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Background: Swimming is commonly recommended as postoperative rehabilitation following total hip arthroplasty (THA) and total knee arthroplasty (TKA). So far, in vivo hip and knee joint loads during swimming remain undescribed. Methods: In vivo hip and knee joint loads were measured in 6 patients who underwent THA and 5 patients who underwent TKA with instrumented joint implants. Joint loads, including the resultant joint contact force (FRes), torsional moment around the femoral shaft axis or the tibial axis (MTors), bending moment at the middle of the femoral neck (MBend), torsional moment around the femoral neck axis (MTne), and medial force ratio (MFR) in the knee, were measured during breaststroke swimming at 0.5, 0.6, and 0.7 m/s and the breaststroke and crawl kicks at 0.5 and 1.0 m/s. Results: The ranges of the median maximal FRes were 157% to 193% of body weight for the hip and 93% to 145% of body weight for the knee during breaststroke swimming. Greater maxima of FRes (hip and knee), MTors (hip and knee), MBend (hip), and MTne (hip) were observed with higher breaststroke swimming velocities, but significance was only identified between 0.5 and 0.6 m/s in FRes (p = 0.028), MTors (p = 0.028), and MBend (p = 0.028) and between 0.5 and 0.7 m/s in FRes (p = 0.045) in hips. No difference was found in maximal MFR between different breaststroke swimming velocities. The maximal FRes was significantly positively correlated with the breaststroke swimming velocity (hip: r = 0.541; p < 0.05; and knee: r = 0.414; p < 0.001). The maximal FRes (hip and knee) and moments (hip) were higher in the crawl kick than in the breaststroke kick, and a significant difference was recognized in FRes Max for the hip: median, 179% versus 118% of body weight (p = 0.028) for 0.5 m/s and 166% versus 133% of body weight (p = 0.028) for 1.0 m/s. Conclusions: Swimming is a safe and low-impact activity, particularly recommended for patients who undergo THA or TKA. Hip and knee joint loads are greater with higher swimming velocities and can be influenced by swimming styles. Nevertheless, concrete suggestions to patients who undergo arthroplasty on swimming should involve individual considerations. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence. [ABSTRACT FROM AUTHOR]

Introduction: After hip surgery, it is the orthopedist’s decision to allow full weight bearing to prevent complications or to prescribe partial weight bearing for bone ingrowth or fracture consolidation. While most loading conditions in the hip joint during activities of daily living are known, it remains unclear how demanding physiotherapeutic exercises are. Recommendations for clinical rehabilitation have been established, but these guidelines vary and have not been scientifically confirmed. The aim of this study was to provide a basis for practical recommendations by determining the hip joint contact forces and moments that act during physiotherapeutic activities. Methods: Joint contact loads were telemetrically measured in 6 patients using instrumented hip endoprostheses. The resultant hip contact force, the torque around the implant stem, and the bending moment in the neck were determined for 13 common physiotherapeutic exercises, classified as weight bearing, isometric, long lever arm, or dynamic exercises, and compared to the loads during walking. Results: With peak values up to 441%BW, weight bearing exercises caused the highest forces among all exercises; in some patients they exceeded those during walking. During voluntary isometric contractions, the peak loads ranged widely and potentially reached high levels, depending on the intensity of the contraction. Long lever arms and dynamic exercises caused loads that were distributed around 50% of those during walking. Conclusion: Weight bearing exercises should be avoided or handled cautiously within the early post-operative period. The hip joint loads during isometric exercises depend strongly on the contraction intensity. Nonetheless, most physiotherapeutic exercises seem to be non-hazardous when considering the load magnitudes, even though the loads were much higher than expected. When deciding between partial and full weight bearing, physicians should consider the loads relative to those caused by activities of daily living. [ABSTRACT FROM AUTHOR]

Understanding the sources of error is critical before models of the musculoskeletal system can be usefully translated. Using in vivo measured tibiofemoral forces, the impact of uncertainty in muscle-tendon parameters on the accuracy of knee contact force estimates of a generic musculoskeletal model was investigated following a probabilistic approach. Population variability was introduced to the routine musculoskeletal modeling framework by perturbing input parameters of the lower limb muscles around their baseline values. Using ground reaction force and skin marker trajectory data collected from six subjects performing body-weight squat, the knee contact force was calculated for the perturbed models. The combined impact of input uncertainties resulted in a considerable variation in the knee contact force estimates (up to 2.1 BW change in the predicted force), especially at larger knee flexion angles, hence explaining up to 70% of the simulation error. Although individual muscle groups exhibited different contributions to the overall error, variation in the maximum isometric force and pathway of the muscles showed the highest impacts on the model outcomes. Importantly, this study highlights parameters that should be personalized in order to achieve the best possible predictions when using generic musculoskeletal models for activities involving deep knee flexion., Competing Interests: AM was employed by Aesculap AG. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Hosseini Nasab, Smith, Maas, Vollenweider, Dymke, Schütz, Damm, Trepczynski and Taylor.)