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What constitutes ACL graft failure and how do you measure it?

ACL graft failure is not necessarily a case of sudden rupture of the graft. The graft may fail in different ways, eg the graft may stretch or the fixation devices may migrate.

In deciding whether or not revision surgery is necessary, one needs to take a number of factors into consideration -

The patient's subjective evaluation of instability

The Cincinnati Knee Rating System, for which the reliability, validity and responsiveness have been established (ref 1), is of value in evaluating from the patient's perspective of their symptoms, functional ability, and occupational levels after cruciate ligament surgery. The overall score (on a scale of 0 to 100 points) is based on twenty factors, of which the functional element records the patient's ability with respect to:

  • walking
  • stairs
  • squatting and kneeling
  • straight running
  • jumping and landing
  • hard twists/cuts/pivots

The surgeon's objective evaluation of laxity

Three objective measurements are of particular value in assessing the integrity of a cruciate graft -

Lachman test

In the Lachman test, with the patient lying on his/her back, the surgeon grasps the femur in one hand above the joint - with the thumb above the patella and the fingers behind the femur, while the other hand grasps the tibia in a corresponding position below the patella. The surgeon pulls the tibia forward in relation to the femur, assessing the degree of laxity of the femur and tibia in relation to one another.

Pivot-shift test

The pivot-shift test is a test to assess the integrity of both the anterior cruciate ligament and and also the other key structures that contribute to the knee's stability. This test determines two factors: the amount of anterior tibial translation and internal tibial rotation. It is graded on a scale of 0 to 3, with 0 indicating no pivot and a normal functioning ACL. A grade of 3 indicates complete loss of the ACL and the secondary restraints to these knee motions.

The patient lies on his/her back with the hip flexed to 30 degrees. The surgeon may bend the patient's knee to 20 degrees and tuck the foot under the surgeon's arm to hold it stable. One hand rests lightly on the outer aspect of the knee, and the other holds the lower leg and controls the process. The knee is slowly flexed and gently inwardly rotated.

If the test is positive, one sees or feels a sudden pivot of the tibia bone on the outer side due to structural instability.

KT-2000

The KT-2000 is an instrument that measures the amount of anterior tibial translation of the knee when the tibia is pulled forward in relation to the femur. The test is done on both knees (with the patient lying on his/her back), with comparisons made between each knee. Via previous research (ref 2, 3, 4), the normal amount of difference in anterior tibial translation between a right and left knee is no more than 3 mm. A finding of 3 to 5 mm of increased anterior tibial translation indicates partial loss of ACL function, and 6 mm or greater, complete loss of ACL function.

Based on the findings of the Lachman, pivot-shift, and KT-2000 tests, the graft can be classified as -

  • functional
  • partially functional
  • nonfunctional

We classify partially functional grafts as those with a KT-2000 reading of 3-5.5 mm, a Lachman test only slightly positive with a hard stop, and a negative pivot-shift.

We classify non-functional grafts as those with 6 mm or more of anterior tibial displacement with the KT 2000, a positive Lachman test with a soft end point, and a fully positive grade 2 or 3 pivot-shift test.

Confirmatory radiographic evaluation

X-rays assess both the placement of the femoral and tibial graft tunnels, and any narrowing of the patellofemoral and tibiofemoral joints (to look for signs of joint surface deterioration or arthritis). In knees with failed ACL grafts, it is also important to determine if the patient's legs are abnormally bowed outwards (varus) or inwards (valgus), as this problem can cause reconstructions to fail. The surgeon first assesses the overall lower limb alignment with the patient standing. If it appears abnormal, then special x-rays are taken of both legs that go from the hips to the ankles. Measurements are then made of the weight bearing line, or where the forces are absorbed in the knee joint. The patient may have to undergo an operation called an osteotomy to realign the lower leg if the forces are not going through the center of the knee. Without this procedure, any graft (ACL, PCL, posterolateral) reconstruction has a high risk of failure.


References

1 Barber-Westin SD, Noyes FR, McKloskey JW. Rigorous Statistical Reliability, Validity, and Responsiveness Testing of the Cincinnati Knee Rating System in 350 Subjects with Uninjured, Injured, or Anterior Cruciate Ligament-Reconstructed Knees. Am J Sports Med. 1999;27:402-416.

2 Wroble RR, Van Ginkel LA, Grood ES, Noyes FR, Shaffer BL. Repeatability of the KT-1000 arthrometer in a normal population. Am J Sports Med. 1990;18:396-9.

3 Daniel, D. M.; Malcolm, L. L.; Losse, G.; and et al.: Instrumented measurement of anterior laxity of the knee. Journal of Bone and Joint Surgery, 67A: 720-726, 1985.

4 Daniel, D. M.; Stone, M. L.; Sachs, R.; and Malcom, L.: Instrumented measurement of anterior knee laxity in patients with acute anterior cruciate ligament disruption. American Journal of Sports Medicine, 13(6): 401-407, 1985.

Updated: 27 Apr, 2013
ABOUT THE AUTHOR

Dr Frank R Noyes

Knee Surgeon
Degrees: 
MD

Based at the Cincinnati Sportsmedicine and Orthopaedic Center in the USA, Dr Frank Noyes is one of the world's most prominent figures when it comes to knee surgery. A prolific researcher and writer, he has published over 200 studies and articles in the world's top orthopaedic journals and...

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