Does your menstrual cycle actually affect your knee?

For many women, the timing is too consistent to ignore: knee pain that flares predictably around a period or mid-cycle, then quietens again. That pattern has a plausible biological explanation.

Reproductive hormones — primarily estradiol and relaxin — measurably alter joint laxity and pain sensitivity across the cycle. Research in regularly cycling women confirms that genu recurvatum and general joint laxity are significantly higher at ovulation than in the early follicular phase, and that elevated laxity persists into the luteal (pre-menstrual) week. Estradiol also modulates pain directly at the joint level, influencing inflammatory signalling and neurotransmitter activity — not merely the mechanics of how the kneecap tracks.

What the evidence does not yet include is a clinical trial that tracked patellofemoral pain severity across every cycle phase. The connection rests on strong adjacent science rather than a direct study, and that gap is worth acknowledging. It does not, however, undermine the biology. The mechanisms are real; how strongly they manifest in any one individual varies considerably.

Why PFPS is more common in women

Anatomy sets an important baseline before hormones enter the picture. A wider pelvis — characteristic of female skeletal structure — increases the Q-angle, which is the angle between the pull of the quadriceps and the line of the patellar tendon. A larger Q-angle draws the kneecap laterally with every step, applying uneven pressure to the cartilage surface beneath it over thousands of repetitions.

Weaker hip abductors and quadriceps compound this. Both muscle groups are critical to keeping the kneecap tracking centrally in its groove, and both tend to be relatively weaker in women, particularly during periods of inactivity or after injury. Research in women with patellofemoral pain found that hip stabiliser strength correlated meaningfully with self-reported lower extremity function (r=0.408, p=0.002). Patellar maltracking, flat feet, and prior minor knee trauma can each add further load.

Perhaps the most clinically important structural feature is the pain-mechanics feedback loop. When PFPS pain intensifies, it alters the way the foot strikes the ground — heightened pain correlates strongly with increased rearfoot eversion and plantar pressure asymmetry (r=0.835, p<0.001). Any trigger that amplifies pain, including a hormonal one, does not act on a neutral system; it acts on a joint already under structural stress, and risks reinforcing that stress.

What estrogen and relaxin do to the knee joint

Two mechanisms operate simultaneously — one mechanical, one neurochemical — and the distinction matters for what any treatment can realistically address.

The mechanical pathway

Estradiol peaks at ovulation and measurably loosens connective tissue. In regularly cycling women, both genu recurvatum and general joint laxity are significantly higher at ovulation than at the early follicular baseline (p=0.011 and p=0.031 respectively). In women with pre-existing knee hyperextension, anterior knee laxity under controlled loading rises further — significantly so at 89 N and 133 N loads (p=0.025 and p=0.018). Practically, the stabilising structures around the kneecap become slightly more elastic at exactly the moment they are needed most.

Generalised laxity then remains elevated into the luteal (pre-menstrual) phase, not just at the ovulation peak, extending the window of structural vulnerability into the days before a period. Estradiol also reduces periarticular muscle stiffness in regularly cycling women, so the dynamic muscular protection around the patella diminishes at the same time the joint itself is at its loosest.

Relaxin compounds this: it peaks at ovulation and persists into menstruation, reducing collagen cross-linking and degrading extracellular matrix through TGF-β/Smad pathway suppression. The direct evidence is concentrated in ACL research, but because the mechanism targets connective tissue broadly, the medial patellofemoral ligament and surrounding knee stabilisers are equally susceptible — making the perimenstrual window one of compounded structural looseness, not merely a brief hormonal blip.

The pain-sensitivity pathway

Estrogen also acts on the knee's pain circuitry directly, regulating inflammatory responses and altering neurotransmitter signalling at the joint level. When estrogen drops or fluctuates during menstruation, the pain threshold falls — a neurochemical event, not a mechanical one. This is why NSAIDs may ease perimenstrual knee pain through anti-inflammatory action without touching the underlying joint laxity: two distinct problems, even when they peak at overlapping points in the cycle.

Which part of your cycle is the higher-risk window

Translated into practical timing, two windows stand out — though neither affects every woman identically.

The peri-ovulatory window (roughly days 12–16 in a 28-day cycle) combines peak estradiol with peak relaxin: the point at which the joint-loosening mechanisms described above are most concentrated. A 2023 systematic review concluded that the ovulatory phase carries elevated musculoskeletal injury risk in female athletes, attributing this to the convergence of increased laxity and reduced neuromuscular control.

The perimenstrual window (roughly days 26–2) is a separate vulnerability. General joint laxity remains elevated from the luteal phase into this period, while falling estrogen may simultaneously lower pain thresholds through inflammatory and neurotransmitter pathways — meaning pain can feel amplified even without any new structural change.

Neither window reliably predicts how much a given woman will notice. A 2024 scoping review of 39 studies found that between 2.8% and 100% of female athletes reported cycle-related performance impairment — a range that reflects genuine biological variation more than inconsistent methodology. A 2023 umbrella review found no consistent evidence that menstrual phase uniformly affects acute strength performance.

The most practical step is a simple symptom diary: logging pain intensity, activity, and cycle day over two or three months tends to reveal a personal pattern far more reliably than any generic calendar rule.

Managing PFPS when your cycle is a factor

Regardless of where someone falls in their cycle, the rehabilitation core remains unchanged: progressive hip abductor and quadriceps strengthening to restore patellar tracking, graded load management, and orthotics where biomechanical correction is indicated. These are the evidence-based foundations, and hormonal variation does not alter them.

What the cycle evidence does support is a careful adjustment of how those sessions are structured around higher-risk windows. Around ovulation and during the perimenstrual days, a longer, more deliberate neuromuscular warm-up makes mechanical sense — the stabilisers are at their most elastic and the pain threshold is lower. Temporarily scaling back high-impact or plyometric elements is a reasonable precaution during these periods; stopping activity entirely is rarely warranted.

NSAIDs taken for period pain act on the same prostaglandin pathways driving knee inflammation, so a concurrent benefit at the joint is plausible and worth knowing about — though no trial has examined this specifically in PFPS, and it remains an observation rather than a studied indication.

Where a supervised rehabilitation programme has been completed and pain persists, injection therapy — PRP or hyaluronic acid — is an option for refractory or structurally complicated cases, but as a downstream escalation, not a substitute for the rehabilitation work.

Cycle-phased rehabilitation protocols are a logical direction for future research but have not yet been validated in clinical trials. It is not an established clinical approach — and presenting it as one would go beyond what the current evidence supports.

When a specialist assessment makes sense

Most cycle-linked knee flares settle within a few days and respond to load reduction and NSAIDs — for these, urgent specialist input is not needed.

Several patterns do warrant escalation:

• Pain that persists beyond the cycle window rather than returning to a baseline
• Swelling, locking, or giving way, which suggest structural involvement beyond patellofemoral irritation
• Symptoms that worsen progressively from one cycle to the next
• No meaningful improvement after 6–8 weeks of consistent self-management

When a specialist is involved, assessment begins with clinical history — including cycle pattern, symptom timing, and activity load — followed by movement and loading examination. Targeted imaging is added only if structural pathology is suspected; an MRI finding alone is not a diagnosis, and incidental cartilage changes can be present without being the source of pain.

Assessment also distinguishes PFPS from conditions with overlapping presentations: patellar tendinopathy, focal chondral lesions, and early patellofemoral osteoarthritis each follow different management pathways, and separating them matters before treatment begins.

For anyone whose symptoms fit the escalation criteria above, a structured specialist assessment is available through londoncartilage.com.

1. [1] The Mechanism by Which Estrogen Level Affects Knee Osteoarthritis Pain in Perimenopause and Non-Pharmacological Measures. (2025). https://doi.org/10.3390/ijms26062391 https://doi.org/10.3390/ijms26062391
2. [2] A preliminary study exploring the change in ankle joint laxity and general joint laxity during the menstrual cycle in cis women. (2021). https://doi.org/10.1186/s13047-021-00459-7 https://doi.org/10.1186/s13047-021-00459-7
3. [3] Comparison of anterior knee laxity, stiffness, genu recurvatum, and general joint laxity in the late follicular phase and the ovulatory phase of the menstrual cycle. (2021). https://doi.org/10.1186/s12891-021-04767-8 https://doi.org/10.1186/s12891-021-04767-8
4. [4] Relationship Between Anterior Knee Laxity and General Joint Laxity During the Menstrual Cycle. (2021). https://doi.org/10.1177/2325967121993045 https://doi.org/10.1177/2325967121993045
5. [5] The role of relaxin in anterior cruciate ligament injuries: a systematic review. (2023). https://doi.org/10.1007/s00590-023-03618-7 https://doi.org/10.1007/s00590-023-03618-7
6. [6] Relaxin in fibrotic ligament diseases: Its regulatory role and mechanism. (2023). https://doi.org/10.3389/fcell.2023.1131481 https://doi.org/10.3389/fcell.2023.1131481
7. [7] Menstrual Cycle and Sport Injuries: A Systematic Review. (2023). https://doi.org/10.3390/ijerph20043264 https://doi.org/10.3390/ijerph20043264
8. [8] Patellofemoral pain syndrome. https://en.wikipedia.org/?curid=12033023 https://en.wikipedia.org/?curid=12033023
9. [9] Menstrual Cycle Changes Joint Laxity in Females — Differences between Eumenorrhea and Oligomenorrhea. (2022). https://doi.org/10.3390/jcm11113222 https://doi.org/10.3390/jcm11113222
10. [10] Current evidence shows no influence of women's menstrual cycle phase on acute strength performance or adaptations to resistance exercise training. (2023). https://doi.org/10.3389/fspor.2023.1054542 https://doi.org/10.3389/fspor.2023.1054542