Background/Purpose: Anterior or posterior cruciate ligament (ACL/PCL) ruptures are thought to lead to early knee osteoarthritis (KOA) and thus considered scientifically valuable “models” of pre-radiographic change. Further, longitudinal studies can be initiated at a precise set-point, which is the time of the trauma. Quantitative measurement of cartilage thickness change with MRI provides a powerful and sensitive tool for longitudinal analysis of structural cartilage change before, during, and after the onset of radiographic KOA. Because ACL/PCL rupture frequently occurs in young athletes, the purpose of this study was to obtain reference data of normal longitudinal subregional femorotibial cartilage thickness change in such subjects, specifically at the end of adolescence.

Methods: The knees of the dominant leg (the one used for take off) of 18 young top volleyball athletes (Olympic center Berlin) were examined. One participant was retrospectively excluded because of a history of ACL rupture, and one because of an imaging artifact. The age range (n=16; 8 female, 8 male) was 15-17 y at baseline. MR images were acquired using a 3D VIBE with water excitation, at baseline and two years later. Femorotibial cartilage thickness was measured by manual segmentation, using the images and commercially available software (Chondrometrics GmbH, Ainring, Germany). Cartilage thickness data were computed in the medial (MFTC) and lateral femorotibial compartment (LFTC), in tibial and femoral cartilages, and in 16 femorotibial subregions.

Results: Of the 16 subjects, 11 displayed open epiphyses at baseline, and all showed closed epiphyses at follow-up. In the MFTC, a cartilage thickness increase of +114±126µm (mean±standard deviation) or +3.3±3.7% was observed, with a standardized response mean (SRM= mean /standard deviation of change) of +0.90. This increase was less in the LFTC (+2.3±2.5%; SRM +0.93); and was greater in the weight-bearing medial femur (+4.4±3.7%; SRM +1.19) than in the medial tibia (+2.0±4.3%; SRM +0.46). The greatest increase was observed in the internal aspect of the medial femur (+5.5±5.8%; SRM +0.94) whereas no increase was seen in the internal aspect of the medial tibia (-0.5±6.6%; SRM -0.07). Over the two years, the subchondral bone area (tAB) increased by 0.8±1.5% in the MFTC and by 1.2±1.2% in the LFTC.

Conclusion: A substantial increase in femorotibial cartilage thickness (and subchondral bone area) was observed in young athletes towards the end of adolescence, i.e. a period during which the epiphyseal line is closing. This increase should be considered when measuring longitudinal cartilage change in young athletes after ACL/PCL rupture. Further studies need to clarify whether the increase is due mainly to normal growth, or to high exercise levels. Longitudinal studies in young adults with cruciate ligament rupture should hence include healthy reference cohorts of similar age (and activity level), to adequately differentiate pathological (post traumatic) change from that occurring physiologically.