Does Every Young Athlete Need Surgery After a Shoulder Dislocation? Understanding Number Needed to Treat (NNT)

When a young athlete dislocates their shoulder for the first time, surgery is often discussed early. But how much additional benefit does surgery provide compared with non-operative management? And does every young male contact athlete really need an operation?

A 2025 systematic review by Cutteridge and colleagues reported a Number Needed to Treat (NNT) of approximately 12 when comparing surgical and non-operative management after a first-time traumatic anterior shoulder dislocation. But what does that number actually mean?

Understanding NNT is an important part of interpreting research and helping patients make informed treatment decisions.

Let's dif into this further.

What Is Number Needed to Treat (NNT)?

Number Needed to Treat, or NNT, is a statistical measure used to describe the benefit of one treatment compared with another. It tells us how many people would need to receive a particular treatment, rather than an alternative, for one additional person to experience a beneficial outcome over a specified period.

In the case of shoulder instability after a first time dislocation, we would ask:

How many patients need to undergo early shoulder stabilisation surgery, rather than non-operative management, to prevent one additional shoulder re-dislocation?

NNT helps put the additional benefit of surgery into perspective. But it's important to remember that it doesn't tell us which individual patient will benefit from that treatment.

What Does the Research Tell Us About Shoulder Surgery?

Cutteridge et al. (2025) published a systematic review and meta-analysis comparing operative and non-operative management following a first-time traumatic anterior shoulder dislocation.

The review included:

• 21 studies involving 5,142 patients.

• A mean patient age of 23 years.

• A predominantly male population (87%).

• An average follow-up of approximately 46 months.

The researchers reported the following average re-dislocation rates:

The authors also reported:

• Relative risk reduction: 34.26%

• Absolute risk reduction: 8.4 percentage points

• Number Needed to Treat: 11.93, rounded to 12

These results suggest that surgical intervention reduces the likelihood of another shoulder dislocation compared with non-operative management. But how do we interpret the size of that benefit?

Understanding the Difference Between Absolute and Relative Risk Reduction

Sometimes the statistics can become confusing.

Imagine reading a headline stating:

"Surgery reduces the risk of another shoulder dislocation by 34%."

That sounds impressive. And the relative reduction in risk is certainly important. But it doesn't mean that 34 out of every 100 patients will avoid another dislocation because they had surgery.

To understand the actual difference in outcomes, we need to look at absolute risk reduction.

Let's Imagine 100 Patients

Using the approximate average re-dislocation rates reported by Cutteridge and colleagues:

Without surgery:

Around 25 out of 100 patients experience another shoulder dislocation.

That means approximately 75 do not experience another dislocation during the study follow-up period.

With surgery:

Around 16 out of 100 patients experience another shoulder dislocation.

That means approximately 84 do not experience another dislocation.

The absolute difference is approximately nine fewer re-dislocations per 100 patients treated surgically.

This is the important difference between relative and absolute risk.

Relative risk reduction describes the proportional reduction in risk.

Absolute risk reduction describes the actual difference between treatment groups.

Both are useful, but absolute risk reduction is particularly helpful when explaining treatment benefits to patients.

How Do We Calculate Number Needed to Treat?

The calculation is relatively straightforward.

NNT = 1 ÷ Absolute Risk Reduction

The important detail is that absolute risk reduction must be expressed as a decimal rather than a percentage.

Cutteridge et al. reported an absolute risk reduction of 8.4 percentage points. Converted to a decimal, this is 0.084. Therefore:

NNT = 1 ÷ 0.084 = 11.9

When expressed as a whole number, NNT is rounded up to 12.

What Does an NNT of 12 Mean?

It means that approximately 12 patients would need to undergo surgical management rather than non-operative management to prevent one additional re-dislocation, on average, over the follow-up period represented by the research.

It does NOT mean:

• Surgery only works in one out of 12 patients.

• The other 11 patients have unsuccessful surgery.

• Every patient undergoing non-operative management will experience another dislocation.

• We can identify precisely which patient will benefit from surgery.

The number describes an average additional treatment benefit across a group of patients.

It is not a prediction of an individual patient's outcome.

Importantly, NNT does not measure surgical complications, recovery burden, costs or other potential harms. Those need to be considered separately.

Does Every 16-Year-Old Rugby Player Need Shoulder Surgery?

Consider a common clinical scenario.

A 16-year-old male rugby player experiences his first traumatic anterior shoulder dislocation. He wants to return to competitive rugby as soon as possible. His surgeon recommends early stabilisation because of his age, sex and participation in contact sport. Is that a reasonable recommendation? Potentially, yes.

Young age, male sex and contact sports are recognised risk factors for recurrent shoulder instability.

There is also evidence that early surgical stabilisation substantially reduces recurrence in some high-risk populations.

However, being a 16-year-old male contact athlete should not replace an individual assessment and a shared decision-making process.

We need to ask additional questions.

What is this athlete's individual risk of recurrence?

What about other risk factors including:

• Bony Bankart lesions
• On track vs Off track lesions
• Kinesiophobia
• Immobilisation
• Pain levels?

We also need to consider:

• What are the consequences of another dislocation?
• What are his sporting goals, and what level does he intend to return to?
• What are his preferences after understanding the potential benefits and harms of each treatment option?

The average NNT of 12 does not answer all these questions.

Why Population Averages Don't Always Apply to Individual Patients

One of the most important limitations of NNT is that it depends on the population being studied. Patients with a higher baseline risk of recurrence may experience a greater absolute benefit from an effective treatment.

For example, imagine two groups of patients. In one group, the risk of recurrence without surgery is 20%. In another, the risk is 60%. If surgery produced the same proportional reduction in risk in both groups, the absolute benefit would be greater in the group starting with a 60% risk. That would produce a lower NNT.

This is a hypothetical illustration, not an estimate of surgical benefit for either group.

The principle is important: NNT is not necessarily the same for every patient.

We should be cautious about applying one number from a broad systematic review to every young athlete with a shoulder dislocation.

An Important Limitation of the Cutteridge Review

There is another reason we need to interpret an NNT of 12 carefully.

Although the review included more than 5,000 patients, approximately 72% came from one large retrospective observational study. That study reported a 20% re-dislocation rate in both its operative and non-operative groups, substantially influencing the overall average results. The authors reported considerable heterogeneity between studies, meaning the studies differed substantially in their populations, methods and findings.

Perhaps most importantly, the review's subgroup analysis of three randomised controlled trials demonstrated a much larger benefit from surgery. Among the 92 patients included in these trials, the reported re-dislocation rates were:

• Arthroscopic stabilisation: 8.89%

• Non-operative management: 51.06%

That is an absolute difference of approximately 42 percentage points, substantially larger than the absolute risk reduction reported across the broader review. The randomised trials were small, so there is uncertainty around the precision and generalisability of these estimates. Nevertheless, their results strongly favoured surgical stabilisation.

This is why we cannot selectively use an NNT of 12 to argue that surgery is unnecessary.

Equally, we should not use the larger treatment effects from a small subgroup of trials to suggest that every young athlete must undergo surgery. Different studies answer slightly different questions, in different populations, using different treatment approaches. Good evidence-based practice requires us to understand those differences.

Re-dislocation Is Not the Same as Recurrent Shoulder Instability

Another important feature of the Cutteridge review is that the primary outcome was re-dislocation rather than recurrent instability. These aren't the same outcome.

Re-dislocation refers to another complete dislocation of the shoulder joint.

Recurrent instability may also include subluxation episodes, feelings of apprehension, or episodes where the patient perceives the shoulder to be slipping or giving way.

This distinction matters because reported recurrence rates can look very different depending on the outcome being measured. A patient who never experiences another complete dislocation may still have symptoms of instability that limit their sporting participation or quality of life. When discussing the evidence with patients, clinicians need to explain exactly what outcome the research is measuring.

Can We Predict Who Is at Risk of Recurrent Shoulder Instability?

Rather than relying entirely on population averages, clinicians can also consider individual prognostic factors.

One example is the Predicting Recurrent Instability of the Shoulder (PRIS) tool, developed through research led by Dr Margie Olds. PRIS uses clinical and patient-related factors to help estimate the likelihood of recurrent instability following a first-time traumatic anterior shoulder dislocation.

Validation research showed that PRIS was particularly useful for identifying patients less likely to experience recurrence, although its ability to identify every patient who would experience another episode was more limited. It is important to understand that PRIS is a prognostic tool, not a treatment-effect calculator.

It does not tell us how much an individual patient's recurrence risk would decrease with surgery. However, prognostic information can contribute to a more informed discussion about the potential treatment options.

Explore the PRIS tool

Surgery or Rehabilitation: Making an Informed Decision

Early surgical stabilisation can be an effective way to reduce the risk of recurrent shoulder dislocation, particularly in younger, higher-risk populations. But not every patient will experience another dislocation without surgery. And not every patient who undergoes surgery will remain free from instability. Rehabilitation also remains important, whether a patient chooses surgical or non-operative management. Effective shoulder rehabilitation should address more than isolated muscle strength. It should progressively develop:

• Control: The ability to coordinate and stabilise the shoulder through movement.

• Capacity: The strength, endurance and power needed to tolerate physical activity.

• Confidence: The athlete's trust in their shoulder and ability to perform without excessive apprehension.

• Demand: The ability to tolerate the speed, fatigue, contact and unpredictability of their chosen sport.

The rehabilitation programme should reflect the demands that the athlete needs to return to. However, evidence about the average outcomes of non-operative management does not automatically tell us how effective any particular rehabilitation programme will be. That question requires its own research.

What Should Physiotherapists Take Away From This?

The most important lesson from NNT is not whether surgery is good or bad. It is that clinicians need to understand the size of a treatment benefit before recommending it to an individual patient. An NNT of 12 tells us something important about the average additional benefit of surgery in the broader population included in the Cutteridge review.

But it does not tell us which 16-year-old rugby player should undergo surgery. For that, we need to consider the best available treatment evidence, individual prognosis, clinical findings, potential treatment harms and patient preferences. Physiotherapists should be comfortable discussing the evidence with surgeons, patients and families.

That includes asking questions about absolute risk reduction, NNT and how well the published research applies to the individual in front of us.

Understanding the statistics doesn't tell us which treatment to recommend. It helps us ask better questions and make better-informed decisions.

Ultimately, that is what evidence-based shoulder care should be about.

Reference

Cutteridge J, Dixon J, Garrido P, Peckham N, Smith C, Woods A, Gwilym S. (2025). A systematic review and meta-analysis of operative versus non-operative management for first time traumatic anterior shoulder dislocation in young adults. Shoulder & Elbow. 17(2):130–139.

https://doi.org/10.1177/17585732241254693

Chesnaye et al., 2026. How to intepret the number needed to treat for clinicians. Nephrol Dial Transplant. 41, 4370444 https://doi.org/10.1093/ndt/gfaf168 

Flawless Motion is committed to supporting evidence-informed shoulder instability management, rehabilitation and return to activity. This article is intended for education and does not replace individual clinical assessment or shared decision-making with a qualified healthcare professional.