Lumbar spondylolysis is one of the common causes of low back pain in adolescents. 4 The incidence rate is 3–10% in adolescents and 6% in adults. 20,21 More than 80% of lumbar spondylolysis appear in L4 and L5. 4 Patients with lumbar spondylolysis mostly like sports or engage in sports, dancing and other industries. The specific cause of spondylolysis may be stress fractures caused by long-term fatigue on the basis of isthmic dysplasia. For the treatment of symptomatic lumbar spondylolysis in adolescents, active measures should be taken to avoid further problems such as intervertebral disc degeneration, herniation, lumbar instability or spondylolisthesis. If early diagnosis of lumbar spondylolysis is made in adolescents, measures such as wearing a lumbosacral brace and restricting movement will most likely result in isthmic healing, 22 but those who do not heal should be actively treated by surgery. Main indication for surgical repair of lumbar spondylolysis is that low back pain is not relieved after at least 6 months of non-surgical treatment, including activity modification, bracing, and physical therapy. Aggravation of pain, deterioration of neurological symptoms and progressive listhesis also are indications for surgical consideration. In the present study, our patient group, due to severe low back pain, failure of conservative treatment for more than 3 months, isthmus dissection, osteosclerosis and nonunion, needed surgical treatment.
There are many surgical methods for lumbar spondylolysis. In 1968, Kimura described an isolated bone graft that directly repaired the isthmus defect without internal fixation, retained segmental activity, but required postoperative cast and long bed rest. 23 Later, Scott 24 proposed the use of wire under the lamina and transverse processes, which has been improved by several authors over the years. 25,26 In 1970, Buck27 first used screw internal fixation and bone grafting to repair defects directly, and subsequently other approaches with special constructs and temporary fixations were reported. 28,29 There were also posterolateral bone graft fusion, cross-segmental pedicle screw fixation and other methods. Patients with spondylolisthesis or disc herniation can be treated with pedicle screw fixation and interbody fusion. 30
The treatment of young patients with lumbar spondylolysis with isthmus debridement, bone grafting, and pedicle screw laminar hook fixation has achieved satisfactory results, 17,18,31 which proves that pedicle screw-laminar hook system has strong fixation and is conducive to bone graft fusion. It is an intra-segmental fixation and does not affect the lumbar interbody movement and the kinematics of the adjacent segment. Studies 32–34 have reached a consensus that lumbar intramuscular approach can reduce the dissection of paravertebral muscles, reduce the denervation of paravertebral muscles, preserve the structure of muscle ligament complex, reduce postoperative pain and recover quickly. However, the current pedicle screw-laminar hook fixation system is not specifically designed for lumbar spondylolysis. Before the hook is installed, the muscles around the spinous process and lamina need to be separated, resulting in severe tissue damage. At the same time, the installation of the system is difficult because the lamina, hook and pedicle screw are not on the same plane.
To solve these problems, we designed a new anatomical hook-rod instrument (Fig. 4), which combined with pedicle screw to form anatomical hook-rod-pedicle screw system. The system can be installed by intermuscular approach, which has the advantages of less trauma and convenient operation. At the same time, the system is firmly fixed, which is favorable for bone graft fusion. According to the anatomy of lumbar spine, the spinous process is at a certain angle with the lamina, the lamina is inclined backward and upward, and the lower edge of lamina and the tail of pedicle screw are at a certain angle with the sagittal plane. According to the above anatomical features, the hook and the rod are inclined in these three directions. The hook is completely matched with the lamina, which is conducive to the installation of the hook at the lower edge of the lamina, and the rod is easy to connect with the universal pedicle screw. Of course, the angles of L4 and L5 are different. We have designed a series of hook-rods with different angles, which are convenient for operation. In this study, 15 cases of young patients with lumbar spondylolysis were treated with isthmus repair, bone grafting, anatomical hook-rod-pedicle screw fixation, and achieved satisfactory results. At the same time, the injury was small, and the operation was simple and convenient.
Autologous iliac bone graft is the "gold standard" in bone grafting, 35 and pain in the iliac bone donor area is a common complication after iliac bone removal. 36 There are many reasons for postoperative pain in the donor area, such as bone defect, adhesion, osteoporosis and cutaneous nerve injury in the donor area. A bone block with cortex and cancellous bone is taken from the posterior superior iliac spine and can be trimmed to a suitable size to meet the needs of bone grafting in the isthmus. To solve the problem of donor site pain, we used the allogeneic bone with tissue-engineered human bone morphogenetic proteins (BMPs) to fill the defect area of posterior superior iliac spine. Allogeneic bone contains BMPs, which can induce new bone formation and promote bone growth. During the follow-up, bone growth was found in the defect of posterior superior iliac spine, as shown in (Fig. 2), and the pain in the bone donor area disappeared.
The application of isthmus debridement, bone grafting and anatomical hook-rod-pedicle screw system fixation in young patients with lumbar spondylolysis has the advantages of less trauma, simple operation and satisfactory curative effect. However, it is not suitable for the cases of lumbar spondylolysis with spondylolisthesis. In addition, it is not also suitable for the cases with missing lamina, bone dysplasia and lumbar disc degenerative diseases. This new hook-rod-pedicle screw system is undergoing biomechanical testing and has been patented in China (Patent No.: ZL201721043286.7). This is a small sample observation study, and further large sample and prospective studies are needed to prove the superiority and reliability of the system.