## 4 Discussion  
Our research aimed to assess the validity and absolute reliability of using the TraumaMeter v.873 software for measuring LLR angular values, which was necessary to confirm the usefulness of the software in clinical practice. The most notable findings of the present study were the high inter- and intra-observer validity and reliability of the adapted TraumaMeter v.873 tool for assessing the angular values at the lower extremities. When analysing the measurement errors (not the angular values of the HKA, which we necessarily assumed to be different between the two knees) and after examining the 26 right and 26 left knees, we determined that the mean intra- and inter-observer measurement errors were equal in both cases. For instance, a measurement error may vary depending on how an X-ray is presented to an observer (laterality and anteroposterior or postoanterior acquisition [35]) and whether the measurements were taken on one or the other side of a knee. This result allowed us to use the total number of medical images considered in the study (n = 52) as a sample of the population of knees that could be measured with the TraumaMeter software, further increasing the statistical power and exceeding the Hopkins criteria for calculating the absolute precision [28]. Daily clinical practice and research require the measurement of variables. Each measurement process requires a measuring instrument that must be validated. For such validation, an instrument must be reliable [43]. Our study was designed to validate a semi-automatic instrument for measuring lower limb angular values in LLRs. In the late 1980s and early 1990s, several authors established criteria for the determination of angular values relevant to the phenotypic characterisation of the lower limbs and for the calculations required for conservative management or surgical planning [10; 11; 44]. It is also worth noting that it was the intention of a group of rehabilitors, led by [PERSON], to standardise the methodology for such measurements [12; 45]. This interest in validity and reliability was heightened by the enormous variability in lower limb alignments in osteoarthritic knees and the alignment changes during the arthritic process [41; 46]. Interest in coronal plane angle measurements has increased significantly over the last decade (perhaps motivated by new alignment philosophies in TKA surgeries and because of the growing interest in classifying the knees according to their constitutional alignment [2; 5; 6]). The reliability of different systems for measuring the same angular values (mHKA), as we have determined, has also been evaluated by other authors. For example, [PERSON] et al. [47] aimed to assess the intra- and inter-observer reliability of lower limb alignment measurements obtained manually from hardcopy radiographs compared with measurements obtained using the Philips Easy Vision system (Philips, Eindhoven, The Netherlands). Four raters (two radiologists and two orthopaedic surgeons) blindly measured each of the 42 hardcopy radiographs and computer images on two separate occasions, separated by at least two weeks. Intra-observer reliability for the mechanical axis data measured on the PACS ranged from an intraclass correlation coefficient (ICC) of 0.93 to 0.99, and the inter-observer reliability ranged from an ICC of 0.93 to 0.97. In a prospective study comparing alignments measured on LLRs and computer tomography with intra-operative computer navigation measurements in 40 patients, [PERSON] et al. [9] observed excellent intra-observer correlations in all cases (>0.98), with a coefficient of repeatability of <1.1\({}^{\circ}\). Three observers measured the alignments on LLRs three times using a computer PACS system's Cobb angle measure (Centricity EnterpriseWeb, version 3.0, GEMedical systems, North Miami Beach, FL, USA). For pre-operative alignments as measured by LLRs, the inter-observer correlation was >0.974 (range of 0.974-0.994, \(p\) < 0.001), with the coefficient of repeatability being 2.8\({}^{\circ}\)[9]. [PERSON] et al.