Partial ACL Injury

One of the treatment dilemmas that the sports physician is faced with is that of the partial tear of the anterior cruciate ligament.

The definition of the partial tear is:

  • History of injury to the anterior cruciate ligament
  • Positive Lachman test with a firm end point
  • Negative pivot shift test
  • Arthroscopic evidence of injury to the anterior cruciate ligament.
  • KT-1000 side to side difference of < 5 mm.

The natural history of the partial tear is controversial. There have been reports that suggest that both conservative and operative treatment give good results. The paper by Noyes had a 50% incidence of instability in high demand sports participation athletes with a anterior cruciate ligament tear > 50%. They also had a 75% incidence of re-injury. This suggests that patients in high demand sports require reconstruction.

The paper by Freunsgaard had good results with conservative treatment in patients who avoided high demand athletics.

Buckley reported that the degree of anterior cruciate tear did not correlate with outcome. Only half of their patients were able to resume their previous level of sports.

Clinical Assessment

  • Clinical Examination
  • Lachman test
  • Pivot shift test
  • KT-1000
  • MRI
  • Arthroscopy and examination under anaesthesia.

Lachman Test

The lachman test is positive, but has more excursion than the normal side, with a firm end point.

Pivot Shift Test

The pivot shift test must be negative for the partial tear to be treated conservatively. If the test is positive, the patient has a anterior cruciate deficient knee, and should be treated as such.

The KT-1000 Arthrometer

The KT-1000 arthrometer will normally show a side to side difference of < 5 mm. The slope of the curves that are pulled with the KT-2000 demonstrate the difference.

This graft is a force displacement curve. On the vertical axis is the force applied to the knee, 15, 20, 30 pounds; on the horizontal axis is the mm of displacement.

The curve on the left shows the normal anterior cruciate ligament. The middle curve shows that there is initially more displacement, but then has a firm restraint to anterior translation. This corresponds to the firm end point to the Lachman test. The third curve on the right is the anterior cruciate deficient knee with complete rupture. The harder the pull, the more the displacement.


It is difficult to estimate the degree of tearing with the MRI, and it is not very useful to diagnosis partial tears of the anterior cruciate ligament. This MRI shows a small band where the anterior cruciate ligament should be. It is difficult to estimate how much of the ligament is still present.

Arthroscopic Assessment

The arthroscopic assessment of the anterior cruciate ligament tear is difficult for 2 reasons. First, it is hard to see the ligament without removing the synovium and fat pad. Second, it is only an estimate of the degree of tearing of the ligament. The interstitial component of the tear is impossible to calculate. It seems to be best to try and estimate whether the tear is less than, or greater than 50%. A hook probe must be used to examine the ligament proximally to see where the ligament is attached to the side wall, to the roof or to the posterior cruciate ligament. The best position is to be attached to the side wall in the normal site of the anterior cruciate ligament. The most common situation is to see the ligament attached to the posterior cruciate ligament.

The upper photo shows the use of the hook to examine the ligament proximally. This example is lax, but is less than a 50% tear. This amount of ligament should allow a return to sports, especially if there is a negative pivot shift test. The lower photo is the appearance of the ligament after the synovium has been removed. It has attenuated down to a small band attached to the side wall. This may give a 1+ Lachman test, and a negative pivot shift test, but would not stand up to vigorous pivoting activities.

Treatment Options

The treatment options are:

  • Give up or modify sports activities

    The patient who can modify his sports activities and avoid pivotal sports will do well with a partial anterior cruciate ligament injury. This is the only parameter that the individual has control over, and that point should be emphasized when counseling athletes.

  • Brace and arthroscopy

    The use of a brace with activity modification can be successful. Sometimes the patient will still have giving way sensation, but this may be due to a meniscal injury. The best outcome for the young patient is to have a meniscus repair.

  • ACL Reconstruction

    If there is a positive pivot shift test, and the athlete wants to be active in pivotal sports, they should consider anterior cruciate ligament reconstruction.

Indications for Surgery

  • Competitive pivotal athlete in soccer, rugby
  • Clinical Instability
  • History of giving out
  • Positive Lachman and pivot shift test
  • KT-1000 > 5 mm side to side difference

Outcome Determinants

  • Activity Level
  • Stability of Knee
  • Meniscal Damage
  • Chondral Damage


1.Noyes FR, Mooar LA, Moormand CT, McGinnniss. Partial tears of the anterior cruciate ligament. J Bone Joint Surg 1989; 71B:825-833 2.Fruensgaard S, Johanne\sen HV. Incomplete ruptures of the ACL. J Bone Joint Surg 1989; 71B:526-530 3.Buckley SL, Barrack RL, Alexander AH. The natural history of conservatively treated partial ACL tears. Am J Sports Med 1989; 17;221-225