Recent Evolution of Cruciate Ligament Surgery of the Knee

There have been many recent improvements in cruciate ligament surgery of the knee. The anterior cruciate ligament (ACL) reconstruction has been changed from isometric placement1-4) to anatomical position. Anatomical ACL reconstruction is currently considered more effective in the recovery of biomechanical and kinematic function of the knee joint, reduction of rotatory instability, and prevention of secondary degenerative arthritis. In the past 20 to 30 years, a relatively vertical femoral tunnel was placed at the 11 o'clock position and a relatively posterior tibial tunnel was created at the center of the insertion site of the posterolateral bundle (PLB) to avoid graft impingement by the femoral anterior intercondylar roof during ACL reconstruction. This was performed from the tunnel in the tibial PLB to that in the femoral anteromedial bundle (AMB), creating a mismatch.

Some recent studies have shown that single-bundle reconstruction using an anatomical center between the AMB and the PLB is comparable to double-bundle reconstruction in terms of biomechanical benefits.5, 6) There is still controversy over comparative advantages between anatomical double-bundle reconstruction and single-bundle reconstruction. Some studies suggest that double-bundle reconstruction is more effective in restoring biomechanical function of the knee than single-bundle reconstruction whereas others document there are no clinical differences between the procedures.7)

However, double-bundle reconstruction is technically more difficult to perform in patients with small stature and requires longer operative time. In these patients, the tunnel is often placed at the center of the tibial and femoral footprints of the ACL (anatomical reconstruction), but transtibial femoral tunnel drilling becomes almost impossible with this technique. Thus, a far anteromedial portal (accessory anteromedial) that is approximately 2 cm medial to the anteromedial portal and just above the meniscus is created as a working portal for femoral tunnel drilling.8) One of the challenges during this procedure is to obtain adequate visualization for tunnel drilling with the knee in 120° flexion. For enhanced visualization, an endo-reamer placed in a transparent plastic tube can be used for femoral tunnel drilling, which also facilitates joint irrigation and bone debris removal. Making an outflow in the high anteromedial area prior to knee flexion can also be helpful for obtaining proper visualization during surgery.9, 10) Alternative options include creating a femoral tunnel through an incision in the posterolateral aspect of the femur or the outside-in femoral tunnel drilling using a reverse reamer or a fl ip cutter (Arthrex Inc., Naples, FL, USA), which does not necessitate 120° flexion of the knee during surgery.

On the other hand, some recent reports showed that an ACL injury can heal spontaneously even when the ACL fibers are torn if the synovial sheath that surrounds the damaged ACL is preserved relatively intact and anterior displacement of the knee is avoided for a certain period of time.11, 12)

In addition, remnant-preserving techniques in ACL reconstruction would result in the recovery of proprioception13-15) and remnant tensioning techniques, albeit more technically challenging and time-consuming, could provide good results.16, 17) I observed that the ACL remained attached to the femur and tibia in 27.4% (90 in 324) of the patients in my clinic and thought that remnant-preserving techniques could be effective even when the damaged ACL is attached to the posterior cruciate ligament (PCL) through separation and pull-out suture.

PCL reconstruction received less coverage in the literature in the past and was thought nearly a decade behind ACL reconstruction. However, there have been some recent studies that are indicative of a growing interest in PCL reconstruction and improvement in treatment outcomes. Before 1995, attempts to perform isometric PCL reconstruction often resulted in postoperative posterior laxity.

Burn et al.18) reported that posterior laxity could be reduced when reconstruction was performed distal to the isometric point.19) Afterwards, distal femoral tunnel placement has been performed frequently, which contributed to improvement in treatment outcomes. I observed that chronic PCL injuries could be successfully treated when PCL reconstruction was performed using tensioning of the remnant PCL and accompanied by AMB reonstruction.20, 21)

In an acute or subacute stage, the PCL has a higher likelihood of spontaneous healing than ACL does because some portion of the PCL or at least the meniscofemoral ligament is preserved in most PCL injuries. In particular, isolated partial PCL injuries can be treated with conservative treatment using cylinder cast immobilization and a brace with tibial supporter including elastic spring to prevent posterior translation of the tibia.22)

Many MRI studies have shown that the PCL can heal itself because the ligament is surrounded by thick synovial sheath that is hardly torn completely and the meniscofemoral ligament remains attached to the lateral meniscus. In some studies, healing of the 72-86% torn PCL ligaments were confirmed on MRI taken 6 months after injury.23-26) Therefore, in order to obtain good PCL reconstruction results, care should be taken to promote self-healing capacity of the PCL by causing minimal damage to the remnant PCL during reconstruction and performing anterolateral bundle reconstruction. If a femoral tunnel is located less than 1-2 mm apart from the articular surface by placing guide pin 5-6 mm proximal to the articular cartilage at the 11-11:30 or 12:30-1 o'clock position and if a tibial tunnel is created by placing a guide pin at the center of or lateral to the distal tibial insertion of the PCL to minimize damage to the remnant PCL, the ligament graft can pass along the medial border of the remnant PCL towards the femoral tunnel that is located anteromedial to the PCL. With this technique, I observed that single-bundle PCL reconstruction or augmentation could result in satisfying outcomes.27, 28) In addition, the remnant PCL can work as a soft tissue cushion between the ligament graft and the bone at the entrance to the tunnel preventing killer turn effect.

Regarding tunnel drilling, tunnels should be placed slightly eccentrically because the graft is fixed under tension in both ACL and PCL reconstruction. In addition, combined injuries to the posterolateral structures should be taken into consideration. Posterolateral rotatory instability (PLRI) can be observed in 12.5% of the ACL injuries20) and in 65-83% of the PCL injuries.21) Considering that concomitant PLRI is an important determinant of ACL and PCL reconstruction, PLRI should be assessed prior to reconstruction.29, 30)

In the absence of remnant PCL on arthroscopy or MRI, double-bundle reconstruction is recommended. However, double bundle reconstruction has rarely been described as more advantageous than single bundle reconstruction in the literature. In addition, PLRI assessment should be performed on several occasions and become a routine procedure during surgery with the patient under anesthesia. In cases where PLRI is combined with a PCL injury, reduction of the knee should be performed prior to assessment because PLRI may not be noticed due to the posterior sagging of the proximal tibia.31, 32)