T. Hopf et al., ACL LESION WITH KNEE-JOINT EFFUSION - WHY CAN LACHMANS SIGN NOT BE ELICITED, Zeitschrift fur Orthopadie und Ihre Grenzgebiete, 134(5), 1996, pp. 418-421
In acute anterior cruciate ligament (ACL) lesions with effusion of the
knee joint it is often difficult to realize a positive Lachman sign.
It was suggested that the tension of the joint capsule may reduce tibi
al displacement although the ACL is completely disrupted. In 10 cadave
r knee joints the ACL was dissected and the capsule was closed again.
By a canula the knee joints were filled with isotonic saline solution
in steps of 20 mi up to 100 mi. Before and after dissection of the ACL
and during filling the joint we measured the anterior tibial displace
ment by use of the MEDmetric KT 1000 arthrometer. In a second series w
e examined 5 patients with acute effusion of the knee joint before and
after puncture of the effusion. We detected the electromyographic act
ivity of the quadriceps muscle and the hamstrings during the KT 1000 t
est and patellar reflex. In the cadaver tests we found no reduction of
the anterior tibial translation while filling the joint with saline s
olution. The electromyographic examinations showed a reflectory action
in the quadriceps muscle and in the hamstrings when the Lachman test
was performed. In the quadriceps muscle the electromyographic amplitud
e was reduced after puncture; the hamstrings showed a drastically redu
ced amplitude and duration of the signal. When patellar reflex was per
formed we recorded an electromyographic action in both muscle groups,
too. Puncture could only reduce the signals of the hamstrings. Our res
ults suggest that the reduction of the anterior drawer and the Lachman
test in acute effusion is caused not mechanically by the tension of t
he capsule but by a reflectory muscle action of the hamstrings.