Longitudinal change in patellofemoral cartilage thickness, cartilage T2 relaxation times, and subchondral bone plate area in adolescent vs mature athletes

Highlights

• First longitudinal study of patellar cartilage thickness/composition during growth.

• Patellofemoral cartilage thickens in late adolescence with no sex differences.

• Patellar cartilage growth accompanied by T2 increases in adolescent women, not men.

• These cartilage changes help interpret findings in subjects after knee trauma.

Abstract

Objective

Patellofemoral cartilage changes have been evaluated in knee trauma and osteoarthritis; however, little is known about changes in patellar and trochlear cartilage thickness, T2 relaxation-time and subchondral bone plate area (tAB) during growth. Our prospective study aimed to explore longitudinal change in patellofemoral cartilage thickness, T2 and tAB in adolescent athletes, and to compare these data with those of mature (i.e., adult) athletes.

Materials and methods

20 adolescent (age 16 ± 1 years) and 20 mature (46 ± 5 years) volleyball players were studied over 2-years (10 men and 10 women each group). 1.5T MRI 3D-VIBE and multi-echo spin-echo sequences were acquired at baseline and 2-year follow-up. Using manual segmentation and 3D reconstruction, longitudinal changes in patellar and trochlear cartilage thickness, patellar cartilage T2 (mono-exponential decay curve with five echoes [9.7–67.9 ms]), and patellar and trochlear tAB were determined.

Results

The annual increase in both patellar and trochlear cartilage thickness was 0.8% (95% confidence interval [CI] 0.6, 1.0) and 0.6% (0.3, 0.9), for adolescent males and females respectively; the longitudinal gain in patellar and trochlear tAB was 1.3% (1.1, 1.5) and 0.5% (0.2, 0.8), and 1.6% (1.1, 2.2) and 0.8% (0.3, 0.7) for adolescent males and females, respectively (no significant between-sex differences). Mature athletes showed smaller gains in tAB, and loss of <1% of cartilage thickness annually. While no significant sex-differences existed in adolescent patellar T2 changes, mature males gained significantly greater T2 than mature females (p = 0.002–0.013).

Conclusions

Patellar and trochlear cartilage thickness and tAB were observed to increase in young athletes in late adolescence, without significant differences between sexes. Mature athletes displayed patellar cartilage loss (and T2 increases in mature males), potentially reflecting degenerative changes.

Introduction

Knee injury is a well-established risk factor for accelerated cartilage pathology and longer-term development of knee osteoarthritis (KOA) [1]. As candidate biomarkers for radiographic KOA incidence, typical cartilage parameters evaluated following injury include cartilage morphology (e.g., volume, thickness) and spin–spin relaxation times (T2). Cartilage T2 reflects cartilage composition and has been shown to be sensitive to water and collagen content, and collagen anisotropy [2].

Most reports of posttraumatic cartilage changes published thus far have focused on the tibiofemoral joint. Patellofemoral joint changes are typically under-recognised following knee trauma [1], despite being a potentially important source of knee symptoms [3]. Recently, posttraumatic longitudinal changes in the patellofemoral joint of adolescents and young adults have been highlighted (i.e., after anterior cruciate ligament [ACL] rupture), with patellofemoral cartilage demonstrating significant thinning [4] and prolongation of T2 values [5], and this more so than any other region in the knee. However, an absence of longitudinal reference data on cartilage morphological and compositional development in young athletes limits interpretation of longitudinal changes in patellofemoral cartilage under pathological conditions, typically a traumatic knee injury in physically active adolescents.

A single study has thus far generated longitudinal data on patellar cartilage growth, measuring patellar volume over approximately 1.5 years in 74 males and females aged 9–18 years [6]. While peak growth appeared greater among young men than young women, the focus on cartilage volume as a morphometric outcome is limited in that it remains unclear whether the observed gain in cartilage volume was due to an increase in (mean) cartilage thickness or due to growth of bone and subchondral bone plate area. Preliminary cross-sectional studies of patellar cartilage T2 relaxation times and thickness in non-athletic symptomatic 5–22 year old children and adolescents have suggested that cartilage compositional properties may depend on age and sex during growth, and that T2 varies from the bone interface to the cartilage surface [7], [8]. As a result, these studies have concluded that longitudinal evaluations of layer-specific patellofemoral cartilage in adolescents are needed. Such evaluations are particularly important in asymptomatic physically active adolescents as they can serve as reference data for evaluation of longitudinal changes in physically active adolescents with ACL or other injuries.

For the tibiofemoral joint, longitudinal changes in cartilage thickness, subchondral bone plate area, and cartilage T2 times over two years have recently been reported in adolescent volleyball athletes and were compared to mature athletes [9], [10]. The distinct properties of patellofemoral cartilage (i.e., patellar cartilage being the thickest cartilage throughout the human body and it being potentially more vulnerable to biochemical and biomechanical changes from physical activity than tibiofemoral cartilage [11]) suggest that its development may differ from other regions in the knee. Therefore, the aims of our prospective study were to determine: i) whether the longitudinal change of patellofemoral cartilage thickness, deep and superficial layer cartilage T2 relaxation-time, and subchondral bone plate area in adolescent athletes differs from that in mature athletes with a similar loading history; and ii) if differences exist in longitudinal cartilage maturation rates between male and female athletes.