Reference: June 2026 | Issue 6 | Vol 12 | Page 23
Total hip and knee replacements remain amongst the most successful surgical procedures, with satisfaction rates over 90 per cent and implant survivorships of 20-25 years in 60 per cent of patients. However, up to 5 per cent of patients have an unsatisfactory outcome, typically due to risks associated with surgery such as infection, dislocation, nerve injury, leg length discrepancy, blood clots, cardiac, and respiratory complications. Improving outcomes further and reducing the risk of these complications continues to focus on surgical technique, implant technology, and perioperative care.
Optimising comorbidities prior to joint replacement is one area of renewed interest, particularly in primary care, where there is now good evidence of improved outcomes in patients with modifiable risk factors such as body mass index, diabetes, smoking, and malnutrition. This will be more relevant as our demographics shift to an older population who will have higher rates of comorbidities.
In Ireland, we are predicting a significant rise in the number of patients requiring hip and knee replacements in the public system (2,500 versus 12,500) by 2050 and the majority of these patients will be over 50 and likely to have comorbidities. Optimising these patients prior to surgery will be important in maintaining good outcomes and reducing the risk of complications.
Patients are also often keen to engage in this process, contribute to the outcome of their joint replacement, often asking what they can do to improve the chance of a good outcome after their hip or knee replacement. This can provide both motivation and opportunity in the pre-operative period before a joint replacement to optimise any co-morbidities which may continue after surgery.
Body mass index
The effect of body mass index (BMI) on outcomes after total hip and knee replacement has been extensively studied, with evidence that patients who have a significantly raised BMI (>40Kg/m2) in particular have an increased risk of complications such as revision, infection, and dislocation (all approximately two times more likely; 1 per cent versus 2 per cent absolute risk).
The evidence for patients with BMI 30-40Kg/m2 is less clear, with smaller effects seen. There is much debate and variance in practice in the orthopaedic community about offering joint replacements to patients with a BMI greater than 40Kg/m2, with some centres viewing a BMI >40Kg/m2 as being an absolute contraindication to surgery. Other centres and surgeons offer surgery regardless of BMI and accept the increased risks once the patient is aware.
A third strategy is to address modifiable risk factors and patients should be given an opportunity and assistance to reduce their BMI prior to joint replacement surgery and proceeding with joint replacement even if the BMI remains over 40Kg/m2 despite intervention. This ideally should involve a weight loss programme that encompasses the option of pharmacotherapy (eg, GLP-1 agonists), dietetic nutrition therapy, and behavioural change support.
There is now emerging evidence that novel pharmacotherapy agents (eg, GLP-1 agonists) are having a significant effect in reducing BMI in these patients, which in turns reduces the risk of complications such as infection (2.1 per cent versus 3 per cent) and readmission to hospital. Apart from reducing the risk of complications after joint replacement surgery, pharmacotherapy has also resulted in improved symptoms, delaying the timing of surgery in some cases.
The STEP 9 trial has shown significantly improved weight loss, knee symptoms, and function in obese patients who were treated with semaglutide versus placebo (diet and exercise guidance). In my view, patients who are obese (BMI >40Kg/m2 in particular) should be offered a weight management programme prior to hip and knee replacement surgery to optimes outcomes and reduce the risk of complications after surgery.
Diabetes
Approximately 5 per cent of our population is diabetic, with prevalence expected to increase as our population ages. Poorly controlled diabetes has been demonstrated to be associated with poorer outcomes after total hip and knee replacement. Chronically raised blood sugar levels directly increase the risk of infection (wound, implant) and longer length of hospital stay. Indirect effects, such as impaired circulation, also contributes to infection and poor wound healing. Studies have demonstrated increased risks of infection (odds ratio [OR] 2.28), CVA (OR 3.42), UTI (OR 1.47), blood transfusion requirement (OR 1.19) and death (OR 3.23).
For patients with a HbA1c greater than 7 per cent surgery should be postponed until their diabetic control is improved. This typically involves input from the primary carer for their diabetes, ie, their general practitioner or endocrinologist. Perioperative control of blood sugars is also important in avoiding complications, and for some patients, endocrinology-led perioperative management is required.
Smoking
Approximately 17 per cent of the Irish population are smokers, according to the latest Healthy Ireland survey (2026). Along with increased risks of cardiovascular disease, multiple cancers, respiratory disease, and diabetes, smoking has also been shown to have a negative impact on outcome after total hip replacement.
A systematic review of 67,897 patients has shown that patients who are active smokers in the year up to their total hip replacement have an increased risk of respiratory complications (OR 1.32), infection (OR 1.31) and increased length of stay (OR 1.17). Smoking is a modifiable risk factor and patients should again be informed of the risk of having a total hip replacement whilst smoking and given an opportunity and help with smoking cessation.
Kidney disease
Approximately 10 per cent of the Irish population have chronic kidney disease, varying from mild to severe (stages 1 to 5). A large meta-analysis of 100,000 patients has shown an increased risk of complications such as mortality (OR 1.89) and infection (OR 1.37). Risks were increased in patients who were on dialysis, in particular mortality (OR 4.2) and risk of revision (OR 2.15). Patients, thus, need preoperative risk stratification and optimisation to inform them of and reduce the risks of total joint replacement surgery.
Optimisation involves avoiding inappropriate hydration, avoiding hypotensive events, and nephrotoxic medications perioperatively. In patients on dialysis, the risks are higher though dialysis itself is not a contraindication to proceeding with joint replacement. It is imperative, however, that patients with moderate to severe chronic kidney disease are managed perioperatively by a renal physician in a high care environment such as high dependency or intensive care, with dialysis available as required.
Neurological disease
As our population ages, the prevalence of conditions such as Parkinson’s disease, dementias, multiple sclerosis, and movements disorders is increasing. This encompasses a wide spectrum of disorders which can result in muscle imbalance (contractures, paresis, or flaccidity), impaired co-ordination and balance. These patients were traditionally considered to be at a high risk of dislocation and other complications, with joint replacement generally avoided.
We have carried out a systematic review of the evidence on this heterogenous patient group and have shown an increased risk of dislocation (10.6 per cent versus the standard 1 per cent) in patients with neurological disorders. However, we have also found significant improvements in hip function and quality of life. Improved outcomes are seen where surgery is carried out by high volume surgeons, use of specialised implants, risk stratification, involvement of all relevant care providers in an MDT format and careful preoperative optimisation. Patients with these conditions should be considered for joint replacement, an appropriate risk assessment carried out, and patients informed of both potential benefits and risks.
Malnutrition
Malnutrition as defined by serological markers (albumin <3.5g/dL or lymphocyte count <200mg/dL or transferrin <200mg/dL) has been shown to be present in up to 20 per cent of patients undergoing total hip and knee replacement. Furthermore, these patients have been shown to be at a higher risk of postoperative complications such as delayed wound healing, wound infection, cardiac and respiratory complications, mortality and extended hospital stay. This is in keeping with a trend seen in all surgical procedures where nutrient, mineral and vitamin deficiencies are associated with poor wound healing and associated complications. Malnutrition again is a modifiable co-morbidity and when suspected should be assessed by serology as per above. Appropriate interventions such as protein rich supplemental drink can then be provided or ideally formal review and management by a dietician.
Summary
In summary, as our population ages, the prevalence of patients with common co-morbidities such as diabetes and obesity undergoing total hip and knee replacement is also increasing. As we strive to improve outcomes after total hip and knee replacement, there has been considerable focus on assessing the risks to these patients in particular and also how these risks can be mitigated. There is good evidence now available that describes the risks associated with many of these co-morbidities which is important information to share with patients.
There is also good evidence where risks are modifiable, eg diabetes, obesity, joint replacement surgery should be delayed until an effort has been made to optimise the co-morbidity, particularly in the setting of primary care where possible. This typically involves evidence supported interventions such as multimodal weight loss programmes where certain objective thresholds are targeted (eg, BMI). In other conditions it involves risk stratification and entering in a shared care decision with patients about the risk of joint replacement surgery specific to their co-morbiditie(s).
References available on request
