Femoral tibial rotation may alter tibial tubercle-trochlear groove distance measurements
Key takeaways:
- Knee joint internal and external rotation may alter tibial tubercle-trochlear groove distance measurements.
- Tibial tubercle-trochlear groove distance is key to determine whether anteromedialization is needed.
Internal and external rotation of the tibia in relation to the femur may alter tibial tubercle-trochlear groove distance, a key indicator for surgical decision-making in patients with patellar instability, according to results.
“Rotation ‘through the knee’ or femoral tibial rotation may be an underrecognized consequence of long-standing patellar instability,” Daniel W. Green, MD, MS, FAAP, FACS, told Healio.
Green and colleagues analyzed eight human cadaveric knees to assess the impact of knee joint internal/external rotation on tibial tubercle-trochlear groove (TT-TG) distance, a key measurement to determine whether tibial tubercle anteromedialization is needed, according to the abstract. Researchers used CT scans, 3D models and linear regression to assess the relationship between rotation and TT-TG measurements.
Researchers found an average of 23° of knee joint internal/external rotation, which changed TT-TG distance by a range of 12.1 mm, enough to alter surgical decision-making, according to the abstract. They noted TT-TG distance averaged 14.21 mm at neutral rotation.
“An increase in ‘through the knee’ rotation has been found in severe cases of patella instability. This study documented that in normal knees the average ‘through the knee’ rotation was 23°, and for each degree of rotation ‘through the knee’ the TT-TG measurement changed by 0.52 mm,” Green said. “Thus, an increase of 10° of ‘through the knee’ external rotation would lead to an increase in TT-TG measurement of 5.2 mm,” he added.
Green noted that TT-TG measurements may vary based on a patient’s position during 3D imaging.
Perspective
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Daniel W. Green, MD, and colleagues point out how much TT-TG distance depends on positioning on imaging for which TT-TG distance is based. A few degrees difference, in many surgeons’ hands, will make the difference between moving a tibial tubercle or not. Thus, his observations are very important.
We should all be extremely cautious about decisions made on 2-dimensional images, and we should be in discussion with our radiology colleagues to ensure images are in full extension and neutral rotation.
Better still, we should look at less variable proximal criteria such as the entry point-transition point angle as described recently by Kristin E. Yu, MD, in Arthroscopy Techniques.
I applaud Dr Green’s work.
Reference:
Yu KE, et al. Arthroscopy Techniques. 2023;doi:10.1016/j.eats.2023.02.004.
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Green DW. Intra-articular femorotibial rotation is associated with tibial tubercle-trochlear groove distance. Presented at: International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine; June 18-21, 2023; Boston.
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