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BLOG: Does position of femoral attachment influence outcome after MPFL reconstruction?
In a paper we recently published, we observed that a non-anatomic femoral attachment in medial patellofemoral ligament reconstructive surgery does not always lead to a poor outcome. In fact, many patients with non-anatomic medial patellofemoral ligament reconstructions have an excellent clinical outcome not only at short-term, as some authors have shown, but also at long-term follow-up, as we have seen in our recently published study.
In this way, a member of our study group (Joan C. Monllau, MD) has analyzed a series of 36 medial patellofemoral ligament (MPFL) reconstructions (mean follow-up 37.6 months, range 27 months to 74.5 months) with gracilis tendon autograft using the adductor magnus tendon as a pulley for femoral fixation (non-anatomic reconstruction) and found good clinical results and without signs of patellofemoral osteoarthritis. In a previous cadaver study, we found the biomechanical behavior of the non-anatomic reconstruction using the adductor magnus as a pulley was similar to that of the anatomic reconstruction.
Vicente Sanchis-Alfonso
Failure vs excellent results after MPFL reconstruction
The relevant question we must ask is: Why will some non-anatomic MPFL reconstructions fail, whereas other non-anatomic reconstructions will have excellent results at long-term follow-up? This question has been answered in the paper we have just published. We have found it is the mechanical behavior of the graft that determines success or failure. The relevant fact is the graft is isometric between 0° and 30° (less than 5 mm of length difference between both knee flexion angles). Beyond 60° of knee flexion, the graft became progressively lax and isometry is lost. MPFL must function as a tether in early flexion without being tight at any point if the patella is centered in the groove, and this can be achieved through non-anatomic attachments. But in order to achieve this aim, we must do several proofs intraoperatively to evaluate the mechanical behavior of the graft, which is tedious and increases the surgical time.
Christina Ramirez-Fuentes
The choice of a femoral anatomic attachment point is a reproducible, quick and easy way to achieve the ideal mechanical behavior of the graft and, therefore, the success of the surgical reconstruction. Thereby, the best way of maximizing outcomes and providing the patient with the best chance to obtain a long-term success is to use an anatomic femoral attachment point. Therefore, the first author strongly advises to always perform anatomic femoral attachments in MPFL surgery. I only use the non-anatomic reconstruction using the adductor magnus as a pulley in children and adolescents with open growth plates and in complex cases of revision MPFL reconstruction with multiple tunnels in the femur.
Choose the right femoral attachment point
Therefore, the question is: How do we choose the femoral attachment point so that it can be anatomic? The most popular method to determine the anatomic femoral fixation point, which is routinely used ORs around the world, is the radiologic method described by Schoettle and colleagues in 2007. It is interesting to mention that in their study, Schoettle and colleagues analyzed eight frozen cadaver knees of an unknown age and the presence of trochlear dysplasia was not mentioned. Moreover, the gender of the analyzed knees was also unknown. In this sense, we must keep in mind that chronic lateral patellar instability is more frequent in female patients and many of them have a trochlear dysplasia.
It has been demonstrated that an exact anatomic femoral tunnel placement cannot be achieved with the radiologic method published by Schoettle and colleagues. C-arm identification of the femoral graft placement according to the Schoettle’s method is a useful and witty way to locate the femoral attachment point and to reproduce an ideal mechanical behavior of the graft; however, it is only an approximation and should not be the sole basis for femoral attachment location if we want to get a real anatomic attachment point. The only accurate way we can be sure of an anatomic femoral placement of the graft to perform an accurate execution of an MPFL reconstruction is to make a large enough incision to unequivocally identify the most important anatomic landmark, the adductor tubercle.
According to Fujino and colleagues, the femoral attachment of the MPFL is distal to the apex of the adductor tubercle and parallel with the long axis of the femur; the mean linear distance between the two points being 10.6 mm, and the position of the insertion site is consistent in all knees. Our previous paper illustrates two important points: first, that studies of normal cadavers cannot be assumed to reflect anatomy in recurrent dislocators; and second, that radiographic landmarks are not accurate enough.
References:
Fujino K, et al. Knee Surg Sports Traumatol Arthrosc. 2015;doi:10.1007/s00167-013-2797-0.
McCarthy M, et al. Iowa Orthop J. 2013;33:58-63.
Monllau JC, et al. Clinical and radiological outcomes after a quasi-anatomical reconstruction of medial patellofemoral ligament with gracilis tendon autograft. Knee Surg Sports Traumatol Arthrosc. (In press).
Pérez-Prieto D, et al. Knee Surg Sports Traumatol Arthrosc. 2015;doi:10.1007/s00167-015-3865-4.
Sanchis-Alfonso V, et al. Knee Surg Sports Traumatol Arthrosc. 2015;doi:10.1007/s00167-015-3523-x.
Sanchis-Alfonso V, et al. Knee Surg Sports Traumatol Arthrosc. 2015;doi:10.1007/s00167-015-3905-0.
Schoettle PB, et al. Am J Sports Med. 2007;doi:10.1177/0363546506296415.
Servien E, et al. Am J Sports Med. 2011;doi:10.1177/0363546510381362.
Ziegler CG, et al. Am J Sports Med. 2015;doi:10.1177/0363546515611652.
Disclosures: Sanchis-Alfonso and Ramírez-Fuentes report no relevant financial disclosures.