Femoral Neck Fractures Biomechanics: Difference between revisions

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<div class="editorbox"> '''Original Editor '''- [[User:Bahnam Sabah|Bahnam Sabah]] '''Top Contributors''' - {{Special:Contributors/{{FULLPAGENAME}}}}</div>
<div class="editorbox"> '''Original Editor '''- [[User:Bahnam Sabah|Bahnam Sabah]] '''Top Contributors''' - {{Special:Contributors/{{FULLPAGENAME}}}}</div>


== Background ==
== Introduction ==
Femoral neck fractures can be detrimental to a person’s health. The occurrence of a femoral neck fracture is associated with decreased quality of life, increased morbidity, disability, and mortality in the elderly population.<ref name=":0">Nasiri Sarvi M, Luo Y. [https://link.springer.com/article/10.1007/s00198-017-4138-5 Sideways fall-induced impact force and its effect on hip fracture risk: a review]. Osteoporosis international. 2017 Oct;28(10):2759-80.</ref> What is also concerning about femoral neck fractures is the occurrence of non-union between the femoral neck and the femoral head. This reduces the distribution of blood flow to the femoral head which is a cause for [[Avascular Necrosis|avascular necrosis.]]<ref name=":1">Fuchs RK, Kersh ME, Carballido-Gamio J, Thompson WR, Keyak JH, Warden SJ. [https://link.springer.com/article/10.1007/s11914-017-0343-6 Physical activity for strengthening fracture prone regions of the proximal femur]. Current osteoporosis reports. 2017 Feb;15(1):43-52.</ref>
[[File:Hip fracture.jpeg|thumb|NOF regions]]
[[Femoral Neck Hip Fracture|Hip fractures]] are one of the most frequent fractures presenting to the emergency department and orthopedic trauma teams. Note, hip fracture and [[Femoral Neck Hip Fracture|neck of femur (NOF) fracture]] both relate to the same type of injury. A NOF fracture occurs just below the head of femur.


Fracture risk is determined by the bone strength and the applied load. The main predictor of bone strength is the bone mineral density at the femoral neck. The bone mineral density can indicate fracture risk and it can be obtained via dual x-ray absorptiometry.<ref name=":2">Augat P, Bliven E, Hackl S. [https://journals.lww.com/jorthotrauma/FullText/2019/01001/Biomechanics_of_Femoral_Neck_Fractures_and.6.aspx Biomechanics of femoral neck fractures and implications for fixation]. Journal of orthopaedic trauma. 2019 Jan 1;33:S27-32.</ref>Other factors that determine fracture risk are bone geometry, cortical bone thickness, and cortical bone density.<ref name=":2" /> The cortical bone matrix has a direct effect on the overall mechanical strength of the bone. Bone porosity, which can be assessed through a bone biopsy, is a strong predictor of mechanical strength.<ref name=":2" />   
The [[Hip Anatomy|hip joint]] contact forces are in excess of 500% body weight (BW) and can be as high as 509 kg of force during during ADL's, however spontaneous fractures typically do not occur in healthy individuals. Falls in the elderly account for most NOF fractures, and the incidence of NOF fractures is increasing today as the proportion of the elderly population worldwide increases.<ref>Radiopedia Neck of femur fracture Available:https://radiopaedia.org/articles/neck-of-femur-fracture-1?lang=us (accessed 9.12.2022)</ref>   


Geometrically, the normal femoral neck-shaft angle is between 124-135⁰.  Femoral neck-shaft angle that is below 120⁰ is considered '''cox vara'''. If the femoral neck-shaft angle is above 135⁰ is considered '''coxa valga'''. Having a femoral neck-shaft angle that is outside of the normal range increases the risk of a femoral neck fracture.<ref name=":3">Kani KK, Porrino JA, Mulcahy H, Chew FS. [https://link.springer.com/article/10.1007/s00256-018-3008-3 Fragility fractures of the proximal femur: review and update for radiologists]. Skeletal radiology. 2019 Jan;48(1):29-45.</ref> Additionally, increased hip axis length (measured along the femoral neck axis and is defined as the distance from the inferolateral aspect of the greater trochanter to the inner pelvic brim), increased neck length, decreased cortical thickness, and decreased cross-sectional area of the femoral neck are all factors that can increase the risk of fracture.<ref name=":2" /><ref name=":3" />
== Etiology ==
[[File:Femoral neck-shaft angle.jpg|thumb|300x300px|Femoral neck-shaft angle|alt=]]


#[[Effects of Ageing on Bone|Ageing,]] [[osteoporosis]], or metastatic lesions, may weaken bone tissue to such an extent that spontaneous [[Femoral Neck Hip Fracture|femoral neck fractures (NOF)]] occur. The initiation of [[fracture]] is typically at the superior aspect of the femoral neck, a region with less [[Bone Cortical And Cancellous|cortical]] thickness, and travels along through the trabecular bone.<ref name=":4">Basso T, Klaksvik J, Syversen U, Foss OA. [https://www.sciencedirect.com/science/article/pii/S0020138312001283 Biomechanical femoral neck fracture experiments—a narrative review]. Injury. 2012 Oct 1;43(10):1633-9.</ref>
#[[Bone Stress Injuries|Femoral neck stress fractures]] occur when homeostatic remodelling can not keep up with the strain that is put on the bone. This is often due to repetitive loading of bone with abnormal forces and sudden increase in training volume or activity.<ref name=":7">Robertson GA, Wood AM. [https://www.thieme-connect.com/products/ejournals/html/10.1055/s-0043-103946 Femoral neck stress fractures in sport: a current concepts review]. Sports Medicine International Open. 2017 Feb;1(02):E58-68.</ref> Femoral neck stress fractures are associated with activities like long-distance running, gymnastics, and ballet.<ref name=":7" /> The cyclical loading of the tissue leads to decreased tissue tolerance. The micro-fractures that occur on the bone cannot be repaired fast enough and turn into fractures.<ref name=":6" />


The initiation of fracture is typically at the superior aspect of the femoral neck, a region with less cortical thickness, and travels along through the trabecular bone.<ref name=":4">Basso T, Klaksvik J, Syversen U, Foss OA. [https://www.sciencedirect.com/science/article/pii/S0020138312001283 Biomechanical femoral neck fracture experiments—a narrative review]. Injury. 2012 Oct 1;43(10):1633-9.</ref> The ageing process reduces bone mineral density and cortical bone thickness, which is why the prevalence of femoral neck fracture is higher in the elderly population.<ref name=":4" />
== Fracture risk ==
=== Biomechanics Involved ===
[[File:Bone Mass.jpeg|thumb|456x456px|Bone mass/Age graph]]
Fracture risk is determined by the bone strength and the applied load.  


=== Forces ===
* Bone strength: [[Bone Density]] at the femoral neck and the cortical bone thickness and bone density.
The femoral neck experiences the highest stress loads within the femur. <ref name=":6">Neubauer T, Brand J, Lidder S, Krawany M. [https://www.tandfonline.com/doi/abs/10.1080/15438627.2016.1191489 Stress fractures of the femoral neck in runners: a review.] Research in Sports Medicine. 2016 Jul 2;24(3):283-97.</ref> Forces that are acting on the femoral neck are externally, and internally generated forces.<ref name=":2" /><ref name=":4" /> Externally generated forces are a result of ground reaction forces that translated from the ankle to the femoral neck as a result of the vertical impact and typically stay below 1.3 times body weight during low-speed walking. <ref name=":2" /> Internally generated forces are a result of the muscles acting on the bone to accomplish the desired movements and maintain balance. Internally generated forces are typically 2-3 times body weight during low-speed walking. <ref name=":4" />  
* Bone porosity: assessed through a bone biopsy, strong predictor of mechanical strength.
* Bone geometrically: normal femoral neck-shaft angle is between 124-135⁰.  Having a femoral neck-shaft angle that is outside of the normal range increases the risk of a femoral neck fracture ([[Coxa Vara / Coxa Valga|coxa vara or coxa valga]]) .
* Increased hip axis length (measured along the femoral neck axis and is defined as the distance from the inferolateral aspect of the greater trochanter to the inner [[Pelvis|pelvic]] brim), increased neck length.<ref name=":2">Augat P, Bliven E, Hackl S. [https://journals.lww.com/jorthotrauma/FullText/2019/01001/Biomechanics_of_Femoral_Neck_Fractures_and.6.aspx Biomechanics of femoral neck fractures and implications for fixation]. Journal of orthopaedic trauma. 2019 Jan 1;33:S27-32.</ref><ref name=":3">Kani KK, Porrino JA, Mulcahy H, Chew FS. [https://link.springer.com/article/10.1007/s00256-018-3008-3 Fragility fractures of the proximal femur: review and update for radiologists]. Skeletal radiology. 2019 Jan;48(1):29-45.</ref>


The internal and external forces produce bending and torsional moments that act on the femoral neck. The bending moments at the femoral neck are a product of vertical loading during daily activities.<ref name=":2" /> The bending moment creates compression on the inferior aspect of the femoral neck and tension at the superior aspect of the femoral neck.<ref name=":2" /> The majority of the vertical loading force is transferred through vertically oriented trabeculae that are located at the inferior aspect of the femoral neck.<ref name=":3" />
== Biomechanics: Forces ==
[[File:Internal and external architecture.jpg|thumb|Internal and external architecture of the femoral neck]]
[[File:Femoral neck-shaft angle.jpg|thumb|437x437px|Femoral neck-shaft angle|alt=]]
The level of strain at the femoral neck is reported to be 500-2000 micro-strains for day-to-day activities.<ref name=":2" />  The bone strain is largest at the inferior aspect of the neck. This results in a larger thickness of the bone cortex compared to the superior aspect.<ref name=":2" /> The superior aspect of the femoral neck experiences increased strain during activities like stair climbing where there is an increase in hip flexion and abduction. The increased strain is due to the increase of torsion at the femoral neck.<ref name=":4" /> 
The NOF experiences the highest stress loads within the femur. <ref name=":6">Neubauer T, Brand J, Lidder S, Krawany M. [https://www.tandfonline.com/doi/abs/10.1080/15438627.2016.1191489 Stress fractures of the femoral neck in runners: a review.] Research in Sports Medicine. 2016 Jul 2;24(3):283-97.</ref> Forces that are acting on the femoral neck are:  


[[Bone Stress Injuries|Femoral neck stress fractures]] occur when homeostatic remodelling can not keep up with the strain that is put on the bone. This is often due to repetitive loading of bone with abnormal forces and sudden increase in training volume or activity.<ref name=":7">Robertson GA, Wood AM. [https://www.thieme-connect.com/products/ejournals/html/10.1055/s-0043-103946 Femoral neck stress fractures in sport: a current concepts review]. Sports Medicine International Open. 2017 Feb;1(02):E58-68.</ref> Femoral neck stress fractures are associated with activities like long-distance running, gymnastics, and ballet.<ref name=":7" /> The cyclical loading of the tissue leads to decreased tissue tolerance. The micro-fractures that occur on the bone cannot be repaired fast enough and turn into fractures.<ref name=":6" />
# Externally generated: a result of ground reaction forces that translated from the ankle to the NOF as a result of the vertical impact and typically stay below 1.3 times body weight during low-speed walking. <ref name=":2" />
[[File:Running-1705716 1920.jpg|thumb|alt=]]
# Internally generated: a result of the muscles acting on the bone to accomplish the desired movements and maintain balance. Internally generated forces are typically 2-3 times body weight during low-speed walking. <ref name=":4" />


=== Fracture Categories ===
The internal and external forces produce bending and torsional moments that act on the NOF (reported to be 500-2000 micro-strains for day-to-day activities)<ref name=":2" />
Femoral neck stress fractures are subdivided into two categories:  


* Category one is compressive type fractures that occur at the inferior aspect of the femoral neck. This type of fracture occurs when the forces applied to the bone are higher than the plastic properties of the bone.<ref name=":7" />  
* The bone strain is largest at the inferior aspect of the NOF, resulting in a larger thickness of the inferior aspect of NOF bone cortex compared to the superior aspect.<ref name=":2" />
* Category two is tensile type fractures that occur at the superior aspect of the bone. In normal conditions, the gluteus medius and minimus muscles counteract the high-tension forces acting on the femoral neck. However, tension femoral neck stress fracture occurs when the muscles are fatigued, and the tensile forces are translated predominantly by the bone.<ref name=":7" /> 
* The superior aspect of the femoral neck experiences increased strain during activities like stair climbing where there is an increase in hip flexion and abduction. The increased strain is due to the increase of torsion at the femoral neck.<ref name=":4" />
Sideway falls are a leading cause of [[Hip Fracture|hip fracture]] in the elderly population.<ref name=":0" /> Sideways falls, on the greater trochanter, induce a compressive type of load to the femoral neck.<ref name=":2" /> The factors that are involved in falls that contribute to fractures are femoral strength, fall velocity, and effective mass.<ref name=":0" /> Femoral strength is significantly reduced in a sideways fall scenario. The loading configuration determines the amount of force required to induce a fracture on the femoral neck. The force required to induce a fracture during a single leg stance is 7214N vs 3462N during a sideways fall ±1520N. The femoral neck can withstand a much greater force during vertical loading vs lateral loading on the greater trochanter.<ref name=":0" />  


Fall velocities greater than 3m/s can induce a fracture on the femoral neck. Falls due to a slip or stumble have higher fall velocity than falls due to incorrect shifting of weight.<ref name=":0" /> The effective mass is the part of the body that moves downwards and creates the impact load. A fall from a standing position is going to have a larger effective mass than a fall from a kneeling position.<ref name=":0" />
=== Categories ===
 
[[File:Internal and external architecture.jpg|thumb|Internal and external architecture NOF|alt=|424x424px]]
=== Prevention ===
NOF stress fractures are subdivided into two categories:  
The first measure of treatment is knowing the signs of a femoral neck stress fracture. Knowing how the fracture presents can lead to early diagnosis and avoid further complications.<ref name=":6" /><ref name=":7" /> The onset of pain occurs at the hip or groin area during activities of weight-bearing. Pain can also radiate to the anterior thigh, gluteal region and even down to the knee. There is a gradual increase in pain throughout the activities.<ref name=":7" /> This stage is when antalgic gait is likely to present due to the pain. Eventually, pain is also noticed during periods of rest and at night. In later stages, cracking and popping can be felt in the groin region which often leads to a complete fracture of the femoral neck.<ref name=":7" />
[[File:Taichi.jpg|thumb|Taichi exercise ]]
In long-term care facilities, a multicomponent exercise program has been proven to reduce the risk of falls for the participants. This can be an effective measure to reduce the occurrence of a fracture at the femoral neck.<ref name=":8">Karlsson MK, Magnusson H, von Schewelov T, Rosengren BE. [https://link.springer.com/article/10.1007/s00198-012-2256-7 Prevention of falls in the elderly—a review]. Osteoporosis international. 2013 Mar;24(3):747-62.</ref> The benefits of the exercise program are improved balance control, improved muscular strength, and muscular endurance. The most effective exercise program should incorporate balance training, strength training followed by flexibility, and endurance training.<ref name=":8" /> Alternatively, Tai chi exercise has been proven to reduce bone mineral density loss in regions of the femoral neck. This can be an effective measure to maintain bone strength and reduce fracture risk.<ref>Zou L, Wang C, Chen K, Shu Y, Chen X, Luo L, Zhao X. [https://www.mdpi.com/221090 The effect of Taichi practice on attenuating bone mineral density loss: A systematic review and meta-analysis of randomized controlled trials]. International journal of environmental research and public health. 2017 Sep;14(9):1000.</ref> 
 
[[Vitamin D Deficiency|Vitamin D]] supplementation has also been proven to reduce the occurrence of falls in long-term care facilities. This measure works best when combined with a multifaceted approach combining Vitamin D supplements with Calcium supplements, education on fall prevention, and balance exercise training.<ref name=":8" />


# Compressive type: occur at the inferior aspect of the NOF. This type of fracture occurs when the forces applied to the bone are higher than the plastic properties of the bone.<ref name=":7" /> eg Sideway falls (leading cause of [[Femoral Neck Hip Fracture|hip fracture]] in the elderly).<ref name=":0">Nasiri Sarvi M, Luo Y. [https://link.springer.com/article/10.1007/s00198-017-4138-5 Sideways fall-induced impact force and its effect on hip fracture risk: a review]. Osteoporosis international. 2017 Oct;28(10):2759-80.</ref> Induce a compressive type of load to the femoral neck.<ref name=":2" /> The factors that are involved in falls that contribute to fractures are femoral strength, fall velocity, and effective mass.<ref name=":0" /> Femoral strength is significantly reduced in a sideways fall scenario. The loading configuration determines the amount of force required to induce a NOF fracture. The force required to induce a fracture during a single leg stance is 7214N vs 3462N during a sideways fall ±1520N. The NOF can withstand a much greater force during vertical loading vs lateral loading on the greater trochanter.<ref name=":0" />; Fall velocities > 3m/s can induce a NOF fracture. Falls due to a slip or stumble have higher fall velocity than falls due to incorrect shifting of weight.<ref name=":0" /> A fall from a standing position is going to have a larger effective mass than a fall from a kneeling position.<ref name=":0" />
# Tensile type: occur at the superior aspect of the bone. Occurs when the muscles are fatigued, and the tensile forces are translated predominantly by the bone. In normal conditions, the gluteus medius and minimus muscles counteract the high-tension forces acting on the NOF.<ref name=":7" />
== References ==
== References ==
<references />
<references />
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[[Category:Hip]]
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[[Category:Hip - Bones]]
[[Category:Hip - Bones]]
[[Category:Biomechanics]]

Latest revision as of 12:08, 19 December 2022

Original Editor - Bahnam Sabah Top Contributors - Lucinda hampton, Lilian Ashraf, Bahnam Sabah, Kim Jackson, Aminat Abolade and Kendal Marriott

Introduction[edit | edit source]

NOF regions

Hip fractures are one of the most frequent fractures presenting to the emergency department and orthopedic trauma teams. Note, hip fracture and neck of femur (NOF) fracture both relate to the same type of injury. A NOF fracture occurs just below the head of femur.

The hip joint contact forces are in excess of 500% body weight (BW) and can be as high as 509 kg of force during during ADL's, however spontaneous fractures typically do not occur in healthy individuals. Falls in the elderly account for most NOF fractures, and the incidence of NOF fractures is increasing today as the proportion of the elderly population worldwide increases.[1]

Etiology[edit | edit source]

  1. Ageing, osteoporosis, or metastatic lesions, may weaken bone tissue to such an extent that spontaneous femoral neck fractures (NOF) occur. The initiation of fracture is typically at the superior aspect of the femoral neck, a region with less cortical thickness, and travels along through the trabecular bone.[2]
  2. Femoral neck stress fractures occur when homeostatic remodelling can not keep up with the strain that is put on the bone. This is often due to repetitive loading of bone with abnormal forces and sudden increase in training volume or activity.[3] Femoral neck stress fractures are associated with activities like long-distance running, gymnastics, and ballet.[3] The cyclical loading of the tissue leads to decreased tissue tolerance. The micro-fractures that occur on the bone cannot be repaired fast enough and turn into fractures.[4]

Fracture risk[edit | edit source]

Bone mass/Age graph

Fracture risk is determined by the bone strength and the applied load.

  • Bone strength: Bone Density at the femoral neck and the cortical bone thickness and bone density.
  • Bone porosity: assessed through a bone biopsy, strong predictor of mechanical strength.
  • Bone geometrically: normal femoral neck-shaft angle is between 124-135⁰. Having a femoral neck-shaft angle that is outside of the normal range increases the risk of a femoral neck fracture (coxa vara or coxa valga) .
  • Increased hip axis length (measured along the femoral neck axis and is defined as the distance from the inferolateral aspect of the greater trochanter to the inner pelvic brim), increased neck length.[5][6]

Biomechanics: Forces[edit | edit source]

Femoral neck-shaft angle

The NOF experiences the highest stress loads within the femur. [4] Forces that are acting on the femoral neck are:

  1. Externally generated: a result of ground reaction forces that translated from the ankle to the NOF as a result of the vertical impact and typically stay below 1.3 times body weight during low-speed walking. [5]
  2. Internally generated: a result of the muscles acting on the bone to accomplish the desired movements and maintain balance. Internally generated forces are typically 2-3 times body weight during low-speed walking. [2]

The internal and external forces produce bending and torsional moments that act on the NOF (reported to be 500-2000 micro-strains for day-to-day activities)[5]

  • The bone strain is largest at the inferior aspect of the NOF, resulting in a larger thickness of the inferior aspect of NOF bone cortex compared to the superior aspect.[5]
  • The superior aspect of the femoral neck experiences increased strain during activities like stair climbing where there is an increase in hip flexion and abduction. The increased strain is due to the increase of torsion at the femoral neck.[2]

Categories[edit | edit source]

Internal and external architecture NOF

NOF stress fractures are subdivided into two categories:

  1. Compressive type: occur at the inferior aspect of the NOF. This type of fracture occurs when the forces applied to the bone are higher than the plastic properties of the bone.[3] eg Sideway falls (leading cause of hip fracture in the elderly).[7] Induce a compressive type of load to the femoral neck.[5] The factors that are involved in falls that contribute to fractures are femoral strength, fall velocity, and effective mass.[7] Femoral strength is significantly reduced in a sideways fall scenario. The loading configuration determines the amount of force required to induce a NOF fracture. The force required to induce a fracture during a single leg stance is 7214N vs 3462N during a sideways fall ±1520N. The NOF can withstand a much greater force during vertical loading vs lateral loading on the greater trochanter.[7]; Fall velocities > 3m/s can induce a NOF fracture. Falls due to a slip or stumble have higher fall velocity than falls due to incorrect shifting of weight.[7] A fall from a standing position is going to have a larger effective mass than a fall from a kneeling position.[7]
  2. Tensile type: occur at the superior aspect of the bone. Occurs when the muscles are fatigued, and the tensile forces are translated predominantly by the bone. In normal conditions, the gluteus medius and minimus muscles counteract the high-tension forces acting on the NOF.[3]

References[edit | edit source]

  1. ↑ Radiopedia Neck of femur fracture Available:https://radiopaedia.org/articles/neck-of-femur-fracture-1?lang=us (accessed 9.12.2022)
  2. ↑ 2.0 2.1 2.2 Basso T, Klaksvik J, Syversen U, Foss OA. Biomechanical femoral neck fracture experiments—a narrative review. Injury. 2012 Oct 1;43(10):1633-9.
  3. ↑ 3.0 3.1 3.2 3.3 Robertson GA, Wood AM. Femoral neck stress fractures in sport: a current concepts review. Sports Medicine International Open. 2017 Feb;1(02):E58-68.
  4. ↑ 4.0 4.1 Neubauer T, Brand J, Lidder S, Krawany M. Stress fractures of the femoral neck in runners: a review. Research in Sports Medicine. 2016 Jul 2;24(3):283-97.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Augat P, Bliven E, Hackl S. Biomechanics of femoral neck fractures and implications for fixation. Journal of orthopaedic trauma. 2019 Jan 1;33:S27-32.
  6. ↑ Kani KK, Porrino JA, Mulcahy H, Chew FS. Fragility fractures of the proximal femur: review and update for radiologists. Skeletal radiology. 2019 Jan;48(1):29-45.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Nasiri Sarvi M, Luo Y. Sideways fall-induced impact force and its effect on hip fracture risk: a review. Osteoporosis international. 2017 Oct;28(10):2759-80.
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