The Müller type cemented hip prosthesis, also called self-locking prosthesis, is one of the most extensively copied and
utilized hip prostheses. Considering the implantation of the cemented stem, the author originally suggested achieving a
press fit between the stem and endostal cortex by implanting a prosthesis of the largest possible size. Analyzing our group
of patients who undergo aseptic stem revision, we try to quantify the term „press fit“ by measuring the filling of the femoral
canal by the metal stem, the so-called canal-fill ratio. Our preliminary results suggest that press-fit is achieved when
the stem occupies more than 90% of the canal diameter in the anterior-posterior projection

Gordan Gulan

Hari Jurdana

English

Gulan, Gordan

Jurdana, Hari

Repository of the University of Rijeka

Coll. Antropol. 31 (2007) 1: 195–198Original scientific paperThe Canal Fill Ratio as a Factor Influencing theAseptic Loosening of the Müller-Type CementedStem – Preliminary ReportGordan Gulan and Hari JurdanaClinic for Orthopaedic Surgery Lovran, Faculty of Medicine University of Rijeka, CroatiaA B S T R A C TThe Müller type cemented hip prosthesis, also called self-locking prosthesis, is one of the most extensively copied andutilized hip prostheses. Considering the implantation of the cemented stem, the author originally suggested achieving apress fit between the stem and endostal cortex by implanting a prosthesis of the largest possible size. Analyzing our groupof patients who undergo aseptic stem revision, we try to quantify the term „press fit“ by measuring the filling of the femo-ral canal by the metal stem, the so-called canal-fill ratio. Our preliminary results suggest that press-fit is achieved whenthe stem occupies more than 90% of the canal diameter in the anterior-posterior projection.Key words: Müller, cemented stem, canal fill ratioIntroductionIn 1977, Müller introduced his cemented straightstem hip prosthesis. It was recommended that the stembe tapered using the largest possible size for a particularfemur, achieving a press-fit between the medial and lat-eral walls of the femur and the prosthesis. The Müllerprosthesis has been extensively copied and is still one ofthe most frequently used implants in some Europeancountries.In a follow-up study, this stem revealed promisingclinical results, including a 10-year survival rate1–2, 4–11.Patients and MethodsPatientsAmong all revised hip prostheses in the period be-tween 2000 and 2005, we analyzed a homogenous groupof 26 patients. All received a hip prosthesis between 65and 70 years of age due to hip arthrosis.The level of physical activity was similar in all pa-tients and all were properly implanted with both compo-nents of the Müller type prosthesis, produced by Lima®.All patients had only one hip prosthesis. 18 patients werefemale and 8 were male. The survival rate of the ce-mented stem was defined as the period between primaryhip arthroplasty and the clinical sign of loosening. Crite-ria for revision required vital patients, pain, and if possi-ble, radiological evidence indicating a loosening of thefemoral component. We excluded patients with radiologi-cal indications alone, such as radiolucent lines or stemsubsidence through the axial load because this is no lon-ger considered to indicate definitive loosening, given thatthe stability of a tapered stem increases with subsidence,which explains the high survival rate of these types ofstems2.Operative TechniqueAll operations on 15 patients were performed in ourclinic, by the same surgical team. In 11 patients the pri-mary implantation was done at other institutions. Allwere evaluated and controlled largely in our clinic. In allpatients the transgluteal surgical approach to the hipwas used without trochanteric osteotomy. After reamingthe acetabulum, the polyethylene cup of correspondingsize was cemented using the finger-packing technique.The femoral canal was prepared according to the manu-facturer’s instructions and rasped until cortical resis-195Received for publication December 14, 2006tance was felt. The stem had the same cross-sectional di-mensions as the rasp. After reaming, the femoral canalwas cleaned, dried and occluded with bone plaque. Astem of the same size as the rasp was introduced usingPalacos® bone cement. All had a 28mm diameter head,and all were produced by the same manufacturer.Plain Radiography AnalysisWe analyzed plain x-rays taken after primary hiparthroplasty of all patients who underwent femoral stemrevision surgery alone or in combination with acetabularrevision due to aseptic loosening.With the aim to observe the ratio between the femoralcanal and the stem, we analyzed only the AP projectionbecause proper stability and the proposed stem positionshould be achieved in this plane.We identified the diameter of the canal-stem ratio asan important factor in the longevity of the cementedstem. The diameter of the canal was defined as the dis-tance between the endostal cortex, which is perpendicu-lar to the long axis of the femoral canal. The stem diame-ter was defined as the distance between two peripheralpoints at a level perpendicular to the long axis of the fem-oral canal. We measured the canal fill ratio at the level atwhich the stem was nearest to the endostal cortex, andaccording to the Green zones3.We also analyzed stem alignment, measuring the de-viation between the long axis of the stem and the femoralcanal.We divided the patients into two groups, according tothe radiographic measurement of the stem/canal diame-ter ratio. The first group comprised patients in whom thestem occupied more than 90% of the femoral canal at ei-ther level. To the contrary, the second group comprisedpatients in whom the stem occupied less than 90%. Weanalyzed only the stem implanted in a neutral position orin a position less than 5 degrees of varus or valgus, whichwe determined to be the border beyond which there is asignificantly higher risk of progressive loosening4.ResultsIn the examined groups there were 8 male and 18 fe-male patients. The gender distribution in the first groupwas 5 male and 11 female patients, while in the secondgroup there were 3 male and 7 female patients. Using thegender representation test, a comparison of the twogroups did not yield results of statistical significance.In both groups intimate contact of the stem with thefemoral wall was achieved, but in the first group theradiolucent line, which represents the residual layer ofthe cancelous bone, was somewhat larger. In this groupthe stem occupied 70–90% of the femoral canal at thelevel measured (Figure 1). In the second group the stemoccupied 90%–100% of the femoral canal.Configuration of the femoral canal determined thelevel and the length of the closest contact of the stemwith the inner part of the femoral canal in the AP projec-tion. In both groups this was in the lower part of thestem, which corresponds to the upper half of the Gruenzones 3 and 5. In the first group the most intimate con-tact was achieved with the lateral side of the femoral ca-nal, while in the second group the distance between lat-eral and medial walls was equal.G. Gulan and H. Jurdana: The Canal Fill Ratio, Coll. Antropol. 31 (2007) 1: 195–198196Fig. 1. X-ray of the Müller type cemented hip prosthesis with astem occupying <90% of femoral canal diameter: A – directly afterimplantation; B – loosened 5 years later.The time of revision in the first group was 6.7 years(2.2 – 9.5). In the second group, the average time of revi-sion was 8.5 years (6.5 – 12), due to aseptic loosening.Statistically (one way ANOVA), the survival rate in thesecond group was thus significantly longer compared tothe first group.DiscussionThe Müller-type stem has dual fixation: self-inter-locking, based on the anchoring principle, and by cementwhich fills the remaining space and acts only as a filter5.According to Morscher and Wirz, due to its fixation sys-tem, Müller’s stem may be called a “hybrid stem”2,5. Themain disadvantage of this stem type is the large func-tional joint space that allows particles of any origin toreach almost every part of the prosthesis and initiate theloosening process2,5.Aseptic loosening is the main long-term reason for thefailure of THA prostheses and accounts for 80% of revisioncases6. Most of the literature describing theMüller-type hipprosthesis shows a satisfactory survival rate varying from88.8%7 to 97%8 during a 10-year follow-up period.The acetabular component made of polyethylene wasrecognized as the weakest link in the chain, especially inconcurrence with a metal head of a 32mm diameter9.With regard to the acetabular component, aseptic loosen-ing increases exponentially after the sixth or seventhpostoperative year10. In contrast, femoral loosening ap-pears to increase at a relatively constant rate10, and re-mains a significant cause of the early failure of total hipreplacement8. Additionally, the survival rate was approx-imately 85% in a 10-year follow up period in the study ob-tained by Biemant1.Analyzing all our patients in both groups separately,based on the femoral canal fill ratio, the survival rate wasstatistically significant between groups. In the groupwhere the stem occupied more than 90% of the femoralcanal the average revision time was 8.5 years, while inthe other group the average revision time was 6.3.The mean time of revision due to aseptic loosening ofthe cemented hip prosthesis published by Havinga et allwas 6.3 years11. The same average revision time was ob-served in our first group, but with a somewhat narrowrange. In this group we observed only the aseptic loosen-ing of the stem. Havinga does not mention in his paperwhich component(s) was revised. If he significantly re-vised the femoral part, this could be another indirect evi-dence that the stem is responsible for early aseptic loos-ening of the cemented hip prosthesis.In the second group, with longer average revisiontime, we observed the loosening of both prosthesis com-ponents in seven patients. Where both prosthesis compo-nents have been revised we could not determine whichcomponent started loosening first. The longevity of theseseven prostheses, where both components had been re-vised, was higher than in any other. This observation isalso in agreement with the observation that the stem isresponsible for early loosening.Our preliminary results suggest that if the stem occu-pies less than 90% of the femoral canal it can be fit, butnot pressed enough against the inner part of the femoralwall, which appears to be critical in the development ofearly aseptic loosening in Müller-type cemented stem(Figure 2). Based on this finding, the femoral stem whichoccupies less than 90% of the femoral canal may be con-sidered undersized.In conclusion, we would like to emphasize the chal-lenge and importance of femoral canal preparation. Oneof the important steps in this process is preoperativeplanning. However, preoperative planning is not entirelyreliable, due to potential mismatch between X-ray and invivo findings. Surgeons must also rely on auscultatorsand tactile sensation during canal preparation, alwaysaiming to implant the largest possible stem, and alwayskeeping in mind that the stem should fit in the femoralcanal and not vice-versa.G. Gulan and H. Jurdana: The Canal Fill Ratio, Coll. Antropol. 31 (2007) 1: 195–198197Fig. 2. Schematic illustration of the implanted cemented Müller-typefemoral stem: A – press-fit implantation; B – fit implantation.R E F E R E N C E S1. BIEMANT JJ, Rev Chir Orthop Reparatrice Appar Mot, 81 (1995)380. — 2. MORSCHER EW, WIRZ D, Acta Orthopedica Belgica, 68 (2002)1. — 3. GRUEN TA,. McNEICE GM, AMSTUTZ HC, Clin Orthop RelatRes, 141 (1979) 17. — 4. EBRAMZADEH E, SARMIENTO A, McKEL-LOP HA, LLINAS A, GOGAN WJ, Bone Joint Surg, 76-A (1994) 77. — 5.WIRZ D, DANIELS AU, GOPFERT B, MORSCHER EW, Orthop Clin NAm, 36 (2005) 63. — 6. MALCHAU PH,. HERBERTS P, AHNFELT L,Acta Orthop Scand, 64 (1993) 497. — 7. MOLLENHOFF, G, DAVID A,WALZ M, Zentralb Chir, 120 (1995) 716. — 8. WILSON-McDONALC J,MORSCHER EW, Arch Orthop Trauma Surg, 109 (1990) 14. — 9. , , B, ,72 (1990) 518. — 10. MORSHER EW, SCHMASSMANN A, Arch OrthopTrauma Surg, 101 (1983) 137. — 11. HAVINGA ME, SPRUIT M, AN-DERSON PG, VAN DIJK-VAN DAM MS, PAVLOV PV, VAN LIMBEEK J,J Arthroplasty, 16 (2001) 33.G. GulanClinic for Orthopaedic Surgery Lovran, Medical Faculty University of Rijeka, M. Tita 1, 51415 Lovran, Croatiae-mail: gordan.gulan@medri.hrISPUNJENOST FEMORALNOG KANALA STEMOM KAO ^IMBENIK U NASTANKUASEPTI^KE NESTABILNOSTI MÜLLEROVOG TIPA CEMENTIRANE PROTEZE KUKA– PRETHODNO PRIOP]ENJES A @ E T A KMullerov tip cementirane endoproteze zgloba kuka jedna je od naj~e{}e kori{tenih endoproteza zgloba kuka u po-jedinim Europskim zemljama. Originalna metoda implantacije cementiranog femoralnog dijela podrazumjeva posti-zanje dobrog kontakta izme|u kosti i metalnog dijela proteze tijekom njenog implantiranja – »press fit«. To se posti~ena na~in da se implantira {to je mogu}e ve}i femoralni dio proteze. U na{oj grupi bolesnika u kojih je zamjenjen ce-mentirani femoralni dio proteze poku{ali smo kvantificirati izraz »press fit« na na~in da smo mjerili ispunjenost fe-moralnog kanala stemom u bolesnika kod kojih je proteze zamijenjena zbog nastanka asepti~ke nestabilnosti. Na{i prvirezultati ukazuju da se »press fit« posti`e onda, ako je na nekoj od mjerenih razina kanal vi{e od 90% ispunjen fe-moralnom komponentom.G. Gulan and H. Jurdana: The Canal Fill Ratio, Coll. Antropol. 31 (2007) 1: 195–198198

The Canal Fill Ratio as a Factor Influencing the Aseptic Loosening of the Müller-Type Cemented Stem – Preliminary Report

Repository of the University of Rijeka, Faculty of Medicine

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Coll. Antropol. 31 (2007) 1: 195–198Original scientific paperThe Canal Fill Ratio as a Factor Influencing theAseptic Loosening of the Müller-Type CementedStem – Preliminary ReportGordan Gulan and Hari JurdanaClinic for Orthopaedic Surgery Lovran, Faculty of Medicine University of Rijeka, CroatiaA B S T R A C TThe Müller type cemented hip prosthesis, also called self-locking prosthesis, is one of the most extensively copied andutilized hip prostheses. Considering the implantation of the cemented stem, the author originally suggested achieving apress fit between the stem and endostal cortex by implanting a prosthesis of the largest possible size. Analyzing our groupof patients who undergo aseptic stem revision, we try to quantify the term „press fit“ by measuring the filling of the femo-ral canal by the metal stem, the so-called canal-fill ratio. Our preliminary results suggest that press-fit is achieved whenthe stem occupies more than 90% of the canal diameter in the anterior-posterior projection.Key words: Müller, cemented stem, canal fill ratioIntroductionIn 1977, Müller introduced his cemented straightstem hip prosthesis. It was recommended that the stembe tapered using the largest possible size for a particularfemur, achieving a press-fit between the medial and lat-eral walls of the femur and the prosthesis. The Müllerprosthesis has been extensively copied and is still one ofthe most frequently used implants in some Europeancountries.In a follow-up study, this stem revealed promisingclinical results, including a 10-year survival rate1–2, 4–11.Patients and MethodsPatientsAmong all revised hip prostheses in the period be-tween 2000 and 2005, we analyzed a homogenous groupof 26 patients. All received a hip prosthesis between 65and 70 years of age due to hip arthrosis.The level of physical activity was similar in all pa-tients and all were properly implanted with both compo-nents of the Müller type prosthesis, produced by Lima®.All patients had only one hip prosthesis. 18 patients werefemale and 8 were male. The survival rate of the ce-mented stem was defined as the period between primaryhip arthroplasty and the clinical sign of loosening. Crite-ria for revision required vital patients, pain, and if possi-ble, radiological evidence indicating a loosening of thefemoral component. We excluded patients with radiologi-cal indications alone, such as radiolucent lines or stemsubsidence through the axial load because this is no lon-ger considered to indicate definitive loosening, given thatthe stability of a tapered stem increases with subsidence,which explains the high survival rate of these types ofstems2.Operative TechniqueAll operations on 15 patients were performed in ourclinic, by the same surgical team. In 11 patients the pri-mary implantation was done at other institutions. Allwere evaluated and controlled largely in our clinic. In allpatients the transgluteal surgical approach to the hipwas used without trochanteric osteotomy. After reamingthe acetabulum, the polyethylene cup of correspondingsize was cemented using the finger-packing technique.The femoral canal was prepared according to the manu-facturer’s instructions and rasped until cortical resis-195Received for publication December 14, 2006tance was felt. The stem had the same cross-sectional di-mensions as the rasp. After reaming, the femoral canalwas cleaned, dried and occluded with bone plaque. Astem of the same size as the rasp was introduced usingPalacos® bone cement. All had a 28mm diameter head,and all were produced by the same manufacturer.Plain Radiography AnalysisWe analyzed plain x-rays taken after primary hiparthroplasty of all patients who underwent femoral stemrevision surgery alone or in combination with acetabularrevision due to aseptic loosening.With the aim to observe the ratio between the femoralcanal and the stem, we analyzed only the AP projectionbecause proper stability and the proposed stem positionshould be achieved in this plane.We identified the diameter of the canal-stem ratio asan important factor in the longevity of the cementedstem. The diameter of the canal was defined as the dis-tance between the endostal cortex, which is perpendicu-lar to the long axis of the femoral canal. The stem diame-ter was defined as the distance between two peripheralpoints at a level perpendicular to the long axis of the fem-oral canal. We measured the canal fill ratio at the level atwhich the stem was nearest to the endostal cortex, andaccording to the Green zones3.We also analyzed stem alignment, measuring the de-viation between the long axis of the stem and the femoralcanal.We divided the patients into two groups, according tothe radiographic measurement of the stem/canal diame-ter ratio. The first group comprised patients in whom thestem occupied more than 90% of the femoral canal at ei-ther level. To the contrary, the second group comprisedpatients in whom the stem occupied less than 90%. Weanalyzed only the stem implanted in a neutral position orin a position less than 5 degrees of varus or valgus, whichwe determined to be the border beyond which there is asignificantly higher risk of progressive loosening4.ResultsIn the examined groups there were 8 male and 18 fe-male patients. The gender distribution in the first groupwas 5 male and 11 female patients, while in the secondgroup there were 3 male and 7 female patients. Using thegender representation test, a comparison of the twogroups did not yield results of statistical significance.In both groups intimate contact of the stem with thefemoral wall was achieved, but in the first group theradiolucent line, which represents the residual layer ofthe cancelous bone, was somewhat larger. In this groupthe stem occupied 70–90% of the femoral canal at thelevel measured (Figure 1). In the second group the stemoccupied 90%–100% of the femoral canal.Configuration of the femoral canal determined thelevel and the length of the closest contact of the stemwith the inner part of the femoral canal in the AP projec-tion. In both groups this was in the lower part of thestem, which corresponds to the upper half of the Gruenzones 3 and 5. In the first group the most intimate con-tact was achieved with the lateral side of the femoral ca-nal, while in the second group the distance between lat-eral and medial walls was equal.G. Gulan and H. Jurdana: The Canal Fill Ratio, Coll. Antropol. 31 (2007) 1: 195–198196Fig. 1. X-ray of the Müller type cemented hip prosthesis with astem occupying <90% of femoral canal diameter: A – directly afterimplantation; B – loosened 5 years later.The time of revision in the first group was 6.7 years(2.2 – 9.5). In the second group, the average time of revi-sion was 8.5 years (6.5 – 12), due to aseptic loosening.Statistically (one way ANOVA), the survival rate in thesecond group was thus significantly longer compared tothe first group.DiscussionThe Müller-type stem has dual fixation: self-inter-locking, based on the anchoring principle, and by cementwhich fills the remaining space and acts only as a filter5.According to Morscher and Wirz, due to its fixation sys-tem, Müller’s stem may be called a “hybrid stem”2,5. Themain disadvantage of this stem type is the large func-tional joint space that allows particles of any origin toreach almost every part of the prosthesis and initiate theloosening process2,5.Aseptic loosening is the main long-term reason for thefailure of THA prostheses and accounts for 80% of revisioncases6. Most of the literature describing the Müller-type hipprosthesis shows a satisfactory survival rate varying from88.8%7 to 97%8 during a 10-year follow-up period.The acetabular component made of polyethylene wasrecognized as the weakest link in the chain, especially inconcurrence with a metal head of a 32mm diameter9.With regard to the acetabular component, aseptic loosen-ing increases exponentially after the sixth or seventhpostoperative year10. In contrast, femoral loosening ap-pears to increase at a relatively constant rate10, and re-mains a significant cause of the early failure of total hipreplacement8. Additionally, the survival rate was approx-imately 85% in a 10-year follow up period in the study ob-tained by Biemant1.Analyzing all our patients in both groups separately,based on the femoral canal fill ratio, the survival rate wasstatistically significant between groups. In the groupwhere the stem occupied more than 90% of the femoralcanal the average revision time was 8.5 years, while inthe other group the average revision time was 6.3.The mean time of revision due to aseptic loosening ofthe cemented hip prosthesis published by Havinga et allwas 6.3 years11. The same average revision time was ob-served in our first group, but with a somewhat narrowrange. In this group we observed only the aseptic loosen-ing of the stem. Havinga does not mention in his paperwhich component(s) was revised. If he significantly re-vised the femoral part, this could be another indirect evi-dence that the stem is responsible for early aseptic loos-ening of the cemented hip prosthesis.In the second group, with longer average revisiontime, we observed the loosening of both prosthesis com-ponents in seven patients. Where both prosthesis compo-nents have been revised we could not determine whichcomponent started loosening first. The longevity of theseseven prostheses, where both components had been re-vised, was higher than in any other. This observation isalso in agreement with the observation that the stem isresponsible for early loosening.Our preliminary results suggest that if the stem occu-pies less than 90% of the femoral canal it can be fit, butnot pressed enough against the inner part of the femoralwall, which appears to be critical in the development ofearly aseptic loosening in Müller-type cemented stem(Figure 2). Based on this finding, the femoral stem whichoccupies less than 90% of the femoral canal may be con-sidered undersized.In conclusion, we would like to emphasize the chal-lenge and importance of femoral canal preparation. Oneof the important steps in this process is preoperativeplanning. However, preoperative planning is not entirelyreliable, due to potential mismatch between X-ray and invivo findings. Surgeons must also rely on auscultatorsand tactile sensation during canal preparation, alwaysaiming to implant the largest possible stem, and alwayskeeping in mind that the stem should fit in the femoralcanal and not vice-versa.G. Gulan and H. Jurdana: The Canal Fill Ratio, Coll. Antropol. 31 (2007) 1: 195–198197Fig. 2. Schematic illustration of the implanted cemented Müller-typefemoral stem: A – press-fit implantation; B – fit implantation.R E F E R E N C E S1. BIEMANT JJ, Rev Chir Orthop Reparatrice Appar Mot, 81 (1995)380. — 2. MORSCHER EW, WIRZ D, Acta Orthopedica Belgica, 68 (2002)1. — 3. GRUEN TA,. McNEICE GM, AMSTUTZ HC, Clin Orthop RelatRes, 141 (1979) 17. — 4. EBRAMZADEH E, SARMIENTO A, McKEL-LOP HA, LLINAS A, GOGAN WJ, Bone Joint Surg, 76-A (1994) 77. — 5.WIRZ D, DANIELS AU, GOPFERT B, MORSCHER EW, Orthop Clin NAm, 36 (2005) 63. — 6. MALCHAU PH,. HERBERTS P, AHNFELT L,Acta Orthop Scand, 64 (1993) 497. — 7. MOLLENHOFF, G, DAVID A,WALZ M, Zentralb Chir, 120 (1995) 716. — 8. WILSON-McDONALC J,MORSCHER EW, Arch Orthop Trauma Surg, 109 (1990) 14. — 9. , , B, ,72 (1990) 518. — 10. MORSHER EW, SCHMASSMANN A, Arch OrthopTrauma Surg, 101 (1983) 137. — 11. HAVINGA ME, SPRUIT M, AN-DERSON PG, VAN DIJK-VAN DAM MS, PAVLOV PV, VAN LIMBEEK J,J Arthroplasty, 16 (2001) 33.G. GulanClinic for Orthopaedic Surgery Lovran, Medical Faculty University of Rijeka, M. Tita 1, 51415 Lovran, Croatiae-mail: gordan.gulan@medri.hrISPUNJENOST FEMORALNOG KANALA STEMOM KAO ^IMBENIK U NASTANKUASEPTI^KE NESTABILNOSTI MÜLLEROVOG TIPA CEMENTIRANE PROTEZE KUKA– PRETHODNO PRIOP]ENJES A @ E T A KMullerov tip cementirane endoproteze zgloba kuka jedna je od naj~e{}e kori{tenih endoproteza zgloba kuka u po-jedinim Europskim zemljama. Originalna metoda implantacije cementiranog femoralnog dijela podrazumjeva posti-zanje dobrog kontakta izme|u kosti i metalnog dijela proteze tijekom njenog implantiranja – »press fit«. To se posti~ena na~in da se implantira {to je mogu}e ve}i femoralni dio proteze. U na{oj grupi bolesnika u kojih je zamjenjen ce-mentirani femoralni dio proteze poku{ali smo kvantificirati izraz »press fit« na na~in da smo mjerili ispunjenost fe-moralnog kanala stemom u bolesnika kod kojih je proteze zamijenjena zbog nastanka asepti~ke nestabilnosti. Na{i prvirezultati ukazuju da se »press fit« posti`e onda, ako je na nekoj od mjerenih razina kanal vi{e od 90% ispunjen fe-moralnom komponentom.G. Gulan and H. Jurdana: The Canal Fill Ratio, Coll. Antropol. 31 (2007) 1: 195–198198

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The Canal Fill Ratio as a Factor Influencing the Aseptic Loosening of the Müller-Type Cemented Stem – Preliminary Report

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