Comparison of knee joint functional laxity after total knee replacement with posterior cruciate-retaining and cruciate-substituting prostheses

UTTERWORTH EINEMANN

Copyright

Q 1996 Pubhshed

The Knee Vol. 2, No. 4, pp. 195-199, 1995 by Elsevier Science Ltd. All rights reserved Printed m Great Britain 0968-0160195 $10.00 + 0.00

PII: S0968-0160(96)00006-3

Comparison of knee joint functional laxity after total knee replacement posterior cruciate-retaining and cruciate-substituting prostheses Y Ishii’, K Terajima2, R 6 Gustilo3 ‘Department of Orthopaedic University, Niigata Japan; Medical Center, Minneapolis,

Y Koga I, H E Takahashi’ Surgery; 30rthopaedic Minnesota,

‘Department Biomechanics USA

with

J E Bechtold3,

of Mechanical Laboratory,

Engineering, Hennepin

Niigata County

Summary The objective of this laxity with implants patients, or substituted (PCL-S) in ten patients. the presence of the (screw home movement) with active extension and were measured exhibited both screw design exhibited only reproduce the normal compared to a PCL-S

Key words: Knee cruciate ligament, The Knee

Vol.

study which

was to measure three-dimensional knee motion or functional either retained the posterior cruciate ligament (PCL+) in ten for excised PCL with a posterior stabilized articulating surface The intent was to identify the specific influence and significance of PCL under active flexion and extension. Internal-external rotation and anterior-posterior tralnslation (femoral rollback phenomena) and flexion were chosen to characterize knee joint functional laxity, using an instrumented spatial linkage. Knees with a PCL+ implant home movement and femoral rollback, while knees with a PCL-S femoral rollback. A knee with a PCL+ implant was more able to kinematics of the screw home movement and femoral rollback, design. Copyright @ 1996 Published by Elsevier Science Ltd.

joint functional posterior cruciate

2, No. 4, 195-199,

laxity, screw home retention, posterior

movement, rollback cruciate substitution

phenomena,

posterior

1995

Introduction Controversy exists with total knee replacement (TKR) as to whether the posterior cruciate ligament (PCL) should be retained (PCL+), or excised and substituted for PCL with a posterior stabilized articulating surface (PCL-S). Although clinical studies have reported satisfactory results with both designs’-16, the particular significance of PCL retention has yet to be identified biomechanically in viva. Knee motion analysis is one objective method for evaluating the difference between PCL retention or substitution. Functional laxity of the knee can be characterized by anterior-posterior translation (femoral rollback) and internal-external rotation (screw home movement)“. A comparison of femoral Accepted: April 1996 Correspondence and reprint requests to: Department of Orthopaedic Surgery, Niigata Medicine, 1 Asahimachi Niigata City, Niigata,

Yoshinori University 951 Japan

Ishii MD, School of

rollback and screw home movement between PCL+ and PCL-S patients was made using a goniometric method which measures three-dimensional motion. The purpose of this study is to compare the difference in functional laxity between PCL+ and PCL-S patients, and to identify the specific influence and significance of the presence of PCL. Patients and methods We evaluated 9 patients with 10 implants (PCL+) and 9 patients with 10 PCL-S implants. These prostheses (Genesis Total Knee SystemTM, Smith & Nephew Richards, Inc., Memphis, TN, USA) have symmetrical femoral condyles with an increasing radius of curvature with extension. The tibia1 plateau is anatomically shaped and asymmetrical, with the medial condyle larger than the lateral one. The average time to follow-up was 26.4 (range 8-52)

196

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months for the PCL+ knees (5 men and 4 women), and 16.2 (range 6-25) months in the PCL-S knees (4 men and 5 women). The mean age for PCL+ patients was 67.5 (range 65-70) years and 68.4 (range 67-75) years for PCL-S patients. All patients could flex from full extension to at least 95”, and no patients had any clinical complaints of pain or instability. There were no significant difference in sagittal and coronal plane alignment between the PCL+ and PCL-S groups. A six degree of freedom electrogoniometer or instrumented spatial linkage (EL), was used to measure knee motion. ISL had a linear accuracy of &500 urn, am angular accuracy of kO.5”. The ISL was applied to the lateral aspect of tibia and femur with aluminum plates, and straps (Figure 1). To transfer the measured motion from the ISL to the femur and tibia, bi-planar radiographs were taken with the knee in full extension”. Three rotations (internal-external rotation), adduction-abduction, flexion-extension) and three translations (anterior-posterior, proximal-distal, medial-lateral) of the tibia relative to the femur can be measured simultaneously with the ISL. Of these six parameters, anterior-posterior (AP) translation and internal-external rotation during active flexion and extension were selected to characterize functional laxity because of the relevance to femoral rollback and screw home motion, respectivelyi7.

Figure 1. The electrogoniometer was applied to lateral aspect of the tibia and femur with aluminium plates and straps. Note the motion sensing potentiometers and the biplanar radiographic markers: a, 90” flexion; b, full extension.

b

a

Femoral , sagittal

, Femoral coordinate origin

Femoral . reference

Tibia1 coordinate origin refernce point

plane

C

Lateral femoral 801

view of condyle

(90” flex.) . .

Femoral

origin

(90” flex.) /

I

70

60 Lateral 3

g

40 view

of

femoralcondyle (0” flex.)

4020

Femoral (O” flex.)

040 Post.

-20

0

20 (mm)

40

origin

60 Ant.

Reference points for rotation: the femoral coordinate origin was defined as the midpoint between the centres of both condyles, and the tibia1 coordinate origin was defined as the centre of the tibia1 plateau. b, Reference points of translation: the tibia1 coordinate origin was defined as the centre of the tibia1 plateau, and the femoral coordinate origin was defined as midpoint between the contacts on the femoral and tibia1 components in the sagittal plane. c, Simulated locus of the femoral origin relative to the contact point between the femoral and tibia1 components in sagittal plane during flexion. The ellipses represent the lateral view of the femoral condyle at each flexion angle. If knee joint motion consists of sliding without rolling, and the contact point does not move, the femoral origin moves forward relative to the contact point (or the tibia1 origin moves backward relative to the contact point). Therefore, if the femoral origin is chosen at the midpoint between the centre of the femoral condyle, this misleading shift due to the component geometry creates differences between the measured data and the observed femoral rollback phenomena, because forward sliding and backward rolling occur simultaneously. For this reason, location of the femoral origin should be changed to make the data coincide with observed clinical findings. Figure

2a.

Internal-external rotation was defined using a helical axis system (aligned with the tibia)i’. The origin of the femur was defined as the midpoint between the centres of both condyles. The origin of the tibia was defined as the centre of the tibia1 plateau (Figure 2a). For anterior-posterior translation, the origin of the tibia was the same as for internal-external rotation, and the origin of the femur was midway between the contact points on the femoral and tibia1 components in the sagittal plane (Figure 2b). Defining the femoral origin for anterior-posterior translation as a midway point

lshii et al.: Functional

Internal-external

between the centres of the condyles made it appear that the femur moved forward with flexion, although femoral rollback was actually at the center of the condyles, caused it to move forward with flexion although rollback was actually observed. This misleading shift in origin is due to the decreasing radius of curvature as the femoral component flexes (Figure 2~). Knee motion was measured with the patients seated and actively extending their knee from 90” flexion to complete extension. The measurements were repeated three times for each subject. These internal-external rotation and anterior-posterior translation patterns as a function of flexion angle were averaged for each subject in each group, and various descriptive peak magnitudes of rotation and translation were identified. Ten age-matched volunteers with normal knees were also included in the study as a control group. A global comparison of each of these motion components over the three test groups was obtained by analysis of variance. Pairwise comparisons were -made while taking multiple comparisons into account (Dunkan).

Anterior-posterior

It remains controversial

deviations of the external and standard deviations

PcL+

3.2 t 8.8 t

significance

2.9* 10.9+

(a) “‘---=--I 30

Rot.

Flexion

I 60

Angle

rotation occurring of anterior-posterior

0.9 10.5

between 30” translation

Normal

10 f 2.2** + 8.5’

3.5 18.3

controls 10 c 2.4”” + 8.8+*

at P < 0.05.

lnternallexteinal

Ii sO

as to whether retaining the

PCL--s

10

*‘**‘+,*statistical

Figure motion Screw

translation

Discussion

Table 1. Screw home motion as defined by the means and flexion and extension, and rollback as defined by -the means between extension and 90” flexion

Ext.

rotation

Both the PCL+ and PCL-S groups exhibited femoral rollback, with a mean translation of 8.8 mm in the PCL+ group (Figure 4a) and 10.5 mm in the PCL-S group (Figure 4b). The normal group’s mean femoral rollback was 18.3 mm (Figure 4~). The magnitude of the rollback for the normal group was approximately twice that of the prosthetic groups. The differences in rollback were significant between the normal group and the prosthetic groups. There were no significant differences between the PCL+ and PCL-S groups (Table 1).

The mean values (and standard deviations) of these changes in translation and rotation magnitudes between 30” flexion and extension were tabulated in Table 1 for the normal control subjects, and the PCL+ and PCL-S groups.

home (deg.) (mm)

197

In the PCL+ and normal groups, a screw home like movement (continuous external rotation between 30 flexion and extension) was observed. The mean range of external rotation between 30” of extension was 3.2” for the PCL+ group (Figure 3a) and 3.5” in the normal group (Figure 3~). The knee with PCL-S implants did not exhibit a screw home movement (mean of 0.9 external rotation) (Figure 3b). Although there were no significant differences between the PCL+ and normal groups, there were significant differences between PCL-S group, and normal and PCL+ group (Table 1).

Results

Number Screw Rollback

laxity after TKR

(b) 20

(deg.)

3. Means and standard deviations of 10 knees with a PCL retaining home motion of 10 normal knees.

Ext.

PCL-s

r

5k

<

Ro’t.

rotation Int.Rot.(deg.)Normal

Control

(c) 207

I

i

30

Flexion

of internal-external design. b, Screw

60

Angle home

Ext.

(deg.)

rotation motion

as a function of 10 knees

I 30

II sO

9

Rot.

Flexion

I 60

Angle

s

(deg.)

of flexion angles. a, Screw home with a PCL substituting design. c,

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The

Vol. 2, No. 4, 1995

Knee

Anterior/Posteriortranslation (4 30r

PcL+

I 30

II 2oO

Post. Figure

,

I 60

and standard

(cl

PCL-s

Int.Rot.(deg.)

I 90

Flexion Angle (deg.) 4. Means

(h) 30(

Post. deviations

Flexlon Angle (deg.)

of anterior-posterior

PCL improves the function and durability of total knee replacements. There appear to be no compelling clinical advantage of retaining PCL compared with excising it and substituting for its function with a posterior stabilized implant design’*2,5,‘0. Both types of prostheses have demonstrated good clinical results’-‘6. L’Insalata and Laskin’ reported on the equally good clinical results with both retention and substitution of the posterior cruciate ligament when the Genesis was used in a randomized, prospective, double blind study. In this study, PCL+ and PCL-S patients were compared with respect to the difference in functional knee joint laxity, which was characterized by internalexternal rotation (screw home movement) and anterior-posterior translation (rollback phenomena) with active flexion and extension. The purpose of this study was to identify the specific influence and significance of the presence of the PCL. In relation to screw home movement, Whiteside et al.” reported in an in vitro study that the normal screw home pattern of coupled external rotation with extension was restored when the ligaments were correctly tensioned in a PCL retaining TKR. Our study also demonstrated that knees with a PCL+ design maintained a screw home motion, while PCL-S implant did not. The presence of the PCL in a PCL+ design may serve to induce the screw home movement. Also, the rotational stresses may be absorbed not only by the tibia1 plateau, but also by the bone-ligament interface. However, the PCL-S implant, which did not exhibit a screw home movement, may restrain rotational torque at the posterior stabilizing cam, which may produce tensile and compressive stresses at the bone-cement interface. Werner et a1.21also concluded that a TKR should not replace the ligament’s function of resisting rotational stresses. In relation to femoral rollback, the PCL and posterior stabilizing cam seemed to perform the same function, since they both allowed the same amount of rollback. The rollback in the prosthetic knees was half of that in the normal group. This could be due to the different geometry between the prosthetic knee and the normal knee. Increased friction between metal and plastic as compared with normal cartilage

translation

203!T----- 30 60 Post. Flexion Angle (deg.) as a function

of flexion

9t

angles.

may also play a role. Shearing stresseson the tibia1 tray in PCL+ knee will be transmitted at both the boneligament interface and the bone-cement interface, while in the PCL-S implant shear can only be transmitted at the bone-cement interface. Sledge and Walker22 also supported the PCL-retaining prosthesis because the posterior stabilized design transferred forces, which were to the bone-cement interface, normally absorbed by the PCL. Since our study was a motion analysis of active flexion and extension, we still require studies which measure functional laxity to investigate the effect of muscle forceZ3 and during gait2” on the differences between PCL+ and PCL-S implant designs. Although our exoskeletal linkage technique assumes that there are perfectly rigid attachments between the ISL and underlying bones, the skin motion and muscular activity can actually cause the ISL to shift relative to the femur and tibia. This creates errors in the measured motion. However, the reproducibility and reliability of the ISL were documented by Townsend et aI.‘5, Shiavi et a1.26 and Terajima et al.27. Furthermore, this procedure is non-invasive and has the advantage of being able to be used in clinical studies. In conclusion, considering that current TKA prostheses have been designed to reproduce the kinematics of the normal knee, including the screw home movement and femoral rollback, the PCL+ design more closely approaches that ideal than the PCL-S implant. However, although the screw home movement and femoral rollback are characteristic movements of knee joint, they are also thought to produce shear stresseson the tibia1 plate28, and possibly contribute to loosening of the tibia1 component. A future aim is to develop new prosthetic designs and materials which can reproduce the screw home movement and femoral rollback with lower shear stresses,such as occurs in the normal knee. References 1

Becker MW, Insall JN, Faris PM. Bilateral total knee arthroplasty. One cruciate retaining and one cruciate substituting. Clin Orthop 1991;271: 122-124

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13 14

Bourne MH, Rand JA, Ilstrup DM. Posterior cruciate condylar total knee arthroplasty: Five-year results. Clin Orthop 1988; 234: 129-133 Colizza WA, Insall JN, Scuderi GR. The posterior stabilized total knee prosthesis, Assessment of polyethylene damage and osteolysis after a ten-year-minimum follow-up. J Bone Joint Surg(Am] 1995; 77A: 1713-1720 Figgie HE, Goldberg VM, Heiple KG, Moller HS, Gordon NH. The influence of tibial-patellofemo-ral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg[Am] 1986; 68A: 1035-1040 Hirsch HS, Lotke PA, Morrison LD. The posterior cruciate ligament in total knee surgery. Save, sacrifice, or substitute? Clin Orthop 1994: 309; 6468 Insall JN, Lachiewicz PF, Burstein AH: The posterior stabilized condylar prosthesis: A modification of the total condylar design. J Bone Joint Surg[Am] 1982; 64A: 1317-1323 L’Insalata JC, Laskin RS, Bono J. Ganz SB. A prospective randomized comparison of posterior cruciate ligament retaining and posterior stabilized total knee arthroplasty. Orthop Trans 1995; 19: 450 Malkani AL, Rand JA, Bryan RS. Total knee arthroplasty with the kinematic condylar prosthesis. A ten year follow-up study. J Bone Joint Surg[Am] 1995; 77A: 423-431 Maloney WJ, Schurman DJ. The effects of implant design on range of motion after total knee arthroplasty: Total condylar versus posterior stabilized total condylar designs. Clin Orthop 1992; 278: 147-152 Rand JA, Ilstrup DM. Survivorship analysis of total knee arthroplasty: Cumulative rates of survival of 9200 total knee arthroplasties. J Bone Joint Surg[Am] 1991: 73A 397-409 Ritter MA, Herbst SA, Keating EM, Faris PM, hlleding JB. Long-term survival analysis of a posterior cruciateretaining total condylar total knee arthroplasty. Clin Orthop 1994: 309; 135-145 Scott WN, Rubinstein M, Scuderi G. Results after knee replacement with a posterior cruciate-substituting prosthesis. J Bone Joint Surg[Am] 1988; 70A: 1163-1173 Scuderi G. Insall JN. The posterior stabilized knee prosthesis. Orthop Clin North Am 1989; 20: 71-78 Stern SH, Insall JH. Posterior stabilized prosthesis. Results after follow-up of nine to twelve years. .J Bone Joint Surg[Am] 1992; 74A: 98&986

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