RESUMO
BACKGROUND: It is the aim of this study to conceptualize a scheme for patellar-height analysis suitable for knees without and with implanted endoprosthesis. Furthermore, patellar-height and change of patellar-height by total-knee-arthroplasty (TKA) should be studied and correlated with clinical outcomes. We hypothesize that not only True-Patella-Infera (TPI) but also Pseudo-Patella-Infera (PPI) might be correlated with elevated anterior-knee-pain and reduced range-of-motion. METHODS: Several patellar-height indices were measured by three independent raters in two passes. Indices were analyzed and intra- and interobserver agreements were determined. For radiographic and clinical evaluation of 92 knee arthroplasties, the Insall-Salvati Index (ISI) and the Caton-Deschamps Index (CDI) were used to determine patellar-height and especially the amounts of TPI and PPI. Patellar-height was correlated with clinical outcome parameters: pain, ROM, Oxford Knee Score, Knee Society Score, Kujala Score, SF-36, Tegner and Lysholm. RESULTS: All used patellar-height indices demonstrated good intra- and interobserver agreement. Low preoperative ROM was correlated with low postoperative ROM after primary TKA. Postoperatively, 2.2% of the patients had a TPI and 9.8% had a PPI. Patella infera was not correlated with reduced subjective or objective clinical outcome parameters. CONCLUSIONS: Preoperative ROM is a good predictor of postoperative ROM after primary TKA. Patellar-height analysis can be sufficiently performed using the ISI and the CDI, respectively the derived CDI (dCDI) in cases with implanted endoprosthesis. As an alternative to the CDI/dCDI, the BPI/mBPI can be used. There seems to be a certain threshold of acceptable patellar-height reduction, in which clinical outcome is not deteriorated.
RESUMO
PURPOSE: The original Caton-Deschamps index (oCDI) detects functional patella height. It cannot be used in knees with an implanted endoprosthesis. The "modified Caton-Deschamps index" (mCDI) for knee arthroplasty can miss pseudo-patella-infera (PPI), which is common after TKA. A derivate of the oCDI could be a simple analogue to the index published in 1982 using a modified tibial reference point at the anterior proximal point of the inlay, which can indirectly be located on the lateral knee radiograph. It was the aim of this study to determine the intra- and inter-rater agreement of a derived Caton-Deschamps index (dCDI) for knee arthroplasty. We hypothesized that the derived Caton-Deschamps index (dCDI) is a reliable radiological measure for patella height in knee arthroplasty. METHODS: Several patella height indices were measured by three independent raters in two passes. The second pass was performed after 6 weeks in random order. Intra- and inter-observer agreements were determined and analyzed using the intraclass correlation coefficient (ICC). For radiographic evaluation, digital lateral radiographs of 150 knees before and after primary TKA were used. RESULTS: We found high interrater reliability for all analyzed indices. We found the highest agreements for the ISI preop (ICC = 0.914) and postop (ICC = 0.920), respectively. We also found very good intra-rater reliability for the CDI (ICCpreop = 0.954), dCDI (ICCpostop = 0.945), ISI (ICCpreop = 0.960; ICCpostop=0.940) and BPI (ICCpreop = 0.969; ICCpostop = 0.955). Fourteen cases (9.3%) with insignificant PPI were found. CONCLUSION: The derived Caton-Deschamps index (dCDI) can easily be used in knee arthroplasty and demonstrated high intra- and interrater agreement, which was similar to other commonly used and established patella height indices.