Epiphyseal Arterial Network and Inferior Retinacular Artery Seem Critical to Femoral Head Perfusion in Adults With Femoral Neck Fractures

Background

A better understanding of the blood supply of the femoral head is essential to guide therapeutic strategies for patients with femoral neck fractures. However, because of the limitations of conventional techniques, the precise distribution and characteristics of intraosseous arteries of the femoral head are not well displayed.

Questions/purposes

To explore the characteristics and interconnections of the intraosseous vessel system between different areas of the femoral head and the possible blood supply compensatory mechanism after femoral neck fracture.

Methods

The three-dimensional (3-D) structures of the intraosseous blood supply in 30 uninjured normal human femoral heads were reconstructed using angiography methods and microCT scans. The data were imported in the AMIRA^® and MIMICS^® software programs to reconstruct and quantify the extra- and intraosseous arteries (diameter, length). In a separate experiment, we evaluated the residual blood supply of femoral heads in 27 patients with femoral neck fractures before surgery by analyzing digital subtraction angiography data; during the study period, this was performed on all patients in whom hip-preserving surgery was planned, rather than arthroplasty. The number of affected and unaffected subjects included in the three groups (superior, inferior, and anterior retinacular arteries) with different types of fractures (Garden Types I–IV) were recorded and analyzed (Fisher’s exact test) to reflect the affected degrees of these three groups of retinacular arteries in patients after femoral neck fractures.

Results

The main results of our cadaver study were: (1) the main blood supply sources of the femoral head were connected by three main network structures as a whole, and the epiphyseal arterial network is the most widely distributed and the primary network structure in the femoral head; (2) the main stems of the epiphyseal arteries which were located on the periphery of the intraosseous vascular system have fewer anastomoses than the network located in the central region; (3) compared with the round ligament artery and anterior retinacular artery, the inferior retinacular artery has a relatively large caliber. Digital subtraction angiography of the 27 patients with hip fractures indicated that the inferior retinacular arterial system had a high likelihood of being unaffected after femoral neck fracture (100% [14 of 14] in nondisplaced fractures and 60% [six of 10] in Garden Type III fractures).

Conclusions

The epiphyseal arterial network and inferior retinacular arterial system appear to be two important structures for maintaining the femoral head blood supply after femoral neck fracture. Increased efforts to protect these key structures during surgery, such as drilling and placing internal implants closer to the central region of the femoral head, might be helpful to reduce the effect of iatrogenic injury of the intraosseous vascular system.

Clinical Relevance

3-D anatomic evidence of intraosseous arterial distribution of the femoral head and the high frequency with which the inferior retinacular arteries remained patent after femoral neck fracture lead us to consider the necessity of drilling and placing internal implants closer to the central region of the femoral head during surgery. Future controlled studies might evaluate this proposition.

     

螺旋CT评价股骨颈骨折后股骨头血运的临床研究

目的探讨应用64排螺旋CT薄层增强扫描技术,观察股骨颈骨折后股骨头血液循环的变化,从而为预测股骨颈骨折后股骨头缺血性坏死提供影像学依据。方法选择2007年9月至2009年12月收治的30例股骨颈骨折患者。术前行双侧髋关节64排螺旋CT薄层增强扫描,健侧髋关节设为自身对照组。观察旋股内侧动脉、旋股外侧动脉、支持带动脉,测量双侧上述血管的管径和长度,计算比较血管容积。结果 GardenⅢ型股骨颈骨折患侧旋股内侧动脉、旋股外侧动脉以及头下型、基底型股骨颈骨折患侧旋股外侧动脉血管容积较健侧明显降低,差异具有统计学意义（GardenⅢ型旋股内侧动脉t=-2.379,P〈0.05;GardenⅢ型旋股外侧动脉t=-3.052,P〈0.05;头下型旋股外侧动脉t=-2.578,P〈0.05;基底型旋股外侧动脉t=-7.908,P〈0.05）。GardenⅠ型、GardenⅡ型以及经颈型骨折双侧血管容积比较,差异无统计学意义。GardenⅠ型、GardenⅡ型、GardenⅢ型股骨颈骨折3组间对比,各组患侧血管容积差异无统计学意义。头下型、经颈型、基底型股骨颈骨折3组间对比,各组患侧血管容积之间差异无统计学意义。支持带动脉因CT分辨率不足未能完全显示。结论股骨颈骨折可改变旋股内侧动脉和旋股外侧动脉血管容积,从而影响股骨头的血液循环状态,是股骨颈骨折后发生股骨头缺血坏死的病理基础之一。64排螺旋CT薄层增强扫描技术是一种直接、实时、无创的观察股骨头血液循环的方法,对评价股骨头血运,预测股骨颈骨折预后及选择治疗方案有一定的参考价值。由于CT分辨率不足,不能清晰显示及测量支持带动脉的血管容积,使其临床应用价值受到一定的局限。     

基于三维重建的股骨头支持带血管的显微外科定位研究及临床意义

目的通过对股骨头血供的灌注和三维重建对股骨头支持带血管进行定位,探讨应用显微外科技术对股骨颈骨折后通过支持带血管进行探查和修复,以重建股骨头血供的可行性及临床意义。方法采用新鲜成人股骨头标本25例进行显微解剖及动脉灌注,应用Micro-CT扫描及三维软件重建股骨头血运,以360°角度盘及骨性解剖标志进行定位,并测量相关的临床数据。结果股骨头血供由上、下、前3组支持带动脉血管供应,其在股骨头内形成互相连接的动脉网,3组血管在角度盘的定位分别为288°-342°、192°-226°、118°-155°。结论来源于旋股内侧动脉的上、下支持带血管是股骨头的主要供血动脉,其走行位置较为恒定,在股骨颈骨折切开复位术中可根据骨性标志定位支持带血管,以探查、判断股骨头血运损伤情况。     

The Vascular Network in the Femoral Head and Neck After Hip Resurfacing

The purpose of this study was to determine whether femoral neck fracture after cemented resurfacing hip arthroplasty (RHA) arises from intraosseous vascularity around the femoral head-neck junction. We implanted a replica of the femoral head component into osteoarthritic femoral heads and compared the intraosseous vascularity network between the femoral heads with and without the RHA procedure using microangiography through a retinacular artery with micro–computed tomography. Our results showed no significant difference in the vascularity around the femoral head-neck junction between the groups with and without the RHA procedure. These results suggest that deterioration of the intraosseous vascular network around the head-neck junction after RHA was not severe enough to induce complete avascularity.     

股骨颈骨折后选择性血管造影评价股骨头血液循环

目的 探讨选择性血管造影检查对评价股骨颈骨折后早期股骨头血液循环损伤及影响因素的价值。方法采用选择性旋股动脉及支持带动脉造影(DSA)，对9例2～23天内单侧股骨颈骨折患者血管损伤和血液循环改变进行评价。结果髋关节囊内出血2例，骨内出血4例，下、后支持带动脉损伤和血管移位各3例。患髋牵引时，除外下支持带动脉，其他支持带动脉无显影或仅显示起始部主干，相应股骨头颈部几无灌注成像，静脉显影延迟；髋关节维持伸直内旋位或囊内注入生理盐水后造影，所有支持带动脉无明确显影或仅显示其主干，股骨头颈部无灌注、染色，静脉显影延迟。结论选择性旋股内、外侧动脉DSA技术是一项准确评价股骨颈骨折后股骨头血液循环损伤及影响因素的微创性检查方法；股骨头血液循环受髋关节体位、囊内压和牵引等因素影响；牵引可导致或加重股骨颈骨折后股骨头缺血。     

A Method to Visualize and Quantify the Intraosseous Arteries of the Femoral Head by Vascular Corrosion Casting

ObjectiveTo describe a method to display the three‐dimensional distribution of intraosseous arteries in the femoral head by vascular corrosion casting.MethodsAn experimental study was done to expose the intraosseous arteries of the femoral head by a microperfusion corrosion method between January 2021 and May 2021. Specimens were 23 swine femoral heads (12 female specimens and 11 male specimens, where age of swine ranged from 8 to 12 months, and the weight was approximately 150 kg). The femoral heads were microperfused with the vascular casting resin through retinacular arteries, and the bone of the femoral head was dissolved with 50% sodium hydroxide and 10% hydrochloric acid and rinsed under the microscope until the vessel casts were completely exposed. The distribution and anastomosis of the arteries in the femoral head were observed under direct vision and microscopy. The diameter of the artery in the femoral head was measured at 0.5 cm after its entry into the bone of the femoral head with a microscale under the microscope. The number of internal arteries with diameter ≥0.05 mm was counted. The number and diameter of the main trunk of the epiphyseal arteries in the femoral head between male and female swine were compared.ResultsThe vascular casting specimen of the swine femoral head was successfully produced by using epoxy resin as a casting agent, and the three‐dimensional intraosseous vascular structures were clearly visible. The number of epiphyseal arteries in male and female swine was 8.55 ± 2.15 and 8.83 ± 2.15 (t = −0.31, p = 0.38), respectively. The diameters of the superior epiphyseal arteries in male and female swine were 0.35 ± 0.09 and 0.31 ± 0.08 mm (t = 1.03, p = 0.16), the diameters of the inferior epiphyseal arteries were 0.47 ± 0.05 and 0.49 ± 0.09 mm (t = −0.57, p = 0.29), and the diameters of the anterior epiphyseal arteries were 0.34 ± 0.08 and 0.33 ± 0.13 mm (t = 0.32, p = 0.37). There was no significant difference in the number and diameter of the main trunk of intraosseous arteries between male and female swine (p > 0.05). The main trunk of intraosseous arteries formed an anastomosis in the center of the femoral head. Among 23 swine femoral head samples, three types of intraosseous anastomosis were observed, including 13 (57%) posterior superior‐posterior inferior, seven (30%) posterior inferior‐anterior, and three (13%) uniform intraosseous anastomosis.ConclusionThe microperfusion corrosion method can produce the vascular casting specimen of swine femoral head revealing the three‐dimensional structure of the intraosseous artery, which clearly shows the origin, course and branches, and diameter, as well as the anastomosis, of nutrient arteries in the femoral head. This method provides a simple and rapid technique for quantifying and visualizing intraosseous arteries.     

Role of the Extraosseus Blood Supply in Osteoarthritic Femoral Heads?

Blood perfusion to the femoral head might be endangered during the surgical approach or the preparation of the femoral head or both in hip resurfacing arthroplasty. The contribution of the intramedullary blood supply to the femoral head in osteoarthritis is questionable. Therefore, the contribution of the extraosseous blood supply to osteoarthritic femoral heads was measured intraoperatively to question if there is measurable blood flow between the epiphysis and metaphysis in osteoarthritic hips in case of extraosseus vessel damage. At defined points during surgery we acquired the epiphyseal and metaphyseal femoral head perfusion by high-energy laser Doppler flowmetry. Complete femoral neck osteotomy sparing the retinacular vessels to simulate intraosseous blood disruption showed unchanged epiphyseal blood flow compared to initial measurement after capsulotomy. The pulsatile signal disappeared after transection of the retinacular vessels. Based on these acute measurements, we conclude intramedullary blood vessels to the femoral head do not provide measurable blood supply to the epiphysis once the medial femoral circumflex artery or the retinacular vessels have been damaged. We recommend the use of a safe surgical approach for hip resurfacing and careful implantation of the femoral component to respect blood supply to the femoral head and neck region in hip resurfacing arthroplasty. Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution has approved or waived approval for the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research. This study was performed at the Department of Orthopaedic Surgery, University of Berne and Department of Orthopaedic Surgery, Balgrist, University of Zurich, Switzerland.     

The arterial supply of the lesser metatarsal heads: a vascular injection study in human cadavers

The possibility of avascular changes of the metatarsal heads following forefoot surgery has been previously documented. The aim of this study was to investigate the arterial supply of the lesser metatarsal heads with regard to osteotomies of these bones. We used epoxy resin injections and a modified Spalteholz technique in human cadaveric specimens to demonstrate the intraosseous and extraosseous blood supply of the lesser metatarsals. The metatarsal heads had two arterial sources: 1. The dorsal metatarsal arteries, which arose from the dorsalis pedis artery, and 2. The plantar metatarsal arteries, which are branches of the posterior tibial artery. These two vessels typically anastomosed at two sites about the metatarsal heads, forming a vascular ring and provided an extensive extraosseous arterial network around the metatarsal heads. Small arterial branches of this network run distally on the metatarsal cortex to enter the bone of the metatarsal head. The nutrient arteries traversed the cortex of the metaphysis close to the capsular and ligamentous insertions to provide multiple branches for the supply of the subchondral bone. Extensive capsular stripping during metatarsal head osteotomies results in damage to the medial and lateral head vessels.     

Circulatory and vascular changes in the hip following traumatic hip dislocation.

An experimental study of the extraosseous and intraosseous vascular and circulatory changes following traumatic hip dislocation in dogs and rabbits is reported. The observations were made by dissection, angiography and histology following posterior dislocation and reduction at varying intervals. Traumatic dislocation of the hip causes extraosseous circulatory disturbance in the hip resulting in intraosseous circulatory deficiency in the femoral head. The sites of the vascular lesions are the extraosseous branches of the femoral circumflex arteries and their extraosseous branches of the epiphyseal and metaphyseal arteries and the retinacular artery of the circulus vasculosus articularis. The types of the vascular damage are irreversible tear of the minority of vessels along the ruptured capsule and teres ligament, and the compression, traction and spasm of the majority of intact vessels which are reversible by early reduction. In prolonged dislocation the circulatory disturbance persists or worsens due to additional pathological changes such as posttraumatic inflammatory changes, fixed deformity in the dislocated position, thrombosis, fibrosis and occlusion of vessels which may eventually cause an ischemic necrosis of the femoral head. Early reduction within several hours after dislocation restores nearly normal regional anatomy and relieves vessels from compression, traction or spasm and restores extra and intraosseous circulation. It also prevents or minimizes thrombosis, fibrosis and occlusion of vessels and avascular necrosis of the femoral head.     

Fracture of the femoral neck. II. Relative importance of primary vascular damage and surgical procedure for the development of necrosis of the femoral head

The opinion is widely held that interruption of the arterial flow through the retinacular arteries to the femoral head is the main cause of avascular necrosis after fracture of the neck. In this study the state of the vascular supply to the femoral head was assessed--prior to osteosynthesis--by means of intramedullary pressure measurements in the femoral head and neck in 72 patients with medial neck fractures. The patients were followed 2 or 3 years or until avascular necrosis became evident. The relative importance of primary avascularity and surgical technique for the development of necrosis suggests that damage to the retinacular arteries may not be the single decisive factor in the pathogenesis of femoral head necrosis. Proper fracture reduction with extensive contact between the cancellous bone surfaces and stable fixation seemed to be more important, probably because they offer the best possibilities for re-establishment of transosseous blood flow across the fracture site.     

股骨颈骨折对局部血供的损伤及评估——解剖基础及其临床运用进展

股骨颈骨折内固定的稳定性可在很大程度上通过手术技巧及内固定排布和植入骨替代物等方法获得,但当前医疗技术水平尚无法完全逆转骨折产生的血供损伤。因此,在围手术期,全面评估股骨颈骨折后局部残余血供以避免医源性损伤成为了目前研究的热点。关于股骨颈骨外层面血供的解剖研究相对成熟,其运用主要涉及旋股内侧动脉和支持带动脉的评估,但不同损伤程度的预后需要进一步探索。当前,临床上尚无法直接观察到骨面的滋养孔,但可根据其分布的密集次序、进行合理的术前规划,尽可能保护残存血供,以避免后续股骨头坏死的发生。而骨内血供的解剖基础及临床研究主要聚焦于头颈结合区,以探究股骨头坏死的机制。但关于股骨颈的其它区域骨内血管分布及交联机制仍需要进一步探究。此外,后续研究可根据骨外血管走行、滋养孔分布及骨内血管网的特征建立完善的基于三层次结构综合的血供评估体系,用于辅助股骨颈骨折的治疗。     

Intraosseous arterial architecture in nontraumatic avascular necrosis of the femoral head. Microangiographic and histologic study.

To determine the vascular architecture of nontraumatic avascular necrosis of the femoral head (ANFH), 38 femoral heads procured from 31 ANFH patients were studied by microangiographic and histologic methods. Microangiography showed that the head was consistently stratified into three zones: the normal vascular, the reparative vascular, and the avascular. Microangiographic abnormalities were closely correlated with the histologic changes in each zone. The extent of the necrotic area proved to depend on the extent and number of involved intraosseous nutrient arteries. Circumscribed necrosis accompanied interruption of the lateral epiphyseal arteries in their intra-capital portion. Extensive necrosis resulted from multiple vascular involvement, which included not only the lateral epiphyseal arteries, but also the superior and inferior metaphyseal arteries. Histologic examination of different levels of the nutrient arteries revealed many intraosseous pathologic vascular changes in apposition to the ischemic episode of the femoral head. Interruption of the blood supply causing ANFH occurs in the intracapital arteries probably because of vascular wall damage, and the extent of necrosis depends on the number of the involved nutrient arteries and their proximity to the intracapital site of origin.     

Revascularization of the femoral head by anastomosis of superior retinacular vessels for the treatment of femoral neck fracture: A case report

The purpose of this report is to present a method of revascularization of the femoral head for the treatment of femoral neck fracture in a young adult. The patient is a 22‐year‐old male with the femoral neck fracture of Garden type III. We performed an open reduction with internal fixation of the fracture and repaired the superior retinacular vessels using microsurgical techniques to achieve revascularization to the femoral head. A desensitized‐digital subtraction angiography examination showed that the blood supply from the superior retinacular artery to the femoral head was re‐established three months after surgery. The X‐ray showed that the femoral head had a normal shape without any necrotic lesions or sclerotic changes at four months follow‐up and the bone achieved good union without redisplacement of the fracture site. This case showed that revascularization of the femoral head by microsurgery could be feasible in treatment of certain type of femoral neck fracture. © 2016 Wiley Periodicals, Inc. Microsurgery 36:426–429, 2016.     

A microangiographic study of idiopathic osteonecrosis of the femoral head

Microangiography was performed on 31 femoral heads with idiopathic osteonecrosis to investigate the pathogenesis of this disease from the aspect of circulation disturbance. Microangiography showed the following: (1) the interruption of the superior retinacular arteries in the extraosseous area; (2) the presence of numerous newly formed vessels of varying diameter arising from the stumps of the interrupted superior retinacular arteries; (3) compensatory hypertrophy and large-area invasion of the inferior retinacular arteries and the ligamentum teres arteries, both of which medially enter the affected head; and (4) the blockage of revascularization, which occurred along the area of subchondral fracture and collapse at the weight-bearing region. These findings strongly suggest that revascularization is aborted by the subchondral fracture and collapse caused by weight bearing. It was assumed that interference with revascularization occurred repeatedly in the repair process of affected heads due to the influence of subchondral fracture and collapse caused by weight bearing.     

Vascular supply of the femoral head in sheep—Implications for the ovine femoroacetabular impingement model

Sheep hips have a natural non‐spherical head similar to a cam‐type deformity in human beings. By performing an intertrochanteric varus osteotomy, cam‐type femoroacetabular impingement can be induced experimentally. In sheep, the aspherical portion is located superiorly—exactly matching the region where the superior retinacular vessels enter the femoral head–neck junction in human beings. In order to fully exploit the potential of this experimental FAI model, a safe osteochondroplasty of the superior asphericity would need to be done without the risk of avascular necrosis. The aim of this study was to describe the vascular anatomy of the femoral head in sheep from the aorta to the retinacular vessels in order to perform safe femoral osteochondroplasty of the superior femoral asphericity in sheep. Sixty‐two ovine hips were analyzed using CT angiography (30 hips), post mortem intravascular latex injection (6 hips), vascular corrosion casting (6 hips), and analysis of the distribution of vascular foramina around the femoral head–neck junction in macerated ovine femora (20 hips). The ovine femoral head receives its blood supply from anterior retinacular arteries from the lateral femoral circumflex artery, and from posterior retinacular arteries from the medial femoral circumflex artery. The superior aspherical portion is free of vessels. Detailed knowledge about vascular anatomy of sheep hips is of clinical significance since it allows to perform osteochondroplasty of the superior aspherical portion in the experimental ovine FAI model safely without the risk of osteonecrosis. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2340–2348, 2018.

     

Delayed Presentation of Lateral Femoral Circumflex Artery Injury Post Cannulated Hip Screw Surgery –A Case Report

An elderly patient underwent cannulated hip screw surgery for a subcapital neck of femur fracture.Nine days post surgery, she was noted to have collapsed with a falling haemoglobin level. Computed tomography revealed a large haematoma to the thigh. Further angiography showed active bleeding from one of the branches of the lateral femoral circumflex artery (LFCA),which we postulate was caused by the sharp tip of a version guidewire used during fracture fixation surgery. Iatrogenic injury during hip fracture fixation is a rare event,particularly to the circumflex branches of the profunda femoris artery (PFA), and may occur from hard wire use intraoperatively or from the fracture itself. The LFCA branches laterally from the PFA, runs anterior to the femoral neck,where we suspect it was injured in our case.Whilst a version wire is a useful radiological guide intra-operatively,manually clearing a passage for its insertion into the femoral head/neck junction and using the blunt end is recommended. A combination of acute swelling in the operated region and falling haemoglobin post surgery should alert the clinician to possible vascular injury.Compared to duplex ultrasonography,CT angiography remains the gold standard in its specificity and sensitivity for diagnosing arterial injuries.With early recognition and prompt radiological intervention, this rare complication of fracture fixation surgery can be treated without the need for further surgery.     

A study of vascular changes on disintegration and repair of the femoral head with advanced osteoarthritis of the hip

Microangiography was performed on 65 femoral heads with advanced osteoarthritis to investigate the vascular changes on disintegration and repair of the femoral head. Affected femoral heads were removed during prosthetic replacement. A needle was inserted into the nutrient vessel of the extraosseous area and the contrast medium was injected by manual pressure through the needle. After slicing the femoral head, decalcification was performed and Spalteholz's preparations were prepared. Anastomosis between the superior and inferior retinacular arteries was found in all cases. Hypertrophy and hypervascularity of the retinacular arteries were observed on the weight bearing region. On the cystic lesion corresponding to the weight bearing region, numerous arteries were extended around the cyst. On the surface of the eburnated femoral head, the peripheral arteries coursing to the joint was not tapered and dilatation of these arteries was demonstrated. On some areas of the head, however, repairing arteries reaching to the joint surface lay horizontally. From this result, it was assumed that numerous arteries proliferated to the eburnated area and to around the cyst for repairing reaction, but that these were damaged by mechanical stress.     

Selective medical circumflex femoral arteriography in idiopathic ischemic necrosis of the femoral head in adults (author's transl)]

It is generally accepted that the medial circumflex femoral artery nourishes about two-thirds to four-fifths of the femoral head. In order to study the arteries in the idiopathic ischemic necrosis of the femoral head in adults, selective medial circumflex femoral arteriography was performed on 24 affected hips and 14 normal hips. This method enabled the better visualization of the medial circumflex femoral arterial system than the conventional femoral or internal iliac arteriography. The affected hips showed similar vascular patterns compared to normal hips. Anastomoses between the ascending branch or the medial circumflex femoral artery and the gluteal arteries, however, were rarely found in the affected hips. In the affected hips, various pathologic changes were demonstrated angiographically mainly in the portion of the ascending branch and the retinacular arteries. The existence of some degree of vascular insufficiency of the femoral head was assumed. However, complete occlusion of the medial circumflex femoral artery and its main branches that might cause head necrosis was seldom observed.     

应用选择性血管造影技术评价股骨颈骨折后股骨头血供情况及其对临床治疗的指导作用

目的探讨应用选择性血管造影（digital subtraction angiography,DSA）评价股骨颈骨折后早期股骨头血液循环损伤情况,以指导临床治疗。方法采用DSA对25例单侧股骨颈骨折的髋部进行旋股动脉及支持带动脉造影,按DSA结果分型,分别为Ⅰ、Ⅱ、Ⅲ型,以了解各型病例术前、术后的股骨头血供。结果 DSAⅠ、Ⅱ型病例无股骨头坏死,DSAⅢ型病例均出现股骨头坏死。结论 DSA可为股骨颈骨折的治疗提供更多、更有力的临床依据。     

The surgical anatomy of the blood supply to the femoral head: description of the anastomosis between the medial femoral circumflex and inferior gluteal arteries at the hip

The inferior gluteal artery is described in standard anatomy textbooks as contributing to the blood supply of the hip through an anastomosis with the medial femoral circumflex artery. The site(s) of the anastomosis has not been described previously. We undertook an injection study to define the anastomotic connections between these two arteries and to determine whether the inferior gluteal artery could supply the lateral epiphyseal arteries alone. From eight fresh-frozen cadaver pelvic specimens we were able to inject the vessels in 14 hips with latex moulding compound through either the medial femoral circumflex artery or the inferior gluteal artery. Injected vessels around the hip were then carefully exposed and documented photographically. In seven of the eight specimens a clear anastomosis was shown between the two arteries adjacent to the tendon of obturator externus. The terminal vessel arising from this anastomosis was noted to pass directly beneath the posterior capsule of the hip before ascending the superior aspect of the femoral neck and terminating in the lateral epiphyseal vessels. At no point was the terminal vessel found between the capsule and the conjoined tendon. The medial femoral circumflex artery receives a direct supply from the inferior gluteal artery immediately before passing beneath the capsule of the hip. Detailed knowledge of this anatomy may help to explain the development of avascular necrosis after hip trauma, as well as to allow additional safe surgical exposure of the femoral neck and head.