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D. I. CLARK,. C. E. CROFTS,. M. SALEH. From the University. ofSheffield and Royal. Hallamshfre. Hospital,. Sheffield. The rigidity of a sliding compression screw.
FEMORAL

NECK

COMPARISON

OF

D.

The rigidity

of a sliding

A SLIDING

I. CLARK,

the University

From

FRACTURE

compression

SCREW

C.

ofSheffield

E.

and

screw

FIXATION WITH

CROFTS,

M.

Royal

and three

LAG

SCREWS

Hospital,

Sheffield

SALEH

Hallamshfre

cannulated

lag screws

in the treatment

of subcapital

fractures was compared in five pairs of female cadaver femora. There were no significant differences between the compressive sfrength, bone density, cortical thickness or Singh index of the bones in each pair. A subcapital fracture was standardised using a perpendicular saw cut across the femoral neck. A urnaxial ‘load

test system’

with force

at a frequency fixation

afforded factor

important

and length

of 0.5 Hz

from

by the sliding in the stabifity

measurement

facifities

0 to 3 times

body-weight.

compression of the bone

screw implant

and

F#{248}nstelien 1987). However, compared fixation devices subjects (Van Audekercke

most in vitro using femora et a! 1979;

two

into

account.

et

a!

1980;

et

The

by using paired a static loading

Engesaeter

et

a!

1984).

reports

which

femora system This

an

offemoral

D. I. Clark, Department Newcastle

in vitro neck

study

fractures

MB, ChB, BMed Sci, of Anatomy, University upon Tyne NE2 4HH,

C. E. Crofts,

Department of Sheffield, 2JF, England.

method

which

is

using

investigated (1) paired

BSc, PhD, University Lecturer of Medical Physics and Clinical Engineering, Royal Hallamshire Hospital, Glossop Road,

© 1990

British 030l-620X/90/S1SS

J Bone Joint

VOL.

should be sent

to Dr

D. I. Clark.

Editorial Society ofBone and $2.00 Surg [Br] 1990; 72-B :797-800.

72-B, No. 5, SEPTEMBER

1990

Joint

Surgery

the femora!

Anatomy Demonstrator of Newcastle, Framlington England.

M. Saleh, MSc(Bio Eng), FRCS, FRCS Ed, SeniorLecturer, ofSheffield, Honorary Consultant, Sheffield Health Authority Department of Orthopaedics, Northern General Hospital, Road, Sheffield 55 7AU, England.

Correspondence

Bone

the

same

to simulate

stressing applied in vivo difference between the was

quality

the single

most

Place,

University Sheffield 510 University Barnsley

patient

and

(2) a dynamic

AND

as a previous arthroplasty, were excluded from the stored

properties

at

of the

loading

walking.

METHODS

Fourteen pairs of femora were obtained over the age of 60. Those with known hip

-

a femoral fracture or a tumour study. The specimens were

20#{176}C. Prior

right

from females pathology such

and

to testing,

left

femora

the mechanical were

investigated

by measuring bone density (Dal#{233}n, Hellstr#{246}m and Jacobson 1976), cortical thickness (Griffiths, Swanson and and

Freeman 1971), the Singh using a static compression

The frozen

walking. We report

fixation

screws.

from

initially

from the (Mizrahi

unsatisfactory since in life the fixation device must be able to withstand the cyclical loading pattern associated with

to mimic cyclical was no significant

MATERIALS

is

taken

lag

heads

a! 1987). The the Yariation in the different individuals

not

three

regime

MacKechnie-Jarvis 1983 ; Elmerson limitation of this technique is that mechanical properties of bone from overcame this problem same patient employed

There

unit.

The importance of bone quality in the fixation of femora! neck fractures has been emphasised by in vitro studies (Franke! 1960; Van Audekercke et a! 1979; Husby, H#{248}iseth and studies have from different

was used

Singh three

index was independent

index test.

(Khairi

et a! 1976)

bones were radiographed in pairs. The assessed for each proximal femur by observers and the femora! shaft

cortical thickness measured 120 mm below the greater trochanter using vernier calipers. After the bones had been radiographed they were returned to their storage environment. Using a ND 2100 bone density scanner, readings were taken from the proximal two-thirds of each femur, and from the femoral shaft sections. As soon as the measurements had been made a!! the bones were again returned to storage. Before mechanical testing, the bones were defrosted for six hours at room temperature, carefully cleaned of muscle and soft tissue, and rehydrated with warm saline. The mechanical tests were performed on a Mayes material testing machine (Fig. 1). Static compression tests

were

carried

out

on

six

pairs

of

femoral

shaft

797

D. I. CLARK,

798

sections. diameter

After the bones of each specimen

each sample was length to diameter

adjusted ratio

had defrosted, were measured.

pairs of randomly selected and fitted with two different

at a rate were

to give a 4 to 1 The

for

.

of 3 mm/mm.

performed

on

femora artificially fixation devices.

M. SALEH

Failure of the system was defined as the point at which a deflection of 125% of the value recorded at 30 cycles was observed (a figure set for the proposed British Standard

the length and The length of

using a band-saw of approximately

specimen was loaded to failure The maximum load was recorded. Cyclical compression tests

C. E. CROFTS,

femora!

specimens graphed

head

prostheses

were refrozen to determine the

BSI

after pattern

DD91

:1986).

testing and of failure.

The

later

radio-

five

fractured After the

RESULTS

bones had defrosted, one specimen from each pair was selected at random for fixation with a sliding compression screw, whilst the other was fixed with three self-tapping

Bone quality. In order difference in the bone pretest investigations

)

c r

-jet

that there was no paired femora, four : static compres-

LLR

a

a

-

a

a

.

to be certain quality of the were performed

-

fl,

-

JJJ.JJ#{149}#{149}. .

rOr

1E i.:. i.

.

..

0

:iu iJ:i;i

d#{149}#{149}O

i:i’’ I Fig.

Figure grips.

1

-

cannulated reduction,

The

Mayes

material

testing

lag screws. In order both devices were

unfractured femur. artificially produced neck. Purpose-built anatomical angle the test machine

were The

Hz until recorded deflections

Fig.

in our

experiments.

to achieve an anatomical initially inserted into the

of 20#{176} from the vertical (Fig. 2). The specimen

fracture

1

as used

They were removed and a fracture using a saw cut perpendicular to the grips to hold the bone at an

the lower grip. Each bone was during testing. Each specimen from 0 to 3 times body-weight 0.5

machine

occurred.

were fitted was placed

to in

covered with damp paper was loaded sinusoidally (2. 1 kN) at a frequency of

The load and displacement

graphically and from a digital after 1 and 30 cycles were

display. recorded.

Figure

2

-

The

proximal

femur

held

between

2

the

purpose-built

sion tests, bone density measurements, the Singh index and cortical thickness as measured radiographically. Statistical analysis revealed no significant difference between the right and left femora (Table I). Rigidity. The deflections recorded during the fatigue testing Table

of the five pairs of proximal femora II. There was no significant difference

deflections bones fixed there

was

recorded after the with compression no significant

three

first or 30th cycles for the or lag screws. In addition,

difference

of cycles required to produce with a sliding compression

are given in between the

between

the

number

failure in the femora screw and those fixed

fixed with

lag screws. THE

JOURNAL

OF BONE

AND

JOINT

SURGERY

FEMORAL

The

results

quality

in Table

(Singh

index

pair

of fixed

of each

deflection years) and

(number had the

and

III

compare

bone

density)

bones.

The

the

age

with

bone density of the five pairs. By deflection occurred in bones from (65 years) with the best bone quality

6) and

a high

bend in any the trabecular

Table from

bone

mode.

The

strength(kN)

Bone

(g/cm2)

density

sliding

of the

compression

bone

quality

thickness

largest

screws

in the

to collapse and head.

of At

and

left

femora

Left

14.24±2.79

12.53

0.97 ± 0.06

12

(mm)

right

not

0.96±

0.05

14

5.2±0.26

5.2±0.30

14

7.21 ±0.27

6.97 ± 0.36

site

impacted with the screw sliding down head then began to shear across the

due

to the

screw

barrel

cutting

through

the

femora! neck trabecu!ar bone (Fig. 3a). During loading the three cannulated lag screws were forced back down the drilling of

holes.

the

femora!

sheared

across

converged deformation

A crush neck the

fracture

then

of the

occurred.

fracture

line

inferior

surface

Finally

and

and rotated downwards of any implant was

the

(Fig. observed.

the

screw 3b).

head

threads No

plastic

DISCUSSION The rigidity lag screws

ofthe used

Richards currently

neck

fractures

have

the

population

at

females exclude

±2.4

799

the fracture barrel. The

first

fracture

(84 the

did

Right

6

Singhindex Cortical

the

FIXATION

the

density.

Pairs tested Compressive

bone

contrast, the the youngest (Singh index

of the tests. Failure was due bone in the femora! neck

I. Comparison the same patients

FRACTURE

deflection

4) were from the oldest subject weakest bone (Singh index 3) and

lowest smallest subject Failure

and

against

pair

NECK

from

over bone the

made

been

compared.

risk,

femora

In order were

to reflect

obtained

from

the age of 60 (Lewinnek et a! 1980). To quality as a source of error, paired femora

same

pair were pretesting

compression screw and three in the treatment of femoral

subject

were

shown to be investigations.

to reduce

tested.

The

bones

from

matched mechanically by In addition an attempt

experimental

variables

each four was

to a minimum

by

using a standardised fracture (Klenerman and Marcuson 1970) and ensuring an anatomical reduction. A saw cut perpendicular to the neck was chosen in accordance with Klenerman’s observations that subcapita! a similar angle. During walking, the angle load on the femora! head has been shown

fractures have ofthe resultant to be 10#{176} to 15#{176}

from the midline (Inman 1947; Elson and Charn!ey 1968). The offset angle of the femora! shaft is 7#{176} to 10#{176} (Williams et a! 1989). The optimum loading angle for the femora! vertical; than

head in vitro is therefore 17#{176} to 25#{176} from the 20#{176} was chosen in this study. A cyclical rather a static

simulate weight Fig. Mode screws.

of failure.

3a Figure

Fig. 3a

of the

-

sliding

screw.

reasons. theoretical

3b

Figure

3b

-

of the

lag

1967; cond!y,

Table II. femora

Deflections

recorded

during

fatigue

testing

ofthe

proximal

Table each

loading

regime

was

applied

walking. A loading regime (2. 1 kN acting sinusoidally) First, three times body-weight load acting on the hipjoint Crowninshield, the

British

Brand

and

Standards

III. Age, bony quality pair of fixed femora

is within (Rydell Johnston

Institute and

deflection

Deflection

Deflection

used

1 cycle

30 cydes

Pair

1

71

Compression Lag

7.20 2.88

12.93 11.18

2

65

Compression Lag

1.65 1.74

4.71 3.45

Compression Lag

3.44

3

65

after (mm)

after (mm)

order

the peak 1966 ; Paul 1978).

testing

Bone Pair

Age (yr)

66 67

1

71

55 65

2

65

4.71 3.45

6 6

0.96

65

6.45 5.71

6 6

0.75 0.69

of cycles to failure

1.94

6.45 5.71

65 38

3

Deflection

after

Singh

density

3Ocycles(mm)

index

(g/cm2)

12.93 11.18

5 6

0.95 0.98

1.00

4

84

Compression Lag

18.50 11.40

24.97 22.21

S 3

4

84

24.97 22.21

3 3

0.53 0.56

5

81

Compression Lag

2.75 2.94

4.30

75 150

5

81

4.30

4 4

0.89 0.79

VOL.

72-B,

No. 5, SEPTEMBER

1990

5.46

5.46

to

Se-

recommends under

Number

Screw

Age (yr)

in

of 0 to 3 times bodywas chosen for two

a of

800

D. I. CLARK,

2. 1 kN femoral

sinusoidal

loading

heads. The choice

biomechanical et a! 1981). orientation optimum

of the

pattern three

investigations Mizrahi found

when

lag

screws

inferior showed

tance ofpara!le! screw placement. Both found no improvement in fixation if screws were used. The compression sliding barrel for controlled impaction (Clawson 1964). Its blunt nose preventsjoint Biomechanical

testing better 1961).

provide improved demonstrated by

has

was

based

shown

on

to be the the impor-

authors, however, more than three hip screw has a at the fracture site penetration.

that

a large

threaded

internal fixation than a triflanged The advantage of the side plate

fixation Haboush

to

the

(1952).

femora! In both

shaft devices

to was the

initial event in failure was impaction ofthe This underlines the importance of parallel

femoral neck. placement of

the lag screws sliding action

the

allowing permitted

backing out, and by the compression

hip

controlled screw.

Franke! (1960) showed that in saw cut femoral neck fractures fixed in vitro, the bone absorbed 75% of the load applied to the femoral head and the device the remaining findings

25%. The results in Table III confirm and suggest bone quality to be the most

M. SALEH

shown that in influencing

testing

(Mizrahi et a! 1980 ; Rubin a triangular three-screw

of two superior and one configuration, whilst Rubin

screw provides nail (Brodetti

fatigue

C. E. CROFTS,

Frankel’s important

factor

in the rigidity ofthe bone implant unit. Using an unphysiological static load and femora! heads from different subjects, other workers have shown that both the sliding compression screw and three lag

No benefits commercial article.

in any party

the same a sliding

results three larger fying

paired

femora!

subject compared two Von Bahr compression screw (Engesaeter

static loading difference was

confirm

to use

regime found

of our study, Engesaeter’s

heads

from

lag screws with et a! 1984). A

was used and no significant between the two devices. The using static

a dynamic test results

loading regime and show that

parallel screws provide as rigid a fixation as the sliding compression screw. In addition, by quantithe mechanical strength of the femora, we have

factor

received or will be received or indirectly to the subject

from a of this

screws Scand

BSJ.

Draft for development. Method for determination of endurance properties of stemmed femoral components of hip joint prostheses 1986. BSI(DD91 :1986).

Oawn

DK. Trochanteric fractures treated fixation method. J Trauma 1964; 4:753-6.

Crowninshield RD, Brand RA, Johnston velocity and age on hip kinematics 132:140-4.

and

Dal#{233}nN, Hellstr#{246}m L-C, Jacobson mechanical strength of the femoral 47:503-8.

by the

sliding

RC. The kinetics.

screw

Elson

RA, Charnley J. The prosthetic replacement 6:19-27.

B. Bone mineral neck. Acta Orthop

direction of the hip

plate

effects of walking C/in Orthop 1978; content Scand

ElmersonS, Andersson CB, Pope MH, Zetterberg C. Stability in femoral neck fractures : comparison of four fixation vivo and in cadavers. Acta Orthop Scand 1987 :8:109-12. of the resultant joint. Med and

and 1976;

of fixation devices in

force in total Biol Eng 1968;

Engesaeter LB, Asserson 0, Molster A, et al. Stability of femoral osteotomies fixed by Von Bahr screws or by compression hip EurSurgRes 1984; l6suppl2:37-40.

VH.

Frankel neck.

Mechanical Acta Orthop

factors for internal Scand 1960; 29 :21-42.

fixation

of the

Criffiths WEC, Swanson SAy, Freeman MAR. Experimental fracture of the human cadaveric femoral neck. J Bone [Br] 1971 ; 53-B:136-43.

Husby

T, Hoiseth A, F#{248}nstelien E. Strength fixation : comparison of six techniques Scand 1987; 58 :634-7.

VT. Functional

aspects

BoneJointSurg Khaki

of the

of femoral in cadavers.

abductor

Joint

L, Marcuson

RW.

Intrascapular 1970;

J Bone Joint Surg [Br]

52-B

AC. Femoral compared.

fractures :514-7.

neck fracture Med 1983

J R Soc

Mizrahi

J, Hurlin RS, Taylor transfer and optimum pin Muller screws, of fractured 1980; 18:319-25.

Paul

JP. Forces Mech Engrs

Rubin

R, Trent P, Arnold W, Burstein experimental femoral neck fractures Trauma 1981 ; 21 :1036-9.

of the

hip.

;

of the

J

fixation 76:643-8.

: rigidity

in the

human

body.

A. Knowles : a biomechanical

NW. Forces acting on the femoral head-prosthesis strain gauge supplied prostheses in living persons. Scand 1966; 37 (Suppl 88):l-132.

Van

Audekercke R, Martens study on internal fixation 1979; 141 :203-12.

M, Muller of femoral

R, Dyson Churchill

Edinburgh,

THE

of the and a C/in of five

JK, Solomon L. Investigation of load configuration in the internal fixation, by femoral necks. Med Bio/ Eng Comput

transmitted by joints 1967; 18l(3J):8-13.

PL, Warwick

neck

The significance of hip fractures.

Rydell

ed.

Orthop

Robb JA, et al. Femoral trabecular-pattern content measurement by photon absorption JBone Joint Surg [Am] 1976; 58-A :221-6.

Lewinnek CE, Kelsey J, White AA, Kreiger NJ. comparative analysis of the epidemiology Orthop 1980; 152:35-43.

Williams 37th

fracture

Acta

1947; 29:607-19.

MRA, Cronin JH, index and bone mineral in senile osteoporosis.

MacKechnie-Jarvis techniques

fatigue Surg

fractures

neck

muscles

neck screw. femoral

Haboush EJ. Photoelastic stress and strain analysis in cervical ofthe femur. Bu//Hosp Joint Dis 1952; 13:252-8.

Klenerman femur.

it does not allow of the different

important

study on the use of nails and bolt of the femoral neck. Ada Orthop

in the fixation of fractures 1961 ; 31 :247-71.

found both devices equally effective. Husby et a! (1987) showed that the sliding compression screw was superior to three lag screws, whilst Elmerson et a! (1987) found the reverse, three lag screws providing better fixation

the results since in bone quality

form have been related directly

A. An experimental

Inman

significantly influenced for possible variations femora under test. The only report

was the most of fixation.

REFERENCES

Brodetti

screws have a superior holding power to the Smith Peterson nail (Brodetti 1961 ; Van Audekercke et a! 1979). However, when comparing parallel lag screws to the sliding compression screw there is disagreement. Van Audekercke et a! (1979) and MacKechnie-Jarvis (1983)

than the Richards sliding compression screw. A!! these studies used unmatched femoral heads from a range of male and female subjects. This factor could have

bone quality the outcome

JOURNAL

Proc

Inst

pinning study.

OF BONE

LH. 1989

AND

J

: a study on Ada Orthop

JC, Stuyck J. Experimental neck fractures. C/in Orthop

M, Bannister Livingstone,

of

Gray’s

Anatomy.

:435.

JOINT

SURGERY