Knee

Albumin and complications in knee arthroplasty

While assessing patients who are undergoing elective primary total joint arthroplasty, surgeons strive to stratify risks and thereby optimise outcomes for patients. Much thought has been given to body mass index (BMI) as a predictor of both outcomes and complications, with some surgeons and healthcare systems using an upper BMI threshold to deny surgery due to the risk of increased post-surgical complications. A study team in Philadelphia (USA) set out to establish if there is a more subtle predictor of complications than the blunt tool that is BMI.¹ However, this study of more than 77 000 patients importantly points out that other parameters such as serum albumin are arguably more important for assessing patients. Low serum albumin (< 3.5 mg/dL) was associated with increased surgical site infections (all levels), and many other major complications such as pneumonia, unplanned intubation, progressive renal insufficiency, cardiac arrest, and septic shock. Interestingly, morbid obesity was not associated with increased transfusion rates, while low albumin was. This does beg the question: is it the obesity itself or the often associated nutritional issues that are the most important determinant in outcomes in the obese?

Tantalum: a knee fixation for all seasons?

As candidates for arthroplasty are becoming younger and younger, and living longer, the burden of revision surgery will increase into the future. Durable fixation in revision situations with poor bone stock is likely to be one of the major challenges of the next few decades. One of the responses of the implant industry to this challenge has been the development of porous metal implants, most commonly tantalum. An arthroplasty group in New York (USA) has been using tantalum cones in the proximal tibia to address revision-related bone defects in proximal tibial metaphysis.² There are a number of short-term series but no longer-term outcome studies relating to these implants, therefore their report of five- to eight-year follow-up is of interest. Although these authors report just 18 knees at this longer stage of follow-up, the results themselves are promising. The authors report a combination of radiological outcomes and clinical outcomes (Knee Society Score) for this cohort of revision knee arthroplasties undertaken for both septic and non-septic indications. In total there were 26 individual tantalum cones: 13 each of tibial and femoral implanted for five cases of aseptic loosening, and 13 reimplantations for deep infection. There were two long-term failures requiring reoperation, both for infection, and the rest of the implants showed no evidence of loosening or migration of any kind with excellent improvement in post-operative results (31 points to 77 points). While these are clearly early and limited results, some inferences can be drawn from them. We would advise caution when using tantalum cones in septic revision scenarios, as patients have a higher likelihood of reinfection, and as the cones integrate so well, removal in the light of infection may be very difficult. These are promising early results from a small series, but clearly more work is required here.

Dynamic knee alignment

Historically, the goal of TKA has been to restore neutral limb alignment with a square flexion/extension gap. There has, however, been a spate of recent studies focusing on the variations in alignment that occur with joint position, degree of weight bearing and gender. Despite advances in computer navigation and patient-specific instrumentation, there is still a cohort of patients that are unsatisfied following TKA, and some authors are attributing these cases to alteration of the patient’s normal limb alignment. Various studies have reported on the variation of limb alignment between genders and different positions; however, the weakness of many of these studies is that they report on patients with OA and after TKA. A study team from Glasgow (UK) and Madhapur (India) describe the variation in alignment of 132 patients (264 knees) in healthy volunteers. The researchers used the Orthopilot navigation system to measure the femorotibial mechanical angle (FTMA) across a range of positions. The mean supine alignment was a varus angle of 1.2°, which increases to 3.4° on standing. Alignment differed significantly between males and females (p = 0.008). This study³ has its inevitable limitations such as using cutaneous trackers rather than bony attachments, however, prior to this study, normal variations in alignment using the FTMA between gender and flexion position were unknown. Currently, the goal of TKA is to restore neutral limb alignment. However, based on this study, this aim may not be correct, as the majority of ‘normal’ people do not have neutral alignment, and intra-operative neutral alignment may translate to varus alignment in weight bearing. The authors conclude that limb alignment is dynamic and suggest that variations between gender and posture should be considered prior to TKA. There are, nonetheless, still a number of unknowns. It is not yet clear how arthritic change varies position and, indeed, if restoring a more physiological axis can give better clinical results.

Tibial component design in UKA

Unicompartmental knee arthroplasty (UKA) is gaining in popularity due to the excellent functional results, despite concerns over its longevity. There is however a paucity of data comparing different UKA implant designs and survival rates. Researchers in Montréal (Canada) set out to unpick the potential pros and cons of metal-backed or all-polyethylene tibial components in fixed bearing unicompartmental knee designs.⁴ They conducted a single blind randomised trial at a single institution comparing the two tibial implant designs. Their study concerned 45 patients (63 knees), all of whom underwent a UKA using an Accuris UKA system, and patients were randomised to either a cemented all-polyethylene or metal-backed modular tibial component. Follow-up was reported to 6.4 years, by which point 11 of the 27 (41%) patients in the all-polyethylene group had undergone revision, the majority (n = 10/11) for aseptic loosening, with Kaplan-Meier survivorship analysis at seven years giving a survival of just 56.5% compared with 93.8% in the metal-backed group. Despite the poorer survival rate, the all-polyethylene group had significantly better mean WOMAC scores (13.4 vs 23), but similar KOOS scores (68.8 vs 62.6). While the authors argue that each design has its own advantages and disadvantages, with failure rates like this, the all-polyethylene implant can be said to be not to be fit for purpose.

Managing the tidal wave of revision knee arthroplasty

For a fair few years there have been predictors of a rising unmet need for revision knee arthroplasty. Given the growing prevalence of total knee arthroplasties, combined with increased patient life span and increasing rates of osteoarthritis, it does look like there may be a ‘perfect storm’ brewing. While the revision rate following TKA is very low, these procedures can be challenging, with loosening associated with bone loss. In an interesting view of what the future may hold, and how to address the potential difficulties associated with this revision burden, researchers in Edinburgh (UK) reviewed the evidence to date.⁵ Perhaps the key question orthopaedic surgeons must ask, given the burden of an increased number of patients undergoing TKA and high numbers of unsatisfied patients or failures after TKA, is how do we improve clinical outcomes for the growing number of dissatisfied patients? The authors of this article suggest that based on the increased criteria for TKA, a re-revision procedure will become increasingly common. With one in ten patients who were younger than 55 years old at the time of primary TKA having their first revision around age 65, it is reasonable to suppose that 20% of these patients will require a second revision by the age of 75. The authors suggest that future resources should be focussed on supporting specialist groups that can provide specialised care for patients requiring revision TKA.

Scoring pain in TKR

The goal of total knee arthroplasty (TKA) is to restore function and decrease pain. The much discussed problem of the ‘5%’ of patients who develop persistent pain following TKA has troubled knee surgeons for decades. Assessing pain can be difficult, and the results vary markedly depending on the instrument used. It is traditional to utilise a range of knee-specific outcome scores such as the Knee Injury and Osteoarthritis Outcome Score (KOOS) or more generic measures such as the Visual Analog Score (VAS). There are, however, a range of other pain specific scales including measures of somatisation and neuropathic pain. In this retrospective review, researchers from Lund (Sweden) attempted to shed some light on the difficult subject of scoring pain post total knee arthroplasty.⁶ Their study population consisted of 2123 patients identified from the Swedish Arthroplasty Register whose operations were carried out at two units in Sweden. The cohort all had pain and functional scores recorded pre-operatively and one year post-operatively. This report concerns 220 patients who reported increased or unchanged pain following surgery, with 50 (23%) reporting increased or unchanged pain on both the VAS and KOOS. Patients who experienced no pain relief on either pain scale tended to have high anxiety or depression indices pre-operatively. Interestingly, the scores used to assess pain dramatically altered the results, with the VAS scale resulting in twice the number of patients reporting no pain relief following a TKA compared with using the KOOS to assess pain (55 vs 115 patients, respectively). The authors suggest that when considering pain assessment following TKA, the level of pre-operative pain should be taken into account, with those with lower pre-operative pain scores appearing to have the least benefit post-operatively, as would be expected. They also make the observation that the observed relief in pain may vary depending on the instrument used to measure pain.

Does anyone have a ‘normal’ tibial slope?

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With coronal plane geometry causing quite a stir in the collected scientific press at the moment, and a gathering of supporters of so-called ‘anatomic alignment’ in knee arthroplasty pointing out that many patients may in fact have far from normal alignments in the coronal plane, we were delighted to see this paper from a study team in Balikesir (Turkey) who took on the challenging task of analysing 13546 CT scans with the express intention of describing the sagittal plane alignment – and, specifically, the normal posterior tibial slope.⁷ Using scans of osteoarthritic knees, the researchers calculated the posterior tibial slope angle in established disease. They established a wide range of alignments exist, with an average posterior tibial slope of 7.2°±3.7° (range, -5° to 25°) with little difference between sexes. Given accepted normal ranges, the authors would have classified around a third of patients as outliers. Although the authors conclude that “these data can be useful to determine optimum techniques and methodology to perform more accurate TKA,” we would venture that these data are no more compelling than those for other variants of ‘anatomic’ knee alignment. What we do not know is if the variation really is normal, causative of the disease process or symptomatic of knee disease. We know that in varus OA, the loss of medial joint space is part of the disease process, not normal variation. Before implanting knee arthroplasties with as much as 24° of posterior slope, we would really like to see a well-designed study establishing the normal alignment of these joints in patients without OA.

Cross-linked polyethylene in TKA A five-year clinical study

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The goal of an everlasting joint replacement seems a remote one at the moment in knee arthroplasty. While ceramic articulations in the hip have provided bearings that essentially don’t suffer enough wear to be clinically relevant in the lifetime of most patients, the same technology is not suitable for knee arthroplasties. Even the now relatively standard highly cross-linked polyethylene (XLPE) has some potential drawbacks in the knee. A process that makes the polyethylene more brittle and susceptible to the delamination and fatigue failure seen in TKA has led some naturally suspicious surgeons to doubt its benefits. Combined with concerns about the biologically-active particulate load actually increasing (while total volumetric wear decreases), we may have some very justified concerns about its use in TKA. In a pragmatic approach to addressing some of these concerns, clinicians in Indianapolis (USA) have reported their results in posterior-stabilised knee arthroplasties (where wear on the peg raises some particular concerns).⁸ The authors report the results of 114 consecutive posterior-stabilised total knee replacements, of which 50 utilised conventional polyethylene and 64 XLPE. Outcomes at five years seem to suggest a slight advantage to the XLPE group, with superior KSS scores and SF-36 physical performance scores. There was no difference in radiographic evidence of osteolysis or macroscopic failure of the tibial insert. In this mid-term follow-up study, there were no deleterious effects associated with using highly cross-linked polyethylene in PS TKA designs at five-year follow-up. The potential benefits in terms of reduced wear debris will, we hope, be addressed in a report of the next five years’ results!

Spacers and infected revision arthroplasties

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The use of the antibiotic-loaded spacer (either custom or pre-fabricated) as part of a two-stage revision for proven infected knee arthroplasties is considered the ‘gold standard’ the world over. The combination of dead-space management, antibiotic elution and maintenance of soft tissue envelope makes the spacer an essential tool for the revision arthroplasty surgeon. A study team in Philadelphia (USA) examined their own series of over 500 cases of revision arthroplasties treated with a two-stage ‘spacer’-based approach. In their series,⁹ the use of the spacer facilitated reimplantation of a definitive joint replacement in 417 patients, with around 80% of these successfully treated. The authors waited on average around four months to reimplant a total joint arthroplasty. Overall, 87 cases (17.3%) did not result in successful reimplantation. In those where it was not possible to revert to an arthroplasty, 14% underwent amputation or a Girdlestone’s procedure, with 5% requiring arthrodesis and the remainder retaining the spacer (83%). The authors make the very valid point that despite the general view that two-stage revision arthroplasty with a spacer yields good results, the rates of failure of salvage are still surprisingly high.

Dialysis and arthroplasty

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In a short and to-the-point paper, surgeons in Baltimore (USA) set out to examine the success or otherwise of arthroplasty in patients who are undergoing haemodialysis for renal failure.¹⁰ As survival for patients with end-stage renal failure is increasing, there is a mounting burden of patients with a variety of underlying pathologies requiring renal transplantation. Using the national inpatient sample of over 6 million patients who had undergone hip or knee arthroplasties, 2934 patients who were dialysis-dependent were compared with 6 186 475 patients who were not. Outcomes were assessed in terms of inpatient mortality and complications. With regards to hip arthroplasty, dialysis patients were younger, had higher inpatient mortality rates (1.88% vs 0.13%) and complication rates (9.98% vs 4.97%). As perhaps might be expected, dialysis was an independent risk factor for mortality (OR 6.66) and complications (OR 1.53). There was a similar story in the knee arthroplasty group, and although patients were similar in age (66.7 vs 66.8 years) the investigators still identified higher inpatient mortality rates (0.92% vs 0.10%) and overall complication rates (12.48% vs 5.00%). We agree wholeheartedly with the authors’ view that “Arthroplasty should be approached with caution” in these patients, and clearly patients wanting TKA or THA should have a clear and frank discussion on the risks specific to dialysis.