A trial to compare two different surgical techniques used to prevent the unstable knee cap from further episodes of dislocation in patients at significant risk or recurrence.

All patients will be undergoing a surgical reconstruction of the medial patellofemoral ligament, performed by an orthopaedic surgeon. The operation takes 60-90 minutes to perform. The first part of the operation is an arthroscopy and then the reconstruction is performed if appropriate. Patients are randomised using a computer program, at this stage. Arm 1 of the study, will undergo a reconstruction of the medial patellofemoral ligament using one of their own hamstrings. Arm 2 will have a similar procedure performed, except a ligament made of polyethylene terephthalate is used instead of the autograft. The two procedures differ only in the nature of the graft use. The operation is performed with the patient under a general anaesthetic. All patient have a standard arthroscopy performed, via two portals in the knee (one anteromedial and one anterolateral). A complete arthroscopic assessment of the knee is performed and any cartilage lesions noted and / or treated. Following this a small incision is made along the medial border of the patella and a second on over the medial epicondyle (ME) of the distal femur. The graft (LARS or hamstring) is attached to the medial border of the patella using 2 x bioabsorable suture anchors and then passed along the course of the native MPFL, immediately superficial and apposed to it, to its attachment at the medial epicondyle, where it is attached to the ME using a third anchor. The anchors used are bioabsorbable. For patients in Arm 1, the hamstring graft is harvested via a small incision placed over the attachment of the gracilis tendon to the proximal medial tibial, and a tendon harvested used to separated the tendon from its muscle, resulting in a tendon graft approximately 20cm long and 3mm in diameter. For patients in Arm 2, the artificial ligament is used instead of the hamstring graft. The results of the randomisation and the operation performed by the operation performed, are recorded and any discrepancy will be noted during the follow-up. All patients are placed in a range of motion brace for 2 months post surgery, in which they are allowed to bear full weight. They both follow the same physiotherapy-supervised rehabilitation program which commences around 2 weeks post surgery. The latter requires 1 x 1 hour physiotherapy weekly for a total of 8 weeks. These are 1 on 1 physiotherapy sessions. The physiotherapist instructs the patient in quadriceps recruitment and control exercise, as well as co-contractions in the range 0-45dg for 3 weeks, and then 0-90dg for the following 3 weeks. They come out of the brace at 2 months post surgery, and progress their strength and balance. Running in straight lines is possible around 3 months post surgery and return to full sport can vary from 4-6 months post surgery.