Mechanical Failures of Rotating Hinge Total Knee Arthroplasty - 15% rate of Hinge Mechanism Fracture at mean of 31 Months

Figure 5: (a) AP view of right rHTKA of patient B at follow up 18 months. (b) magnified view of medial joint line showing gapping between medial femoral condyle and tibial insert.

Figure 6: Fluoroscopy of right rHTKA of patient B with (a) valgus stress in extension demonstrating gapping medially, and (b) with varus stress demonstrating more subtle gapping laterally.

Patient C

This patient had a history of previous revision TKA, presented with a recurrence of infection. First stage revision was performed with implantation of a temporary antibiotic spacer in February 2019, and after treatment with IV antibiotics and a period of quiescence while not taking antibiotics, the second stage was completed in September 2019. At that time due to bone loss and flexion–extension imbalance a Legion rHTKA prosthesis was used. In July 2020 the patient was seen with worsening pain in the knee in the absence of trauma. The knee had evidence of recurrence of infection clinically and biochemically and so underwent a repeat staged revision procedure at another unit.

Patient D

A patient with a previously revised TKA (2 stage revision for infection) in 2006. He developed some progressive tibial subsidence so underwent 2 stage revision to a Legion rHTKA, the second stage in March 2017, without any complications. At the one year follow up a check x-ray suggested that the tibial insert retaining screw may have backed out. The patient was entirely asymptomatic, so the situation was monitored. At the 2 year follow up there was no change in the screw position and the patient remained asymptomatic. The patient re-presented in June 2021 with worsening left knee pain and swelling affecting his gait. There was no history of trauma. Check radiographs of the knee were unchanged, and the patient was placed on regular review. Four months later the patient complained of worsening pain and instability in the knee, and radiographs clearly showed fracture of the femoral link (Figure 7). In January 2022 a limited revision of the hinge mechanism was performed, using a thinner tibial insert in an attempt to reduce the stress over the construct. The femoral and tibial components were found to be well fixed at the time of revision. At the one month post operative review the patient was experiencing symptoms of instability and repeat radiographs showed anterior tilting of the post sleeve (Figure 8) similar to that seen in patient A, indicating failure of the hinge mechanism. The patient subsequently underwent knee arthrodesis.

Figure 7: lateral radiograph of rHTKA of patient C demonstrating fracture of the link bush

Figure 8: lateral radiograph of rHTKA of patient C taken 4 weeks post revision of hinge mechanism, demonstrating anterior tilting of the hinge sleeve relative to the tibial baseplate, indicating further mechanical failure of the hinge mechanism.

Lesser Constrained Implants

For comparison, during the same time period we identified 157 legion implants performed within the unit that were not hinge linked. These had an overall revision rate of 6% (n=9), revisions according to indication can be seen in table 3. A Kaplan Meier graph comparing the hinged and non-hinged prostheses can be seen in figure 9, a Log-Rank test showed this difference to be statistically significant (p=0.033).

Table 3: Indications and subsequent revisions of non-hinge Legion TKA cases

Figure 9: Kaplan Meier graph comparing hinged and non-hinged Legion implants

Discussion

This case series demonstrates a revision rate of 18% for the Legion rHTKA system, and a 15% rate of early mechanical failure of the hinge mechanism at mean of 30.8 months from implantation. The management of instability and bone loss in knee arthroplasty is a challenge which may be met with a number of different reconstruction methods. These include cementing techniques, bone grafting, metal augmentation, metaphyseal fixation with cones or sleeves, custom-made implants and prosthesis of increasing constraint, which include hinge-type implants. [6] Hinged rotating knee replacements, if used in the management of non-tumour associated reconstruction, have reported good clinical results and improved quality of life for patients. [7,8] The Legion rHTKA is utilised in our centre for patients, in both complex primary and revision settings. Instability and early mechanical failure in rHTKAs, though infrequent, have been reported and pose a clinically significant complication as it often necessitates further intervention. [9,10] Other authors have previously reported instability with the Legion rHTKA. Van Laarhoven et al observe a 3.5% incidence of instability in their cohort of 169 patients. [11] On stress testing the Legion rHTKA in varus/valgus they observed excessive tilting of the link-bush mechanism. They also observed that if the joint is under distraction (when not under axial load) the force distribution between condyles and tibial liner is lost. The stress is therefore, placed purely upon the short link-bush system. This mechanism of failure is the same as was seen in patient B, as demonstrated by the varus/valgus tilt and condylar lift-off seen in figures 3 and 4. In their cohort, they managed this instability successfully with a brace in 50% of cases, and the remaining were managed with limited revision of the liner and hinge mechanism, with no mention of further revisions. Limited revision of the sleeve/bolt connection was attempted in 2 cases, and both rHTKAs went on to rapidly fail. In both patients B and D a liner exchange was performed as well to alter tension in the soft tissue envelope and offload the hinge mechanism, but the outcome was unsuccessful. Van Laarhoven did not report their duration of follow up although it can be inferred that it could be up to 6 years and there was no stated follow up for those who had undergone limited revision. In their conclusion, van Laarhoven et al do not recommend the use of the Legion rHTKA in specific patients (multidirectional instability, posterior capsule insufficiency, grossly imbalanced flexion extension gaps, extensor mechanism insufficiency, or revision of a more rigid rHTKA system) due to the tilting and wear observed by the less rigid design of the Legion compared to other devices such as the RT-PLUS (Smith and Nephew). Perrin and Turgeon report on their experience with the Legion rHTKA system [12] in 39 implants with 2 years follow up. They report a 2-year survival of 90.7%, with only one patient (2.5%) experiencing early failure of the hinge mechanism after a fall. There were no traumatic events documented for any of the failures in our study, and in 2 of the 3 patients who experienced hinge failure (the first time) the time to failure occurred several years after implantation. Perrin et al do not record their long term results. Failure of the hinge mechanism in rHTKAs is reported to be exceedingly rare. [13] Bornes et al [14] report on outcomes of 115 rHTKAs with a mean follow up of 3 years and only report one episode of hinge component failure out of 115 (0.9%). The rHTKA in their series are various designs, 35 of which were Legion rHTKAs, however, the authors do not specify which model of rHTKA experienced mechanical failure. In another series of 86 rHTKAs [15] with a mean follow up of 5 years there was only one hinge related failure (Link rotating hinge, Waldemar LINK GmbH and Co, Hamburg, Germany). Cottino et al [16] report on 408 rHTKAs (varying models, no Legions included) with mean follow up 4 years and identified 10 mechanical failures (2.5%), although they do not elaborate on the nature of the failure. Bruce et al report on 53 NexGen rHTKAs with a mean follow up of 7.6 years with only one hinge failure, treated successfully with revision of the modular hinge components [17]. Several case series for other implants do not report on any instances of hinge failure for implants including NexGen (Zimmer Biomet) [18-20]. Modular Rotating Hinge System (Stryker) [12], MUTARS GenuX MK, (Implantcast GmbH) [21] GMK Hinge (Medacta international) [22]. One reported method of failure of rHTKAs is dislocation of the hinge mechanism [23,24] indeed in some rHTKA designs the femoral and tibial components are not technically connected, but linked by a post that can rotate and piston within a barrel on the opposing part such as with the S-ROM NOILESTM (DePuy Synthes). Dislocations are avoided by ensuring a large ‘jump distance’ however with a severely compromised soft tissue envelope, this jump distance can be exceeded. Other rHTKA designs have avoided this complication by incorporating a mechanical link between the femoral and tibial components, as is seen in the Legion. 

In the Legion, the rotating hinge mechanism consists of a linkbush mounted on an axle between the condyles of the femoral component. This femoral link has multiple polyethylene linings, sagittally between itself and the femoral component (referred to as the hyper-extension stop), itself and the axle, and axially it rotates around a post-sleeve which engages with the tibial component via a morse taper, and has secondary fixation via a post-bolt which screws into the tibial component using a torque wrench (Figure 1). According to the manufacturer, there is a requirement for 96% of the load through the implant to occur via condylar loading to remove the stress placed upon the femoral link [25]. We hypothesise that for this 96% condylar loading to occur, the soft tissue envelope must be of sufficient competency so as to exert some compression across the tibial insert even during the swing phase of gait. However, if the soft tissue envelope cannot be relied upon to provide such a force, as is possible with multiply revised knees or those without competent collateral ligaments, this condylar loading may not occur. In such a situation excessive forces would be transmitted across the hinge mechanism and in turn lead to stress hardening of the hinge components and ultimately, fracture. This is what we hypothesise happened in the case of patient D when the femoral link fractured (Figure 7).

Patients A, B and D all demonstrated loosening of the post sleeve within the tibial component. For this to occur the fixation must fail in 2 places, the appropriately torqued post bolt must become loose; there is evidence of this in Figure 4a (top centre) with focal wear of the polyethylene bushing between the femoral link and the femoral component. The morse taper must then disengage from the tibial component sufficiently for the small metal tab at its distal aspect to fracture off, and become entrapped such that the morse taper cannot re-engage, allowing the anterior tilt of the post seen in figures 3 and 8. We suggest that a significantly attenuated soft tissue envelope could allow this at times when the leg is lifted (e.g. during swing phase of gait) and if combined with repeated axial rotations could lead to loosening of the post bolt and ultimately the morse taper.

Limitations

There are several arthroplasty surgeons in our unit performing revision operations and therefore it is difficult to standardise the treatment for all. Patients also have varying indications for revision surgery and therefore their post operative plan and result will vary. Another limitation to our study includes its retrospective study design.

Further prospective work with a standardised approach and post operative stress radiographs at set time intervals could detect any instability or impending catastrophic implant failure. There are no patient reported outcomes measures, however this was outside of the scope of this study.

Conclusion

Despite design advancements and evidence that supports the use of rotating hinge arthroplasty in knee revision surgery, this subset of patients presents complex surgical challenges placing them at risk for complication. Rotating hinge systems such as the Legion have their place in knee arthroplasty both in the complex primary and revision setting but may not have the durability required for some patients. We present five instances of early mechanical failure of the Legion rHTKA in three patients and propose the method of failure. This series emphasises the importance of careful implant selection for patients with gross instability or significantly attenuated soft tissue envelope. Long-term prospective studies with standardized follow-up protocols, including stress radiographs, are warranted to further evaluate the characteristics of rHTKAs in such patients and guide improvement in hinge knee arthroplasty technology and better define its indications for use in this patient cohort.

At present, we believe that major revision units should not rely on a single hinge system to cover all potential hinge cases. Each case requires careful evaluation, and a hinge knee system selected which best fits the patient’s needs. We advise caution when considering use of this prosthesis for patients with multiply revised knees or those with gross instability. In cases of mechanical failure, we would recommend caution if considering limited revision of the hinge mechanism. While this is potentially a less invasive option, in this series it was unsuccessful in 2 out of 3 cases.

Acknowledgements

Acknowledgements go to Miss Lia Nadimi, student of mathematics at Warwick University who assisted with creating the Kaplan Meier graph.

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