The low prevalence of hip OA in Asian and black populations in their native countries; the low incidence of total joint replacement for primary OA in Asian, black, and Hispanic populatio
Trang 1Osteoarthritis (OA) of the hip is
manifested as degeneration of the
tissues of the hip joint, including
hyaline cartilage, fibrocartilage,
bone, and synovium Hip arthritis
can result from several different
patterns of joint failure Underlying
pathologic changes due to
condi-tions such as osteonecrosis, trauma,
sepsis, Paget’s disease, and
rheuma-toid arthritis can produce
degenera-tion of the joint Condidegenera-tions such as
developmental dysplasia of the hip
(DDH) and slipped capital femoral
epiphysis (SCFE) leave the patient
with predisposing anatomic
abnor-malities that can later result in os-teoarthritic changes When any of these conditions can be identified (Table 1), the degenerative process
is termed “secondary OA.” When neither an anatomic abnormality nor any specific disease process can
be identified, the condition is called
“primary OA,” which is, therefore, a diagnosis made by exclusion
Clinical and epidemiologic stud-ies indicate that OA of the hip is a distinct entity that behaves
different-ly from OA in other synovial joints.1
Patients who have undergone total hip replacement (THR) because of a
Dr Hoaglund is Professor (Emeritus) of Ortho-paedic Surgery, University of California at San Francisco Medical Center, San Francisco Dr Steinbach is Professor of Radiology and Ortho-paedic Surgery, University of California at San Francisco Medical Center.
Reprint requests: Dr Hoaglund, Department
of Orthopaedic Surgery, UCSF Medical Center,
500 Parnassus Avenue (MU 320-W), San Francisco, CA 94143-0728.
Copyright 2001 by the American Academy of Orthopaedic Surgeons.
Abstract
Primary osteoarthritis (OA) of the hip has a distinct etiology and epidemiology
compared with other types of arthropathy in the hip joint Arthritis of the hip can
be secondary to conditions such as osteonecrosis, trauma, sepsis, or rheumatoid
arthritis Certain conditions, such as congenital hip disease and slipped capital
femoral epiphysis, involve predisposing anatomic abnormalities; in such cases, the
term “secondary OA” is used When either an anatomic abnormality cannot be
determined or other specific causative entities are not identified, primary OA is
the diagnosis of exclusion The prevalence of hip OA is about 3% to 6% in the
Caucasian population and has not changed in the past four decades In contrast,
studies in Asian, black, and East Indian populations indicate a very low
preva-lence of hip OA Statistics on patients who underwent total hip replacement for
primary OA in San Francisco and Hawaii demonstrate a virtual absence of the
condition in Asians and low rates in the black and Hispanic populations Family
studies from Sweden, Britain, and the United States show increased rates of hip
OA in first-degree relatives of the index patient when compared with the normal
population Occupations requiring heavy lifting, farming, and elite sports
activi-ty are associated with increased rates of hip OA The low prevalence of hip OA in
Asian and black populations in their native countries; the low incidence of total
joint replacement for primary OA in Asian, black, and Hispanic populations in
North America; and the familial association of hip OA in Caucasians all suggest
that genetic factors may be involved in the occurrence of this disease.
J Am Acad Orthop Surg 2001;9:320-327
Etiology and Epidemiology
Franklin T Hoaglund, MD, and Lynne S Steinbach, MD
diagnosis of primary OA rarely undergo total knee replacement, and vice versa.2 In two other studies, Japanese and Hong Kong Chinese populations had virtually no pri-mary OA of the hip but a consider-able incidence of knee OA.3,4
Epidemiology
The modern search for the causes of
OA started with the work of British scientists Kellgren and Lawrence, who carried out epidemiologic stud-ies encompassing several ethnic groups in a number of geographic areas, including western European and specifically British Caucasians, African and Jamaican blacks, and Native Americans.5-7 Responses to questionnaires and the clinical findings in randomly selected pop-ulations were evaluated, and radio-graphs of various joints were
Trang 2ex-amined with the use of
standard-ized grading.5-7 Patients were
con-sidered to have generalized OA if
three or more joint groups were
involved Evaluation of these data
was the basis for an atlas that is
still used today to characterize the
various degrees of OA.5
These researchers found that the
incidence of OA was not related to
latitude or longitude The highest
prevalence of OA occurred in the
Caucasians It was noted that OA
pref-erentially affected the distal
inter-phalangeal joints and the first
carpo-metacarpal joints of the hands, the
knees, and the first
metatarsopha-langeal joints Comparisons between
ethnic groups were not particularly
helpful in delineating the etiology of
OA; however, the marked ethnic and
racial differences in the incidence
of hip OA were important
observa-tions.6
Population Studies
Lawrence and Sebo6studied the
comparative incidence of
radio-graphic OA of the hip by evaluating
pelvic radiographs of European
Caucasians, blacks, and Native
Americans from nine geographic areas The term “radiographic OA”
was used because there was no intent to distinguish primary or sec-ondary OA from other specific causes
of hip disease Kellgren’s grading system was used to characterize the degree of hip arthritis as absent (grade 0), doubtful (grade 1), mini-mal (grade 2), moderate (grade 3),
or severe (grade 4) The incidences
of grade 2-4 and grade 3-4 OA were higher in the Caucasian males than
in the females (Table 2) The rate of moderate and severe OA in Cau-casians was three to four times that
in blacks and Native Americans
Hoaglund et al4 also evaluated conventional radiographs of the hands, knees, and hips of 500 Hong Kong Chinese subjects An ex-tremely low rate of OA of the hip (1%) was found, but the incidence
of hand OA was similar to that in European Caucasians A second study was done 20 years after the original study Pelvic radiographs
of 999 Hong Kong Chinese men ob-tained during intravenous pyelog-raphy demonstrated no change in the incidence of hip OA.8
In another study, a group of 51,777 East Indians who visited an orthopaedic clinic in India were examined.9 The incidence of OA was found to be less than 0.1% Pelvic radiographs of American Caucasians demonstrated that the prevalence of hip OA in patients over 54 years of age was 2.7% to 3.5%,10which is lower than the rate seen in European Caucasians.6-11
In a Swedish study,12pelvic radio-graphs obtained during double-contrast colon examinations were evaluated The overall incidence of hip OA was 3.4% in 1964 There has been no change in this rate over the past four decades, as demonstrated
in follow-up studies performed in
1984 and 1993.13
In summary, population studies show that the rate of moderate to severe primary or secondary OA of the hip in Caucasians is 3% to 6%, compared with 1% or less in East Indians,9 blacks, Hong Kong Chinese, and Native Americans The prevalence has not changed in four decades, suggesting that genetic and/or environmental factors remain constant
Hip Disease in Hip Surgery Patients
Specific causes of hip disease and OA in patients who underwent hip surgery in the 1940s and 1950s have been evaluated.14-16 The rela-tive incidence of various hip dis-eases described in these series is quite different from the current incidence During that era, 20% to 50% of surgical cases were due to Legg-Calvé-Perthes disease, DDH,
or SCFE One might have expected
a higher incidence of adults pre-senting with a painful hip due to arthritic changes from these causes, because there was no prophylactic treatment for these conditions or good early surgical reconstruction
at that time
There has been an ongoing de-bate about whether the high rate of
Table 1
Causes of Secondary OA and Their Radiographic Appearance
Condition Radiographic Features*
Osteonecrosis Sclerosis, lucency, flattening of femoral head
Paget’s disease Osseous enlargement, trabecular coarsening,
cortical thickening Inflammatory arthropathy Joint-space narrowing, osteopenia, erosion
Traumatic remodeling Distortion of osseous contour with sclerosis
and remodeling Degenerative dysplasia Shallow acetabulum with increased acetabular
of the hip index, subluxation, or dislocation
Slipped capital femoral Medial and/or posterior displacement of
epiphysis femoral head, convexity at head-neck
junction, short femoral head, coxa vara, short broad femoral neck
* In addition to joint-space narrowing and osteophytes.
Trang 3secondary OA in that period
con-tinues today Studies of THR
pa-tients in Europe and the United
States have provided information
about the frequency of all causes of
hip arthritis in various populations
The prevalence data were
compa-rable among Caucasian population
groups in the United States,
Scan-dinavia, and western Europe The
rate of THR varied from
approxi-mately 60 per 100,000 persons in
the Mayo Clinic data to 140 per
100,000 in Norway17 (Table 3)
When other specific causes of hip
disease were excluded, it was noted
that primary OA was the underlying
disorder in nearly 90% of
osteoar-thritic hips Similar published
statis-tics for Africa, South America, Hong
Kong, or Japan are not available
The rate of THR for all residents
of San Francisco has been
mea-sured for the years 1984 through
1988 using data from the 17 hospi-tals in or near the city (Table 4).22
Preoperative pelvic radiographs were evaluated for arthritis with-out the examiner’s knowledge of the gender or race of the patient
Total hip replacement statistics for Caucasians were compared with those for the sizable non-Caucasian populations (i.e., Asian, Hispanic, and black) Caucasians had a rate
of THR of 75 per 100,000 persons, blacks had half the incidence, and Asians had only one tenth There were markedly lower rates of THR performed because of primary OA
in non-Caucasians; for example, the rate was 1.3 per 100,000 for the Chinese population, compared with 43 per 100,000 for Caucasians
The rates of THR for the other causes of hip disease, including secondary OA, were not signifi-cantly different among the various ethnic groups
This study was repeated in Ha-waii,23 with its large Asian and Pacific Islander population (750,000 persons) In the total Hawaiian population, medical insurance is available to more than 90% of the patients, thus minimizing the effect
of access to care as a factor The re-sults of this study confirmed the markedly higher rates of THR in Caucasians, who predominantly had primary OA (Table 4) The rate
of THR for secondary OA in the Caucasian population was not sig-nificantly different from the rates for the Chinese, Filipino, Hawaiian, and Japanese populations
Incidence of Predisposing Anatomic Abnormalities
In 1965, Murray24suggested that secondary OA was more common than primary OA In that study, ra-diographs were evaluated looking for evidence of DDH or femoral head tilt Previous DDH was found
in 37% of British women with OA, and a femoral-head tilt deformity was noted in 74% of British men with OA (Table 5) His conclusion that OA was in fact secondary 90%
of the time has been supported by subsequent analysis of the data in uncontrolled series of hip surgery patients in the United States25,26and South Africa.27 However, there is now considerable information from more recent surgical series that argues against such a high inci-dence of either DDH or SCFE as the cause of OA
Measurements of the center-edge (CE) angle in blacks (who are rela-tively unaffected by DDH and hip OA) are the same as those in Cau-casians.28(The CE angle is a mea-sure of hip socket coverage A low angle indicates a shallow socket, which can predispose to secondary OA) In one study, acetabular depth measurements and CE angles in British patients were the same in normal and osteoarthritic hips.29
The incidence of DDH based on CE angle measurements in Hong Kong Chinese men was not different from that in British men,8 yet osteoar-thritic hips are much less frequent
in the Chinese Although Japanese persons have significantly smaller
Table 2
Incidence of Hip OA in Male
and Female Subjects in
Population Studies 6
Incidence (M/F), % Grades Grades Subjects (No.) 2-4 3-4
Caucasian (1,451) 20/12 6.5/5.75
Black (503) 2.3/3 1/1.6
Native
American (545) 9/8.0 2.7/1.6
Table 3
Relation Between THR and Primary OA in Various Nations 17-21
Sweden Norway Denmark Finland USA United Kingdom France Belgium Rate of THR per 100,000 persons 130 140 82 58 60 54 108 116
* NA = data not available
Trang 4CE angles than British persons, they
have much less hip OA.30
Lane et al31 found no difference
in the incidence of an abnormal CE
angle between American Caucasian
women with OA of the hip and
those without it (4% to 5% in each
group) In this population, DDH
did not account for more than a few
osteoarthritic hips
If primary OA of the hip is due to
a subtle dysplasia, it should be seen
frequently in Japanese persons, with
their extremely high rate of dysplasia;
however, primary OA is rare in that
population.3,32 The incidence of DDH
in Caucasians is 0.5% If OA
devel-oped in all children with DDH, this
would account for only one eighth of
the cases of OA in the Caucasian
pop-ulation Hawaiian Japanese women
have the same rate of THR for
dys-plastic OA as Caucasian women, but
their rate of THR performed for
pri-mary OA is only one tenth of that for
Caucasian women.23
In summary, when controlled
studies of acetabular measurements
are done and the rates of DDH and
OA for each racial subgroup are
considered, DDH accounts for only a
small percentage (5% to 10%) of hip
OA in Caucasians
Since the original publications of
Harris,26Murray,24Stulberg and
Harris,25and Solomon,27which sug-gested that OA was often caused by SCFE (Table 5), there has been new information that SCFE or subclinical SCFE does not account for the high rate of primary OA The tilt defor-mity seen in the adult with OA has been shown to be due to a remod-eling process that causes progres-sion of osteophytes, rather than to
an old epiphyseal slip.33 Goodman
et al34identified a subtle or subclini-cal slip deformity in 8% of cadaver bone specimens from a large collec-tion of disarticulated femora and pelves There are some similarities
of this subclinical SCFE to SCFE, such as a lower incidence in women,
increased left-side prevalence, and increased incidence in specimens from black subjects However, clini-cal SCFE in the adolescent occurs in only 1 of every 800 boys (an inci-dence of only 0.125%) Whether subclinical SCFE is a forme fruste of SCFE remains to be proved Even if
it is, anatomically normal femora accounted for more than 80% of the
OA in their series Furthermore, although there is little primary OA
in the black and Polynesian popula-tions, as well as a low incidence of THR performed because of OA,22,23
these populations have two to four times the rate of SCFE in Cauca-sians
Table 4
Rates of THR for Secondary and Primary OA by Ethnic/Racial Background in Two Studies 22,23*†
Chinese Japanese Filipino Caucasian Hispanic Black Hawaiian San Francisco study22
Women 1.8/1.4 2.9/2.9 0.9/3.1 6.7/52.6 0/6.2 1.1/19.2 …
Hawaii study23
Women 0.31/0.84 0.17/0.24 0.06/0.25 0.29/2.35 … … 0/0.30
* Adapted with permission from Hoaglund FT, Oishi CS, Gialamas GG: Extreme variations in racial rates of total hip arthroplasty for
primary coxarthrosis: A population-based study in San Francisco Ann Rheum Dis 1995;54:107-110 Also adapted with permission
from Oishi CS, Hoaglund FT, Gordon L, Ross PD: Total hip replacement rates are higher among Caucasians than Asians in Hawaii.
Clin Orthop 1998;353:166-174.
† Values are expressed as rates for secondary OA/primary OA per 100,000 population/yr.
Table 5 Incidence of OA Due to DDH and Femoral-Head Tilt in Men and Women
in Four Studies 24-27
Stulberg Murray24 Solomon27 Harris26 and Harris25
Women
Men
Trang 5Body Weight
Bioengineering studies have
shown that forces across the hip
joint are multiplied by a leverage
system involving muscles pulling
against the weight of the body For
example, an individual standing on
one foot has a force across the hip
joint of three to four times his or
her body weight Therefore,
obesi-ty could be contributory in the
eti-ology of primary OA of the hip
Although OA of the knee has
been shown to be consistently related
to obesity, there have been
conflict-ing results regardconflict-ing the
relation-ship of body weight to the
develop-ment of OA of the hip Saville and
Dickson35found no difference in the
average body weight of patients
with primary or secondary OA of
the hip compared with control
sub-jects Spector36 and Tepper and
Hochberg37 found no relationship
between body weight or body-mass
index and the occurrence of hip OA
However, other studies have shown
an increased risk of OA of the hip
in obese individuals.38,39 The
con-flicting findings concerning body
weight and hip OA may be related
in part to the fact that patients gain
weight as a result of the immobility
imposed by a painful hip
Occupational Factors
The physical demands of work
have been estimated to account for
40% of cases of hip OA,40and
carry-ing heavy loads has been associated
with an increased rate of hip OA
Axmacher and Lindberg41 found
that farmers were at increased risk
for hip OA in studies conducted in
England, Sweden, and France—all
countries that are known to have
high rates of hip OA However, the
researchers pointed out that farmers
are usually members of families that
have been involved in farming for
many generations; therefore,
heredi-tary factors cannot be ruled out
Studies conducted in Sweden in-dicated an increased risk of OA in patients who had been involved in track, field, and racket sports as well
as among soccer players (especially those who played professionally).42
The findings from these studies support the hypothesis that sports may exacerbate hereditary predis-position to OA of the hip
Other Anatomic Considerations
There is a known association be-tween arthritis and previous DDH
in patients with the mechanical fac-tors that predispose to secondary
OA, such as an acetabular abnor-mality or femoral anteversion
Therefore, investigations have also been done to determine the role of femoral anteversion alone in pa-tients with primary OA of the hip
However, small studies involving cadaver specimens and patients with hip arthropathy have shown variable results.43-46 In cadaver specimens without OA, there was
no correlation between femoral anteversion and acetabular angles
A study of Hong Kong Chinese cadaver bones showed a high inci-dence of femoral anteversion com-pared with specimens obtained from Caucasian subjects.47 Inas-much as hip OA is rare in the Hong Kong Chinese population, this ob-servation is inconsistent with ante-version being a factor in primary
OA of the hip
Femoral anteversion in osteo-arthritic and normal subjects has been measured with the use of biplanar and/or conventional (AP and cross-table lateral) radio-graphs; a mild increase in antever-sion was found in some series but not in others.43 This increase in femoral anteversion could be due
to measurement error Using ac-curate CT techniques, Reikerås et
al46found no difference in femoral anteversion between control sub-jects and a series of Caucasian pa-tients with OA
Family Studies
In 1984, Lindberg48 studied 289 siblings of 184 Swedish patients who had undergone THR for primary coxarthrosis Coxarthrosis occurred
in 8% of siblings This represents a
statistically significant (P<0.05)
increase over the rate of 3.8% in con-trol subjects
In an unpublished study, 72 pa-tients with primary OA who un-derwent THR responded to a writ-ten family questionnaire Analysis
of the responses confirmed Lind-berg’s findings Of the 238 first-degree relatives over the age of 50, 13% reported a THR or symptoms
of hip pain consistent with OA of the hip This is significantly higher than the 3% to 6% prevalence of OA
of the hip diagnosed radiographi-cally
In black patients in San Francisco, the incidence of THR for primary
OA was only 30% of that for Cau-casian patients.22 This is the same as the incidence of Duffy or GM blood groups reported for black persons
in the western part of the United States.49 (All Europeans have Duffy blood groups, but black Africans do not have them.) Therefore, the dif-ference between the rates of THR for primary OA in Caucasians and in blacks is consistent with a genetic etiology
In a prospective cross-sectional survey of 264 British patients who underwent THR for idiopathic OA
of the hip, the familial prevalence
of THR was ascertained with a questionnaire distributed to their siblings.50 By using spouses as a control group, the researchers cal-culated the relative risk of THR in siblings as 1.86 (95% CI, 0.93 to 3.60) With the use of the threshold liabil-ity model, the heritabilliabil-ity of end-stage OA of the hip was estimated
to be 27%
Twin studies in women have shown that the heritability rates of
OA of the knee and hand are 49% and 65%, respectively.51 In more
Trang 6recent twin studies of OA of the hip,
women showed a 50% heritability
(95% CI, 20% to 74%).52
In summary, two different factors
appear to be involved in the etiology
of OA First, the lower rates of
pri-mary OA in population studies of
non-Caucasians and the difference
in rates of THR for primary OA in
patients with various racial
back-grounds living in a common
envi-ronment suggest that it is a disease
primarily of Caucasians Second,
the relatively high incidence of the
disease in siblings of Swedish and
English patients who underwent
THR because of primary OA
sug-gests that genetic factors are
opera-tional as well
Radiographic Criteria
In the studies performed by
Hoaglund and co-workers in San
Francisco22and Hawaii,23the
radio-graphs were read without
knowl-edge of the race of the patient The
rate of secondary OA in the
Cau-casian population was not
signifi-cantly different from the rates for
Chinese, Filipino, Hawaiian, and
Japanese subjects
The use of radiographic criteria
has been criticized as being generally
inadequate to establish that a case
classified as primary OA is actually
secondary OA For example, DDH
is thought to be underrepresented
in women with primary OA, and
SCFE or a variation of it is thought
to be underrepresented in men
However, evaluation of the
radio-graphs of equivalent large Japanese
and Caucasian populations have
demonstrated that these criteria can
be used to distinguish between
pri-mary and secondary OA
The cumulative rates of THR for
secondary OA (measured in cases
per 100,000 person-years) are similar
for Japanese women (0.17) and
Caucasian women (0.29), but the
rate for primary OA in Japanese
women was only one tenth (0.24) of
that for the Caucasian women (2.35)
If large numbers of cases of primary
OA are in fact secondary OA, there should be sizable numbers in the Japanese women as well as in the Caucasian women
The statistics for men show the same disparity The rate of sec-ondary OA in Japanese men is 0.6, in contrast to the rate of 0.11 for Cau-casian men If no variant of SCFE were distinguished on the basis of radiographic criteria, comparable numbers of primary OA would be seen in both Caucasian and Japanese men However, the rate of THR for Caucasians with primary OA is 29 times that for the Japanese men, but the rate of SCFE in Japanese men is only one half to one fifth of that in Caucasians
It seems clear, therefore, that use
of radiographic criteria did not lead
to underrepresentation of DDH in the female subjects Similarly, use of those criteria did not lead to under-representation of SCFE or subclinical SCFE in male subjects
Summary
Contributions to our understanding
of the etiology of OA of the hip have come from international popu-lation studies, joint replacement reg-istries, epidemiologic investigations, and, more recently, analysis of fam-ily pedigrees to investigate genetic factors in this disease Attempts to elucidate the etiology of OA of the hip depend on our ability to recog-nize and separate this condition from other causes of hip disease, as well as our ability to distinguish secondary OA from primary OA
Secondary OA of the hip occurs when a condition such as DDH, SCFE, or Legg-Calvé-Perthes disease results in a predisposing anatomic abnormality that leads to hip degen-eration due to mechanical factors A specific diagnosis of secondary OA
is dependent on radiographic diag-nosis and is more sensitive in the
early stages of degeneration, before
it progresses and remodeling occurs Radiographic studies of both Cau-casian and Asian patients with and without OA suggest that a specific diagnosis can be made Disagree-ment may arise in specific cases, but
in a large series such cases should not affect the overall conclusions
It is noteworthy that studies of the Asian populations in San Fran-cisco and Hawaii showed similar prevalences of all types of hip ar-thritis in those who underwent THR but virtually no underlying primary
OA As the same radiographic cri-teria were applied to all races, the high incidence in Caucasians indi-cates that the conditions are separa-ble at least 90% of the time
The contribution of subclinical SCFE to the overall incidence of pri-mary OA is small.34 In a study of cadaver femora and pelves, the un-derlying anatomy was normal in 83% of the specimens, and only 8% had subclinical SCFE Interestingly, grade 2 OA developed in only 37%
of the femora with subclinical SCFE; therefore, it appears that something other than the anatomic deformity
is the main etiologic factor underly-ing OA
The results of comparison studies
of Caucasian, black, Native Ameri-can, and Hong Kong Chinese popu-lations; the joint replacement statis-tics; and the comparative rates of THR in American non-Caucasian populations indicate that primary
OA is a disease primarily of Cauca-sians of European ancestry Inci-dence rates do not appear to have changed in the past four decades, suggesting that the etiologic factors have not changed Although some studies suggest that factors such as obesity, high-performance athletics, strenuous occupations, and femoral neck anteversion may be contribu-tory to OA, there is also evidence to the contrary The minimal inci-dence of THR for primary OA in American Asians compared with
Trang 7Caucasians living in a similar
envi-ronment suggests a genetic etiology
Apparently normal hip anatomy
is present in more than 80% of
pa-tients in whom OA develops, and only a small percentage of patients with subclinical SCFE are subse-quently found to have OA
There-fore, it is reasonable to postulate an underlying defect in articular carti-lage or bone that leads to the even-tual development of OA
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