Anatomy • Largest sesamoid bone • Thick articular cartilage proximally • Articular surface divided into medial and lateral facets by longitudinal ridge • Distal pole nonarticular
• Blood Supply – Primarily derived from geniculate arteries
Biomechanics • The patella undergoes approximately 7 cm of translation from full flexion to extension • Only 13-38% of the patellar surface is in contact with the femur throughout its range of motion
Biomechanics • The patella increases the moment arm about the knee – Contributes up to 30% increase in force with extension
• Patella withstands compressive forces greater than 7X body weight with squatting
Biomechanics • Twice as much torque is needed to extend the knee the final 15 degrees than to extend from a fully flexed position to 15 degrees of flexion
History • Direct blow to the anterior knee (dashboard injury) • Fall from height • Rapid knee flexion with quadriceps resistance
Physical Examination • Pain, swelling, contusions, lacerations and/or abrasions at the site of injury • Palpable defect • Assessment of ability to extend the knee against gravity or maintain the knee in full extension against gravity
Radiographic Evaluation • AP & Lateral – Patella alta or baja – Note fracture pattern • Articular step-off, diastasis
• Special views – Axial or sunrise
• CT Scan -Occult fractures
Radiographic Evaluation • Bipartite Patella – Obtain bilateral views – Often involves superolateral corner – Accessory ossification center
Etiology • Allows prediction of outcome • Direct trauma – Dashboard injury – Increasing cases with penetrating trauma – Often with comminution and articular damage
• Indirect trauma – Violent flexion directed through the extensor mechanism against a contracted quadriceps – Results in simple, transverse fractures
Nonoperative Treatment • Indicated for nondisplaced fractures – 40 years old • Usually 0-2 cm above the superior pole • Level often associated with age – Rupture occurs at the bone-tendon junction in majority of patients > 40 years old – Rupture occurs at midsubstance in majority of patients < 40 years old
Quadriceps Tendon Ruptures • Risk Factors – – – –
Chronic tendonitis Anabolic steroid use Local steroid injection Inflammatory arthropathy – Chronic renal failure – Systemic disease
History • Sensation of a sudden pop while stressing the extensor mechanism • Pain at the site of injury • Inability/difficulty weightbearing
Physical Exam • Effusion • Tenderness at the upper pole • Palpable defect above superior pole • Loss of extension • With partial tears, extension will be intact
Quadriceps Tendon Rupture Radiographic Evaluation • X-ray- AP, Lateral, and Tangential (Sunrise, Merchant) – Distal displacement of the patella
• MRI – Useful when diagnosis is unclear
Treatment • Nonoperative – Partial tears and strains
• Operative – For complete ruptures
Operative Treatment • Reapproximation of tendon to bone using nonabsorbable sutures with tears at the muscultendonous junction – Locking stitch (Bunnel, Krakow) with No. 5 ethibond passed through vertical bone tunnels – Repair tendon close to articular surface to avoid patellar tilting
Operative Treatment • Midsubstance tears may undergo end-to-end repair after edges are freshened and slightly overlapped – May benefit from reinforcement from distally based partial thickness quadriceps tendon turned down across the repair site (Scuderi Technique)
Treatment • Chronic tears may require a V-Y advancement of a retracted quadriceps tendon (Codivilla VY-plasty Technique)
Postoperative Management • Knee immobilizer or cylinder cast for 5-6 weeks • Immediate vs. delayed (3 weeks) weightbearing as tolerated • At 2-3 weeks, hinged knee brace starting with 45 degrees active range of motion with 10-15 degrees of progression each week
Complications • Rerupture • Persistent quadriceps atrophy/weakness • Loss of motion • Infection
Patellar Tendon Rupture • Less common than quadriceps tendon rupture • Associated with degenerative changes of the tendon • Rupture often occurs at inferior pole insertion site
Anatomy • Patellar tendon – Averages 4 mm thick but widens to 5-6 mm at the tibial tubercle insertion – Merges with the medial and lateral retinaculum – 90% type I collagen
Blood Supply • Fat pad vessels supply posterior aspect of tendon via inferior medial and lateral geniculate arteries • Retinacular vessels supply anterior portion of tendon via the inferior medial geniculate and recurrent tibial arteries • Proximal and distal insertion areas are relatively avascular and subsequently are a common site of rupture
Biomechanics • Greatest forces are at 60 degrees of flexion • 3-4 times greater strain are at the insertions compared to the midsubstance prior to failure • Forces through the patellar tendon are 3.2 times body weight while climbing stairs
History • Often a report of forceful quadriceps contraction against a flexed knee • May experience and audible “pop” • Inability to weightbear or extend the knee
Physical Examination • Palpable defect • Hemarthrosis • Painful passive knee flexion • Partial or complete loss of active extension • High riding patella on radiographs
Radiographic Evaluation • AP and Lateral X-ray – Patella alta seen on lateral view • Patella superior to Blumensaat’s line
• Ultrasonagraphy – Effective means to determine continuity of tendon – Operator and reader dependant
• MRI – Effective means to assess patellar tendon, especially if other intraarticular or soft tissue injuries are suspected – Relatively high cost
Classification • No widely accepted means of classification • Can be categorized by: – Location of tear • Proximal insertion most common
– Timing between injury and surgery • Most important factor for prognosis • Acute- within two weeks • Chronic- greater than two weeks
Treatment • Surgical treatment is required for restoration of the extensor mechanism • Repairs categorized as early or delayed
Early Repair • Better overall outcome • Primary repair of the tendon • Surgical approach is through a midline incision – Incise just lateral to tibial tubercle as skin thicker with better blood supply to decrease wound complications
• Patellar tendon rupture and retinacular tears are exposed
Early Repair • Frayed edges and hematoma are debrided • With a Bunnell or Krakow stitch, two ethibond sutures or their equivalent are used to repair the tendon to the patella • Sutures passed through three parallel, longitudinal bone tunnels and tied proximally
Early Repair • Repair retinacular tears • May reinforce with wire, cable or umbilical tape • Assess repair intraoperatively with knee flexion
Postoperative Management • Maintain hinged knee brace which is gradually increased as motion increases (tailor to the patient) • Immediate vs. delayed (3 weeks) weightbearing as tolerated • At 2-3 weeks, hinged knee brace starting with 45 degrees active range of motion with 10-15 degrees of progression each week • Immediate isometric quadriceps exercises • All restrictions are lifted after full range of motion and 90% of the contralateral quadriceps strength are obtained; usually at 4-6 months
Delayed Repair • > 6 weeks from initial injury • Often results in poorer outcome • Quadriceps contraction and patellar migration are encountered • Adhesions between the patella and femur may be present • Options include hamstring and fascia lata autograft augmentation of primary repair or Achilles tendon allograft
Postoperative Management • More conservative when compared to early repair • Bivalved cylinder cast for 6 weeks; may start passive range of motion • Active range of motion is started at 6 weeks