What is the significance of a positive Lachman's test result in assessing Anterior Cruciate Ligament (ACL) integrity and what are the treatment options for an ACL injury?

Lachman Test: Clinical Significance and ACL Injury Management

Test Performance and Interpretation

The Lachman test is the most reliable clinical examination for detecting ACL rupture and should be your primary physical examination maneuver when evaluating suspected ACL injury. 1

Proper Technique

• Position the patient supine with the knee flexed to 20-30 degrees 1
• Stabilize the distal femur with one hand while applying anteriorly directed force to the proximal tibia with the other hand 1
• Assess for anterior tibial translation and end-feel quality, comparing to the contralateral knee 1
• The test is more sensitive than the anterior drawer test for ACL rupture 1

Grading Positive Results

When the Lachman test is positive, grade the severity as follows 2, 3:

• Grade I: Proprioceptive appreciation only (subtle increased translation)
• Grade II: Visible anterior translation of the tibia
• Grade III: Passive subluxation of the tibia with patient supine
• Grade IV: Patient can actively sublux the proximal tibia

Diagnostic Limitations

• The predictive value of a positive test is only 47%, while a negative test has 70% predictive value 4
• A negative Lachman test is more useful for ruling out ACL injury than a positive test is for confirming it 4
• Intratester and intertester reliability is moderate (Kappa values 0.42-0.69), meaning examiner variability exists 4

Biomechanical Insight

• During the Lachman test, the lateral compartment contributes more to anterior tibial translation than the medial compartment 5
• ACL rupture causes increased anterior translation coupled with tibial internal rotation 5

Imaging After Positive Lachman Test

Initial Imaging

• Obtain plain radiographs first if Ottawa knee rules are positive (focal tenderness, inability to bear weight) 6
• Radiographs rule out fractures and assess for joint effusion >10mm on lateral view, which should prompt MRI in patients <40 years old 6

Advanced Imaging

• MRI is superior for soft tissue evaluation and should be obtained when radiographs are negative but ACL injury is suspected 6
• MRI has 93.5% detection rate for soft-tissue injuries in acute knee trauma 6
• MRI shortens diagnostic workup, reduces additional procedures, and improves quality of life in the first 6 weeks 6
• CT can detect ACL tears with 79-100% sensitivity but MRI remains superior for meniscal and ligamentous injuries 6

Treatment Options for ACL Injury

Young, Active Patients (<30 years) in Cutting/Pivoting Sports

For patients participating in cutting and pivoting sports with complete ACL tears, ACL reconstruction with autograft is the most appropriate treatment to prevent instability, protect menisci, and reduce risk of subsequent cartilage damage. 6

Appropriate Treatment Options (AAOS Rating 7-9) 6:

• ACL reconstruction with autograft (Rating: 8) - preferred option
• ACL reconstruction with allograft (Rating: 7)
• Activity modification without reconstruction (Rating: 7) - only if patient accepts risk

Graft Selection 7:

• Patellar tendon (BTB) autograft: Choose to reduce risk of graft failure or infection
• Hamstring tendon autograft: Choose to reduce risk of anterior knee pain or kneeling pain
• Single or double bundle techniques show similar results 7

Timing of Surgery 7:

• Early reconstruction is preferable in young, active patients to provide knee stability and protect menisci
• Risk of additional cartilage and meniscus injuries increases after 3 months from initial injury
• Delayed reconstruction is acceptable if patient initially chooses conservative management but develops instability

Patients with Lower Activity Demands

May be appropriate (AAOS Rating 4-6) for sedentary or low-demand patients 6:

• Supervised rehabilitation program without reconstruction (Rating: 6)
• Self-directed exercise program without reconstruction (Rating: 6)
• ACL functional knee brace without reconstruction (Rating: 6)

Critical caveat: These options lack sufficient evidence for return to cutting/pivoting sports due to high instability risk and associated meniscal/chondral damage 6

Special Considerations

Concomitant Meniscal Injury

• Meniscal repair should be the first option whenever technically possible, as it results in similar clinical outcomes to isolated ACL injuries 7
• Partial meniscectomy increases osteoarthritis risk (OR=1.87) 7
• Total medial meniscectomy dramatically increases osteoarthritis risk (OR=3.14) 7
• Combined ACL and medial meniscus lesions carry significantly higher risk for knee osteoarthritis than isolated lesions 7

Minor Osteoarthritic Changes

• The presence of minor osteoarthritic changes does not influence treatment decision-making 6, 7

Postoperative Management

• Adequate rehabilitation with open and closed kinetic chain exercises for quadriceps recovery is fundamental 7
• Functional knee orthoses are NOT recommended for routine use after primary isolated ACL reconstruction, as they provide no clinical benefit 7
• Address modifiable osteoarthritis risk factors including weight control and quadriceps strengthening 7

Key Clinical Pitfalls

• Do not rely solely on the Lachman test: Its moderate reliability means MRI confirmation is essential before surgical planning 4
• Do not delay surgery beyond 3 months in young, active patients, as risk of secondary injuries increases 7
• Do not perform meniscectomy when repair is feasible: This substantially increases long-term osteoarthritis risk 7
• Do not assume conservative management is safe for cutting/pivoting athletes: High instability risk leads to meniscal and chondral damage 6