GLP-1 Weight Loss Drugs Are Reshaping Orthopaedic Surgery

The rise of GLP-1 receptor agonists — semaglutide (Ozempic/Wegovy), tirzepatide (Mounjaro/Zepbound), and the newer dual and triple agonists — is one of the biggest stories in medicine right now. These drugs are producing sustained weight loss of 15-25% of body weight in clinical trials, and their use has exploded globally. In Australia alone, PBS prescriptions for GLP-1 agonists increased by over 300% between 2024 and 2025.

For orthopaedic surgeons, this is not just a pharmacology curiosity. It is fundamentally changing the patient population walking into our clinics, the timing of surgical intervention, and the perioperative risk profile of our cases.

The Obesity-Osteoarthritis Connection

The relationship between obesity and osteoarthritis is well established. Each kilogram of excess body weight places approximately 4 kg of additional force across the knee joint during walking. A patient with a BMI of 40 is experiencing forces equivalent to carrying an additional 80 kg on their knees with every step.

This is not just a mechanical story. Adipose tissue is metabolically active, producing pro-inflammatory cytokines (IL-6, TNF-alpha, leptin) that accelerate cartilage degradation through systemic inflammation. Obesity-related osteoarthritis is therefore both a mechanical and a biochemical disease.

Historically, the clinical challenge has been clear: many patients who need a knee replacement most are also the patients at highest risk for complications due to their weight. A BMI above 40 is associated with significantly higher rates of periprosthetic joint infection, wound complications, VTE, and all-cause revision. For background on arthroplasty indications and outcomes, see our topics on total hip arthroplasty and total knee arthroplasty. Many units set a BMI threshold (typically 35 or 40) below which they prefer patients to be before proceeding with elective arthroplasty.

What GLP-1 Drugs Are Changing

The practical impact is playing out in several ways:

Patients are hitting BMI thresholds. For years, telling a patient with a BMI of 45 to "lose weight before surgery" was almost cruel — conventional diet and exercise programmes achieve sustained weight loss of only 3-5% on average, nowhere near enough to bring a morbidly obese patient to a safe surgical window. GLP-1 agonists are changing this calculus. A 20% weight reduction in a patient with a starting BMI of 45 brings them to a BMI of 36 — well within most units' surgical thresholds.

Some patients are delaying or avoiding surgery entirely. Weight loss reduces both the mechanical and inflammatory burden on joints. Anecdotally and in early registry data, some patients who were listed for knee replacement have reported sufficient symptom improvement after significant weight loss that they have deferred or cancelled surgery. Whether this represents genuine disease modification or just symptom relief remains to be seen.

Perioperative complications are trending down. Early data from high-volume arthroplasty centres in the United States suggests that patients who have achieved significant weight loss on GLP-1 drugs prior to surgery have complication rates more comparable to non-obese patients than to their pre-weight-loss BMI peers. This makes biological sense — they have less metabolic inflammation, better glycaemic control, and often improved cardiovascular fitness.

The Concerns

Not everything about this trend is positive. Several important surgical concerns have emerged:

Anaesthetic risk with delayed gastric emptying. GLP-1 agonists slow gastric motility. This means patients may have residual gastric contents at the time of induction, increasing aspiration risk. Current anaesthetic society guidelines recommend holding semaglutide for at least one week before elective surgery, and tirzepatide for at least one week. Some anaesthetists are requesting pre-operative gastric ultrasound to confirm an empty stomach.

Muscle mass loss. GLP-1-induced weight loss is not purely fat loss. Studies consistently show that 30-40% of weight lost is lean body mass, including muscle. For arthroplasty patients, pre-operative muscle mass is a strong predictor of post-operative functional recovery. A patient who loses 25 kg but arrives to surgery sarcopenic may actually rehabilitate more poorly than expected.

Nutritional deficiency. Significant appetite suppression can lead to protein malnutrition, vitamin D deficiency, and iron deficiency — all of which impair wound healing and bone metabolism. Pre-operative optimisation protocols now need to include nutritional screening for patients on GLP-1 therapy.

Rebound weight gain. Long-term adherence data is still maturing, but studies suggest that most patients regain significant weight if they discontinue the medication. This raises questions about the durability of pre-operative weight loss and whether patients need to remain on these drugs long-term to maintain benefit.

The Australian Perspective

In Australia, semaglutide for weight management (Wegovy) was listed on the PBS in 2025 for patients with a BMI of 30 or greater (or 27 with comorbidities), subject to specialist initiation. Tirzepatide is expected to follow. This means access is broadening, but cost remains a barrier — monthly out-of-pocket costs for patients on general prescriptions can still exceed AUD $100 even with PBS subsidy.

From a health system perspective, the potential to reduce the volume of joint replacements — or at least reduce the complication rate — has enormous implications for surgical waiting lists and hospital budgets. The average cost of a primary knee replacement in the Australian public system is approximately AUD $23,000. If even 5-10% of currently listed patients achieve sufficient symptom improvement to defer surgery, the savings are substantial.

What Surgeons Should Do Now

1. Screen for GLP-1 use in every pre-operative assessment. This is now as important as asking about anticoagulants.
2. Coordinate with anaesthesia early regarding fasting protocols and drug hold periods.
3. Assess body composition, not just BMI. A patient who has lost 20 kg but is now sarcopenic needs a different prehabilitation plan than one who has maintained muscle mass.
4. Optimise nutrition proactively. Check albumin, pre-albumin, vitamin D, and iron studies in all patients who have had significant recent weight loss.
5. Counsel patients honestly. GLP-1 drugs are powerful tools, but they are not a substitute for surgery in end-stage arthritis. Setting realistic expectations about what weight loss can and cannot achieve is essential.

The Bigger Picture

The GLP-1 revolution is the first time in decades that a medical therapy has had the potential to meaningfully change the demand curve for one of the highest-volume surgical procedures in the world. Whether that potential is fully realised depends on long-term efficacy data, drug pricing, and health system willingness to invest in pre-operative optimisation pathways.

For orthopaedic surgeons and trainees, this is a space that demands close attention. The patients walking into your clinic in 2026 are measurably different from those of five years ago, and your practice needs to evolve accordingly.