Drill channel positions of cruciate ligament reconstruction

The anatomical drill canal placement is probably the most significant factor for a satisfactory outcome after an anterior cruciate ligament replacement.

The primary goal of cruciate ligament surgery is to restore the stability of the knee joint with unrestricted mobility of the operated knee joint in relation to the healthy knee joint. The anatomical placement of the upper and lower leg drill tunnel is an indispensable prerequisite for this. The anatomical positioning of the ACL replacement should lead to a better long-term result with the aim of a reduced risk for the development of joint wear (arthrosis).

Anatomy & Function Anterior Cruciate Ligament

The importance of the anteromedial bundle (AM bundle) and posterolateral bundle (PL bundle) in anterior cruciate ligament reconstruction

What is the anatomical drill channel position?

One of the critical steps in anterior cruciate ligament reconstruction is the anatomical placement of the femoral drill canal - the so-called footprint of the anterior cruciate ligament on the thigh. If this is missed during the operation, this can be the main reason for a revision surgery of the plastic.

The area of origin or footprint is described on the thigh as an oval or crescent shape with a longitudinal diameter of approximately 18mm and a transverse diameter of approximately 11mm , which are divided into two bundles: the anteromedial (AM) bundle and the posterolateral (PL) bundle. Both bundles fulfil different functions: During knee flexion, the AM bundle is tense; during extension and rotation close to the knee joint, the posterolateral bundle is tense.

There are several clues and methods for the surgeon to correctly position the femoral tunnel:

The "Resident's Ridge" defines the upper limit of the femoral ACL attachment. Thelateral bifurcate ridgedivides the AM and PL bundle fibres of the ACL. However, the cross-sectional area of the PL and AM bundles is variable from patient to patient, so the location of the Lateral Bifurcate Ridge, if present, does not necessarily represent the true centre of the ACL femoral attachment site. However, the positioning of the tunnel in relation to the time is also used, e.g. for the right side the 10 o'clock position, for the left side the 2 o'clock position (in the case of the single bundle technique of ACL plastic surgery), but the most precise anatomical landmark for the arthroscopic ACL reconstruction is the native residual limb or even the ligament parts still present.

Arthroscopic orientation points on the thigh for anatomical tunnel drilling in ACL plastic surgery

• Resident's Ridge: arthroscopic landmark for anatomical tunnel drilling in ACL surgery
• Lateral bifurcat ridge: separation of AM bundle (anteromedial bundle) and PL bund le (posterolateral bundle)

Tunnel positions after anterior cruciate ligament reconstruction

Since the anterior cruciate ligament has a great influence on the knee joint kinematics, incorrect tunnel bores lead to functional restrictions, especially of mobility and stability. We have shown the possible femoral tunnel positions for better understanding:

Anatomical tunnel position

A tunnel position is described as anatomical if it lies exactly in the area of origin of the anterior cruciate ligament. This borehole position should be aimed for and implemented in every anterior cruciate ligament reconstruction operation.

Semianatomical tunnel position

Semi-anatomical tunnel positions (partially anatomical tunnel positions) are the most unfavourable. The borehole often tends to be very high, in the area of origin of the AM bundle (anteromedial bundle) and sometimes also too far forward, but touches the area of origin of the anterior cruciate ligament to varying degrees. In this case, it is often not possible to perform a replasty of the anterior cruciate ligament in one surgical session. Filling the drill canal with an autologous bone graft is often unavoidable.

Extraanatomical tunnel position

Extra-anatomical (non-anatomical) tunnel position refers to the complete malposition of the drill channel outside the area of origin of the anterior cruciate ligament. If this tunnel position is shown in the preoperative X-ray and/or CT images as well as in the arthroscopic image, it is possible to carry out the replasty in the same surgical session with new creation of the drill channels in the anatomical drill tunnel position.

Restoring the anatomy of the cruciate ligament has the highest priority in anterior cruciate ligament reconstruction!

Non-anatomical femoral tunnel after anterior cruciate ligament reconstruction - effect on mobility and stability

Femoral drill channel too far forward

According to our documentation, the most frequently cited technical error is a drill channel on the upper leg side that is placed too far forward:

This results in a relative shortening of the graft with an increase in stress on the plastic during flexion. As a result of the shortening of the graft, increased forces act on the plastic, which on the one hand cannot be influenced initially after the operation in the clinical examination as a restriction of movement in knee joint flexion in comparison to the healthy knee joint despite physiotherapeutic treatment. In the further course, there is usually a "wearing out" (elongation) of the plastic, it loses its stability and thus its function. However, the lower leg tunnel, which was drilled in the correct anatomical position, shows considerable tunnel widening:

→ Restriction of the ability to bend (movement restriction with graft failure - anterior cruciate ligament insufficiency).

Lateral X-ray after ACL plastic with bioscrew fixation

Femoral drill channel too vertical

However, a drill canal placed too far back or too vertically on the thigh side can also lead to postoperative problems. The consequences are often deficits in extension and, if the drill channel is placed too vertically, increased rotational instability (rotational instability), which can often be clinically demonstrated in a positive pivot-shift test.

→ Restriction of the ability to extend and increased rotational instability (rotational instability)

X-ray image after ACL plastic with button fixation femoral high ("high noon ")

Lower leg drill channel too far forward

However, the correct positioning of the lower leg drill channel is also crucial for the result of an ACL plastic:

If the drill channel on the lower leg side is too far forward, the graft may become trapped at the roof of the intercondylar fossa as the knee joint is extended, a so-called notch impingement. Notch impingement can cause not only an extension deficit and graft elongation but also abrasions on the graft and thus lead to weakening of the graft. The femoral drill canal also shows up outside the area of origin of the anterior cruciate ligament.

→ Limitation of extensibility and graft failure (anterior cruciate ligament insufficiency)

Lateral X-ray after ACL plastic with bioscrew fixation

 

→ Our procedure for revision surgery after anterior cruciate ligament reconstruction