Blood Is Thicker Than Water: Commentary on an article by Lionel E. Lazaro, MD, et al.
They found that the farther the superior margin of resection was extended posteriorly, the greater the loss in femoral head perfusion. The specimens in their standard-resection group (resection anterior to the 12 o’clock position) demonstrated a mean decrease in femoral head perfusion of 5%. The minimally extended resection group (resection extended just posterior to the 12 o’clock position by ≤10°) demonstrated a mean decrease in femoral head perfusion of 9%. In contrast, the extended-resection group (resection extending an average of 41.3° posterior to the 12 o’clock position) demonstrated a mean decrease in perfusion of 28%. The authors found that these differences in femoral head perfusion were significant across the groups. It is also important to note that their quantitative findings are consistent with what is already known in the literature regarding the anatomy of the blood supply to the femoral head2.
Although the results of this study are compelling, the reader should also take into account that the methods only focus on varying resection margins based on the clock face. Additionally, the maximum depth of resection was 10 mm. In clinical practice, resection margins can vary with respect to the proximal and distal extents3 as well as depth. The depth of resection performed in this study was deeper than that noted in the literature. For example, Aoki et al.4 recently described a trough technique in which the depth of resection was between 3 to 5 mm in most cases, with some exceptions for larger cam lesions. Philippon et al.5 described a depth of resection of 5 to 7 mm. One can argue that the depth of resection can also affect femoral head perfusion. Perhaps variables such as depth of resection as well as the proximal-distal extent of resection can be investigated in future studies quantifying their effects on femoral head perfusion.
Lazaro and colleagues were astute in mentioning that the results of the study should be interpreted with caution. Although they were able to quantify the decrease in femoral head perfusion, the threshold at which a loss in femoral head perfusion becomes clinically important is unknown. Additionally, beyond the extent of resection during a hip arthroscopy procedure, there may be other factors that contribute to the development of osteonecrosis. These may include traction time, increased intra-articular pressure, amount of traction, and direct injury to the vessels from other instruments used during a hip arthroscopy.
It is important to recognize that determining the extent of resection during a femoral osteochondroplasty can be challenging. Not only can over-resection lead to vascular compromise but it can also lead to violating the suction-seal effect between the labrum and the femoral head. Under-resection can result in persistent cam lesion impingement, which can fail to alleviate symptoms and lead to revision hip arthroscopy. Proper preoperative planning, including a thorough evaluation of radiographs and advanced imaging, can help the surgeon determine the extent of resection needed.