Tuesday, November 22, 2011

High Flex Designs - a walk in the clouds


High flex TKR has caught the common man’s imagination. And the Orthopaedic surgeon is all set to take advantage. Promises of unimaginable postoperative flexion are easily made. The medical rep gives guarantees to the doctor and the doctor to the patient. The newspapers are flooded with this miracle of modern science and technology.
Is this all true? Or is it a fairy tale we are all weaving?
Mehin et al in a recent Meta-analysis studied high flex versus conventional implants.  They included only randomised clinical trials. They found no improvement in flexion with high flex implants.
Nutton et al also studied this. They did a prospective double-blind randomised controlled trial. They studied 56 patients. They found no difference in flexion.
NgFY et al also could not find better flexion in the high flex group nor could Kim et al.
Murphy et al did a review where they included 9 studies. Again high flex implants failed to show more flexion.
I think we need to be careful with high flex implants. Tall claims are made on shaky foundations.
Don’t get me wrong. We are achieving better postoperative flexion nowadays. But are we giving the prosthetic design too much credit?
It all matters. The preoperative range of motion, the severity and type of disease, the surgical skill (meticulous ligament balancing and proper implant position) and the patients’ compliance with postoperative physiotherapy.
So let’s come down from the clouds and do our part – balance, rotate and align them well. Then the magic of flexion will happen. Happy replacing!!

Friday, November 11, 2011

VARUS BEFORE - VARUS AFTER??


Knee Replacement has always been about alignment. A recent article by Pagnano et al shook the very foundations of knee replacement by claiming that alignment is a poor predictor of the durability of the implant. Ritter et al however think otherwise. They too studied a huge no of knees (6070) and concluded that alignment is after all important.
I am worried about alignment as I don’t have the luxury of navigation yet. I came across this interesting article. The authors claim that preoperative varus deformity predisposes to varus malposition of the implants. Furthermore, they say that more the varus, more is the risk of malposition. However this is not true for valgus knees in which malposition and malalignment were rare. (I find that difficult to digest)
They used an intramedullary guide for both the femur and the tibia. With varus bowing in the tibia, intramedullary guides can go wrong. This was studied by Teter et al. However they also concluded that extramedullary instrumentation is no better.
Dennis et al recommended that the extramedullary guides should be distally positioned over the center of the talus (3 mm medial to the midpoint of the ankle) to avoid varus tibial resection.
Coming back to the article in question, the authors could not specify the reasons for the varus postop alignment. It is obviously a technical issue. It is an error of the instrumentation or an error of the surgeon’s technique.
The take home message would be to be careful about alignment. Plan properly. Check and recheck during surgery. And be more careful whilst operating varus knees. Happy Replacing!! 

Wednesday, November 9, 2011

Does postoperative limb alignment affect implant survival in TKR? Does better alignment achieved by Navigation TKR reallly affect implant survival?


The effect of post-operative mechanical axis alignment on the survival of primary total knee replacements after a follow-up of 15 years.

J Bone Joint Surg Br. 2011 Sep;93(9):1217-22.
Bonner TJ, Eardley WG, Patterson P, Gregg PJ
Source: Queen Elizabeth Hospital, Sheriff Hill, Gateshead, Tyne and Wear NE9 6SX, UK. t.bonner10@imperial.ac.uk

Abstract:
Background:  Correct positioning and alignment of components during primary total knee replacement (TKR) is widely accepted to be an important predictor of patient satisfaction and implant durability. The apparent benefits of achieving a neutral mechanical axis (angle of 0°) of the lower limb during TKR surgery has encouraged surgeons and manufacturers to invest time and resources into achieving this alignment target. This retrospective study reports the effect of the post-operative mechanical axis of the lower limb in the coronal plane on implant survival following primary TKR.

Materials and Methods: A total of 501 TKRs in 396 patients were divided into an aligned group with a neutral mechanical axis (± 3°) and a malaligned group where the mechanical axis deviated from neutral by > 3°.

Results: At 15 years' follow-up, 33 of 458 (7.2%) TKRs were revised for aseptic loosening. Kaplan-Meier survival analysis showed a weak tendency towards improved survival with restoration of a neutral mechanical axis, but this did not reach statistical significance (p = 0.47). The pre-operative alignment, type of fixation and primary pathology did not predict either the accuracy of alignment of the mechanical axis or the survival pattern in either group

Discussion: Interest in the accurate positioning and alignment of arthroplasty components has been the subject of controversy, particularly following the development of computer navigated surgery. Justification for using computer navigation and its cost-effectiveness is based on the implication that accurate alignment improves implant survival, thereby reducing the rate of costly revision, but the evidence supporting this is scarce. In present Study the effect of post-operative alignment of the mechanical axis, measured using long-leg radiographs, on the long-term risk of revision surgery demonstrate only a weak relationship between alignment and the risk of revision surgery. Thus, the reported cost-benefit ratio of computer navigated TKR surgery using 3° as the primary outcome measure alone may exaggerate its benefit, with the effect of computer-navigated TKR on long-term implant survival remaining unproven.

Conclusion: We found that the relationship between survival of a primary TKR and mechanical axis alignment is weaker than that described in a number of previous reports.

LEVEL OF EVIDENCE: Level -  IV

IORG Arthroplasty Update

Tuesday, November 1, 2011

All - Polyethylene tibial component has finally proved its metal (by avoiding metal)

Initial total knee prosthesis had an all polyethylene tibial component. They went out of favour because of fears of subsidence and early failure. Metal backed components were introduced with claims of better load distribution to the proximal tibia and consequently less subsidence and loosening.
However advantages of the all polyethylene tibia cannot be ignored. The component is monoblock thereby completely eliminating backside wear. Moreover it is cheaper making the surgery more cost effective.
So what is the current status of the all polyethylene tibial component?
A ten year randomized controlled trial comparing all poly with metal backed components found no difference in the two components. They studied 566 knees.
Blumenfeld et al in a literature review recommended all poly components in older patients and less active younger patients. The only disadvantages they mentioned were an inability to change liner thickness after final component cementing and inability to use constrained inserts. Also poly exchange is not possible.
Another study in JBJS Am published in 2010 also supports the use of all poly tibial components.

As always there is another side of the coin. So check for yourself and decide. Happy replacing!!