Keywords
patella - knee prosthesis - arthroplasty, replacement, knee
Introduction
Osteoarthrosis (OA) is the most common joint disease worldwide, affecting ∼ 10% of
men and 18% of women > 60 years old. It causes destruction of articular cartilage
and progressively leads to chronic pain and joint deformity.[1]
[2]
[3]
[4]
In the approach of the disease, after failure of conservative treatment, considering,
among other factors, the significant pain and loss of the quality of life of the patient;
TKA may be indicated as a therapeutic option. TKA is a surgery for the treatment of
advanced osteoarthrosis and has been increasingly used due to good results in pain
relief and re-establishment of function.[3]
[4]
[5]
[6]
[7]
Changes in patellar height after TKA may interfere with and cause clinical and functional
implications in patient outcomes. Thus, we consider it important to evaluate the variation
in patellar height in TKA surgery, which is the objective of our study.[8]
[9]
[10]
[11]
[12]
[13]
The indication of replacement of the articular surface of the patella during TKA is
controversial, and it is the option of the surgeon to use the patellar component or
not.[14]
There are studies that have not shown benefits in the use of the patellar component
in TKA.[15] There are also studies showing that the rate of reoperation due to patella complications
is higher when it is not replaced. Due to the controversial results, there is still
no consensus in the literature on this subject.[16]
[17]
Thus, we also tried to determine in the present study whether the replacement of the
patella can influence the change in its height in the postoperative period.
Material and Methods
The present study was evaluated and approved by the Brazil platform and the ethics
committee of the institution (CAAE: 39030220.0.0000.5128).
A retrospective evaluation was performed with 362 radiographs of 325 patients submitted
to primary TKA, from the electronic medical records of the hospital network of our
institution, of patients undergoing TKA in the period from 2014 to 2020, by 2 surgeons
of the service. The inclusion criteria considered were: patients with primary arthrosis,
without previous open surgical procedures that could interfere with patellar height,
with good radiological documentation before and after surgery (profile with flexion
between 20 and 80°, as described in the original article by Caton et al.).[13] The exclusion criteria were patients whose pre- or postoperative radiographs were
not found in the records, patients submitted to TKA for secondary arthrosis, patients
whose radiographs were considered inadequate to perform the correct technique of patellar
height measurement, previous lesions in the knees that led to alteration of patellar
height, revision prostheses, and complications in the immediate postoperative period
that could interfere with the usual rehabilitation.
Profile radiographs were evaluated using the modified Caton-Deschamps patellar height
index.[13] After proper selection of our sample, pre- and postoperative radiographs of 100
knees submitted to TKA were evaluated in 90 patients, who were divided into 2 groups,
considering the use or not of the patellar component.
The surgical technique and access route used were similar in all patients, the only
variable being the option of replacing the patella or not.
The Caton-Deschamps index modified for TKA is used to evaluate patellar height by
analyzing radiography in a strict knee profile ([Fig. 1]). We chose this method because of its ease of execution before and after TKA, using
anatomical landmarks that will not be altered by surgery. This allows the comparison
of patellar height with better accuracy and reproducibility. It uses one line in the
projection of the posterior cortical of the tibia and another line perpendicular to
the first, projected at the height of the head of the fibula. Thus, the distance between
the point of this line that touches the anterior cortical of the tibia to the lowest
point of the articular surface of the patella (TA line) is measured. Later, this value
is divided by the size of the articular surface of the patella (AP line). It is noteworthy
that this method is used only to compare the pre with the postoperative period of
TKA, without setting a low or high patella limit.[13] When the line (blue in [Fig. 1]) is drawn in the projection of the posterior cortical of the tibia and the other
line perpendicular to the first, projected at the height of the fibula head, it is
possible to measure the distance between the point of this line that touches the anterior
cortical of the tibia to the lowest point of the articular surface of the patella
(t-line) in green in [Fig. 1]. Later, this value is divided by the size of the patella joint surface (AP line)
in yellow in [Fig. 1].
Fig. 1 Modified Caton-Deschamps index to define the variation of patellar height in the
postoperative period of knee arthroplasty. Description in the text.
We performed the measurement up to 20 days postoperatively so as not to induce a variation
in height that may occur with a longer time elapsed from surgery.
The preoperative index result was compared with the postoperative period to evaluate
whether there was a change in patellar height in all knees. Then, a comparison of
height variation was performed in both groups, with and without patellar replacement.
Results
The sample of the tests consisted of 90 patients, with a total of100 knees submitted
to TKA surgery. The majority was female (n= 59; 65.3%); 52 of the TKAs were performed (52%) in the right knee, 38 (38%) in the
left knee, and 10 (10%) in both knees, with a mean age of 68.8 (±7.2) years old; the
minimum age was 44 years old and the maximum was 85 years old ([Table 1]).
Table 1
|
Variables
|
n
|
%
|
|
Age (mean ± SD)
|
68.8 ± 7.2
|
|
Gender
|
|
|
|
Male
|
31
|
34.4
|
|
Female
|
59
|
65.3
|
|
Operated knee
|
|
|
|
Right
|
52
|
52.0
|
|
Left
|
38
|
38.0
|
|
Both
|
10
|
10.0
|
|
Type of surgery
|
|
|
|
No patella
|
54
|
54.0
|
|
With patella
|
46
|
46.0
|
The result of the Caton-Deschamps index modified for TKA, before and after surgery,
is found in [Table 2]. The statistical analysis of the pre- and postoperative moments for comparations
for the total sample showed that there was a statistically significant difference;
the preoperative index was superior to that of the postoperative period, evidencing
a mean lowering of patellar height. The mean preoperative index was 1.41 (± 0.25,)
and the mean postoperative index was 1.31 (±0.25), p < 0.001.
Table 2
|
Variable
|
n
|
Pre
|
Post
|
Average of differences
|
95%CI
|
p-value
|
|
|
CDM index: mean (±SD)
|
|
|
|
CDM index
|
100
|
1.41 (±0.25)
|
1.31 (±0.25)
|
0.1
|
0.05–0.15
|
< 0.001
[*]
|
|
Group
|
|
|
|
|
|
|
|
No patella
|
54
|
1.52 (±0.22)
|
1.40 (±0.24)
|
0.12
|
0.05–0.18
|
< 0.001
[*]
|
|
With patella
|
46
|
1.28 (±0.21)
|
1.20 (±0.21)
|
0.08
|
0.01–0.15
|
0.023
[*]
|
|
Average difference
|
|
0.24
|
0.2
|
|
|
|
|
95%CI
|
|
0.15–0.32
|
0.11–0.29
|
|
|
|
|
p-value
|
|
< 0.001
[**]
|
< 0.001
[**]
|
|
|
|
In the analysis, comparing the indexes of the groups with and without patella replacement,
no statistically significant difference was observed. For the group without replacement,
the Caton-Deschamps index modified for mean TKA was 1.52 (±0.22) in the preoperative
moment, and 1.40 (± 0.24) in the postoperative check, p < 0.001. For the group with patellar replacement, the Caton-Deschamps index modified
for mean TKA was 1.28 (±0.21) in the preoperative and 1.20 (±0.21) in the postoperative
moment, p = 0.023 ([Table 2]).
The groups (with and without patella) are homogeneous in terms of gender (p = 0.815) and age (p = 0.682) ([Tables 3] and [4]). No statistically significant difference was found in the Caton-Deschamps index
modified for TKA before and after surgery in relation to the group with and without
patellar replacement, p = 0.510. The mean difference of the Caton-Deschamps index modified for TKA in the
group without patellar replacement was 0.11 and it was 0.08 in the group with patellar
replacement, with no significant difference. ([Table 5]).
Table 3
|
Type of surgery
|
n
|
Mean
|
Standard deviation
|
Standard error of mean
|
|
Age
|
Without patella
|
54
|
68.5556
|
8.00864
|
1.08984
|
|
With patella
|
46
|
69.1522
|
6.21814
|
.91681
|
Table 4
|
Type of surgery
|
Total
|
|
Without patella
|
With patella
|
|
Gender
|
Female
|
n
|
34
|
30
|
64
|
|
%
|
63.0%
|
65.2%
|
64.0%
|
|
Male
|
n
|
20
|
16
|
36
|
|
%
|
37.0%
|
34.8%
|
36.0%
|
|
Total
|
n
|
54
|
46
|
100
|
|
%
|
100.0%
|
100.0%
|
100.0%
|
Table 5
|
CDM index
|
n
|
Average
|
Standard deviation
|
Average difference
|
95%CI
|
p-value
[*]
|
|
Difference from post to pre
|
Without patella
|
54
|
0.11
|
0.24
|
0.03
|
−0.13
|
0.06
|
0.510
|
|
With patella
|
46
|
0.08
|
0.24
|
|
Discussion
The variation in patellar height after TKA has been discussed in the literature for
its possibility of influencing the clinical and functional results of this procedure.
The option of replacing or not the articular surface of the patella is also a frequent
discussion.[14]
[15]
[16]
[17]
Cabral et al.[12] evaluated 203 post-TKA knees, comparing different methods of patellar height and
found good reproducibility between the Insall-Salvati, the Blackburne-peel and the
Caton-Deschamps methods. Moreover, despite stating that patellar height tends to decrease
postoperatively, they did not find a significant difference in the methods studied,
and the median patellar heights were normal. This result differs from that found in
our study, which found a significant difference between pre- and postoperative height,[12]
p < 0.001.
Jawhar et al.[8] evaluated 107 knees after TKA in a period of 1 week and 1 year postoperatively,
finding a variation of > 10% of patellar height in a significant number of patients.
These results are in line with ours.
Meneghini et al.[11] evaluated the patellar height of 1,055 primary arthroplasties using the Insall-Salvati
index. They also found a significant reduction in patellar height in 50% of the cases
and found low patella (< 0.8) in 9.8% of knees. The reduction in height was associated
with worsening of functional scores.
Prudhon et al.[10] also demonstrated that in 80% of post-TKA patients there is a lowering of patellar
height; however, the lowering was < 15% and did not impact functional results or range
of motion (ROM) IKS, which differs from the findings of Meneghini et al.[11]
Bugelli et al.[18] evaluated the following parameters in 208 knees of 158 patients after TKA: patellar
height, functional scores, visual anterior pain scale and ROM. They found an elevation
of the articular interline, with the patella distally diverted in relation to the
trochlea, which was termed as pseudo low patella in 55 cases (26.4%). When there is
a real shortening of the patellar tendon, it was considered as true low patella. These
authors concluded that this (pseudo low patella) is a relatively common complication,
but it did not influence functional scores, visual pain scale or range of motion between
groups.
Aguirre-Pastor et al.[19] evaluated 354 post-TKA patients. Postoperatively, 286 (80.7%) patients had normal
height, 17 (4.8%) had true low patella, and 51 (14.4%) had pseudo low patella. There
was no difference in functional scores between the normal group and the low pseudo
patella. However, the true low patella group had significantly worse scores. They
concluded that true low patella, although less frequent, can lead to worse results.
We did not find in the literature similar articles that compare the variation of patellar
height after TKA between groups of patients who replaced and did not replace the patella,
which was the objective of our study. Our finding that there was no significant variation
in the height regardless of patella replacement is interesting in the sense of giving
the surgeon freedom to choose the technique he prefers.
A limitation of the present study was that we did not make an analysis comparing the
relationship of patellar height with the satisfaction index or functional scores of
patients, which may be the subject of a future study.
Conclusion
The present study showed that TKA surgery leads to a decrease in patellar height in
the postoperative period. Replacing or not the patella in patients undergoing TKA
did not result in significant variation in patellar height.
