Influence of Risky Pathoanatomy and Demographic Factors on Clinical Outcomes After Isolated Medial Patellofemoral Ligament Reconstruction: A Regression Analysis

Abstract

Background: Multiple studies have demonstrated that a number of demographic and pathoanatomic characteristics are associated with patellofemoral instability, recurrence of instability, and less satisfactory results following medial patellofemoral ligament reconstruction (MPFL-R). Despite the growing volume of research, the relationship of risk factors to patient-reported outcome after MPFL-R is unclear. Purpose: To determine if certain pathoanatomic and demographic factors predict disease-specific quality-of-life outcome after isolated MPFL-R for symptomatic patellofemoral instability. Study Design: Cohort study; Level of evidence, 3. Methods: The study analyzed 224 isolated MPFL-Rs. Demographic data were collected, including age at first dislocation, sex, and presence of bilateral instability. Pathoanatomic risk factors included the presence of high-grade trochlear dysplasia, tibial tubercle–trochlear groove (TT-TG) distance, patella alta ratio, Beighton score, and patellar tilt. Other factors included femoral tunnel position accuracy and WARPS/STAID score. Descriptive analyses were conducted, followed by calculation of individual Spearman rank correlation coefficients for the predictor variables versus the Banff Patellofemoral Instability Instrument (BPII) scores. A multivariable regression with stepwise selection was employed to establish the final model predicting BPII score, with all significant variables for alpha ≤ .05 included in the final model. Results: The cohort of 224 patients included 66 (29.5%) males and 158 (70.5%) females, with a mean age of 24.1 years and a mean body mass index of 23.9 kg/m2. The mean age of first patellar dislocation was 15.7 years, and 41.4% of patients had bilateral instability. Pathoanatomic variables within the cohort included the following: high-grade trochlear dysplasia = 41%; mean TT-TG = 14.6 mm, with 16.8% of patients demonstrating a TT-TG ≥18 mm; mean Caton-Deschamps ratio = 1.09, with 22% of patients demonstrating a ratio ≥1.2; and positive Beighton score = 37.5%. The mean BPII score at postoperative 2 years was 67.1 out of 100. A stepwise elimination in the regression model demonstrated no statistically significant 3- or 2-way relationships. Assessment of individual variables indicated that bilateral symptoms ( P = .004), higher age at first dislocation ( P = .024), and femoral tunnel position >10 mm from the Schöttle point ( P = .042) were statistically significant predictors of lower quality-of-life scores. The R2 value for the regression analysis model was 0.07. Conclusion: In this large cohort of patients undergoing isolated MPFL-R for symptomatic lateral patellofemoral instability, a multivariable forward stepwise regression demonstrated that bilateral symptoms, femoral tunnel position, and age at first dislocation were statistically significant predictors of lower postoperative BPII scores. No anatomic risk factors were predictive of quality-of-life outcome score 2 years after MPFL-R surgery. The R2 value indicated that there were many other important contributing factors affecting BPII outcome scores than those explored in this study.

Identifying Patients With Patella Alta and/or Severe Trochlear Dysplasia Through the Presence of Patellar Apprehension in Higher Degrees of Flexion

“…12 Commonly cited clinical thresholds for bony procedures include a TT-TG distance of greater than 16 mm or a CD index of greater than 1.2; however, the original surgical "a la carte menu" that established these criteria predates the surgical option of MPFL reconstruction. 8 There are few outcome studies of MPFL reconstruction evaluating the influence of TT-TG distance and patella alta on isolated MPFL reconstruction; however, several recent retrospective cohort studies 4,10,15,18,24 have demonstrated little influence of TT-TG distance and moderate patella alta on the outcomes of MPFL reconstruction. These studies suggest that isolated MPFL reconstruction can be successful in cases with a higher CD index and TT-TG distance than previously thought.…”

Patient-Reported Outcomes After Revision Surgery for Failed Medial Patellofemoral Ligament Reconstruction: A Matched-Pair Analysis Including Correction of Predisposing Factors

“…31 In particular, the incidence of femoral tunnel malpositioning has been reported to range from 31% to 67%. 10,37 Although previous studies were inconclusive regarding the effect of and correlation between poor femoral tunnel malpositioning and clinical outcome scores, 23,37 a recent investigation by Hiemstra et al 18 confirmed that femoral tunnel positioning >10 mm from the Schöttle point correlates with lower postoperative BPII 2.0 scores. These findings are in accordance with the results obtained in this study, in which femoral tunnel malpositioning was found in 75% of the patients with a postoperative knee flexion deficit and in 27% of patients who experienced patellar redislocation.…”

“…Magnetic resonance imaging data were obtained for all patients in the study group and the control group, as were routine radiographs, including standing long leg axis and true lateral view of the knee joint with ≤3 mm of overlap between the femoral condyles. 18 Data were evaluated for the following: severity of trochlear dysplasia (absent, low grade [Dejour type A], or high grade [Dejour type B-D]) 11 ; patellar height, with Caton-Deschamps index ≥1.2 recorded as elevated 9 ; tibial tuberosity–trochlear groove (TT-TG) distance, with >16 mm recorded as elevated 2 ; tibial tuberosity–posterior cruciate ligament (TT-PCL) distance, with >24 mm recorded as elevated 36 ; and varus-valgus alignment. 22 Femoral tunnel accuracy was measured from the center of the tunnel to the center of the Schöttle point, with an increment of 10 mm indicating malpositioning.…”

“…22 Femoral tunnel accuracy was measured from the center of the tunnel to the center of the Schöttle point, with an increment of 10 mm indicating malpositioning. 18…”

“…22 Femoral tunnel accuracy was measured from the center of the tunnel to the center of the Schöttle point, with an increment of 10 mm indicating malpositioning. 18 In revision cases (study group) and in primary stabilization cases (control group), concomitant trochleoplasty was considered in patients with Dejour type B or D trochlear dysplasia in combination with a positive J-sign and a reversed dynamic patellar apprehension test 44 result 50°; concomitant TTO was considered when the TT-TG distance exceeded 20 mm, when the TT-PCL distance z exceeded 24 mm, and/or when the Caton-Deschamps index was 1.3. Femoral derotation osteotomy or valgus correction osteotomy was considered when femoral antetorsion exceeded 25°and valgus deformity was 4°.…”