BLOG: MPFL, MPFC, MQTFL reconstruction: Patellar stabilization and alphabet soup
The term medial patellofemoral ligament has traditionally been used to refer to the primary static stabilizer to lateral patellar translation. Found between layers two and three in the medial knee, the anatomy of this ligament has been described as originating in the saddle between the medial epicondyle and adductor tubercle, and attaching to the medial border of the patella. Numerous reconstructive techniques of the medial patellofemoral ligament have been described in the treatment of patellar instability, and subsequent studies have identified the critical role of anatomic fixation of the graft to optimize its function and minimize complications.
More recently, John P. Fulkerson, MD, described a set of fibers that existed proximal to the fibers of what we knew to be the medial patellofemoral ligament (MPFL). As these attached to the quadriceps tendon, he named this the medial quadriceps tendon femoral ligament (MQTFL), and described a reconstruction technique that involves attaching the graft to the medial quadriceps tendon. He has reported good results with this technique, while emphasizing the added benefit of eliminating the risk of patella fracture, which is arguably the most catastrophic complication that can occur as a result of this procedure.
In trying to understand the disparity between the existing literature and these new anatomic findings, I utilized a similar dissection technique by exposing the medial soft tissue from the articular surface to dissect 28 knees. In doing so, I found most knees had a combination of these fibers that stemmed from the same origin and attached in a fan-shaped pattern to both structures, although some knees had fibers extending to only the patella (MPFL) and others had fibers attaching to only the quadriceps tendon (MQTFL). I reported on the variability of these fibers in this series, in which 57.3% +/- 19.5% of fibers attached to the patella, while the remainder attached to the quadriceps tendon. This confirmed the descriptions of several other studies that more recently have described the presence of proximal MPFL fibers that attach to the quadriceps tendon.
Later that year we sought to identify the midpoint of this fan-shaped attachment, to guide anatomic graft placement during reconstruction with a single-stranded graft. While studying this, we referred to this structure as the medial patellofemoral complex (MPFC), to allow for the anatomic variability in the attachment sites to the patella and/or quadriceps tendon. Despite this variability, we found that the midpoint of this complex was reproducibly found at the junction of the medial border of the quadriceps tendon and superior articular border of the patella, which can be used to potentially guide graft fixation on the patella or quadriceps tendon during reconstruction for patellar stabilization.
Regardless of the name, MPFL, MPFC or MQTFL reconstruction, when a surgeon chooses to perform patellar stabilization, the tenets of medial soft tissue reconstruction remain constant. First, it is paramount that bony malalignment be addressed concurrently, to avoid increased risk of failure through altered mechanics on the graft. Stephen described the inability of MPFL reconstruction to properly restore patellar kinematics in the setting of tibial tuberosity to trochlear groove (TT-TG) distance greater than 15mm. Similarly, Redler and colleagues showed that increased TT-TG distance of greater than 20 mm and patella alta (CD ratio > 1.2) significantly altered MPFL isometry during knee range of motion from 20° to 70° of flexion, suggesting that a soft tissue procedure alone may not be enough to maintain patellar stability in the setting of malalignment.
Secondly, despite the broad attachment of this structure on the patella and/or quadriceps tendon, the function of the ligament has shown to be sensitive to the position of the femoral tunnel, and much effort has been focused on accurately determining and recreating its position during surgery. Elias and Cosgarea have shown through computational modeling that errors in femoral tunnel malpositioning by as little as 5 mm can lead to changes in patellofemoral contact pressures. Stephen and colleagues also found in their cadaveric study that femoral tunnels positioned proximal or distal to the anatomic origin can result in increased peak and mean medial patellofemoral pressures, as well as increased medial patellar tilt.
Finally, while anatomic positioning of the graft is important, the tension placed on the graft during fixation is equally critical. In the same study mentioned above, Stephen and colleagues demonstrated that while a graft tensioned to 2 N restored normal patellofemoral pressures and tracking, grafts tensioned with 10 N or 30 N caused significant increases in medial patellofemoral joint pressures and medial tilt. As Jack Farr and others have noted, the "tension" on the graft should be thought of as "removing the slack from the graft," as the idea of “tensioning” can lead to overtightening and subsequent overconstraint of the patella.
In summary, there have been advances in our understanding of the medial soft tissue anatomy that have led to the variable terminology of MPFL, MQTFL and MPFC. Due to the broad attachment of these fibers on both the patella and quadriceps tendon, a single stranded graft can be placed either on the quadriceps tendon or the patella, near the junction of the medial quadriceps tendon and the proximal patella to recreate the anatomy of these fibers. Despite the evolving name of the procedure, the position of the femoral tunnel, the “tension” (or lack thereof) placed on the graft and the consideration of concurrent procedures to address excessive bony malalignment, remain constant and critical elements in the surgical treatment of patellar instability.
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Miho J. Tanaka, MD, is assistant professor of orthopedic surgery and director of the Women's Sports Medicine Program at The Johns Hopkins Hospital in Baltimore. Disclosure: Tanaka reports no relevant financial disclosures.