Dial Test | Arcuate Sign | Combined PCL | Reconstruction
PLC STRUCTURES
Critical Must-Knows
- PLC = primary restraint to EXTERNAL ROTATION and VARUS
- Dial test at 30 degrees only = isolated PLC. At 30 AND 90 degrees = combined PCL
- Arcuate sign on X-ray = avulsion of PLC attachment to fibula
- Missing PLC injury = ACL/PCL graft failure
- Reconstruct rather than repair for best outcomes
Clinical Pearls
- "Varus thrust gait = chronic PLC deficiency
- "Common peroneal nerve at risk (20%+ injuries)
- "LaPrade anatomic reconstruction = gold standard
- "Address varus alignment with osteotomy before/with PLC
Clinical Imaging
Imaging Gallery
Critical Exam Concepts
Dial Test is KEY
Dial test at 30 and 90 degrees distinguishes isolated PLC (30 only) from combined PCL/PLC (30 and 90). Critical for surgical planning.
Commonly Missed
PLC injuries often missed. Always check with PCL and ACL injuries. Missing PLC leads to cruciate graft failure.
Peroneal Nerve
Common peroneal nerve injury in 20%+ of PLC injuries. Check foot drop, lateral leg sensation. Document preoperatively.
Reconstruct Not Repair
Reconstruction superior to repair. Isolated repairs have high failure rates. LaPrade anatomic reconstruction is gold standard.
Dial Test Interpretation
| Finding | 30 Degrees | 90 Degrees | Diagnosis |
|---|---|---|---|
| Normal | Symmetric | Symmetric | No injury |
| Isolated PLC | Greater than 10 degree increase | Symmetric | PLC injury only |
| Combined PCL/PLC | Greater than 10 degree increase | Greater than 10 degree increase | PCL + PLC injury |
FAPPLC Structures
| F | FCL Fibular collateral ligament (primary varus) |
| A | Arcuate complex Posterolateral capsule |
| P | Popliteus complex Popliteus tendon, popliteofibular ligament |
| F | FCL Fibular collateral ligament (primary varus) |
| A | Arcuate complex Posterolateral capsule |
| P | Popliteus complex Popliteus tendon, popliteofibular ligament |
Hook:FAP structures form the PLC!
VERSEPLC Function
| V | Varus restraint FCL is primary varus restraint |
| E | External rotation restraint Popliteus controls ER |
| R | Recurvatum restraint PLC resists hyperextension |
| S | Secondary ACL backup Helps control anterior translation |
| E | Extension tightening PLC tightens in extension |
| V | Varus restraint FCL is primary varus restraint | S | Secondary ACL backup Helps control anterior translation |
| E | External rotation restraint Popliteus controls ER | E | Extension tightening PLC tightens in extension |
| R | Recurvatum restraint PLC resists hyperextension |
Hook:The PLC controls VERSE directions of instability!
DRIVEPLC Examination
| D | Dial test At 30 and 90 degrees |
| R | Reverse pivot shift PLC-specific test |
| I | Instability varus Test at 0 and 30 degrees |
| V | Varus thrust gait Observe walking |
| E | External rotation recurvatum Supine, lift great toe |
| D | Dial test At 30 and 90 degrees | V | Varus thrust gait Observe walking |
| R | Reverse pivot shift PLC-specific test | E | External rotation recurvatum Supine, lift great toe |
| I | Instability varus Test at 0 and 30 degrees |
Hook:DRIVE through PLC examination!
Overview and Epidemiology
Commonly Missed Injury
PLC injuries are frequently missed on initial presentation. Have high index of suspicion with PCL and ACL injuries. Missing PLC leads to cruciate graft failure - must address all injured structures.
Epidemiology
- 16% of knee ligament injuries
- 60-70% with cruciate injury
- Usually high-energy trauma
- Sports: football, soccer, skiing
- MVCs common cause
Mechanism
- Varus force: Direct blow to medial knee
- Hyperextension: With varus component
- External rotation: On planted foot
- Knee dislocation: Multiligament pattern
- Contact sports: Direct lateral blow
Pathophysiology and Mechanisms
PLC Anatomy (LaPrade)
Fibular Collateral Ligament (FCL):
- Origin: Lateral femoral epicondyle
- Insertion: Lateral fibular head
- Primary varus restraint
Popliteus Complex:
- Popliteus tendon: Femoral origin, inserts on tibia
- Popliteofibular ligament: Connects popliteus to fibula
- Primary external rotation restraint
Posterolateral Capsule: Static stabilizer, arcuate ligament.
Always Check Peroneal Nerve
Common peroneal nerve injury occurs in 20%+ of PLC injuries. Check ankle dorsiflexion and toe extension. Document sensation. Nerve injury affects rehabilitation and prognosis.
Classification Systems
PLC Injury Grading
| Grade | External Rotation | Varus | Implication |
|---|---|---|---|
| I | Less than 5 degree increase | Minimal | Sprain, intact structures |
| II | 5-10 degree increase | Moderate | Partial tear |
| III | Greater than 10 degree increase | Significant | Complete rupture, surgery indicated |
Grade based on dial test asymmetry compared to contralateral side.
Clinical Assessment
History
- Mechanism: Varus blow, hyperextension, MVA
- Pain: Lateral and posterolateral knee
- Instability: Varus, giving way
- Gait: Varus thrust (chronic)
- Nerve symptoms: Foot drop, numbness
Examination
- Dial test: 30 and 90 degrees (KEY)
- Varus stress: 0 and 30 degrees
- External rotation recurvatum: Lift toe
- Reverse pivot shift: Clunk on extension
- Peroneal nerve: Motor and sensory
Dial Test Technique
Patient prone, knees flexed 30 degrees (then 90). Externally rotate both feet simultaneously. Compare tibial thigh angle. Greater than 10 degree asymmetry = positive. At 30 degrees only = isolated PLC. At 30 AND 90 = combined PCL.
Key Clinical Pearls
Varus thrust gait: Lateral thrust during stance phase. Indicates chronic PLC deficiency and significant laxity.
External rotation recurvatum test: Patient supine, lift great toe. Positive = tibia drops into hyperextension and external rotation.
Differential Diagnosis
Distinguishing PLC from Mimics
| Condition | Key discriminator | Best test | Pitfall |
|---|---|---|---|
| Isolated PLC | Dial positive at 30 only; varus laxity | Dial at 30 and 90; varus stress | Easily missed when subtle |
| Combined PCL + PLC | Dial positive at 30 AND 90; posterior sag | Posterior drawer + dial | Operating on PCL alone |
| Isolated PCL | Posterior sag; dial symmetric | Posterior drawer | Mislabelling as PLC |
| Isolated LCL/FCL | Varus laxity at 30 without rotational laxity | Varus stress at 30 | Underestimating popliteus involvement |
| Multiligament dislocation | Gross instability, possible vascular injury | ABI, CT angiography | Missing limb-threatening ischaemia |
| Common peroneal palsy alone | Foot drop without major laxity | Motor/sensory exam, NCS | Attributing all weakness to pain |
Investigations
MRI Assessment
Sensitivity: Good for PLC but structures can be subtle.
Key structures:
- FCL: Coronal images
- Popliteus: Sagittal and coronal
- Popliteofibular ligament: Often difficult to see
- Arcuate complex: Posterolateral capsule
Associated injuries: Peroneal nerve edema, bone bruise, cruciate tears.
Arcuate Sign
Arcuate sign = avulsion fracture of fibular head/styloid on plain X-ray. Pathognomonic for PLC injury. Indicates avulsion of FCL and/or biceps femoris. Suspect multiligament injury.
Management Algorithm
PLC Injury Management
Treatment Pathway
Document neurovascular status. MRI for full injury pattern. Assess alignment.
Limited evidence. Bracing, rehabilitation. Monitor for progressive laxity.
Anatomic reconstruction preferred. Address all injured structures. Early surgery (within 3 weeks) if combined.
Assess for varus thrust. May need HTO before or with PLC reconstruction.
Surgical Technique
Anatomic PLC Reconstruction
Graft: Achilles allograft with bone block, or split semitendinosus.
Tunnels:
- Femoral: At FCL and popliteus origins (separate tunnels)
- Fibular: At FCL insertion
Technique:
- Reconstruct FCL from femur to fibula
- Reconstruct popliteus and popliteofibular ligament
- Graft crosses from fibula to tibial sulcus
Anatomic reconstruction restores both varus and rotational stability.
Peroneal Nerve Protection
Common peroneal nerve at risk during PLC reconstruction. Meticulous dissection required. Identify and protect nerve throughout. May be scarred/displaced in chronic cases.
Complications
| Complication | Cause | Prevention | Management |
|---|---|---|---|
| Peroneal nerve injury | Traction, direct | Identify and protect | Observation, EMG, may recover |
| Residual laxity | Technical error, missed structure | Anatomic reconstruction | Revision |
| Stiffness | Scarring, immobilization | Early ROM | Physiotherapy, MUA |
| Failure | Missed varus alignment | Correct alignment | HTO then revision |
Peroneal Nerve Outcomes
Peroneal nerve injury occurs in 20%+ of PLC injuries. Complete lesions have poor recovery. Incomplete lesions may recover over 6-12 months. Consider nerve exploration/grafting if no recovery at 3-6 months.
Postoperative Care
PLC Reconstruction Rehabilitation
Brace locked in extension. Non-weight bearing. Avoid external rotation.
Progressive flexion. Partial weight bearing. Quad strengthening.
Full ROM. Weight bearing progression. Closed chain exercises.
Sport-specific preparation. Pool running. Proprioception.
Functional testing. Full sport when strength and stability restored.
Rehabilitation Cautions
Avoid external rotation stress early - this stresses the PLC reconstruction. Avoid varus stress. Progress slower if combined with other reconstructions.
Outcomes and Prognosis
Outcome Factors
Good outcomes: Anatomic reconstruction, early surgery, all structures addressed, alignment corrected.
Poor outcomes: Isolated repair, delayed surgery, missed varus alignment, incomplete reconstruction, peroneal nerve injury.
Long-Term
If untreated or undertreated: Progressive varus deformity, lateral compartment OA, cruciate graft failure.
If addressed appropriately: Good return to activity, stable knee, preserved function.
Controversies and Areas of Uncertainty
Anatomic vs Fibular-Based Reconstruction
The LaPrade anatomic two-graft technique reconstructs FCL, popliteus and popliteofibular ligament. Fibular-based (Larson) techniques are simpler and reconstruct FCL and popliteofibular ligament only. Anatomic methods better restore rotation biomechanically, but high-level comparative clinical data are limited and many surgeons obtain good results with a hybrid approach.
Acute Repair vs Reconstruction
Reconstruction is more durable overall (repair failure around 37% vs 9%). However, a good acute bony avulsion with healthy tissue can be primarily fixed. The threshold for choosing repair over reconstruction in the acute setting remains debated.
Staged vs Single-Stage Alignment
With genu varus, some advocate osteotomy first (a proportion then avoid ligament surgery), others perform combined realignment and reconstruction. Optimal sequencing, especially in multiligament knees, is unresolved.
Graft Choice and Nerve Outcomes
Allograft versus autograft, optimal tensioning angle, and whether early peroneal nerve exploration changes outcomes are all areas without consensus. Complete peroneal lesions still carry a poor prognosis regardless of approach.
Evidence Base and Key Studies
Quantitative Posterolateral Attachment Anatomy
- Cadaveric study (10 fresh-frozen knees) mapping the FCL, popliteus tendon, popliteofibular ligament and lateral gastrocnemius attachments
- FCL femoral attachment averaged 1.4 mm proximal and 3.1 mm posterior to the lateral epicondyle; fibular attachment 8.2 mm posterior to the anterior fibular head
- Popliteus femoral attachment lies in the proximal-anterior fifth of the popliteal sulcus, always anterior to the FCL (mean separation 18.5 mm)
- Popliteofibular ligament had constant anterior and posterior divisions at the fibular styloid
Anatomic PLC Reconstruction (Biomechanical Validation)
- In-vitro biomechanical study in 10 cadavers describing a 2-graft technique reconstructing the FCL, popliteus tendon and popliteofibular ligament
- Restored varus stability versus the sectioned (grade III) state at 0, 30, 60 and 90 degrees of flexion
- Restored external rotation control, with no significant difference from the intact knee at any flexion angle
- Became the reference anatomic reconstruction technique
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Scenario 1: Acute Combined Injury
"A 25-year-old motorcyclist presents after an MVC. He has a swollen knee. Posterior drawer shows Grade III laxity. Dial test shows 20 degrees increased external rotation at both 30 and 90 degrees compared to the opposite side. He has ankle dorsiflexion weakness. What is your assessment and management?"
Scenario 2: Chronic PLC with Varus Thrust
"A 35-year-old presents with lateral knee instability for 2 years after a rugby injury. He walks with a noticeable varus thrust. Dial test shows 15 degrees increased external rotation at 30 degrees, symmetric at 90 degrees. X-rays show varus alignment (mechanical axis 5 degrees varus). What is your approach?"
Scenario 3: Arcuate Sign
"A 22-year-old presents after a knee hyperextension injury during soccer. X-ray shows a small avulsion fracture of the fibular head. He has tenderness posterolaterally. Dial test is positive at 30 degrees only. What is your management?"
MCQ Practice Points
Dial Test Interpretation
Q: Dial test positive at 30 degrees only vs 30 and 90 degrees? A: 30 degrees only = isolated PLC. 30 and 90 degrees = combined PCL + PLC. At 90 degrees, intact PCL prevents external rotation.
Primary Function
Q: What are the primary functions of the PLC? A: Varus restraint (FCL primary) and external rotation restraint (popliteus primary). Also resists hyperextension.
Arcuate Sign
Q: What is the arcuate sign? A: Avulsion fracture of fibular head on X-ray. Pathognomonic for PLC injury. Indicates avulsion of FCL/biceps attachment.
Repair vs Reconstruction
Q: Why is reconstruction preferred over repair for PLC? A: Repair has 37% failure rate vs 9% for reconstruction. Reconstruction anatomically restores all structures.
Peroneal Nerve
Q: What nerve is at risk with PLC injuries? A: Common peroneal nerve - 20%+ injury rate. Check ankle dorsiflexion and lateral leg sensation. Document preoperatively.
Varus Alignment
Q: Why is varus alignment important in PLC injuries? A: Varus increases load on PLC. Must correct with HTO before or with reconstruction, or reconstruction will fail.
Guidelines, Registries & Global Practice
Global Epidemiology
- PLC injury accounts for roughly 16% of knee ligament injuries
- Up to 60-70% occur with a cruciate injury (rarely truly isolated)
- Common peroneal nerve involvement in 15-25% of cases
- Typical patient is young and male (mean age mid-20s to early 30s in published series)
- High-energy mechanisms predominate: road traffic trauma, contact sport, knee dislocation
Society & Consensus Position
- No single dedicated international society guideline exists; practice is driven by expert consensus and series
- ESSKA / European consensus: reconstruct rather than repair grade III injuries; address all structures anatomically
- AANA / AOSSM (North America): anatomic reconstruction is the reference standard for chronic and most acute grade III injuries
- AO / multiligament-knee principles: ankle-brachial index in suspected dislocation, early surgery, reconstruct the PLC/FCL
- Broad agreement that missed varus malalignment must be corrected before or with reconstruction
Side-by-Side Practice Positions
| Question | European consensus (ESSKA) | North American (AOSSM/AANA) | Multiligament / AO principles |
|---|---|---|---|
| Grade III treatment | Anatomic reconstruction | Anatomic reconstruction | Reconstruct PLC/FCL, not repair alone |
| Acute repair | Selective (good bony avulsion) | Selective; reconstruction favoured | Repair carries higher failure |
| Timing | Early (within ~3 weeks) | Early for combined injuries | Early after vascular clearance |
| Varus malalignment | Correct (staged or combined) | Correct before/with reconstruction | Realign to protect the graft |
Registry & Resource Context
- National knee-ligament registries (e.g. Scandinavian and UK datasets) capture mainly ACL; isolated PLC is under-represented, so high-quality outcome data come from specialist series
- Allograft is widely used in North America; many European and resource-limited settings rely on autograft (hamstring, peroneus longus, quadriceps) due to allograft cost and availability
- MRI and stress radiography availability shape how confidently PLC is diagnosed pre-operatively
High- vs Limited-Resource Practice
- High-resource: anatomic multi-tunnel reconstruction, intra-operative fluoroscopy, allograft, structured bracing and physiotherapy
- Limited-resource: autograft, fibular-based (Larson-type) or hybrid techniques, greater reliance on clinical examination and plain films
- Universal priorities everywhere: document the peroneal nerve, exclude vascular injury in dislocations, and never miss the PLC alongside a cruciate tear
Orthopaedic Exam Relevance
PLC injuries are high-yield viva topics. Know the dial test interpretation, arcuate sign significance, and why reconstruction is preferred. Be prepared to discuss combined injuries and the importance of addressing alignment.
POSTEROLATERAL CORNER INJURIES
Clinical summary
PLC Structures (FAP)
- •FCL: Primary varus restraint
- •Arcuate complex: Posterolateral capsule
- •Popliteus complex: External rotation restraint
- •Popliteofibular ligament connects them
Dial Test Critical
- •Test at 30 AND 90 degrees
- •Positive at 30 only = isolated PLC
- •Positive at 30 AND 90 = combined PCL + PLC
- •Greater than 10 degree asymmetry = positive
Key Findings
- •Arcuate sign: Fibular head avulsion = PLC
- •Varus thrust gait: Chronic PLC deficiency
- •Peroneal nerve injury: 20%+ cases
- •Combined injuries most common
Treatment Principles
- •Reconstruction superior to repair (37% vs 9% failure)
- •LaPrade anatomic technique gold standard
- •Early surgery (within 3 weeks) preferred
- •Address varus alignment or reconstruction fails
Exam Pearls
- •Commonly missed injury - high suspicion
- •Always check with PCL and ACL injuries
- •Document peroneal nerve status
- •Early surgery prevents contracture