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Patella Fracture

Patella fracture is a frequently observed knee traumatization. It is either a result of force directly exerted on the patella itself or occurs when quadriceps forcefully contract.


The predominant symptom manifesting after a patella fracture is knee pain [7]; the patient's medical history will illustrate the way in which the traumatization was sustained: direct force, indirect force or a combination of those.

Displaced fractures usually present with abnormal appearance of the knee and the dislocated pieces may as well be palpable. Medial and lateral retinacula disruption may also be present, accompanied by hemarthrosis.

  • Most of them are asymptomatic and are discovered incidentally. Bipartite patella is sometimes misdiagnosed as a patella fracture, because the x-ray images of both these conditions may appear very similar.[ncbi.nlm.nih.gov]
  • Mean follow-up in asymptomatic patients was 8 months (range, 3-18 months) and in patients with implant-related problems was 17 months (range, 10-36 months). Four patients were lost to follow-up.[ncbi.nlm.nih.gov]
  • Most remain asymptomatic. They are classified into three types: Type I - inferior pole, Type II - lateral margin, Type III: - superolateral. Type III is most common.[orthopaedicsone.com]
  • He was 4/5 lame on the left hind and appeared to be partially collapsing in the stifle when fully weight bearing. Radiographs (X-Ray) Radiographs show a fracture of the patella (knee cap).[cavecreekequine.com]
  • Osteonecrosis of the knee is also associated with certain conditions and treatments, such as obesity, sickle cell anemia, lupus, kidney transplants, and steroid therapy.[arlingtonortho.com]
  • […] weeks Displaced fractures with 2 mm of step-off or 3 mm of distraction are treated surgically Common technique involves insertion of two Kirschner wires and a looped wire Partial or total patellectomy may be used for severe comminution Complications Sepsis[learningradiology.com]
  • INTRODUCTION: Titanium-nickel shape memory alloy (Ti-Ni SMA) is characterized by shape-memory effect, super-elasticity, excellent fatigue behavior, corrosion resistance, acceptable biocompatibility and high damping capacity.[ncbi.nlm.nih.gov]
  • A potentially impaired joint can be aspirated, which will help diagnose hemarthrosis or a joint effusion; the latter leads to the aspiration of fluid containing fat globules.[symptoma.com]
  • If there is an effusion at the knee and aspiration reveals hematoma with fat droplets inside, suspicion should rise about an osteochondral fracture even if nothing is detected on the radiographs in AP and lateral projections.[casesjournal.biomedcentral.com]
  • […] pt's ability to maintain knee extended against gravity; - there should be minimal displacement of fragments (2-3 mm) - minimal disruption of the articular surface (2-3 mm) - transverse undisplaced fracture of the patella is an avulsion frx; - should aspirate[wheelessonline.com]
  • Aspiration of the hemarthrosis and instillation of local anesthetic will the diagnostic usefulness of this test. A thorough examination of the ipsilateral extremity should ensue to evaluate for associated injury.[orthopaedicsone.com]
Knee Pain
  • In this confusing presentation, a high index of suspicion for patella fracture should be maintained for patients with knee pain and osteoporosis on x-ray with a dysplastic syndrome. Copyright 2011 Elsevier B.V. All rights reserved.[ncbi.nlm.nih.gov]
  • […] more often girls Other possible causes of anterior knee pain include: Arthritis Pinching of the inner lining of the knee during movement (called synovial impingement or plica syndrome) Symptoms Anterior knee pain is a dull, aching pain that is most often[mountsinai.org]
  • Knee pain following a Patella fracture is quite common, even after the fracture has healed. Many people find that a Knee Brace or Support helps to provide warmth and alleviates their knee pain symptoms.[physioroom.com]
  • In this case, the patient complained of left knee pain after x-ray films revealed a fracture-like line in the left patella. The patient was then diagnosed as having a patella fracture.[ncbi.nlm.nih.gov]
  • DOCTOR EXAMINATION deformity swelling contusion 8. INVESTIGATIONS 9.[slideshare.net]
  • A MRI may be used to show bone contusions and injuries to nearby muscles and tendons. Causes of Patella Fractures The most common cause of a patella fracture is a fall onto the kneecap, often in a slip and fall accident or staircase fall.[ebtrialattorneys.com]
  • […] avulsion of the inferior pole of the patella If the x-ray beam is oriented horizontally and image is obtained cross-table, a fat-fluid level ( lipohemarthrosis ) may be present CT is used when a fracture is suspected but not visible MRI can show bone contusions[learningradiology.com]
  • Abrasions, contusion over the anterior aspect of the knee, or both may be present Examination reveals effusion of knee in a closed fracture .[boneandspine.com]
  • Diagnostic methods that a physician may use to help diagnose a Patellar Fracture include: Physical examination: A thorough physical examination is important in identifying any noticeable deformities, swelling, and contusions in the injured knee.[dovemed.com]
Knee Effusion
  • Conclusion To us it is vital to obtain CT scan of the patient's knee if there is an ipsilateral femoral fracture with an ipsilateral knee effusion and a punction which reveals hematoma even in the absence of a fracture line seen in AP and lateral projections[casesjournal.biomedcentral.com]
  • (Hunt 2005) Clinical Findings: Osseous fractures present with a knee effusion, point tenderness at the fracture site, and the inability to extend the knee fully without pain. Patella alta is frequently present as well.[posna.org]
Anterior Knee Pain
  • […] more often girls Other possible causes of anterior knee pain include: Arthritis Pinching of the inner lining of the knee during movement (called synovial impingement or plica syndrome) Symptoms Anterior knee pain is a dull, aching pain that is most often[mountsinai.org]
Flexion Contracture
  • At 1 year postoperatively, she ambulated with a cane, with range of motion examination revealing 5 degrees flexion contracture and 80 degrees flexion.[ncbi.nlm.nih.gov]
  • However, patients with fixed flexion contractures of the knee, in spite of the fracture pattern are candidates for conservative treatment.[boneandspine.com]


A patella fracture usually manifests with intense knee pain and a medical history involving a direct blow to the kneecap, an indirect strain, such as the one sustained by a fall, or a combination of these forces. Dislodged bone may be observable with a bare eye, especially in the cases of open fractures.

The first step towards evaluating a potential patella fracture is radiographic imaging. X-rays obtained from a lateral, anteroposterior and axial perspective are widely used to provide critical information about the skeletal structures underneath tissue. Radiographic depiction assesses the direction of the fracture, its type, possible comminution and other important features. Magnetic Resonance Imaging helps to evaluate osteochondral fractures, sleeve fractures [8] and generally fractures that prove difficult to characterize with other than MRI examinations.

A patient also needs to be evaluated for the presence of hemarthrosis and damage to the extensor mechanism, namely the medial and lateral retinacula. A potentially impaired joint can be aspirated, which will help diagnose hemarthrosis or a joint effusion; the latter leads to the aspiration of fluid containing fat globules. Lidocaine can be administered intra-articularly, in order to reduce the pain and allow for a more extensive examination of the patient's ability to extend the knee against gravity.


Fractures that do not involve displacement respond to conservative treatment at a rate of nearly 90%. The patient does not benefit from any surgical intervention and is treated with a cylinder cast that is kept for 4 to six weeks, depending on the specific characteristics of the fracture. An assessment is carried out after the initial period has passed and is sign of healing are evident, the cast is removed and the patient is required to use a removable brace. the decision of cast discontinuation is based on the results of the clinical examination (painless knee, even when palpated) and radiologic findings which are compatible with union.

Gradual strengthening of the arthrosis should be attempted alongside physiotherapy to restore the range of movement. A patient can stop using a removable brace when they are able to flex their knee joint over 90 degrees and raise their leg freely against gravity.  

Fractures that involve displacement do not benefit from conservative treatment and require surgical intervention instead. The precise technique is decided depending on the particular characteristics of each fracture and greatly depends on whether it is an open fracture, if arthrotomy has been sustained and if ligaments will have to be repaired as well. At any case, a thorough examination and detection of the damage is mandatory before deciding upon the best surgical treatment. A widely used surgical technique generally involves the conversion of tensile force into a compressive one, with the use of a tension band, thereby helping the patella to regain continuity faster [9] [10]. Open fractures are operated as an emergency condition.

Antimicrobial treatment is also administered prophylactically before a patella reconstructive surgery. In a case of open wound, further antibiotics are introduced into the therapeutic scheme. Tetanus shots are also mandatory if a wound is open. An orthopedic surgeon should always consider the possibility of infection before proceeding to surgery and treat it appropriately.


Surgical intervention is expected to result in a successful repair of patella continuity and functionality. The more extensive the damage sustained by the structure, the more time it will require to reach a stage of complete recovery; even less severe traumatizations can result in significant complications, such as patellofemoral arthrosis [5]. 10-20% of the patients who undergo open reduction internal fixation also experience displacement of the patella segments following surgery, which is believed to be the case when the separated parts are not fixed together properly by a surgeon [6]. Hardware prominence is also possible in some cases.


In general, the patella is an anatomical structure that is susceptible to injuries, due to the fact that it is located subcutaneously and is therefore not as protected from extreme forces as other structures are. There are three possible causes of a patella fracture:

  • Direct force
  • Abrupt tensile force
  • A combination of the above

Direct force exerted on the patella usually produces a comminuted fracture, as the regional anatomical structures are obliged to absorb the force. This may result in the traumatization not only of the patella, but of the cartilage and femoral condyles as well.

Should the patella sustain tensile-type force, such as the type sustained when the quadriceps contact violently in hyperflexion, the most common fracture acquired is a nondisplaced fracture. Lastly, if the traumatization is a result of the two forces combined, fractures of various types can occur, i.e. tansverse, displaced fractures that become comminuted at a later stage.


Patella fractures represent 1% of all traumatizations sustained by the skeleton.

Sex distribution
Age distribution


The patella is a small triangular bone which covers the joint between the femoral bone and tibia. The conjoined tendons of the four quadriceps muscles, known as the quadriceps tendon encases the structure and assumes the function of the patella tendon. The forces sustained by the patella when the quadriceps muscles contact are able to strain the former at such an extent that an indirect fracture can occur.

The vastus medialis is one of the four quadriceps muscles of the thigh, which function in unison. Its tendon is extended to form the medial patellar retinaculum, which is itself linked to the upper-and-towards-the-midline part of the patella. Respectively, the lateral patellar retinaculum is formed by the last part of the vastus lateralis and is also attached to the patella. The lateral and medial retinacula are responsible for a person's ability to flex the knee, an ability that is preserved if both structures are unharmed after an injury.

Patella fractures are a result of direct forces exerted on the patella or indirect forces induced by the surrounding tendons. Typically, indirect fractures are a result of abnormal or excessive knee flexion. If a major fall occurs for example, the joint is forced to absorb great pressure, which will result either in the rupture of the tendons or in a transverse patella fracture [2]. Displacement is a frequent finding is these types of fractures, whereas direct traumatization induces a comminuted fracture, articular traumatization and, most likely, open fractures [3]. Both types of forces may be exerted, which cause bone displacement alongside tissue traumas.

Regarding the regional perfusion, the three largest branches of the geniculate artery are responsible for providing the knee with the required volume of blood. Since the superior and inferior medial geniculate arteries penetrate the knee joint, a patella fracture may severely compromise the knee blood supply, leading to an avascular necrosis [4].


In order to prevent a patella fracture, one should regularly exercise, giving emphasis to the strengthening of the knees: surrounding muscles are able to protect the patella if a person maintains good physical status. Suitable protection like kneepads are required, if one participated in a sport likely to cause knee injuries.


The patella bone is otherwise known as the "kneecap" bone. It is a structure located in the front part of the joint of the knee, at the point where the femoral bone and the tibia are joined together. The joint itself alongside the part of the patella that lies above it are enclosed by the articular cartilage, which lubricates the structures in order to allow for smoother motion, minimal friction and damage to the bones.

The patella can sustain various types of fractures. Depending on their morphology, primary patella fractures are divided in transverse, vertical, osteochondral, sleeve and marginal [1], with the fracture located at the top, lower part or center of the patella.

Depending on the severity of the fracture, it can be stable, displaced, comminuted or open. Stable fractures are those whereby the two separated parts remain in place and correct alignment. In a displaced fracture, alignment is impaired and surgical intervention is necessary before the bone starts to heal. On the other hand, comminuted fractures involve shattering of the patella into 3 pieces or more. Finally, open fractures are the severer type: the bone has torn out of the skin and adjacent structures have also sustained massive damage.

Patient Information

A patella fracture is an injury to the patella, commonly known as the kneecap. A fracture can have various degrees of severity and may also be accompanied by damage to the surrounding ligaments, muscles and tendons.

Patellar fractures are sustained in three different ways. the first one involves a direct blow to the patella, usually forceful. the second one is an indirect mechanism, whereby the patella is injured when the thigh muscles contract very violently; the quadriceps (thigh muscles) are connected to the kneecap, so their abrupt and violent contraction strains the patella to such an extent, that a fracture can occur. This can happen when falling from a considerable height. The third mechanism involves a combination of the two aforementioned ways.

Typical symptoms include knee pain, regional tenderness and swelling, knee bruises, inability to extend ones knee, defects visible with a bare eye (bone protruding, dislodged patellar pieces) and numbness. A patella fracture is diagnosed with the help of an x-ray obtained at different angles, possibly an MRI and a thorough physical examination.

Patella fractures may be treated both surgically and non-surgically, depending on the case. Generally, fractures where the patella has broken but all the damage is minimal and the segments still remain in their original place does not need surgery. The patient initially wears a cast for 1-1.5 month and then, if recovery is proceeding, discontinues the cast use and starts to wear a removable brace. Gradually, a person regains their ability to flex the knee and perform a fully-ranged knee motion. Fractures where the bone segments are out of place need to be operated on, in order to reconstruct the patella or remove some of the pieces that cannot be placed in their right position.

Antibiotic treatment is administered before and shortly after surgery, in cases of bone exposed through the skin, or, generally, when infection is clinically evident.



  1. Moretti B, Speciale D, Garofalo R, et al. Spontaneous bilateral fracture of patella. Geriatr Gerontol Int. 2008 Mar; 8(1):55-8.
  2. Harris RM. Fractures of the patella and injuries to the extensor mechanism. In: Bucholz, RW, Heckman, JD, Court-Brown CM, eds. Fractures in Adults. Ed 6. Philadelphia, PA: Lippincott Williams and Wilkins; 2006; 1969–1998.
  3. Carpenter JE, Kasman R, Matthews LS. Fractures of the patella. Instr Course Lect. 1994; 43:97–108.
  4. Harris, RM. Fracture of the patella. In: Rockwood and Green's Fractures in Adults, Bucholz, RW, Heckman, JD (Eds), Lippincott Williams & Wilkins, Philadelphia 2002; p.1775.
  5. Sorensen KH. The late prognosis after fracture of the patella. Acta Orthop Scand. 1964; 34:198–212.
  6. Nummi J. Fracture of the patella: a clinical study of 707 patellar fractures. Ann Chir Gynaecol Fenn Suppl. 1971; 179:1–85.
  7. Goldberg VM, Figgie HE, Inglis AE, et al. Patellar fracture type and prognosis in condylar total knee arthroplasty. Clin Orthop Relat Res. 1988 Nov; (236):115-22.
  8. von Engelhardt LV, Raddatz M, Bouillon B, et al. How reliable is MRI in diagnosing cartilaginous lesions in patients with first and recurrent lateral patellar dislocations?. BMC Musculoskelet Disord. 2010 Jul 5; 11:149.
  9. Berg EE. Open reduction internal fixation of displaced transverse patella fractures with figure-eight wiring through parallel cannulated compression screws. J Orthop Trauma. 1997 Nov; 11(8):573-6.
  10. Fortis AP, Milis Z, Kostopoulos V, et al. Experimental investigation of the tension band in fractures of the patella. Injury. 2002 Jul; 33(6):489-93.

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Last updated: 2018-06-22 07:51