THE POSITION OF THE NUTRIENT FORAMEN AND DIRECTION OF THE NUTRIENT CANAL IN THE LONG BONES OF THE MADDER-FED PIG BY CARRICK G. PAYTON, M.D. Lecturer and Senior Demonstrator in Anatomy, University of Birmingham INTRODUCTION THE external opening of the nutrient canal, usually referred to as the nutrient foramen, has a particular position and the canal a certain direction constant for each bone. Because of confusion of these two points in the literature on the subject, I wish to stress the fact that the position of the foramen and the direction of the canal are two distinct and separate phenomena of the nutrient artery, and may be the result of independent mechanisms. The literature available is small in amount, deals mainly with direction of the canal, and gives the impression that investigators have assumed that both phenomena are caused by this direction. In this account the position of the nutrient foramen and the direction ofthe canal will be dealt with separately. Throughout this paper use has been made of the data contained in two previous papers on the growth of the diaphyses and epiphyses of the long bones in the madder-fed pig (1, 2). MATERIAL AND METHODS Observations and measurements are made from the limb bones of a dozen madder-fed pigs used in my recent publication on diaphysial growth(1). The age of the pigs varied from 80 to 587 days. These pigs had been treated by the "indirect madder method," whereby the madder is withheld for a period before killing, and consequently the new bone of this non-madder period shows up white against a background of maddered bone. Particulars of age, madder period and non-madder period are noted in Table I. Table I. Duration in days with and without madder feeding. Age at death Madder period Non-madder period Pig No. days days days 14 80 72 8 15 91 77 14 16 108 84 24 17 126 105 21 12 140 61 28 1 169 68 29 2 197 97 28 3 225 125 28 4 279 153 54 6 362 207 84 9 475 271 126 8 587 394 116 Position ofNutrient Foramen and Direction ofNutrient Canal 501 Longitudinal sections were cut through the long axes of the diaphyses and the plane of the section was chosen to pass through the nutrient foramen. HISTORY BWrard (3), almost 100 years ago, noticed that the direction of the nutrient canals in the human being was constant for a given bone. He noticed that in the upper limb the canals were directed towards the elbow and in the lower limb away from the knee. He advanced no theories concerning these observa- tions, but remarked that the nutrient artery entering the bone divided into two branches, ascending and descending, the branch continuing in the direction of the main artery was the larger, and therefore, because of the better blood supply, caused union to occur first of all between the diaphysis and epiphysis towards which it flows. Thus the canal is slanted towards that end at which the epiphysis is first united to the shaft. In this series of pig bones the direction of the nutrient canal has been noted and this is considered with regard to the end of the diaphysis which first unites with its epiphysis (Table II). Table II. The direction of the nutrient canal in relation to the end of the diaphysis which unites with its epiphysis first. In humerus canal directed away from distal. end ofdiaphysis which unites with its epiphysis first ,, radius ,, towards proximal ,. VP .. ,, ulna ,, towards proximal ,. .. .. femur ,, away from proximal ,. VP Pt tibia ,, towards distal ,. ., .. fibula ,, towards distal ,. .J. 9 It is to be noted from Table II that for the bones of the pig the humerus and femur disagree with Berard's statement. In contrast with Berard's idea, Humphry (4) demonstrated, by means of madder staining in the pig's bones, the unequal growth of the two ends of the diaphysis, and stated that the obliquity of the canal was not the cause but the effect of the unequal growth. This unequal growth at the two ends would cause an unequal drag on the periosteum which is fixed to the two ends of the bone. Humphry's dragging theory is disputed by Piollet(5), who states that in the human foetus the nutrient arteries are directed first perpendicularly to the bone's long axis and then later all proceed distally in the bone, while still later the arteries of the radius, ulna and femur change their direction, so that in the adult all the arteries are found directed away from the growing ends as the result of unequal growth of the diaphysis in which growth is peripheral, while growth of soft parts is interstitial. Thus both Humphry and Piollet associate the obliquity of the nutrient canal with the unequal growth of the diaphysis. In Table III the direction of the canal in respect to the greater growing end of the diaphysis is noted for this series of bones. 502 Carrick G. Payton Table III. To show the relation between the direction of the nutrient canal and the end of the diaphysis with the greater growth. In humerus canal directed proximally and proximal end of diaphysis is greater growing end radius ,, proximally ,, distal , . ulna ,, proximally ,, distal femur ,, distally ,, distal ,.9 pi- tibia ,, distally ,, proximal ,. .. fibula ,, distally ,, proximal ,. .. It is seen from Table III that the nutrient canals in the pig's humerus and femur are directed towards the end of the diaphysis with the greater growth, in contrast to Piollet's and Humphry's statements. Various authors, in addition to the foregoing, have supported (6) or dis- agreed (7) with these statements without, however, adding to our knowledge. The text-books of anatomy generally quote either 1Wrard's (8) orHumphry's and Piollet's (9) theories. A few of them remark that the reason for the obliquity seems obscure. Since the nutrient canals as observed in the long bones of the pig do not agree with any of the above theories, is it just possible that this apparent agreement for the human long bones is one of mere coincidence? GENERAL OBSERVATIONS In the pig's humerus the nutrient foramen is situated on the posterior surface near the junction of the middle and distal thirds of the shaft. The canal is directed proximally into the bone. The outer end of the canal comes into relation with the lower edge of a layer of new bone which is being laid down on the exterior of the posterior part of the shaft (fig. 1). It will be noticed that the nutrient canal of the humerus does not enter the shaft so obliquely as is the case in the other bones, because the canal is involved in a modelling process at the distal end of the diaphysis. It has been shown (l) that new bone is added to the distal end of the diaphysis and that most of this new bone is rapidly absorbed on the anterior and posterior aspects of this extremity to form the coronoid and olecranon fossae. Owing to the distal extremity growing downwards and forwards the olecranon fossa becomes the deeper of the two fossae and requires to be filled in on its proximal aspect to enable the shaft of the humerus to extend in a distal direction. Conse- quently a layer of new bone is found on the posterior part of the olecranon fossa extending proximally on the posterior surface of the shaft as far as the nutrient foramen. In this way the nutrient foramen is sandwiched between two edges of new bone-one, the distal edge of new bone added to the shaft, and the other, the proximal edge of new bone added to the olecranon fossa. This peculiar position of the canal between two layers of new bone in addition to lessening the obliquity of the canal may also modify any movement of the canal in respect to the layer of new bone round the shaft; but reference to this point is made later. In the radius the nutrient foramen is situated on the posterior surface of the shaft near the junction of the proximal and middle thirds. The canal is i . Fits. 3;. ltAl L. 4. I'iL. .5. Jg ja . Figs. 1-6 are respectively longitudinal sections cut through the nutrient canals of humeral, radial, ulnar, femoral, tibial and fibular diaphyses of Pig. No. 4. Age 279 days. The areas of bone unstained by madder are represented white and indicate new bone laid down during the non-madder period of 54 days. Bone stained by madder is black or stippled. 504 Carrick G. Payton directed proximally into the bone. The external end of the canal lies at the lower edge of new bone which is being added to the outside of the posterior part of the shaft (fig. 2). In the ulna the nutrient foramen is situated on the anterior surface of the shaft near the middle. The canal is directed proximally into the bone. The inner end of the canal lies in relation to the upper margin of new bone which is being added to the inside of the anterior part of the shaft (fig. 3). In the femur the nutrient foramen is situated on the anterior surface of the shaft near the junction of the proximal and middle thirds. The canal is directed distally into the bone. The outer end of the canal lies in relation to the proximal margin of new bone which is being added to the outside of the shaft (fig.