A7 Post-intervention biomechanical alterations

Topic

The musculoskeletal system can undergo lasting physical changes stemming from two distinct triggers: a surgical procedure or prolonged immobilization. Both surgical procedures and prolonged immobilization directly alter the musculoskeletal system—albeit through different mechanisms—and both result in the same four physical changes described by this model.

The first physical change in the musculoskeletal system is an alteration in joint geometry: a surgical procedure can directly modify the shape or alignment of a joint, whereas prolonged immobilization allows joint geometry to progressively adapt to the fixed position in which the joint is held.

The second change is a reduction in force-generating capacity due to disuse: when prolonged immobilization prevents a muscle from contracting normally, this lack of use progressively diminishes the muscle's force-generating capacity, even if the surgical procedure did not directly involve that specific muscle.

The third change is a loss of joint range of motion due to soft-tissue contracture: when the soft tissues surrounding a joint remain shortened during prolonged immobilization, they contract and no longer allow the joint to move through its previous range of motion, even after the immobilization is removed.

The fourth change is an alteration in load distribution: both surgical procedures and prolonged immobilization modify the support points and mechanical levers upon which the musculoskeletal system acts, thereby changing how loads are distributed across various joints and muscles.

However, not every type of surgery affects these four factors—joint geometry, force-generating capacity, joint range of motion, and load distribution—in the same way; each specific surgical procedure alters one or more of these parameters relative to the musculoskeletal system's normal state, while leaving the others unchanged. Recognizing the specific parameters modified by each procedure makes it possible to anticipate—for each individual—exactly how their musculoskeletal system has changed following surgery or prolonged immobilization, rather than assuming that every intervention alters the musculoskeletal system in the same way.

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