Patella Fractures

Updated: Aug 23, 2022
Author: Alexandra K Schwartz, MD; Chief Editor: Thomas M DeBerardino, MD, FAAOS, FAOA 


Practice Essentials

Patella fractures account for approximately 1% of all skeletal injuries. They become problematic if the extensor mechanism of the knee is nonfunctional, articular congruity is lost, or stiffness of the knee joint ensues.[1]  To avoid these problems, the surgeon must achieve anatomic restoration of the joint and must allow early motion.

In the 1800s, treatment of patella fractures was controversial. Owing to a lack of adequate fixation techniques, surgical experience, and imaging, treatment most often consisted of extension splinting. This led to poor results because of intra-articular incongruity, nonunion, and poor motion.

Initial attempts at operative stabilization of these fractures yielded satisfactory repair rates lower than 50%. Treatment then progressed to excision of fractured patellar fragments or of the entire patella. Despite encouraging early results, long-term follow-up revealed degenerative changes in the femoral condyles and decreased quadriceps power.

With the introduction of the AO group (Arbeitsgemeinschaft für Osteosynthese, or Association for the Study of Osteosynthesis) in the 1950s, a new technique for fixation of these fractures was developed. The concept of the anterior tension band technique was introduced. This allowed stable fixation, early motion, and improved rates of bony union.


The patella is the largest sesamoid bone in the body. It is contained within the extensor mechanism, consisting of the quadriceps tendon proximally and the patellar ligament distally. At this location, it serves to increase the extensor moment by nearly 30%. The patella is covered at its proximal aspect by thick cartilage. Owing to its relatively small size, the patellofemoral joint is exposed to the highest contact stress of any weightbearing joint. Therefore, any aberration in its anatomy or alignment may lead to symptomatic degenerative changes.


The subcutaneous location of the patella makes it prone to injury. Fractures occur as a result of a compressive force (as occurs with a direct blow), a sudden tensile force (as occurs with hyperflexion of the knee), or a combination of these. Various fracture patterns result, depending on the mechanism of injury. The most common patterns are often described as stellate or transverse; less common patterns include vertical, marginal, osteochondral, and sleeve fractures.

Sleeve fractures are seen exclusively in the pediatric population.[2] On radiographs, sleeve fractures are represented by a small bony avulsion fracture. However, they are actually larger than they appear on radiographs because they are surrounded by a significant portion of articular cartilage.

A direct blow to the patella most often results in a stellate fracture. The compressive forces applied to the patella result in a comminuted pattern. The energy of the blow is absorbed by the fracture and may cause damage to the articular cartilage of both the patella and the femoral condyles. Free osteochondral lesions therefore must be excluded. About 65% of these fractures do not involve the extensor retinaculum. If the extensor mechanism has not been disrupted and if intra-articular stepoff is less than 2 mm, the fracture may be treated nonoperatively.

Another mechanism of injury to the patella is a tensile force, as is sustained with hyperflexion of the knee with an eccentric contraction of the quadriceps. Approximately 35% of these are nondisplaced fractures with an intact retinaculum. This type of fracture, with less than 2 mm of intra-articular stepoff, can be treated with a nonoperative modality.

A combination of these two mechanisms can lead to a variety of other fracture patterns. A displaced transverse fracture can have comminution if a blow to the knee occurs after the tensile force. For instance, a hyperflexion moment to the knee resulting in a transverse fracture pattern can be followed by a fall onto the knee, which causes comminution.


The prognosis depends primarily on the quality of articular restoration.[3] Any intra-articular incongruities lead to posttraumatic arthritis. To a certain extent, the prognosis also depends on the amount of chondral damage sustained at the time of injury. Some of these changes are irreversible; anatomic restoration of the joint minimizes the long-term degenerative changes. Functional outcome depends on the ability to achieve early, pain-free, stable range of motion (ROM). If arthrofibrosis develops, it may necessitate manipulation with the patient under anesthesia or arthroscopic release of adhesions.

Rabalais et al compared two tension-band techniques, with stainless-steel wire and ultrahigh-molecular-weight polyethylene cable, in transverse patella fractures in eight cadaver knees.[4]  Fixation consisted of figure-eight and parallel wire configurations, along with Kirschner wires (K-wires) and polyethylene cable. The parallel wire configuration showed better results than the figure-eight construct in monotonic and cyclic loading models, and the ultrahigh-molecular-weight polyethylene cable and the 18-gauge steel wire performed similarly.

El-Sayed et al reported on arthroscopic-assisted reduction and fixation of displaced transverse fractures of the patella in 14 patients.[5]  Patients were treated by means of arthroscopic-assisted closed reduction of the fracture with percutaneous screw fixation. Patella fractures were found to unite in a mean of 7 weeks. All 14 patients regained full extension of the knee, and full ROM was achieved in 12 patients, with two patients experiencing a 10º loss of flexion.

Wright et al performed materials testing on No. 5 FiberWire suture and 18-gauge stainless-steel wire tension by using them both for band fixation on a transverse patellar fracture model and performing three-point bending tests.[6]  The investigators found that FiberWire maintained its initial stiffness until failure and that during three-point bend testing, double-strand FiberWire had a higher failure load than stainless-steel wire when the suture was tied and locked under tension created by a modified Wagoner hitch.

Dargel et al compared interfragmentary compression with tension-band wiring.[7]  They concluded that fragment fixation is an acceptable technique for treating osteosynthesis of a transverse patella fracture.

Muzaffar et al successfully treated minimally displaced two-part patellar fractures with percutaneous K-wire fixation and compression that was subsequently augmented with a cast.[8]

In a retrospective study of 72 patients with transverse patella fractures treated with either a modified tension band (n = 37) or a titanium cannulated lag screw (n = 35), Wang et al found that the parallel titanium cannulated lag screw technique yielded better results; accordingly, they recommended that this technique be considered as an alternative method for treating transverse patella fractures.[9]

Larsen et al examined 30-day, 6-month, and 1-year mortality in 6096 Danish patients (mean age, 48.9 y) with 6114 patella fractures versus a matched reference population.[10] Overall mortality was 0.7% at 30 days (1.3% for patients >65 y), 1.8% at 6 months (3.9% for patients >65 y), and 2.8% at 1 year (6.2% for patients >65 y). In comparison with the reference population, the relative risk of mortality in patients older than 65 years was 1.9% at 30 days, 1.0% at 6 months, and 0.9% at 1 year. The authors concluded that patella fractures in elderly patients were not associated with increased mortality.




An individual who has sustained a patella fracture usually presents with pain in the affected knee. The history reveals a direct blow to the knee, a fall, or a combination of the two. Overlying abrasions, ecchymosis over the anterior aspect of the knee, or both may be present.

Physical Examination

Any lacerations must be assumed to communicate with the joint until this assumption is disproved by the saline load test. Because the retinaculum may have a large tear, it may be necessary to inject a significant amount of saline (up to 100 mL) to exclude an open joint. An accompanying intra-articular effusion may be present, which, if aspirated, will reveal fat globules. If the fracture is displaced, a defect is palpable at the fracture site.

The extensor mechanism must always be evaluated. As a result of the pain associated with the injury and hemarthrosis, the patient may be unable to perform a straight leg raise. Aspiration of the hemarthrosis under sterile conditions and the instillation of lidocaine may relieve the pain sufficiently to allow performance of a reliable examination. Disruption of the extensor mechanism renders the patient unable to extend the knee against gravity and usually implies that a tear is present in the medial and lateral quadriceps expansion.



Imaging Studies

Most patella fractures can be adequately visualized and classified by using standard anteroposterior (AP), lateral, and axial (Merchant or sunrise) radiographs of the knee (see the images below). The AP view helps in assessing the fracture pattern and the direction of displacement, whereas the lateral and Merchant views assist in evaluating the amount and location of comminution.

Preoperative anteroposterior radiograph of patella Preoperative anteroposterior radiograph of patella fracture.
Preoperative lateral radiograph of patella fractur Preoperative lateral radiograph of patella fracture.
Preoperative sunrise radiograph of patella fractur Preoperative sunrise radiograph of patella fracture. Note that vertical fracture is not appreciated on anteroposterior and lateral views.

Occasionally, oblique views or computed tomography (CT) may be indicated for assessment of osteochondral fractures and intra-articular fragments. If a stress fracture is suspected, bone scanning may be helpful for making the diagnosis.


Aspiration of a hemarthrosis followed by instillation of intra-articular lidocaine may relieve the pain related to the fracture and permit a more thorough evaluation of extensor mechanism disruption. This measure is not usually necessary, but if it is, it must be performed under sterile conditions to minimize the risk of infection.



Approach Considerations

Indications for operative treatment of a patella fracture include the following:

  • Disruption of the extensor mechanism
  • Articular incongruity with more than 2 mm of stepoff
  • More than 3 mm of separation between primary fracture fragments

Relative contraindications for closed treatment of patella fractures include the following[11, 12, 13] :

  • Open fractures
  • Intra-articular displacement with disruption of the extensor mechanism

Contraindications for operative repair of patella fractures include the following:

  • Preexisting lack of active extensor function
  • Fixed flexion contractures of the knee

Future treatment options may include osteochondral allograft reconstructions of the patella for posttraumatic arthritis. Bioabsorbable fixation methods may reduce the frequency of hardware-related symptoms.

Nonoperative Therapy

If the fracture is not displaced and the extensor mechanism is intact, the fracture may be treated by means of immobilization. This usually involves placing the affected extremity in a cylinder cast for 4-6 weeks. The patient is allowed to bear weight in the cast.

Once radiographic evidence indicates union and clinical signs of healing (nontender to palpation) are present, the patient is changed to a removable brace. A hinged knee brace is used during ambulation. A program emphasizing range of motion (ROM) and strengthening is then implemented. Once the patient is able to perform a straight leg raise without extensor lag and has greater than 90º of knee flexion, brace use may be discontinued. With proper patient selection, good results can be expected in approximately 90% of patients with nondisplaced fractures.

Surgical Therapy

For displaced patellar fractures, surgical treatment is warranted to maximize the potential for successful outcomes. Operative treatment aims to restore extensor function, align articular incongruities, and allow early motion. Operative treatment is carried out on an emergency basis if the fracture is open or if an associated traumatic arthrotomy is present.

Preparation for surgery

Evaluation of the extent of comminution is critical in preoperative planning. The various possible implants should be available, and the choice may be dictated by the fracture pattern. In addition, the patient should be informed of the possible need for fragment excision (see the image below) and patellar ligament advancement to the remaining patella if he or she has irreparable comminution.

Chondral fragments from comminuted patella fractur Chondral fragments from comminuted patella fracture.

Operative details

Fixation can be accomplished in a variety of ways. The most common method is a tension-band technique (see the images below). The biomechanical principle of tension-band fixation is to convert a tensile force into a compressive force while the knee is flexed. If a fractured patella were to be brought through a range of motion, tension and distraction would be present at the fracture site. By placing a tension band at the anterior surface, this tensile force is converted into a compressive force, thereby aiding in fracture healing.[14, 15, 4, 16, 17]

Postoperative anteroposterior radiograph of patell Postoperative anteroposterior radiograph of patella fracture.
Postoperative lateral radiograph of patella fractu Postoperative lateral radiograph of patella fracture.
Postoperative sunrise view of patella fracture. Ve Postoperative sunrise view of patella fracture. Vertical fracture is stabilized with lag screw.

The tension-band technique often begins with placing two parallel Kirschner wires (K-wires). (Some surgeons prefer a crossed-pin configuration to a parallel configuration.[18] ) Placement of K-wires is not mandatory but is often performed to aid with rotational control. These wires can be placed outside-in after the fracture is reduced and provisionally stabilized with a reduction clamp.

Another technique by which to place K-wires is the inside-out technique. This involves drilling the wires through the fracture site prior to reduction. Once the wires are passed through the fracture, the wire end nearest the fracture surface is made flush with the fracture. The fracture is then reduced, and the wires are advanced across the fracture. The ideal level of the pins is in the center of the patella, approximately 5 mm below its anterior surface. Intraoperative fluoroscopy may be used to guide placement of hardware.

Once the K-wires are placed, a 1-mm or 1.25-mm tension-band wire is placed as close to the border of the patella as possible. Keeping the tension band at the anterior half of the patella is very important. The tension band is made into a figure-eight or figure-zero shape. It should lie as close to bone as possible throughout its entire course. A 14- or 16-gauge intravenous (IV) catheter facilitates the passage of the wire through the soft tissue.

The figure-zero configuration has more stability against torsional force. However, it can cut into the retinacula, and if this should occur, the tension band would be lost. This is especially true if the wire is at the posterior half of the patella. For this reason, most surgeons prefer the figure-eight configuration.

As the tension band is tightened with the knee extended, the articular surface must be evaluated. This can be performed by using fluoroscopy or by palpating the undersurface of the patella through the medial and lateral retinacular defects.

After fracture fixation, the arc of motion is assessed. This should be done while the undersurface of the patella is palpated through the medial and/or lateral retinacular defects.

The twisted ends are cut in such a way as to leave approximately 1 cm of wire. These ends are then bent over with a large needle driver, then rotated so that they lie within soft tissue. They should not be left proud, because they can cause irritation of the overlying skin.

The K-wires are also cut. The proximal ends are bent over, again by using a large needle driver. The ends are rotated so as to lie within the quadriceps tendon and are advanced until the ends contact the proximal pole of the patella. The distal ends are then cut to avoid prominence within the patellar ligament.

Circumferential cerclage wires[19]  are helpful for stellate fractures. A 1-mm cerclage wire may be placed around the periphery of the patella. If this measure is combined with tension-band fixation, the circumferential cerclage should be placed first. Suture-tape cerclage using a tensioner has been described for transverse patella fracture.[20]

Modifications of the tension-band technique include the use of cannulated screws instead of K-wires.[21]  This may allow compression across stable fractures. After placement of cannulated screws from distal to proximal, the 1-mm or 1.25-mm wire is passed through the center of the cannulated screws, and the wire ends are twisted as described above.

A case-control study by Liu et al (N = 90; minimum follow-up, 2 y) compared the clinical outcomes of three techniques for the treatment of transverse patella fractures: K-wire with tension band (KTB; n = 30), cannulated-screw tension band (CSTB; n = 30), and ring-pin tension band (RPTB; n = 30).[22]  CSTB was found to be superior to KTB and RPTB for reducing the incidence of postoperative complications, as well as advantageous for accelerating fracture healing, reducing pain, increasing ROM, and improving functional recovery.

Tension-band wiring is possible only after the fracture has been converted to a two-part fracture. Additional fracture fragments can be secured by using supplementary small fragments or mini-fragment screws. This, in essence, allows conversion of a comminuted fracture to a two-part fracture. A hybrid approach to patella fractures with multiple osteochondral fragments has been described in which fixation of one of the osteochondral fragments is combined with the use of particulated juvenile articulate cartilage to fill the remaining patellar defect.[23]

Wurm et al prospectively evaluated clinical outcomes in 35 patients with patella fractures who were treated with an angular stable patella plate rather than tension-band wiring.[24] Only one implant-related complication occurred, and none of the patients had any deficits in extension capabilities. Patients classified their knee function in daily life as an average of 77% of their pretrauma function; only kneeling or squatting was a problem for some. The authors suggested that the patella plate may yield reduced complications and improved functional outcome versus tension-band wiring, especially for patients with a multipart or comminuted fracture or with osteoporotic bone.

Yao et al reported excellent clinical outcomes (excellent-to-good rate, 92.6%) with the titanium-nickel shape-memory patella concentrator (TNSMPC) in combination with cannulated compression screws for the treatment of C2 and C3 patella fractures in 54 patients.[25]

If the fracture is at the most proximal or distal pole, adequate fixation may not be achievable with hardware. In such cases, nonabsorbable heavy suture material can be used for the repair. This involves placing several sets of suture in the patellar or quadriceps tendon, using a locking and running stitch (eg, a Krackow stitch[26] ). The suture ends are then brought through the patella via drill holes and tied securely at the opposite end of the fracture. A five-pointed star lattice suture fixation technique for transverse patella fractures has been described by Tang et al.[27]

In rare instances (eg, cases of severe and irreparable comminution), a partial or a total patellectomy must be performed. Because the long-term outcomes with these techniques are poor, they should be used only as a last resort. With a partial patellectomy involving at least one third of the patella, a loss of motion of approximately 18° can be expected. With a total patellectomy, loss of motion, loss of strength, and knee instability with stair-climbing occur. Therefore, it is essential to try to salvage as much patella as possible in all fractures.

After fixation of a patella fracture, closing the arthrotomy and repairing the retinacula are vital. These measures add to the healing of the extensor mechanism and help prevent patellar subluxation. A drain may be placed into the knee joint before closure. The patient is then placed in a well-padded sterile dressing, and a knee immobilizer or hinged knee brace is locked in extension.

Postoperative Care

First-generation cephalosporins are given before the surgical incision and for approximately 24 hours postoperatively. The standard protocols for any open fracture should be followed, with aminoglycosides added for contaminated open wounds. Tetanus shots should be updated as indicated for open fractures. Contaminated open wounds may require several repeat irrigations. If the capsule was penetrated, the knee joint should be closed over a drain.

Routine surgical incisions may be followed in an outpatient setting. Sutures or staples generally are removed at 14-21 days. Open fracture wounds should be inspected approximately 48 hours after surgery. Persistent drainage or erythema should warn the surgeon of possible underlying infection. Infection should be aggressively treated (eg, with IV antibiotics, surgical irrigation and debridement, or both).

Postoperative rehabilitation is dependent on the fracture pattern, the stability of fixation, and the status of the soft tissue. Early ROM may be initiated if the fracture pattern allowed stable fixation and no wound problems exist. However, comminuted fractures with less than optimal fixation should be monitored closely for stability and progressive signs of radiographic healing.

Direct communication between the surgeon and the therapist is essential to ensure proper rehabilitation. All patients should be counseled regarding the importance of attaining and maintaining full knee extension. Patients should avoid using pillows under the knee; rather, they should place a heel roll or towel to allow gravity to act on the knee.



Infection rates as high as 2-10% have been reported. Wound healing also may be problematic, especially with associated soft-tissue lesions. This high rate is attributable to the subcutaneous location of the patella, with lack of overlying soft tissue. To allow healing, the knee often must be immobilized so that further stress on the soft tissue is avoided. Deep infections necessitate surgical debridement and prolonged antibiotic therapy. Untreated infections can lead to septic arthritis and a poor prognosis.


Stiffness often occurs after prolonged immobilization. If the patient is amenable to early motion, physical therapy may be initiated once the soft tissues have stabilized. Patellar mobilizing exercises are mandatory to allow better tracking of the patella. If arthrofibrosis ensues, additional procedures (eg, manipulation under anesthesia or arthroscopy) may be required.

Hardware prominence

Hardware prominence can largely be prevented by means of careful intraoperative technique. Wire ends should lie within soft tissue and not immediately subcutaneously. As many as 15% of patients with symptoms require hardware removal once the fracture is healed.

Prominent wires at the anterior surface of the patella near the prepatellar bursa can lead to prepatellar bursitis. Therefore, it is important to ensure that K-wires and cerclage wires are shortened as much as possible.

Loss of fixation or reduction

Loss of fixation or reduction can occur in as many as 20% of fractures treated with internal fixation. It often is due to inadequate fixation, unrecognized comminution, or aggressive postoperative therapy. If only minimal displacement occurs, the fracture may be treated with immobilization until healing occurs. With loss of extensor mechanism or unacceptable incongruity, the fracture must be revised with hardware or by a partial patellectomy.