morphology of acetabulum

52

CLINICAL ORTHOPAEDICS AND RELATED RESEARCHNumber 393, pp. 52–65© 2001 Lippincott Williams & Wilkins, Inc.

Morphologic features of the hips, in particularthose features germane to determination of ac-etabular and femoral anteversion angles andfemoral head offset, were studied in 50 male and50 female human skeletons with bilateral normaljoints. Four distinct configurations were identi-fied relative to the anterior acetabular ridge. Themajority (121, 60.5%) were curved; 51 (25.5%)were angular; 19 (9.5%) were irregular; andnine (4.5%) were straight. The acetabular an-teversion angle measured 19.9� � 6.6� (range,7�–42�) and was significantly larger in females(21.3� � 7.1�) versus males (18.5� � 5.8�). Thenotch acetabular angle, which can be identifiedeasily intraoperatively, was defined as the anglecreated at the intersection of a line from the sci-atic notch along the posterior acetabular ridgeand a line from the posterior to the anterior ac-etabular wall. This angle is almost perpendicular(89.0� � 3.5�) and, therefore, may provide an ac-

curate estimate of acetabular anteversion duringcup placement. Awareness of the anatomic dif-ferences between genders for acetabular ante-version angle, anterolateral bowing of the femur,and neck shaft angle may help reduce the rela-tively higher incidence of dislocation in femalesand may lead to different implant designs formale and female patients.

It is important to know the normal acetabularand femoral anteversion for proper implantpositioning and to prevent dislocation in totalhip arthroplasty.2,10 Adequate anteversion pro-vides for a satisfactory functional range of mo-tion. The acetabulum is not a simple hemi-spheric shape. As a result, the acetabularanteversion angle would seem to be influencedby the point of measurement along a possiblycurved or angular configuration. Neither stan-dard radiographs nor two-dimensional com-puted tomography (CT) scans allow for accu-rate determination of anatomic configuration3

and, therefore, assuming acetabular wall con-figuration has some influence, accurate mea-surement of the anatomic anteversion anglecannot be determined. Three-dimensional CTscanning has potential for detection of varia-

The Frank Stinchfield Award

Morphologic Features of the Acetabulum and Femur

Anteversion Angle and Implant Positioning

Masaaki Maruyama, MD; Judy R. Feinberg, PhD; William N. Capello, MD; and James A. D’Antonio, MD

From the Department of Orthopaedic Surgery, ChushinMatsumoto National Hospital, Matsumoto, Nagano,Japan.This research was supported by Stryker Howmedica Os-teonics, Rutherford, NJ.Reprint requests to Masaaki Maruyama, MD, Depart-ment of Orthopaedic Surgery, Chushin Matsumoto Na-tional Hospital, 811 Kotobuki Toyooka, Matsumoto,Nagano 399-0021, Japan.

tions in configuration,1 although this technol-ogy currently is not used routinely nor is itcost-effective for routine use as a preoperativeassessment tool to aid in intraoperative deter-mination of anteversion. Despite the potentialimportance of acetabular ridge features, therehave been no reports on how differences inanatomic structure influence measurement ofacetabular anteversion.

A similar problem exists for accuratemeasurement of the medial offset of the fem-oral head. Offset measurement is affected byfemoral anteversion and bowing, neither ofwhich can be appreciated adequately on two-dimensional radiographs. Accurate assess-ment is complicated by the fact that most pa-tients with advanced osteoarthritis of the hipcannot internally rotate their hip on radio-graphs obtained preoperatively and therefore,the offset is influenced by the inability to at-tain the necessary derotation of the femur.Several studies of proximal femoral anatomyhave regarded the femoral shaft as straight inthe standard anteroposterior (AP) view.8,21,23

It is well known that the femoral shaft hassome anterior bowing and clinically other con-figurations have been seen.

The overall incidence of dislocation afterprimary total hip arthroplasty averages between2% and 3%.18 Several risk factors have beenidentified. There is a definite predilection in fe-male patients with some studies reporting ratesdouble that of male patients.10,12,19,27 Compo-nent positioning has been linked directly to in-cidence of dislocation. Fackler and Poss6 re-ported a significant increase in postoperativedislocations when femoral offset was decreasedby inserting the femoral component with a val-gus neck shaft angle. Cup orientation is partic-ularly critical. Lewinnek et al13 described a safezone of acetabular component orientation as alateral opening of 40� � 10� with anteversion of15� � 10� to decrease the likelihood of disloca-tion after total hip arthroplasty. Surgical ap-proach also can affect proper positioning of theacetabular component. For example, it has beenshown that the surgeon tends to place the cup in5� to 7� less anteversion with a posterior ap-

proach.17 Positioning the patient in the lateraldecubitus position during total hip arthroplastycan allow the pelvis to rotate forward and resultin placement of the cup in a retroverted posi-tion.18 Yet, despite all of these reports as to theimportance of controlling the amount of ante-version, there have been no reports of how tomeasure anteversion in an accurate and consis-tent manner. External alignment guides havebeen shown to be helpful in reproducing ab-duction but inaccurate regarding anteversionof the acetabular component.7 Recently a com-puter-assisted and image-guided system (Hip-Nav, Center for Orthopaedic Research, Pitts-burgh, PA) was developed and is being testedclinically for precise planning and placement ofthe acetabular component in total hip replace-ment surgery.9

The aims of the current study were to: (1)evaluate in detail the morphologic features ofthe pelvis and femur particularly for configu-ration of the acetabular anterior and posteriorcolumns and the medial offset of the femoralhead relative to the configuration of the femo-ral shaft; (2) evaluate any differences attribut-able to gender; and (3) determine whetherthere is any practical way to accurately assessacetabular anteversion intraoperatively eitherdirectly or indirectly.

MATERIALS AND METHODS

SpecimensThis study was done in collaboration with the De-partment of Physical Anthropology at the Cleve-land Museum of Natural History. The departmenthouses the Hamann-Todd Osteological Collection,which was amassed between 1912 and 1938 byDrs. C.A. Hamann and T.W. Todd of the WesternReserve University, Department of Anatomy, andit contains 3100 skeletons of the unclaimed dead ofthe Cleveland area.16 Only normal pelves and fe-murs were included for this study. Specimens withosteoarthritis of the hip, evidence of previoustrauma to the pelvis or femur, or skeletal disorderssuch as multiple epiphyseal dysplasia or osteogen-esis imperfecta were excluded. Because gender dif-ferences were considered a primary aim of thestudy, the sample group consisted of 50 female and

Number 393December, 2001 Acetabular and Femoral Structure 53

50 male skeletons with age and race distributionselected to be similar to the population having to-tal hip arthroplasty in the United States. Speci-mens were selected randomly based on the follow-ing conditions: five were younger than 40 years,five were between 40 and 49 years, 15 were be-tween 50 and 59 years, 15 were between 60 and 69years, and 10 were 70 years or older. Twenty per-cent of the skeletons in each age group were fromAfrican-Americans. The average age was 57.9 �12.2 years (range, 28–82 years) for males and 57.5� 13.5 years (range, 18–82 years) for females. Twohundred normal femur and pelvis combinations(100 male, 100 female) were studied. All measure-ments were done by one author (MM).

The individual bones (iliums, sacrums, and fe-murs) were stored in separate areas in the museum,and therefore required reconstruction for this study.The pelves were reconstructed using a thin clay(0.5 to 1.5 cm, proportional to the size of thepelvis)25 and rubber bands. An anatomic frontalplane of the pelvis was defined by the anterosupe-rior iliac spines and by the pubic symphysis. Thisplane is nearly vertical during upright sitting,standing, and walking.1,15 In this study, the pelviswas laid on a flat glass table (craniograph) in aprone position so that the anterosuperior iliacspines and the pubic symphysis were in contactwith the glass. The glass table was regarded as theanatomic frontal plane. The femur was placed on anosteometric board in the supine position so that theposterior aspects of the medial and lateral femoralcondyles and the base of the femoral neck were indirect contact with the board.

Acetabular MeasurementsThe acetabular anteversion angle was measured atthe center of the acetabulum in a vertical plane tothe glass table (horizontal plane) along the anteriorto posterior ridges.14 For acetabula that were notstraight, the long axis of the anterior wall was con-verted to a straight line, and the midpoint then wasestablished along that line. The inward wing of theilium was evaluated by measuring the angle createdat the intersection of a line from the posterior to theanterior iliac spines and the glass table on a hori-zontal plane. The superior to inferior inclination ofthe acetabulum was measured in a parallel plane tothe glass table.

The notch acetabular angle was defined as theangle created at the intersection of a flat line fromthe sciatic notch along the posterior acetabular ridge

and a line from the posterior to the anterior acetab-ular ridge. Because the line from the sciatic notchalong the posterior acetabular ridge had an inclina-tion, the notch acetabular plane is not horizontal.

Pelvic dimensions were measured as the fol-lowing: height (HP), AP width (APW), mediolat-eral width (MLW), and distance between the rightand left acetabular floors (DAF). The ratio (per-cent) of distances between the acetabular floors andAP width (DAF/MLW) was calculated for eachpelvis.

Femoral MeasurementsFemoral anteversion was defined based on the pre-vious works of Billing5 and Murphy et al.20 Thelong axis of the femur (FLA) is the line defined bytwo points: the center of the knee (the centroid ofthe distal femoral metaphysis on a cross sectionthrough the femoral condyles) (K), and the centerof the base of the femoral neck (the centroid of thefemoral diaphysis on a cross section through thebase of the femoral neck) (O) (Fig 1). The axis ofthe femoral neck (FNA) is the line defined by twopoints: the center of the femoral head (C), and thecenter of the base of the femoral neck (O). This axisbisects and passes through the midline between theanterior and posterior borders of the femoral neck(Fig 1). In this study, neutral rotation of the femurwas defined by the posterior condylar line. Directbone measurement was done using a craniometeron the osteometric board for determination of theanteversion angle from the proximal (�) and distal(�o) views.

In addition to the anteversion angle, the follow-ing dimensions were measured directly from the fe-murs: femoral neck-shaft angle (�) (Fig 1), AP di-ameter of the femoral head (HAP), craniocaudaldiameter of the femoral head (HCC), AP diameter ofthe femoral neck (NAP), and the craniocaudal di-ameter of the femoral neck (NCC).

The reconstructed pelvis was combined with thefemurs to recreate the hips so static radiographscould be obtained of all specimens. First, the rightand left femurs were placed in neutral rotation andan AP radiograph was taken. Then both femurswere put in a position such that each femur wasderotated (commonly internally rotated) around itslong axis by the angle of anteversion from the dis-tal view. Anteroposterior and lateral radiographswere taken in this derotated position. The tube wasset on the pubic symphysis with a tube-to-film dis-tance of 47.5 inches. Radiographic magnification

Clinical Orthopaedics54 Maruyama et al and Related Research

was corrected by comparing the actual with the ra-diographic diameter of the femoral head. The fol-lowing dimensions were measured from the radio-graphs: the distance between the right and leftfemoral head centers (HC), the femoral neck-shaftangle based on the AP radiograph in neutral (�0)and derotated (�1) positions, and the medial offsetof the femoral head based on the AP radiograph inthe neutral ( j0) and derotated ( j1) positions. Forconsistency of measurement, the total length of thefemur from the top of the greater trochanter to thebase of the condyles (GT) was measured for each

femur and then divided into tenths. The axis of theproximal femur (FPA) was set as a line connectingthe midpoints of the mediolateral width of the fe-mur at a distance of 2⁄10 and 3⁄10 from the top of thegreater trochanter.

Anterior bowing angle (�), based on the lateralradiograph of the hip in the derotated position, wasmeasured as the angle between the following twoaxes: a femoral axis at the proximal 2⁄10 and 3⁄10

lengths and a femoral axis at the 6⁄10 and 8⁄10 lengths(Fig 2A). Lateral bowing angle of the femur (�)was determined by direct bone measurement fromthe distal-to-proximal view (Fig 2B). The lateralbowing angle from the anterior-to-posterior viewin neutral rotation (�0) was defined as an angle be-tween the axis of the proximal femur (FPA) at the2⁄10 and 3⁄10 positions and a line connecting the inter-section of the neck and proximal femur axes and thecenter of the femoral condyles (Fig 2C). In the samemanner, the lateral bowing angle from anterior toposterior in derotation (�1) was defined as the lateralbowing of the femur in the derotated position. Basedon the AP radiograph of the bilateral hips with a neu-trally rotated femur, the angle (�0) was defined as theangle between the femoral axis at 2⁄10 and 3⁄10 pointswith the axis at 4⁄10 and 5⁄10 points. Therefore, a posi-tive number indicated varus and a negative numberindicated valgus. The same angle with the femurderotated is denoted by �1. This varus or valgus an-gle essentially is the degree of discrepancy betweenthe previously described definition of the long axisof the femur and the long axis as determined consid-ering the effect of bowing in the AP plane.

Statistical AnalysisStatistical analyses for comparison of morphologicfeatures between males and females were done us-ing unpaired t tests or chi square analysis. Compar-isons from right to left femur were done usingpaired t tests. Correlations between variables werecalculated using the Pearson product moment coef-ficient of correlation (r). The significance level wasset at 0.05. The statistical package used was Mi-crosoft® Excel and its statistical software (Mi-crosoft Corporation, Redmond, WA).

RESULTS

Morphologic Features of the PelvisFour distinct configurations of the anterior ac-etabular ridge were identified and denoted ascurved, straight, angular, or irregular (Fig 3).


Fig 1. Placement of the femur on an osteometricboard (OB) with the condylar plane (CP) parallelis shown. Points of orientation include the centerof the femoral head (C), the center of the base ofthe femoral neck (O), the center of the knee (K),and the posterior aspects of the medial (M) andlateral (L) femoral condyles. The anteversionplane (AVP) is shown as are the long (FLA) andfemoral neck (FNA) axes of the femur. (FPA: axis of the proximal femur; FCA: axis of the fem-oral condyles.) Pertinent measurements in thisposition include the femoral neck shaft angle (�)and the femoral anteversion angle from distalview (�0).


Most of the pelves (121; 60.5%) had a curvedconfiguration, 51 (25.5%) were angular, 19(9.5%) were irregular, and nine (4.5%) werestraight. Of the 100 pelves examined, 51 had thesame configuration of both anterior acetabularridges and 49 had differing configurations fromone side to the other. There were no differencesbetween genders regarding either breakdown ofconfigurations seen (57 males and 64 femaleshad curved configurations; p .087) or side-to-side similarities or differences (29 male and 22female pelves had the same configuration bilat-erally; p .161). All posterior columns were asimple hemicircle or straight classification.

The anteversion angle of the acetabulum wasmeasured as 19.9� � 6.6� (range, 7�–42�). Thecorrected acetabular angle for the acetabulathat were not straight was approximately 6.2�smaller than the uncorrected acetabular angle on

average. The acetabular anteversion angle wassignificantly greater in females than males(21.3� versus 18.5�; p .002). The inward wingand inclination angles also were significantlygreater in females than in males (60.5� versus58.7�; p .005; 38.9� versus 37.8�; p .038, re-spectively). The notch acetabular angle was al-most perpendicular, measuring 89.0� � 3.5�(range, 77�–100�). As with the other anglesmeasured, the average notch acetabular anglefrom females was greater than the average notchacetabular angle from males (89.6� versus 88.4�;p .014). There were no significant differencesbetween right and left sides for males or femalesfor any of the measured pelvic angles. Therewere no significant differences found in the an-teversion angle and the notch acetabular anglebetween younger ( 60 years) and older (� 60years) group within each gender.

A B C

Fig 2A–C. The anterior bowing angle of the femur (�) as would be seen on a lateral radiograph isshown. Lateral bowing angle of the femur (�) from the distal-to-proximal view along the plane of thefemoral long axis (LB) and relative to the plane of the femur on the osteometric board (OB) is shown.Lateral bowing angle of the femur (�) from the anterior-to-posterior view is shown. The axes of the prox-imal femur (FPA) and the femoral neck (FNA) are shown for orientation.


Measurements for the pelvis are shown inTable 1. The distance between the acetabularfloors (DAF) was significantly larger in femalesthan males, although the height (HP), AP width(APW), and mediolateral width (MLW) were

significantly smaller in females than in males.The resultant DAF/MLW ratio was greater infemales than in males (44.6% versus 40.8%; p .001). The DAF/MLW ratio correlated sig-nificantly with the acetabular anteversion angle

Fig 3A–D. The four anterior acetabular ridge configurations are shown. (A) The straight type was seenin 4.5%, (B) the curved type was seen in 60.5%, (C) the angular type was seen in 25.5%, (D) and theirregular type was seen in 9.5% of the acetabula.

A B

C D

TABLE 1. Pelvic Size Measurements

Measurement (cm) Total Group Males Females p Value

Height of pelvis 21.0 � 1.4 (18.2–24.8) 22.0 � 1.1 (18.3–24.8) 20.0 � 1.0 (18.2–22.5) 1 � 10 29

Anteroposterior width 13.4 � 1.0 (11.0–16.0) 13.6 � 1.0 (11.0–16.0) 13.1 � 0.9 (11.3–15.2) 0.0002of pelvis

Mediolateral width 26.9 � 1.8 (23.0–31.2) 27.3 � 1.8 (23.4–31.2) 26.6 � 1.7 (23.0–31.0) 0.0058of pelvis

Distance between 11.5 � 0.9 (9.6–14.7) 11.1 � 0.7 (9.6–12.7) 11.8 � 0.9 (10.2–14.7) 2 � 10 9

right and left acetabular floors

DAF/MLW (%) 42.7 � 3.4 (33.3–55.5) 40.8 � 2.3 (33.3–45.3) 44.6 � 3.3 (36.4–55.5) 2 � 10 17

Average � standard deviation (range); DAF/MLW Ratio between the distance between the right and left acetabular floors andmediolateral width of the pelvis.


(r .448, p 3 � 10 6 in males; r .317, p .0013 in females) and with the inward wingangle of the ilium (r .311, p .0016 in males;r .399, p .00004 in females). This ratio cor-related with the inclination angle in females (r .356; p .0003) but not in males (r .0962; p .3461). The ratio and the notch ac-etabular angle were inversely correlated in fe-males (r .268; p .0071) but not in males(r .116; p .2489).

Morphologic Features of the FemurEach of the femoral angles and dimensionsmeasured are summarized in Tables 2 and 3 forthe total group and for comparative differencesbetween males and females. Three distinct con-figurations of the femoral shaft were identifiedin the AP view (Fig 4). Of the 200 femurs, in aneutral rotation, 162 (81%) had lateral bowing.The average angle of lateral bowing (�) on di-rect bone measurement was 12.9� � 9.6�, withthe angle averaging 5.6� larger in males than infemales (p .001). Thirty-two (16%) had adouble or S curve, and six (3%) had medialbowing. All double or S curves had lateral bow-

ing proximally and medial bowing distally.With the femur in the derotated position, 124(62%) were classified as having lateral bowing,32 (16%) with a double curve, and 44 (22%)with medial bowing. By rotating the femurfrom neutral to the derotated position, the di-rection of bowing in 38 (19%) femurs appearedto change from lateral to medial. In the neutraland derotated positions, femoral shaft configu-ration differed between males and females withthe females having a greater occurrence of me-dial bowing (six versus 0 in neutral rotation and29 versus 15 in derotation; p .05). All but sixof the 100 specimens had the same configura-tion bilaterally in the neutral position, and allbut 15 had the same femoral configuration inderotation. If the lateral bowing angle from an-terior to posterior (�) measured � 2� or less andthe femur had minimal lateral bowing, more fe-males than males had straight femurs (38 ver-sus 16, respectively; p .001). The anteriorbowing angle of the femur �) averaged 9.7� �2.3�, with males averaging approximately 1.3�more anterior bowing than females as measuredon the lateral radiograph (p .001).

TABLE 2. Angular Measurement of the Femur

Angle (degrees) Total Group Males Females p Value

Anteversion 9.8 � 8.5 ( 15 to �34) 9.8 � 9.0 ( 15 to �30) 9.8 � 8.0 ( 12 to �34) 0.954(proximal view) (�)

Anteversion 11.6 � 9.1 ( 30 to �34) 11.1 � 10.3 ( 30 to �34) 12.2 � 7.8 ( 5 to �34) 0.399(distal view) (�0)

Neck-shaft (�) 125.0 � 4.8 (106–137) 124.7 � 5.3 (106–135) 125.3 � 4.2 (115–137) 0.395Neck-shaft—NR* (�0) 124.2 � 6.0 (107–141) 123.2 � 6.3 (107–134) 125.3 � 5.4 (112–141) 0.014Neck-shaft—IR* (�1) 122.8 � 5.7 (106–140) 121.8 � 6.1 (106–134) 123.8 � 5.2 (111–140) 0.0158Anterior bowing* (�) 9.7 � 2.3 (4–17) 10.3 � 2.0 (6–16) 9.0 � 2.4 (4–17) 5.7 � 10 5

Lateral bowing (�) 12.9 � 9.6 ( 20 to �37) 15.7 � 8.7 (0–37) 10.1 � 9.7 ( 20 to �35) 3.3 � 10 5

distal to proximalLateral bowing 3.5 � 2.3 ( 1 to �13) 4.2 � 2.3 (0–12) 2.8 � 2.1 ( 1 to �13) 1.5 � 10 5

(�0)—NR anterior to posterior

Lateral bowing 1.5 � 2.6 ( 5 to �11) 2.2 � 2.6 ( 2 to �11) 0.8 � 2.4 ( 5 to �8) 0.0001(�1)—IR anterior to posterior

Varus-valgus—NR* 1.7 � 1.8 ( 4 to �9) 1.6 � 2.0 ( 4 to �6) 1.7 � 1.6 ( 2 to �9) 0.736(�0) (varus �)

Varus-valgus—IR* 0.8 � 1.7 ( 4 to �5) 0.7 � 1.8 ( 4 to �5) 0.9 � 1.7 ( 4 to �5) 0.570(�1) (varus �)

NR neutral rotation; IR internal rotation (derotated position); * measured from radiographs; Average � standard deviation (range).

The anteversion angle (�) of the femoralneck was 9.8� � 8.5� (range, 15�–34�) fromthe proximal view and 11.6� � 9.1� from thedistal view with no difference between malesand females. There was no significant correla-tion between either the anterior or the lateralbowing angles and the anteversion angle.

The femoral neck shaft angle (�) averaged125� � 4.8� on direct bone measurement.Compared with direct bone measurement, thefemoral neck shaft angle averaged 122.8� �5.7� in internal rotation (p .001) and 124.2�� 6.0� in neutral rotation (p .01) on radio-graphic assessment. Females had a more val-

gus femoral neck-shaft angle on radiographicassessment than males in neutral and internalrotation. (p .05).

The medial offset of the femoral head ( j)was significantly larger when measured in in-ternal rotation versus neutral rotation (47.2 �6.1 mm versus 44.6 � 6.7 mm, respectively; p .0001). The medial offset on the radiographwas influenced greatly by the anterolateralbowing of the femoral shaft and anteversion ofthe femoral neck.

On radiographic measurement, there was nodifference in the distance between the right andleft femoral head centers in males and females;


TABLE 3. Femoral Size Measurements

Measurements Total Group Males Females p Value

Distance between 18.7 � 1.3 (15.2–23.0) 18.7 � 1.1 (16.2–21.3) 18.8 � 1.4 (15.2–23.0) 0.646right and left centers of femoral heads (cm) (Hc)

Fem head 44.9 � 3.9 (36.9–55.0) 47.9 � 2.7 (42.5–55.0) 42.0 � 2.4 (36.9–47.9) 1.1 � 10 38

diameter—AP plane (mm) (HAP)

Fem head 45.3 � 3.9 (37.4–55.5) 48.3 � 2.8 (42.5–55.5) 42.4 � 2.4 (37.4–49.0) 2.5 � 10 37

diameter—CC plane (mm) (HCC)

Fem neck 24.6 � 2.4 (19.6–31.3) 26.0 � 1.9 (20.9–31.3) 23.1 � 2.0 (19.6–28.6) 2.4 � 10 21

diameter—AP plane (mm) (NAP)

Fem neck 32.1 � 3.3 (25.0–40.5) 34.4 � 2.4 (29.5–40.5) 29.8 � 2.5 (25.0–37.8) 6.9 � 10 29

diameter—CC plane (mm) (NCC)

Femur length to 41.3 � 2.9 (33.1–49.7) 43.0 � 2.5 (36.7–49.7) 39.5 � 2.3 (33.1–44.9) 4.7 � 10 20

top of gr troch (cm) (GT)

Femur length to 43.2 � 3.0 (34.2–51.5) 44.9 � 2.6 (38.5–51.5) 41.4 � 2.4 (34.2–46.4) 1.2 � 10 19

top of fem head (cm) (H)

Deviation from 2.4 � 1.5 ( 0.7 to �7.7) 2.0 � 1.5 ( 0.6 to �7.7) 2.9 � 1.3 ( 0.7 to � 6.4) 8.3 � 10 6

mechanical axis to H (cm) (D)

Medial offset of 44.6 � 6.7 (28.5–64.5) 47.2 � 6.4 (30.0–64.5) 41.9 � 5.9 (28.5–61.5) 6.2 � 10 9

fem head—NR (mm) (j0)

Medial offset of 47.2 � 6.1 (32.0–65.0) 50.1 � 5.3 (36.0–65.0) 44.3 � 5.4 (32.0–63.0) 8.0 � 10 13

fem head—IR (mm) (j1)

Fem femoral; AP anteroposterior; CC craniocaudal; Gr Troch greater trochanter; Mechanical axis distance from the mid-point between the femoral condyles to center of femoral head; NR neutral rotation; IR internal rotation (derotated); Average �standard deviation (range).


however, the diameters of the femoral headand femoral neck in females were significantlysmaller than those of the males in the AP andcraniocaudal planes (p .0001). The neck-to-head ratios (NAP/HAP, NCC/HCC) were calcu-lated as 54.7% � 3.0% in the AP plane and70.8% � 3.4% in the craniocaudal plane, andthese ratios did not differ between males andfemales. The overall length of the femurs ondirect bone measurement revealed an average3.5 cm difference in males greater than females(p .0001). The distance (D) from the mid-point between the femoral condyles distallyand the midpoint of the femoral head proxi-mally was greater in females than males (2.9cm versus 2 cm; p .001) because the longaxis of the femur is more valgus in females.

Because gender differences commonly wereobserved, it was decided to examine whetherage was a significant factor within each gender

group. Each gender group was subdivided intotwo age groups ( 60 or � 60 years) of 50 fe-murs (25 bilateral specimens). The average ageof the young male group was 48.2 � 8.3 years(range, 28–58 years). The average age of theolder male group was 67.6 � 6.2 years (range,60–82 years). The average age of the young fe-male group was 47.4 � 10.9 years (range,18–59 years) and 67.6 � 6.3 (range, 60–82years) in the older female group. There were nodifferences found in any parameters betweenyounger and older males. In females, the devi-ation angle as a component of lateral bowing in-creased significantly from 6.9� � 10.9� inyoung females to 13.4� � 7.1� in older females(p .001) (Table 4). The varus angle (�) alsoincreased with age, whereas the neck shaft an-gle, on direct bone measurement and radio-graphic measurement, decreased with age in fe-males (p .05).

Fig 4A–C. The three femoral shaft config-urations as seen in neutral rotation in theAP plane are shown. (A) Lateral bowingwas most common, occurring in 81% of thefemurs. (B) Sixteen percent of the femurshad a double curve with a lateral bowingproximal and medial bowing distal, and (C)medial bowing was seen in 3% of femurs.A B C

DISCUSSION

The current authors identified anatomic fea-tures of the acetabulum and femur not previ-ously described, which may be relevant in thedesign and implantation of hip implants. Thevariations in configuration of the anterior ac-etabular wall and in bowing of the femur pro-vide new information that affects the accuracyof the current methods of measurement of ac-etabular and femoral anteversion. The poste-rior acetabular ridge almost always forms asimple semicircle. However, the anterior ridgeeither is curved, angular, straight, or irregu-larly configured. Because of these variations,the amount of anteversion is affected by thepoint of measurement along the anterior ridge.In the anatomic model, the anteversion anglevaried by an average of 6.2� when nonstraightanterior ridges were converted to a straightconfiguration, therefore, the anteversion angleis dependent on the point of measurementalong the ridge. This finding is important be-cause the configuration of the anterior acetab-ular ridge is not discernible on a standard two-dimensional radiograph nor is it possible todiscern intraoperatively through palpation be-cause of soft tissue, the presence of osteo-phytes, or both. Because greater than 95% ofthe 200 acetabula in this study had nonstraightanterior ridges, had they undergone total hiparthroplasty, the amount of acetabular ante-

version easily could have been underestimatedin these cases depending on the point of deter-mination along the acetabular walls intraoper-atively. The presence of osteophytes, in par-ticular those along the anterior acetabularridge, could result in an overestimation of thenotch acetabular angle.

Medial offset of the femoral head is mea-sured based on the assumption that the longaxis of the femur is straight. Because standardradiographs of the hip usually only include theproximal femur, measurements that are takenhave only the proximal femur available to de-termine the long axis. Noble et al22 defined themedullary axis using the proximal femur as aline passing through the midpoints of themedullary canal at 20 mm proximal and distalto the canal isthmus. However, because otherauthors4,24 described changes in the medullarycanal with aging and osteoporosis, the extra-cortical borders were used to define the femo-ral axes in this study. The amount of offset wasinfluenced by rotation of the femur seen on theradiograph because of femoral anteversionwith the value of the offset in derotation sig-nificantly larger than in neutral rotation. Dero-tation of the femur was useful in negating theeffect of the femoral anteversion; however, itoften is not possible to position the patientwith end-stage hip arthritis who has yet tohave surgery in a derotated position. There-fore, the amount of offset may be underesti-


TABLE 4. Younger ( 60 years) Versus Older (60� years) Age Comparisons inGender Groups

Dimensional Parameter Younger Males Older Males Younger Females Older Females

Anteversion angle (�0) 11.6 � 9.9 10.5 � 10.7 13.5 � 8.6 10.8 � 8.6Neck shaft angle (�) 125.6 � 4.4 123.8 � 6.0 126.1 � 4.2 124.4 � 4.2*Neck shaft angle (�0) 123.8 � 5.7 122.7 � 6.9 126.7 � 5.6 123.9 � 4.9**Neck shaft angle (�1) 122.4 � 5.1 121.3 � 6.9 124.8 � 5.6 122.7 � 4.5*Medial offset (j0) (mm) 46.2 � 5.7 48.2 � 6.9 40.7 � 6.1 43.2 � 5.4*Medial offset (j1) (mm) 49.3 � 4.6 50.8 � 5.9 43.9 � 5.5 44.7 � 5.3Anterior bowing angle (�) 10.3 � 2.1 10.3 � 1.9 8.9 � 2.4 9.2 � 2.3Lateral bowing angle (�) 14.5 � 9.4 16.9 � 7.9 6.9 � 10.9 13.4 � 7.1***Lateral bowing angle (�0) 4.0 � 2.2 4.5 � 2.2 2.3 � 2.5 3.3 � 1.6*Lateral bowing angle (�1) 1.8 � 2.5 2.6 � 2.7 0.1 � 2.7 1.5 � 1.7**

*p � 0.05; **p � 0.01; ***p � 0.001; (all others not statistically significant).

mated on the standard radiograph, obtainedpreoperatively.

Medial offset also was found to be influ-enced by not only the anteversion of the fem-oral neck but also by the anterolateral bowingof the femoral shaft. The long axis of the prox-imal femur was altered depending on rotationattributable to the bowing. It is known that thefemur has an anterior bowing of the shaft. Thecurrent authors, however, described an aver-age lateral bowing of approximately 13� with81% of femurs having lateral bowing. The ef-fect of lateral bowing on the apparent long axisof the femur was a change toward varus of 3.5�in neutral rotation and 1.5� in the derotated po-sition. In the current study, the lateral bowingangle was measured based on neutral rotationas determined from the posterior condylarline. However, if neutral rotation were to bedetermined from the transepicondylar line,then the lateral bowing angle possibly couldappear decreased. Clinically, the effect of lat-eral bowing would mean that an implantplaced in apparent neutral alignment, as deter-mined by viewing the radiograph of the prox-imal femur, actually would be in slight varusregarding the true long axis of the femur in themajority of cases (Fig 5). It is not knownwhether this slight varus positioning could af-fect the longevity of the implant adversely al-though varus orientation of the stem led to in-creased failure with the Charnley low frictionarthroplasty.11

Numerous differences were found betweenmorphologic features of male and femalepelves and femurs. The overall height andwidth of the pelvis and the overall femorallength were larger in males, yet the distancesbetween the right and left acetabular floors andthose between the femoral head centers werelarger in females. The acetabular anteversionangle was greater in females, which is similarto the reported findings of others.14,15 No gen-der differences were found relative to amountof femoral anteversion, and no correlation wasfound between acetabular and femoral antever-sion angles, which is in agreement with previ-ous reports.3,26 Males had a significantly greater

medial offset of the femoral head and greateranterior and lateral bowing of the femoralshaft. In neutral rotation, medial bowing of thefemur was seen in six females and no males.There were no significant differences betweenyounger and older males for femoral dimen-


Fig 5A–B. (A) A standard AP radiograph asused in preoperative planning for total hip arthro-plasty is shown. (B) The postoperative radiographof the same femur shows the femoral componentplaced in a slightly varus postion.

A B

sions. However, older females had significantlyincreased lateral bowing in the proximodistaland AP views and a decreased neck shaft anglethan the younger female group. Noble et al22

found similar differences between younger andolder females relative to changes in the femur.

Proper component positioning in total hiparthroplasty relative to the amount of acetabu-lar and femoral anteversion is important in pre-venting postoperative dislocation. Althoughthis orientation is critically important, it is ex-tremely difficult to assess intraoperatively.Even with proper acetabular component posi-tioning, excessive anteversion or retroversionof the femoral component can lead to compo-nent dislocation.6 Furthermore, the most com-mon error in femoral malpositioning is exces-sive anteversion.6 The most important factor inminimizing the rate of dislocation under thesurgeon’s control is positioning of the compo-nents in total hip arthroplasty.17

The results of this anatomic study may ex-plain why component positioning relative toanteversion is so difficult. On the acetabularside, the anteversion angle is influencedgreatly by the point of measurement and con-figuration of the anterior acetabular ridge. Theanteversion angle, when measured with theabove considerations, differed significantlybetween males and females. On the femoralside, the complexity of the bowing of the fem-oral shaft could influence femoral componentpositioning relative to anteversion and medialoffset. The anterior and lateral bowing anglesdiffered significantly between males and fe-males, and these angles differed depending onthe rotation of the hip. Although there was nodifference between males and females regard-ing the varus-valgus angle of the femur, therewas a significant increase in the lateral bowingangle in older females compared with youngerfemales.

The notch acetabular angle (the angle cre-ated at the intersection of the line from the sci-atic notch to the posterior acetabular ridge andthe line from the posterior to anterior acetabu-lar ridge) was measured in this study using aspecial tool that was placed between the sci-

atic notch and the posterior acetabular ridge.This notch acetabular angle has been used bytwo authors (JAD, WNC) to estimate theamount of acetabular anteversion necessaryfor accurate cup placement. With the patient inthe lateral decubitus position and the surgeon


Fig 6. The pelvis is viewed from cranial to caudal.Lines 1 and 2 are parallel to the long axis of thetool that was used to measure the notch acetab-ular angle on the anatomic specimen. In theanatomic model, the tool was hooked onto thesciatic notch along the posterior acetabular ridge.Line 1 passes along the posterior acetabularridge and the top of the sciatic notch and isshown for orientation purposes. Line 2 is a trans-lation of that line to the center of the acetabulum.Line 3 lies across the anterior and posterior wallsof the acetabulum. The broken Line 4 depicts anincreased anteversion angle from the anatomicanteversion. Line 4 angles toward the top of thesciatic notch. Therefore, placing a cup parallel toLine 2 would result in placement in anatomic an-teversion and placing a cup parallel to Line 4would result in approximately 10� to 15� more an-teversion than anatomic anteversion.

on the anterior or abdominal side of the pa-tient, the surgeon palpates using the index fin-ger along a line from the posterior wall of theacetabulum to the greater sciatic notch. A rodis placed parallel to the index and a mark ismade on the posterosuperior aspect of the ac-etabulum using electrocauterization. This an-gle, as determined in this study by direct bonemeasurement, averages 89� with a small stan-dard deviation. Therefore, because that lineessentially is perpendicular to the plane of theface of the acetabulum, reaming for a hemi-spherical cup parallel to that line would resultin placement of the cup in anatomic antever-sion for that patient. However, if the surgeonwishes to place the acetabular component inincreased anteversion, particularly when usinga posterior approach, the direction of thereaming and insertion of the cup will be diver-gent from that line and will angle toward thetop of the sciatic notch instead of the center ofthe ilial wing. A schematic drawing of how thedesired anteversion angle is determined intra-operatively is shown in Figure 6. The fact thatthe notch acetabular angle was measured asnearly perpendicular in the 200 pelves in thisstudy suggests that this angle is an accurate es-timation of acetabular anteversion and that theuse of this technique intraoperatively may aidthe surgeon in determining more accurateplacement of the acetabular component. Be-cause an improperly angled cup is a recog-nized cause of dislocation, the incidence ofdislocation after primary total hip arthroplastymay be reduced with use of this technique.

This study of 200 pelves and femurs identi-fies morphologic details not previously de-scribed. In particular, four distinct configura-tions of the anterior acetabular ridge wereidentified and the influence of these configura-tions on the accuracy of anteversion anglemeasurement was shown. Similarly, bowingof the femur was found to be more complexthan previously thought. In addition to an an-terior bow, femurs were found to have a lateralbow, and in some cases and depending on ro-tation, this additional bow appeared to be me-dial. Detailed measurements of dimensions re-

vealed differences between males and femalesand between younger and older females,which may help to explain the increased inci-dence of dislocation after total hip arthro-plasty in females. These results have implica-tions relative to implant design in that normalanatomy has a wide variation of configura-tions, and therefore one implant design maynot be adequate for all cases. In particular,differences in male and female anatomy re-garding anteversion angles may indicate thateither different implants or different guide-lines for implant positioning are needed. Fur-thermore, it was shown that hip rotation influ-ences critical measurements used in implantpositioning. The use of the notch acetabularangle as an indirect estimate of acetabular an-teversion may be a useful tool to decrease theincidence of dislocation after primary totalhip arthroplasty.

AcknowledgmentsThe authors thank Bruce Latimer, PhD, Curator,and Lyman M. Jellema, Collections Manager, De-partment of Physical Anthropology, ClevelandMuseum of Natural History, for their excellent as-sistance.

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morphology of acetabulum

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