ROLE OF DYNAMIC MRI IN THE ASSESSMENT OF PATELLA TRACKING – NEW METHOD USING ACTIVE RESISTED QUADRICEPS CONTRACTION

Abstract

70 patients who underwent dynamic MRI scanning for chronic anterior knee pain were retrospectively evaluated. All patients had been symptomatic for over a year. 43 patients had been treated conservatively and 27 had undergone surgical procedures (arthroscopy -13, lateral release- 9, tibial tubercle transfer 5). The extent of subluxation, tilt and cartilage abnormalities on MRI scans, during resisted extension were assessed. Functional scoring (Oxford, Lysholm and Tegner scores) was done through questionnaires and correlated with the radiological findings.

54 (77%) patients were found to have some patellofemoral abnormality on the scans. Subluxation was the most common finding with mild subluxation in 30, moderate in 18 and severe in 17 knees. Mild tilt was seen in 26 knees and moderate to severe tilt in 14 knees. Tilt was found in association with subluxation except in 8 cases. Grade 1 and 2 cartilage wear were seen in 13 knees and Grade 3 and 4 in 21 knees.

The “Tibial Tubercle to Trochlear Groove distance” (TTD) was measured in all knees and correlated with subluxation. The average distance was 13.5mm, 13.6mm and 18.8mm for mild, moderate and severe subluxation respectively. All patients with a TTD _ 20mm had moderate or severe subluxation. The specificity of a TTD _ 20mm for severe maltracking was 100% but the sensitivity was only 42%.

The TTD appears to be the single most significant parameter determining patella tracking. We have proposed an algorithm for the surgical and non-surgical treatment of chronic anterior knee pain. We recommend lateral release for those with moderate and severe subluxation and a tibial tubercle transfer as well in those with a TTD _ 20mm. The functional scores did not zshow a significant correlation with the grading of subluxation.