Discussion
MPFL Repair: Indications and Surgical Technique
Although optimal management of first-time patellar dislocation continues to be a topic for debate, the frequency of recurrent instability,7,27 particularly in young patients, has led some to advocate early surgical management.9,28 A clear indication for early operative intervention is the presence of a large osteochondral lesion that can undergo fixation or is causing persistent mechanical symptoms with recurrent effusion (Figures 1A, 1B).
Numerous open and arthroscopic MPFL repair techniques have been described.10,30-33 Nevertheless, comparative studies are limited, and the greatest debate about MPFL repair continues to be appropriate indications. Arthroscopic MPFL repair can be technically demanding and can fully visualize only patella-based injuries. In addition, all-arthroscopic repair techniques may place suture material in the joint, which causes concern regarding suture irritation. As a result, the majority of MPFL repair techniques described in the literature use an open approach, which typically includes a 4-cm to 5-cm longitudinal incision along the medial aspect of the patella. Sharp dissection is carried down through the medial retinaculum to the underlying joint capsule. The plane between the medial retinaculum and the underlying joint capsule is bluntly developed posteriorly until the medial epicondyle and the adductor tubercle are palpated. For a patella-based rupture, the MPFL is defined within layer 2, and 2 suture anchors are placed within the superior third of the patella. Although there are other patellar fixation methods, suture anchors provide adequate fixation with minimal risk of iatrogenic patellar fracture. With anchors in place, horizontal mattress sutures are placed in the stump of the MPFL. For femoral-based ruptures, the same surgical exposure is used to identify the MPFL. However, depending on the size of the incision and the mobility of the tissue, a second incision can be made posterior and parallel to the first—best achieved using a spinal needle to fluoroscopically localize Schöttle’s point.16 An incision is made in line with the spinal needle, and dissection is continued down to the previously developed extracapsular plane. Under fluoroscopic guidance (Figure 3), 1 or 2 suture anchors are placed at Schöttle point, and horizontal mattress sutures are placed through the avulsed MPFL femoral origin.
MPFL Imbrication: Indications and Surgical Technique
MPFL reconstruction is the technique of choice in recurrent patellofemoral instability when no other procedures are required. When combined with distal realignment procedures, distal femoral osteotomy, open patellofemoral cartilage resurfacing procedures, or trochleoplasty, MPFL imbrication can be considered in place of MPFL reconstruction. Recurrent patellofemoral instability is influenced by various factors, including static soft-tissue restraints, dynamic muscle action, and bony anatomy, only one of which is directly addressed with MPFL imbrication. Relying on native tissues without a graft increases the risk for recurrent instability because of concern that the already attenuated native tissues will stretch out further, particularly in the presence of hyperlaxity. Although the significance of trochlear dysplasia in patellofemoral instability was first noted by Dejour and colleagues,34 the presence of trochlear dysplasia has been shown to negatively influence outcomes of isolated MPFL imbrication.35 Because of the relative frequency of trochlear dysplasia and axial or coronal plane malalignment in patients with chronic or recurrent patellar instability, MPFL imbrication typically is not performed on its own, and it is best used in conjunction with a distal realignment procedure or distal femoral osteotomy. MPFL reconstruction should be performed instead of MPFL imbrication in patients with severe trochlear dysplasia, in patients with hyperlaxity signs, and in young patients who participate in cutting or pivoting sports.
When distal realignment procedures are performed for axial alignment, or distal femoral osteotomy is performed for severe genu valgum, patellofemoral laxity is tested after the bony correction is completed. If the patella is still dislocatable, MPFL reconstruction provides the most predictable outcome. If laxity is increased, but the patella remains in the trochlea, typically MPFL imbrication is adequate.
Similar to MPFL repair, both open and arthroscopic techniques have been described in the literature.36-38 As MPFL imbrication is most commonly performed in conjunction with large open procedures, this procedure can often be incorporated with other open incisions. In addition, open MPFL imbrication allows for precise control and tensioning of the medial retinacular structures, which is not always easily achieved by arthroscopic methods.
If a separate incision is required, a 4-cm to 5-cm longitudinal incision is made along the medial border of the patella, just as described for MPFL repair. The medial retinacular tissue, including the MPFL, is identified and isolated extracapsularly. Imbrication can be performed with sutures only (using a cuff of tissue along the medial border of the patella and placing pants-over-vest sutures in the adjacent tissue) or with sutures and anchors (more similar to MPFL repair described earlier). In either scenario, adequately tensioning the MPFL and associated medial retinaculum is essential in order to restore the checkrein function of the attenuated MPFL. Although typically described in the setting of MPFL reconstruction, the MPFL can easily be overtensioned during MPFL imbrication. This potential pitfall can be avoided by recognizing that forces over 2 N will overtension medial structures and thereby increase contact pressures at the medial patellar facet.39 The complication can easily be prevented simply by placing the knee in 30° flexion and centering the patella in the trochlear groove while performing the MPFL imbrication.