Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Instability

Andrew J. Cosgarea, MD

Miho J. Tanaka, MD

John J. Elias, PhD

Dr. Cosgarea or an immediate family member serves as a board member, owner, officer, or committee member of the Patellofemoral Foundation. Dr. Tanaka or an immediate family member serves as a board member, owner, officer, or committee member of the American Academy of Orthopaedic Surgeons, the American Orthopaedic Society for Sports Medicine, and the Arthroscopy Association of North America. Neither Dr. Elias nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

INTRODUCTION

The medial patellofemoral ligament (MPFL) is the primary passive soft-tissue restraint to lateral patellar instability.¹ It has been shown both clinically and radiographically that the MPFL tears when the patella dislocates.² The other crucial stabilizing components of the knee extensor mechanism are the bony restraints (especially the lateral trochlear ridge) and the dynamic soft-tissue restraints (especially the vastus medialis obliquus). Recently, emphasis has been placed on additional surrounding soft-tissue restraints including the medial quadriceps tendon femoral ligament (MQTFL), medial patellotibial ligament (MPTL), and medial patellomeniscal ligament (MPML).³^,⁴ MPFL reconstruction is one of a large number of different surgical procedures that have been described to restore patellar stability. Studies reporting short-term and midterm results of MPFL reconstruction confirm excellent patient satisfaction and low recurrent instability rates.⁵^,⁶^,⁷^,⁸ Sometimes other procedures can be better suited to addressing the pathoanatomy. For example, patients with excessive tibial tuberosity lateralization may need a medializing tibial tuberosity osteotomy, and patients with extreme patella alta may need a distalizing osteotomy.

PATIENT SELECTION

Indications

MPFL reconstruction is indicated for patients with symptomatic recurrent patellar instability when the primary etiologic factor is medial soft-tissue insufficiency. MPFL reconstruction may also be indicated as a concomitant procedure when bony procedures alone are not sufficient to restore functional stability.

A thorough assessment of the patient’s history, description of symptoms, and physical examination are crucial in determining when to perform surgical stabilization. Patients who report recurrent painful episodes of lateral subluxation or dislocation associated with the classic twisting mechanism and exhibit apprehension with lateral translation on physical examination are the best candidates. A course of physical therapy designed to strengthen core, hip, and quadriceps musculature may negate the need for surgery, especially for patients with demonstrable weakness and only one or two previous instability episodes. Patients with substantial patellofemoral pain independent of instability episodes are likely to have continued anterior knee pain even after successful stabilization.

Contraindications

The primary contraindication to MPFL reconstruction is medial patellar instability; this instability is usually an iatrogenic problem found after overaggressive lateral retinacular release, but it may also be seen as a primary problem, especially in patients with hyperlaxity syndromes. Active infection is another contraindication to MPFL reconstruction. Patients who are skeletally immature require a modification of this procedure to minimize the risk of epiphyseal plate injury at the femoral attachment site adjacent to the distal femoral physis.⁹

PREOPERATIVE IMAGING

It is crucial that the appropriate radiographic studies be obtained before recommending a specific surgical procedure. In addition to standard AP and notch views, the sunrise view is obtained at 45° and the lateral view is obtained at 30° of knee flexion. For patients in whom tibiofemoral osteoarthritis is suspected, the notch view is replaced by a PA view in 45° of flexion. The lateral radiograph is used to quantify the relative patellar height (Figure 1). Patients with extreme patella alta (Caton Deschamps Index > 1.4) may benefit from a distalizing tibial tuberosity osteotomy. Trochlear dysplasia can also be seen on the lateral radiograph as the “crossing sign” (Figure 2). Patellofemoral degenerative changes and joint space narrowing seen on the sunrise view may suggest the need for an anteromedializing osteotomy to decrease joint reactive forces.

MRI is most useful for assessing the integrity of the articular surfaces. If localized high-grade chondral
lesions are identified, then the surgeon can plan for concomitant cartilage débridement marrow stimulation or osteochondral replacement procedures. When high-grade lateral patellofemoral chondral abnormalities are noted, an osteotomy that unloads the lateral patellofemoral joint (eg, an Elmslie-Trillat medialization osteotomy) may be indicated as an isolated or concomitant procedure. When a high-grade inferior pole lesion is noted, an osteotomy that unloads the inferior pole (eg, Fulkerson anteromedialization osteotomy) may be considered.

FIGURE 1 The lateral radiograph is used to determine relative patellar height. The Caton Deschamps Index is a measurement of patellar height, calculated by dividing the distance from the inferior articular pole of the patella to the anterior margin of the tibia (A), by the articular length of the patella (B).

FIGURE 2 Lateral radiograph of a knee shows the “crossing sign” (arrow), indicative of trochlear dysplasia.

FIGURE 3 CT scan of a knee with superimposed axial cuts through the level of the trochlear groove and tibial tuberosity. The tibial tuberosity-trochlear groove (TT-TG) distance is the distance between vertical lines drawn through these landmarks.

CT scans are particularly useful for determining trochlear morphology and measuring malalignment, as determined by tibial tuberosity lateralization. The tibial tuberosity-trochlear groove (TT-TG) distance is measured on superimposed axial CT cuts through the distal femur at the level of the Roman arch and the proximal tibia at the level where the tuberosity is most prominent (Figure 3). The distance between vertical lines drawn through the base of the trochlear groove and the anterior prominence of the tuberosity is measured. Normal values are up to 15 to 20 mm. More recently, dynamic CT scanning has been used to assess maltracking. In contrast to traditional CT scans, where static images are obtained at specific flexion angles, dynamic CT scans are imaged while the patient actively flexes and extends the knee, which allows the surgeon to not only quantify the amount of maltracking but also determine the flexion angle where the lateral translation of the patella is greatest.

PROCEDURE

Patient Positioning/Examination Under Anesthesia

The patient is placed supine on the operating table. The procedure always begins with an examination under anesthesia, including assessment of limb alignment, hip rotation measurement, and a formal knee ligament
evaluation. A crucial part of the examination under anesthesia is the glide test, which is used to manually assess the amount of lateral translation of the patella (Figure 4). Lateral translation is quantified in quadrants (100% lateral translation equals four quadrants). It is very important to compare this translation to that of the contralateral knee. Assuming that the contralateral knee has normal lateral translation (no previous episodes of instability), the goal will be to set the tension of the MPFL graft on the surgical side to allow an amount of translation equal to that of the normal side. The tilt test is used to determine the tightness of the lateral retinaculum. The examiner should be able to evert the patella to a horizontal position by pushing up manually on the lateral facet of the patella. Although usually not necessary, a lateral retinacular release may be performed using an open or arthroscopic technique if the lateral retinaculum is determined to be excessively tight. This can be the case if a combined MPFL reconstruction with tibial tubercle osteotomy is performed. In this setting, it is not uncommon to increase compression of the lateral facet of the patella.

FIGURE 4 Photograph shows the glide test, which is performed during the examination under anesthesia to determine passive lateral patellar translation.

FIGURE 5 Intraoperative photographs of medial patellofemoral ligament (MPFL) reconstruction. A, Bony landmarks are marked on the surface of the skin. The proximal X is over the adductor tubercle, and the distal X is over the medial femoral epicondyle. B, A locking stitch is woven through the patellar end of the graft. C, An incision is made along the medial border of the patella.

Surgical Technique

After prophylactic intravenous antibiotics are administered and a tourniquet is placed around the thigh, a diagnostic arthroscopy is performed. Arthroscopic evaluation is necessary to assess patellar tracking and, in particular, to determine the location and degree of any chondral abnormalities. If high-grade (Outerbridge grade 3 or 4) chondral lesions are noted on the lateral facet or the inferior pole of the patella, consideration should be given to performing a concomitant medializing (eg, Elmslie-Trillat) or anteromedializing (eg, Fulkerson) tibial tuberosity osteotomy. If an osteotomy is indicated, it should be performed before the MPFL reconstruction.

After the examination under anesthesia and diagnostic arthroscopy are completed, bony landmarks are marked on the surface of the skin (Figure 5, A). The leg is exsanguinated with an elastic bandage, and the tourniquet is inflated (the tourniquet is optional). Hamstring graft harvest begins with an incision directly over the pes anserine bursa. Blunt dissection is performed, small vessels are electrocauterized, and the superior edge of the sartorial fascia is exposed. The tips of the scissors are placed under the sartorial fascia, which is then sharply released off its insertion on the proximal medial tibia. The sartorial fascia is everted, exposing the underlying gracilis tendon.

The gracilis tendon is dissected free from the sartorial fascia and semitendinosus tendon. If the gracilis is too small, the semitendinosus is harvested. The end of the tendon is tagged with a locking stitch. An open-ended tendon stripper is then used to harvest the tendon. The surgeon must be careful during harvest to release any accessory bands that can promote premature transection of the hamstring tendon. Hamstring allograft may be
preferable in patients undergoing revision surgery or in those with connective tissue disorders.

The graft is brought to the rear table for preparation. Muscle is scraped off the hamstring tendon at the musculotendinous junction using curved scissors. Additional tissue is then débrided sharply to create a smooth graft of the appropriate size. The graft is then passed through a sizer to measure its diameter. A 4- to 5-mm diameter is more than adequate. A No. 2 nonabsorbable suture is woven through the distal end of the graft using a locking technique (Figure 5, B).

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