Physeal-Sparing Medial Patellofemoral Ligament Reconstruction With Quadriceps Turndown and Patellar Tendon Transfer

Patellar instability is a common problem in the pediatric population. When surgery is indicated, skeletal immaturity poses unique challenges due to the risk of deformity or limb length discrepancy if the physis are injured. Therefore, the optimal combination of procedures in prepubescent patients with patellar instability remains unclear. Several stabilization procedures have been described for the treatment of patellar instability. The medial patellofemoral ligament (MPFL) or similar structures are commonly reconstructed, as they function as the primary restraint to lateral translation in early flexion and are commonly incompetent after lateral patellar dislocations. Traditional MPFL reconstruction can pose a risk to the distal femoral physis in skeletally immature patients because of the proximity of the insertion of the MPFL to the physis. Therefore, modified techniques are necessary. Distal realignment procedures have been used as accessory operations and, when necessary, must consider the presence of the proximal tibial physis. This article describes physeal-sparing MPFL reconstruction with quadriceps autograft and patellar tendon transfer for the management of patellofemoral instability in the skeletally immature patient.

Introduction

Patellar dislocations are common in the pediatric population, with incidence ranging from 29 to 43 per 100,000 patients, accounting for 2%-3% of all knee injuries. ^, Risk factors for patellar instability include anatomic factors, such as patella alta, trochlear dysplasia, excessive femoral anteversion, genu valgum, an increased tibial tubercle to trochlear groove (TT-TG) distance, and others. Furthermore, skeletal immaturity, ligamentous laxity, and prior patellar dislocation are associated with an increased risk of recurrence. ^,

Several classification systems have been proposed for patellar instability. Prior studies have used classifications split into 4 categories based on clinical scenarios: syndromic, obligatory, fixed, and traumatic dislocations. Each category has a different pathophysiology that influences surgical considerations. Traumatic instability, the most common type, results in excessive patellar translation in extension that typically improves with progressive flexion. Syndromic dislocation can be associated with soft tissue laxity, osseous deformity, neuromuscular imbalances, or other systemic issues. Obligatory dislocation results in instability when the knee is flexed, but more concentric reduction in extension. Fixed dislocations cannot be reduced. The underlying pathophysiology as well as patient and family expectations must be considered when planning treatment for each type of instability. This article will focus on 2 techniques that can be applied to any of the aforementioned types of patellar instability in skeletally immature patients.

Surgical Indications

Nonoperative management is often indicated in skeletally immature patients with first-time acute patellar dislocation without evidence of intra-articular loose bodies or osteochondral fracture requiring intervention. Standard practice includes bracing, activity restriction, and physical therapy targeted at proprioceptive training as well as strengthening the core and lower extremity muscles.

Operative management is generally indicated in skeletally immature patients with acute patellar dislocation with associated loose bodies or for recurrent dislocations. These are mostly relative indications, and the care of each patient requires shared decision making with the patient and family based on the risk of recurrence, patient activity level, family preferences, and the ability to successfully participate in rehabilitation postoperatively. The primary goal of surgical treatment is to prevent future instability. Previous studies have demonstrated that there is an increased risk of osteoarthritis and diminished knee function with successive instability, further suggesting the importance of early treatment. ^, ^, Finally, inability of a child to return to their desired activity level can have substantial implications on quality of life and mental health. ^, Therefore, consideration of early treatment is important in this population despite the challenges posed by the presence of open physes.

Surgical Considerations

Prior to surgery, diagnostic imaging generally includes anteroposterior (AP), lateral, and axial (“sunrise”) radiographs of the knee, magnetic resonance imaging (MRI), bone age films, and standing alignment radiographs to assess for coronal plane deformity. Importantly, a thorough physical exam is critical during preoperative assessment. Important elements include, but are not limited to, assessment of passive patellar mobility at various degrees of flexion, patellar tracking with active knee motion, presence of a “J sign”, the patellar apprehension test, evaluation of femoral anteversion and tibial torsion, as well as calculation of the Beighton-Horan score to assess for ligamentous laxity.

As previously mentioned, a plethora of anatomic and physiologic factors may predispose specific patients to patellar instability. Radiographic measurements of some of these factors include, but are not limited to, tibial tubercle to trochlear groove distance (TT-TG), patellar tendon-lateral trochlear ridge distance (PT-LTR), evaluation of trochlear dysplasia, and assessment of patellar height (especially patella alta). The patellofemoral cartilage is also evaluated closely on MRI, as the presence of chondral lesions may impact treatment. While TT-TG, PT-LTR, and patellar height measurements have demonstrated good interrater reliability, studies have demonstrated poor interrater reliability when evaluating skeletal maturity and trochlear dysplasia. The authors recommend assessing bone age via hand x-rays or by the knee MRI system proposed by Politzer et al. Regarding axial measures like TT-TG distance, the criteria utilized for older or larger skeletally mature patients may not be appropriate for prepubescent children. For example, a TT-TG distance of 18 mm may affect patellar tracking and stability drastically differently in a 6-foot-tall adult than in a 4.5-foot-tall child. Finally, there is ongoing debate regarding which anatomic factors should be corrected through surgical means and when these factors should be corrected in skeletally immature patients.

Some of the most-commonly employed and effective treatments for patellofemoral instability used in skeletally mature patients, such as osteotomies, cannot be utilized in patients with open physes due to risk of physeal disruption. This article describes a physeal sparing distal realignment procedure involving patellar tendon transfer typically performed in combination with physeal-sparing MPFL reconstruction with quadriceps autograft for skeletally immature patients. While this article focuses on 2 specific procedures, others like hemiepiphysiodesis or de-rotational osteotomies may be indicated depending on patient specific factors.

The senior author typically performs patellar tendon transfer for similar indications as tibial tubercle osteotomy in skeletally mature patients. While a TT-TG distance greater than 20 mm is commonly accepted as excessive in skeletally mature patients, a measurement of 15 mm can sometimes be excessive in prepubescent children. The exact TT-TG “cutoff” in this patient population is unclear. Therefore, this measurement is supplemented by others, like the PT-LTR distance, the presence of a J-sign on physical examination, and patellar instability in higher ranges of knee flexion. When all of these factors suggest excessive lateralization of the distal extensor mechanism, the senior author will typically recommend distal realignment via patellar tendon transfer. This technique is preferred over others, such as the Roux-Goldthwaite procedure, because it translates the entire distal extensor mechanism rather than just a portion of it, does not cause direct damage to the patellar tendon itself, and provides reliable healing due to intact periosteum distally and a robust periosteal flap medially. Preoperative MRI should be scrutinized for chondral lesions of the patella as large central or proximal lesions may be a contraindication for patellar tendon transfer. MPFL or a similar reconstruction is generally indicated for lateral patellar instability in extension and early knee flexion. The senior author utilizes various MPFL or medial patellofemoral complex techniques depending on patient characteristics. The quadriceps turndown technique obviates the need for allograft or patellar drilling and benefits from the robust nature of the quadriceps tendon.

Surgical Technique

The patient is placed in the supine position. A thigh tourniquet is applied on the operative limb. Diagnostic arthroscopy is performed to evaluate for intra-articular pathology.

Distal Realignment Via Patellar Tendon Transfer

Distal realignment is performed prior to MPFL reconstruction in order to ensure optimal tension of the MPFL. A midline incision is made over the anterior aspect of the proximal tibia, starting at the tibial tubercle and proceeding distally ( Fig. 1 ). The medial and lateral borders of the patellar tendon are defined, and the tendon’s attachment point to the tibial tubercle is identified. The patellar tendon is carefully dissected off the tibial tubercle sharply while ensuring that the tubercle apophysis is not violated. The tendon is fully elevated, but the associated distal periosteum remains attached to the tibia ( Fig. 2 ). A Krackow-type suture can be run up and down the patellar tendon for improved control of the tendon.

Next, a full-thickness flap of periosteum is elevated off the medial tibia adjacent to the elevated patellar tendon ( Fig. 3 ). A planned medialization is marked on the medial tibial cortex based on preoperative measurements, including the TT-TG distance and patellar tendon-lateral trochlear ridge (PT-LTR). The target medial translation is dependent on each patient’s initial TT-TG measurement, preoperative anatomy, and tracking after medialization. Generally, the goal is to achieve a TT-TG distance of 8-10 mm in skeletally immature patients. The extensor mechanism is then translated medially under the periosteal flap to the previously marked line and provisionally sutured to the periosteum. Patellar stability and tracking are then assessed and should demonstrate decreased lateral patellar translation without maltracking during passive motion. If substantial patella alta is present, the tendon can also be translated distally according to preoperative measurements. If patella alta is not present, care must be taken to avoid distal translation and potential patella baja. The knee is positioned in approximately 30 degrees of flexion, and nonabsorbable suture is used to further affix the extensor mechanism to the overlying periosteal flap ( Fig. 4 ). The tails of the patellar tendon sutures can be incorporated into a suture anchor for additional fixation if desired, but this is typically not necessary. Patellar mobility is then reevaluated throughout the arc of motion and should be improved in greater degrees of flexion. If maltracking is noted or insufficient realignment was achieved, the sutures can be removed and the extensor mechanism realignment can be adjusted. Pearls and pitfalls of this technique are shown in Table 1 .

Table 1

Pearls and Pitfalls of Distal Realignment Via Patellar Tendon Transfer

Pearls	Pitfalls
Maintain a full-thickness sleeve of patellar tendon and periosteum, taking care to leave the periosteum intact distally.	Do not perform stabilization procedures like MPFL reconstruction prior to distal realignment.
Mark the anticipated distance of translation on the medial tibial cortex after elevating the periosteum.	Do not violate the tibial tubercle apophysis or utilize electrocautery around the proximal tibial physis.
After translating the tendon and placing provisional sutures, check patellar tracking prior to finalizing fixation.	Avoid detachment of the patellar tendon or periosteum distally. Similar fixation strategies can be used if this occurs, but heightened attention to patellar height and medialization will be required.
A suture anchor can be used for supplementary fixation, especially if the tendon is inadvertently detached distally. However, anchors are typically not necessary.	Do not medialize the patellar tendon excessively, as this will negatively impact patellar tracking. Sutures can be revised if necessary.
Very young patients may exhibit significant apprehension or anxiety early during the rehabilitation process. While motion restrictions are important to ensure successful periosteal healing, early knee motion should be encouraged to avoid stiffness.	Avoid excessive distal translation of the patella when fixing the patellar tendon in patients with patella baja or normal patellar height.

Physeal-Sparing MPFL Reconstruction (Quadriceps Turndown Technique)

Following the distal realignment, MPFL or other medial patellofemoral complex reconstruction is performed to address residual patellar instability in early flexion, especially between 0 and 30 degrees. This procedure is performed after patellar tendon realignment so that the MPFL is tensioned optimally.

A 3 cm midline incision is made, starting near the center of the patella and proceeding proximally. Subcutaneous dissection is followed by incision of the paratenon overlying the quadriceps tendon. A Cobb elevator is used to clear any fat overlying the tendon. Excellent visualization of the entire width and length of the tendon is critical. Prior to harvesting the quadriceps graft, a small medial parapatellar incision is made through the retinaculum near the proximal-medial edge of the patella. The medial tissue planes are dissected layer by layer until the second layer of the knee is exposed. This contains the native MPFL and is just superficial to the joint capsule. This plane is developed in blunt fashion towards the medial aspect of the distal femur. The interval should be sufficiently wide and free of adhesions in order to ensure smooth graft passage. The medial edge of the patella can be decorticated with a curette or rongeur to optimize the osseous healing surface.

Next, a 9- or 10-mm parallel blade is used to incise the quadriceps tendon, starting about 2 cm proximal to the superior pole of the patella and proceeding proximally. The superficial half of the tendon is isolated in blunt fashion. This partial-thickness plane is advanced proximally and distally. After confirming adequate graft length, the strip of superficial quadriceps tendon is detached proximally ( Fig. 5 ). Typically, a quadriceps tendon length of 70 mm from the proximal pole of the patella is sufficient for this technique. However, maximizing this length is critical in order to ensure that it will ultimately reach its femoral attachment for reliable fixation. Traction sutures are inserted into the detached end of the graft. A fresh scalpel is used to elevate the strip of quadriceps tendon graft off the proximal patella, taking care to never fully detach it, especially as the tissue thins distally. Dissection typically stops near the junction of the proximal third and distal two-thirds of the patella, although lateral dissection is carried slightly more distal than medial in order to facilitate folding of the graft. The graft is then folded medially onto the anterior patella. With light-to-moderate tension held on the graft, nonabsorbable suture is used to stitch the folded portion of the graft into the surrounding patellar periosteum. Horizontal mattress sutures are placed along the superior and inferior edges of the graft, with full-thickness passes through the surrounding periosteum ( Fig. 5 ). The knots are tied on the patella rather than on top of the graft to avoid prominence. Holding tension on the graft while tying knots helps minimize truncation of the graft as the knots are tightened. Patellar fixation is then assessed by applying more tension to the graft.

Under fluoroscopic guidance, a 2.4 mm pin is inserted percutaneously into the medial aspect of the distal femur at Schottle’s point (just anterior to an extrapolation of the posterior femoral cortex and just proximal to Blumensaat’s line). A perfect lateral radiograph is critical to ensure accurate pin placement. Care is taken to avoid the distal femoral physis when advancing the pin laterally ( Figs. 6 A and B). As the senior author typically prefers a knotless, double-loaded suture anchor for on-lay fixation in the femur, the pin only needs to be advanced as far as the length of the anchor. The trajectory of the pin should still be slightly distal and anterior to avoid the physis. Preoperative MRI should be evaluated carefully prior to surgery to assess the degree of ossification at the medial femoral cortex. In very young patients, this area is often incompletely ossified. In such patients, suture-based anchors may be at higher risk of pull-out. Therefore, a hard-body anchor or small interference screw should be considered in such situations. In general, a small-profile implant is ideal given the small size of these patients, nearby physis, and minimal osseous disruption in case revision is eventually needed in this high-risk population. Several fluoroscopic views are obtained to confirm that the physis is not violated and that the pin does not cross through the intercondylar notch. The undulating nature of the distal femoral physis should be appreciated on both AP and lateral knee radiographs. While Schottle’s point may appear to be within the physis on a lateral view ( Figs. 6 A), the medial and lateral “valleys” of the physis slope proximally ( Figs. 6 B). Therefore, identification of Schottle’s point on lateral fluoroscopy is generally safe, provided that pin and implant placement are aimed away from the physis.

Once acceptable pin position is confirmed, a small incision is made around the pin. A clear plane is established between this incision and the previously dissected medial path for eventual graft passage. In order to confirm isometry, the graft can be passed through the medial interval and wrapped around the pin. Minimal tension change should be noted with passive knee motion. Once isometry is confirmed, the anchor is placed. Since the diameter of the aforementioned suture-based anchor is 2.6 mm (with further expansion once it is deployed intra-osseously), the provisional 2.4 mm pin tract serves as a pilot hole for it. Accordingly, the pin is removed and the anchor is inserted into the medial femoral cortex.

The graft is passed through the 2 loops of the knotless anchor ( Fig. 7 ). Adequate tension is held on the graft so that patellar mobility is normalized. With optimal tension applied to the graft, the graft is marked at a relatively static landmark (ie, where it meets the anchor or where it meets the skin) in order to ensure that it is not over-tensioned. The knee is then placed in 30 degrees of flexion. With appropriate tension maintained on the MPFL graft and the patella itself manually held within the trochlear groove, the tensioning strands from the anchor are used to sequentially cinch the suture loops onto the graft. Prior to fully tightening these sutures, patellar mobility and graft tension are confirmed. The loops are then definitively cinched onto the graft to provide on-lay fixation on the femur. Patellar mobility and tracking are reassessed through passive knee motion to ensure there is less than 2 quadrants of translation. The patella should be unable to be manually dislocated at any amount of knee flexion, and tracking should be smooth throughout the entire arc of motion. Construct stability is also assessed with direct visualization. The knee should be able to flex to at least 90 degrees without any implant or suture pull-out. Pearls and pitfalls of this technique are shown in Table 2 . Lengthening of the lateral retinaculum may be considered at this point if there is residual lateral patellar tilt. When necessary, this is typically performed after realignment and stabilization in typical cases of acute traumatic instability. However, in the setting of obligate or fixed dislocations, extensive lateral lengthening may be an important initial step.

Table 2

Pearls and Pitfalls of Physeal-Sparing MPFL Reconstruction With Quadriceps Turndown Technique

Pearls	Pitfalls
Ensure excellent visualization of the entire length and width of the quadriceps tendon.	Do not perform MPFL reconstruction before distal realignment procedures.
Develop the correct medial plane for graft passage, which is extra-articular, just superficial to the joint capsule. This can be confirmed arthroscopically prior to femoral fixation.	Do not detach the graft from the anterior surface of the patella, as the tissue thins distally. If this occurs, the detached end may be sutured to the patellar periosteum, or a suture anchor can be used in the medial edge of the patella.
Utilize a partial-thickness graft to avoid excessive insult to the quadriceps and graft prominence. A graft diameter of 6 to 7 mm is generally adequate.	Avoid a graft <70 mm in length. A longer harvest incision or a small, proximal counter incision can be made for optimal graft detachment.
Prior to detaching the tendon proximally, ensure adequate graft length. Approximately 70 mm of graft (measured proximally from the superior pole of the patella) is typically sufficient.	Malpositioning of the femoral attachment point can occur if a perfect lateral x-ray is not utilized for guidance.
Apply mild to moderate medial traction on the graft while suturing it to the patellar periosteum in order to avoid shortening as the knots are tied.	Avoid entering the distal femoral physis and intercondylar notch by starting the MPFL femoral tunnel at Schottle’s point and angling approximately 15° inferior and anterior.
During patellar fixation, place knots on the patella rather than the graft to avoid prominence.	Take note of the undulating nature of the distal femoral physis on the AP radiograph.
Implants that allow for on-lay fixation (ie, anchors with suture loops that can be cinched over the graft) obviate the need for a very long graft.	In very young patients, suture-based anchors may pull out if the medial distal femur is incompletely ossified. Consider utilizing small, hard-body fixation (ie, suture anchors or bioabsorbable screws) for femoral fixation in these patients.
Confirm graft isometry prior to final fixation.	Avoid over-tightening the MPFL graft to ensure normal patellar mobility and avoid maltracking.