Knee

Dexamethasone and knee arthroplasty

One thing that most patients have in common when they undergo a total knee arthroplasty (TKA) is that they suffer from acute surgical pain in the post-operative period. The mainstay of pharmacological relief is opioids, however, the side effects of nausea, vomiting, sedation and constipation, as well as ineffective pain relief, have led to the use of a multimodal approach in the majority of centres to relieve pain following a TKA. The inability to control post-operative pain is not only distressing for the patient but can affect the patient’s surgical outcome, increase the patient’s hospital stay and may affect their ability to complete their post-operative rehabilitation.Dexamethasone is a long-acting glucocorticoid that has an anti-inflammatory effect by inhibiting peripheral phospholipase which reduces the pain-aggravating products from the cyclooxygenase and lipoxygenase pathways. They also inhibit cytokine gene expression and other pain mediators, thereby reducing pain secondary to inflammation. With a half-life ensuring efficacy for 48 hours, dexamethasone potentially has a lot to recommend it as a peri-operative analgesic adjunct. On the flip side of the coin are concerns about steroid use and stress ulcers in the peri-operative period, combined with concerns about immunosuppression in the knee potentially leading to higher infection rates. Previous research reports the effectiveness of dexamethasone in reducing pain following a number of general surgical procedures. Previous studies in TKA have involved multiple doses of dexamethasone being administered peri-operatively whereas these authors from Flint, Michigan (USA) set out to establish the effect of their protocol in the context of a single 8 mg dose of dexamethasone.¹ This retrospective comparative cohort study reports the outcomes of a 55-patient treatment group (who received dexamethasone) and a 47-patient standard care group. There were no differences in anaesthetic type between the two groups, and the primary outcome measure was oral opioid use within three days of operation. The dexamethasone treatment group required a significantly smaller quantity of oral opioids throughout the three-day period and reported lower pain scores at 24 hours. This is the first study to focus on the use of a single pre-operative dose of dexamethasone, however, in common with many other studies in orthopaedic surgery, it is let down by its methodology. It was a retrospective non-randomised study. There are now a number of studies suggesting the potential of dexamethasone to reduce pain following a TKA, and a proper randomised study is certainly warranted before this technique becomes more widespread, especially given the potential for adverse effects.

Patient-specific instruments in TKA: a systematic review and meta-analysis

TKA satisfaction scores are good but are consistently eclipsed by those of hip arthroplasty. For the patient and surgeon alike, it is disappointing when expectations are not met, not to mention the socioeconomic impact that this may have. Dissatisfaction is a complex multifactorial problem, however, there has been some focus on component alignment as a potential cause. Patient-specific instrumentation (PSI) is said to allow more accurate component alignment, coupled with reduced operating time and facilitating work flow in the operating theatre. Cross-sectional MRI or CT imaging is used to develop a 3D model of the patient’s anatomy and produce disposable pinning or cutting blocks which are used intra-operatively to align the components correctly. While meta-analyses have been published before on the subject, they did not include more recent studies, and the authors were keen to include those in order to obtain a more representative impression of how successful PSI has been in improving TKA outcome. A review team in Brussels (Belgium) and Männedorf (Switzerland) undertook the mammoth task of reviewing the literature for PSI.² They identified a total of 44 studies reporting 2866 TKAs that used PSI and 2956 that used standard instrumentation. Interestingly, there was a significantly higher probability of malalignment with the use of PSI for the tibial component in the sagittal plane but a lower probability of femoral component malalignment in the coronal plane with PSI, which translated into an important 30% greater chance of tibial component malalignment with PSI compared with standard instrumentation. This meta-analysis revealed a slight advantage regarding blood loss (perhaps due to the lack of intramedullary instrumentation) and operative time. There were six studies that reported enough data for meta-analysis of the post-operative Knee Society Score, demonstrating a significant, although marginal, improvement in the functional component of the score in the PSI group. Similar to previous meta-analyses, this study struggled with the heterogeneity of the data and a possible publication bias, however, it is the largest study of its type to date. It did show that PSI is associated with an increased risk of tibial component malalignment and, similar to previous studies, there was no evidence that PSI is associated with an improved clinical outcome. There is therefore little evidence to support the routine use of PSI in standard primary TKA, however, it does have its uses. For patients with previous femoral shaft fracture or severely abnormal femoral geometry, PSI may have a role.

Robotic-assisted medial unicompartmental knee arthroplasty

In the never-ending quest to improve surgical outcomes through improved accuracy of component position, there has been a push from implant companies to develop technology to improve accuracy of component positioning. Three technologies continue to be developed and pushed hard, namely computer navigation, patient-specific instrumentation and, on the even more expensive end, robotic-assisted surgery. Arguing that a key determinant in outcome for unicompartmental knee arthroplasty is the accuracy of surgical approach, authors in New York, New York (USA) have published their multicentre study reviewing the outcomes of 1135 patients who underwent robotic-assisted TKA.³ There were outcome data available for 909 knees at an average of around 30 months of follow-up. Of those available for review, there were 11 known knees reported as revised (98.8% survival). In the worst-case scenario, where all 35 who declined participation had failed, the survival would be 96%. These results in the best case are better than the vast majority of published series and, especially given the size of this cohort, it does give one pause for thought. Although robotic-assisted surgery has never been seen to have much of an advantage here at 360, given that we now know unicompartmental knee arthroplasty perhaps isn’t an operation where the implant tolerances are particularly lax, this paper certainly gives some pause for thought.

Predicting dissatisfaction following TKA in the young

We have already touched briefly this month on the difficulty of the dissatisfied TKA patient, with strategies for improvement in other papers focusing on accurate component position. In an excellent paper from Edinburgh (UK), the authors focus instead on the age-old practice of ‘picking winners’.⁵ We all know it when we see one, that patient who will do incredibly well, just as we know the patients protesting a ‘high pain threshold’ have anything but.This paper focuses on the assessment of 177 serial TKAs undertaken in 157 consecutive patients under the age of 55 years. The core of this study is the collation of demographic information (age, gender, body mass index (BMI), social deprivation), diagnostic information (indication, range of movement, Kellgren-Lawrence grade) and surgical details (prior knee surgery, implant), as well as attempting to predict the likely functional outcome (as measured by the Oxford Knee Score and SF-12). Pre- and post-operative scores, along with one-year outcome scores, were available. There was a range of factors that appeared to predict dissatisfaction following surgery, including low Kellgren-Lawrence grade, low pre-operative Oxford Knee Score, previous surgeries, high BMI and post-traumatic arthritis. Although the authors included a multivariable model for outcomes, this was of little use to the study question as they included change in pre- and post-operative functional scores which remained independently predictive of dissatisfaction. However, clearly this is not a co-variate as the improvements in self-reported functional scores and satisfaction are likely to be dependent. Perhaps the most helpful message here is to avoid offering TKA to patients with Kellgren-Lawrence grade I or II osteoarthritis, as the dissatisfaction rates are around 60%.