Periprosthetic patella fractures in total knee replacement and revision surgeries: how to diagnose and treat this rare but potentially devastating complication—a review of the current literature

A comprehensive narrative review of the current literature on PPPFs examining epidemiology, risk factors, clinical manifestations, classification systems, diagnosis, management, outcomes, and preventive strategies was performed. The search was conducted using the PubMed, EMBASE, and SCOPUS databases.

The PPPFs are a patellar complication in TKA [11] and represent the second most common periprosthetic fracture around the knee, after supracondylar femur fractures [12]. The PPPFs may occur in both resurfaced and non-resurfaced patella. Resurfacing is one of the most important predisposing factors, with a PPPFs prevalence of about 0.2–21% higher in the resurfaced patella than in the non-resurfaced one (Fig. 1) [3, 4, 8, 9]. Chalidis et al. [4] in their systematic review, reported a rate of 0.9% (5 cases) of fractures that occurred in a non-resurfaced patella, while the remaining 577 cases (99.1%) occurred in a patella resurfaced (Fig. 2).

PPPFs may occur intraoperatively, but in most cases, they are observed in the postoperative follow-up with an incidence that increases sharply during rTKA [3‐5, 13]. In the Mayo Clinic joint registry, Berry reported that PPPFs are more frequent in rTKA than in primary TKA [5]. Furthermore, PPPFs usually occur in the first few years after TKA [1‐4]. Chalidis et al. [4] described a mean time from surgery to fracture occurrence of 18.5 months.

Several studies recorded a male prevalence and identified the male sex as an independent risk factor [1, 3, 8]. Ortiguera and Berry [1] reported a prevalence of 1.01% and 0.40% in men and women, respectively, consistent with Parvizi et al. [3] series, where PPPFs occurred with a 2:1 ratio of males to females. These data differ from other periprosthetic knee fractures, which frequently occur in osteoporotic women [1, 8, 12]. The reason is unclear, but a possible cause is that men usually have a higher body weight and activity level, leading to greater forces damaging the extensor apparatus [1, 3, 8, 9]. Contrary to previous papers, other authors [6, 14] have reported a female prevalence, explained by a higher osteoporosis rate in women.

The PPPFs may be traumatic or not [1‐4, 8‐10]. Although the literature seems to be a trend to atraumatic causes, there is much heterogeneity [1‐4, 8‐10, 14]. Chalidis et al. [4] described only 11.7% of cases associated with a traumatic event, whereas the recent case series by Govil et al. [14] reported that 66% of PPPFs were trauma related. The traumatic fracture may occur due to direct trauma, such as a fall on the knee, or indirect one, for example, an eccentric muscle contraction [1, 9, 15]. Ortiguera and Berry described several indirect mechanisms, like standing from a deep-seated position, hyperflexion, and knee overload [1]. Excluding traumatic cases, the literature strongly accords that the PPPF etiology is multifactorial [3, 4, 8, 9]. Nontraumatic PPPFs, therefore, are much more common than traumatic PPPFs, and most of them are related to fatigue fractures due to thinning of the native bone by loosening the patellar component or excessive original resection resulting from failure with the surgical technique. Several authors [3, 4, 8, 9] classified risk factors into three main groups: patient-related, implant-related, and surgical technique-related risk factors (Table 1).

PPPFs may be asymptomatic at clinical presentation and be discovered on radiographs during outpatient follow-up [1, 4, 8‐10]. Chalidis et al. [4] reported that more than 80% of PPPFs are diagnosed when symptoms occur, mainly consisting of anterior knee pain associated with swelling and patellar tenderness [9, 14]. Patients may complain of other manifestations, such as knee instability with extensor system weakness [9]. Diagnosis is usually made by anteroposterior and lateral X-ray view and Merchant X-ray view [9, 12, 14]. A CT scan may be performed to evaluate better any implant loosening and fracture morphology [12, 14]. Technetium-99m (Tc-99m) bone scan could be performed to discover occult fractures or to distinguish an old fracture from a recent one [9, 14]. Finally, the patient’s history, blood tests, and comparison with previous radiographs are critical in directing the surgeon to aseptic loosening, infection-related loosening, or upcoming implant failure [12].

Several classification systems for PPPFs are described in the literature, but the most widely used are those of Goldberg et al. [6] and Ortiguera and Berry [1].

Goldberg’s classification categorizes fractures according to fracture pattern, extensor mechanism integrity, and patellar component stability (Fig. 3). Type I is characterized by patellar fractures with intact extensor apparatus and implant stability, while in type II, one or both previously mentioned elements are damaged. Type III is divided into IIIa, in which the fracture of the inferior pole of the patella is associated with a patellar tendon injury, and IIIb, in which the same fracture pattern has an intact patellar tendon. Type IV consists of patellar fracture-dislocations [6].

Ortiguera and Berry’s classification is the most recent (Fig. 4) (Table 2); it considers the amount of residual patellar bone, implant stability, and extensor apparatus integrity. Type I fractures have a stable implant and an intact extensor apparatus; type II disrupts the extensor mechanism; type III has a mobilized implant but an intact extensor apparatus. The latter group is further divided into IIIa, characterized by a good amount of residual bone reserve for revision, and IIIb, with poor bone reserve, defined as a bone thickness of < 10 mm or marked comminution of the patellar component. If disruption of the extensor mechanism and a loosened component are concomitant, it is classified as type II [1].

Considering atraumatic fatigue fractures, Windsor et al. [10] associated the fracture pattern with the causative mechanism. Horizontal fractures were related to patellar maltracking and dislocation, while vertical ones passed through the patellar fixation holes. Comminuted and dislocated fractures were usually a whole of transverse and vertical fractures [10].

Conservative treatment consists mainly of immobilization in extension, with a cast or brace, for four to six weeks, depending on the fracture type; full or partial weight-bearing is allowed [1‐4, 6‐10, 14]. Surgical procedures may include open reduction and internal fixation (ORIF), partial or complete patellectomy with the extensor apparatus repair, patellar component revision, or extensor apparatus reconstruction [1‐9, 14, 27‐29].

Although several algorithms were developed, in the literature, there is a general trend in favor of nonsurgical treatment, except in cases of implant loosening or extensor apparatus failure (Table 3) [1, 4]. In Chalidis et al. [4] systematic review, 68.8% of PPPFs received non-operative treatment, and only 31.2% of patients underwent surgery. Conservative management is favored in most cases because of the higher number of complications associated with surgery, such as the infection rate reported in 19.2% of revision surgeries [4]. Conservative treatment is characterized by good functional results without pain, patellar, or extensor instability, with few cases of minimal extensor delay of about 5° [1‐4, 9, 14]. Although knee function was restored, non-union or fibrous union was detected in many cases on radiographic follow-up [1, 8]. Conversely, surgery is required in type II and III PPPFs, according to Ortiguera and Berry’s classification, characterized by extensor mechanism failure or implant loosening (Fig. 5) [1]. In type II fractures, surgical options are patellar fragments ORIF, partial or complete patellectomy with extensor apparatus repair, augmentation with adjacent tendons, or reconstruction with extensor allograft in cases of severe extensor tendon rupture and residual extension lag (Fig. 6) [1‐4, 8, 9, 14, 15]. Type III fractures involving implant loosening require operative treatment, especially in symptomatic patients [1‐4, 8, 9]. The most appropriate management is related to residual bone stock: type IIIa fractures undergo implant revision or resection arthroplasty, while type IIIb requires implant removal with partial or complete patellectomy [1, 4, 28, 29]. However, the complication rate is high; Ortiguera and Berry [1] described more than half of type III fractures as symptomatic at the last follow-up, while Parvizi et al. [3] reported that two out of three type III PPPFs required reoperation. Sometimes, in low functional demands and non-symptomatic patients, even PPPF type II and III may be treated conservatively due to the high complication rate associated with surgical procedures [1, 4].

Intraoperative PPPFs and fractures occurring in non-resurfaced patella deserve a separate analysis. Intraoperative PPPFs could be synthesized during surgery, and the patella should be later resurfaced if symptoms appear [11], whereas non-resurfaced PPPFs are generally treated as traumatic patellar fractures [3, 8, 30].

Windsor et al. [10] in their study, treated PPPFs surgically or conservatively based on fracture patterns and displacement. The authors divided fractures into the transverse, vertical, and comminuted, and further into displaced or nondisplaced with 2 cm as the displacement limit. Vertical, comminuted, and transverse fractures with less than 2 cm displacement could be treated conservatively; on the contrary, both transverse patella fractures with displacement greater than 2 cm and severely comminuted fractures associated with extension lag and quadriceps weakness should be managed surgically [10].