Background Instability of the distal radioulnar joint (DRUJ) is a complication that can occur following distal radius fracture or malunion. We have observed that residual radial translation of the distal radius, relative to the radial shaft, may be a causal factor of DRUJ instability, even once the traditional radiographic parameters (volar tilt, radial inclination, and ulnar variance) have been restored. Residual radial translation of the distal fragment may cause detensioning of the distal interosseous membrane (IOM) and pronator quadratus with poor apposition between the ulnar head and sigmoid notch. This may potentially lead to persistent instability of the ulnar head following internal fixation. Residual radial translation deformity is at risk of being overlooked by the wrist surgeon as there is no existing radiographic parameter that accurately measures this deformity. Patients and Methods In this study, 100 normal wrist radiographs were reviewed by three fellowship-trained orthopedic surgeons to develop a simple and reproducible technique to measure radial translation. Results Utilizing the method described, the point of intersection between the ulnar cortex of the shaft of the radius and the lunate left a mean average of 45.48% (range 25–73.68%) of the lunate remaining on the radial side. In the majority of cases more of the lunate resided ulnar to this line. High levels of agreement with inter-rater (intraclass coefficients = 0.967) and intra-rater (intraclass coefficients = 0.79) reliability was observed. Conclusions The results of this study can be used to define a normal standard against which residual radial translation can be measured to assess the reduction of distal radius fractures. This new parameter aids in the development of surgical techniques to correct residual radial translation deformity. In addition, awareness and correction of this potential malreduction at the time of surgery may decrease the need for other procedures on the ulnar side of the wrist to improve DRUJ stability, such as ulnar styloid fixation, TFCC repair, or ligamentous grafting. Level of Evidence Level II (Diagnostic)
Shoulder replacement is a reliable treatment for the relief of pain and improvement of function in patients with glenohumeral arthritis, rotator cuff arthropathy, osteonecrosis and fracture. Limited data is available comparing revision rates for the different types of shoulder replacement when used in younger patients. This study aims to compare the survivorship of hemi resurfacing, stemmed hemiarthroplasty, total shoulder arthroplasty and reverse total shoulder arthroplasty in younger patients using data from a large national arthroplasty registry.
Subscapularis tendon plays an important role in shoulder stability and functions. There has been much interest recently in the prevalence of subscapularis tears and outcomes following repair of subscapularis tears. We aimed to assess whether there is an increase in pick up rate of subscapularis tears in patients who underwent arthroscopic rotator cuff repair following routine additional use of a 70° arthroscope during shoulder arthroscopy.A retrospective review of a single surgeons practice was performed to assess the frequency of identifying and repairing subscapularis tears among a cohort of 58 consecutive arthroscopic rotator cuff tears performed over a 12 months period. The patients' had an age ranged between 42 and 71 years (mean 54.4). The case mix was a combination of degenerative and traumatic tears. All-arthroscopic procedures had an additional assessment with a 70° arthroscope, in addition to routine assessment with a 30° arthroscope. The follow-up ranged from 30 to 120 days. The prevalence of subscapularis tendon tears was noted intraoperatively. This was compared to the pre-operative incidence as determined by the various clinical examination and radiological techniques.Of the 58 arthroscopic rotator cuff repairs, subscapularis tear was identified in 25 patients (43.1%). Among the imaging modalities used pre-operative magnetic resonance imaging scanning reported a subscapularis tear in 71.4% and pre-operative ultrasound scanning reported a tear in 78.6.The use of a 70° arthroscope can facilitate the recognition and management of subscapularis tears which may not be recognized with a routine 30° shoulder arthroscope. A combination of high index of suspicion, judicious use of pre-operative imaging and careful arthroscopic assessment aids identification of subscapularis tendon tears.
Fractures of the distal radius are common. Closed reduction and moulded casting is often the first line treatment. Malunion after casting is not uncommon and can lead to discussion on acute surgical fixation versus delayed corrective osteotomy if symptomatic. However, it is unclear if late surgery will provide similar outcomes as early intervention.We performed a single centre, age matched, case series comparison study, comparing outcomes of patients who had undergone early fixation (ORIF) versus those who had undergone late corrective osteotomy (CO) following distal radius fracture.Twenty-six patients were available for review, 13 in each group. Fracture patterns were similar. Reviewing CO versus ORIF; patients achieved a mean DASH; 22 versus 18 (P = 0.355), PRWE; 35 versus 26 (P = 0.237), and VAS 2 versus 2 (P = 0.490). Grip strength was significantly better in those who had undergone ORIF; 2% versus -22% (P ≤ 0.001). Range of motion was generally better with primary fixation but of doubtful clinical importance, reviewing CO versus ORIF; Flexion 46° versus 60° (P = 0.045), extension 55° versus 64° (P = 0.137), pronation 73° versus 85° (P = 0.078), supination 84° versus 84° (P = 0.747), flexion/extension arc 101 versus 124 (P = 0.017), ulnar/radial deviation arc 42° versus 59° (P = 0.01), pronation/supination arc 157° versus 168° (P = 0.118). Ulnar variance was significantly improved in the ORIF group; +0.5 mm versus +2 mm in the CO group (P = 0.023). Radial inclination, radial height and volar tilt were not significantly different between either group.Our findings suggest that patient measured outcome of corrective osteotomy is not inferior to early internal fixation.III (Case Series Comparison).
History The diagnostic spectrum from rotator cuff tendinopathy through cuff tear arthropathy causes pain and disability that can result in surgical intervention [15]. In 1931, Codman and Akerman [5] proposed that degenerative changes of the tendons initiate rotator cuff tears. Subsequently, in 1949, Armstrong [1] proposed that mechanical impingement of the rotator cuff tendons under the acromion causes supraspinatus syndrome. Neer [21] also postulated that mechanical impingement was responsible for up to 95% of rotator cuff tears and reported successful treatment with anterior acromioplasty [20]. Regardless of the etiology, acromioplasty is commonly used as a surgical adjunct for the treatment of rotator cuff tendinopathy and tears. In 1986, Bigliani and colleagues [3] were the first to classify acromial morphology and correlate it with rotator cuff tears. They described three types of acromion: Type I (flat), Type II (curved), and Type III (hooked) (Fig. 1). A Type IV acromion was later described as a convex acromion [28]. Bigliani et al. [3] and other authors [2, 6–8, 10, 13] have reported that Type III acromia have been associated with rotator cuff tears. Conversely, other authors have found no such correlation [23, 24]. Since Bigliani et al.'s [3] original description, there have been other attempts to quantify acromial morphology. Bigliani et al. [3] and Kitay [12] described the acromial slope, a measure of anterior acromial slope and the relationship between increased acromial slope and rotator cuff tears. In the same paper, Kitay [12] also described acromial tilt, the angle between a line drawn connecting the most posterior point of the inferior acromion to the most anterior point of the inferior acromion and a line drawn connecting the same most posterior point of the inferior acromion to the inferior tip of the coracoid process. Decreased acromial tilt was associated with rotator cuff tears [12]. Nyffeler et al. [22] described the acromial index, a ratio of the distance from the glenoid plane to the acromion divided by the distance from the glenoid plane to the lateral aspect of the humeral head. The authors observed that the acromion of patients with a rotator cuff tear appeared to have a more lateral extension, thus a greater acromial index, than that of patients with an intact cuff [22]. Most recently, the critical shoulder angle (CSA) was described, which not only includes acromial morphology but also considers glenoid morphology [16]. The authors observed patients with rotator cuff tears were more likely to have a CSA > 35° than a control group of patients without rotator cuff tears. Although there have been numerous attempts to find an association between rotator cuff tears and scapular morphology [2, 3, 12, 17, 18], there is no consensus as to the role of scapular morphology in the etiology of rotator cuff tears.Fig. 1: This diagram shows the Bigliani classification of acromial morphology: (A), Type I (flat); (B), Type II (curved); and (C), Type III (hooked). Reprinted with permission from Bright AS, Torpey B, Magid D, Codd T, McFarland EG. Reliability of radiographic evaluation for acromial morphology. Skeletal Radiol. 1997;26:718–721.Purpose The original purpose of the Bigliani classification [3] was to describe acromial morphology and determine whether it was associated with rotator cuff tears. To our knowledge, the Bigliani classification of acromial morphology was the first classification system to try to define acromial morphology. One goal was to facilitate communication among clinicians and to support further research on the relationship between acromial morphology and rotator cuff tendinopathy. However, as we have already noted, this relationship has been questioned (particularly with respect to the concept of impingement syndrome) [2, 23, 24]. In addition, problems with reliability of the Bigliani classification [2, 4, 9, 31] have been reported. Taken together, these concerns should cause both clinicians and researchers to use the Bigliani classification with caution, if at all. In the same publication, Bigliani et al. [3] aimed to determine if there was any correlation between acromial morphology and the presence of rotator cuff tears. Bigliani et al. [3] found that 69.8% of full-thickness rotator cuff tears had Type III acromia, 24.2% had Type II acromia , and 3% had Type I acromia. Further studies have reported conflicting results; some found correlations between acromial morphology and rotator cuff tears [3, 7, 13], and others did not [23, 24]. Later attempts to identify whether acromial morphology types were associated with impingement syndrome were made [2, 6], although this was not originally a purpose of the classification system. Two studies [2, 6] observed that there was no correlation between impingement syndrome and acromial morphology. Because of the proposed correlation between rotator cuff tears and Type III acromia, it was theorized that patients with Type III acromia may be at risk of having impingement syndrome [19]. Classification In 1986, Bigliani et al. [3] described three distinct types of acromial morphology after taking lateral radiographs of 140 shoulders from 71 cadavers. They described Type I as flat, Type II as curved, and Type III as hooked (Fig. 1). No further attempt was made to further define the three different acromial morphology types. Bigliani et al. [3] also observed that acromial morphology and rotator cuff tears were associated with two additional factors. There was an association between increasing acromial slope, which increased from Type I to Type III acromia, and rotator cuff tears, as well as between anterior acromial spurs and rotator cuff tears. Both observations have been verified by further research from several authors [2, 3, 9, 12]. Validation As we suggested earlier, the main problem with the Bigliani classification is that although its intraobserver reliability has varied–sometimes (though not always [4]) achieving kappa values in the good-to-excellent range [11, 25, 27]–its interobserver reliability has been consistently fair-to-poor [4, 9, 11, 23, 25, 27, 31]. This means that it is not suitable as a clinical communication tool among surgeons or clinician-scientists. In one study, in which six fellowship-trained shoulder surgeons reviewed 126 scapular outlet view radiographs (a scapular Y view with 10° of caudal tilt) of the shoulder observed good-to-excellent intraobserver reliability (κ = 0.888) and poor-to-fair interobserver reliability (κ = 0.516) [11]. Several further small studies observed that interobserver reliability was poor (κ = 0.25-0.41) [9, 25, 27, 31]. In another study, which again found only fair interobserver (κ = 0.35) reliability, both interobserver and intraobserver reliability were found not to vary according to surgeon experience level (from PGY-2 resident to fellowship-trained shoulder surgeon), or whether the observers were surgeons or radiologists [4]. Taken together, the interobserver reliability of the Bigliani classification of acromial morphology as reported by multiple studies is fair at best, regardless of level of expertise and training, and as such it should not be used to facilitate communication by orthopaedic surgeons, radiologists, or researchers. The use of MRI to identify acromial morphology has also been studied. One small study compared a single oblique midsagittal MRI image in the plane of acromion and scapular outlet view radiographs of 32 shoulders in patients who had undergone impingement syndrome treatment [29]. Three shoulder surgeons independently reviewed MRI and radiographs. They graded acromial morphology almost identically when radiographs and MRI were compared, with 31 of 32 (97%) having the same acromial type. The authors concluded that MRI was as accurate as radiographs at determining acromial morphology [29]. A similar study compared the value of different MRI planes independently and in combination for assessment of acromial morphology compared with a scapular outlet view radiographs [14]. They found that scapular outlet view radiograph had fair agreement (κ = 0.55) but was superior to any single MRI image position that did not achieve higher than poor agreement (κ = -0.1 to 0.44). However, a combination of two MRI images showed good agreement (κ = 0.66)[14]. This conflicts with the previous study [29], which found that single MRI images were not different from scapular outlet view radiographs. This difference in agreement between the two studies may be due to the already well-documented poor-to-fair interobserver reliability, and as such, to an inability to use the Bigliani classification effectively for research purposes. Although more MRI images showed improved interobserver agreement, employing MRI to identify acromial morphology should be used with caution, if at all. There is conflicting evidence regarding Bigliani's original observation that rotator cuff tears were associated with Type III acromia [2, 3, 6–8, 10, 13, 17, 23, 24]. Many authors have found a correlation between Type III acromia and rotator cuff tears [2, 3, 6–8, 10, 13]. In one meta-analysis, patients with Type III acromia were more likely to present with rotator cuff tears [18]. By contrast, several other studies found that Bigliani Type III acromia were no more likely to have a rotator cuff tear than shoulders with a Type II or I acromia [17, 23, 24]. On balance, we consider the relationship between acromial morphology as defined by the Bigliani classification and rotator cuff pathology to be weak, if it is present at all. It is not possible to know whether this is because of a flawed anatomic premise (that a more-hooked acromion is more likely to damage the rotator cuff) or because of the considerable problems reported with the reliability of this classification system [4, 9, 11, 25]. Limitations Different observers must be able to agree on the same classification when reviewing the same data (interobserver reliability) before a classification system should be used for clinical decision-making, communication between surgeons, prognosis, or research. Because the interobserver reliability of the Bigliani classification system [3] is only poor-to-fair (κ = 0.28-0.516 [4, 9, 11, 25]), it therefore should not be used for any of these purposes. Some of its problems may derive from the system's subjective descriptions. The original Bigliani classification does not give objective definitions of flat, curved, or hooked acromia, and thus it entirely depends upon each surgeon's subjective interpretation. Two studies found that by using standardized criteria to define Type I, Type II, or Type III acromia, the interobserver reliability improved from poor (κ = 0.25 -0.28) to good-to-excellent (κ = 0.62- 0.77) [25, 27]. Whether their finding that standardization of this sort improves the system's interobserver reliability must be verified by others. Some skepticism may be necessary in this regard, given how sensitive the system appears to be to the quality of the imaging. One study found that the interpretation of acromial morphology is influenced by the angle of the beam in the sagittal, coronal, and axial planes [26]. There is a dearth of research evaluating the effectiveness of the treatment of patients with rotator cuff pathology according to differences in acromial morphology. A single, small study observed that patients with Type III acromia were more likely to undergo surgery after undertaking nonoperative treatment of shoulder impingement than patients with either Types I or II acromia [30]. The utility of this study is limited because it was a small, single-surgeon case series using a questionable shoulder impingement diagnosis [30]. And until or unless surgeons and clinician-scientists find ways to improve the interobserver reliability of the Bigliani classification system, we believe it should not be used to estimate patients' prognoses. Conclusions The Bigliani classification of acromial morphology is of some historical importance as the first system to classify acromial morphology. However, although it is widely used, we believe it should not be. Its interobserver reliability has generally been in the fair-to-poor range [4, 9], which means that two observers are unlikely to classify the same acromion similarly; consequently, this system simply has no place in clinical communication, determination of prognosis, or research (other than research to try to improve upon the ways we classify the acromion). Attempts to improve reliability have been made using objective criteria to define the distinct types of acromial morphology and were somewhat successful [25, 27], but these findings must be reproduced by others before we should consider them convincing.
History Periprosthetic joint infections (PJIs) after arthroplasty cause morbidity and contribute to mortality; they also increase the costs of treatment, both to the patient and the healthcare system [27]. The risk of THA and TKA infection is often quoted in the literature as less than 2% [23]. Most patients who develop a PJI can be treated, however, as many as 30% [11] of these patients will have persistent infection despite appropriate treatment. Decision making about the best treatment approach for these patients remains controversial. Widely accepted management of PJI is a two-stage revision with a targeted antibiotic regimen [27]. Other surgical interventions include débridement and implant retention (DAIR), with or without modular component exchange, and single-stage direct-exchange revision arthroplasty. Excisional arthroplasty and amputation as an index operation typically are reserved for unusual circumstances. McPherson et al. [20] were the first to propose a clinical staging system for knee PJI. This system has three components: infection type, systemic host grade, and local extremity grade (Table 1). The premise behind this classification was the authors' subjective experience with patients with systematic comorbidities that predispose a patient to infection (or that can potentiate its persistence) were more difficult to treat, as were those with local soft-tissue compromise [20]. Their initial paper retrospectively applied the staging system to 70 infected TKAs, and they reviewed outcome measures including the Knee Society Scores, complications, amputations and permanent resections after treatment. Subsequently, McPherson et al. [21] applied the same system to infected THAs treated with a two-stage revision, with a similar observation; patients who were healthier at baseline and who had fewer local findings suggestive of severe infection or poor tissue healing ability (like soft-tissue abscess or sinus formation) were more likely to have successful reimplantation after PJI.Table 1.: McPherson Staging system for prosthetic joint infectionBefore the publication of McPherson et al.'s classification [20], no systems dedicated to PJI had been described. Grouping orthopaedic-related infections based on duration, the host's systemic condition, and the host's local condition was not unique [6, 14, 17, 30], McPherson and his team though, in 1999, were the first to apply this to arthroplasty. However, similarities can be drawn between McPherson's classification [20] and the Cierny and DiPasquale [5], and the Cierny and Mader [6] classification system of osteomyelitis in the long bones, which was later modified and adapted to grade PJI. Both systems stratify patients based on their current morbid state, related to both systemic and local health. Purpose Treatment of PJI is challenging and can lead to functional impairment, pain, and even death. The development and application of an objective and clinically relevant system, like McPherson's classification, provides important information to facilitate communication, research, prognosis and treatment decisions. Currently, the McPherson classification system is recommended by the Musculoskeletal Infection Society for grading PJI, and there is no internationally accepted equivalent [1]. Using the McPherson classification to identify those patients who might achieve eradication of PJI with a single-stage procedure could provide a cost benefit to health systems, as well as an easier course of treatment for patients to endure [12, 27]. This classification system may help clinicians to identify patients who are at a higher risk for failed surgical management, which may result in outcomes including arthrodesis and amputation. Description The McPherson staging system for PJI incorporates three distinct parameters: infection type (temporal phase), systemic host grade, and local extremity grade (Table 1); these are then used together to assign a status; for example, II, B, and 1 (compromised host, with acute hematogenous infection (< 4 weeks) of the joint, and uncompromised skin at the surgical site). Stratification of patients by the McPherson system starts with the duration of infection, using 4 weeks as a division point for acute and chronic infection. Acute infections are further divided into early postoperative and hematogenous infection. The number and type of medical comorbidities are used to segregate patients into grades (A) uncompromised, (B) compromised, and (C) substantially compromised host status groups. Compromising systemic factors either impair the immune system or the body's synthetic and anabolic capacity or drive a continuous inflammatory state (Table 2).Table 2.: Systemic and Local Wound factors in patients at risk for prosthetic joint infectionThe assessment of the local and extremity status again highlights issues of soft-tissue coverage, delivery of essentials for metabolism and immune function, and skin integrity. Based on these parameters, the extremity is graded as 1, 2, or 3 (uncompromised, compromised, and severely compromised, respectively), depending on the number of comorbidities associated with the limb. Validation Although widely used, the McPherson staging system for periprosthetic infection has not been validated with intra- and interobserver studies in the current evidence. The objective nature of the system would suggest that little variability would be encountered. Studies investigating the reliability of the system to predict patient outcome have been typically small, retrospective, and variable in their findings. Despite these shortcomings, the International Consensus Group on Orthopaedic Infections advocates the use and further development of this system [1, 10]. Since McPherson's first description of this system [20] and their series of TKA and THA [20, 21], multiple studies have used this system to report success or failure of treatment. To date, there are no well-designed prospective series applying this system; most are retrospective case series, and many focus on the McPherson host grade alone in patients either with acute or chronic infections, with variable local extremity grading. Two-stage exchange arthroplasty for infection is a commonly recommended procedure to cure infections. In a review of 245 patients with infected TKAs treated with two-stage revision arthroplasty, the application of the McPherson classification identified three factors that were associated with an increased risk of re-infection: McPherson host grade C, previous revision surgery, and a BMI greater than 30 kg/m2 [24]. The latter two parameters suggest a worse McPherson extremity grade, but in their direct comparison of Grade 2 and 3 limbs, no difference was found (no Grade 1 limbs were treated). In a series that replicated the original McPherson THA paper [21], 60 Type III infections were treated with a two-stage hip revision [2]. The authors found that worsening of the host's status was related to a higher risk of a postoperative draining sinus, and the local extremity grade was positively associated with wound healing complications [2]. Interestingly, host grade was not associated with an increase in one or more complications, or a difference in amputation and reimplantation rates nor death during a 24-month follow-up period. This may be related to the low sample size, a difference in patient group heterogeneity, or different treatment protocols (exclusive use of spacers [2] versus resection and spacers [21]). A study on the outcomes of 92 patients with infected primary THAs, with a rigorous application of the classification system and a minimum of 2 years of follow-up concluded that only patients with McPherson Grade I/A/1 could or should be considered for single-stage revision [32]. This study is the largest published THA series on this subject, and in particular, the largest using all three facets of the scoring system. It provides support for the use of the system when deciding between a single-stage or two-stage THA revision. The use of débridement and implant retention (DAIR) to treat acute PJI remains controversial. In a review of 90 patients with acute PJI after THA at a single center who underwent DAIR, 17% (15 of 90) of THA revisions failed due to acute reinfection and underwent either resection arthroplasty or revision DAIR; failure proportions increased with the host's grade (Host grade A 8%, Host grade B 16% [p = 0.04], Host grade C 44% [p = 0.006]) [4]. They were unable to identify a positive relationship between the temporal infection type (that is, McPherson Type I or II) or the local extremity grade regarding failure to eradicate infection (component removal or repeat DAIR due to infection recurrence). Affirming that for THA host grade should be considered when offering DAIR procedures; local extremity grade may be of less importance around the hip due to good soft tissue coverage. Conversely, in the treatment of acute infection (McPherson Types I and II) using the DAIR technique in a series of 134 patients with infected primary TKAs, McPherson's host grade was not shown to be associated with an increased risk of subsequent infection or component removal [31]. The protocol used in this study included antibiotics for the life of the implant. Mortality of these patients was 15% by 2-year follow-up, of which grade C hosts had an increased risk of death (HR 18.4 (95% confidence interval 3.9 to 87.2); p < 0.001) compared with grade A hosts, as did grade B hosts (HR 7.4 (95% CI 1.6 to 33.3); p = 0.01) [31]. The notion that single-stage and DAIR-type procedures carry a high risk of recurrent infection in compromised hosts was supported in a review of chronically infected (Type III) lower-limb arthroplasties in immunocompromised patients [15]. Thirteen of the 24 Grade B hosts had a recurrence of infection, and three of five Grade C hosts had a recurrence. No Grade A hosts were included as controls. Two studies from the Mayo Clinic reviewed patients undergoing a second two-stage exchange arthroplasty for PJI after TKA and THA [3, 9]. Although both studies had small groups (45 TKA patients and 19 THA patients), the repeat two-stage TKA results showed that the chance of success (prosthesis retention without subsequent procedures) in Grade A hosts was only 70% (7 of 10), falling to 50% (10 of 20) in Grade B hosts and 0% in Grade C hosts (0 of 2) [9]. In contrast, within the repeat two-stage THA group, there was no association between the host's grade and reinfection risk after THA [3]. This was likely influenced by the small cohort. Other studies on the treatment and salvage of infected arthroplasty support that local limb conditions and systemic factors should be considered [19, 24, 29]. A review of 38 two-stage TKA revisions identified that local limb conditions affect infection clearance, with increased infection recurrence in extensively scarred limbs, and those with chronic venous insufficiency [29]. Additionally, systemic factors such as chronic pulmonary disease, low preoperative lymphocyte count, and diabetes mellitus increase risk of unsuccessful infection eradication and wound complications [8, 18]. Limitations A primary limitation of the McPherson classification is the paucity of studies confirming its inter- and intra-observer reliability. Despite this shortcoming, this system does have international acceptance and continues to be reported in current scientific literature. The McPherson classification of PJI is comprehensive but lacks some defining criteria that may ultimately affect the outcome [13]. The elements of the "ideal" staging system are proposed to include clinical presentation, etiopathogenesis, anatomo-pathologic findings, host type, micro-organisms, bone defects, and soft tissues [25]. Similar conclusions have been made regarding osteomyelitis of the long bones [14]. McPherson's system addresses three of these: duration (clinical presentation), host status, and soft tissues. The McPherson classification does not account for the infecting organisms and resistance profiles, which are important to consider when treating infected arthroplasty. Two-stage [28] and DAIR [26] procedures have a high failure rate in those with infections with multi-resistant organisms. A counterargument was presented in a study of 37 TKAs infected with methicillin-resistant Staphylococcus aureus or Staphylococcus epidermidis, among which only 11% of patients had reinfection with the same organism after two-stage revision; the overall reinfection rate was 24% [22]. In addition to factors affecting host status (Table 2), other authors have suggested there may be more affecting variables; however, to what extent each host comorbidity drives the host's inability to overcome infections and operative complications is unknown. These include coronary artery disease, anemia, psychiatric disease, and sleep apnea [8]. Few studies have examined the management of massive bone loss in patients with PJI. Minor bone loss during reimplantation can be addressed with cement, sleeves, or distal-fit prostheses, whereas patients with massive bone loss may need a megaprosthesis. Successful treatment of infected THA and TKA with megaprostheses has been reported in a small series at 83% (24 of 29) [7]. Bone loss around the infected implant may be less of a concern than it is in the management of osteomyelitis of the long bones and may not need to be included in hypothesized classification systems of PJI. A logical assumption is that older patients are likely to do worse than younger patients, but some authors suggest that patients younger than 60 years may also be at risk [28, 31]. A review of DAIR in patients with chronically infected TKAs concluded that patients younger than 60 years had both an increased risk of subsequent infections and a need for component removal [31]. In another analysis of infected TKAs, the results showed that the mean age of patients who successfully underwent two-stage revision was higher than that of patients with reinfection (mean success 74 years, mean failure 65; p = 0.01) [28]. Because both of these studies were retrospective, the underlying nature of the poorer outcome in younger patients may be due to selection bias and prevention of "sicker, older" patients from completing their surgical protocols. The distinction between a Type II and III infection is the presence of infection symptoms for more than 4 weeks; some suggest this temporal period must be reduced. Symptoms for less than 48 hours was identified to improve infection clearance in patients undergoing a DAIR procedure, in a study of 99 patients [16]. Conclusions The McPherson classification system provides a way to group patients with infected THAs and TKAs. It provides a tool to communicate host and infection characteristics in what is a very complex and specialized field. Of significant concern is the seemingly widespread, international use of this classification despite an absence of validation studies. Two-stage revision for infected arthroplasty is commonly accepted as necessary for the treatment of periprosthetic infection, but it is laden with risk and burden to the patient. The use of the McPherson staging system has led to existing literature which suggests that DAIR and single-stage revision arthroplasty for infected THA and TKA can be favorably considered in McPherson Type I/A/1 patients. Caution and consideration of treatment goals should be strongly considered if providing DAIR or single-stage revision to patients with host Grade B or C, or those with Type III infections. Demographic changes among future arthroplasty patients means the development of a robust, validated system to stratify failed septic arthroplasties for determining a treatment regimen will continue to be important. Within the literature to date, robust studies of periprosthetic classification systems are absent. This provides opportunity for future research, although this will remain difficult due to low numbers of patients with infected arthroplasties. Many treatment protocols are based on innominate regimes proposed through expert opinions and available studies. The McPherson classification system attempts to address this issue, although it remains an unvalidated system, supported by only small case series. Although the McPherson classification system is accepted by a number of relevant large international groups, we caution the use of this system until research validating its use exists.
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