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 Diagnosis Clinical: history of TKA + inability to perform straight leg raise + palpable tendon defect Confirmed with radiographs (patella alta/baja, fracture) and/or MRI or ultrasound PJI must be ruled out in all cases before surgical planning Assess component fixation status on radiographs and CT Classify patellar fractures to guide treatment Treatment Nonoperative knee immobilizer x6 weeks indications partial EM rupture with preserved active extension type I patellar fracture (intact EM, well-fixed component) non-displaced patellar fracture with intact extensor mechanism [QID 219997] extensor lag < 20° with nondisplaced fracture absolute contraindications to surgery: active PJI, medically unfit for surgery sedentary, low-demand, elderly patients unwilling to accept surgical risk technique extension splint or immobilizer brace cylinder cast for non-compliant patients drop-lock brace if no intention of healing weight-bearing as tolerated in brace serial radiographs every 4–6 weeks transition to progressive ROM after 6–8 weeks once healing confirmed outcomes good to excellent for Type I patellar fractures ~69% of periprosthetic patellar fractures treated conservatively Operative primary repair with suture indications acute rupture (< 2 weeks) of quadriceps or patellar tendon with intact patella and patellar component rarely indicated for patellar tendon alone due to high failure rate quadriceps tendon acute repair may equal allograft outcomes if < 2 weeks contraindications chronic rupture (> 6 weeks) – insufficient tissue quality; reconstruction required inadequate patellar bone stock active PJI outcomes patellar tendon repair: 63% complication rate – largely abandoned quadriceps tendon repair: 25% complication rate reconstruction (allograft, autograft, or synthetic) indications complete EM disruption with inability to perform SLR chronic EM rupture (> 6 weeks) failed primary repair type II periprosthetic patellar fracture patellar tendon rupture – preferred over primary repair techniques achilles tendon allograft whole EM allograft synthetic material semitendinosus autograft outcomes residual extensor lag synthetic outcomes similar to allograft arthrodesis 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 Techniques Primary repair indications acute (< 2 weeks) intact patella and component adequate tissue rarely indicated due to consistently poor outcomes approach direct anterior midline incision technique end-to-end repair with heavy non-absorbable sutures (#5 FiberWire or equivalent) suture anchors into proximal pole of patella for tendon-to-bone repair bone tunnels through patella for quadriceps-side repairs augmentation with allograft strongly recommended due to high re-rupture rate repair performed with knee in full extension postoperative cylinder cast or brace in full extension for 6-8 weeks progressive ROM after cast removal outcomes largely abandoned for patellar tendons due to poor poutcomes relative to reconstruction 63% complication rate in patellar tendons 25% complication rate in quadriceps tendon some studies show quadriceps tendon repair can be as successful as allograft reconstruction if injury <2 weeks chronicity Reconstruction with Achilles tendon allograft indications patellar tendon rupture intact patella and patellar component patella mobile within 3–4 cm of joint line Quadriceps tendon rupture chronic rupture with significant proximal retraction allograft fresh-frozen achilles tendon allograft with calcaneal bone block inferior results with freeze-dried allografts technique midline anterior incision to expose entire EM creation of rectangular trough in proximal tibia to receive calcaneal bone block bone block is press-fit into tough and fixed with cerclage wires or cortical screws proximal portion of graft is sutured into native EM tissue tensioning of the graft is performed in full knee extension postoperative cylinder cast in full extension for 6-8 weeks, then progressive ROM outcomes residual extensor lag unacceptable range of motion dependence on assistive devices persistent instability Reconstruction with whole extensor mechanism (EM) allograft indications complete EM rupture with deficient or absent patella failed prior reconstruction requires adequate proximal tibial bone stock (5 cm) and sufficient quadriceps tendon (5 cm) allograft contains quadriceps tendon, patella, patellar tendon, and proximal tibial bone block allograft should be fresh-frozen technique midline incision and dissection to expose entire host EM full-thickness medial and lateral subcutaneous flaps midline incision through remaining host quadriceps and patellar tendons midline bisection of patella with saw to split patella in half; resect patellar remnants tibial bone block fashioned to fit into rectangular trough on host proximal tibia, secured with screws or wires allograft pulled proximally under host quadriceps while pulling maximal tension on native quadriceps distally in full extension allograft sutured proximally into overlying host quadriceps with heavy nonabsorbable sutures allograft patella is not resurfaced elevated medial and lateral flaps of host EM are sutured over top of EM allograft postoperative cylinder cast in full extension for 6-8 weeks, then progressive ROM complications inferior results found with freeze-dried allografts outcomes residual extensor lag unacceptable range of motion dependence on assistive devices persistent instability Reconstruction with synthetic material indications patellar tendon insufficiency with intact patella, patellar component, and quadriceps tendon immunocompromised patients (avoids allograft disease transmission) shown to have similar clinical outcomes to allograft at lower cost synthetic material options synthetic polypropylene mesh (Marlex) woven polyester ligament (LARS) technique medial parapatellar arthrotomy after full-thickness subcutaneous flaps medially and laterally distal end of synthetic mesh placed into trough in proximal tibia and secured with screw and or cement fixation proximal end of mesh is tunneled along lateral aspect of host patellar tendon from superficial to deep and secured to quadriceps tendon proximally mesh covered with medial and lateral flaps of host tissue postoperative cylinder cast in full extension for 6-8 weeks, then progressive ROM complications residual extensor lag unacceptable range of motion dependence on assistive devices persistent instability advantages vs. allograft: similar outcomes [218132, 219933] lower cost [220158, 217844] decreased risk of disease transmission [220458] higher availability Reconstruction with medial gastrocnemius rotational flap indications EM rupture with inadequate anterior soft-tissue coverage technique medial parapatellar arthrotomy after full-thickness subcutaneous flaps medially and laterally medial half of gastrocnemius mobilized from musculotendinous junction of Achilles tendon through a separate medial incision muscle belly tunnelled subcutaneously around medial border of tibia fascia of gastrocnemius is secured to atnerior tibial periosteium achilles tendon sutured to distal aspect of quadriceps tendon postoperative casting of knee in full extension for 6-8 weeks prior to beginning ROM complications residual extensor lag unacceptable range of motion dependence on assistive devices persistent instability pros/cons provides extra soft tissue coverage of the anterior knee increases vascularity Open reduction internal fixation (ORIF) of patella indications type II with EM disruption and adequate bone type IIIa with symptomatic loose component and bone ≥ 10 mm technique direct anterior approach; anatomic reduction cannulated screw fixation or tension band wiring revision of patellar component at time of ORIF for Type IIIa type IIIb (< 10 mm bone): patellectomy or component removal without revision (patelloplasty) complications AVN nonunion hardware failure (wire migration to popliteal fossa reported) infection Knee arthrodesis indication salvage for failed reconstruction active PJI precluding reimplantation massive bone loss technique options long intramedullary nail – preferred; provides rigid fixation external fixator – infected cases or significant bone loss fusion position: 0–15° flexion, 5–7° valgus, neutral rotation Complications Persistent extensor lag > 30° most common complication, 45% of cases risk factors: chronic rupture, delayed treatment, inadequate tensioning at reconstruction treatment: physical therapy; rarely re-operation if severe Re-rupture of EM 25% of cases higher with primary repair alone vs. augmented reconstruction higher with freeze-dried vs. fresh-frozen allograft treatment: revision reconstruction Infection 23% of cases following surgical reconstruction risk factors: immunosuppression, diabetes, prior infection, allograft use, prolonged OR time diagnosis: elevated CRP/ESR, knee aspiration, intraoperative cultures treatment: two-stage revision (explantation + antibiotic spacer → reimplantation after eradication) Residiual limited ROM / stiffness mandated 6–8 week immobilization leads to flexion loss average postoperative ROM typically 75–90° treatment: aggressive PT after brace removal; MUA rarely indicated Persistent instability / dependence on assistive devices common long-term sequela; many patients require a cane or walker Patellar AVN disruption of geniculate anastomotic ring can cause AVN resulting in late stress fracture risk: lateral retinacular release, V-Y turndown Hardware failure (ORIF cases) wire breakage, screw loosening, migration to popliteal fossa (reported complication) high nonunion rate with periprosthetic patellar fractures Prognosis Outcomes after EM reconstruction are universally challenging with high complication rates functional success rates 50–68% at 3–5 years 54% 5-year implant survivorship common sequelae: residual extensor lag, limited ROM, dependence on assistive device, instability Favorable prognostic factors: acute rupture treated early (< 2 weeks) fresh-frozen allograft (vs. freeze-dried) intact patellar component at reconstruction adequate bone stock absence of infection Negative prognostic factors: active PJI or prior infection chronic disruption with scarred, retracted tissues multiple prior knee surgeries significant systemic comorbidities (renal failure, diabetes, RA) freeze-dried allograft use inadequate patellar bone stock Natural history without treatment: progressive extensor lag and functional decline instability, falls risk, inability to ambulate independently nonoperative management in poor surgical candidates: functional but limited outcome with assistive device dependence