Moreover, it
`may well be that the genetic factor in the etiol¬
`ogy of congenital dislocation of the hip is related
`to the degree of capsular laxity at birth, rather
`than to any of the othe