Studying the bow posture in detail leads us first and most obviously to the knees. When the knee joint is extended (fig. 5.24) it is almost invulnerable to injury because all of its component parts fit together perfectly and protect the joint from torques and impacts from all directions. The flexed knee joint is another matter. Its internal and external supporting ligaments have to become loose to permit flexion, and any tension superimposed on the flexed joint, whether from extension, twisting, or even additional flexion, can make the joint vulnerable to injury.
Standing postures, even with the knees flexed, are rarely a problem. The knee joint is the largest and strongest joint in the body, and toting our weight around from place to place is its forte. Under ordinary circumstances it can support tremendous muscular stresses—hopping up and down a flight of stairs on one foot, running down a mountain, and for those who are prepared, jumping to the ground from heights of five feet or more. All of these activities require only moderate flexion, and the knee joint is made to order for them. The problem comes with yoga backward bending postures that flex the knee under unnatural circumstances.
The bow posture is a case in point. The beginning pose must start with a flexed knee joint which is then forced into extension from an awkward and unfamiliar prone posture. Indeed, it is hard to imagine a more unnatural or demanding role for this joint than to use it as the primary tool for lifting into the bow. The intermediate and advanced postures are not so much of a problem because they make more efficient use of the erector spinae muscles, the hamstrings, and the respiratory and pelvic diaphragms for coming up into the posture. They use knee extension merely to aid the lift, and they do so from a less completely flexed position than in the beginner's bow.
The two advanced cobra poses stress the knees in an entirely different way. We come into these postures with the knees straight., which does not stress them at all, but once the rest of the body is settled we can take the additional option of bending the knees and pulling the feet toward the r'gure 5.23. In this advanced how (the string of the bow is drawn to the rear at the junction °f the hands and the ankles), the lumbar region is extended 90° and the hips are hyperextended. The quadriceps femoris muscles are not nearly so important as in the beginner's how; they can "elp initiate coming up as an option, but they are not "iportant as prime movers for 'he final pose.
head. This increases tension on the quadriceps femoris muscles at the sam< time the joint ligaments start to become lax. Unfamiliar and disquieting sensations wai n us promptly to be wary, and only after much experienci will students not have misgivings about completing this last refinement o the cobra. To understand how the strongest joint in the body can be s vulnerable to injury, we must examine the anatomical components of th knee that often create problems. We'll begin with the menisci.
The two bones that stand in end-to-end apposition to one another in tl knee joints, the tibia and the femur, can withstand the repetitive shocks walking and running because they are well cushioned. The lower ends f the femurs (femoral condyles) and the upper ends of the tibias (tibi I condyles) are covered with thick layers of articular hyaline cartilage th t
femur medial head of gastrocnemius femur vastus lateralis quadriceps femoris tendon patella patellar tendon vastus medial is adductor magnus tendon medial (tibial) collateral ligament sartorius tendon gracilis tendon head libula semitendinosus tendon popiiteus tibia lateral (fibular) collateral ligament latera ead of ga: oc-nemiL
Figure 5.24. On the left is an anterior view of a superficial dissection of the ri> <' extended knee joint, and on the right is a posterior view (from Sappey).
5. RAtXBEKfíllW POSTURES loy have a slippery surface for permitting flexion and extension. In addition, donut-shaped wafers of fibrocartilage called the medial and lateral tnenisci (or medial and lateral semilunar cartilages), cushion the mating surfaces of the condyles (fig. 5.25). Torn menisci are difficult to treat because they have lost their blood supply by the time we reach our mid-20s, and if they are damaged after that time, usually in dance or athletics, they are essentially irreparable. This is why "torn cartilages" are greeted so apprehensively by adult athletes.
The menisci move freely during the course of flexion. This is not oi-dinarily a problem because we assume that they will come back into their home position when the knee joint is subsequently extended. But that does not always happen, and if it doesn't the menisci can get crushed by the opposing condyles. This might happen when you kick a ball or start to get up from a squatting position, and if you ever encounter unusual resistance to extension under such circumstances, carefully sit down and massage the knee before you try to straighten it. If you crush the menisci the only remedy may be trimming them surgically, if not removing them outright.
medial femoral condyle posterior cruciate ligament anterior cruciate ligament lateral femoral condyle medial (tibial) collateral ligament medial meniscus (semilunar cartilage)
tibia fibula tibia femur suprapatellar bursa quadriceps femoris tendon patella lateral meniscus
posterior cruciate ligament
patellar tendon cut end of anterior cruciate ligament infrapatellar bursa tibia fibula tibia
£'gure 5.25, On the left is an anterior view of a deep dissection of the flexed left ¡'"ee joint, and on the right is a sagittal cut through the extended knee joint lr,°ni Sappey).
medial meniscus (semilunar cartilage)
posterior cruciate ligament patellar tendon cut end of anterior cruciate ligament infrapatellar bursa medial femoral condyle posterior cruciate ligament anterior cruciate ligament lateral femoral condyle femur suprapatellar bursa quadriceps femoris tendon patella lateral meniscus
medial (tibial) collateral ligament
The femur and tibia meet together in a hinge, and two internal ligaments, tl anterior and posterior cruciate ligaments (fig. 5.25), keep the bones in aligi -ment. Viewed from the side, the cruciate ligaments form an X. The anterii r cruciate ligament runs from the back of the femur to the front of the til a and constrains anterior displacement of the tibia in relation to the fern r, while the posterior cruciate ligament runs from the front of the femur to t e back of the tibia and constrains posterior displacement of the tibia.
The cruciate ligaments, especially the anterior cruciate ligament, e commonly stretched or torn in knee injuries, and even though they do it lose their blood supply entirely, as do the menisci, they are still so pot ly vascularized that they do not easily heal. Many professional foot I J] careers have been brought to an abrupt end by an anterior cruciate inji y. Envision a linebacker in a crouched position, clipped from behind by tn opponent who throws his full weight against the top of the unsuspoc ig tibia. This will certainly tear the anterior cruciate ligament. It would lie surprising, to say the least, to hear of anyone injuring a cruciate ligan nt doing advanced hatha yoga postures, but someone with an old injury m lit find that certain postures bear watching.
the medial and lateral collateral ligaments
The other two commonly injured ligaments in the knee are the medial 'id lateral collateral ligaments (fig. 5.24-25), which are important acce.- >ry ligaments on the medial and lateral aspects of the joint capsules. Thest ire frequently injured by weekend athletes playing sports in which the be is wrenched and twisted in a direction at cross-purposes to foot positio It might, be touch football, racquetball, or any sport in which your consciou *ss is directed away from your foundation. The collateral ligaments are • en sprained under such conditions, meaning that some of their connective ti ue fibers have been torn away from their bony attachments. Such injurie ire slow to heal. If someone says they have a "trick knee," it is often all r a long history of collateral ligament sprains. As with cruciate ligar 'nt injuries, yoga postures are less likely to create new injuries than to in ate old ones.
the patella and bursae
The main role of the patella, or kneecap (figs. 5.24-25), is to make extei ion of the knee joint more efficient. It is a sesamoid bone, that is. a bone iat is inserted in a tendon, in this case between the quadriceps femoris ter on and the patellar tendon (fig. 5-24>- During flexion it slides down the 11 >er-
condylar notch, a deep vertical gutter between the femoral condyles he articular end of the femur); during extension it acts like a pulley on he
5 HIBOTIM, POSTl'HES
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