summary TKA Extensor Mechanism (EM) Ruptures are traumatic periprosthetic injuries that consist of quadriceps tendon injuries, patella fractures, or patellar tendon injuries. Diagnosis can be made clinically in a patient with a history of a TKA who is unable to perform a straight leg raise. Radiographs may show patella alta (patellar tendon rupture) or patella baja (quadriceps tendon rupture). Treatment is generally surgical repair versus reconstruction, depending on available patella bone stock and chronicity of injury. Nonoperative management is reserved for poor surgical candidates and partial disruptions. Epidemiology Incidence overall EM failure incidence 0.1-2.5% of all TKAs; revision TKA carries higher risk quadriceps rupture 0.1% patellar tendon rupture 0.17% patella fracture 0.05% in unresurfaced cases and 0.2-21% in resurfaced cases patellar tendon ruptures are the most common type Demographics presents in typical TKA demographic (mean age 65-75) patellar tendon ruptures more common in females patellar fractures more prevalent in men Risk factors multiply operated knees 3-4 prior surgeries increases risk for EM rupture including prior TKA, revision TKA, patellar realignment surgery, high tibial osteotomy systemic conditions renal disease, diabetes mellitus, rheumatoid arthritis, peripheral vascular disease, obesity medications testosterone replacement therapy flouroquinolone antibiotics intraoperative technical factors stiff knees with inadequate exposure - patellar eversion risk aggressive resection of the patella residual bone < 12 mm increases fracture risk lateral retinacular release - risk to the superior lateral geniculat artery V-Y quadriceps turndown - disrupts proximal blood supply component malrotation - excessive patellofemoral forces excessive joint line elevation maximum acceptable elevation is 4 mm implant factors single-peg vs tri-peg patella fixation single-peg carries a higher fracture risk femoral component with thicker anterior flange Etiology Pathophysiology iatrogenic / intraoperative injury avulsion of patellar tendon from tibial tubercle during forced flexion of stiff knee excessive lateral retinacular release – disrupts superior lateral geniculate artery V-Y turndown for difficult exposure – disrupts proximal quadriceps blood supply manipulation under anesthesia post-TKA postoperative traumatic injury direct blow to anterior knee (patella fracture) eccentric loading of compromised extensor mechanism quadriceps tendon: most commonly tears 1–2 cm proximal to superior patellar pole (watershed zone) avascular necrosis (AVN) of patella disruption of anastomotic geniculate ring causes AVN and risks stress fracture risk: lateral retinacular release, V-Y turndown Associated conditions medical renal failure, diabetes, rheumatoid arthritis, peripheral vascular disease orthopaedic periprosthetic joint infection (PJI) – must always be ruled out before reconstruction component malrotation or loosening arthrofibrosis Anatomy Extensor mechanism quadriceps tendon patella patellar tendon tibial tubercle Muscles quadriceps muscle group rectus femoris – superficial layer; fibers continue over patella into patellar tendon vastus medialis – deep medial layer; medial patellar stabilizer vastus lateralis – deep lateral layer; lateral patellar stabilizer vastus intermedius – deepest layer Tendons quadriceps tendon distal confluence of the quadriceps muscle complex inserts onto proximal pole of patella superficial fibers from rectus femoris continue over patella to patellar tendon watershed zone 1–2 cm proximal to superior patellar pole most common rupture site patellar tendon originates from inferior pole of patella average 4-6mm thick, 5 cm long insterts into tibial tubercle Blood Supply genicular arteries primary blood supply to patella and patellar tendon superior medial, superior lateral, inferior medial, inferior lateral geniculate arteries form anastomotic ring inferior genicular arteries supply patellar tendon superior lateral genicular artery at risk with injury to lateral retinacular release recurrent anterior tibial artery contributes to supply of patellar tendon clinical relevance: disruption of anastomotic ring --> AVN --> patellar stress fracture watershed area of quadriceps tendon 1-2 cm proximal to superior pole of patella Biomechanics patellofemoral joint forces vary with activity 0.5 x body weight - walking 3.1 x body weight - ascending/descending stairs 7 x body weight - squatting patella increases quadriceps mechanical advantage 30-50% via lever arm effect Classification Ortiguera & Berry Classification – Periprosthetic Patellar Fractures most widely used classification based on three criteria: extensor mechanism integrity, patellar component fixation, bone stock quality **ERROR CREATING TABLE** Presentation History history of prior TKA (primary or revision) acute onset: traumatic fall, direct blow, forced flexion, manipulation under anesthesia insidious onset: chronic/attritional rupture, AVN-related fracture Symptoms inability to perform active knee extension or straight leg raise (most common) anterior knee pain knee instability or buckling audible pop at time of injury (acute rupture) Physical exam inspection knee effusion / hemarthrosis soft-tissue swelling about anterior knee extensor lag – inability to actively extend against gravity patella alta (patellar tendon rupture) or patella baja (quadriceps tendon rupture) palpation palpable defect in the tendon at rupture site tenderness over anterior knee of patellar fracture site range motion passive ROM may be preserved active extension lost weakness with attempted extension against gravity special tests straight leg raise inability indicates complete EM disruption Imaging Radiographs recommended views AP, lateral, and Merchant (axial patellar) views findings patella alta - patellar tendon ruptures (Insall-Salvati ratio > 1.2) patella baja - quadriceps tendon ruptures (Insall-Salvati ratio < 0.8) posterior tibial subluxation bony avulsions prior radiographs can aid in determination of component migration or loosening loosening: osteolysis, radiolucent lines, component migration component position, joint line level measurements Insall-Salvati ratio lateral knee X-ray in 30° of flexion patellar tendon length to maximum length of patella normal: 0.8 to 1.2 CT indications evaluation of femoral and tibial component rotation characterization of patellar fracture fragmentation and bone stock quality component loosening assessment MRI indications imaging modality of choice for confirming and characterizing extent of tendon disruption useful when clinical diagnosis is uncertain (partial vs. complete tear) evaluation of patellar AVN – detects earlier than plain radiographs metal artifact reduction sequences (MARS) to minimize implant artifact Ultrasound indications bedside assessment of quadriceps or patellar tendon continuity dynamic evaluation of tendon gap benefits no metallic artifact; low cost; readily available findings disruption of tendon continuity hematoma tendon retraction gap Studies Labs all patients with EM rupture after TKA must be evaluated for PJI prior to any reconstruction ESR, CRP knee aspiration cell count, differential, Gram stain, cultures alpha-defensin or synovial leukocyte esterase when PJI is suspected BMP, CBC, HbA1c for preoperative optimization Differential Periprosthetic Joint Infection (PJI) key differentiator: elevated ESR/CRP, positive aspiration, systemic signs of infection must always be ruled out before operative reconstruction Isolated component loosening pain without extensor lag radiographic loosening, radiolucent lines active extension typically preserved Patellar clunk syndrome fibrous nodule in suprapatellar pouch painful clunk at 30–60° flexion during extension no extensor lag treated with arthroscopic debridement Patellar maltracking or subluxation lateral tilt or subluxation on Merchant view component malrotation on CT extension intact J-sign on exam Arthrofibrosis restricted passive AND active ROM without extensor lag Treatment Nonoperative knee immobilizer x6 weeks indications partial quadriceps tendon rupture fracture of the patella in which the extensor mechanism remains intact Operative direct repair with suture indications partial patellar tendon avulsion (< 30%) primary repair and augmentation with graft indications complete laceration of patellar tendon with adequate patellar bone stock extensor mechanism reconstruction indications complete laceration of patellar tendon without adequate patellar bone stock and deficient soft tissues chronic extensor mechanism (patella or quadricep tendon) disruption reconstruction with synthetic polypropylene (ie. Marlex mesh) has been shown to have similar clinical outcomes at a lower cost than allograft techniques reconstruction with synthetic polypropylene is recommended in patients with immune-compromise knee arthrodesis indications salvage option for multiple failures of extensor mechanism reconstruction, especially if complicated by infection