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The Journal of Bone and Joint Surgery (American). 2007;89:2285-2296. doi:10.2106/JBJS.G.00132 © 2007 The Journal of Bone and Joint Surgery, Inc.
Periprosthetic Patellar Fractures
1 Department of Orthopaedic Surgery, Hospital of the University of Pennsylvania,
3400 Spruce Street, Philadelphia, PA 19104
Investigation performed at Pennsylvania Hospital, Philadelphia,
Pennsylvania
The patella is the largest sesamoid bone in the skeleton. Located within an expansion of the quadriceps tendon, the patella allows an increased functional lever arm of the quadriceps and enhances the mechanical advantage of the extensor mechanism of the knee. In addition, it provides an articulating surface with a low coefficient of friction, protects the native and prosthetic knee from trauma, protects the quadriceps tendon and extensor mechanism from frictional irritation, and affects the cosmetic appearance of the knee1. Because of its biomechanical importance, any problems involving the patella or the patellar component of a total knee prosthesis can have a substantial effect on overall knee function. In fact, patellar complications following total knee arthroplasty have been a well-documented source of discomfort and disability2-6. Although infrequent, periprosthetic fractures of the patella remain a challenge for even the most experienced joint reconstruction surgeons. This is largely due to the discouraging results that are common following the treatment of all but nondisplaced patellar fractures. Even with meticulous anatomic fracture reduction, healing, and reconstitution of the extensor mechanism, return to prefracture function is rare7. Most studies on periprosthetic patellar fractures have involved a small number of patients, have lacked discrimination between intraoperative and postoperative fractures and between those associated with revisions and those associated with primary total knee arthroplasties, have not been consistent with regard to follow-up assessment measures, have failed to identify the pretreatment integrity of the patellar bone, and have involved use of disparate treatment techniques. This list of confounders is further confused by a lack of a standardized classification system for these fractures, a standardized rating system for assessing knee function and predicting prognosis following treatment, and a reliable management strategy. In this article, we discuss periprosthetic patellar fractures after total knee arthroplasty, review the classification systems, and put into perspective the treatment algorithms that will potentially optimize the outcome of management of this complication.
Periprosthetic patellar fractures may be the most common fractures complicating total knee arthroplasty7. The reported prevalence ranges from as low as 0.11% to as high as 21.4%8,9. According to epidemiological data in the Mayo Clinic Joint Registry, a periprosthetic patellar fracture occurred in association with 0.68% of 12,000 primary total knee arthroplasties over a thirteen-year period10. As a result of the variability in the prevalence of this fracture, values reported in the literature should be used only as a guideline to estimate the prevalence of periprosthetic patellar fractures (Table I).
In published series of patellar fractures, there is considerable variability with regard to implant type, treatment of the posterior cruciate ligament, prevalence of lateral releases performed, use of cement, inclusion of revisions, and prevalence and method of patellar resurfacing, all of which can independently affect the fracture prevalence and pattern. Periprosthetic patellar fractures are more likely to occur postoperatively than intraoperatively, and they are more frequent after revision total knee arthroplasties7,8,11. Berry11 reported that the rate of postoperative patellar fracture after revision total knee arthroplasty (1.8%) was more than double that after primary total knee arthroplasty (0.7%) and was nine times higher than the rate of intraoperative fracture during revision total knee arthroplasty (0.2%) (Table II)11.
Periprosthetic patellar fractures are typically diagnosed on the basis of a combination of the history, physical examination, and plain radiographs. While there may be a history of trauma, there is often no episode preceding the pain. Patients may report anterior knee pain, especially with certain activities such as ascending or descending stairs. Patients may not show the signs or symptoms typically seen with acute traumatic patellar fractures in the native knee and they may have no symptoms at all (Fig. 1). Bourne12 reported that, in his series, three of four patients with a vertical, laterally based periprosthetic fracture without disruption of the extensor mechanism were asymptomatic. A majority of these fractures are discovered incidentally on radiographs during a routine postoperative follow-up examination. More than 80% of patients with a periprosthetic patellar fracture seen by Tria et al.3 (nine knees) and Insall et al.13 (eight knees) were asymptomatic and were diagnosed on the basis of routine follow-up radiographs. In a series of eighty-five periprosthetic patellar fractures, 44% caused either minimal or no symptoms at the time of diagnosis10.
When patients are symptomatic, the classic clinical manifestation is anterior knee pain with patellar tenderness on direct palpation. There may be an effusion as well as extensor weakness, instability, or difficulty ascending or descending stairs, with a fear of falling14. With this scenario, it is necessary to evaluate the knee with formal anteroposterior, lateral, and skyline radiographs (Figs. 2-A and 2-B). Although most fractures are diagnosed with use of radiographs, a technetium-99m bone scan may be employed to determine whether a fracture is old or new or to diagnose occult fractures. Old asymptomatic fractures do not require treatment; however, it is important to realize that bone scans may be positive for up to two years following a periprosthetic patellar fracture14.
Classification systems in orthopaedic surgery allow effective communication between clinicians, help them to make management decisions, provide insight regarding projected outcomes, and assist in the advancement of clinical research. Ultimately, a universal system for categorizing injuries must focus on the variables that influence treatment strategy. Important components affecting the management of periprosthetic patellar fractures include the degree of fracture fragment displacement, the stability of the fixation of the patellar prosthesis, the location and pattern of the fracture, the integrity of the extensor mechanism, and the quality and vascularity of the remaining bone stock. Presently, there is no universally accepted validated classification system that can provide functional outcome measures or be used as an adjunct to clinical treatment algorithms. Several classification systems, involving use of disparate radiographic and clinical variables, have been utilized in an attempt to determine the appropriate treatment and predict prognosis7,10,15,16.
Several predisposing factors may increase the risk of a periprosthetic patellar fracture occurring during or after a total knee arthroplasty. It is important to classify these factors on a temporal basis (intraoperative or postoperative) in the setting of primary or revision total knee arthroplasty. The risk of a patellar fracture in association with a total knee arthroplasty is lower intraoperatively than it is in the postoperative period. Predisposing intraoperative factors include overzealous clamping of the patella during the resurfacing, overreaming of the patella, slippage of the reamer, aggressive bone resection with <10 to 15 mm of patellar bone stock left remaining, thermal injury and bone necrosis due to polymethylmethacrylate cement, and revision of the patellar component, particularly in a patient with poor bone stock (Figs. 2-A and 2-B)7,8,12,17,18.
Trauma
Anatomic Factors
Technical Factors Several authors have evaluated devascularization of the patella during the index procedure as a possible etiology of patellar fractures after total knee arthroplasty, although a clear link has not been absolutely established. The vascular supply to the patella may be disrupted secondary to lateral retinacular release for the treatment of patellar maltracking, resection of the infrapatellar fat pad22, and the standard median parapatellar arthrotomy.
Sacrifice of a branch of the superior lateral geniculate artery during lateral release has been reported to be a risk factor for patellar osteonecrosis and subsequent patellar fracture following total knee arthroplasty. Scuderi et al.23 reported a lack of isotope uptake in nine of sixteen knees in which a lateral release had been performed at the time of a primary total knee arthroplasty compared with only three of twenty knees treated without a lateral release. While this finding demonstrated a correlation between lateral release and loss of the blood supply to the patella, it was clinically unimportant, with only one patellar fracture occurring in that series. Tria et al.3 reported eighteen patellar fractures after 504 primary total knee arthroplasties. All patients with a patellar fracture had undergone a lateral release at the time of the index procedure, again raising the question of whether lateral release was associated with patellar avascularity. This concept has been supported by clinical1,16 and histological6 findings, with demonstration of osteonecrosis of the patella following lateral release. However, Ritter and Campbell24 were unable to find a connection between lateral retinacular release and osteonecrosis or patellar fracture. In a review of 555 primary total knee arthroplasties, they found that a lateral release had not been performed in seventeen of eighteen that were associated with a patellar fracture.
Osteolysis and loosening of the patellar component place the patella at risk for fracture because of poor bone quality. Both increased osseous resection and disruption of the anterior cortex during patellar preparation can compromise the remaining bone stock. Inadequate osseous resection, overstuffing of the anterior compartment (as a result of an under-resected patella or an anteriorized femoral component), and patellar maltracking can also increase the risk of a postoperative patellar fracture as a result of transfer of higher contact stresses to the patella. Femoral and tibial component malalignment, either rotational or angular, can promote abnormal loading of the patellofemoral compartment, resulting in subluxation, dislocation, or fracture of the patella21.
Patient Factors Rheumatoid arthritis may be an independent risk factor for periprosthetic patellar fractures, particularly in the presence of a very thin and eroded patella. It may be best to avoid resurfacing in these cases7. However, Grace and Sim8 found no significant difference in the fracture prevalence between knees with osteoarthritis (12%, six of fifty) and those with rheumatoid arthritis (18%, six of thirty-three). This was confirmed in another study that showed no significant difference between the two groups, with a patellar fracture occurring in six of seven and nine of eleven knees, respectively1. Nevertheless, resurfacing should be avoided in cases in which severe patellar erosion has left <10 mm of patellar bone19. It is arguable whether gender is an independent risk factor for patellar fracture. Seventy-three (62%) of 117 patellar fractures seen in association with nearly 17,000 primary total knee arthroplasties listed in the Mayo Clinic Joint Registry were in men11. It has been speculated that male gender is associated with higher activity levels and greater body weight, leading to increased extensor mechanism force and patellofemoral stresses25. However, other authors have reported a predominance of patellar fractures in women, attributing this phenomenon to the higher overall prevalence of osteoporosis in women1,15,26.
Implant Design Issues
Periprosthetic fractures are more likely after revision total knee arthroplasty, which may be considered an independent risk factor for patellar fracture7. Engh and Ammeen14 found that removal of a stable patellar component from osteoporotic bone can lead to intraoperative patellar fracture during revision surgery. This is particularly true during the revision of a well-fixed metal-backed patellar component when stress-shielding has resulted in osteoporosis and diminished bone stock. Again, it is advisable not to resurface the patella during revision surgery when the residual patellar thickness is <10 mm; this is found in approximately 30% to 40% of knees undergoing revision total knee arthroplasty19. Berry11 found that men had an increased rate of patellar fracture following revision total knee arthroplasty. Of fifty-three fractures seen in association with more than 2900 revision total knee arthroplasties, thirty (57%) were in men. In a separate study, Berry and Rand found that patellar fracture was one of the most common complications following isolated revision of the patellar component in forty-two knees2. There were five late patellar fractures, four of which were in patients who had had a lateral retinacular release during either a primary total knee arthroplasty or a revision of the patellar component. Because of the risk of patellar fracture, all-polyethylene patellar components should not be revised unless they are loose, substantially worn, or malpositioned20. Stress-shielding from a metal-backed patellar component or osteolysis from metallosis can predispose a patella to fracture at the time of implant removal, and patients should be informed about this risk.
The location and pattern of the fracture, the integrity of the extensor mechanism, the stability of the patellar component, and the quality of the remaining bone stock are considered when determining the appropriate treatment of a periprosthetic patellar fracture. Treatment options include nonoperative management; open reduction and internal fixation, occasionally in combination with partial or total patellectomy; revision total knee arthroplasty with replacement of all three components; or isolated revision of the patellar component. Complete reconstruction of the extensor mechanism with an allograft may be needed when the fracture and the extensor mechanism are irreparable. An asymptomatic, nondisplaced patellar fracture that is not associated with an extensor lag and is associated with an intact patellar component may require no specific treatment other than observation or immobilization in a cast or brace1,10,12,14,26. A symptomatic, nondisplaced transverse fracture that is associated with an intact patellar component and an intact extensor mechanism can be treated in a cylinder cast or a knee brace locked in extension for six weeks, and weight-bearing can be allowed immediately (Figs. 4-A, 4-B, and 4-C). Vertical patellar fractures are associated with lower rates of disruption of the extensor mechanism and thus can be treated with cast immobilization if they are symptomatic. A displaced transverse fracture through the middle third of the patella should be repaired, but tension band wiring may be difficult to achieve in the presence of a patellar component (Figs. 5-A,5-B,5-C,5-D)12,14. If the component is loose, it should be removed to facilitate stabilization of the fracture and repair of the extensor mechanism. A cylinder cast can be worn for eight to twelve weeks, until there is radiographic and clinical evidence of fracture-healing.
The treatment for a fracture of the superior or inferior pole of the patella is similar to that for a quadriceps tendon or patellar tendon disruption, respectively. The clinical outcome of a stable repair of the extensor mechanism with use of a locking stitch, with or without partial patellectomy, is more predictable than that after use of pins, wires, or screws. Sutures are routed through vertically oriented drill holes in the patella and are secured over a bone bridge over the proximal or distal edges of the patella; a tension band technique may be used to further protect an avulsion fracture of the inferior pole by routing the wire through the tibial tubercle14. If the knee cannot be passively flexed to 75° without disrupting or putting undue tension on the surgical repair, then consideration should be given to augmentation of the extensor mechanism with a semitendinosus or iliotibial band tendon autograft, allograft, or xenograft14. Reconstruction of the extensor mechanism with an allograft is an alternative that has been used to treat disruption of the extensor mechanism following total knee arthroplasty. The indications for this treatment modality have been extrapolated to include a periprosthetic patellar fracture associated with disruption of the extensor mechanism. Burnett et al.28 compared two separate techniques of allograft reconstruction of the extensor mechanism in patients followed for a minimum of two years. Thirteen patients in whom the allograft had been tightly tensioned in full extension exhibited an average postoperative extensor lag of 4.3° (range, 0° to 15°) with an average Hospital for Special Surgery knee score29 of 88 points. This group was compared with a second group of seven patients in whom the allograft had been minimally tensioned; all of those patients had a clinical failure, with an average postoperative extensor lag of 59° (range, 40° to 80°) and an average Hospital for Special Surgery knee score of 52 points. The difference between the two groups was significant (p < 0.0001). Neither group had a loss of postoperative knee flexion, which was 104° and 108°, respectively (p < 0.549). Although this study included a small number of patients, allograft reconstruction of the extensor mechanism with tensioning of the graft to treat a potentially catastrophic complication following total knee arthroplasty yielded favorable clinical results. Loose components should be removed routinely; stable components should be removed only if removal is necessary to achieve adequate fracture stabilization. A patellar implant should not be used to resurface a patella that has undergone previous operative fixation of a fracture because the implant may weaken the repair and impart greater stress on the extensor mechanism; this may increase the risk of nonunion or refracture. Hemispherical trabecular metal patellar components (Zimmer, Warsaw, Indiana) have been used for primary fracture fixation during patellar component revision with some success, but further study is necessary30. Windsor et al.27 classified periprosthetic patellar fractures as vertical, transverse, or comminuted, with subdivision into nondisplaced and displaced types. In the majority of vertical fractures, cemented patellar buttons remain well fixed to one of the two minimally displaced fracture fragments. On the basis of this finding, vertical and comminuted fractures, regardless of displacement, and transverse fractures that are displaced <2 cm can be treated with six weeks of immobilization in a cylinder cast or a brace locked in extension. According to current protocols, nonoperative treatment is not acceptable for fractures with 2 cm of displacement unless there is no compromise of the extensor strength or the range of motion1. When a fracture is associated with disruption of the extensor mechanism and an extensor lag as seen on clinical examination, open reduction and internal fixation should be considered, with the methods varying according to the location of the fracture. Fixation with metal cerclage wire with retinacular repair can be employed when the patellar component precludes adequate exposure of the fracture site; this treatment should be followed by cast or brace immobilization. Specific details of the operative repair depend on the quality of the bone stock, the location and pattern of the fracture, and the stability of the patellar component. When the patellar component is loose, removal without replacement is often necessary since the remaining bone stock is usually inadequate to accommodate a new implant. Removing the component and leaving an osseous shell (patelloplasty) may predispose the patient to the development of residual anterior knee discomfort and crepitus, and patients should be advised about this possibility. Severely comminuted patellar fractures with substantial displacement and an extensor lag may require a partial patellectomy with repair of the disrupted retinaculum and removal of the patellar component. Alternatively, an allograft reconstruction of the extensor mechanism may be necessary (Figs. 5-A,5-B,5-C,5-D). Brick and Scott1 recommended surgical intervention for periprosthetic patellar fractures with displacement in excess of 2 cm, an extensor lag, and loosening or displacement of the patellar implant. Open reduction and internal fixation should not be repeated after an initial attempt fails. Partial patellectomy, with repair of the quadriceps tendon or patellar tendon, should be considered when there are small displaced proximal or distal fragments. Total patellectomy should be considered a salvage option for severely comminuted fractures and failed fixation.
Ortiguera and Berry10 recommended a treatment algorithm for periprosthetic patellar fractures based on a useful contemporary classification (Table IV). Type-I fractures (implant and extensor mechanism intact) are treated nonoperatively. Type-II fractures (implant intact and extensor mechanism disrupted) require repair of the extensor mechanism with partial patellectomy or open reduction and internal fixation of the fracture. Type-III fractures (implant loose) are subdivided into Types IIIa (good remaining patellar bone stock) and IIIb (poor remaining patellar bone stock). If the patient is sufficiently symptomatic, operative intervention should be considered, with patelloplasty being an option. Type-IIIa fractures may be treated with component revision or component resection arthroplasty, and Type-IIIb fractures can be treated with implant removal and patelloplasty or total patellectomy.
Tria et al.3 reported their experience with eighteen patients who had a total of ten nondisplaced and eight displaced patellar fractures. Nine of the ten nondisplaced fractures were treated nonoperatively with analgesics and some decrease in physical activity, but no immobilization. The tenth nondisplaced fracture required excision of the fracture fragments because of nonunion after conservative treatment. Of the eight displaced fractures, four were associated with an intact extensor mechanism and patellar component, with minimal symptoms, and were treated nonoperatively with decreased activity and no immobilization. Three of the remaining four displaced fractures were associated with disruption of the extensor mechanism. Two patients underwent implant removal, and one had a patellectomy. The fourth patient refused surgery. The average recovery of flexion was 110° (range, 90° to 125°) compared with 112° on the contralateral side. No other outcomes were reported in that series.
Grace and Sim8 reported on twelve periprosthetic patellar fractures. Four of the twelve fractures were minimally displaced (<5 mm), had little to no comminution, and were associated with an intact patellar button. These four were all treated nonoperatively with either a long leg knee immobilizer or a cylinder cast for six weeks, and three of the four patients had a satisfactory result. The remaining eight fractures (in seven patients) were displaced (>5 mm) and had excessive comminution or a loose patellar button. All of these fractures were managed operatively; a total patellectomy was done in four; a partial patellectomy, in two; tension band wiring, in one; and circumferential wiring, in one. Five of seven patients had a satisfactory result according to The Hospital for Special Surgery knee rating scale29. The average postoperative flexion arc was 87°. In eleven of the entire group of twelve cases, there was less than a 5° difference in the extensor lag when compared with the prefracture state. The authors reported complications in five of the twelve cases, including ipsilateral quadriceps rupture, secondary fatigue fracture, a wound infection, fibrous nonunion, and synovial cyst formation. Hozack et al.26 reported on twenty-one fractures and concluded that nonoperative treatment of nondisplaced fractures yielded satisfactory results whereas patellectomy produced good but not excellent results, with decreased quadriceps strength in three of four cases. The result was poor for four of six displaced fractures treated with patellectomy, two of the four treated with fragment excision, and both of the fractures treated with internal fixation. Quadriceps strength was preserved with nonoperative treatment of nondisplaced fractures, but it decreased when patellectomy was done for persistent instability and pain. Goldberg et al.15 reported on thirty-six fractures. Fourteen that were classified as Type I (a marginal fracture with an intact extensor mechanism and implant-bone interface) and two that were classified as Type IIIb (a fracture of the inferior pole of the patella without rupture of the patellar tendon) were treated nonoperatively with knee immobilization and partial weight-bearing with crutches, followed by a rehabilitation program with active range-of-motion and quadriceps-strengthening exercises. In all sixteen cases, the result was good or excellent according to the University Hospitals of Cleveland quantitative functional knee score31, with an average arc of motion of 100°. There were six Type-II fractures (disruption of the extensor mechanism or implant-bone interface), and all were treated operatively. Of eight Type-IIIa fractures, seven underwent repair of a ruptured patellar tendon associated with superior patellar migration; one patient refused surgery and had a poor result. There were six Type-IV fracture-dislocations, and all were treated operatively. In the total series of thirty-six cases, twenty-two had an overall good or excellent result (average arc of motion, 100°) and fourteen (four treated nonoperatively and ten treated operatively) had a fair or poor result, with an average arc of motion of 80° and an extensor lag of >10°. On the basis of this study, Goldberg et al. concluded that patients with a fracture that is not associated with a dislocation of the patella, loosening of the implant, or complete disruption of the extensor mechanism usually will recover function with nonoperative management. Brick and Scott1 reported that all six of their patients who had a nondisplaced fracture treated with immobilization for six weeks had a satisfactory result. However, eleven of fifteen displaced fractures treated with internal fixation failed to heal. They concluded that nonoperative treatment may be successful for 50% to 80% of periprosthetic fractures of the patella, depending on the variables discussed earlier. In a study of seventy-eight fractures by Ortiguera and Berry10, thirty-eight were Type I and thirty-seven of those were treated with observation, a brace, or a cast. In this group, 82% (thirty-one) of the cases remained asymptomatic, one patient required excision of a symptomatic nonunion, arthrofibrosis developed in one, and the patellar implant eventually loosened in one. One Type-I fracture was initially treated operatively. Eleven of twelve Type-II fractures were treated with repair of the extensor mechanism and partial patellectomy or open reduction and internal fixation. One was treated with a brace, and the patient was still asymptomatic at the five-year follow-up evaluation, despite a 5° extension lag. The result was a failure for five of the six fractures managed with open reduction and internal fixation and repair of the extensor mechanism. The results were not specified for the five fractures that were treated with partial patellectomy and repair of the extensor mechanism. There was a 50% complication rate in association with the management of Type-II fractures, with a revision required in five of the eleven cases. Seven of the twelve knees with a Type-II fracture had instability, pain, or weakness at the time of the last follow-up. There were twenty-eight Type-III fractures (associated with loosening of the patellar implant), which were treated operatively if the patient was symptomatic. The type of operation selected was based on the quality of the remaining bone stock. Of the twelve Type-IIIa fractures (implant loose, with good remaining bone stock), four were treated with observation; five, with open reduction and internal fixation (with resection of the patellar component); two, with component resection and patelloplasty; and one, with patellar component revision. Six Type-IIIb fractures (implant loose, poor remaining bone stock) underwent partial or complete patellectomy, five were treated with component resection and patelloplasty, and one was treated with patellar component revision. There were eight complications following treatment of Type-III fractures, including failure of fixation, an extensor lag in excess of 15°, nonunion, infection, instability, and arthrofibrosis. Three knees required a revision operation. Keating et al.32 reviewed the results following 177 fractures and found that operative treatment was generally associated with a high complication rate and nonoperative treatment generally led to good results. However, these results were confounded by the severity of the fracture, the integrity of the extensor mechanism, and the quality of the residual patellar bone. Of twenty-two Type-1 fractures (all vertical fractures and fractures associated with an intact extensor mechanism and a stable implant) and twenty-two Type-2A fractures (horizontal fractures with separation of the fracture fragments of <1 cm associated with disruption of the extensor mechanism and a stable or unstable implant), all but two were treated nonoperatively, with good results. According to the Knee Society Scoring system33, the patients with a Type-1 or 2A fracture had, on the average, pain scores of 44 and 49 points, knee scores of 85 and 92 points, and 120° and 117° of flexion, respectively, and no extensor lag. One patient in each group underwent excision of an extruded patellar button, and a deep infection developed in one of them. Fourteen of seventeen Type-2B fractures (those with separation of the fracture fragments of >1 cm) were treated nonoperatively. A residual extensor lag was present in three of those cases. Operative treatment was performed for three of the Type-2B fractures. Two were treated with open reduction and internal fixation, and there was postoperative nonunion despite good clinical results. In the final group of 114 Type-3 fractures (an intact extensor mechanism and an unstable implant), only six were treated operatively. Two of the patients had a subsequent deep wound infection, and one had secondary component loosening six months postoperatively. The remainder of the Type-3 fractures were treated nonoperatively, and at the time of follow-up the average pain score was 43 points, the average knee score was 83 points, and the average range of knee flexion was 116°. Laskin34 reported his experience with the management of patellar fractures in the setting of revision total knee arthroplasty. Because a majority of fractures occur in an avascular patella, attempting repair is often futile. As a result, Laskin recommended removal of the implant and performance of a patelloplasty. During this procedure, all small fragments of bone are removed except for the small fragment adjacent to the patellar tendon. The remaining patellar bone stock is thinned to a wafer, and the retinaculum is then repaired. At the two-year follow-up evaluations after twelve patelloplasties that had been done at the time of revision total knee arthroplasties, two of ten patients complained of anterior knee pain, only one patient could ascend and descend stairs, the average extensor lag was 10°, and the average range of knee flexion was 120°.
Nonoperative treatment, usually with an initial period of immobilization, of a minimally displaced fracture associated with an intact patellar component and extensor mechanism can often produce satisfactory results with low morbidity. In an overwhelming number of cases, operative treatment of periprosthetic patellar fractures yields relatively poor results. Suboptimal outcomes with high complication rates have typically been reported in the literature, and little improvement in functional outcomes has been demonstrated even with newer operative techniques. Operative intervention is still required to treat some fractures that are associated with loosening of the patellar component, considerable fracture displacement, and disruption of the extensor mechanism. Specifically, Type-II fractures require repair of the extensor mechanism with treatment of the fracture by patellectomy or open reduction and internal fixation. Type-III fractures necessitate surgical intervention with revision of the patellar component, resection of the component, patelloplasty, or total patellectomy. In addition, early or late allograft reconstruction of the extensor mechanism should be considered. All patients should be advised about the risk of failure of surgical reconstruction of periprosthetic patellar fractures. Avascularity of the patella may also affect treatment. Newer strategies for fracture fixation, such as the use of trabecular metal implants that allow simultaneous fracture fixation and resurfacing and the use of bone graft in conjunction with bone morphogenetic proteins, may help to redefine operative management of these challenging fractures.
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Introduction
Epidemiology
Periprosthetic
patellar fractures may be the most common fractures complicating total knee
arthroplasty. 
