Surgical Management of Patellofemoral Instability in the Skeletally Immature Patient

Lauren H. Redler, MD; Margaret L. Wright, MD

Disclosures

J Am Acad Orthop Surg. 2018;26(19):e405-e415. 

In This Article

Surgical Techniques

Surgical Considerations

In the pediatric population, a thorough understanding of the distal femoral and proximal tibial physes, as well as the TT apophysis, is critical when considering the multitude of available surgical techniques. The distal femoral physis has a characteristic undulating structure with relatively proximal medial and lateral borders (Figure 1). It is the largest and fastest growing physis in the body and contributes 70% of the femoral length and 37% of overall lower limb growth, which amounts to approximately 1 cm per year during skeletal immaturity. This growth plate fuses between the ages of 14 and 16 years in females and 16 and 18 years in males. The proximal tibial physis contributes approximately 55% of the length of the tibia and 25% of the length of the entire limb. On average, the proximal tibial physis contributes 0.65 cm of growth per year. This physis fuses between the ages of 13 and 15 years in females and 15 and 19 years in males. The TT apophysis fuses between the ages of 13 and 15 years in females and 15 and 19 years in males. The patella begins to ossify at age 3 years in females and 4 to 5 years in males. Growth disturbance as a result of injury of the patellar physis after MPFL reconstruction has not been reported. However, reconstruction technique and patellar fixation should be carefully considered in young patients and is discussed in more detail later.

Figure 1.

AP radiograph of a skeletally immature knee showing the undulating course of the distal femoral physis.

The femoral insertion of the MPFL is variable in pediatric patients, although radiographic and cadaver studies have found that in most patients, the midpoint of the femoral attachment is just distal to the physis.[18,19] Grafts placed proximal to the physis have the unique complication of proximal migration of the insertion after reconstruction and high tension across the physis. Fluoroscopic guidance is mandatory to avoid physeal violation and to determine appropriate tunnel placement. Care should be taken to confirm that the trajectory of the guide pin is completely distal to the physis on the AP view, given the concave shape of the distal femoral physis[20] (Figure 2). Although growth of the distal femoral epiphysis arises from the secondary subchondral growth plate, and is theoretically at risk of injury during creation of tunnels in the epiphysis, the concern for tethering of the distal femoral physis outweighs this issue, and thus, epiphyseal tunnels remain the location of choice. It is also important to consider the perichondrium of the physis because it is sensitive to injury. Caution must be exercised to avoid violation of the perichondrium during both surgical dissection and tunnel placement.

Figure 2.

A, AP intraoperative fluoroscopic image showing drilling of the femoral socket away from the physis. B, Lateral intraoperative fluoroscopic image showing the drill located at the Schottle point. C, Postoperative coronal magnetic resonance image showing the location of the interference screw on the distal medial femur distal to the physis. (Courtesy of Beth E. Shubin Stein, MD, New York, NY.)

Distal Realignment Procedures

Distal realignment procedures include the Modified Roux-Goldthwait, Galeazzi, and Nietosvaara techniques. These procedures are often combined with proximal realignments, including medial imbrication and lateral retinacular release.

The modified Roux-Goldthwait procedure is performed by detaching the lateral half of the patellar tendon from the TT and passing it medially under the patellar tendon. The tendon is sutured to the medial tissues and periosteum at the junction of the medial TT and pes anserine insertion. A lateral release, sometimes with medial imbrication, is also performed. In an early study of 30 knees that underwent the procedure, 26 knees had excellent results based on the Insall criteria[21] (Figure 3).

Figure 3.

Schematic drawing of the modified Roux-Goldthwait distal realignment technique. (Reproduced with permission from Weeks KD III, Fabricant PD, Ladenhauf HN, Green DW: Surgical options for patellar stabilization in the skeletally immature patient. Sports Med Arthrosc Rev 2012;20[3]:194–202.)

The Galeazzi semitendinosus tenodesis is performed by harvesting the semitendinosus tendon, leaving it attached at its distal insertion, and sewing it in an oblique manner to the inferomedial patella. A 2012 study of 34 knees treated with the procedure found that 35% required a second surgery and 82% had recurrent subluxation or dislocation, so it has largely been abandoned for more effective and anatomic reconstruction procedures[22] (Figure 4).

Figure 4.

Schematic drawing of the Galeazzi semitendinosus tenodesis distal realignment technique. (Reproduced with permission from Weeks KD III, Fabricant PD, Ladenhauf HN, Green DW: Surgical options for patellar stabilization in the skeletally immature patient. Sports Med Arthrosc Rev 2012;20[3]:194–202.)

Nietosvaara et al[23] described a more anatomic modification of the Galeazzi distal reconstruction, in which the semitendinosus and gracilis are left attached at the pes insertion, passed through a medial longitudinal patellar bone tunnel from inferior to superior, and then fixed to the femoral insertion of the MPFL with an interference screw. Although this technique seems promising in the original case series, long-term outcome studies have not yet been performed[23] (Figure 5).

Figure 5.

Schematic drawing of the Nietosvaara distal realignment technique. (Reproduced with permission from Weeks KD III, Fabricant PD, Ladenhauf HN, Green DW: Surgical options for patellar stabilization in the skeletally immature patient. Sports Med Arthrosc Rev 2012;20[3]:194–202.)

Soft-tissue Procedures

MPFL Repair. The MPFL is the primary restraint against lateral patellar translation and is stretched or torn in dislocation events, most commonly at the patellar origin.[19] Direct MPFL repair does not require patellar bone tunnels and poses minimal risk of femoral physeal injury. However, biomechanical tests of MPFL repair show weakness compared to the native ligament and MPFL reconstruction.[24] Patients who undergo MPFL repair are more likely than those who undergo reconstruction to have recurrent dislocation, and they are nearly as likely as patients who are treated nonsurgically to have recurrent dislocation.[23,25,26] MPFL repair is therefore only considered in patients with an initial dislocation who are undergoing a procedure for additional injuries (ie, osteochondral repair).

Hamstring MPFL Reconstruction. MPFL reconstruction is favored in patients with recurrent instability because the chronically injured medial retinacular structures are insufficient to prevent recurrent dislocation. Anatomic MPFL reconstruction procedures for skeletally immature patients have been described, with multiple fixation techniques available in the patella and femur to avoid injury to the physis. A recent meta-analysis found that anatomic grafts have the lowest recurrence rate when a double-limb graft configuration is used.[7] Similar outcome scores and rates of recurrent instability have been reported in both autograft and allograft hamstring reconstruction in skeletally immature patients.[7,20,27]

Patellar fixation using bone tunnels, docking technique, interference screw, or suture anchor fixation has been described.[20,28] Creation of a bony sulcus and suture anchor fixation are gaining favor because they avoid the risk of patella fracture (Figure 6). In addition, if cartilage restoration procedures (eg, osteochondral fracture fixation, OATS [osteochondral allograft transfer system], minced chondral allograft) are concurrently performed on the patella, creation of bone tunnels in the patella increases the possibility of the tunnels communicating and compromising the repair. The graft is placed between the capsule and medial retinaculum and fixed to the Schottle point at 30° flexion using an interference screw, suture button, or suture anchor technique. A schematic demonstrating hamstring MPFL reconstruction is shown in Figure 7, F.

Figure 6.

Intraoperative photographs demonstrating the placement of suture anchors (A) for fixation of the hamstring graft (B) to the medial border of the patella (asterisk) during medial patellofemoral ligament reconstruction.

Figure 7.

Schematic drawing of several physeal-sparing medial patellofemoral ligament reconstruction techniques: hemiquadriceps tendon transfer (A), hemipatellar tendon transfer (B), adductor tendon pedicle graft (C), hamstring graft using MCL as a pulley (D), hamstring graft using adductor tendon as a pulley (E), and double-limb hamstring allograft using patellar and femoral sockets (F). (Reproduced with permission from Gausden EB, Green DW: Medial patellofemoral ligament reconstruction: Hamstring technique, in Cordasco FA, Green DW, eds: Pediatric and Adolescent Knee Surgery. Philadelphia, PA, Wolters Kluwer, 2015, pp 140–147.)

Quadriceps and Patellar Tendon Reconstruction. Additional options beyond free tendon grafting include patellar and quadriceps tendon grafts, which eliminate patellar fixation, thus obviating the risk of patella fracture from bone tunnels that place the proportionally smaller patellar at higher risk. A 10- to 12-mm slip of the middle third of the superficial quad tendon is dissected and left attached at its insertion on the proximal patella. The tendon is subperiosteally dissected more distally on the lateral side so that when rotated, the attachment is primarily at the superomedial patella. A stay suture is placed to maintain an anatomic patellar origin, and then it is passed through the subvastus space and fixed to the medial femur[29] (Figure 7, A). A small series has shown good outcomes with minimal recurrence of dislocation in skeletally mature patients.[30] No long-term outcome studies have been performed in pediatric patients.

Some authors have described the use of a pedicled medial patellar tendon graft to reconstruct the MPFL[31,32] (Figure 7, B). The medial third of the patellar tendon is detached from the TT. The tendon is subperiosteally dissected to the proximal third of the patella to maintain an anatomic MPFL origin. The tendon is rotated, and a stay suture is placed to prevent further detachment from the patella. The graft is passed in the subvastus space and fixed to the femoral insertion.[32] Similar to the quadriceps tendon technique, outcomes of the pedicled medial patellar tendon technique in young, skeletally immature patients have not been reported and therefore may not apply to pediatric patients.

The use of a combined quadriceps and patellar tendon graft in an effort to create adequate tension throughout knee flexion has been described. Setting the graft length to appropriately establish graft tension is a challenge in any MPFL reconstruction technique, because placing the femoral insertion of the graft too proximally or distally can increase tension in flexion and extension, respectively, causing stress on the medial trochlea and patellar cartilage. The combined quadriceps and patellar tendon graft uses both the superficial quadriceps tendon and the patellar tendon to reconstruct the MPFL and medial patellotibial ligament (MPTL).[33] The superficial quadriceps tendon is harvested, and the MPFL reconstruction is performed as described earlier. The medial patellar tendon is also harvested, leaving the proximal end attached to the inferior patella, and it is attached to the tibia more medially to reconstruct the medial patellotibial ligament. With two points of fixation, there may be a secondary restraint to graft loosening. Hinckel et al[33] have specifically advocated for the use of a combined quadriceps and patellar tendon graft in patients with flexion instability, in children with unmodifiable anatomic risk factors, and for knee hyperextension associated with generalized ligamentous laxity. With this technique, it is important to consider both the tibial and femoral physes when determining the location of the MPFL and MTFL fixation sites.

Adductor Tendon Reconstruction. Because of the proximity of the adductor tubercle to the femoral insertion of the MPFL, the adductor tendon is also an ideal graft for MPFL reconstruction (Figure 7, C). The medial two thirds of the adductor magnus tendon are harvested, leaving it attached to the adductor tubercle, and the tendon is passed between the capsule and medial retinaculum and secured to the superomedial patella. A variation of this technique is to create a small bone tunnel in the distal femur from the MPFL insertion to the adductor tubercle, through which the graft can be passed to provide a more anatomic femoral insertion. Compared with patellar and quadriceps tendon MPFL reconstruction techniques, the adductor tendon graft was found to have similar outcomes and no recurrences of patellar instability.[34]

An important technical point to consider when performing this technique is that the tendon harvester should be pointed medially when harvesting the adductor tendon graft, which minimizes the risk of injury to the saphenous nerve and vessels passing through the adductor canal. In a cadaver study, Jacobi et al[35] explored the potential anatomic dangers of this technique. They found that the neurovascular bundle of the adductor hiatus, the saphenous nerve, and the saphenous branch of the descending genicular artery are typically approximately 10 cm away from the instruments during the graft harvest.

Sling Procedures. In an effort to maximize the ability to create an anatomic graft while minimizing the risk of femoral physeal injury, the use of sling procedures for MPFL reconstruction in pediatric patients has been described. Monllau et al[36] described a technique using gracilis autograft, in which the adductor tendon insertion is used for the femoral MPFL attachment point. Two tunnels are drilled through the patella in a V shape (Figure 7, E). The gracilis tendon is passed through one bone tunnel, under the VMO, around the adductor magnus tendon near its femoral insertion, back across the medial knee, and through the second patellar tunnel, and the ends are sutured together.

A similar technique has been described using the femoral MCL (medial collateral ligament) insertion. A free hamstring graft is fixed to the patella and then passed medially and under the posterior third of the femoral insertion of the MCL. The graft is then looped back over the MCL and sutured to the anterior patellar retinaculum.[37] A variation of this technique is to leave the semitendinosus attached to its pes insertion site. The free end of the graft can then be passed behind the femoral attachment of the MCL and sutured to the anterior patellar retinaculum. When performing the MCL sling techniques, care should be taken to avoid iatrogenic injury to the MCL, although no MCL injuries have been reported in the literature to date (Figure 7, D).

Although these techniques are appealing because they avoid tunnels on the medial femur and minimize the risk of growth disturbance, results have been mixed. One study found a higher risk of patellar instability after the adductor sling procedure compared to anatomic techniques.[38] A study of the adductor tendon reconstruction compared to the adductor sling procedure using hamstring autograft found no difference in postoperative instability or complications, but found that patients who had undergone the sling procedure were more likely than those who underwent reconstruction using the adductor magnus tendon to return to sports and had subjectively better outcome scores.[39] Longer follow-up of the same patients found that 11 of 15 had an excellent outcome with the sling procedure and only one required further surgery.[39]

Medial Quadriceps Tendon Femoral Ligament Reconstruction. Anatomic studies have shown variability in the patellar origin of the MPFL, with some patients having greater attachment to the VMO and quadriceps tendon as opposed to the patella directly.[40] A separate structure just superior to the MPFL, the medial quadriceps tendon femoral ligament (MQTFL), has been identified. It originates from the deep aspect of the quadriceps tendon and inserts superior to the MPFL.[41] MQTFL reconstruction is an alternative to MPFL reconstruction that avoids the use of patellar tunnels.

MQTFL reconstruction is performed with either semitendinosus autograft or allograft. The graft is fixed just anterior to the adductor tendon insertion with an interference screw or suture anchor. A second parallel incision is made over the medial patella and quadriceps tendon, and the graft is passed extracapsularly. The graft is sutured to the distal aspect of the medial quadriceps tendon, and patellar tracking is observed throughout range of motion to evaluate graft tension. In a series of 17 skeletally mature patients who underwent an MQTFL reconstruction for instability, none had recurrence at 1 year postoperatively.[41] A combination MPFL-MQTFL reconstruction technique is gaining popularity, sparking interest in renaming it the medial patellofemoral complex (Figure 8).

Figure 8.

Intraoperative photograph of the knee demonstrating a combined MPFL and MQTFL reconstruction. MPFL = medial patellofemoral ligament, MQTFL = medial quadriceps tendon femoral ligament. (Courtesy of Mininder S. Kocher, MD, MPH, Boston, MA.)

Lateral Release. Lateral release has not been found to be effective when performed in isolation, likely because it does not improve patellar tracking. However, in some cases, it may be an effective addition to medial soft-tissue procedures. Indications for a lateral release in combination with medial procedures include abnormal patellar tilt, defined as the inability to evert the patella to neutral, and TT-TG distance >20 mm. It is important to distinguish abnormal patellar tilt, which represents true lateral tightness, from lateral patellar tilt seen on imaging in all cases of patellar instability as a result of injured incompetent medial tissues. It is vital to avoid excessive lateral release because medial instability after lateral release has also been described.[42] Lateral release may also be indicated in patients with obligatory or fixed patellar dislocation because these patients have tight lateral restraints that limit the ability to maintain patellar reduction.[2]

Complications

Although MPFL reconstruction techniques are currently the standard of care for pediatric patients with patellofemoral instability, complications remain a considerable challenge. One of the largest series of young patients (aged <21 years) undergoing MPFL reconstruction reported an overall complication rate of 16.2%.[12] The most common complications were loss of complete knee flexion and recurrent patellofemoral instability. In the patients with loss of flexion, all improved with manipulation under anesthesia and nearly all had anterior placement of the femoral insertion point identified on MRI.[12] One study found that the primary radiographic risk factor for recurrent dislocation was the severity of trochlear dysplasia.[43] Although specific methods of fixation and graft type have not been associated with complications after anatomic reconstruction, patella fracture is a known complication of the bone tunnels used for patellar fixation. Six cases of patella fracture (4.3%) were identified in one series, and five of the six required surgical fixation.[44]

Although uncommon, this is an important consideration when choosing the technique of MPFL reconstruction, especially in younger patients with a less ossified patella and small margin for error. This may sway the surgeon to use techniques that do not require patellar bone tunnels (quadriceps or patellar tendon autograft or suture anchor fixation).

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