Short-Term Consequences of Long-Term Evolutionary Benefits:

Over the long-term, bipedal locomotion provides such a profound evolutionary advantage that it outweighs even significant negative consequences to the individual. In fact, many of the most common medical complaints of modern humans relate directly to the physiological realities of the transition of anatomical systems originally designed for quadruped locomotion to the later evolution of bipedalism. Chronic lower back pain, for example, afflicts approximately 80% of the human population. According to physiologists, this is a direct function of the changed role of a spinal column originally designed as an arched support connecting two sets of load-bearing limbs to a vertically- loaded column supporting the compression load required by the shift to bipedalism.

Likewise, the transition to the narrower hips necessary for efficient bipedal locomotion is the source of significant potential problems affecting the connective tissues, particularly in the knee. Specifically, the change in angle formed by limbs in relation to the narrower bipedal hips significantly increases the potential shearing force on the ligaments of the knee. In fact, this phenomenon...

In that regard, possibly the most dramatic modern consequences of the evolutionary adaptations necessitated by bipedal locomotion relate to the comparative difficulty which human females experience in childbirth compared to our closest simian relatives. Whereas other primates give birth relatively easily and without assistance, human birth requires complicated fetal movement corresponding to the extremely narrow and twisted shape of the human birth canal that until the modern medical era, made childbirth a significant risk to the life of the mother.
Conclusion:

The evolution of bipedal locomotion in humans illustrates the degree to which behavior generates adaptive evolution as well as the profound short-term consequences sometimes required to reap the long-term benefits of certain adaptations. Ultimately, many of our present day medical complaints can be directly traced to the fact that we walk upright on two legs rather than to our choices of life style and recreational pursuits.