The anthropometric variations of the knee in different races are well-known and documented in the literature. Most studies were done on a national basis using different dimensions of the knee (Table 3). In this study, we measured the medial and lateral PTS and analyzed the measurements based on genders and age groups in the Turkish population.
According to our results, the mean medial and lateral PTS measurements show variations between genders without statistical significance. In similar studies which were done in other populations, demonstrated significant gender-based differences in PTS.
Hudek R. et al. reported that minimum values of medial PTS were -1,2° (range -1,2° to 11°, mean: 4,6°±2,4°) that value was 5° smaller than our findings and minimum values of lateral PTS was -4,3° (range -4,3° to 12,8°, mean: 5,0°±3,6°) that value was 9° smaller than our findings in Swedish adults. Similarly, we found important difference in study which mean medial PTS in male subjects was 3,7 (range -3° to 10°, mean: 3,7°±3,1°) that angle was 4° smaller than our results and mean lateral PTS in male subjects was 5,4° (range 0° to 9°, mean: 5,4°±2,8°) this angle was 2° smaller than our results that were done in England. But on the other hand, our results show a similarity with the results of studies that were done in South Korea and Italy. Han H. et al. showed that mean medial PTS in South Korean subjects was 6,1°±1,7° and mean lateral PTS was 6,8°±1,8° all those close to values we found. A study that was done in Italy showed that mean medial PTS in male subjects was 7,6°±3,3° and mean lateral PTS was 7,5°±3,5° almost same results that we found in male subjects. Also, Haddad B. et al. found that the medial and lateral PTS was significantly different in Asian subjects compared with other ethnic groups.
In the study using MRI, Hashemi J. et al. found that the medial and lateral PTS was statistically greater in female subjects than male subjects. Additionally, Haddad B. et al. reported that PTS was greater in female subjects than male subjects but they did not report a significant difference between medial PTS and lateral PTS. In our study, we did not find any significant differences between lateral PTS and medial PTS as well as within the genders similarly studies.[11,12]PTS of medial and lateral tibial plateau with rising age can be expected to increase due to degeneration on the tibial plateau. But we couldn’t find any correlation between the age and other variables (medial PTS, lateral PTS) similarly following studies.[10-12]
Despite the tibiofemoral joint has an asymmetrical, complex, three-dimensional structure; generally, PTS is evaluated from lateral knee radiographs after uni-total knee arthroplasties or tibial osteotomies in daily clinic routine. As we mentioned before, medial and lateral PTS can not be truly distinguished from plain radiographs due to its nature; superimposing.[5,10,14,15] The accurate measurement method of PTS must be contained exact localization of the center of articular surfaces. On MRI measurement, the medial and lateral plateau of the tibia can be assessed separately. Differences between the assessing medial, lateral tibial plateau and lateral radiographs were reported in cadaveric, CT and MRI imaging studies.[16-18] We found differences between our results and other results that were done in Turkey with a lateral radiographic method. Mean and standard deviation of PTS of the radiographic study was 13,4°±3,2°; this angle was 6° greater than our result. Besides the all positive features of MRI measurement, Hudek R. et al.stated that cost and total time consumption of a routine knee MRI is approximately five times greater than for a lateral radiograph based on the accounting data of their clinic. But they also stated that MRI scans can be applicable to daily clinic routine due to it allows to assessment of medial and lateral plateaus separately with reliable method.
One of the importance of PTS in daily life is it has a close relationship with anterior tibial translations of the knee. This relationship is shown in a cadaveric study  especially, with the application of compressive load to the knee. Knee produces anteriorly directed shear force then shifting to anteriorly with the application of compressive load and the amount of shifting is greater in anterior cruciate ligament resected knees than in intact knees. Additionally, Dejour H. and Bonnin M. stated in their studies that tibia had a 6 mm anterior translation for a 10° increase in PTS.
Gender-specific prostheses, primarily designed according to characteristic features of the female knee joint. Their main differences based on three anatomic differences which are narrower mediolateral diameter, the anterior ﬂange of the prosthesis was modiﬁed to include a recessed patellar sulcus and reduced anterior condylar height (to avoid “overstuffing” during knee flexion) and a lateralized patellar sulcus (to accommodate the increased Q-angle associated with a wider pelvis). According to a meta-analysis, no statistically significant differences were observed between the gender-specific prostheses and unisex prostheses designs regarding pain, range of motion (ROM), knee scores, satisfaction, preference, complications, and radiographic results. Also in our study, we did not found any statistically significant differences between genders in the Turkish population. Our results showed that gender-specific prosthesis is not useful in the Turkish population-based on PTS measurements.
Moreover, in total knee arthroplasty operations, PTS is critical for the proper size of prostheses and determining its last sagittal alignment and also for patients to benefit from this operation. A decrease in the slope of medial and lateral tibial plateau results in insufficient flexion of the knee, early overloading of polyethylenes in the tibial plateau. Then, it causes early anteroposterior laxity, increased polyethylene wear. Dorr et al. found that 90°-110° knee flexions can be reachable when PTS would be in a range of 5°-10°. If the posterior inclination of tibia turns through anteriorly, knee flexion would be quite insufficient in which the posterior cruciate ligament was preserved knees.Blunn GW. et al. reported that knee anatomy should be reshaped as original as possible, deviations from this will cause excessive movements on the polyethylene and early wearing of polyethylene.
According to the study, tibial slope also should be considered when high tibial osteotomy operation is planned, leveling of cutting point in the surgery and it can affect the functional level of a patient, the success of surgical treatment, the contribution of physical therapy. Dejour H. and Bonnin M. showed that evaluation of sagittal plane such as the frontal plane is necessary before high tibial osteotomy is performed in patients which have gonarthrosis and varus or valgus deformities together, late outcomes of high tibial osteotomy are very poor in the increased PTS patient group.
This study has several limitations. One of them is all measurements were done just once time by one observer and one co-observer. Thus, we could not have a chance to assess differences in the interobserver and intraobserver variations and calculate the reliability of the measurements. Medial and lateral tibial slope measurements could be repeated, the first time starting the study and the second time 2 weeks after and with the more than one observer. On the other hand, we couldn’t obtain the weight and height of subjects to assess whether there is a relationship between PTS and other anthropometric measurements. Differences between our findings and other studies could be based on these other variations in anthropometric features. Routine knee MRIs are included the distal femur and proximal tibia so we tried the identify tibial longitudinal axis from this limited area. Measurement of PTS from the tibial mechanical axis could provide more accurate results but determining of tibial mechanical axis requires MRI of the whole tibia. We don't think that this limitation will not affect a general minimum and maximum values in large scale subjects or subject-to-subject variations.