LARS Ligaments compared to hamstring tendon graft
To reconstruct the medial patellofemoral ligament (MPFL) the traditional approach has seen surgeons using the hamstring tendon as the graft. However, A/Prof Al Muderis differs from the conventional approach and has modified a minimally invasive surgical technique to reconstruct the MPFL. Instead of using the hamstring tendon as the graft, A/Prof Al Muderis uses LARS ligaments (Ligament Augmentation and Reconstruction System). LARS ligaments are artificial ligaments used for the intra or extra-articular reconstruction of ruptured ligaments. Used to reconstruct a torn MPFL they are designed to mimic the normal anatomic ligament fibres in the knee. The intra-articular longitudinal fibres resist fatigue and allow fibroblastic growth. The extra-articular woven fibres provide strength and resistance to stretch.
LARS ligaments can be used in conjunction with suturing to the remaining section of the ruptured ligament or as a stand-alone reconstruction.
The ligaments are precisely selected according to the weight and activity level of each patient.
Using LARS ligaments can reduce surgery time considerably because no additional harvesting of grafts is needed. Thus the patient can expect a faster return to full function compared to after MPFL reconstruction using hamstring tendon grafts. This is largely due to LARS ligaments allowing the original ligament tissues to heal in the absence of traction.
MPFL Reconstruction Surgical Procedure:
The first part of the procedure includes knee arthroscopy to remove any loose bodies and fix any other intra-articular pathologies that may be associated with the injury.
The second part of the procedure includes a minimally invasive open approach to the patella. A 3-4cm vertical skin incision is made over the outer one third of the patella. Through this incision a lateral release of the patella is performed and then under image intensifier a 5mm horizontal drill is guided over a guide wire through the centre of the patella.
A patella tendon type LARS ligament is then passed through the patella drill hole from lateral to medial using a special wire passer. The lateral end of the LARS ligament is sutured to the lateral edge of the patellar at the insertion site using a strong suture to prevent pull through the ligament. Usually the LARS ligament has a metal pin like button, which adds stability to the structure.
Using an image intensifier, a second 1-2cm incision is made over the natural attachment of the MPFL. Using long forceps, a tunnel is created in the soft tissue between the two incisions. The LARS ligament is then passed through this soft tissue tunnel.
Under the image intensifier a second 5mm drill tunnel over a guide wire is made and the LARS ligament is then passed through this second tunnel entering at the medial side and exiting at the anterolateral corner of the distal femur.
In a skeletally immature patient this tunnel has to be accurately positioned in the epiphysis to avoid injury to the growth plate.
The patient’s knee is then positioned at full flexion with the patella fully engaged within the femoral trochlea (femoral groove). The LARS ligament distal end is gently tugged to avoid over loosening or over tightening. Then over a blunt guide wire a 6mm interference screw is inserted through the inside incision. The knee is then taken through a range of motions to check tracking and patella stability. The distal end of the LARS ligament is then trimmed and final radiographs are taken. The wound is closed in layers and a bandage dressing is then applied with no need for a brace.