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Medial patellofemoral ligament (MPFL) injuries are common in children and young adults. In patients with recurrent patellar dislocations with normal lower-extremity alignment, anatomic reconstruction of the MPFL has been shown to restore patellar stability. We describe a technique that creates an anatomic reconstruction using a dual docking technique into the patella. Our technique is simple and efficacious for reconstructing the MPFL without implant fixation in the patella, allowing a maximal bone-tendon interface for healing.
Technique Video
See video under supplementary data.
The medial patellofemoral ligament (MPFL) has been shown to be the primary stabilizing soft-tissue structure of the patellofemoral joint. Several studies, both anatomic and biomechanical, have shown that the MPFL is the most important restraint to lateral patellar translation from 0° to 30° of flexion.
Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: Surgical technique and clinical outcome.
The purpose of this Technical Note and accompanying video (Video 1) is to describe an MPFL reconstruction technique that uses a patella dual docking tunnel technique to create an anatomic reconstruction.
Diagnosis and Preoperative Planning
Examination should include evaluation for an effusion, which may indicate intra-articular pathology. Tenderness over the medial epicondyle can indicate an injury to the MPFL. Patellar mobility is assessed in full extension and compared with the contralateral side, with patellar apprehension and lateral patellar quadrant translation with a firm versus soft endpoint. Patellar tracking is assessed by evaluating for the J sign. Limb alignment is assessed for the presence of femoral anteversion, genu valgum, and external tibial torsion. Hip and quadriceps muscular strength should be assessed. Generalized ligamentous laxity is assessed with evaluation for the presence of elbow and knee recurvatum, metacarpal hyperextension, passive apposition of the thumb to the volar forearm, and active forward flexion of the trunk with the knees fully extended so that the palms of the hands rest flat on the floor.
Radiographic evaluation should include standard anteroposterior, lateral, and axial weight-bearing views. Careful evaluation for intra-articular bodies and osteochondral fractures should be performed. The lateral radiograph can be used to assess for patellar height and depth of the femoral trochlea. The axial radiograph can be used to assess the femoral sulcus angle, congruence angle, lateral patellofemoral tilt angle, lateral shift ratio, and absolute lateral patellar displacement.
Computed tomography is used to measure the tibial tubercle and trochlear groove distance. Magnetic resonance imaging can be used to evaluate other injuries after a patellar dislocation, including a bone contusion on the lateral femoral condyle and medial patella, as well as an MPFL tear and articular cartilage injury.
Indications and Contraindications
There is debate in the literature concerning when surgical intervention is indicated for patellar instability. Our indications include recurrent instability despite a trial of nonoperative treatment that typically includes patella-stabilizing braces and physical therapy to include quadriceps, hip, and core muscle strengthening. In patients with osteochondral injuries and intra-articular bodies, arthroscopy is indicated for the treatment of these injuries and concomitant MPFL reconstruction. Contraindications to an isolated MPFL reconstruction include limb rotation and alignment abnormalities.
Technique
The patient is placed supine on the table. An intraoperative examination is performed to confirm clinical findings. We perform a single-portal diagnostic arthroscopy from the superolateral portal of the knee,
allowing us to evaluate the cartilage, patellofemoral tracking, and laxity of the medial joint restraining ligaments. Arthroscopic treatment of any noted abnormalities is performed as necessary through standard portals (Table 1).
Table 1Pearls and Pitfalls
Pearls
Pitfalls
Indications
A full history should be obtained and a physical examination performed to identify risk factors for failure of reconstruction.
Isolated MPFL reconstruction with concomitant malalignment can result. Failure to recognize systemic disease or syndromes can occur.
Arthroscopic evaluation
The surgeon should visualize the ability to manually reduce the patella into the trochlear groove.
Failure to recognize intra-articular pathology that should be treated concordantly can occur.
Femoral tunnels
Intraoperative fluoroscopy should be used to identify femoral tunnel landmarks. The surgeon should consider the femoral tunnel position relative to the distal femoral physis in skeletally immature patients.
An imperfect lateral radiograph of the distal femur to assess the starting point can lead to improper tunnel placement.
Patellar tunnels
Palpation of the patella articular surfaces while drilling can provide tactile feedback for the direction of drilling.
Superficial tunnels can lead to fracture. The surgeon should avoid reaming across the entire length of the patella to avoid fracture risk. The surgeon should avoid large-diameter tunnels to avoid fracture as well as tunnel convergence.
Graft docking
The interosseous portion of the graft should be made shorter than the tunnel to ensure that the tunnel is not filled before adequate tension is achieved.
Graft tensioning
Tensioning with the knee in flexion allows the patella to articulate within the trochlear groove, which can help prevent over-tightening of the graft.
The surgeon should avoid over-constraining to create gross tilting or preventing at least 2 to 3 patellar quadrants of translation.
We use a semitendinosus allograft doubled over. The folded end is sutured together with a locking stitch with the free ends exiting the end of the graft. Two FiberWire sutures (Arthrex, Naples, FL) are run through the 2 graft limbs individually. The diameters of the folded end and 2 graft limbs are measured and used to size the femoral tunnel and patellar tunnels, respectively. The graft is placed on a tensioning device and wrapped in a moist sponge. An example of our graft after preparation is shown in Figure 1.
Fig 1Graft preparation using Acufex tensioning device (Smith & Nephew). To the left is the single arm that will be inserted into the distal femur; to the right are the 2 arms that will be inserted into the patella.
We place a Beath pin against the skin and confirm the location of the tip. Care should be taken during this step in skeletally immature patients because the femoral attachment of the MPFL is near the distal femoral physis and may need to be adjusted if a physeal-sparing approach is indicated.
A skin incision is made, and the Beath pin, starting at the correct insertion site, is advanced across the femur parallel to the knee joint and out the lateral skin surface (Fig 2). We aim slightly proximally and anteriorly to avoid the risk of violating the intercondylar notch and trochlea, as well as to avoid damage to the neurovascular structures. If more than 2 cortices are encountered during passing of the pin, then fluoroscopy can be used to determine whether the femoral trochlea or notch has been violated and the pin should be redirected. A cannulated reamer, corresponding to the measured diameter of the folded graft end, is used to drill over the pin to a depth of 25 mm. Multiple structures attach near the femoral attachment of the MPFL, including the superficial medial collateral ligament, posterior oblique ligament, medial head of the gastrocnemius, and adductor magnus tendon.
To our knowledge, the clinical significance of potentially injuring these structures while reaming has not been elucidated. A looped suture is then shuttled through the femur using the Beath pin, pulling the pin out laterally. The looped end is left medial to shuttle the sutures from the folded graft end out the femur. The graft is tensioned into the femoral tunnel. A guide pin is placed into the tunnel, and an interference screw (Arthrex) is used to secure the graft into the femoral tunnel; the surgeon should then ensure that the graft is securely fixed (Fig 3).
Fig 2(A) Lateral radiograph of a knee with anterior to the left and posterior to the right with the pin at our femoral tunnel location, anterior to the posterior cortical line (asterisk) and superior to the Blumensaat line (arrow). (B) Clinical photograph of a left knee in a patient positioned supine with the Beath pin entering through a medial incision, drilled into the femoral tunnel starting location.
Fig 3Photograph of a left knee in a patient positioned supine with proximal to the left and distal to the right. The semitendinosus graft (arrow) is being secured into the medial femoral tunnel. The guidewire (asterisk) for an interference screw is in place.
A 3- to 5-cm longitudinal incision is made over the medial third of the patella. We dissect sharply down to bone and elevate the fascia. Using a long-handle hemostat, we dissect between layers 2 and 3 of the medial soft tissue,
ensuring to remain extra-articular. If there is any concern, confirmation is made arthroscopically. The dissection is carried to and out of the medial femoral incision. Two free looped sutures are passed through this retinacular tunnel and used to shuttle both graft limbs through the tunnel, exiting adjacent to the patella (Fig 4).
Fig 4Photograph of a left knee in a patient positioned supine with proximal to the left and distal to the right. One limb of the semitendinosus graft (arrow) is being shuttled through the medial knee retinacular tunnel, exiting adjacent to the patella. The second limb (asterisk) has not yet been shuttled.
We mark the site of our patellar tunnels and be sure to center in the anterior-to-posterior axis. We plan on inserting 2 Beath pins that are spaced at least 1 cm apart and usually in the superior third and middle third of the patella. Minor changes in tunnel location may occur depending on graft size. Two Beath pins are inserted to and through the patella, coming out of the skin laterally. We keep the pins parallel to avoid pin convergence and prevent tunnel communication and potential fracture. We confirm that the pins are extra-articular with fluoroscopic images (Fig 5). If unclear, we encourage arthroscopic confirmation. Using a cannulated drill, we then drill over the pins to a depth of 2 cm. The drill size corresponds to the graft limb diameter and is typically between 3.5 and 4.5 mm in diameter. We confirm an adequate bony bridge (Fig 6).
Fig 5(A) Photograph of a left knee in a patient positioned supine with proximal to the left and distal to the right. The medial aspect of the patella with the 2 tunnel sites is marked (arrows). Two Beath pins are drilled through the patella at these sites. (B) Lateral fluoroscopic image of a left knee after the Beath pins (arrows) have been drilled from medial to lateral across the patella. The image confirms that the pins remain extra-articular as they cross the patella.
Fig 6Photograph of a left knee in a patient positioned supine with proximal to the left and distal to the right. We prepare to drill our tunnel with a 4.0-mm cannulated reamer (asterisk). The reamer has been marked at 2 cm (arrow). We visually confirm that the spacing is adequate such that the tunnels do not meet.
The free ends of the grafts are held against the patella, and we mark the graft limbs at the point of bony contact and about 18 mm distal to this location (making the interosseous portion of the graft shorter than the tunnel ensures that we do not fill the tunnel before adequate tension is achieved). We run a suture in locking technique between these 2 points and cut the excess. The free ends are trimmed to ensure easy passage into the tunnels (Fig 7).
Fig 7Photographs of a left knee in a patient positioned supine with proximal to the left and distal to the right. (A) Measurement of graft limbs. We mark the graft 2 cm distal (arrowhead) to the point at which it makes contact with the medial cortex of the patella (arrow). (B) Suturing of grafts with a straight needle (asterisk) and a looped FiberWire suture from the point of contact with the medial cortex of the patella (arrow) to the marked point 2 cm distal (arrowhead).
We make a lateral incision over the Beath pins, where they exit laterally, at this time to prevent inadvertent suture amputation after the suture has been shuttled. The graft limb sutures are shuttled through the patella, using the Beath pins, and out of the lateral incision. The graft limbs are individually “docked” into their respective tunnels. It is important to ensure that the grafts are secured into their tunnels and not held up at the entrance (Fig 8). The sutures exiting laterally are tied to the other limb under minimal tension with the knee in 30° of flexion, with the patella held centrally in the trochlea. We tension the graft at 30° because the graft is longest in this position. There has been much debate and research into the ideal knee position while tensioning.
The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction.
We believe that the ideal location may vary with differing patient anatomy and tunnel locations. Ultimately, the native MPFL, although firmly attached, is not under tension at rest and only begins to undergo tension as the knee goes into flexion. We aim to mimic this by ensuring that there is minimal tension as we tie our sutures. We examine the knee in full extension and flexion to ensure supple knee range of motion. In addition, we ensure that the patella has no gross tilting or medial over-constraint. However, excessive lateral translation at this time should be corrected. One can compare the operative knee with the contralateral (unaffected) limb if there is concern. The patient is placed in a hinged knee brace and is allowed to flex the knee to 90° and fully bear weight with the knee in full extension.
Fig 8(A) Photograph of a left knee in a patient positioned supine with proximal at the top and distal at the bottom. Both graft limbs have been secured into their respective patellar tunnels (asterisks) on the medial aspect of the patella. (B) Sutures coming out of the lateral incision after they have been passed through the patella from medial to lateral. The sutures from the different graft limbs are tied to each other.
described 2 functional bundles of the MPFL. Use of a 2-limb graft technique, as we describe, as opposed to single–graft limb patellar insertion allows for more accurate re-creation of these bundles and insertion on the MPFL.
Mechanical studies have shown the importance of the MPFL in its contribution to the restraining force against lateral displacement of the patella, contributing 53% to 60% of restraining force against lateral patellar translation.
The importance of this ligament in chronic lateral patellar instability in a patient with normal osseous anatomy and limb alignment has led to the development of various surgical techniques to reconstruct the MPFL with variations in graft choice, anatomic versus nonanatomic reconstruction, and fixation methods.
Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: Surgical technique and clinical outcome.
A femoral tunnel that is too proximal may lead to graft laxity in extension and over-tensioning in flexion, a femoral tunnel that is too distal may lead to graft over-tensioning in extension and laxity in flexion, and tunnel placement too anterior can cause overloading of the medial patellofemoral cartilage.
The fixation method to the patella can be generalized as tunnel versus suture fixation. A systematic review showed a higher risk of recurrent dislocation or subluxation (4.8% vs 3.3%) and hypermobility or apprehension (24% vs 8.6%) with suture fixation.
We describe a technique that re-creates an anatomic reconstruction of the MPFL at both the femoral and patellar attachments. Our method of fixation, using a dual docking technique, has potential benefits (Table 2). It creates 2 incomplete transverse tunnels that do not rely on implants for fixation. The docking technique is well described for ulnar collateral ligament reconstruction of the elbow and has been shown to have favorable outcomes.
Our use of this technique allows for increased surface area for graft-to-bone healing. Our dual docking technique also simplifies tunnel placement by obviating the need to converge tunnels, potentially decreasing surgical time and decreasing risk of fracture. A single-tunnel MPFL docking technique has been described and shown to have good outcomes.
However, we believe that a more anatomic re-creation of the MPFL broad insertion on the patella may be of benefit, especially in the very active patient. In addition, docking the grafts individually allows for the use of 2 smaller tunnels as opposed to 1 larger tunnel. Other authors have described 4-tunnel fixation in the patella. The benefit of our technique is the ability to accurately restore the anatomy while limiting the chance of fracture caused by 4 tunnels. Potential limitations of our described method include dual-tunnel placement, which may lead to increased risk of fracture compared with single-tunnel or suture anchor fixation. Improper angling and positioning of the Beath pin may cause inadvertent iatrogenic chondral damage if it penetrates the joint. In conclusion, we describe a surgical technique with potential benefits creating an anatomic reconstruction of the MPFL using 2 patellar tunnels to secure each graft limb.
Table 2Advantages and Disadvantages
Advantages
Anatomic reconstruction
Not reliant on implants in patella
Docking technique allows greater surface area for graft-to-bone contact
Parallel tunnels in patella simplify previously described techniques
Disadvantages
Dual tunnels may lead to increased risk of fracture
Tensioning can be difficult with docking technique
Medial patellofemoral ligament (MPFL) dual patella docking technique in a left knee with the patient placed in the supine position. Arthroscopy begins by use of a superolateral portal. A looped semitendinosus allograft is used for the MPFL reconstruction. A single femoral tunnel location is identified with fluoroscopy and drilled with a cannulated reamer. Two patellar tunnels are drilled 2 cm deep with cannulated reamers, and the location is confirmed with fluoroscopy. The folded end of the graft is shuttled into the femoral tunnel, and the 2 remaining graft limbs are docked into the patellar tunnels. The grafts are tensioned and tied over the lateral cortex of the patella with the knee in 30° of flexion.
Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: Surgical technique and clinical outcome.
The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction.
The authors report that they have no conflicts of interest in the authorship and publication of this article. Full ICMJE author disclosure forms are available for this article online, as supplementary material.
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