Primary cam morphology conceptual definition statements based on its attributes, empirical referents, antecedents and consequences
| Conceptual definition with examples of heterogenous empirical referents (operationalising) | Attribute/empirical referent/antecedents/consequences |
| Primary cam morphology | Concept and terminology |
| is a cartilage or bony prominence (bump) | Attribute 1 (tissue type) Antecedent (acquired during maturation) |
| of varying size | Attribute 2 (size) |
| at any location around the femoral head-neck junction of the hip | Attribute 3 (site) |
| which changes the shape of the femoral head from spherical to aspherical | Attribute 4 (shape) |
| It often occurs in asymptomatic male athletes in both hips, and is reported per hip, per person or both | Attribute 5 (ownership) |
| We distinguish between cartilage and bone on MRI. We see primary cam morphology and measure its size, site and shape on two-dimensional imaging (AP pelvis and lateral radiographs) and/or three-dimensional imaging (CT scan/MRI). The size and shape are measured in individual hips as a continuous or dichotomous outcome measure. The most common outcome measure is the alpha angle as a continuous variable (mean, SD degrees or median; IQR) or a dichotomous variable (primary cam morphology is present when the alpha angle is above a certain cut-off value) on two-dimensional radiographs (AP pelvis or lateral hip) or three-dimensional imaging. The location (site) depends on the imaging and how it is reported: for example, femoral head-neck junction, anterosuperior, 1.30 o’clock position (eg, ‘3 Tesla MRI: 3D multiplanar reconstructions producing radial images around the axis of the femoral neck at 30° intervals; using the primary outcome measure as the maximum cartilage alpha angle from 11 o'clock through to 3 o'clock to account for variation in the location of cam morphology at the femoral head-neck junction of the hip’).23 Regression models (with, eg, generalised estimating equations) would allow data from both hips to be included in the same data set to account for potentially related observations between hips from the same person, and to assess changes in morphology over time, to account for correlation between measurements from the same research participant at different stages (attribute 5). | Empirical referents for attributes 1–5 |
Primary cam morphology likely* develops during skeletal maturation in young adolescents (with no history of current or previous hip disease), as a normal physiological skeletal response to high-load sporting activity and other unconfirmed risk factors
Epiphysial extension is measured on 3 T MRI as the distance the epiphysis extends along the femoral neck expressed as a ratio of femoral head diameter using custom-developed software on the radial slices at 11 o’clock, 12 o’clock, 1 o’clock, 2 o’clock and 3 o’clock or the physeal tilt quantified as the ratio of epiphysial extension on either side of the physis at the different o’clock positions. | Antecedents (risk factors and pathogenesis) |
| When developed, primary cam morphology has likely* no hip disease consequence in the majority of individuals.44 Long-term prospective research on prognosis is needed to confirm this. In some individuals, however, the regular abutment of primary cam morphology against the hip socket (acetabular rim) may cause
We define these hip diseases as a consequence of primary cam morphology based on clinical history and examination as well as imaging findings. | Consequences |
*Supported by current—although limited—prospective research evidence.
AP, anteroposterior.