The knee that has hurt for months: why it is not 'growing pains'

Among adolescents with recurrent knee pain, 72% are girls, the median duration of pain is 24 months, and five years later 40.5% still hurt — with 60% of those having stopped or cut back on sport. Patellofemoral pain does not go away by 'growing out of it': it goes away when someone takes it seriously and doses the load. The data, and what changes in the gym.

There is one injury in young female athletes that appears on no medical report and costs no single match: it costs years. It is the knee that has hurt for months — on stairs, in a squat, after twenty minutes sitting at a school desk — filed away as growing pains, or as something that "will sort itself out once she stops growing". The research says the opposite: in adolescents followed over time, five years later 40.5% still hurt, and 60% of them had stopped or cut back on sport because of the knee (Rathleff et al., 2019).

Key points

  • Among adolescents with at least monthly knee pain, 363 out of 504 are girls (72%) and the median duration of pain is 24 months; only 59% had sought healthcare (Rathleff et al., 2013).
  • Two years later, 55.9% still have knee pain; with patellofemoral pain the relative risk is 1.26 versus other types of knee pain (Rathleff et al., 2016).
  • Five years later: 40.5% still in pain (versus 13.2% of controls), 60% stopped or reduced sport, 15% say the knee influenced their choice of job (Rathleff et al., 2019).
  • It is not rare: annual prevalence of patellofemoral pain in adolescents is estimated at 28.9% (Smith et al., 2018).
  • What worked was not rest: it was modifying the load and then strengthening. In the 12-week pathway with 151 girls and boys aged 10-14, 86% successful outcomes at 12 weeks and 81% at one year (Rathleff et al., 2019).

How common is knee pain in young female athletes?

Far more common than the number of girls who mention it would suggest. The most cited systematic review with meta-analysis on the topic pooled 23 studies and estimates an annual prevalence of patellofemoral pain of 28.9% in adolescents, versus 22.7% in the general population; in adolescent amateur athletes, incidence over a single season ranges from 5.1% to 14.9% (Smith et al., 2018, PLOS ONE). The authors themselves flag that the estimates rest on few studies and inconsistent definitions: treat the exact figure with caution, but not the order of magnitude.

Population data point the same way. In a sample of 2,953 Danish adolescents aged 12-19, knee pain was reported by 35.0% of girls versus 27.9% of boys, and almost-daily pain at any site by 23.8% versus 13.3% (Rathleff et al., 2013, BMC Pediatrics).

And when you look only at those with recurrent knee pain, the imbalance becomes obvious: among 504 adolescents aged 15-19 with at least monthly knee pain, 363 were girls — 72% (Rathleff et al., 2013, BMC Musculoskeletal Disorders). In the same cohort, 68.3% of the pain had an insidious onset, i.e. no trauma to point to.

This is exactly the kind of pain that enters no statistic in youth sport: no episode, no collision, no day on which it started.

What patellofemoral pain is, and what it is not

It is diffuse pain around or behind the kneecap, triggered by loading the knee in flexion: stairs, squats, jumps, running, and — the detail that often gives it away — sitting for long periods with the knees bent. Whoever has it cannot point to it with one finger: she points with a whole hand, "around here".

It needs to be told apart from two things we have already covered, because management differs:

One thing to say plainly: this article is not a diagnostic tool. Knee pain in an adolescent girl has several possible causes — some trivial, some not — and the distinction is made by a healthcare professional. What matters here is something else: that this kind of pain is not a reason to wait.

Does adolescent knee pain go away on its own?

In most cases it does not, and this is the question the literature has answered best. One study followed Danish adolescents with knee pain for two years: at follow-up, 55.9% still reported pain. Those classified with patellofemoral pain had a relative risk of 1.26 of still hurting compared with other types of knee pain. The study's title is a question — is knee pain during adolescence a self-limiting condition? — and the authors conclude that in most cases the pain is still present after two years and therefore may not be self-limiting (Rathleff et al., 2016, Am J Sports Med).

At five years the picture had not straightened out (Rathleff et al., 2019, BMJ Open):

It is worth being precise about the population: these are Danish adolescents aged 15-19 of both sexes, recruited from the school population rather than from registered athletes. They are not 13-year-olds in an Italian club, and the numbers do not transfer one to one. But the direction — pain that over time takes away the sport rather than itself — is measured, not assumed.

There is a second finding, this one specific to girls, that makes waiting even harder to defend: female adolescents with patellofemoral pain have lower pressure pain thresholds than pain-free peers, including at body sites far from the knee (Rathleff et al., 2013, JOSPT). In other words, pain lasting months does not stay a local problem — it changes how the nervous system processes stimuli, as we described in how pain changes during puberty.

Why almost nobody takes it to a doctor

Because it feels too small to bother anyone with, and too normal to be a problem. In the cohort of 504 adolescents with at least monthly knee pain, the median duration of pain was 24 months and only 59% had sought healthcare; 18% were under treatment at the time of the questionnaire (Rathleff et al., 2013, BMC Musculoskeletal Disorders).

The most instructive detail, though, is another. Among girls, those with traumatic-onset pain sought help in 80% of cases; those with insidious-onset pain in only 55.7%. In boys the difference between onset types was minimal (47.9% versus 49.5%).

Put bluntly: an accident seems to be needed before it feels allowed to ask. It is the same dynamic that keeps urine leakage during jumping and menstruation in front of a coach unspoken — a symptom without an event to justify it does not feel serious enough to name. And pain that is never named is pain nobody can dose.

What works: not rest, but measured load

In the studies, stopping was not what worked: modifying the load and then strengthening was. This is the counter-intuitive part, and the most useful one in the gym.

The study closest to the age band that matters followed 151 adolescents aged 10-14 with patellofemoral pain through a 12-week pathway: activity modification in weeks 1-4, home exercises from week 5 to 8, graded return to sport from week 9 to 12, with only four supervised sessions, each of which a parent also had to attend. Self-reported successful outcomes were 86% at 12 weeks, 77% at 6 months and 81% at 12 months; hip and knee strength rose by 20-33% and return to sport reached 81% at one year (Rathleff et al., 2019, Am J Sports Med).

A limit to state up front: that study has no control group, so on its own it cannot show that the effect came from the intervention rather than from time. The randomised evidence comes from an older population: in a cluster trial of 121 adolescents aged 15-19, adding supervised exercise during school hours to education alone increased the odds of recovery at 12 months (OR 1.73; 95% CI 1.02-2.93; NNT 11), and the effect grew at 24 months (OR 2.52; NNT 5). More exercise sessions per week, higher odds of recovery (Rathleff et al., 2015, Br J Sports Med).

On the type of work, the international consensus statement is clear: exercise therapy is recommended, in particular the combination of hip-focused and knee-focused exercise; joint mobilisations in isolation and electrophysical agents (ultrasound, electrical currents and the like) are not recommended (Collins et al., 2018, Br J Sports Med). One honest note: that consensus concerns the general patellofemoral pain population, largely adult — in adolescents the evidence is the studies above.

The practical point that holds it all together: a knee does not heal by staying still, it heals by getting the right dose. It is the same principle behind early specialisation and overuse: load is not the enemy, unmanaged load is.

And the knee that hurts below the kneecap (Osgood-Schlatter)?

Different picture, same approach. Pain localised over the tibial tuberosity — the bony prominence just below the kneecap, where the patellar tendon attaches — is typical of adolescence during growth and is called Osgood-Schlatter disease. Here too, the idea that you just need to wait has been tested: in a prospective study of 51 adolescents aged 10-14 (51% girls), a 12-week pathway using a load-progression ladder for the patellar tendon, strengthening exercises and a graded return to sport produced 80% self-reported successful outcomes at 12 weeks and 90% at 12 months (Rathleff et al., 2020, Orthop J Sports Med).

This too is a study without a control group and in a small sample: not proof of efficacy, but a consistent signal. And the message is the same, worth repeating: load progression is an intervention; waiting is not.

What a club can do, starting Monday

None of these is a medical prescription. They are organisational and language choices, within reach of anyone who coaches:

Where BAB fits

BAB does not diagnose, does not treat and does not decide when someone returns to play. It does something almost nobody does today: it makes duration visible. An athlete privately logs pain, perceived load, energy and recovery, and sees a line form — not the single bad day, but the six weeks in which that knee kept coming back. Clubs receive only aggregated, anonymous signals, never an individual's health data.

Because in this story the decisive number is not pain intensity. It is 24 months — the median time it takes for these knees to finally reach somebody.

Sources

This article is for information and education only and does not constitute medical advice or a diagnostic tool. The cohorts cited involve adolescents of both sexes, mostly Danish and aged 15-19, and do not transfer directly to a 13-14 year-old athlete. Knee pain persisting beyond two to three weeks, or accompanied by swelling, the knee giving way or locking, or following trauma, should be assessed by a paediatrician, sports physician or physiotherapist: decisions on load and return to activity belong with whoever is looking after the athlete clinically.

Does adolescent knee pain go away on its own with growth?

Often it does not, and this is the question the research has answered most clearly. In a Danish cohort of adolescents followed over time, 55.9% of those reporting knee pain at baseline still reported it two years later; those classified with patellofemoral pain had a relative risk of 1.26 of still having pain compared with other types of knee pain. The authors explicitly conclude that adolescent knee pain, and patellofemoral pain in particular, 'may not be self-limiting' (Rathleff et al., 2016). At five years, 40.5% (95% CI 35.4-45.6) still had pain versus 13.2% of those pain-free at baseline, and among those still in pain, 60% had stopped or reduced sport because of the knee (Rathleff et al., 2019). Population: Danish adolescents aged 15-19 of both sexes, not specifically 13-14 year-old athletes.

What is patellofemoral pain and how do you recognise it?

It is diffuse pain around or behind the kneecap, triggered by activities that load the joint in flexion: stairs up and down, squatting, jumping, running, and also sitting for a long time with the knees bent. Unlike a stress fracture it cannot be pointed to with one finger on a precise spot of bone, and unlike an ACL rupture it does not start with a single traumatic episode: in the Danish cohort, 68.3% of adolescent knee pain had an insidious onset, i.e. no trauma (Rathleff et al., 2013). One caveat: this article is not a diagnostic tool. Knee pain in an adolescent girl has several possible causes, and the distinction is made by a healthcare professional, not by a symptom list.

Is rest the treatment?

Complete rest is not what worked in the studies: what worked was modifying the load and then strengthening. In a prospective study of 151 adolescents aged 10-14 with patellofemoral pain, a 12-week pathway built on activity modification in weeks 1-4, home exercises from week 5 and a graded return to sport from week 9 produced 86% self-reported successful outcomes at 12 weeks and 81% at 12 months, with hip and knee strength up by 20-33% (Rathleff et al., 2019). Note that this study had no control group, so on its own it does not prove the intervention works. The randomised evidence comes from an older group: in 121 adolescents aged 15-19, adding supervised exercise to education increased the odds of recovery at 12 months (OR 1.73; 95% CI 1.02-2.93) and more so at 24 months (OR 2.52), with a number needed to treat of 5 (Rathleff et al., 2015).

Why does knee pain seem to affect girls more?

Because in population data they report it more often. In a sample of 2,953 Danish adolescents aged 12-19, knee pain was reported by 35.0% of girls versus 27.9% of boys, and almost-daily pain at any site by 23.8% versus 13.3% (Rathleff et al., 2013). In the cohort of adolescents with at least monthly knee pain, 363 out of 504 were girls — 72% (Rathleff et al., 2013). One further finding, measured in girls only: female adolescents with patellofemoral pain have lower pressure pain thresholds than pain-free peers, including at sites far from the knee (Rathleff et al., 2013, JOSPT). That is not evidence of fragility: it is a sign that pain lasting months changes how the nervous system processes stimuli, which makes waiting even harder to justify.

When should she see a doctor?

Knee pain lasting more than two or three weeks, returning at every session, making her avoid stairs, squats or jumps, or costing her training sessions, should be assessed by a healthcare professional: a paediatrician, sports physician or physiotherapist. Some signs warrant assessment without waiting: swelling, the knee giving way or locking, pain after trauma, night pain, or pain that can be pointed to with one finger on a precise spot of bone. The reason not to wait is not alarmism, it is statistics: the median duration of pain in adolescents who eventually seek help is 24 months, and only 59% had sought care at all (Rathleff et al., 2013). Time is not an ally here.