No abstract

The moment arm is a crucial parameter for understanding musculoskeletal dynamics as it defines how linear muscle force is transformed into a moment. Yet, for the quadriceps tendon this parameter cannot be directly calculated, as the patella creates a dynamic fulcrum. Thus, the effective quadriceps moment arm (EQma) was developed to define the quadriceps force to tibial moment relationship. In vivo data in regards to the EQma are lacking and the critical question of how patellofemoral kinematics may influence the EQma remains unresolved. Therefore, the purpose of this study was to quantify the in vivo EQma during a knee extension exercise in asymptomatic controls and to correlate the EQma with sagittal plane patellofemoral kinematics. While subjects (30F/10M, 26.5±5.6 years, 167.5±10.2 cm, 62.6±10.7 kg) cyclically flexed-extended their knees within the MR scanner, dynamic cine-phase contrast and cine MR images were acquired. From these data, patellofemoral kinematics, the ratio of the patellar tendon to quadriceps force, the patellar tendon moment arm, and the EQma were quantified. The EQma trended upwards (32.9–45.5mm (females) and 31.5–47.1mm (males)) as the knee angle decreased (50°–10°). The quadriceps had a mechanical advantage (ratio of patellar to quadriceps tendon forces>1.0) for knee angles ≤ 20°. The EQma did not correlate with sagittal plane patellofemoral kinematics. As this is the first study to characterize the EQma in vivo during dynamic volitional activity, in a large group of asymptomatic controls, it can serve as a foundation for future knee joint models and to explore how pathological conditions affect the EQma.

BackgroundIn total knee arthroplasty (TKA) for valgus knees, the decision to use a constrained implant is often made intraoperatively depending on the extent of soft tissue releases performed and residual soft tissue imbalance. The purpose of this study is to determine if preoperative radiographic criteria of valgus knees can predict the extent of soft tissue releases required and the level of constraint needed to balance the knee during TKA.MethodsA single surgeon's 807 consecutive TKA standing hip-knee-ankle radiographs from 2007-2012 were analyzed. One hundred eighty-seven valgus knees were identified and annotated. Statistical univariate and multivariate analyses were performed for both outcomes, lateral release and articulation, to assess the association with risk factors of gender, age, and preoperative radiographic markers of valgus deformity. A P-value <.05 represented a significant difference between groups.ResultsUse of a constrained articulation was associated with increased valgus deformity (mechanical hip-knee-ankle angle, P < .0001) and extent of lateral soft tissue release (P < .0001). No relationship existed between the use of a constrained articulation and age or gender (P > .05). A preoperative anatomic tibiofemoral valgus angle of >16.8° was associated with the use of a constrained articulation during surgery.ConclusionsOur data demonstrate that preoperative radiographic characteristics of the valgus knee can be utilized to predict the extent of lateral soft tissue release and whether a constrained articulation will be required in TKA. This will provide surgeons with useful information to offer accurate preoperative counseling to patients and to ensure that the appropriate prosthetic parts are available during surgery.

Background: The direct anterior approach (DAA) has been used successfully in total hip arthroplasty with many benefits including improved radiographic positioning of components, earlier ambulation, as well as decreased narcotic consumption, length of stay, dislocation rate, discharge to rehabilitation facility (vs. home) and 30-day readmission. Hip resurfacing can be a successful surgical option for the properly selected patient as it can preserve bone stock and provide excellent function including improved activity levels as compared with total hip arthroplasty. Traditionally hip resurfacing has been performed via an extensile posterior approach, but the benefits of DAA can be applied to resurfacing though not without a learning curve. Case Presentation: Here we report the surgical technique of hip resurfacing performed supine on a Hana table via the DAA and include key steps to ensure adequate exposure and minimize complications.