You are in: eMedicine Specialties > Orthopedic Surgery > KNEE Patella FracturesArticle Last Updated: Mar 16, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Alexandra K Schwartz, MD, Associate Clinical Professor, Chief, Division of Orthopedic Trauma, Director of Residency Program, Department of Orthopedic Surgery, University of California at San Diego Alexandra K Schwartz is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Medical Association, and Western Orthopaedic Association Editors: Robert D Bronstein, MD, Associate Professor, Department of Orthopedic Surgery, University of Rochester School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Shepard R Hurwitz, MD, Executive Director, American Board of Orthopaedic Surgery; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Carlos J Lavernia, MD, FAAOS, Adjunct Clinical Professor, Department of Orthopedic Surgery, University of Miami School of Medicine; Medical Director, Orthopedic Institute at Mercy Hospital Author and Editor Disclosure Synonyms and related keywords: patella fractures, patella fracture, patellar fracture, broken patella, broken knee bone, fractured knee INTRODUCTIONSection 2 of 12
  History of the ProcedureIn the 1800s, treatment of patella fractures was quite controversial. Owing to lack of adequate fixation techniques, surgical experience, and imaging, treatment most often was 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 rates of satisfactory repair of less than 50%. Treatment methods 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 for stable fixation, early motion, and improved rates of bony union. ProblemPatella fractures become problematic if the extensor mechanism of the knee is nonfunctional, articular congruity is lost, or stiffness of the knee joint ensues. In order to avoid these problems, the surgeon must achieve anatomic restoration of the joint and must allow early motion. FrequencyPatella fractures account for approximately 1% of all skeletal injuries. EtiologyThe subcutaneous location of the patella makes it prone to injury. Fractures occur as a result of a compressive force such as a direct blow, a sudden tensile force as occurs with hyperflexion of the knee, or from a combination of these. A variety of 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, or sleeve fractures. Sleeve fractures are seen exclusively in the pediatric population. 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 pattern. 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. Approximately 65% of these fractures do not involve the extensor retinaculum. If the extensor mechanism has not been disrupted and if intra-articular step-off is less than 2 mm, the fracture may be treated with a nonoperative modality. 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 step-off, can be treated with a nonoperative modality. A combination of these 2 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. ClinicalThe patient usually presents with pain in the affected knee. The history reveals a direct blow to the knee, a fall, or a combination of both. Overlying abrasions, ecchymosis over the anterior aspect of the knee, or both may be present. Any lacerations must be assumed to communicate with the joint until 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 enough to perform a reliable examination. Disruption of the extensor mechanism results in the inability to extend the knee against gravity and usually implies that a tear is present in the medial and lateral quadriceps expansion. INDICATIONSSection 3 of 12
Indications for operative treatment include disruption of the extensor mechanism, articular incongruity with more than 2 mm of step-off, or more than 3 mm of separation between primary fracture fragments. RELEVANT ANATOMYSection 4 of 12
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. Due 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. CONTRAINDICATIONSSection 5 of 12
Relative contraindications to closed treatment of patella fractures include open fractures and intra-articular displacement with disruption of the extensor mechanism. Contraindications to operative repair of patella fractures include a preexisting lack of active extensor function, septic arthritis, and fixed flexion contractures of the knee. WORKUPSection 6 of 12
Lab Studies
Imaging Studies
Diagnostic Procedures
TREATMENTSection 7 of 12
Medical therapyIf the fracture is not displaced and the extensor mechanism is intact, the fracture may be treated with 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 once clinical signs of healing (nontender to palpation) are present, the patient is changed to a removable brace. A hinged knee brace is used while ambulating. A program emphasizing range of motion and strengthening is then implemented. Once the patient is able to perform a straight leg raise without extensor lag and has greater than 90° 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 therapyDisplaced patellar fractures warrant surgical treatment to maximize the potential for successful outcomes. Operative treatment aims to restore extensor function, align articular incongruities, and allow early motion. Operative treatment is emergent if the fracture is open or if an associated traumatic arthrotomy is present. Preoperative detailsEvaluation 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 Image 1) and patellar ligament advancement to the remaining patella if he or she has irreparable comminution. Intraoperative detailsFixation can be accomplished in a variety of ways. The most common method is a tension band technique. 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. The tension band technique often begins with placing 2 parallel Kirschner wires (K-wires). 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 the shape of a figure of 8 or figure of 0. It should lie as close to bone as possible throughout its entire course. A 14- or 16-gauge intravenous catheter facilitates the passage of the wire through the soft tissue. The figure-of-0 configuration has more stability against torsional force. However, it can cut into the retinacula, and thus, 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-of-8 configuration. While tightening the tension band with the knee extended, the articular surface must be evaluated. This can be performed using fluoroscopy or by palpating the undersurface of the patella through the medial and lateral retinacular defects. Following fracture fixation, the arc of motion is assessed. This should be performed while the undersurface of the patella is palpated through the medial and/or lateral retinacular defects. The twisted ends are cut, leaving approximately 1 cm of wire remaining. These ends are then bent over with a large needle driver, and the ends are rotated to 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 using a large needle driver. The ends are rotated 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 are helpful for stellate fractures. This involves placement of a 1-mm cerclage wire around the periphery of the patella. If combined with tension band fixation, the circumferential cerclage should be placed first. Modifications of tension band technique include the use of cannulated screws instead of K-wires. This may allow for 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 in the previous section. Tension band wiring is only possible after the fracture is converted to a 2-part fracture. Additional fracture fragments can be secured using supplementary small fragments or mini-fragment screws. This, in essence, allows conversion of a comminuted fracture to a 2-part fracture (see Images 2-7). If the fracture is at the most proximal or distal pole, adequate fixation may not be achieved with hardware. In such cases, nonabsorbable heavy suture 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, such as a Krackow stitch. The suture ends are then brought through the patella using drill holes. The ends then are tied securely at the opposite end of the fracture. In rare cases, a partial patellectomy or total patellectomy must be performed, such as in cases of severe and irreparable comminution. These techniques should be used only as a last resort because the long-term outcomes with these techniques are poor. With partial excision of at least one third of the patella, a loss of motion of approximately 18° can be expected. With total patellectomy, loss of motion, loss of strength, and knee instability with stair climbing occur. Therefore, attempt salvage of as much patella as possible in all fractures. After fixation of a patella fracture, closing the arthrotomy and repairing the retinacula are vital. This adds to the healing of the extensor mechanism and helps prevent patellar subluxation. A drain may be placed into the knee joint prior to closure. The patient is then placed into a well-padded sterile dressing and a knee immobilizer or hinged knee brace is locked in extension. Postoperative detailsPerioperative first-generation cephalosporins are given prior to the surgical incision and for approximately 24 hours postoperatively. Follow standard protocols for any open fracture, with aminoglycosides added for contaminated open wounds. Update tetanus shots as indicated for open fractures. Contaminated open wounds may require several repeat irrigations. Close the knee joint over a drain if the capsule was penetrated. Follow routine surgical incisions in an outpatient setting. Sutures or staples generally are removed at 14-21 days. Inspect open fracture wounds approximately 48 hours after surgery. Persistent drainage or erythema should warn the surgeon of possible underlying infection. Implement aggressive treatment for infection (ie, intravenous antibiotics and/or surgical irrigation and debridement). Postoperative rehabilitation is dependent on the fracture pattern, stability of fixation, and status of the soft tissue. Early range of motion may be initiated if the fracture pattern allowed for 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 therapist is essential to ensure proper rehabilitation. Counsel all patients on the importance of attaining and maintaining full knee extension. The patient should avoid using pillows under the knee. Rather, a heel roll or towel should be placed to allow gravity to act on the knee. COMPLICATIONSSection 8 of 12
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. In order to allow healing, the knee often must be immobilized to avoid further stress to the soft tissue. Deep infections require surgical debridement and prolonged antibiotic therapy. Untreated infections can lead to septic arthritis with a poor prognosis. Stiffness This often occurs following prolonged immobilization. If the patient is amenable to early motion, initiate physical therapy once the soft tissues have stabilized. Patellar mobilizing exercises are mandatory to allow better tracking of the patella. If arthrofibrosis ensues, additional procedures, such as manipulation under anesthesia or arthroscopy, may be required. Hardware prominence This is best avoided by careful intraoperative techniques. Wire ends should be within soft tissue and not immediately subcutaneous. Up to 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, ensuring that K-wires and cerclage wires are shortened as much as possible is important. Loss of fixation/loss of reduction This can occur in up to 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. OUTCOME AND PROGNOSISSection 9 of 12
Prognosis depends primarily on the quality of articular restoration. Any intra-articular incongruities lead to posttraumatic arthritis. A certain component of 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. If arthrofibrosis develops, it may require manipulation with the patient under anesthesia or arthroscopic release of adhesions. FUTURE AND CONTROVERSIESSection 10 of 12
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. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Article Last Updated: Mar 16, 2006 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
