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BLOG: Anisometry of MPFL reconstruction in the setting of patella alta, increased TT-TG distance
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There is a paucity of information about whether, in the setting of patella alta and/or increased tibial tubercle-trochlear groove, it is necessary to transfer the tibial tubercle to attain an isometric medial patellofemoral ligament reconstruction and thus a stable patella.
In this Patellofemoral Update, Lauren H. Redler, MD, and Beth E. Shubin Stein, MD, discuss results of cadaveric testing that showed increased tibial tubercle-trochlear groove (TT-TG) and patella alta significantly altered medial patellofemoral ligament (MPFL) isometry.
The perspective on this topic is from David Dejour, MD, of Lyon, France. He cautions surgeons to use both radiographic and slice imaging for accurate measurements in the patellofemoral joint prior to performing surgery.
Patellofemoral Update focuses on the causes, prevention and treatment of patellofemoral disorders. The blog is sponsored by the Patellofemoral Foundation whose mission is to improve the care of individuals with anterior knee pain through targeted education and research. The Patellofemoral Foundation offers additional online education resources on its website.
Members of the Patellofemoral Foundation review and add clinical perspective to recently published studies on the causes, prevention and treatment of patellofemoral disorders. The twice monthly blogs are edited by John P. Fulkerson, MD, and can be found on www.healio.com/orthopaedics. To read all the Patellofemoral Update blogs, click here.
Perspective
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David Dejour, MD
The treatment for objective patellar dislocation requires the correct identification of all the factors involved. This is necessary for success.
This interesting cadaveric study by Redler and Shubin Stein confirms that patella alta and high tibial tubercle-trochlear groove (TT-TG) distance lead to an anisometric behavior of the reconstructed medial patellofemoral ligament (MPFL), which will lead to failure.
In my practice, the evaluation of sagittal patellofemoral engagement index, as discussed in my 2013 study, can serve as a useful tool along with the existing methods of evaluating patellar height. It shows the borderline case where the classical radiographic index is nearly normal, but due to a low engagement of the patella, the patient has a functional patella alta.
Thus, mild tibial tubercle distalization allows the patella to be engaged in the trochlea and improves the biomechanical behavior of the new MPFL. It is important to remember the distalization leads to an automatic medialization of 4 mm due to the tibial shape.
This study confirms the fundamental value of using the X-ray measurement (for trochlear dysplasia, patellar height) combined with slice imaging measurement (for TT-TG, sagittal engagement index) prior to performing any patellofemoral surgery.
Reference:
Dejour D, et al. Orthop Traumatol Surg Res. 2013;doi:10.1016/j.otsr.2013.10.008.
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