What Works
Tier 1
High confidenceAssume the corner is torn until imaging says otherwise
About 60% of these ligament injuries carry a tear of the posterolateral corner, and rebuilding the back ligament alone does not restore normal knee movement when the corner is also gone.
Evidence: STRONG. Systematic review of combined injuries plus a meta-analysis of biomechanical studies (Vaquero-Picado 2017; Kim 2018).
When the corner is badly torn, rebuilding beats stitching it back together
This is a surgical decision rather than a rehab one, but the person who spots the injury in time is usually the one who determines whether it can still be done well.
Evidence: STRONG. Failure 21.9% after repair versus 7.1% after reconstruction across 288 patients, and the same direction and size in two further reviews (Dean 2023; Chahla 2016; Vicenti 2019).
Tier 2
Moderate confidenceQuadriceps-focused loading that protects against backward shin slide
The thigh muscle at the front pulls the shin forwards, which is exactly the direction the injured ligament used to control. Bending work is done with the shin supported so it cannot drop backwards.
Evidence: MODERATE for direction, LOW for dose. The mechanical reasoning is sound. No trial has tested it (Kim 2013).
Bracing during non-surgical management
Evidence: MODERATE and imprecise. Large improvements, but from single studies, and this group had the highest rate of eventually needing surgery of any injury studied at 16.4% (2025 bracing review).
Early surgery, within 3 weeks, for multi-ligament injuries
Evidence: MODERATE. Better function scores than delayed surgery, pooled across mixed-quality studies (Vicenti 2019).
Tier 3 — the rehab timelines, and why they are weaker than they look
Published programmes typically allow the knee to bend to 90 degrees somewhere between 4 and 8 weeks, delay full weight through the leg until about 6 weeks, brace for 6 to 8 weeks, and withhold hamstring machine work for anywhere from 6 to 24 weeks.
Those numbers come from counting up what 34 published surgeon programmes happened to say, not from testing them. A parameter appearing in 70% of programmes means 70% of authors chose it, not that it beat the alternative. The hamstring window spanning 6 to 24 weeks is the clearest sign that no defensible single answer exists.
Practical position: if you have had surgery, follow your surgeon's programme, because consistency with the person who saw the tissue beats anything you read online. If you have not, work from the principle rather than the calendar.
Exercise Prescription
Only for a confirmed isolated low-grade injury that has been imaged, with no corner involvement and no red flags. If the corner is involved, or imaging has not happened yet, the right action is the referral, not the exercises.
| Exercise | How | Sets × reps | Frequency |
|---|---|---|---|
| Quad sets | Lie flat, leg straight. Tighten the front thigh and press the back of the knee down. Hold 5 seconds | 3 × 10 | 2-3× daily |
| Straight leg raise | Tighten the thigh, keep the knee locked, lift the leg about 30cm, lower slowly | 3 × 10 | Daily |
| Supported heel slide | Slide the heel towards you with a rolled towel behind the top of the shin so it cannot drop backwards | 2 × 10 | Daily |
| Sit-to-stand | Stand and sit slowly, controlling the way down with the thigh | 3 × 8 | Daily |
| Wall sit | Back to wall, shallow bend only, hold | 3 × 20 sec | Daily |
| Step-down control | From a low step, lower the other foot slowly to the floor and return | 3 × 8 each | Every other day |
Why almost all of it targets the front of the thigh: that muscle pulls the shin forwards, which is the exact job the torn ligament used to do. It is the one muscle group that directly compensates for this specific injury.
What Doesn't Work
- Clearing a suspicious knee on hands-on examination. No test for this ligament has an established accuracy figure, and this is what generates the delay.
- Stitching an acute badly torn corner when rebuilding is an option. Two to four times the failure rate across three independent reviews.
- Rebuilding the back ligament alone when the corner is also torn. It does not restore normal knee movement.
- Early unsupported hamstring machine work. It loads the injured ligament in the exact direction it is weakest. Note honestly that the timing of when to reintroduce it is convention, not evidence.
- Presenting the non-surgical route as consequence-free. Symptomatic arthritis ran about six times higher than matched controls over twelve years.
Return to Training
- Full pain-free straightening, and bending within 10 degrees of the other side
- No swelling 24 hours after a full session
- Thigh strength within 10% of the uninjured side on a repeatable measure
- Single-leg step-down performed with control, no inward or outward collapse, at the depth your activity needs
- No sense of instability on stairs, slopes or when slowing down, for 2 consecutive weeks
- No outward bowing of the knee when walking or loading on one leg
- Nerve examination intact and written down (foot lifting, big-toe lifting, sensation between the first two toes)
- Surgeon clearance for any knee that was operated on
Honest caveat: no trial has validated a return-to-activity threshold for this injury. These criteria are built from the outcome measures the research actually uses plus standard lower-limb principles. Defensible, but not a validated battery.
Red Flags — Get Seen Urgently
- You cannot lift your foot or big toe upwards, or the top of your foot and the web between your first two toes feels numb. Nerve injury occurred in roughly 1 in 4 of these injuries when surgery was needed, and fewer than 4 in 10 of those recovered fully. Get seen urgently.
- Your foot or lower leg is pale, cold or numb, or the calf pain is severe and out of proportion. Emergency department, same day.
- A very high-energy injury, and the knee feels loose in several directions. This can mean the knee dislocated and went back in on its own, which is a blood-vessel emergency. Emergency department.
- The knee visibly bows outwards when you walk. Urgent orthopaedic referral. Do not start an exercise programme first.
- Any of the above in a child or teenager still growing. Different management pathway.
Refer to: emergency department for suspected dislocation or any circulation problem. Orthopaedics urgently for any nerve deficit, outward bowing on walking, or a suspected severe corner injury.
The Takeaway
If you took a hard blow to the front of your shin, or fell onto a bent knee, ask for imaging even if the examination was normal and even if it barely hurts. The hands-on tests for this ligament have never been shown to be accurate enough to rule it out, and this is the injury that gets missed for over a year.
What This Actually Means
A knee ligament that usually tears alongside a second one, and the second one is what gets missed.
Think of a tent held up by a back guy-rope and a corner guy-rope. Snap the back rope and the tent leans but still stands, so nobody panics and nobody checks the rest. The catch is that whatever snapped the back rope usually snapped the corner rope too, and if you replace only the back one the tent still leans, because the corner was quietly doing a job nobody measured. That is why a knee can still feel loose after a technically perfect repair, and why the fix has to start with finding out which ropes actually went.
- What this actually is: a ligament at the back of your knee that stops your shin sliding backwards, and it is known for hurting far less than the damage would suggest.
- What most people get wrong: treating it as one injury, when roughly 6 in 10 of them come with a torn corner on the outside of the knee.
- Start here: get it imaged, then train the front of your thigh, because that muscle does the same job as the ligament you tore.
Conviction
ModerateConfidence varies a lot by claim, so it is worth separating them.
High confidence: that these injuries usually are not alone, that rebuilding a badly torn corner beats stitching it, and that the hands-on tests have no established accuracy. That last one is confidence in a gap rather than in a number.
Moderate confidence: that rebuilding the back ligament alone cannot stabilise a knee with a torn corner (the evidence is laboratory mechanics rather than patient outcomes), that non-surgical management suits confirmed isolated low-grade injuries, and that early surgery helps in multi-ligament injuries.
Low confidence: every specific rehab timeline on this page, and ultrasound as a rule-out test in general hands.
What would change my mind about the surgery decision
A multi-centre randomised trial in acute isolated moderate-to-severe injuries, at least 200 people, excluding multi-ligament patterns, comparing bracing plus structured thigh-focused rehab against early reconstruction plus the same rehab, with assessors blinded and the main measure being side-to-side backward shin movement on kneeling stress x-rays at 24 months. If the non-surgical group matched the surgical group, the case for operating on isolated severe injuries would drop to low.
What would change my mind about the examination tests
One adequately powered study of the posterior drawer and dial tests against a surgical reference in 300 or more consecutive freshly injured knees, reporting how often each test catches the injury and how often it correctly clears it, with confidence intervals. That would turn the largest gap on this page into a usable number. It is cheap, it is obvious, and it has not been done.
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Join The VerdictThe Full Picture — Anatomy, Diagnosis & Evidence
What's Actually Going On
The posterior cruciate ligament is made of two bundles, plus two smaller ligaments that run alongside the meniscus, and together they are the main restraint stopping the shin bone sliding backwards on the thigh bone. The usual mechanisms are a backwards force into the front of the shin (a dashboard in a car crash, a fall onto a bent knee with the foot pointed down) or forcing the knee into extreme bend.
The posterolateral corner sits on the outside-back of the knee and resists the knee bowing outwards and the shin rotating outwards. Its main parts are the outer collateral ligament, the popliteus tendon and the popliteofibular ligament.
The reason the two belong on one page is that roughly 60% of these ligament injuries carry a corner tear, and laboratory work on cadaver knees showed that rebuilding the ligament alone fails to restore normal movement when the corner is also torn, whether the surgeon uses a single-bundle or double-bundle technique. Add the corner reconstruction and the leftover looseness comes under control.
The cost of missing it shows up in the timelines. Corner injuries paired with the front cruciate reached surgery at an average of 4.43 months. Corner injuries paired with this back ligament took an average of 18.4 months, and the authors put the gap down to how long it took to make the diagnosis.
How to Identify It
What raises suspicion: a backwards sag of the shin when the knee is bent to 90 degrees with the foot supported, loss of the normal small step where the shin bone sits forward of the thigh bone, bruising over the front of the upper shin matching the impact, and outward bowing of the knee during walking. Pain is often modest, which is exactly why these get waved through.
An honest gap, stated plainly. Every hands-on test for this ligament (posterior drawer, sag sign, quadriceps active test, dial test, varus stress, external rotation recurvatum, reverse pivot shift) has no published figure for how often it catches the injury or correctly clears it. The definitive review screened 1,307 papers, included 11 studies covering 11 different tests, and concluded the accuracy is largely unknown, with the data too inconsistent to even combine.
That is not a reason to stop examining. It is a reason to stop treating a normal examination as clearance. Anyone quoting you a percentage for these tests should be able to show you the source.
Telling it apart from the more famous injury: a torn front cruciate makes the knee give way when pivoting, and the shin sags forwards. This one makes the knee feel unsafe going down stairs and slopes, and the shin sags backwards. There is a trap here worth knowing: if the shin is already sitting backwards, pulling it forwards can read as a positive test for the front ligament when the front ligament is fine. Establish where the shin is resting before you test anything.
What actually settles it: kneeling stress x-rays of both knees compared side by side (a completely torn ligament averages about 8mm more movement than the healthy side), varus stress x-rays for the corner, and an MRI where the request specifically asks about the posterolateral corner rather than just the cruciates. Worth noting that only 3 of 8 studies in the published surgical literature bothered to take those comparison x-rays, which tells you how patchily this is done even by specialists.
The Debate
There is no clinical practice guideline for this condition. Not an old one, not a disputed one. None. The closest document is an expert consensus statement built from 27 specialists, and its treatment section reached only 70% agreement, the lowest of its four sections. So the honest framing is consensus versus evidence, not guideline versus trial.
Repair versus rebuild. Stitching a badly torn corner back together used to be considered reasonable where the tissue allowed. Three independent reviews now put its failure rate at roughly two to four times that of rebuilding it (21.9% against 7.1% in the largest). The direction is settled. Rebuild.
Is the non-surgical route as good as it sounds? Most people with a confirmed isolated low-grade injury do get back to activity without surgery, which is true and reassuring. Alongside that, symptomatic arthritis ran about six times higher than matched people over twelve years, and about 1 in 6 braced knees ended up in surgery anyway. Both facts are true because they measure different things on different clocks. Present both.
Honest Limitations
The rehab literature is a survey of habits, not a body of evidence
The programme timings everyone quotes come from counting what 34 published surgeon programmes said. Nobody compared any two of them against each other. The window for reintroducing hamstring work spans 6 to 24 weeks, which is a four-fold range on a single number.
Every published success rate is judged by the surgeons who did the operations
Success is defined by the investigators' own examination or x-ray, and blinded assessment is essentially absent. Expect real-world failure rates at or above the published ones, on both paths.
The studied population is not the outpatient population
These cohorts are high-energy trauma and multi-ligament surgical patients. The person who turns up three weeks after a fall, still walking, never scanned, is barely represented anywhere. The natural-history evidence for exactly that person is a single 48-patient study.
The Nuance
Surgery versus conservative, with the numbers. For confirmed isolated low-grade injuries, most people return to activity without an operation. For severe corner injuries operated on early, success ran about 81% with a 19% failure rate; for long-standing corner injuries rebuilt later, about 90% success. In multi-ligament knees, surgery beat non-surgical management on function scores (85 against 67) and return to sport (41% against 18%).
The honest version. The decision that matters here is not really surgery versus rehab. It is whether anyone properly looked for the corner injury before that conversation started, because the entire case for the non-surgical route depends on the injury being genuinely isolated, and that assumption is wrong about 60% of the time.
What to expect if the corner is involved. People whose corner injury came with this back ligament, rather than the front one, saw their activity level drop measurably compared to before the injury, and took about 21 weeks to get back to work against 11 weeks for the front-ligament group. Complications after corner surgery are not rare either: around 20% overall, most commonly stiffness needing a further procedure.
One structural detail worth knowing. The natural backward slope of the top of your shin bone affects the risk. A flatter slope was linked to both tearing this ligament in the first place and to the graft failing afterwards, with roughly a 1.3-fold increase in failure odds for each degree flatter. It does not change how you rehab, but it does explain why some knees fail twice.
Sources
- Peccin et al., 2005, Cochrane Database of Systematic Reviews — searched for trials of any treatment for this injury and found zero eligible randomised trials. Review withdrawn in 2012. (Highest-tier methodology, empty result.)
- Kopkow et al., 2013, Journal of Orthopaedic & Sports Physical Therapy — 1,307 papers screened, 11 studies, 11 different hands-on tests; accuracy "largely unknown", data too inconsistent to combine. (Systematic review of diagnostic accuracy.)
- Vaquero-Picado & Rodríguez-Merchán, 2017, British Medical Bulletin — approximately 60% of these ligament injuries carry a corner tear; no randomised trial exists. (Systematic review.)
- Kim et al., 2018, KSSTA — meta-analysis of 5 laboratory studies; rebuilding the ligament alone cannot restore normal knee movement when the corner is torn. (Meta-analysis, laboratory not clinical.)
- Dean et al., 2023, KSSTA — 288 patients; failure 21.9% after repair versus 7.1% after reconstruction. (Largest and most recent direct comparison.)
- Chahla et al., 2016, American Journal of Sports Medicine, Parts 1 and 2 — acute corner injuries 81% success across 134 patients; long-standing 90% across 456. (Two systematic reviews.)
- Gwinner et al., 2014, Orthopaedics & Traumatology: Surgery & Research — average 18.4 months to surgery for these combined injuries versus 4.43 months for the front-cruciate equivalent. (Systematic review.)
- Sanders et al., 2017, KSSTA — population study, 48 patients, average 12.2 years follow-up; symptomatic arthritis roughly six times more likely than matched controls. (Population-based cohort.)
- Krych-indexed group, 2022, KSSTA — nerve palsy in 23.4% of operated corner injuries, concentrated in lower-corner injuries; only 36.4% recovered completely. (Retrospective cohort.)
- Ahn et al., 2016, Journal of the AAOS — states plainly that no high-quality evidence exists on immobilisation, weight-bearing, bracing or rehabilitation for this injury. (Evidence-based review.)
- Chahla et al., 2019, KSSTA — expert consensus statement, 27 specialists; treatment section reached only 70% agreement. (Expert consensus, lowest evidence tier.)
- Kim et al., 2013, Archives of Orthopaedic and Trauma Surgery — tabulation of 34 published rehabilitation programmes; hamstring restriction window ranged 6 to 24 weeks. (Literature review of protocols, not trials.)