Reliability and validity of the Unified Classification System for postoperative periprosthetic femoral fractures around cemented polished taper-slip stems

Abstract

Aims This aim of this study was to assess the reliability and validity of the Unified Classification System (UCS) for postoperative periprosthetic femoral fractures (PFFs) around cemented polished taper-slip (PTS) stems. Methods Radiographs of 71 patients with a PFF admitted consecutively at two centres between 25 February 2012 and 19 May 2020 were collated by an independent investigator. Six observers (three hip consultants and three trainees) were familiarized with the UCS. Each PFF was classified on two separate occasions, with a mean time between assessments of 22.7 days (16 to 29). Interobserver reliability for more than two observers was assessed using percentage agreement and Fleiss’ kappa statistic. Intraobserver reliability between two observers was calculated with Cohen kappa statistic. Validity was tested on surgically managed UCS type B PFFs where stem stability was documented in operation notes (n = 50). Validity was assessed using percentage agreement and Cohen kappa statistic between radiological assessment and intraoperative findings. Kappa statistics were interpreted using Landis and Koch criteria. All six observers were blinded to operation notes and postoperative radiographs. Results Interobserver reliability percentage agreement was 58.5% and the overall kappa value was 0.442 (moderate agreement). Lowest kappa values were seen for type B fractures (0.095 to 0.360). The mean intraobserver reliability kappa value was 0.672 (0.447 to 0.867), indicating substantial agreement. Validity percentage agreement was 65.7% and the mean kappa value was 0.300 (0.160 to 0.4400) indicating only fair agreement. Conclusion This study demonstrates that the UCS is unsatisfactory for the classification of PFFs around PTS stems, and that it has considerably lower reliability and validity than previously described for other stem types. Radiological PTS stem loosening in the presence of PFF is poorly defined and formal intraoperative testing of stem stability is recommended. Cite this article: Bone Joint J 2021;103-B(8):1339–1344.

Epidemiology and characteristics of femoral periprosthetic fractures

“…16 The classification has been subsequently validated, 25 although its validity and reliability in differentiating loose from fixed cemented polished taper stems has been questioned. 26 The COMPOSE femoral PPF cohort was predominantly UCS type B, 76% hip and 58% knee, in keeping with previous published series of PPFs around hip arthroplasty where the reported incidence of B type fractures ranged from 70% to 78%, 27,28 and with Swedish registry data (86%). 13 Type A fractures are often under-reported or excluded from cohort studies examining PPFs as they may be treated nonoperatively and/or be managed in an outpatient setting.…”

Management and outcomes of femoral periprosthetic fractures at the hip

“…For B2 and B3 fractures, the proportions of patients undergoing revision (B2 77%; B3 77%) were lower than the 87% (B2) and 96% (B3) reported in the Cochrane Review by Khan et al 12 The difference in the proportion of patients undergoing revision for B1 and B2/B3 PPFs may to be due to the contemporary use of taper-slip cemented femoral stem designs. 13 The taper-slip stem design requires controlled subsidence within an intact cement mantle and therefore, when the cement-implant interface is broken, the implant is by definition loose and may require revision. In uncemented, proximally well-fixed implants, a fixation alone may be appropriate.…”

“…In uncemented, proximally well-fixed implants, a fixation alone may be appropriate. 9,13 National standards for the treatment of hip fragility fractures stipulate that these injuries should be operated on within 36 hours of admission. 14 COMPOSE data demonstrated that for all fractures, the median time between admission and surgery across 27 NHS sites was four days.…”

Periprosthetic femoral fracture type and location are influenced by the presence of an ipsilateral knee arthroplasty implant: A case-control study of 84 interprosthetic femoral fractures

“…Finally, VCS grade was assessed using plain radiographs only. Although the VCS is a well validated, reliable classification system [32][33][34], we acknowledge that stem stability can sometimes only be established intraoperatively, especially for polished taper-slip stems [35]. However, in this retrospective series, intraoperative stability was frequently not recorded.…”