Relationship of the Posterior Condylar Line and the Transepicondylar Axis: A CT-Based Evaluation

Posterior condylar referencing, a common method for determining femoral axial orientation during total knee arthroplasty (TKA), relies upon an assumed consistent relationship between the posterior condylar line (PCL) and the transepicondylar axis (TEA) of 3 degrees rotation. A total of 3,010 computed tomography (CT) scans and three-dimension (3D)-reconstructions for presurgical creation of patient-matched TKA instrumentation were analyzed. Demographic data and five anthropometric measurements (hip–knee angle [HKA], distal femoral angle [DFA], proximal tibial angle [PTA], tibial slope [TS], and PCL–TEA relationship) were recorded for each scan. A logistic regression model was fit to assess interaction between the PCL–TEA relationship and demographic and radiological variables. The mean (standard deviation [SD]) PCL–TEA was +2.9 degrees (0.8 degree). The range varied between +0.5 and +16.5 degrees. In 2,758 knees (91.6%), the PCL–TEA was within 3 ± 1 degrees, whereas 252 knees (8.4%) fell outside this range. There were no significant demographic or anthropometric differences between those knees with PCL–TEA relationship between 3 ± 1 degrees and those falling outside that range. The posterior condyles of diseased knees undergoing TKA can be reliably used to indirectly reference the TEA of the distal femur with an error of only 1 degree in 92% of patients.

iAssist versus conventional total knee arthroplasty in patients with varus and valgus deformities

<p class="abstract"><strong>Background:</strong> Accelerometer and gyroscope based iAssist system's accuracy in restoring the hip knee angle (HKA) in valgus and varus deformity patients is compared to that of conventional system.</p><p class="abstract"><strong>Methods:</strong> In this retrospective study we compared the HKA of 26 patients in iAssist group with that of 26 patients in conventional group. The knee joints were evaluated with full leg length radiographs.<strong></strong></p><p class="abstract"><strong>Results:</strong> The iAssist group patients’ post-operative hip knee angle was much near to our target angle when compared to that of patients in conventional technique group.</p><p class="abstract"><strong>Conclusions:</strong> iAssist brings the high accuracy associated with large console CAS systems with lower costs and helps surgeons in low volume hospitals achieve specific intra operative goals with the familiarity of conventional guides.</p>

An investigation of kinematic and kinetic variables for the description of prosthetic gait using the ENOCH system

Gait patterns, joint angles, floor reaction forces and joint moments during walking were investigated for normal subjects and above-knee and below-knee amputees. The investigation showed that the hip-knee angle diagram as well as different symmetry diagrams (e.g. left knee angle versus right knee angle) provide an easily interpreted means of evaluating abnormalities in the gait pattern. It was further concluded that a combined gait pattern-force vector diagram is valuable for the evaluation of the joint moments. Floor reaction forces and muscular moments at the joints were also included in the analysis. The joint moments at the knee were quite different for both above-knee and below-knee amputees as compared to the normal subjects. Some interesting trends were also found concerning the knee stability of the amputees. A system called ENOCH was used for the measurement and analysis. This system consists of a minicomputer connected on-line to equipment for measurement of displacement (Selspot) and floor reaction forces (Kistler). A graphic computer terminal (Tektronix) was used for the result presentation.