In this systematic review, we identified a number of hip joint parameters and physical activities that are closely linked to hip contact stress. Numerous studies have been given to understanding hip biomechanics, particularly in the context of hip contact stress. The management of contact stress is contingent on the extent to which loads are distributed across the hip articular surface.[22, 24] It is widely theorized that body weight, along with any additional loads, significantly contributes to hip joint contact stress.[44, 45] Engaging in activities that involve carrying heavy objects and/or assuming different joint positions can potentially introduce additional loads and alter the biomechanical aspects as well.[42, 46] Previous studies have sought to investigate the essential role played by body weight and physical activity in influencing hip joint contact stress.[28, 42]
In a standing position, the hips bear the weight of the head, trunk, and upper limbs, which accounts for approximately 62% of an individual's body weight. The body's center of gravity is approximately aligned with the vertical axis passing through the heads of the femurs, slightly above the midpoint of the axis connecting these two points. In this position, the maintenance of balance requires minimal or negligible muscular effort. Assuming the lower limbs are of equal length, each hip joint carries approximately 31% of the body's weight. This force acts vertically and symmetrically on both sides of the hip joint.[14, 32]
When standing on one leg, the hip on that side carries the weight of the head, trunk, upper leg, and lower leg on the other side. This weight is concentrated at the center of gravity and is exerted on the hip as an axial load. The axial load is typically calculated as 81% of the total body weight. The center of gravity of the whole body aligns vertically with the foot acting as a support on the ground. The center of gravity of the individual body parts is located further away from the loaded hip. The axial load causes eccentric forces in the hip, which can result in tilting of the hip towards adduction in relation to the femur.[39, 42] During walking, each hip supports a portion of the body weight, including the head, trunk, upper limbs, and legs that are swung during each period of single support. This repetitive force on the hip during the gait cycle can be likened to swinging a hammer or performing an oscillatory movement. This force oscillates near the coronal plane at the hip joint. Additionally, other complex biomechanical processes come into play during activities such as running, sitting, squatting, and walking up and down stairs, each with their own unique forces on the hip joint.[5, 25, 43]
Another aspect of the hip joint's biomechanical process cannot be ignored, as it is closely related to the anatomical characteristics of the joint itself. Various parameters of the hip joint have been extensively studied and found to play a significant role in determining its biomechanics, particularly in relation to hip joint contact stress. Parameters such as femoral anteversion (FAV), femoral neck length (FNL), femoral neck shaft angle (FNSA), femoral head radius (FHR), and joint gap have all been investigated in this regard. Additionally, certain radiological parameters, including the acetabular inclination, acetabular index, and center-edge angle (CEA), have also been found to influence the femoral head coverage provided by the acetabulum and demonstrate a correlation with the contact area.[13, 14, 30]
With regard to hip joint parameters and physical activity as contributing factors of hip joint contact stress in relation to hip OA, we performed this systematic review to analyze the results of previous studies.
Hip Joint Parameter on Hip Contact Stress
We identified 11 relevant articles that examined the relationship between hip joint parameters and joint contact stress. These studies assessed various hip joint parameters, including whole-body alignment (WBA), femoral anteversion (FAV), femoral head radius (FHR), femoral neck length (FNL), neck-shaft angle (NSA), and center-edge angle (CEA). The findings of these studies indicated that changes in these hip joint parameters can lead to alterations in hip joint contact stress.
Femoral Anteversion (FAV)
Femoral anteversion refers to the rotational alignment of the femoral neck and head relative to the femoral shaft.[47] Higher femoral anteversion angles have been associated with increased contact stress on the anterior portion of the hip joint.[34, 47] This increased stress might be due to alterations in the alignment and distribution of forces across the joint surfaces.[14, 34] However, it is important to note that the femoral anteversion is just one of many factors that can influence hip contact stress, and the relationship may vary among individuals.[21, 47]
Four studies investigated the impact of varying degrees of femoral anteversion (FAV) on hip contact stress. The results, as depicted in Fig. 2, show that the peak of hip contact stress differs depending on the angle of FAV. The variability in the findings might be attributed to differences in methodology and calculation approaches used in each study. In the study by Matej Daniel et al. (represented by the red line), they observed a consistent increase in peak contact stress with increasing FAV angle. However, in the other four studies (Meyer et al. - represented by the yellow line, Altai et al. - represented by the green line, and Heller et al. - represented by the purple line), different hip joint parameters were used to measure hip contact stress, resulting in an inconsistent correlation between FAV angle and peak hip contact stress when analyzed separately.
Weight Bearing Area (WBA)
The weight-bearing area refers to the portion of the hip joint surface that is subjected to the load or pressure during weight-bearing activities.[14, 17] The greater the weight-bearing area, the more the load is distributed across a larger surface, which can help reduce hip contact stress.[22, 24] Conversely, a smaller weight-bearing area concentrates the load on a smaller surface, increasing the hip contact stress. Therefore, a larger weight-bearing area is generally associated with lower hip contact stress, while a smaller weight-bearing area can lead to increased stress on the hip joint.[14, 17]
Five studies explored the impact of whole-body alignment (WBA) on hip joint contact stress, as illustrated in Fig. 3. Similar to the first graph, the second graph demonstrates that only one study (Matej Daniel et al. - represented by the red line) found a consistent correlation between WBA and hip contact stress. Thus, this study reported that hip joint contact stress consistently decreased with larger WBAs. However, the other four studies (Alex M. Meyer - represented by the green line, Assasi et al. - represented by the purple line, Andrew E. Anderson et al. - represented by the yellow line, and M.D Harris - represented by the blue line) displayed scattered values of hip contact stress, it likely due to the influence of other parameters in each calculation.
Center Edge Angle (CEA)
Center-edge angle (CE angle) is a measurement used to assess the coverage of the femoral head within the acetabulum. It quantifies the relationship between the center of the femoral head and the lateral edge of the acetabular socket.[14, 48] The center-edge angle has a notable effect on hip contact stress. A lower center-edge angle, indicating decreased coverage of the femoral head by the acetabulum, can lead to increased hip contact stress. This is because a lower angle is associated with reduced joint stability and a higher risk of hip dislocation. Conversely, a higher center-edge angle, indicating better coverage of the femoral head by the acetabulum, generally reduces hip contact stress. A more favorable angle provides improved joint congruency and stability, distributing forces more evenly across the joint.[18, 48, 49]
Three studies exploring the role of Center Edge Angle (CEA) to evaluate hip joint contact stress, but did not find any consistent effect between the degree of CEA and hip contact stress. Furthermore, there was no evident correlation between changes in the CEA and hip contact stress (Fig. 4). The discrepancy observed in these three studies may be attributed to the inclusion of other measurement variables, which could lead to inconsistent findings regarding the relationship between CEA variations and hip contact stress.
Femoral Neck Shaft Angle (FNSA)
The FNSA angle, also known as the angle of inclination, is the angle formed between the femoral neck and the femoral shaft. It plays a significant role in determining the biomechanics of the hip joint.[15, 50] A greater femoral neck shaft angle, often referred to as coxa valga, has been associated with increased contact stress on the superior portion of the hip joint due to changes in the distribution of forces across the joint surfaces. Conversely, a smaller femoral neck shaft angle, known as coxa vara, has been associated with increased contact stress on the inferior portion of the hip joint. This altered stress distribution can result in increased loading on specific areas of the joint.[15, 50]
Figure 5 shows the three studies on FNSA and its effect on hip contact stress. However, we cannot conclude a constant correlation between FNSA degree and hip contact stress. Lenaerts et al. (red line) showed that a high hip contact stress was obtained in the range of FNSA between 128° and 132°.
Femoral Neck Length (FNL)
The FNL has an important effect on hip contact stress. Generally, a longer femoral neck can increase hip contact stress, while a shorter femoral neck can decrease it.[14, 41] This relationship is primarily due to the biomechanics of the hip joint. A longer femoral neck changes the lever arm and alters the forces acting on the hip joint during activities such as walking or running. This can result in increased stress on the hip joint, potentially leading to conditions like hip impingement or osteoarthritis. On the other hand, a shorter femoral neck can reduce the lever arm and redistribute the forces, potentially decreasing hip contact stress.[23, 41]
Two studies analyzed the various degree of FNL affecting hip contact stress. Lenaerts, et al. (red line) showed an elevation of hip contact stress with the increase in FNL (Fig. 6).
Femoral Head Radius (FHR)
The FHR also plays a significant role in hip contact stress. A larger femoral head radius generally leads to lower hip contact stress, while a smaller femoral head radius can increase it.[14, 15] The femoral head radius affects the surface area over which forces are distributed in the hip joint. With a larger radius, the load is spread over a larger area, resulting in reduced stress on the joint, this can be beneficial in minimizing the risk of hip joint pathology and maintaining joint health. Conversely, a smaller femoral head radius concentrates the forces on a smaller area, leading to increased contact stress within the joint. Increased stress may contribute to conditions such as hip impingement, labral tears, or early-onset osteoarthritis.[13, 14]
Two studies calculated the effect of FHR and showed its negative effect on hip joint contact stress. However, we cannot conclude a constant correlation because these studies did not use FHR as a single parameter to measure hip contact stress (Fig. 7).
Physical Activity on Hip Contact Stress
In this systematic review, 21 articles were selected to examine the role of physical activity on hip joint contact stress. These studies focused on analyzing the forces exerted on the hip joint during various activities such as walking, running, and ascending and descending stairs. The results revealed variations in hip contact force, mean hip contact stress, and peak hip contact stress (Fig. 8). Some studies also investigated the forces at different phases of walking. Additionally, an analysis was conducted to determine the correlation between walking and running speed and hip CF. The findings indicated that higher speeds of walking or running result in increased hip CF, as depicted in Fig. 9.
Walking speed can have an effect on hip contact stress, but the relationship is complex and influenced by various factors. Generally, walking in a faster speed increasing the force and load on the hip joint, potentially leading to higher contact stresses. This is because a faster walking pace leads a higher impact force and greater muscle force on hip joint during step.[51, 52] However, it is important to note that the hip joint is a complex structure influenced by multiple factors, such as individual anatomy, joint health, and biomechanics. Other factors, like body weight, stride length, and gait mechanics, can also affect hip contact stress. Moreover, the body has adaptive mechanisms that can help mitigate the impact of higher walking speeds on hip joint loading.[36, 38]