Revista de Medicina Desportiva (English) November 2018 | Page 28

Rev. Medicina Desportiva informa, 2018; 9(6):26-28.
Patellar Instability in
Children and Adolescents
Dra. Catarina Neto Pereira 1 , Dra. Patrícia Rodrigues 2 , Dr. Delfin Tavares 3
1
Resident doctor on Orthopedics and Traumatology at the Hospital Professor Doutor Fernando Fonseca
(HFF), 2 Orthopedic and Traumatology Specialist at the Hospital Dona Estefânia (HDE), 3 Director of the
Orthopedic Ward at the Hospital Dona Estefânia. Lisboa
RESUMO / ABSTRACT
Patellar Instability is the most common pathology of the knee during growth. After the first episode
of patellar dislocation there are about 40% of recurrences. Conservative treatment is the preferred
strategy for the first time, but in cases with concomitant anatomic predisposition and relapse,
surgical reconstruction may be considered. In these cases, when there is skeletal immaturity, the
reconstruction of the medial femoro-patellar ligament may be sufficient, associated or not with soft
tissue procedures, with the aim to have permanent stabilization of the patella or, at least, a gain of
time for the accomplishment of a definitive bone procedure. Recurrent dislocations of the patella lead
to changes in the cartilage, hence early treatment is important. Although it is still a controversial
subject, the reconstruction of the medial femoro-patellar ligament has been shown to be effective
in the treatment of patellar instability, with the advantage of being able to use a surgical technique
that does not damage the growth cartilage.
PALAVRAS-CHAVE / KEYWORDS
Patellar instability, femoropatellar ligament, children/teenagers
Introduction
The patelofemoral pathologies are
among de most frequent causes of
pain in children and adolescents and
the patellar instability is the most
frequent pathology in the knee dur-
ing the growing process. 1 The global
incidence is about 50 in 100 000
children and adolescents per year,
with a peak at the age of 15 years
old. 2,3 The majority of the patellar
dislocations have a lateral deviation,
with about 40% of recurrences after
the first episode of dislocation. Two
thirds of the subjects have open phy-
sis, which limits the type of surgery
for patellar stabilization. 2,4
The treatment of the acute dislo-
cations, like in the adults, is typically
conservative, except if there is an
osteochondral injury. The surgical
treatment is recommended on cases
of recurrence. 1
Probably, the most important
patellar stabilizer is the medial
femoropatelar ligament (MFPL),
that promotes more than 50% of
the medial restriction. It has been
demonstrated that in the majority
of the dislocations the MFPL has
suffered some degree of injury 1 , and
the its avulsion usually occurs at the
patellar insertion. 2,5 Anatomic vari-
ations, like changes on the Q angle,
26 november 2018 www.revdesportiva.pt
distance tibial tuberosity-trochlear
groove, are associated to an increase
of stress over the MFPL that predis-
poses to patellar dislocation. 1
Predisposing factors
The identification of anatomic
factors that predispose to patellar
dislocation is of paramount impor-
tance to decide the best treatment
for the patient. The ligament laxity
is a commonly found factor on the
females and on subjects with col-
lagen disease. On the other hand,
the fibrosis of the vastus lateralis
is also considered a risk factor. It is
believed that the increased Q angle
contributes for the lateralization of
the patella, however there is a poor
clinical correlation, and Q angle
could be decreased. 2
Trochlear dysplasia (Figure 1) that
is considered a major predisposing
factor for patelofemoral instability 9 ,
is defined as geometric abnormal-
ity in the shape and in the depth
of the trochlear groove, especially
on the proximal area where the
patella bone fits on the trochlea. 6,7
It has been demonstrated that the
trochlear cartilaginous trochlear
angle is already created at birth, but
the bone trochlea gains its depth
during adolescence. 6,8 This fact
presents an enormous relevance in
the evaluation for the treatment the
patients with patelofemoral instabil-
ity. The type of trochlear dysplasia
can be classified on the profile of the
X-rays according Dejour’s principles:
the presence of the crossing sign,
proximal groove flattened or con-
vex, step-off between the trochlea
and the anterior cortex of the distal
femur and flattening of the lateral
femoral condyl. 2,9
The X-rays are technician depend-
ent and frequently they fail to dem-
onstrate the proximal trochlear dys-
plasia, this is, the location where the
trochlea articulates with the patella
bone on the first 20-30° of knee flex-
ion. 7,10 The CT scan studies can help
to have a better interpretation of the
trochlear dysplasia components.
There is a high percentage of pate-
lla alta (Figure 2) in patients with
recurrent dislocations. According to
Insall, on patients with closed physis
the profile X-ray with the knee at 45°
of flexion determines if the patella is
high or low, but in the patients with
open tibial proximal physis it is pref-
erable the Caton-Deschamps Index
(CDI), that is the relation between
the length from proximal anterior
border of the tibia and the most
inferior point of the articular surface
of the patella bone and the length of
the articular surface of the patella,
and a CDI bigger than 1,45 (patella
alta) is an important predictive fac-
tor of patella instability. 2
The distance from the tibial
tuberosity-trochlear groove (TT-TG)
is used to determine the degree of
lateralization of the tibial tuber in
relation to the deepest area of the
trochlear groove. A distance bigger
than 20mm measured in the CT
scan, with the knee in full exten-
sion, is considered pathological and
it is a risk factor for instability. 6,7 The
increase of the distance TT-TG is
rarely present as isolated in patients
with patellar instability and usually
is associated with other risk factors. 7
The femoral anteversion (Fig-
ure 3) and tibial rotation are other
risk factors to be evaluated in the
patient. The femoral torsion is
calculated with the angle between
a line that runs thought the center
of the femoral head and the center
of the femoral neck and a posterior