Total Knee Arthroplasty Using Bicruciate-Stabilized or Posterior-Stabilized Knee Implants Provided Comparable Outcomes at 2 Years: A Prospective, Multicenter, Randomized, Controlled, Clinical Trial of Patient Outcomes.

BACKGROUND: The bicruciate-stabilized (BCS) knee arthroplasty was developed to replicate normal knee kinematics. We examined the hypothesis that patients with osteoarthritis requiring total knee arthroplasty (TKA) will have better functional outcome and satisfaction with the BCS implant compared with an established posterior cruciate-stabilized implant. METHODS: This multicenter, randomized, controlled trial compared the clinical outcomes of a BCS implant against an established posterior cruciate-stabilized implant with 2-year follow-up. Of the patients awaiting primary knee arthroplasty for osteoarthritis, 228 were randomized to receive either a posterior-stabilized or BCS implant. Primary outcomes were knee flexion and Oxford Knee Score. Secondary outcomes were rate of complications and adverse events (AEs). Tertiary outcomes included Knee Society Score, University of California, Los Angeles, activity score, Patella scores, EQ-5D, 6-minute walk time, and patient satisfaction. RESULTS: Complete data were recorded for 98 posterior-stabilized implants and 97 BCS implants. Twelve patients had bilateral knee implants. There was no difference between the groups for any of the measures at either 1 or 2 years. At 2 years, knee flexion was 119 ± 0.16 and 120 ± 1.21 degrees for the posterior-stabilized and BCS implants, respectively, (mean, standard error, P = .538) and Oxford Knee Scores were 40.4 ± 0.69 and 40.0 ± 0.67 (P = .828), respectively. There were similar device-related AEs and revisions in each group (AEs 18 vs 22; P = .732; revisions 3 vs 4; P = .618). CONCLUSION: There was no evidence of clinical superiority of one implant over the other at 2 years.

Stability of Uncemented Cups - Long-Term Effect of Screws, Pegs and HA Coating: A 14-Year RSA Follow-Up of Total Hip Arthroplasty.

Screws, pegs and hydroxyapatite-coating are used to enhance the primary stability of uncemented cups. We present a 14-year follow-up of 48 hips randomized to four groups: press-fit only, press-fit plus screws, press-fit plus pegs and hydroxyapatite-coated cups. Radiostereometric migration measurements showed equally good stability regardless cup augmentation. The mean wear rate was high, 0.21 mm/year, with no differences between the groups. Seven hips had radiographical osteolysis but only in hips with augmented cups. Cups without screw-holes compared with cups with screw-holes resulted in better clinical outcome at the 14-year follow-up. Thus, augmentation of uncemented cups with screws, pegs, or hydroxyapatite did not appear to improve the long-term stability compared with press-fit only.

Less wear with aluminium-oxide heads than cobalt-chrome heads with ultra high molecular weight cemented polyethylene cups: a ten-year follow-up with radiostereometry.

PURPOSE: Wear is a major contributor to osteolysis and aseptic loosening of total hip replacements (THR). Both alumina (Al(2)O(3)) and cobalt-chrome (CoCr) femoral heads are commonly used. We investigated wear comparing alumina heads to cobalt-chrome heads against conventional cemented polyethylene (PE) cups for up to ten years. METHODS: Linear wear was measured with radiostereometry (RSA). Our material was derived from two prospective randomised trials that investigated fixation of femoral stems, not wear, and was evaluated retrospectively (Level III). RESULTS: The mean (95% CI) proximal head penetration was 0.96 mm (0.68-1.23) in the cobalt-chrome group and 0.42 mm (0.30-0.53) in the alumina group at ten years (P = 0.001). The mean (95% CI) 3D penetration was 1.07 mm (0.79-1.35) and 0.53 mm (0.38-0.63), respectively, at ten years (P = 0.001). CONCLUSION: Alumina heads performed better than cobalt-chrome heads in this study after ten-year follow-up.

No adverse effects of submelt-annealed highly crosslinked polyethylene in cemented cups: an RSA study of 8 patients 10 yaers 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.

10-year results of a new low-monomer cement: follow-up of a randomized RSA study.

BACKGROUND AND PURPOSE: The properties and performance of a new low-monomer cement were examined in this prospective randomized, controlled RSA study. 5-year data have already been published, showing no statistically significant differences compared to controls. In the present paper we present the 10-year results. METHODS: 44 patients were originally randomized to receive total hip replacement with a Lubinus SPII titanium-aluminum-vanadium stem cemented either with the new Cemex Rx bone cement or with control bone cement, Palacos R. Patients were examined using RSA, Harris hip score, and conventional radiographs. RESULTS: At 10 years, 33 hips could be evaluated clinically and 30 hips could be evaluated with RSA (16 Cemex and 14 Palacos). 9 patients had died and 4 patients were too old or infirm to be investigated. Except for 1 hip that was revised for infection after less than 5 years, no further hips were revised before the 10-year follow-up. There were no statistically significant clinical differences between the groups. The Cemex cement had magnitudes of migration similar to or sometimes lower than those of Palacos cement. In both groups, most hips showed extensive radiolucent lines, probably due to the use of titanium alloy stems. INTERPRETATION: At 10 years, the Cemex bone cement tested performed just as well as the control (Palacos bone cement).

Comparison of cementing techniques of the tibial component in total knee replacement.

A few studies have shown that cementing the stem enhances fixation of the tibial baseplate in total knee replacement (TKR). Even the horizontal technique has been shown to provide good fixation. We used radiostereometry to study migration of the tibial component in 30 knees operated with Profix TKR. The knees were randomised for either complete (both under the baseplate and around the stem) or horizontal (only under the baseplate) cementing of the tibial component. At two years the tibial baseplate rotated externally a median of 0.18 degrees in the uncemented stem group and internally a median of 0.23 degrees in the cemented stem group. The tibial baseplate subsided 0.14 mm in the cemented stem group, and no translation was seen in the uncemented stem group. The differences in migration were small and probably without clinical significance. The findings do not favour either of the cementing techniques in TKR.

Validation of a low-dose hybrid RSA and fluoroscopy technique: Determination of accuracy, bias and precision.

Analyzing skeletal kinematics with radiostereometric analysis (RSA) following corrective orthopedic surgery allows the quantitative comparison of different implant designs. The purpose of this study was to validate a technique for dynamically estimating the relative position and orientation of skeletal segments using RSA and single plane X-ray fluoroscopy. Two micrometer-based in vitro phantom models of the skeletal segments in the hip and knee joints were used. The spatial positions of tantalum markers that were implanted into each skeletal segment were reconstructed using RSA. The position and orientation of each segment were determined in fluoroscopy images by minimizing the difference between the markers measured and projected in the image plane. Accuracy was determined in terms of bias and precision by analyzing the deviation between the applied displacement protocol and measured pose estimates. Measured translational accuracy was less than 100 microm parallel to the image plane and less than 700 microm in the direction orthogonal to the image plane. The measured rotational error was less than 1 degrees . Measured translational and rotational bias was not statistically significant at the 95% level of confidence. The technique allows real-time kinematic skeletal measurements to be performed on human subjects implanted with tantalum markers for quantitatively measuring the motion of normal joints and different implant designs.

Mobile vs. fixed bearing unicondylar knee arthroplasty: A randomized study on short term clinical outcomes and knee kinematics.

The literature contains limited yet controversial information regarding whether a fixed or a mobile bearing implant should be used in unicompartmental knee arthroplasty (UKA). This randomized study was to further document the performance and comparison of the two designs. Fifty-six knees in 48 patients (mean age of 72 years) undergoing medial UKA were randomized into a fixed bearing (Miller/Galante) or a mobile bearing (Oxford) UKA. The 2 year clinical outcomes (clinical scores), radiographic findings, and weight bearing knee kinematics (assessed using RSA) were compared between the two groups. The mobile bearing knees displayed a larger and an incrementally increased tibial internal rotation (4.3 degrees, 7.6 degrees, 9.5 degrees vs. 3.0 degrees, 3.0 degrees, 4.2 degrees respectively at 30 degrees, 60 degrees, 90 degrees of knee flexion) compared to the fixed ones. The medial femoral condyle in the mobile bearing knees remained 2 mm from the initial position vs. a 4.2 mm anterior translation in the fixed bearing knees during knee flexion. The contact point in the mobile bearing implant moved 2 mm posteriorly vs. a 6 mm anterior movement in the other group. The mobile bearing knees had a lower incidence of radiolucency at the bone implant interface (8% vs. 37%, p < 0.05). The incidence of lateral compartment OA and progression of OA at patello-femoral joint were equal. No differences were found regarding Knee Society Scores, WOMAC, and SF-36 scores (p > 0.05). This study indicates that mobile bearing knees had a better kinematics, a lower incidence of radiolucency but not yet a better knee function at 2 years.

Decreased precision for BMD measurements in the prosthetic knee using a non-knee-specific software.

Non-knee-specific software has been widely used for bone mineral density (BMD) measurement at the knee, which coincide with a higher measurement error. This study was conducted to test whether software developed for BMD measurement at the hip could be used in the knee by using dual-energy X-ray absorptiometry (DXA) and whether knee rotational alignment or differences in soft tissue substitutes would influence the precision of the BMD measurement. Twelve knees operated with total knee arthroplasty were included. The knees were scanned four to six times each in four rotational positions using DXA with either a Plexiglas rod or rice bags as a soft tissue substitute. The BMD was measured in one manually defined region at the proximal tibia by using the software of Orthopedic. The precision (coefficient of variation) at the knee was 5.1-9.0% when using the Plexiglas rod and 7.3% when using rice bags. The poor precision was mainly explained by inconsistency in tissue baseline establishment and/or by low baseline bone density (Adj R2 = 0.78-0.90, p < 0.000). Neither intentional rotation of the knee nor using different soft tissue substitutes significantly altered the precision. The results suggest that the use of a non-knee-specific software in the prosthetic knee is not appropriate.

Does a bipolar hemiprosthesis offer advantages for elderly patients with neck of femur fracture? A clinical trial with 261 patients.

BACKGROUND: Previous studies comparing unipolar and bipolar hemiarthroplasty for treatment of displaced intracapsular femoral neck fractures in elderly patients have often lacked methodological power and yielded conflicting clinical results. The objective of this study was to compare the clinical outcomes from each implant in a randomized cohort of elderly patients with intracapsular fracture of the femoral neck treated with a cemented hemiprosthesis. METHODS: This study is a clinical trial of 261 patients (82.0 ± 7.9 years) who were randomly assigned to one of the two treatment groups: group 1 (n = 133) received a cemented bipolar implant and group 2 (n = 128) received a unipolar head with the same stem. At 12 months post-surgery, pain and functional abilities were quantified by blinded assessors using the Oxford and Harris Hip Scores, Verbal Numerical Rating Score and Six-Minute Walk. The Mann-Whitney U-test and t-test for independent samples were used to compare results between the groups (P < 0.05). RESULTS: There were no significant differences in any clinical scores between the groups. Results from the Six-Minute Walk indicated no difference in functional walking ability or endurance (P = 0.446) between the groups. Self-selected pain ratings also did not differ between groups (P = 0.236). Patients receiving the unipolar prosthesis had significantly reduced abduction (P = 0.0001) and internal rotation (P = 0.047) in the operated hip compared to the non-operated hip. CONCLUSION: These short-term results suggest that unipolar implants share many of the advantages of the bipolar prosthesis but can be manufactured at substantially lower cost. These implants may be appropriate for the less-active elderly patient, particularly when used with bone cement.

Roentgen stereophotogrammetric analysis and clinical assessment of unipolar versus bipolar hemiarthroplasty for subcapital femur fracture: a randomized prospective study.

BACKGROUND: Hemiarthroplasty is a well-established treatment for displaced subcapital fracture, but controversy exists about the optimal implant type. Bipolar hemiarthroplasty has proposed advantages over unipolar hemiarthroplasty in terms of better clinical results and decreased wear of acetabular cartilage. METHODS: This study is a randomized prospective study of 51 patients (52 hips) receiving either bipolar or unipolar hemiarthroplasty for displaced subcapital fractures. The outcome measurements were clinical scores and Roentgen stereophotogrammetric analysis (RSA) analysis to determine the rate of acetabular wear. RESULTS: Twenty-three patients completed 2-year follow-up. The RSA data demonstrated that there was slightly less acetabular wear by bipolar prostheses than by unipolar. The combined mean three-dimensional wear of the bipolar prostheses was 0.6 mm compared with 1.5 mm for the unipolar prostheses (P= 0.04). The bipolar group generally achieved higher scores in terms of the Harris Hip Score, Western Ontario and McMaster University Index of Osteoarthritis (WOMAC) questionnaire and 6-min walk test. These results were statistically significant at 3 months but not at 12 and 24 months. CONCLUSION: This study suggests that while the bipolar prosthesis performs slightly better than the unipolar in terms of acetabular cartilage wear and clinical outcomes, it remains debatable whether the benefits are worth the increased cost of the prosthesis.

Periprosthetic changes in bone mineral density in 5 stem designs 5 years after cemented total hip arthroplasty. No relation to stem migration.

Changes in bone mineral density (BMD) at the proximal femur were evaluated in 83 cemented total hip arthroplasties (THAs) 5 years after surgery. The BMD changes were compared among 5 stem designs and were related to the stem migration. A greater BMD decrease was found in Scientific Hip Prosthesis (Biomet, Bridgend, UK) and SPII CoCr stems (Link, Hamburg, Germany) than in Exeter (Howmedica, London, UK), Spectron (Smith & Nephew, Memphis, Tenn), and SPII Titanium stems (P < .05), and the stiffer SPII CoCr stems (Link) had a larger bone loss than the SPII Titanium stems (Link). However, no overall relationship was found between the BMD changes and stem migration or stem stiffness.

Capsular-enhanced repair of the short external rotators after total hip arthroplasty.

Higher dislocation rates have been reported with the posterior approach to the hip. Empirical studies suggest that careful repair of the posterior structures significantly reduces this risk. However, studies examining the integrity of repair using plain radiographs and metallic markers have reported high failure rates. To explain this discrepancy, we performed a study using radiostereometric analysis to assess the repair. Ten patients were recruited. Markers were placed into the capsule and bone. The capsule and conjoined short external rotators were repaired through drill holes in bone. At 3 months, stress radiostereometric analysis radiographs were taken in internal and external rotation. Eight of 10 patients had a mean of 3.51-mm difference in separation, suggesting that the repair was intact. We recommend careful repair of posterior structures when using the posterior approach to reduce the risk of dislocation.

Very low wear of non-remelted highly cross-linked polyethylene cups: an RSA study lasting up to 6 years.

BACKGROUND AND PURPOSE: Highly cross-linked polyethylenes (PEs) all appear to reduce wear dramatically in laboratory studies, although there is substantial variation in this respect between manufacturers. Nonremelted cross-linked PE is almost as tough as unirradiated PE, but is not completely stable and can oxidize in vivo, as has been shown in recent retrievals studies. We had reported low wear and good clinical performance after 2 years for 10 non-remelted highly crosslinked PE cups compared to 16 conventional PE cups sterilized by gamma-in-air. METHOD: Because of possible degradation by free radicals, we followed up both cohorts for 5 years (conventional PE) and 6 years (highly cross-linked PE). RESULT: Mean (CI) proximal head penetration over the observation time was linear and measured 0.08 (0.02-0.13) mm for cross-linked PE and 0.42 (0.23-0.62) mm for conventional PE, and total penetration was 0.23 (0.1-0.35) mm and 0.75 (0.05-1.4) mm respectively. After subtracting creep, the annual wear for non-remelted highly cross-linked PE was below 6 microm. The cups had equally low migration and few radiolucencies. INTERPRETATION: The theoretical possibility of oxidation in non-remelted highly cross-linked PE may not show clinically. However, it may be that cemented cups with their thicker PE are more forgiving than metal-backed cups with thin PE moving in the locking mechanism. So far, we can conclude that the Crossfire highly crosslinked polyethylene cups performed very well clinically, with extremely low wear even after almost 6 years. This is reassuring, but care should be taken in extrapolating these results to other cross-linked PEs or uncemented cups where toughness of PE is more of an issue.

The constrained acetabular component for hip instability.

One hundred four hips in 107 patients undergoing revision arthroplasty of the hip were identified at risk of dislocation and treated with the constrained cup. Radiostereometric analysis was performed to assess prosthesis migration. Mean follow-up was 3.0 years (range, 2.0-4.8). At last review, 19 patients had died and 6 were lost to follow-up. There were 5 revisions for cup loosening and a further 4 with radiographic evidence of loosening. There were 3 dislocations and 3 dissociations in 5 patients. Radiostereometric analysis demonstrated that cup migration at 24 months was up to 0.82 mm of translation and 1.58 degrees of rotation. Our results confirm that the constrained acetabular component is a highly effective option for the treatment for patients with instability of the hip. The aseptic loosening rate was higher than previously reported.

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 linersgamma-sterilized in air and 32-mm ceramic heads were used. 8 patients died within 12 years, leaving 50 patients with a complete 12 year 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.

No increased migration in cups with ceramic-on-ceramic bearing: an RSA study.

UNLABELLED: Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness, microseparation, and sensitivity to impingement. To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration. Sixty one patients (61 hips) undergoing THA for osteoarthritis were randomized to ceramic on ceramic (Ce/Ce) or cobalt-chromium on cross-linked polyethylene bearings (PE) in the same uncemented cup shell. Migration was followed with RSA. At 2 years we observed similar mean cup translations in the 3 directions (0.07-0.40 mm vs. 0.05-0.31 mm, Ce/Ce vs. PE), as well as similar rotations around the 3 axes (0.31-0.92 degrees vs. 0.57-1.40 degrees). WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found. The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons. Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months. Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene, and they seem an equally safe choice. However, the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender. LEVELS OF EVIDENCE: Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

Less invasive total hip arthroplasty: description of a new technique.

We describe a new technique and aim to justify its use in total hip arthroplasty. The incision is short and there is minimal soft tissue dissection: piriformis and most of quadratus femoris remain intact. A meticulous capsular repair is performed. Patients are mobilized without restrictions. One hundred total hip arthroplasties by the standard posterior approach (group 1) were compared with 100 by the less invasive approach (group 2). Minimum follow-up was 2 years. Mean blood loss in group 1 was higher (P < .0001) and inpatient stay longer (P < .0001). There was greater improvement in WOMAC scores for up to 1 year in the less invasive group (P = .027). In conclusion, the less invasive approach is safe and the functional benefits last up to 1 year.

In vivo wear and migration of highly cross-linked polyethylene cups a radiostereometry analysis study.

In 50 cemented hip arthroplasties, wear and migration of the polyethylene (PE) cups were measured with radiostereometric analysis for a period of 2 years. Twenty had a normal gamma-in-air-sterilized PE, another 20 had a PE sterilized with 30000 Gy followed by heat stabilization (Duration; Stryker Orthopaedics, Mahwah, NJ), and 10 had highly cross-linked PE cups irradiated with 100000 Gy (Crossfire; Stryker Orthopaedics). In the initial 2 months, head penetration (creep) was 63 microm on average for the 3 groups. From 2 to 24 months, the mean proximal head penetration (wear) was 156 microm for standard PE, 138 microm for stabilized PE (P = .45), and 23 microm for highly cross-linked PE (P < .001; analysis of variance). The low in vivo wear rate for highly cross-linked cups was not at the expense of higher migration or less favorable clinical outcome and looks promising.

The cone hip stem: a prospective study of 13 patients followed for 5 years with RSA.

We operated on 13 patients (14 hips) with dysplastic hips, mean age 42 (28-58) years, with a cementless Cone stem and followed them for 5 years, using the Merle d'Aubigné clinical score, conventional radiography and repeated radiostereometry analyses. The clinical scores improved markedly at 4 months and still more throughout the study. None of the patients complained of thigh pain. No stem showed radiographic subsidence, but 3 stems had radiolucent zones probably indicating fibrous ingrowth. Micromigration was measured at 4 months, 1, 2 and 5 years. The mean subsidence after 5 years was 0.27 mm and the mean posterior micromigration of the head was 0.74 mm. Most of the micromigration took place within the first 4 months. We conclude that the uncemented Cone stem used in dysplastic hips has shown a good clinical outcome so far and was found to be stable on conventional radiographs and using RSA technique.