Imageless robotic-assisted total knee arthroplasty is accurate in vivo: a retrospective study to measure the postoperative bone resection and alignment.

PURPOSE: Conventional instruments for total knee arthroplasty (TKA) have limited accuracy. The occurrence of outliers can negatively influence the clinical outcome and long-term survival of the implant. Orthopaedic robotic systems were developed to increase the accuracy of implant positioning and bone resections. Several systems requiring preoperative imaging have shown a higher degree of precision compared to conventional instrumentation. An imageless system needs less preoperative time and preparation and is more cost effective. Aim of this study was to find out whether this system is as precise, reproduces accurately the surgeon's planning and reduces the occurrence of outliers. METHODS: This retrospective study included the first 71 robotic-assisted TKA and 308 conventional TKA in 374 patients. Intraoperatively planned and actual bone resections were compared. Postoperative alignment, measured on full leg weight bearing radiographs, was related to the respective planning and statistically compared between the groups. RESULTS: Baseline characteristics (age, BMI, ASA, preoperative Knee Society Score and deformity) between both groups were comparable. According to the planned alignment, the postoperative mean difference was - 1.01° in the robotic versus 2.05° in the conventional group. The maximum deviation was - 2/+ 2.5° in the robotic and - 6.6/ + 6.8° in the conventional group. According to the plan, there were no outliers above ± 3° in the robotic versus 24% in the conventional group. The mean difference between planned and measured bone resection was 0.21 mm with a maximum of 2 mm. The 95% confidence interval was at each position 1 mm or below. CONCLUSIONS: The described imageless robotic system is accurate in terms of coronal alignment and bone resections. In precision, it is superior to conventional instrumentation and could therefore be used to evaluate new alignment concepts.

Polymer Networks for Enrichment of Calcium Ions.

In this study, solvogels containing (2-((2-(ethoxycarbonyl)prop-2-en-1-yl)oxy)-ethyl) phosphonic acid (ECPA) and N,N'-diethyl-1,3-bis-(acrylamido)propane (BNEAA) as the crosslinker are synthesized by UV induced crosslinking photopolymerization in various solvents. The polymerization of the ECPA monomer is monitored by the conversion of double bonds with in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The morphology of the networks is characterized by in situ photorheology, solid state NMR spectroscopy, and scanning electron microscopy (SEM) of the dried gels. It is demonstrated that the storage modulus is not only determined by the crosslinker content in the gel, but also by the solvent used for preparation. The networks turn out to be porous structures with G' being governed by a rigid, phase-separated polymer phase rather than by entropic elasticity. The external and internal pKa values of the poly(ECPA-co-BNEAA) gels were determined by titration with a specially designed method and compared to the calculated values. The polymer-immobilized phosphonic acid groups in the hydrogels induce buffering behavior into the system without using a dissolved buffer. The calcium accumulation in the gels is studied by means of a double diffusion cell filled with calcium ion-containing solutions. The successful accumulation of hydroxyapatite within the gels is shown by a combination of SEM, energy-dispersive X-ray spectroscopy (EDX) and wide-angle X-ray scattering (WAXS).