Combined MPFL Reconstruction with Tibial Tubercle Osteotomy and Repair of Patellar Cartilage Defect with Particulated Juvenile Articular Cartilage
Authors: Dennis Elizabeth R. , Marmor William A. , Shubin Stein Beth E. 
Published: November 2022

Background:
Medial patellofemoral ligament (MPFL) reconstruction with tibial tubercle osteotomy (TTO) and particulated juvenile articular cartilage (PJAC) grafting can be performed in combination for the treatment of recurrent patellar instability with associated patellar cartilaginous defects.

Description:
Preoperative planning is an essential component for this procedure. Measurement of the tibial tubercle to trochlear groove (TT-TG) distance and the Caton-Deschamps index (CDI) allows for determination of the degree of medial and anterior translation and helps to identify whether distalization is necessary. The procedure begins with a thorough examination under anesthesia to determine range of motion, patellar tracking, translation, and tilt. A diagnostic arthroscopy is performed, at which time patellar tracking is again assessed and the patellar and trochlear cartilage are evaluated. A medial parapatellar incision is made, and the layer between the capsule and retinaculum is identified. This layer will serve as the location for the MPFL graft passage. The medial patella is decorticated to prepare for graft fixation. The patella is then everted, and the cartilaginous defect is prepared and sized. The PJAC graft is prepared on the back table based on these measurements. The MPFL graft is then anchored to the decorticated medial patella. Attention is then turned to performing the TTO. The patellar tendon is isolated and protected. The osteotomy shingle is created with a combination of sagittal saw and osteotomes, followed by shingle translation and fixation. Attention is then turned to performing the MPFL graft fixation on the femur. An incision is made, the area of the sulcus between the medial epicondyle and adductor tubercle is identified, and a pin is placed. Graft isometry is assessed, pin placement is confirmed, and a socket is created. After thorough irrigation, the patella is then everted and the PJAC graft is implanted and set with fibrin glue. Finally, the MPFL graft is passed through the previously identified layer and docked into the medial femur at its isometric point.

Alternatives:
Nonoperative treatment of first-time patellar instability can often include physical therapy, bracing, and activity modification. However, recurrence rates can be high, especially in a subset of high-risk patients with characteristics such as age of <25 years, trochlear dysplasia, patella alta, and coronal plane malalignment. For patients with recurrent patellar instability, a well-executed MPFL reconstruction restores stability while the TTO serves to unload the lateral and/or inferior patellar cartilage and correct osseous malalignment. Additional techniques, such as a distal femoral osteotomy and trochleoplasty, have been suggested to address patellar tracking and trochlear dysplasia. For patients who have sustained cartilaginous injury from their previous dislocations, PJAC can be utilized to restore the patellofemoral cartilage. Alternative operative treatments of cartilaginous defects include matrix-induced autologous chondrocyte implantation (MACI), mosaicplasty, osteochondral allograft, microfracture, and—in later stages of disease—patellofemoral arthroplasty.

Rationale:
The MPFL is an important medial stabilizer in the knee, with high rates of injury in patients who have experienced patellar instability. When an MPFL reconstruction is combined with a TTO, it can stabilize the patella while simultaneously correcting osseous malalignment and unloading the patellofemoral joint. Additionally, use of PJAC is advantageous for patients with patellar chondral defects because it is a single-stage technique, has low technical difficulty, and can be customized to accommodate large lesions.

Expected Outcomes:
MPFL in combination with TTO and PJAC provides patellar stabilization and overall improvements in pain and function, with low rates of recurrent instability. A recent study by Franciozi et al. showed significant improvement in functional outcome scores at a minimum of 2 years with no recurrent subluxations or dislocations
1
. Another study by Krych et al. showed an 83% rate of return to sport in patients who underwent MPFL reconstruction combined with TTO
2
. With respect to PJAC grafts, a study by Grawe et al. assessed the maturation of PJAC implanted into patellar chondral defects, demonstrating that the matured grafts paralleled the characteristics of the surrounding native cartilage. In addition, the authors reported that 73% of patients who completed follow-up magnetic resonance imaging at 2 years postoperatively had good defect fill, defined as >66%
3
.

Important Tips:

A lateral release may be necessary if the patella is unable to be everted parallel with the table. Typically, 80% of patients with instability do not need a lateral release, whereas 80% of patients with malalignment and isolated patellar osteoarthritis do need a release.MPFL graft isometry should be assessed by manually placing the patella in the center of the trochlea and flexing the knee to roughly 70°. The graft should slacken in subsequent deeper flexion and should never tighten.When customizing the TTO to obtain the necessary anatomic alignment, the surgeon can achieve additional medialization by dropping their hand to create a flatter cut, while additional anteriorization can be created with a steeper cut.Once the cartilage defect has been prepared and measured, a mold can be created to allow for concomitant PJAC preparation on the back table earlier in the procedure.

Acronyms and Abbreviations:

TT-TG = tibial tubercle to trochlear groove distanceMPFL = medial patellofemoral ligamentTTO = tibial tubercle osteotomyPJAC = particulated juvenile articular cartilageMACI = matrix-induced autologous chondrocyte implantationOR = operating roomIV = intravenousK-wires = Kirschner wiresCPM = continuous passive motionMRI = magnetic resonance imagingOA = osteoarthritisASA = acetylsalicylic acid (aspirin)DVT = deep vein thrombosisPPX = prophylaxisNWB = non-weight-bearingFWB = full weight-bearingPOD = postoperative day