The next most common reason for revision was patellofemoral problems (50%), while nearly 60% of patients were found to have multiple causes for failure¹.

TKR is the treatment of choice for advanced multi-compartmental OA, but 10-30% of patients report ongoing pain and dissatisfaction, often resulting in revision surgery¹,². The burden of revision TKR is increasing in many countries, and the rate of revision in national joint registries now ranges from 3 to 12%, depending on the observation period and the criteria for a ‘revision’ TKR being applied¹.

Most literature on the causes of revision TKR has been based on national registry data. Often this analysis is limited to a single cause per revision, and employs no standardised methodology for accurately diagnosing the cause of failure¹. “This impedes the careful identification or exclusion of all possible failure modes¹.”

The objective of this study was to assess the most common reasons for primary TKR failures in a large single-centre series using a published, standardised diagnostic algorithm¹. Data from a specialised knee centre was collected prospectively for patients presenting with persistent post-TKR pain between 2015 and 2020. Revision was defined as a “secondary surgical procedure…where by the complete primary implant or parts thereof are replaced by new components¹.”

The failure categories used were:

• Aseptic loosening

• Peri-prosthetic infection

• Instability

• Wear/osteolysis

• Arthrofibrosis/stiffness

• Malalignment

• Patellofemoral problems and/or extensor mechanism insufficiency

• Peri-prosthetic fracture

• Irritation of ITB

• Others

Where more than one cause of failure was observed all causes were recorded.

The mean time to revision TKR was 3.6 years. 98/49% were performed within the first 2 years of the index surgery. 102/51% occurred later than 2 years from the primary procedure¹.

Being a knee centre specialising in painful TKR, most patients (86%) came via tertiary referrals from other centres/surgeons. A total of 87 different surgeons performed the primary TKRs making up the cohort for this study¹.

As well as the most common failure modes, the authors also explored any correlation between the failure modes. Interestingly, they observed a strong positive correlation between patellofemoral problems/extensor mechanism insufficiency and malalignment (p < 0.01) and wear/osteolysis and ‘unexplained’ pain (p < 0.01)¹.

The findings that instability and patellofemoral problems were the most common causes for revision differ from the findings of previous literature¹. The authors were not surprised by this observation because the majority of the revisions in this instance were tertiary referrals to a centre specialising in painful TKR. They concluded that: “due to the standardised diagnostics following a validated algorithm for painful patients after TKR in the setting of a knee centre, it is likely that the identified failure modes might differ from those based on registries and studies carried out in less specialised institutions¹.”