The simplest method to classify CAM lesions

Abstract

CAM lesions are now seen as a significant pathology that could cause osteoarthritis of the hip joint. Currently there is no gold standard for classifying these lesions. We aim to show a simple method for classifying these lesions based on shape and position. Using CT 3D reconstruction, 91 preoperative CT scans from patients who had undergone hip arthroscopy for femoroacetabular impingement, were reconstructed to produce 3D images. Two senior hip surgeons have devised a simple four type classification system from previous experience. The system highlights the position and shape of different CAM lesions present in patients. The two senior surgeons and one junior surgeon reviewed the scans individually to assess whether the system could be used at all levels of surgical experience. The two senior surgeons agreed on which type of CAM lesion was present in all 91 cases. Intra observer reliability scores for the senior surgeons were 0.90 and 0.91. The junior surgeon reviewed the scans and disagreed on eight cases. This gave a Kappa co-efficient score of 0.87, which confirms a reliable system. We believe this classification system is simple and reproducible. It will aid surgeons in pre and intra-operative management of CAM lesions. Surgeons will be able to select the optimal portal placement and resect less capsule depending on the exact CAM lesion identified. This will potentially reduce complications and improve outcomes in junior hip arthroscopy surgeons.

Fig. 1.

Alpha angle measurement using AP hip radiograph.

Fig. 2.

AP view of hip joint. The red line shows the femoral head neck junction. If the lesion crosses this red line from the neck into the head then it must be the anterolateral head neck lesion or anterior head neck junction lesion. It cannot be the anterolateral neck or anterior neck lesion.

Fig. 3.

3D CT lateral view of hip. If the lesion is seen on the lateral view in the neck region (red rectangle) then it must be either the anterolateral head neck type or the anterolateral neck type. If a lesion is not present in the red rectangle it must be either the anterior head neck junction lesion or anterior neck lesion only.

Figs. 4 and 5.

Anterolateral Head Neck Lesion. The arrows highlight the lesion on both views. This lesion crosses the head neck junction and is seen on the lateral view so it can only be the anterolateral head neck lesion rather than the anterolateral neck lesion, which does not cross the head neck junction.

Fig. 5.

See Figure 4.

Fig. 6 and 7.

Anterolateral neck lesion. This lesion does not cross the head neck junction, but can be seen on both the AP and lateral views.

Fig. 7.

See figure 6.

Fig. 8.

Anterior neck lesion. This lesion is only seen on the AP view and does not cross the head neck junction.

Fig. 9.

Anterior head neck junction lesion. This lesion is only seen on the AP view but crosses the head neck junction so is not just the anterior neck lesion seen in Figure 8.