Kjell G. Nilsson

Hydroxyapatite coating versus cemented fixation of the tibial component in total knee arthroplasty

Fifty-three consecutive patients (57 knees; mean age, 69 years) entered a prospective randomized study to compare the fixation of hydroxyapatite (HA)-coated (29 knees) with cemented (28 knees) tibial components in the Tricon II total knee arthroplasty. The quality of the fixation during 5 years postoperatively was evaluated with radiostereometric analysis (RSA). Three HA-coated implants were revised: 2 owing to infection, and 1 owing to early delamination of the coating and clinical loosening. Eight patients (9 knees) died, 1 patient sustained a stroke, and 1 patient refused investigations after 1 year. In the 40 patients (19 HA-coated, 21 cemented) remaining at 5 years, the magnitude of the micromotion between the HA-coated and cemented groups did not differ. The HA-coated implants displayed most of the migration within the initial 3 months then stabilized, whereas the cemented implants showed an initially lower, but over time continuously increasing migration. Between 1 and 2 years, 4 of 24 HA-coated and 10 of 23 cemented implants migrated >0.2 mm and were categorized unstable, which has been shown to have a prognostic value as regards future aseptic loosening. Progressive radiolucent lines developed in 2 cemented knees, which both were categorized unstable. If HA-coated implants can sustain the forces that threaten the fixation in the early period after implantation, a strong and enduring fixation may be obtained.

Abnormal kinematics of the artificial knee : roentgen stereophotogrammetric analysis of 10 Miller-Galante and five New Jersey LCS knees

The in vivo kinematics of two types of unconstrained, posterior cruciate ligament retaining knee prostheses were analyzed 1 year postoperatively using roentgen stereophotogrammetric analysis. Ten knees had the Miller-Galante and five the New Jersey LCS design. The Miller-Galante knees displayed decreased adduction during active flexion when compared with normal knees. In both types of prostheses, there was decreased medial and increased proximal and posterior displacement. The abnormal kinematics probably reflect the design of the articular surfaces, the absence of the anterior cruciate ligament, and the dysfunction of the posterior cruciate ligament.

Increased varus-valgus tilting of screw-fixated knee prostheses: Stereoradiographic study of uncemented versus cemented tibial components*

Twenty-six women and three men (34 knees) with osteoarthrosis were operated with the Miller-Galante I (Zimmer, Warsaw, IN) knee prosthesis. The patients were randomized to either cemented or uncemented fixation of the tibial component. All patients received a TiVaAl alloy tibial plate with four pegs and titanium fiber-mesh undersurface. In the uncemented knees four screws were added. The fixation of the tibial component was determined by roentgen stereophotogrammetric analysis during the first 2 postoperative years. Rotations of the entire tibial component were recorded, as well as proximal or distal translation of various parts of the prosthetic edge corresponding to subsidence and lift-off. The uncemented components displayed almost all rotation and translation during the first 6 weeks, whereas the cemented ones displayed a more gradually increasing migration during the 2 years. Tibial component rotation about the sagittal axis was significantly increased in the uncemented knees throughout the investigation period. This corresponded to increased subsidence medially or laterally in the uncemented knees, whereas lift-off was equal in the two groups. Thin (8.5 mm) uncemented tibial components displayed more subsidence than the thicker ones at the medial or lateral edge 3 months after surgery.

Uncemented HA-coated implant is the optimum fixation for TKA in the young patient.

Fixation of the tibial component in total knee arthroplasty in younger patients remains controversial. We evaluate the results of three different types of fixation of the Profix total knee arthroplasty in a randomized controlled trial of 97 consecutive knees (85 patients) with osteoarthrosis or inflammatory arthritis with 2-year followup of all patients. We randomized patients to three different types of fixation of the tibial component: cemented, uncemented (HA coated) with screws, or uncemented (HA coated) without screws. We performed clinical evaluations and radiostereometric analysis at 6 weeks, and 3, 6, 12 and 24 months postoperatively. The knees in the uncemented groups migrated more than those in the cemented group during the first 3 months, but at 2 years we observed no differences. The uncemented implants displayed all migration within the first 3 months. The cemented implants did not stabilize but had continuously increasing migration during the followup. Cementless implants without screws did not migrate more than implants with screws and displayed similar pattern of migration, indicating screws do not improve fixation. Uncemented fixation using hydroxyapatite-coated implants without screws seems to be the best solution for the younger patient. Level of Evidence: Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

Knee motion in total knee arthroplasty : a Roentgen stereophotogrammetric analysis of the kinematics of the tricon-M knee prosthesis

The three-dimensional kinematics of the Tricon-M knee prosthesis during active knee flexion and extension were recorded in 11 patients with arthrosis or rheumatoid arthritis using roentgen stereophotogrammetric analysis. Twenty-three normal knees constituted the control group. The prosthetic knees displayed the same degrees of freedom regarding rotational and translational movements as the normal knees, although the kinematics were different. A combination of internal rotation, abduction, and lateral translation of the tibia was recorded during flexion, and the reversed movements were recorded during extension. During the first 25 degrees of flexion, these movements were small, reflecting the high congruency between the articular surfaces, while beyond 25 degrees they increased. The normal knees displayed a combination of internal rotation, adduction, and medial translation of the tibia during flexion and the reversed movements during extension. The prosthetic knees also exhibited an increased posterior displacement during increasing flexion when compared with the normal knees. There was a correlation between the positioning of the femoral component in the sagittal plane and the recorded anterior/posterior translations. In conclusion, the kinematics of the Tricon-M knee prosthesis significantly differ from the normal knee, probably because of the design of the prosthesis and the absence of the cruciate ligaments.

Mobile bearings do not improve fixation in cemented total knee arthroplasty.

Mobile bearings were introduced to improve wear and knee kinematics. By uncoupling the forces generated at the articulation from the implant-bone interface this would, theoretically, also improve the fixation of the implant to bone. We did this study to evaluate whether mobile bearings improve the fixation of the tibial component to bone. Fifty-two consecutive knees in 47 patients (average age, 72 years; range, 62-84 years) with primary osteoarthrosis were randomized into two groups to receive a cemented total knee arthroplasty with either a fixed-bearing or mobile-bearing tibial component. The quality of fixation was analyzed with radiostereometric analysis for up to 2 years. Mobile bearings did not improve fixation. Both magnitudes and directions of component rotations were similar, and the number of implants with continuous migration was almost identical. Both implant types had a combination of subsidence and lift-off, but where the mobile bearing implants displayed more of subsidence, the fixed bearing knees showed more lift-off. It might be that the somewhat stiffer cobalt-chromium baseplate or the different joint conformity used in the mobile-bearing knees counteracts any potential effects of the mobile bearing. Level of Evidence: Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

No adverse effects of submelt-annealed highly crosslinked polyethylene in cemented cups: An RSA study of 8 patients 10 years after surgery

Background and purpose Highly crosslinked polyethylene (PE) is in standard use worldwide. Differences in the crosslinking procedure may affect the clinical performance. Experimenatal data from retrieved cups have shown free radicals and excessive wear of annealed highly crosslinked PE. We have previously reported low wear and good clinical performance after 6 years with this implant, and now report on the 10-year results. Patients and methods In 8 patients, we measured wear of annealed highly crosslinked PE prospectively with radiostereometry after 10 years. Activity was assessed by UCLA activity score and a specifically designed activity score. Conventional radiographs were evaluated for osteolysis and clinical outcome by the Harris hip score (HHS). Results The mean (95% CI) proximal head penetration for highly crosslinked PE after 10 years was 0.07 (–0.015 to 0.153) mm, and the 3D wear was 0.2 (0.026 to 0.36) mm. Without creep, proximal head penetration was 0.02 (–0.026 to 0.066) mm and for 3D penetration was 0.016 (–0.47 to 0.08) mm. This represents an annual proximal wear of less than 2 µm. All cups were clinically and radiographically stable but showed a tendency of increased rotation after 5 years. Interpretation Wear for annealed highly crosslinked PE is extremely low up to 10 years. Free radicals do not affect mechanical performance or lead to clinically adverse effects. Creep stops after the first 6 months after implantation. Highly crosslinked PE is a true competitor of hard-on-hard bearings.

Porous-coated cups fixed with screws. : A 12-year clinical and radiostereometric follow-up study of 50 hips.

Background Excellent mid-term results have stimulated the use of hemispherical porous-coated cups in hip replacement. With longer follow-up, there have been problems related to polyethylene wear and liner fixation, and osteolysis has been documented in reports of selected cases. We evaluated the clinical and radiographic results of 50 patients followed for 12 years. Patients and methods 58 consecutive patients (58 hips), mean age 55 years, were operated with Harris-Galante (HG) I or II cups using line-to-line fit and additional screw fixation. Polyethylene linersγ-sterilized in air and 32-mm ceramic heads were used. 8 patients died within 12 years, leaving 50 patients with a complete 12year follow-up. 23 of the cups were also evaluated with radiostereometry (RSA) for migration, liner stability, and wear. Results All metal shells were still in situ after 12 years. 4 hips had been revised due to femoral loosening. In these revisions, the liner had been exchanged due to wear and/or instability, resulting in a cup survival rate of 89%. 28 cups displayed osteolytic lesions, mainly in relation to screws. RSA revealed minimum translations, but in many cases there were pronounced liner rotations suggesting unstable liners within the metal shell. The annual proximal wear was 0.09 mm and the three-dimensional wear was 0.16 mm. Interpretation RSA can predict the long-term performance of cup fixation. Low migration during the initial years after implantation indicates excellent long-term results regarding fixation of the metal shell. The main problem with this design appears to be liner instability and osteolysis, factors that are probably interrelated. Because these phenomena are clinically silent, we recommend regular follow-up of patients with HG cups to avoid sudden loosening and complicated revisions.

Inferior performance of Boneloc® bone cement in total knee arthroplasty: A prospective randomized study comparing Boneloc® with Palacos® using radiostereometry (RSA) in 19 patients

We compared Boneloc bone cement with conventional cement (Palacos) in fixating the tibial component during 2-5 years in 19 patients with gonarthrosis undergoing total knee arthroplasty in a prospective randomized study. Boneloc displayed significantly larger migration, subsidence and lift-off than Palacos. The difference was identifiable already within 3 months postoperatively, but became significant at 12 months. In the Boneloc group, all components showed subsidence of the posterior part and lift-off of the anterior part of the tibial component, whereas in the Palacos group, the locations of subsidence and lift-off were evenly distributed about the edge of the implant. At 5 years, both Boneloc knees so far investigated were clinical failures with high migration rates. We conclude that, even in total knee arthroplasty, there is a substantial risk that Boneloc leads to inferior clinical results, but later than in hip replacements.

Cemented versus uncemented fixation of the femoral component of the NexGen CR total knee replacement in patients younger than 60 years: a prospective randomised controlled RSA study.

The optimal mode of femoral fixation in total knee arthroplasty (TKA) remains controversial, especially for the young patient. In a prospective randomised study we compared the magnitude and pattern of the fixation of cemented versus uncemented femoral components during 2 years in patients younger than 60 years. Forty-one knees in 41 patients were randomised to receive a NexGen (Zimmer, Warsaw, USA) cruciate-retaining TKA with either a cemented or an uncemented non HA-coated femoral component. The patients were examined by radiostereometric analysis (RSA), as well as clinical and radiological evaluation. The magnitude and pattern of migration as measured by RSA did not differ significantly between the cemented and uncemented fixation during the 2-year follow-up, nor were there any differences between the groups in clinical parameters. These findings suggest that an uncemented and non HA-coated femoral component may behave equally as well as a cemented one in the long-term.