joint motion area related to prosthesis component

Joint motion area related to prosthesis component position in total HIP arthroplasty

JOINT MOTION AREA RELATED TO PROSTHESIS COMPONENT POSITION IN TOTAL HIP ARTHROPLASTY Adrian PACIOGA, Doru D. PALADE, Stanca COMŞA, National Institute for Research and Development in Mechatronics and Measurement Technique, Bucharest, Pantelimon Road 6-8, Romania

Abstract – The total hip arthroplasty is the most common procedure for hip reconstruction, but even if it has a great success rate it also has some limitations regarding compromises that must be made, which can lead to post operative complications and could affect patient’s life quality and implant’s lifetime. Utilization of a personalized implant permits restoration of the original anatomy with maximization of the contact surface between bone and prostheses, which leads to the optimization of load distribution. The authors realized a 3D proximal femur modelling, designed an adequate personalized prostheses and realized computational simulation of the assembly, in order to anticipate the joint motion area related to acetabular cup position. We must outline that because the reconstruction was made keeping the natural rotation centre of the femoral head, the influence of the anteversion of the stem was not analysed. Key words – personalized prostheses, motion area simulation. 1. Introduction

2. Method description

The idea of a personalized hip implant is not so new on the international scale and there are some preoccupations regarding personalized implant manufacturing, using classic and non-conventional technologies. The new laser sintering machines have brought an unexpected excitement among researchers in this domain. In the history of total hip arthroplasty (THP) many different positions for the acetabular cup and the femoral stem component have been recommended. For the acetabular component, in different studies an abduction of 30° to 50° and an anteversion of 0° to 30° were suggested. Charnley, the pioneer in arthroplasty advocated a 45° of acetabular abduction, a 0° anteversion and a maximum 5° femoral anteversion for the stem [1,2]. Muller proposed that the combined anteversion of the cup and stem should not exceed 25° to 30°, while Ranawat opined for 20° to 30° for this combined anteversion in males and up to 45° in females [3]. Different positions of the prosthesis components lead to different results regarding joint motion area and have impact upon implant’s durability and stability. The data obtained in the course of this study help doctors to predict the prosthetic joint motion resulting from acetabular cup position.

For motion area evaluation, the 3D models of the proximal femur, hemipelvis, the spherical joint, the plastic liner and the acetabular cup were computed. The authors have used the CT scan data of the patient A.M., whose 3D model of the proximal femur was obtained using the commercial soft 3D DOCTOR, and importing the obtained surfaces in SolidWorks 2009, in order to compute the solid model. The assembly for joint area evaluation was obtained by fixation of the hemipelvis, on which the acetabular cup and the liner were inserted using concentricity mates between cup and the acetabular fossa and parallelism between their plan faces. The subassembly formed by the proximal femur, personalized stem and spherical joint was then inserted using only a concentricity mate between the joint and the liner. This single constraint allowed free rotation of the femur-prosthesis subassembly in order to determine the maximum angles of motion without interferences. Next, the reference planes used for characterization of the position of the different body parts were materialized: sagittal, frontal and transverse planes (see fig.1) The sagittal plane was placed at half of the distance between femoral heads (the distance was measured on the radiographic image of patient’s A.M. hip). The other two planes were constructed perpendicular to the first one and passing through the femoral head centre

The Romanian Review Precision Mechanics, Optics & Mechatronics, 2010 (20), No. 38

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Fig. 1: Materialization of the reference planes Taking in account the controversies regarding the position of the acetabular cup, in order to study the influence, we orientated it in 30°, 40°, 45°, 50° abduction and 0°,10°,20°, 30° anteversion. All the 16 resulted combinations were then examined for maximum joint motions in five directions (associated with hip dislocation), as follows [6]: Study I: Maximum external rotation in 0° flexion and 0° abduction; Study II: Maximum flexion in 0° rotation and 0° abduction; Study III: Maximum flexion in 10° adduction and 10° internal rotation;

Study IV: Maximum internal rotation in 90° flexion and 0° abduction; Study V: Maximum internal rotation in 90° flexion and 10° abduction. For exemplification, the study of maximum flexion in 10° adduction and 10° internal rotation was used to simulate the function of getting up from a low chair without keeping the knees apart [4,5]. The assembly was displaced/rotated until the impingement between prosthetic elements (acetabular cup - stem neck or acetabular cup - stem neck) or bones (femur - hemipelvis) occurred. The contact type was recorded in the results table, the bone impingement was noted with “A” and prosthetic impingement with “B”. In order to orientate the acetabular cup to the desired angles, 16 dedicated planes were created. Also, in order to force the displacement of the stemfemur subassembly in the desired directions other auxiliary plans and rotational axes were created, temporary mates being assigned to the subassembly. 3. Results and discussions Appreciation of the maximum joint motion angle was made by measuring the difference between the initial position (stand up) and the final one when impingement occurred (see fig. 2). The interferences between the elements of the assembly were evidenced using the “Interference detection” command, available in SolidWorks 2009.

a. Maximum external rotation b. Maximum flexion Fig. 2: Measurement of the maximum angle The launch of the “Interference detection” command, opens a dialog window were the interferences are listed and the zone is highlighted in red for an easy and rapid location. The programme also calculates the volume of the superimposed elements (see fig. 3). In table 1, the computed maximum joint motion angles are presented for patient A.M. hip 148

with personalised femoral stem. The motion areas are presented for all five studies defined in the first paragraph, for all the possible combinations of the acetabular cup positions (16 positions). In order to outline the correspondence between the results in table 1 and the variation diagrams (see fig. 4), the table lines were shaded in the colours of corresponding curves.



Fig. 3: Interference detection

Contact type

Motion area

Contact type

Motion area

Contact type

Motion area

Contact type

Study V

Motion area

50º

Study IV

Contact type

45º

Study III

0º 10º 20º 30º 0º 10º 20º 30º 0º 10º 20º 30º 0º 10º 20º

55,1° 55,1° 48,9° 35,8° 55,1° 55,1° 46,9 33,1 55,1 55,1 44,5 30,6 55,1 55,1 41,9

A A B B A A B B A A B B A A B

B B B A B B B A B b A A A A A

16,6° 22,9° 27,3° 30,1° 24,2° 30,3° 34,5° 36,7° 31,5° 35,1° 36,7° 36,7° 35,7° 36,7° 36,7°

B B B B B B B A B B A A B A A

13,1° 18,6° 22,6° 24,7° 22,3° 26,9° 30,2° 30,9° 27,4° 30,1° 31,9° 31,9° 31,3° 31,9° 31,9°

B B B B B B B B B B A A B A A

26,8

113,7 128,9 ° 138,8 ° 144,3 ° ° 129,1 138,4 ° 143,5 ° 146,2 ° ° 144,9 148,5 ° 148,5 ° 148,5 ° ° 148,5 148,5 ° 148,5 ° 148,5 ° °

B B B B B B B B B A A A A A A

30º

107,4 119,4 ° 128,5 ° 133,1 ° ° 118,9 127,1 ° 130,5 ° 133,1 ° ° 128,5 131,5 ° 133,1 ° 133,1 ° ° 133,1 133,1 ° 133,1 ° 133,1 ° °

B

Max. ext. rotation: 0°flexion 0°abduction[°]

40º

Study II

Motion area

30º

Study I

Acetabular anteversion

Acetabular abduction

Table 1: Joint motion area depending on acetabular cup position

A= A=A= A

55

A

A

36,7°

A

31,9°

A

A= A=A=A

B B 45

B B B

35

B

30° acetabular abduction 40 acetabular abduction°

B

45° acetabular abduction

B


25 0

10

20

30

Acetabular anteversion [°]


149

150

140 A 130 B

120

A

A= A

B

B

B

B

A= A= A= A

B

B


110


B

45° acetabular abduction 50° acetabular abduction

Max. flexion:10°adduction 10°int. rotation [°]

Max. flexion: 0° rotation 0° abduction [°]


100 0

10

20

A

150

A= A

A= A B

B

B 140

B

130

B

B

B

B

120

B


110

40° acetabular abduction 45° acetabular abduction 50° acetabular abduction

100 0

30

10


20

30


B 35

B

A

A= A

B

A

B

30

A=A= A

B B

25

B B

20 30° acetabular abduction

B


15

45° acetabular abduction 50° acetabular abduction 10

Max. int. rotation: 90°flexion 10°adduction[°]

40

40

Max. int. rotation: 90°flexion 0°abduction [°]

A= A

35

B 30

B

A

A= A

B

B

A= A B

B

25

B B

B 20

B

30° acetabular abduction 40° acetabular abduction

15


B

50° acetabular abduction 10

0

10

20


30

0

10

20

30


Fig. 4: Diagrams of the joint motion area variation Using the 3D model the authors demonstrated that external rotation in neutral position of the femur decreases as acetabular cup anteversion and abduction increases. For anteversion of 0° and 10°, the maximum external rotation is the same for all positions of the acetabular cup, respectively 55.1° the impingement in this case taking place between the femur and the pelvis. The decrease of the motion area depending on acetabular orientation is not so significant, the biggest difference being of 9°. One can see on the diagram that the global influence obtained by anteversion modification is more significant. Acetabular abduction had little effect upon maximum external rotation. The joint flexion in 0° rotation and 0°femoral abduction increased as acetabular abduction and anteversion increased. When the acetabular cup was placed in 30° abduction and 0° anteversion, the model allowed the smallest flexion angle (107.4°), and the maximum value was obtained for 50° abduction, when a bone impingement was obtained.

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The same relationship between the acetabular anteversion/abduction and the maximum flexion angle was observed when the femur was positioned in 10°adduction and internally rotated 10°, in order to simulate the function of getting up from a lower seat [4,5]. In this case, the maximum flexion angle increases with more than 15° keeping the shape of the curves. One can observe that the maximum flexion increases from 133.1° (bone impingement), to 148.5° (prosthetic impingement). The increase of abduction and adduction of the acetabular cup, also leaded to an increase of the internal rotation angle, the maximum values (with bone impingement) being obtained for abduction greater then 40° and anteversion of 30°. Placing the femur in 10° adduction leads to a decrease of the previous obtained values for internal rotation, the maximum decrease being 4.8°. We can also observe the modification of impingement type from bone to prosthetic for the abduction of 40° and anteversion of 30°.


Joint motion area related to prosthesis component position in total HIP arthroplasty 4. Conclusions The 3D model of the right hip joint obtained from a CT scan of patient A.M., was utilized to study the relationship between the position of the acetabular cup and the femur motion area determined by the impingement between the elements of the assembly (bone and prosthetic elements). The models were obtained using the 3D DOCTOR commercial soft and then the contours exported in SolidWorks 2009, were the joint area simulation took place. For the simulation, a Fujitsu Siemens computer with Intel Core Duo 2,4GHz processor, 4GB RAM and NVIDIA QuadroFX570 video card was used. The research was made for 16 possible positions of the acetabular cup and five directions associated with hip dislocation, as mentioned in the method description paragraph [6]. Specific implant designs can be studied using this method, and an unlimited number of implant positions and joint motions can be examined using this method. The realised study has some imperfections regarding following matters: The simulation didn’t take in account the soft tissues from the hip joint which could influence the range of motion or the moment of impingement;

a. 30º abduction 0º anteversion

The study does not consider the reaction forces from the hip joint; The obtained results can be modified depending on the osteotomy technique which is associated to the patient specific anatomy The 3D model was obtained from a CT scan of a female patient and the modification of the gender or of the geographic area may modify the results. Data collected in this study showed that femoral joint range of motion in directions usually associated with implant dislocation varies considerably depending on the position of the acetabular cup. In general, flexion and internal rotation of the joint is increased when acetabular cup abduction and anteversion increased, the extreme limits of abduction and anteversion allowing the largest movements. An inverse relationship was detected for the internal rotation, which decreases especially when the acetabular anteversion increases, abduction modifications leading negligible changes. Information obtained by the simulation can be useful to the surgeon whom is useful to know the maximum motion area that can be obtained for a given patient and to select the position of prosthetic components leading to that area.

b. 30º abduction 30º anteversion

c. 45º abduction 10º anteversion

Fig. 5: Protrusion of the acetabular cup for different acetabular positions The surgeon’s goal is to maximize the motion area of in an impulsive or forgetful patient with memory deficiencies who can forget to limit the amplitude of movements to avoid a possible dislocation. Also, in a revision operation, when only the femoral stem is needed to be replaced, the surgeon may decide to replace also the acetabular cup (even if it is firmly set) if he finds that the range of motion is not satisfactory.

Following research carried out, the authors opines for the use of 45°-50° of adduction accompanied by 10°-20° of anteversion, the position providing a bigger range of motion and at the same time a good fill of the acetabular cavity, because for small abduction and large anteversion one can observe the protrusion of acetabular cup beyond the original enclosure (see fig. 5).


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Joint motion area related to prosthesis component position in total HIP arthroplasty 5. References [1] Cameron, H., U.,: Intraoperative alignment, instrumentation and surgical approaches, The technique of surgical approaches, Mosby Year Book, 1992. [2] Hedlundh, U., Hybbinette, C., Fredin, H.,: Influence of surgical approach on dislocations after Charnley hip arthroplasty, The Journal of Arthroplasty, Volume 10, Issue 5, Oct. 1995. [3] McCollum, D., E., Gray, W., J.,: Dislocation After Total Hip Arthroplasty, Journal of Clinical Orthopaedics & Related Research, 1990, Vol. 261.

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[4] Neumann, L., Freund, K., G., Sorensen, K.,: Total Hip Arthroplasty with the Charnley Prosthesis in Patients Fifty-five Years Old and Less. Fifteen to Twenty-one-Year Results, The Journal of Bone and Joint Surgery 78:73-9 (1996). [5] Ritter, M., A.,: A treatment Plane for the dislocated Total Hip Arthroplasty Journal of Clinical Orthopaedics & Related Research, 1980, Vol. 153. [6] Robinson, R., P., Simonian, P., T., Gradisar, I., M., Ching, R., P.,: Joint motion and surface contact area related to component position in total hip arthroplasty, The Journal of Bone And Joint Surgery, Vol. 79-B, No. 1, Ian. 1997.
