Is simultaneous bilateral total hip arthroplasty deleterious in a biomechanical point of view? A comparative gait analysis study

Hip osteoarthritis (HO) is a chronic disease generating pain [1], disability, stiffness, and alteration in gait function [2]. It is established that osteoarthritis is the third most rapidly rising condition associated with disability [3]. According to Global health Metrics, HO affects 40 million people worldwide [4].

Diagnostic of a symptomatic HO may lead to total hip arthroplasty (THA) to improve gait function and quality of life. It has been proven that replacement of the coxo-femoral articulation alleviated pain and stiffness [5]. The goal of THA is to restore the normal pain free function of the hip. Studies are generally based on functional outcomes, range of motion (ROM) and radiological evaluation. It is well known that restoration of leg length, centre of rotation, acetabular and femoral offset increase implants survival and satisfaction [6].

THA is known as the surgery of the century for symptomatic HO [7]. Sequential THA for bilateral HO with generally a 3–6-month interval period is the most used procedure [8]. Since 1996, simultaneous bilateral total hip arthroplasty (SBTHA) is known to be a safe procedure with good outcomes and gave a real improvement in walking abilities in patient with bilateral and symptomatic HO [9].

Walking is a movement based on a cyclic activity: the walking cycle is characterized from a physical point of view by spatio-temporal, kinematic, kinetic, mechanical, and energetic elements [10, 11].

Thus far, most studies compared the effect of unilateral THA (UTHA) on biomechanics against healthy individuals. It has been described by Bahl & al., that patients with OA have a decrease of walking speed, step length, single-limb support time, sagittal and coronal plane hip range of motion (ROM) compared to health population [12]. The aim of this study is to evaluate changes in the walking in UTHA and SBTHA.

To date, with the development of minimal invasive surgery (MIS), it has been well established that SBTHA is safer than two-stage in patients with symptomatic bilateral HO [13, 14]. This procedure reduces the length of hospital stay and is cost effective [15]. Evidence base medicine requires meticulous assessment of treatment; in this sense the World Health Organization (WHO) has created an International Consortium for Health Outcomes Measurement (ICHOM). Patients are nowadays evaluated in their globality through validated questionnaires. Patient-reported outcome measure (PROMS) are valid and reproducible in hip registries such as the Short Form-36 Health Survey (SF-36) that is the most widely used health-related quality of life (QOL) measure in research to date [16]. Oxford Hip score (OHS) is another valid tool for self-assessment of pain and function [17]. Those easy-to-use scores are well spread in the literature and give indirect, though subjective, information about effectiveness of treatment. There are only few prospective comparative studies in the field of biomechanics and dynamic up to now. The lack of data in the literature limits the full integration of ICHOM because we need more objective, independent and dynamic measures to fully attest efficiency. With the technology available in our motion laboratory, it was mandatory to gain more information about SBTHA, to compare the procedure and its effects with the actual gold standard (UTHA). Motion lab system give mechanical, kinematic, kinetic, mechanic, and energetic values that will help us collecting experience data.

Our hypothesis is that SBTHA is offering a better balance motion recovery (because avoidance of protective contralateral reflexes) nevertheless with a higher energetic gait pattern request because of two site surgeries comparing to unilateral procedures.

In total, 30 patients, 46 arthroplastic hips and 60 hips were included. 26 participants passed all tests, 4 patients did not pass the post operatively 3DGLA, one because of time schedule issues, and 3 because of the Covid-19 pandemic regulations. Mean was calculated to assess missing data of patients who did not pass post op 3DGLA because of pandemic regulations. Radiologically, all patients were classified Kellgren and Lawrence grade 3 or 4 on operated sides [24]. Patients were discharge from hospital when they can walk and climb stairs without exterior help. Any physiotherapy was given to patients outside hospital, so they were all able to perform a self-rehabilitation.

Data in the UTHA group are presented in Table 2, data in the SBTHA in Table 3 and changes comparing both groups (UTHA vs SBTHA) in Table 4.

In the unilateral group, pelvis sagittal balance (p = 0.03) is significatively improved, while a significative decrease of Wtot and Wext (p = 0.01) is observed with a better recovery (p < 0.001). Functional outcomes scores are significatively improved (p < 0.001). Note also that the only patient with previous THA on one side, was beyond the UTHA mean pre and post operatively and therefore does not influence the results.

In the bilateral group (SBTHA), speed (p = 0.03) and step length (p = 0.04) are improved. ROM of Knee sagittal stance (p = 0.009), and ROM hip frontal (p = 0.03) increase. The Wint is significatively higher (p < 0.001). Functional outcome scores are significatively better (p < 0.001).

The changes expressed as “post minus pre values” are significantly improved in favour of bilateral group for speed and SF36 PC. The change seems in disfavour of bilateral group for Wint but attributed to an increase of speed in this group.

The study is to our knowledge the first one comparing UTHA and SBTHA based on biomechanical and energetics fields. Data were collected preoperative and at 6 months postoperative by a same high volume hip surgeon, with a single DAA without traction table. This study gains in interest as DAA became more frequently used nowadays, furthermore up to now we did not have any biomechanical information in a DAA SBTHA cohort at 6 months post operatively. Our results attest that surgery has a positive impact in both PROM’s score, biomechanical and energetic fields in both groups. Our hypothesis that SBTHA would generate higher energetic cost is rejected. SBTHA is therefore not deleterious to the patient from a biomechanical and energetical point of view.

Concerning the UTHA group, patients walked pre- and post-operatively at a relatively similar speed, as demonstrated in Colgan et al. [25], however the Wtot and Wext decreased as recovery improved significatively. This may be explained by a reduction in pelvic sagittal ROM. We conclude in this population, that surgery improves the pain free ROM of the hip, therefore patients do not need any extra production of Wext to produce avoidance limping as detailed by van Drongelen et al. [26]. In fact, as the hip becomes pain free, a better flexion of the hip and the knee is balanced through a better pelvic sagittal ROM. Energetic equilibrium between potential and kinematic energy is improved. Restoration of the oscillation of the COM will decrease the Wext needed to produce limping because of pain, stiffness, or both. The whole will allow a better gait pattern and spare mechanical energetics outcome at a same speed. Patients at last, can walk at a same self-selected comfortable speed with a normalized mechanical gait pattern post operatively. This correlates the work of Queen et al. attesting that avoidance of compensatory mechanisms increases hip power on the surgical sides and decreased in the non-surgical side, the whole automatically goes with a decreased in Wext [27].

About kinematics and kinetics parameters, our results are partially in agreement with Rathod et al. which observed at 6 months postoperatively, improvement in flexion/extension ROM, peak of flexion and extension moments. Our values are also improving but not significantly explained by the size of our sample [28].

Concerning the SBTHA group, patient spontaneously walks at a higher speed with a longer step length, mobility of both hips and knees improves gradually. These results are in agreement with Temporiti et al. [29]. Energetics exchange in Wext and Wint is foreseen at an equivalent Wtot. Alleviating pain and stiffness of both hips is having a huge impact on the knee sagittal stance. It is here one of the key elements to be encountered.

After SBTHA, for a same transverse ROM pelvis, step length and speed are increased. In the meantime, the knee stance phase is considerably increased, which attests that patient flex legs much more than preoperatively, just as the hip ROM increases too. Therefore, flexing hips and knees will decrease the necessity of energy output to upper the COM to help passing energy from one leg to the other.

At last, we may say, that patients walk faster, with better mobility closer to normal values, and better energetics distribution. The whole goes in parallel with good PROM’s which attests patients’ satisfactory.

In our population, ROM pelvis sagittal remains equal in our second group. Those measures differ from the work of Milan university attesting a pelvic kinematic profile closer to normative data was found in bilateral patients [30]. This might be explained by two distinct parameters: first, patients are evaluated at six months in our study versus seven days, which might allow patients to adapt to the hip replacement, and second, surgery approaches were different between both studies (DAA vs postero-lateral).