CORR Insights®: Does Cartilage Degenerate in Asymptomatic Hips With Cam Morphology?

Where Are We Now?

Femoroacetabular impingement (FAI) is a common cause of hip pain and a potential risk factor for the development of early osteoarthritis [2]. While this relationship is well established, a sizeable population of asymptomatic individuals exhibit some degree of cam morphology. This raises the question: Is it a matter of “if” or “when” chondral damage occurs in these individuals?

Grammatopoulos and colleagues [3] addressed this question in the current study. The authors found that knowing the natural history of chondral wear may aid physicians in caring for their patients, particularly in terms of counseling patients about prognosis.

The development of chondral wear in patients with FAI depends on multiple factors and varies by individual. The type of anatomic lesion (cam, pincer, mixed, DDH, or subspine) determines which area or areas of cartilage are at greatest risk, while the severity of lesion and presence of coexisting lesions likely also play a role [2]. Additionally, patient-related factors, such as activity level, age, sex, also have been identified as potentially influencing the probability of developing chondral wear [4].

Where Do We Need to Go?

Advanced cartilage imaging sequences such as T1rho identify areas of early chondral matrix depletion prior to their becoming evident on routine clinical MRIs [1]. Orthopaedic surgeons use advanced sequencing to identify areas of “cartilage at risk” prior to the development of osteoarthritis, in the hopes of allowing early intervention. Advanced imaging may also note the presence or absence of early chondral damage in patients with only mild anatomic deformity, as well as highlight at-risk cartilage in patients with mixed lesions.

Further research on quantifying morphologic abnormalities would allow investigators to parse the individual interactions among such abnormalities, as well as examine the relationships and interactions among the type/severity of anatomic lesions and patient activity levels. Computer-assisted modelling may also tailor recommendations based on the predicted interactions between a particular patient’s anatomy and other patient-related factors.

Advanced cartilage imaging sequences are a powerful tool that can help surgeons identify various anatomic and patient-related factors that may contribute to the development of chondral wear in patients with FAI. However, various technical factors must be considered when applying these techniques clinically, and an ideal algorithm for imaging FAI has yet to be established.

Image quality generally determines how finely cartilage can be subdivided when establishing regions of interest (ROIs) and acquiring T1rho images of sufficient quality within a reasonable scan time is challenging. Quality ROIs, particularly in FAI, will result in the most-sensitive detection of early pathologic change, while poorly conceived ROIs may mask pathology. Advances in pulse sequence design can contribute to increased image quality and allow for improved segmentation of cartilage. Analysis of advanced cartilage imaging datasets also presents challenges in terms of how best to normalize individual values (as values may vary from patient to patient), as well as how best to establish a normal value to which the area of suspected pathology may be compared.

How Do We Get There?

In order to evaluate the natural history of chondral wear in patients with FAI, long-term prospective longitudinal studies encompassing a large cohort of patients who are relatively diverse in terms of their anatomic deformity and patient factors would be ideal. While these studies are ongoing (for example, at my institution, NCT# 02408276), smaller and less time-consuming studies may be performed in order to advance and augment the major long-term studies that may eventually come out.

Advances in describing both the quality and severity of anatomic deformities might be accomplished, for example, by further development of imaging based three-dimensional modelling techniques. Such techniques can reliably calculate morphologic values, provide insight into expected areas of impingement based on a given patient’s individual anatomic lesions, and allow surgeons to explore the predicted outcome of virtual interventions [5].

Technical advances in MR pulse sequence design may contribute to improvements in T1rho image quality and offer improved cartilage segmentation [8]. Advanced analysis techniques such as voxel based relaxometry have also been applied to the hip cartilage, and further study of these techniques in patients with FAI may provide an additional powerful method of analyzing quantitative MRIs [6]. Additionally, while conventional analysis of parametric images typically involves calculation of a mean relaxation value and standard deviation for each region of interest, the calculation of texture mapping parameters can provide a more detailed evaluation of variability within each ROI, potentially detecting early tissue disorganization that may not be evident with conventional parametric analyses [7].

Ultimately, any advances in imaging, whether pertaining to osseous morphology or chondral microstructure, should be correlated with patient factors, surgical findings, and clinical outcomes, in order pursue a more-comprehensive understanding of the natural history of cartilage damage in patients with FAI.