Persistent J-Sign Following Distalization with Correction of Patellar Height: A Descriptive study reviewing anatomic factors (195)
Authors: Turkula Stefan , Schmiesing Andrew , Agel Julie , Arendt Elizabeth 
Published: October 2021

Objectives:

The anatomic factors associated with a J-sign (patella dislocation in extension) are debated and likely multi-factorial. With trochlear shape and patella height playing a role. The goal of distalization of the tibial tubercle (dTTO) is normalization of patella height to improve patellar stabilization by earlier trochlear groove engagement. dTTO is felt to diminish or remove the J-sign by ‘by-passing’ the supra-trochlear bump, thus avoiding the need for a trochleoplasty in addition to a dTTO. The objective is to determine if a persistent J-sign after surgical patellar stabilization and adequate patellar height restoration is due to additional anatomic variances that were not surgically addressed.

Methods:

A retrospective chart review of 89 consecutive patients who were treated by a single surgeon for recurrent lateral patella dislocation with medial patellofemoral ligament reconstruction (MPFL-R) and dTTO was undertaken. 63 patients were identified with a pre-operative J-sign and formed the study sample. 40 of these patients had no J-sign post-operatively and 23 patients had a persistent postoperative J-sign. All patients had radiographic measurements made for patella alta (caton-deschamps index [CD]), and magnetic resonance imaging measurements of trochlear depth, sulcus angle, as well as the individual components for measuring trochlear depth (medial, central, and lateral height).

Results:

The average age of patients at time of surgery was 21 years old (range,13-45). Females were 74% of the population. Average BMI was 26 (17-44) and follow-up averaged 16 months. Table 1 demonstrates the between group differences for the statistically significant variables. These included trochlear depth, and lateral-central difference (via components of trochlear depth calculation) (fig 1). If the patient had lateral condylar height < medial condylar height, a J -sign persisted (4 patients). When the post op C/D >/= 1.2, 5/6 (83%) patients had a persistent j-sign. There were 5 re-dislocations in this population: 2/23 (13%) with a persistent J-sign and 3/40 (8%) without. The KOOS was available for all patients at a minimum of 3 months (Table 2). There was no statistically significant domain that demonstrated a difference between the 2 groups. In both groups, the domains with the lowest scores were quality of life, sports, and symptoms.

Conclusions:

Dysplastic trochlea that have a small lateral-central difference (<2mm), a shallower trochlear depth, or a lateral condylar height less than the medial condylar height, are more likely to result in a persistent J-sign. In the setting of these dysplastic trochleas, consideration should be given to address trochlear anatomy at the same time as addressing patella height normalization.In the presence of a J-sign, patella height should be normalized to CD < 1.1 to reduce the likelihood of a persistent J-Sign. Post-Op KOOS scores suggest the persistent J-sign does not impact the functional recovery in these patients. In our cohort, there was no increased risk of re-dislocation with a persistent J-Sign.