Evaluation of accuracy of bone cuts and implant positioning in total knee arthroplasty using patient specific instrumentation.

In the last years new surgical techniques are developing to improve prosthesis positioning, increasing clinical and functional results and reducing invasiveness. In this scenario patient-specific instrumentations have been introduced in order to enhance surgical accuracy and ease of implantation. The purpose of this study was to assess the compliance of the pre-operative planning data with bone resections measured intraoperatively and to evaluate prosthesis positioning in patients undergoing total knee arthroplasty (TKA) using an MRI-based pin-guides instrumentation. Thirty consecutive patients (20 women and 10 men) undergoing 30 total knee replacements (20 right- and 10 left-sided knees) were included in this study. The same cemented cruciate ligament sacrificing prosthesis (NexGen LPS, Zimmer, Warsaw, Indiana, USA) was implanted in all patients by a single surgeon using Patient-Specific Instruments (PSI, Zimmer, Warsaw, Indiana, USA). Femoral and tibial bone resections were measured using a manual caliper intra-operatively and compared with the corresponding pre-operative values. Each patient underwent A CT examination following surgery in order to investigate individual component positioning. None of the cases was converted from PSI technique to conventional TKA and adequate femoral and tibial bone cuts were performed without the need for intraoperative adjustments. Two outliers were detected among the intra-operative bone cuts measurements. In all patients the size of femoral and tibial prosthetic components, hypothesized at preoperative planning, was confirmed intra-operatively. Two outliers were detected among post-operative CT measurements as for components positioning. PSI system can assist in obtaining good component positioning with reduction of outliers. Despite the small number of patients, our data demonstrate the validity of this patient-specific pin-guides system in TKA and may support repeatable improvements in surgical accuracy. Level of evidence: IV.

Proximal translation of > 1 mm within the first two years of revision total hip arthroplasty correctly predicts whether or not an acetabular component is loose in 80% of cases: a case-control study with confirmed intra-operative outcomes.

AIMS: The purpose of this study was to determine the sensitivity, specificity and predictive values of previously reported thresholds of proximal translation and sagittal rotation of cementless acetabular components used for revision total hip arthroplasty (THA) at various times during early follow-up. PATIENTS AND METHODS: Migration of cementless acetabular components was measured retrospectively in 84 patients (94 components) using Ein-Bild-Rontgen-Analyse (EBRA-Cup) in two groups of patients. In Group A, components were recorded as not being loose intra-operatively at re-revision THA (52 components/48 patients) and Group B components were recorded to be loose at re-revision (42 components/36 patients). RESULTS: The mean proximal translation and sagittal rotation were significantly higher in Group B than in Group A from three months onwards (p < 0.02). Proximal translation > 1.0 mm within 24 months had a positive predictive value (PPV) of 90% and a specificity of 94%, but a sensitivity of 64%. Proximal translation > 1.0 mm within the first 24 months correctly identified 76 of 94 (81%) of components to be either loose or not loose. However, ten components in Group B (24%) did not migrate proximally above 1.0 mm within the first 60 months. CONCLUSION: The high PPV of EBRA-Cup measurements of proximal translation (90%) shows that this can be used in early follow-up to identify patients at risk of aseptic loosening. The absence of proximal translation within the first 60 months indicates a component is not likely to be loose at re-revision THA although it does not exclude late aseptic loosening as a cause of failure. Cite this article: Bone Joint J 2017;99-B:465-74.

The diagnostic performance of radiographic criteria to detect aseptic acetabular component loosening after revision total hip arthroplasty.

AIMS: This study aimed to determine the diagnostic performance of radiographic criteria to detect aseptic acetabular loosening after revision total hip arthroplasty (THA). Secondary aims were to determine the predictive values of different thresholds of migration and to determine the predictive values of radiolucency criteria. PATIENTS AND METHODS: Acetabular component migration to re-revision was measured retrospectively using Ein-Bild-Rontgen-Analyse (EBRA-Cup) and manual measurements (Sutherland method) in two groups: Group A, 52 components (48 patients) found not loose at re-revision and Group B, 42 components (36 patients) found loose at re-revision between 1980 and 2015. The presence and extent of radiolucent lines was also assessed. RESULTS: Using EBRA, both proximal translation and sagittal rotation were excellent diagnostic tests for detecting aseptic loosening. The area under the receiver operating characteristic (ROC) curves was 0.94 and 0.93, respectively. The thresholds of 2.5 mm proximal translation or 2° sagittal rotation (EBRA) in combination with radiolucency criteria had a sensitivity of 93% and specificity of 88% to detect aseptic loosening. The sensitivity, specificity, positive predictive value and negative predictive value (NPV) of radiolucency criteria were 41%, 100%, 100% and 68% respectively. Manual measurements of both proximal translation and sagittal rotation were very good diagnostic tests. The area under the ROC curve was 0.86 and 0.92 respectively. However, manual measurements had a decreased specificity compared with EBRA. Radiolucency criteria had a poor sensitivity and NPV of 41% and 68% respectively. CONCLUSION: This study shows that EBRA and manual migration measurements can be used as accurate diagnostic tools to detect aseptic loosening of cementless acetabular components used at revision THA. Radiolucency criteria should not be used in isolation to exclude loosening of cementless acetabular components used at revision THA given their poor sensitivity and NPV. Cite this article: Bone Joint J 2017;99-B:458-64.