Radiological Follow-up of Alternative ACL Reconstruction Technique

Rupture of the ACL has an incidence of 30 cases per 100,000 individuals in the UK. The number of reconstructions performed is increasing as more patients wish to maintain optimum knee function and stability, in older age-groups, than previously seen. The research centre (hospital) presently performs between 100 and 150 ACL reconstructions each year but, thus, this figure is likely to continue to rise.

The ACL performs a role in preventing anterior translation of the tibia on the femur, throughout the range of motion of the knee, but also provides rotational stability. Inadequate post-injury function, or failure, can result in continued feeling of instability (within the knee) and this may prevent return to employment as well as recreational activities. This is of particular importance to heavy manual workers and competitors in change-of-direction sports.

Reconstruction of the ACL most commonly involves the use of autologous hamstring or patellar tendon grafts that are implanted during an arthroscopic procedure. Rehabilitation, following reconstruction, is lengthy as the graft takes months to incorporate and over a year to regain mechanical properties. Therefore, these patients undergo a long period of functional rehabilitation, under the guidance of the physiotherapists, with repeated outpatient surgical follow-up to assess recovery and detect rare (but important) complications of surgery.

As understanding of the anatomy and biomechanics of the ACL has improved, the techniques used to perform this procedure have evolved accordingly. The goals of reconstructive surgery are to restore stability to the knee and allow the patient to return to employment and recreational activities. Research over the last 5 years has increasingly turned to defining the anatomy of this ligament and positioning the graft in an anatomical position. Bony landmarks have been identified for the position of the femoral footprint of the ACL - the intercondylar and bifurcate ridges - making positioning of the graft accurately possible. Appreciation of the importance of the remnant tissue - as an indication of previous attachment and as a conduit for revascularisation of the graft - and these bony landmarks for the tibial and femoral attachments, of the ligament, have led to changes in surgical philosophy and technique.

Of particular interest is the femoral tunnel. Successful ACL reconstruction has clearly been shown to be associated with femoral tunnel positioning so that the graft is centred in the original footprint and replicates the normal biomechanics of the knee. As there is a degree of variation between individuals, previous methods of positioning the graft relative to other structures (or using surrogate measurements) have been superseded by the need to identify these remaining anatomical landmarks. Therefore, operative technique has focussed on femoral footprint identification and centring the graft within this area.