Hip-spine syndrome was first described by Offierski and Macnab in 1983 [1]. It is classified into four types: simple, complex, mixed, and misdiagnosed. The simple type involves degenerative changes in either the hip joint or the spine, with that degeneration being the primary cause of the condition. The complex type involves degenerative changes in both the hip joint and the spine, with both contributing to the pathology. The mixed type refers to the interaction between hip and spinal pathologies, so that the conditions of the hip joint and the spine mutually affect each other. The misdiagnosed type occurs when incorrect treatment is provided due to a lack of awareness of the involvement of both hip and spine pathologies. An anatomical study also has detailed the mutual influence of degenerative changes in the spine and the hip joint [2].
In recent years, researchers have suggested that lumbosacral fusion and long fusion of the lumbar spine can lead to progressive hip osteoarthritis (hip OA) [3, 4]. Additionally, sacroiliac joint (SIJ) fixation has been linked to a two-fold increase in the risk of dislocation after total hip arthroplasty [5], suggesting a mechanical influence on the SIJ between the lumbar spine and the hip joint. Credible reports indicate that 14–30% of low back pain originates from the SIJ [7–9], and extensive study of the nerve supply to the SIJ suggests that not only the SIJ capsule but also the surrounding tissues such as ligaments can manifest pain [10–18]. However, the origin of SIJ pain remains unclear [6, 16, 17]. While excessive motion is restricted by ligaments, the SIJ joint has some limited mobility [6], and increased instability or stress on the posterior ligaments of the SIJ may cause pain and dysfunction. In fact, symptomatic relief has been reported from immobilization by external fixation of the pelvis or injections into the posterior ligaments [19, 20].
There have been reports of increased stress on the SIJ due to lumbosacral fusion [21, 22], as well as reports of increased degeneration of the SIJ [23], strongly indicating an interrelationship between the lumbar spine and the SIJ, and a link between hip OA and SIJ dysfunction has been suggested [24, 25]. Asada et al. analyzed preoperative CT scans of patients with hip OA who underwent total hip arthroplasty (THA) and noted a significantly higher incidence of narrowed joint space, osteophyte formation, and vacuum phenomena in the SIJ compared with a control group [25]. Elucidating the relationship between the hip, spine, and SIJ disorders is thus of considerable clinical importance.
In this study, we formulated two hypotheses: first, that long-term degeneration of the hip joint has a major impact on the SIJ, making it more susceptible to Hip-SIJ syndrome, and second, that patients with the condition termed “Hip-Spine syndrome” show a higher prevalence of SIJ degeneration, suggesting the existence of what we have designated as “Hip-SIJ-Spine syndrome”. We then conducted a comparative study of patients undergoing THA for hip OA and for idiopathic osteonecrosis of the femoral head (ON).
THA for OA is often performed after a long duration of illness, while ON frequently requires THA within a short timeframe. This is the reason for selecting these two conditions for comparison. Furthermore, in our facility, a significant proportion of OA cases are associated with developmental dysplasia of the hip (DDH), and ON often occurs in the unaffected hip joint, making it easier to compare and study in the context of this research.