Page 8 - JCTR-11-3

Journal of Clinical and
Translational Research Lateral patellar instability in deep flexion

constraints to allow the patella to subluxate partially or included. In addition, the references of all included
completely from its position in the femoral trochlea. In studies were analyzed, and the full text of all articles was
1
general, two types of lateral patellar instability are described: reviewed. Furthermore, clinical experience from cases was
(i) instability close to extension or beginning flexion <45° incorporated into the considerations and assessments.
and (ii) instability of the patella in deep flexion >45°.
1,2
Although instability in early flexion is a commonly known 3. Results
type of lateral patellar instability, there is still a general Nine studies were selected based on the criteria for
lack of information, and very little literature is available inclusion in the review. These studies comprised three case
2-4
on instability in deep flexion. In addition, most studies reports, three case series, a book chapter, and two reviews
3
report a combination of both types of instabilities. Patellar (Table 1). The full texts of these articles, related to patellar
instability in deep flexion represents a habitual patellar instability and flexion, were analyzed.
dislocation and must be differentiated from recurrent
patellar instabilities. It occurs only within the range of 50° 3.1. Anatomy
– 80° of knee flexion, with the patella remaining centrally The patellofemoral gliding mechanism is determined by
stable in the proximal trochlea near or close to full the three-dimensional shapes of the trochlear groove and
extension. Therefore, understanding the close relationship patella. The articular part of the trochlea consists of the
2
between anatomy and patellar kinematics during deep lateral and medial facets of the femoral sulcus and exhibits
flexion is necessary to assist clinicians in selecting the most different anatomical aspects in the proximal-distal,
effective treatment to address the pathological factors mediolateral, and anteroposterior directions. 21-23 The
contributing to this form of instability. 2-8
normal trochlea deepens gradually from proximal to distal
Various morphologic abnormalities, such as trochlear and is longer on the lateral side and shorter medially. It
2,23
dysplasia (present in 85% of cases), patella alta, increased begins at the anterior cortex of the distal femur and extends
tibial tubercle-trochlear groove (TT-TG) distance, to the femoral notch. The lateral and the medial facet are
24
rotational abnormalities, external tibiofemoral rotation, separated by the trochlear groove. In the anteroposterior
and soft tissue abnormalities, are well-known factors direction, the lateral trochlear facet is typically higher than
causing lateral patellar instability near full extension. 3-8,14-18 the medial condyle, engaging the patella in the extended
In contrast, relatively little attention has been given to the knee (Figure 2). 21,22,25 This anatomical configuration allows
predisposing factors that trigger instability in deep flexion. the lateral facet to resist forces applied by the quadriceps
The same factors contributing to instability near extension angle effect in extension. In contrast, with increased knee
25
(unusually patella alta, trochlear dysplasia grade C or flexion, the medial facet becomes higher, with a crossing
D, increased TT-TG distance, or a combination of these point of around 50° of flexion (Figure 3). As a result,
25
factors) are commonly described as etiological features. lateral resisting forces decrease in deep flexion due to
19
However, other potential etiological factors remain largely the lowered inclination, causing the patella to track more
unaddressed. laterally. 15,25-27
Given these considerations, it is essential to clearly In this context, the anteroposterior length and depth
distinguish between lateral patellar instability in deep of the terminal sulcus are essential. The terminal sulcus
flexion and instabilities near extension. This requires a is a shallow groove that separates the patellar and tibial
comprehensive evaluation of anatomy, biomechanics, and articular surfaces of the femur. 28,29 Located laterally to
the kinematics of flexion instability to better understand the intercondylar notch, it has a triangular shape with
the changing forces acting in all three-dimensional planes. an indentation up to 1.5 mm depth, which can vary
individually. It does not extend more than 10 mm
30
2. Methodology posterior to the Blumensaat line. 28,31
A systematic literature search was performed through In addition, the lateral femoral condyle shape can
PubMed registries in 2024 according to the Preferred change in patients suffering from patellar instability in
Reporting Items for Systematic Reviews and Meta- deep flexion. Persistent abnormal motion of the patella in
Analyses guidelines using the terms “patellar instability” higher flexion at a young age, caused by a large quadriceps
20
and “knee flexion” (Figure 1). vector, excessive lateral patellar tilt, skeletal deformations,
Inclusion criteria were original studies, book or rotational abnormalities, may form a false sulcus in
chapters, and review articles in English. Computational the middle of the lateral femoral condyle, resulting in
or biomechanical studies, abstracts, and technical subsequent flattening. Furthermore, the shape and
2,4
notes were excluded. Studies of all evidence levels were thickness of the bone and cartilage of the lateral condyle in

Volume 11 Issue 3 (2025) 2 doi: 10.36922/jctr.7131