The incidence of trochlear dysplasia in anterior cruciate ligament tears

The purpose of the present epidemiologic study is to record the radiographic presence of trochlear dysplasia and patella alta in patients who undergo anterior cruciate ligament (ACL) reconstruction as a potential underlying factor for post-operative anterior knee pain (AKP).

All consecutive cases of skeletally-mature ACL-deficient knees that would undergo ACL reconstruction in three different hospitals were prospectively included during a six-month period. Inclusion criteria were acute and sub-acute ACL injury with no previous ipsilateral knee operation. Patients with chronic ACL tears, prior-to-ACL-injury history of patellar instability or other PF disorders were excluded from the study.

A total of 299 knees were included (mean age 32 ± ten years). Forty-four (14.7 %) knees had a positive 'crossing sign' in the lateral X-rays and 255 (85.3 %) had no sign of trochlear dysplasia (p < 0.01). Among the cases with trochlear dysplasia, 41 (93 %) had type A trochlear dysplasia with the presence only of the 'crossing sign' and three (7 %) had type C trochlear dysplasia. Patellar height results included a mean Caton-Deschamps index of 1.0 ± 0.14 (0.5-1.4). Twenty (6.6 %) knees had an index of less than 0.8, and two (0.6 %) knees had an index less than 0.6. In contrast, 15 (5.0 %) knees had an abnormal value of more than 1.2, indicating patella alta.

The most important finding of the study is the increased prevalence of trochlear dysplasia and patella alta in patients with ACL injury, when compared to the incidence of trochlear dysplasia and patella alta in the general population in the literature. This finding could sound as an alert of a possible additional risk factor for post-operative anterior knee pain after ACL reconstruction.