Stryker Triathlon Total Knee Replacement System | Used in Knee replacement | Which Medical Device

Triathlon Total Knee Replacement System

Added Sep 16, 2010

Manufactured by Stryker

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Categorised under: Orthopaedics > Knee > Total knee replacement

Reviews

Reviewed by Mr Craig Gerrand Reviewed Sep 16, 2010

Consultant Orthopaedic Surgeon, Freeman Hospital, Newcastle upon Tyne, UK - Declaration of Interest: The Author is part of a group funded by a Stryker educational grant to evaluate the Triathlon knee system.

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The Triathlon knee system was launched in 2005 by Stryker as a single radius, high flexion knee replacement system. Other features included better anthropomorphic fit and Orthonomic instrumentation (orthopaedic and ergonomic). At the time, Stryker had a number of knee systems on the market including the Kinemax and the Scorpio systems. Cruciate sparing, cruciate substituting, revision designs and a rotating platform version have all since become available. This review concerns the cruciate retaining, fixed platform design with which I have most experience (over 150 knees). I have also been a regular user of the PFC Sigma knee.

The Triathlon knee system was launched in 2005 by Stryker as a single radius, high flexion knee replacement system. Other features included better anthropomorphic fit and Orthonomic instrumentation (orthopaedic and ergonomic). At the time, Stryker had a number of knee systems on the market including the Kinemax and the Scorpio systems. Cruciate sparing, cruciate substituting, revision designs and a rotating platform version have all since become available. This review concerns the cruciate retaining, fixed platform design with which I have most experience (over 150 knees). I have also been a regular user of the PFC Sigma knee.

The femoral and tibial components are cobalt-chrome. In recent years X3 polyethylene (Stryker’s cross-linked polyethylene) has become available and has become standard in our centre.

The instruments come in three trays, and are well-presented and relatively easy to use and learn (figures 1 to 4). Instruments for outsize components (large or small sizes) come in a separate tray.

In use

The instruments are generally thoughtfully designed and are low profile. This is particularly so for the distal femoral cutting block which is elegant in its design and has good all-round visibility, compared with the PFC cutting block for example.

There is a learning curve for some aspects. This includes the tibial cutting jig which can be assembled upside down (figure 5). When measuring the tibial cut, the stylus measures either 2 or 9mm of resection, i.e. 2 mm off the medial side (if worn) or 9 mm from the lateral. In my experience, there is a tendency to under-resect the tibia, and I have had to re-cut it on several occasions. I now tend to leave the tibial pins in until I’m sure the extension gap is right. The handle for the trial tibial tray takes a little getting used to – the reason it inserts in such an unusual way apparently relates to the number of patents on preexisting systems which means that the designers have struggled to come up with a novel solution (figure 6 and 7). The handle which attaches the tower for the keel cutting to the trial tibial tray amusingly says “lock” on it. It doesn’t lock and takes a little care. Likewise, the keel cutter (just like the Scorpio) can have difficulty in hard bone and the tray can lift off the resected tibia as you knock it in. I have heard of a tibial fracture occurring once when the keel cutter was used. Multiple lighter blows with a hammer are probably best here.

The femoral drill has 3 steps to it. Stop at the second. It is rarely necessary to use the thickest diameter of the drill in my opinion – just makes the hole more difficult to plug (Figure 8).

When making the distal femoral cut, the block allows you to select an 8 or 10mm resection. I very rarely use the 10mm option, unless I have revised a cut in a knee with a marked fixed flexion deformity. I find this is different to the PFC, where I was taking 10-12mm routinely, but the Triathlon is thinner distally than the PFC. I did have a minor balancing issue early on when I took 10mm and ended up loose in extension and tight in flexion, which took a PCL recession and a revised tibial slope to balance. Since then I have avoided the 10mm option first off.

The fixed radius design means that posterior referencing is the order of the day. The downside of this is, of course, that there may be a tendency to notch the femur as a result. The designers have compensated for this by designing the anterior cut to diverge from the posterior cut as you go from distal to proximal. It’s not a notch apparently – more of a chamfer. However, I have not had any problems with this. The distal anterior chamfer cut can appear alarming – quite a large piece of bone comes off – but you can rationalise this by considering that the distal cut is a little thinner.

This is a high flexion design and there is an emphasis on removing the posterior osteophytes at the back of the femoral condyles using the posterior osteophyte removal tool, aka the curved osteotome in the set, and this appears to be an important step.

Final implantation is usually problem free (Figure 9). The tibial tray snaps into place quite easily without using the impactor. I thought the tibial insert impactor was marking the polyethylene early on until I realised there is always a transverse groove at the front of the polyethylene. The polyethylene fits very well into the tray and is very difficult to remove without destroying it. The spring wire at the front of the insert is likely very helpful here and it feels more secure than the PFC or the Kinemax inserts have been (Figures 11 to 13).

There were initial problems with the fixation pins supplied with the sets, but the fluted pins with a spiral groove which we now have work well. However, the device which pulls the pins out when you pump the handle almost never works in the intended fashion.

I don’t routinely resurface the patella, and the physiotherapists feel anecdotally the Triathlon is a very patella-friendly knee. However, I have gone back to resurface one or two patellae at a year as I have had to with the PFC from time to time, so the jury is still out on this. When I have, I tend to use the asymmetric patella. The instruments are as good or as bad as any I have seen – you either like using them or you don’t.

Soft tissue balancing is usually straightforward for most knees. Early on there was a suggestion that the knee should go in relatively tight – this is a mistake. I aim for 1-2mm of opening on the medial side with the knee in extension. In flexion, the knee opens up less than the PFC, the j-curve cross section of which gives more flexion gap.

At the end of the case, in deep flexion, the components appear to articulate well with each other. This is different to the PFC, which tends to lift off a little in deep flexion.

Results so far

Results have been really very good so far. I have had the occasional stiff knee, as has been the case when using the PFC system and the occasional patellar resurfacing. Our cohort of patients is in a study, the results of which are awaited and which should demonstrate whether the high flexion design pays off. Patients are generally pleased, and I have had no complaints suggestive of instability through flexion.

Conclusion

In my experience the Triathlon knee system is an excellent device which may improve outcomes for patients undergoing primary knee replacement, although the results of our study are not yet analysed. There is a learning curve which surgeons should be aware of.

Mr Craig Gerrand,
Consultant Orthopaedic Surgeon, Freeman Hospital, Newcastle upon Tyne, UK

Conflict of interest statement: The author is part of a group funded by a Stryker educational grant to evaluate the Triathlon knee system.

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