| Background :In terms of the cause of the fracture,currently people generally believe the fracture occurs in the weak area of femoral neck during lateral fall,and it is caused due to direct stress on greater trochanter.Besides,osteoporosis is a major precipitating factor for occurrence of fracture.Many scholars have made researches on the action of lateral stress on greater trochanter and to result in occurrence of femoral neck fracture.The researches showed that when the lateral stress acted on greater trochanter,the femoral neck was under longitudinal pressure stress,meanwhile,fracture occurred first in the upper weak area of the femoral neck.If the pressure continued to increase,fracture occurs completly.This indicated simulation of the mechanism for lateral fall.Beyond that,many researches focus on bone mineral density of the aged.In these researches,it was believed that the occurrence of femoral neck fracture was related to local bone mineral density decline.In fact,many cases of femoral neck fracture can not be explained with the above-mentioned mechanism.For example,the hip of some patients is not down to the ground when falling down,but rather fall forward.Even some patients are free of specific history of trauma.The femoral neck fracture occurs when they just wrench or without any feeling.Some people have good bone strength,but fracture occurs to them due to very small injury.The previous researches focus on biomechanics of femoral neck or research on specimen of human body,and they indicate the research under ideal status,however,nobody has conducted a research on the damage mechanism of clinical patients of femoral neck fracture.In clinical practice,we discovered that the injury mechanism of patients of femoral neck fracture was different,and there was a large difference in violence size,which could not be explained via direct lateral stress on greater trochanter.Hence,we hope to find some other possible mechanisms for explanation.Kevin M found stress fracture of femoral neck occurred to many new recruits,and it wasrelated to acetabulum retroversion;Goldin M also verified that stress fracture of femoral neck was relevant to anterior femoroacetabular impingement.In clinical practice,we discovered that many patients under femoral neck fracture are combined with CAM malformation,PINCER malformation or concurrence of both.Therefore,we believed that this type of malformation might facilitate occurrence of femoral neck fracture.When performing operation for the patients under femoral neck fracture,we often found that many of such patients were provided with obvious fresh tearing on the anterior superior labrum of the acetabulum,and we believed that such tearing might be generated due to impact between femoral neck and acetabulum.As a result,the purpose of this research is to investigate whether femoral neck fracture is related to femoroacetabular impingement.Methods: A total of 36 out of 74 patients(10 males and 26 females)with a history of femoral neck fractures for less than 4 weeks were recruited from February 2017 to February2018.Patient's data were collected from the medical record system in September 2018.All patients underwent total hip arthroplasty or hemiarthroplasty due to their age,fracture displacement and/or geriatric fracture.The mean age of the included patients was 72.8 years old,range from 50 to 89.Inclusion criteria:1.First femoral neck fracture.2.Medical history less than 4 weeks.3.Barrier-free communication.4.Cardiopulmonary function can withstand surgery.5.No previous history of hip pain.6.No previous history of hip surgery.7.No previous history of hip infection.8.No previous fracture in the pelvis or lower limbs.9.Normal hip joint development.10.No hip osteoarthritis.11.No necrosis in bilateral femoral head.Exclusion criteria:1.There are fractures in other parts combined with trauma.2.Previous history of hip pain.3.Medical history over 4 weeks.4.Communication difficulties.5.Previous surgical history of either side of the hip joint.6.Patients with poor cardiopulmonary function and high risk of operation.7.Previous fracture history of pelvis and lower limbs.8.Dysplasia of hip.9.Necrosis of the femoral head.10.The hip osteoarthritis.11.History of hip infection on either side.Biopsy of labrum: We removed the tore glenoid labrum and delivered them for biopsy.Previous literature suggested that the hyperplasia of granulation tissue and hemosiderin macrophages could be found in patients with acute soft tissue injury.To assess the changes in the hyperplasia of granulation tissue and hemosiderin macrophages,all samples with injuredlabrums were sent to biopsy.The patients were divided into two groups,(i)Labrum tear group(n=22),with the presence of hemorrhage and hematoma in local area of the injured labrums as well as the hyperplasia of granulation tissue and hemosiderin macrophages.Normal labrum group(n=14),in which the labrums were not injured or no hyperplasia of granulation tissue and hemosiderin macrophages.1.Femoral neck fractures and anterior femoroacetabular impingementPatients' age,gender,BMI,muscle injury,injury pattern and trauma severity were recorded.The location of bone contusion and muscle injury around the hip were observed by MRI examination.For the patients who fell sideways,direct trauma of the greater trochanter resulted in a compression type stress fracture of femoral neck.We know the femoral neck is 15 degrees forward,the injury pattern was possibly a posterolateral fall.We divided the fall postures into three ways: Posterolateral descending,anterolateral descending and lateral descending.Therefore,it may be necessary to explain that generally speaking,the damage of the selected cases were low-energy,and there is a difference between relatively low-energy and relatively high-energy traumas.Relatively low-energy trauma was defined as a lateral fall that occurred during walking;while relatively high-energy trauma was a fall characterized by additional acceleration,such as slip,fall from heights,trip,traffic injury,fall and get hurt by heavy objects at the same time.All statistical analyses were in the SPSS version 18.0 software(IBM Corp.,Armonk NY,USA).P value of less than 0.05 was considered statistically significant.2.Femoral neck fracture and hip joint anatomyPatients' age,gender,BMI,femoral head-neck offset,femoral head-neck ratio,alpha angle,1/14,3/14,5/14,7/14 and femoral head center anteversion on the affected side,diameter of the femoral head,acetabular index(AI),cortical index(CI),hip axis length(HAL),and neck stem angle(NSA)were recorded.The scan data were stored in DICOM format,and then imported into MIMICS 19.0 for reconstructing and generating STL files of the pelvis and femur.Unigraphics NX 11.0 software was used to import the 3D reconstructed STL files,in order to establish the coordinate system and place the pelvis completely in a neutral position.The acetabulum was divided into fourteen parts from top to bottom,and the five different angles were defined as follows: 1/14,3/14,5/14,7/14 and the femoral head center.The anteversion angle of the acetabulum was measured.All statistical analyses wereperformed using SPSS version 18.0 software(IBM Corp.,Armonk NY,USA).P value of less than 0.05 was considered statistically significant.Results:1.Femoral neck fractures and anterior femoroacetabular impingementAccording to intraoperative findings,22 patients exhibited a labrum tear.Further reviewing the surveillance videos supported our hypothesis that the affected limbs were in the flexion and internal rotation positions.Magnetic resonance imaging examination revealed bone contusion on the anterolateral margin of the acetabulum with muscle damage surrounding the hip,Especially the short abductor and adductor muscles.At the same time,we could see that the locations of acetabulum contusion were also in the anterior superior quadrant,which were consistent with the location of labrum tear.Among 14 cases without a labrum tear have no obvious performance.Notably,age,muscle injury,injury pattern and trauma severity differed significantly(P <.05)between labrum tear and normal labrum groups,with respect to gender and BMI on the contrary.Based on fall injury data,we found that the injury pattern of cases without a labrum tear was mainly posterolateral,while that of cases with a labrum tear was primarily non-posterolateral.Data on the injury conditions of all patients were collected through the past medical history.A total of 9 out of 14 cases with relatively high-energy trauma were identified in untorn labrum group,including 1 case of falling off a bike,3 cases of slip,1 case of fall and get hurt by heavy objects at the same time,1 case of falling down from a parallel bar,and 2 cases of trip.Meanwhile,3 out of 22 cases with relatively high-energy trauma were identified in labrum tear group,all of which corresponded to a fall downstairs.It was noteworthy that the severity of traumatic injury in patients with labrum tear was significantly lower than those with normal labrum.MRI examination revealed that the labrum tear group displayed significant muscle injuries around the hips,including damages to the short external rotators,obturator externus,pectineus and adductor brevis.When the damage occurs in the internal rotation and bending position,acetabular impingement can be presented.Short external rotation muscle and joint capsule restrict the internal rotation of the hip and prevent further dislocation of the femoral head,obturator externus and adductors magnus also prevent internal rotation of the affected limb,while gluteus medius limits the greater trochanter.Both muscles and joint capsule areequivalent to one end of a lever,and the anterolateral margin of the acetabulum is similar to the fulcrum of the lever,where the femoral neck is located;while the affected limb is equivalent to the other end of the lever.When an external force acts on the affected limb,the more distal the external force is on the lever,the greater of the stress.Patients with normal labrum exhibited no traction in the muscles around the hip or impingement on the hip,and thus,there is no apparent damage on the soft tissues surrounding the hip.The injury pattern of patients without a labrum tear was primarily posterolateral,while the injury pattern of patients with a labrum tear was primarily anterolateral or lateral,suggesting that patients with a labrum tear may have suffered anterior impingement of the hip.In line with our hypothesis,the severity of trauma in labrum tear group was lower than that in untorn labrum group.The most likely explanation is that the injuries in labrum tear group may be due to lever force,whereas those in untorn labrum group may be caused by direct stress.Theoretically,lever is more effective in view of its lower stress(force).2.Femoral neck fracture and hip joint anatomyThere were no significant differences in gender,BMI,femoral head-neck ratio,Cam deformity alpha angle,femoral head diameter,AI,HAL and NSA between labrum tear and normal labrum groups.On the contrary,age,femoral head-neck offset and CI were significantly associated with labrum tear.Notably,the smaller the femoral head-neck offset,the higher the incidence of labrum tear.Besides,there were no significant differences for the five levels of acetabular anteversion between the two groups.However,the mean acetabular anteversion values at the five angles were smaller in labrum tear group compared to untorn labrum group,and the greater differences were observed at 1/14 and 3/14 angles.To eliminate the impact of bone mineral density,we compared the CI values in the two groups,as the value of dual-energy x-ray absorptiometry(DEXA)scan was not assessed in our study group.Notably,In terms of CI value,there was a statistically significant difference between the two groups.The CI value of labrum tear group was higher,indicating that the patients with a labrum tear exhibit better bone quality.Moreover,less stress was imposed for the fracture in labrum tear group,suggesting the possibility of anterior femoroacetabular impingement.Conclusions: It is believed that there might be at least two injury mechanisms underlying femoral neck fracture.One is the common typical sideways fall,in which femoral neckfracture of is attributed by direct trauma to the greater trochanter;the other is femoroacetabular impingement.These two types of injury mechanisms are totally different with respect to the physiological anteversion of femoral neck.In particular,the former occurred in the posterolateral position where there was no femoroacetabular impingement,while the latter involves a fall pattern of lateral or anterolateral,as the affected limb should be in the position of flexion and internal rotation.Further reviewing the surveillance videos supported our hypothesis.For this type of injury,we observed that corresponding injury to the muscles around the hip,and femoroacetabular impingement could result in an acetabular labrum tear and bone contusion on the anterolateral margin of the acetabulum.These findings were verified by MRI examination and intraoperative findings.Besides,it is believed that the abnormal anatomy of the hip,such as femoral head-neck offset may promote femoroacetabular impingement.Previous studies have reported that the use of hip protectors or specific training can reduce the incidence of hip fracture.Thus,novel solutions for preventing femoral neck fracture should be discovered by elucidating the injury mechanisms,which also confers protection against injuries. |
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