Table 1.

Pearls and Pitfalls

Pearls

1.Flexion of the involved knee over leg support or triangle would allow for easy lateral fluoroscopic imaging.

2.Retrograde insertion of guide-pin for transphyseal screw insertion is easier and more precise than antegrade insertion as the starting point is nearer to the physis.

3.The transphyseal screw should be inserted before MPFL graft femoral attachment, so that the screw would not inadvertently damage or interfere with the MPFL graft.

4.A fully threaded screw is preferred for hemiepiphysiodesis as it would facilitate later removal if needed.

5.Gracilis autograft is the graft of choice due to its smaller diameter and hence the need for smaller (3.5 mm) patellar tunnel.

6.A posteromedial approach for graft harvest is cosmetic, easier and safer for the saphenous nerve compared with the traditional anteromedial approach.

7.Graft passage through patellar tunnels can be facilitated by trimming the graft ends or substance, chamfering the tunnels using curved curette, and by using mineral oil.

8.The guide-pin for femoral tunnel should be positioned on the distal femoral physis on the lateral view. This would correspond to the pin being distal to the physis on the anteroposterior view.

9.Once the MPFL graft is placed in the femoral tunnel, the knee is flexed and the pull-through sutures are clamped against the thigh. The knee is then extended and patellar mobility is assessed so as to avoid overtensioning of the MPFL graft.

10.Before final femoral fixation, an arthroscopic evaluation would help to confirm extra-articular position of the graft and to assess MPFL graft function with knee range of motion.

11.Complete insertion of the femoral interference screw is confirmed on fluoroscopic imaging.

Pitfalls

1.The transphyseal screw should pass through the center of the distal femoral physis on a perfect lateral view, so as to avoid any sagittal plane deformity.

2.During dissection on the medial side of patella, care should be taken to avoid joint capsule penetration. If the joint capsule is opened, it can be sutured before placement of the MPFL graft.

3.An 8- to 10-mm bone-bridge should be maintained between the patellar tunnels to prevent the graft from cutting through the tunnels.

4.The guide pin for femoral tunnel should be directed slightly anterior to avoid the intercondylar notch and slightly inferior to avoid distal femoral physis.

5.Dissection near the femoral tunnel entrance should be kept to minimum to avoid injuring the perichondral ring around the physis.

6.During percutaneous insertion of the graft in the femoral tunnel, a nitinol guidewire for interference screw should be placed in the tunnel prior to graft passage.

7.Before final femoral fixation, it should be checked that the MPFL graft has not bottomed out in the femoral tunnel or has not bunched up against femoral tunnel entrance. There should be no slack when the MPFL graft is gently pulled from the patellar side.

MPFL, medial patellofemoral ligament.