Anterior Knee Pain Patients Without Structural Knee Abnormalities and Normal Lower Limb Skeletal Alignment Have a Higher Prevalence of Cam-Femoroacetabular Impingement Syndrome than the General Population.

OBJECTIVES: This study aimed to ascertain the prevalence of cam Femoroacetabular Impingement Syndrome (cam-FAIS) in Anterior knee pain (AKP) patients devoid of both structural patellofemoral joint (PFJ) abnormalities and lower limb skeletal mal-alignment. A secondary objective was to examine pain and disability differences between AKP patients with and without cam-FAIS.

METHODS: A total of 209 AKP patients were screened for eligibility. Inclusion criteria were normal imaging studies and normal lower limb alignment, and exclusion criteria were previous knee surgery and knee and/or hip osteoarthritis. Of those, 49 (23.4%) were eligible and this number matched a previous power analysis to detect statistically significant differences in prevalence of cam-FAIS in a population of AKP patients. The first step in the study sequence was to ask the patient whether they had groin pain. If so, the impingement test was done. Then, the femoral cam morphology defined by an alpha angle greater than or equal to 55 degrees in a 45º Dunn axial view of the hip was ruled out. Additionally, patients completed Kujala and International Knee Documentation Committee (IKDC) functional knee scores for disability assessment. General population control group was obtained from literature.

RESULTS: The study included 9 males and 40 females, with an average age of 36 (20-50, ± SD 8.03) years. Groin pain and positive impingement test were found in 26/49 patients (53%). An alpha angle ≥ 55° was observed in 35/49 patients (71%). A combination of groin pain, positive impingement test and an alpha angle ≥ 55° was seen in 18/49 patients (37%). The AKP patients with groin pain, a positive impingement test and an alpha angle ≥ 55° exhibited statistically similar pain and disability levels as AKP patients without cam-FAIS.

CONCLUSION: The results of this study suggest that AKP patients without structural abnormalities in the PFJ and without lower limbs mal-alignment have a statistically significantly higher prevalence of cam-FAIS than the general population. Moreover, AKP patients with cam-FAIS have a statistically similar degree of pain and disability than AKP patients without it.

STUDY DESIGN: Cross-Sectional Study.

LEVEL OF EVIDENCE: IV.