We present a case series of patients undergoing Arthroscopic Popliteus sling reconstruction with or without associated cruciate ligament reconstruction at our institution between January 2016 and December 2018. The aim of our study was to evaluate the efficacy of arthroscopic Popliteus sling reconstruction in restoring posterolateral corner stability. The study was approved by our institutional review board, and informed patient consent for study inclusion was obtained.
The inclusion criteria were patients with popliteus tendon injury with posterolateral rotary instability as identified by a positive hughston test without FCL injury [varus instability]. Associated cruciate ligament injuries or meniscal injuries were not grounds for exclusion.
Patients who had FCL injury and varus instability were excluded as they were treated with an open FCL repair [in acute setting] or an open FCL reconstruction [Modified Larson] technique. Cases with fractures of the proximal tibia or distal femur, open injury, or associated neurovascular injury were excluded from the study.
Clinically, each patient was assessed preoperatively and under anesthesia using the Lachman and anterior and posterior drawer tests to evaluate for cruciate injury, as well as varus and valgus stress tests both in extension and at 30 0of flexion to assess the competence of the collateral ligaments. The dial, external rotation recurvatum and hughstons tests were also performed to evaluate posterolateral corner injuries.
Stress Radiographs were used to evaluate the posterior sag in cases with PCL injuries. MRI scan was done for all patients to supplement the clinical tests in arriving at an accurate diagnosis.
Patients were followed up at 6 weeks, 3, 6, 12 and 18 months post operatively. The parameters assessed during follow up were the IKDC and Tegner score, the ROM, posterior sag and Hughston test for posterolateral laxity.
Surgical Technique
In the operating room, the injured knee was examined with the patient under anesthesia and laxity elicited was documented. The patient is kept in supine position under spinal anesthesia with the limb secured in a leg holder ensuring that the knee is able to hang up to at least 90 degrees of flexion. The procedure is performed under tourniquet control after exsanguination of the limb. A standard 30 degrees arthroscope is used. Initially a diagnostic arthroscopy is performed to identify associated cruciate/ meniscal injuries using the standard anteromedial and anterolateral portals.
Popliteus Portal
Under direct vision ‘the popliteus portal’ is made using the outside in technique centered over the popliteus femoral footprint at 70 degree of knee flexion. (Fig 1) This portal passes through the skin, subcutaneous tissue, iliotibial tract, capsule, and the synovium. It does not injure any significant neurovascular structure. The portal should be directed in a way which will permit the reaming of femoral tunnel for the graft in the popliteus groove in the lateral condyle of femur, directed in a proximal and anterior direction.
Graft harvesting and preparation
Autologous gracilis tendon from the ipsilateral knee was used for reconstruction of the popliteus sling. In cases with multiligament injury, where graft could not be acquired from the ipsilateral knee, contralateral knee gracilis was harvested for the graft. A minimum of 180 – 200 mm of graft was required for the Popliteus sling reconstruction. After clearing the muscle fibers, the ends of the graft were whipstitched with no.2 fibrewire/ Ethibond for a length of 30mm on either ends.
Tibial tunnel
This bone tunnel is made anteroposteriorly, starting in the distal portion of flat triangular area in between the Gerdy tubercle and the lateral border of patellar tendon insertion. The point of exit for the tunnel is just below the ridge on the posterior aspect of the lateral tibial plateau where it dips into a sulcus, usually at the level of the popliteus musculotendinous junction. The point of exit should also be medial in relation to the lateral wall of the lateral femoral condyle. The tunnel is therefore drilled in a posterolateral direction to avoid it from being directly in line with the neurovascular structures behind.(Fig 2)
An anterior cruciate ligament elbow aimer (Acufex) is used for making this tunnel. (Fig 3)The tip of the aimer is passed through the popliteus portal across the popliteal hiatus (viewing portal being the anterolateral portal)and then onto the posterior aspect of the tibia. The tip of the aimer is used to palpate the popliteus ridge posteriorly and then moved further distally till it dipped into the sulcus. One may need to flex the knee up to 20 – 30 degrees in this step for better visualization. A beath pin is then passed through till it is visualized exiting at the elbow of the aimer. The aimer is removed and the tip of the pin protected by a small curvedscoop passed through the popliteus portal to prevent it from advancing further while reaming. A 6 mm reamer is used. The tunnel is reamed cautiously to avoid a sudden exit from the posterior aspect. The reaming is stopped as soon as the tip of the reamer is visualized. The exit point could be cleared with a shaver passed through the bone tunnel or the popliteus portal.
A suture loop of no.1 prolene mounted on a knot pusher is used to serve as a shuttle for passing the graft. It is inserted through the tunnel advancing the knot pusher and the tip of the prolene loop till it can be visualized exiting posteriorly. A suture retriever is passed through the popliteus portal across the popliteal hiatus to withdraw the prolene suture into the lateral gutter and then further out of the popliteus portal.
Femoral Tunnel
The site for the tunnel is at the anterior end of anatomic insertion site of the popliteus. The insertion site is at the anterior end of the popliteal groove on the femoral condyle, close to where the articular cartilage ends approximately 2cmm distal and anterior to the fibular collateral ligament insertion in line with the femoral axis. A guide pin is passed initially over which a 6mm reamer is drilled.
The pin is directed proximally toward the region between the adductor tubercle and medial epicondyle and angulated anteriorly to exit through the skin in the region between the medial epicondyle and medial border of trochlea. This is to avoid tunneling into the intercondylar notch and having a more conducive angle for the graft at its entry into the tunnel.
Figures 4a and 4b show a Diagramatic representation of Location of femoral and tibial tunnel for the popliteus graft in Anteroposterior and lateral views.
Graft Passage and Fixation
The graft is fed into the Prolene shuttle and pulled across the tibial tunnel through the popliteal hiatus and out of the popliteus portal. The Ethibond is then fed into the eyelet of the beath pin in the femoral tunnel and shuttled across along with the pin out of the skin on the medial side. The graft is pulled into the tunnel with the help of the Ethibond till it reaches the end of the femoral tunnel.
Femoral fixation is done using a biointerference screw (7mm) while maintaining graft tension. Tibial fixation is also done using a bio interference screw (7mm) keeping the knee at 90 degrees flexion correcting the poserolateral sag. This reduction is maintained by keeping the foot in 15 degrees internal rotation and maintaining graft tension while fixation of the graft.
Associated cruciate ligament reconstructions and meniscus surgery were performed following standard procedures.
Postoperative Rehabilitation
The knee is kept non weight bearing for a period of 6 weeks after which partial weight bearing is permitted gradually to full weight bearing by 8 weeks. The knee is placed in a long knee brace in extension with posterior tibial support for a period of 3 weeks. Passive prone ROM is started at 3 weeks post op and the long knee brace is replaced with a ROM knee brace. Isometric quadriceps and short arc quadriceps exercises are started at 3 weeks postoperatively. Isotonic quadriceps, leg press, and gait training is started after 6 weeks. Proprioceptive training is started on regaining quadriceps strength equal to the opposite uninvolved knee. Hamstring strengthening exercises are delayed for 6 months
Follow up Evaluation
All the patients were followed up and evaluated by clinical and radiographic assessment at 6 weeks and 3,6,12,18 months post operatively. The Tegner activity score and International Knee Documentation Committee (IKDC) knee ligament examination form were used for follow-up assessment to document Knee scores. In addition VAS score for pain and a subjective assessment of ROM and stability of the knee using the Posterior sag test and Hughston’s test for posterolateral laxity were also performed and findings were documented.
Statistical Analysis
The data obtained was statistically analyzed with SPSS software (version 13.0; SPSS, Chicago, IL).