Doctor BSWH Department of Radiology Temple, Texas, United States
Case Diagnosis: Anterior cruciate ligament tear diagnosed by Patella Alta and Insall-Salvati Ratio.
Case Description: The mechanism of injury and general radiographic findings associated with ACL tears have been extensively documented. The presence of a patella alta and the utilization of the Insall-Salvati Ratio as an indicator of ACL tears, however, has not been as well studied. The following case demonstrates utilization of the Insall-Salvati ratio to diagnose Patella Alta and increase suspicion for underlying ligamentous instability of the right knee, especially if physical exam findings are inconclusive.
A 17-year-old football player presented to the orthopedic clinic a week after seeing his FNP for right knee pain following a popping sensation. Physical exam findings at that visit were significant for edema and decreased ROM. Patient could still bear weight then, denying other symptoms. Radiographs taken at that visit showed patella alta. At the orthopedic clinic on this visit, with his HPI, new physical exam findings, and patella alta, underlying ligamentous instability and injury were questioned.
Discussions: There is a significant association between an ACL tear and an increased patellar tendon length with a greater Insall-Salvati ratio. Of the various ACL injury studies we evaluated, only one discussed the Insall-Salvati ratio and ACL tear relationship. This study showed a substantially greater Insall-Salvati ratio of 1.16 (median) in patients with ACL tears (n=34) versus 0.99 in control subjects with normal findings (n=36). Our patient's Insall-Salvati ratio was 1.78, leading to a follow-up exam and imaging that subsequently diagnosed an ACL tear.
Conclusions: This case illustrates the potential of patella alta, diagnosed by an elevated Insall-Salvati ratio, as a radiographic indicator for underlying ACL tear or other ligamentous disruption; especially given that outpatient physical exams can be inconclusive in post-traumatic settings.