Our data showed that among 259 elderly patients, the incidence of PJK was 35.9%. Higher age at surgery, larger BMI, significant paraspinal muscle degeneration and poor bone mineral density made DSD patients susceptible to PJK. To our knowledge, this is the first study of PJK risk factors in a large number of elderly patients with DSD.
Anatomical, surgical, radiological and patient-related factors are all involved in the incidence of PJK. Age has been proven to be associated with the incidence of PJK[13, 14]. Age at surgery over 55 is shown to be an independent risk factor for PJK, which is considered to be related to age dependent disc, facet joint and paraspinal muscle degeneration[15]. These degenerative changes are commonly seen in elderly DSD patients over 65 years of age. While greater age was still shown to be an independent risk factor for PJK. In our point of view, greater age brings worse preoperative reserve capacity and postoperative compensatory capacity. Therefore, for DSD elderly patients over 65 years of age, perioperative management is one of the key steps to decrease the risk of PJK. Preoperative evaluation and nutritional support by geriatricians can reduces the incidence of postoperative complications, shortens the duration of in-hospital stay, and contributes to improved perioperative functional status in elderly population[16]. Comprehensive perioperative management such as Enhanced Recovery After Surgery(ERAS) can reduce traumatic impact and accelerate postoperative recovery of patients[17]. Early rehabilitation and functional exercise can accelerate the recovery of paraspinal muscles and reduce the adverse effects of advanced age.
Osseous and soft-tissue failure are the two main pathological changes of PJK[3, 18]. The bone quality and quantity of UIV is closely related to the occurrence of PJK[19, 20]. Fixation failure of UIV and compression fractures of UIV and UIV + 1 are common manifestations of PJK. These osseous failures often lead to clinical symptoms and require surgical intervention. Enhancement techniques such as vertebroplasty at UIV and UIV + 1 have been shown to be a protective factor[21]. Osteopenia and osteoporosis are commonly seen conditions in the elderly, especially for female population. Looker et al. reported a 11% of osteoporosis rate in elderly Americans[22]. Johnston et al. estimated osteoporosis affected one-fifth of women aged 70[23]. The higher osteoporosis rate in the elderly population increases the risk of PJK in DSD patients. Therefore, we recognize the importance of regular anti-osteoporosis treatment in elderly DSD patients. The use of bisphosphonates or biosynthetic parathyroid hormone combined with calcium and vitamin D can effectively maintain the bone quality of elderly patients[24]. Regular anti-osteoporosis treatment could be a momentous factor in preventing mechanical complications including PJK.
Paraspinal muscles have been shown to be an important stabilizer of the spine [25, 26]. Our data regarding patients over 65 years of age indicated both ES and MF degeneration to be risk factors for PJK. These results are consistent with previous studies[15]. As the main components of the posterior spine extensor, ES and MF provide stability to maintain the overall and local sagittal balance of the spine[27, 28]. Paraspinal muscle degeneration caused by aging is commonly seen in elderly population[29]. The weakening of the protective effect of paraspinal muscles increases the risk of PJK. For elderly patients, appropriate surgical techniques can be adopted on the basis of appropriate radiological evaluation to protect the vertebra, ligaments and paraspinal muscles, along with continuous anti-osteoporosis treatment and muscle rehabilitation to reduce the risk of PJK[30]. Appropriate preventive measures are important in reducing the risk of PJK, especially for elderly patients.
Several limitations of our study should be considered. Firstly, this was a retrospective, single-institution study and the result may reflect biases. Secondly, since not all of DSD patients had underwent thoracic MRI, we chose L1/L2 segment as the measurement level of paraspinal muscles. Although the paraspinal muscle degeneration shows consistency between different levels, the L1/L2 level parameters cannot fully represent the state of the paraspinal muscles of the UIV level[31]. Moreover, our data were based on radiological findings, which did not reflect clinical outcomes directly.