Knee joint anterior malalignment and patellofemoral
osteoarthritis: an MRI study
Poster No.:
C-0369
Congress:
ECR 2011
Type:
Scientific Paper
Authors:
N. Tsavalas, E. Vassalou, A. Ntailiani, A. H. H. Karantanas;
Heraklion/GR
Keywords:
Musculoskeletal system, Musculoskeletal joint, MR
DOI:
10.1594/ecr2011/C-0369
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Purpose
1.The anatomic configuration and congruent relationship of the patella and trochlear
groove are considered the biomechanical basis of the normal function of the
patellofemoral joint (PFJ), i.e. knee flexion and extension [1].
2.Developmental or acquired alterations in the anatomy and congruence of the PFJ
may lead to abnormal distribution of patellofemoral stress and predispose patients to
developing PFJ cartilage lesions and subsequent osteoarthritis (OA) [2,3].
3.Knee joint anterior malalignment, also known as patellofemoral malalignment (PFM),
may induce excessive stress on the articular surfaces of the PFJ, and therefore could
potentially lead to aberrant mechanical forces and osteoarthritic changes in the knee [4].
In order to clarify the precise relationship of PFM with PFJ OA we evaluated various
patellofemoral congruency measurements on MRI, correlating the findings with severity
of osteoarthritic manifestations, while adjusting for age, sex and body fat content. We
assumed that increasing PFM would be associated with deteriorating osteoarthritic
lesions (cartilage defects, osteophytes and bone marrow lesions) of the PFJ.
Methods and Materials
PATIENTS
1.We retrospectively reviewed 650 consecutive knee MRI examinations from a total
number of 622 patients referred to our MR department, due to various knee related clinical
conditions, between November 2007 and June 2010.
2.Infants, toddlers and patients with suprapatellar joint recess effusion or a history of
arthroscopic surgery, knee trauma, knee joint tumor or rheumatic arthritis were excluded
from the study. A total of 540 knee MRI examinations from 516 patients were eventually
included in our study.
3.Study population was divided into two age groups: (i) 50 years old or younger (315
patients; age range, 9-50 years; sex ratio, 197 males / 118 females) and (ii) older than
50 years (201 patients; age range, 51-85 years; sex ratio, 49 males / 152 females). This
distinction was essential to account for age-related osteoarthritic changes.
4.Control group included patients with normal cartilage morphology (total of 406
patients, 288 in the younger and 118 in the older age group), while OA group consisted
of patients demonstrating PFJ osteoarthritic features on MRI (total of 110 patients, 27 in
the younger and 83 in the older age group).
Page 2 of 18
IMAGING
1.All examinations were performed with a 1.5 T MRI scanner using a phased-array knee
coil.
2.Axial fat-saturated turbo spin echo (TSE) proton density (PD), sagittal fat-saturated
TSE intermediate-weighted (IM-w), sagittal T2*-w MEDIC and coronal T1-w spin echo
MR sequences were utilized for our study analysis.
MEASUREMENTS
1.The axial fat-saturated PD TSE images were recruited for the evaluation of most of the
studied parameters. Three reference images were selected: (a) Image I at the level of
the greatest anteroposterior diameter of the femoral condyles, (b) Image II at the level of
the greatest transverse diameter of the patella and (c) Image III at the level of the patellar
tendon insertion upon the tibial tubercle [5]. Reference lines were created at image I (Fig.
1A): line A across the anterior aspects of the femoral condyles, between the most medial
and lateral points of the trochlea, line B along the posterior aspects of the condyles and
line C drawn perpendicular to line B through the deepest trochlear point (trochlear apex)
[5].
•
•
•
The femoral sulcus angle (SA) and depth (SD), utilized to assess
trochlear morphology, were measured at image I (Figs. 1B, 1C).
The lateral patella displacement (LPD) and lateral patellofemoral angle
(LPFA), used as patellofemoral congruence indices, were measured at
image II (Figs. 1D, 1E).
TT-TG distance, also used as a patellofemoral congruence index, was
measured at image III (Fig. 1F).
2.The sagittal fat-saturated IM-w TSE sequence was recruited for the evaluation of
another patellofemoral congruence paremeter: the Insall-Salvati index. The image at the
level of the greatest patellar bone length was selected. Patellar length (PL) was measured
from the superior border of the patella to the most posterior point of the proximal insertion
of the patellar tendon excluding osteophytes and enthesophytes. Patellar tendon length
(PTL) was measured between the most posterior points of the proximal and distal
insertions of the patellar tendon. The ratio PTL/PL determined the Insall-Salvati index
(Fig. 2) [5,6,10].
3.Fat thickness (FT) in the medial compartment of the knee was also measured. The
coronal T1-w image at the level of the tibial insertion of the anterior cruciate ligament
was selected for this purpose. The distance (in cm) between the tibial collateral ligament
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(TCL) and the medial cutis was then estimated (Fig. 3). We used FT as an indirect body
fat content index.
4.With a minimal interval of 1 month all measurements were repeated by the same
observer (a fellowship-trained musculoskeletal radiologist) on each knee scan.
OSTEOARTHRITIC FEATURES
1.The fat-saturated IM-w and proton density TSE MR images were reviewed for the
evaluation of patellar and trochlear cartilage morphology. Assessment of cartilage
lesion severity was based upon the International Cartilage Repair Society (ICRS)
classification system (Fig. 4: Table 1) [13]. Grading was conducted by two observers,
the aforementioned fellowship-trained and a senior musculoskeletal radiologist, blinded
to each other's results.
2.The presence of accompanying osteophytes (OST) and bone marrow lesions (BML)
was recorded. BML comprised osteoarthritis-related subchondral bone marrow edema
and/or cysts.
STATISTICAL ANALYSIS
1.The D'Agostino-Pearson, Mann-Whitney and independent samples t tests as well as
the Spearman's rank correlation (rho) and Cohen's kappa coefficients were used.
2.Statistical significant differences and associations were defined by a resulting P-value
of < 0.05.
Images for this section:
Page 4 of 18
Fig. 1: Axial patellofemoral alignment measurements in a 31-year-old man who
underwent knee MRI. (A), (B) and (C) at the level of the greatest anteroposterior diameter
of the femoral condyles (Image I) show the three reference lines, the sulcus angle (SA)
and the sulcus depth (SD) respectively. SA was determined by the intersection of lines
connecting the subchondral bony margins of the medial and lateral trochlear facets to
the trochlear apex [6-9]. SD was defined as the maximum perpendicular distance (in
mm) of the trochlear apex from line A [6,7,10,11]. (D) and (E) at the level of the greatest
transverse diameter of the patella (Image II) show the lateral patella displacement (LPD),
measured perpendicularly to lines D and E, and the lateral patellofemoral angle (LPFA).
LPD was defined as the distance (in mm) between two lines, one from the most medial
point of the patella (line D) and the other from the most medial point of the femoral trochlea
(line E), drawn perpendicular to line A which was copied from image I [6]. A positive value
was recorded if line D was lateral to line E. LPFA was determined by the intersection
of line A and a line created between the apex and the lateral subchondral border of the
patellar cortex [5,7,9]. A positive LPFA was recorded if the angle opened laterally. In this
patient, line D was medial to line E (indicating a relatively medial position of the patella),
thus a negative value was attributed to LPD. On the contrary, a positive angle value was
recorded pointing out the lateral opening of the LPFA. (F) at the level of the distal patellar
tendon insertion (Image III) shows the tibial tubercle-trochlear groove (TT-TG) distance,
measured perpendicularly t# lines C and F. A line bisecting the tibial tubercle through
the midpoint of the patellar tendon insertion (line F) was drawn parallel to line C which
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was copied from image I. The distance (in mm) between these two lines determined the
extent of lateralization of the tibial tubercle [5,7,12].
Fig. 2: Evaluation of Insall-Salvati index in the same 31-year-old patient. Patellar tendon
length (PTL) and patellar length (PL) were measured on the sagittal plane and the ratio
PTL/PL was calculated.
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Fig. 3: Fat thickness (FT) in the medial compartment of the knee of the same 31-yearold patient was measured on the coronal plane perpendicularly to the portion of the TCL
next to the medial interarticular space.
Fig. 4
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Results
1.The prevalence of patellofemoral OA was 21.3%. 31.5% of female and 10.2% of male
patients were affected (Fig. 1: Table 2).
2.Significantly older patients in both age groups and the total study population suffered
from PFJ OA (Fig. 2: Table 3).
3.Grade I and grade IV lesions were more prevalent in the younger (# 50 years) and older
(> 50 years) OA group respectively (Fig. 3: Table 4). Excellent grading agreement (k =
0.868) was found between the two raters.
4.Comparison and differences of all studied measurements between the OA and control
groups are summarized in Tables 5 and 6 (Figs. 4,5) . The intra-rater agreement for each
of these measurements was excellent (k range, 0,828-0,875).
•
•
No statistically significant difference was seen regarding TT-TG
distance and Insall-Salvati index in both age groups as well as FT in the
older patient group. Patella alta was observed in 10% (8/83) of OA patients
as opposed to 3% (4/118) of patients with normal cartilage morphology in
the older age group (Fig. 6), and therefore the limited number of patients
do not allow solid conclusions. A TT-TG distance of more than 10 mm
(considered abnormal [5,7,8,14]) was found in 46% (51/110) of OA patients
in the total study population, 52% (14/27) in the younger and 45% (37/83)
in the older age group compared to 29% (116/406), 28% (80/288) and
30% (36/118) of control patients respectively. Moreover, a TT-TG distance
of more than 15 mm (used as a cutoff value to distinguish symptomatic
patients that can benefit from a distal realignment procedure [12,15,16])
was observed in 11% (12/110) of OA patients in the total study population
and 22% (6/27) in the younger age group compared to 5% (21/406) and 5%
(14/288) of patients with normal cartilage morphology respectively.
Analysis of SA, SD, LPD and LPFA in both age groups as well as FT in
the younger patient group revealed a statistically significant difference. OA
patients in both age groups demonstrated a shallower throchlear groove
(Figs. 7,8) as well as a more laterally positioned and inclined (tilted)
patella (Fig. 9). A positive association between obesity and PFJ OA in the
younger population is indicated.
5.Correlation of increasing cartilage lesion grading with each of the measurements as
well as the presence of PFJ OST and BML is presented in Table 7 (Fig. 10).
•
Increasing SA and LPD as well as decreasing SD and LPFA were
significantly associated with increased PFJ cartilage loss in both age
groups.
Page 8 of 18
•
•
Significant postitive correlation was found between FT and cartilage lesion
grading in the younger patient group.
Advanced cartilage wear in patients > 50 years was associated with
emergence of OST and BML, a finding consistent with the chronic
degenerative course of PFJ OA.
Images for this section:
Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
Fig. 5
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Fig. 6: Fat-saturated IM-w sagittal (A) and PD axial (B) TSE knee MR images in a 54year-old woman with left PFJ osteoarthritis. (A) Patella alta (PTL/PL = 1.32) is seen on
the sagittal plane. (B) Grade III cartilage defects involving the medial facet of the patella
are depicted on the axial plane (white arrow).
Fig. 7: Axial fat-saturated PD TSE knee MR images in a 75-year-old woman with
advanced left PFJ osteoarthritis. (A) A severely shallow trochlear groove (SA = 158.3
degrees / SD = 3.2 mm) is depicted. Lateral femoral condyle subcortical bone marrow
oedema is also noted (white arrow). (B) shows grade IV cartilage defects involving the
lateral facet and apex of the patella with exposure of the underlying subchondral bone
(black arrows) and accompanying subcortical bone marrow oedema (white arrow).
Page 13 of 18
Fig. 8: Axial fat-saturated PD TSE knee MR images in a 69-year-old woman with
advanced left PFJ osteoarthritis. (A) shows a shallow trochlear groove (SA = 148
degrees / SD = 4.2 mm). (B) Severe cartilage loss and accompanying subcortical cysts
involve the lateral patellar facet (white arrow). Patellar subluxation is also present (black
arrow).
Fig. 9: Axial fat-saturated PD TSE knee MR image in a 46-year-old woman with left PFJ
osteoarthritis. A laterally displaced and tilted patella (LPD = 10.6 mm / LPFA = - 16.5
degrees) is seen.
Page 14 of 18
Fig. 10
Page 15 of 18
Conclusion
•In the present study, we have directed our attention on femoral trochlear anatomy and
patellofemoral congruence evaluation, correlating the findings with PFJ OA features
(cartilage lesions, OST and BML). We report significant differences and correlations
regarding the majority of studied parameters, indicating a multivariable association
between patellofemoral malalignment and PFJ OA.
•Considering the recent advances in patellofemoral realignment procedures, great value
can be attributed to the aforementioned alignment parameters concerning PFJ OA
prevention and treatment. A similar benefit can be drawn from obesity control in young
patients.
•In conclusion, we believe that the routine evaluation of SA, SD, LPD, LPFA and, possibly,
TT-TG distance can be beneficial in further understanding of pathogenesis as well as
improvement of prognosis, prevention and treatment of PFJ OA.
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