What did the study look at?
In femoroacetabular impingement syndrome (FAIS), a bony bump at the femoral head-neck junction (cam deformity) rubs against the hip socket during movement. Citing several studies, the authors note that incomplete removal of this bump is the leading cause of failed hip arthroscopy; according to the data they cite, 5% to 10% of hip arthroscopy patients may need revision surgery, and 81% of these revisions show residual impingement. On the other hand, removing too much bone may, rarely, increase the risk of a femoral neck fracture.
The alpha angle is an X-ray measurement that quantifies the size of a cam deformity. The aim of the paper was to give technical tips on using a navigation tool (HipCheck; Stryker) that measures the alpha angle on intraoperative fluoroscopy (live X-ray) images.
How was it done?
This is a surgical technique paper (Technical Note), not a study comparing patient outcomes. The technique is shown in a video and images of a right hip arthroscopy.
- The navigation screen is covered with a sterile sheath, attached to the table so as not to disturb the theatre set-up, and connected to the fluoroscopy unit. No extra preoperative planning or imaging is required.
- After the work inside the joint (such as labral repair) is completed, traction is released and the capsule is opened in a T shape.
- The surgeon marks the femoral head and neck on the touchscreen. Fluoroscopic images are then taken with the hip in 6 standard positions; the system measures the alpha angle on each and stores them as pre-resection values.
- While the bump is removed with an arthroscopic burr, images can be taken at any time to check the amount of bone removed.
- Once dynamic examination shows no impingement, images are repeated in the same 6 positions in the same order and the post-resection values are stored; the capsule is then closed.
What did it find?
As a technique paper, it does not report patient outcomes. The authors highlight the following:
- Fluoroscopy in a single position gives two-dimensional information and cannot show the three-dimensional extent of resection. The reliability of the 6 positions used had previously been shown against computed tomography.
- The 3 views at 0° of flexion help assess the upper-outer part of the bump, and the 3 views at 50° of flexion help assess its front.
- According to the authors, advantages include ease of use, no need for CT or extra instruments on the patient, and a lower risk of under- or over-resection.
- Practical cautions: instruments overlapping the femoral head or neck on the image may distort measurements; pre- and post-resection images must be reproducible in exactly the same way; and the connection should be checked before surgery.
The authors' conclusion
The authors conclude that this navigation system makes it possible to check the adequacy of cam resection during surgery with an objective radiological measurement on fluoroscopic images, before and after resection and at any chosen hip position during the procedure.
Limitations
- Compared with CT-based navigation systems that provide 3D assessment, the system does not markedly reduce dependence on surgical experience.
- As a new system, cost and availability may be problems.
- Incorrect marking of the head and neck, or failure by the surgeon to check the system's measurements, may produce wrong data.
- The authors also note that a surgeon used to the system may feel "blind" if it is not working or not available.
Reference
Gürsoy S, Vadhera AS, Singh H, Perry A, Nho SJ, Chahla J. 2021. Intraoperative Guidance for the Surgical Correction of Cam Deformities Using Hip Arthroscopy Based on Alpha Angle Measurement. Arthroscopy Techniques. 10(5):e1351–e1360. Licence: CC BY-NC-ND 4.0.
DOI: 10.1016/j.eats.2021.01.038
Free full text: PubMed Central PMC8185893
This article summarises a published scientific paper for general information; it does not replace an examination or a personal medical assessment. Please consult your doctor about your symptoms.
