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1979;61:15-23. J Bone Joint Surg Am.JF Crowe, VJ Mani and CS Ranawat    

Total hip replacement in congenital dislocation and dysplasia of the hip

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www.jbjs.org20 Pickering Street, Needham, MA 02492-3157The Journal of Bone and Joint Surgery

Copynghl 1979 by The Journal ofilone and Joins Surgery, Incorporated

ABsm@cr: The results of thirty-one total hip replacementsin twenty4our patients with either severecongenital dysplasia or dislocation, after an averagefollow-upof four years, were excellentin eleven, goodin sixteen, fair in one, and poor in one. The operativetechnique included superolateral bone grafts to increase the acetabular coverage in six hips. Twenty

seven hips required smaller and straighter femoralcomponents than normal. The Incidence of majorcomplications was 19 per cent.

While the indications, techniques, and results in totalhip arthroplasty for patients with idiopathic or traumaticdegenerative arthritis of the hip are well established, therehas been some controversy regarding its advisability andapplication in the patient with degenerative arthritis 5ccondary to congenital dislocation of the hip 1.4•Charnleyand Feagin, in 1973 , advocated the procedure for congenital subluxation but not for congenital dislocation of thehip. One year later, arri4 recommended it for both conditions and discussed the technique of total hip replacement for congenital dislocation . He emphasized thetechnical difficulties in establishing an adequate acetabularbed for the prosthesis.

More recently, Harris and associates described theuse of femoral-head bone-grafting for severe acetabulardysplasia5. Other methods for support of the acetabulumhave also been described3, but follow-up on the involvedpatients has not been extensive.

In this paper we report on thirty-one total hip replacements in twenty-four patients with secondary degenerative arthritis due either to complete congenital dislocation of the hip or to subluxation of severe degree.Follow-up averaged four years . Six of these hips requireda bone graft as part of the reconstruction of theacetabulum. Patients with mild dysplasia (less than 50 percent subluxation) were excluded from the study becausethey did not pose special (specific) technical difficulties.Their procedures were similar to those of the hips with severe osteoarthritis that have been treated by us with totalreplacement arthroplasty.

Materialsand MethodsThe thirty-one total hip replacements were performed

on twenty-four patients at The Hospital for Special Surgery

a 535 East 70th Street, New York, N.Y. 10021.

between November 197 1 and January 1976. The averageage at the time of the operation was fifty-seven years. Theyoungest patient was thirty-five years old and the oldest,seventy-nine. There were twenty-two women and twomen. Fourteen patients (58 per cent) had bilateral involvement with either dislocation or dysplasia and elevenhad bilateral total hip replacement. Four hip replacementsin these eleven patients were excluded from this study because the involved hips did not meet the criteria of morethan 50 per cent subluxation. Therefore, a total of sevenpatients with bilateral total hip replacement are included inthe study. Ten patients with unilateral involvement arealso included. The other seven patients had bilateral involvement, but either one hip was not operated on (threepatients) or it had a total replacement for dysplasia that

was not severe (four patients). The period of follow-upranged from twenty-four to seventy-three months, the average being forty-seven months.

Closed reduction and immobilization had been carried out in fourteen of the twenty-four patients, and openreduction with or without a shelf procedure was done infive. A femoral osteotomy was done in three. Four patientshad more than one procedure.

All patients had had a limp since childhood and manyhad had mild intermittent aches in the groin or thigh region. The pain began to be more severe between the thirdand fifth decade of life, with the peak onset being in thefourth decade. The interval between onset of severe pain

and total hip replacement ranged from two to thirty-fiveyears, with an average of thirteen years.

Nine patients had associated symptomatic degeneration of the knees, and four of them had genu valgum. Tenpatients had symptoms from degenerative joint disease ofthe lumbosacral spine.

Each patient was rated preoperatively according toa previously published system 6.10, consisting of gradesfrom 1 to 10 in four categories: pain, walking, musclepower and motion , and function (Table I) . The average

preoperative disability gradings of the present series ofpatients compare closely with the average preoperativeratings of osteoarthritic hips requiring total hip replacement at our institution. The respective grades were: pain,grade 3; walking, grade 4; muscle power and motion,grade 4; and function, grade 3.

To measure the degree of acetabular dysplasia, twotechniques were used. One was measuring the acetabularangle, which by Sharp's method of measurement is 30 to

15VOL. 61-A, NO. 1, JANUARY 1979

Total Hip Replacement in Congenital Dislocationand Dysplasia of the Hip

BY JOHN F. CROWE, M.D.*, V. JOHN MAN!, M.D.*, AND CHITRANJAN S. RANAWAT, M.D.*, NEW YORK, N.Y.

From The Hospitalfor Special Surgery, Affiliated with The New YorkHospital-Cornell University Medical Center, New York City

16 J. F. CROWE, V. J. MANI, AND C. S. RANAWAT

TABLE I

HOSPITAL FOR SPECIAL SURGERY —¿�HIP RATING SYSTEM*

Pain

0. All the time. Unbearable. Strongmedication frequently.

2. All the time but bearable. Strongmedication occasional . Salicylatesfrequently.

4. None or little at rest. With activities.Salicylates frequently.

6. When starting, then better, or after acertain activity. Salicylates occasional.

8. Occasional and slight.

10. No pain.

Muscle Power and Motion t

0. Ankylosis with deformity.

2. Ankylosis with good functional position.

4. MP —¿�Poor to fair. Arc of flexion less than60 degrees. Restricted lateral and rotarymovement.

6. MP —¿�Fair to good. Arc of fiexion up to90 degrees. Fai4 lateral and rotarymovement.

8. MP —¿�Good or normal. Arc of flexionover 90 degrees. GOOd@lateral and rotarymovement.

10. MP —¿�Normal. Motion —¿�normal oralmost normal.

Walking

0. Bedridden.2. Wheelchair. Transfer activities with walker.

4. No support —¿�house bound or ) MarkedlyOne support —¿�less than one block@ restrictedBilateral support —¿�less than three blocks .3

6. No support —¿�less than one block@ ModeratelyOne support —¿�up to five blocks@ restrictedBilateral support —¿�unrestricted .3

10. No support or appreciable limp —¿�unresthcted

Function

0. Completely dependent and confined.2. Partially dependent.4. Independent. Limited housework, shops limitedly.6. Mosthousework,shopsfreely,desk-typework.8. Very little restriction. Can work on feet.10.Normalactivities.

8. No support—limpOne support —¿�no limp

* Reprinted from Wilson and associates ‘¿�°.t Precedencein ratingwasgivento activemovement,but usuallybothactiveand passivemovementwerethe same.:t Fair lateralmovement:10degreesabduction,10degreesadduction.Fair rotatorymovement:internalrotation10degrees,externalrotation20

degrees.I Good lateralmovement:20 degreesabduction,20 degreesadduction.Goodrotatorymovement:internalrotation20 degrees,externalrotation

40 degrees.

42 degrees in patients with dysplasia. Stulberg and Harrisfound an average of 33 degrees (range, 25 to 41 degrees)in sixty normal individuals. The acetabular angle in ourpatients ranged from 4 1 to 63 degrees , with an average of52 degrees . We did not use the center-edge angle measurement of Wiberg because, although a completely dislocated hip is easy to recognize by Wiberg's method, quantitation of the degree of subluxation is difficult. In patientswith degenerative disease secondary to congenital dislocation or dysplasia of the hip, the lateral end of theacetabulum is not well defined, and difficulty is encountered in defining which point represents the center of thefemoral head because in most cases it is grossly deformed.

The second method that we used was as follows: Weobserved that the junction between the femoral head andneck medially could be located easily in all patients, including those with severe deformity of the femoral head.We studied anteroposterior roentgenograms of the pelvisin fifty normal hips and drew a horizontal line through the

inferior margin of both so-called teardrops (Fig. 1). Thedistance between this and the head-neck junction was ourmeasure of the degree of subluxation of the femoral head.Where there was no subluxation , the distance was close tozero (0.6 centimeter in Fig. 1). We also made mea

surements on the roentgenograms of the normal hips to determine the ratio between the diameter of the femoral head(measured vertically in relation to the length of the pelvis)as measured from the highest point on the iliac crest to theinferior margin of the ischial tuberosity. The normal ratiowas found to be about 1:5 (Fig. 1). When the verticaldiameter of the femoral head was reduced during deformation in the dysplastic hip, the degree of deformity couldbe measured. Because the predicted vertical diameter ofthe femoral head for all practical purposes was 20 per centof the height of the pelvis , a hip was considered to be subluxated 50 per cent or more only if the medial head-neckjunction was situated above the reference line by at least10 per cent of the measured height of the pelvis.

The amount of subluxation thus could be determinedeasily from the anteroposterior roentgenogram of the pelvis, by noting just three easily identifiable landmarks: (1)the height of the pelvis, (2) the head-neck junction in thedysplastic hip, and (3) the inferior margin of each teardrop(the reference line).

Dysplastic hips could then be classified according tothe amount of subluxation: Group I, less than 50 per centsubluxation; Group II, 50 to 75 per cent subluxation (sevenhips); Group III, 75 to 100 per cent subluxation (ten hips);

THE JOURNAL OF BONE AND JOINT SURGERY

1. Mildly

J restricted

17TOTAL HIP REPLACEMENT IN CONGENITAL DISLOCATION AND DYSPLASIA

FIG. 1

Anteroposterior roentgenogram of a patient with a dislocation of the left hip. In the normal right hip the head-neck junction lies 0.6 centimeterbelow the line joining the teardrop. The left hip head-neck junction is 2.8 centimeters above the teardrop, and this represents the degree of subluxation.

The ratio ( 1.5) of the diameter of the femoral head (solid bar on right) and the height of the pelvis (hatched bar on extreme right) representsmeasurements on the normal side. Not much change in this ratio is evident on the involved left side.

and Group IV, more than 100 per cent subluxation (four

teen hips).

Reconstructive Problems and Planningof Surgical Technique

The difficulty associated with total hip replacement inthe dysplastic hip bore a relationship to the severity of thedislocation and subsequent distortion of normal bone andsoft-tissue anatomy I, A hip that was subluxated less than50 per cent (Group I) presented no greater technicaldifficulty at surgery than a hip with severe osteoarthritis,and no cases in Group I were included in this study.

The technical problems of total hip replacement in the

severely dysplastic hip have been discussedpreviously I.3-@ These are related to: (1) the acetabularcomponent of the prosthesis, and (2) the femoral component.

A cetabular Component

The three main considerations to be discussed are the

location, the fixation, and the size.The false acetabulum with which the femoral head

articulated always was shallow and was located at varyinglevels on the ilium. Charnley and Feagin and Harris andco-workers4'@ emphasized that the ilium becomes significantly thinner proximal to the acetabulum and the lackof bone stock there and the shallowness of the falseacetabulum, with the added abductor muscle weakness, allplay a role in the problem of constructing a bed for the

acetabular component of the prosthesis. If the acetabularcomponent is to be well seated and properly positioned,and if the location of the component is considerably abovethe level of the true acetabulum, the lack of bone stock is amajor problem.

The greatest available amount of bone stock is at ornear the level of the true acetabulum. In the great majorityof cases of severe dysplasia, there was insufficient boneavailable for creating an adequate bed at the site of thefalse acetabulum even if a small acetabular component anda small femoral-head component of the prosthesis wereused. Therefore, if at all possible, the prosthesis wasplaced at or near the level of the true acetabulum.

Because of the distorted anatomy, this position oftenwas difficult to identify at the time of surgery. Then it wasessential that one identify the anterior inferior iliac spine,the ischial tuberosity, and the obturator foramen. Whenthe center of the triangle constructed on these landmarkswas marked out, a Cobb gouge was used to begin forminga bed for the acetabulum at that point, with care beingtaken not to perforate the inner table of the ilium. A bedwas gradually enlarged, the anterior and posterior marginslimiting its size. (The extra-small Mira reamer which isnow available is very helpful.) Every attempt was made toreach but not perforate the inner wall of the ilium at thelevel of the triradiate cartilage. The appropriate size of cup(ranging from thirty-three to forty-four millimeters) was

chosen so that there was 75 per cent or more of superiorcoverage with bone. Occasionally, however, a superior os

VOL. 61-A, NO. I, JANUARY 1979

18 J. F. CROWE, V. J. MANI, AND C. S. RANAWAT

FIG. 2

Anteroposterior roentgenogram of a patient with a Trapezoidal-28 total hip replacement showing the bone graft attached to the ilium with twocancellous screws.

teophyte or a previous shelf procedure aided in providingadequate coverage for the component at the level of the

false acetabulum.Harris located the suitable level for placement by pal

pation of the inner wall of the ilium at the time of surgery.He stated that this enabled him to determine the area ofgreatest thickness of the ilium and, therefore, the best location for the acetabular component.

If there was inadequate coverage for a small component after careful reaming, a bone graft was necessary onoccasion to increase the depth of the bed and superior sup

port of the acetabular component. Six hips in this series(20 per cent) had bone grafts used for that purpose. In allof these cases, a portion of the resected femoral head wasutilized as the graft and was attached to the cancellous surface (Fig. 2) at the anterosuperior margin of the preparedbut inadequate acetabular bed, either with cancellousscrews (two hips) or with Steinmann pins (four hips). Thenewly created bed with anterosuperior coverage was thenreamed with an appropriate reamer to conform to the chosen acetabular component and the acetabular prosthesiswas cemented in in the optimum position. In the four hipsin which Steinmann pins were used, the pins were removed after the cement had cured (Figs. 3-A and 3-B). Inall six hips there was no instance of loss of position of thegraft or of fixation. The grafts were not expected to provide support until there was bone healing. There were norevisions done in this series for acetabular failure, butshould revision be necessary, the healed graft would provide bone stock for future reconstruction.

In spite of our achieving proper location of theacetabular bed at the level of maximum bone thickness and

possible superior buttressing with bone graft, the preparedbed often was not large enough to accept a normal-sizedacetabular cup. In this series, twenty-three (77 per cent),of the thirty hips required a small or extra-small acetabularcomponent. In some cases, an offset articulating surfacewas used to obtain better wear qualities in the smallerthan-normal cup.

Obviously, an adequate supply of various sizes ofsmall acetabular components had to be available at thetime of surgery . Three ( 10 per cent) of the thirty hips required extra-small components (thirty-three to thirty-sixmillimeters), which are not routinely available.

Femoral Component

Because the proximal end of the femur also wasdysplastic in these hips, with the femoral head and neckanteverted and with posterior migration of the greater

trochanter1'3, the configuration of the intramedullary cayity was distorted. It was wider in the anteroposterior dimension than mediolaterally. The width of the medullarycavity also was smaller in the patients with dysplastichips3, and there was less curvature in the upper femoral

canal. The width of the canal was further reduced by themore distal level of femoral resection that was necessary toseat the femoral prosthesis well. Therefore, a femoralcomponent with a straighter stem and smaller diameterwas often necessary for these patients. This usually wasevaluated with a template before surgery, and if necessarycustom-fitted femoral prostheses were fabricated. In ourseries, twenty-seven (87 per cent) of thirty-one hips required femoral components that were smaller or straighterthan usual.

THE JOURNAL OF BONE AND JOINT SURGERY

TOTAL HIP REPLACEMENT IN CONGENITAL DISLOCATION AND DYSPLASIA 19

FIG. 3-A

Anteroposterior roentgenogram of a patient with a dislocated right hip.

Results tion three years after the operation. Her results had beenrated excellent a little more than two years postoperalively.

The patient with the fair result (Case 2 1) had intermittent subluxation of the hip, while the patient with the poorresult (Case 10) had recurrent dislocations of the hip, andat the time of writing she had permanent dislocation.

ComplicationsAs might be expected because of the technical

difficulties , postoperative complications were more frequent than with ordinary total hip replacements. Therewere two deaths, as previously described, but these were

The results were classified (Table I) as excellent (32points or more), good (22 to 3 1 points), fair (16 to 21points) , or poor ( 15 points or less) . Follow-up ranged from

twenty-four to seventy-three months, with an average offorty-seven months.

The results were excellent in eleven hips, good in sixteen, fair in one, and poor in one. Two patients who diedwere not included in the over-all results. In one (Case 11)amyotrophic lateral sclerosis developed postoperatively

and she could not walk. Her result was rated poor twoyears postoperatively, just before she died of the disease.

The second patient (Case 4) died of a myocardial infarc

Anteroposterior roentgenogram of a Trapezoidal-28 total hip replacement. The bone graft taken from the femoral head was used to increasesuperior coverage of the cup.

VOL. 61-A, NO. I , JANUARY 1979

Case Age, Sex Group*Type of Prosthesis Follow-upHip-RatingScoret Most RecentCommentsPreoperative(Yrs.)(Mos.)

20 J. F. CROWE, V. J. MANI, AND C. S. RANAWAT

TABLE II

3 54,F

4 65,F

7 57,F8 56,F

9 55,M

10 71,F

11 58,F

12 53,F

13 59,F

20 35,F

21 56,F

22 65,F

23 46,M

24 41,F

II Charnley-Mueller

III Charnley-Mueller

155, FR IIIL IICharnleyCharnley73 691/4/1/4 1/4/1/49/8/5/8 9/8/5/8Good

resultbilat.279,

FIICharnley664/6/5/410/9/7/9Excellent result. Patient on chemother. forbreastcancer664/4/4/79/6/6/6Good

result353/5/6/58/9/8/10Excellent

rating. Died of unrelatedmyocardial infarct 6 mos.later544,

FRLIII IVCharnleyCharnley62 622/5/5/4 2/5/5/410/8/4/610/8/4/7Good

result. No bone graft used.Cup placed high onleft667,

FIVCharnley-Mueller61

615757

51

51

24

49

484/1/4/4

3/5/4/34/6/6/64/6/6/6

4/5/6/8

2/4/4/4

3/3/3/3

4/5/6/3

1/1/4/49/8/6/6

9/8/8/1010/9/9178/9/10/7

8/6/617

3/3/4/2

—¿�

7/8/8/8

9/6/6/6Good

result. Previous right femoral shortcIting to equalize limb length

Excellent resultExcellent bilat. Broken left troch. wire

with overlying bursitis

Good result. Radiolucent tine at femoralbone-cement interface; neg. arthrogram;no progression

Bust. congen. disloc. Refused revisionafter third redisloc. Poor result

Bilat. congen. disloc. Femur fract. required revision with long-stem prosth.Died 2 yrs. postop. of amyotrophiclateral sclerosis

Good result

Good result. Bone graft fixed with Steinmann pins

Good resultbilat.Good

result

Bilat. congen. disloc. with bone graftsfixed with Steinmann pins. Good resultin spite of troch. migration on right.Fell, fractured right femoral stem 40mos. postop.

Excellentbilat.38

38

362/6/4/3

4/4/6/4

4/7/4/48/81717

4/6/6/6

9/8/617Excellent

result

Excellent result. Had bilat. total hip replacement, left with <50% dysplasia

Good result. Bone graft fixed to ilium withtwo screws

Fair result. History of sublux. confirmedon fluoroscopy

Bilat. congen. disloc., left hip fused previously. Bone graft with Steinmann pins.Good result

Excellent result

Osteophytes used for coverage on right.Bone graft fixed with two screws on left.Excellent result

II Charnley

R IV CharnleyL IV Charnley

II Charnley

IV Charnley

IV Charnley

III Charnley

IV Trapezoidal-28

III Trapezoidal-28

II Trapezoidal-28

III Trapezoidal-28

II CharnleyR III Trapezoidal-28L IV Charnley

14 57, F R III Trapezoidal-28L IV Trapezoidal-28

15 67,F IV Charnley

16 70, F R IV Trapezoidal-28L III Charnley

17 35, F R III CharnleyL IV Charnley

18 64, F IV Trapezoidal-2819 63,F IV Charnley

45 6/5/4/644 5/4/3/6

43 4/4/4/443 2/2/2/443 2/2/2/4

41 2/4/4/437 4/6/5/4

40 4/6/6/4

39 3/4/3/4

33 4/6/5/5

28 3/5/5/524 5/5/4/5

9/8/7178/7/8/79/8/6/7

9/6/9/68/4/5/5

10/10/8/1010/9/8/10

9/8/9/8

10/9/6/10

10/9/9/10

10/9/7/910/9/8/9

* See text.

t See Table I.

not considered to be related to the surgery and hence werenot included in the tabulation of incidence of complications from the procedure.

Two patients had clinical thrombophlebitis and oneeach had an urinary-tract infection and sterile wounddrainage. All of these complications resolved understandard treatment.

The major complications were one case each ofmyocardial infarction, pulmonary embolism, dislocation,

subluxation, fracture of the shaft of the femur, andsciatic-nerve palsy (in the same patient who had the dislocation). This represents a 19 per cent complication rate forthis group of patients.

In Case 10, the patient with the poor result, thesciatic-nerve palsy was noted in the immediate postoperative period and the dislocation occurred fifteen days later.A closed reduction with percutaneous abductor tenotomywas performed and the hips were maintained in wide ab

THE JOURNAL OF BONE AND JOINT SURGERY

21TOTAL HIP REPLACEMENT IN CONGENITAL DISLOCATION AND DYSPLASIA

FIG. 4

Case 10. Anteroposterior roentgenogram of a dislocated Charnley total hip replacement. The cup was located vertically. The acetabularangle of the cup measured from the horizontal was 65 degrees.

duction. A second dislocation then occurred while the pa

tient was in bed on the twenty-fifth postoperative day.Again a closed reduction was done and a hip spica wasapplied that was retained for five weeks. The patient then

was discharged and apparently did well until four monthslater, when she was readmitted. Roentgenograms made atthat time revealed that she had been walking with a dislocated hip. Review of the roentgenograms of this hip (Fig.4) revealed the lateral tilt of the acetabular component tobe 65 degrees. A revision of the acetabular component wassuggested but refused. The hip has remained dislocated todate and the patient has continued to walk wearing ashoe-lift.

The patient with the subluxation, Case 21 , complained of mild pain in the groin. Fluoroscopy revealedimpingement of the femoral neck at the acetabulum. No

treatment was given because the pain was mild.The one femoral fracture occurred on the twenty-first

postoperative day while the patient (Case 11) was bearingweight. This fracture required removal of the femoralcomponent and insertion of an extra-long stem. Review ofthe roentgenograms revealed that the lateral part of thefemoral shaft had been weakened due to perforation of thecortex during reaming. This had not been recognized at thetime of operation. This patient was the one who died ofamyotrophic lateral sclerosis.

The two patients with pulmonary embolism andmyocardial infarction recovered uneventfully.

Three patients had breakage of the trochanteric wireswithout migration of the trochanter. They were asymp

tomatic. One patient (Case 16) had breakage of thetrochanteric wires with superior migration of the greatertrochanter, discovered on a routine follow-up examination(Fig. 5). The patient was asymptomatic, and was classified

FIG. 5

Case 16. Anteroposterior roentgenogram of a hip joint with aTrapezoidal-28 total joint replacement. The greater trochanter did notheal and migrated superiorly with wire breakage. This patient had a fracture of the femoral stem forty months postoperatively.

VOL. 61-A, NO. I, JANUARY 1979

22 J. F. CROWE, V. J. MAN!, AND C. S. RANAWAT

as having a good result thirty-six months postoperatively.However, forty months postoperatively she fell, injuringher hip. Roentgenograms made at that time showed nochange from four months earlier, but about a month laterthe hip became painful, and new roentgenograms revealeda fractured femoral stem . The femoral component thenwas replaced. The hip-rating score in this case has re

mained in the ‘¿�‘¿�good‘¿�‘¿�category. Of note is the fact that thefracture occurred in a medium-size Trapezoidal-28femoral stem, a size that is no longer available because it isconsidered mechanically inadequate.

There were roentgenographic features of interest insome cases. Twelve hips showed radiolucent linesaround the acetabular component: eight of the lines weresuperolateral and three were medial . In one hip there wasfibrous union of the trochanter and in three, asymptomaticectopic ossification.

Discussion

The technical difficulties of total hip replacement inthe dysplastic hip have been well emphasized1'2'4@5, butbear repetition.

1. Osteotomy of the greater trochanter is needed asan integral part of the operative technique, and that procedure is universally accepted as a means of obtaining thewide exposure that is required.

2 . Locating the acetabular component at or near thelevel of the true acetabulum will give the most satisfactorybiomechanical result and will make use of the maximumavailable thickness of the ilium. The proper level is judgedby identifying the anterior inferior iliac spine, the ischialtuberosity, and the inferior rim of the acetabulum formedby the superior part of the obturator foramen. No reamingshould be carried out until the landmarks of the trueacetabulum are identified.

3 . The critical measurement to be used in selectingthe proper acetabular component is the anteroposteriorwidth of the true acetabulum, measured after reaming iscompleted. A smaller than usual acetabular component(outside diameter ranging from thirty-three to forty-fourmillimeters) will ordinarily be necessary, as it was in 77per cent of cases in this series.

4. The superior coverage of the true acetabulum isreduced whenever there has been progressive superiormigration of the femoral head. Our data suggest that thereis a linear relationship between the degree of subluxation

of the hip and the diminished width of the ilium. The bonegraft will be needed more often in Group-Ill hips (three out

of ten) than in Group-I! hips (none of seven in this series).This relationship is not valid in patients whose hips havebeen completely dislocated early in life. In these cases apseudo-acetabulum may develop and good bone coveragemay be possible because of it. Only three of our fourteenpatients with dislocation required bone grafts.

When more than 75 per cent coverage of theacetabulum cannot be obtained at the time of surgery,

other methods to improve the coverage besides bonegrafting 1.4.5are available, such as medial displacement ofthe cup' or a Chiari-type@ , but we concur withHarris and associates@ that the best alternative is bonegrafting.

The resected femoral head forms a suitable graft whenfastened to the ilium to create a superolateral buttress forthe acetabulum. The use of bolts as described by Harrisand@ appears to be technically difficultalthough the fixation achieved is superior to that with theuse of screws or pins. However, in our experience, fixing aportion of the resected femoral head to the ilium with twocancellous screws in our two patients was successful, andthis technique has now become our preferred method ofbone-graft fixation. It has been used in fifteen additionalhips and there has been no failure in fixation of the graft oracetabular component to date.

Theoretically, compromise of the medial wall by cxcessive reaming (or by a Chiari osteotomy) creates a potential for axial migration of the prosthesis and loss of position of the acetabular @2or fatigue fracture ofthe weak medial acetabular wall “¿�.This technical error didnot occur in our series.

Careful preoperative planning is essential in selectingthe femoral component. An estimation of the level offemoral resection as related to the lesser trochanter shouldbe made. Templates magnified 20 per cent for direct usefrom roentgenograms , or roentgenograms made with atube-to-plate distance of 183 centimeters, should be usedto determine component size prior to surgery.

The femoral component ordinarily will be smaller andstraighter than usual (87 per cent of hips in our series). Theabnormal configuration of the femoral canal must be takeninto account while reaming in order to avoid fracture andpenetration of the cortex@ In dysplastic hips, the greaterdiameter of the medullary cavity is in the anteroposteriorplane, and may require a custom-made femoral component.

While several different types of prostheses were usedin this series, we are of the opinion that the Charnleymodification (special CDH prosthesis for dislocated hips),or a Charnley prosthesis modified according to measurements made from preoperative roentgenograms,should be used. The inner acetabular diameter of twentytwo millimeters allows the use of a smaller acetabularcomponent (thirty-six-millimeter outside diameter) thathas a sufficient thickness of polyethylene to provide themechanical strength needed.

With one exception , there has been no deteriorationin the quality of the results in our patients as determinedroentgenographically and clinically . The exception is thelate mechanical failure in the one patient (Case 16) whohad a fracture of the femoral stem forty months postoperatively. However, a longer follow-up is needed to show ifloosening of the prosthesis or other types of failure willeventually become evident.

ThE JOURNALOF BONE AND JOINTSURGERY

TOTAL HIP REPLACEMENT IN CONGENITAL DISLOCATION AND DYSPLASIA 23

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1976.3. DUNN, H. K., and HESs, W. E.: Total Hip Reconstruction in Chronically Dislocated Hips. J. Bone and Joint Surg., 58-A: 838-845, Sept. 1976.4. HARRIS, W. H .: Total Hip Replacement for Congenital Dysplasia of Hip: Technique. In The Hip: Proceedings of the Second Open Scientific

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