Summary

To investigate the clinical, histological, and genetic phenotype of superficially fissured cartilage on the femoral head-neck junction at the impingement site in patients with femoroacetabular impingement.

Abstract

Purpose

While an association between femoroacetabular impingement (FAI) and osteoarthritis (OA) has been reported, the mechanistic differences and transition between the two conditions is not fully understood. In FAI cartilage lesions at the femoral head-neck junction can sometimes be visualized during hip arthroscopy. In this study, we evaluated a unique cartilage pattern in FAI patients that we hypothesized may indicate risk for, or predict occurrence of, osteoarthritis. The purpose of this study was to describe a unique dimpled pattern of superficial fissured cartilage lesions on the femoral head-neck junction at impingement site in patients with FAI and to evaluate the clinical, histological and genetic phenotype of this cartilage.

Methods

Six hips (six patients) with dimpled or fissured cartilage were included among patients who underwent hip arthroscopy for treatment of symptomatic FAI from October 2020 through December 2021. This injured cartilage (dimple-pattern group) and normal cartilage (control group) on the femoral head-neck junction were collected from the same patients and evaluated for histological quantification by Mankin scores and expression of proteins related to cartilage degeneration, such as matrix metalloproteinases (MMP)-1,2,3,10, and 12, tissue inhibitor of metalloproteinases (TIMP)-1 and 2, aggrecan neopepitope CS846, and hyaluronic acid, by Milliplex Multiplex Assays.

Results

The mean age of the six hips included was 34.2 ± 12.9 years (range, 19-54), and all FAI subtypes were mixed. Mankin scores for the normal cartilage group and the dimple-pattern group were 0.67 ± 0.82 and 3.3 ± 0.82, respectively. Dimple pattern fissured cartilage showed a significant increase in Mankin score (p=0.031) and a significant increase in protein expression of CS846 (p=0.031) compared to normal cartilage. There were no significant differences in MMPs, TIMPs, or HA levels between the two groups.

Conclusion

The dimple pattern fissured cartilage, compared to normal cartilage, showed histologically significant cartilage degeneration and a significant increase in protein expression of CS846, a biomarker for early OA. This lesion serves as helpful visual indicator of extremely early degeneration of the cartilage of femoral head-neck junction caused by FAI.
Keywords
cartilage defect; femoral head; femoroacetabular impingement; hip arthroscopy