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Surgeon devises a simple new measurement for patellar instability
Measuring the axial patellar tendon angle called easier than other indices of patellofemoral anatomy.
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FLORENCE — An easy-to-reproduce MRI-based measurement of the axial patellar tendon angle could help surgeons better diagnose and treat patellofemoral instability, particularly with dysplasia, a new study suggests.
Benedict J. A. Lankester, FRCS(Tr&Orth), and colleagues in the United Kingdom, evaluated the use of axial knee MRIs for plotting the axial patellar tendon angle (APTA) in patients with and without patellofemoral instability (PFI). The researchers sought to use the technique to better understand the soft tissue anatomy and guide angular corrections of the extensor mechanism.
"Existing measurements of the patellofemoral joint can be unreliable in the presence of dysplasia," said Lankester, who presented the study results at the 8th European Federation of National Associations of Orthopaedics and Traumatology Congress (EFORT).
Lankester and colleagues took axial MRIs of 20 knees with PFI and 20 normal knees. They then assessed the angle between the patellar tendon and the posterior femoral condylar line at three levels — from the proximal tendon to its point of insertion, Lankester said.
"The lines are easy to draw to obtain the angle," he said.
"In normal knees the APTA is 11° of lateral tilt at all levels from the proximal tendon to its distal insertion," the authors wrote in the abstract. "In PFI knees, the APTA is 32° at the proximal tendon, 27° at the joint line and 22° at the distal insertion."
The difference was significant (P=.001) at all levels, they noted.
The patella commonly tilts laterally in PFI, which is matched by the orientation of the patellar tendon, Lankester said.
Since the increased tilt of the tendon only partially corrects at the distal insertion with an abnormal angle of tibial attachment, "When performing distal realignment procedures, angular corrections as well as displacement may be appropriate," he added.
For more information:
- Benedict J. A. Lankester, FRCS, can be reached at Avon Orthopaedic Centre, Southmead Hospital, Bristol BS10 5NB, UK; e-mail: jblankester@aol.com.
- Lankester BJA, Barnet, AJ, Eldridge JD, Wakeley CJ. The axial patellar tendon angel — a simple new measurement in patellar instability. #F234. Presented at the 8th European Federation of National Associations of Orthopaedics and Traumatology (EFORT) Congress. May 11-15. 2007. Florence, Italy.