Knee surgery, whether a total joint replacement or a ligament repair, addresses orthopedic problems by removing damaged tissue and restructuring the joint. However, the procedure itself represents only the first phase of true recovery. The ultimate success of the operation depends heavily on the structured rehabilitation guided by physical therapy. Skipping the prescribed post-operative physical therapy regimen introduces significant, avoidable risks that directly undermine the surgeon’s work.
Restricted Joint Mobility
Following surgery, the knee joint immediately begins a healing process that involves the formation of scar tissue around the surgical site. Without controlled, guided movement, this biological process can quickly lead to a complication known as arthrofibrosis, or a stiff joint. The delicate tissues within the joint capsule become thick and contracted. This unmanaged internal scarring acts like a biological glue, severely limiting the knee’s ability to achieve full flexion (bending) and extension (straightening).
Physical therapy provides a crucial window of opportunity, especially in the first few weeks, to prevent this excessive scar tissue from maturing and becoming dense. Without consistent passive and active range-of-motion exercises, the joint capsule tightens rapidly, leading to a permanent loss of mobility. A significant number of patients experience long-term range-of-motion loss if rehabilitation is neglected. This mechanical block traps the knee in a cycle of stiffness and restriction, making simple movements like climbing stairs or standing up from a chair challenging.
Muscle Atrophy and Instability
A lack of physical activity following surgery causes a rapid loss of muscle mass, known as atrophy, particularly in the quadriceps and hamstring muscle groups. This muscle wasting is compounded by a neurological phenomenon called arthrogenic muscle inhibition (AMI). AMI is a protective reflex where the nervous system temporarily “shuts down” the signals to the muscles surrounding the swollen or painful joint to prevent further damage.
This inhibition, combined with disuse, leads to severe, unchecked weakness and joint instability. Patients can lose over 60% of their quadriceps strength in the first month alone, a much faster rate than simple immobilization would cause. This weakness makes the knee feel unreliable or “wobbly” during weight-bearing activities. The lack of muscle strength also disrupts proprioception, which is the body’s sense of where the joint is positioned in space, increasing the risk of falls or re-injury. Rebuilding this lost strength requires focused, resistance-based exercises that are the foundation of a physical therapy program.
Chronic Pain and Functional Decline
Failure to address joint stiffness and muscle weakness through rehabilitation results in long-term, systemic consequences that affect the body beyond the knee itself. Unmanaged restricted joint mobility and instability force the individual to adopt an altered walking pattern, or gait, to compensate for the dysfunctional joint. This unnatural movement places undue stress on other joints and structures, including the opposite knee, the hips, and the lower back, potentially leading to new injuries or chronic pain in those areas.
Persistent tightness and the resultant mechanical strain contribute to the development of chronic, long-lasting pain that remains long after the surgical incision has healed. If joint stiffness is severe due to neglected rehabilitation, a patient may require an additional invasive procedure. This procedure is often Manipulation Under Anesthesia (MUA), where the surgeon forcefully breaks up the scar tissue. In the most severe instances of functional failure, the inability to regain mobility can ultimately necessitate a complete revision surgery.