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Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 84 - 84
1 Dec 2013
Ismaily S Patel R Suarez A Incavo S Bolognesi MP Noble P
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Introduction

Malpositioning of the tibial component is a common error in TKR. In theory, placement of the tibial tray could be improved by optimization of its design to more closely match anatomic features of the proximal tibia with the motion axis of the knee joint. However, the inherent variability of tibial anatomy and the size increments required for a non-custom implant system may lead to minimal benefit, despite the increased cost and size of inventory.

This study was undertaken to test the hypotheses:

That correct placement of the tibial component is influenced by the design of the implant.

The operative experience of the surgeon influences the likelihood of correct placement of contemporary designs of tibial trays.

Materials and Methods

CAD models were generated of all sizes of 7 widely used designs of tibial trays, including symmetric (4) and asymmetric (3) designs. Solid models of 10 tibias were selected from a large anatomic collection and verified to ensure that they encompassed the anatomic range of shapes and sizes of Caucasian tibias. Each computer model was resected perpendicular to the canal axis with a posterior slope of 5 degrees at a depth of 5 mm distal to the medial plateau. Fifteen joint surgeons and fourteen experienced trainees individually determined the ideal size and placement of each tray on each resected tibia, corresponding to a total of 2030 implantations. For each implantation we calculated: (i) the rotational alignment of the tray; (ii) its coverage of the resected bony surface, and (iii) the extent of any overhang of the tray beyond the cortical boundary. Differences in the parameters defining the implantations of the surgeons and trainees were evaluated statistically.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_13 | Pages 11 - 11
1 Mar 2013
Matthies A Suarez A Karbach L Henckel J Skinner J Noble P Hart A
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There are several component position and design variables that increase the risk of edge loading and high wear in metal-on-metal hip resurfacing (MOM-HR). In this study we combined all of these variables to calculate the ‘contact patch to rim distance’ (CPRD) in patients undergoing revision of their MOM-HR. We then determined whether CPRD was more strongly correlated with component wear and blood metal ion levels, when compared to any other commonly reported clinical variable. This was a retrospective study of 168 consecutively collected MOM-HR retrieval cases. All relevant clinical data was documented, including pre-revision whole blood cobalt and chromium ion levels. Wear of the bearing surfaces was then measured using a roundness-measuring machine. We found four variables to be significantly (p < 0.05) correlated with component wear and blood metal ion levels: (1) cup inclination angle, (2) cup version angle, (3) arc of cover, and (4) CPRD. The correlations between CPRD and both wear and ion levels were significantly stronger than those seen with any other variable (all p < 0.0001). Our study has shown that CPRD is the best predictor of component wear and blood metal ion levels, and may therefore be a useful parameter to help determine those patients who are at risk of high wear and require more frequent clinical surveillance.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_1 | Pages 142 - 142
1 Jan 2013
Matthies A Suarez A Karbach L Isamailly S Henckel J Skinner J Noble P Hart A
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Introduction

Edge loading is a common wear mechanism in Metal-on-Metal (MOM) hip resurfacing and is associated with higher wear rates and the incidence of pseudotumour. The purpose of this study was to develop a method to investigate the contributions of patient, surgical and implant design variables on the risk of edge loading.

Method

We created a mathematical model to calculate the distance from the head-cup contact patch to the rim of the cup and used this to investigate the effect of component position, specific design features and patient activity on the risk of edge loading. We then used this method to calculate the contact patch to rim distance (CPRD) for 160 patients having undergone revision of their MOM hip resurfacing in order to identify any possible associations.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_II | Pages 92 - 92
1 May 2011
Noriega-Fernandez A Hernandez-Vaquero D Suarez-Vazquez A Sandoval-Garcia M Perez-Coto I
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Introduction: Computer assisted-surgery (CAS) brings in a great precision to the alignment of the components and the axis of the extremity in total knee arthroplasty (TKA). On the other hand, even though the MIS technique exerts a lesser aesthetic impact, favours the faster recovery of the patient and preserves the soft parts better, it can also lead to mistakes in the alignment of the implant due to the deficient visualization. Adding CAS to MIS may solve this potential complication.

Objective: To compare the alignment of the components with regard to the mechanical axis in four TKA groups (standard surgery, MIS surgery, standard surgery with CAS, and MIS with CAS).

Materials and Methods: Prospective and randomized study. 100 patients with Alhbäck degree III primary degenerative osteoarthritis of the knee and less than 10° of varus-valgus were included. The patients were randomly distributed in 4 groups of 25 patients each, and the same surgeons performed the surgery. Two CT surviews were performed on every patient, one preoperatively and one during the immediate postoperative period, including hip and ankle, where the femoral, tibial and femoro-tibial axis measurements were carried out.

Results: Mean age was 71.63 years (SD 6.68); 81 % of patients were women. Preoperative mean varus was of 7.57° (SD 1.10). No significant differences were found in the femoro-tibial alignment nor in the components with regard to the mechanical femoral axis between the four groups (Table 1). Nevertheless, significant differences in favour of the MIS-CAS technique group for the alignment of the tibial component with regard to the mechanical tibial axis were found.

Conclusions: The MIS technique allows for a well-aligned TKA implantation. Nevertheless, when CAS is coupled with this technique, the alignment of the tibial component is improved. It is possible for the association of MIS and CAS to become a true advance in TKA implantation.


Orthopaedic Proceedings
Vol. 86-B, Issue SUPP_III | Pages 227 - 227
1 Mar 2004
Hernandez-Vaquero D Suarez-Vazquez A Garcia-Sandoval M Fernandez-Carreira J Perez-Hernandez D
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Aims: To study the utility of a computer assisted orthopaedic surgery (CAOS) wireless system (navigator) in Total Knee Arthroplasty (TKA). Methods: Randomised prospective study. A sample of 40 TKA patients was randomised in two groups: CAOS was used in 20 of them. In the other group standard technique with manual alignment was performed. Femoral angle (formed between the femoral mechanical axis and the femoral component), tibial angle (formed between the tibial mechanical axis and the tibial platform) and femorotibial angle (formed between femoral and tibial mechanical axes) were measured from Computed Tomography Surviews taken in the immediate postoperative period. Results: In the standard group (without navigator) the femoral angle mean was 91.7° (ranged 90 to 94°). Tibial angle mean was 90.2° (87°–95°) and femorotibial angle mean was 175.9° (172°–180°) showing a slight prevalence of varus deviation of the extremity mechanical axis. In the group with navigator the femoral angle mean was 90.2∞ (87–93°), tibial angle mean 89.6°(85°–93°) and femorotibial angle mean 179.2° (177°–182°). There were statistically significant differences between groups for the femoral angle (p=0.001), and the femorotibial angle (p < 0.001). An ideal femorotibial angle (180±3°) was achieved for all the patients of the CAOS group but only 9 patients of the standard technique group reached this objective (p< 0.001). Conclusions: The use of CAOS for TKA favors the implant placement in a position nearer to the ideal mechanical axis.