Determination of the major dimensions of femoral implants using morphometrical data and principal component analysis

Anthropometry of the knee of the Turkish population and the comparison to implant sizes in total knee arthroplasty

BACKGROUND

Total knee arthroplasty (TKA) is one of the most common orthopaedic surgical procedures in the advanced stages of knee arthritis.

OBJECTIVE

The purpose of this study was to define the sex differences in the Turkish population's morphological measurements of the distal femoral and proximal tibial surfaces that form the knee joint and to compare their compatibility with conventional prosthetic implants commonly used in TKA for advanced-stage knee arthritis.

METHODS

Anthropometric data for a total of 240 knees from 240 patients were measured using 3-dimensional computed tomography (3D CT). All morphological data were compared with the dimensions of four conventional knee prostheses commonly used in Turkey.

RESULTS

A comparison of the four tibial components revealed that the majority of female proximal tibias matched with smaller-sized tibial components, whereas those of males matched the larger sizes. Comparing the morphological data with similar values for the four femoral components currently used in Turkey, we found that all the prostheses had similar values.

CONCLUSION

The four conventional prosthetic brands included in this study matched the distal femoral dimensions of both sexes. On the other hand, we need smaller size tibial components for our female population.

Towards the generation of a parametric foot model using principal component analysis: A pilot study

There have been many recent developments in patient-specific models with their potential to provide more information on the human pathophysiology and the increase in computational power. However they are not yet successfully applied in a clinical setting. One of the main challenges is the time required for mesh creation, which is difficult to automate. The development of parametric models by means of the Principle Component Analysis (PCA) represents an appealing solution. In this study PCA has been applied to the feet of a small cohort of diabetic and healthy subjects, in order to evaluate the possibility of developing parametric foot models, and to use them to identify variations and similarities between the two populations. Both the skin and the first metatarsal bones have been examined. Besides the reduced sample of subjects considered in the analysis, results demonstrated that the method adopted herein constitutes a first step towards the realization of a parametric foot models for biomechanical analysis. Furthermore the study showed that the methodology can successfully describe features in the foot, and evaluate differences in the shape of healthy and diabetic subjects.

Preoperative morphometric differences in the distal femur are based on skeletal size in Japanese patients undergoing total knee arthroplasty

PURPOSE

The objectives of this study were to measure the morphometric parameters of preoperative distal femurs to determine the differences by diagnosis and gender after accounting for skeletal size.

METHODS

One-hundred and seventy-nine Japanese patients who underwent total knee arthroplasty (TKA) (25 males and 154 females) were assessed. The anteroposterior length (AP), mediolateral width (ML), aspect ratio (AR), surgical epicondylar axis (SEA) to posterior condylar axis (PCA) angle, and Whiteside to SEA angle were measured on preoperative computed tomography scans. The AP/ML, AR/ML, SEA/PCA, and Whiteside/PCA relationships were evaluated and compared by patient diagnosis and gender. The results were also compared with the sizes of 10 currently available TKA implants in Japan.

RESULTS

The mean AP, ML, AR, SEA/PCA angle, and Whiteside/PCA angle were 58.8 mm, 64.7 mm, 0.91, external rotation (ER) 3.5°, and ER 1.6°, respectively. AP and AR each were significantly correlated with ML (p < 0.001). AP, ML, and AR were not significantly different between patients diagnosed with osteoarthritis and rheumatoid arthritis. AP/ML and AR/ML were significantly correlated within each diagnosis (p < 0.001), but the analysis of covariance showed no significant differences between the diagnoses. AP and ML were significantly longer (p < 0.001) in males (63.6, 72.7 mm) than in females (58.1, 63.4 mm), while AR was smaller in males (0.88 vs. 0.92), with significant correlations for AP/ML (male: p < 0.010, female: p < 0.001) and AR/ML (male: p = 0.002, female: p < 0.001) in each gender. However, the analysis of covariance showed no significant differences between gender in the AP/ML and AR/MR correlations. The AP/ML ratio of our data was similar to the size variations of the 10 TKA implants, but the AR/ML ratio was quite different from almost all the implants.

CONCLUSIONS

No differences in preoperative femur morphometry were found between patients with different diagnoses, but the gender difference in AR was related to the difference in skeletal size between males and females.

LEVEL OF EVIDENCE

Case series with no comparison groups, Level IV.

Is there any relation between distal parameters of the femur and its height and width?

The purpose of this study was to reveal the association whether the distal morphometry of femur had a relation with femur height or width. Sixty-six adult (35 right and 31 left) dry femurs from Caucasians were used in this study. Computed tomography (CT) imaging was applied to obtain measurement values of the femur. Femur height (413.29 ± 28.40 mm) and width (29.86 ± 2.72 mm) were all checked one by one to determine the correlation with the parameters obtained. Both values exposed high rates of correlation with height (26 ± 2.34 mm) and width (20.85 ± 2.76 mm) of femur notch; also, measures of epicondylar, bicondylar and condylar diameters of femur were obtained. Measures were checked if there was a correlation with femur height and width. Differences displayed in distal morphometry of femur according to race and sex are due to other morphometric measures of femur rather than race and sex. We believe that displaying the high rates of correlation of distal morphometry of femur with femur height and width will be the factor which determines the selection and production of prosthesis among the long or short individuals of folks.

Three dimensional morphometry of the knee to design the total knee arthroplasty for Chinese population

Anthropometric data on the proximal tibia and distal femur of 172 normal knees (94 male knees, 78 female knees) were obtained using three dimensional computer tomographic measurements. We measured the tibial mediolateral (tML) and tibial anteroposterior (tAP) dimension in resected proximal tibia surface, femoral mediolateral (fML) and femoral anteroposterior (fAP) dimension in resected distal femur surface. The measurements were compared with the similar dimensions of five total knee prostheses conventionally used in China. We found that in the smaller sized prostheses the tibial mediolateral dimension was undersized, while in the larger size prostheses the tibial mediolateral dimension was overhang. For all sizes of prostheses the femoral mediolateral dimension was overhang. We found a progressively decreased in the aspect ratio (ML/AP %) with an increasing anteroposterior dimension both in the tibia and femur, as compared to the constant aspect ratio shown by the conventional total prostheses. Male had larger values in mediolateral dimension and aspect ratio than female under a given anteroposterior dimension both in the tibia and femur. There were strong correlations between measurements of the tibia and femur. The results of this study may provide guidelines for designing suitable total knee prosthesis for the Chinese population, especially for design of gender-specific prostheses.

What patient and surgical factors contribute to implant wear and osteolysis in total joint arthroplasty?

Total joint arthroplasty has been a successful operation for decades. Our current patients are younger and more active than those in the past. They place higher demands on themselves and have expectations commensurate with their lifestyles. Time-limited longevity with the large number of anticipated total joint replacement procedures and their potential burden to health care is a growing concern. In the past two decades, implant wear and osteolysis have been identified as major causes for the failure of otherwise well-functioning implants. Osteolysis can be divided into several categories: patient-specific, implant-specific, and the result of surgical factors. Although these categories are interrelated and not mutually exclusive, they enable us to build a framework in which to further advance our understanding of osteolysis and apply this information in a clinically relevant manner.

The trochlea is medialized by total knee arthroplasty: an intraoperative assessment in 61 patients

BACKGROUND

A medialization of the femoral component in a total knee arthroplasty (TKA) causes abnormal patellar tracking, which could result in patellar instability, pain, wear, and failure. Previous reports defined medialization in relation to the neutral position of the femoral component, but omitted to compare it to the anatomical position of the trochlea. We assessed intraoperatively whether there is a systematic error of the position of the prosthetic groove relative to the anatomical trochlea.

MATERIAL AND METHODS

A special instrument was developed to measure consecutively the mediolateral position of the anatomical trochlea and the mediolateral position of the prosthetic groove. 3 experienced knee surgeons determined the mediolateral error of the prosthetic groove in primary TKAs in 61 patients.

RESULTS

There was a significant medial error of the prosthetic groove relative to the preoperative position of the trochlea, with a mean medial error of 2.5 mm (SD 3.3)

INTERPRETATION

Our findings indicate that the trochlea is medialized by TKA. Because a conscious medialization of the femoral component in a TKA produces abnormal patellar tracking patterns, further investigations will be needed to analyze the clinical consequences of this medialization of the trochlea.

Morphometrical measurements of resected surface of femurs in Chinese knees: correlation to the sizing of current femoral implants

Morphometrical data were measured in the resected femurs of seventy Chinese patients who underwent total knee arthroplasties. Two measured parameters, the anterior-posterior length of the lateral condyle and the total width of the distal condyle, were compared to the anterior-posterior length and the medial-lateral width of five femoral implants currently used in Taiwan. Three implants (Duracon, NexGen and UKnee) have a larger medial-lateral width than the total width of the resected distal condyle for a given femoral implant anterior-posterior length. These implants tend to overhang the medial-lateral width of resected femurs from Chinese patients. In addition, one femoral implant (Duracon), which has previously been shown to be suitable for use in Caucasian patients, is not suitable in Chinese patients. Our results will allow manufacturers to design femoral implants better suited to Chinese patients.

Small stem Exeter total hip replacement: clinical and radiological follow-up over a minimum of 2.5 years

PURPOSE

To evaluate the clinical and radiological outcome in patients undergoing small stem Exeter total hip replacement.

METHODS

A total of 46 small stem Exeter total hip replacements were performed on 44 consecutive patients (18 men and 26 women) attending the University of Malaya Medical Centre. The mean age at the time of operation was 58 years (range, 24-81 years). Of the 46 procedures performed, 35 were primary total hip replacements and 11 were revision operations, with aseptic loosening of the original implant being the main indication for revision. The main indications for surgery in primary cases were avascular necrosis and rheumatoid arthritis. Clinical and radiographic outcomes were assessed at 6 weeks', 12 weeks', 6 months' follow-up, and annually thereafter. Postoperative cementing technique was also assessed.

RESULTS

The mean follow-up period was 4 years. The mean Oxford Hip Score improved from 46 points preoperatively to 17 points at the final follow-up examination. There were no revision operations, no implant breakages, and no excessive migration of the implants. The potential complications of implant failure due to smaller implant size and increased patient activity were not observed.

CONCLUSION

Due to the smaller size of Asian femora, the small stem Exeter implant is a very useful development. This study suggests that it will perform as well as its larger counterparts.