Evaluation of the patient with patellar instability begins with obtaining a complete history. The physician should determine what types of activities cause painful subluxation or dislocation and the number of episodes. Indirect mechanisms account for most patellar dislocations; for instance, a right-handed softball player might feel a “pop” in her right knee as her body rotates to the left while trying to hit a pitch. Less commonly, a direct blow to the medial aspect of the patella causes the injury.

Physical examination begins with assessment of the tibiofemoral alignment with the patient standing. Excessive valgus alignment may predispose the patient to patellar instability. With the patient supine, the surgeon performs a thorough ligamentous examination. Patients with an elevated “Q” angle have an increased lateral force vector and greater risk for patellar instability, and those with a prominent “J” sign have bony malalignment. The physician tests for patellar apprehension by manually placing a laterally directed force on the medial edge of the patella. The patellar glide test is used to assess patellar laxity by quantifying patellar translation in quadrants. The examiner measures lateral retinacular tightness by using the patellar tilt test. Other pertinent parts of the examination include assessment for tibial torsion, femoral anteversion and vastus medialis weakness. It is also important to identify the area of maximum tenderness of the MPFL because this point usually correlates with the location of the ligament rupture. A standard series of radiographs of the knee includes anteroposterior, lateral (in 30° of flexion), tunnel, and sunrise (in 45° of flexion) views. The lateral view best shows patella alta and trochlear dysplasia, the tunnel view commonly reveals loose bodies in the notch or osteochondritis dissecans lesions, and patellar tilt, and the degree of subluxation is best appreciated on the sunrise view. CT imaging of the knee defines the amount of subluxation and tilt more accurately than does conventional radiography. A characteristic bone bruise pattern involving the medial patellar facet and the lateral femoral condyle is often seen in patients who sustain a patellar dislocation. This pattern is easily detected with MRI, which can also ascertain the extent of articular cartilage damage. The surgeon can use CT or MRI to measure the distance between the tibial tuberosity and the trochlear groove, which is a manifestation of bony malalignment.

The main indication for MPFL reconstruction is recurrent instability in patients with medial soft-tissue deficiency. The literature has shown that nonoperative treatment of acute patellar dislocations provides good-to-excellent outcomes (5). Initial episodes of patellar dislocation should usually be treated nonoperatively; a closed reduction may be necessary if the patella remains dislocated on presentation. The patient can progress quickly (within 1 to 2 weeks) away from the use of crutches and a knee immobilizer through a rehabilitation program that focuses on pain management, soft- tissue swelling control, core and quadriceps strengthening, and proprioception. The patient can return to normal activities when strength and agility allow for functional progression.

Some clinical situations necessitate acute surgical intervention. For instance, patients with a large loose body, concurrent intra-articular abnormality (e.g., meniscal tear), or persistent subluxation after a course
of therapy benefit from early surgical treatment. Patellar dislocations often cause osteochondral loose bodies and should be suspected in patients who experience mechanical symptoms. The loose bodies are often visualized on MRI or even conventional radiographs ordered at the time of initial presentation. Asymptomatic, diminutive loose bodies are treated with observation; larger fragments that could cause mechanical symptoms require removal.

When acute surgical intervention is warranted, the surgeon should consider concomitant MPFL repair. Acute repair affords an opportunity to repair the static restraint, which is torn in most cases. Direct repair does present several challenges that the surgeon should appreciate. For example, it is not always possible to identify the exact location of the MPFL tear and its repair. Although MPFL avulsions from the origin or insertion sites can be treated with suture anchor fixation, correcting midsubstance tears can be more difficult. Imbricating the tissues in the proper location and determining the correct tension is crucial. Overtensioning the tissue leads to pathologic increases in joint reactive forces or ligament failure as a result of overload (6).

In cases of recurrent instability, patients with bony malalignment as the primary abnormality may be better served with isolated or concomitant osteotomy of the tibial tuberosity. The surgeon must account for patient factors that contribute to recurrent patellar dislocation and understand that MPFL reconstruction alone does not provide adequate treatment in all cases. From a practical standpoint, the surgeon must examine whether the primary pathophysiology is bony malalignment or soft tissue insufficiency. Failure to address a bony abnormality during a soft-tissue procedure could lead to failure. An excessive Q angle increases lateral forces, predisposing the patella to dislocation. The surgeon should consider medializing the tibial tubercle if the angle exceeds 20°. Using the preoperative CT or MRI sequences, the surgeon can measure the distance between the tibial tuberosity and the trochlear groove; measurements greater than 15 mm indicate excessive tuberosity lateralization and should make the surgeon consider the addition of a distal realignment procedure (7). The presence of highgrade chondral defects may also predispose the patient to pain and progressive arthrosis. Depending on the location of the lesion, the patient may benefit from an osteotomy to decrease loading forces. Although MRI often shows damage to the articular cartilage, intraoperative arthroscopic examination is the best way to truly determine the extent of the lesion, at which point the surgeon can decide whether or not to proceed with before osteotomy. Patients without excessive bony malalignment who have recurrent symptomatic subluxation or dislocation are the best candidates for MPFL reconstruction (Fig. 62.1).

Numerous techniques have been described for MPFL reconstruction, and the literature does not indicate that any one method is clearly superior to the others (8, 9, 10, 11, 12 and 13). The techniques differ, depending on the source of the graft and the method of fixation. There are various graft options, including semitendinosus (11), gracilis (14), fascia lata (9), adductor longus (15), adductor magnus (8, 16), quadriceps (13, 15), allograft (17), and even artificial mesh (10). Methods of patellar fixation described include tunnels (15, 16, 18), suture anchors (9), and more recently, a docking technique (19). For femoral side fixation, authors have described using sutures to attach the graft to soft tissues (13), staples (10), a bone tunnel with endobutton fixation (18), soft-tissue slings (8), and interference screws (14).