Validation of the Acute Lower Limb Activation Mechanism Test: A Reliable Bedside Diagnostic Tool for Extensor...

Modern clinical practice has become increasingly reliant on imaging modalities to diagnose the extent of soft tissue injuries. We describe and then validate a novel bedside clinical test, the acute lower limb activation mechanism test (ALAM), that can be used to identify an extensor mechanism rupture in those unable to straight leg raise (SLR). Patients who presented with an acute knee injury and were unable to SLR were identified over a 6-year period. Patients meeting the inclusion criteria were examined utilizing the ALAM test and diagnosis subsequently confirmed with ultrasound, magnetic resonance imaging (MRI) or surgery. During the validation study, four surgeons independently examined 10 patients with unilateral soft tissue knee injuries. Surgeons were blinded to the type of injuries present and examined both the normal and pathological knee. Patient randomization followed and the examination was repeated 2-hour later to yield 40 examined knees each. A total of 113 patients (56 female, mean age 47.3 years) presented with unilateral knee pathology. In this original cohort, the ALAM test had high sensitivity (100%; 95% confidence interval: 94.5-100%) and high specificity (93.8%; 82.8-98.7%). The positive predictive value was 95.6%. In the validation study, blinded prestudy MRI diagnoses showed: acute quadriceps rupture (n = 4), acute anterior cruciate ligament tear (n = 3), acute patellar dislocation (n = 1), and medial patellofemoral ligament injuries following recurrent dislocations (n = 2). The ALAM test had 100% sensitivity (95% confidence interval: 63.1-100%), 97.0% specificity (83.8-99%), 100% negative predictive value, and 88.9% positive predictive value (53.8-98.2%). The significance of bedside examinations in conjunction with a detailed history cannot be overemphasized. This study adds to the literature by proposing a validated, noninvasive, highly sensitive and specific bedside test. We advocate the ALAM test be used as part of the orthopaedic surgeons' diagnostic armamentarium, in all patients unable to SLR to reliably detect soft tissue extensor mechanism ruptures.