Is impingement the cause of jumper's knee? Dynamic and static magnetic resonance imaging of patellar tendinitis in an open-configuration system.
BACKGROUND
Chronic overload is considered the main cause of patellar tendinitis, but it has been postulated that impingement of the inferior patellar pole against the patellar tendon during knee flexion could be responsible.


OBJECTIVE
The role of the patellar pole in patellar tendinitis can be determined by dynamic magnetic resonance imaging.


METHODS
Case-control study.


METHODS
We compared 19 knees with patellar tendinitis and 32 asymptomatic knees of age-matched subjects using an open-configuration magnetic resonance imaging system. Dynamic sagittal images were obtained from full extension to 100 degrees of flexion with and without activation of the quadriceps muscle. The following measurements were made from the images: tendon-patella angle, anteroposterior diameter of the tendon, signal difference-to-noise ratio, the shape of the inferior patellar pole, and the location of the patellar tendon insertion.


RESULTS
The tendon-patella angle was not significantly different between groups at any flexion angle, with or without quadriceps muscle activation. The insertion site of the patellar tendon differed significantly but not the shape of the inferior pole of the patella. The volume and the signal difference-to-noise ratio of zones of increased intratendinous signal as well as the anteroposterior diameter of the proximal patellar tendon were increased in symptomatic knees.


CONCLUSIONS
The relationship between the patella and the patellar tendon was identical in both groups; therefore, chronic overload seems to be a major cause of patellar tendinitis.
Schmid
Marius R
MR
Department of Diagnostic Radiology, University Hospital Balgrist, University of Zurich, Forchstrasse 340, CH-8008 Zurich, Switzerland.
Hodler
Juerg
J
Cathrein
Philipp
P
Duewell
Stefan
S
Jacob
Hilaire A C
HA
Romero
José
J
D000328:Adult; D001265:Athletic Injuries / Q000209:etiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology; D010329:Patella / Q000033:anatomy & histology / Q000473:pathology*; D012016:Reference Values; D012420:Running / Q000293:injuries*; D052256:Tendinopathy / Q000209:etiology*; D013710:Tendons / Q000033:anatomy & histology / Q000473:pathology*