INTRODUCTION

The position of the patella relative to the femur is important for the evaluation of patellofemoral joint diseases. Most of patellofemoral joint diseases are based on a mismatch between the patella and femoral components (1). In 1938, on a lateral knee X-ray, Blumensaat described a line, in which the inferior pole of the patella was aligned with a line drawn from the roof of the intercondylar notch to the anterior of the knee joint (2). The vertical height above this line should be measured with the inferior pole of the patella, and the normal distance is defined as zero. Values greater than 10 mm are classified as patella alta (2) (Figure 1).

Patellar height measurements based on the blumensaat line (BL) are not affected by the patellar bone length or the angle between the BL and femoral shaft (BL-FS). Therefore, the BL method is more practical and reliable than indirect methods (3,4). However, some researchers suggest that BL varies at different BL-FS and flexion angles, resulting in inaccurate measurements (5-8).

Although the BL method is reported to be inconsistent with other patellar height measurement methods, the correlation between other measurement methods is also weak (9). In the clinical use of direct methods, BL remains to be an important parameter despite the controversial findings. Therefore, recently, it has been used more as a suitable reference point in newly described methods (3,4).

A limited number of studies, showing the accuracy of the BL method and affected variables, exist in the literature. This study aimed to investigate changes in BL measurements according to gender and age.

METHODS

Patients

The study included 229 patients, aged 18 to 60 years, who presented to our hospital with an anterior knee pain between January 2019 and July 2020 and underwent standard lateral knee radiography at the radiology clinic. Patients who had a history of previous knee surgery and those with developmental knee joint pathology or posttraumatic knee joint deformity, effusion, soft tissue pathology, or severe degeneration were excluded from the study. The demographic data of the patients were recorded.

To standardize the radiological measurements, lateral knee X-rays taken at 30° flexion were examined. The flexion angle was obtained by measuring the angle between the FS and tibia (Figure 2). This ensures that the slack is in the patellar tendon and determines the relationship between BL and inferior pole of the patella (10). Measurements were undertaken directly on the X-rays by the same radiologist for each patient, using the digital picture archiving system (Figure 3). Before the study, approval was received from the clinical research ethics committee of our hospital, and the study was conducted in accordance with the principles of the Declaration of Helsinki. Informed consent was obtained from all individuals participating in the study.

Statistical Analysis

For the descriptive statistics related to the continuous data, mean, standard deviation, median, and minimum and maximum values were used, while discrete data were expressed as percentages. The Shapiro-Wilk test was used to analyze the conformance of the data to a normal distribution. The Mann-Whitney U test was conducted to compare age and knee BL-patella values according to gender. The chi-square test was used in the group comparisons (cross-tables) of nominal variables. The relationship between age and knee BL-patella values was examined using Spearman’s correlation coefficient. IBM SPSS Statistics v. 20 was used for statistical evaluations, and p<0.05 was considered the statistical significance limit.

RESULTS

The ages of the 229 patients included in the study ranged from 18 to 60 years, and the mean age was 41.96±13.41 years. Of the patients, 44.1% were women, with a mean age of 44.90±12.2 years, and 55.9% were men, with a mean age of 39.63±13.89 years. Meniscal tears existed in 40.6% of the patients, degenerative changes, 47.2%, meniscal degeneration, 51.5%, and degeneration in the anterior cruciate ligament, 7.4% (Table 1).

When determining the height of the patella using the BL method, the position of the inferior pole of the patella (high or low) and its distance in millimeters are measured according to BL. In this study, the mean distance between the BL and inferior pole of the patella was 7.62±4.92 mm (7.06±4.59 mm in women; 8.06±5.14 mm in men). There was no significant difference in terms of the BL measurement values between men and women (p>0.05) (Table 2).

In only two (0.9%) of the 229 patients, BL passed straight through the inferior pole of the patella. Patella alta was identified in 49 patients (21.4%) (Figure 4). This condition was seen in 21 (20.8%) female patients and 28 (21.9%) male patients (Table 3). Patella baja was not detected in any patient. There was no significant relationship between the age groups of the patients and these distance values (r=-0.112; p>0.05) (Table 4).

DISCUSSION

Patellofemoral congruence is important for the etiology of anterior knee pain. The use of BL is accepted as a pioneering method in measuring the patellar height (2). According to Jacobsen et al., (10) since BL was first defined, this measurement has not been standardized, and thus, it provides varying results, depending especially on the knee flexion angle. However, Seyahi et al., (4) who compared the accuracy of BL methods in different BL-FS angles, determined that the accuracy of the BL method and size of the patellar bone were not affected by different BL-FS angles, but they also noted that the intercondylar notch depth might impact BL measurements. In this study, we examined whether the depth of the intercondylar notch may vary according to age and gender (11).

For patellar height measurements, many direct methods using patellar and femoral reference points were described, which mostly used BL as the reference point (3,12,13). Therefore, BL remains important in clinical use (11). In Andersen et al., (14) study, where they measured the patellar height based on BL in 256 knees, 207 patients were diagnosed with patella alta. Based on the study, it was revealed that the intercondylar notch roof-femoral diaphyseal angle affected the position of BL relative to the patella, which could provide different values varying from one person to another.

In another study, patella alta or baja was detected on lateral radiograph images, at 30° flexion, in 7.5% of patients. When the correlation of these values with other indirect methods was evaluated, the results were found to be consistent (1). According to the literature, the BL method shows the most significant correlation with the Insall-Salvati method (4,15,16). In a similar study conducted on Turkish patients, patella alta was detected on lateral radiograph images, at 30° flexion, in 9.47% of the patients (11). In the current study, patella alta was detected in 21.4% of the patients, while patella baja was not observed. Compared with the other study in Turkey, due to the higher number of patients in the sample, patella alta was detected in more patients.

Studies existing in the literature show that patellar height measurements may be affected by personal characteristics, such as ethnicity, age, and gender. Karadimas et al. (17) and Leung et al. (18) stated that ethnicity played an important role in patellar height. They reported that patellar height was higher, especially in Arabian, African, and Chinese populations, compared with the European population.

Norman et al. (5) and Egund et al. (19) emphasized that patellar height was affected by gender differences in direct measurements. Farrow et al. (20) stated that the intercondylar notch structure was narrower and shallower in women. The reference point of BL is the roof of the intercondylar notch; therefore, it was considered that the difference in the notch depth between genders might have affected the results (11). Değirmenci et al. (11) found a significant difference in terms of patellar height between genders. They reported that women had a higher patella than men, but the height of the patella did not significantly differ between the age groups (11). Moreover, studies in the literature show that patellar height is not affected by gender differences when measured using the BL method (16,21,22). Thus, there is still no consensus on the effect of gender differences in BL measurements. In this study, no difference was found between genders or different age groups in terms of the patellar height measurements using the BL method.

CONCLUSION

There was no difference between genders and different age groups in terms of BL measurements.

ETHICS

Ethics Committee Approval: The study were approved by the Health Sciences University Dışkapı Yıldırım Beyazit Training and Research Hospital of Local Ethics Committee (Protocol number: 10.08.2020/93/10).

Informed Consent: Consent form was filled out by all participants.

Authorship Contributions

Surgical and Medical Practices: V.K., Concept: H.K., Design: H.K., Data Collection or Processing: H.K., Analysis or Interpretation: H.K., Literature Search: H.K., Writing: V.K.

Conflict of Interest: No conflict of interest was declared by the authors.

Financial Disclosure: The authors declared that this study received no financial support.