The autopsy service of the Legal Medicine Organization in Tehran, in cooperation with the Iran University of Medical Sciences, provided the specimens for this study. Formal institutional review board approval was not required, but the study had the support and approval of our hospital administration.
Twenty hips in twenty adult fresh cadavers (seventeen men and three women) were injected with colored silicone. The technique of silicone injection has been previously described15,16. The exact ages of the subjects were not known; however, the approximate age range was twenty to fifty years. The pelvic and hip region was intact in all cadavers, and they had no history of surgery. To achieve proper filling of the vessels, the arteries proximal and distal to the site of study were ligated. Prior to silicone injection, the vascular tree was irrigated with water. Between 80 mL (for the circumflex arteries) and 180 mL (for the common iliac arteries) of colored silicone was injected until intra-arterial pressure prevented further injection. The common iliac artery was injected by transperitoneal or extraperitoneal abdominal approaches in sixteen cadavers, the internal iliac artery was injected to selectively study the gluteal arteries in two cadavers, and the femoral circumflex arteries were selectively injected in the remaining two cadavers. Twenty-four hours after injection, dissection was performed through anterior and posterior approaches. The ilioinguinal approach with a vertical femoral limb was used for the study of the medial femoral circumflex, lateral femoral circumflex, and obturator arteries. A transtrochanteric lateral approach was used to study the superior and inferior gluteal arteries. Each artery was followed from its origin to the terminal branches (distribution) by stepwise dissection. In the specimens in which the femoral artery system was selectively injected, the gluteal arteries were dissected to look for retrograde filling by means of anastomoses. Therefore, the gluteal arteries were studied in all twenty specimens, and the femoral circumflex arteries were studied in eighteen specimens. The obturator artery was studied in four hips. Particular emphasis was placed on defining the vessels traveling between the capsule and acetabulum superficially or within the capsular tissue. Capsular vessels were defined as arteries entering the extra-articular or intra-articular surface of the capsule and those running within the capsular tissue. To better identify the vessels within the substance of the capsule, a complete circumferential detachment of the capsule from the acetabular rim was performed in ten hips. In the remaining ten hips, only the iliac attachment was transected. The capsulotomies were T-shaped, with the vertical limb placed along the femoral neck and the transverse limb along the acetabular attachment of the capsule. The cut capsular tissues were then inspected for vascular channels.
Source of Funding
There was no external funding for this study.
In all twenty hips, contributions to the hip capsule vasculature arose from the medial femoral circumflex artery, lateral femoral circumflex artery, superior gluteal artery, and inferior gluteal artery. The medial and lateral femoral circumflex arteries provided direct capsular branches to the femoral side of the capsule and ran on the surface of the capsule circumferentially from distal to proximal. Some of these vessels ran superficially as capsular arteries, and the others perforated the capsule to contribute to the blood supply of the femoral neck and head. Also, the superior and inferior gluteal arteries contributed to the vascular supply of the posterior capsule in all twenty hips. The majority of the capsular branches originating from the superior gluteal artery and inferior gluteal artery were the terminal continuations of the corresponding acetabular arteries and ran on the surface of the bone, deep to the gluteus minimus and short external rotator muscles. The contributory vessels from both the gluteal and femoral systems entered the surface of the capsule from the periphery and branched proximally and distally, respectively, toward the deep layer. Superficial anastomoses were detectable between the proximal and distal vessels on the posterior and posterolateral surface of the capsule, but the number, size, and location of these vessels varied.
Medial Femoral Circumflex Artery
In all of the hips, capsular branches derived from the medial femoral circumflex artery supplied the anteromedial capsule and were identified between the pectineus and iliopsoas muscles. Anastomoses between these vessels and small arterial branches that originated from the acetabular side were identified in six specimens. These anastomoses were located deep to or medial to the iliopsoas muscle (Fig. 1-A).
Another branch of the medial femoral circumflex artery, which perforated the capsule inferomedially, entered the joint, and continued as an inferior retinacular artery, was identified in all hips. This arterial branch ran toward the femoral head in the ligament of Weitbrecht (Fig. 1-B). The size and diameter of this artery was highly variable. While the medial femoral circumflex artery continued to run laterally toward the greater trochanter, variable small branches to the posteroinferior aspect of the capsule were identified. The medial femoral circumflex artery contributed the trochanteric branch between the quadratus femoris muscle and the tendon of the obturator externus muscle in all hips. The artery then crossed the tendon of the obturator externus in close contact posteriorly, before it entered the hip joint through the femoral attachment of the posterior capsule (Fig. 2). In addition, the medial femoral circumflex artery had two constant branches (in all hips) that divided at the posteromedial aspect of the greater trochanter and contributed to the vascularization of the hip capsule. The first of these branches exited between the tendon of the obturator externus and inferior gemellus muscle and branched to supply the neighboring muscles and capsule before it continued on to anastomose with the acetabular branch of the inferior gluteal artery. The second branch exited just before the artery penetrated the capsule, continued anteriorly on the surface of the capsule, and sent variable anastomoses with capsular branches of the lateral femoral circumflex artery.
Lateral Femoral Circumflex Artery
After it branched off from the femoral or profunda femoris artery, the lateral femoral circumflex artery was found to lie anterior to the femoral attachment of the capsule and to run laterally toward the greater trochanter, deep to the rectus femoris and tensor fasciae latae muscles. Between the tensor fascia muscle and the abductors, the artery turned proximally and ultimately anastomosed with the supra-acetabular branch of the superior gluteal artery at the anterolateral aspect of the acetabulum.
In all hips, a prominent capsular branch from the lateral femoral circumflex artery that arose between the iliopsoas and rectus femoris muscle was found. This branch divided proximally to supply the anterior capsule as well as the overlying rectus femoris and iliopsoas muscles (Fig. 3). In eight specimens, the terminal branch of this artery anastomosed with vessels coming from the acetabular side near the anterior inferior iliac spine. In the interval between the tensor and the abductor muscles, the lateral femoral circumflex artery supplied multiple branches to the named muscles and the anterolateral capsule. The number and size of these vessels was highly variable. Finally, in all hips studied, the artery anastomosed with the supra-acetabular branch of the superior gluteal artery, deep to the gluteus minimus muscle (Fig. 4).
The lateral femoral circumflex artery contributed to the femoral head and neck blood supply by a single, small arterial branch in five specimens and by two small branches in one specimen. These vessels entered the joint by perforating the femoral attachment of the capsule and then continued proximally, on the anterior surface of the femoral neck.
Superior Gluteal Artery
The superior gluteal artery provided an acetabular branch in all twenty hips and a supra-acetabular branch that fed the roof of the acetabulum in fourteen hips. The supra-acetabular branch was the periosteal segment of an artery that took the form of an arcade and was found to lie under the gluteus minimus muscle. The proximal segment of the supra-acetabular branch was more superficial and had an intramuscular course. After it gave off multiple branches to the acetabulum and capsule, the supra-acetabular artery anastomosed with the terminal branch of the lateral femoral circumflex artery at the anterosuperior aspect of the acetabulum (Fig. 5).
The acetabular branch exited from the main artery at the superior aspect of the sciatic notch and ran deep in the interval between the gluteus minimus and the piriformis. This acetabular branch anastomosed proximally with the supra-acetabular branch of the superior gluteal artery and distally with the acetabular branch of the inferior gluteal artery (Fig. 6).
Inferior Gluteal Artery
In all specimens, the inferior gluteal artery was found to give rise to superficial muscular branches that ran between the piriformis and the superior gemellus and usually crossed the sciatic nerve laterally. The inferior gluteal artery also gave rise to two constant branches that were found to underlie the short external rotators. These branches contributed to the perfusion of the acetabulum and capsule. The proximal branch left the artery at the distal border of the greater sciatic notch, ran under the deep surface of the sciatic nerve, and then ran onto the periosteal surface between the piriformis and the superior gemellus. Deep to these muscles, it split into several smaller branches to supply the posterior aspect of the acetabular bone and capsule. It anastomosed with the supra-acetabular branch of the superior gluteal artery directly or by means of the acetabular branch if present (Fig. 6). The second and distal acetabular branch of the inferior gluteal artery exited at the level of the lesser sciatic notch, crossed the sciatic nerve medially, and ran between the inferior gemellus muscle proximally, the quadratus femoris muscle distally, and the obturator externus muscle medially, toward the posteroinferior aspect of the acetabulum. This artery contributed to the vascularization of the acetabulum and capsule directly and indirectly by means of anastomoses with the medial femoral circumflex artery system and the more proximal branches of the inferior gluteal artery (Fig. 7). We found an anastomosis of this artery with the deep branch of the medial femoral circumflex artery in fourteen hips and with the proximal branch of the inferior gluteal artery in twelve hips. In two hips, this artery was the dominant artery of the femoral head, replacing the deep branch of the medial femoral circumflex artery. When present, this branch of the inferior gluteal artery occupied the more common position of the medial femoral circumflex artery at the level of the greater trochanter.
Anastomoses between the acetabular branches of the gluteal arteries formed an incomplete periacetabular vascular ring on the external surface of the ilium that supplied the main portion of the acetabulum as well as the acetabular part of the capsule. Terminal branches of this incomplete ring continued toward the acetabular rim and traversed the capsule subperiosteally to supply the labrum (Fig. 6). Some of these vessels also continued superficially as capsular arteries. These vessels were highly variable in size, location, and number.
The medial femoral circumflex artery and lateral femoral circumflex artery contributed to the vascularization of the acetabulum by sending respective anastomotic branches to the periacetabular vascular ring at the posteroinferior and the anterosuperior aspect of the acetabulum. These branches completed the vascular ring (Fig. 8). The capsule also received variable perforating branches from the overlying short external rotators and gluteus minimus, posteriorly and posterosuperiorly. No vascular communication was found between the acetabulum and the capsule on the synovial surface of the capsule or within the substance of the capsule.
Obturator Artery
Four hips were dissected for examination of the obturator artery. We could not find any prominent capsular vessels. This artery was studied in the first four hips; however, because of the lack of relevant findings and the difficulty of the added dissection, the obturator artery was not studied in the remaining hips.
The present study demonstrates that the superior gluteal artery, inferior gluteal artery, medial femoral circumflex artery, and lateral femoral circumflex artery all contribute to the blood supply of the hip capsule. We did not find any capsular vessels arising from the obturator artery. However, a definitive statement regarding the contribution of the obturator artery cannot be made since the obturator artery was studied in only four of the twenty hips. Our general findings are summarized in Figure 8. This study adds to the findings of previously published work19-25 and presents some important new contributions and differences.
Beck et al.19 described the major arteries supplying the acetabulum and emphasized the importance of the supra-acetabular branch of the superior gluteal artery in the vascularization of the acetabulum after a Bernese periacetabular osteotomy. They also described anastomoses between the femoral circumflex arteries and the gluteal arteries. Our study supports the findings of Beck et al. In addition, our study clearly shows the contribution by the inferior gluteal artery to the blood supply of the acetabulum and femoral head, which, to our knowledge, has not been described previously.
Yiming et al.23, in a study of ten female cadavers, reported that the extrapelvic aspect of the acetabulum is supplied by the artery of the roof of the acetabulum, a branch of the superior gluteal artery, and the artery of the ischium, a principal branch of the pudendal artery. Our study confirmed the finding of Yiming et al. with regard to the role of the supra-acetabular branch of the superior gluteal artery (the artery of the roof of the acetabulum). However, our findings do not support the role of the internal pudendal artery. We could not find any branch arising from the internal pudendal artery that contributed to the vascularity of the extrapelvic surface of the acetabulum. Instead, we found that the inferior gluteal artery provides a constant supply.
Our study generally confirms the findings reported by Gautier et al.20 concerning the role of the medial femoral circumflex artery as the usual main supplier of the femoral head, but with certain potentially important differences. We found a consistent contribution from the inferior gluteal artery to the perfusion of the femoral head that comes either by means of an anastomosis with the medial femoral circumflex artery, or by means of a direct branch to the hip joint as a retinacular artery. In two of the twenty hips in our study, the inferior gluteal artery was the main artery of the femoral head. We also found a consistent branch from the inferior gluteal artery at the level of the ischial tuberosity that, to our knowledge, has not been previously described. The branch crosses the sciatic nerve posteriorly and makes a constant anastomosis with the medial femoral circumflex artery, and sometimes provides a direct branch to the joint as a provider for the retinacular arteries. Another subtle, but important, difference between our findings and those of Gautier et al.20 is that we identified the inferior retinacular artery to be running along the ligament of Weitbrecht in all of our specimens, whereas Gautier et al. identified this pattern in only two of twenty-four hips. This difference may be explained by the fact that the specimens in our study were from individuals who had been relatively young, allowing an easier and clearer dissection of the vessels. Because of its position relative to the ligament of Weitbrecht, the inferior retinacular artery is more mobile than the other retinacular vessels and may be more likely to escape injury following certain femoral head and neck fractures; also, it can be more easily mobilized and protected during some of the new intra-articular procedures, such as femoral head and neck osteotomies.
Another goal of this study was to determine the possible deleterious effects of capsulotomies on the vascular supply to the femoral head and acetabulum. The femoral head receives its blood supply by means of arterial branches that enter the joint near the femoral attachment of the capsule. Proximal transverse capsulotomies, therefore, appear to be safe vis-à-vis the vascularity of the femoral head. Distal transverse capsulotomies, however, are likely to damage these vessels, especially those near the superolateral and inferomedial attachments.
The acetabulum has an endosteal vascularization by means of the nutrient branch of the iliolumbar artery and the acetabular branch of the obturator artery. Additionally, there is a periosteal blood supply from the gluteal arteries. Terminal branches from the periosteal network supply the labrum and the acetabular portion of the hip capsule. The endosteal blood supply is disrupted in any periacetabular osteotomy. The closer the osteotomy is to the capsular attachment, the higher the risk of disrupting the periosteal blood supply and, thus, the higher the risk of postoperative disturbance of bone perfusion and osteonecrosis. If the periacetabular osteotomy is performed proximal to the supra-acetabular branch of the superior gluteal artery, some part of the blood supply to the acetabulum and hip capsule that comes from the periosteal network should be preserved19,26.
Since the vessels bridging the capsule and the acetabulum run on the extra-articular surface of the capsule, surgical approaches that separate the muscles and tendons from the capsule are likely to damage these bridging vessels. Some authors have advocated performing the periacetabular osteotomy through a lateral approach in order to decrease the risk of acetabular osteonecrosis. Ko et al.2, in a report of thirty-seven patients, concluded that periacetabular spherical osteotomy through a modified Ollier approach usually preserves vascularity to the acetabular fragment. Similarly, Hsieh et al.1, in reporting on a transtrochanteric lateral approach for a modified periacetabular osteotomy in forty-six hips, concluded that the lateral approach is safe with regard to acetabular vascularity. However, the results of the present study indicate that lateral approaches to the hip joint, with or without a trochanteric osteotomy, generally carry additional risk to the vascularity of the acetabular segment by disrupting not only the endosteal and periosteal vessels but also the superficial anastomotic and perforating vessels. In this regard, the anterior approach for periacetabular osteotomy is the approach that is least likely to further compromise the acetabular circulation. However, we believe that once the musculature has been dissected from the hip capsule as part of the lateral approach for periacetabular osteotomy, the addition of a capsulotomy per se should not lead to further compromise of the blood supply to the acetabular fragment. With regard to fracture surgery (e.g., a posterior acetabular wall fracture), it may be advisable to leave the external rotator muscles intact but to elevate them minimally for submuscular plate and screw fixation.
In conclusion, we were able to support the hypothesis that capsular vessels do contribute to the blood supply of acetabular bone, and we demonstrated that these capsular vessels consistently lie between the capsule and the deep surface of the short external rotators. These vessels are, therefore, at risk during posterior approaches to the hip and acetabulum. They are also at risk during some arthroscopic procedures in which multiple percutaneous capsulotomies are performed to create working portals and in procedures in which extensive intra-articular capsulectomy is performed, with either a shaver or diathermy, in order to "raise the roof" and create space for a head and neck osteoplasty. In open procedures, the short external rotators can serve to protect the capsular vessels, along with the medial femoral circumflex artery, or its potential variant, as the dominant supply to the femoral head. If it cannot be avoided entirely, dissection in this area should be undertaken carefully. 