Take-Home Points
- MPFL repair has the best results with isolated ligament avulsions in first-time dislocations. This can be demonstrated on MRI and verified at the time of arthroscopy.
- Recurrent dislocations, even if acute, have a higher failure rate with MPFL repair. In this setting, MPFL reconstruction provides more consistent outcomes.
- In cases of chronic lateral patellar dislocation, imbrication may be enough when other associated procedures have sufficiently stabilized the patella without the need for a strong soft-tissue checkrein.
- Femoral-sided repairs are more challenging due to the need to optimize the insertion point on the femur, as small changes in positioning can cause increased stress on the repaired tissue and lead to failure.
- If a repair is to have a chance to work, it must be performed at the site of the tear. Thus, preoperative planning and intraoperative inspection is important to precisely identify the site, which can involve intrasubstance and multifocal injuries as well as the femoral and patellar complex attachments.
The medial patellofemoral ligament (MPFL) is the primary soft-tissue restraint to lateral patellar translation.1 In cases of first-time acute lateral patellar dislocation, injury to the MPFL is described as the essential lesion, occurring in almost 100% of cases.2-4 Because of the relatively high frequency of recurrent instability after first-time acute lateral patellar dislocation,5-7 much research has been focused on MPFL repair and reconstruction.8-11 Although the clinical results of isolated MPFL repair are highly variable, this variability is likely secondary to relatively inconsistent clinical indications for repair, with repair described for patients with acute as well as chronic or recurrent instability.10-13 From these early successes and failures, much has been learned about the appropriate indications for MPFL repair as well as medial retinacular “reefing” or imbrication in the chronic setting.
Relevant Anatomy
The MPFL is an extracapsular thickening of the medial retinacular structures and can be most consistently identified just distal to the vastus medialis obliquus, running within layer 2 of the medial side of the knee (using the often-referenced layer system popularized by Warren and Marshall14). The MPFL origin on the medial aspect of the femur falls within a well-defined saddle between the adductor tubercle and the medial epicondyle.15 From this relatively narrow origin, the MPFL broadens before attaching to the proximal one-third of the medial aspect of the patella.
Over the past 2 decades, the osseous anatomy surrounding the femoral origin of the MPFL has been of much interest in large part because of the increasing popularity of MPFL reconstruction. Although useful for MPFL reconstruction, the vast amount of literature and our improved understanding of this anatomical region can be extrapolated to MPFL repair. The radiographic landmarks described by Schöttle and colleagues16 have advanced our knowledge of the femoral origin of the MPFL, with fluoroscopic guidance allowing for more limited dissection and increased accuracy of repair for femoral-sided MPFL injuries.
Location of MPFL Injury
Understanding and appreciating the specific location of the MPFL injury are paramount to successful MPFL repair. Unfortunately, the location and pattern of MPFL injury cannot be consistently predicted. Although early surgical dissections described femoral-sided injuries as the most common injury site,4 more recent studies using magnetic resonance imaging (MRI) have described a more even distribution of MPFL injury patterns, which include patella-based ruptures, femoral-based ruptures, intrasubstance ruptures, and multifocal injuries.17 In addition, age and skeletal maturity likely play a role in the MPFL injury location, as skeletally immature patients more often have patella-based ruptures.2,18,19 In acute MPFL repair, MRI appears to be the most accurate imaging modality for determining the patella- or femoral-based injuries most amenable to repair and for identifying clinically significant osteochondral lesions, which are not uncommon after first-time patellar dislocation.20,21
Medial Reefing, Imbrication, and Advancement
Medial reefing, imbrication, and advancement, collectively referred to as proximal realignment procedures, describe a variety of techniques that essentially shorten or tighten the medial retinacular structures.22-24 Although the terms cover a variety of similar surgical techniques and are often used interchangeably in the literature, imbrication, or overlapping of adjacent edges, is the single most accurate term used to define this spectrum of procedures. These procedures historically were performed in the setting of chronic or recurrent patellar instability, with the primary goal being to imbricate the attenuated medial retinaculum, which includes the MPFL. However, the procedure has had good clinical outcomes when performed in isolation for patients with normal bony anatomy.25 Such anatomy is rare in chronic or recurrent dislocators, and these proximal soft-tissue procedures are often combined with other osseous realignment procedures, including distal realignment, trochleoplasty, and distal femoral osteotomy.26