How the gender or morphological specific TKA prosthesis improves the component fit in the Chinese population?

Sub-optimal femoral fit in total knee arthroplasty, a systematic review of human femoral data vs off-the-shelf contemporary femoral components

PURPOSE

The purpose of the current study is to investigate the inadequacy of fit between the human distal femur and the knee implants offerings and describe the available strategies to overcome this issue.

METHODS

A systematic research of the literature was performed to identify studies reporting morphologic measures of the distal femur. Studies were excluded if they included unhealthy knees or the morphological analysis did not report the two key dimensions to identify the patient's unique anatomy: AP length and mediolateral (ML) width. Clinically relevant component overhang or underhang was considered when the metal-bone mismatch was > 3 mm as described in the literature.

RESULTS

Six studies with anthropometric analysis of 1395 distal femurs met the inclusion criteria. The analysis revealed that by employing the available sizes of four current "state-of-the-art" primary off-the shelf (OTS) femoral implants up to 13-41% would show underhang and 9-27% overhang clinically relevant and the introduction of narrower sizes did not reduce this percentage of underhang but improved the overhang rate of 10-15%.

CONCLUSIONS

Whenever an ML/AP mismatch in encountered in the operating room, adaptations are needed, and these bring about deleterious biomechanical and clinical complications. Therefore, this study highlights the need for implants design with multiple ML offerings per AP size, since they provide not only more sizes options but more femoral shapes to match the different ML sizes of the distal femur, compared to designs with single ML offerings for a given femoral AP dimension.

Potential for femoral size optimization for off-the-shelf implants: A CT derived implant database analysis

In total knee arthroplasty, the femoral implant size is chosen mainly based on the femoral anteroposterior (AP) height and mediolateral (ML) width. This choice often is a compromise, due to limited size availability. Inadequate AP fit is expected to alter flexion laxity and thus knee function. Inadequate ML fit entails underhang or overhang, which is linked to worse clinical outcomes. Hence, we aimed to find implant size distributions, which maximize population coverage, and to evaluate the sensitivity regarding error bounds and the number of implant sizes for a database of 85,143 cases. All patients in the database have been provided with a patient-specific implant in the past. For a subset of 1049 cases, three-dimensional preoperative bone surface models were available. These were used to validate whether the implant dimensions were representative of the bone dimensions. Particle Swarm Optimization was used for optimizing the implant size distribution. The deviations between implant and bone measures in the subset were found to be clinically irrelevant. Therefore, the full database of 85,143 cases was used for further analyses. A higher sensitivity of the population coverage regarding the error bounds compared to the number of implant sizes was found. For an exemplary setup of 12 optimized implant sizes and error bounds of ±1.5 mm for AP and ±3 mm for ML, a population coverage of almost 85% was achieved. In contrast, even with 30 implant sizes, a full population coverage could not be reached. Hence, remaining cases should be provided with patient-specific implants.

Minimum Five Years Follow-Up of Total Knee Arthroplasty Using Morphometric Implants in Patients With Osteoarthritis

BACKGROUND

The use of morphometric implants in total knee arthroplasty (TKA) has shown better early clinical outcomes compared to conventional implants. The primary objective of this study is to evaluate the functional outcome and the implant survivorship of a morphometric TKA at a minimum of 5 years of follow-up.

METHODS

From May 2012 to June 2015, all patients undergoing primary TKA with a single design of morphometric posterior-stabilized prosthesis (Persona; Zimmer) in a prospective observational single-center study were evaluated. The Knee Society Scoring System (KSS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were completed preoperatively, 1, 3, and 5 years postoperatively. Kaplan-Meier was used to calculate survivorship of the implants. The average follow-up was 75 months.

RESULTS

In total, 237 TKAs were performed in 235 patients with a mean age of 73 years (49-90). The KSS Knee Score increased from 44.7 (13-64) preoperatively to 93.6 (71-100), the KSS Function Score from 45.8 (17-69) to 92.2 (51-98), and the KSS Satisfaction Score from 26.6 (16-51) to 41 (35-55) at 5 years of follow-up. Similarly, for the KOOS score, a significant improvement of all the subscales was observed at 5 years of follow-up. Implant survival without reoperation at 5 years of follow up was 98.72% (95% confidence interval 0.95-1.00).

CONCLUSION

This is the first study demonstrating that significant improvements of the functional scores with good survivorship can be achieved at a minimum of 5 years of follow-up with TKA using morphometric implants.

Gender differences in femoral trochlea morphology

PURPOSE

This study aimed to analyze the morphology of the anterior femoral condyle using a quantitative three-dimensional reconstruction method. The morphological data were compared between genders.

METHODS

Computed tomography scans of femurs were taken from 90 healthy subjects and then reconstructed in 3D modeling software. Coaxial cutting planes were created at 10° increments to measure the lateral and medial anterior condylar heights (LACH and MACH, respectively), lateral and medial trochlear groove widths (LTW and MTW, respectively), and for trochlear groove tracking. The absolute values and normalized data were compared between male and female subjects. The sulcus angle and deepest point of the trochlear groove at each cross-section were also analyzed to determine the differences in the depth of the trochlear groove.

RESULTS

The absolute dimensions of LACH, MACH, LTW, and MTW were significantly smaller in the female subjects, by 10.5%, 36.9%, 10.3%, and 11.0%, respectively, than in the males (p < 0.05). After normalization, no significant difference was found in the condylar height between the genders. However, the female subjects had a significantly larger value of approximately 7.9% for the normalized trochlear width.

CONCLUSION

Male subjects had greater condylar heights and widths than the female subjects. Although the trajectory of the trochlear groove varied greatly among the subjects, the trochlear groove appeared to be wider and shallower in the female subjects than in the male subjects. These results provide important information for the design of femoral trochlea to fit Asian female patients.

LEVEL OF EVIDENCE

III.

Anthropometric Measurements of Distal Femur to Design the Femoral Component of Total Knee Arthroplasty for the Iranian Population

Background

Acquiring knowledge about anatomic and geometric quantities of bones is among the most vital parameters in orthopedic surgery that has a significant effect on the treatment of various disorders and subsequent outcomes. The aim of this study was to obtain anthropometric information for distal femur in order to compare with similar dimensions of prosthesis used in total knee arthroplasty (TKA) surgery and to design more suitable and optimal components.

Methods

Morphological data of distal femur were measured in 132 knees (81 males and 51 females) using magnetic resonance imaging (MRI). The data included anterior-posterior (AP) length, medial-lateral (ML) width, medial AP (MAP), lateral AP (LAP), MAP to LAP distance in the anterior distal femur namely anterior medial lateral (AML) width, medial and lateral condyle width, and intercondylar notch. The aspect ratio (ML/AP) was also calculated and the results were compared with similar dimensions of currently used knee implants.

Results

Our data showed that men are significantly larger in all dimensions than women. In the distal femur with similar AP lengths in both sexes, women had a smaller ML width than men (P<0.001). Comparison between the distal femur and studied prostheses showed no high correlation and similarity between the femoral component and femoral condyle prostheses in the resected surface of the bone.

Conclusion

The results of this study can provide the data needed to design prostheses suitable for the Iranian population.

Cost-utility analysis of total knee arthroplasty for osteoarthritis in a regional medical center in China

BACKGROUND

To analyze the cost-effective ratio of total knee arthroplasty (TKA) in the osteoarthritis (OA) treatment of at a regional medical center in China.

METHODS

One hundred thirty-nine patients with osteoarthritis who underwent TKA at the Department of Osteoarthritis in Luhe hospital (Tongzhou, Beijing) from January 2011 to January 2012 were followed up. Their health-related quality of life (HRQoL) was evaluated using Short-Form Health Survey (SF) -36 Chinese version, and compared with those of the normal population to assess quality-adjusted life years (QALYs) gained after surgery for its effectiveness of the treatment. The total expense was the cost of patient hospitalization. The cost per QALY was calculated. The cost-benefit ratio (CBR) was expressed as a ratio of each QALY's expenditure to per capita gross domestic product (GDP). Factors affecting the cost, including age, gender, length of stay, and ICU experience, were also considered.

RESULTS

The total hospitalization fee was Ұ8,053,736.68, Ұ57,940.55 in average, of which, 81.59% constituted out-of-pocket expenses. The SF-36 scores were as follows: Physical Function: 25.14, Role Physical: 7.12, Bodily Pain: 9.60, Role emotional: 5.58, Vitality: 19.9, Mental Health: 25.84, Social Function: 9.86 and General Health: 21.15. Compared with normal people of the same age and sex, a total of Ұ2487.74 QALYs and Ұ3237.37/QALY were gained, 10% less than the regional GDP per capita. The cost-effective ratio of TKA for osteoarthritis in China was 1: 10.78. The main cost of the patient was the cost of prosthesis (61.78%). The average cost afforded by patients' themselves was Ұ47,242.64 after the deduction of government subsidies. There were Ұ31,306.64 difference compared with the annual average income of the local people. The cost might be affected by length of stay and ICU experience. Longer stay caused more cost of treatment. Patients who remained in ICU after surgery had higher overall costs and blood transfusion costs.

CONCLUSION

The factors that affect TKA cost are hospital and postsurgical ICU stay. It is cost-effective for regional medical care center to treat osteoarthritis using TKA economically. However, considering the average income of patients in the area, it is necessary to reduce the cost of the treatment.

Effect of Femoral Component Flexion Implantation on the Mediolateral Bone-prosthetic Fit in Total Knee Arthroplasty

OBJECTIVE

Femoral component overhang in total knee arthroplasty (TKA) has been reported in previous studies. The purpose of this study was to evaluate the effect of femoral component flexion implantation on mediolateral bone-prosthetic fit in TKA.

METHODS

Virtual prosthesis implantations were performed on computed tomographic models of 10 Chinese knees with femoral prostheses of the Advance Medial-Pivot knee system (MicroPort Orthopedics, Arlington, TN, USA), with the femoral component positioned at 0°, 3°, or 6° of flexion in the sagittal plane. For each degree of flexion implantation, the differences between the knee and femoral component models on the lateral and medial sides at trochlea (zone 1), anterior-distal condyle (zone 2), posterior-distal condyle (zone 3), and posterior condyle (zone 4) were measured. Positive difference values indicate component overhang, and negative difference values indicate component underhang. The values of component overhang (underhang) in each zone were statistically analyzed across the 3° of flexion implantation.

RESULTS

With a greater degree of flexion implantation, overhang was reduced and even changed to underhang. With 0° of flexion implantation, an overhang exceeding 3 mm existed mainly on the medial side of zone 1 (5.81 mm) and the lateral side of zone 2 (3.39 mm). With 3° of flexion, overhang exceeding 3 mm was observed only on the medial side of zone 1 (3.10 mm), and underhang was observed only on the medial side of zone 4 (-0.32 mm). No overhang exceeding 3 mm was observed for 6° of flexion, while underhang was observed except on the lateral sides of zone 2 (1.32 mm) and zone 4 (1.10 mm) and on the medial side of zone 1 (1.54 mm). A significant difference in overhang values on the lateral and medial sides of zone 1 was observed between 0 and 6° of flexion (P < 0.05).

CONCLUSION

The present study demonstrated that femoral component flexion implantation by 3° can reduce excessive overhang, although 3.10 mm of overhang remained at the medial side of zone 1. Conversely, 6° of flexion implantation can avoid 3 mm of overhang for any zone, but increases the risk of underhang. Slight flexion implantation may be an effective alternative technique to prevent excessive component overhang, especially in the trochlea and anterior region of the distal condyle, in Chinese patients with standard TKA prostheses.

Availability of Additional Mediolateral Implant Option During Total Knee Arthroplasty Improves Femoral Component Fit Across Ethnicities: Results of a Multicenter Study

Background:

Anatomical variation may represent a challenge in achieving a close fit between a prosthesis and a patient’s osseous geometry in total knee arthroplasty (TKA). The purposes of this study were to determine whether the shape of the distal part of the femur differs among ethnicities, whether these differences affect the fit of the femoral component of a standard prosthesis, and whether the additional availability of a femoral component with a reduced mediolateral dimension for the same anteroposterior dimension improves femoral component fit across ethnicities.

Methods:

Femoral dimensions were measured intraoperatively during 967 TKAs performed using the same type of prosthesis in patients of 5 different ethnicities. Aspect ratios were calculated to determine whether the shapes of the femora differed among ethnicities. The component fit (“perfect,” overhang, or underhang) when only standard prostheses were available was compared with the fit when both standard and narrow prostheses were available in all ethnic groups. This enabled us to determine whether the femoral component fit was improved by the additional availability of the narrow version.

Results:

Wide variations in shape were found among ethnicities as were variations among individuals of the same ethnicity. Differences in shape among ethnicities influenced the rate of overhang. However, overhang was more frequent at the trochlear than at the condylar level across all ethnicities. The availability of both the standard and the narrow femoral components improved the rate of a perfect fit in women in 3 of the 5 ethnic groups and reduced the overhang rate in women in all 5 of the ethnic groups. In contrast, only modest improvements in femoral component fit, which were not statistically significant, were seen in men.

Conclusions:

The shape of the distal part of the femur varies not only among ethnicities but also within ethnic groups, leading to a high prevalence of overhang when only standard prostheses are available. The additional availability of a femoral component with a reduced mediolateral dimension for the same anteroposterior size can reduce overhang and improve component fit across ethnicities.

Morphometry of femoral rotation for total knee prosthesis according to gender in a Korean population using three-dimensional magnetic resonance imaging

BACKGROUND

We aimed to evaluate differences in femoral arthometric data for 700 osteoarthritic knees (587 females and 113 males) with respect to gender in a Korean population.

METHODS

We identified and measured the mediolateral (ML) and anteroposterior (AP) lengths, femoral aspect ratio (ML/AP), surgical epicondylar axis (SEA), and Whiteside's line (WL). In addition, the anterior, posterior, and distal bone resections of the implanted femurs were evaluated using SEA and WL as references using a three-dimensional analysis method.

RESULTS

ML and AP lengths significantly differed according to gender. ML dimension and aspect ratio were greater in males than in females for a given AP dimension in the femur. No statistically significant differences in femoral rotation with SEA as a reference were observed between male and female knees; however, a significant difference was shown using WL as a reference and both affected the amount of bone resection irrespective of gender.

CONCLUSION

This study provides important guidelines for gender-specific femoral prosthesis design with different ML and AP aspect ratios and femoral rotation based on SEA and WL for Korean populations.

Distal Femur Morphology of Iranian Population and Correlation With Current Prostheses

Background:

Maintaining proper size and rotation of components of total knee arthroplasty is mandatory for optimal longevity. Ethnical differences may affect the fitness of prostheses that were manufactured mainly based on Caucasian dimensions.

Objectives:

To evaluate the distal femur morphology of the Iranian population at the level of standard cuts simulated via computed tomography.

Patients and Methods:

During 2013, 150 consecutive patients (96 males and 54 females) from the outpatient Department of Orthopedic Surgery of Rasoul Akram Hospital with knee CT scans were studied. We entered cases with apparent normal extremity alignment and bone maturity. Exclusion criteria were history of fracture or conditions affecting knee profile. Standard cuts were simulated on the CT scan using the Marco Pacs program. For each bone, anteroposterior (AP), mediolateral (ML), and aspect ratio (ML/AP) were measured. Values were compared with the sizing of four currently available prostheses.

Results:

The mean age of the patients was 43 years (range: 17 to 80). All isolated parameters were higher in men significantly (P < 0.001). However, the aspect ratio did not show any significant difference (1.51 ± 0.11 vs 1.46 ± 0.1), suggestive of a similar configuration of distal femur profiles between genders. Ultimately, close correlations were observed among simulated cuts and size-matched femoral components of the prostheses. For females, however, components were mostly overhang mediolaterally except for one gender-specific subset. Decrement in the aspect ratio for larger knees was another mismatch with current prostheses that preserve an almost constant ratio throughout all sizes.

Conclusions:

Our findings may be applied by manufacturers to design prostheses more compatible with Asian populations. Alterations to the shape of components should be considered to provide optimal coverage.

No clinical benefit of gender-specific total knee arthroplasty

BACKGROUND AND PURPOSE

There is no consensus regarding the clinical relevance of gender-specific prostheses in total knee arthroplasty (TKA). We summarize the current best evidence in a comparison of clinical and radiographic outcomes between gender-specific prostheses and standard unisex prostheses in female patients.

METHODS

We used the PubMed, Embase, Cochrane, Science Citation Index, and Scopus databases. We included randomized controlled trials published up to January 2013 that compared gender-specific prostheses with standard unisex prostheses in female patients who underwent primary TKAs.

RESULTS

6 trials involving 423 patients with 846 knee joints met the inclusion criteria. No statistically significant differences were observed between the 2 designs regarding pain, range of motion (ROM), knee scores, satisfaction, preference, complications, and radiographic results. The gender-specific design (Gender Solutions; Zimmer Inc, Warsaw, Indiana) reduced the prevalence of overhang. However, it had less overall coverage of the femoral condyles compared to the unisex group. In fact, the femoral prosthesis in the standard unisex group matched better than that in the gender-specific group.

INTERPRETATION

Gender-specific prostheses do not appear to confer any benefit in terms of clinician- and patient-reported outcomes for the female knee.

Increased shape and size offerings of femoral components improve fit during total knee arthroplasty

PURPOSE

Contemporary total knee arthroplasty femoral component designs offer various degrees of fit amongst the global population. The purpose of this study was to assess component fit of contemporary femoral component design families against multiple ethnicities.

METHODS

Using a multi-ethnic dataset including Caucasian, Indian, and Korean subjects, this study investigated component fit in six contemporary femoral component design families (A: Persona™, B: NexGen (®), C: Sigma (®), D: GENESIS™ II, E: Triathlon (®), F: Vanguard (®)). Component overhang/underhang was measured between the resected distal femur and its corresponding component size and compared across design families and ethnicities. The severity of overhang/underhang and propensity of downsizing due to clinically significant overhang were quantified for the overall dataset and each ethnicity.

RESULTS

In all the overhang cases, Designs A and B had significantly lower component overhang than the other designs (p < 0.02). In all the underhang cases, Designs C and E had significantly greater underhang than the other designs (p < 0.01). Component design influenced the occurrence (% bones) of component downsizing due to clinically significant overhang (>3 mm), with the highest incidence observed in Designs D (20.5%) and F (17.7%), and the lowest incidence observed in Designs A (0%) and B (0.4%). Variation in component fit was significantly impacted by designs (p < 0.01) but not ethnicities (n.s.).

CONCLUSIONS

The inclusion of multiple ML/AP shape offerings and the increased number of available sizes in Design A, as compared to other contemporary femoral component design families studied, result in improved femoral component fit across various ethnicities.