THE KNEE 1449 



upper surfaces to their free borders, and then along their under surfaces to the 

 tibia. Between the lateral of these and the upper and back part of the tibia is a 

 prolongation of the synovial membrane to facilitate the play of the popliteus 

 tendon. 



Finally, amid the complications of this synovial membrane, its communication with some 

 of the bursae mentioned below, and occasionally with the superior tibio-fibular joint, is to be 

 borne in mind. In effusion the bony prominences are obliterated, and the patella 'floats.' 

 The knee-joint is easily opened by free lateral incisions lying midway between the margins of 

 the patella and the tuberosities of the condyles, drainage-tubes being passed so as to meet above 

 the patella. The above-mentioned complications of the synovial membrane show that such 

 drainage wiU be often inadequate. By passing a director to the back of the joint and cutting 

 down upon it carefully from the popUteal space, better drainage wiU be given, but opening the 

 joint by an anterior flap is needed where the above fail, and, even then, cleansing of the numerous 

 deep recesses is obviously difficult. 



Structures on the head of the tibia. — From before backward these are: — 

 (1) Transverse ligament. (2) Anterior end of medial meniscus (fibro-cartilage). 

 (3) Lower attachment of anterior crucial. (4) Anterior end of lateral meniscus 

 blending with (3). (5) Posterior extremity of lateral meniscus giving off a strong 

 process to posterior crucial. (6) Posterior extremity of medial meniscus. (7) 

 Posterior crucial ligament. Menisci. — These serve as buffer-bonds and cushions 

 between the contiguous bones. The more frequent displacement of the medial is 

 explained by — (a) its greater fixity, and, therefore, its feeling strains more. Thus, 

 in addition to weaker attachments to the coronary and transverse ligaments, it is 

 connected all along its convex border wdth the inside of the capsule, and strongly 

 with the tibial collateral ligament. The lateral meniscus, on the other hand, is 

 more weakly attached to the capsule, especially opposite to the popliteus tendon, 

 and has no tie to the fibular collateral ligament. (6) When, in the erect position, 

 the knee-joint is rotated laterally and slightly flexed, a common position, an 

 especial strain is thrown upon the very important tibial collateral ligament, and 

 from the above-mentioned connection, on the medial meniscus also. 



Position of knee-joint in disease. — In inflammatory effusion, the position which best 

 accommodates the collection of fluid is one of moderate flexion, the ligaments being now mainly 

 relaxed. Later on, when the ligaments are softened, the hamstrings obstinately displace the 

 leg backward, the tibia being rotated laterally by the biceps. The antero-posterior displacement 

 is always more marked than the lateral. In straightening an anchylosed joint, the resistance of 

 the shortened lateral, crucial, and posterior ligaments, and the facility with which a softened 

 upper epiphysial line of the tibia may give way, must never be forgotten. Erasion and excision. 

 — The extent and compHcations of the synovial membrane render attention to the following 

 points imperative: — (1) Free exposure of the joint usually by an anterior curved incision, the 

 medial extremity of which must not damage the great saphenous vein. (2) The extent of the 

 pouch under the quadriceps, it may be for 5 cm. (2 in.) above the patella, and the lateral recesses 

 under the vasti. The pouches at the back of the joint are far more difficult to deal with, viz., 

 the partial covering of the posterior crucial ligament, the proximity of the popliteal artery, 

 the pouches in relation to the popliteus, gastrocnemii, and back of the femoral condyles. In 

 erasion, the cartilage and bone, where diseased, are removed with a gouge. Owing to the 

 removal, in addition to the synovial membrane, of the fibro-cartilages, and crucial ligaments, 

 and the damage to lateral and patellar ligaments, there is a most obstinate tendency to flexion 

 afterward. In excision, to avoid injury to the epiphj^sis, the section of the femur should not 

 pass higher than through the upper third of the trochlear surface. Of the tibia, only 12 mm. 

 (I in.) should be removed. 



Genu valgum. — Here the natural angle at which the femur inchnes medially to the tibia 

 is increased. As shown by the late v. Mikulicz, this is due to an abnormal growth downward 

 of the medial part of the femoral diaphysis, the epiphysial line being gradually altered from 

 one at right angles to the shaft to one which runs obliquely from without downward and medially. 

 The femur is not only elongated on its medial side, but bent at its lower end, the concavity of 

 the curve being lateral. Other changes have to be remembered. Pes valgus very commonly 

 coexists, and in the tibia there may be a compensatory curve, the concavitj^ being medial, 

 in the lower third, or an analogous alteration in the line of the upper epiphysis may be present, 

 its direction being no longer at a right angle with the shaft, but obUque. In Sir W. Macewen's 

 supra-condyloid osteotomy, a longitudinal incision, about 3.7 cm. (I5 in.) long is made where 

 the following lines meet, viz., one transverse, a finger's breadth above the upper margin of the 

 lateral condyle, and one longitudinal, 1.2 cm. {\ in.) in front of the adductor magnus tendon. 

 The bone is divided in front of the genu suprema and above the superior medial articular artery, 

 above the epiphysial fine and behind the upward extension of the synovial membrane under the 

 quadriceps. 



The folloT\dng bursae about the knee-joint must be remembered. Some, it 

 will be seen, are much more constant than others: — 



