Bulletin 22
The Punt Kick – The Injury List Grows

Hello coaches and sport scientists. Welcome to season 2012 and another series of Bulletin Boards from the ‘The Science of Kicking’. A striking feature of the pre-season has been the number of injuries, the usual hamstring and groins certainly suggesting a lack of preparation during the summer months. Particularly noticeable is the number of patella displacements which can be attributed not only to the speed of the modern game but also to the design of the knee joint, dodgy at best and a real compromise between the need for stability on the one hand and significant mobility on the other.

Cursory observation as one sights down the thighs to the feet reveals that the thigh bone (femur) is not in line with the shin (tibia) but instead angles inwards. This is to accommodate the pelvis and at the same time permit us to stand with our knees together. The resultant angle is known as the physiological valgus, more pronounced in women than in men due to their wider hips. It means that the medial side of the knee is always under greater stress than the lateral side, with the medial ligament and medial cartilage (meniscus) receiving more of a belting than those structures on the lateral side.

Look at the photograph of Jason Ackermanis (fig 1) seen here in the midst of a sudden directional change. With weight taken on his left leg and turning in the opposite direction, he has exacerbated his valgus dramatically. Look also at the line of pull of the quadriceps (red line) as it meets the kneecap and then angles sharply to its insertion at the top of the shin (tibial tuberosity).

With  the medial rotation of the femur continuing as the turn progresses, this angle will increase due to the anchoring of the weight-bearing foot. With the quadriceps contracting powerfully to stabilize the knee, the tendency is for them to take a new line of pull (dotted line) lateral to the knee. As the patella is in fact part of the quadriceps tendon, it will be subjected to a powerful lateral destabilizing force which may be strong enough to cause the patella to skip out of its trough along which it slides and relocate to the lateral side of the knee. The mechanics of this action is explained in the diagram of the pulley below (fig 3).

Look now at Buckley executing a similar turn but this time turning toward the side of the stabilizing leg (fig 2). The result is a straightening of the physiological valgus which has the quadriceps pulling in a straight line with little danger of dragging the patella laterally. Fortunately our quadriceps are designed in such a way as to retain the patella within its groove (fig 4). Here we see the lower fibres of the vastus medialis arranged in such a way as to exert a ‘pull’ on the patella toward the medial side and prevent it slipping sideways. Of course this muscle must be strong enough to resist the forces demonstrated by Ackermanis and experienced by players in the faster game of today. Of course any movement of the patella laterally must result in stretching and tearing of soft tissues on the medial side of the knee. These ‘holding’ tissues will never return to their original length and there will be the ever-present danger of recurrent patella dislocation. Hence, preseason training regimes must target the quadriceps with appropriate exercises to strengthen the vastus medialis in particular. The offshoot will be more powerful kicking. Speak to your club physiotherapist. More next month.

 


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