[ 61 ] THE VASCULARIZATION OF THE RABBIT FEMUR AND TIBIOFIBULA By M. BROOKES AND R. G. HARRISON Department of Anatomy, University of Liverpool Previous investigations of the vascularization of bone have largely centred on the respective contributions of arterial blood to long bones derived from the periosteal network, the principal nutrient artery and arteries entering a bone at its extremities. The older authors paid much attention to the periosteal network (e.g., Barkow 1868; Langer, 1876), and Testut (1880) gave it primary functional significance. In more recent times this has been disputed. On the basis of injection experiments made as a preliminary to perfusion studies, Drinker, Drinker & Lund (1922) thought fit to neglect it altogether, while Johnson (1927) granted it only subsidiary impor- tance. Their views are supported by Harris (1933), Kistler (1984), Wood-Jones (1946), Marneffe (1951), Watson-Jones (1952) and Laing (1953) who all give the principal nutrient artery a pre-eminent place in the schema of bone vascularization. Gray (1954), Testut & Latarjet (1948), Cunningham (1951) and Ham (1932) allow a free anastomosis between the terminals of this artery and the periosteal system, while only rarely is it stated to be solely of haemopoietic function (Houang, 1934). The arteries entering the extremities of a long bone (Hunter, 1743) are generally given a supporting role in bone nutrition. With the exception of arteries entering the human femoral head and neck, there are few works in which these arteries are the subject of exact anatomical description (Marneffe, 1951; Fracassi, 1954). If great emphasis has been placed on the arterial supply of bone, venous drainage has attracted little attention. Langer (1876) first pointed out that there are more veins leaving bone than entering arterial twigs. Lamas, Amado & da Costa (1946) have remarked upon the large 'venous lakes' existing in the cancellous bone at the extremities of long bone, while Marneffe (1951) describes a central venous channel extending the length of the medulla. In this connexion it is to be recalled that both Rustizky (1872) and Bizzozero (1869) observed a central medullary vein, the former in frogs, the latter in a rabbit tibia. In view of the inadequacy of accounts of bone vascularization, of the rabbit in particular (Krause, 1884), it was decided to undertake an investigation of the blood supply of the rabbit femur and tibiofibula. MATERIALS AND METHODS Twenty-one fully grown rabbits were used, average weight 3 kg. Each was sacri- ficed by intravenous injection of Nembutal into an ear vein, and injected intravas- cularly with varying dilutions of Micropaque (Damancy and Company Ltd.), a 50 % suspension of barium sulphate. After fixation in 10 % formol saline solution, Micropaque is quite hard and does not run. Because of its white colour, the part could easily be dissected with the aid of a binocular microscope to determine every 62 M. Brookes and R. G. Harrison vessel that pierced bone, its source, and site of penetration. Other specimens were injected with thorotrast and fixed in 70 % alcohol. The arterial system of the hind-limb was filled via the abdominal aorta; venous filling was effected through the external iliac, lateral circumflex femoral, and long saphenous veins. A polythene cannula was used for arterial injection, but hypo- dermic needles are more suitable for veins, since they can be used to pierce the venous valves obstructing the retrograde pathway. Following dissection, the individual bones were stripped of all extra-osseous tissue including periosteum (Delkeskamp, 1915; Trueta & Harrison, 1953), to permit clear visualization of intra-osseous vessels alone, and to avoid confusion arising from the superimposition of vessels in soft tissues. This procedure did not remove periosteal arterial twigs from the cortex since, as will be shown later, minute vessels leaving the cortex to enter the periosteum are still demonstrable in profusion. Decalcification for 5 days in a mixture of 5 % formol saline and 5 % nitric acid followed. The bone was then radiographed on Kodaline film, and selected specimens were subjected to microradiography using Kodak maximum resolution plates, and a microfocus radiographic unit incorporating the Ehrenberg and Spear tube. GROSS OBSERVATIONS Femur: arterial supply (Text-figs. 1 and 2) The medial circumflex femoral artery has a branch which passes laterally on the hip joint to terminate as a contribution to the trochanteric anastomosis. From it, anterior cervical arteries descend into the femoral neck. Another branch of the same artery concerned in the nutrition of the femur is the artery of the trochanteric fossa which passes downwards and laterally behind the neck to sink into a foramen in the depths of the fossa. It gives off ascending branches associated with the posterior aspects of the lesser trochanter and femoral neck, and the greater trochanter respectively, which thereby receive nutrient twigs. There are no nutrient arteries serving the third trochanter. The posterior subcapital artery arises from the artery of the trochanteric fossa or directly from the medial circumflex femoral, and sinks into a foramen just below the rim of the head. From it posterior cervical arteries descend into the neck. Besides anterior and posterior cervical arteries the neck of the femur is pierced by numerous small vessels derived from the anastomosis in the trochanteric fossa. This anastomosis is formed by branches of the medial and lateral circumflex femoral arteries and a vessel of small calibre which runs on obturator internus, the trochan- teric branch of the internal pudendal artery. The principal nutrient artery of the rabbit femur springs from the root of the lateral circumflex femoral artery. In one specimen it sprang directly from the femoral, distal to the lateral circumflex femoral artery. It passes downwards for 2 cm. before disappearing in the nutrient foramen situated on the medial surface of the shaft just below the lesser trochanter. It has a branch which provides twigs to the periosteum of the lesser trochanter and the substance of pectineus, and continues downwards in close association with the insertions of add. brevis, longus et magnus. It anastomoses below with the A. suprema genu. The vascularization of the rabbit femur and tibiofibula 63 The A. suprema genu divides into articular and muscular branches. The former descends medial to the lower end of the femur. It gives off a superior medial genicu- lar artery which forms a loop running round the periphery of the medial aspect of the inferior extremity of the bone. Anastomotic channels traverse the area enclosed n.i.-- --------- f a. a.a.f. - g.t.a.- I.t. m.c.f.a. t- - a.a.f. p.s.a.- I.c.f.- P -- M.C.f a. -------- p.s.a. --------- p.c.a. c.a.c.f. a.t.f. ~-~~~~|- a.t.f. -- t.i.p.a a.s.g. su.m. i.a. -t-- a.i.a. __. i.m.g.a. Text-fig. 1. Drawing of arterial supply of the Text-fig. 2. Drawing of arterial supply of the rabbit femur; anterior aspect. The following rabbit femur; posterior aspect. key applies to Text-figs. 1 and 2: m.c.f.a. medial circumflex femoral artery a.a.f. artery to acetabular fossa n.i. nutrient to ilium a.b. articular branch p.c.a. posterior cervical arteries a.c.a. anterior cervical arteries pop.a. popliteal artery a.i.a. anterior intercondylar artery p.s.a. posterior subeapital artery a.s.g. arteria suprema genu sap.a. saphenous artery a.t.f. artery to trochanteric fossa s.l.g.a. superior lateral genicular artery an.t.t. anastomosis round third trochanter s.m.g.a. superior medial genicular artery c.a.c.f. circulus arteriosus capitis femoris s.p.a. suprapatellar arteries f.a. femoral artery su.l. lateral supracondylar artery g.t.a. arteries to greater trochanter su.m. medial supracondylar artery i.a. intercondylar artery t.an. trochanteric anastomosis i.m.g.a. inferior medial genicular artery t.i.p.a. trochanteric branchof internalpudendal l.c.f. lateral circumflex femoral artery artery. l.t. ligamentum teres 64 M. Brookes and R. G. Harrison by the loop. From this plexiform arrangement nutrient twigs are given off which are radially disposed in relation to the circle whose centre is the medial epicondyle of the femur. Anteriorly, on the suprapatellar surface of the femur where descending nutrients pierce the anterior surface of the metaphysis, the medial condylar loop joins its fellow from the other side. This lateral condylar loop is formed by the condylar branch of the superior lateral genicular artery, which springs from the femoral about 1 cm. above the condyles, and divides into muscular and condylar branches. The popliteal artery gives origin to medial and lateral supracondylar arteries, which pass outwards supplying fine nutrient twigs to the posterior face of the in- ferior metaphysis, and to the condyles. They join the medial and lateral condylar loops. From the popliteal or anterior tibial artery, a large middle genicular artery arises, which pierces the joint capsule, passes above the point of crossing of the cruciate ligaments, and sinks into a foramen in the anterior wall of the intercondylar notch. Femur: Venous drainage A single vena comitans accompanies each artery. At the surface of the bone at either end, the nutrient venous radicles are more numerous than the arterial, and some occupy their own canals, not sharing the space with an incoming artery. A simple circulus venosus is formed on the superficial surface of each condyle. The femoral intercondylar vein joins the tibial intercondylar veins to drain into the anterior tibial vein. Tibiofibula: arterial supply (Text-figs. 3 and 4) The superior tibial epiphysis is pierced in the prespinal portion of the intercondy- lar ridge by two anterior tibial intercondylar arteries, derived from the articular branch of the A.