Precision and Accuracy of Identification of Anatomical Surface Landmarks by 30 Expert Hip Arthroscopists
We conducted a study to assess 30 expert hip arthroscopists’ ability to identify common surface landmarks used during hip arthroscopy. Thirty hip arthroscopists independently performed a blinded examination of an awake supine human volunteer for identification of 5 surface landmarks: anterior superior iliac spine (ASIS), tip of greater trochanter (GT), rectus origin (RO), superficial inguinal ring (SIR), and psoas tendon (PT). The examiners applied the labels ASIS, GT, RO, SIR, and PT to the landmarks. An ultrasonographer performed a musculoskeletal ultrasound examination and applied labels as well, and a photographer documented the examiner labels after obtaining overhead and lateral digital images with use of fixed camera mounts. Digital overlay composite images of arthroscopist and ultrasonographer labels were analyzed. Direction and distance of inaccurately placed labels were compared with known values for neurovascular structures previously reported for common arthroscopic portals. Average distance from examiner-applied labels to ultrasonographer-applied labels was 31 mm for ASIS, 24 mm for GT, 26 mm for RO, 19 mm for SIR, and 35 mm for PT. Interobserver variability of examiner-applied labels was recorded as areas of 95% predictive interval: 65 cm2 for ASIS, 16 cm2 for GT, 221 cm2 for RO, 38 cm2 for SIR, and 29 cm2 for PT. Examiner labels demonstrated the highest potential for injury because of anterior portal inaccuracy. Expert hip arthroscopists varied in their ability to accurately and precisely identify common surface landmarks about the hip, using only manual palpation.
Take-Home Points
- Surface landmarks are routinely used for physical examination and surgical technique.
- Common surface landmarks used in establishing arthroscopic portals may be more difficult to accurately identify than previously thought.
- The greater trochanter was the surface landmark most precisely identified by expert examiners.
- Ultrasound examination identified landmarks varied from landmarks identified by palpation alone.
Anatomical surface landmarks about the hip and lower abdomen are often referenced when placing arthroscopic portals and office-based injections.1-3 However, the degree to which these landmarks can be reproducibly identified using only visual inspection and palpation is unknown.
Safe access to the hip joint and surrounding structures during hip arthroscopy has been a focus in the orthopedic literature. Authors have described anatomical relationships of recommended portals to neurovascular and other anatomical structures.4-6 This information has been reported in millimeters to centimeters of safety based on cadaver dissection studies.4-7We conducted a study to assess expert hip arthroscopists’ ability to identify, using only physical examination techniques, the anatomical structures used for reference when creating safe starting points for arthroscopic access. We hypothesized that variance in examiner-identified points would exceed safe distances from neurovascular structures for the most commonly used hip arthroscopic portals. The volunteer in this study provided written informed consent for print and electronic publication of this article.
Methods
In this study, we prospectively assessed 30 expert hip arthroscopic surgeons’ ability to identify commonly referenced surface landmarks on the adult male hip, using only inspection and manual palpation. Surgeons were defined as experts on the basis of their status as hip arthroscopy instructors at the Orthopaedic Learning Center (Rosemont, IL) for the Arthroscopy Association of North America and industry-sponsored hip arthroscopy education faculty (Arthrex). Five surface landmarks were selected for their relevance to publications on safe portal placement2-5: anterior superior iliac spine (ASIS), tip of greater trochanter (GT), rectus origin (RO), superficial inguinal ring (SIR), and psoas tendon (PT).
A healthy adult male volunteer was placed supine on an examination table and exposed distally from the mid abdomen, with the perineum and the genital area covered bikini-style. An expert musculoskeletal ultrasonographer used a handheld musculoskeletal ultrasound transducer (Sonosite) to identify the 5 landmarks. Short- and long-axis images of each structure were obtained. The examiner applied a round (1 cm in diameter), uniquely colored adhesive label to the skin over each location. A professional photographer using a Canon digital camera and fixed mounts made precise overhead and lateral images. The positional integrity and scale of these images were confirmed with referral to constant anatomical skin features. Images were archived for analysis (Figure 1A).
After the ultrasonographer’s labels were removed, each of the 30 expert hip arthroscopic surgeons identified the structures by static physical examination (inspection and palpation only) and applied the same colored labels to the skin. 
Imaging software (Adobe Photoshop Creative Suite 5.1) was used to superimpose the digital images of the examiner labels on those of the ultrasound-verified anatomical labels (Figure 1C). Measurements were then taken with digital calipers to determine average distance from ultrasound label; accuracy within 10 mm of verified ultrasound label; true average location (TAL) determined by 95% confidence interval (CI); and interobserver variability calculated by 95% prediction interval, which determined the probability of where an additional examiner data point would lie.
In the second arm of the study, examiner data were compared with previously published data on arthroscopic portal safety. 
Results
Average absolute distance from examiner labels to ultrasonographer labels was 31 mm for ASIS, 24 mm for GT, 26 mm for RO, 19 mm for SIR, and 35 mm for PT (Figure 2).
