[Reprinted from the Transactions of the American Orthopedic Association, September, 1893.] ETIOLOGY OF THE DEFORMITIES OCCURRING IN KNEE-JOINT DISEASE. a. M. PHELPS, NEW YORK* Propositions : 1. In diseases of the condyles of the femur or the head of the tibia, the leg always assumes a flexed position to a greater or less extent. 2. After the limb flexes the foot rotates outward, and rotation increases with flexion. 3. In diseases confined to the patella the limb never flexes. 4. In disease of the synovial sac, or fibrous capsule, anteriorly unattended with diseases of the condyles-cartilage, lateral, or crucial ligaments, the limb remains straight. In diseases of the entire joint, including the cartilages, the leg always flexes, whether there is fluid present or not. I must qualify these propositions by saying that certain patho- logical changes which may have taken place, may modify these deformities. But such exceptional deformities are always easily accounted for, as, for instance, that seen in Charcot's disease, or in cases attended by complete destruction of either condyle or either side of the tibia. My observations have been made in a large number of cases upon which I have operated in the Post-Graduate and City Hospitals, New York City, and the Mary Fletcher Hos- pital, Burlington, Vermont, and I found that the foregoing propo- sitions were correct, with an occasional exception, as already noted. Many German and English experimenters have tried to account for flexion upon the fluid hypothesis. It is true that when the knee- joint is forcibly injected it will flex slightly, to give the greatest possible capacity to the capsule, but this is insufficient to explain the deformities. 2 DEFORMITIES IN KNEE-JOINT DISEASE. Barwell does not attempt to explain them, but says (Barwell, p. 106 Wood's Library, 1881), "It is true that the flexors are probably in all limbs stronger than extensors, but in fact a mere examination will show that on the flexor side muscles are rigid, and on the oppo- site side flaccid. Our knowledge is as yet insufficient to account for this phenomenon." The fluid hypothesis is wrong-why ? 1. Because by far the largest per cent, of knee-joint diseases are unattended by fluid effusions. Still the same picture of deformity is seen as in those cases attended by large effusions. 2. Cases of disease, extra-capsular, located in the epiphysis of the femur, or in the head of the tibia in which the joint was not found involved at the time of aspiration, presented the same pic- ture of deformity. 3. Large serous effusions, from synovitis or other causes, are fre- quently unattended with flexion. 4. After the joint is evacuated in large effusions the limb should again assume the straight position, but it does not. These are the chief and valid reasons why the fluid hypothesis is incorrect. The statement of Barwell, just quoted, is incorrect. I have care- fully weighed the muscles acting upon the leg, and find that the flexors weigh eight pounds and the extensors fourteen pounds in the subject examined. The quality of fibre of these muscles being equal, and other things taken into consideration, the extensors would be stronger than the flexors, in the proportion of fourteen to eight, while the limb is in the straight position, as neither group would have the advantage of leverage. Experiments to Demonstrate the Relative Strength of Each Group. Experiment I. A man was strapped to a table, the popliteal space at the end of the table and leg extending over. He could sustain 136 pounds suspended from his foot. Turned on his face, the patella at the edge of the table and limb extended, he could now only sustain 36 pounds suspended from the heel. These results correspond very closely to similar ones attained by Haughton, of Dublin. (See Haughton's Animal Mechanics.') A. M. PHELPS. 3 Experiment II. Subject standing, right leg flexed to right angle, he could hold suspended from heel 90 pounds. In other words, the flexor group were 55 pounds stronger when the leg was flexed than when straight. Experiment III. Subjects standing against bar which crossed the legs at right angles behind at the popliteal spaces, the left toe of foot against a spike in the floor to prevent slipping. A strap around ankle of left leg adjusted to spring scales, which were pulled upon from behind, showed a resistance of the extensor group of muscles of 240 pounds. Same subject was strapped on his back, leg hanging at right angles over the edge of the table. The same scales were now pulled upon under the table, and it was found that a pull of 80 pounds would flex the leg still further, a difference of 150 pounds of resist- ance in the quadriceps group of muscles between the leg flexed and extended. Then we have this formula for extensor and flexor group: 1. Flexors, first experiment, 35 pounds. Extensors, same experiment, 136 pounds. Difference of power of each operating with equal ad- vantage, = 90 pounds. 2. Flexors, same experiment, leg flexed, greatest advantage of flexors, 90 pounds. Extensors, leg straight, greatest possible advantage for ex- tensors, = 240 pounds. Experiment III. Difference, = 150 pounds. Difference in favor of flexor, limb straight or flexed, 55 pounds. Difference in power of extensors, limb flexed or straight, 150 pounds. This proves that the extensors are stronger than the flexors, the proportion being 240 to 90, the limb being straight to give ex- tensors the greatest advantage, and flexed to give the flexors a similar advantage. The limb when flexed, so modifies the strength of these groups as to make the proportion in favor of the flexors as 90 is to 80. The extensors lose in power as the limb flexes, while the flexors increase in power in about the same proportion. We all remember the futile effort of one boy to bend the other's leg by putting his 4 DEFORMITIES IN KNEE-JOINT DISEASE. knee in the popliteal space, and grasping the foot, the other boy on his face. And again, sitting on a fence while hunting, the toes under or behind a rail, one can easily lower himself backward until the head is on the ground, and can quite easily again resume the upright position. The power exerted by the quadriceps group of muscles in such a case, acting as a pulley over the end of the femur, raising a weight of 150 pounds on the end of a lever (the femora) of nearly two feet, must be enormous, amounting to hundreds'of pounds. We will now examine a knee-joint. It is a hinge which, when- in the straight position is firmly fixed, owing to the tension of the lateral and crucial ligaments. This forces the articular surfaces firmly together and prevents lateral motion. The leg flexed, there is lateral motion of the joint, which increases as the leg flexes, and not only lateral but rotary motion. This is due to the relaxation of the crucial and lateral ligaments by flexion. Another fact, the patella and a portion of the capsular, anteriorly receives its nerve supply from the obturator, and possibly from the anterior crural. The other portion of the joint is supplied from the great sciatic. The great sciatic supplies the flexor group, while the obdurator and anterior crural supplies the extensor group. A clinical fact is, that when the entire joint is attacked with acute inflammation, all the muscles surrounding it are affected by spasm. Still flexion rapidly takes place, whereas disease of the condyles always produces great spasm and rapid atrophy of the flexors, while the extensors remain quiescent. Diseases limited to the patella produce spasm and atrophy of the quadriceps extensor femoris, and the limb remains straight. Understanding that the extensors are stronger than the flexors ; that the muscles about the joint are equally affected by spasm when the entire joint is diseased, why does not the leg remain straight ? Before attempting to answer the question, I desire to call your attention to these diagrams. Fig. 1, a lever with a joint ata. Both hands pulling 10 pounds, the bar would not flex. But in Fig. 2, the bar being flexed at a right angle, puts one string on the lever and the other around the pulley. This gives to the string acting on the lever a tremendous advantage, quite easily calculated. This is exactly what takes place when the leg flexes, and ex- A. M. PHELPS. 5 plains the difference in power as illustrated by my experiments. The same mechanics applies to the anatomy of the leg, roughly represented by a rude pencilling (Fig. 3). A photograph of one of Fig. 1. Fig. 2. my dissections shows the biceps acting on the head of the fibula, the limb straight, and also the extensors and patella. Fig. 5, the same in flexion: biceps acting on a lever, and extensor over a pulley Fig. 3. (head of the femur). The muscles being dried, do not give an accu- rate idea of their position while contracted, as they fall in curves on flexion. Fig. 6. The same leg straight, showing inside flexors acting on the tibia. Fig. 7. The same leg flexed. It will be seen that 6 DEFORMITIES IN KNEE-JOINT DISEASE. these flexors increase in power as the leg flexes, by being placed on a lever, and the extensors decrease by being wound around the head of the femur. Q. Why does the leg flex when the entire joint is diseased, and all muscles are equally affected by spasm 2 A. When the leg is straight the tension upon the lateral and crucial ligaments produce great pressure between the articular carti- Fig. 4. Fig. 5. lage. This produces great pain, and the patient to relieve this flexes the leg to relax these ligaments. This at once relieves intra-articular pressure. But the flexion of the leg has put the flexors on a lever and the extensors on a pulley. The flexion now having the advant- age, will continue to flex the leg. Q. Why does the leg rotate outward 2 A. Flexion by relaxing the lateral and crucial ligaments permits free lateral and rotary motions at the knee-joint. The biceps inserted A. M. PHELPS. 7 into the head of the fibula, and being the stronger of all the flexor group, and having the advantages of direction and leverage, rotates the leg outward. Q. Why does the leg never flex in diseases of the patella alone? A. Because the reflexes from the area of disease are transmitted through the obturator and ant. crural nerves, which supply only the quadriceps. A voluntary effort to relieve pain is also present. Fig. 6. Fig. 7. Q. Why are the extensors relaxed in disease confined to the head of the tibia and condyles of the femur posteriorly? A. The reflexes from the area of disease are transmitted through the great sciatic, which nerve supplies the flexors. Exceptional de- formities are produced from pathological destruction of bone or soft parts. Conclusions.-Typical deformities are produced by change of leverage and action of muscles due to 8 DEFORMITIES IN KNEE-JOINT DISEASE. 1. A voluntary effort to relieve pressure and pain. 2. Involuntary spasm and contraction of muscles, which increases the deformity by advantage of leverage due to flexion. 3. Nervous irritation of groups of muscles due to localized lesion in or about the joint. 4. Exceptional deformities are produced by pathological destruc- tion of bone or soft parts. 5. Outward rotation of the leg is produced by spasmodic con- traction of the biceps after flexion has taken place. Flexion allows lateral and rotary motion at the joint.