N Reina1, S Putman2, R Desmarchelier3, E Sari Ali4, P Chiron5, M Ollivier6, J Y Jenny7, D Waast8, C Mabit9, E de Thomasson10, C Schwartz11, P Oger12, L E Gayet13, H Migaud2, N Ramdane14, M H Fessy3. 1. Institut locomoteur (ILM), hôpital Pierre-Paul-Riquet, CHU de Toulouse, 31059 Toulouse, France. Electronic address: reina.n@chu-toulouse.fr. 2. Hôpital Salengro, CHU de Lille, place de Verdun, 59000 Lille, France. 3. Service de chirurgie orthopédique et traumatologique, hospices civils de Lyon, centre hospitalier Lyon-Sud, université de Lyon, 69002 Pierre-Bénite, France. 4. Service de chirurgie orthopédique et traumatologique, hôpital la Pitié-Salpétrière, 47-83, boulevard de l'Hôpital, 75013 Paris, France. 5. Institut locomoteur (ILM), hôpital Pierre-Paul-Riquet, CHU de Toulouse, 31059 Toulouse, France. 6. Service de chirurgie orthopédique et traumatologique, hôpital St. Marguerite, 13009 Marseille, France. 7. Service de chirurgie orthopédique et traumatologique, hôpital de Hautepierre, CHU de Strasbourg, 67091 Strasbourg, France. 8. Service de chirurgie orthopédique et traumatologique, Hôtel-Dieu, 1, place Alexis-Ricordeau, 44093 Nantes, France. 9. Service de chirurgie orthopédique et traumatologique, CHU Dupuytren, avenue M.-Luther-King, CHU de Limoges, 87000 Limoges, France. 10. Institut mutualiste Montsouris, 42, boulevard Jourdan, 75014 Paris, France. 11. Centre d'orthopédie clinique des 3-frontières, 68300 Saint-Louis, France. 12. Hopital A.-Mignot, 177, route De-Versailles, 78150 Le Chesnay, France. 13. Service de chirurgie orthopédique et traumatologique, CHU de Poitiers, 86021 Poitiers, France. 14. Unité de biostatistique, pôle de santé publique, CHRU de Lille, 59000 Lille, France.
Abstract
BACKGROUND: Various factors contribute to instability of total hip arthroplasty (THA), with implant orientation being a major contributor. We performed a case-control study with computed tomography (CT) data to determine whether: 1) orientation contributes to THA instability and 2) a safer target zone for stability than Lewinnek's classic safe zone can be defined. MATERIAL AND METHODS: We included prospectively 363 cases of THA dislocation that occurred during the calendar 2013 year in 24 participating hospitals. Of the 128 dislocations that occurred in patients who underwent THA at these centers, 56 (24 anterior, 32 posterior) had CT scans, thus were included in the analysis. The control group was matched 4:1 based on implant type, year of implantation, age, sex, bearing types and THA indication. Of the 428 matched control THA cases, 93 had CT scans. In all, the CT scans from 149 cases (56 unstable, 93 stable) were analyzed to determine the acetabular cup's inclination and anteversion, and the femoral stem's anteversion. RESULTS: In the unstable THA group, cup inclination was 46.9°±7.4°, cup anteversion was 20.4°±10.8° and stem anteversion was 14.2°±9.9°. In the stable THA group, cup inclination was 44.9°±5.3° (P=0.057), cup anteversion was 22.1°±5.1° (P=0.009) and stem anteversion was 13.4°±4.4° (P=0.362). The optimal total anteversion (cup+stem) of 40-60° was achieved in 16.5% of unstable THA cases and 13.9% of stable THA cases, thus this parameter does not predict stability (odds ratio [OR] of 0.40, P=0.144). The cup was positioned in Lewinnek's safe zone in 44.6% of patients in the unstable group and 68.2% of those in the stable group (OR 3.74, P=0.003). A target zone defined as 40-50° inclination and 15-30° anteversion was better able to distinguish between unstable cases (23.2%) and stable cases (71.6%) resulting in an OR of 13.91 (P<0.001). DISCUSSION: Implant positioning was the only risk factor for instability found in this study. Moreover, our findings reinforce the theory put forward by other authors that Lewinnek's safe zone is not specific enough to differentiate between stable and unstable THA implantations. The target zone for acetabular cups proposed here (40-50° inclination and 15°-30° anteversion) is related to a lower risk of instability. This orientation can be used as a guide, but must be combined with other technical elements to optimize stability. By balancing stability and biomechanics, the 40-50° inclination and 15°-30° anteversion target zone redefines the optimal positioning window. LEVEL OF EVIDENCE: III case-control study.
BACKGROUND: Various factors contribute to instability of total hip arthroplasty (THA), with implant orientation being a major contributor. We performed a case-control study with computed tomography (CT) data to determine whether: 1) orientation contributes to THA instability and 2) a safer target zone for stability than Lewinnek's classic safe zone can be defined. MATERIAL AND METHODS: We included prospectively 363 cases of THA dislocation that occurred during the calendar 2013 year in 24 participating hospitals. Of the 128 dislocations that occurred in patients who underwent THA at these centers, 56 (24 anterior, 32 posterior) had CT scans, thus were included in the analysis. The control group was matched 4:1 based on implant type, year of implantation, age, sex, bearing types and THA indication. Of the 428 matched control THA cases, 93 had CT scans. In all, the CT scans from 149 cases (56 unstable, 93 stable) were analyzed to determine the acetabular cup's inclination and anteversion, and the femoral stem's anteversion. RESULTS: In the unstable THA group, cup inclination was 46.9°±7.4°, cup anteversion was 20.4°±10.8° and stem anteversion was 14.2°±9.9°. In the stable THA group, cup inclination was 44.9°±5.3° (P=0.057), cup anteversion was 22.1°±5.1° (P=0.009) and stem anteversion was 13.4°±4.4° (P=0.362). The optimal total anteversion (cup+stem) of 40-60° was achieved in 16.5% of unstable THA cases and 13.9% of stable THA cases, thus this parameter does not predict stability (odds ratio [OR] of 0.40, P=0.144). The cup was positioned in Lewinnek's safe zone in 44.6% of patients in the unstable group and 68.2% of those in the stable group (OR 3.74, P=0.003). A target zone defined as 40-50° inclination and 15-30° anteversion was better able to distinguish between unstable cases (23.2%) and stable cases (71.6%) resulting in an OR of 13.91 (P<0.001). DISCUSSION: Implant positioning was the only risk factor for instability found in this study. Moreover, our findings reinforce the theory put forward by other authors that Lewinnek's safe zone is not specific enough to differentiate between stable and unstable THA implantations. The target zone for acetabular cups proposed here (40-50° inclination and 15°-30° anteversion) is related to a lower risk of instability. This orientation can be used as a guide, but must be combined with other technical elements to optimize stability. By balancing stability and biomechanics, the 40-50° inclination and 15°-30° anteversion target zone redefines the optimal positioning window. LEVEL OF EVIDENCE: III case-control study.
Authors: Pouria Rouzrokh; Taghi Ramazanian; Cody C Wyles; Kenneth A Philbrick; Jason C Cai; Michael J Taunton; Hilal Maradit Kremers; David G Lewallen; Bradley J Erickson Journal: J Arthroplasty Date: 2021-02-16 Impact factor: 4.435
Authors: Joost H J van Erp; Thom E Snijders; Harrie Weinans; René M Castelein; Tom P C Schlösser; Arthur de Gast Journal: Arch Orthop Trauma Surg Date: 2021-06-08 Impact factor: 2.928
Authors: Nicholas L Kolodychuk; Jesse A Raszewski; Brian P Gladnick; Kurt J Kitziger; Paul C Peters; Bradford S Waddell Journal: Arthroplast Today Date: 2022-08-15