Biomechanics of a collum-fixated short stem in total hip arthroplasty

Background

Biomechanical reconstruction of the hip significantly impacts the clinical outcome and implant survival. Our knowledge is limited of the ability of neck-stabilised prostheses to restore hip biomechanics. We hypothesised that hip biomechanics, specifically leg length and global offset (GO), may be restored to an acceptable range using the Primoris™ stem.

Methods and material

In this retrospective study, we analysed 152 patients who underwent total hip replacement (THA) using the short collum-fixated stem Primoris™.The primary outcomes were hip parameters measured by x-ray following THA using the Primoris™ stem. After surgery, the biomechanical parameters used were measured at the arthroplasty and the native contralateral side of the same x-ray. The X-rays were taken one year after the patient's surgery.1. GO.2. Leg length discrepancy (LLD).3. Neck shaft angle (NSA).

Results

We recorded an average GO of -3.4 mm (standard deviation (SD) 7.2) and an average LLD of +3.8 mm (SD 6.4). Furthermore, we registered an average 14-degree NSA increase (SD 7.4).

Conclusion

The Primoris™ neck-stabilised stem enabled hip anatomy restoration to a favourable range with respect to GO and LLD as the average difference fell within ±5 mm. However, the stem tended to be implanted in valgus.

Medium-term clinical and radiographic outcomes of a cementless prosthesis with a 140° neck-shaft angle in reverse total shoulder arthroplasty

BACKGROUND

The design of humeral implants has evolved from the initial Grammont design, notably regarding the neck-shaft angle (NSA) and through the use of cementless prostheses. Stress shielding was frequently reported with cementless implants, the 2 main risk factors being humeral stem misalignment and high filling ratios. Our hypothesis was that standard length cementless stems with an NSA of 140° would facilitate good alignment with moderate filling ratios, thereby limiting stress shielding and ensuring good clinical outcomes.

METHODS

A single-center retrospective study was conducted of patients who underwent reverse total shoulder arthroplasty between January 2015 and August 2017, with at least 2 years' follow-up. Clinical evaluations included range of motion measurements and Constant and subjective shoulder values scores. Frontal alignment was assessed in terms of the angle (α) between axes of the stem and of the humerus. Filling ratios were measured in the metaphysis of the humerus, in the diaphysis, and at the distal end of the stem and considered excessive above 0.7. Stress shielding was evidenced radiographically by the observation of medial cortical narrowing, medial metaphysis thinning, lateral metaphysis thinning or under-the-baseplate osteolysis.

RESULTS

Eighty-two shoulders were included and 70 had radiographic follow-up data available. The mean patient age was 78 years and 63/81 patients (78%) were female. The mean follow-up time was 39 ± 7 months. The mean α angle was 1.4° ± 0.9° and was less than 5° in all cases. The mean metaphyseal, diaphyseal, and distal filling ratios were 0.61 ± 0.06, 0.70 ± 0.08, and 0.64 ± 0.09, respectively. The mean Constant score improved from 28 ± 11 preoperatively to 64 ± 14 at last follow-up. The mean subjective shoulder values score at last follow-up was 81 ± 12. Seventy-nine percent of patients (55/70) had at least 1 form of stress-shielding related, which were not associated with clinical outcomes, apart from lateral metaphysis thinning, which was associated with lower active anterior elevation (mean, 106° ± 30° vs. 126° ± 28°; P = .01) and lower Constant scores (mean, 56 ± 17 vs. 65 ± 14; P = .06).

CONCLUSION

The use of cementless reverse shoulder prostheses with a NSA of 140° was associated with good clinical outcomes at 2 years' follow-up. The prosthesis stem was correctly aligned with the humeral axis and the filling ratios were <0.7 in all cases. Stress-shielding was common but, apart from lateral metaphysis thinning, this had no impact on clinical outcomes.

Humeral head size predicts baseplate lateralization in reverse shoulder arthroplasty: a comparative computer model study

Background

In reverse shoulder arthroplasty (RSA), the ideal combination of baseplate lateralization (BL), glenosphere size (GS), and glenosphere overhang (GOH) with a commonly used 145° neck shaft angle (NSA) is unclear. This is the first study evaluating correlations of body height (BH), humeral head size (HS), glenoid height (GH), and association of gender with best glenoid configurations for range of motion (ROM) maintaining anatomic lateralization (aLAT) for optimized muscle length in 145° and less distalized 135° RSA.

Methods

In this computer model study, 22 computed tomographies without joint narrowing were analyzed (11 male/female). A standardized semi-inlay 145° platform stem was combined with 20 glenoid configurations (baseplate [B] 25, 25 + 3/+6 lateralized [l], 29, 29 + 3/6l combined with glenosphere 36, 36 + 2 eccentric [e], 36 + 3l, 39, 39 + 3e, 39 + 3l , 42, 42 + 4e). Abduction-adduction, flexion-extension, external rotation-internal rotation, total ROM (TROM), and total notching relevant (TNR) ROM were computed, best TROM models respecting aLAT (-1 mm to +1 mm) and HS/GH recorded. Second, the 145° models (Ascend Flex stem; Stryker, Kalamazoo, MI, USA) were converted and compared to a 135° inlay RSA (New Perform stem; Stryker, Kalamazoo, MI, USA) maintaining GOH (6.5-7 mm) and aLAT.

Results

Best 145° models had eccentric glenospheres (mean BL: 3.5 mm, GOH 8.8 mm, GS 38.1 mm, distalization 23 mm). The 135° models had concentric glenospheres, mean BL 3.8 mm, GOH 6.9 mm, GS 39.7 mm, and distalization 14.1 mm. HS showed the strongest positive correlation with BL in 145° and 135° models (0.65/0.79). Despite reduced GOH in smaller females with a 135° NSA, adduction, external rotation, extension, TNR ROM, and TROM were significantly increased (P = .02, P = .005, P = .005, P = .004, P = .003), abduction however reduced (P = .02). The same trends were seen for males.

Conclusion

HS is a practical measure in surgery or preoperatively, and the strong positive correlation with BL is a useful planning aid. Despite reduction of GOH, conversion to a less distalized 135° NSAinlay design is powerful to maintain and even significantly increase all components of TNR ROM (extension/external rotation/adduction) in small females with the drawback of reduced abduction which may however be compensated by scapula motion. Lateralization with a less distalized 135° RSA optimizes muscle length, may facilitate subscapularis repair, and maintains highest rigid body motion.

Effectiveness of locking compression plate for proximal humeral fracture in elderly patients without structural bone grafting: age group of 65-79 compared to 80 and above

PURPOSE

This study shows the effectiveness of locking compression plate for proximal humeral fractures in elderly patients over 80 years old without structural bone grafting compared age group of 65-79 (Group 1) with 80 and above (Group 2).

METHODS

This study included sixty-one patients who underwent using locking compression plate for proximal humeral fractures between April 2016 and November 2021. The patients were divided into two groups. The neck shaft angle (NSA) was checked at immediately after surgery, at 1 month and the final follow-up visit. The NSA changes in the two groups were compared using the independent t-test. In addition, multiple regression analysis was used to find out which factors affect NSA changes.

RESULTS

In group 1, the mean difference between NSA immediately after surgery and 1 month after surgery was 2.74°, and group 2 was 2.89°. In group 1, the mean difference in NSA for 1 month after surgery and at the last follow-up was 1.43°, and group 2 was 1.75°. No significant difference was observed in the NSA changes between two groups (p = 0.59, 0.173). Bone marrow density and four-part fracture type were significant difference in NSA changes (p = 0.003, 0.035). The disabilities of the arm, shoulder and hand scale (DASH scale), age, medical support, diabetes and three-part fracture type were no significant in NSA changes.

CONCLUSIONS

Using locking compression plate without structural bone grafting is a good option in elderly patients over 80 years old and can help achieve radiological results similar to patients which age group of 67-79.

Computer-assisted analysis of functional internal rotation after reverse total shoulder arthroplasty: implications for component choice and orientation

PURPOSE

Functional internal rotation (IR) is a combination of extension and IR. It is clinically often limited after reverse total shoulder arthroplasty (RTSA) either due to loss of extension or IR in extension. It was the purpose of this study to determine the ideal in-vitro combination of glenoid and humeral components to achieve impingement-free functional IR.

METHODS

RTSA components were virtually implanted into a normal scapula (previously established with a statistical shape model) and into a corresponding humerus using a computer planning program (CASPA). Baseline glenoid configuration consisted of a 28 mm baseplate placed flush with the posteroinferior glenoid rim, a baseplate inclination angle of 96° (relative to the supraspinatus fossa) and a 36 mm standard glenosphere. Baseline humeral configuration consisted of a 12 mm humeral stem, a metaphysis with a neck shaft angle (NSA) of 155° (+ 6 mm medial offset), anatomic torsion of -20° and a symmetric PE inlay (36mmx0mm). Additional configurations with different humeral torsion (-20°, + 10°), NSA (135°, 145°, 155°), baseplate position, diameter, lateralization and inclination were tested. Glenohumeral extension of 5, 10, 20, and 40° was performed first, followed by IR of 20, 40, and 60° with the arm in extension of 40°-the value previously identified as necessary for satisfactory clinical functional IR. The different component combinations were taken through simulated ROM and the impingement volume (mm³) was recorded. Furthermore, the occurrence of impingement was read out in 5° motion increments.

RESULTS

In all cases where impingement occurred, it occurred between the PE inlay and the posterior glenoid rim. Only in 11 of 36 combinations full functional IR was possible without impingement. Anterosuperior baseplate positioning showed the highest impingement volume with every combination of NSA and torsion. A posteroinferiorly positioned 26 mm baseplate resulting in an additional 2 mm of inferior overhang as well as 6 mm baseplate lateralization offered the best impingement-free functional IR (5/6 combinations without impingement). Low impingement potential resulted from a combination of NSA 135° and + 10° torsion (4/6 combinations without impingement), followed by NSA 135° and -20° torsion (3/6 combinations without impingement) regardless of glenoid setup.

CONCLUSION

The largest impingement-free functional IRs resulted from combining a posteroinferior baseplate position, a greater inferior glenosphere overhang, 90° of baseplate inclination angle, 6 mm glenosphere lateralization with respect to baseline setup, a lower NSA and antetorsion of the humeral component. Surgeons can employ and combine these implant configurations to achieve and improve functional IR when planning and performing RTSA.

LEVEL OF EVIDENCE

Basic Science Study, Biomechanics.

Femoral neck shaft angle measurement on plain radiography: is standing or supine radiograph a reliable template for the contralateral femur?

INTRODUCTION

Neck-shaft angle (NSA) is of paramount importance to orthopedic surgeons due to its implications for various pathologies of the hip and femur. The primary aim of the study was to establish if NSA measurement may be affected by imaging position (standing and supine) and provide evidence regarding whether the contralateral NSA can be used as a template. The secondary aim was to determine a reference value and precisely understand the effects of sex on NSA measurement.

MATERIALS AND METHODS

We measured bilateral NSA in a retrospective study of 200 standing and 200 supine anteroposterior pelvis radiographs that met the inclusion criteria, while paying special attention to bilateral hip symmetry. The overall inter-rater reliability was 0.688 (CI 0.128-0.851). Matching was performed according to sex (exact matching) and age. Paired t-test, Pearson correlation coefficient, and independent sample t-test were used (p < 0.01).

RESULTS

A total of 400 pairs of femoral necks were reviewed, comprising of 200 males and 200 females. In the upright radiograph, the overall mean NSA was 131.21° ± 4.72°. There was no significant difference between right and left femur NSA among the patients (p = 0.95). On both sides, male NSA was higher than female NSA (p < 0.001). In supine radiograph, the overall mean NSA for the supine position was 133.06° ± 5.71°. There was a significant difference between NSA of the right and left femur among the patients in the supine position (p < 0.001). On supine radiographs there was no statistically significant difference between male and female NSA (p = 0.85).

CONCLUSION

Our findings indicated no significant variability in upright radiographs between the right and left NSA. In contrast, significant asymmetry between the right and left NSA was found in the supine radiographs. However, this study does not provide definitive clinical evidence, and further clinical-oriented research is required.

LEVEL OF EVIDENCE

Level III; retrospective comparative study.

The relationship between the ''Fujisawa point'' and anatomical femorotibial angle following simulated open wedge high tibial osteotomy

Background

We evaluated the relationship between the weight-bearing line (WBL) ratio and anatomical femorotibial angle (FTA) by simulated open wedge high tibial osteotomy (OWHTO). This study evaluated the correlation between the ‘‘Fujisawa point’’ and FTA, and identified factors which caused deviations between the two measurement methods. We hypothesized that the Fujisawa point corresponded with 170° of the FTA.

Methods

Preoperative antero-posterior full-length lower limb radiographs of 82 patients were obtained for the OWHTO to place the WBL ratio at a target of 62.5% of the width of the tibial plateau (Fujisawa point). The coronal alignment was measured pre- and post-planning. The patients were divided into two groups by the post-planning FTA: a correspondence group (168.5°≦FTA≦171.5°) and a non-correspondence group (FTA < 168.5°, 171.5° < FTA). The relationship between the Fujisawa point and the FTA was analyzed with multivariate regression analysis.

Results

The post-planning FTA was 169.8 ± 1.1° and within 170 ± 1.5° in 69 cases (84.1%) when the WBL ratio was 62.5%. The neck shaft angle was 128.1 ± 5.2° in the correspondence group, and 122.3 ± 6.3° in the non-correspondence group. The multivariate linear regression analysis revealed that the neck shaft angle was the only factor that predicted the correspondence of the Fujisawa point with the FTA at 170° (p = 0.006, odd 1.28).

Conclusions

The post-planning FTA converged at 170° when the WBL ratio passed through the Fujisawa point and the neck shaft angle was the only predictor.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05734-7.

Significance of Tip Apex Distance in Intertrochanteric Fracture femur managed with Proximal femoral nailing

INTRODUCTION

Tip Apex distance (TAD) is well established method of prediction of outcome in intertrochanteric fractures managed by Dynamic Hip Screw. This retrospective study was done to assess the significance of Tip Apex Distance in the management of the intertrochanteric fractures by Proximal femoral nail.

MATERIAL AND METHODS

The study was done in a tertiary care centre where 174 follow-up patients operated for intertrochanteric fractures with proximal femoral nail were included in the study. The radiological outcome of patients was assessed using the neck shaft angle, neck length and the offset whereas the functional status was assessed using the Harris hip score and the Lower extremity functional scoring system. These functional and radiological outcomes were compared with the TAD for any significant findings.

RESULTS

The tip apex distance on the postoperative X-ray was found to be 22.93+3.88mm. The Lower Extremity Functional Score was found to be 70.71+8.153. The Harris Hip Score was found to be 85.408+9.586. Change in the neck length as compared to the uninjured hip was found to be 1.46+1.705. Change in the offset and neck shaft angle was 1.38+1.567 and -2.61+1.27 respectively. There were 8 cases of screw cut out and 8 cases of superficial infection.

DISCUSSION

The Harris hip score and the LEFS increased with decreasing values of the Tip Apex distance. The Neck shaft angle, Neck length and the offset all decreased with the increase in the Tip Apex Distance. The Harris hip score and the LEFS decreased with the decrease in the Neck shaft angle, Neck length and the offset. On examining the 2 groups one with TAD <25mm and the other with TAD >25mm it was seen that both functionally and radiologically, the outcome was better in the group having TAD<25mm.

CONCLUSION

This study indicates that the Tip Apex Distance can be used as a useful predictor of the outcome of the proximal femoral nail in intertrochanteric fractures.

LEVEL OF EVIDENCE

IV.

Femoral morphology is associated with development of knee pain after hip fracture injury among older adults: A nine-year retrospective study

Introduction

We aimed to clarify differences in femoral morphology associated with post-hip fracture knee pain (PHFKP).

Methods

Medical records and radiographic examinations were retrospectively reviewed to determine the relationship between PHFKP development and femoral morphology. Leg length discrepancy (LLD) and neck-shaft angle discrepancy (NSAD) were measured from hip radiographs.

Results

202 were enrolled, of whom 64 (31.7%) developed PHFKP. The PHFKP group showed more varus NSA. Intertrochanteric femoral fractures (γ-nail or CHS) displayed a more varus NSA.

Conclusions

Femoral morphology (varus NSA) may be involved in the development of PHFKP.

[Comparison of 127° small and 135° large stem angle prostheses in total hip arthroplasty]

OBJECTIVE

To investigate the effect of total hip arthroplasty(THA) with the prosthesis of 127° small neck stem angle and 135° large neck stem angle.

METHODS

From January 2014 to June 2016, 84 patients with THA were selected, including 44 males and 40 females, aged 45 to 72(53.4±8.1) years old, 68 patients with necrosis of the femoral head(32 on the left and 36 on the right), 16 patients with serious osteoarthritis of the hip caused by other reasons, and the course of disease was 9 to 36 (24.0±5.5) months. Forty-two patients in each group were evaluated by Harris score, visual analog score(VAS), length measurement of lower limbs, biomechanical evaluation of different angles of the neck stem. The complications and quality of life 24 months after operation were compared.

RESULTS

Two patients in each group were lost, the rest were followed up for 30 to 36 (33.0±1.6)months. The Harris score and the length of both lower limbs were measured before and 1, 6, 12, 24 months after operation. The difference of Harris score and the length of both lower limbs in the two groups was significantly improved compared with that before operation(P<0.05), but there was no significant difference between the two groups(P>0.05). There was no significant difference between the two groups in VAS score before operation (P>0.05), but the VAS score of the group with large neck stem angle was significantly lower than that of the group with small neck stem angle(P<0.05). There was no significant difference in the incidence of postoperative complications between the two groups (P>0.05). The quality of life of the patients in the two groups after 24 months was significantly higher than that before operation (P<0.05).

CONCLUSION

THA with large and small neck stem angle prosthesis can better recover the function of hip joint, but large neck stem angle can reduce the degree of postoperative pain and improve the quality of life of patients.

Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties?

BACKGROUND

Shorter humeral stems were developed to improve bone preservation, vascularity and osteointegration in reverse total shoulder arthroplasty (RSA). While some studies examined the relationship between canal filling and radiographic changes, none evaluated the association between stem alignment and canal fill ratio (CFR).

HYPOTHESIS

The hypothesis was that stem misalignment after RSA would be associated with lower CFR.

PATIENTS AND METHODS

The authors retrospectively reviewed immediate postoperative radiographs of 157 patients, comprising 56 men (36%), who underwent RSA with a short uncemented stem with neck shaft angle (NSA) default of 145°. The parameters included postoperative NSA and metaphyseal CFR, both measured with excellent inter-observer agreement. Uni- and multivariable linear regressions were performed to determine associations between postoperative NSA and 5 variables (CFR, gender, age, BMI, and surgical approach).

RESULTS

Postoperative NSA was 149°±8°, exceeding 5° of varus in 15 shoulders (9%) and 5° of valgus in 60 shoulders (38%), and CFR was 58%±8%. CFR was lower in shoulders with varus stem alignment (54%±6%) than shoulders with neutral stem alignment (59%±8%, p=0.033). Multivariable regression revealed that postoperative NSA increased with age (beta: 0.20; p=0.008), was higher for shoulders operated with the subscapularis- and deltoid-sparing approach (beta: 3.82; p=0.040) but lower for men (beta: -4.14; p=0.002).

CONCLUSIONS

Stem misalignment exceeded 5° in 47% of the shoulders. Women, older age, and subscapularis- and deltoid-sparing approach are associated with greater risks of valgus stem positioning, while lower CFR seems to be associated with greater risks of varus stem positioning.

LEVEL OF EVIDENCE

IV; case series.

CT based measurement of anatomical dimensions of femur and its relevance in nail designs for proximal femoral fractures

Introduction

The purpose of this study was to obtain computed tomography (CT) based measurements of femoral dimensions in adults, to identify its relevance with intramedullary nails used in the management of proximal femur fractures and to suggest a best fitting implant dimensions to our population. To best of our knowledge our study would be first to compile different CT based dimension in single study.

Methods

In our retrospective study of 50 femurs, CT based femoral dimensions measured in standardized cuts and compared with previous studies and commonly available proximal femur intramedullary devices.

Results

68.4 was the mean age in our study, neck shaft angle (NSA) was 127.2±5.2⁰, anteversion 11.2±7.4⁰, endosteal isthmus diameter was 11.9 ± 1.7 mm, anterior radius of curvature (ROC) was 116.8 ± 20 mm, horizontal femoral offset 37.5 ± 4.6 mm, medio-lateral angle 7.8±1.6⁰, with good inter and intra observer correlation. Femoral length and neck width was positively correlated to head diameter, horizontal femoral offset with medio-lateral (ML) angle. One of the 50 femur studied had the parameters in the range of available implant and could match appropriately.

Conclusion

CT based dimensions in our population is different from other population. Based on this study, a design modification of nails used in present day management of proximal femur fractures has been recommended.

Comparison of radiological and functional outcome of unstable intertrochanteric femur fractures treated using PFN and PFNA-2 in patients with osteoporosis

INTRODUCTION

Presently, unstable intertrochanteric femur fractures are treated commonly with intramedullary nailing devices. Various designs of intramedullary nail are introduced. The conventional Proximal Femoral Nail has given diverse outcome. Complications have also been noted with this implant. Newer designs like Proximal Femoral Nail Antirotation-2 have been introduced for Asian population. The aim of our study was to compare the radiological and functional outcome of unstable intertrochanteric femur fracture treated with conventional Proximal Femoral Nail and Proximal Femoral Nail Antirotation-2 in osteoporotic patients.

MATERIALS AND METHODS

Patients presenting with unstable intertrochanteric femur fracture (AO classification) and Singh's index ≤ 3 were included. Patients were assigned to the groups based on the implant used for treatment (PFN and PFNA2 group). Post-operative radiographs were used to assess the quality of reduction, by calculating neck shaft angle. The quality of fixation was assessed, by calculating tip apex distance and Cleveland index. The duration of surgery, blood loss, number of fluoroscopic images taken and length of hospital stay were noted. Patients were followed up for 6 months, and complications were noted. The functional outcome was compared using modified Harris hip score. The data analysis was done using Student's unpaired t test/Mann-Whitney U test and Chi-square test/Fisher's exact test. A p value less than 0.05 was considered significant.

RESULTS

Seventy-eight patients with unstable intertrochanteric fractures and Singh's index < 3 were included. Thirty-seven were treated with PFNA2 and 41 with PFN. The average age in PFNA2 group was 69.51, and PFN group was 70.804. Nine patients in PFNA2 group and 10 patients in PFN group had tip apex distance more than 25 mm. Twelve patients in PFNA2 group and 14 Patients in PFN group had sub-optimal implant position as per Cleveland index. The difference in neck shaft angle between uninjured and operated side was more than 10° in four patients of PFNA2 group and seven patients of PFN group. The average Harris hip score was 74.55 for PFNA2 group and 69.88 for PFN group. Four complications were seen in PFNA2 group and 5 in PFN group.

CONCLUSION

The functional outcome (p = 0.102) achieved with both the implants was similar. Good functional outcome can be achieved, when the radiological parameters are restored, i.e. TAD < 25 mm, Cleveland index in centre-centre position and neck shaft angle difference < 5°. The overall complications, in the set-up of osteoporosis, seen with both the implants were similar (p = 0.44). PFNA2 group showed better results in terms of perioperative morbidity.

Detection of primary screw perforation in locking plate osteosynthesis of proximal humerus fracture by intra-operative 3D fluoroscopy

PURPOSE

The purpose of this study was to identify the rate of primary screw perforations after osteosynthesis of proximal humerus fractures with intra-operative 3D fluoroscopy and to analyse the rate of secondary screw perforations as well as complications, outcome, and revision surgeries after a minimum of 12 months.

MATERIALS AND METHODS

Thirty-three patients (20 female, 13 male, median age 67 years, range 35-85 years) with displaced proximal humerus fractures were included. After reduction and fixation, an intra-operative 3D fluoroscopy was performed to evaluate primary screw perforations (PS) and screws with "near perforation" (nPS). These screws were changed intra-operatively. Patients were followed-up for a minimum of 12 months. Clinical and radiological parameters, such as secondary screw perforation, secondary loss of reduction, or functional outcome, were investigated.

RESULTS

In six patients (18.2%), humeral head screws were changed due to primary PS (n = 2) or nPS (n = 4) after the intra-operative 3D fluoroscopy. Follow-up revealed an adapted constant score (%CMS) of 76.2% after a mean follow-up of 17.7 months. Two secondary screw perforations were observed (6%). Loss of reduction was observed in eight patients (24.2%).

CONCLUSION

The intra-operative 3D reveals a high rate of primary screw perforations or near perforations. Immediate change of these screws may lead to a lower rate of secondary screw perforations and, therefore, reduce post-operative complications.

Rewriting the tip apex distance for the proximal femoral nail anti-rotation

INTRODUCTION

The proximal femur nail anti-rotation (PFNA-II) (Synthes GmbH, Oberdorf, Switzerland) is the most commonly used implant for intramedullary nailing of unstable intertrochanteric fractures in our centre. However, mechanical failure of the bone with respect to the implant is a cause of concern due to its significant morbidity especially in the elderly. To date, factors for fixation failures are not well defined in the literature. This study aims to evaluate the factors that predispose to cut out of the PFNA implant and to provide a guide for surgical fixation.

PATIENTS AND METHODS

This study was a retrospective analysis of 340 patients who underwent PFNA-II insertion from 2011 to 2013 in our centre. Intraoperative image intensifier images were used for calculation of tip apex distance, neck shaft angles, determination of Cleveland zones. Demographic data was collected on patients age and gender. The fractures were classified based on AO-OTA classification (Marsh et al., 2007) [1]. Patients were followed up for a minimum of 4 months and union of the fracture or until a complication occurred. Risk ratio for cut out was also compared with each statistically significant variable to determine the cut-off point.

RESULTS

The incidence of cut out was 6.7% Tip apex distance, neck shaft angles and female gender were statistically significant for cut out. The study found that tip apex distance beyond 27mm increased the risk of cut out. Neck shaft angles less than 128° also increased the risk of cut out. Posterior and superior blade position in the femoral head and AO 31A3 fractures trended towards significance for cut out but were not statistically significant.

CONCLUSION

To avoid cut out, one should aim for a tip apex distance of not more than 27mm and preserve a neck shaft angle of more than 128°. Risk stratification of the patient allows the surgeon to take greater caution in the post-operative period to detect early cut out.

A balanced approach for stable hips in children with cerebral palsy: a combination of moderate VDRO and pelvic osteotomy

BACKGROUND

Hip reconstructive surgery in cerebral palsy (CP) patients necessitates either femoral varus derotational osteotomy (VDRO) or pelvic osteotomy, or both. The purpose of this study is to review the results of a moderate varisation [planned neck shaft angle (NSA) of 130°] in combination with pelvic osteotomy for a consecutive series of patients.

METHODS

Patients with CP who had been treated at our institution for hip dysplasia, subluxation or dislocation with VDRO in combination with pelvic osteotomy between 2005 and 2010 were reviewed.

RESULTS

Forty patients with a mean follow-up of 5.4 years were included. The mean age at the time of operation was 8.9 years. The majority were non-ambulant children [GMFCS I-III: n = 11 (27.5 %); GMFCS IV-V: n = 29 (72.5 %)]. In total, 57 hips were treated with both femoral and pelvic osteotomy. The mean pre-operative NSA angle of 152.3° was reduced to 132.6° post-operatively. Additional adductor tenotomy was performed in nine hips (16 %) at initial operation. Reimers' migration percentage (MP) was improved from 63.6 % pre-operatively to 2.7 % post-operatively and showed a mean of 9.7 % at the final review. The results were good in 96.5 % (n = 55) with centred, stable hips (MP <33 %), fair in one with a subluxated hip (MP 42 %) and poor in one requiring revision pelvic osteotomy for ventral instability.

CONCLUSIONS

This approach maintains good hip abduction and reduces soft-tissue surgery. Moderate varisation in VDRO in combination with pelvic osteotomy leads to good mid-term results with stable, pain-free hips, even in patients with severe spastic quadriplegia.

The femoral neck-shaft angle on plain radiographs: a systematic review

OBJECTIVE

The femoral neck-shaft angle (NSA) is an important measure for the assessment of the anatomy of the hip and planning of operations. Despite its common use, there remains disagreement concerning the method of measurement and the correction of hip rotation and femoral version of the projected NSA on conventional radiographs. We addressed the following questions: (1) What are the reported values for NSA in normal adult subjects and in osteoarthritis? (2) Is there a difference between non-corrected and rotation-corrected measurements? (3) Which methods are used for measuring the NSA on plain radiographs? (4) What could be learned from an analysis of the intra- and interobserver reliability?

MATERIAL AND METHODS

A systematic literature search was performed including 26 publications reporting the measurement of the NSA on conventional radiographs.

RESULTS

The mean NSA of healthy adults (5,089 hips) was 128.8° (98-180°) and 131.5° (115-155°) in patients with osteoarthritis (1230 hips). The mean NSA was 128.5° (127-130.5°) for the rotation-corrected and 129.5° (119.6-151°) for the non-corrected measurements.

CONCLUSION

Our data showed a high variance of the reported neck-shaft angles. Notably, we identified the inconsistency of the published methods of measurement as a central issue. The reported effect of rotation-correction cannot be reliably verified.

Bone cross-sectional geometry is not associated with atypical femoral fractures in Asian female chronic bisphosphonate users

INTRODUCTION

Atypical femoral fractures (AFF) tend to occur in Asian women with prolonged bisphosphonate exposure. Hip geometry is thought to contribute to the risk of AFF formation. We examined the hip structural geometry parameters in Asian female chronic bisphosphonate users who sustained an AFF and compared them to chronic bisphosphonate users who did not sustain any femoral fracture (NFF) and bisphosphonate-naïve patients who sustained an osteoporotic femoral fracture (OFF).

MATERIALS & METHODS

Thirty-one patients with AFFs were gender and age-matched to 31 patients with NFFs and 49 patients with OFFs. The Hip Structural Analysis parameters analyzed were bone mineral density (BMD), cross-sectional area (CSA; a metric of resistance to axial compression), section modulus (SM; a metric of resistance to tensile loads), average cortical thickness (ACT; mean thickness of the femoral cortices), buckling ratio (BR; an index of likelihood of local buckling), and neck shaft angle (NSA; the angle between the neck and shaft axes). The regions analyzed were three cross-sections measured at the narrowest femoral neck diameter, the intertrochanteric area, and the proximal femoral shaft. One-way ANOVA with Bonferroni adjustment for multiple comparisons was used to compare parameters between the three patient groups, with statistical significance defined as p<0.05.

RESULTS

There were no statistical differences in parameters between patients with AFFs and patients with NFFs at all measured regions. Patients with AFFs and NFFs had statistically higher BMD, CSA, ACT, SM values and lower BR values at the NN and IT regions than patients with OFFs. Additionally, patients with NFFs had statistically higher SM values at the IT region than patients with OFFs, while patients with AFFs had statistically higher BMD, CSA, and ACT values at the FS region. All other measured parameters were not statistically different between the groups.

CONCLUSIONS

Chronic bisphosphonate users with and without AFFs had similar femoral structural geometries. Unlike in other populations, varus neck shaft angles were not found to be associated with AFFs in Asian female chronic bisphosphonate users. Thus, bone cross-sectional geometry is not likely to be associated with AFFs in Asian female chronic bisphosphonate users. Hip Structural Analysis does not show an increased predilection for tensile failure in AFFs.

The influence of stem offset and neck shaft angles on the range of motion in total hip arthroplasty

PURPOSE

To evaluate the influence of stem offset and neck shaft angles on the range of motion before component impingement (ROMCI) and bony impingement (ROMBI), and the types of impingement in total hip arthroplasty (THA).

METHODS

Using the computed tomography data of 101 patients who underwent THA, three-dimensional dynamic motion analysis was performed using a modular implant (Kinectiv(®) stem) that enabled adjustment of offset and leg length independently. We defined offset as horizontal offset (HO) and leg length as vertical offset (VO), and measured the ROMCI and ROMBI in flexion (Flex), internal rotation (Int-R) and external rotation (Ext-R) with the configuration of each horizontal/vertical offset.

RESULTS

We found that HO lengthening increased the ROMCI and ROMBI in Flex and Int-R by delaying bony impingement, although excessive lengthening had minimal effect. On the contrary, VO lengthening decreased the ROMCI and ROMBI in Flex and ROMCI in Int-R. As for Ext-R, VO lengthening had positive effects on the ROMCI and ROMBI, whereas lengthening of HO had negative effects on the ROMCI and ROMBI.

CONCLUSIONS

We demonstrated that the appropriate long offset with a low shaft angle increased the ROM in Flex and Int-R, and a high neck shaft angle increased the ROM in Ext-R. We should use implants properly in accordance with the types of impingement for avoiding dislocations in THA.

Impact of hip anatomical variations on the cartilage stress: a finite element analysis towards the biomechanical exploration of the factors that may explain primary hip arthritis in morphologically normal subjects

BACKGROUND

Hip arthritis is a pathology linked to hip-cartilage degeneration. Although the etiology of this disease is not well defined, it is known that age is a determinant risk factor. However, hip arthritis in young patients could be largely promoted by biomechanical factors. The objective of this paper is to analyze the impact of some normal anatomical variations on the cartilage stress distributions numerically predicted at the hip joint during walking.

METHODS

A three-dimensional finite element model of the femur and the pelvis with the most relevant axial components of muscle forces was used to simulate normal walking activity. The hip anatomical condition was defined by: neck shaft angle, femoral anteversion angle, and acetabular anteversion angle with a range of 110-130°, 0-20°, and 0-20°, respectively. The direct boundary method was used to simulate the hip contact.

FINDINGS

The hydrostatic stress found at the cartilage and labrum showed that a ±10° variation with respect to the reference brings significant differences between the anatomic models. Acetabular anteversion angle of 0° and femoral anteversion angle of 0° were the most affected anatomical conditions with values of hydrostatic stress in the cartilage near 5MPa under compression.

INTERPRETATION

Cartilage stresses and contact areas were equivalent to the results found in literature and the most critical anatomical regions in terms of tissue loads were in a good accordance with clinical evidence. Altogether, results showed that decreasing femoral or acetabular anteversion angles isolatedly causes a dramatic increase in cartilage loads.

Locking plate for proximal humeral fracture in the elderly population: serial change of neck shaft angle

Background

We conducted this radiographic study in the elderly population with proximal humeral fracture aiming to evaluate 1) the serial changes of neck-shaft angle after locking plate fixation and 2) find relationship between change in neck shaft angle and various factors such as age, fracture pattern, severity of osteoporosis, medial support and initial reduction angle.

Methods

Twenty-five patients who underwent surgical treatment for proximal humeral fracture with locking plate between September 2008 and August 2010 are included. True anteroposterior and axillary lateral radiographs were made postoperatively and at each follow-up visit. Measurement of neck shaft angle was done at immediate postoperative, 3 months postoperative and a final follow-up (average, 11 months; range, 8 to 17 months). Severity of osteoporosis was assessed using cortical thickness suggested by Tingart et al.

Results

The mean neck shaft angles were 133.6° (range, 100° to 116°) at immediate postoperative, 129.8° (range, 99° to 150°) at 3 months postoperative and 128.4° (range, 97° to 145°) at final follow-up. The mean loss in the neck-shaft angle in the first 3 months was 3.8° as compared to 1.3° in the period between 3 months and final follow-up. This was statistically significant (p = 0.002), indicating that most of the fall in neck shaft angle occurs in the first three months after surgery. Relationship between neck shaft angle change and age (p = 0.29), fracture pattern (p = 0.41), cortical thickness (p = 0.21), medial support (p = 0.63) and initial reduction accuracy (p = 0.65) are not statistically significant.

Conclusions

The proximal humerus locking plate maintains reliable radiographic results even in the elderly population with proximal humerus fracture.