This document presents a new method for assessing patellar height before and after total knee arthroplasty (TKA). Previous methods of measurement were inaccurate. The new Caton-Deschamps index measures the ratio of the articular surface to a tibial reference point, eliminating errors from abnormalities. Testing showed good intra- and inter-observer reliability. Results found the patella was lower after TKA in most cases due to femoral and tibial cuts. Moderate lowering did not affect function, but higher positioning or major lowering required further study to understand functional consequences. The new index allows detecting true versus pseudo patella infera to better understand TKA outcomes.

1. Patellar height
assessment in TKA:
a new method.
How does the vertical patella position
influence the TKA outcome?
Jacques Caton
Jean louis Prudhon
Régis Verdier
Lyon - France

2. INTRODUCTION
Joint reaction forces in flexion
between groove and patella are
modified by patellar height.
“Patella is the engine break of the
knee” J. Caton
Downstairs load bearing is equal to 5
times the body weight
Knee flexion pain?

3. Background
• Assessment of the patellar height is very
important before and after a total knee
arthroplasty (TKA)
Figgie HE, 3rd, Goldberg VM, Heiple KG, Moller HS, 3rd, Gordon NH. The influence of tibial-
patellofemoral location on function of the knee in patients with the posterior stabilized condylar
knee prosthesis. J Bone Joint Surg Am. 1986;68(7):1035-40.
Koshino T, Ejima M, Okamoto R, Morii T. Gradual low riding of the patella during postoperative
course after total knee arthroplasty in osteoarthritis and rheumatoid arthritis. J Arthroplasty.
1990;5(4):323-7.
Grelsamer RP. (2002) Patella baja after total knee arthroplasty: is it really patella baja? J
Arthroplasty 17: 66-9

4. Blumensaat
(1938)
Bernageau,
Goutallier
(1984)
Labelle, Laurin
(1977)
Biedert,
Albrecht (2006)
Femoral reference
Patella height measurement methods

5. Tibial reference
Insall, Salvati
(1971)
Caton,
Deschamps
(1981)
Blackburne,
Peel (1977)
Grelsamer
(1994) (Insall-
Salvati modifié)
Patella height measurement methods

6. Mixt Femoral Groove and Tibial Marks :
Koschino – Sugimoto
for children only
Chareangholvanich - Narkbunnam
Picard – Saragaglia Leung – Wail
Patella height measurement methods

7. Origine of the Caton-Deschamps Index
Caton 1st time (1977) Blackburne & Peel (1977) Caton & Deschamps 1981
César

8. Insall & Salvati, 1971?
Blackburne and Peel, 1977
Why Insall&Salvati and Blackburne&Peel index have not a precise
accuracy?

9. 3 Major Points of our Method :
1. Articular surface measurement
(AP) eliminates patellar
abnormalities (Patella Magna,
Osteophytes etc...)
2. (AT) T mark eliminates tibial or
tibial tuberosity abnormalities
3. Ratio AT/AP eliminates
problems range of motion
(flexion degrees, 10 to 80°)
Caton-Deschamps index

10. • For TKA patella height measurement is
difficult and no previous described methods
were perfect.
• And even if original Caton&Deschamps index
is one of the most used in TKA, this index is
not very accuracy: why?

11. Caton-Deschamps index and TKA (2007)
• Original CD
index (AT/AP)
• Modified index
AT’/AP
(J. Caton)
T’

12. (a) Preoperative CD and mCD index
(b) Postoperative mCD index
Postero-stabiilzed TKA New Wave (groupe lépine - France)
a b

14. • Patella vertical
height before
and after TKA
• 2007 Hermès PS

15. Validation of the measurement method
– 30 consecutive TKA implanted from
april 2014 to april 2015
– New Wave postero stabilized rotating
cementless THA (groupe lépine TM)
– 3 different observers :
• on each knee, each observer performed
twice with a minimal interval of 3 weeks
• Five measurements to calculate 3 index
(preoperative CD and mCD pre and post
opérative)
• Overall, 900 values were measured

16. Statistical analysis
– Data collected on Excel®
– According to :
• Shrout, PE and Fleiss, FL (Psychol Bull 1979)
• Langlois, J and Hamadouche, M. (BJJ 2016)
Repeatibility intra-observer Intraclass correlation and
reproducibility-Inter-observer intraclass correlation coefficient :
Good and very-good results if 0.6< ICC< 0.8

17. Results
CD
Preoperative
mCD
Postoperative
mCD
JC
ICC 0.59 0.57 0.63
95%CI [0.30-0.78] [0.27-0.77] [0.32-0.81]
JLP
ICC 0.67 0.60 0.75
95%CI [0.41-0.82] [0.31-0.79] [0.54-0.87]
RV
ICC 0.69 0.58 0.68
95%CI [0.44-0.84] [0.28-0.78] [0.43-0.84]
Repeatability -
Intra-observer
Intraclass
Correlation
Coefficient of CD
and mCD patellar
height index
CD
Preoperative
mCD
Postoperative
mCD
ICC 0.64 0.72 0.68
95%CI [0.42-0.80] [0.56-0.84] [0.43-0.83]
Reproducibility -
Inter-observer
Intraclass
Correlation
Coefficient of CD
and mCD patellar
height index

18. Results
Preoperative and postoperative mCD Index
Globally the height of patella is lower after TKA ( 80 %)
Mean difference between pre and postoperative mCD was 0.19 (12.2%)

19. • For TKA 3 measurements of patella height are
necessary
• In case of TKA only, it is very important to know
the patella position before TKA by original
Caton&Deschamps (oCD) index to detect more
reliably a true patella infera which can cause
approaches difficulties
• The new modified index (mCD) is a relative
assessment to compare patella height before TKA
and after TKA: Is vertical patella position be
modified by TKA? What are consequences?

20. 67 y.o. female
Severe overweight
Charnley C
Function score 25
Knee score 8
ROM 0/120

22. How does the vertical
patella position influence
the TKA outcome?

23. Material method
– 60 consecutive TKA implanted
from april 2014 to april 2015
– New Wave postero stabilized
rotating cementless THA
(groupe lépine TM)
– One senior surgeon

24. Material method
– Patella replacement in all cases
– Domical shape
– full Poly Cemented component
– Data collected on file maker Pro
– Modified Caton-Deschamps
index: 4 evaluators (validated
method by intra and inter-
obervers Intraclass correlation
coefficient)

25. 29 females, 31 males
Age: 70.5 (53-86)
Status
Aetiology
Surgical approach 0 5 10 15 20 25 30
Medial OA
lateral OA
Tri comp OA
Ligament injury
post traumatic
Rhumatoid A
PF OA
Tibial osteotomy
TT transfer
other
72%
21%
2%
5%
Antero medial
antero lateral
partial ATT osteotomy
ATT osteotomy
0
5
10
15
20
25
normal mild
obesity
severe
obesity
morbid
obesity
Material method

26. – IKS Score: (knee
+function) pre
and post op
– ROM: pre and
post op
– Original Caton
Deschamps
index pre op
– Modified Caton
Index: pre and
post op
Material method

28. results
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
AxisTitle
modified Index pre op vs post op
Pre op mean modified index : 1.32
Post op mean modified index: 1.13
Globally the height of patella is lower after TKA 14.39% in
81.66 % cases

29. results
Modified patellar height and knee function
Group 1 : major patella lowering more than 0,19 20 cases
Group 2 : medium patella lowering from 0 to 0,19 29 cases
Group 3 : normal or rising higher than 0 11 cases
group 1 group 2 group 3 p value
n = 20 29 11
IKS knee 93.4 92.7 92.00 0.91
IKS function 86.5 89 89 0.80
Lag of
extension
0.44 0.1 1.36 0.03
Max. flexion 128.5 128.4 127.3

30. 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
AxisTitle
«right in the target »
Focus on some results…

31. AP 1.9
AT° 2.1
Index modifié 1.1
AP 2.2
AT° 2.4
INDEX 1.1
Pre op
IKS knee 15
IKS
function
20
ROM 0/120
Post op
IKS knee 82
IKS function 75
ROM 3/120

32. 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
AxisTitle
« poor shot »
Focus on some results…

33. AP 1.9
AT° 3.2
Index
modifié
1.7
AP 2.4
AT° 2.5
INDEX 1,05
Pre op
IKS knee 49
IKS function 60
ROM 0/120
Post op
IKS knee 60
IKS function 62
ROM 5/120

34. Discussion: further questions to
answer
• Patella infera or pseudo patella infera?
– Patella tendon shortening
– Proximal joint line elevation
• Incidence on knee function ?
Correlations between IKS, ROM and joint line
• How to prevent it ?
• Work is on process …

35. J Arthroplasty. 2002 Jan;17(1):66-9.
Patella baja after total knee arthroplasty: is it really patella baja?
Grelsamer RP.
Surg Technol Int. 2004;12:231-8.
Patella baja and total knee arthroplasty (TKA): etiology, diagnosis, and
management.
Chonko DJ, Lombardi AV Jr, Berend KR.
Knee Surg Sports Traumatol Arthrosc. 2015 Dec;23(12):3601-6. doi:
10.1007/s00167-014-3257-1. Epub 2014 Sep 2.
Prevention of pseudo-patella baja during total knee arthroplasty.
Seo JG, Moon YW, Kim SM, Park SH, Lee BH, Chang MJ1, Jo BC.
Discussion - References
International orthopaedics 2016 DOI 10.1007/s00264-016-3256-6
Patellar height assesment in total knee arthroplasty:a new method
Caton JH, Prudhon JL, Aslanian T, Verdier R

36. • True patella infera is detected most reliably by the original CATON-
DESCHAMPS (CD) (AT/AP) index before TKA, whereas a pseudo
patella infera can be detected only by the mCD index pre- and post-
TKA.
• These results could be also compared to functional results of the
TKA, with potential limitation of motion and potential pain in case of
true postoperative patella infera with extensor mechanism lesions.
• In case of pseudo patella infera with a normal length of the patellar
tendon, the problem is probably secondary to the femoral and tibial
cuts.
• Is it a mild raising of the joint line or a major raising with a significant
knee mechanic problem?
Discussion: further questions to
answer

37.  Is it a mild raising of the joint line or a major raising with a significant knee mechanic
problem?
 If lowering patella is moderate (<14%) we have not observed functional consequences
 If patella is higher after TKA, results are not so very good
 Need for future evaluations … Work in progress
Conclusion
Preoperative Postoperative

38. Thank you for your attention