Summary A traumatic rupture of the patellar tendon caused by a tension overload during activity in a patient at risk. Diagnosis can be confirmed by physical exam and radiographs for complete tears. Partial tears may need an MRI to confirm the diagnosis. Treatment for complete tears is timely surgical repair to optimize the chance of healing. Partial tears with an intact extensor mechanism may be treated with immobilization. Epidemiology Incidence rare affects < 1 per 100,000 people annually Demographic most commonly in 3rd and 4th decade male > female Anatomic location quadriceps tendon rupture is more common than patella tendon rupture (2:1 ratio) Risk factors may see weakening of collagen structure systemic diseases associated with bilateral ruptures diabetes mellitus systemic lupus erythematous rheumatoid arthritis chronic renal disease local patellar degeneration (most common) previous injury patellar tendinopathy other corticosteroid injection Etiology Pathophysiology mechanism of injury tensile overload of the extensor mechanism sudden quadriceps contraction with knee in a flexed position (e.g., jumping sports, missing step on stairs) most ruptures occur with knee in flexed position greatest forces on tendon when knee flexion > 60 degrees ratio of patellar tendon force to quads tendon force >1 at <45° and <1 at >45° at smaller flexion angle, patellofemoral contact point is at distal pole of patella, giving quads tendon a mechanical advantage pathoanatomy 3 patterns of injury avulsion with or without bone from the proximal insertion/inferior pole of patella (most common) strain at tendon-bone interface is 3-4x strain at midsubstance midsubstance distal avulsion from the tibial tubercle pathobiology rupture is usually the result of end stage or long-standing chronic tendon degeneration Associated conditions orthopedic conditions tibial tubercle avulsion patella fractures TKA extensor mechanism rupture Anatomy Extensor mechanism of the knee quadriceps tendon patella patellar tendon tibial tubercle Blood supply infrapatellar fat pad retinacular structures (medial and lateral inferior geniculate arteries) Biomechanics Forces in patellar tendon ascending stairs is 3x body weight to rupture a normal tendon is 17x body weight Classification Anatomic incomplete tear intact extensor mechanism in some cases can be treated noperatively complete tear patella alta with palpable defect treated with surgical repair Presentation History history of jumping event with sudden quadriceps contraction with knee in a flexed position (e.g., jumping sports, missing step on stairs) patient will often hear/feel a popping sensation Symptoms infrapatellar pain immediate swelling difficulty weight-bearing Physical exam inspection elevation of patella height usually associated with a large hemarthrosis and ecchymosis localized tenderness palpable gap below the inferior pole of the patella motion reduced ROM of knee (and difficulty bearing weight) due to pain if only tendon is ruptured and retinaculum is intact, active extension will be possible but will have extensor lag of a few degrees provocative tests straight leg raise unable to perform active straight leg raise or maintain passively extended knee Imaging Radiographs recommended views AP and lateral of the knee knee in flexion (ideally 30 degrees) optional views merchant or skyline findings patella alta seen in complete rupture various measurements indicating patella alta Insall-Salvati ratio is > 1.2 normal between 0.8 and 1.2 Blackburne-Peel ratio > 1.0 normal between 0.5 and 1.0 Caton Deschamps ratio > 1.3 normal between 0.6 and 1.3 MRI indications differentiate partial from complete tendon rupture most sensitive imaging modality findings site of disruption, tendon degeneration, patellar position, and associated soft tissue injuries Ultrasound indications suspected acute and chronic injuries findings effective at detecting and localizing disruption operator and user-dependent Diagnosis Complete tears can be confirmed by physical exam and radiographs for complete tears. Partial tears partial tears may need an MRI to confirm the diagnosis. Treatment Nonoperative immobilization in full extension indications partial tears with intact extensor mechanism modalities immobilization hinged knee brace locked in extension for 6 weeks with weight bearing rehabilitation progressive active flexion / passive extension protocol Operative primary repair indications complete patellar tendon ruptures ability to approximate tendon at site of disruption techniques end-to-end repair transosseous tendon repair suture anchor tendon repair rehabilitation locked extension brace with immediate weight bearing for 6 weeks early motion protocol at 7-10 days with focus on passive extension and active flexion outcomes biomechanical studies have shown less gap formation with suture anchor repair compared to transosseous repair clinical studies have shown a significant decrease in re-rupture rate with use of suture anchor compared to transosseous repair. tendon reconstruction indications severely disrupted or degenerative patella tendon chronic tears > 6-8 weeks out from injury techniques ipsilateral semitendinosus or gracilis autograft central quadriceps tendon-patellar bone autograft contralateral bone-patellar tendon-bone autograft or allograft Techniques Nonoperative Treatment - Immobilization protocol similar to post-operative protocol below Direct primary repair approach longitudinal midline incision expose rupture and adjacent retinacula debride the ends of the rupture for subacute tears (> 2 weeks out from injury) quadplasty or scar tissue release to facilitate tendon approximation technique end-to-end technique approximate tendon at site of rupture nonabsorbable sutures are woven with locking stitch transosseous tendon repair suture the patellar tendon to the patella with a #5 non-absorbable transosseous suture drill 2 trans-patellar bony tunnels and pass the sutures through tunnels and tie over the top of patella can be protected with a cerclage wire or nonabsorbable tape between patella and tibial tuberosity suture anchor tendon repair number of anchors debatable most authors advocate for at least 2 anchors higher ultimate load to failure and less gap formation compared to transosseous suture fixation postoperative rehabilitation weight bearing may weight bear early with protected knee brace locked in extension goal of brace free ambulation by 6 weeks early motion begins at 7-10 days controlled initiation of knee ROM at 7-10 days exercises to optimize range of motion and minimizes stress on the repair include passive extension and active closed chain flexion (heel slides) prone open chain knee flexion goal of brace free ambulation, full knee extension, and 120 degrees of knee flexion by 6 weeks, and return to sport full return to sport at 6 months Tendon reconstruction approach retracted patella may require extensive surgical release quadplasty release of scar tissue technique graft sources autograft ipsilateral gracilis, semitendinous, and quadriceps autografts have all been used allograft tendon or ligament technique free ends of the tendons are passed through transosseous hole of the patella, and then through a transosseous hole within the tibial tubercle to make a complete circle graft Complications Knee stiffness incidence most common complication risk factors delay in surgical treatment delay in initiating post-operative range of motion treatment manipulation under anesthesia (MUA) if flexion is <120° at 6-12 weeks post-op lysis of adhesions if flexion is < 120° after >12 weeks post-op Re-tear incidence ~8% with transosseous direct primary repair 1-2% following suture anchor repair treatment primary repair if acute and adequate tendon quality remains reconstruction chronic lesions poor tendon quality Infection incidence ~2% following surgery Quadriceps atrophy incidence 2nd most common complication does not compromise return of strength treatment physical therapy Prognosis Outcome with treatment excellent outcomes seen with early repair Prognostic variables most important prognostic factor for complete tears is timing of repair