Special Considerations for Pediatric Patellar Instability

Parikh and Lykissas recently published a comprehensive classification system of 4 defined types of patellar dislocation in addition to voluntary patellar instability and syndromic patellar instability (Table).⁶⁰ The 4 types are Type 1, first-time patellar dislocation; Type 2, recurrent patellar instability; Type 3, dislocatable; and Type 4, dislocated. Type 2 is further subdivided into Type 2A, which presents with positive apprehension signs, and Type 2B, which involves instabilities related to anatomic abnormalities.⁶⁰ A distinction is also made between Type 3A or passive patellar dislocation and Type 3B habitual patellar dislocation.⁶⁰

The classification system proposed by Green and colleagues is more simplified with 3 main categories (Table) of pediatric patellar dislocation: traumatic (acute or recurrent), obligatory (either in flexion or extension), and fixed laterally.^71,72 The acute traumatic categorization refers to patients who experienced an initial dislocation event due to trauma whereas recurrent traumatic involves repeated patella dislocations following an initial incident. Studies report that between 60% to 70% of these acute traumatic dislocations occur as a result of a sports-related incident.^2,33,73 Obligatory dislocations occur with every episode of either knee flexion or extension, depending on the subtype. Obligatory patella dislocation in flexion typically cannot be manipulated or relocated into the trochlea while the knee is fixed but does reduce into the trochlea in full extension. Fixed lateral dislocations are rare, irreducible dislocations in which the patella stays dislocated laterally in flexion and extension. These dislocations often present with other congenital abnormalities. Each of these categories can be further specified as syndromic if the dislocation is associated with genetic or congenital conditions including skeletal dysplasia, Ehlers-Danlos syndrome, cerebral palsy, Marfan disease, nail-patella syndrome, Down syndrome, Rubenstein-Taybi syndrome, and Kabuki syndrome.^{51-54,61,74-76}

SURGICAL TECHNIQUES IN SKELETALLY IMMATURE PATIENTS

While nonsurgical, conservative treatment involving physical therapy and activity modification is recommended for most patients who experience first-time traumatic patellar dislocations, many patients experience complicating factors that indicate them for surgery. These factors include recurrent dislocation, risk factors for patellofemoral instability, underlying malalignment issues, and congenital deformities. When evaluating these factors, particularly patellofemoral instability, the authors recommend assessing osteochondral lesions, age, skeletal maturity, number of previous dislocations, family history, and anatomic risk factors.^2,5,77-79 Extra care should be taken when considering surgical treatment for skeletally immature patients at elevated risk for recurrent instability as the risk of cartilage damage in these cases is high.^80-82

Recently, there has been a reported increase in surgical treatment for patellar instability in the skeletally immature.⁸³ This finding may be attributed to heightened awareness of factors that indicate patients for surgical treatment and increased familiarity of surgeons with newer techniques.⁸³ Many surgical techniques have been described to address patellar instability involving both soft-tissue procedures and bony corrections.⁸⁴ In this article, we discuss the various surgical techniques for MPFL reconstruction, quadricepsplasty, and distal realignment. These procedures can be paired with any number of additional procedures including, but not limited to, lateral retinacular release or lengthening, chondroplasty, TT osteotomy (in skeletally mature patients), and removal of loose bodies.⁸³

There is a need for more comprehensive studies, particularly randomized controlled trials, to evaluate the outcomes for both surgical and nonsurgical treatments for first-time dislocations. In the current literature, only very recently have surgical treatments shown outcomes that are more positive. In 2009, Nietosvaara and colleagues⁸⁵ conducted a randomized controlled trial of nonoperative and operative treatment of primary acute patellar dislocation in both children and adolescents. After a long-term mean follow-up of 14 years, there was not a significant difference between the groups in recurrent dislocation and instability, subjective outcome, or activity scores.⁸⁵ In a subsequent review of 5 studies including 339 knees, Hing and colleagues⁸⁶ also found similar results in both the operative and nonoperative cohorts at risk of recurrent dislocations, Kujala scores, and reoperations. However, a recent systematic review comparing redislocation rates and clinical outcomes between surgical and conservative management of acute patellar dislocation reported more positive outcomes for the surgical cohort.⁸⁷ This review included 627 knees, 470 of which received conservative management, 157 of which received operative treatment. The conservative cohort was followed for an average of 3.9 years and had a 31% rate of recurrent dislocation while the surgical group was followed for a mean 4.7 years and experienced a 22% redislocation rate.⁸⁷ This study indicates that operative management for acute first-time dislocations may be the preferred treatment option.

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