Patellar dislocation commonly occurs as a result of trauma sustained during physical activity but may occur with minimal trauma in patients with predisposing anatomy.

Patellar dislocation tears the medial patellofemoral complex or stretches it beyond normal function.

The medial patellofemoral complex includes multiple soft-tissue structures that provide resistance to lateral patellar translation, of which the medial patellofemoral ligament (MPFL) is the most important component near full extension, where it provides 50% to 60% of the resistance to lateral translation of the patella.¹

The MPFL runs from the medial femoral condyle in the saddle between the adductor tubercle and the medial epicondyle to the proximal medial border of the patella, with some fibers extending proximally where they insert into the vastus intermedius tendon.²

Multiple classification systems of patellar instability have been described. In regard to surgical decision making, one must consider two main questions: (1) whether the patient is a first-time dislocator or has suffered multiple dislocations and (2) whether the patient has relatively normal osseous anatomy that would allow for treatment with isolated MPFL reconstruction, or whether significant osseous abnormalities are present that would require the performance of concomitant procedures.

Patients present with a history of recurrent lateral patellar dislocation or a single patellar dislocation with subsequent episodes of lateral subluxation and feelings of instability.

Indications for MPFL reconstruction following a first-time acute patellar dislocation are rare (Table 7.1). One may consider this procedure in the setting of a history of a contralateral patellar dislocation that required surgical stabilization or in cases where an osteochondral fragment is to be repaired.

Physical examination prior to surgery should demonstrate patellar apprehension with lateral patellar translation near full knee extension. Apprehension generally resolves as the knee is flexed and the patella enters the trochlear groove, which provides osseous stability. Apprehension that persists beyond 30°, and especially 60°, of knee flexion indicates the presence of significant trochlear dysplasia, patella alta, or both and should lead to consideration of the need for associated procedures to correct this anatomy.

The patient should also demonstrate increased lateral patellar translation near full knee extension. One should be hesitant to perform MPFL reconstruction in the absence of increased lateral patellar translation.

Patellar tracking can also be assessed dynamically by having the patient range the knee and observing for the presence of lateral patellar translation near full extension (J-sign). The presence of a large J-sign is another indicator of the presence of abnormal bony
anatomy that may predispose to failure of isolated MPFL reconstruction if not adequately addressed.

The tightness of the lateral retinaculum should also be assessed by evaluation of medial patellar translation and the degree to which the patella can be everted. If medial translation is less than two quadrants or if the patella cannot be everted to a neutral position, lateral lengthening³ or limited lateral release should be considered in addition to MPFL reconstruction.

Patients’ ligamentous laxity should be assessed, and those with increased laxity (generalized hyperlaxity) as assessed with Beighton or similar criteria should be considered at high risk to stretch out any soft-tissue reconstruction procedures. In such patients one should have a lower threshold for considering the addition of a bony procedure. The use of autograft for reconstructions in these patients should be avoided.

Plain radiographs should be obtained in all patients and include a true lateral view of the knee in 20° to 30° of flexion to assess patellar height via the calculation of the Caton-Deschamps index⁴ or Insall-Salvati ratio.⁵ An axial view near full knee extension (Merchant view) can provide insight into patella tilt. Axial views in high degrees of knee flexion are useful to assess for the presence of patellofemoral osteoarthritis.

Full-length lower extremity films are useful for assessment of overall alignment and should be obtained in skeletally immature patients and those patients in whom significant varus or valgus is suspected on the basis of a physical examination.

Cross-sectional imaging (computed tomography or magnetic resonance imaging [MRI]) is useful to further assess trochlear anatomy (sulcus angle and the presence and location of a supratrochlear bump or spur) and allow for measurement of the tibial tubercle-trochlear groove (TT-TG) distance.⁶

MRI also allows for evaluation of the articular cartilage surfaces and assessment of cartilaginous overlap in the patellofemoral joint (patellotrochlear index).⁷

While MPFL reconstruction is frequently successful in restoring knee stability and function, some patients may require additional procedures to treat other anatomic factors associated with instability.¹⁰ Attention must be paid to these factors preoperatively and additional procedures planned as indicated. The details of risk factors and procedures to address them are discussed in subsequent chapters.

Several techniques and graft choices are available for MPFL reconstruction, each with its pros and cons. For this technique, one must assess the patella and femur to ensure that no prior tunnels or hardware could complicate implant placement.

A preoperative discussion with the patient should also include a discussion of graft choice options. Either a free hamstring autograft or allograft (peroneus longus, semitendinosus, or gracilis) can be utilized with this surgical technique.

Large C-arm

One free suture used for graft passage

Two differently colored nonabsorbable high-strength sutures for tagging graft ends (eg, #2 Fiberwire and #2 Tigerwire [Arthrex])

Bioabsorbable screw-in suture anchor for patella (two)

Bioabsorbable interference screw for femur (such as DePuy Mitek Milagro Advanced)

Soft-tissue graft

Allografts are a viable option for MPFL reconstruction given the ligament’s extra-articular location.

Peroneus longus tendon, semitendinosus, and gracilis allografts are all excellent options for MPFL reconstruction with this technique.

Hamstring autografts are also an excellent option, although there is some morbidity associated with hamstring harvest.

We prefer peroneus longus or semitendinosus allograft to decrease harvest-site morbidity; allograft is strongly suggested in the setting of generalized ligamentous laxity.