Modes of ACL Reconstruction Failure
Failure of ACL reconstruction surgery may be due to recurrent instability, arthrofibrosis, or infection. Recurrent instability after ACL reconstruction occurs in approximately 8% of patients and is the most common reason for ACL reconstruction failure. Reconstruction failure may be subclassified as technical, biologic, or traumatic, or as resulting from laxity in secondary ligamentous restraints.[3]
Technical Failure
Of all these possible causes for failure, technical error appears to be the most common, accounting for 77% to 95% of all cases of ACL failure.[3,4] By far the most commonly cited technical error in ACL reconstruction has been nonanatomic tunnel placement, accounting for 70% to 80% of technical failures, with an improperly placed femoral tunnel being the root cause in most cases.[2,3] The femoral tunnel is often placed in a position that is too anterior, resulting in graft constraint in flexion and laxity in extension (Fig 1).[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21] The key to avoiding anterior femoral tunnel placement is adequate visualization of the over-the-top position before tunnel placement. The femoral tunnel may also be placed too posteriorly, resulting in loss of fixation due to posterior wall blowout and constraint in extension due to nonisometric tunnel position, but this is less common.[3,5,6] In addition, placement of the femoral tunnel in a position that is too central (at the 12 o'clock position) results in a nonanatomic graft that may not restore the rotational component of stability provided by the ACL, leading to a persistently positive pivot shift, despite objective anterior/posterior stability.[2,3,6,9] Tibial tunnel placement is a less common cause for ACL failure, but improper positioning may still lead to persistent instability. A tibial tunnel placed too anteriorly may lead to impingement and graft rupture or constraint in flexion, and a posteriorly placed tunnel may lead to laxity in flexion.[2,3,5,6] Other types of technical error include improper graft tensioning, insufficient graft material, and inadequate graft fixation.[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21] A graft that is undertensioned will result in excess laxity and persistent instability, and an overtensioned graft can result in a constrained knee with delayed graft incorporation. The exact amount of tension required remains poorly defined, and determining the appropriate tension intraoperatively remains a clinical challenge. The use of synthetic grafts, poorly harvested autografts, or poorly selected allografts may result in insufficient graft material, which can lead to ACL reconstruction failure.[22] Synthetic grafts are no longer used in the United States, but appropriate attention to meticulous harvesting technique can avoid autograft problems, and allograft donors should be screened for donor age and sterilized by nondamaging techniques to ensure adequate graft material. Finally, inadequate graft fixation may lead to persistent instability, and the operating surgeon must have a variety of primary and secondary fixation options available to deal with technical challenges. In the case of poor bone stock appreciated intraoperatively, interference screws may provide inadequate fixation, and the use of post-washer or button fixation may be appropriate. Interference screw divergence may decrease pullout strength and should be avoided by appropriate matching of the screw placement angle with that of the femoral and tibial tunnels.[23] Finally, if Endobutton (Acufex, Mansfield, Mass) fixation is utilized, appropriate deployment technique with confirmatory radiographs can avoid soft tissue placement, which has been reported as a cause of failure using this type of fixation.[24]
Figure 1.
(Left) Arthroscopy photo of notch anatomy at time of ACL revision surgery. Thick arrowhead shows site of previous interference screw placement in excessively anterior position; short, thin arrowhead shows site of previous graft placement in anterior position; long, thin arrowhead shows "resident's ridge" anterior to actual over-the-top position, indicated by probe. (Right) Arrow and probe indicate over-the-top position, which is significantly posterior to previously placed hardware and graft.
Figure 1.
(Left) Arthroscopy photo of notch anatomy at time of ACL revision surgery. Thick arrowhead shows site of previous interference screw placement in excessively anterior position; short, thin arrowhead shows site of previous graft placement in anterior position; long, thin arrowhead shows "resident's ridge" anterior to actual over-the-top position, indicated by probe. (Right) Arrow and probe indicate over-the-top position, which is significantly posterior to previously placed hardware and graft.
Biologic Failure
Biologic failure is the lack of complete incorporation and ligamentization of the graft material during the healing phase of ACL reconstruction and is generally the result of infection or allograft rejection response. Biologic failure should be considered when instability occurs without antecedent trauma or an identifiable technical error.[2,3] Infection has been shown to occur in approximately 0.3% of ACL reconstructions and is generally treated with operative irrigation and debridement, intravenous antibiotics, and occasionally with graft removal and delayed revision reconstruction.[25] With regard to allograft use, ligamentization has been shown to be delayed and less uniform, and bone-tunnel osteolysis may occur. Freeze-dried allografts cause some level of immune reaction in 60% of cases; fresh allografts may also incite a rejection response, and processing with gamma irradiation, freeze drying, or ethylene oxide sterilization biomechanically weakens the grafts and delays incorporation.[2,3,26]
Traumatic Failure
Traumatic failure may occur in the early postoperative period, or later, after return to full activity. Early failure occurs before complete graft incorporation and may be due to overly aggressive rehabilitation or noncompliance with postoperative activity restrictions. Late failure results from a traumatic episode after complete healing has occurred and has been noted to occur in 5% to 43% of ACL reconstruction failures.[2] In either early or late traumatic failure, technical error must always be considered as a possible underlying factor.
Failure Due to Associated Laxity
Associated ligamentous instability must be addressed at the time of ACL reconstruction to avoid graft failure.[10,11,21] A high index of suspicion should be maintained in the revision scenario for subtle posterolateral instability, and a detailed examination under anesthesia should be performed in this setting to assist in diagnosis. Isolated ACL reconstruction in this scenario results in increased graft stresses and gradual recurrence of instability after an initially stable reconstruction. Acute lateral collateral and posterolateral ligamentous injuries should have primary repair with or without augmentation; high-grade medial collateral ligament sprains with posteromedial corner injuries should be repaired or allowed to heal before reconstruction; and complete posterior cruciate ligament (PCL) ruptures should undergo simultaneous or staged reconstruction. In the patient with varus knee alignment, consideration should be given to initial or combined high-tibial osteotomy to correct mechanical alignment. Finally, meniscal allograft transplantation may be considered in the meniscus-deficient patient to avoid posttraumatic osteoarthritis and possibly restore some of the secondary stabilization effect provided by the native meniscus.
Arthrofibrosis
Arthrofibrosis is the remaining cause of ACL failure, which has not been addressed. In general, failure to obtain range of motion in the postoperative period equal to that which was present preoperatively may be considered arthrofibrosis. This may vary among patients but is usually assessed in comparison with the flexibility of the uninjured knee. Arthrofibrosis has been associated with ACL reconstruction in the acute scenario and with prolonged postoperative immobilization.[5,6] It may also be due to technical error, with an overconstrained knee resulting from improperly positioned tunnels or a graft placed in excess tension.[3,5,6] Regardless of the cause, full range of motion must be obtained before proceeding with revision ACL reconstruction, and staged surgery may be necessary in this scenario.
J South Orthop Assoc. 2002;11(1) © 2002 Southern Medical Association
Cite this: Revision Anterior Cruciate Ligament Reconstruction Surgery - Medscape - Mar 01, 2002.
