INTRODUCTION

In Total Knee Arthroplasty (TKA), the neutral overall limb alignment (NOLA), i.e. the mechanical alignment of the lower limb within 0°±3°, is targeted for achieving good clinical/functional results. The kinematic overall limb alignment (KOLA), which uses the axis through the centres of the femur posterior condyles modelled as cylinders, represents a novel approach for achieving better soft tissue balance.

Patient-specific instrumentation (PSI) is nowadays offered as an effective technology in TKA to obtain better lower limb alignments than those via conventional guides (CON). Although relevant results are still inconsistent, the benefits claimed include shorter operative time, reduced surgical instrumentation, and accurate preoperative planning.

The aim of this study was to report the preliminary clinical and radiological results of TKA patients operated via NOLA-PSI and KOLA-PSI. Comparisons between them and with the results obtained via NOLA-CON were performed.

Computer-assisted techniques in total knee replacement (TKR) have been introduced to improve bone cuts execution and relevant prosthesis components positioning. Although these have resulted in good surgical outcomes when compared to the conventional TKR technique, the surgical time increase and the use of additional invasive devices remain still critical. In order to cope with these issues, a new technology in TKR has been introduced also for positioning prosthetic components according to the natural lower-limb alignment. This technique is based on custom-fit cutting block derived from patient-specific lower-limb scan acquisition. The purpose of this study is to assess the accuracy of the custom-fit technology by means of a knee surgical navigation system, here used only as measurement system, and post-operative radiographic evaluations. Particularly, the performances of two different custom-fit cutting blocks realized from as many scan acquisitions have been here reported.

Thirty patients affected by primary knee osteoarthritis were enrolled in this study. Fifteen patients were implanted with GMK® (Medacta-International, Castel San Pietro, CH) and as many patients with Journey® (Smith&Nephew, London, UK). Both TKR designs were implanted by using custom-fit blocks for bone cut executions provided by the same TKR manufacturers according to a pre-operative web planning approved by the surgeon. Particularly, the cutting block for the former design was built from CT scan acquisition of the hip, knee and ankle, whereas that for the latter design from MRI scans acquisition of the knee and X-ray lower-limb overview. A knee surgical navigation system (Stryker®-Leibinger, Freiburg, Germany) was used for recording intra-operative alignment of bone cuts as performed by means of the custom-fit cutting blocks and relevant component positioning. Prosthetic components alignments were also assessed post-operatively on X-ray images according to a shape-matching technique. The accuracy of the custom-fit blocks was evaluated through the comparison between pre-operative planning, and intra/post-operative data. Discrepancies above 3° and millimeters were considered as outliers.

Within the patient cohort, nine cases were fully analyzed at the moment and here reported. Over them and except for one case, the discrepancy between pre-operative planned femoral/tibial resection level on the frontal plane and the corresponding measured intra-operatively was within 3 mm, being 5 mm in the worse case. Two outliers were observed for the corresponding femoral/tibial cut rotational alignment. Particularly, in one patient, the discrepancy in femoral cut alignment was of 8° in flexion and 6° in external rotation; in another patient this was of 4° in extension and 4° in external rotation in the femoral and tibial cut alignment, respectively. Post-operative radiographs evaluations for the final prosthetic components revealed that femoral/tibial alignment were within 3° in all cases, except for those patients that were already outliers.

These preliminary results reveal the efficacy of the custom-fit cutting block for TKR. These were generally fitted properly and final prosthetic components were accurately placed, although some discrepancies were observed. This new technology seems to be a valid alternative to conventional and computer-assisted techniques. More consistent conclusions can be deduced after final evaluation of all patients.