gms | German Medical Science

Objectives: Musculoskeletal regeneration is essential for the functional outcome and patient mobility after total knee arthroplasty (TKA). Increasing prevalence of TKA in younger, active patients emphasizes the importance of implant longevity and rapid treatment recovery. Little is known regarding the long-term effects of TKA on skeletal muscle architecture and its impact on in vivo knee joint loadings. The aim of the present study was thus to assess the association of changes in skeletal muscle characteristics with forces acting in the tibiofemoral joint.

Methods: Instrumented knee prostheses [1] were used for precise in vivo measurements of tibiofemoral joint contact forces in 8 patients [5 men, 3 women, mean age, 69 years (60-75), BMI, 29.7 kg/m2 (25-36)] receiving unilateral TKA. Patients underwent radiological assessments prior to surgery and up to 3 years postoperatively. Knee joint loadings were quantified from 8 to 50 months postoperatively during daily activities, including walking, stair climbing and standing exercises. To examine knee muscle composition, axial computed tomography scans of the lower thigh were analyzed, using Amira-Avizo and ImageJ software, to quantify individual muscle damage as a result of surgery. Hence, skeletal muscle volume (SMV), cross sectional area (CSA) and mean radiation attenuation characteristics of lean muscle and intramuscular adipose tissue were calculated.

Results and conclusion: Overall and surprisingly, a decrease in SMV was observed for the quadriceps femoris, vastus lateralis and vastus medialis muscle. These lower postoperative SMV measures were, thereby, associated with a reduction in intramuscular adipose tissue content. Low muscle attenuation values, as a measure of high muscle fat content, were inversely correlated to the CSA across all muscles analysed, indicating fatty atrophy. In all investigated thigh muscles, increased joint contact forces in level walking were significantly correlated with lower mean muscle radiation attenuation values and, hence, a higher muscle fat content.

TKA should enhance mobility and, in combination with postoperative training, contribute to an improved muscle status, which protects the artificial joint from high loads. Our data shows, however, that the protective effect of the periarticular muscles is reduced in the case of postoperative muscle atrophy. Furthermore, the preliminary results of our study show the importance of training or treating muscles in order to avoid postoperative atrophy and thereby higher joint loads.