EFFECT OF FEMORAL OFFSET ON RANGE OF MOTION AND ...

EFFECT

OF

FEMORAL

ABDUCTOR

OFFSET

MUSCLE

ON

STRENGTH

RANGE

OF

AFTER

MOTION

TOTAL

AND

HIP

ARTHROPLASTY BRIAN

J. McGRORY,

From

BERNARD

the Mayo

Clinic

At a minimum 64 patients standard

and

of one

with 86 anteroposterior

F. MORREY,

Mayo

year total

THOMAS

Foundation,

after hip hip

Rochester

operation,

abduction positively and the

(p

(THA) radiographs

the

0.046). Abduction strength with both femoral offset length of the abductor lever arm =

(p = 0.005). Using strength correlated

multiple regression, abduction with height (p = 0.017), gender

(p

of

0.0005),

=

range

abductor lever Our findings THA

allows

greater J Bone

arm (p suggest

both

Joint

Received

Surg

22 June

fiexion

(p

0.060). that greater

=

0.047)

and

the

=

an increased

abductor

decrease

by

of isometric with

femoral

range

offset

of abduction

after

AN,

MIGUEL

E. CABANELA

the

incidence

of impingement

pelvis. An increase in femoral the lever arm of the abductor ically, increase the mechanical the abductors. Finally, a greater stability

by

tissue

preventing

of the

impingement

Femoral

offset

has

been

shown

to

mum

of one

these

questions.

year

after

surgery

in an

AND

after

revision

23

March

1995

We

reviewed

one

of

64 patients

two

surgeons

year

(mean

one

years

two

months)

year

who

had

after

surgery,

included

was

offset

stabilise

interest

as the

in femoral

perpendicular

long axis of the femur femoral head. Charnley

said

offset

distance

and the centre (1979) considered

under the control of the surgeon ment surgery; the more lateral

as a factor

between

the

of rotation of the it to be a factor

at the time of hip replaceposition

of

the

range

to increase

the

femur

of motion

with and

replacements

and

at one

Ornstein

excluded

Resident Portland, USA.

P0

Box

1260,

33

B. F. Morrey, MD, Chairman, Department of Orthopaedics T. D. Cahalan, RN’, Physical Therapist K-N. An, PhD, Director, Biomechanics Laboratory M. E. Cabanela, MD, Professor of Orthopaedics Mayo Clinic and Mayo Foundation, 200 First Street Minnesota 35905, USA. should

be sent

01995 British Editorial Society 0301-620X/95/61066 $2.00

VOL.

77-B,

No. 6, NOVEMBER

to Dr B. F. Morrey. of Bone

1995

and Joint

Surgery

Sewall

Street,

of 86 THAs

avoid

confounding

Patients were

year

1985;

(Insall

et

Parsley,

who also

would

factors

al

1983;

and

have

excluded;

had the

of rheumatoid strength

to travel

one-year

more

patients

with

a diagnosis

by the two the project

Rochester,

were

77.7

were

seen

kg (44.5 to 109.1) in follow-up from

followshown to Parker

1992).

We

arthritis

to

measurements. than 500 miles

assessment

is often carried out locally. patients had been operated on over from 1988 to 1989, during which

had been performed was obtained and

of

analysis

Schurman,

Dwyer

of rheumatoid

for

such

a two-year 263 THAs arthritis)

surgeons. Informed consent and consent process were

approved by the IRB of the Mayo Clinic. There were 36 women and 28 men and the was 60 years (22 to 87). Their average weight SW,

examina-

on a power

Engh in

by

of one to three

testing. The number

based

patients with a diagnosis

(excluding B. J. McGrory, MD, Senior Orthopaedic Associates of Portland, Maine 04104-1260,

a total

calculation (see statistical section). The minimum up was chosen because results for THA have been

patients The period,

Correspondence

hip

to answer

by radiography,

joint

was

attempt

(BFM, MEC) at a minimum nine months, range one year

in total hip arthroplasty (THA) (Yanagimoto 1991; Abraham and Dimon 1992; Steinberg and Harris 1992; Davey et al 1993; Rothman et al 1993; Wong et al 1993). Femoral

offset

with

METHODS

strength

greater

correlate

stability (Fackler and Poss 1980; Huk et al 1993), but we know of no clinical study which has related the range of motion or abduction strength to femoral offset after THA. We therefore reviewed 64 consecutive patients at a mini-

PATIENTS

; Accepted

recent

is defined

soft-

1995;77-B:865-9.

1994;

been

improving

and

abductor

has

on the

tension.

tion, and standard

There

femur

offset (and consequently of muscles) will also, theoretadvantage and strength of femoral offset will increase

and

strength. [Br]

KAI-NAN

USA

we studied

arthroplasties and pelvic

and measurement of range of motion and abduction strength. The femoral offset correlated positively range of correlated (p = 0.0001)

D. CAHALAN,

median age and height

and 168 cm (140 to 190). All April 1, 1989 to April 1, 1993

and no evaluations were excluded. replaced in 48 (55.8%) and the was osteoarthritis in 57 (66.3%),

The right hip had been left in 38. The diagnosis post-traumatic deformity 865

B. J. MCGRORY,

866

in nine

(10.5%),

avascular

necrosis in five (5.8%), arthritis following slipped

(2.3%),

developmental

in two, and systemic lupus were 70 primary and 16 (20.9%)

femoral

B. E MORREY,

dysplasia

in nine

T. D. CAHALAN,

(10.5%),

Paget’s disease in two capital femoral epiphysis

were

cemented

and

68 unce-

There were 34 (39.5%) Osteonics Omnifit (Osteonics Corp. Allendale, New Jersey), 14 (16.3%) Osteonics Onmiflex, 13 (15.1%)

Zimmer

surgeon. Radiological

Mayo-Money

(Zimmer

Inc.

Warsaw,

Zimmer

Harris precoat, 5 (5.8%) Zim5 (5.8%) Zimmer Bias, and eight other of varying design chosen by the

assessment.

Anteroposterior

pelvic

and

a vertical line the body-weight

corrected

M. E. CABANELA

through lever

the symphysis pubis was arm. These measurements

hip

recorded as were then

for magnification. assessment.

A complete

examination

the recording of the patients’ height, thigh circumference on the affected

mented. An anterolateral approach was used in 32 (37.2%) and a posterior approach in 54; trochanteric osteotomy was not used. A variety of femoral prostheses was employed.

Indiana), 7 (8.2%) mer Harris-Galante, prostheses (9.3%)

AN,

Functional

erythematosus in two. There revision operations. Eighteen

components

K-N.

weight, side.

included

and

maximum

The ranges of motion in flexion, abduction, adduction, internal rotation, and external rotation were measured using a goniometer by a single observer (TDC). Strength. Three measurements of isometric abduction strength at 0#{176} (neutral) were made for each THA by the

Motion.

method previously described (Cahalan et al 1989). A Cybex II isokinetic dynamometer (Lumex, Ronkonkoma, New York) was modified to allow adjustment of the loading level arm to provide a comfortable position for the patient and maximal stability to produce optimal strength. A body stabilisation

frame

was

developed

and

used

to allow

sub-

radiographs were taken on the day of examination using a 100 mm magnification marker with the ankles 20 cm apart and the feet 15#{176} internafly rotated. The femoral offset and

jects to stand with support when testing abduction strength. The Cybex machine was calibrated at weekly intervals. We used the numerical average of three measurements as the

the abductor lever arm were measured (BJM) from each radiograph (Fig.

abductor

distance

from

the centre

of rotation

by a single observer 1). In addition, the of the femoral

head

to

strength

for data

Statistical analysis. of 84 THAs should

analysis.

A power analysis showed that provide at least an 80% chance

tical power) of detecting any correlation range of motion or strength, accepting

a study (statis-

between offset and an r value of 0.30.

Linear regression beta coefficients and corresponding ability using StatView software (Abacus Concepts Berkeley, California) were determined for femoral versus

range

gender,

and

diagnosis, fixation, height,

ponent abduction

lever which

of motion,

age,

lever

arm. of

arm,

time

strength

versus

from

surgery,

and

comoffset,

body-weight

multiple regression to determine found to have significant inter-

the most

were

abduction

revision, surgical approach, weight, thigh circumference,

We then used the variables

relationships

for

probInc, offset

important.

RESULTS

Radiological averaged

aged

assessment.

The

corrected

averaged 9.2 cm (7.8 to 10.7). Femoral offset correlated positively the abductor lever arm (p = 0.0001; r body-weight

lever

arm

or the abduction lever Functional assessment Motion. The average Fig. 1 Diagram

showing

abductor

lever

measurements of femoral offset (A) and the arm (B). Femoral offset is the perpendicular distance from the centre line of the femur to the centre of rotation of the femoral head. Abductor lever arm is the perpendicular distance from a line tangential to the greater trochanter to the centre of rotation of the femoral head. The tangential line corresponds to the abductor shadow on the radiograph (from Steinberg and Harris 1992, with permission).

standard

deviation

analysis

showed

positively r = 0.22; correlation tion, Strength.

between

femoral

3.9 cm (2.3 to 5.5), the abductor lever 4.8 cm (3.4 to 7. 1) and the body-weight

range

is shown that

related Fig. 3). between

or internal

did arm.

not

=

correlate

of

femoral

offset

lever

with

either

arm

offset

range

I. Simple was

aver-

with the length of 0.43; Fig. 2). The with

motion

in Table

offset arm

and

regression

significantly

and

to range of abduction (p = 0.046; We could demonstrate no significant femoral offset and hip flexion, adduc-

or external

rotation.

There was a highly significant positive correlation femoral offset (and consequently abductor lever THE

JOURNAL

OF BONE

AND

JOINT

SURGERY

EFFECT

OF FEMORAL

OFFSET

ON RANGE

OF MOTION

AND ABDUCTOR

a)

5.5

AFTER

TOTAL

HIP

ARTHROPLASTY

867

a)

a5

#{149}#{149}e#{149}

0

ao

STRENGTh

P-o.0001

7.0

E E

MUSCLE

.

0

%IP

#{149}#{149}#{149}#{149} S 0

4.5 4D

C 0

#{149}

...S

3.5

:

#{149}$#{149},#{149}

.5.

.

ao 25

3

3S

4

45

5

4.5

5.5

offset (cm)

Femoral

Femoral Fig.

Fig. 2 Femoral

offset

related

to length

of abductor

lever

arm.

Femoral

80

arm) and The other

S

.0

P=0.0001 70

C a)

%

.5

S

:

.C

are

I

55 S

S S

2

2.5

5

as

3

4.5

4

Femoral offset Fig. Femoral

offset

related

thigh

circumference, revision

weight

lever

each 5

53

(cm)

6

I.

Range

after

abductor

strength.

THA

in degrees Standard Range

deviation

Flexion

99.8

48 to 121

15.3

Abduction

25.7

10 to 45

7.7

Adduction

19.8

8 to 35

5.7

26.5

7 to 51

9.2

24.9

6 to 48

8.1

rotation

External

rotation

Table II. Factors which correlated with strength abduction after THA by simple regression p value

Patient

height

Patient

gender

Femoral

female)

ROM* weight

Flexion

ROM*

Abductor Patient *

>

offset

Abduction Patient

(male

lever diagnosis

range

arm (OAt

>

others)

of motion

VOL.

77-B,

No.

1995

arm

advantages

of isometric

to

time

of arthroplasty,

the

femoral

combody-

approach,

from the

variables

surgery. relative

because

Multiple

importance

a number

of

of them

statistical data for each variable are Of the four, only the length of the

is under

the

of increasing include

mechanical the

an

advantage

instability

because

first,

to our

a clinical

control

of the

surgeon.

for of better

knowledge,

femoral

increased the

range

offset

at THA

of

motion,

abductors

soft-tissue to address

and

tension. the

first

are better

decreased Our

two

study issues

setting.

Table Ill. after THA

Factors which correlated with by multiple regression analysis

strength

o f isometric

abduction

Standardised r value

0.0001

0.72

Patient

height

0.0001

0.71

Patient

gender

0.0001

0.40

Femoral Abduction

0.00)

0.35

Patient

0.004

0.32

Flexion

ROM*

0.005

0.30

Abductor

lever

0.03

0.24

Patient

range

(male

>

female)

offset

#{216}#{216}#{216}#{216}9 0.36

tosteomritis 6, NOVEMBER

and

for

surgical

to determine

The III.

to side

of cement age,

Abductor

analysis.

related

DISCUSSION

*

tosteoarthritis

arm, used

lever

reported

Average

Internal

multivariate

use

were inter-related. presented in Table

abductor

Fig. 4). strength

4

to isometric

of hip motion

and

surgery,

was

of abduction.

II.

of the significant

The Table

to range

was not significantly

regression

S

3

related

variables

ponent,

(cm)

strength (p = 0.0001 ; r = 0.40; which correlated with abductor

in Table

shown

strength

S 5 S.

offset

abductor factors

Additional

S

20 10

S

S

:...

S

offset

ROM* weight

diagnosis of motion

arm (OAt

>others)

coefficient

p value

r value

0.47

0.017

0.95

0.44

0.0005

0.86

0.030

0.74

0.67

0.16

0.098

0.78

0.19

0.13

0.87

0.18

0.047

0.74

0. 16

0.060

0.68

0.012

0.89

0.68

is in

868

B. J. MCGRORY,

The

relationship

between

stability after hip arthroplasty Poss 1980; Huk et al 1993). postoperative lute offset

of

dislocation 4. 1 cm

increasing

B. F. MORREY,

femoral

offset

has been shown In our series there

(1.1%) (series

T. D. CAHALAN,

and

(Fackler and was a single

in a patient with average 3.9 cm).

an absoWe can

significantly (p = 0.046).

(Chamley 1979; range of abduction

greater in patients with We could not, however,

greater show

ing, and therefore decrease as well as the overall joint Other

authors

have

that

this

Kelikwas

method lever arm, the offset. for walk-

the energy requirement reactive force.

inferred

been

femoral offset any correlation

with other planes of motion. Charnley considered that the most effective available to the surgeon to improve the abductor and therefore the biomechanics, was to increase This should decrease the abductor force required

for gait

relationship

is true

from apparent abductor weakness and lurch evident in patients with poor offset (Tauber et al 1980; Kelikian et al 1983; Rothman et al 1993). We identified a variety of factors among length

that correlated with abductor which were femoral offset of the abductor lever arm

regression abductor flexion,

showed strength and

abductor

factors found were related

strength after THA, (p = 0.0001) and the (p = 0.005). Multiple

that the four most important after THA were height, gender, lever

arm

to be significant to these four.

(Table

ifi).

by simple

factors range

All

regression

stem

strains.

the

in of

other

analysis

by

be interpreted overall, there

bone cement in cemented cases. These potential concerns have recent

scientific

femora containing lated gait. Direct

reports.

Davey

been

et al (1993)

cemented measurements

allayed

by

loaded

femoral components of strain were

two

in simumade using

strain in the proximal medial cement mantle was not significantly increased. Wong et al ( 1993) used finiteelement analysis and a canine uncemented THA model to demonstrate that both the abductor force and hip reaction were

Although

significantly stress

was

reduced slightly

with

higher

an increase at the distal

increase

of bone

in femoral

offset.

Both

effect of an by a reduction

experimental

was

not

mdi-

reports

increasing bending in hip force.

results,

component et al (1993).

in bone

ingrowth

the

clinical

concern

loosening They showed

has been a 6% rate

cautiously; there were significantly

were only five loose stems more males in the high-

femoral offset. Our data allow after THA with reported (Cahalan nificant relationship

us to compare the abduction strength that for normal volunteers, previously et al 1989). We demonstrated the sigof gender to strength, but could not

identify the age-dependent volunteers. We believe patient

in our

series

by Cahalan

study

may

to

‘older

group’

of the

years

of age).

Of the

(over

for men

actual

diagnoses,

Conclusions.

be in the 40

is compared between the latter have lower

of 24.6% due

evident because

measurements reported greatest correlation. When

strength patients

be

lying

would

relationship this was

et al (1989)

anthropomorphic height had the abduction and THA

that

age

the effect We have

and

in both studies, gender-specific

normal volunteers actual strengths by

37.8%

for women.

difference,

the

of surgery,

or other

shown

that

in normal all but one

effect

femoral

This

of

under-

factors.

offset

correlated

with increase in range of abduction and strength of abduction correlated positively

femoral

offset

and

the

length

of the

that with

abductor

lever

We would like to thank Amy Weaver, MS. Department of Biostatistics, for her advice and help with the statistical analysis of data. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

cadaver

strain gauges on the bone and the metal as well as in the cement mantle. It was possible to quantify the effect of changing offset on both abductor force and the resultant force, as well as on the strains in the cement, the bone and the prosthesis. Increased femoral offset gave substantial reductions in both abductor and resultant forces, and the

force

excessive

offset group, and the actual femoral offset was not reported, only the prosthesis offset. This is obviously important in that varus or valgus prosthesis positioning affects actual

both arm.

increased strain in the medial proxparticularly in the medial proximal

a change

these

an

the amount

of loosening in femora with implant offset of 38 mm or more, against a 2% rate in those with less offset, in 146 patients followed for two to six years. These results must

because metals

however, could cause imal femur, and more

produce

of increasing femoral expressed by Rothman

positively objective

of currently used increase in offset,

not

cate that the adverse moment was neutralised

an average

fatigue resistance Harris 1992). An

M. E. CABANELA

it did

affected

The advantages of increased stability, range of motion, and abduction strength are conferred by an increased femoral offset, but a possible disadvantage is an increase in the out-of-plane bending moment in the prosthesis. This effect in the stem is generally not important in modem THAs of the increased (Steinberg and

AN,

In addition,

Despite

therefore make no definitive statement on hip stability. The lateral position of a hip with greater offset has said to allow an increase in motion ian et al 1983) and we found that

the

K-N.

in offset. portion

of

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