An anteroposterior and/or a notch view projection is then performed to confirm the location of Schottle’s point, distal to the physis. Because the origin of the MPFL is posterior to the condyle, the notch view should be used to visualize Schottle’s point in relation to the physis in the coronal plane. This location has been confirmed to approximate the origin of the MPFL by published anatomic studies. If the graft measures 6 mm, an ideal distance of 5 to 8 mm distal to the physis will ensure a tunnel location with a proximal margin 2 to 4 mm distal to the physis. In our experience, Schottle’s point is approximately 5 to 7 mm distal to the physis, and rarely do we adjust our position. The guide wire is placed on the medial femoral condyle at this point and then angled 30° proximal to distal to allow tunnel trajectory distal to the undulating physis (Figure 8).
A 6-mm reamer is used over the guide wire to a depth of 20 mm. The newly created tunnel is now exposed and visualized. The graft is folded over at the center aspect and marked 20 mm from the tip of a Bio-tenodesis screwdriver (Arthrex). A 6.25 × 15 mm Bio-tenodesis screw is used. The graft and the screw are inserted into the condyle, and the appropriate graft fixation is confirmed by longitudinal tension placed upon the graft.
The hemostat or the passing suture previously placed into the blind pouch below the native MPFL is used to pass the graft immediately superficial to the synovial lining, in an extra-articular location. The ends of the graft are now exposed through the incision adjacent to the patella. The knee is confirmed to be flexed to approximately 45° on the surgical positioning triangleor at the flexion position determined during diagnostic arthroscopy at which the patella engages the trochlea. The graft is set to length alongside the medial surface of the patella at the position of the suture anchor, and a single stitch is placed through both ends of the graft at this adjacent position using a free needle (Davis Tonsil ½ Circle Taper Point; Vessel Medical). A hemostat is placed on the single suture throw to provisionally secure the graft in this trial position. This allows the surgeon to trial and examine the MPFL graft in extension, 45° of flexion, and terminal flexion. The goal is to provide a check rein to lateral translation of the patella and provide a firm endpoint to avoid further dislocation without overtension of the graft that may lead to increased contact pressures in the patellofemoral joint.
Once appropriate graft position is confirmed, using the double-loaded suture, we prefer to secure each limb separately to the decorticated medial patella. One end of the suture is threaded through the graft once and will act as a post. The other end of the suture is threaded through the graft 3 times in a modified Mason-Allen stitch. With the knee in that same position of flexion, the knot is tied and the graft is secured to the medial side of the patella. For secondary fixation, the remaining ends of the graft are passed below the periosteum on the anterior surface of the patella. Using a 0 Vicryl (Ethicon US), the periosteal flaps are sutured on top of the graft, incorporating the residual graft. The ends are cut and a repeat dynamic examination is performed to confirm the position of the patella and the patellar tracking and to ensure that overtensioning did not occur. Following irrigation, a standard closure is performed. The patient is placed in a hinged knee brace and cryotherapy is applied (Polar Care, Breg Inc).
POSTOPERATIVE PROTOCOL
For the initial or the acute postoperative phases, an emphasis on edema control, early quadriceps activation, and range of motion is recommended. We recommend weight-bearing as tolerated with the leg locked in extension until adequate quadriceps control is achieved. The patient must be able to perform 10 straight leg raises without an extension loss to be cleared to weight-bear as tolerated without motion restriction in the brace. Full motion is allowed immediately.
OUTCOMES
In our experience using isolated MPFL reconstruction in the skeletally immature patient, we have had no evidence of physeal arrest, leg-length inequality, or angular deformity, and only11.4% of patients have had recurrent instability. The mean Kujala score in this cohort was 90.4, with a mean Tegner activity of 7, after the procedure. All failures in our cohort had had severe trochlear dysplasia.