ARTICULAR CARTILAGE THICKNESS IN PEDIATRIC AND ADOLESCENT KNEES DECREASES WITH AGE AND SKELETAL MATURITY: IMPLICATIONS FOR OSTEOCHONDRAL GRAFTING PROCEDURES

Abstract

Background:Quantifying native cartilage thickness in pediatric and adolescent knees can help match donor and recipient sites for articular cartilage restoration procedures such as osteochondral autograft transplantation (OATS) and osteochondral allograft transplantation (OCA).Hypothesis/Purpose:The purpose of the current study was to quantify articular cartilage thickness in pediatric and adolescent knees using magnetic resonance imaging (MRI). We hypothesized that cartilage thickness is inversely correlated with skeletal maturity and age.Methods:One hundred and twenty MRI scans were evaluated in a cohort of patients 9 to 18 years old without osteochondral lesions, chondral wear or pathology, intraarticular fractures, history of knee surgery, or inflammatory arthropathy. Measurements of articular cartilage thickness at the medial femoral condyle, lateral femoral condyle, lateral trochlea, and patella were made on axial, coronal, and sagittal MRI scans (Figure 1). Skeletal maturity was categorized as ‘open’, ‘closing’, or ‘closed’ based on the status of the proximal tibial and distal femoral growth plates. Descriptive statistics was used to evaluate cartilage thickness by age and sex. Independent samples t-test, analysis of variance (ANOVA), and linear regression were performed to investigate for associations with sex, skeletal maturity, and age.Results:On the femur, cartilage was thickest at the lateral trochlea with mean articular thickness of 4.2 ± 1.4 mm in males and 3.6 ± 1.3 mm in females (p=0.015) (Table 1). Skeletally immature patients with open physes had significantly thicker cartilage at the medial femoral condyle, lateral femoral condyle, and lateral trochlea compared to patients with closing and closed physes (Figure 2). Linear regression analysis also revealed a significant association between femoral cartilage thickness and age (Figure 3). Age explained 63% of the variance at the medial femoral condyle (B=6.1, p<0.001), 64% of the variance at the lateral femoral condyle (B=4.9, p<0.001), and 68% of the variance at the lateral trochlea (B=8.2, p<0.001) (Table 2). In contrast, cartilage thickness at the patella did not significantly vary by age, sex, or skeletal maturity (Figures 2 and 4).Conclusion:There is a strong inverse association between increasing age and cartilage thickness of the femoral condyles and lateral trochlea. In particular, pediatric knees demonstrate relatively thick cartilage at the lateral trochlea that decreases with age. This information will help surgeons understand recipient site anatomy and identify appropriate donor site tissue for articular cartilage restoration procedures such as OATS and OCA in children and adolescents.Tables:Table 1.Mean articular cartilage thickness of the femur and patellaCombined (n=120)Male(n=40)Female(n=60) p valueMedial femoral condyle3.2 ± 1.03.5 ± 1.02.9 ± 0.80.001Lateral femoral condyle2.8 ± 0.72.9 ± 0.72.7 ± 0.70.056Lateral trochlea3.9 ± 1.44.2 ± 1.43.6 ± 1.30.015Median ridge of patella4.2 ± 0.94.4 ± 0.94.1 ± 0.90.080Medial facet of patella4.7 ± 1.04.8 ± 1.04.6 ± 0.90.320Lateral facet of patella4.6 ± 0.84.7 ± 0.84.5 ± 0.80.185Table 2.Linear regression of articular cartilage thickness of the femur and patella by ageR2 B p valueMedial femoral condyle0.636.1<0.001Lateral femoral condyle0.644.9<0.001Lateral trochlea0.688.2<0.001Median ridge of patella0.024.80.090Medial facet of patella0.045.50.032Lateral facet of patella0.0014.50.741Figures:Figure 1.Measurements of patellofemoral articular cartilage thickness Measurements of articular cartilage thickness were made on (A) coronal, (B, C) sagittal, and (D) axial magnetic resonance imaging (MRI) of the knee. For the medial femoral condyle, cartilage thickness was measured at five regions: midpoint of the medial condyle (MFC) and midpoints of Cahill zones 1 (MID1), 2 (MID2), B (MIDB) and C (MIDC). Similarly, measurements of cartilage thickness of the lateral femoral condyle were made at the midpoint of the lateral condyle (LFC) and midpoints of Cahill zones 4 (MID4), 5 (MID5), B (MIDB), and C (MIDC). Measurement of the lateral trochlea was made at midpoint of Cahill zone A (MIDA). Measurements on the patella were made at the midpoint of the medial facet (MF), midpoint of the lateral facet (LF), and the median ridge (MR) on axial and sagittal MRI scans. Figure 2.Mean articular cartilage thickness of the femur and patella by growth plate statusFigure 3.Mean articular cartilage thickness of the femur by ageFigure 4.Mean articular cartilage thickness of the patella by age