Technique: Distal Realignment Tibial Tubercle Osteotomy

Brian Grawe

Jacqueline Munch

Beth Shubin Stein

INTRODUCTION

Instability of the patellofemoral joint is a relatively common and often a challenging condition to treat in the pediatric and adolescent patient population.¹,² A population-based study by Nietosvaara and colleagues³ has demonstrated the annual incidence rate of acute patellar dislocation to be 0.04% (43 in 100,000) in those younger than 16 years of age. A myriad of potential risk factors have been implicated as precipitating etiologic features for both initial and recurrent patellofemoral instability, with some studies estimating the risk of recurrence, after a primary patellar dislocation event, to be as high as 49% to 69%.⁴,⁵ The risk factors for recurrent lateral patellar instability can be defined as either demographic or anatomic. Female gender, sports participation, and a personal or family history of instability are important demographic variables. Anatomic risk factors of patellar instability include patella alta, an increased Q angle, generalized ligamentous laxity, vastus medialis weakness, and excessive pes/planus/subtalar joint pronation.⁵ More recent work has demonstrated skeletal immaturity and trochlear dysplasia to be significant risk factors in terms of predictors of failure after initial nonoperative management.⁵ From a conceptual point of view, pediatric and adolescent patients can be grouped into four distinct classes: syndromic, obligatory, fixed lateral, and traumatic.² The latter faction can be further subdivided into first time or recurrent, and it is this traumatic group that the subsequent chapter concentrates its attention.

Maintenance of a stable concentric reduction must be the principal goal of treating any dislocation of the patellofemoral joint, as the potential long-term sequelae of instability include knee pain, decreased activity level, recurrent instability/dislocation, chondral injury, and subsequent patellofemoral arthritis.⁶ The traditional nonoperative approach of closed reduction, joint immobilization, and subsequent rehabilitation, although appropriate for a first-time dislocator, does not always consistently eliminate the risk of recurrence. Frequently, patients require surgical intervention if they go on to sustain a second instability event in order to prevent continued recurrence. Although controversy still exists regarding the indications, timing, and type of procedure to be performed for pediatric and adolescent patients with patellofemoral instability, a tailored surgical plan must be devised that accounts for history, age, status of physes, degree or presence of chondral injury, osseous alignment, and soft tissue injury.⁷ The purpose of this chapter is to review the indications and surgical technique associated with distal osseous realignment surgery for pediatric and adolescent patients with patellofemoral instability. This chapter focuses on the authors’ preferred method of treatment for tibial tubercle osteotomy (TTO).

TREATMENT

Indications

The presence of an unstable osteochondral lesion is generally the most accepted absolute indication for immediate surgery after a first-time acute patellar dislocation. Most authors would agree that symptomatic recurrent patellofemoral instability is a surgical problem that must be addressed with proximal, distal, or combined realignment. The decision to transfer the tibial tubercle, in patients with recurrent patellar dislocation, is based on a thorough clinical and radiographic assessment of the patient’s anatomy. Although there is a paucity of evidence surrounding the radiographic parameters associated with TTO, many authors will use specific thresholds based on measurements that assess for both the height of the patella and presence of excessive lateral position of the tuberosity in relation to the trochlear groove. The presence and degree of cartilage wear and trochlear dysplasia must be noted on preoperative imaging studies as well, as these factors can ultimately affect joint stability and any proposed surgical plan.⁸ Taken in concert with a thorough clinical history and physical examination, these radiographic parameters can be used to determine the amount and plane (anterior, medial, or distal) of correction needed to effectively obtain a stable and pain-free patellofemoral joint after tibial tubercle transfer.

Patellar height is best assessed via a true lateral radiograph of the patellofemoral joint. Alternatively, sagittal slices through the joint, as seen on magnetic resonance imaging (MRI) or computed tomography (CT), can also be used to measure vertical height of the patella. Various methods and ratios have been devised by a variety of authors to evaluate patellar height that
include the Blumensaat method, the Insall-Salvati index, the Blackburne-Peel index, and the Caton-Deschamps index (CD index). The CD index is generally accepted as the most accurate diagnostic measurement as well as the most germane index regarding assessing patellar height before and after transfer. This ratio consists of plotting the distance between the inferior edge of the patellar joint surface and the anterosuperior angle of the tibia against the intra-articular length of the patella. It relies on identifiable and reproducible anatomic landmarks, is less dependent on knee flexion angles, and should be therapeutically altered after transfer of the tubercle.⁹ A normal CD index is typically defined as 1, with the values of less than 0.8 and greater than 1.2 being considered pathology great enough to warrant surgical correction.⁷

Quantitatively, the amount of lateral displacement of the tibial tubercle can be measured in one of two ways and must be defined on advanced axial imaging studies (CT or MRI). The conventional and most accepted method involves measuring the linear distance between the tibial tubercle and the trochlear groove on superimposed axial imaging, Dejour’s so called tibial tubercle-trochlear groove (TT-TG) distance.⁸ A second and more novel method, which similarly involves measuring known anatomic landmarks on superimposed images, is called the tibial tubercle-posterior cruciate ligament (TT-PCL).¹⁰ The TT-PCL measures the distance between the tibial tubercle and the posterior cruciate ligament and, secondary to its limited use in the literature, will not be discussed in this chapter. Careful measurement of the TT-TG can be accomplished by taking advantage of the roman arch of the trochlear groove and either the most proximal or distal portion of the tubercle. A linear distance is then measured between two lines that are perpendicular to posterior femoral condyle and pass through the middle of trochlear groove and the tibial tubercle, respectively.¹¹ Numerous authors have published on the measurement’s reliability and acceptable correlation between CT and MRI.¹² However, there is limited data regarding normal values for TT-TG distance, and a cutoff magnitude of greater than 20 mm is generally regarded as the lower threshold of normal prior to medialization of the tibial tubercle.

The concept of trochlear dysplasia, as originally classified by Dejour and colleagues,¹³ can be assessed on the lateral radiograph and will not be discussed in detail, as it is outside of the scope of this chapter. It must be recognized that the crux of this pathology lies within a flattened or convex geometrical shape of the trochlear and can portend a higher risk of recurrent patellofemoral instability.

Contraindications

There are a few important contraindications to TTO which are also germane to pediatric and adolescent patients with recurrent patellar instability. Principally, the presence of an open tibial tubercle apophysis is a contraindication to any distal osseous realignment procedure. The theoretical risk of premature physeal disruption/closure and possible subsequent genu recurvatum deformity are the primary concern for surgeons treating patients with a patent apophysis and concomitant patellofemoral instability. Admittedly, the literature is scarce in terms of this reported complication, and as a result, there is no steadfast age of remaining growth that can be considered an absolute cutoff for TTO consideration. Most of the trepidation, surrounding osteotomy in the skeletal immature patient, results from the knowledge garnered from orthopedic surgeons who have treated the recurvatum sequelae associated with traumatic fractures of the tibial tuberosity.¹⁴ A comprehensive understanding of the physeal anatomy about the knee is imperative when treating pediatric and adolescent patellofemoral instability, and in the case of a pathologically abnormal patellar height or TT-TG distances, alternative procedures such as the Roux- Goldthwait, Galeazzi, Nietosvaara technique, or distal patellar tendon transfer can be used to correct the aforementioned malalignment parameters.² We prefer to stage these patients, addressing all soft tissue incompetencies while the patient is skeletally immature, and perform a final TTO after skeletal maturity is achieved. It must be noted that apophyseal closure of the tibial tuberosity usually commences at ages 15 and 17 years for females and males, respectively.¹⁵

Other relative contraindications also exist and essentially follow the general principles of any other lower extremity surgery. These contraindications include, but are not limited to, infection, open wound near the operative site, and active medical comorbidities that preclude surgical intervention.

Operative

Numerous techniques and methods for TTO have been developed, since Roux’s first description of tuberosity transfer in 1888,¹⁶ and nuances exist that can make each surgeon’s specific approach different. Furthermore, a whole industry has arisen with different manufacturing companies developing cutting guides and systems to aid in surgical accuracy and efficiency. The tubercle can be transferred in multiple directions, and the vector that is chosen depends on the pathology that needs to be addressed. Medialization and distalization are the two directions that are most commonly discussed when addressing patellar instability. Anterior and posterior transfers, the so-called Maquet and Hauser procedures, will not be discussed in this chapter, as the former is employed for relief of patellar overload and the latter is of historic interest only.

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