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CURRENT CONCEPTS
Double Bundle Medial Patellofemoral Ligament Reconstruction
David Sadigursky, MD, MSc
Manoel Victorino Hospital/Faculty of the COT Hospital
Salvador, Bahia, BRAZIL
The medial patellofemoral ligament (MPFL) is the major restraint that prevents lateral translocation of the patella. In most patients, the MPFL is torn during acute patellar dislocation. Because of this, several surgical techniques have been described for the treatment of patellar instability. Surgical treatment is accepted as necessary for the restoration of the stability of the MPFL.
Despite the biomechanical importance of MPFL reconstruction, its value was appreciated only relatively recently, particularly over the last two decades. Although a wide range of techniques have been described for MPFL reconstruction, with different graft sources and fixation methods, accumulating evidence shows good clinical results of this surgery, with a very low recurrence rate of instability.
A major concern is the consequence of a graft positioning error in MPFL reconstruction. Small errors of 5 mm in the ideal position or graft tension > 2N are known to lead to increased joint forces on the medial facet of the patella, increasing the risk of pain and degeneration of the patellar cartilage. This leads to the need for techniques that can distribute the graft tension on the patella, reproducing the anatomy more closely.
However, Sandmeier et al. and Parker et al. showed that isolated MPFL reconstruction was unable to restore normal patellar tracking through medium and maximum flexion. Failure to restore proper anatomy or isometry of the MPFL may be responsible for this issue, thus limiting the long-term success of such reconstruction.
In 2010, Kang et al. introduced the concept of MPFL bands. The ligament has a thin layer that connects the femoral condyle to the supramedial border of the patella. From the femoral origin, MPFL fibers become larger, forming two bands, named by the authors as the inferior straight bundle (ISB) and superior oblique bundle (SOB). However, the two bands do not separate completely, forming a single structure. The lower fibers act as the static restraint, and the upper fibers act in the dynamic stabilization of the patella owing to their close association with the vastus medialis obliquus tendon.
MPFL reconstruction has become the technique of choice for most authors since the 1990s, even in cases where trochlear dysplasia and patella alta are identified. Isolated MPFL reconstruction has been shown to be a suitable and effective technique for the correction of patellar instability, except in cases where the tibial tuberosity-trochlear groove (TTTG) distance is longer than 20 mm.
In 2010, Kang et al. described the anatomy and function of the MPFL and their two bands. The superior oblique bundle together with the vastus medialis obliquus exerts traction on the patella, medially promoting a dynamic restraint. Meanwhile, the lower inferior straight bundle acts as a static restraint to balance the resulting lateral forces that act on the patella, caused by the Q angle. Thus, reconstruction of the two bands could increase the stability during the first flexion angles around 30°. The function of the MPFL at greater angles requires more elucidative studies.
Despite the MPFL being the primary stabilizer against patellar dislocation between 30 – 40° of flexion, Philippot et al. described the role of the medial patellotibial (MPTL) and the medial patellomeniscal (MPML) ligaments acting on the rotation, tilt, and dislocation at angles greater than 45°. The reconstruction of the MPTL is gaining popularity both in patients with open physes and in adults. During the arc of motion from total extension to flexion of 90°, the MPTL and MPML contribute 28% – 48% against the lateralization of the patella, 23% – 71% against tilt, and 32% – 92% against rotation. This finding cannot be disregarded in the planning of the correction of patellar instability. Despite the growing interest in the reconstruction of MPTL, with the aim of reducing dislocation of the patella at larger angles, possibly eliminating the inverted J sign, no data so far show the superiority of clinical outcomes in the combined reconstruction of the MPFL and MPTL with the double- or single-bundle technique.
Applying the MPFL reconstruction technique with the use of metal anchors has shown that the resistance is appropriate for achieving restraint against dislocation of the patella, especially in the early knee flexion angles. The MPFL tensile strength is relatively low, around 208 N, making the implant useful in fixing the graft. Mountney et al. showed no significant difference in tensile strength between the passage of the graft through bone tunnels and anchor fixation. Comparing the bone tunnels and anchor fixation, Hapa et al. did not find differences, although anchor fixation showed less stiffness. Bone tunnels were also demonstrated to enable better integration of the graft. As stated by Song et al., tendon-to-bone healing also occurs in the anchor fixation technique, as a bone bed in the medial border of the patella is made to accommodate the graft, which is then covered by the layer of periosteum and medial retinaculum.
Patellar fracture and cartilage perforation were described as among the possible complications of the patellar bone tunnel fixation technique. These complications were not found in studies that used anchor fixation. This fact is due to the non-perforation of the patella with drills, which require greater technical precautions in order to avoid these complications, particularly in patients with smaller patellae, such as Asians or people of short stature.
22 ISAKOS NEWSLETTER 2015: Volume I