I personally think North is a bit too quick to attribute chondromalacia. But below is info, posted at Runners World online, about that particular injury...
Chondromalacia Definition: A softening or wearing away and cracking of the cartilage under the kneecap, resulting in pain and inflammation. The cartilage becomes like sandpaper because the kneecap is not riding smoothly over the knee.
Symptoms: Pain beneath or on the sides of the kneecap. "It's a soreness, a nagging discomfort," says Dave Apple, M.D., an orthopedic surgeon at Atlanta's Piedmont Hospital. Pain can worsen over a year or so and is most severe after you run hills. Swelling is also present. In severe cases, you can feel--and eventually hear--grinding as the rough cartilage rubs against cartilage when the knee is flexed.
Causes: Excessive pronation (when the arch collapses too much and the foot rotates too far inward) can cause the kneecap to twist sideways. Fatigued or weak quadriceps muscles, which aid in proper tracking of the kneecap, can prevent the kneecap from tracking smoothly. A muscle imbalance between weak quads and tighter hamstrings can also pull the kneecap out of its groove. Hill running (especially downhills) can aggravate the condition, as can running on the same side of a cambered road, or, in general, overtraining.
Self-Treatment: Stop running. Ice the knee for 15 minutes two or three times a day. Use a flexible, frozen gel pack that wraps around the knee (or, in a pinch, try a bag of frozen vegetables). Take aspirin three times a day for 12 weeks. "Aspirin has been found to block further breakdown of cartilage," says Apple. Also try self-massage on the sore spots around the knee. Once the pain and swelling are gone, strengthen quadriceps by doing "step-downs". Stand on a step or box at least 4 inches high. Keep your right quadriceps tight while you lower the left leg slowly toward the floor. Then raise it back up to the box, and relax. Repeat 40 times with each leg. Continue increasing repetitions in increments of five every two days, all the way up to 60 reps.
Don't forget to stretch quadriceps and hamstrings. When you start running again, you also might try wearing a rubber sleeve with a hole that fits over the kneecap, which can help the knee track better.
You should be back to easy running in four to six weeks.
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