Introduction:
The hip is the largest weight bearing joint which makes it prone to excessive loading. It is the second joint following the knee which is commonly affected by the osteoarthritis (OA). (Felson 1988). OA of the hip is a degenerative joint disease characterised by pain on weight bearing and negatively impacts the health-related- quality of life. (Ackerman 2017). It is common in the elderly population, especially after 60 years of age and is a result of a breakdown of the articular cartilage due to mechanical overload (Shane Anderson and Loeser 2010, Tibor and Ganz 2014). The loads on the hip are increases in patients with hip OA during walking causing an overload. (Liao et al. 2019).
Walking is both a common and biomechanically complex activity of daily living (Pirker and Katzenschlager 2016). Gait is a pattern of walking and gait analysis is the measurement of walking with the use of an instrument to produce viable data that can be interpreted (Baker 2006). The gait cycle is categorised into stance phase and swing phase. Alteration in any of the components of these phases can disrupt the normal biomechanics causing load disturbances. These alterations are analysed in the form of parameters of spatial and temporal variations, kinematics, kinetics, oxygen consumption and electromyographic activities (Baker 2006). This paper aims to compare the biomechanics of gait in hip OA patients and healthy individuals without any hip pathology based on the spatial, temporal, kinematic and kinetic differences. For this paper, all the studies included had patients with unilateral hip OA of moderate to severe stage, age group of above 45 years, and above and studies which showed statistically significant results.
Spatial and temporal Parameters:
Reininga et al (2012) compared spatiotemporal parameters of hip OA and healthy subjects and reported that the walking speed of subjects with hip OA was slower. Constantinou et al (2014) reported that hip OA patients walked with 26% slower self-selected gait speed compared to the healthy control which was attributed to shorter stride length. They also added that the affected leg showed shorter step length and stance duration compared to the unaffected leg. MP;Gore (2014) while reporting coxalgic gait and its patient-related variations also reported slower walking speed in hip OA patients and suggested that shorter step length and slower cadence were responsible for the decrease in speed. Additionally, they reported prolonged gait cycles in these patients. TATEUCHI (2019) denied that decreased cadence contributed to the reduction of speed and concluded slower speed was a result of decrease in the step and stride length was due to the reduced stance phase of the affected limb obliging the unaffected limb to make ground contact immediately for double support. Whereas, there were no significant differences in the step length and cadence amongst the two groups in the study by Reininga et al. (2012) Hence, slower gait speed was reported in all studies although their justification varied. A shorter stride length may also be an adaptation to reduce the overall forces acting on the body during walking. This is done by a reduction in the vertical acceleration which keeps fluctuating the forces while taking longer strides (Levine and Whittle 2015, pp.68).
Kinematics and Kinetics:
Kinematic is a movement or change in a movement whereas kinetic is the entity that has given rise to the movement. Kinetic can be a force, pressure, muscle activity, energy consumption or anything that causes or alters the movement. In this paper, the alterations in the gait pattern will be described as the kinematics and kinetics in planes of movement. Major differences were observed in the sagittal plane and the frontal plane.
Sagittal Plane:
These differences are best observed laterally. Lamontagne et al (2009) suggested that the sagittal plane deviations in the gait of patients with hip OA might be a protective mechanism. Greater contact stresses were seen in the anterior and superior parts of the joint when compared to the posterior part during the stance phase (Harris et al. 2011). This can be attributed to increased peak hip flexion which causes unequal distribution of forces in the joint and leads to further damage to the articular cartilage (Kumar et al. 2017). As a result of which patients with progressing hip OA walked with more peak hip flexion and less peak hip extension during the stance phase (Kumar et al. 2017). TATEUCHI (2019) showed similar findings stating the hip extension angle is decreased in all stages of hip OA, it is due to early pain avoidance in early stages and can eventually lead to hip flexion contracture in later stages. Meyer et al (2015). while studying the biomechanical gait characteristics of hip OA patients also confirmed an overall decrease in hip excursion, mainly extension and a flexed hip pattern in the terminal stance. The study also observed compensation in surrounding joints stating forward bending of the trunk, flexed knee pattern and increased ankle dorsiflexion were seen in the terminal stance. TATEUCHI (2019) also addressed the knee stating that while the knee is extended until the loading response, extension decreases during the mid-stance and terminal stance. Along with forward trunk bending anterior pelvic tilt was more relied on rather than hip extension in these patients which might be associated with a greater risk of degenerative spondylolisthesis in them (Ibara et al. 2020). This was a compensatory mechanism to provide enough coverage to the anterior femoral head which is reduced during late stance (Fujii et al. 2012). This justification was further supported by the fact that these patients show less disassociated pelvis and thigh movements which explains the chain-like pattern of flexion (Ibara et al. 2020).
Frontal Plane:
These alterations are best observed from the back or front during gait. Brunton (2015) studied the frontal plane pelvic motion in hip OA and concluded that there is a higher frontal plane asymmetry in patients with hip OA when compared to healthy individuals. The pelvic range of motion is significantly reduced in them. As a result of which they demonstrate greater thoracic movements as compensation during fast walking while their healthy counterparts demonstrated greater pelvic movements (Reininga et al. 2012). The thoracic movements in the frontal plane mainly includes lateral leaning of the trunk towards the affected side which starts as a compensatory mechanism for hip pain and stiffness and eventually leads to hip abductor weakness in the later stages (Meyer et al. 2015). Abductor muscle weakness is commonly observed in patients with hip OA which gives rise to Duchenne’s limp and Trendelenburg gait (Reininga et al. 2012, Arokoski et al. 2017). The trunk lateral bending is seen towards the OA side in the stance phase when the affected leg is on single limb support. The trunk becomes upright and aligned with double limp support in cases of unilateral affection, failure of this alignment causes waddling gait which is seen in bilateral hip abductor weakness. This compensatory mechanism is to reduce the load on the abductor muscles to produce force. The lateral bend helps to keep the centre of gravity nearer to the hip joint of the stance (affected) limb hence, reducing the moment arm for hip abductor muscles (Levine and Whittle 2015, pp. 66-67).
Moreside et al. (2018) studied erector spinae activity and trunk motions in hip OA patients and concluded that with the progression of the stages of OA, trunk activity in the frontal and sagittal planes increases. The results established that the erector spinae are significantly active throughout the gait phase with more activity on the affected side, they discussed that this may influence the low back pain prevalence in these patients. Along with reduced hip abduction, decrease in peak hip adduction and external rotation also indicate patient’s effort of unloading (Nérot and Nicholls 2017). Another reason for internal rotation decrease is the gluteus medius weakness demonstrated at the mid stance (Meyer et al. 2015). Although symmetry is an important factor of normal gait pattern for its energy efficiency, asymmetry in the spatial and temporal parameters of gait is seen due to the asymmetric distribution of forces in the foot causing unequal weight bearing in the hip (Cichy and Wilk 2022). This asymmetrical loading leads to increased load on the unaffected limb and subsequent progression of the condition (Farkas et al. 2018).
In conclusion, walking is a common activity of daily living, tends to increase the cumulative load on the hip. Patients with unilateral hip pain show a variety of gait biomechanics differences in the comparison to healthy individuals without hip OA. Reduced walking speed along with shorter step and stride length is observed. The stance phase on the affected leg is significantly decreased. Asymmetry is seen in the foot contact pressure and weight bearing in both limbs. Decreased hip extension and increased flexed pattern of the hip to reduce pain on loading of the hip is a primary compensatory mechanism seen. Associated alterations in the surrounding body segments like forward bending of the trunk, anterior pelvic tilting, knee flexion and ankle dorsiflexion are commonly seen. Hip abductor weakness causes limping and lateral trunk bending in these patients. Weakness of other muscles around the hip and knee is also present. If not addressed promptly, the initial adjustment for the avoidance of pain may soon turn into persistent joint stiffness, muscle weakness and contractures.
Clinical Implications:
The use of certain components like the speed and asymmetry of gait are feasible and efficient outcomes to assess the progress of treatment in hip OA patients (Constantinou et al. 2014). Training in cadence-increasing strategy will be beneficial in relieving the hip of certain loads and help in increasing the functionality of the patients (Tateuchi et al. 2021). Pain reduction and weight bearing training should be synchronised to reduce the asymmetry between the limbs. Wearing a hip brace has shown a reduction in the compressive joint reaction force on the hip joint and also acts as a support to the muscles as it pulls the hip into the abduction and external rotation (Nérot and Nicholls 2017). Strengthening protocol for the muscles around the hip especially the hip abductors and extensors should be implemented. Maintenance of the mobility of the joint and prevention of the hip flexor contracture is necessary for gait biomechanics. As the loads are increased on the contralateral limb, rehabilitation of the unaffected leg should also be given attention. Patients with the pre-arthritic hip disease should undergo preventive treatment as gait alterations are prominent in them as well (Lewis et al. 2021).
Research Question:
The gait abnormality of forward bending is often considered as compensation for the inadequacy of knee extensors. During the stance phase as the leg starts to bear the weight the ground reaction force vector passes behind the knee joint axis producing a force external in nature in an attempt to bend the knee. The quadriceps being the knee extensor opposes this movement by producing an internal force of extension. When the quadriceps is weak subject tends to bend anteriorly to move the centre of gravity forward resulting in the passage of the ground reaction force vector in front of the knee joint giving rise to an external extension force (Levine and Whittle 2015, pp. 69). In patients with hip OA, both forward bending and flexed knee pattern is seen. The association of hip OA and quadriceps weakness is not well explored in the literature. A correlation study can be proposed to see the association between forward trunk movements and quadricep strength in these patients. The results may be resourceful for inculcating knee muscle strengthening in these patients and also correcting the trunk alterations which might be a cause of low back pain in them.
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