Disconnect Between Knee Pain and Joint Morphology

Key finding
• Three-dimensional (3D) image analysis demonstrated no statistically significant differences in joint morphology between older people with and those without patellofemoral pain (PFP).

Background
While previous studies demonstrated structural differences within the patellofemoral joint between asymptomatic individuals and those with PFP, these findings were predominately based on 2-dimensional (2D) radiographic methods. Unfortunately, 2D measurements are unable to control for the position of the leg within the image; a solution to this imaging shortfall is to use 3D quantitative analysis.

Led by Benjamin T. Draw of the Leeds Institute of Rheumatic and Musculoskeletal Medicine in the UK, this study used modern 3D image analysis technology to investigate any differences in joint morphology for individuals with and without PFP in a large cohort.

The study
Data were taken from the Osteoarthritis Initiative (OAI) database, a multicenter, prospective, observational study. The PFP group was selected based on pain reported by the participant using a knee pain map, knee pain when using the stairs taken from the WOMAC pain subscale question, and a tibiofemoral joint Kellgren-Lawrence (KL) grade of 0 in at least one knee. Participants with a history of knee surgery were excluded.

There were 115 participants in the PFP group (mean age, 59.7 years; 58.2% women), and 438 in the control group (mean age, 63.6 years; 52.9% women).

A linear discriminant analysis (LDA) of 3D shape explored whether any overall 3D shape or spatial position of the bones could discriminate between those with PFP and those without. The validity of this approach was assessed by determining whether the method could discriminate between men and women, who are known to have different bone shapes.

The results
“Our findings suggest that when commonly used patellofemoral imaging features are examined using careful 3D quantification, no statistically significant differences are found between a group with and without PFP,” the researchers conclude.

The results of the LDA also showed that overall 3D shape was unable to significantly discriminate between the group with and without PFP. By contrast, however, the overall 3D shape was able to significantly discriminate between men and women with a classification of 90.6%, which confirmed the validity of the 3D measures.

Implications for future research
There are some limitations to this study. Mainly, the analysis was conducted on a sample older than a typical PFP patient; thus, further work is needed to see if these findings could be replicated in a younger PFP population. In addition, a larger sample may be necessary to detect differences considering the high dimensionality of the data. However, the finding that there is no association of the 3D imaging features with PFP is robust in this analysis.

A growing evidence base also suggests that this issue is influenced by gender. A recent review of imaging literature in PFP shows that 80% of studies with mixed gender cohorts failed to report women and men separately. “Previous studies may simply have been describing differences related to their gender mix,” the researchers caution. “It is recommended that future studies follow the lead of recent studies by reporting gender separately or conducting single gender analyses.”

References:

Drew BT, Bowes MA, Redmond AC, et al. Patellofemoral morphology is not related to pain using three-dimensional quantitative analysis in an older population: data from the Osteoarthritis Initiative.Rheumatology. 2017;56:2135-2144.