APPLICATION OF CALCULATING THE MAXIMUM PERMISSIBLE LOAD ON THE FEMUR AFTER OSTEOSYNTHESIS

Yamshchikov O.N., Emelyanov S.A., Emelyanova N.V.

Derzhavin Tambov State University, Institute of Medicine, Tambov, Russia 

The surgical technique is the main method for treatment of such severe injuries as transtrochanteric fracture of the femoral bone [1, 2]. The studies by T.N. Vorontsova (2016) show the importance of surgical treatment and need for standardization of management techniques for patients with proximal femoral fractures [3]. Moreover, the postsurgical management lasts for several months than negatively influences on function of joints and the whole extremity. So, Ryabchikov et al. (2013) note that techniques for recovery of locomotor system functioning, which are used by orthopedic surgeons and rehabilitation physicians, often do not comply with requirements of modern medicine [4]. According to the opinion by V.F. Miroshnichenko (1975) and A.N. Shimbaretsky (1985), the appropriate restorative treatment after osteosynthesis of the hip and the leg is realized at the background of already developed joint contractures in almost all patients [5, 6].
Currently, the osteosynthesis, which allows the dosed load to the extremity before achievement of complete union, is used more often [7, 8]. However, there are some opinions that some older patients can not limit the load to the operated extremity when walking, but they can limit the load to the injured extremity [8, 9]. Most publications relating to treatment of fractures of femoral bones describe only common techniques for postsurgical recovery: remedial gymnastics, kinesitherapy, mechanotherapy, physiotherapy etc. The descriptions of the offered rehabilitation programs with clear substantiation of techniques and criteria of efficiency encounter more seldom. So, O.V. Nikitina (2010) indicates that correct movement mode and weigh load during subsequent movement present the basis for rehabilitation procedures. However, she notes that movements are realized with orientation to patient’s personal feelings in the early postsurgical period [10].
N.V. Belinov (2017) developed and systematized the six-staged rehabilitation program for traumatic injuries to the proximal femoral bone [11]. The postsurgical movement mode and the parameters of load to the extremity vary in dependence on a fixation technique, presence of osteoporosis, and rates of fracture union. It indicates the appropriateness of the individual approach to extremity load with consideration of these parameters [12].
The recent publications describe some techniques for computer modeling of load to the extremity after osteosynthesis [13-15]. It is impossible to imagine the correction of the movement mode correction and intensity of training of movements in extremity joints without consideration of a degree of fracture union. So, A.B. Slobodskoy (2003) and A.Yu. Popov (2006) used a technique for calculation of optical density difference (ODD) of bone tissue in the fracture site [16, 17]. Also the use of computer techniques for estimation of the bone regenerate and the osteoreparation processes has been described [18, 19]. However, the objective criteria for calculation of safe load to the extremity in various periods of fracture union have not been offered.
In the recent literature, we did not find any publications relating to mathematical calculation of load to the extremity with consideration of numerical values of fracture union. Therefore, there is the unsolved problem of individual approach to the movement mode and load to extremities after osteosynthesis on the basis of objective numerical data.
Objective – to conduct the analysis of time course of recovery of range of motions in the hip joint after fixation of hip fracture with use of numerical calculation of load to the femoral bone. 

MATERIALS AND METHODS

The patients were distributed into two groups to study the influence of the offered technique for calculating the load to the femoral bone on the time course of recovery of range of motions in joints after osteosynthesis. The comparison group included 20 patients with transtrochanteric fractures 31A1 according to AO/ASIF [20]. The degree of postsurgical load to the femoral load was estimated according to the standard criteria and subjective assessment by the traumatologist. The main group included 20 patients with transtrochanteric fractures. The load to the extremity was determined after estimation of the maximal load. The patients of the main group received the presurgical computer modeling of osteosynthesis with estimation of appropriate load to the extremity. The comparison group included 45 % of men, the main group – 40 %. The mean age of the patients was 66.8 in the comparison group, and 68.5 in the main group. In the comparison group, 5 % of patients were younger than 40, and 5 % were older than 80. In the main group, 5 % of patients were older than 80.
We used the following algorithm for calculation of maximum allowable load (MAL) to the femoral bone in the required period of restorative treatment after osteosynthesis. First of all, we calculated the difference in loads (DL) between initial maximal allowable load (IMAL) in the period before initiation of fracture union. The load was calculated during computer modeling of osteosynthesis and in full load (FL) to the extremity, which was equal to the patient’s body mass: DL = FL – IMAL. The presurgical computer modeling of osteosynthesis includes the calculation of the values of tension and displacement in the interfragmental space after fracture fixation with a metal construct. The maximal allowable load was the load, which did not cause the displacement exceeding the displacement for the model of the femoral bone without displacement; the values of equivalent tension in the fracture site did not exceed the corresponding values of the same region of the bone without a fracture. The calculated value of the maximal allowable postsurgical load to the bone varies depending on multiple fractures (gender, age, body composition, concurrent diseases etc.) determining the structural and anatomical features of the bone, and a type of a fracture. Therefore, the value of the postsurgical maximal allowable load to the extremity was calculated individually for each patient.
Then, these X-ray images were used for calculation of fracture union coefficient α in the definite time interval: α = 2 – ODD. ODD was measured with the technique by A.B. Slobodskoy (2003) and A.Yu. Popov (2006). The essence of the technique consists in the fact that optical density of the fracture site in presence of diastasis is similar with optical density of soft tissues. While the fracture unites, the optical density of the fracture site approaches the optical density of cortical layer that can be determined with PC graphics editor for estimation of X-ray images. ODD is the ratio of optical density of the cortical layer to optical density of the fracture site. It reaches 1 in complete union.
After estimation of α ratio, the final maximal allowable load to the extremity was calculated with the formula: MAL = IMAL + (DL × α). For α ≤ 0.1, it was considered that fracture union was absent, and the load corresponded to initial maximal allowable load, which was calculated with results of computer modeling. For α ≥ 0.8, fracture union was considered as complete, and the full load to the extremity was allowed.
The recovery of the extremity function after femur fractures was estimated with deficiency of movement range in the hip joint over time. The deficiency of movement volume in the hip joint after femur fracture was conducted with the mean value of volume in active flexion, extension and abduction in the joint with percentage of values of the healthy extremity. The mean summary estimation of deficiency of movement volume was carried out on the days 15, 30, 60, 90, 150 and 180 after surgery. All patients received the fixation with dynamic hip screw (DHS).
All patients gave their informed consent at the moment of admission in compliance with requirements of the Federal law No. 152-FZ, June 27, 2006, (edited on February 22, 2017) “About personal data”. It corresponds to Helsinki Declare, 1964, revised in 2013, to the Rules for Clinical Practice in the Russian Federation, confirmed by the Order of Russian Health Ministry on June 19, 2003, No. 266. The data were anonymised.
The statistical analysis was conducted with SPSS Statistics 21. The mean arithmetic, error in the mean, and t-test of reliability of difference of two values were measured. The critical level of significance (p) was 0.05 for testing the statistical hypotheses.

RESULTS

The estimation of movement volume in the operated extremity identified a deficiency in movement volume in more than 40 % of patients of both groups two weeks after surgery. The main cause of limitation of active movements was pain syndrome. The movement volume in the hip joint was not more than 30 % of normal values in 10 % of patients in the main group and in 15 % of patients in the comparison group due to evident pain syndrome within the first 15 days after surgery. All patients became active from the second day after surgery, when sitting in the bed was allowed, as well as walking with crutches from the third day. One should note that patients could stand up and move with crutches only in presence of a doctor in a half cases in both study groups, avoiding the excessive load to the extremity. In absence of a doctor, the patients preferred not to stand from the bed, even after detailed consultations. All patients received the training of movements in the lower extremities from the first days after surgery. From 30th day after surgery, the deficiency in volume of movements in the joint was noted (the table).

Table. Time course of restoration of range of motions in hip joint

Groups	Total number of patients (n)	Deficit in range of motions in joints in % of normal
		15th day	30th day	60th day	90th day	120th day	150th day	180th day
Main group	20	44.45 ± 3.17	33.25 ± 2.61	21.05 ± 1.42	10.75 ± 1.19	8.1 ± 0.71	3.5 ± 0.77	2.1 ± 0.71
Comparison group	20	47.8 ± 3.52	36.25 ± 2.47	30.4 ± 2.42	24.4 ± 1.67	15.5 ± 1.24	10.4 ± 1.05	8.3 ± 0.85

Note: * – reliability of differences for comparison group, p < 0.05.

The differences in deficiency of movement volume were less than 4 % (t = 0.83, p = 0.41) in both groups before 30 days after surgery. However after 30 days, the main group showed a higher increase in movement volume as compared to the comparison group. On 60th day after surgery, the deficiency in movement volume of the operated extremity was 9.4 % lower in the main group than in the comparison group (t = 3.33, p = 0.002). On 90th day after surgery, the deficiency in movement volume of the operated extremity was 13.65 % lower than in the comparison group (t = 6.66, p < 0.05). It shows more intensive activation and training of movements in patients of the main group. 180 days after surgery, the deficiency in movement volume in the hip joint was higher by 6.2 % in the comparison group (t = 5.6, p < 0.05). In the late postsurgical period, the differences in hip movement volume were determined by more intensive activation in patients of the main group over all months of the follow-up. In the main group, all patients were able to know more precise and safer values of weigh load to the extremity, i.e. they could allow higher functioning of the extremity.

DICUSSION

The attempts to objectify the data on stability of osteosynthesis and degree of fracture union were made by various authors. So, the technique of dynamic estimation of difference in optical density was firstly used in the traumatology unit of 16th Central Military Special Hospital of Ministry of Defense of the Russian Federation. A.Yu. Popov (2006) used the calculations of difference in optical density of bone tissue in fracture site in various time intervals of treatment, and offered a classification of fracture union degrees according to optical properties of bone tissue in fracture site. The use of this technique allowed more appropriate approach to estimation of fracture union, but no technique was offered for calculation of load to the extremity [17]. As for foreign literature, we did not find any examples of numerical calculation of the load on the basis of fracture union degrees and features of osteosynthesis. Therefore, we offer to use these findings for calculation of safe loads to the extremity in various periods of fracture union with use of computer modeling of safe displacements in tension in fixation site.
The use of the offered technique for patients after osteosynthesis of the transtrochanteric fracture of the femur influenced on a degree of recovery of movement volume in the hip joint after surgery. So, the deficiency in movement volume in the early period (1-3 months after surgery) can be explained by traumatic potential of surgery, pain syndrome and soft tissue edema, i.e. by causes which can be removed only over time. We think it explains the highest intensity of dynamics of recovery of movement volume in this period. In the later period, when the fracture union completes, the higher significance is given to forming scars. Therefore, this time interval is associated with precise calculation of possible loads to the extremity without risk of disorders in the fracture union, and with possibility for maximal movement activity.
One can suppose that the increase in volume of active movements in the joint after osteosynthesis mainly depends on mental status of the patient. When the patient knows that the recommended load to the extremity is calculated precisely, and the risk of a recurrent fracture is absent, and the decrease in the load can slow down the treatment, than the desire to be too cautious and not to load the extremity disappears. More active activation and load to the extremity give more movements and increase the patient’s activity. It is more evident in older patients who spare their injured extremities, when the volume of active and passive movements varies significantly, considering the fact that the longer period of immobilization gives more severe functional disorder.
According to our opinion, the calculation of postsurgical loads on the basis of numerical values is perspective for clinical using, but one should note some features of calculation which limit the use: need for standardized radiologic control of the fracture union process, presence of possibility for ODD measurement, realization of computer modeling of osteosynthesis, which requires for significant recourses, with several hours of calculation with high efficiency servers. Possibly, the improvements in computing technologies will solve the above-mentioned problems. 

CONCLUSION

The use of the technique for calculation of maximally allowable load to the femur after osteosynthesis, with use of data on fracture union degrees and values of computer modeling, allows the best conditions for patient’s activation and for acceleration of recovery of movement volume in the operated extremity. 

ACKNOWLEGEMENT

For the assistance in realization of computer modeling, the authors thank the employees of Chernyshevsky Saratov State University represented by Golyadkina A.A. 

Information on financing and conflicts of interests

The study was conducted without sponsorship. The authors declare the absence of any clear or potential conflicts of interests relating to publication of this article.

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