Summary. Computer assisted surgery (CAS) during total knee arthroplasty (TKA) is known to improve prosthetic alignment in coronal and sagittal plane. In this systematic review, no evidence is found that CAS also improves axial component orientation when used during TKA. Introduction. Primary total knee arthroplasty (TKA) is a safe and cost-effective treatment for end-stage knee osteoarthritis. Correct prosthesis alignment is essential, since malpositioning of the prosthesis leads to worse functional outcome and increased wear, which compromises survival of the prosthesis. Computer assisted surgery (CAS) has been developed to enhance prosthesis alignment during TKA. CAS significantly improves postoperative coronal and sagittal alignment compared to conventional TKA. However, the influence of CAS on rotational alignment is a matter of debate. Therefore purpose of this review is to assess published evidence on the influence of CAS during TKA on postoperative rotational alignment. Patients and Methods. This review was performed according to the PRISMA Statement. An electronic literature search was performed in Pubmed, Medline and Embase on studies published between 1991 and April 2013. Studies were included when rotational alignment following imageless CAS-TKA was compared to rotational alignment following conventional TKA. At least one of the following outcome measures had to be assessed: 1) rotational alignment of the femoral component, 2) rotational alignment of the tibial component, 3) tibiofemoral mismatch, 4) the amount of rotational outliers of the femoral component, 5) the amount of rotational outliers of the tibial component. Study selection was performed in two stages and data extraction and methodological quality assessment was conducted independently by two reviewers. Standardized mean difference (SMD) with 95% confidence interval (95% CI) was calculated for continuous variables. The SMDs were interpreted according to Cohen: an SMD of 0.2–0.4 was considered a small effect; 0.5–0.7 was considered moderate; and ≥ 0.8 was considered a large effect. For the comparison of the amount of outliers for femoral and tibial component rotation, the Odds ratio (OR) and 95% CI was calculated. The OR represents the odds of outliers occurring in the CAS group compared with the conventional group. An OR of < 1 favors the CAS group. The OR is considered statistically significant when the 95% CI does not include the value of 1. Results. Seventeen studies met the inclusion criteria. One study was considered of high, 15 studies of medium and one study of low methodological quality. SMD for rotation of the femoral component was −0.07 (−0.19–0.04). For rotation of the tibial component, the SMD was 0.11 (−0.01–0.24). Regarding tibiofemoral mismatch, the SMD was −0.27 (−0.57–0.02). For femoral outliers, the OR was 1.05 (0.78–1.43) and for tibial outliers the OR was 1.12 (0.86–1.47). Discussion / Conclusion. Results of this review show no evidence that CAS-TKA leads to better rotational alignment of the femoral or tibial component or tibiofemoral mismatch. Also no evidence was found that CAS results in a decrease of the amount of outliers regarding femoral or tibial component orientation. However, these conclusions have to be interpreted with caution. The number of included studies was low and strong heterogeneity existed between the studies. Of the 17 included studies, only one study was considered of high methodological quality. Moreover, different methods for assessing tibial component rotation have been used in the studies included

The aim of this project is to test the parameters of Patient Specific Instruments (PSIs) and measuring accuracy of surgical cuts using sawblades with different depths of PSI cutting guide slot. Clear operative oncological margins are the main target in malignant bone tumour resections. Novel techniques like patient specific instruments (PSIs) are becoming more popular in orthopaedic oncology surgeries and arthroplasty in general with studies suggesting improved accuracy and reduced operating time using PSIs compared to conventional techniques and computer assisted surgery. Improved accuracy would allow preservation of more natural bone of patients with smaller tumour margin. Novel low-cost technology improving accuracy of surgical cuts, would facilitate highly delicate surgeries such as Joint Preserving Surgery (JPS) that improves quality of life for patients by preserving the tibial plateau and muscle attachments around the knee whilst removing bone tumours with adequate tumour margins. There are no universal guidelines on PSI designs and there are no studies showing how specific design of PSIs would affect accuracy of the surgical cuts. We hypothesised if an increased depth of the cutting slot guide for sawblades on the PSI would improve accuracy of cuts. A pilot drybone experiment was set up, testing 3 different designs of a PSI with changing cutting slot depth, simulating removal of a tumour on the proximal tibia. A handheld 3D scanner (Artec Spider, Luxembourg) was used to scan tibia drybones and Computer Aided Design (CAD) software was used to simulate osteosarcoma position and plan intentioned cuts. PSI were designed accordingly to allow sufficient tumour. The only change for the 3 designs is the cutting slot depth (10mm, 15mm & 20mm). 7 orthopaedic surgeons were recruited to participate and perform JPS on the drybones using each design 2 times. Each fragment was then scanned with the 3D scanner and were then matched onto the reference tibia with customized software to calculate how each cut (inferior-superior-vertical) deviated from plan in millimetres and degrees. In order to tackle PSI placement error, a dedicated 3D-printed mould was used. Comparing actual cuts to planned cuts, changing the height of the cutting slot guide on the designed PSI did not deviate accuracy enough to interfere with a tumour resection margin set to maximum 10mm. We have obtained very accurate cuts with the mean deviations(error) for the 3 different designs were: [10mm slot: 0.76 ± 0.52mm, 2.37 ± 1.26°], [15 mm slot: 0.43 ± 0.40 mm, 1.89 ± 1.04°] and [20 mm: 0.74 ± 0.65 mm, 2.40 ± 1.78°] respectively, with no significant difference between mean error for each design overall, but the inferior cuts deviation in mm did show to be more precise with 15 mm cutting slot (p<0.05). Simulating a cut to resect an osteosarcoma, none of the proposed designs introduced error that would interfere with the tumour margin set. Though 15mm showed increased precision on only one parameter, we concluded that 10mm cutting slot would be sufficient for the accuracy needed for this specific surgical intervention. Future work would include comparing PSI slot depth with position of knee implants after arthroplasty, and how optimisation of other design parameters of PSIs can continue to improve accuracy of orthopaedic surgery and allow increase of bone and joint preservation