|Beitragstitel||The external obturator footprint as a landmark in total hip arthroplasty through a direct anterior approach: CT-based analysis in 200 patients|
Background: Anatomical landmarks for templating of total hip arthroplasty (THA) that are visible both during surgery and on the pre-operative radiograph are rare. If surgery is performed through a direct anterior approach the external obturator tendon (EO) is consistently visible, particularly the cranial part of its insertion. To use this point as a reference the exact position and dimensions of the footprint needs to be known.
Aim: First, to determine the location and dimension of the EO footprint on ap pelvis radiographs by correlating the EO anatomy in CT scans with conventional radiographs. Second, measure the precision with which the EO-footprint on pelvic radiographs can be determined on standard radiographs.
Methods: Pelvic CT scans of 200 patients were analyzed. Scans of patients <18yrs or after previous hip surgeries were excluded. The EO tendon was identified in the coronal plane; the height of its footprint, and its distance to the tip of the greater trochanter was measured and identified on virtual radiographs. The EO footprint was classified as “grooved” or “flat” depending on its appearance in the sagittal plane. Further, the distance between the EO footprint and the anatomical axis of the femoral diaphysis was measured. The EO footprints were marked on plain x-rays by two readers in a subset of 50 patients and transferred to the respective CT scan to compare it to its true position.
Results: The EO tendon was visible on all scans. The cranio-caudal dimension of the footprint was 6.4±1.4mm (range 3.0 to 11.8). Its distance to the tip of the greater trochanter was 16.0±3.1mm (range 10.1 to 29.2). In the axial plane, the distance of the EO footprint to the anatomical axis of the femur was 5.2±3.7mm (range -5.6 to 14.5). The EO footprint was grooved in 157 cases (78.5%) and flat in 43 cases (21.5%). There was no difference between the mean error (difference between x-rays and CT scan) between the two raters (0.3, -0.06 to 0.6 mm; p=0.105; intraclass correlation coefficient 0.84).
Conclusion: The footprint of the EO tendon on the greater trochanter is consistently visible on CT scans and on virtual radiographs. The EO footprint can be localized on plain x-rays with an acceptable accuracy. As the variability of the footprint dimension is small, this structure might be a useful landmark in THA, particularly when performed through a direct anterior approach.