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Patellar Fracture
From WikiSM
Contents
Other Names
- Patella Fracture
- Knee Cap Fracture
- Patella sleeve fracture
- Bipartite Patella
- Tripartite Patella
Background
- This page refers to fractures of the Patella
History
Epidemiology
- Represents ~1% of all fractures (need citation)
- Most commonly occur in ages 20 to 50 years[1]
- Incidence in men is twice that of women[2]
- Majority are closed, up to 7% are open
- Periprosthetic fractures are a known complication of total knee arthroplasty[3]
- incidence of 0.68% in unresurfaced patellae and up to 21% resurfaced patellae
Pathophysiology

Lateral radiograph of the with a mid body patella fracture. Note the two fragments are being pulled proximally and distally by their respective tendons.[4]
- Fracture Patterns
- Simple 2-part caused by direct blow is most common
- The majority of patellar fractures are closed
Etiology
- Majority of cases due to direct trauma to flexed knee[5]
- MVC represent 78.3% of cases
- Work-related 13.7%
- Domestic accidents 11.4%
- Sports related fractures are uncommon
- Indirect injury
- Rapid knee flexion against contracted quad muscle leads to eccentric contraction, failure
- In pediatrics, can see patellar sleeve fracture
Associated Injuries
- Patellar Dislocation
- Associated with Osteochondral Defect of the Patella
- Open fractures or high speed fractures associated additional injuries[6]
- Femoral Neck Fracture
- Acetabular Fracture
- Hip Dislocation
- Knee Dislocation
- Additional Knee Injuries
Pathoanatomy
- Patella
- Responsible for knee extension by functioning as a lever arm
- The Quadriceps Tendon inserts proximally, and the distal pole becomes the Patellar Tendon
Risk Factors
- Unknown
Differential Diagnosis
- Fractures
- Dislocations & Subluxations
- Patellar Dislocation (and subluxation)
- Knee Dislocation
- Proximal Tibiofibular Joint Dislocation
- Muscle and Tendon Injuries
- Ligament Pathology
- Arthropathies
- Bursopathies
- Patellofemoral Pain Syndrome (PFPS)/ Anterior Knee Pain)
- Neuropathies
- Other
- Bakers Cyst (Popliteal Cyst)
- Patellar Contusion
- Pediatric Considerations
- Patellar Apophysitis (Sinding-Larsen-Johnansson Disease)
- Patellar Pole Avulsion Fracture
- Tibial Tubercle Avulsion Fracture
- Tibial Tuberosity Apophysitis (Osgood Schalatters Disease)
- Proximal Tibial Metaphyseal Fracture
- Proximal Tibial Physeal Injury
Clinical Features
- History
- Some traumatic mechanism should be apparent
- Patient will endorse knee pain
- Painful knee extension and possibly inability to extend
- Physical Exam: Physical Exam Knee
- Inspection will likely reveal significant swelling and joint effusion, be sure to note any skin abrasions
- There may be an obvious defect depending on the fracture pattern
- The distal and proximal fragments may be seperated
- There is typically a palpable defect on the bone
- Inability to actively extend knee
- Special Tests
- Consider Saline Load Test if suspected open fracture
Evaluation

This AP view shows a well rounded, corticated bony fragment in the superlateral patella, aka a bipartite patella[7]
Radiographs
- Standard Radiographs Knee
- Typically sufficient to identify injury
- AP, Lateral, Sunrise
- Findings
- Lateral is best view for transverse
- Sunrise is best for vertical fracture
- If patella baja or alta is present, consider quadriceps or patellar tendon rupture
- Bipartite Patella
- Can be mistaken for fracture
- Most individuals have 1 ossification center, however up to 23% have accessory ossification center(s)
- Bipartate patella represents failure of second ossification center to fuse
- Typically seen in superolateral position
- Occurs in about 2% of individuals, and 50% of patients are bilateral
- Tripartite Patella similarly, failure of 2 accessory ossification centers to fuse
CT
- Indicated for surgical decision making in unclear or complex fracture patterns
- May be helpful for stress fracture, nonunion or malunion
MRI
- Indicated if soft tissue injuries are suspected
- In children, can be used instead of CT
Classification
AO/ASIF Classification
- Extra-articular
- 34-A1: Avulsion
- 34-A2: Isolated body
- Partial articular
- 34-B1: vertical, lateral
- 34-B2: vertical, medial
- Complete articular
- 34-C1: transverse
- 34-C2: transverse plus second fragment
- 34-C3: complex
Management
Prognosis
- Goals of treatment
- Maintain extensor mechanism
- Maintain anatomic alignment of patellofemoral articulation
- Overall paucity of data on outcomes
- Most experts agree non- or minimally displaced transverse fractures managed conservatively have the best outcomes
- Comminuted fractures have thw worst outcomes
- 30-50% suffer from persistent anterior knee pain, 15-30% from functional impairment[8]
- Lazaro et al study of 30 patients who underwent ORIF of patella fracture[9]
- 80% of patients reported persistent anterior knee pain
- Despite radiographic healing, near anatomic reduction, reliable reconstruction of extensor mechanism and physical therapy
- LeBrun et al studied long term surgical outcomes at median of 6.5 years[10]
- 52% of patients required hardware removal, 28% reported implant-related pain
- 15% of patients lacked 5° of extension, 38% of patients lacked some flexion
- Mean extension deficit of 26%, loss of power was 30%
Nonoperative
- Indications
- Only if the extensor mechanism is intact (can perform straight leg raise)
- Typically includes stable, non-displaced fractures
- Vertical fracture patterns
- Stress views
- Consider stressing under 60° of flexion to confirm stability
- Immobilization
- Initially Knee Immobilizer
- More functionally in a Hinged Knee Brace which can be locked
- Early mobility
- Start at 2-3 weeks, allow up to 40° flexion
- Early weight bearing in full extension
Operative
- Indications
- Preserve patella whenever possible
- Extensor mechanism failure (unable to perform straight leg raise)
- Open fractures
- Fracture articular displacement >2 mm
- Displaced patella fracture >3 mm
- Patella sleeve fractures in children
- Technique
- ORIF with tension band construction
- Partial Patellectomy (only if ORIF not possible)
- Total patellectomy (rare)
Rehab and Return to Play
Rehabilitation
- Needs to be updated
Return to Play
- Needs to be updated
Complications
- Loss of extensor mechanism
- Anterior knee pain
- Symptomatic hardware (up to 50%)
- Hardware Migration
- Hardware failure
- Weakness
- Loss of reduction (22%)
- Nonunion (<5%)
- Osteonecrosis
- Infection
- Stiffness
- Patellofemoral Pain Syndrome
- Eventually Patellofemoral Osteoarthritis
- Nonoperative risks
- Loss of full extension due to non-union
- Stiffness
- Incongruity of patellofemoral articulation
See Also
- Internal
- External
- Sports Medicine Review Knee Pain: https://www.sportsmedreview.com/by-joint/knee/
References
- ↑ Wild, M., J. Windolf, and S. Flohé. "Patellafrakturen." Der Unfallchirurg 113.5 (2010): 401-412.
- ↑ Boström A. Fracture of the patella. A study of 422 patellar fractures. Acta Orthop Scand Suppl. 1972;143:1–80
- ↑ Märdian S, Wichlas F, Schaser KD, Matziolis G, Füchtmeier B, Perka C, Schwabe P. Periprosthetic fractures around the knee: update on therapeutic algorithms for internal fixation and revision arthroplasty. Acta Chir Orthop Traumatol Cech. 2012;79(4):297–306.
- ↑ Case courtesy of Dr Jeremy Jones, Radiopaedia.org, rID: 6461
- ↑ Nummi J. Fracture of the patella. A clinical study of 707 patellar fractures. Ann Chir Gynaecol Fenn Suppl. 1971;179:1–85.
- ↑ Catalano JB, Iannacone WM, Marczyk S, Dalsey RM, Deutsch LS, Born CT, Delong WG. Open fractures of the patella: long-term functional outcome. J Trauma. 1995 Sep;39(3):439–444.
- ↑ Case courtesy of Dr Mostafa El-Feky, Radiopaedia.org, rID: 22347
- ↑ Levack B, Flannagan JP, Hobbs S. Results of surgical treatment of patellar fractures. J Bone Joint Surg Br. 1985 May;67(3):416–419.
- ↑ Lazaro LE, Wellman DS, Sauro G, Pardee NC, Berkes MB, Little MT, Nguyen JT, Helfet DL, Lorich DG. Outcomes after operative fixation of complete articular patellar fractures: assessment of functional impairment. J Bone Joint Surg Am. 2013 Jul;95(14):e96
- ↑ LeBrun CT, Langford JR, Sagi HC. Functional outcomes after operatively treated patella fractures. J Orthop Trauma. 2012 Jul;26(7):422–426.
Created by:
John Kiel on 7 July 2019 06:17:40
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Last edited:
4 October 2022 15:44:16
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