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Standard knee radiographs (antero-posterior,
profile, and axial) are mandatory to evaluate the
type and displacement of the fracture. The
differential diagnosis is a patella bipartita which
is present in 2 to 3% of the population [1].
Computed tomography may help to precise the
type and comminution of the fracture. MRI
allows evaluation of the patellar cartilage which
can be very damaged even in “in situ” fractures.
Treatment
The goal of the treatment is to restore extensor
mechanism continuity and the patello-femoral
congruency. Treatment depends on the type of
fracture : displaced (2-3mm articular step-off or
1-4mm fracture displacement) or not [3]. Non-
surgical treatment is only for non-displaced
fractures (vertical or transverse) and consists of
knee immobilisation with a brace in extension
for 4-6 weeks, weight-bearing and isometric
quadriceps contractions are allowed. Displaced
fractures must be treated surgically (open
reduction and internal fixation). Transverse
fractures must be fixed adequately to resist
quadriceps traction force. Tension band
osteosynthesis with two longitudinal parallel
K-wires and a fashion-of-eight wire is
recommended [17]. A polar cerclage can be
added to increase stability [4]. In case of fracture
of the patellar nose, the bony fragment can be
excised and its patellar tendon fibers reinserted
on the patella via transosseous sutures or
anchors.Inanycase,evenwithverycomminutive
fracture, patellectomy should be avoided
because the quadriceps strength is decreased by
more than 49%. Post-operative complications
are loss of reduction or fixation (8%), non-union
(1%), knee stiffness, patello-femoral arthritis.
Acute patellar tendon
ruptures
Anamnesis and incidence
Acute patellar tendon ruptures are less
frequent than quadriceps tendon ruptures.
About 80% of patients with patellar tendon
ruptures are less than 40 years-old [23].
Rupture most often occurs at the lower border
of the patella and sometimes at its insertion on
the anterior tibial tuberosity. As for the
quadriceps tendon, mid-body tendon ruptures
are rare and often associated to a systemic
inflammatory disease, chronic metabolic
disorders, anabolic steroid abuse, local steroid
injections, and most commonly progressive
degenerative processes. In athletes, patellar
tendinopathy (jumper’s knee) and sequelas of
Osgood-Schlatter enthesopathy are risk
factors for ruptures [11]. Patellar tendon may
tear when a high load is suddently applied to
the tendon. The dynamic load during sport is
much higher than any static load. In a healthy
patient (without any systemic pathology or
patellar tendinopathy), the patellar tendon
breaking point is 17.5 times the body weight.
To compare, climbing stairs loads the patellar
tendon of 3.3 times the body weight [19] and
jumps 7 to 8 times the body weight. The most
frequent mechanism is landing from a jump:
deceleration with sudden eccentric contraction
of the quadriceps, while the foot is anchored
on the ground and the knee is flexed. Patients
feel the tear or a painful knee buckling,
followed by a functional disability. Direct
traumas can also cause patellar tendon tears
when the patellar tendon is tight by quadriceps
contraction. Bilateral patellar tendon tears are
rare and often associated to systemic disease
(systemic lupus erythematosus, rheumatoid
arthitis, diabetes mellitus, hyperparathyroidy)
with chronic inflammation and amyloid
deposits in the tendons. Corticosteroids often
prescribed in those diseases may alter collagen
synthesis and tendons vascularisation [21].
However, a systemic cause of bilateral rupture
reported in the literature were found in only
60% of cases [10].
Acute extensor mechanism rupture may be a
complication of surgical procedures as total
knee arthroplasty, anterior cruciate ligament
recontruction with patellar tendon autograft
(patellar tendon rupture 0.3%; patellar fracture
0.03%) [2], tibial intramedullary nailing
through the patellar tendon.