A High-Grade J Sign Is More Likely to Yield Higher Postoperative Patellar Laxity and Residual Maltracking in Patients With Recurrent Patellar Dislocation Treated With Derotational Distal Femoral Osteotomy

Abstract

Background: It has been speculated that the patellar J sign may have a negative effect on the clinical outcomes of patients with recurrent patellar dislocation (RPD). Purpose: To (1) evaluate clinical outcomes, postoperative patellar stability, and patellar maltracking correction in patients with RPD treated with derotational distal femoral osteotomy (DDFO) and combined procedures and (2) investigate the influence of J sign severity on the clinical outcomes. Study Design: Cohort study; Level of evidence, 3. Methods: Between January 2015 and December 2016, a total of 78 patients (81 knees) with RPD, a positive J sign, and an excessive femoral anteversion angle (FAA; ≥30°) were surgically treated with DDFO and combined procedures. J sign severity was graded according to a previously described classification system (grades 1-3). Routine radiography and computed tomography were performed on every patient to evaluate the patellar height, trochlear dysplasia, genu valgum, tibial tuberosity–trochlear groove distance, patellar lateral tilt angle, and patella–trochlear groove distance. The patellar lateral shift distance during stress radiography was measured preoperatively and postoperatively to quantify medial patellofemoral ligament (MPFL) graft laxity under anesthesia, and “MPFL residual graft laxity” was defined as the patellar ridge surpassing the apex of the lateral femoral trochlea. Patients were evaluated using the Kujala, International Knee Documentation Committee (IKDC), and Lysholm scores preoperatively and postoperatively. Patients were allocated into 3 subgroups in terms of the severity of the J sign: low-grade group 1 (grade 1; n = 19), low-grade group 2 (grade 2; n = 16), and high-grade group (grade 3; n = 12). Subgroup analyses were performed to investigate the influence of a high-grade J sign on the clinical outcomes. Results: Among the 78 patients (81 knees), 47 patients (47 knees) met the inclusion criteria. The mean follow-up time was 26.1 ± 1.7 months. The mean preoperative and postoperative FAAs were 36.2°± 5.3° and 10.0°± 2.1°, respectively, with a mean correction angle of 26.2°± 5.9°. At the final follow-up, all patient-reported outcomes improved significantly, and subgroup analyses showed that the high-grade group had significantly lower Kujala scores (75.6 vs 85.3 for low-grade group 1 [ P < .001] and 83.4 for low-grade group 2 [ P = .001]), Lysholm scores (77.6 vs 84.6 for low-grade group 1 [ P = .003]), and IKDC scores (78.6 vs 87.3 for low-grade group 1 [ P = .001] and 84.3 for low-grade group 2 [ P = .033]) than the low-grade groups. The total rate of MPFL residual graft laxity was 8.5% (4/47), and the prevalence of the postoperative residual J sign was 38.3% (18/47). Subgroup analyses showed significant differences between the high-grade group and the 2 low-grade groups with regard to the MPFL residual graft laxity rate (33.3% vs 0.0% for low-grade group 1 [ P = .016] and 0.0% for low-grade group 2 [ P = .024]), residual J sign rate (91.7% vs 15.8% for low-grade group 1 [ P < .001] and 25.0% for low-grade group 2 [ P < .001]), and patellar lateral shift distance (14.2 vs 8.1 mm for low-grade group 1 [ P = .002] and 8.7 mm for low-grade group 2 [ P = .007]). Conclusion: In a group of patients treated for RPD with a positive preoperative J sign and increased FAA (≥30°), patients with a preoperative high-grade J sign had inferior clinical outcomes, more MPFL residual graft laxity, and greater residual patellar maltracking.

Medial Patellofemoral Ligament Reconstruction With or Without Derotational Distal Femoral Osteotomy in Treating Recurrent Patellar Dislocation With Increased Femoral Anteversion: A Retrospective Comparative Study

“…The Digital Imaging and Communications in Medicine data from the hip-knee-ankle CT scan were reconstructed into 3-dimensional models using Mimics Research 20.0 (Materialise) to detect rotational deformities of the lower extremity according to a method described previously. 31 The FAA was defined as the angle formed between the axis of the femoral head-neck and distal femur, and the external tibial torsion angle was assessed by measuring the rotational angle of the proximal tibia relative to the distal tibia. The present study showed an interobserver agreement of 0.9° for femoral anteversion and 0.7° for external tibial torsion angle.…”

“…The Caton-Deschamps Index was used to measure patellar height. 23 Trochlear dysplasia was detected on the true lateral view of the knee and classified according to the Dejour classification system; 5 severe trochlear dysplasia was defined as type B or D. 31 All patients were examined using axial CT for the measurement of the TT-TG distance according to the method described by Camp et al 3 To detect the presence of valgus/varus deformity, the femorotibial angle was measured on the whole-leg standing anteroposterior radiograph. All these radiological parameters were measured by 2 independent examiners (H.Z., Z.J.Z.)…”

“…DDFO was performed according to a method described previously. 31 A standardized lateral subvastus approach at the distal femur was used. A self-designed osteotomy goniometer was employed to determine the rotation angle of the osteotomy, which was marked using 2 Kirschner wires (Youke).…”

“…The Tegner score, Kujala score, Lysholm score, and International Knee Documentation Committee score were assessed preoperatively and at the final follow-up. The preoperative J-sign was graded according to a method described previously 31 : grade 1, >1 quadrant of patellar motion; grade 2, >2 quadrants of patellar motion; and grade 3, complete patellofemoral dislocation. In the present study, a grade 3 J-sign was categorized as a high-grade J-sign, and a grade 0/1/2 J-sign was categorized as a low-grade J-sign.…”

“…Axial stress fluoroscopy was used to assess the patellar medial laxity index with the knee flexed at 30° (all knees in the DDFO group and 52 knees in the control group). 28,31 First, a stress-free radiograph of the patellofemoral joint was obtained. Second, maximum manual pressure was applied to the medial side of the patella, displacing it laterally, to obtain the maximum lateral stress radiograph.…”