Validation of the Acute Lower Limb Activation Mechanism (ALAM) Test: A Reliable Bedside Diagnostic Tool for Extensor Mechanism Ruptures

Introduction 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). Methods Patients who presented with an acute knee injury and were unable to SLR were identified over a six-year period. Patients meeting the inclusion criteria were examined utilising the ALAM test and diagnosis subsequently confirmed with ultrasound, MRI or surgery. During the validation study, four surgeons independently examined ten 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 randomisation followed and the examination was repeated two-hours later to yield 40 examined knees each. Results 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 pre-study 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%). Conclusion The significance of bedside examinations in conjunction with a detailed history cannot be overemphasised. This study adds to the literature by proposing a validated, non-invasive, 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.