The most important finding of the present study is that the periosteal thickness changed at the region corresponding to the apex of the turning point of the femoral metaphysis in all cases. Therefore, the periosteum might support the hinge of MCWDFO within the area surrounded by the bony landmark and the upper border of the posterior part of the lateral condyle of the femur (Fig. 11).
Our pilot study showed the presence of the GLH on the posterolateral side of the distal femur. A previous cadaveric study of 20 human knees showed that the upper and lower margins of the femoral attachment of the GLH were 9.1 ± 0.9 mm above and 8.0 ± 1.4 mm below the upper border of the posterolateral region of the lateral femoral condyle [9]. Similarly, the present study revealed that the GLH was attached to the posterolateral side of the femur; however, the GLH was attached distally and posteriorly to the hinge and seemed to play a small role in stabilizing the hinge point. In contrast, another study revealed a different origin of the GLH [16], indicating the presence of morphological diversity and the need for further research.
Dissection of the lateral distal femur revealed the presence of the joint capsule and periosteum directly attached at the lateral side of the distal femur. A previous cadaveric study of 20 fresh-frozen human knees showed minimal soft tissue attachment around the hinge point of MCWDFO [12]. However, despite the presence of thick periosteum in the distal femur, the authors concluded that the soft tissue plays only a small supportive role in the stabilization of the osteotomy hinge, although no specific reason or details were given [12]. The radiological analysis revealed that the joint capsule was only partially attached to the hinge point of MCWDFO and was fragile enough to be easily detached during dissection. Furthermore, histological examination showed sparse fibrofatty tissue between the synovial surface of the joint cavity and the periosteum; thus, the joint capsule seemed to play a small role in stabilizing the hinge point. In contrast, thick periosteum was present around the metaphysis region, which may provide additional support to the osteotomy hinge.
The mean periosteal thicknesses of the metaphysis and diaphysis in the present study were similar to those in a cadaveric study of 18 femoral diaphyses, which revealed thicknesses of the cambium and fibrous layers of 23 ± 2.5 µm and 77 ± 8.8 µm, respectively [19]. No previous anatomical study has revealed the periosteal thickness of the distal femur, especially around the hinge point of MCWDFO. The present study is the first to compare the periosteal thickness between the metaphysis and diaphysis of the femur. Periosteal expansion occurs throughout life. The rate of expansion is fastest in puberty and becomes slower in adulthood [20, 21]. However, the decreased serum estradiol levels in postmenopausal women are correlated with changes in the periosteal diameter, and the rate of expansion accelerates again after menopause [22]. In the present study, the periosteal thickness in the region of the diaphysis was also significantly correlated with age; a similar tendency was observed in the region of the metaphysis, but there was no significant correlation. Sex-related differences could not be investigated because of the small sample size.
The periosteum also thickens in response to mechanical stress from components of the enthesis, such as ligaments, tendons, and muscles, and the resultant expansion of the periosteum increases the strength of bone and decreases the risk of fracture [23, 24]. In the present study, a strong correlation was observed between the periosteal thickness and the AP dimension of the femur, the total length of the femur, and height. Generally, increases in these measurements are directly proportional to the mechanical stress and load. However, it has also been reported that the periosteal thickness increases as a compensatory response to osteoporotic bone [24]. Thus, it should be emphasized that the thickness of the periosteum does not necessarily guarantee the mechanical stability of the structure, including the bone and further study is needed to understand the effect of periosteal thickness on mechanical strength.
The graphically visualized results of the periosteal thickness in the present study showed that the periosteal thickness of the distal lateral femur tended to rapidly decrease from the metaphyseal region toward the diaphyseal region. Furthermore, the overlayed images showed that the periosteal thickness changed at the part corresponding to the apex of the turning point of the femoral metaphysis in all cases. These alterations might be explained by the differences in bony geometry between the metaphysis and diaphysis and the difference in the soft tissue structure surrounding these bones. The bony landmark corresponding to the apex of the turning point of the femoral metaphysis is clinically important because it is easy to recognize and can be referred to intraoperatively during osteotomy as well as during preoperative planning and postoperative evaluation.
The present study has several limitations. First, the mean age of the cadavers was 78.8 ± 9.3 years (range, 61–91 years), which was relatively older than the typical patient undergoing MCWDFO. However, age seemed to have little influence on the anatomical location of the joint capsule attachment or the morphological features of the turning point of the periosteal thickness. Second, the cadavers had been fixed with formalin. Although the joint capsule was fragile enough to be easily detached during dissection, changes in mechanical features associated with tissue fixation were not considered. Third, the strength of the periosteum was not evaluated because of the formalin fixation of the cadavers. Nevertheless, this is the first report of quantitative measurements of the periosteal thickness around the hinge point of MCWDFO. Fourth, a detailed anatomical evaluation of the femoral attachment of the GLH was not performed. However, in the present study, the GLH was attached distally and posteriorly to the hinge and seemed to play a small role in stabilizing the hinge point.
Lastly, this was a 2D study and did not include 3D structural imaging of the hinge point or the femoral bone morphology. Therefore, further study is needed based on these findings of this present study.