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Lachman test of the knee

Name of test

Lachman test

What it tests

ACL integrity

How to do it

  • Stand next to the supine patient, on the side of the exam table.
  • Grasp the lateral thigh just above the knee with your upper (contralateral) hand. See Figure 1
  • Hold the tibia medially with your lower (ipsalateral) hand. See Figure 2
  • Put your lower thumb on the joint line. See Figure 3
  • Steady the leg with your upper hand and gently lift it, asking the patient to keep the foot on the table, such that the knee flexes to 30 degrees.See Figures 4 and 5
  • Ask the patient to relax.
  • Gently yet suddenly apply a juddering force to the tibia in an attempt to subluxate it forward. See Figure 6
  • Assess in your mind the extent of excursion and the 'quality' of the end point

The normal response

There should be a firm restraint to anterior translation. See Figure 7 The tibia should not move forward much (the same amount as found on the other side) See Figure 8 and it should come to a strong stop, the so-called "good end point" as the ACL reaches its maximum length Again, this end point on the injured leg should be comparable to the normal side.

What it means if not normal

ACL deficiency is suggested

Grades of laxity defined by amount of anterior tibial translation relative to contralateral knee:

Grade I: 1-5mm
Grade II: 6-10mm
Grade III: >10mm


  • This should be the first test performed, while the patient while still relaxed.
  • Lachman does not tell acute from chronic
  • You may be fooled by hamstring spasm (false negative) or generalized laxity (false positive)
  • you may be fooled by a displaced meniscal tear, which blocks excursion. Hint: full extension is also blocked
  • watch this video



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