- Email: [email protected]
Alignment of total knee arthroplasty: the relationship to radiolucency around the tibial component
Mpd.
Alignment of total knee arthroplasty: relationship to radiolucency around component LA. Harvey*,
M.P. Manningt,
S.A.C.
Sampath&
Eng.
Phys. Vol.
17, No. 3. pp. 182-187. 1995 Elsevier Science Ltd for BES Printed in Great Britain 1350-4533/95 $10.00 + 0.00
the the tibial
R. Johnson§
and M.A. Ellofl
* Walton Hospital, Rice Lane, Liverpool 9, UK; t Whiston Hospital, Whiston, Nr. Prescot, Lanes, UK , +’ Dept. of Orthopaedic Surgery, Liverpool University, UK; §The Knee Research Unit, The Wirral Knee Centre, BUPA Murrayfield Hospital, Holmwood Drive, Wirral, Merseyside, L61 lAU, UK, 1 Department of Mechanical Engineering, Liverpool University, UK Received
April
1993, accepted
October
1993
ABSTRACT Between January 1982 and July 1985, 122 cemented ‘Accord’ total knee replacements were performed. number, 21 were lost to follow-up because of death (in 16), revision (2) due to infection, and failure to The post-operative alignment of 101 prostheses were compared to the incidence of radiolucencies around component at 5 years follow-up. The mechanical axis was used as a reference. The mean alignment valgus with a standard deviation of 2.48”. Some 72% of knees were within P and 94% within alignment. Using two methods of assessing radiolucencies there was a non-signaficant relationship between ment and radiolucencies. The alignment tolerance with this prosthesis is, therefme, at least 5”.
Keywords:
Total knee replacement,
alignment,
Med. Eng. Phys., 1995, Vol. 17, 182-187,
tibia1 loosening
April
INTRODUCTION
The accuracy of alignment of a total knee arthroplasty is an important factor in its likely success or failure. Jeffrey et aL7 reported that an error of alignment of more than 3” from the mechanical axis significantly increased the incidence of loosening the ‘Denham’ knee replacement. However, Smith et aZ.‘O, reporting a series of ‘Insall-Burnstein’ knee arthroplasties, were unable to confirm the importance of alignment in the long-term survival of the prosthesis. Elloy et nZ.’ reported the results of alignment in a series of 101 ‘Accord’ arthroplasties. Alignment of this prosthesis was achieved by making the femoral and tibia1 bone cuts over long, 6 mm diameter, intramedullary rods and inserting the prosthesis over these same rods. A 7” tibio-femoral valgus angle was imposed upon all cases. The mean alignment was 0.67” of valgus from the mechanical axis (standard deviation 2.47”) with 73% of cases falling within 3” of the mechanical axis and 98% within 5”. Using the same technique, we have reviewed 122 cases with cemented Correspondence and reprint requests to: Mr R. Johnson, Knee Research Unit, where the work was carried out. 0 Crown copyright (1995).
Out of this attend (3). the tibial was 0.99 5” of true the align-
at The
tibia1 components with a minimum follow up of 5 years, to establish whether errors of alignment have a significant effect on the rate of radiological loosening of the prosthesis and, if possible, to determine acceptable tolerances. MATERIAL23
AND METHODS
A total of 122 consecutive ‘Accord’ (JohnsonElloy) total knee replacements (DePuy lnt. Warsaw) in 101 patients were performed between January 1982 and July 1985. Some 21 knees have been lost to follow up by virtue of death (16)) revision (2 infections) and failure to attend (3). Therefore 101 knees in 81 patients were available for review. The mean age was 64.5 years (range 38-83 years) and 69 of the patients were female and 12 were male. The diagnosis was osteoarthritis in 46 knees and rheumatoid arthritis in 55. Radiological assessment involved full length weight bearing, AP, lateral and skyline views on discharge from hospital. The AP, lateral and skyline views were repeated at six months and at annual follow-up. The X-rays were performed in the following manner. Both the lateral and AP radiographs were
taken with the knee in extension. The centre of the beam was directed at a point 2.5 cm below the apex of the patella, on a 43 X 18 cm cassette at a distance of 100 cm, to include the lower third of the femur and the upper third of the tibia. Long leg X-rays were taken with a long (105 X 35 cm) cassette holder with three (35 X 35 cm) films and screens. The patients stood on a wooden frame with arm supports and their back to the cassette. The legs were pos-
Apparent valgus Total error Em =
Figure
1
Apparent
valgus
total
error
itioned so that the patella faced directly forwards. In difficult cases, e.g. severe rheumatolds, the position of the knee was ignored. The cassettes were positioned so that the edges of adjacent films were in direct contact. After processing the X-rays, the three films were taped together on an X-ray viewing box, ensuring no errors were introduced due to malpositioning of the bones. The mechanical axis is used as the reference and the results reported in degrees of devi-
Et + Ef
E,,,, = Et + Z$
183
A/P
LATERAL
Some 10 zones, 5 AP and 5 lateral around the tibia1 component (fig~e 2) were observed for radiolucent lines on the 5 year post-operative Xrays. Assessment of radiolucencies was by two methods. Firstly, they were divided into four groups based on th e thickness of the radiolucent lines. These were: no radiolucency, O-1 mm, l2 mm and greater than 2 mm thickness. The second method used was the Knee Society Roentgenographic Evaluation System” with score groups of 0, 1-4, 5-9 and 10 or greater. Statistical comparisons between the various subsets of alignment data were performed using the Mann Whitney U test. A value of the two-tailed PC 0.05 was considered to indicate a significant difference. RESULTS
Figure
‘2
Ten zones
around
tibia1 component
ation from this axis, a positive sign indicating valgus and a negative varus. The mechanical axis was drawn on the X-ray ([email protected] I). A line (HA) was drawn from the centre of the head of the femur to the centre of the ankle, the centre of the head of the femur being determined by the use of concentric rings. The angle of alignment was measured as follows: (1) A line (HK) was drawn on the X-ray from the centre of the head of the femur to the centre of the prosthesis. (2) A line (KA) was drawn on the Xray from the centre of the ankle, i.e. bisecting the talus, to the centre of the prosthesis. 13) The centre of the prosthesis was the intersection of the tibia1 stem axis and a line joining the flat femoral condyles. The angle of error is the summation of the errors at the ankle (&) and at the hip (4) as meason E;igLlre 1. The measured error ured & = & + 4.. In a perfectly aligned knee this angle should be 0”. If there is Rexion or hyperextension combined with rotation of the knee in relation to the X-ray beam, an apparent valgus or varus deformity is produced. Internal rotation produces a valgus deformity and external rotation a varus deformity; this artefact is sLlperimposed on any actual valgus or varus misalignment. radiological Correcting for these apparent deformities depends on measuring, on the long leg X-rays, the angles of misalignment at the hip and ankle (4. and &). The total measured alignment error on the X-ray (I;,,, = Ef + &). If the rotation and flexion of the prosthesis produced by radiological misalignment is subtracted from, or added to this, then the true misalignment can be calculated. The calculations for correction of these radiological misalignments have been described by Etloy et al:’
184
At the 5 year follow-up 67 knees, 32 rheumatoid and 35 osteo-arthritic, had no radiolucent lines in any zone. Some 14 knees, 8 rheumatoid and 6 osteoarthritic, had radiolucency of O-l mm thickness in 1 or more zones. Of these 14 cases, 9 had radiolucency in 1 zone alone and were otherwise well fixed. Only 1 patient had more than 5 zones affected. Some 19 knees, 14 rheumatoid and 5 osteoarthritic, had radiolucency l-2 mm thick. In 16 of the 19 cases, less than 5 zones were involved and in 3 cases a total of 8, 9 and 10 zones respectively were involved. Only 1 knee had radiolucency greater than 2 mm in all zones around the prosthesis. The analysis of the radiolucent lines in the 101 knees is presented in boozes f and 2. The mean alignment of all knees was 0.99” val us. Standard deviation 2.48”, with a maximum of $ * valgus, and 4.62” varus. This is consistent with the previously reported results*. The mean valgus for the rheumatoid knees was 1.57O, standard deviation 2.37”, and for the osteo-arthritic knees 0.32, standard deviation 2.54”. Some 72% of the knees were within 3” and 94% were within 5” of true alignment. For both rheumatoid and osteo-arthritic knees, alignment was compared with both the thickness of radiolucency (fig~es 3a, 36) and the Knee Society Scores (F&Wes 4a, 4b). Comparisons between the alignments of the four groups of patients with different thicknesses of radiolucency showed no significant differences P > 0.05. Similarly the alignment for the different Knee Society scores also showed no significant differences P > 0.05. The results show that accurate alignment is produced by using long 6 mm intramedullary rods. The incidence of radiolucencies around the tibia1 component is low and there is no significant relationship between radiolucencies and the alignment. DISCUSSION A number of authors have discussed ship between the alignment of total ments and the likelihood of failure. have, however, been contradictory. between papers are difficult because
the relationknee replaceThe results Comparisons of the num-
Lucency Width mm
Coronal Alignment of The Accord Knee rheumatoid Arthritis - 55 Knees Alignment a h
6
2
-- I.5
0
1.9
1 0.7
2 -4i
4.6 --
T -- 25
4
--
0.x
-L
2.3
-- 3.1 I 0
5 o-
1
O-2
I
2-t
LucencyWidth mm
ber of different arthroplasties used and because t.he technique of measuring the alignment has either been not stated”, assessed, climcally with a goniometer’ ‘, radiographically using short les films”.’ or radiographically using long leg films”‘-‘. Ecker ~1 01.” described a radiographical index of prosthesis positioning and found a correlation between positioning and the early clinical result. Insall’, whilst not presenting any data, predicted ~~nsatisfacto~ results if alignment was not within 5” of ‘the ideal’. Lewallen et aZ.“, in a 10 year review of 209 polycentric (Gunston) total knee arthroplasties, found that the failure rate doubled with valgus alignment of more than 8” or any varus misalignment of the anatomical axis. More a series of 115 recently, Jeffrey vt al.’ reporting Denham knee replacements, found that an error of alignment of more than approximately 3” from the mechanical axis produced a significant increase in the rate of loosening at a median follow-up of 8 years. However, Tew and Waugh’ ’ reported that half of their failures were in correctly aligned knees, but with a wide variation of between 2” varus and 12” valgus. Smith PE aL”’ reviewed 65 Insall-Burnstein arthroplasties with a
mean follow-up of approxinlately 4 years and found no relationship between alignment and progressive radiolucent lines. The results in this paper show a mean accuracy of 1” of valgus and a standard deviation of 2.48”. Some 72% of the knees were within 3” and 94% were within 5” of the mechanical axis. It is arguable that the low incidence of radiolucencies indicate that, with this prosthesis the tolerance for the alignment is at least 5”. It may, however, be due in part to the design of the prosthesis which is aimed at reducing shear forces on the tibia1 fixation. Prosthetic design has been shown to have an important influence on torque transmission across the knee .joint”. Significant torsional force is applied to the knee during normal walking”. If there is any constraint to these torsional forces imposed by a prosthetic design they will be transmitted via the tibia1 component to the bone cement interface which will affect the fixation of the tibia1 component. When constrained prostheses such as the Denham are used, the alignment toierances are
185
The relationship
to radiolucenq
around
the tibia1 component:
Coronal
R. Johnson et al
Alignment of The Accord Osteoarthritis - 46 Knees
Knee
Alignment
Knee Society Score
Coronal Alignment of The Accord Knee Rheumatoid Arthritis - 55 Knees Alignment 8
1 6
6 4
3.1
2
--
--
1.5
1.7
--
1
1.6
lo.1
0
0.1 - 0.8
-2
I -4 I
-3.4
- 2.3
Score 0
Score 1 - 4
I
Score 5 - 9
I
Score 10 +
Knee Society Score Figure 4 RA knees
Table
1
(a) Coronal
Analysis
alignment
of thickness
in relation
of radiolucency
RA
Table
2
Analysis
of Knee
Society
in 101 knees
32 8 14 1
35 6 5 0
67 14 19 1
55
46
101
Society
score
Knee RA
scores in OA knees.
Thickness of Radiolucency OA Totals
Radiolucency
Nil O-l mm 1-2 mm 2+ mm
to Knee
scores in 101 knees
(b) Coronal
alignment
in relation
to Knee
Society
scores in
probably lower than with less constrained prostheses. The design of the Accord total knee replacement with its conical tibia allows for a largely unconstrained range of motion. The ability of the meniscus to rotate and sublux under the control of the soft tissues alone converts most of the forces on the tibia into compressive loads; the interposed bone cement being best able to withstand this type of force. The authors feel that accurate alignment is essential, but the design of the prosthesis in reducing torsional and shear forces on the fixation is also a most important factor in the long term survival of the prosthesis.
Society Radiolucency Scores OA Totals
REFERENCES 0
l-4 5-9
10+
186
32 13 7 3
35
0
67 21 10 3
55
46
101
8
3
1. Bargren JH, Blaha JD, Freeman MAR. Alignment in total knee arthroplasty. Clin Orth & Rel Res 1983; 173: 178-83. 2. Cameron HU, Hunter GA. Failure in total knee arthroplasty. mechanisms, revisions and results. Clin Orth L? Rel Res 1982; 170: 141-46. 3. Ecker ML, Lotke PA, Windsor RE & Cella JP. Long-term
4.
5.
6. 7.
8.
results after total condylar knee arthroplasty. C/in Otih U Rel Res 1987; 216: 151-S. Elloy MA, Manning MP, Johnson R. The accuracy of intramedullary alignment in total knee replacement. ,/ BioMed Erg 1992; 14: 363-70. Ewald FC. The Knee Society total knee arthroplast? Roentgenographic evaluation and scoring system. Clin Orth C3 Rel Kes 1989; 248: 9-12. Insall JN. Sqq~ o/the Knee. Churchill Livingstone 1984. Jeffrey RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. ,I BonPJoint Surg 1991: 73B: 709-14. Lewallen DG, Bryan KS, Peterson LFA. Polycentric total
9. 10. 11.
I <‘, -
knee arthroplasty. a ten year follow-up study. J Bone Joint surg 1984; 66-A: 1211-18. Morrison JB. Function of the knee joint in various activities. J BioMed l+gn,g 1969; 4: 573-8. Smith JL, Tulles HS, Davidson JP. Alignment of total knee arthroplasty. J Arthro~lnsty 1989: 4 (Suppl 55). Tew M, Wdugh W. Tibia-femoral alignment and the results of knee replacement. ,J BovrJoint Surg 1985; 67-B: 551-G. Werner F. Foster D. Murray DG. The influence of design on the transmission of torque across knee prostheses. J BoneJomt Surg 1978: 60-A: 343-H.
187
Alignment of total knee arthroplasty: relationship to radiolucency around component LA. Harvey*,
M.P. Manningt,
S.A.C.
Sampath&
Eng.
Phys. Vol.
17, No. 3. pp. 182-187. 1995 Elsevier Science Ltd for BES Printed in Great Britain 1350-4533/95 $10.00 + 0.00
the the tibial
R. Johnson§
and M.A. Ellofl
* Walton Hospital, Rice Lane, Liverpool 9, UK; t Whiston Hospital, Whiston, Nr. Prescot, Lanes, UK , +’ Dept. of Orthopaedic Surgery, Liverpool University, UK; §The Knee Research Unit, The Wirral Knee Centre, BUPA Murrayfield Hospital, Holmwood Drive, Wirral, Merseyside, L61 lAU, UK, 1 Department of Mechanical Engineering, Liverpool University, UK Received
April
1993, accepted
October
1993
ABSTRACT Between January 1982 and July 1985, 122 cemented ‘Accord’ total knee replacements were performed. number, 21 were lost to follow-up because of death (in 16), revision (2) due to infection, and failure to The post-operative alignment of 101 prostheses were compared to the incidence of radiolucencies around component at 5 years follow-up. The mechanical axis was used as a reference. The mean alignment valgus with a standard deviation of 2.48”. Some 72% of knees were within P and 94% within alignment. Using two methods of assessing radiolucencies there was a non-signaficant relationship between ment and radiolucencies. The alignment tolerance with this prosthesis is, therefme, at least 5”.
Keywords:
Total knee replacement,
alignment,
Med. Eng. Phys., 1995, Vol. 17, 182-187,
tibia1 loosening
April
INTRODUCTION
The accuracy of alignment of a total knee arthroplasty is an important factor in its likely success or failure. Jeffrey et aL7 reported that an error of alignment of more than 3” from the mechanical axis significantly increased the incidence of loosening the ‘Denham’ knee replacement. However, Smith et aZ.‘O, reporting a series of ‘Insall-Burnstein’ knee arthroplasties, were unable to confirm the importance of alignment in the long-term survival of the prosthesis. Elloy et nZ.’ reported the results of alignment in a series of 101 ‘Accord’ arthroplasties. Alignment of this prosthesis was achieved by making the femoral and tibia1 bone cuts over long, 6 mm diameter, intramedullary rods and inserting the prosthesis over these same rods. A 7” tibio-femoral valgus angle was imposed upon all cases. The mean alignment was 0.67” of valgus from the mechanical axis (standard deviation 2.47”) with 73% of cases falling within 3” of the mechanical axis and 98% within 5”. Using the same technique, we have reviewed 122 cases with cemented Correspondence and reprint requests to: Mr R. Johnson, Knee Research Unit, where the work was carried out. 0 Crown copyright (1995).
Out of this attend (3). the tibial was 0.99 5” of true the align-
at The
tibia1 components with a minimum follow up of 5 years, to establish whether errors of alignment have a significant effect on the rate of radiological loosening of the prosthesis and, if possible, to determine acceptable tolerances. MATERIAL23
AND METHODS
A total of 122 consecutive ‘Accord’ (JohnsonElloy) total knee replacements (DePuy lnt. Warsaw) in 101 patients were performed between January 1982 and July 1985. Some 21 knees have been lost to follow up by virtue of death (16)) revision (2 infections) and failure to attend (3). Therefore 101 knees in 81 patients were available for review. The mean age was 64.5 years (range 38-83 years) and 69 of the patients were female and 12 were male. The diagnosis was osteoarthritis in 46 knees and rheumatoid arthritis in 55. Radiological assessment involved full length weight bearing, AP, lateral and skyline views on discharge from hospital. The AP, lateral and skyline views were repeated at six months and at annual follow-up. The X-rays were performed in the following manner. Both the lateral and AP radiographs were
taken with the knee in extension. The centre of the beam was directed at a point 2.5 cm below the apex of the patella, on a 43 X 18 cm cassette at a distance of 100 cm, to include the lower third of the femur and the upper third of the tibia. Long leg X-rays were taken with a long (105 X 35 cm) cassette holder with three (35 X 35 cm) films and screens. The patients stood on a wooden frame with arm supports and their back to the cassette. The legs were pos-
Apparent valgus Total error Em =
Figure
1
Apparent
valgus
total
error
itioned so that the patella faced directly forwards. In difficult cases, e.g. severe rheumatolds, the position of the knee was ignored. The cassettes were positioned so that the edges of adjacent films were in direct contact. After processing the X-rays, the three films were taped together on an X-ray viewing box, ensuring no errors were introduced due to malpositioning of the bones. The mechanical axis is used as the reference and the results reported in degrees of devi-
Et + Ef
E,,,, = Et + Z$
183
A/P
LATERAL
Some 10 zones, 5 AP and 5 lateral around the tibia1 component (fig~e 2) were observed for radiolucent lines on the 5 year post-operative Xrays. Assessment of radiolucencies was by two methods. Firstly, they were divided into four groups based on th e thickness of the radiolucent lines. These were: no radiolucency, O-1 mm, l2 mm and greater than 2 mm thickness. The second method used was the Knee Society Roentgenographic Evaluation System” with score groups of 0, 1-4, 5-9 and 10 or greater. Statistical comparisons between the various subsets of alignment data were performed using the Mann Whitney U test. A value of the two-tailed PC 0.05 was considered to indicate a significant difference. RESULTS
Figure
‘2
Ten zones
around
tibia1 component
ation from this axis, a positive sign indicating valgus and a negative varus. The mechanical axis was drawn on the X-ray ([email protected] I). A line (HA) was drawn from the centre of the head of the femur to the centre of the ankle, the centre of the head of the femur being determined by the use of concentric rings. The angle of alignment was measured as follows: (1) A line (HK) was drawn on the X-ray from the centre of the head of the femur to the centre of the prosthesis. (2) A line (KA) was drawn on the Xray from the centre of the ankle, i.e. bisecting the talus, to the centre of the prosthesis. 13) The centre of the prosthesis was the intersection of the tibia1 stem axis and a line joining the flat femoral condyles. The angle of error is the summation of the errors at the ankle (&) and at the hip (4) as meason E;igLlre 1. The measured error ured & = & + 4.. In a perfectly aligned knee this angle should be 0”. If there is Rexion or hyperextension combined with rotation of the knee in relation to the X-ray beam, an apparent valgus or varus deformity is produced. Internal rotation produces a valgus deformity and external rotation a varus deformity; this artefact is sLlperimposed on any actual valgus or varus misalignment. radiological Correcting for these apparent deformities depends on measuring, on the long leg X-rays, the angles of misalignment at the hip and ankle (4. and &). The total measured alignment error on the X-ray (I;,,, = Ef + &). If the rotation and flexion of the prosthesis produced by radiological misalignment is subtracted from, or added to this, then the true misalignment can be calculated. The calculations for correction of these radiological misalignments have been described by Etloy et al:’
184
At the 5 year follow-up 67 knees, 32 rheumatoid and 35 osteo-arthritic, had no radiolucent lines in any zone. Some 14 knees, 8 rheumatoid and 6 osteoarthritic, had radiolucency of O-l mm thickness in 1 or more zones. Of these 14 cases, 9 had radiolucency in 1 zone alone and were otherwise well fixed. Only 1 patient had more than 5 zones affected. Some 19 knees, 14 rheumatoid and 5 osteoarthritic, had radiolucency l-2 mm thick. In 16 of the 19 cases, less than 5 zones were involved and in 3 cases a total of 8, 9 and 10 zones respectively were involved. Only 1 knee had radiolucency greater than 2 mm in all zones around the prosthesis. The analysis of the radiolucent lines in the 101 knees is presented in boozes f and 2. The mean alignment of all knees was 0.99” val us. Standard deviation 2.48”, with a maximum of $ * valgus, and 4.62” varus. This is consistent with the previously reported results*. The mean valgus for the rheumatoid knees was 1.57O, standard deviation 2.37”, and for the osteo-arthritic knees 0.32, standard deviation 2.54”. Some 72% of the knees were within 3” and 94% were within 5” of true alignment. For both rheumatoid and osteo-arthritic knees, alignment was compared with both the thickness of radiolucency (fig~es 3a, 36) and the Knee Society Scores (F&Wes 4a, 4b). Comparisons between the alignments of the four groups of patients with different thicknesses of radiolucency showed no significant differences P > 0.05. Similarly the alignment for the different Knee Society scores also showed no significant differences P > 0.05. The results show that accurate alignment is produced by using long 6 mm intramedullary rods. The incidence of radiolucencies around the tibia1 component is low and there is no significant relationship between radiolucencies and the alignment. DISCUSSION A number of authors have discussed ship between the alignment of total ments and the likelihood of failure. have, however, been contradictory. between papers are difficult because
the relationknee replaceThe results Comparisons of the num-
Lucency Width mm
Coronal Alignment of The Accord Knee rheumatoid Arthritis - 55 Knees Alignment a h
6
2
-- I.5
0
1.9
1 0.7
2 -4i
4.6 --
T -- 25
4
--
0.x
-L
2.3
-- 3.1 I 0
5 o-
1
O-2
I
2-t
LucencyWidth mm
ber of different arthroplasties used and because t.he technique of measuring the alignment has either been not stated”, assessed, climcally with a goniometer’ ‘, radiographically using short les films”.’ or radiographically using long leg films”‘-‘. Ecker ~1 01.” described a radiographical index of prosthesis positioning and found a correlation between positioning and the early clinical result. Insall’, whilst not presenting any data, predicted ~~nsatisfacto~ results if alignment was not within 5” of ‘the ideal’. Lewallen et aZ.“, in a 10 year review of 209 polycentric (Gunston) total knee arthroplasties, found that the failure rate doubled with valgus alignment of more than 8” or any varus misalignment of the anatomical axis. More a series of 115 recently, Jeffrey vt al.’ reporting Denham knee replacements, found that an error of alignment of more than approximately 3” from the mechanical axis produced a significant increase in the rate of loosening at a median follow-up of 8 years. However, Tew and Waugh’ ’ reported that half of their failures were in correctly aligned knees, but with a wide variation of between 2” varus and 12” valgus. Smith PE aL”’ reviewed 65 Insall-Burnstein arthroplasties with a
mean follow-up of approxinlately 4 years and found no relationship between alignment and progressive radiolucent lines. The results in this paper show a mean accuracy of 1” of valgus and a standard deviation of 2.48”. Some 72% of the knees were within 3” and 94% were within 5” of the mechanical axis. It is arguable that the low incidence of radiolucencies indicate that, with this prosthesis the tolerance for the alignment is at least 5”. It may, however, be due in part to the design of the prosthesis which is aimed at reducing shear forces on the tibia1 fixation. Prosthetic design has been shown to have an important influence on torque transmission across the knee .joint”. Significant torsional force is applied to the knee during normal walking”. If there is any constraint to these torsional forces imposed by a prosthetic design they will be transmitted via the tibia1 component to the bone cement interface which will affect the fixation of the tibia1 component. When constrained prostheses such as the Denham are used, the alignment toierances are
185
The relationship
to radiolucenq
around
the tibia1 component:
Coronal
R. Johnson et al
Alignment of The Accord Osteoarthritis - 46 Knees
Knee
Alignment
Knee Society Score
Coronal Alignment of The Accord Knee Rheumatoid Arthritis - 55 Knees Alignment 8
1 6
6 4
3.1
2
--
--
1.5
1.7
--
1
1.6
lo.1
0
0.1 - 0.8
-2
I -4 I
-3.4
- 2.3
Score 0
Score 1 - 4
I
Score 5 - 9
I
Score 10 +
Knee Society Score Figure 4 RA knees
Table
1
(a) Coronal
Analysis
alignment
of thickness
in relation
of radiolucency
RA
Table
2
Analysis
of Knee
Society
in 101 knees
32 8 14 1
35 6 5 0
67 14 19 1
55
46
101
Society
score
Knee RA
scores in OA knees.
Thickness of Radiolucency OA Totals
Radiolucency
Nil O-l mm 1-2 mm 2+ mm
to Knee
scores in 101 knees
(b) Coronal
alignment
in relation
to Knee
Society
scores in
probably lower than with less constrained prostheses. The design of the Accord total knee replacement with its conical tibia allows for a largely unconstrained range of motion. The ability of the meniscus to rotate and sublux under the control of the soft tissues alone converts most of the forces on the tibia into compressive loads; the interposed bone cement being best able to withstand this type of force. The authors feel that accurate alignment is essential, but the design of the prosthesis in reducing torsional and shear forces on the fixation is also a most important factor in the long term survival of the prosthesis.
Society Radiolucency Scores OA Totals
REFERENCES 0
l-4 5-9
10+
186
32 13 7 3
35
0
67 21 10 3
55
46
101
8
3
1. Bargren JH, Blaha JD, Freeman MAR. Alignment in total knee arthroplasty. Clin Orth & Rel Res 1983; 173: 178-83. 2. Cameron HU, Hunter GA. Failure in total knee arthroplasty. mechanisms, revisions and results. Clin Orth L? Rel Res 1982; 170: 141-46. 3. Ecker ML, Lotke PA, Windsor RE & Cella JP. Long-term
4.
5.
6. 7.
8.
results after total condylar knee arthroplasty. C/in Otih U Rel Res 1987; 216: 151-S. Elloy MA, Manning MP, Johnson R. The accuracy of intramedullary alignment in total knee replacement. ,/ BioMed Erg 1992; 14: 363-70. Ewald FC. The Knee Society total knee arthroplast? Roentgenographic evaluation and scoring system. Clin Orth C3 Rel Kes 1989; 248: 9-12. Insall JN. Sqq~ o/the Knee. Churchill Livingstone 1984. Jeffrey RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. ,I BonPJoint Surg 1991: 73B: 709-14. Lewallen DG, Bryan KS, Peterson LFA. Polycentric total
9. 10. 11.
I <‘, -
knee arthroplasty. a ten year follow-up study. J Bone Joint surg 1984; 66-A: 1211-18. Morrison JB. Function of the knee joint in various activities. J BioMed l+gn,g 1969; 4: 573-8. Smith JL, Tulles HS, Davidson JP. Alignment of total knee arthroplasty. J Arthro~lnsty 1989: 4 (Suppl 55). Tew M, Wdugh W. Tibia-femoral alignment and the results of knee replacement. ,J BovrJoint Surg 1985; 67-B: 551-G. Werner F. Foster D. Murray DG. The influence of design on the transmission of torque across knee prostheses. J BoneJomt Surg 1978: 60-A: 343-H.
187