When the leg is extended it does not lie in the same line as the thigh, but, owing to the obliquity of the latter, forms an angle of about 170 with it. The patella is generally easily recognized, particularly when the limb is extended, its inner border being more prominent than the outer. In the extended position it is very mobile, and advantage may be taken of this to displace it sufficiently laterally to permit of examination of the outer edge of the external condyle and inner edge of the internal for evidences of lipping, which occurs in rheumatoid arthritis, etc. On either side of the patella, and between it and the femoral condyle, is a depression, which in stout persons may be obliterated by fat, which in the extended position, with the rectus relaxed, may be united to its neighbour by a shallow depression along the upper margin, the whole forming a horseshoe, called the peripatellar depression. Under this depression are situated the lateral and superior pouches of synovial membrane of the joint, and when these are distended from any cause, the depression is replaced by a swelling, roughly horseshoe in shape, which may obliterate the patellar outline. When the knee is flexed, the patella at first is rendered prominent, and then sinks deeply into the intercondyloid notch, where it becomes firmly fixed, protecting the articulation, and assisting the tubercle of the tibia to bear the weight of the body in kneeling. In this flexed position the upper portion of the trochlear surface of the femur can be palpated ; the condyles separate from the head of the tibia and become more distinct, and the ligamentum patella? is rendered tense. On the outer side of the knee the tendon of the biceps may be felt posteriorly, descending to be inserted into the head of the fìbula, which is about a finger's breadth below the articular margirtfof the tibia, and on a level with the prominent external tuberosity of the tibia. Into this latter is inserted the ilio-tibial band of fascia lata, which becomes very prominent when the knee is actively extended. Immediately in front of the biceps tendon, near its insertion, the upper part of the external lateral ligament of the knee may be felt when the limb is very slightly flexed.
The internal condyle of the femur is much more prominent than the external, and marking its upper limit, and the position of the epiphyseal line, is the adductor tubercle into which the tendon of the adductor magnus is inserted. Where any difficulty is experienced in finding the tubercle, the limb should be forcibly adducted, and the finger then run down along the prominent adductor tendon to the tubercle. The sartorius and the tendon of the gracilis, the former anterior, pass behind the internal condyle, and then curve forwards, to be inserted into the upper and inner surface of the shaft of the tibia. As they cross the joint the tendon of the semitendinosus lies close but posterior to them, the interspace being occupied by the long saphenous vein and nerve, and the superficial branch of the anastomotica magna.
The skin of the front of the knee is dense, while the subcutaneous tissue contains but little fat, and being lax permits of considerable movement of the skin when the knee is extended. This mobility assists in protecting the joint from various injuries, and is utilized in certain operations on the knee to render the line of incision very oblique by first pulling down the skin prior to incising it. Where the flexed knee is struck over the bone by a blunt instrument, a clean-cut wound may result. The front of the knee is supplied with blood by the anastomotic, four articular branches of the popliteal, and anterior tibial recurrent, and with nerves from the third lumbar segment ; and the fact that the joint is supplied by branches of the same vessels, and with nerves from the same spinal segment through the obturator nerve, is advanced by some as an argument in favour of the application oí blisters to the front of the knee in various joint affections. The superficial lymphatics lie on the inner side, accompanying the long saphenous vein,