Management of periprosthetic patellar fractures A systematic review of literature

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1 Injury, Int. J. Care Injured (2007) 38, Management of periprosthetic patellar fractures A systematic review of literature Byron E. Chalidis a, Eleftherios Tsiridis a, Adamantios A. Tragas a, Zois Stavrou b, Peter V. Giannoudis a, * a Academic Department of Trauma & Orthopaedics, School of Medicine, University of Leeds, LGI University Hospital, Clarendon Wing, Great George St, Leeds LS1 3EX, UK b Evagelismos Hopsital, Athens, Greece Accepted 27 February 2007 KEYWORDS Periprosthetic fractures; Patellar resurfacing; Lateral release; Malalignment; Infection; Non-union Summary Despite advances in surgical technique and implant design, complications involving the extensor mechanism and patellofemoral joint after total knee arthroplasty (TKA) continue to be the most common cause of pain and the most commonly cited reason for revision surgery. Periprosthetic patellar fractures occur in 1.19% of all reported cases after TKA, with a clear correlation with resurfacing of the patella. In 88.32% of the cases reported the fracture is not associated with a traumatic event and it is identified at the follow-up examination during the first 2 years after knee replacement. Predisposing factors for fracture include lateral release, excessive bone removal, peg fixation and cementation, improper patellar tracking and prosthesis malpositioning. More than 50% of fractures are associated with a loose implant which complicates the fracture management. Non-operative treatment seems to offer acceptable functional results and pain relief, especially in cases of minimal displacement and stable implant fixation. However, when surgical reconstruction is undertaken, open reduction and internal fixation with tension band or cerclage wiring should not be the first choice of treatment as the rate of failure and subsequent nonunion may be as high as 90%. # 2007 Elsevier Ltd. All rights reserved. Introduction Since its advent in the late 1960s, total knee arthroplasty (TKA) has proven to be an effective * Corresponding author. Tel.: ; fax: address: pgiannoudi@aol.com (P.V. Giannoudis). treatment for knee osteoarthritis, providing adequate relief of pain, improvement of joint flexibility and increase in limb mobility. Although the experience with arthroplasty has become further refined, various complications including infection, thrombophlebitis, component loosening, malalignment, periprosthetic fractures, patellofemoral pain and extensor mechanism /$ see front matter # 2007 Elsevier Ltd. All rights reserved. doi: /j.injury

2 Management of periprosthetic patellar fractures 715 dysfunction may significantly compromise the final outcome. 15 Patellofemoral complications constitute a major source of failure after TKA, causing varying degrees of pain and disability. 22 Fracture, excessive wear or loosening of the patellar component, subluxation and radiolucency 36 occur in approximately 1.5% to over 24% 5 7,12,13,17,27,32 of knee replacements and are responsible for as much as 90% of revision surgery procedures. 3,17,18,38 Patellar fracture is the second most frequent periprosthetic fracture of the knee joint after the femur 2 and may occur in both unresurfaced 7,15 and resurfaced 2,3,7,9 13,15,19 24,26,29,30,34 36,40,43 cases. Multiple aetiological factors such as limb or prosthesis malalignment, lateral release, patellar component design and excessive resection of bone have been implicated in the pathogenesis of fracture. 7,8,12,13,19,29,34 The factors which guide treatment management are the location and displacement of the fracture, the integrity of the extensor mechanism, the stability of implant fixation and the remaining bone stock quality. 16 Treatment options range from non-operative methods to open reduction and internal fixation, component resection and partial or complete patellectomy. 29 Determining optimal treatment can be complex, and fracture management may be quite difficult. 4,29 Surgical intervention is usually reserved for patellar maltracking, disturbance of extensor function and loosening of the patellar component. 42 However, infection, non-union and failure of metalwork may complicate the operative treatment, leading to modest or poor results. 29,30 In the present study, the published trials referring to periprosthetic patellar fractures were examined and specific outcomes of interest were addressed and further evaluated. Materials and methods There are several studies in the available literature which address periprosthetic patellar fracture after total knee replacement. 2,3,7,9 13,15,19 24,26,29,30,34 36,40,43 The majority of these reports had relatively small sample sizes and were probably underpowered to determine the optimal fracture management. 29 No prospective randomised studies exist comparing treatment methods. In this review we have analysed the available clinical studies of periprosthetic patellar fractures according to a specific methodological procedure in order to record the incidence rate, the available epidemiological data and the most important factors involved in the pathogenesis and treatment of these fractures. Research methodology We searched for articles in the English literature with no time limitation using the Pubmed and Cochrane search engines. The key words used were: patella fracture, total knee replacement, periprosthetic fractures, failure of patellar component and extensor mechanism dysfunction. All the search results were analysed and the reference lists of retrieved articles were also screened for available information. Because of the limited number of the published papers we did not set restrictions on the quality of data or the duration of follow-up. However, we excluded all the case report studies or trials with less than five patients. Data extraction For each report, information was gathered on characteristics of the trial and study population. Furthermore, the type of fracture, potential predisposing factors, and the time between arthroplasty and fracture were also recorded. Finally, we extracted data related to methods of treatment, incidence of non-union, infection rate, range of knee motion and extensor lag. Statistical analysis The SPSS program 12.0 (SPSS Inc., Chicago, IL, USA) was used for the statistical analysis of the data. A weight case estimation was used for the analysis of values. For example, the mean incidence of fracture was weighted according to the number of cases in each paper. The data were analysed using the chisquare test; p values less than 0.05 were considered to be statistically significant. Results Eligible studies demographic data Twenty-three studies were found. 2,3,7,9 13,15,19 24,26,29,30,34 36,40,43 Fourteen studies included less than 20 cases, 3,7,9 11,15,19,21,23,26,30,34,40,43 7 studies included between 20 and 100 cases 12,13,20,24,29,35,36 and 2 trials included 177 and 178 cases, respectively. 2,22 In total, there were 752 periprosthetic patellar fractures in 693 patients for further analysis. The mean age was 69.5 years with a range of years.

3 716 B.E. Chalidis et al. Table 1 Author Demographic data No. of fractures No. of patients Female Incidence Follow-up (mean, months, range) Scott et al (83.3%) 1.6% Ritter et al * N/A 1.7% N/A Ritter et al * N/A 3.4% (12 84) Ritter and Campbell N/A 3.2% N/A Parvizi et al (33.3%) N/A 21.6 Ortiguera and Berry (33.8%) 0.68% 43.2 (24 120) Keating et al N/A 3.8% 60 Healy et al N/A 2.4% 37 (24 108) Hozack et al (72.2%) N/A 15.3 (2 79) Insall et al * N/A 11% Goldberg et al (80%) N/A 54 (30 108) Grace and Sim (72.7%) 0.15% 28 (2.5 64) Clayton and Thirupathi N/A 5.4% N/A Figgie et al (80%) N/A 54 (30 108) Chang et al (37.5%) N/A 20 (2 78) Brick and Scott * 13 (86.6%) 0.5% N/A Berry and Rand N/A 12% 42 (24 96) Chun et al (66.7%) 1.14% 32 (3 57) Tria et al (66.7%) 3.6% Berry * 67 (39.4%) 0.9% N/A Le et al (66.7%) 1.4% 87.6 ( ) Lynch et al N/A 1.8% 42 (29 87) Larson et al N/A 3% 64.8 (24 120) N/A: not available. * No specific reference in text. Thirteen papers provided data on the gender of patients. 2,7,9,10,12,15,20,21,24,29,30,40,43 Out of a total of 441 patients there were 210 males (47.6%) and 231 females (52.4%). All the retrieved studies with the providing epidemiological data are shown in Table 1. According to the available articles, the incidence ranged between 0.15 and 12% in revision cases. 3,9,10,12,13,15,19 24,26,29,30,36,40,43 The mean incidence of periprosthetic patellar fracture after total knee replacement was 1.19% (median value = 0.9%) (Table 1). Classification Many classification systems have been suggested for periprosthetic patellar fractures after TKA. 13,20,29 The classification schemes took into account parameters such as fracture displacement or location and fixation status of the patellar component. The most commonly used classification system is based on both the stability of the patellar implant and the integrity of the extensor mechanism, and it provides a guide to the management (Table 2). 29 Data for this fracture classification were available from three studies reporting on 265 fractures. 22,29,30 The most frequent fracture type was Type III with 54.7% (145 fractures), then Type I and Type II with 25.3% (67 fractures) and 20% (53 fractures), respectively ( p < 0.001) (Table 3). Time from knee replacement, patellar resurfacing, trauma Twenty-two from the 23 trials provided some information as to whether or not the patella had been resurfaced or not during the knee arthroplasty. 3,7,9 13,15,19 24,26,29,30,34 36,40,43 Only 5 cases out of a total Table 2 Type Type I Type II Type III a b Ortiguera and Berry classification of periprosthetic fractures of the patella Features Intact extensor mechanism and stable implant Disruption of extensor mechanism with or without implant in place Intact extensor mechanism and loosening of patellar component Reasonable remaining bone stock Poor bone stock

4 Management of periprosthetic patellar fractures 717 Table 3 Number of fractures according to Ortiguera and Berry classification Author Type I Type II Type III Total Parvizi et al Ortiguera and a Berry 29 Keating et al b Total of 582 (0.9%) fractures occurred in a non resurfaced patella, whereas in the remaining 577 cases (99.1%) a polyethylene or metal-backed patella prosthesis had been implanted ( p < 0.001) (Table 4). Relevant details on the mechanism of fracture were reported in 16 studies. 7,10,12,13,15,20 22,24,29,30,34 36,40,43 Out of a total of 539 fractures, in only 63 cases (11.68%) was a predisposing traumatic event directly associated with the fracture. In the remaining 476 fractures (88.32%) there was no reported injury and the diagnosis was made retrospectively as part of the routine follow-up examination ( p < 0.001) (Table 4). According to the data from 17 studies, 7,9 13,15,19,20,23,29,30,34 36,40,43 the mean period of time between knee arthroplasty and fracture was 18.5 months. Although fractures may be reported up to 12 years after total knee replacement, most fractures occurred during the first or second year after the resurfacing of the patella (Table 4). Lateral release. a 78 from 85 followed-up fractures. b 175 from the total of 177 fractures. The effect of lateral retinacular release in the occurrence of periprosthetic patella fractures was addressed in 16 studies (Table 5). 3,7,11 13,15,19,20,22,24,29,34 36,40,43 A total incidence of Table 4 Data related to trauma, patellar resurfacing and time from total knee arthroplasty (TKA) Author Traumatic event Resurfaced patella Time from TKA Scott et al. 40 No Yes Range 3 37 months (average 13 months) Ritter et al. 35 No Yes Range 6 12 months Ritter et al. 36 No Yes Range 6 12 months Ritter and Campbell 34 No Yes Average 1 year Parvizi et al out of 12 Yes Range years (average 3.5 years) Ortiguera and Berry out of 78 (38%) Yes Range 1 6 years Keating et al. 22 No Yes N/A Healy et al. 19 N/A Yes Average 10 months Hozack et al out of 21 Yes Range 0 41 months (average 9.8 months) Insall et al. 21 No Yes N/A Goldberg et al. 13 No Yes 80% at 2 years Grace and Sim 15 5 out of 12 9 out of 12 Range 9 36 months (average 19.3 months) a ; range 1 74 months (average 20.1 months) a Clayton et al. 11 No data Yes Average 1.4 years Figgie et al. 12 No Yes 80% at 2 years Chang et al. 9 No data Yes Range 4 88 months (average 21 months) Brick and Scott 7 8 out of 15 b 13 out of 15 Range 0 48 months (average 8.6 months) Berry and Rand 3 No data Yes N/A Chun et al out of 17 Yes Range 1 72 months (17.5 months) 65% during first year Tria et al out of 18 Yes Range 3 22 months (average 11 months) Le et al. 24 No Yes N/A Lynch et al. 26 No data Yes N/A Larson et al. 23 No data Yes 1 5 years (average 2.5 years) a Group I: after lateral release, Group II: without release. b 2 cases after manipulation.

5 718 B.E. Chalidis et al. Table 5 Correlation between lateral release and periprosthetic patellar fractures Author No. of fractures Lateral release cases Incidence (%) Scott et al Ritter et al Ritter et al Ritter and Campbell Ortiguera and Berry Keating et al Healy et al Hozack et al Goldberg et al Grace and Sim Clayton et al Figgie et al Brick and Scott Berry and Rand Tria et al Le et al % (268 out of 523 fractures) was found among all the available studies, and in some papers the rate was raised to %. 3,19,35,40,43 Methods of treatment We found 19 papers with data on the treatment of periprosthetic patellar fractures; 3,7,9 13,15,19 22,24,26,29,30,34,40, % (349 out of 507 fractures) of cases were treated non-operatively with observation or cast application. The remaining 31.17% (158 fractures) cases underwent operative treatment with a variety of techniques, including open reduction and internal fixation (ORIF), resection arthroplasty and patelloplasty, partial or total patellectomy according to fracture type (avulsion of distal or proximal pole, transverse, comminuted fractures) and the stability of the implant ( p < 0.001) (Table 6). Infection non-union The incidence of postoperative infection after surgical treatment of periprosthetic patellar fractures was clearly mentioned in eight studies (Table 7). 7,10,11,15,22,26,29,30 The mean infection rate was 19.2%. Table 6 Incidence of conservative and surgical treatment in the total of fractures Author Operative Conservative Total Scott et al Ritter and Campbell Parvizi et al Ortiguera and Berry Keating et al Healy et al Hozack et al Insall et al Goldberg et al Grace and Sim Clayton et al Figgie et al Chang et al Brick and Scott Berry and Rand Chun et al Tria et al Le et al Lynch et al Total

6 Management of periprosthetic patellar fractures 719 Table 7 Infection rate of operative treatment, nonunion of internal fixation and outcome according to knee motion Author Infection rate Nonunion rate Extension lag (8) Range of motion (ROM) Scott et al. 40 N/A 100% (1 out of 1) Range Parvizi et al % (1 out of 12) N/A 1 patients <58, 11 patients >108 1 patient: average 1108, 8 patients: range , Ortiguera and Berry % (2 out of 32) 90% (10 out of 11) 64 patients 08, 3 patients <108, 3 patients10 208, 1 patients >208 Keating et al % (4 out of 13) 100% (2 out of 2) 3 patients >208, 2 patients10 208, 172 patients <108 Hozack et al. 20 N/A 100% (2 out of 2) 14 patients 08, 4 patients10 208, 3 patients >208 Goldberg et al. 13 N/A N/A 14 patients >108, 22 patients <108 3 patients: range <808 Range Average 1208, 1178, 1168 in Types I, II, III Range patients: average patients: average 808 Grace and Sim % (1 out of 8) 50% (1 out of 2) All (12 patients) <108 Average 878 Clayton et al % (1 out of 5) No ORIF In 4 out of 6 patients. N/A Details N/A Figgie et al. 12 N/A N/A N/A 22 patients: average 1008, 14 patients: average 808 Chang et al. 9 No ORIF No ORIF All (8 patients) <108 Average 1048 Lynch et al N/A 14 patients <108, 1 patients >108 Chun et al % (1 out of 3) N/A N/A Brick and Scott % 1/1 N/A N/A 6 patients: average1008, 9 patients: N/A According to information from seven studies, the mean non-union rate after internal fixation with tension-band technique or cerclage wire was 92%, leading to poor results in the majority of cases (Table 7). 10,15,20,22,26,29,40 Outcome Extensor lag was reported in nine studies 7,9,13,15,20,22,29,30,40 and range of knee motion in ten studies. 7,9,12,13,15,20,22,29,30,40 There were divergent results on the mobility of the knee joint after conservative or operative treatment. In the majority of cases an extensor lag of no more than 108 and a limitation of flexion of approximately were described (Table 7). Discussion Fracture of the patella after total knee arthroplasty is an infrequent complication in both unresurfaced and resurfaced patellae, with a reported prevalence from 0.15 to 12% in revision cases. 3,9,10,12,13,15,19 22,24,26,29,30,36,40,43 According to our study the mean incidence rate is 1.19 and 99% of the total fracture cases had been resurfaced. Although many issues have been addressed in recent literature regarding the mechanism and pathogenesis of periprosthetic patellar fractures, the causes and management of patellar fractures after arthroplasty remain illdefined. 15 It seems that multiple aetiological factors may be responsible for patellar fractures after total knee arthroplasty (Table 8). Biomechanical, vascular, technical, thermal and traumatic causes 15 have been implicated in the pathogenesis of fracture, and questions about the ideal type of implant and the appropriate amount of bone resection are still under discussion. 29 Forces across the patellofemoral joint are strongly related to patellar height and length and, during certain activities, may exceed the forces generated across the tibiofemoral joint. Throughout normal level walking on even ground, the patellofemoral joint is subjected to forces from 1 to 1.5 times body weight. This may be increased to 3 4 times of body weight when going up or down stairs and may reach as high as 7 times body weight during squatting. 26 With increasing knee flexion, the patellofemoral contact point moves from distal to proximal on the patellar surface, with a concomitant proportional decrease in the patellar ligament/ quadriceps tendon stress ratio. 7 For that reason

7 720 B.E. Chalidis et al. Table 8 Factors associated with increased rate of periprosthetic patellar fracture Bone-patient factors Surgery-related factors Osteoporosis Limb malalignment Osteolysis Prosthesis malpositioning Bone loss Patellar maltracking High activity level Excessive bone resection Knee hyperflexion Lateral release Rheumatoid arthritis Unwarranted fat pad removal Revision surgery Cementless implants Central peg designed implant most patients became symptomatic on stairs or on rising from a chair. 25 The blood supply to the patella is via intraosseous and extraosseous vascular systems. 39,43 The extraosseous system includes a peripatellar ring that receives contributions from six sources: the supreme genicular, medial superior genicular, medial inferior genicular, lateral superior genicular, lateral inferior genicular and anterior recurrent arteries. The intraosseous system consists of midpatellar and polar vessels. This vascular network is at risk throughout knee arthroplasty and median parapatellar arthrotomy, fat pad removal and lateral release may contribute to patellar devascularisation. 26 As the medial genicular arteries are divided in a standard medial parapatellar incision, the extensor complex is reliant on the blood supply from the lateral genicular vessels. The lateral superior genicular artery may be damaged when a lateral retinacular release is performed, contributing to the poor supply to the quadriceps tendon proximally to the patella. 15,43 Furthermore, removal of the fat pad to increase exposure may damage the anastomosis between the inferior medial and lateral vessels, which lie posterior to the polar branches running toward the centre of the anterior surface of the patella. 26,39 Studies have demonstrated that a combination of lateral release and excessive fat pad removal may jeopardise the vascular net and polar vessels integrity. 11,15 Patellar hypovascularity and osteonecrosis are associated with an increased tendency to fracture, especially in the elderly and in patients who have long-standing rheumatoid arthritis. 11,43 In our study, 51.2% of fractures were associated with lateral retinacular release. It is generally recommended that lateral release must be performed at a distance from the patella to preserve the lateral vessels, most importantly the superior lateral genicular artery, and the fat pad should be retained if possible. 11,15 Technical factors such as excessive patellar bone resection, creation of a large central defect or violation of the anterior cortex may create a stress concentration effect and predispose the patella to fracture. Furthermore, the cytotoxic, lipolytic and thermal effects of polymethylmethacrylate have been suggested as being detrimental to bone integrity. The heat of polymerisation may exceed the coagulation temperature of the tissue proteins (about 67 8C). Although the heat of a large cement bolus can reach 100 8C, the temperature at a bonecement interface has been reported to be between 55 and 70 8C. 1,44 A thicker patella after surgery has been reported to cause loss of flexion and lateral subluxation of the patella, whereas a thinner patella after surgery is thought to cause patellar stress fracture and anteroposterior instability of the knee. 28 Ritter et al. 36 found that a difference in postoperative patellar thickness compared with preoperative patellar thickness had no statistical effect on patellar fractures, loosening of the patellar component, radiolucency at the bone-cement interface or postoperative flexion. However, the majority of authors agree that during the preparation of the patella, a minimal amount of articular surface must be removed and attempts should be made to preserve the peripheral cortex of both the medial and lateral facets. 11,15,40,45 Reuben et al. 33 found that a patellar thickness of less than 15 mm increased the strain in the anterior patellar region and the risk of fracture. Finally, Bourne 4 and Windsor et al. 45 pointed out that resurfacing of a patella less than 10 to 15 mm thick and overreaming were significant predisposing factors for periprosthetic fracture. Tibial and femoral implant malalignment (either angular or rotational) and improper patellar tracking can dramatically increase forces on the patellofemoral articulation and may increase the risk of fracture. 2,13 Figgie et al. 12 reported that in 36 knees with patellar fracture there were 20 and 16 knees with major or minor implant malalignment, respectively. The degree of the improper fit and alignment of the components determined the severity and prognosis of the subsequent patellar fracture. Specific patellar designs with a large central peg have been thought to contribute to patellar fracture. 20 The cam mechanism itself increases the force on the patella, especially in knee flexion of more than 958 because of the additive effect of quadriceps and patellar tendon contracture. 21 Thus, a greater range of motion may subject the implant to more severe loading. 21 Moreover, mostly metalbacked uncemented patellar components 13,19,37,41 or implants with large central pegs 11,14,23,37,40 have been associated with an increased risk of patellar

8 Management of periprosthetic patellar fractures 721 fractures. Recently Larson et al. 23 found that patellar components with a single central peg design may encompass a higher prevalence of patellar fracture than a three-peg patellar component. Patients with periprosthetic fractures of the patella were asymptomatic in 88.32% of cases and the fractures were identified during routine followup examinations. After a fracture is discovered, previous radiographs should be analysed to assess whether patellar component loosening was present before the fracture. However, it is often not feasible to determine whether the patella fractured before the prosthesis became loose or the prosthesis became loose before the patella fractured. 36 Windsor et al. 45 reported that fatigue fractures occur spontaneously without significant trauma and may be subdivided into horizontal, vertical and comminuted-displaced types. The horizontal type is caused by improper patellar tracking and may be associated with patellar dislocation; the vertical type invariably passes through the patellar fixation hole. Comminuted and displaced fractures are usually a combination of transverse or vertical types of fracture. Treatment options include splintage, open reduction and internal fixation with or without prosthetic revision, partial patellectomy combined with patellar ligament or quadriceps repair, and total patellectomy. 7 Fracture displacement and comminution, extensor mechanism integrity, remaining bone stock and stability of component fixation determine the therapeutic management (Table 9). 13,22,29,30,42 In the available literature 68.83% of fractures were addressed non-operatively and 31.17% by operative means. In cases of periprosthetic patellar fractures with a stable implant and an intact extensor mechanism, non-operative treatment is associated with good results. 22,29,30 This should start with a brace locked in extension or alternatively with a cylinder cast until radiological signs of healing are apparent. 30 Keating et al. 22 reported a mean flexion of 1208, extensor lag, less than 58 and minimal pain in 21 patients with Type I fracture who were treated non-operatively. Although osseous union is not always apparent, ununited marginal fractures rarely cause significant pain and discomfort during mobilsation. 29 Fractures associated with disruption of the extensor mechanism are usually treated operatively regardless of the stability of the patellar component Restoration of the extensor function of the knee should be achieved as a non-invasive treatment strategy results in impairment of knee extension. 42 However, surgical intervention has a modest outcome and it is associated with high complication rates. 11,15,20,22,29,30 According to our data, ORIF failed in 92% of cases and the final result was poor. Simple ORIF should not be routinely recommended because avascular fracture fragments have little if any healing potential and surgical complications of non-union, infection, failure of fixation and subsequently patellectomy have often been described (Fig. 1). 22,42 For this reason, reestablishment of the continuity of the extensor mechanism by excision of small poor-quality osseous fragments (patellectomy) and repair of the remaining extensor tendon to bone may be considered, despite the potential for residual extensor lag and quadriceps weakness. 24,40,43 This has led many authors to Table 9 Algorithm of management of periprosthetic patellar fractures

9 722 B.E. Chalidis et al. include non-operative treatment in their armamentarium, even in cases of marked fracture displacement. 21,22,40 Periprosthetic patellar fractures with loosening of the patellar component require surgical intervention for removal of the loose implant. 29 Afterwards, the decision for implant revision is individualised according to the quality and magnitude of the remaining bone stock. In cases of adequate bone thickness of more than 10 mm, reimplantation of the patellar component and patelloplasty is a viable and acceptable method of treatment. 31 However, when severe bone deficiency is present, patellar resection arthroplasty with partial or total patellectomy is a reasonable therapeutic option. 42 Ortiguera and Berry 29 reported 29% of complications in fractures with loosening of the patellar component (Type III), 11% of reoperation; 54% were still symptomatic at the last follow-up. At the time of patellar resection Figure 1 (a) Displaced periprosthetic fracture of the left patella 6 months after TKA. (b) ORIF with tension-band wiring led to symtomatic fracture non-union. (c) Three months later the patient was referred to our centre for further management. After metalwork removal, there was a gap between proximal and distal parts of the patella. Patellar prosthesis was stable and poor bone stock was available. (d) Distal partial patellectomy and reapproximation of patellar tendon to proximal fragment was selected as the final method of treatment.

10 Management of periprosthetic patellar fractures 723 arthroplasty, tibial and femoral component stability and axial and rotational alignment should be assessed, and if major problems are identified, appropriate measures should be taken. 31 Conclusion Treatment of periprosthetic patellar fracture is challenging, with a high complication rate and low satisfaction outcome. Numerous factors must be taken into account to decide on the optimal method of treatment. Patients must be warned about the possibility of a poor outcome and further surgery. Surgical treatment, when selected, should provide an uncomplicated and uneventful result aiming to achieve both stability of the implant and restoration of the extensor mechanism. However, the increased postoperative incidences of nonunion, infection and reoperation render conservative treatment the most realistic management. References 1. Berman AT, Reid JS, Yanicko Jr DR, et al. Thermally induced bone necrosis in rabbits. 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