Axial and Lateral Radiographs in Evaluating Patellofemoral Malalignment

Abstract & Commentary

Synopsis: Combining AP, lateral, and axial views helps to best understand a patient’s patellofemoral alignment.

Source: Murray TF, et al. Axial and lateral radiographs in evaluating patellofemoral malalignment. Am J Sports Med 1999;27(5):580-584.

Murray and associates performed a prospective study to determine the effectiveness of lateral and axial x-rays to detect patellofemoral problems. History, physical examination, and radiographs were obtained for both knees of 431 patients (862 knees). Patients with 217 asymptomatic knees without patellofemoral problems in either knee served as the controls. Radiographs included standard axial patellar (AP) views, AP views in 30° of knee flexion, and standing lateral films at 0° and 30° of flexion. The presence of patellar tilt or subluxation was noted on the axial view. The lateral views were taken with precise overlap of the posterior femoral condyles, which allowed the determination of the relationships between the medial border of the patellar, the median ridge, and the lateral ridge in an attempt to assess patellar tilt. This is termed the Maldagne lateral view.

Sixty-two percent of the patients with patellar dislocations demonstrated subluxation on the axial view, while 98% demonstrated malalignment on the extended lateral view. Eighteen percent of the control knees had evidence of subluxation on the axial view, where 35% demonstrated subluxation on the extended lateral view.

The axial view demonstrated 62% sensitivity for previous dislocation, while the lateral view taken in full extension demonstrated 98% sensitivity. Specificity for prior dislocation was 82% for the axial view, 93% for the flexed lateral view, and 65% for the extended lateral view. Murray et al concluded that with the high sensitivity on the lateral view for detecting a patellar dislocation, a normal result on the full extension lateral view can virtually eliminate any question of previous dislocation. Given the high specificity on the axial view and lateral view with knee flexion, those two views combined can confirm a clinical impression of patellofemoral malalignment.

COMMENT BY JAMES P. TASTO, MD

Radiography of the patellofemoral joint has been well described in the literature and probably the most popular and commonly quoted article is that written by Merchant et al.1 These axial views are taken with the knee in approximately 45° of flexion with a specifically designed cassette. This is the view that most of us are familiar with. This is in contrast to the older, conventional "sunrise" view, which was an axial view taken with the knee in about 60-70° of flexion. The "sunrise" view has been fairly well discounted in the orthopaedic literature as giving little useful information on subluxation, dislocation, or tilt since the patella is deeply seated in the groove at that degree of flexion. There have been a lot of papers written concerning CT, MRI, and even dynamic MRI, but these tests are quite costly and in today’s environment are probably not practical.

Maldague and Malghem originally described the radiographic anatomy on lateral films and the ability to detect malalignment in the literature, and Malghem and Maldague have taken this information and converted it into an excellent study.2,3

When viewing the patella on lateral radiographs in full extension and 30° of flexion, three specific categories are isolated. Grade I alignment (normal) shows a slight concavity of the patellar median ridge and lateral facet relative to the femoral condyles. For grade II alignment (slight subluxation), the median ridge and lateral facet are overlapped, producing a dense, relatively straight line. Grade III alignment (more subluxed) demonstrates a convex median ridge and lateral facet surface, with the lateral facet being located closer to the femur.

This paper helps the clinician to use conventional AP, lateral, and axial radiographs to support his/her clinical impression of patellar malalignment without the need for more expensive studies. However, these x-ray findings do not have significant correlation with patellofemoral pain. The difficulty in this particular radiographic assessment lies in training the x-ray technician to be able to overlap the medial and lateral posterior femoral condylar outlines. If this is not done, then the radiograph cannot be adequately assessed. Murray et al originally used fluoroscopy for this study, but in practice merely have trained their technicians to manually line up the knee so that reproducibility can be obtained. I would suggest that we all spend a little time to train our radiology technicians to take these views and add them to our armamentarium, as this may help us better assess and treat patellofemoral disorders that commonly present in the office.

References

1. Merchant AC, et al. Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg Am 1974;56:1391-1396.

2. Maldague B, Malghem J. Apport du cliché de profil du genou dan le depistage des instabilities rotuliennes: Rapport prelimanair. Rev Chir Orthop 1985;71(Suppl 2):5-13.

3. Malghem J, Maldague B. Le profil du genou; Anatomie radiologiques differentielle des surfaces articulaires. J Radiol 1986;67:725-735.

A grade III alignment film of the patellofemoral joint has a high degree of sensitivity with which of the following clinical conditions?

a. patellar subluxation and dislocation.

b. patellar alta.

c. chronic patellofemoral pain.

d. normal finding.