Sonography of injury of the posterior cruciate ligament of the knee.

OBJECTIVE

To describe the sonographic appearance of injury of the posterior cruciate ligament (PCL) of the knee.

DESIGN AND PATIENTS

Eleven patients (6 men, 5 women) with an average age of 36 years (range 17-70 years), referred for magnetic resonance (MR) imaging evaluation of knee pain, had PCL injury according to standard MR imaging criteria. Sonography was performed after the MR examination by the author, who was aware of the MR findings. Both the affected and contralateral asymptomatic PCL were scanned sonographically in the longitudinal plane with a curvilinear transducer, and their diameters were measured on the scanner using electronic calipers. Bilateral PCL sonography and measurement were also performed on 12 patients with other acute knee injuries but normal PCLs according to MR imaging ("non-PCL-injured knee cohort"), and on 10 normal volunteers.

RESULTS

All PCLs were hypoechoic, regardless of injury. The injured PCLs had an average diameter of 0.88 cm (range 0.54-1.21 cm), while the contralateral PCLs had an average diameter of 0.51 cm (range 0.30-0.84 cm) (signed rank test, P<0.001). One patient also had focal discontinuity of the PCL. There was no statistical difference between the diameters of the right and left PCLs of the non-PCL-injured knee cohort (signed rank test, P=0.1) nor between those of the volunteers (signed rank test, P=0.6). The average difference in diameter between the injured and contralateral PCLs was statistically significant versus the difference between the non-PCL-injured knee cohort's PCLs (Mann-Whitney test, P=0.0001) and versus the difference between the volunteers' PCLs (Mann-Whitney test, P=0.0001).

CONCLUSION

PCL injury is manifested sonographically either as enlargement of the entire ligament, appreciated by comparison with the contralateral normal PCL, or by focal disruption of the ligament.