Tunnel placement in Anatomical ACL reconstruction

Tunnel placement in Anatomical ACL reconstruction: (using 4 strand Hamsting tendons)

By Dr. Ravi Kirubanandan,

Consultant Orthopaedic Surgeon

For Appointments and queries contact  09629240084/ nexusortho@yahoo.com

The position of femoral tunnel placement have changed many times in the past decade. Accurate placement of the tunnels appears difficult to achieve. Studies have shown that in more than 50% of patients the tunnels have been poorly placed. The aim of this article is suggest, a reproducible tunnel placement using standard intra-operative landmarks for the use of 4-strand ACL reconstructions. The radiological understanding of the tunnel positions as explained.

Native ACL location:

Centre of the origin as seen on lateral radiographs was located on the femur at a mean of 66% from the anterior edge of Blumensaat’s line (inter- condylar root line). The tibial attachment was located at the junction of the anterior and middle thirds of the tibial plateau.

Knee Arthroscopy - Intra-articular landmarks:

Femoral tunnel:

Identification of the ridge between the AM & PL bundle is the key. The recommended entry point is just posterior to the ridge. But this is difficult to reproduce between surgeons and every other surgery. The new method is using a ruler to measure the AP length of the femoral condyle (visulalisation is done via a 3^rdportal). The mean mid point between the bony margin excluding the articular surface is identified and entry point made with an awl. The height of the entry point from the inferior articular surface is 2mm + ½ of the graft width.

 Tibial tunnel:

The lateral tibial spine and anterior horn of lateral meniscus identifier. 5 mm medial to this juncture of Lateral tibial spine and ant. Horn of lateral meniscus is the marker for the tip aimer jig. The other method is to identify the remenant of ACL stump as a landmark.

Anterior placement of tibial tunnel = Impingement in extension + Cyclops lesion formation

Radiological understanding of Tunnels:

Femoral tunnel:

Lateral view: The position of the femoral tunnel was assessed on the lateral radiographs (Fig. 1). The length of Blumensaat’s line was measured and the points of intersection between it and the anterior and posterior borders of the femoral tunnel were identified. Based on these measurements, the position of the centre of the femoral tunnel was calculated and then expressed as a percentage of the total length of Blumensaat’s line.

AP view: Angle of inclination of the femoral tunnel can be measured in the AP view. Vertical placement of the tunnel leads to increased rotational instability and degenerative radiological changes. This issue was primarily related to the trans-tibial placement of femoral technique.

By placing the tunnel using the anatomical method based on intra-articular landmarks, clearly avoids the placement vertically.

Vertical Femoral tunnel placement = rotational instability and early OA changes

Tibial Tunnel:

Lateral view: Placement of the tibial tunnel was assessed on the lateral radiographs (Fig. 1) as follows: the length of the tibial plateau was determined and the positions of the anterior and posterior borders of the tibial tunnel were identified relative to the anterior edge of the plateau. This allowed the position of the centre of the tunnel to be calculated and then expressed as a proportion of the total length of the tibial plateau.

AP view: Placement of the tibial tunnel was assessed on AP radiographs (Fig. 2) by measuring the total width of the tibial plateau. The distances from the medial edge of the medial tibial plateau to both the medial and lateral borders of the tibial tunnel were measured.

Posterior Tibial tunnel placement = early graft rupture

So what is the ideal radiological positioning of the tunnels ?

Femoral Tunnel : Taking 0% as the anterior and 100% as the posterior extent, the femoral tunnel with a mean of 86%  along Blumensaat’s line

Tibial tunnel : with 48% along the tibial plateau.

Recommended radiological position of the tunnels in a) the coronal and b) the sagittal views after reconstruction of the anterior cruciate ligament.

Ref:

1. Pinczewski L, Tashiro S et al; Radiological landmarks for placement of the tunnels in single-bundle reconstruction of the anterior cruciate ligament.  J Bone Joint Surg [Br] 2008;90-B:172-9.

2. Pictures – drawn by Author, Dr. Ravi Kirubanandan.