THE KNEE-JOINT 295 



In flexion the ligament um patellae and anterior portion of the capsule are on the stretch; 

 so also is the posterior crucial in extreme flexion, though it is not quite tight in the semiflexed 

 state of the joint. All the other ligaments are relaxed (fig. 325, C, D), although the relaxation 

 of the anterior crucial ligament is sUght in extreme flexion (fig. 327). Flexion is only checked 

 during Ufe by the contact of the soft parts, i. e., the calf with the back of the thigh. 



Rotation medially is checked by the anterior crucial hgament; the collateral ligaments 

 being loose. 



Rotation laterally is checked by the collateral ligaments; the crucial ligaments have no 

 controlling effect on it, as they are untwisted by it. 



Sliding movements are checked by the crucial and collateral ligaments — sliding forward 

 especially by the anterior, and sliding backward by the posterior crucial. 



Muscles which act upon the knee-joint. — Flexors. — Biceps, semimembranosus, semiten- 

 dinosus, sartorius, gastrocnemius, plantaris, and popUteus. Extensor. — Quadriceps extensor. 

 Medial Rotators. — Sartorius, gracilis, semitendinosus, semimembranosus, popliteus. Lateral 

 Rotator. — Biceps. 



3. THE TIBIO-FIBULAR UNION 



The fibula is connected with the tibia throughout its length by an interosseous 

 membrane, and at the upper and lower extremities by means of two joints. 

 Very little movement is permitted between the two bones. 



(a) The superior tibio-fibular joint. 

 (6) The middle tibio-fibular union. 

 (c) The inferior tibio-fibular joint. 

 (a) The Superior Tibio-fibular Joint 



Class. — Diarthrosis. Subdivision. — Arthrodia. 



The superior tibio-fibular joint is about 6 mm.(| in.) below, and quite distinct 

 from, the knee at its upper and anterior part; but at its posterior and superior 

 aspect, where the border of the lateral condyle of the tibia is bevelled by the pop- 

 liteus muscle, the joint is in the closest proximity to the bursa beneath the tendon 

 of that muscle, and is only separated from the knee-joint by a thin septum of 

 areolar tissue. There is often a communication between the synovial cavities of 

 the two joints. The ligaments uniting the bones are: — 



Articular capsule. Anterior tibio-fibular. 



Posterior tibio-fibular. 



The articular capsule is a well-marked fibro-areolar structure; it is attached 

 close round the articular margins of the tibia and fibula. In front it is shut off 

 completely from the knee-joint by the capsule of the knee and the coronary liga- 

 ment; but behind, it is often very thin, and may communicate with the bursa 

 under the popliteus tendon. 



The anterior tibio-fibular (capitular) ligament (fig. 326) consists of a few fibres 

 which pass upward and medially from the fibula to the tibia. It lies beneath the 

 anterior portion of the tendon of the biceps. 



The posterior tibio-fibular (capitular) ligament (fig. 317) consists of a few fibres 

 which pass upward and medially between the adjacent bones, from the head of 

 the fibula to the lateral condyle of the tibia. 



The superior interosseous ligament consists of a mass of dense yeUow fibroareolar tissue, 

 binding the opposed surfaces of the bones together for 2 cm. (f in.) below the articular facets. 

 It is continuous with the interosseous membrane along the tibia. 



The biceps tendon is divided by the fibular collateral ligament of the knee; of the two 

 divisions the anterior is by far the stronger, and is inserted into the lateral condyle of the tibia 

 as well as to the front of the head of the fibula, and thus the muscle, acting on both bones, tends 

 to brace them more tightly together; indeed, it holds the bones strongly together after all other 

 connections have been severed. 



The synovial membrane which lines the joint sometimes communicates with the knee-joint 

 through the bursa beneath the popUteus tendon. 



The arterial supply is from the inferior lateral articular and recurrent tibial arteries. 



The nerve-supply is from the inferior lateral articular, and also from the recurrent branch 

 of the common peroneal. 



Relations. — In front, the upper ends of the tibialis anterior, the extensor digitorum longus, 

 and the peroneus longus. Behind, the tendon of the popliteus overlapped by the lateral head 

 of the gastrocnemius. Laterally, the biceps tendon and the common peroneal nerve. Below 

 and medially, the anterior tibial vessels. 



The movements are but slight, and consist merely of a gliding of the two bones upon each 

 other. The joint is so constructed that the fibula gives some support to the tibia in transmitting 



