The Lachman maneuver is a specific physical examination technique used to assess the stability of the knee joint. It is widely considered the most reliable clinical test for evaluating the integrity of the Anterior Cruciate Ligament (ACL). This ligament connects the thigh bone (femur) to the shin bone (tibia), preventing the tibia from sliding too far forward beneath the femur. The test challenges the ACL’s ability to restrain this forward movement, providing insight into its condition following an injury.
Performing the Lachman Maneuver
The Lachman maneuver is performed with the patient lying on their back to ensure the muscles around the knee are relaxed. The knee is gently bent to a slight angle, typically between 20 and 30 degrees of flexion. This bending relaxes the hamstring muscles, which could otherwise mask a ligament injury by preventing the tibia from moving forward.
The examiner uses one hand to stabilize the patient’s thigh (femur). With the other hand, the examiner grasps the upper part of the shin bone (proximal tibia). A quick, firm force is then applied to the tibia, attempting to pull it forward (anteriorly) relative to the fixed femur. The examiner monitors the amount of forward movement and the quality of the resistance felt at the endpoint.
Defining a Positive Result
A positive Lachman maneuver is characterized by two distinct findings suggesting ACL damage. The first is increased anterior translation: the tibia slides forward excessively compared to the opposite, uninjured knee. This comparison is necessary because knee ligaments naturally vary slightly in laxity.
The second finding is the absence of a firm, distinct “endpoint” when the tibia is pulled forward. In a healthy knee, the intact ACL abruptly stops the forward motion, perceived as a solid, hard stop. When the ACL is torn, this resistance is lost, and the examiner feels a soft, mushy, or completely absent endpoint instead.
To quantify this laxity, clinicians use a grading system based on anterior movement relative to the opposite knee. Grade 1 laxity (0 to 5 mm) suggests a partial tear or mild sprain. Grade 2 laxity corresponds to 6 to 10 mm of movement. Grade 3 laxity (11 to 15 mm or more) indicates severe instability, often representing a complete ligament rupture.
Confirmation and Severity of ACL Injury
The finding of a positive Lachman test is a highly reliable clinical indicator, possessing a sensitivity of 87% and a specificity around 93% for diagnosing an acute ACL tear. A positive result strongly suggests the ACL has been sprained or torn, with the degree of laxity correlating directly to the injury’s severity.
While the physical examination is accurate, it is usually followed by diagnostic imaging to confirm the nature and extent of the injury. Magnetic Resonance Imaging (MRI) is the standard tool, providing detailed images of the soft tissues inside the knee. The MRI confirms the diagnosis of an ACL tear, determines if the tear is partial or complete, and identifies associated injuries. It is common for an ACL tear to occur alongside damage to structures like the menisci or bone bruising.
Management Options Following Diagnosis
Following the confirmed diagnosis of an ACL injury, the treatment strategy is determined by several factors, including the patient’s age, activity level, and the presence of accompanying knee injuries. Generally, there are two primary management pathways: non-operative treatment or surgical reconstruction.
Non-operative treatment, often chosen for individuals with lower activity demands or partial tears, focuses on intensive physical therapy. Rehabilitation strengthens the muscles surrounding the knee (quadriceps and hamstrings) to compensate for the lost ACL stability. This approach aims to restore function and prevent episodes of the knee giving way during daily activities.
For active individuals who participate in sports requiring pivoting, cutting, and jumping, surgical reconstruction is often recommended to restore mechanical stability. This procedure involves replacing the torn ligament with a tissue graft. The decision is personalized, carefully considering the patient’s goals for returning to their desired level of physical activity.