Differences in femur geometry and bone markers in atypical femur fractures and the general population

Update on Atypical Femoral Fractures

➤ Atypical femoral fractures (AFFs) are stress fractures between the lesser trochanter and the metaphyseal flare that are most commonly related to prolonged (3 to 5 years) antiresorptive medication use.➤ An important finding is a visible transverse line in the lateral cortex, known as the "dreaded black line." Complete fractures are transverse and have minimal comminution.➤ Prodromal symptoms including hip, groin, thigh, and knee pain are present in more than one-half of cases and are usually misdiagnosed.➤ Nonoperative treatment for all patients with AFF includes withdrawal of bisphosphonates, assessment for secondary causes of osteoporosis, and optimization of vitamin D and calcium.➤ Incomplete fractures without a visible line can initially be treated nonoperatively with protected weight-bearing.➤ Intramedullary nailing is indicated for complete fractures and incomplete fractures with a visible fracture line. Delayed healing after fixation should be anticipated.➤ Treatment with parathyroid hormone (PTH) analogs (teriparatide and abaloparatide) after AFF prevents other fractures in high-risk patients, but the effect on healing of the fracture is unclear.

Effect of different constraining boundary conditions on simulated femoral stresses and strains during gait

Finite element analysis (FEA) is commonly used in orthopaedic research to estimate localised tissue stresses and strains. A variety of boundary conditions have been proposed for isolated femur analysis, but it remains unclear how these assumed constraints influence FEA predictions of bone biomechanics. This study compared the femoral head deflection (FHD), stresses, and strains elicited under four commonly used boundary conditions (fixed knee, mid-shaft constraint, springs, and isostatic methods) and benchmarked these mechanics against the gold standard inertia relief method for normal and pathological femurs (extreme anteversion and retroversion, coxa vara, and coxa valga). Simulations were performed for the stance phase of walking with the applied femoral loading determined from patient-specific neuromusculoskeletal models. Due to unrealistic biomechanics observed for the commonly used boundary conditions, we propose a novel biomechanical constraint method to generate physiological femur biomechanics. The biomechanical method yielded FHD (< 1 mm), strains (approaching 1000 µε), and stresses (< 60 MPa), which were consistent with physiological observations and similar to predictions from the inertia relief method (average coefficient of determination = 0.97, average normalized root mean square error = 0.17). Our results highlight the superior performance of the biomechanical method compared to current methods of constraint for  both healthy and pathological femurs.

Is there genetic susceptibility for atypical femoral fractures?

The mechanisms underlying AFF remain unclear, with hypotheses including bone turnover suppression and morphological variation. Recent studies have suggested a potential genetic susceptibility to AFF. A scoping review was conducted using PubMed to identify studies published since 2016. Twenty-one studies were identified, focusing on histological and genetic analysis of AFF patients and Bisphosphonates users. Biopsies and imaging modalities were used to assess histological and morphometric parameters, while genetic sequencing was performed to identify variants in target genes. Genetic studies identified variants in geranylgeranyl diphosphate synthase 1 (GGPS1) and CYP1A1 genes, which play roles in osteoclast function and drug metabolism, respectively. Functional analysis revealed reduced enzymatic activity in mutant variants of these genes, which could be further inhibited by BP use. Other genes, such as ATRAID, ALPL, and COL1A2, were also associated with AFF. Histomorphometric studies supported the hypothesis of bone turnover suppression in AFF, with alterations in tissue mechanical properties and microarchitecture observed, particularly in cortical bone. The findings suggest a potential genetic susceptibility to AFF, with variants in GGPS1 and CYP1A1 genes affecting osteoblast and osteoclast function. Bone turnover suppression and altered tissue properties contribute to the pathogenesis of AFF.

The additive effect of vitamin K supplementation and bisphosphonate on fracture risk in post-menopausal osteoporosis: a randomised placebo controlled trial

This study assessed whether vitamin K, given with oral bisphosphonate, calcium and/or vitamin D has an additive effect on fracture risk in post-menopausal women with osteoporosis. No difference in bone density or bone turnover was observed although vitamin K1 supplementation led to a modest effect on parameters of hip geometry.

PURPOSE

Some clinical studies have suggested that vitamin K prevents bone loss and may improve fracture risk. The aim was to assess whether vitamin K supplementation has an additive effect on bone mineral density (BMD), hip geometry and bone turnover markers (BTMs) in post-menopausal women with osteoporosis (PMO) and sub-optimum vitamin K status receiving bisphosphonate, calcium and/or vitamin D treatment.

METHODS

We conducted a trial in 105 women aged 68.7[12.3] years with PMO and serum vitamin K1 ≤ 0.4 µg/L. They were randomised to 3 treatment arms; vitamin K1 (1 mg/day) arm, vitamin K2 arm (MK-4; 45 mg/day) or placebo for 18 months. They were on oral bisphosphonate and calcium and/or vitamin D. We measured BMD by DXA, hip geometry parameters using hip structural analysis (HSA) software and BTMs. Vitamin K1 or MK-4 supplementation was each compared to placebo. Intention to treat (ITT) and per protocol (PP) analyses were performed.

RESULTS

Changes in BMD at the total hip, femoral neck and lumbar spine and BTMs; CTX and P1NP did not differ significantly following either K1 or MK-4 supplementation compared to placebo. Following PP analysis and correction for covariates, there were significant differences in some of the HSA parameters at the intertrochanter (IT) and femoral shaft (FS): IT endocortical diameter (ED) (% change placebo:1.5 [4.1], K1 arm: -1.02 [5.07], p = 0.04), FS subperiosteal/outer diameter (OD) (placebo: 1.78 [5.3], K1 arm: 0.46 [2.23] p = 0.04), FS cross sectional area (CSA) (placebo:1.47 [4.09],K1 arm: -1.02[5.07], p = 0.03).

CONCLUSION

The addition of vitamin K1 to oral bisphosphonate with calcium and/or vitamin D treatment in PMO has a modest effect on parameters of hip geometry. Further confirmatory studies are needed.

TRIAL REGISTRATION

The study was registered at Clinicaltrial.gov:NCT01232647.

Incomplete Diaphyseal Atypical Femoral Fracture due to Increased Anterolateral Bowing: Treatment with Corrective Osteotomy and Intramedullary Nailing with Augmented Plate Fixation

BACKGROUND

Increased anterolateral bowing of the femur is associated with atypical femoral fractures among older patients (including both those receiving and those not receiving treatment with bisphosphonates) as well as a greater likelihood of occurring in the diaphyseal versus the subtrochanteric region. Prophylactic intramedullary (IM) nailing is recommended for the treatment of incomplete atypical femoral fractures, which are radiographically evident. However, this bowing deformity is considered to be a major obstacle to IM nailing as it may be associated with postoperative complications. Corrective osteotomy combined with IM nailing straightens the exaggerated curvature of the femur. We hypothesized that this technique may lead to the safe and rapid healing of incomplete diaphyseal atypical femoral fractures, thereby reducing lateral tensile stress.

METHODS

From October 2015 through March 2020, 17 female patients (20 femora) with a mean age of 76.1 years (range, 68 to 86 years) underwent a surgical procedure for the treatment of an incomplete diaphyseal atypical femoral fracture associated with anterolateral bowing. The surgical technique consisted of minimally invasive osteotomy and reconstruction with use of IM nailing, with or without an augmentation plate. Preoperative and postoperative radiographic findings (lateral and anterior bowing angles, anterolateral bowing grade, and lateral distal femoral angle [LDFA]) were compared. Primary union, time to union, and complications were evaluated as the outcomes.

RESULTS

Primary bone union was achieved in 19 of the 20 femora at a mean of 24.9 weeks (range, 20 to 40 weeks). There were 2 instances of delayed union, which healed at 36 and 40 weeks. The lateral bowing angle, anterior bowing angle, and LDFA significantly improved postoperatively (from 12.0° to 3.3°, from 17.3° to 11.5°, and from 93.5° to 88.8°, respectively) (p < 0.001). There was 1 instance of nonunion, which healed after plate augmentation without a bone graft.

CONCLUSIONS

Given the pathophysiology of elevated lateral tensile stress, corrective osteotomy and IM nailing may be an acceptable solution for the treatment of incomplete diaphyseal atypical femoral fractures associated with increased anterolateral bowing.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.