Numerous surgical procedures have been described for the treatment of patellar instability, most with generally favorable success rates. The medial patellofemoral ligament (MPFL), the primary soft tissue passive restraint to pathologic lateral patellar displacement,¹ is torn when the patella dislocates.^2,3 There has been a great deal of interest recently in soft tissue procedures that address the MPFL. Techniques have been described to repair^2–5 or reconstruct^6–9 the MPFL in an attempt to restore its function as a checkrein. Regardless of which approach is taken, successful surgical treatment requires that the surgeon have a thorough understanding of the relevant anatomy and a working knowledge of patellofemoral biomechanics.

Preoperative Considerations

History

Patellofemoral complaints are among the most common problems encountered by physicians treating knee disorders, and instability is a distinct subset that is usually amenable to surgical treatment. Instability represents a continuum ranging from minor incidental subluxation episodes to traumatic dislocation events. Patients with frequent subluxation episodes and patients with dislocation usually experience substantial knee pain, swelling, and stiffness, resulting in interruption of their normal occupational and recreational activities.

Patellar dislocations can occur from an indirect twisting mechanism as the upper body rotates while the foot remains planted on the ground or, less commonly, from a direct blow to the medial aspect of the patella during contact sports or motor vehicle accidents when the patella is driven laterally. The patella may be spontaneously reduced as the knee is extended, or it may require a formal reduction maneuver. With initial dislocation episodes, the pain and swelling are caused by soft tissue and articular surface damage. The resulting hemarthrosis and quadriceps weakness may take several weeks to resolve. The degree of morbidity tends to decrease in patients who sustain multiple recurrent episodes.

Subluxation episodes are usually less dramatic and manifest as a feeling of instability and pain. Patients often describe the sense that the knee may “give out.” These episodes usually occur with trunk rotation during physical activity and result in a variable degree of pain and swelling. The pain is usually anterior and may be bilateral, especially in patients with malalignment or diffuse ligamentous laxity. The most important clinical determination to be made is whether the pain described by the patient is associated with patellar instability, because the common clinical entity of isolated anterior knee pain (patellofemoral pain syndrome) is nearly universally treated nonoperatively.

Some authors recommend MPFL repair after first-time patellar dislocation.³ We usually treat an initial subluxation or dislocation episode nonoperatively but may repair an acute MPFL tear when surgery is indicated for concomitant intra-articular disease (such as an osteochondral fracture, large loose body, or meniscus tear). MPFL repair may also be used to treat recurrent instability. With repeated instability episodes, the MPFL becomes attenuated and functionally incompetent. To reestablish the normal checkrein effect, the MPFL is tightened by cutting, shortening, and reattaching it at the patellar or femoral insertion or by midsubstance imbrication.

MPFL repair or reconstruction is contraindicated in patients with medial instability or isolated anterior knee pain. In patients with substantial medial patellofemoral degenerative changes, great care should be taken not to overtighten the MPFL because doing so will result in excessive medial joint pressure and is likely to exacerbate patellofemoral pain.

Surgical Technique

Anesthesia and Positioning

The procedure is performed on an outpatient basis with use of general or regional anesthesia techniques. The patient is positioned supine on a standard operating room table. A vertical thigh post is used to facilitate arthroscopic evaluation and is removed before the reconstruction is started. A tourniquet is placed around the proximal thigh on the operative side, and a compressive thigh-high stocking is placed on the contralateral leg. Prophylactic intravenous antibiotics are administered before incision.

Examination

Examination Under Anesthesia

Once adequate anesthesia has been established, a comprehensive examination is performed. It is usually easier to characterize patellar stability, translation, and tilt when the patient is anesthetized. With the knee in extension, the position of the patella is determined at rest and with a lateral translation force applied (Fig. 88-2A). Even an unstable patella will not stay dislocated unless the knee is maintained in a flexed position. It is important to compare the amount of translation on the symptomatic side with the normal lateral patellar translation in the contralateral knee. The examiner should use his or her thumb to push the patella laterally and assess the amount of translation as well as the consistency of the end point. It is also important to measure medial translation (Fig. 88-2B). Rarely, medial instability may be confused with lateral instability, especially if the patient has had an overaggressive previous lateral retinacular release. It is also important to assess the patient for lateral retinacular tightness. If the examiner is unable to evert the lateral edge of the patella to the neutral or horizontal position, and if the patient’s symptoms and preoperative radiographs are consistent with excessive lateral pressure, consideration should be given to a concomitant arthroscopic lateral retinacular release.