Fracture, Patella
Aaron J. Provance
BasicsMechanisms of injury:
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Direct trauma: Often comminuted but minimally displaced; associated with fractures of the tibia, femur, and hip, as well as posterior hip dislocation
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Indirect trauma: Exertional loading of the extensor mechanism beyond the tensile strength of the patella; often with unexpected knee flexion; frequently transverse with significant displacement and disruption of the extensor retinaculum
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Pediatric sleeve fractures: Cartilage of the inferior pole of the patella is pulled off, often with a small avulsed bone fragment. This occurs with a vigorous contraction of the quadriceps muscle group when the knee is in a flexed position (1)[C].
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Patellar subluxation or dislocation: Associated with osteochondral fractures of the medial facet of the patella; avulsion fractures of the medial aspect of the patella can occur at the attachment of the medial retinaculum.
Epidemiology
Incidence
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1% of all fractures
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Usually 20–50 yrs of age
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Patellar sleeve fractures occur between 8 and 12 yrs of age.
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Osteochondral fractures are common in the adolescent years.
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Incidence of osteochondral fractures (patellar and femoral) in patients with first-time traumatic dislocations was found to be 24% in a recent systematic review (2)[A].
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Predominant gender: Male > Female (2:1)
Diagnosis-
Transverse (50–80%): Usually displaced, of the middle and lower thirds; in the adult population, most patellar fractures sustained during sports participation are of the transverse type (3)[C]. They often result from a strong quadriceps contraction, such as in a partial fall or in jumping sports; also with associated direct trauma.
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Stellate (30%): Usually comminuted and nondisplaced; often secondary to high-impact direct trauma in sport or motor vehicle accidents
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Longitudinal (12–25%): Due either to trauma (especially of the lateral facet) or to subluxation/dislocation of the patella; often in adolescents, with resulting osteochondral fragments
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Sleeve fractures: Significant articular cartilage and a small bony fragment avulsed from the distal pole; often difficult to see on plain films; may have an ipsilateral patella alta
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Stress fractures: Usually elderly, osteopenic patients with anterior knee pain after minor trauma
History
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Activity (partial fall, exertional strain, etc.)
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Trauma (object, direction, force)
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Subluxation or dislocation
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Popping or snapping
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Locking or joint instability
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Loss of range of motion
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Difficulty weight-bearing
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Speed and extent of swelling
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Characterization of pain
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Constitutional symptoms, especially with delayed presentation or evidence of infection
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Previous knee injuries
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Past medical and surgical history
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Medications and allergies
Physical Exam
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Signs and symptoms include:
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Tenderness to palpation and pain with passive motion of the patella
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Hemarthrosis or diffuse soft tissue swelling of the knee
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Limited range of active leg extension owing to disruption of soft tissues
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Physical examination includes the following:
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Pain and tenderness with palpation
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Pain with passive motion
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Palpable step-off defect
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Effusion or soft tissue swelling
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Distal neurovascular status
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Full range of active knee extension implies preservation of extensor mechanism.
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Rule out associated injuries, especially hip, femur, leg, and ankle.
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Soft tissue injuries, contamination, or signs of infection
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Stress testing of ligaments should be delayed until after radiographic evaluation if there are concerns of growth plate injury in children.
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Open fractures should be ruled out owing to the risk of osteomyelitis and septic arthritis; saline may be injected intraarticularly after aspiration of hemarthrosis to test for suspected communication with soft tissue injuries.
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Patellar apprehension test is used to help identify acute patellar dislocation.
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Diagnostic Tests & Interpretation
Imaging
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Anteroposterior (AP) and lateral radiographs: Used to evaluate patella, distal femur, proximal tibia, and soft tissues. The AP view can help to determine fracture lines, and the lateral view can help to determine the number of fragments and commination (3)[C].
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Axial (sunrise, merchant) views: Help to identify osteochondral medial patellar avulsion and other longitudinal fractures. Comparison views of the contralateral side should be used to help determine fractures. Sunrise view (90 degrees of flexion) can be very difficult to obtain with lack of range of motion (ROM) and pain. Merchant view (30–60 degrees of flexion) may be easier to obtain acutely.
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CT scan: Used to detect suspected occult fractures
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Bone scan: Used to evaluate stress reactions, stress fractures, and osteomyelitis
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MRI: Used to evaluate suspected soft tissue injuries and patellar sleeve and osteochondral fractures. MRI is a critical tool for evaluating the severity of an osteochondral defect and assessing the true extent of injury to the extensor mechanism with patellar sleeve fractures (1)[C].
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All patients with first-time traumatic dislocations should be suspected of having an osteochondral injury until proven otherwise by MRI, CT scan, or continued clinical examination (2)[A].
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Osteochondral fractures have been reported to be missed on 30–40% of initial radiographs based on MRI studies and surgical findings (2)[A].
Differential Diagnosis
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Bipartite patella: Usually bilateral and not associated with point tenderness, with rounded edges at the proximal lateral corners of the patellae
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Acute patellar dislocation: Moderate to large hemathrosis and positive apprehension sign; may or may not have underlying osteochondral defect
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Proximal tibia or distal femur fractures: Should be ruled out radiographically with plain films
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Occult physeal injuries: May require MRI if not apparent on plain films
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Anterior cruciate ligament tears: May present with moderate to large hemarthrosis; similar mechanism of injury as patellar dislocation, but with usually less extraarticular swelling
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Meniscal tears: May present with hemathrosis and lack of ROM; tenderness usually along medial or lateral joint line
Treatment-
Acute management:
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Analgesia
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Aspiration of hemarthrosis may be followed by injection of local anesthesia to facilitate assessment of the extensor mechanism. Presence of fatty globules is indicative of an osteochondral defect or occult patellar fracture (2)[A].
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Consider aspiration of tense anterior hematomas.
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Ice and elevation to control swelling (avoiding prolonged, direct application)
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Anti-inflammatory and/or low-potency narcotic medications for pain control
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Immobilization: Splinting and support in position of comfort (usually slight flexion) to minimize quadriceps contraction and fracture distraction
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Nonoperative treatment:
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Displacement of <3 mm in any plane and <2 mm of the articular surface, as well as full range of active knee extension
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The athlete's ability to straight-leg raise against gravity is crucial when selecting treatment options (3)[C].
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Compressive dressings and aspiration of hemarthrosis (if present) before cast application may help to control edema and discomfort.
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Immobilization in full extension in a long-leg cast with weight-bearing as tolerated for 3–6 wks
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Weekly radiographs should be obtained to evaluate for possible fracture displacement and appropriate healing (3)[C].
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Progressive ROM and strengthening are used until the patient can perform a straight-leg raise against gravity without extension lag (3)[C].
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P.235
Additional Treatment
Additional Therapies
Special considerations: Open fractures: IV antibiotics and emergent referral for extensive irrigation and debridement, usually followed by internal fixation
Surgery/Other Procedures
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Displacement of >2 mm of articular step-off or >3 mm in any plane of fracture separation
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Disruption of extensor mechanism is indicated by lack of full extension against gravity.
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Open reduction with internal fixation (ORIF): Modified tension-band wiring with either circumferential wire loops or infragmentary wires or screws (depending on fragment configuration) in conjunction with repair of medial and lateral retinaculum; small fragments might not be amenable to surgical fixation and need to be resected (3)[C].
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Partial patellectomy: Indicated with severe patellar comminution or inability to restore a smooth articular surface; involves repair of retinaculum and reinsertion of patellar or quadriceps tendon into remaining patellar fragment near its articular surface
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Total patellectomy: Reserved for severe comminution precluding retention of any significant (>25%) patellar fragments; involves soft tissue repair with shortening of the quadriceps tendon; loss of knee extension strength (up to 40%) is frequently reported.
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Inferior pole avulsion fractures: The normal height of the patella can be maintained by preserving the patellar pole. In a recent study, internal fixation with use of a basket plate provided better clinical results than pole resection and patellar tendon repair (4)[B].
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Osteochondral fractures: Difficult to detect on plain films; usually heal if nondisplaced but require arthroscopic removal or screw fixation if displaced; associated patellar instability may be surgically corrected at the same time.
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Surgery may be delayed with extensive or contaminated soft tissue injury.
Ongoing Care-
Immobilization: Long-leg cast for nonoperative treatment and for 3–6 wks after partial or total patellectomy; immediate joint motion if intraoperative fracture stability is achieved (3)[C]
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Weight bearing as tolerated in a cast or locked brace: Reduces quadriceps contraction and fragment distraction
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Isometric exercises and straight-leg raises: Started within days of cast application or surgical fixation.
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ROM exercises such as continuous passive motion may be started immediately after stable internal fixation with a delay of 3–6 wks for immobilization in nonoperative treatment and after unstable fracture repair. Exercises should be delayed no more than 6 wks to reduce pain and improve ROM. Active flexion and passive extension are performed until the fracture is healed and then progress with resistance exercises (3)[C].
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Resistance exercises: Several months of resistance exercises may be required to achieve full strength and ROM.
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Return to play when bony healing is demonstrated on AP, lateral, and merchant radiograph views, complete extension is obtained, complete and painless range of motion are achieved, 90% of quadriceps strength is achieved, and balance and proprioception are restored (3)[C].
Follow-Up Recommendations
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Check ROM and strength as compared with the contralateral side.
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Repeat plain films (AP, lateral, and merchant) to document signs of healing with callus formation and periosteal reaction.
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Functional testing prior to return to sport.
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Orthopaedic referral whenever criteria for nonoperative treatment are not met
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Emergent referral with evidence of an open fracture
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Anti-inflammatory and/or low-potency narcotic medications for pain control
Complications
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Patellofemoral arthritis is the most common complication. Risk factors include incongruence of the articular surface and damage to articular cartilage. Treatment includes anti-inflammatory medications and physical therapy, with patellectomy and tibial tubercle elevation reserved for severe cases.
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A slight decrease in flexion is common but not usually clinically significant. Early postoperative motion and physical therapy help to maintain ROM, with manipulation under anesthesia and arthroscopic lysis of adhesions required if unsuccessful.
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Painful hardware: Common complication; managed by removal after fracture union (minimum 6 mos) or tendon healing (minimum 3 mos)
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Infection: Local care for superficial infections; osteomyelitis or septic osteoarthritis may require IV antibiotics with surgical irrigation and debridement, removal of loose hardware, and delayed closure.
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Radiographic evidence of avascular necrosis consists of a sclerotic area evident 1–2 mos after injury, usually of the proximal fragment; mostly asymptomatic, resolving spontaneously.
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Loss of fixation: Often owing to unrecognized comminution; requires surgery if fragments are significantly displaced
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Nonunion: Very uncommon; repeat surgery indicated if symptomatic.
References
1. Dupuis CS, Westra SJ, Makris J, et al. Injuries and conditions of the extensor mechanism of the pediatric knee. Radiographics. 2009;29:877–886.
2. Stefancin JJ, Parker RD. First-time traumatic patellar dislocation: a systematic review. Clin Orthop Relat Res. 2007;455:93–101.
3. Bharam S, Vrahas MS, Fu FH. Knee fractures in the athlete. Orthop Clin North Am. 2002;33:565–574.
4. Veselko M, Kastelec M. Inferior patellar pole avulsion fractures: osteosynthesis compared with pole resection. Surgical technique. J Bone Joint Surg Am. 2005;87 (Suppl 1):113–121.
Additional Reading
Cohn SL, Sotta RP, Bergfeld JA. Fractures about the knee in sports. Clin Sports Med. 1990;9:121–139.
CodesICD9
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822.0 Closed fracture of patella
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822.1 Open fracture of patella
Clinical Pearls
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Most athletes with patellar fractures return to play the following season (3–6 mos) with little residual deficit. Return of function is more limited with comminuted, high-impact mechanisms of injury. Strength of terminal knee extension will be reduced by ∼15–30% if patellectomy is required.
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If criteria for nonoperative treatment are met, studies have shown a failure rate of <5% for fractures managed nonoperatively.
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Many patients have some residual complaints, but most report good to excellent results overall after ORIF. Slightly fewer achieve this level of satisfaction after partial patellectomy, and fewer still after total patellectomy.