condition explainer
LCL & PCL Injuries Explained — The Often-Missed Knee Ligaments
This article is for educational purposes only. It is not medical advice. If you’re experiencing knee pain, consult a healthcare professional.
The knee has four major stabilising ligaments. Two get most of the attention — the ACL and MCL. The other two — the LCL (lateral collateral ligament) and PCL (posterior cruciate ligament) — get injured less often but are also missed more often. Patients sometimes spend weeks being treated for a generic “sprain” before someone identifies what’s actually torn.
This article covers what these two ligaments do, the specific mechanisms that injure them, why diagnosis matters, and what treatment looks like.
The lateral collateral ligament (LCL)
The LCL runs along the outside of the knee, connecting the femur to the fibula (the smaller bone on the outer side of the lower leg). It’s the mirror-image of the MCL — but it’s a much smaller, cord-like structure and not as well-supported by surrounding tissue.
The LCL resists varus stress — forces that would push the knee outward.
How LCL injuries happen
- Direct blow to the inside of the knee pushing the joint outward (less common than blows to the outside)
- Non-contact hyperextension with rotation — often during awkward landings
- Knee dislocation — most LCL tears are part of a larger injury pattern, including the posterolateral corner (PLC), a complex of structures behind and to the outside of the knee
- Severe twisting injuries — particularly in skiing, contact sports, motor vehicle accidents
Symptoms
- Pain and tenderness directly over the lateral knee
- Swelling on the outer side (often less than ACL-related swelling because it’s largely extracapsular)
- Looseness or instability when the knee is loaded with the foot planted
- Possible peroneal nerve symptoms — numbness, tingling, or weakness in the outer lower leg and foot. The peroneal nerve runs near the LCL and can be stretched or injured in severe LCL/posterolateral corner injuries. Foot drop in this setting is a red flag.
Why LCL injuries get missed
- The lateral structures are smaller and harder to examine than the medial side
- MRI interpretation of the posterolateral corner requires specific expertise
- Patients often have a constellation of complaints that the LCL component gets folded into
LCL injury treatment
For isolated Grade I-II LCL sprains — and these are uncommon as isolated injuries:
- PRICE protocol for the first 1-2 weeks
- A hinged brace can provide stability and confidence during early healing
- Progressive return to activity over 4-8 weeks similar to MCL grades
For complete LCL tears or combined posterolateral corner injuries — surgical reconstruction is usually recommended. The lateral side has poorer healing potential than the medial side, and untreated posterolateral corner instability often leads to chronic problems with cutting, rotational activities, and eventual cartilage damage.
A complete LCL or PLC injury that’s missed initially and presents 6-12 months later with chronic instability is much harder to treat than a recognised acute injury.
The posterior cruciate ligament (PCL)
The PCL runs inside the joint, behind the ACL. Its job is to prevent the tibia from sliding backward relative to the femur — the opposite of the ACL.
The PCL is actually a thicker, stronger ligament than the ACL. It takes a substantial force to injure it.
How PCL injuries happen
- “Dashboard injury” — the classic mechanism. In a car accident, the bent knee strikes the dashboard, driving the tibia backward.
- Falling onto a bent knee — the most common mechanism in everyday life
- Hyperflexion — knee bent forcibly beyond normal range
- Sports — soccer, rugby, mixed martial arts; often combined with other knee injuries
Symptoms
PCL injuries are sneaky. Many patients have:
- Modest pain — sometimes surprisingly little
- Mild to moderate swelling that settles in days
- Vague back-of-knee discomfort especially going down stairs or downhill
- A feeling that the knee is “wobbly” but not the dramatic giving-way of ACL injuries
- Difficulty squatting deeply or kneeling
Patients are often able to continue some activity, which is part of why PCL injuries get missed. The chronic consequence — long-term posterior instability — accumulates cartilage damage if the knee remains lax.
The posterior drawer test
A clinician examines the PCL by flexing the knee to 90 degrees and pushing the tibia backward — the posterior drawer test. Significant backward displacement compared with the uninjured side suggests PCL injury.
MRI confirms the diagnosis and reveals associated injuries.
PCL injury treatment
PCL injury management has shifted in recent years.
Grade I-II isolated PCL injuries — usually managed non-operatively:
- Initial relative rest, ice, and quadriceps activation work
- Quadriceps strengthening is especially important — strong quads help compensate for PCL deficiency by holding the tibia forward
- Avoid early hamstring strengthening (the hamstrings pull the tibia backward, the same direction the missing PCL was preventing) — focus on quads first
- A PCL-specific brace that supports the back of the tibia can be used early
- Most patients return to function in 6-12 weeks
Grade III isolated PCL tears — still often managed non-operatively, with surgical reconstruction reserved for symptomatic patients who don’t respond.
Combined PCL injuries (PCL+ACL, PCL+posterolateral corner, multi-ligament knee dislocations) — surgical reconstruction is usually recommended.
Long-term, chronic PCL deficiency increases the risk of patellofemoral and medial compartment cartilage damage. This is part of why even “successfully managed” non-operative PCL injuries warrant long-term joint care — strength work, sensible activity choices, and managing any subsequent osteoarthritis aggressively.
What both injuries share — why they get missed
Both LCL and PCL injuries can present without the dramatic symptoms of an ACL tear:
- Less of an immediate “pop”
- Less rapid swelling
- Less obvious instability in straight-line activity
- Patient can often weight-bear and even continue activity
The result is that emergency department visits or early clinical assessments often miss them. A “knee sprain” that doesn’t improve in 4-6 weeks, or that has persistent back-of-knee or outer-knee pain, deserves re-examination — ideally by a clinician with sports medicine or orthopaedic background.
Imaging guidance
If you suspect either injury — or if a generic “knee sprain” isn’t improving — appropriate imaging matters:
- X-ray — rules out fractures, particularly avulsion fractures at ligament attachments
- MRI — the test for ligament integrity, with the proviso that posterolateral corner injuries are easily under-read by general radiologists. If a posterolateral corner injury is suspected clinically, sub-specialist interpretation matters.
- Stress radiographs — sometimes used for chronic PCL evaluation
Useful tools during recovery
The right knee support depends on the injury and grade:
- Hinged knee brace — for isolated MCL or LCL injuries in the early healing phase, blocks valgus or varus stress while allowing motion. See hinged knee brace options.
- PCL-specific brace — supports the back of the tibia; used for isolated PCL injuries during early recovery
- Compression sleeve — useful later in recovery for proprioception and mild support
- Cold therapy — through the first 1-2 weeks helps swelling control. See cold therapy options.
When to seek urgent care
For any suspected ligament injury — including LCL and PCL:
- Inability to bear weight
- Rapidly increasing swelling
- Numbness, tingling, or weakness in the foot (rule out nerve injury, especially with LCL/PLC mechanism)
- Pale or cool foot, weak pulses (vascular emergency — knee dislocation can damage the popliteal artery)
- Knee that won’t fully straighten
Multi-ligament knee injuries can be associated with vascular and nerve injuries that need immediate attention.
Recommended products for this condition
Affiliate disclosure: As an Amazon Associate, Knee Joint Relief earns from qualifying purchases. The picks below are products we’d recommend based on the conditions and treatment options discussed in this article. They are not medical advice — please consult a healthcare professional for guidance specific to your situation.
McDavid 422 Hinged Knee Brace — Range-of-motion support during early healing
DonJoy Iceman Classic3 Cold Therapy Unit — Cold therapy for swelling control
Related reading
- Ligament Injuries category
- ACL Tear: Signs, Surgery & Rehab
- MCL Sprain: Grading & Recovery
- Knee braces & supports
- Therapy devices
- Methodology
Sources
- American Academy of Orthopaedic Surgeons (AAOS)
- Mayo Clinic — Collateral Ligament Injuries; PCL Injuries
- Cleveland Clinic Health Essentials
- PubMed: LaPrade RF et al. “The reproducibility and repeatability of varus stress radiographs.” J Bone Joint Surg Am. 2008
- PubMed: Bedi A, Musahl V, Cowan JB. “Management of Posterior Cruciate Ligament Injuries.” J Am Acad Orthop Surg. 2016
For citations, see our methodology.