Glossary · Anatomy

Lateral collateral ligament (LCL)

The lateral collateral ligament (LCL) is a fibrous cord on the outer (lateral) side of the knee, running from the lateral femoral epicondyle to the fibular head, where it resists varus stress and contributes to posterolateral rotational stability.

Verified May 8, 2026 · 8 sources ↓

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Definition

Source · Editorial summary grounded in 8 cited references ↓

Also called the fibular collateral ligament, the LCL is one of the four primary knee ligaments and the primary soft-tissue restraint against varus (bow-legged) force across the joint. It originates at the lateral femoral epicondyle and inserts on the proximal fibular head, traveling slightly posterior to the joint line and running independently of the joint capsule—a feature that distinguishes it from the medial collateral ligament. Because it is a cord-like, extra-articular structure, it is not visible during standard knee arthroscopy without deliberate posterolateral portal placement.

The LCL functions within a broader structural neighborhood called the posterolateral corner (PLC), which also includes the popliteofibular ligament, arcuate ligament, fabellofibular ligament, and biceps femoris tendon. The PLC anatomy is variable between individuals, which has direct consequences for surgical planning and pre-authorization documentation. LCL injury almost always warrants evaluation of co-existing PLC pathology, and isolated LCL tears are uncommon.

LCL and PLC injuries are the least frequent of all major knee ligament injuries, yet they carry outsized clinical risk when missed: untreated posterolateral instability is one of the leading causes of ACL or PCL reconstruction failure. Grading follows the standard ligament injury scale (Grade I–III), and grade directly drives both the treatment algorithm and medical-necessity criteria for surgical intervention.

Why it matters

Accurate LCL documentation directly affects claim outcomes and coverage decisions. Payers—including those following Providence Health Plan MP434 criteria and similar CMS-aligned policies—require grade-based instability findings on physical exam plus imaging confirmation before approving CPT 27427 (ligament reconstruction/repair). Billing 27427 without documented grade (I, II, or III), laterality, and a clear description of whether isolated LCL or concurrent PLC involvement is present is a common driver of prior-authorization denials and post-payment audits. Additionally, because LCL reconstruction is routinely performed alongside other knee procedures (PCL repair, ACL reconstruction), coders must evaluate NCCI procedure-to-procedure (PTP) bundling edits and apply appropriate modifiers only when the services are genuinely separate and not contiguous—failing to do so triggers either underpayment or improper unbundling.

Common mistakes

Where people most often go wrong with this concept.

Source · Editorial brief grounded in cited references ↓

Billing CPT 27427 for LCL reconstruction without documenting the instability grade (I, II, or III) in the operative or clinic note—many payers require Grade III, or Grade II with failed 6-week conservative care, as a medical-necessity threshold.
Failing to document whether the LCL injury is isolated or involves the posterolateral corner (PLC); concurrent PLC injury changes medical-necessity criteria and may support additional CPT codes.
Confusing the knee LCL (femur-to-fibula, CPT 27427) with the elbow lateral collateral ligament (humerus-to-radius, CPT 24343/24344)—the same abbreviation 'LCL' appears in both anatomic regions and can cause incorrect code selection.
Attempting to separately report arthroscopic visualization of the posterolateral compartment when it is integral to the primary reconstructive procedure, triggering NCCI PTP bundling.
Using modifier 59 to bypass NCCI edits on contiguous-structure LCL/PLC procedures performed at the same encounter—NCCI guidance specifies that modifiers are generally inappropriate for procedures on contiguous structures at the same session.
Omitting laterality on both the ICD-10-CM diagnosis code and the operative note, which delays adjudication and can result in claim rejection.

Related codes

Codes commonly involved when this concept appears in practice.

CPT

Modifiers

59 Distinct procedural service XS Separate structure RT Right side LT Left side 51 Multiple procedures

Frequently asked questions

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01What is the difference between LCL repair and LCL reconstruction, and does it affect CPT coding for the knee?

For knee procedures, both repair (using local tissue) and reconstruction (using a tendon graft) are reported under CPT 27427. Unlike the elbow—where repair (24343) and reconstruction (24344) have separate codes—the knee collateral ligament codes do not split by technique in the same way. However, the operative note should still clearly distinguish the method because payers may request records, and the distinction affects medical-necessity review.

02Can the LCL be evaluated arthroscopically?

Standard knee arthroscopy does not provide a direct view of the LCL because it is an extra-articular structure. Posterolateral portal placement can allow indirect assessment, but MRI remains the primary imaging modality for confirming LCL and PLC tears before surgical planning.

03When is LCL reconstruction considered medically necessary?

Most payer policies aligned with CMS guidance require either Grade III LCL instability on exam, or Grade II instability with imaging-confirmed isolated tear and failure of at least six weeks each of physical therapy and bracing. Documentation of all three elements is essential to avoid denial of CPT 27427.

04Why do LCL injuries frequently involve other structures?

The LCL sits within the posterolateral corner (PLC), a complex of multiple ligaments and tendons. A force strong enough to stress the LCL past its limit typically loads the entire PLC simultaneously. Isolated LCL tears are uncommon; concurrent PLC injury should be assumed and ruled out with imaging and thorough physical examination.

05Is 'LCL' always the knee lateral collateral ligament in orthopedic coding?

No. Surgeons and operative notes use 'LCL' for both the knee lateral collateral ligament (femur to fibula) and the elbow lateral collateral ligament (humerus to radius). The correct CPT codes differ substantially—27427 for the knee versus 24343 or 24344 for the elbow—so coders must confirm anatomic site from context before assigning codes.

06What ICD-10-CM codes are used for an acute LCL knee sprain?

Acute LCL knee sprains are coded from the S83.4xx category. Laterality and encounter type must be specified—for example, S83.401A (unspecified sprain of lateral collateral ligament of right knee, initial encounter) or S83.402A (left knee, initial encounter). Choose the most specific subcategory supported by documentation.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

When Mira detects LCL in the operative or clinic note, verify and flag the following before claim submission: 1. GRADE DOCUMENTED? The note must state Grade I, II, or III instability based on physical examination. Grade drives medical-necessity criteria for CPT 27427; absence of grading is a top denial trigger. 2. LATERALITY CAPTURED? Confirm left (LT) or right (RT) modifier is applied and that the ICD-10-CM code includes the correct laterality digit (e.g., S83.401A right vs. S83.402A left for unspecified sprain, initial encounter). 3. ISOLATED LCL OR PLC INVOLVEMENT? If the surgeon documents concurrent posterolateral corner (PLC) pathology, a second procedure code (e.g., 27429 or an additional 27427) may be appropriate—but verify NCCI PTP edits before reporting both. Do not apply modifier 59 for contiguous structures at the same session. 4. REPAIR vs. RECONSTRUCTION? Local-tissue repair and tendon-graft reconstruction are distinct; both map to CPT 27427 for the knee LCL (unlike elbow LCL, which has separate codes 24343/24344). Confirm the operative note specifies technique. 5. ELBOW vs. KNEE DISAMBIGUATION: If the note is for an elbow procedure, 'LCL' refers to the radial/lateral collateral ligament of the elbow → CPT 24343 (repair) or 24344 (reconstruction). Do not route to 27427. 6. CONSERVATIVE CARE FOR GRADE II: Payer policies (e.g., Providence MP434-style criteria) require ≥6 weeks of PT and ≥6 weeks of bracing before surgical authorization for Grade II LCL injuries. Confirm the note documents this history if applicable.

See Mira's approach

The medial collateral ligament (MCL) is a broad, flat band of connective tissue on the inner (medial) side of the knee that resists valgus stress and stabilizes the tibiofemoral joint. It runs from the medial femoral epicondyle to the proximal medial tibia and is the most commonly injured knee ligament.

Anterior cruciate ligament (ACL) Anatomy

The anterior cruciate ligament (ACL) is a primary intra-articular stabilizing ligament of the knee that resists anterior tibial translation and rotational forces. It is one of the most commonly injured knee structures in orthopedic practice, and its repair or reconstruction drives a distinct set of CPT, ICD-10-CM, and modifier decisions.

Posterior cruciate ligament (PCL) Anatomy

The posterior cruciate ligament (PCL) is a strong intra-articular ligament connecting the medial femoral condyle to the posterior tibial plateau, functioning primarily to prevent the tibia from translating posteriorly on the femur. It is roughly 1.3–2 times thicker and up to twice as strong as the ACL, making isolated PCL tears less common than ACL injuries.