By James Donaldson
Consultant Orthopaedic Surgeon
Joint Reconstruction Unit
Patient-specific hip and knee replacements are a relatively modern concept and are increasingly being used in an effort to improve clinical and functional results and long-term implant survival.
Patient-specific instruments (PSI) are custom made on a case-by-case basis, specific to both the anatomy of the patient and the surgical plan created by the surgeon.
Each patient requires pre-operative cross-sectional imaging with either a low dose CT scan or MRI. Computer software is then used to generate a virtual, or 3D printed, model of the patient’s anatomy, which allows the surgeon to accurately plan the position, size and orientation of the implant. Once the plan is finalised engineers work with the surgeon to design the patient specific instrumentation and/or implant to be used during the surgery.
In the knee, customised cutting blocks are manufactured from a pre-operative three-dimensional model of the knee and lower limb. This allows the surgeon to plan the procedure in great detail making adjustments to the proposed bony cuts in
any plane (sagittal, coronal and axial). Custom cutting guides, that accurately fit the patient’s anatomy, are then 3D printed and sterilized for surgical use (Fig 1A).
The PSI guide can take into account bony deformities (Fig 1B) or abnormal knee shapes and sizes. The guide allows the joint to be prepared to accommodate a pre-determined implant size in the optimal position. The proposed benefits include a more reproducible and accurate postoperative alignment, decreased surgical operating time, faster patient recovery and a more efficient surgical procedure.
PSI again aims to improve the accuracy of the surgical procedure and reconstruct the hip to as near normal as it can be. The more accurate positioning of both the femoral and acetabular components should result in improvements in the patient’s functional outcome and recovery, as well as reduce potential complications including leg length inequality, abnormal muscle tension, dislocation and peri-prosthetic fracture.
Similar to the knee, patient-specific cutting blocks and guides are created to cut the femoral neck and to optimize the acetabular preparation and cup implantation. Orientation, size, rotation, offset and leg length can all be optimised during the delivery of the pre-operative patient-specific surgical plan.
Revision hip and knee reconstruction is becoming increasingly common and brings with it its own unique surgical challenges. Bone loss, infection, component malposition, soft tissue and muscle deficiency all add an extra element of complexity.
Greater accuracy and the execution of a more detailed pre-operative plan are crucial in the revision setting. Advances in technology and implant design allow a bespoke solution for individual patients to be made, making use of available bone and filling defects with porous bone-adhering titanium. In this way, many joints can now be reconstructed that may have previously been deemed un-reconstructable (Fig 2).
The surgeons on the Joint Reconstruction Unit at the Royal National Orthopaedic Hospital receive referrals nationally and see some of the most complex primary and revision hip and knee cases in the UK. They have unparalleled experience with cutting-edge technologies, both from an academic and clinical perspective, including patient-specific instruments and components.
For more information contact please contact the Royal National Orthopaedic Hospital Private Patient Unit: 020 8909 5114