The Patellofemoral Joint Tal Laor, MD Department of Radiology Cincinnati Children’s Hospital Medical Center Patellofemoral Joint Disorders • Overuse pain • Transient patellar dislocation • Arthritis Patellofemoral Joint Disorders • Overuse pain • Transient patellar dislocation • Arthritis Transient Patellar Dislocation • Common in children, adolescents • Lateral dislocation • Spontaneous reduction • Predisposing factors • Associated injuries http://ortho-teaching.feinberg.northwestern.edu/ Transient Patellar Dislocation • Highest incidence 10-17 year olds • Half experience anterior knee pain after episode managed conservatively • High rate of recurrent dislocations • Persistent symptoms, degenerative changes Predisposing Factors • Most factors are congenital/developmental • Osseous –Patellar configuration, location –Femoral (trochlea) –Tibial (tubercle) • Soft tissue Patellar Factors www.boundless.com Patella • Sesamoid bone • Medial, lateral facets • Odd facet (80%): far medial O L M Goodfellow J, et al. JBJS 58-B 1976 Patella • Sesamoid bone • Medial, lateral facets • Odd facet (80%): far medial • Shape medial, lateral facets (Wiberg classification) I II L M III Patella Alta • Associated with instability • Insall-Salvati ratio – Patellar tendon/patellar length – Lateral radiograph in 30° flexion – Standing increases quadriceps contraction and adds to “alta” Modified Insall-Salvati ratio (mIS) Insall-Salvati ratio (IS) Caton-Deschamps Index (CDI) PL TL Normal: IS = 0.8-1.2 Normal: mIS = mean 1.25 (>2 is alta) Normal: CDI = 0.8-1.2 Caton J, Deschamps G, et al. Rev Chir Orthop Reparatrice Appar Mot. 1982;68(5):317-25. alta baja 35.6mm 52.6 mm 1.48 0.78 Patella Alta - MRI • Shortest length deepest patellar tendon: anteroinferior to postero- superior patella on mid- sagittal image • > 1.32 M, 1.52 F (adults) • > 1.3 in children 59 ÷ 35.1 = 1.68 Lateral Patellar Subluxation and Tilt • Axial radiographs • Knee at 20°-45° flexion (30°) Sunrise Merchant eorif.com youtube.com eorif.com patellavision.com J Bone Joint Surg Am 1974 (56) 1391 Joan and Alan Merchant, MD (2013) Merchant View Merchant View Congruence Angle (for patellar subluxation) -6° in normal subjects, > 16° is abnormal lat + med - +20° Merchant AC, et al. J Bone Joint Surg Am 1974 (56) 1391 Lateral Patellofemoral Angle (for patellar tilt) • Line along anterior medial and lateral trochlear surfaces • Line along lateral patellar facet • Should open laterally • If lines are parallel or angle opens medially = abnormal patellar tilt opens medially: abnormal patellar tilt Femoral (Trochlear) Factors • Superior trochlea most important for stabilization • Adults: estimated 3 cm above joint • 3 cm might not work for children • Dysplasia estimated in 85% of patients with patellar dislocation Sulcus Angle normal approx 138-142° Merchant AC, et al. J Bone Joint Surg Am 1974 (56) 1391 Sulcus Angle normal approx 138-142° 147° Merchant AC, et al. J Bone Joint Surg Am 1974 (56) 1391 158° Trochlear Facet Asymmetry • Medial /lateral x 100 • < 40% = trochlear dysplasia L M approx 30% 23mm 7mm Lateral Trochlear Inclination • Line along bone of lateral trochlea (most cephalad image with articular cartilage) and line along posterior femoral condyles • Angle < 11° is abnormal 7° Trochlear Depth • AP lengths of femoral condyles • AP length at deepest groove and line along posterior condyles A B • [A + B]/2 - C C • ≤ 3mm = abnormal 2.7 Ventral Trochlear Prominence normal Pfirrmann CWA, et al. Radiology 2000; 216:858-864. Ventral Trochlear Prominence • Measured on midsagittal image • Supratrochlear femoral cortex • Ventral-most cartilage 9.8 mm of trochlear floor • > 8 mm abnormal (75% sensitivity, 83% specificity for trochlear dysplasia) Tibia (Tubercle) Position of Tibial Tubercle Tibial Tubercle-Trochlear Groove distance (TT-TG) • Anterior-most tubercle (or central superior-most tendon) relative to deepest trochlear groove • CT or MRI (2.8-3.8 mm difference) • Osseous vs cartilaginous landmarks TT-TG www.innerbody.com Tibial Tubercle-Trochlear Groove Distance (TT-TG) Tibial Tubercle-Trochlear Groove Distance (TT-TG) normal < 15 mm, 15-20 mm borderline, > 20 mm considered abnormal (lower mean value in skeletally immature children ~ 8mm) Affect of Skeletal Maturation and Gender • Greater trochlear depth in boys* • Different measurements with age, approach adult measurements* • During skeletal growth, age and gender do not affect osseous morphology** *Mundy A, et al Pediatr Radiol 2105. 46:255-262. **Kim HK, et al. Pediatr Radiol 2014. 44: 141-148. Soft Tissue Stabilizers Soft Tissue Stabilizers • Medial retinacular thickenings make retinacular ligaments • Medial patellofemoral VMO ligament (MPFL) strongest MPFL passive stabilizer • From medial distal femur (anterior to adductor tubercle, near MCL) to superior 2/3 Patellomeniscal ligament patella Patellotibial ligament radsource.us MPFL • Trilaminar –Crural fascia: most superficial –Middle: tendinous fibers of VMO –Deepest: MPFL Diram B, et al . AJR 2008; 191:490–498 MPFL • Trilaminar –Crural fascia: most superficial –Middle: tendinous fibers of VMO –Deepest: MPFL Diram B, et al . AJR 2008; 191:490–498 MPFL • Trilaminar –Crural fascia: most superficial –Middle: tendinous fibers of VMO –Deepest: MPFL Diram B, et al . AJR 2008; 191:490–498 MPFL • Trilaminar –Crural fascia: most superficial –Middle: tendinous fibers of VMO –Deepest: MPFL • Joint capsule Diram B, et al . AJR 2008; 191:490–498 MPFL • Often appears bilaminar Diram B, et al . AJR 2008; 191:490–498 Acute Transient Patellar Dislocation • Predisposing factors • Osteochondral injuries during dislocation/relocation –Patella –Lateral femoral condyle • Soft tissue injuries • Heme- or lipohemarthrosis Articular Cartilage • Osteochondral injuries –Usually patellar medial facet –Occasionally anterolateral femoral condyle –Both (6%) • Grading articular cartilage injury –Size in 2 dimensions, depth –T2 maps, dGEMRIC, Na imaging • Check for articular bodies Soft Tissue Injuries • MPFL tear –Patellar, femoral, mid substance tears –Partial, complete, location, association with fracture fragment? • Vastus medialis obliquus muscle tear MPFL Vastus Medialis Obliquus Muscle Tear Predictors of Recurrent Instability after First-Time Dislocation • Radiographic study • Trochlear dysplasia • Skeletal immaturity • Patella alta: CDI > 1.45 • Contralateral dislocation ** Consider early surgical intervention Jaquith BP, et al J Pediatr Orthop 2015. Treatment of Transient Patellar Dislocation • Conservative –Usually for first time dislocators –Patellar-stabilizing orthotic after swelling improves –Early mobilization –Medial stabilizer strengthening PT Treatment of Transient Patellar Dislocation • Surgical –Functional limitations –Repeat episodes –Chondral, osteochondral injuries, intra-articular bodies –Major stabilizer tears Treatment of Transient Patellar Dislocation • Types –Lateral retinacular release (reduce tension) –MPFL repair or reconstruction –Patellar repositioning (tibial tubercle transfer) Patellofemoral Joint Transient Patellar Dislocation • Predisposing factors • Patellar, femoral, tibial factors • Osteochondral injuries • Soft tissue injuries • Treatment Thank you!.