Loading of the artificial knee during early rehabilitation and physiotherapy : an in vivo study.

Aims: This retrospective observational study aimed to determine the in vivo joint loads in the knee after total knee arthroplasty during early postoperative rehabilitation involving different physiotherapy exercises and to analyze how these loads change over the first three weeks postoperatively.

Methods: Nine patients (six males, three females) with a primary instrumented total knee replacement participated in the study. A total of 19 selected physical therapy exercises of varying load levels were performed on the ninth (SD 3) and 21st (SD 6) postoperative day. During these sessions, the peak resultant knee contact force (F_{res max}) and loading patterns were measured to assess joint loading dynamics.

Results: F_{res max} varied across different exercises, ranging from a minimum of 15% body weight (% BW) during seated leg swings to a maximum of 195% BW during stair ascent. Joint loads increased from the ninth to the 21st postoperative day for all activities, except for a few relaxed status exercises where a decrease was observed. Load-bearing activities with crutches had the highest knee joint loads.

Conclusion: All exercises remained below the forces of walking on ground level indicating safety for the postoperative rehabilitation. Physical therapists should consider these loads in relation to daily activities when designing treatment plans also referring to the different loads in different exercises.