Inferior outcomes seen in patients with recurrent patellar dislocation and high-grade J sign
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Among patients treated for recurrent patellar dislocation, patients with perioperative high-grade J sign had inferior clinical outcomes, more residual medial patellofemoral ligament residual graft and greater residual patellar maltracking compared with patients who had a low-grade J sign, according to study results.
Researchers identified 78 patients with recurrent patellar dislocation, a positive J-sign and an excessive femoral anteversion angle who underwent derotational distal femoral osteotomy and combined procedures. There were 47 patients included in the study. The mean follow-up was 26.1 months. The patellar height, trochlear dysplasia, genu valgum, tibial tuberosity-trochlear groove distance, patellar lateral tilt angle and patella-trochlear groove distance were evaluated with routine radiography and CT. Preoperatively and postoperatively, the patellar lateral shift distance was measured during stress radiography to quantify medial patellofemoral ligament (MPFL) graft laxity under anesthesia. Investigators noted MPFL residual graft laxity occurred when the patellar ridge surpassed the apex of the lateral femoral trochlea. Kujala, IKDC and Lysholm scores were used to preoperatively and postoperatively evaluate patients. With regard to severity of the J sign, patients were placed into either a low-grade group 1, low-grade group 2 or high-grade group. The impact of a high-grade J sign on clinical outcomes was determined with subgroup analyses.
Results showed the mean preoperative femoral anteversion angle was 36.2° and the postoperative femoral anteversion angle was 10°. All patient-reported outcomes significantly improved at the final follow-up. Patients in the high-grade group had significantly lower Kujala scores compared with the low-grade 1 group and low-grade 2 group. They also had significantly lower Lysholm scores and IKDC scores. The MPFL residual graft laxity was 8.5%. Investigators noted the prevalence of a postoperative residual J sign was 38.3%.
According to subgroup analyses, the residual graft laxity rate was significantly different between the high-grade group and the low-grade group 1 and low-grade group 2 (33% vs. 0% vs. 0%, respectively), as were the residual J sign rate (91.7% vs. 15.8% and 25%. respectively) and patellar lateral shift distance (14.2 mm vs. 8.1 mm and 8.7mm, respectively). – by Monica Jaramillo
Disclosures: Zhang report no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
Perspective
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Laurie A. Hiemstra, MD, PhD, FRCSC
The physical examination of patellofemoral instability always includes the evaluation of the J-sign, a commonly used but poorly understand indication of the lateral force vector on the patella during active leg extension. Zhang and colleagues have taken on the significant task of exploring the effect of the severity of the J-sign in patients with recurrent lateral patellofemoral instability and increased femoral internal rotation who have undergone a femoral de-rotation osteotomy and combined stabilizing procedure.
These authors have effectively demonstrated that a severe J-sign is a poor prognosticator both for failure of an MPFL reconstruction and for poorer clinical outcomes. In this series of 47 patients, they found a 38.3% incidence of residual J-sign even when the femoral internal rotation was corrected. Ultimately, they conclude that a severe J-sign is indicative of more significant pathoanatomy and therefore, it is more difficult to reduce the lateral force vector on the graft leading to laxity and poorer clinical outcomes. These authors have reinforced that in the treatment of patellofemoral instability in the setting of significant bony pathoanatomy, surgical results will depend on correcting as much as possible while balancing the extent of morbidity for the patient.
The challenge of this study is the difficulty of oversimplifying the classification of a complex sign that may have multiple different etiologies or combined etiologies. The confounding variables of trochlear dysplasia, patella alta and quadriceps abnormalities that may contribute to the J-sign need to be explored and would require a larger sample size and more robust classification systems.
These authors have reinforced that the failure to eliminate the lateral force vector on the patella will stretch out a soft tissue graft. In simple terms, the worse the deformity and symptoms, the bigger the operation is needed to restore functional anatomy and biomechanics of the patellofemoral joint.
Alberta, Canada
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