Nutrient Foramina of The Human Patellar Bone. A Novel Macroscopic Morphology Classification

Methods and Materials: The local Municipal authorities of Volos city gave the permission for the conduction of our study. After a thorough research of 201 skeletons 104 patellas entered our study. A macroscopic cartography be three independent researchers was performed. A statistical analysis followed with the aim to design a patellar cartography in the anterior surface and to classify the bone according to NFs.


Introduction
Patella is the largest sesamoid bone of the human body, contained within the tendon of the quadriceps femoral muscle in front of the knee. The distance from the lower pole to the insertion of the tendon at the tibial tuberosity is about equal to the midsagital height of the patella. The prepatellar bursa separates the bone from the skin. The patellofemoral joint is a part of the knee joint. The normal anatomical position of the patellar bone is rather difficult to be determined, as the position of the tibial tuberosity may vary [1][2][3]. Blackburne and Peel in 1977 compared the height of the patella from the tibial plateau to its articular length, demonstrating a ratio of 0.8 to refer to normal position, indicating any deviation as a clinical problem [4].
The majority of the patellar bones, about 60%, are depicted as roughly triangular in shape, concerning the outline of the bone.
However, oblique, elliptical and circular shapes may be found too [5]. The base is placed superiorly and the apex inferiorly, the later lying just proximal to the line of the knee joint in the anatomical with hyaline cartilage, is separated into 3 facets, the medial, the lateral and the odd facet. The anterior surface is covered by the aponeurosis of the quadriceps tendon and bears 10-12 nutrient foramina lying between longitudinal fissures, markings made by the quadriceps tendon.
Experimental cadaveric studies demonstrated that the patellar bone improves the biomechanical efficiency of knee extension, especially towards the end of its range. It has the ability to hold the patellar tendon away from the axis of the movement, thus increasing the pull of the quatriceps muscle. In general, the patella has a protective role for the anterior aspect of the knee joint; it serves as the insertion for the quadriceps tendon and finally functions as a fulcrum to maximize the efficiency of the extensor mechanism [6].
The patellar bone receives centripetal blood supply from the genicular arteries. The superior vessels are lying anterior to the quadriceps tendon and the inferior vessels are passing posterior to the patellar ligament [7], while further studies demonstrated that the most significant blood supply to the bone penetrates the inferior pole along the infrapatellar fat pad.
The patella is a bone which experiences complex, dynamic loading patterns and may be fractured due to the infliction of direct or indirect forces. The mechanism of injury indicates the fracture pattern. A series of non-operative and surgical methods are available for the fracture management. Complications are rare and the bone fragments' union rates, based on the Bostman grading scale, are high, after surgical fixation. Non-union cases and infection are rare complications, more likely to happen in open fractures [8][9]. Moreover, osteonecrosis of the patella is reported as high as 25%, though presenting no important clinical outcomes [7,10]. A compromise of the blood supply itself not only prevents bone healing but it constitutes an additional factor for a novel fracture. Hence, this research endeavors to cartograph the nutrient foramina (NF) of the anterior surface of the patellar bone, and create a classification index which may be helpful, in patellar fractures and patelloplasty.

Results
Nutrient foramina (NF) in the anterior surface of the patella bone are described in numbers above ten per bone. Our study indicates a mean of 12.564 and 12.383 NF for the right and left patella bones respectively (Table 1) Table 2. Therefore, a significant difference of the mean number of NF is indicated for the upper (p<0.001) and left (p=0.01) areas between male and female subgroups ( Table 2).    (Table 4). However, the comparison between the right and left side patellar bones shows that the right side bones present a significant difference of the mean num-

Discussion
The subject of fractures and re-fractures (later-secondary or post-operative) of the patella has attracted many writers. Various lesions of the vascular blood supply of the patella bone may result to total knee arthroplasty, artificial patella or partial patellectomy.
The "peripatellar arterial ring" is wrongfully considered as a true ring, having really an incomplete nature. Nine arteries participate to its formation, alongside with the presence of a rich extrinsic vascular plexus, that gives off nutritional patellar arteries [10]. Studies demonstrated that the dominant central arteries are branches of the lateral inferior genicular artery, while the auxiliary inferior marginal arteries derive largely from the anterior tibial recurrent vessels. Thus, they reinforce the concept of an overwhelming inferior-lateral blood path to the patella. Therefore, transverse fractures of the bone are so prone to delayed union, avascular necrosis of the proximal fragment [11][12] or a severe disturbance of the blood supply during a lateral release of the patella in total knee arthroplasty [13]. Surprisingly our dry bone sample presented high numbers of NFs in the upper part of the bone, a finding which may alter the above-mentioned concept concerning the avascular necrosis of the proximal fragment.
Even though a pattern in patella blood supply already exists, the distribution of the nutrient arteries entering the bone through its NFs in not thoroughly studied. No classification of the bone exists regarding its NFs. Several branches arise from the peripatellar arterial "ring" at the lower pole of the patella and run proximally on the anterior surface of the bone in a series of furrows, enter-ing through the NFs [9][10][11][12]. Those small vessels penetrate the bone in the middle third region [7,14]. However, our study demonstrated the appearance of NFs to the proximal and distal parts as well.
Nonetheless, the type 1 of NFs cartography constituted the 69% of the total sample, presenting a linear NF distribution in the middle part of the bone.
There is a second blood supply network for the patella bone, arising this from the polar vessels which are branches of the infrapatellar anastomosis behind the patellar ligament. They pierce the area between the ligamentum patellae and the articular surface, running upwards, being anastomosed with the nutrient arteries of the anterior surface, supplying the distal third of the bone [1,15].
Our sample presented NFs both in the anterior and posterior surfaces of the distal third of the bone (Figure 7). Our study calculated a mean of almost 12.5 vascular/nutrient foramina per bone as the nutrient arteries for the patella reach it via the quadriceps tendon, while the majority of the researchers consider the number 12 as the limit [1,7,15]. However, others simply indicate no number, only mentioning that many NFs exist in the anterior surface [16].
In our sample, consisting of older adults of rural origin, an interrupted blood stream due to trauma or overuse (many years of

Conclusion
Nutrient arteries of the anterior surface of the patella, despite of their significance in blood supply of the kneecap, are rather undervalued in recent studies concerning the area. They play an important role in the re-organisation of a broken bone, or during knee surgical interventions. Our study aimed to categorize the patella bone in agreement with the NFs cartography in a new morphology classification. Bigger sample and further research are needed to connect blood supply with clinical anatomy of the knee joint.