ARTICULATIONS BETWEEN THE TIBIA AND FIBULA 



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groove rests on the articular margin in front of the lateral process of the tibial intercondyloid 

 eminence. Into the groove on the medial condyle is fitted the anterior part of the medial meniscus, 

 while the anterior cruciate ligament and the articular margin in front of the medial process of 

 the tibial intercondyloid eminence are received into the forepart of the intercondyloid fossa of 

 the femur. This third phase by which all these parts are brought into accurate apposition is 

 known as the "screwing home," or locking movement of the joint. 



The complete movement of flexion is the converse of that described above, and is therefore 

 preceded by an external rotation of the femur which unlocks the extended joint. 



The axes around which the movements of flexion and extension take place are not precisely 

 at right angles to either bone; in flexion, the femur and tibia are in the same plane, but in exten- 

 sion the one bone forms an angle, opening lateralward with the other. 



In addition to the rotatory movements associated with the completion of extension and the 

 initiation of flexion, rotation inward or outward can be effected when the joint is partially flexed; 

 these movements take place mainly between the tibia and the menisci, and are freest when the 

 leg is bent at right angles with the thigh. 



Movements of Patella. The articular surface of the patella is indistinctly divided into seven 

 facets upper, middle, and lower horizontal pairs, and a medial perpendicular facet (Fig. 353). 

 When the knee is forcibly flexed, the medial perpendicular 

 facet is in contact with the semilunar surface on the lateral 

 part of the medial condyle; this semilunar surface is a pro- 

 longation backward of the medial part of the patellar surface. 

 As the leg is carried from the flexed to the extended position, 

 first the highest pair, then the middle pair, and lastly the 

 lowest pair of horizontal facets is successively brought into 

 contact with the patellar surface of the femur. In the ex- 

 tended position, when the Quadriceps femoris is relaxed, the 

 patella lies loosely on the front of the lower end of the femur. 



During flexion, the ligamentum patellae is put upon 

 the stretch, and in extreme flexion the posterior cruciate 

 ligament, the oblique popliteal, and collateral ligaments, 

 and, to a slight extent, the anterior cruciate ligament, 

 are relaxed. Flexion is checked during life by the contact 

 of the leg with the thigh. When the knee-joint is fully 

 extended the oblique popliteal and collateral ligaments, 



the anterior cruciate ligament, and the posterior cruciate ligament, are rendered tense; 

 in the act of extending the knee, the ligamentum patellae is tightened by the Quadriceps 

 femoris, but in full extension with the heel supported it is relaxed. Rotation inward is checked 

 by the anterior cruciate ligament; rotation outward tends to uncross and relax the cruciate liga- 

 ments, but is checked by the tibial collateral ligament. The main function of the cruciate liga- 

 ment is to act as a direct bond between the tibia and femur and to prevent the former bone from 

 being carried too far backward or forward. They also assist the collateral ligaments in resisting 

 any bending of the joint to either side. The menisci are intended, as it seems, to adapt the surfaces 

 of the tibia to the shape of the femoral condyles to a certain extent, so as to fill up the intervals 

 which would otherwise be left in the varying positions of the joint, and to obviate the jars which 

 would be so frequently transmitted up the limb in jumping or by falls on the feet; also to permit 

 of the two varieties of motion, flexion and extension, and rotation, as explained above. The 

 patella is a great defence to the front of the knee-joint, and distributes upon a large and tolerably 

 even surface, during kneeling, the pressure which would otherwise fall upon the prominent ridges 

 of the condyles; it also affords leverage to the Quadriceps femoris. 



When standing erect in the attitude of "attention," the weight of the body falls in front of 

 a line carried across the centers of the knee-joints, and therefore tends to produce overextension 

 of the articulations; this, however, is prevented by the tension of the anterior cruciate, oblique 

 popliteal, and collateral ligaments. 



Extension of the leg on the thigh is performed by the Quadriceps temoris; flexion by the Biceps 

 femoris, Semitendinosus, and Semimembranosus, assisted by the Gracilis, Sartorius, Gastroc- 

 nemius, Popliteus, and Plantaris. Rotation outward is effected by the Biceps femoris, and rota- 

 tion inward by the Popliteus, Semitendinosus, and, to a slight extent, the Semimembranosus, the 

 Sartorius, and the Gracilis. The Popliteus comes into action especially at the commencement 

 of the movement of flexion of the knee; by its contraction the leg is rotated inward, or, if the 

 tibia be fixed, the thigh is rotated outward, and the knee-joint is unlocked. 



FIQ. 353. Posterior surface of the 

 right patella, showing diagrammatically 

 the areas of contact with the femur in 

 different positions of the knee. 



III. Articulations between the Tibia and Fibula. 



. The articulations between the tibia and fibula are effected by ligaments which 

 connect the extremities and bodies of the bones. The ligaments may consequently 



