Knee Region – Comprehensive Study Notes

Functional Anatomy of the Knee

• Largest synovial joint; bicondylar hinge joint that must provide both mobility (flexion/extension, axial rotation) and stability for weight-bearing tasks.
• Functional compartments
  • Medial tibio-femoral
  • Lateral tibio-femoral
  • Patello-femoral
  • Superior tibio-fibular joint (routinely examined in foot/ankle disorders).
• Osseous & arthrokinematic considerations
  • Accessory motions: anterior–posterior glide, medial–lateral glide, compression–distraction.
  • Roll–slide mechanics; screw-home mechanism (terminal extension couples tibial ER/femoral IR).
  • Tibio-femoral closed-packed = full extension + ER; open-packed ≈ $25^{\circ}$ flexion.
• Ligaments
  • Intra-articular: ACL, PCL, transverse ligament → low healing capacity.
  • Extra-articular: MCL, LCL → comparatively higher healing potential.
• Menisci
  • Wedge-shaped fibrocartilage anchored to tibial plateau via anterior/posterior horns.
  • Peripheral vascularity good; central third avascular.
  • Medial: C-shaped, firmly attached to capsule & MCL → higher injury rate.
  • Lateral: almost circular, more mobile.
• Dynamic & passive soft tissues
  • Muscles: Quadriceps, hamstrings, gastrocnemius, popliteus.
  • Tendons: Patellar, biceps femoris, semimembranosus, pes anserinus (sartorius, gracilis, semitendinosus).
  • Numerous bursae around patella, pes, ITB, etc.

Clinical Assessment Goals

• Identify structure(s) injured, extent of damage, and immediate disability → guides safe, timely management.
• Process integrates:
  • Comprehensive patient interview
  • Focused physical examination & special tests
  • Interpretation of swelling onset, behaviour of symptoms, special questions, and personal factors.

Patient Interview Framework

Body Chart

• Exact pain location → suggests injured tissues (localised vs diffuse; superficial vs deep).
• Palpable tenderness (e.g.
  • MCL/LCL along joint line).
• Swelling timing clues:
  • Immediate $0!–!2$ h haemarthrosis: ACL rupture, patella dislocation, major osteochondral lesion, fracture.
  • Gradual $6!–!24$ h synovial effusion: meniscus tears, peripheral MCL/meniscus, degenerative OA.

Behaviour of Symptoms

• Constant vs intermittent; activity limitation;
• Aggravating/easing factors key to differential (e.g. overuse tendinopathy worsens with load, improves with rest).
• $24$-h pattern reveals inflammatory vs mechanical picture.
• Severity/irritability rated mainly by pain & swelling response.

Special Questions

• Swelling, locking, clicking, instability/giving-way, grinding.
• Locking/clicking → meniscus flap/bucket-handle, loose body, PF pain, chondromalacia.
• Instability → ligamentous laxity (acute) or muscle weakness/degeneration (chronic).

Personal Factors

• Age, gender, weight, physical conditioning, occupation, sport type, genetics, comorbidities & social context shape pathology prevalence and management.

History Typing

• Acute/traumatic vs gradual/non-traumatic onset.
• Mechanism (direction, speed, position, contact vs non-contact).
• Pain/disability at injury, swelling latency, contributory changes (activity, environment), prior injuries.

Acute / Traumatic Knee Injuries

Common Region-Specific Traumas

• Anterior: patella dislocation, quadriceps or patellar tendon rupture, quad strain.
• Medial: MCL tear, medial meniscus.
• Lateral: LCL, lateral meniscus, posterolateral corner (PLC).
• Posterior: hamstring strain.

Less Common / Red-Flag Traumas

• Tibial plateau or tibial spine fracture; superior Tib/Fib injury; fat-pad impingement; osteochondritis dissecans (adolescents); CRPS-1; quadriceps rupture.

Ligament Injury Grading

• Tensile overload ⇒
  • Grade I: few collagen fibres disrupted.
  • Grade II: considerable proportion torn; some laxity.
  • Grade III: complete rupture.

Anterior Cruciate Ligament (ACL)

• Provides $\approx85\%$ (at $90^{\circ}$ flex) & $87\%$ (at $30^{\circ}$) resistance to anterior tibial translation; also restrains rotation & frontal-plane motion in extension.
• $60!–!80\%$ non-contact (pivot, decel, single-leg land); mechanism: tibial ER, valgus, $10!–!30^{\circ}$ flexion while trunk IR.
• Female risk $2.4!–!9.7$× male.
• Presentation: audible pop, immediate large effusion, extreme pain, giving-way; often associated bone bruise or “terrible triad” (ACL + MCL + medial meniscus).

Collateral Ligaments

• MCL: resists valgus & extension; secondary anterior restraint. Injured by valgus load in partial flexion.
• LCL: resists varus; secondarily controls A-P translation. High-energy varus trauma, rarely isolated.
• Clinical: sharp localised pain, swelling/bruise after $1!–!2$ days; instability during pivot/lateral moves.

Meniscal Tears

• Compression + rotation in flexion (weight-bearing). Medial > lateral.
• Acute (20–30 yrs, significant force), acute-on-chronic (> 40 yrs, degenerative), or purely degenerative.
• S/S: twisting MOI, joint-line pain, gradual <24 h effusion, locking/clicking/giving-way, loss of extension.

Posterior Cruciate Ligament (PCL)

• Resists $\approx94\%$ posterior tibial translation at $90^{\circ}$, $96\%$ at $30^{\circ}$; controls ER $90!–!120^{\circ}$.
• MOI: direct tibial blow (dashboard, tackle), fall onto flexed knee, hyperextension.
• Often concomitant (ACL, PLC, meniscus, chondral). $60\%$ with PLC disruption.
• Vague posterior pain, mild effusion, sag sign, pain descending/kneeling.

Posterolateral Corner (PLC)

• Key stabilisers: LCL, popliteus & popliteofibular lig., arcuate & oblique popliteal lig., fabellofibular lig., posterolateral capsule, biceps femoris tendon, lateral gastroc, ITB.
• MOI: anteromedial blow, hyperextension-varus-rotation.
• Findings: side-to-side instability near extension, varus laxity $30^{\circ}$ & $0^{\circ}$, positive dial test, peroneal nerve symptoms.

Patella Dislocation

• Lateral displacement tearing medial patellofemoral ligament; peaks $10!–!17$ yrs; females > males.
• Predisposing: trochlear dysplasia, patella alta/tilt, weak VMO.
• Spontaneous reduction in extension; large haemarthrosis, medial tenderness, apprehension test positive. Differentiate from ACL rupture.

Gradual / Overuse Knee Conditions

Anatomical Distribution

• Anterior: Patellar tendinopathy, Osgood Schlatter, Sinding-Larsen-Johansson, fat-pad impingement.
• Medial: Degenerative meniscus, medial OA, PF pain.
• Lateral: ITB friction, lateral meniscus, lateral OA.
• Posterior: Baker’s cyst, lateral meniscus posterior horn, biceps femoris tendinopathy.

Additional “Not-to-Miss” Gradual Causes

• Biceps femoris tendinopathy, common peroneal neuropathy, superior Tib/Fib injury, slipped capital femoral epiphysis, Perthes, DVT, tumours, referred lumbar/hip pain, neural mechanosensitivity, synovitis.

Patellofemoral Pain (PFPS)

• Pain around/behind patella; load increases with knee flexion: walking $0.5$ BW, stairs $7!–!8$ BW.
• Requires coordinated VMO & VL activation for tracking.

Contributing Factors

• Extrinsic: sudden load ↑, running technique/speed, surface, footwear.
• Intrinsic Local: lateral displacement/tilt, soft-tissue tightness, quad weakness/VMO timing.
• Intrinsic Remote: ↑ femoral IR, hip add, dynamic valgus, tibial ER, trunk/pelvic control, pronated foot, sagittal deficits.

Clinical Picture

• Diffuse anterior/peripatellar pain, aggravated by sitting, stairs, squats, running; gradual onset.
• Feels patella “moves laterally”, clicks/grinds, occasional giving-way.

Patellar Tendinopathy (“Jumper’s Knee”)

• Non-inflammatory cell-mediated tendon pathology; presents as inferior pole pain during/after energy-storage tasks.
• Typical pain pattern: start-up pain → settles after warm-up → returns post-activity or next morning.

Pathology Continuum (Cook & Purdam)

1. Reactive: acute overload → reversible thickening/stiffness.
2. Tendon disrepair: matrix breakdown & neovessels; partly reversible.
3. Degenerative: large cell death, disorganisation; irreversible, rupture risk.

• Stage-specific demographics: reactive (younger or sedentary ↑ load), disrepair (any age), degenerative (older, long history, elite overuse).

• Clinical comparison with PFPS (Brukner & Kahn)

  • PFPS: vague/peripatellar, aggravated by knee flexion WB, may respond to PF taping.
  • Tendinopathy: point tenderness inferior pole, pain with jumping/early squat, decline squats provoke.

Adolescent Anterior Knee Pain

• Osgood-Schlatter: traction apophysitis at tibial tuberosity during growth spurt (boys $13!–!15$, girls $10!–!12$). Tender tubercle, activity-related pain; self-limiting.
• Sinding-Larsen-Johansson: analogous lesion at inferior patellar pole.

Fat Pad (Hoffa) Impingement

• Highly nociceptive; repeated hyperextension or direct blow.
• Exquisite tenderness just inferior to patella, worsened by active/passive extension with overpressure; “puffy” swelling; quad inhibition.

Iliotibial Band Friction Syndrome

• ITB rubs over lateral femoral epicondyle or inflamed bursa at $15!–!30^{\circ}$ flexion.
• Aching lateral knee in runners/cyclists; tenderness $1!–!2$ cm proximal joint line; possible TFL/GLUTE tightness or dominant VL.

Baker’s (Popliteal) Cyst

• Synovial fluid herniation between medial gastrocnemius & semimembranosus; often secondary to intra-articular pathology.
• Palpable posteromedial mass, pain at end-range flexion, limited ROM, painful squat/kneel.

Knee Osteoarthritis (OA)

• Degenerative changes in tibio-femoral and/or patello-femoral cartilage, subchondral bone & synovium.
• Risk: previous trauma (ligament/meniscus), obesity, sports, genetics.
• Early: diffuse ache, swelling, crepitus, rest stiffness, joint-line tenderness.
• Progressive: ↑ pain, mechanical symptoms (click, lock), morning stiffness >30 min, atrophy, deformity/varus-valgus mal-alignment.

Forces Acting on Patella & PF Joint

• Patellar tendon:quadriceps force ratio varies with flexion; graph indicates force peaks at $1.5$ near $50^{\circ}$.
• Patello-femoral joint contact force increases steeply with flexion—from $\approx500$ N at $30^{\circ}$ to >2000 N at $120^{\circ}$ (Huberti & Hayes).

Linking Interview Findings to Pathology

• Immediate large effusion + audible pop + pivot landing = likely ACL.
• Gradual <24 h effusion + locking + joint-line tenderness = probable meniscus.
• Sharp valgus trauma + medial pain = MCL.
• Vague anterior pain worsening with stairs/squats = PFPS.
• Inferior pole point pain during jumps = patellar tendinopathy.
• Posteromedial mass with OA history = Baker’s cyst.

Ethical & Practical Considerations

• Early accurate diagnosis prevents secondary damage (e.g. unstable ACL → meniscal degeneration).
• Adolescents with traction apophysitis need load modification rather than aggressive strength programs.
• Long-term PF instability after first dislocation informs decision for surgical vs conservative management.
• Obesity & lifestyle factors must be addressed in OA for sustainable outcomes.

Connections to Foundational Principles

• Tissue healing times: intra-articular ligament (poor) vs extra-articular (better) ↔ informs rehab timelines.
• Biomechanical chain: hip/trunk control influences knee valgus and PF load → reinforces proximal strengthening in PFPS protocols.
• Tendon mechanobiology: load management manipulates continuum stage (reactive ↔ disrepair) aligning with therapeutic exercise prescription.

Summary of Key Equations & Numbers

• Screw-home: terminal $\approx5^{\circ}$ ER of tibia in open-chain extension.
• ACL anterior restraint: $85.1\%$ at $90^{\circ}$ flexion; $87.2\%$ at $30^{\circ}$ (Butler et al.).
• PCL posterior restraint: $94.3\%$ at $90^{\circ}$; $96\%$ at $30^{\circ}$.
• PF joint load: walking $0.5$ BW → stairs $7!–!8$ BW.
• ITB friction angle: peak irritation $15!–!30^{\circ}$ flex.
• Growth-spurt traction apophysitis ages: boys $13!–!15$, girls $10!–!12$.

Recommended Reading

• Brukner & Kahn 5th Ed., Vol 1: Ch 35 (Acute Knee Injuries), Ch 36 (Anterior Knee Pain), Ch 37 (Lateral/Medial/Posterior Knee Pain).