Prof. N. Reha Tandoğan, M.D. - Asım Kayaalp, M.D.
Anterior Cruciate Ligament (ACL) injuries are one of the most common knee injuries in athletes. Surgical treatment is required in most athletes to achieve pre-injury sports performance. Here we review a recently described technique, “All inside ACL reconstruction”.

Why do we need new techniques in ACL reconstruction?

Figure 1: Preparation of a single hamstring tendon graft.
Figure 1: Preparation of a single hamstring tendon graft.
The foundations of modern ACL reconstruction techniques have been laid in the 1990’ies. Advances in instruments, surgical techniques and improved understanding of the anatomy & motion of the knee have led to improvements in the way ACL surgery is performed. Current techniques have a success rate of over 90%, however, 5-10% of the patients do not achieve satisfactory outcomes. Although most patients can perform sports activities after ACL reconstruction, return to pre-injury sports level is between 40-60%. New methods have been developed in recent years to increase the success rate of surgery, to ensure a rapid and pain free recovery and cause minimal damage to normal structures. Advances in implant design, tunnel placement used to reconstruct the ACL, rehabilitation techniques and return to sports criteria have occurred in recent years. One of these advances is the technique of “All-inside ACL reconstruction”. Only a single hamstring tendon is harvested in this technique, thus preserving the knee flexor muscle strength. This is in contrast to classical techniques in which 2 hamstring grafts are harvested, which may lead to weakness in the explosive muscle strength necessary for sprinting and jumping. ACL reconstruction involves using a tendon graft placed in anatomical tunnels fixed under appropriate tension. All-inside techniques utilize special drills to decrease the amount of bone removed during surgery. This leads to decreased pain and less bleeding after surgery.

Why is a single hamstring tendon harvest important?

Very high forces are needed to injure the strong anterior cruciate ligament, and the resulting tear is usually not a clean cut but an extensive damage to the fibers of the ligament in a spaghetti like fashion. Therefore, repair of the ACL is not feasible in most of the cases (except for boney avulsions) and the ligament needs to be reconstructed using a strong tissue made of collagen fibers. This tissue is called a “graft” and several tendons of the muscles around the knee can be used as graft material. These tendon grafts are cleaned of muscle tissue, folded into 3 or 4 and placed in bone tunnels mimicking the insertion sites of the original ACL. The grafts are fixed on both ends using implants under appropriate tension. Three commonly used grafts are the tendons of the hamstring, patellar tendon or the quadriceps muscles. The most widely used are the tendons of the hamstring muscles that bend the knee and course from the hip to the knee on the back of the leg. Two of the four hamstring tendons are harvested in classical techniques. These tendons are folded in two resulting in a long 4 strand graft. Grafts with a diameter less than 8mm’s have been associated with inferior outcomes. Double hamstring tendon grafts folded in 2 are usually larger than 8 mm. However, harvest of two hamstring tendons may result in muscle weakness in athletes that require explosive muscle force such as sprinters and jumpers. This can be overcome by harvesting a single hamstring tendon, which is folded into 4 strands, resulting a 7.5 cm long graft with a 9-10 mm diameter graft (Figure 1). Modern small profile implants can be used to safely fix these grafts at the bone tunnels in both ends (Figure 2). Using a single tendon graft minimizes the loss of hamstring muscle strength that is very important for high level athletes.

Figure 2: Modern low profile adjustable button implants are used to fix the graft at both ends.
Figure 2: Modern low profile adjustable button implants are used to fix the graft at both ends.

What are the advantages of all inside ACL reconstruction techniques?

Short sockets instead of full length tunnels are created into the bones during all-inside ACL reconstruction. This can be done by using specialized small diameter drills that can be expanded to a 9-10 mm diameter in the joint during surgery (Video 1). 25-30 mm sockets can be created without penetrating the outer wall (cortex) of the bone. This results in less bleeding and pain after surgery. Less bleeding means a lower risk of infection. The graft is fixed into these tunnels under appropriate tension using low profile button devices. The staples and screw-washer implants used in classical techniques may cause pain and skin irritation in some patients and may need to be removed. The low profile implants used in all-inside ACL reconstructions obviate the need for implant removal. Smaller skin cuts can be used for all-inside techniques, this also improves the cosmesis.

Video 1: All-inside ACL reconstruction.

Is all inside ACL reconstruction more difficult for the patient/surgeon?

All inside ACL reconstruction techniques result in less pain and rapid recovery after surgery compared to the classical technique. There is no increase in the operation time. However, the surgical technique is more complex than the classical one, and surgeon experience is an important factor for a successful outcome. Specialized instruments and equipment are also needed for this type of surgery.

How are the outcomes of all inside ACL reconstructions?

The mid term outcomes of all inside ACL reconstructions are comparable to other modern ACL reconstruction techniques (1,3). However, the early postoperative period is more comfortable in patients with all inside ACL reconstructions. The harvest of a single hamstring graft results in superior knee flexor muscle strength, which is important for sports requiring explosive muscle force during sprints. The avoidance of a large diameter screw in the tibial tunnel results in less bone loss and tunnel widening; this is an advantage should a subsequent surgery be required (2).


  1. Connaughton AJ, Geeslin AG, Uggen CW. All-inside ACL reconstruction: How does it compare to standard ACL reconstruction techniques? J Orthop. 2017 Mar 19;14(2):241-246.
  2. Monaco E, Fabbri M, Redler A, Gaj E, De Carli A, Argento G, Saithna A, Ferretti A. Anterior cruciate ligament reconstruction is associated with greater tibial tunnel widening when using a bioabsorbable screw compared to an all-inside technique with suspensory fixation. Knee Surg Sports Traumatol Arthrosc. 2018 Nov7. doi: 10.1007/s00167-018-5275-x.
  3. Blackman AJ, Stuart MJ. All-inside anterior cruciate ligament reconstruction. J Knee Surg. 2014 Oct;27(5):347-52.

© Prof. Dr. Reha Tandoğan - Op. Dr. Asım Kayaalp