To The Editor:
We read with interest the recent paper "The Reproducibility and Repeatability of Varus Stress Radiographs in the Assessment of Isolated Fibular Collateral Ligament and Grade-III Posterolateral Knee Injuries. An in Vitro Biomechanical Study" (2008;90:2069-76), by LaPrade et al., which aimed to address the lack of quantitative data on the diagnosis of posterolateral knee ligament injuries. We commend the authors for attempting to provide a more objective clinical assessment of these injuries. We question, however, whether the conclusions drawn from the study are supported by the evidence presented.
The authors conclude that their study establishes a "feasible, cost-effective objective measurement tool" that can be used to evaluate patients in a clinical setting. However, this in vitro study involved the use of cadaveric knees from a predominantly elderly age group (average age, 71.6 years). These specimens may not represent the knee ligament behavior of younger patients, in whom this type of injury is more prevalent1.
The experimental setup of the knee also raises some questions. First, was there any rotational control of the knee during the measurement of the lateral compartment gap? Lack of rotational control can introduce potential error2. Second, are the authors suggesting that this model be adapted for clinical use? If so, then it would be extremely difficult to control the amount of knee flexion during clinical examination, which again could lead to radiographic errors2.
In view of these concerns, we question whether these in vitro results can realistically be applied to the clinical setting and particularly to the degree of accuracy suggested. It is difficult to be convinced that a difference of 1 to 2 mm can differentiate between an isolated fibular collateral ligament injury and a grade-III posterolateral injury, especially given the range of measurements for clinician-applied varus stress.
LaPrade and colleagues have written extensively in this field, and their publications have included a report on magnetic resonance imaging3. Do the authors believe that the proposed method of using stress radiographs is a realistic alternative to clinical examination and magnetic resonance imaging scanning? It would certainly be an interesting clinical comparison that could potentially validate their in vitro measurements.