Background Recently, patient-specific guides (PSGs) have been introduced, claiming a significant improvement in accuracy and reproducibility of component positioning in TKA. Despite intensive marketing by the manufacturers, this claim has not yet been confirmed in a controlled prospective trial. Questions/purposes We (1) compared three-planar component alignment and overall coronal mechanical alignment between PSG and conventional instrumentation and (2) logged the need for applying changes in the suggested position of the PSG. Methods In this randomized controlled trial, we enrolled 128 patients. In the PSG cohort, surgical navigation was used as an intraoperative control. When the suggested cut deviated more than 3°from target, the use of PSG was abandoned and marked as an outlier. When cranial-caudal position or size was adapted, the PSG was marked as modified. All patients underwent long-leg standing radiography and CT scan. Deviation of more than 3°from the target in any plane was defined as an outlier. Results The PSG and conventional cohorts showed similar numbers of outliers in overall coronal alignment (25% versus 28%; p = 0.69), femoral coronal alignment (7% versus 14%) (p = 0.24), and femoral axial alignment (23% versus 17%; p = 0.50). There were more outliers in tibial coronal (15% versus 3%; p = 0.03) and sagittal 21% versus 3%; p = 0.002) alignment in the PSG group than in the conventional group. PSGs were abandoned in 14 patients (22%) and modified in 18 (28%). Conclusions PSGs do not improve accuracy in TKA and, in our experience, were somewhat impractical in that the procedure needed to be either modified or abandoned with some frequency. Level of Evidence Level I, therapeutic study. See instructions for authors for a complete description of levels of evidence.

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Minimally invasive surgery has recently been introduced in TKA surgery. The purpose of this study was to evaluate the effect of eversion of the patella, on safety and functional result after TKA. In a prospective, randomised, double blinded trial, 60 patients were divided in two groups: group A underwent TKA through a standard medial parapatellar arthrotomy, with patellar eversion. Group B underwent the same exposure, except for the fact that the patella was subluxed laterally. All other treatment protocols were identical. Outcomes were measured until 1 year postoperatively. Radiographic evaluation included AP, lateral, skyline and full leg standing radiographs. VAS, WOMAC score, Knee Society Knee and Function score were performed. Active and passive range of motion (ROM) and knee proprioception was measured. All patients underwent isokinetic strength testing. The mean passive ROM changed from 121 degrees preoperatively to 121 degrees postoperatively in group A, compared to 118 degrees -131 degrees respectively in group B at 1 year (P = 0.003). The mean active ROM changed from 112 degrees to 115 degrees in group A, and from 108 degrees to 125 degrees in group B (P = 0.005). All other parameters were not significantly different. Patellar dislocation without eversion for exposing the knee during TKA is a safe procedure and improves ROM at 1 year postoperatively.

ResultsThe post-cam mechanisms analyzed in this study are very variable in terms of design features. This leads to large variations in terms of the flexion angle at which the post and cam engage maximal contact force, contact pressure and contact area. We found that more functional postcam mechanisms, which engage at lower flexion angle and have a similar behavior as normal PCL function, generally show more normal rollback and tibial rotation at the expense of higher contact forces and pressures. All designs show high contact forces. A positive correlation was found between contact force and initial contact angle. Conclusion Post-cam contact mechanics and kinematics were documented in a standardized setting. Post-cam contact mechanics are correlated with post-cam function. Outcomes of this study can help to develop more functional designs in future. nevertheless, a compromise will always be made between functional requirements and risk of failure. We assume that more normal knee kinematics leads to more patient satisfaction because of better mobility. Understanding of the post-cam mechanism, and knowing how this system really works, is maybe the clue in further development of new total knee designs.

Diagnostic study, Level III.