The knee is a complex structure comprised of several separate but complementary joints. Normal movement in this region requires coordinated efforts of both the hinging tibiofemoral and gliding patellofemoral joints. Proper joint alignment and adequate spacing, optimal tension in key soft tissues, and coordinated contraction of dynamic stabilizers all contribute to optimal knee function.
Patellofemoral Joint Anatomy
The patella is a triangular-shaped bone situated on the front of the knee. The posterior surface articulates with the femoral groove, a deep furrow located on the anterior surface of the distal femur. Both the posterior surface of the patella and the anterior surface of the femoral groove are covered in articular cartilage, a specialized type of connective tissue that provides a smooth, lubricated surface that reduces friction and distributes forces.
The patella is a sesamoid bone, meaning it develops and remains embedded within a tendon where it passes over a joint. The patella is embedded in the large, thick patellar tendon, a unified junction of the quadriceps muscles that crosses the tibiofemoral joint then inserts at the tibial tuberosity. In addition to the vertically oriented patellar tendon, several ligaments surround the patella and help maintain optimal lateral positioning within the femoral groove. This network of ligaments is referred to as the patellar retinaculum.
Patellofemoral Joint Mechanics
The primary movements of the knee—flexion, extension, and slight rotation—are the result of movement at the tibiofemoral joint. The large condyles of the femur roll along the surface of the tibial plateaus to achieve this hinging motion. As the knee flexes, the patella glides inferiorly within the femoral groove. Conversely, as the knee extends, the patella glides superiorly.
Dynamic positioning of the patella throughout the broad range of movement of the tibiofemoral joint helps stabilize the patellar tendon, distributes force loading on the femoral condyles, and significantly increases the mechanical advantage and force production by adjusting the angle of pull and resultant leverage of the quadriceps muscles. Force production for knee extension is increased by about 50 percent due to the mechanics of the patellofemoral joint.
Also known as patellar tracking, ideal positioning of the patella relative to the femoral groove throughout the full range is essential to smooth motion, minimal friction, and maximum force production. Adequate slack in the patellar tendon, proper tension balance in the patellar retinaculum, and coordinated contraction of the quadriceps, pes anserine, and biceps femoris muscles all contribute to proper patellar tracking.
Pathology and Purpose of Soft-Tissue Intervention
Improper patellar tracking is a common cause of knee pain and dysfunction. Postural deviations such as genu varum (bow-legged) or genu valgum (knock-kneed) may result in altered angles of pull on the patellar tendon and impact patellar tracking.
Soft-tissue imbalances may also affect patellar tracking. Excessive tension from the iliotibial band, vastus lateralis, or biceps femoris may shift or tilt the patella laterally. Excessive tension in the pes anserine or vastus medialis may shift or tilt the patella medially. Additionally, excessive tension and shortening of the quadriceps group limits the inferior glide of the patella and places excessive friction on the articular cartilage when loaded. The patellar retinaculum also requires optimal balance between mobility and stability in order to function properly.
Improper patellar tracking often leads to pain with loading activities, such as walking, running, squatting, or climbing stairs. There may be notable crepitus, a grating or grinding sensation that accompanies movement. Crepitus is an indication that the articular cartilage has been compromised, and is an early sign of osteoarthritis.
Soft-tissue manipulation may have limited impact on more prominent postural deviations in the lower extremities but is effective in restoring optimal mobility and balanced tension in the associated retinaculum and muscles surrounding the knee. Additional therapies may be required to address improper muscle activation and coordination with specific activities.
Christy Cael is a licensed massage therapist and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (Lippincott Williams & Wilkins, 2009). Contact her at christy_cael@hotmail.com.