Image-free computer navigation systems build a frame of reference of a patient's knee from anatomical landmarks entered by the surgeon during the initial stage of total knee arthroplasty. We performed tibial cuts on 70 sawbones using computer navigation. All landmarks were marked identically except for the tibial mechanical entry point, which was marked correctly in 10 bones and with offsets of 5, 10, and 15 mm medially and laterally in the others. The actual coronal angle of the tibial cuts was measured directly and compared to the final angle given by the navigation system. Significant deviations of the coronal angle were observed in the trial groups. Landmarking errors during navigated TKA can lead to inaccurate tibial bone cuts. This navigation system did not have an iterative software method to verify landmarking errors that can lead to inaccurate tibia bone cuts. Keywords: computer assisted orthopedic surgery; total knee arthroplasty; navigation system; saw bones; landmarkingThe outcome of total knee arthroplasty (TKA) is particularly sensitive to variations in surgical technique. 1,2 Incorrect implant positioning and improper limb alignment may lead to implant loosening. A number of alignment mistakes can occur during the bone cuts and prosthesis implantation. Tibial bone cuts that are in varus by >38 are associated with rapid failure and reduced functional results. 3-5 Patellar instability can be caused by malrotation of the femoral prosthesis. 6 Errors of this type are estimated to occur in at least 10% of TKA even when performed by experienced surgeons using modern mechanical alignment systems (intramedullary or extramedullary methods). Outliers are especially common when severe bony deformity or dysplasia exists. 7,8 The use of computer assisted orthopedic surgery (CAOS) for TKA has reduced the number of outliers in mechanical axis alignment. 9 There are three main types of navigation systems: pre-op image-based (CT-based), intra-op image-based (radiograph, no CT), and intra-op image-free (no CT or radiograph). 10 Image free navigation avoids the expense and radiation associated with pre-op CT and the extra OR time and personnel required for intra-op radiographs. A critical aspect of image-free CAOS TKA is the data acquisition stage, during which data are collected to build a reference frame of the patient's knee. Trackers attached to the bones are seen by the system throughout surgery and allow it to provide real-time spatial anatomic information. Most systems prompt the surgeon to visually select several anatomic landmarks by using a mechanical pointer attached to an infrared tracker: mechanical entry point of the distal femur (entry point of the femoral medullary canal), mechanical entry point of the proximal tibia (entry point of the tibial medullary canal), anterior femoral cortex, posterior and distal portions of the femoral condyles, medial and lateral tibial plateau, tibial tuberosity, and medial and lateral malleoli. The femoral epicondylar axis and Whiteside's line are also often u...

Purpose Potential sources of inaccuracy in leg length discrepancy (LLD) measurements commonly arise due to postural malalignment during radiograph acquisition. Preoperative planning techniques for total hip arthroplasty (THA) are particularly susceptible to this inaccuracy, as they often rely solely on radiographic assessments. Owing to the extensive variety of pathologies that are associated with LLD, an understanding of the influence of malpositioning on LLD measurement is crucial. In the present study, we sought to characterize the effects of varying degrees of lateral pelvic obliquity (PO) and mediolateral limb movement in the coronal plane on LLD measurement error (ME). Methods A 3-D sawbones model of the pelvis with bilateral femurs of equal-length was assembled. Anteroposterior pelvic radiographs were captured at various levels of PO: 0°, 5°, 10°, and 15°. At each level of PO, femurs were individually rotated medio-laterally to produce 0°, 5°, 10°, and 15° of abduction/adduction. LLD was measured radiographically at each position combination. For all cases of PO, the right-side of the pelvis was designated as the higher-side, and the left as the lower-side. Results At 0° PO, 71% of tested variations in femoral abduction/adduction resulted in LLD ME < 0.5-cm, while 29% were ≥ 0.5-cm, but < 1-cm. ME increased progressively as one limb was further abducted while the contralateral limb was simultaneously further adducted. The highest ME occurred with one femur abducted 15° and the other adducted 15°. Similar magnitudes of ME were seen in 98% of tested femoral positions at 5° of PO. The greatest ME (~ 1 cm) occurred at the extremes of right-femur abduction and left-femur adduction. At 10° of PO, a higher prevalence of cases exhibited LLD ME > 0.5-cm (39%) and ≥ 1-cm (8%). The greatest errors occurred at femoral positions similar to those seen at 5° of PO. At 15° of PO, half of tested variations in femoral position resulted in LLD ME > 1-cm, while 22% of cases produced errors > 1.5-cm. These clinically significant errors occurred at all tested variations of right-femur abduction, with the left-femur in either neutral position, abduction, or adduction. Conclusion This study aids surgeons in understanding the magnitude of radiographic LLD ME produced by varying degrees of PO and femoral abduction/adduction. At a PO of ≤5°, variations in femoral abduction/adduction of up to 15° produce errors of marginal clinical significance. At PO of 10° or 15°, even small changes in mediolateral limb position led to clinically significant ME (> 1-cm). This study also highlights the importance of proper patient positioning during radiograph acquisition, demonstrating the need for surgeons to assess the quality of their radiographs before performing preoperative templating for THA, and accounting for PO (> 5°) when considering the validity of LLD measurements.

As the number of total knee arthroplasties (TKAs) increases, it is reasonable to expect the number of revision TKAs (rTKAs) to rise in parallel. The patient-related and societal burdens of rTKA are poorly understood. Therefore, the purpose of this study was to determine temporal changes in: (1) the incidence of rTKA; (2) patient and hospital characteristics; (3) complications, hospital lengths of stay (LOSs), and discharge dispositions; and (4) costs, charges, and payer types. All patients who underwent rTKA between 2009 and 2016 were identified from the National Inpatient Sample database using International Classification of Diseases, Ninth Revision and Tenth Revision codes and were studied. Univariate analyses were performed to compare the incidence of rTKA, patient and hospital characteristics, LOS and discharge dispositions, as well as costs, charges, and payer types. A multivariate logistic regression model was built to compare the odds of complications in 2009 and 2016. Over our study period, there was a 4.3% decrease in the incidence of rTKA. The mean age of patients who underwent rTKA was 65 years and a majority were female (58%). Mean hospital LOS decreased from 4.1 days in 2009 to 3.3 days in 2016 (p < 0.001). The rate of several complications decreased significantly over our study period including myocardial infarction, cardiac arrest, transfusion, pneumonia, urinary tract infection, and mortality. A significantly lower percentage of rTKA patients were discharged to a skilled nursing facility in 2016 (26.5%) compared with 2009 (31.6%; p < 0.001). There was an 18.7% increase in the mean costs, and a 43.3% increase in the mean charges (p < 0.001). Over the study period, there was a decrease in the incidence of rTKAs. Despite potential improvements in primary TKA, the burden associated with rTKA remains large. This report can be used to help educate medical providers about outcomes that may result from a primary and/or revised TKA.

Several studies have shown that computer-navigated TKA reduces the rate of outliers. Thirty-one consecutive patients were operated on by the same surgeon using a computer assisted navigation system. Data collected by the system included the final mechanical axis of the extremity (HKA angle) and the coronal angle of the tibial and femoral implants. These same values were measured using CAD software on full weight-bearing long X-rays taken 6 weeks post-surgery. Deviations were observed when X-ray measurements were compared to intra-operative data collected from the navigation system. A statistically significant difference was found in the tibial cut (1.29 AE 1.35 ; p < 0.0001) and in the HKA (1.59 AE 2.36 ; p ¼ 0.0007). Outliers of more than 3 were observed in the coronal plane of the tibial implant in 9.6% of patients, in the coronal plane of the femoral implant in 6.4% of patients, and in the HKA angle of 29% of patients. Our results indicate that the use of navigation alone is insufficient to prevent outliers beyond an acceptable range of 3 .