Lumbar spondylolysis is a widespread disease and the main cause of low back pain in young people. It most commonly is present at the L5 segment bilaterally.19 Currently, there are two main types of repair operations for spondylolysis: one is direct repair using segmental internal fixation and bone grafting in the isthmus; the other is fusion of the affected vertebra with adjacent vertebrae using intersegmental internal fixation. For patients with simple spondylolysis without obvious spondylolysis, various surgical methods such as Buck screw technique and pedicle screw-hook technique are often used. However, these internal fixation methods are non-intersegmental and therefore cannot solve problems such as lumbar spondylolysis and lumbar-sacral sagittal imbalance. For lumbar spondylolysis with spondylolisthesis in youth, the previous experience was to perform interbody fusion by removing the disc. However, interbody fusion may sacrifice a motor unit to induce adjacent segment degeneration, which is often an awful outcome for young people. Faced with possible complications, many scholars have modified isthmus repair surgery. For example, Huang et al proposed a surgical method of isthmic bone graft repair combined with temporary intersegmental pedicle screw,15 and Berjano et al proposed a novel technique with pedicle screws, rod and polyester band. 20However, the author believes that all the above surgical methods have advantages and disadvantages.
Based on the underlying pathological mechanism of lumbar spondylolysis and previous literature reports, the author believes that the key to the repair of lumbar spondylolysis lies in: 1) The hyperplasia tissue at the broken end of the isthmus should be fully removed and bone graft be performed according to the scope of the bone defect. The direct fixation of the isthmus was realized by using compression screw technology, so as to restore the continuity and integrity of the bone while ensuring the stability of the isthmus;12,13 2) For mild lumbar spondylolisthesis and lumbosacral sagittal imbalance, we need to use intersegmental fixation to reduce spondylolisthesis and rebuild the spine-pelvis balance, so as to avoid the stress concentration on the intervertebral disc or isthmus area which resulting in disc degeneration and poor bone fusion.15,16
According to the above ideas, we proposed a novel technique for spondylolysis repair based on Buck technique supplemented by temporary segmental pedicle screw fixation. By comparing the CT images before and after the operation, we can confirm that Buck technique can directly repair the isthmus defect with bone grafting and restore the complete lumbar posterior arch (Fig. 5). Meanwhile, we can observe based on radiographs that temporary intersegmental fixation played a significant role on the reconstruction of sagittal balance of the lumbosacral vertebra (Fig. 6). It can reduce stress concentration on the defect area of the pars interarticularis and indirectly promote bone fusion. In particular, considering that the Buck technique directly occupied a portion of the bone graft space through the isthmus section, we modified the details of the procedure to reduce the occupying effect of the Buck screw by replacing a slightly smaller diameter Herbert screw(φ = 3mm), which have many advantages for repairing nonunion or stress fractures.21,22 In addition, in order to prevent the degeneration of intervertebral disc or adjacent segments which caused by long-term intersegmental fixation, patients will be regularly followed up after surgery (Fig. 7). Within 1 year of healing of the lumbar isthmic fracture, pedicle screws will be removed to obtain better ROM values, during which time rehabilitation will be strengthened to restore as much range of motion in the lumbar spine as possible.23
While Buck technique's effectiveness is undisputed, the most controversial aspect of the technique involves the temporary fixation of moving segments with intersegmental pedicle screws. Here we have our opinions as follows. As a three-column spinal fixation, the biomechanical properties of pedicle screws should better control intersegmental extension and rotational stresses.24 There was a very interesting clinical and biomechanical study showed that the spondylolysis originates ventrally in the interarticular region, simply because higher stresses were found in the ventral caudate during repeated hyperextension and rotation activities in all loading modes.25 At the same time, some studies show that the imbalance of lumbosacral sagittal position may play an important role in the pathological process of lumbar spondylolysis in adolescent population. 5,6,26 LL and SS were positively correlated with lumbar spondylolisthesis rate in that an excessively large angle of LL and SS leads to lumbar center of gravity moves forward, while the support point of gravity moves backward.7 The stress of lumbosacral will be concentrated in the isthmus of the 5th lumbar vertebra, resulting in a large shear force on the isthmus. Loss of sagittal balance in the lumbosacral region and morphological abnormalities may be responsible for high involvement of L5. High frequency and intensity of stress applied to the lumbar spondylolisthesis can lead to the gradual progression of the spondylolisthesis from microfractures to complete fractures and chronic nonunion. Moreover, Jeon et al believed that pedicle screw fixation in a short period of time did not affect the recovery of lumbar motion.27 Therefore, we can conclude that temporary intersegmental internal fixation is feasible for the repair of isthmus.
Absolutely, our current research also has many limitations and deficiencies. First of all, the number of case samples in this study is insufficient, so we need more patients and control groups in the later study to compare the therapeutic effect of the current proposed technology with that of the traditional technology. Second, this new surgical method requires two surgeries to complete, and the treatment cycle may be too long to meet the needs of some young patients for rapid recovery. Finally, the Buck technique requires difficult nailing techniques and extensive surgical experience, so it is hoped that this kind of surgery can be carried out smoothly in the future with the assistance of computer navigation and neural monitoring technology.28