An Anterior Spike Decreases Bone-Implant Micromotion in Cementless Tibial Baseplates for Total Knee Arthroplasty: A Biomechanical Study

BACKGROUND

Cementless tibial baseplates in total knee arthroplasty include fixation features (eg, pegs, spikes, and keels) to ensure sufficient primary bone-implant stability. While the design of these features plays a fundamental role in biologic fixation, the effectiveness of anterior spikes in reducing bone-implant micromotion remains unclear. Therefore, we asked: Can an anterior spike reduce the bone-implant micromotion of cementless tibial implants?

METHODS

We performed computational finite element analyses on 13 tibiae using the computed tomography scans of patients scheduled for primary total knee arthroplasty. The tibiae were virtually implanted with a cementless tibial baseplate with 2 designs of fixation of the baseplate: 2 pegs and 2 pegs with an anterior spike. We compared the bone-implant micromotion under the most demanding loads from stair ascent between both designs.

RESULTS

Both fixation designs had peak micromotion at the anterior-lateral edge of the baseplate. The design with 2 pegs and an anterior spike had up to 15% lower peak micromotion and up to 14% more baseplate area with micromotions below the most conservative threshold for ingrowth, 20 μm, than the design with only 2 pegs. The greatest benefit of adding an anterior spike occurred for subjects who had the smallest area of tibial bone below the 20 μm threshold (ie, most at risk for failure to achieve bone ingrowth).

CONCLUSIONS

An anteriorly placed spike for cementless tibial baseplates with 2 pegs can help decrease the bone-implant micromotion during stair ascent, especially for subjects with increased bone-implant micromotion and risk for bone ingrowth failure.

A Biomechanical Comparison of the Effect of Baseplate Design and Bone Marrow Fat Infiltration on Tibial Baseplate Pullout Strength

BACKGROUND

Early clinical results of a new total knee arthroplasty (TKA) implant design show promise for improved outcomes and patellofemoral function scores. However, reports of early tibial component-cement interface debonding requiring revision have been published. This study investigated the biomechanical properties of three different tibial baseplates to understand potential causes of failure.

METHODS

PFC Sigma (control), Attune (1st generation) and Attune S+ (2nd generation) tibial baseplates were implanted into 4th generation sawbone tibia models using a standardized technique. Three of each baseplate were cemented with and without additional bovine bone marrow fat. All models were tested to failure with measured axial distraction force. Implant type, presence or absence of bovine marrow and load to failure were all recorded and compared. Two-way ANOVA followed by post-hoc pairwise comparisons were used to determine statistical significance, which was set to P < .05.

RESULTS

The 2nd generation tibial baseplates required significantly more force to failure. The presence of bovine marrow significantly reduced the pullout force of the implant designs overall. No significant difference was detected between the 1st generation and control baseplates. Failure mode for each model was also noted to be different irrespective of the presence or absence of bone marrow fat.

CONCLUSION

The 2nd generation baseplates required significantly more force to failure compared with older designs. The presence of bone marrow during cementation of a tibial base plate significantly decreased axial pullout strength of a tibial baseplate in this laboratory model. All 1st generation baseplates exhibited debonding at the cement-implant interface.

Medial Tibial Stress Shielding: A Limitation of Cobalt Chromium Tibial Baseplates

BACKGROUND

Stress shielding is a well-recognized complication associated with total knee arthroplasty. However, this phenomenon has not been thoroughly described. Specifically, no study to our knowledge has evaluated the radiographic impact of utilizing various tibial component compositions on tibial stress shielding.

METHODS

We retrospectively reviewed 3 cohorts of 50 patients that had a preoperative varus deformity and were implanted with a titanium, cobalt chromium (CoCr), or an all polyethylene tibial implant. A radiographic comparative analysis was performed to evaluate the amount of medial tibial bone loss in each cohort. In addition, a clinical outcomes analysis was performed on the 3 cohorts.

RESULTS

The CoCr was noted to have a statistically significant increase in medial tibial bone loss compared with the other 2 cohorts. The all polyethylene cohort had a statistically significantly higher final Knee Society Score and was associated with the least amount of stress shielding.

CONCLUSION

The CoCr tray is the most rigid of 3 implants that were compared in this study. Interestingly, this cohort had the highest amount of medial tibial bone loss. In addition, 1 patient in the CoCr cohort had medial soft tissue irritation which was attributed to a prominent medial tibial tray which required revision surgery to mitigate the symptoms.

Migration of a cemented fixed-bearing, polished titanium tibial baseplate (Genesis II) at ten years : a radiostereometric analysis

AIMS

The purpose of the present study was to examine the long-term fixation of a cemented fixed-bearing polished titanium tibial baseplate (Genesis ll).

PATIENTS AND METHODS

Patients enrolled in a previous two-year prospective trial (n = 35) were recalled at ten years. Available patients (n = 15) underwent radiostereometric analysis (RSA) imaging in a supine position using a conventional RSA protocol. Migration of the tibial component in all planes was compared between initial and ten-year follow-up. Outcome scores including the Knee Society Score, Western Ontario and McMaster Universities Arthritis Index, 12-item Short Form Health Survey, Forgotten Joint Score, and University of California, Los Angeles Activity Score were recorded.

RESULTS

At ten years, the mean migration of the tibial component was less than 0.1 mm and 0.1° in all planes relative to the post-operative RSA exam. Maximum total point movement increased with time (p = 0.002) from 0.23 mm (sd 0.18) at six weeks to 0.42 mm (sd 0.20) at ten years.

CONCLUSION

The low level of tibial baseplate migration found in the present study correlates to the low rate of revision for this implant as reported in individual studies and in joint replacement registries.

TAKE HOME MESSAGE

Overall, the implant was found to be well fixed at ten years, supporting its continued clinical use and the predictive power of RSA for determining long-term fixation of implants. Cite this article: Bone Joint J 2016;98-B:616-21.

Contribution of Surface Polishing and Sterilization Method to Backside Wear in Total Knee Arthroplasty

The purpose of this study was to compare the relative contributions of backside wear from polished and roughened tibial baseplates and different sterilization methods. Three groups of tibial inserts of the same design were matched: roughened gamma-air (RGA), polished gamma-air (PGA), and polished gas-plasma (PGP). Visual damage scoring and micro-CT deviation maps were used for evaluation. Total backside damage was higher (P=0.045) in RGA (13.8±3.4) compared to PGA (8.7±3.4) and PGP (8.2±4.8). Backside wear rates were greatest (P=0.02) in RGA (0.038 mm/year), followed by PGA (0.012 mm/year), and lowest in PGP (0.009 mm/year). Use of a roughened tibial baseplate had a greater effect on wear magnitude than sterilization method.

MRI Based Comparison of Tibial Bone Coverage by Five Knee Prosthesis: Anthropometric Study in Indians

This MRI based study evaluates morphological differences of proximal tibia (total cross-sectional area, mediolateral and anteroposterior distance) 8-10 mm distal to the lateral tibial plateau. We evaluated the difference in the coverage of the tibial surface between symmetric and asymmetric tibial trays and difference in coverage between males and females. 150 patients who underwent MRI scans for sports related soft tissue injury without osteoarthritis were studied. The tibial trays of the 5 total knee arthroplasty designs (4 symmetric and 1 asymmetric) were scanned. Mean total tibial coverage of all designs was more than 80%. Asymmetric baseplate had maximum total tibial coverage and maximum rate of optimal fit, with only 2% absolute overhang posterolaterally. Females had better tibial coverage as compared to males.