[Radiologic assessment of femoro-patellar instability. Personal experience and review of the literature].
OBJECTIVE
To propose a simple and reproducible radiological evaluation of patellofemoral instability to enable the orthopaedic surgeon to choose the best therapy.


METHODS
We have evaluated retrospectively the radiographs and CT examinations of 25 patients, 15 female and 10 male, aged between 18 and 32 years. They underwent surgical treatment for patellar instability in the past 4 years. Lateral retinacular release has been performed in every patient, medial transposition of the anterior tibial tuberosity has been performed in 23 patients and in 5 of them also its distal replacement, proximal Insall's realignement was performed in 20 cases and only 1 patient underwent trochleoplasy. Preoperative conventional radiographs included antero-posterior view, true lateral view (exact superimposition of the posterior trochlear edges) and axial views at 30 degrees of knee flexion. On lateral view, the patellar height was evaluated based on Caton-Deshamps index and trochlear dysplasia assessed using the methods suggested by Dejour. A CT examination of both knees was performed: the images were taken first with knees in extension, with and without quadriceps contraction, then in flexion at 20 degrees. Patellar "bascùle" angles were measured both with quadriceps relaxed and contracted as an index of quadriceps dysplasia; the TAGT in extension was evaluated as an index of the degree of lateral position of the anterior tibial tuberosity. Preoperative conventional and CT findings were compared with those obtained postoperatively at 30.4 months from the surgical intervention.


RESULTS
All patients were free from complaints after surgery. In 5 patients a high patella was corrected by distal realignement of anterior tibial tuberosity. A trochlear dysplasia with different degrees of severity was present in all cases and it was not modified by surgical treatment, with the exception of the patient who underwent trochleoplasty. In the 20 patients who underwent proximal Insall's realignment, patellar "bascùle" angles--pathological before surgery--were restored to normal values with the exception of 3 cases. In 23 patients who underwent medial transposition of anterior tibial tuberosity, the values of the TAGT were all normalized: nevertheless, in three patients low values of the TAGT were found after surgery and this condition may predispose to the development of medial patellofemoral by iperpression syndrome.


CONCLUSIONS
In patients suffering from patellofemoral instability, a radiological protocol which includes conventional radiographs in two projections and a CT examination both in extension, with and without quadriceps contraction, and in flexion at 20 degrees supplies all the information needed for evaluating patellar height and mobility, trochlear dysplasia, valgism of the knee and the degree of excessive lateral position of the anterior tibial tuberosity. Careful evaluation of such abnormalities is important for selecting the best surgical treatment for each patient. It's a simple, quick, and accurate protocol that may be reproduced, even using different radiographic equipment. The collaboration between the radiologist and the orthopaedic surgeon is crucial for the correct interpretation of radiological findings, which must be evaluated together with clinical findings so that an adequate therapeutical plan could be proposed.
Cusmano
F
F
Istituto di Scienze Radiologiche, Università degli Studi, Casa di Cura Città di Parma, Parma.
Adravanti
P
P
Pedrazzini
M
M
Ampollini
A
A
Pavone
P
P
D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000601:surgery; D007719:Knee Joint; D008297:Male; D010329:Patella; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed