We reviewed 90 3D CT scans of 82 patients who have undergone or are awaiting arthroscopic surgery for femero-acetabular impingement, both retrospectively and prospectively. A method to determine the presence and severity of pincer lesion was established during routine reconstruction of 3D CT scans of hips.

The width of the anterior inferior iliac spine (AIIS) was measured at the widest point. The distance from the base of the AIIS to the acetabular rim directly inferiorly was also measured (rim distance). The rim distance was divided by the AIIS width to give a ratio (figure 1). The ratio gives a numerical appreciation of the severity of the pincer lesion (pincer ratio). We have categorized these lesions into type 1 (ratio <0.3), type 2 (ratio 0.31 -0.6), and type 3 (ratio >0.61) (figure 2).

Our results show a large variation in the pincer ratio (0.06- 3.13), with a mean value of 0.521, and 95% CI 0.438 - 0.604. 53% of hips had a positive cross over or line join sign on AP radiograph. There was excellent inter-observer correlation with high kappa co-efficient values during categorization of lesions (figure 4). There does not appear to be a correlation between the presence of a crossover sign and the degree of severity of pincer ratio when ratios are categorized as type 1 (<0.3), type 2 (0.31 - 0.6), and type 3 (>0.61) (p=0.533) (figure 5).

We believe this is a reproducible method of determining the severity of a pincer lesion. We propose that the pincer ratio could be used to influence the choice of resection technique.

This systematic approach is valuable in preoperative planning and should aid the surgeon when making decisions regarding the degree of rim recession.

Figure 1

59af4767d6b7bce1128c24bb44ef9812 300x300
D373482a4a526b4bb85f4a3f48bfbe61 300x300

Figure 2

B621301e2bf9171164bdbaf5a590e2dc 300x300

Type 1

Db786c0f042c782c31200e35f161beec 300x300

Type 2

99858b433beda179236bfa5a64f9b056 300x300

Type 2.

Figure 3 Numbers of each type of pincer lesion

  Type 1 (<0.3) Type 2 (0.31-0.6) Type 3 (>0.61)
n 36 40 15

Figure 4 Kappa co-efficient values following categorization of lesion

Type 1 lesion k= 0.95
Type 2 lesion k= 0.93
Type 3 lesion k= 0.96

Figure 5 Presence of crossover sign for each lesion type. No correlation found (p=0.533)

Crossover sign on AP Type 1 lesion Type 2 lesion Type 3 lesion
Present 9 11 4
Absent 27 29 11
Total 36 40 15


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