Loss of Motion

Motion loss is one of the most common and potentially debilitating complications following ACL reconstruction.¹⁹ Specifically, extension loss is encountered more frequently and is less tolerated than flexion loss.²⁸ The cause of motion loss may be attributed to a number of causes, such as time from injury to ACL reconstruction, tunnel position on the tibia and femur, excessive graft tension, extensor mechanism and patellar tendon scarring, arthrofibrosis, multiple ligament injury, and prolonged immobilization.²³

The cause of motion loss must be addressed prior to proceeding with revision ACL reconstruction. Although prevention is the best strategy, early recognition of developing stiffness allows for the appropriate conservative or surgical intervention to provide the best outcome. Importance is placed on maximizing knee range of motion, decreasing inflammation, and improving muscle strength prior to revision ACL reconstruction.

Assessment of tunnel placement, graft impingement, and fibrosis location can be ascertained by physical examination, diagnostic imaging, and surgical visualization. A systematic evaluation of the knee, as described by Millet and colleagues,³⁰ allows for careful débridement of fibrotic structures through arthroscopic or open procedures. When motion loss is significant, a staged revision procedure may be indicated.

Persistent Pain

Persistent pain after ACL reconstruction is often multifactorial. Articular cartilage loss, meniscal pathology, prominent hardware, neuromas, graft site morbidity, prolonged inflammatory response, painful scars, and infection have all been implicated as confounding variables. Often, the exact source of pain is difficult to ascertain. However, selection of an optimal treatment plan relies on accurately determining the cause.

Recurrent Instability

Instability after ACL reconstruction can be divided into three categories: traumatic failure, atraumatic failure, and failure caused by graft malposition or fixation loss. Analysis of these categories relies on careful history, physical examination, imaging, and review of prior operative reports.

Patients with traumatic failure report a single traumatic event in a previously well-functioning stable knee. The mechanism is often the same as that occurring in a native rupture of the ACL. Instability that occurs in the early postoperative course may be the result of trauma to the ACL before full graft incorporation.²³ Other studies have shown that returning to athletics prior to full return of neuromuscular coordination and strength may increase the risk of recurrent injury.^15,17 In most of these cases, it can be assumed that the primary reconstruction was appropriately performed, and thus the same tunnels may be reused for the revision. It is crucial, however, to consider the primary reconstruction graft type and ensure appropriate graft selection for the revision procedure. Controversy exists regarding the ideal graft type for revision surgery.³²

Atraumatic failure of ACL reconstructions can occur for a number of reasons. Although the primary reconstruction may have been technically acceptable, the progressive return of instability in the absence of trauma may still occur. Causes for this failure include failure of graft biologic integration, improper graft tension, failure of bone healing, or missed associated instabilities, such as persistent medial laxity or posterolateral corner deficiency.* Determining the type of graft tissue used in the primary operation is important to avoid similar problems in the revision setting. For example, Singhal and associates³⁸ have reported unacceptably high reoperation rates with the use of allograft tibialis anterior tissue in patients younger than 25 years. Studies have also shown high levels of gamma irradiation (4 Mrad) in some allograft tissue may weaken the graft structural properties leaving it prone to failure.³⁵ Tunnel widening may also be present as a result of mechanical and biologic factors related to graft motion within the tunnel and release of inflammatory cytokines.⁴⁴ A thorough physical examination to assess for other instability patterns that can predispose an ACL reconstruction to early failure should be performed. Secondary causes of instability should be addressed at the time of revision to provide the best chance for an optimal outcome.

With no evidence of concomitant pathology, the location of the tibial and femoral tunnels should be assessed with preoperative imaging. In many cases, the tunnel position is optimal and the same tunnels may be used for the revision procedure. If tunnel widening is present, a decision should be made as to whether the widening can be addressed at the time of revision with techniques that will be outlined later in the chapter or whether a two-stage procedure is required.

The third cause of recurrent instability is a malpositioned graft or loss of graft fixation (Table 49-1). Errors in surgical technique related to placement of tunnels and graft fixation are the most common cause of failure in ACL reconstruction.^15,17 Graft malposition can occur on both the tibial and femoral sides, although anterior femoral tunnel placement is the most common error. Anterior femoral tunnel placement leads to flexion deficits and early graft failure as a result of excessive tension and impingement in extension. This failure can occur when using an endoscopic technique secondary to difficulty visualizing the over the top position. Revision surgery may require placement of a new tunnel posterior to the original anterior tunnel. If preexisting hardware is not impeding proper tunnel placement, the prior hardware should be left in place to avoid creating a larger defect. When a posterior femoral tunnel position with femoral cortical compromise is identified as the primary problem, revision using a two-incision, outside-in technique to create divergent tunnels is recommended. If this technique is not possible, a two-stage revision should be considered. Central femoral tunnel positioning may produce a vertical graft that provides anteroposterior stability without rotational control.^9,27 This problem can manifest on physical examination with a negative Lachman examination and a persistent pivot shift. If adequate bone stock remains, a proper femoral tunnel can be created with an endoscopic or two-incision technique. Recent discussion regarding anatomic ACL reconstruction has identified femoral tunnel placement lower on the intracondylar notch as a potential solution to this issue.^7,10 The use of an accessory anteromedial portal has also been described as a means of drilling a more anatomic femoral tunnel site.¹⁸ Independent drilling of femoral and tibial tunnels has recently been shown to outperform conventional transtibial drilling in a cadaver model.³⁹ However, Rue and coworkers³⁴ have demonstrated that it is technically possible to create an obliquely oriented single-bundle femoral tunnel down the femoral wall through a tibial tunnel angled approximately 60 degrees from the proximal tibial joint surface. This correlates with a femoral tunnel approximately midway between the anteromedial and posterolateral bundle origins of the ACL.

Table 49-1 Common Technical Errors and Results

Errors in tibial tunnel placement can also lead to graft failure. A tibial tunnel placed too anteriorly will result in graft impingement on the intracondylar notch in extension and early graft failure.^20,21 A posterior position will result in a vertical graft and loss of rotational control.⁸ Posterior tibial tunnel placement can also lead to excessive laxity in flexion and impingement on the posterior cruciate ligament. Specifically, when using an endoscopic technique, it is important to consider the affect of coronal plane obliquity of the tibial tunnel on femoral tunnel position. In cases of tibial tunnel malposition, an attempt can be made to drill a properly oriented tibial tunnel if adequate bone stock is present.⁴¹ Kopf and colleagues²⁴ have reported in a meta-analysis that there is wide variability in the location of the footprint of the ACL and stressed the importance of using anatomic landmarks when creating tunnels.

Loss of graft fixation may occur secondary to poor bone quality, screw breakage, screw divergence, or graft damage during screw insertion. Poor bone quality may require other revision techniques, including compaction drilling or bone grafting. Additional fixation may be warranted such as the use of a suspensory device such as the EndoButton (Smith & Nephew, Andover, Mass) on the femoral side. A lateral screw post or ligament button may be placed through a separate incision. This technique may also be used on the tibia. Nevertheless, aperture fixation should be used whenever possible because interference screws have been shown to be stronger than staples, suture fixation around a post, or a soft tissue washer with screw fixation.^15,40 However, interference screws can be complicated by poor fixation in osteopenic bone, disruption of the bone plug, and transection of the graft. If graft damage occurs during femoral screw placement, the graft can be reversed so that the tibial bone block is placed on the femoral side and soft tissue fixation techniques are used on the tibial side.