FRACTURES OF THE PATELLA AFTER TOTAL KNEE REPLACEMENT

PERIPROSTHETIC FRACTURES AFTER MAJOR JOINT REPLACEMENT

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FRACTURES OF THE PATELLA AFTER TOTAL KNEE REPLACEMENT Robert B. Bourne, MD, FRCSC

Patellar fractures complicating total knee arthroplasty are uncommon (approximately 1%), but they represent one of the most common periprosthetic total knee arthroplasty fract u r e ~ . ' - Most ' ~ of these patellar fractures (75%) are vertical and laterally based without disruption of the extensor mechanism and are often an incidental finding on postoperative skyline radiographs (Fig. 1).These fractures may occur during a primary or revision total knee replacement or postoperatively as a result of trauma, avascular necrosis, fatigue, or a combination of these factors. Patellar fractures may occur with or without patellar resurfacing (see Figs. 1-5). Patellar fractures are usually characterized by the competence of the extensor mechanism, involvement of the patellar implant, and anatomic location.* When a patellar fracture occurs in association with a total knee replacement, treatment can be demanding, and the clinical result can be compromised (Fig. 2). This article describes the predisppsing factors and management principles of patellar fractures complicating total knee arthroplasty.

nontraumatic causes. A number of patient, surgical, and implant factors may predispose to patellar fracture (Table 1). Trauma may cause a patellar fracture and may be direct or indirect. A direct fall on the knee with a total knee arthroplasty may result in a fracture that may or may not compromise patellar implant fixation or the integrity of the extensor mechanism. Indirect causes include an eccentric quadriceps muscle contraction associated with a stumble, resulting in a transverse avulsiontype fracture, which once again may or may not affect patellar implant fixation or extensor mechanism function (Fig. 3).

PREDISPOSING FACTORS Patellar fractures in association with a total knee replacement may be due to traumatic or

Figure 1. A skyline radiograph of an asymptomatic patient taken at a routine follow-up check-up. Surprisingly,this patient remains asymptomatic 5 years later.

From London Health Sciences Centre, University of Western Ontario, London, Ontario, Canada

ORTHOPEDICCLINICS OF NORTH AMERICA VOLUME 30 NUMBER 2 APRIL 1999

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Figure 2. A lateral radiograph illustrating the complexity associatedwith some patellar fractures followingtotal knee replacement. Note the patellar fracture, disrupted extensor mechanism, dysvascular patella, and anteroposteriorlyunstable total knee replacement.

Figure 3. A lateral radiograph demonstrating a transverse patellar fracture in association with a total knee replacement caused by a stumble and eccentric quadriceps contraction, resulting in a disrupted extensor mechanismand loose patellar implant.

INTRAOPERATIVE PATELLAR FRACTURES

total knee arthroplasty, the use of biconvex patellar implants in primary or revision thicknesses can be helpful in minimizing patellar resection and restoring patellar height.

Patellar fractures may occur during routine primary total knee replacement but are more prevalent in revision arthroplasty. Attempts to resurface a patella less than 10 to 15 mm thick, overzealous use of patellar clamps, patellar reamer slippage, and overreaming all contribute to intraoperative patellar fractures (Fig. 4). In fact, in the author’s experience, it is often wiser not to resurface the patella in 30%to 40% of revision total knee arthroplasties in which patellar thickness is less than 10 to 15 mm because of the risk of patellar fracture. When patellar resurfacing seems feasible during primary cases with thin patellae or in revision

POSTOPERATIVE, NONTRAUMATIC PATELLAR FRACTURES Nontraumatic, postoperative patellar fractures after total knee arthroplasty often are associated with dysvascular bone and are similar to stress fractures (Figs. 5 and 6). These fractures may be transverse or longitudinal (usually laterally based). Patient, implant, and technical factors are all predisposing issues (see Table 1).Weak bone resulting from osteo-

Table 1. PREDISPOSING FACTORS TO PATELLAR FRACTURE AFTER TOTAL KNEE REPLACEMENT ~

Patient Factors

Implant Factors

Technical Factors

Osteoporosis Rheumatoid arthritis Male sex High activity level Excessive range of motion

Patellar replacement/nonreplacement Central peg Cementless implants PCL-substituting prosthesis Inset design Osteolysis

Excessive resection Inadequate resection Anterior patellar perforation Revision Malalignment Patella subluxation Devascularization of patella

PCL = Posterior cruciate ligament.

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Figure 5. Postoperative, nontraumatic patellar fracture in a patient who did not have the patella resurfaced. Note the sclerosis of the patella suggesting dysvascularity and the vertical nature of the fracture with lateral subluxation of the lateral fragment.

Figure 4. Intraoperative patellar fracture in a patient with a thin, sclerotic patella. The patellar reamer fractured the patella, necessitating open reduction and internal fixation and not resurfacing the patella.

treatment algorithm used at the author's institution for patellar fractures associated with a total knee replacement. Transverse and vertical fractures predominate, but in cases of avascular necrosis of the patella, combinations of fracture patterns may emerge-

porosis or overreaming and resection is an obvious cause. Male sex, high activity levels, and excessive range of motion are other factors implicated. Implant factors include a central peg, cementless patellar implants, and posterior cruciate ligament-substituting implants. Technical factors are usually important and include inadequate soft tissue balancing, femoral or tibia1 component rotational malalignment, patellar devascularization, lateral retinacular release, excessive patellar resection, and inadequate patellar resection. The role of patellar devascularization warrants special emphasis (see Figs. 2 and 5). Scuderi et all4 performed technetium bone scans after total knee replacement. They demonstrated cold patellae in 56.4% of patients who had undergone a lateral retinacular release and in 15%of patients who did not. pitter and CampbelP could not replicate these findings, so debate still exists. MANAGEMENT PRINCIPLES

Goldberg et a14 developed a useful classification of patellar fractures after total knee replacement based On the integrity Of the extenSOT Inecfianism and fixation of the patellar component (Table 2). Figure 7 represents the

Figure 6. Avascular necrosis of the patellar in a symptomatic patient 26 months after total knee replacement before revision surgery.

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Table 2. CLASSIFICATION OF PATELLAR FRACTURES Extensor mechanism intact, not extending t o implant interface Extensor mechanism disrupted o r extension to implant interface Inferior pole fracture Patellar ligament rupture Patellar ligament intact Fracture-dislocations

Type 1 Type 2 Type 3 a b Type 4

Data from Goldberg VM, Figgie HE, Inglis AE, et al: Patellar fracture type and prognosis in condylar total knee arthroplasty. Clin Orthop 236:115, 1988.

Patellar fractures with extensor mechanism disruption or patellar implant loosening (or both) necessitating operative treatment had poorer results (60% unsatisfactory). Satisfactory results have been reported in only 33% of type 11, 38% of type IIa and 33% of type IV patellar fractures. Total knee component alignment has also been demonstrated to be important. If major malalignment of components was present combined with a patellar fracture, only 28% had a successful outcome compared with 94% satisfactory results in patients with only minor malalignment.3,4

RESULTS OF PERIPROSTHETIC PATELLAR FRACTURES CONCLUSIONS The type of periprosthetic patellar fracture influences the clinical result? Patellar fractures not associated with disruption of the extensor mechanism or loosening of the patellar implant may be treated nonoperatively (i.e., knee immobilizer, partial weight bearing for 4 to 6 weeks, then rehabilitation) with good or excellent results (Table 3-type I and IIIb fractures).

Patellar fractures associated with total knee replacement are uncommon. Patient, implant, and technical predisposing factors should be identified, such that the risk of patellar fractures might be minimized. A classification system based on the criteria of extensor mechanism integrity, patellar component fixation, and anatomic location is useful in guiding

Table 3. PATELLAR FRACTURE TYPES AND EFFECT ON OUTCOME Type

N

Knee Score (100)

Range of Motion

I I1 IIIa

13 6 8 2 6

Excellent 75 (42-100) 63 (40-93) 100 (100) 67 (41-85)

100" (85"-125") 90" (7O0-11Oo) 90" (45"-110") 100" (85"-125") 75" (60"-100")

IIIb IV

Data from Goldberg VM, Figgie HE, Ingus AE, et al: Patellar fracture type and prognosis in condylar total knee arthroplasty. Clin Orthop 236115,1988.

PATF.LT.AR FRACTUBE Transverse Fracture

Vertical Fracture

Stable Fixation

,

1

Unstable Fixation

1

yMec@nis;

Intact

Disrupted

Intact

I

I

I

Closed Treatment -Cylinder -Splint

Open Fixation -Wires -Screws

Remove Prosthesis

Qr Revise

,

Disrupted

Stable Fixation

I

I

Intact

Unstable Fixation Extenso;Mecm

Disrupted

I

I

I

Remove Prosthesis and Internal Fixation M Patellectomy

Closed Treatment - early motion

open Repair

I

1

Intact

I

, Disrupted

I

Remove Remove Prosthesis Prosthesis - early and motion Internal Fixation QI:

Patellectomy

Figure 7. Treatment algorithm used at London Health Sciences Centre to treat periprosthetic fractures of the patella in association with total knee replacement.

FRACTURES OF THE PATELLA AFTER TOTAL KNEE REPLACEMENT

treatment and anticipating the clinical outcome. Patellar fractures requiring operative treatment often yield unsatisfactory results. Prevention is the best treatment and includes proper total knee replacement alignment, soft tissue balancing, patellar height restoration, and implant selection.

References 1. Brick GW, Scott R D The patello-femoral component of total knee arthroplasty. Clin Orthop 231:163,1988 2. Cordeiro EN, Costa RC, Corazzato JG, et al: Periprosthetic fractures in patients with total knee arthroplasties. Clin Orthop 252182, 1990 3. Figgie HE, Goldberg VM, Figgie MP, et al: The effect of alignment of the implant on fractures of the patella after condylar total knee arthroplasty. J Bone Joint Surg Am 71:1031,1989 4. Goldberg VM, Figgie HE, Inglis AE, et al: Patellar fracture type and prognosis in condylar total knee arthroplasty. Clin Orthop 236:115,1988 5. Grace JN, Sim FH: Fracture of the patella after total knee arthroplasty. Clin Orthop 230:168,1988 6. Healy WL, Wasilewski SA, Takei R, et a1 Patello-femoral complications following total knee arthroplasty:

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Correlation with implant design and patient risk factors. J Arthrop 10:197, 1995 7. Hozack WJ, Gall SR, Lotke PA, et al: Treatment of patellar fractures after total knee arthroplasty. Clin Orthop 236:123, 1988 8. Insall JN, Haas SB: Complications of total knee arthroplasty. In Insall JN (ed): Surgery of the Knee. New York, Churchill Livingstone, 1996, p 891 9. Leblanc J M Patellar complications in total knee arthroplasty: A literature review. Orthop Rev 18:296, 1989 10. Lynch AF, Rorabeck CH, Bourne RB: Extensor mechanism complications following total knee arthroplasty. J Arthroplasty 2135,1987 11. Rand JA, Coventry MB: Stress fractures after total knee arthroplasty. J Bone Joint Surg Am 62:226, 1980 12. Ritter MA, Campbell E D Post-operative patella complications with or without lateral release during total knee arthroplasty. Clin Orthop 219:163, 1987 13. Scott RD, Turoff N, Ewald FC: Stress fracture of the patella following duopatellar total knee arthroplasty with patellar resurfacing. Clin Orthop 170:147, 1982 14. Scuderi GR, Scharf SC, Meltzer LP, et al: The relationship of lateral release to patella viability in total knee arthroplasty. J Arthroplasty 2209, 1987 15. Tria AJ, Harwood DA, Alicea JA, et a1 Patella fractures in posterior stabilized knee arthroplasties. Clin Orthop 299:131, 1994 16. Windsor RE, Scuderi GR, lnsall JN: Patella fractures in total knee arthroplasty. J Arthroplasty 4(suppl):563, 1989

Address reprint requests to Robert B. Bourne, MD, FRCSC London Health Sciences Centre University Campus 339 Windermere Road London, Ontario N6A 5A5