Elsevier

Journal of Orthopaedics

Volume 14, Issue 4, December 2017, Pages 582-588
Journal of Orthopaedics

Original Article
Biomechanical model based evaluation of Total Hip Arthroplasty therapy outcome

https://doi.org/10.1016/j.jor.2017.09.002Get rights and content

Abstract

Objective

Total-hip-arthroplasties are performed to treat patients with osteoarthritis. Surgical planning is usually based on specific radiographs. These information could also be used as data for biomechanical modelling.

Methods

Models are rarely used during clinical practice. Our aim was to analyze model-based the pre- and postoperatively hip-biomechanic. Pre- and postoperative X-rays of 30 patients were examined by using 4 biomechanical-models.

Results

The received results showed variations e.g. an increase and decrease of hip-load pre- and postoperative.

Conclusion

With the data of these models it would be possible to integrate the amplitude and orientation of the hip-joint-resultant-force into the therapeutical approach.

Introduction

Total Hip Arthroplasty (THA) is an established and effective treatment for osteoarthritis (OA). In Germany there are more than 215,000 THA interventions per year (in 2014) carried out, and more than 36,000 secondary revision interventions per year were performed [1]. Furthermore, THA has been performed on a large number of patients worldwide. It is among the most frequently executed orthopaedic operations, and is an increasingly common and successful operation of the last decades [2], [3], [4]. Today the average lifetime of a hip prosthesis is approximately 15 years [5], [6].

In THA an accurate alignment and exact positioning of the hip prosthesis is a major factor affecting the longevity of a hip implant [7], [8]. The hip joint is one of the most important weight-bearing joints in the human body, and it has an important biomechanical function: it enables a physiological bi-pedal gait and mobility, respectively, for a lifetime. During daily routine activities, forces up to 8 times bodyweight (BW) (during stumbling) are transferred between the femoral head and the acetabulum [9]. Abnormal repetitive loading of the hip joint results in the breakdown of articular cartilage, thereby, destroying the normal function of the joint [10].

Postoperative complications after THA are dependent on multiple factors. Dislocation [6], [11] and abrasion behavior of the prosthesis components [6], [12] are one of the most common postoperative complications.

Musculoskeletal loading plays an important role in the primary stability of THA. Thus; simulation of the pre- and post-operative magnitude of the resultant hip joint force R is of interest to analyze hip biomechanics after THA. Biomechanical models can be used to get an impression about the patient specific intervention outcome. Simple 2D-models (e.g. Pauwels [13], [14], [15], Debrunner [16], Blumentritt [17], [18]) and more complex 3D-models (e.g. Iglič et al., [19]), are available for estimation of the magnitude and the orientation of R depending on their geometrical and anthropometrical parameters.

For a successful THA it is essential to consider biomechanical factors in the anatomical features of the hip. During THA surgery, a couple of (biomechanical relevant) geometrical parameters influence the specific (biomechanical) operation outcome e.g. position of the hip rotational centrum (HRC), angle (inclination and anteversion) of the acetabular cup, caput-collum-diaphyseal angle of the hip stem (CCD-angle and neck angle, respectively), femoral offset and lever arms. Consequently, the positioning of the HRC influences the local loading situation at the implant–implant interface (head and cup) and the bone interface. For example, a slightly superior, posterior and medial HRC after total hip replacement can be associated with markedly higher joint forces [20].

Furthermore, the orientation and position of the acetabular cup is an important factor for satisfactory long-term results after THA [21]. Correct implantation of the THA is crucial with respect to long-term results and survival rate [22]. This is the reason why consideration of biomechanical aspects during THA is recommendable, and allows a high accuracy especially in cases with anatomical variations such as hip dysplasia and coxa valga/vara.

Radiographs and clinical examination are the most important tools for the indication and follow up evaluation of THA [23]. It is possible to use the radiographs also to acquire anatomical/geometrical parameters for the biomechanical modelling. A preoperative planning and a postoperative examination of the therapy outcome e.g. of implant position under biomechanical aspects based on radiographs can be of enormous helpful for the surgeon [7].

We wanted to show how helpful the use of a biomechanical model could be. In our case, we used the mathematical models for a retospective analysation of THA therapy outcome. The objective of this study was in general the investigation of the resulting hip joint force R and their orientation calculated by the mathematical models of Pauwels, Blumentritt, Debrunner and Iglič. Then the differences between pre- and postoperative joint load can be quantified, and the therapy outcome can be shown. In detail, we wanted to show, that a biomechanical model can be easily implemented in a clinical workflow for therapy planning and outcome analysation. The objective was the investigation and comparison of the postoperative restauration in regard to the preoperative situation. We wanted to proof, if the postoperative outcome (amplitude and orientation of R) is similar or better (ideal: amplitude of R decreased and orientation approximately perpendicular on the cup of R) to the preoperative situation.

Furthermore, we evaluated the models of Pauwels, Blumentritt, Debrunner and Iglič in the way that we compare the results to measurments of the Orthoload-database (www.orthoload.com) for the one leg stance. Mathematical assessments derived from the model computations will be directly compared to a generated reference basis of in-vivo measurements obtained from instrumented hip implants. Thus, it is possible to get an impression of the validity of the mathematical models.

Section snippets

State of the art

Musculoskeletal models of the lower limb are widely used to predict the resultant joint force R in the hip joint as an alternative to instrumented implants [24], [25]. Simple analytical mathmatical models are applied to predict hip joint biomechanics, and therefore, use the equations of statics to solve for resultant joint reaction forces. The models are based on the angles and length measurements in planar one leg standing anterior-posterior (a.p.) X-ray images of the hip and pelvis,

Material and methods

Pre- and postoperative X-rays of 30 patients (14 male patients (MP)

  • with an average body weight of 90.14 kg (SD ± 19.66 kg) and with an average body weight force of 884N (±193N), respectively, and with an average height of 1.72 m (SD ± 0.07m); furthermore, 16 female patients (WP)

  • with an average body weight of 77.25 kg (SD ± 11.26 kg) and with an average body weight force of 758N (SD ± 110N), respectively, and an average height of 1.67 m (SD ± 0.09m)), which had to undergo a primary THA, were included and

Results

The resulting hip forces were related to the respective BW (Table 1). This was done both for the pre- and postoperative load, allowing hence an easier comparison between the different results.

The evaluation of the CCD angle showed only in 3 patients that no change of the CCD angle has been observed postoperatively. The CCD angle was rather increased than decreased. The CCD angle affects the leg length and the introduction of force in the femur with respect to the exposure of the femoral neck.

Discussion

Knowledge of biomechanical conditions of the individual hip is important for several reasons: understanding the function of the normal and diseased hip joint, assessing the condition of the hip, preoperative planning, evaluating the effects of the treatment, optimizing implant design and performance, and improving the treatment outcome.

The quality of the outcome after THA treatment depends on various factors. We performed a retrospective comparison of the achieved intervention outcomes

Conclusion

In our mind there is a strong need for a biomechanical model of the hip joint, which includes a valid computation algorithm to calculate the hip-contact forces in the context of surgery planning. It will help for a better understanding of the function of normal and diseased joints and the optimal position and orientation of the prothesis components. At present the therapy outcome differ from the possible optimum. There are too many (mechanical) parameters, which cannot be completely and

Declaration of conflicting interest

The Authors declare no conflict of interest.

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