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Adult Reconstruction

Posterolateral Approach to the Knee

Comprehensive guide to the posterolateral approach to the knee for FRCS exam preparation

Core Procedure
intermediate
By OrthoVellum Medical Education Team

Reviewed by OrthoVellum Editorial Team

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High Yield Overview

POSTEROLATERAL KNEE APPROACH

PLC Reconstruction | Tibial Plateau | CPN Protection

Critical Posterolateral Knee Approach Points

Common Peroneal Nerve

Most commonly injured nerve at knee. Palpable behind biceps tendon. Winds around fibular neck ~2-3cm distal to head. Identify and protect before deep dissection.

Interval

Between biceps femoris (posterior) and iliotibial band (anterior). Both structures insert on fibular head/Gerdy's tubercle area.

Structures Accessed

LCL, popliteus tendon, posterolateral capsule, arcuate ligament, popliteofibular ligament. Lateral tibial plateau (posterior column).

Knee Flexion

Flexing the knee relaxes the CPN and makes dissection safer. Position the knee in 45-90° flexion during dissection around the posterolateral corner.

At a Glance

The posterolateral approach to the knee provides access to the posterolateral corner (PLC), lateral tibial plateau, and proximal fibula through the interval between biceps femoris (posterior) and iliotibial band (anterior). The common peroneal nerve (CPN) is the critical structure at risk—it wraps around the fibular neck 2-3cm distal to the head and must be identified early before deep dissection. Knee flexion to 45-90° relaxes the CPN and facilitates safer dissection. Primary indications include PLC reconstruction (LCL, popliteus, popliteofibular ligament), lateral tibial plateau fractures (posterior column), and peroneal nerve exploration. The approach can be extended distally for fibular access.

Mnemonic

FIBCPN Safety

Memory Hook:FIB = Fibular neck, Identify early, Behind Biceps!

Indications and Position

Indications:

  • Posterolateral corner (PLC) reconstruction/repair
  • LCL reconstruction
  • Lateral tibial plateau fractures (posterior column)
  • Biceps tendon repair
  • Proximal fibula excision/biopsy
  • Peroneal nerve exploration

Patient Position:

  • Supine with bump under contralateral hip
  • Lateral decubitus
  • Knee flexed 45-90° during dissection

Overview

Posterolateral Knee Approach Overview

The posterolateral approach provides essential exposure for the posterolateral corner (PLC), lateral tibial plateau, and peroneal nerve.

Key Concepts:

  • Access to posterolateral corner structures (LCL, popliteus, PFL)
  • Common peroneal nerve (CPN) is critical structure at risk
  • Interval between biceps femoris and iliotibial band
  • Essential for multiligament knee injury management
  • Can be extended distally for proximal fibula access

Historical Context:

  • PLC anatomy described by LaPrade and colleagues
  • Anatomic reconstruction techniques now standard
  • Recognition that PLC injuries often missed leading to ACL/PCL failure

Anatomy

Surface Anatomy

Palpable Landmarks:

  • Fibular head: Key landmark, palpable posterolaterally
  • Biceps femoris tendon: Inserts on fibular head
  • Lateral femoral epicondyle: LCL origin
  • Iliotibial band: Palpable anterolaterally
  • Common peroneal nerve: Palpable behind biceps

Incision Planning:

LandmarkPosition
Proximal extent5 cm above joint line
CenterOver fibular head
Distal extentAlong fibular neck
OrientationCurved or oblique

Classification

Posterolateral Approach Variations

VariationDescriptionIndication
Standard posterolateralBiceps-ITB intervalPLC reconstruction
Extended posterolateralIncludes fibular neck exposureCPN exploration, fibula access
Posterolateral + lateralCombined for plateauBicondylar fractures
Fibular head excisionThrough posterolateralProximal fibula tumors

Interval Options:

  • Anterior: ITB to biceps (main working interval)
  • Posterior: Biceps to lateral gastrocnemius (deeper access)

History

Preoperative History

Mechanism of Injury:

  • Direct blow to anteromedial tibia (varus force)
  • Hyperextension injury
  • Contact sports, motor vehicle accident
  • Low-velocity: isolated PLC; High-velocity: multiligament

Key History Elements:

ElementSignificance
Instability"Giving way" with pivoting, stairs
Pain locationPosterolateral knee
SwellingOften minimal with isolated PLC
Neurological symptomsFoot drop, numbness (CPN injury)
Previous surgeryACL/PCL failure may indicate missed PLC

Examination

Physical Examination

Observation:

  • Varus thrust during gait (lateral thrust)
  • Recurvatum with standing
  • Swelling, ecchymosis posterolaterally

Palpation:

  • Tenderness over fibular head
  • LCL along its course
  • Biceps femoris tendon

Neurovascular:

  • Essential: Check CPN function
  • Ankle dorsiflexion, toe extension (deep peroneal)
  • First web space sensation
  • Foot eversion (superficial peroneal)

Investigations

Imaging Studies

Radiographs:

ViewFinding
APSegond fracture (pathognomonic), fibular head avulsion
LateralArcuate sign (fibular head avulsion)
Stress viewsVarus opening, increased ER
Long legVarus alignment assessment

MRI (Gold Standard):

  • LCL tear: Location and quality
  • Popliteus tendon: Musculotendinous vs insertion
  • Popliteofibular ligament: Often difficult to visualize
  • Associated injuries: ACL, PCL, meniscal
  • Bone bruise pattern: Posteromedial (varus injury)

Management

📊 Management Algorithm
Management algorithm for Approach Posterolateral Knee
Click to expand
Management algorithm for Approach Posterolateral KneeCredit: OrthoVellum

Non-operative Management

Indications:

  • Grade I, II injuries
  • Elderly, low-demand patients
  • Significant comorbidities

Protocol:

PhaseManagement
Acute (0-2 weeks)Hinged brace, protected weight bearing
Intermediate (2-6 weeks)ROM exercises, quadriceps strengthening
Late (6-12 weeks)Progressive strengthening, proprioception

Bracing:

  • Hinged knee brace locked in extension initially
  • Progress ROM as healing occurs
  • Long-term lateral unloader brace if residual varus

Surgical Technique

Incision: Curved incision over posterolateral knee, centered on fibular head. Approximately 8-12cm.

Interval: Develop between iliotibial band (anterior) and biceps femoris (posterior).

CPN Identification: Critical first step. Palpate CPN behind biceps tendon. Identify and protect. The nerve winds around the fibular neck 2-3cm distal to the fibular head.

Knee Flexion: Keep knee flexed to relax CPN.

Structures at Risk

Critical Structures

Common Peroneal Nerve (CPN): Posterior to biceps tendon, winds around fibular neck. Most commonly injured nerve at knee. Injury causes foot drop. Identify and protect in all cases.

Lateral Inferior Genicular Artery: May be encountered deep in dissection.

Popliteal Vessels: Lie medially but at risk with deep dissection toward joint.

Complications

Common Peroneal Nerve Injury

Risk Factors:

  • Preoperative CPN palsy (traction injury)
  • Varus malalignment
  • Revision surgery
  • Inadequate nerve protection

Presentation:

DeficitNerve Affected
Foot drop (dorsiflexion weakness)Deep peroneal
Toe extension weaknessDeep peroneal
First web space numbnessDeep peroneal
Lateral leg/foot numbnessSuperficial peroneal
Eversion weaknessSuperficial peroneal

Management:

  • Observation: Most neurapraxias recover
  • EMG/NCS at 6 weeks, 3 months
  • AFO for foot drop
  • Exploration if no recovery at 3-6 months

Postoperative Care

Immediate Postoperative Care

Day 0-1:

  • Hinged brace locked in extension
  • Ice, elevation
  • DVT prophylaxis
  • Check CPN function (critical)

Protection Phase (Weeks 0-6):

WeekActivity
0-2Brace locked extension, NWB or TTWB
2-4Brace 0-90°, TTWB
4-6Brace 0-120°, progress WB

Key Points:

  • Protect graft healing
  • Avoid varus stress
  • Check wound, neurovascular status

Outcomes

Functional Outcomes

PLC Reconstruction Results:

OutcomeResult
Stability restoration80-90%
Return to sport (any level)70-80%
Return to previous level50-60%
Patient satisfaction75-85%
Residual laxity10-20%

Scoring Outcomes:

  • Lysholm score: Average improvement 30-40 points
  • IKDC: Majority achieve normal/near-normal
  • Tegner: Often reduced by 1-2 levels

Evidence Base

Key Studies

StudyYearFinding
LaPrade et al2003Described anatomic PLC landmarks
Stannard et al2005Repair vs reconstruction outcomes
Levy et al2010Anatomic reconstruction technique
Kim et al2011Single vs double bundle PLC
Geeslin et al2016Long-term reconstruction outcomes

Level of Evidence:

  • Mostly Level III-IV studies
  • Few RCTs in PLC literature
  • Anatomic techniques now preferred (expert consensus)
  • Biomechanical studies support anatomic reconstruction

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Posterolateral Knee Approach

EXAMINER

"Describe the posterolateral approach to the knee and how you protect the common peroneal nerve."

EXCEPTIONAL ANSWER
The posterolateral approach to the knee is used primarily for posterolateral corner (PLC) reconstruction, LCL surgery, and lateral tibial plateau fractures. The patient is positioned supine with a bump under the contralateral hip to externally rotate the leg, or in lateral decubitus. I keep the knee flexed 45-90° during dissection as this relaxes the common peroneal nerve. The incision is curved, centered over the fibular head. The interval is between the iliotibial band anteriorly and biceps femoris posteriorly. The critical first step is identification and protection of the common peroneal nerve. The CPN is palpable just posterior to the biceps tendon. It winds around the fibular neck approximately 2-3cm distal to the fibular head. This is the most commonly injured nerve at the knee and damage causes foot drop. I identify it early before any deep dissection and protect it throughout. With the nerve protected, I can access the lateral collateral ligament running from the lateral femoral epicondyle to the fibular head, the popliteus tendon, the arcuate complex including the popliteofibular ligament, and the posterolateral capsule. For PLC reconstruction, I would create tunnels in the fibula and lateral femur and pass grafts to reconstruct the LCL and popliteofibular ligament. The approach can be extended distally for access to the proximal fibula and lateral tibia.
VIVA SCENARIOChallenging

Scenario 2: PLC Reconstruction Tunnel Placement - Technical Decision-Making

EXAMINER

"You are performing an anatomic posterolateral corner reconstruction in a 28-year-old rugby player who sustained a grade III PLC injury 5 weeks ago (varus stress with hyperextension mechanism). MRI shows complete tears of the LCL, popliteus tendon, and popliteofibular ligament. He has an associated ACL tear which you plan to reconstruct in a staged procedure after the PLC has healed. You have successfully exposed the posterolateral corner via the standard approach (IT band-biceps interval), identified and protected the common peroneal nerve, and prepared your allograft (Achilles tendon allograft for LCL reconstruction, hamstring allograft for popliteofibular ligament). You are now preparing to drill your femoral tunnels for the LCL and popliteus reconstructions. You need to place two femoral tunnels: one for the LCL at the lateral femoral epicondyle, and one for the popliteus tendon in the popliteal groove. Your assistant asks about the exact anatomic location for these tunnels and expresses concern about tunnel convergence (tunnels being too close together risking fracture). How do you determine the isometric points for tunnel placement and how do you avoid tunnel convergence?"

EXCEPTIONAL ANSWER
This requires precise understanding of the anatomic landmarks for PLC reconstruction based on the work of LaPrade and colleagues who defined the isometric points for anatomic PLC reconstruction. For the LCL femoral tunnel: The isometric point is 1.4mm proximal and 3.1mm posterior to the lateral femoral epicondyle. I use the lateral epicondyle as my primary landmark - I can palpate this prominently on the lateral femoral condyle. Using fluoroscopy, I place a guide wire at this precise location (1.4mm proximal, 3.1mm posterior to the center of the epicondyle). For the popliteus femoral tunnel: This is located in the popliteal groove (popliteal sulcus) which lies anterior and distal to the LCL insertion. The popliteal groove is approximately 18mm anterior to the LCL femoral insertion when measured along the joint line. I identify the popliteal groove by palpation (it's a depression in the lateral femoral condyle anterior to the epicondyle) and confirm with fluoroscopy. Regarding tunnel convergence: This is a legitimate concern as placing two femoral tunnels in close proximity risks fracture or tunnel coalescence. The key is the different depths and orientations of the tunnels. The LCL tunnel is drilled from lateral to medial aiming toward the opposite cortex (trans-femoral tunnel), while the popliteus tunnel is typically shorter and oriented differently (can be socket or trans-femoral depending on technique). I use fluoroscopy in both AP and lateral planes to visualize tunnel trajectories before drilling. I ensure at least 5-10mm of bone bridge between the tunnels to prevent convergence. If using interference screws, I plan tunnel diameter accordingly (typically 7-9mm tunnels with corresponding interference screws). An alternative technique to avoid convergence is using the 'LaPrade technique' with separate smaller tunnels, or using cortical suspensory fixation which allows smaller tunnels. For fibular tunnel placement: I drill a tunnel in the fibular head for the LCL distal insertion (anatomic insertion site on posterolateral fibular head) and a separate tunnel for the popliteofibular ligament if doing anatomic reconstruction. After tunnel preparation, I pass the grafts: LCL graft from femoral epicondyle to fibular head, and popliteofibular graft from popliteal groove to fibular insertion. I tension and fix the grafts with the knee at 30-60° of flexion in neutral rotation - this is critical as the PLC structures are isometric at this position. I use interference screw fixation in the tunnels (typically 7-8mm screws), ensuring the grafts are tensioned appropriately to restore varus and rotational stability without over-constraining the knee. Intraoperatively I check knee stability with varus stress testing and dial test to confirm adequate reconstruction.
VIVA SCENARIOCritical

Scenario 3: Iatrogenic Common Peroneal Nerve Injury - Critical Complication Management

EXAMINER

"You are performing a posterolateral corner reconstruction in a 32-year-old motorbike accident victim who sustained a knee dislocation 3 weeks ago (multiligament injury: ACL, PCL, and PLC all torn, vascular injury ruled out, no baseline neurological deficit). You have made your posterolateral approach through the IT band-biceps interval and identified the common peroneal nerve posterior to the biceps tendon. The nerve appears normal and you have been protecting it with a Penrose drain looped around it. You are now drilling the fibular tunnel for the LCL insertion. Despite careful technique, your drill suddenly advances more than expected and you feel a 'pop'. On inspection, you realize the drill has partially transected the common peroneal nerve - approximately 40-50% of the nerve diameter has been cut by the drill, with nerve continuity maintained in the remaining fascicles. The patient begins moving his foot spontaneously under anesthesia. You have not yet completed the PLC reconstruction and still need to address the ACL and PCL in a staged procedure. How do you manage this intraoperative CPN injury and what are the implications for the patient's outcome?"

EXCEPTIONAL ANSWER
This is a devastating iatrogenic nerve injury requiring immediate recognition, documentation, repair, and honest post-operative counseling. Common peroneal nerve injury is the most feared complication of the posterolateral approach, and iatrogenic injury during surgery is associated with worse outcomes than pre-existing traumatic injuries. My immediate management: (1) I would immediately stop drilling and assess the extent of nerve injury. In this case, I have a partial nerve transection (40-50% diameter) with continuity maintained in remaining fascicles. This is a Sunderland grade IV-V injury depending on whether the remaining fascicles are intact (grade IV) or if there is complete loss of continuity requiring re-anastomosis (grade V). (2) I would inform my assistant and anaesthetist of the complication, request microsurgical instruments if available (loupes at minimum, ideally operating microscope), and prepare for nerve repair. The key decision is whether to repair NOW intraoperatively, or to plan delayed nerve repair with a specialist peripheral nerve surgeon. The gold standard is immediate primary repair if the surgeon is competent in microsurgical nerve repair - acute repair within 72 hours has better outcomes than delayed repair. (3) For nerve repair technique: I would sharply debride the damaged nerve ends back to healthy fascicular architecture (may need to convert this to a complete transection to get clean ends for repair). I would perform primary neurorrhaphy using 8-0 or 9-0 nylon sutures under magnification (loupes minimum 2.5-3.5x, ideally microscope). The repair should be tension-free - if there is a nerve gap greater than 2-3cm after debridement, primary repair is not feasible and I would need nerve grafting (sural nerve autograft) or conduit. In this case, with partial transection, I may be able to preserve the intact fascicles and repair only the damaged portion, which has better outcomes than complete transection repair. (4) After nerve repair is secured, I face the critical decision of whether to complete the PLC reconstruction. The options are: (A) Complete the PLC reconstruction as planned - risks additional nerve trauma from continued dissection, graft passage, and fixation. The nerve repair may be compromised by further manipulation. (B) Abort the PLC reconstruction and stage it for later - requires second surgery exposing patient to additional anesthetic and surgical risks, but protects the nerve repair. (C) Modify the PLC reconstruction to a less invasive technique - e.g., simplified reconstruction avoiding the area of nerve injury. My approach: I would complete a modified PLC reconstruction avoiding further dissection near the nerve repair. This likely means completing the LCL and popliteus reconstruction using alternative fixation methods (e.g., suture anchors rather than fibular tunnel if that was the site of injury), and protecting the nerve repair site. I would NOT abort the procedure entirely as the PLC instability must be addressed to prevent ACL/PCL graft failure. However, I would modify my technique to minimize risk to the nerve. (5) Post-operatively: I must immediately inform the patient and family of the nerve injury when the patient wakes up. Documentation in the operation note must be meticulous: exact nature of injury, repair performed, prognosis discussed. I would examine CPN function immediately post-op (ankle dorsiflexion, toe extension, first web space sensation, foot eversion). If there is complete foot drop (expected given the injury), I would provide an ankle-foot orthosis (AFO) and refer to physiotherapy for foot drop management. I would arrange baseline EMG/NCS at 3-6 weeks (too early immediately post-op), and serial studies at 3 months, 6 months, and 12 months to monitor for reinnervation. Prognosis counseling: Iatrogenic CPN injury with partial transection repaired primarily has approximately 40-60% chance of meaningful recovery (grade 3 or better motor function) but full recovery is rare. Complete motor recovery occurs in only 10-20% of cases. Recovery timeline if it occurs is 6-12 months minimum (regeneration rate 1-2mm per day, so for CPN to reinnervate tibialis anterior approximately 20-25cm distance requires 100-125 days minimum, plus additional time for functional recovery). Many patients are left with permanent foot drop requiring long-term AFO. If there is no recovery by 12 months, I would consider tendon transfers (tibialis posterior transfer to dorsum of foot) or ankle fusion for salvage. Regarding the multiligament reconstruction plan: This complication may alter my surgical staging. I would likely delay the ACL/PCL reconstruction for longer (3-6 months rather than 8-12 weeks) to allow nerve healing and determine CPN recovery trajectory before subjecting the patient to further knee surgery. Prevention is key: This injury could have been prevented by (1) better CPN mobilization before fibular drilling, (2) using a drill guide or fluoroscopic guidance for tunnel placement, (3) drilling with incremental depth checks, (4) protecting the nerve with retractors during drilling. The fact that the nerve was looped with Penrose suggests I identified it, but clearly protection was inadequate during the critical step of fibular tunnel drilling.

MCQ Practice Points

Exam Pearl

Q: What are the surgical indications for the posterolateral approach to the knee?

A: Primary indications: Posterolateral corner (PLC) reconstruction; LCL repair/reconstruction; Popliteus tendon repair; Posterolateral tibial plateau fractures (Schatzker VI, Moore I); Fibular head fractures; Arcuate ligament complex repair; Revision multiligament surgery. Essential for addressing posterolateral rotatory instability and varus-posterolateral instability patterns.

Exam Pearl

Q: What is the key structure at risk in the posterolateral approach and how is it protected?

A: The common peroneal nerve (CPN) is the most critical structure. It courses around the fibular neck, approximately 2cm distal to fibular head. Protection: (1) Identify and protect nerve early in dissection; (2) Avoid excessive traction; (3) Release peroneus longus fascia to mobilize nerve if needed; (4) Maintain knee in flexion during dissection. CPN injury causes foot drop (ankle dorsiflexion, toe extension weakness) and lateral leg numbness.

Exam Pearl

Q: What are the components of the posterolateral corner (PLC)?

A: Three main static stabilizers: (1) LCL (fibular collateral ligament) - primary restraint to varus; (2) Popliteus tendon - resists external rotation and posterolateral translation; (3) Popliteofibular ligament - connects popliteus to fibular head. Additional structures: Arcuate ligament, lateral capsule, fabellofibular ligament, posterolateral capsule. The PLC resists varus stress, external rotation, and posterior translation of the lateral tibia.

Exam Pearl

Q: What is the interval used in the posterolateral knee approach?

A: Two main intervals: (1) Anterior interval: Between iliotibial band (ITB) and biceps femoris - exposes LCL, lateral femoral condyle. (2) Posterior interval: Between biceps femoris and lateral gastrocnemius - exposes popliteus, posterolateral capsule, fibular head. The CPN lies along posterior border of biceps, requiring identification before posterior dissection. The lateral geniculate vessels mark the joint line.

Exam Pearl

Q: How do you test for posterolateral corner insufficiency clinically?

A: Dial test: Prone, compare tibial external rotation at 30° and 90° knee flexion. Increased ER at 30° only = isolated PLC; at both 30° and 90° = combined PLC + PCL. Posterolateral drawer: Increased posterolateral translation. Reverse pivot shift: Knee reduced in extension, subluxes posterolaterally in flexion. Varus stress at 30°: Increased opening indicates LCL insufficiency. External rotation recurvatum test: Tibia rotates externally and knee hyperextends with gravity.

Australian Context

Australian Epidemiology

Incidence:

  • PLC injuries occur in 2-16% of acute knee injuries
  • Higher incidence in multiligament injuries
  • Contact sports (AFL, rugby) significant mechanism
  • Motor vehicle accidents common in severe cases

At-Risk Activities:

ActivityMechanism
AFL/RugbyDirect tackle, varus stress
Motor vehicleDashboard injury
SkiingHyperextension, rotation
WorkplaceCrush, falls

POSTEROLATERAL KNEE APPROACH

High-Yield Exam Summary