Patellofemoral Instability

It is a pleasure to introduce this special focus section of the Journal of Knee Surgery presenting topics related to the patellofemoral joint. Diane Dahm, MD, Special Focus Section, Guest Editor, has assembled experts in the field of patellofemoral joint pathology addressing interesting and timely topics. We present a brief summary of these articles in this introduction.

Drs. Ries and Bollier present the topic of patellar instability in the pediatric and adolescent patient. Patellofemoral instability (PFI) is a common problem in the adolescent population. Patellar stability depends on a dynamic interplay between bony and soft tissue restraints. Several pathoanatomical factors increase the likelihood of patellar instability: patella alta, trochlear dysplasia, malalignment, and deficient proximal medial restraints. Treatment for first-time patella dislocations is typically nonoperative and includes bracing, early range of motion, and physical therapy. The only absolute indication for early surgery is a large osteochondral fragment that can be fixed. Surgical stabilization is indicated for chronic patellar instability and includes both proximal and distal realignment options. Medial patellofemoral ligament reconstruction is the treatment of choice in most adolescent patients with patella instability. Distal bony realignment procedures are reserved for skeletally mature adolescents.

Drs. Grawe and Shubin Stein present the indications and techniques for tibial tubercle osteotomy. This article highlights that osteotomy of the tibial tubercle is a versatile procedure that can be utilized for several common pathologies about the patellofemoral joint. Most commonly, tuberosity transfer is employed for the treatment of patellar instability or symptomatic overload of the patella. The osteotomy can be combined with soft tissue realignment procedures or cartilage reconstructive techniques. A precise understanding of the surgical anatomy and the biomechanics of the patellofemoral articulation is essential for producing a successful outcome during surgery. Tailoring the direction of transfer to the pathoanatomy of each patient is critical to producing a durable and lasting result following a tibial tubercle osteotomy. When evaluating a patient for a possible transfer, a thorough history and physical evaluation must be undertaken, along with imaging of the patellofemoral joint. Several useful advanced imaging techniques can also be used to guide the surgeon toward the most appropriated osteotomy for the patient.

Drs. Prince, King, Stuart, Dahm, and Krych present a timely article discussing the treatment of patellofemoral cartilage lesions in the young active patient. This article emphasizes that articular cartilage lesions of the patella and trochlea are commonly encountered in the young and active patient. These defects can be classified as chondral or osteochondral, and then further described according to size, location, and etiology. Early surgical intervention is often indicated for traumatic injuries resulting in osteochondral damage, including acute patellofemoral dislocation. For chronic lesions, initial treatment involves exhaustive nonoperative measures and surgery is reserved for patients with persistent symptoms. A thorough history, physical examination, and imaging are essential to select the best surgical option. Cartilage restoration procedures are combined with optimization of background factors such as patellofemoral alignment and congruity to achieve success. Advanced surgical techniques such as cell-based therapies have evolved into a reliable strategy for management of these lesions.

Drs. Ryzek and Schottle discuss the indications and surgical technique for trochleoplasty. This article highlights that PFI is a pathological knee syndrome that frequently affects young patients. The patellofemoral joint's structural morphology is the determining factor in the extent of PFI. Structural factors that play leading roles in patellofemoral stability can be classified into static (bone morphology), passive (ligamentous) and active (muscular). The predominant static factor leading to patella dislocation and thus patellofemoral dysfunction is trochlear dysplasia, which is the point of focus in this article. After orienting clinical examinations, MRI can provide the best information about trochlear dysplasia which includes trochlear shape, orientation, and tibial tubercle to the trochlear groove distance. Convex trochleas or trochlea dysplasia with PFI at flexion over 30 degrees are indications for performing a deepening trochleoplasty to correct for static pathomorphology. The focus of this article is the pathology of trochlear dysplasia, its role in PFI, the correct indication for trochleoplasty as a primary intervention and the role of a simultaneous MPFL reconstruction.

Drs. Lewallen, McIntosh, and Dahm present the demographics of patients with a first time patellofemoral dislocation, and identify risk factors for recurrent instability. This was a single institution, IRB approved, retrospective review of > 2,000 patients with a patellar dislocation between 1998 and 2010. Inclusion criteria consisted of the following: (1) no history of patellofemoral subluxation or dislocation of the affected knee; (2) X-rays within 4 weeks of the initial instability episode; and (3) a dislocated patella requiring reduction, or history/findings suggestive of acute patellar dislocation. Clinical records and radiographs were reviewed assessing patella alta, trochlear dysplasia, and skeletal maturity. A total of 326 knees (312 patients) met the aforementioned criteria. There were 145 females (46.5%) and 167 males (53.5%), with an average age of 19.6 years (range, 9–62 years). Overall, 35 patients (10.7%) were treated with surgery after the initial dislocation. All others were initially managed nonoperatively. Of these 291 patients, 89 (30.6%) had recurrent instability; 44 (49.4%) of which eventually required surgery. Several risk factors for recurrent instability were identified, including the following: younger age (p < 0.01), immature physes (p < 0.01), sports-related injuries (p < 0.01), patella alta (p = 0.02), and trochlear dysplasia (p < 0.01). Overall, 69% of patients with a first time patellofemoral dislocation will stabilize with conservative treatment. However, patients younger than 25 years of age with trochlear dysplasia have a 60 to 70% risk of recurrence by 5 years. This information is helpful when counseling patients on their risk for recurrent instability and determining the most appropriate treatment plan.

The purpose of this Special Focus Section of the Journal of Knee Surgery is to provide experienced knee surgeons, general orthopedic surgeons, fellows, residents, medical students, and other health care professionals with an interest in the patellofemoral joint with an overview for the evaluation and treatment of these complex knee injuries. I thank Diane Dahm, MD, for her efforts in creating this Special Focus Section for the Journal of Knee Surgery.