Long-term clinical results of alumina ceramic medial pivot total knee arthroplasty: a 10-year follow-up study.

BACKGROUND: The newly-designed alumina ceramic medial pivot total knee prosthesis was introduced to reduce polyethylene wear and better fit the anatomical morphology of the Asian population. This study aimed to clarify the long-term clinical results of alumina medial pivot total knee arthroplasty over a minimum follow-up period of 10 years. METHODS: The data of 135 consecutive patients who underwent primary alumina medial pivot total knee arthroplasty were analyzed in this retrospective cohort study. Patients were examined over a minimum 10-year follow-up period. The knee range of motion, Knee Society Score (KSS) knee score, Knee Society Score function score, and radiological parameters were assessed. The survival rate was also evaluated by using reoperation and revision as endpoints. RESULTS: The mean follow-up period lasted 11.8 ± 1.4 years. Patients who were not followed accounted for 7.4% of the total cohort. Knee and function scores of KSS improved significantly following total knee arthroplasty (P < 0.001). In 27 individuals (28.1%), a radiolucent line was observed. Aseptic loosening occurred in three cases (3.1%). The survival rates for reoperation and revision were 94.8% and 95.8% 10 years after the operation, respectively. CONCLUSIONS: During a minimum 10-year follow-up period, the present model of alumina medial pivot total knee arthroplasty showed good clinical outcomes and survival rates.

The posterior tibial slope does not influence the flexion angle in posterior-stabilized mobile-bearing total knee arthroplasty.

BACKGROUND: It remains uncertain whether an increase in the tibial slope leads to better flexion in posterior-stabilized (PS) total knee prostheses. PURPOSE: To compare the intra-operative flexion angle between standard and an additional 10° posterior slope inserts. PATIENTS AND METHODS: Between December 2014 and February 2015, 22 patients (25 knees) who underwent PS mobile-bearing primary total knee arthroplasty (TKA) were included. Flexion angles were measured using either standard or specially-made inserts. Differences in flexion angles between the two situations were analyzed to determine the relationship between changes in flexion angle and pre-operative flexion angle or body mass index (BMI), and between intra- and post-operative flexion angle. RESULTS: The difference between the average flexion angle of standard inserts and specially-made inserts was not statistically significant. Although the correlations between changes in flexion angle due to insert difference and flexion angle, pre-operative flexion angle or BMI were not significant, there was a positive correlation between intra-operative and post-operative flexion at 2 years. CONCLUSION: The results showed an additional posterior tibial slope by 10° did not affect the intra-operative flexion angle. Surgeons performing PS mobile-bearing TKA do not need to excessively slope the tibial bone cutting to improve the post-operative flexion angle. LEVEL OF EVIDENCE: I, Experimental study.

Clinical results of alumina medial pivot total knee arthroplasty at a minimum follow-up of 10years.

BACKGROUND: The medial pivot total knee prosthesis with alumina ceramic femoral components was introduced to reproduce physiological knee kinematics and reduce polyethylene wear. The five-year clinical outcomes of alumina medial pivot total knee arthroplasties (TKA) have previously been reported. The purpose of this study was to provide the longer-term clinical results at a minimum follow-up of 10years. METHODS: The clinical results of 70 alumina medial pivot TKA in 51 consecutive patients, with a minimum follow-up period of 10years, were evaluated. RESULTS: Mean follow-up was 11.8years (range 10 to 13). Alumina medial pivot TKAs improved the patients' Knee Society knee scores, function scores, and postoperative ranges of motion compared with their pre-operative statuses (P<0.05 for each). Revision surgery was required in one knee due to a postoperative fracture of the tibial plateau after a fall that occurred two years postoperatively. Osteolysis and femoral component loosening was identified in one case after the initial five-year time point of analysis. The survival rate was 99.1% at 10years. CONCLUSIONS: This study demonstrated excellent clinical results for patients receiving the alumina medial pivot prosthesis at a minimum follow-up period of 10years.

Meniscal Bearing Dislocation of Unicompartmental Knee Arthroplasty with Faint Symptom.

We experienced two cases of atypical lateral dislocations of meniscal bearing in UKA (unicompartmental knee arthroplasty) without manifest symptoms. The dislocated bearing, which jumped onto the wall of tibial components, was found on radiographs in periodic medical examination although they could walk. Two thicker size bearing exchanges were promptly performed before metallosis and loosening of components. Continual examination is important to mobile bearing type of UKA because slight or less symptoms may disclose such unique dislocation. One case showed malrotation of the femoral component on 3D image. Anteroposterior view hardly disclosed the malrotation of the femoral component. Epicondylar view is an indispensable view of importance, and it can demonstrate the rotation of the femoral component. The the femoral distal end is wedge shaped and is wider posteriorly. If the femoral component is set according to the shape of medial condyle, the femoral component shifts to medial site compared with tibial component in flexion. It can account for such rare dislocation as follows. If excessive force applies on most medial side of the bearing during flexion, the lateral part of the bearing pops and the force squeezes it laterally simultaneously. Finally, the bearing jumps onto the lateral wall of the tibial component.

Joint gap measurement in total knee arthroplasty using a tensor device with the same articulating surface as the prosthesis.

BACKGROUND: We developed a new tensor to measure the joint gap throughout knee flexion during total knee arthroplasty (TKA). This tensor has the same articular shape as that of the tibial liner, including the post structure and the curvature of femorotibial articular surface, to measure the gap intraoperatively under the same conditions as after TKA. The present study aimed to examine the precision of the new tensor for gap measurement after implantation. METHODS: We performed TKA using the modified gap technique in four cadaveric knees and measured the gaps using the new tensor. The intra-observer and inter-observer error of the tensor was analyzed using 168 measurements of the gaps as determined at least twice by two surgeons. In addition, the gaps in rotating-platform posterior-stabilized TKA were measured at seven positions with the knee bending from extension to full flexion. RESULTS: The inter-observer and intra-observer errors were 0.8 and 0.3 mm, respectively, indicating precise and reproducible gap measurement. The gaps before implantation in reduced patellar position were 12.1 mm at extension and 12.5 mm at 90° flexion. The gaps after implantation were 9.1, 12.9, 13.1, 13.5, 13.8, 13.3, and 10.1 mm at 0°, 30°, 45°, 60°, 90°, 120°, and full flexion, respectively. CONCLUSIONS: The new tensor provides precise and reproducible measurements. Although the joint gap before implantation was parallel and equal at extension and 90° flexion, the joint gap after implantation was variable throughout knee flexion. This feature of the gap should be considered during the operation.

The intact posterior cruciate ligament not only controls posterior displacement but also maintains the flexion gap.

BACKGROUND: The PCL is a strong stabilizer of the knee and provides posterior stability to the tibia. However, sagittal alignment of the PCL with the knee at 90° flexion suggests the PCL might play a role not only in posterior stabilization but also in maintaining the flexion gap. QUESTIONS/PURPOSES: We determined whether the intact PCL helps maintain the flexion gap. METHODS: We examined axial radiographs and gravity sag views of 17 patients with chronic isolated unilateral PCL injury. The flexion gap was defined as the mean value of the medial and lateral distances between the femoral and tibial bones on the axial radiograph. Increase in the flexion gap and posterior laxity were determined by comparing the patients' injured and contralateral uninjured knees. RESULTS: The flexion gap of PCL injured knees (median, 7.5 mm; range, 5.3-11.5 mm; medial median, 6.2 mm; medial range, 3.7-8.3 mm; lateral median, 7.9 mm; lateral range, 5.3-11.5 mm) was larger than that seen in uninjured knees (median, 5.0 mm; range, 4.0-7.6 mm; medial median, 4.6 mm; medial range 3.4-7.1 mm; lateral median, 5.6; lateral range, 4.5-11.2 mm). The increment in the medial distance was similar to that in the lateral distance. Posterior laxity of injured knees was 9.1 (median); 5.4 to 15.2 (range) mm greater than that of uninjured knees. We found no correlation between posterior laxity and the flexion gap increment. CONCLUSIONS: Our data suggest the intact PCL controls posterior displacement and maintains the flexion gap.

Posterior condylar cartilage may distort rotational alignment of the femoral component based on posterior condylar axis in total knee arthroplasty.

PURPOSE: Among several anatomical references, the posterior condylar axis is the most apparent landmark to decide the femoral rotation for total knee arthroplasty. External rotation based on the posterior condylar axis requires condylar twist angle in order to set the femoral component parallel to trans-epicondylar axis although the angle is not constant. The angle during surgery differs from the pre-operative measurement on epicondylar view, because X-rays do not show the posterior condylar residual cartilage thickness. The thickness should be measured for the accurate femoral rotation. METHODS: We investigated the two twist angles on preoperative X-ray and during surgery, and the impact of residual cartilage on the setting of rotational angle of the femoral component in 184 knees in 112 patients with varus osteoarthritis (mean femorotibial angle: 185 ± 6.9 from 169 to 205°). RESULTS: The twist angle during surgery was 5.2 ± 1.3° (1.5-8.5°) and the angle on X-ray was 6.5 ± 2.3° (0.6-13.5°). The rotational angle influenced by the residual cartilage was calculated to be 1.7 ± 1.3° (0.0-4.6°). The discrepancy in the two twist angles was close to the rotational angle. There were, however, wide variations in all angles. CONCLUSION: The results suggested the importance of considering the influence of the residual cartilage and the individual variation in determining the femoral component setting. Multiple reference frames for femoral component rotation or combination with gap technique may help to minimize malalignment which may lead to poor clinical outcome.

Mid-term clinical results of alumina medial pivot total knee arthroplasty.

PURPOSE: The medial pivot total knee prosthesis has been designed to reproduce physiological knee kinematics. It has been reported that alumina ceramic femoral components reduce polyethylene wear. Thus, medial pivot total knee prostheses with alumina ceramic femoral components were introduced. The purpose of this study was to evaluate the clinical results of patients who underwent newly introduced alumina medial pivot total knee arthroplasties (TKA). METHODS: We evaluated the clinical results of 107 alumina medial pivot TKAs in 80 consecutive patients with a mean follow-up period of 5 years. RESULTS: Alumina medial pivot TKAs provided significant improvements in the patients' Knee Society knee scores, function scores and post-operative ranges of motion compared with their pre-operative statuses (each, P < 0.05). There was no statistical correlation between the change in maximum knee flexion and the increase in posterior condylar offset. Revision surgery was required in one knee due to a post-operative fracture of the tibial plateau after a fall that occurred 2 years postoperatively. No knees had aseptic loosening, osteolysis, or ceramic fractures. The survival rate was 98.6% at 5 years. CONCLUSIONS: This study demonstrates satisfactory mid-term clinical results for patients receiving the alumina medial pivot prosthesis. LEVEL OF EVIDENCE: Therapeutic study, Level IV.

Anterior knee pain after total hip arthroplasty in developmental dysplasia.

Little has been reported on knee pain after total hip arthroplasty (THA). The purpose of this study was to investigate the incidence and mechanism of knee pain after THA. Two hundred fifty-two patients with hip dysplasia were clinically and radiographically assessed for knee pain before and after THA. Incidences of knee pain and patellofemoral alignment were analyzed with reference to postoperative change in leg length, femoral anteversion, and the femoral offset. Anterior knee pain was present in 16 patients (7.3%). Lateral patellar tilt was increased in all patients with knee pain and significantly larger compared to that seen in patients without knee pain. The increased patellar tilt disappeared within 3 months, but symptoms in 4 patients persisted for more than 3 months. The patellar tilt was significantly related to the amount of leg lengthening. This study demonstrates that THA influences the patellofemoral joint via leg lengthening and causes anterior knee pain.

Repair of experimentally induced large osteochondral defects in rabbit knee with various concentrations of Escherichia coli-derived recombinant human bone morphogenetic protein-2.

Effective therapies for the regeneration of large osteochondral defects are still lacking; however, various approaches have been used. We evaluated the efficacy of Escherichia coli-derived dimeric recombinant human BMP-2 (E-rhBMP-2) for the repair of large osteochondral defects in a rabbit model. Osteochondral defects made in the femoral patellar groove of the knee were treated by transplanting gelatin sponges onto which no or various doses of E-rhBMP-2 were loaded. The outcomes were compared with those of an untreated control group four, 12 and 24 weeks after transplantation. At early time points, the cartilage tissue was repaired in a dose-dependent manner, and bone repair was accelerated in the defects treated with high doses of E-rhBMP-2. At 24 weeks, the repair of cartilage tissue was better with E-rhBMP-2 treatment, even at low doses, than without E-rhBMP-2 treatment. Our findings suggest that the use of E-rhBMP-2 improves and accelerates the repair of osteochondral defects in a rabbit model.

Local delivery of rolipram, a phosphodiesterase-4-specific inhibitor, augments bone morphogenetic protein-induced bone formation.

Recombinant human bone morphogenetic protein (rhBMP) is a promising therapeutic cytokine for the induction of bone formation, but a weak response in humans remains a major hurdle in its therapeutic application. We have previously reported an rhBMP-2-induced increase in the bone mass of mice receiving systemic rolipram, a specific inhibitor of phosphodiesterase-4. To overcome the side effects of systemic administration of rolipram, we examined the effects of its local release. Polyethylene glycol discs were used as a delivery system. The discs were impregnated with rhBMP-2 and rolipram and implanted into the dorsal muscle pouches in mice. Bone formation was assessed by measuring the bone mineral content (BMC) of the formed bone. First, to determine the optimal dose of rolipram, we added 0-5000 nmol rolipram and 5 microg rhBMP-2 to the pellets and found that 500 nmol rolipram was the most effective concentration for inducing bone formation after 4 weeks. Second, to examine the time course of bone formation, we implanted 5 microg rhBMP-2 with 0 or 500 nmol rolipram and killed mice 5, 7, 10, 14, or 21 days after implantation. Bone formation was accelerated in the rolipram group. Finally, to determine the rolipram-induced increase in the effect of BMP, BMC obtained after treatment with 5 microg rhBMP-2 and 500 nmol rolipram was compared with that obtained after treatment with 5-9 microg rhBMP-2 without rolipram, 4 weeks after implantation. The results indicated that 500 nmol rolipram enhanced the effect of rhBMP-2 by almost 1.5-fold. In summary, locally released rolipram enhanced the capacity of rhBMP-2 to induce bone formation, an effect previously reported with systemic administration. These findings may decrease the cost and increase the efficacy of rhBMP-2 treatment.

The risk of notching the anterior femoral cortex with the use of navigation systems in total knee arthroplasty.

Use of navigation systems has recently been introduced in total knee arthroplasty (TKA) to achieve more reliable prosthetic alignment. In the sagittal plane, there are two important requirements for navigation systems: (1) perpendicular cut to the femoral mechanical axis and (2) prevention of notching of anterior femoral cortex. These two requirements, however, may conflict. The angles between the line of the anterior femoral cortex and four sagittal femoral mechanical axes for navigation systems using radiographs of the entire lower extremity, while standing were measured and compared. These four sagittal axes simulated on the radiographs in navigation systems were in extension relative to the line of the anterior femoral cortex in 40-85% of cases in male and 65-100% in elderly female. The present study showed that navigation systems have the potential risk for notching of anterior femoral cortex.

Low levels of steroid-metabolizing hepatic enzyme (cytochrome P450 3A) activity may elevate responsiveness to steroids and may increase risk of steroid-induced osteonecrosis even with low glucocorticoid dose.

BACKGROUND: The main purpose of this study was to examine the relationships among osteonecrosis, steroid-metabolizing hepatic enzyme (cytochrome P450 3A; CYP3A) activity, and steroid dose to determine whether it is possible to prevent osteonecrosis in animals with low hepatic CYP3A activity by reducing exogenous steroid doses. METHODS: Japanese white rabbits (n = 103) were divided into three groups: a group with CYP3A activity induction (by intramuscular phenobarbital injection, n = 31), a group with CYP3A activity inhibition (by oral itraconazole administration, n = 30), and a control group (n = 42). Three weeks later, all rabbits received a methylprednisolone injection. Each group was divided into two subgroups by dosage of methylprednisolone (5 or 10 mg/kg body weight). Three weeks after methylprednisolone injections, the animals were killed and histological examination was performed to determine the incidences of osteonecrosis in the six subgroups. RESULTS: Incidence in the inhibition subgroup with 5 mg/kg steroid was higher than that in the induction subgroup receiving 10 mg/kg steroid. Thus, suppression of CYP3A activity significantly increased vulnerability to steroid-induced osteonecrosis, while increased CYP3A activity reduced this vulnerability. CONCLUSIONS: These findings suggest that low CYP3A activity may be vulnerable to the effect of steroids and increase risk of osteonecrosis, even with a low dose of steroid.

Arthroscopy for evaluation of polyethylene wear after total knee arthroplasty.

BACKGROUND: The purpose of this report is to demonstrate the severity of polyethylene wear by arthroscopy after total knee arthroplasty (TKA). METHODS: Polyethylene wear of TKA prostheses was evaluated endoscopically in eight knees (six patients). Arthroscopy was indicated when the patients had persistent but slight hydroarthrosis and instability confirmed by stress radiography, but these findings were insufficient for a consensus on polyethylene revision. The average interval between primary TKA and arthroscopy was 9 years 3 months. RESULTS: All knees had unexpectedly widespread, severe polyethylene wear characterized by delamination. Based on arthroscopic visualization of the damage to the polyethylene, all patients consented to undergo isolated polyethylene surface revision surgery. The severity of polyethylene wear was worse than anticipated at the evaluation arthroscopy. After a mean follow-up of 5 years 6 months, all knees were stable and symptom-free. CONCLUSIONS: The usefulness of arthroscopy is validated in certain groups of patients with polyethylene wear when diagnosed with careful clinical examination and stress radiography.

Sagittal alignment of the lower extremity while standing in Japanese male.

There is little information available regarding the sagittal mechanical axis of the lower extremity of normal subjects under weight-bearing conditions. The purpose of this study was to determine the sagittal alignment of the lower extremity under such conditions. Anteroposterior and lateral radiographs were taken of the 20 lower extremities of 10 healthy male Japanese volunteers (mean age, 27 years) while standing. The coronal mechanical axis passed through 33.9% medial to the proximal tibial articulating surface. The sagittal mechanical axis passed through 38.0% anterior to the distal femoral condyle and 27.9% anterior to the proximal tibial articulating surface, and also passed 5.2 mm anterior to the intercondylar notch. Our study therefore showed that the coronal and sagittal mechanical axes of the lower extremity do not always pass through the center of the knee. This has important implications for alignment in surgery of lower extremities such as total knee arthroplasty and osteotomy.

Characteristics of Hylamer polyethylene particles isolated from peri-prosthetic tissues of failed cemented total hip arthroplasties.

Polyethylene wear particles are one of the most important factors affecting the results of total hip arthroplasty. Hylamer, a highly crystalized ultra-high-molecular-weight polyethylene, has been used in total hip arthroplasty for wear reduction, but has exhibited high wear rate and excessive osteolysis. The aim of the present study was to examine Hylamer wear particles in peri-prosthetic tissues with osteolysis obtained from two cases of failed cemented total hip arthroplasty at 8 and 6 years after operation. Polyethylene particles were isolated, and examined using a scanning electron microscope and image analyzer. Total numbers of Hylamer polyethylene particles in the two cases were 5.6 x 10(9) and 8.0 x 10(9) g(-1). Particle sizes (in equivalent circle diameter) for the two cases were 1.07 +/- 0.06 microm and 1.16 +/- 0.05 microm, and particle shapes (roundness) were 3.05 +/- 0.22 and 3.76 +/- 0.28. The Hylamer polyethylene particles were larger in size and more elongated and their number was larger, compared with the corresponding reported values for particles generated from conventional polyethylene. This increase in particle number and elongation may lead to early osteolysis in total hip arthroplasty with Hylamer.

Flexion gap preparation opens the extension gap in posterior cruciate ligament-retaining TKA.

It has been reported that preparation of the flexion gap results in significant widening of the prepared extension gap in posterior stabilized (PS) total knee arthroplasty (TKA). To date, there is a paucity of data regarding cruciate ligament-retaining (CR) TKA. Changes in the extension gap caused by preparation of the flexion gap were measured in 42 varus osteoarthritic knees undergoing CR TKA. The extension gap was first prepared and then measured before and after preparation of the flexion gap. The extension gap increased significantly on both the medial and lateral sides (18.8-20.0 and 21.7-22.7 mm, respectively) (P < 0.01). Preparation of the flexion gap also resulted in significant widening of the extension gap on CR TKA. However, amount of extension gap increase in CR TKA was smaller than previous reports on PS TKA.

Preparation of the flexion gap affects the extension gap in total knee arthroplasty.

Changes in the extension gap caused by the preparation of the flexion gap were measured in 50 varus osteoarthritic knees undergoing total knee arthroplasty. The extension gap was first prepared and then measured before and after preparation of the flexion gap. The extension gap increased significantly on both the medial and lateral sides (19.3 +/- 0.3 to 22.0 +/- 0.3 and 21.9 +/- 0.3 to 24.0 +/- 0.3 mm, respectively, mean +/- SE, both P < .0001). The increase was greater medially (P = .0014), and in the knees with more varus deformities (> or = 10 degrees, P = .0075). Thus, preparation of the flexion gap resulted in significant widening of the extension gap, especially on the medial side. The medial release should be stepwise and conservative to achieve adequate soft tissue balance.

Polyethylene wear particle generation in vivo in an alumina medial pivot total knee prosthesis.

Polyethylene wear particle generation is one of the most important factors affecting mid- to long-term results of total knee arthroplasties. It has been reported that the medial pivot total knee prosthesis (MP) design and alumina ceramic femoral component reduce polyethylene wear. The aim of this study is to evaluate in vivo polyethylene wear particle generation in the newly introduced alumina MP, in comparison with a metal MP. Synovial fluid was obtained from 11 knees with alumina MP and 15 knees with metal MP at nine months after the operation. Polyethylene particles were isolated, and examined using scanning electron microscope and image analyzer. Total number of particles in each knee was 7.10+/-2.86x10(6) in alumina (mean+/-standard error), and 5.70+/-2.82x10(7) in metal MP (p=0.048). Particle size (equivalent circle diameter) was 0.78+/-0.04 microm in alumina, and 0.66+/-0.06 microm in metal MP (p=0.120). Particle shape (aspect ratio) was 1.52+/-0.05 in alumina, and 1.88+/-0.11 in metal MP (p=0.014). Apart from the femoral component, the material and manufacturing method of polyethylene insert differed between the two groups, although the sterilization method was the same. Alumina MP generated fewer and rounder polyethylene wear particles than metal MP in early clinical stage, and could potentially reduce prevalence of osteolysis and aseptic loosening.