Validation of a computerized model for a new biomechanical concept- the fossa-foveolar mismatch- the answer to lesions of the ligamentous fossa-foveolar complex in the hip?

Abstract

Background: Hip-preserving surgery in young patients frequently reveals lesions of the ligamentum teres (LT). Histological and clinical evidence supports that those lesions could be source of intraarticular hip pain. It has been hypothesized that LT degeneration could be linked to the abnormal positioning of the fovea outside the lunate surface during various daily motions. We introduce the "fossa-foveolar mismatch" (FFM) by determining the trajectory of the fovea in the fossa during hip motions, enabling a comparison across diverse hip-pathomorphologies.

Aims: to determine (1) intraobserver reliability and (2) interobserver reproducibility of our computer-assisted 3-dimensional (3D) model of the FFM.

Materials and methods: All patients with joint preserving surgery for femoroacetabular impingement syndrome (FAIS) or developmental dysplasia of the hip (DDH) at our institution (11. 2015-08.2019)were initially eligible. We employed a simple random sampling technique to select 15 patients for analysis. Three-dimensional surface models based on preoperative computed tomography (CT) scans were built, the fossa virtually excised, the fovea capitis marked. Models were subjected to physiological range of motion with validated 3D collision detection software. Using a standardized medial view on the resected fossa and the transparent lunate surface, the FFM-index was calculated for 17 motions. It was obtained by dividing the surface occupied by the fovea outside of the fossa by the total foveolar tracking surface. Three observers independently performed all analyses twice. (1) Intraobserver reliability and (2) interobserver reproducibility were calculated using intraclass correlation coefficients (ICCs).

Results: (1) We obtained excellent intraobserver ICCs for the FFM-index averaging 0.92 with 95% CI 0.77-0.9 among the three raters for all motions. (2) Interobserver reproducibility between raters was good to excellent, ranging from 0.76 to 0.98.

Conclusions: The FFM-index showed excellent intraobserver reliability and interobserver reproducibility for all motions. This innovative approach deepens our understanding of biomechanical implications, providing valuable insights for identifying patient populations at risk.

Keywords: 3D model; Acetabular fossa; Active patients; Biomechanical; CT; Fossa-foveolar mismatch; Fovea capitis; Hip; Hip morphology; Hip pain; Hip preserving surgery; Intraclass correlation coefficient; Ligamentum teres; Range of motion; Validation.

Fig. 1

The fossa-foveolar mismatch is illustrated by displaying (A) no fossa-foveolar mismatch and (B) presence of a fossa-foveolar mismatch with a pathologic foveolar tracking pattern for the motion of everyday life internal/external rotation in 90 degrees flexion

Fig. 2

The flow diagram displays the inclusion and exclusion criteria of our study cohort

Fig. 3

(A) Based on CT of the pelvis and distal femur; (B) we created a 3D model; (C) The acetabular fossa was digitally removed; (D) the fovea was identified and manually exaggerated; (E) finally, the model was subjected to standardized movements within physiological range of motion and the foveolar tracking pattern was determined

Fig. 4

The foveolar tracking pattern for all analyzed motions is illustrated showing an example of a high and low FFM index

Fig. 5

The forest plots show the (A) intraobserver reliability and (B) interobserver reproducibility of the FFM index for the different motions. Flex/Ex: Flexion/Extension; Ab/Ad: Abduction/Adduction; IR/ER: Internal/External rotation; 90 Flex IR/ER: Internal/External rotation in 90° flexion; Ant Imp test: Anterior Impingement test; Post Imp: Posterior Impingement test; Position 30° IR: FFM index in 30° internal rotation position; Position 30° ER: FFM index in 30° external rotation position;