Patellar Clunk Syndrome in a Current High Flexion Total Knee Design

The Journal of Arthroplasty 28 (2013) 1846–1850
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The Journal of Arthroplasty
journal homepage: www.arthroplastyjournal.org
Patellar Clunk Syndrome in a Current High Flexion Total Knee Design
Sanjay R. Agarwala, MS, Mch (Orth), Ganesh S. Mohrir, DNB (Orth), Aashish G. Patel, MS (Orth)
Department of Orthopedics, P.D.Hinduja National Hospital, Mahim (W), Mumbai, India
a r t i c l e
i n f o
Article history:
Received 1 August 2012
Accepted 21 March 2013
Keywords:
knee arthroplasty
patella clunk
high flexion
fibre-like
open arthrotomy
arthroscopy
a b s t r a c t
This retrospective study of 208 (204 patients) total knee arthroplasties evaluated the incidence of patellar
clunk syndrome for two high-flex posterior stabilized knee prostheses; a high-flex fixed bearing prosthesis
and a high-flex mobile bearing prosthesis. Patients were followed for up to two years and were evaluated for
patellar clunk and component position. Knees receiving the mobile bearing had a significantly higher
(p b 0.001) incidence of patellar clunk (15%) than knees receiving the fixed bearing (0%). There was a
significantly higher incidence of patellar clunk in males (34.1%; p b 0.01) compared to females (8.6%). Fibrous
nodules were treated surgically in 11 of the knees with patellar clunk. The design of this particular mobile
bearing knee seems to contribute to patellar clunk syndrome.
© 2013 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) patients from certain ethnicities
have a cultural need for a high degree of knee flexion. A number of
high-flexion knee prostheses are now available that theoretically
meet the requirement for a greater degree of knee flexion in these
patients. However, the presence of patellofemoral complications such
as patellar clunk is commonly reported for certain high-flexion
prostheses, particularly those that are cruciate substituting [1,2].
Patellar clunk occurs when a pannus like synovial mass is suddenly
released from its entrapment in the intercondylar box of the femoral
component during extension of the knee. It has historically been
thought that the synovial mass is formed either by impingement of
the patellar button on the quadriceps tendon if the patellar
component is located too far proximally, or by impingement of the
proximal aspect of the femoral component on the quadriceps tendon
if the patellar component is too small [3,4]. For this reason it is
recommended that the patellar component is placed distal to the
centre of the patella and that the largest patellar prosthesis that fits
without overlap is chosen. However, in the presence of good surgical
technique it is now thought that prosthesis design is the major factor
in causing patellar clunk syndrome [5].
Two high-flexion prostheses that offer design modifications to
minimise the occurrence of patellar clunk are the fixed bearing
NexGen Flex prosthesis (Zimmer, Warsaw, IN, USA) and the mobile
bearing P.F.C Sigma RP-F prosthesis (DePuy, Warsaw, IN, USA). To our
knowledge, this is the first study that compares these two implants
The Conflict of Interest statement associated with this article can be found at http://
dx.doi.org/10.1016/j.arth.2013.03.019.
Reprint requests: Sanjay Agarwala, MS, Mch (Ortho), Department of Orthopedics,
P.D. Hinduja National Hospital, Mahim (W), Mumbai-400016, India.
0883-5403/2810-0031$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.arth.2013.03.019
with regard to the incidence of patellar clunk syndrome in a
population with a need for greater flexion to enable cross-legged
sitting and squatting.
The study was initiated when a patient reported to follow-up with
a distressful click around the knee after Total Knee Arthroplasty.
Another patient with similar symptoms of clunk followed soon after.
We hypothesized that the incidence of patellar clunk syndrome was
more common in a high-flexion, rotating platform prosthesis as
opposed to a high-flexion, fixed bearing design.
Materials and Methods
Following approval of Institutional review board this retrospective
study was conducted. Between January 2006 and December 2007, a
total of 242 consecutive primary total knee arthroplasty were
performed in 238 patients. TKAs were performed with posterior
stabilised high flexion total knee prostheses by a single surgeon.
Sixteen patients with rheumatoid arthritis and 18 patients operated
with non high-flexion posterior stabilised designs were excluded.
Thus, 204 patients with 208 TKAs were identified in this retrospective
study. Two types of prostheses, namely the NexGen LPS-Flex (fixed
bearing) and P.F.C Sigma RP-F (mobile bearing), were used. The
prosthesis was chosen in consultation with the patient according to
the recommendations of the surgeon, based on the insurance and
financial considerations of the patient as there was a cost differential
between the implants. The retrospective review identified 105
patients with 107 P.F.C Sigma RP-F TKAs and 99 patients with 101
NexGen LPS-Flex TKAs that were suitable for analysis. Ethics approval
from the hospital Institutional Review Board was granted prior to
initiation of this retrospective study.
S.R. Agarwala et al. / The Journal of Arthroplasty 28 (2013) 1846–1850
All surgeries were performed using an anterior midline incision
and medial parapatellar approach following application of a tourniquet. Tibial resection was performed with 7 degrees of posterior slope
for the NexGen LPS-Flex design and 0 degree posterior slope for the
P.F.C Sigma RP-F, as described in the manufacturers’ instructions.
Anterior referencing was used for the femoral component sizing and 3
degrees of external rotation was applied in reference to the posterior
condyles. Ligament balancing was performed and range of movement
and patellar tracking was checked using the “no thumb test.” The
synovial plicae, patellar fat pad and synovium from the under surface
of the quadriceps tendon were excised carefully. When maltracking of
the patella was present, lateral retinacular release was performed
using the inside-out technique. This procedure was required in eight
patients (three in P.F.C Sigma RP-F group, five in the Nexgen LPS-Flex
group). All the patellae were resurfaced with an all-polyethylene
component and all components were fixed in situ with cement.
Patients were mobilised from the next day following surgery and
drains were removed after 48 hours.
Patients were followed for a maximum of two years from the time
of surgery. They were routinely assessed at 4 weeks, 12 weeks,
6 months, 1 year and 2 years. Presence of the patellar clunk syndrome
was clinically defined as a visible or audible clunk that may be painful
on extending the knee from 30–40 degrees of flexion [4]. The InsallSalvati ratio [6], the position of the proximal pole of the patella from
the joint line [7] and the relative anteroposterior position of tibial tray
[8] were measured on true lateral radiographs. Radiological assessment was performed on the institutional PACS system (Picture
archiving and communication system). Insall-Salvati ratio is the
ratio of patella tendon length to the length of patella. The mean
position of the proximal pole of the patella was measured with
reference to the distal end of femoral prosthesis/joint line. The relative
antero-posterior position of the tibial tray was the perpendicular
distance from the upper anterior corner of the tibial tray to the
patellar tendon. Standardized Merchant’s view of patella was not
available in all patients. This was done in cases diagnosed with
patellar clunk syndrome to rule out patellar component position as
one of the cause for clunk. Range of movement was also assessed at
each follow up. It was measured using goniometer on the lateral side
of the leg with the proximal arm placed from the lateral trochanter to
the lateral epicondyle and distal arm placed from lateral epicondyle to
the lateral malleolus.
The differences between the two treatment groups were
evaluated by independent t-tests for continuous variables. Continuous data which were not normally distributed were analyzed by
non-parametric ranking tests and proportional values were analyzed by a Pearson chi-square test or a Fischer’s exact test at low
response frequencies. A p-value of 0.05 was used to determine
statistical significance.
1847
Table 1
Patient Demographics and Findings.
Age (years ± SD)
Gender (F/M)
Affected side (L/R/Bilateral)
Mean Insall Salvati ratio ± SD
Mean tibial tray position ± SD
Mean proximal pole position ± SD
Range of Movements
P.F.C Sigma RP-F
NexGen LPS-Flex
63.2 ± 8.5
81/26
55/50/2
1.07 ± 0.06
4.8 ± 0.2
49.5 ± 1.4
125.7 ± 5.1
63.2 ± 8.8
82/19
58/41/2
1.06 ± 0.05
4.8 ± 0.2
49.6 ± 1.4
126 ± 5
L – left, R – right, SD – standard deviation.
detectable effect of age, range of movement, Insall Salvati Ratio, the
relative tibial tray position and the relative position of the proximal
pole of the patella. However, there was a significantly greater
incidence of patellar clunk syndrome in males (34.1%; p b 0.01)
compared to females (8.6%). The odds of developing patellar clunk
syndrome in male patients were five times higher than for female
patients, with risk four times higher than female patients. The average
time to onset of symptoms was nine months (range: 6 to 11 months).
Average patellar tilt angle in cases with patellar clunk was 3.65
(range 2.8–4.2).
All sixteen knees with patellar clunk syndrome were initially given
conservative management. Five knees responded and the remaining
11 knees were treated surgically. Arthrotomy was performed in five
knees (Fig. 1a, b) and arthroscopic resection was performed in six
knees (Fig. 2a, b). All knees had a fibrous nodular mass at the superior
pole of the patella. Five patients also had a nodule at the inferior pole.
Results
A total of 208 TKAs (101 in the NexGen LPS-Flex group and 107 in
the P.F.C Sigma RP-F group) were retrospectively analysed. Two
hundred patients had unilateral knee replacements and four patients
had bilateral knee replacements (Table 1).
The patient demographics, Insall Salvati ratio, position of the
proximal pole of the patella from the joint line and the relative
anteroposterior position of tibial tray, range of movements were
similar between the groups (Table 3). Patellar clunk syndrome was
diagnosed in 16 knees, all of which received the P.F.C Sigma RP-F
prosthesis. There were no cases of patellar clunk in the knees that
received the NexGen LPS-Flex prosthesis. The difference in the
incidence of patellar clunk between the groups was statistically
significant (p b 0.001).
When within group analysis of the incidence of patellar clunk
syndrome was performed for the P.F.C Sigma RP-F group, there was no
Fig. 1. (A) Knee arthrotomy showing presence of synovial mass over superior pole
of patella prior to mass resection. (B) Knee arthrotomy showing after resection of
synovial mass.
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Table 2
Femoral Component Features.
Design Features
Nexgen LPS Flex Zimmer
Box
dimension
Trochlear
angle
Posterior
condyle
Lateral flange
Same with all sizes
Increases with increase in size
PFC Sigma RPF Depuy
Same with all sizes
Increases with all sizes
Bone resection and size
remains same
Smooth
Bone resection and size increases
with size
Ridge is present
Discussion
Fig. 2. (A) Knee arthroscopy showing presence of synovial mass prior to arthroscopic
debridement. (B) Knee arthroscopy showing after debridement of the synovial mass.
After excision of the nodules, the transected synovium was cauterised.
In all cases, histopathology of the nodules found a foreign body giant
cell reaction and mild chronic granulomatous inflammation (Fig. 3).
Some of the giant cells contained polarisable, refractile ‘fibre-like’
foreign material within the cytoplasm. Complete relief of the patellar
clunk syndrome was achieved postoperatively. No recurrence of
patellar clunk was reported from the time of treatment to the final
follow-up. The average time between treatment of patellar clunk and
final follow-up was 12 months.
The reported aetiologies for patellar clunk syndrome include:
excessive surgical trauma, femoral component design, an excessively
high position of the patellar component causing impingement of the
patellar prosthesis against the quadriceps tendon, inadequate synovial tissue debridement at the junction of the quadriceps tendon and
the upper pole of the patella, abnormal patellar tilt, abnormal patellar
tracking, alteration in the joint line of 8 mm or less, and patellar
height from the joint line of 10–30 mm [4,6–13].
Our study supports the aetiology of implant design as patellar
clunk syndrome was only evident in the mobile bearing P.F.C Sigma
RP-F implant compared with no patellar clunk being evident in the
knees receiving the fixed bearing NexGen LPS-Flex implant. This is
consistent with other studies that have also reported no cases of
patellar clunk syndrome with the NexGen LPS [11,12,14]. Earlier
designs of posterior stabilised knee prostheses, such as the Insall
Burstein II (Zimmer, Warsaw, Indiana) and the AMK PS (DePuy)
were associated with a high incidence of patellar clunk syndrome
(3.9% to 13.5%) [8,11,15]. The NexGen Legacy knee (Zimmer,
Warsaw, IN, USA), is a fixed bearing knee replacement, with
modifications from the Insall-Burstein II knee such as a raised lateral
flange, a deepened trochlear groove, and a more posteriorly and
proximally positioned femoral cam that decreases the chance of soft
tissue entrapment on knee flexion and thus lessens the risk of
patellar clunk [11,12,16]. The incidence of patellar clunk syndrome
with the NexGen Legacy knee has been evaluated in a small study
with a short term follow up [12], and in a larger series of patients
[14]. In both studies there were no cases of patellar clunk syndrome
in the patients receiving the NexGen Legacy implant. The NexGen
Flex implant, which is an implant that is commonly used in our
practice, retains the features of the NexGen Legacy knee that are
believed to minimise patellar clunk and in addition has been
modified to allow greater knee flexion with a deepened and
extended patellar groove to reduce shear forces on the patella whilst
ensuring full patellofemoral contact during deep flexion.
The Rotating Platform High-Flex Knee (P.F.C Sigma RP-F; DePuy,
Warsaw, IN, USA), which is offered as an alternative to the NexGen
Flex implant in our practice, has also been developed with features
to improve patellar tracking; however, unlike the fixed bearing
prostheses, its mobile bearing mimics the natural movement of the
Table 3
Tibial Insert Features.
Fig. 3. Histological section demonstrating presence of foreign body giant cells
containing fibre-like foreign material (arrows).
Features
Nexgen LPS Flex Zimmer
Type of Polyethylene
Sterilization
Packaging
UHMWPE
Gamma irradiation
Packed in nitrogen
environment using
high oxygen barrier
materials
Remains same
Tibial Post Height &
width
PFC Sigma RP-F Depuy
UHMWPE
Gamma irradiation
Vacuum packaged in i
mpermeable foil pouch
under hydrostatic pressure
Increases with increase in size
UHMWPE – ultra high molecular weight polyethylene.
S.R. Agarwala et al. / The Journal of Arthroplasty 28 (2013) 1846–1850
knee which allows greater knee flexion. The patella component in
both designs is an all polyethylene with an asymmetrical oval dome
shape in RP-F and circular dome in LPS-Flex. The differentiating
design features between RP-F and LPS-Flex are mentioned in
Tables 2 and 3.
Both PFC Sigma PS and RP design known to have patellofemoral
complications with incidence around 12 to 13% [17,10]. Fukunaga et
al. [10], reported a high incidence of patellar clunk syndrome (13.3 %)
with the mobile-bearing posterior stabilised P.F.C Sigma RP knee
replacement (DePuy, Warsaw, IN, USA). However, modification of the
conventional P.F.C Sigma implant to include a deeper trochlear groove
and a smoother transition of the intercondylar box successfully
resolved the patellar clunk syndrome with no cases detected
compared with 12% in the conventional design [5]. Interestingly the
authors of this study claim that the design modifications do not
reduce the formation of the synovial mass, but rather better
accommodate such a mass once formed. Therefore, although the
knees receiving the NexGen LPS-Flex implant had no evidence of
patellar clunk, it is possible that, although not diagnosed) they also
had some degree of fibrous nodule formation. If this is the case then it
could be argued that the nodule was also accommodated better by the
design of the NexGen LPS-Flex implant.
This is first study to look for incidence of patellar clunk in PFC
Sigma RP-F design. Femoral component design or mobile bearing
insert may be responsible for patellar clunk. We feel posterior tibial
slope may not be the contributing factor for clunk as both designs
have different surgical techniques. Further in vivo kinematic studies
may be helpful to know the cause.
Certain features of our study such as mean time of occurrence of
patellar clunk, and the success of conservative and surgical
therapies are consistently reported in the literature. The sterilization method of polyethylene in both designs is with gamma
radiation. (Table 3) Aspects from our study that are not consistently
reported in the literature include a greater prevalence of males than
females with patellar clunk in the mobile bearing group and the
presence of foreign (refractile, fibre-like) material in the giant cells
of the synovial masses (Fig. 3). It is well accepted that polyethylene
wear particles elicit an inflammatory reaction which causes
osteolysis and eventual aseptic loosening of prostheses. There are
also some case reports, although few in number, which describe
extraosseous granulomatous reactions to polyethylene wear particles following knee replacement. Wang et al. [18], described a
foreign body type reaction in the synovial tissues surrounding a
failed tibial component after 10 years of implantation in an 85year-old male patient. The tibial insert was severely worn and
fractured and the patellar component also demonstrated wear of
the polyethylene surface. Polarised light microscopic examination of
the granuloma demonstrated the presence of birefringent extracellular polyethylene particulate material. Waite et al. [19], described
an inflammatory mass in the posterior thigh following knee
replacement which caused acute sciatic nerve palsy. In this patient
the TKA was well fixed, but again the tibial insert demonstrated
wear and delamination. The foreign body giant cell reaction present
in the fibrous nodules found in the patients from our study was
similar to the histopathological reaction described in these case
reports. This finding would indicate that aetiology for fibrous
nodule formation on the superior aspect of the patellar button is
polyethylene wear.
Hamilton et al. [20], reported a trend towards a higher incidence of
patellar clunk in patients with larger femoral components. Given that
males generally have a larger distal femur than females [21], it could
be expected that males also have a higher incidence of patellar clunk,
as was found in this study; however, as no anthropometric
measurements of the knee were made in this study, accurate
conclusions on the relationship between gender, femoral component
size and patellar clunk cannot be made.
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A limitation of this study was that the patients were not
randomised to each treatment group. However, given the fortuitous
similarity in patient demographics, Insall-Salvati ratio, position of the
tibial tray and the proximal pole of the patella, it is unlikely that this
had a significant effect on the findings of this study. This study may
have been strengthened with the use of functional MRI or CT for
precise measurement of femoral and tibial component rotation, and
for better determination of the process of fibrous nodule formation
and therefore the etiology of the patellar clunk syndrome in affected
patients. Strength of this study was the consistency in the surgical
technique that could be achieved in both groups due to the
involvement of only one surgeon. Both designs have been developed
based on general morphology of North American patients which may
or may not vary from Asian population. Further studies needs to be
done to establish design related problems in different races.
In conclusion, prosthesis design has an important role in the
incidence of patellar clunk syndrome. We were not able to detect any
patellar clunk complications in this study with the NexGen LPS-Flex
prosthesis indicating that the modifications to allow greater knee
flexion with this device do not have a detrimental effect on
patellofemoral complication rate. On the other-hand, despite modifications to reduce the incidence of patellofemoral complications with
the P.F.C Sigma RP-F prosthesis, there appears to remain a patellofemoral complication rate that is higher than the reported rates from
the early IB type prostheses but similar to other reports studying this
device. A redesign reported recently may assist in alleviating these
complications with this implant [5].
Acknowledgments
The authors wish to thank Alexandra Pearce for assistance with
manuscript preparation.
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