Knee Joint Biomechanics Quiz

Runner's Knee (PFPS)

• Objectives: Students will be able to review knee joint anatomy, recognize anterior knee pain syndrome, identify its causes, and plan appropriate rehabilitation.

Knee Joint Anatomy

• Bones: Tibia, Femur, and Patella
• Articulations: Tibiofemoral and Patellofemoral
• Ligaments: MCL, LCL, ACL, and PCL
• Menisci: Medial and Lateral menisci
• Articular Cartilage: Covers joint surfaces

Knee Joint Alignment

• Femoral Mechanical Axis: Center of the femoral head to the center of the knee.
• Femoral Anatomical Axis: Center of the femoral shaft to the center of the knee joint. It deviates 6° outward from the mechanical axis.
• Genu Valgum (Knock-Knee): Excessive valgus alignment of the knee, potentially resulting in a Q-angle larger than normal.
• Genu Varum (Bowleg): Characterized by a bowed appearance of the legs, with the knees aligned in varus.

Screw-Home Mechanism

• Rotation: Knee rotates approximately 5-10 degrees during the last phase of extension.
• Mechanism Differences: Rotation during knee extension is different than general axial rotation at the knee. It is a coupled rotation, linked mechanically to flexion and extension.
• Factors: Shape of femoral condyles, passive tension in the anterior cruciate ligament, and lateral pull from the quadriceps tendon.

Knee Joint Positions

• Closed Packed Position: Full extension and external tibial rotation (tibiofemoral joint). Full knee flexion (patellofemoral joint).
• Resting Position: 25° of flexion (tibiofemoral joint). Full extension (patellofemoral joint).
• Capsular Position: Flexion more limited than extension (both joints).

Patellar Tracking

• Path & Area: Patellar contact on the femur varies during knee flexion and extension. At 135° of flexion, the patella rests on the medial & lateral facets. At 90° of flexion, it rests on the superior pole. Between 90° to 60° flexion, the patella occupies the greatest contact area with the trochlear groove (30% of total surface area). In full extension, it rests above the intercondylar groove, against the supra-patellar fat pads.
• Normal Alignment: Maintained by iliotibial band & lateral retinaculum laterally, vastus medialis medially, patellar tendon inferiorly, and quadriceps tendon superiorly.
• **Natural Bowstringing Force:**The lateral traction forces on the patella are caused by the iliotibial band, lateral patellar retinacular fibers, and overall quadriceps force. Medial directed forces include the vastus medialis and medial patellar retinacular fibers.
• Abnormal Positions: Frog-eye, squinting, rotated inward/outward, patella alta, patella baja.
• Stress: Maximum stress on the patella occurs during 60-75° of flexion

Special Tests

• Patellar Gliding: Assessing patellar translation in the resting position. Measure displacement in quadrants. Less than one quadrant indicates tightness of lateral structures. More than three quadrants indicates hypermobility
• Patellar Apprehension: Evaluating for lateral instability. Positive test = lateral translation produces pain or discomfort.
• Patellar Tilting: Measuring the patellar tilt relative to the axis.
• Patellar Grinding: Investigating for pain or crepitus during patellar glide.

Patellofemoral Pain Syndrome (PFPS)

• Definition: Anterior knee pain, diffuse, dull, and aching. It results from changes in the patellofemoral joint, outside of any other medical pathology.
• Epidemiology: Common in runners, young athletes, basketball players, and bicyclists, especially women.

Causes of PFPS

• Overuse: Repetitive movements, especially with increases in activity levels
• Trauma: Knee injury or impacts
• Abnormal Forces: Abnormal biomechanics may initiate a cascade of issues.
• Muscle Imbalance (Weakness or Tightness): Imbalance between thigh muscles, tight hamstrings, tight quadriceps, weak vastus medialis oblique (VMO)
• Patellar Tracking Disorders: Including patella alta, patella baja, iliotibial band issues and femoral anteversion issues
• Foot Issues: Pronated feet, pes cavus/flat foot issues
• Excess Weight: Increased stress on the knee joint

History of PFPS

• Location: Specific area of knee pain
• Aggravating Activities: Activities that provoke pain
• Associated Symptoms: Giving way, swelling, catching/popping/grinding sensations, stiffness

Physical Examination

• Standing Exam: Assess lower extremity alignment, focusing on femoral position when feet are together.
• Dynamic Exam: Evaluating knee response during walking, stair climbing, and squatting.
• Special Tests: Patellar gliding, apprehension, tilting, and grinding tests to identify tightness of lateral structures.

Treatment

• Rest: Reduce activity levels associated with pain.
• Strengthening: Quadriceps (especially VMO), hip adductors, hamstrings, gastrocnemius, and hip external rotators.
• Stretching: Hamstrings, gastrocnemius, ITB, and quadriceps.
• Taping: Patellar taping
• Proprioception Training: Improved body awareness and balance
• Myofascial Release: Addressing tightness of the Iliotibial band (ITB).
• Foot Orthotics: If foot pronation contributing to knee pain

Prevention

• Stay in Shape: Maintain appropriate fitness level.
• Stretching: Before & after exercise
• Gradual Training Increase: Avoid sudden increases in activity levels.
• Proper Running Gear: Use supportive shoes and other gear (as appropriate).
• Proper Running Form: Correct running mechanics.

Differential Diagnosis

• Fat Pad Syndrome: Irritation of infra-patellar fat pad from overuse or trauma.
• Quadriceps Tendonitis: Overuse or repeated jumping.
• IT Band Friction Syndrome: Irritation of the IT band over the lateral femoral condyle, often associated with tightness of tensor fasciae latae (TFT).
• Prepatellar Bursitis: Repeated kneeling, or minor trauma.
• Chondromalacia Patellae: Cartilage damage due to abnormal stress to the patella.
• Patellofemoral Osteoarthritis: Radiographic changes associated with degereration.
• Osgood-Schlatter Disease: Inflammation of the tibial tubercle, especially in adolescents.