It is often said that when many operations are recommended to treat a single problem such as patellar instability, that means no one knows which is best. Perhaps it means something different. Perhaps it means that there has been an evolution and a variety of opinions about the underlying pathology that must be addressed surgically to restore stability and function.

It has long been recognized that lateral dislocation of the patella can occur near extension from a direct blow to the medial patella or from an indirect mechanism in which muscular force produces the load necessary to result in dislocation.¹

It has long been understood that medial parapatellar soft tissues must generally be torn to allow the patella to dislocate laterally. The earliest reference to this is in 1885 from Pick, who noted: “Professor Steubel considers the subject of the mechanism of dislocation of the patella, and from experiments on the dead body concludes that it can only occur in joints whose ligaments have been previously relaxed.”²

An insightful publication from Gallie and Lemesurier,³ in 1924, recognized the need to restore medial stability. It was their opinion that repair of the medial soft tissues was not as effective as reconstruction with graft tissue, and their prescient article describes six medial patellofemoral ligament (MPFL) reconstruction cases using fascia lata and one with Achilles autograft. Their article also recognized that underlying alignment and bony deformities play a role in patellofemoral instability. Diagrams from their article are remarkably similar to contemporary MPFL reconstruction (Figure 1.1).

For those who felt that the variable of joint alignment and the alignment of muscular force was the primary instigating factor in patellar instability, it made sense to design surgery to realign the extremity and balance the muscular vectors.

Many anatomic factors have been addressed surgically to correct coronal plane valgus alignment, patellar height, an excessively valgus vector of the quadriceps, and rotational deformity of the femur and tibia. Multiple studies and measures have been applied to discern normal ranges and to try to associate these factors with patellar instability. When associations have been determined between anatomic factors and increased incidence of patellar instability, it has been hypothesized that correction of those factors should address the symptoms. However, just because a finding is noted to occur more often in patients with a given condition such as patellar instability, it does not mean that that finding must be corrected to effectively treat the problem.

A landmark study on patellar instability by Henri Dejour et al,⁴ in 1994, documented trochlear dysplasia, patella alta, patellar tilt, and increased tibial tuberosity-trochlear groove distance. All these factors were much more common in their study population of patients with acute and recurrent patellar instability. For some providers, this has become an algorithm of defining these factors and addressing each of them in an “à la carte” fashion when surgery is needed.

These factors have been addressed by soft-tissue procedures medially to restore constraint, correct perceived abnormalities of the quadriceps muscle alignment, and release or lengthen soft tissues on the lateral side of the patella.

Bony procedures have been devised and popularized to reshape the trochlea (trochleoplasty) and address patella alta and increased tibial tubercle-trochlear groove distance by tibial tuberosity transfer. However, as a profession, we still lack the data to know definitively which factors must be treated when and in what combination for any individual patient.

Historically, open surgery to balance the quadriceps with medial imbrication and lateral release was popular. Tibial tuberosity medialization became popular next. With the advent of arthroscopy and the interest in minimally invasive surgery, isolated lateral release was used and then as it became evident that this was insufficient, arthroscopic attempts at medial imbrication were added.

Despite discussion of the laxity that is now considered to be such a key concept in evaluation and treatment of patellar instability, treatment in the early part of the 20th century focused largely on alignment and anatomic factor correction.

As orthopedic understanding and treatment began to focus more on traumatic joint laxity initially with anterior cruciate ligament injury,⁵ these concepts were applied to the patellofemoral joint first by Fithian⁶ using instrumented measurement and Teitge,⁷ who evaluated patellar instability by stress radiography in a landmark 1996 study (Figure 1.2). Currently, it is still not common practice to measure patellofemoral laxity by instrumentation or radiographs.

Multiple studies have since explored the location of the medial tears on magnetic resonance imaging and shown that tears can occur at the femoral or patellar attachment sites or in the midsubstance. Repair or reconstruction of these soft tissues has often been used in addition to correction of underlying anatomic risk factors.

Although there is some evidence that repair of the MPFL can be successful,⁸,⁹ attention has turned again toward reconstruction of the MPFL as described initially by Gallie.³

Publications in the early 1990s by Avikainen and Ellera-Gomes utilized adductor tendon autograft and artificial ligament, respectively, to restore medial patellar constraint¹⁰,¹¹ (Figure 1.3). Much attention has subsequently been paid to various techniques and graft choices to restore ligament stability medially. While MPFL reconstruction has grown in popularity, complications from inaccurate graft placement and tensioning can be catastrophic for patients and difficult to revise.

A personal recollection from Dr. Bob Teitge of the renaissance of MPFL reconstruction is included as an addendum to this chapter.

Other authors have just addressed the risk factors of alignment and not included any medial repair or reconstruction. Some have preferred addressing the medial laxity primarily and not addressing some or all of the underlying “risk factors.” A detailed recounting of these studies and associated opinions is beyond the scope of this chapter.

Many clinical studies combine these operations in nonuniform retrospective reports and do not help us understand exactly what is the minimum treatment needed to be effective.

So where do we stand now as a profession in trying to sort out what to do for these patients who can be severely disabled by this problem? We are left with expert opinions as our gold standard in the absence, as yet, of scientifically proven data relating specific surgeries to specific outcomes while rigorously defining the necessary anatomic variables.

To help answer these questions as well as possible given the current scope of our understanding, the American Orthopedic Society for Sports Medicine and the Patellofemoral Foundation sponsored a workshop project designed to seek a consensus and expert opinions from an experienced group of well-published and widely recognized patellofemoral “experts” from the fields of orthopedic surgery, physical therapy, and basic science.¹² This group worked for over a year to reach a consensus on a variety of topics with a goal of providing concise guidance to practicing surgeons on the state of current expert opinion.

The workshop group came up with helpful definitions of patellofemoral stability and instability:

Factors that were found to be important in maintaining patellar stability were felt to include intact medial and lateral patellar retinaculum (soft-tissue constraints), the articular shape of patella and trochlea, normal patella height, and normal axial and coronal skeletal alignment.

Conversely, factors leading to instability were patholaxity of the medial and/or lateral patellar soft-tissue constraints, decreased constraint as a result of abnormal shape of the patella and/or trochlea (usually trochlear dysplasia), patella alta, abnormal skeletal alignment valgus and/or torsional (such as excessive femoral anteversion, external tibial torsion, foot hyperpronation, and genu valgum), and deficient proximal muscular strength and control, resulting in abnormal lower extremity kinematics (ie, excessive hip internal rotation, knee valgus, etc).

The workshop group also carefully discerned opinions about the key points of the history, physical examination, and imaging in patients with the symptoms of patellar instability (Tables 1.1,1.2,1.3). A full discussion of these recommendations is beyond the scope of this introductory book chapter except to emphasize that

meticulous clinical evaluation is the cornerstone of good care for these patients.