A double patellar tendon is an extremely rare anomaly, thought to be related to the embryological development of the patella and patellar tendon. It may appear as a crossed or uncrossed-doubled tendon on imaging 1-4.
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Epidemiology
Double patellar tendon appears to be a rare anomaly with only a few cases reported in the literature 1-4.
Associations
The crossed-doubled patellar tendon has been associated with Hoffa fat pad impingement in one case 3.
Diagnosis
The diagnosis can be conveniently made by imaging favourably by MRI 1-4.
Clinical presentation
A potential contribution of the double patellar tendon to knee pain remains possible, though confounding factors exist 1.
Pathology
For a double patellar tendon, two courses are described either a crossed or uncrossed type both characterized by completely separated bands and insertions 1-3.
The crossed type features a medially originating band that follows a superficial normal course with a typical distal insertion at the tibial tuberosity and a more lateral originating band with a deep course crossing the former superficial band posteriorly, inserting at the medial portion of the proximal tibial with a distal broadening 1,3.
The uncrossed type is characterized by two parallel bundles, one of which originates more medially from the patella and inserts on the medial proximal tuberosity, with a deeper course partly covered by the more lateral originating and descending superficial part, which inserts on the lateral aspect of the proximal tibial tuberosity 2.
Radiographic features
MRI
MRI is the imaging modality of choice, can demonstrate the double patellar bands and the course and insertional anatomy of the two bands as well as the option of detecting related pathology.
The crossed-doubled version displays the superficial band with a typical course and a deep portion crossing the superficial portion on its posterior surface separated by a thin fat stripe 1,3.
The uncrossed-double version also displays superficial and deeper situated portions that are separated by a thin fat stripe, but in contrast to the crossed version, they run parallel and insert ipsilaterally 2.
In both situations, the bands should display an otherwise normal anatomy.
Radiology report
The radiology report should include a description of the following:
course
insertional anatomy
related pathology
History and etymology
The first description of a crossed-doubled patellar tendon on imaging was made by the Radiologist Alexander Loicides and his colleagues at the Medical University of Innsbruck, Austria in 2016 1. The uncrossed doubled form was first described by the British Radiologist Syed Mohammad Ali Haydar and his colleagues at St. Thomas Hospital London, United Kingdom in 2019 2.
Differential diagnosis
The main differential diagnosis includes the following clinical conditions:
status post tendon harvest
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