Special Considerations for Pediatric Patellar Instability

ADDUCTOR MAGNUS TENDON TRANSFER

This technique is a double-bundle MPFL reconstruction that uses a pedicled graft of the distal adductor magnus tendon and suture anchors or incomplete osseous sockets to recreate the MPFL anatomically (Figure 5). Avikainen and colleagues⁹⁶ and Sillanpää and colleagues¹²⁵ described this procedure as a progression from the original single-strand adductor magnus transfer technique. First, maintaining the distal insertion, a graft of approximately 14 cm to 18 cm is harvested from the adductor tendon and then passed through a subcutaneous tunnel between the distal vastus medialis obliquus and the superficial joint capsule. The graft is then looped at the medial patella so that the distal bundle runs back to the adductor tubercle.¹²⁵ With the knee at 30° of flexion to assure proper tension, the graft is secured at both the patella and near the adductor tubercle with suture anchors.¹²⁵ Hambridge and colleagues¹²⁶ compared a similar adductor magnus transfer with other pedicled techniques including bone-quadriceps tendon autograft and bone-patellar tendon allograft and found positive results for all 3 methods of reconstruction.

HEMI-PATELLA TENDON TRANSFER

In a similar technique to the adductor tendon transfer, the medial section of the patellar tendon is harvested from the TT and run from its proximal insertion at the medial patella to the medial femoral attachment via a subcutaneous tunnel. The free end of the graft is then secured with suture anchors or incomplete osseous sockets with the knee at 30° of flexion.¹²⁷

HAMSTRING GRAFT WITH ADDUCTOR TENDON AS A PULLEY

Several techniques opt to use a more dynamic model of MPFL reconstruction in which the adductor tendon or medial collateral ligament (MCL) is used as a pulley for the hamstring graft (Figure 6).^128,129 The site of the pulley approximates the normal attachment of the MPFL to the femur and so acts as an effective anatomic replica of the MPFL origin. A semitendinosus graft is harvested and is prepared with continuous sutures, and 2 tunnels to secure the graft are drilled into the patella. The graft is then run subcutaneously from the medial side of the patella to the adductor magnus tubercle into which an osteoperiosteal tunnel is drilled at its distal femoral insertion. The graft is looped through the adductor tunnel and secured with sutures. Proper knee kinematics was ensured by placing the knee at 30° of flexion as the ends of the tendon are secured to the patella.^114,130

HAMSTRING GRAFT WITH MCL AS A PULLEY

The MCL can also be used as a pulley rather than the adductor tendon. The semitendinosus graft is harvested and prepared and the patella drilled as it is in the previous technique. The MCL was fashioned into a pulley by making a slit in its posterior one-third. The semitendinosus graft is looped through this slit, and both ends of the graft are held in place with suture anchors on the surface of the patella.¹²⁹

ADDITIONAL PROCEDURAL COMBINATIONS

Depending on the needs of the individual patient, MPFL reconstruction, and other patellar stabilization techniques can also be combined with additional procedures. Arshi and colleagues⁸³ conducted a review of 6190 adolescents surgically treated for patellar instability and reported the most common additional procedures performed at the time of the stabilization. They found 43.7% of the population underwent lateral retinacular release, which while not effective as an isolated technique to treat patellar instability, has often been used in combination with MPFL reconstruction.^131-133 There is currently a lack of consensus regarding the success of adding a lateral release to the reconstruction. Some studies report no difference while others report a decrease in stability after lateral release.^90,134-136 While lateral retinacular release has been shown to decrease the force required to displace the patella, it can be surgically indicated in certain patients undergoing MPFL reconstruction.¹³¹ The authors advocate that if the lateral retinaculum is tight such that centralized patellar tracking is inhibited following the reconstruction, or if the patella cannot be pushed passively from a laterally tilted position to the neutral horizontal position, lateral retinacular lengthening should be performed to improve kinematics.¹³²

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