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Although cervical and lumbar disc arthroplasty have entered the clinical setting, there are still concerns regarding the short and long term complications arising from hypermobility of current prosthesis designs. Reconstruction of the ALL is a potential solution to disc arthroplasty hypermobility.

While the overall design principals of total disc replacement (TDR) prostheses have improved over the years, many available devices have semi- or non-constrained dynamics in an attempt to restore the normal range of motion [7]. This however comes with a risk of hypermobility in the motion segment, which combined with the inherent iatrogenic damage to the anterior longitudinal ligament (ALL) during insertion, disturbs the physiological kinematics of the spine [8910]. These factors have been speculated to cause clinically significant secondary consequences to the operated spinal motion segment and adjacent segments in the short and long term [11121314151617]. Indeed, there have been several reports of anterior prosthesis migration following TDR, speculated to be a direct consequence of the disrupted ligamentous structures [1215].

Cervical and lumbar interbody fusion techniques have become a routine surgical approach to effectively manage various degenerative pathologies of the spine including discogenic back and neck pain, spondylosis, segmental instability and deformity [18]. However, adjacent segment degeneration is an established long-term complication of cervical and lumbar fusion [145]. Immobilization of a spinal motion segment transfers increased loading and biomechanical stress to the adjacent motion segments, thereby accelerating the degenerative process.

Restoring the physiological kinematics of a spine motion segment requires consideration of the role of spinal ligaments in stabilizing and regulating the motion of the tri-joint complex, which are often compromised during surgical dissection. The ALL has been demonstrated to be an important stabilizer of the motion segment during extension and lateral bending but at the same time, is routinely divided during anterior discectomy and prosthesis insertion [10]. The non-physiological kinematics introduced by current prosthesis designs in conjunction with loss of the ALL is speculated to cause clinically significant hypermobility, especially in extension, of the operated segment and excessive loading of the facet joints and implanted device [11152728]. There has been speculation on the use of the lateral approach for TDR, but this has not been well explored and there is the theoretical risk of lumbosacral plexus injury with this approach.

Long term secondary consequences of facet degeneration in the operated and adjacent levels due to segmental hypermobility following disc arthroplasty have also been described. van Ooij et al. [15] reported 11 cases of facet joint arthrosis following lumbar disc arthroplasty with pain aggravated in extension. Though the authors acknowledge that this facet arthrosis could be pre-existing, they speculate abnormal segmental kinematics from the Charite disc prosthesis, even in the absence of device subsidence or sub-optimal placement may introduce or accelerate facet degeneration. In the same study, 3 cases of excessive lordosis at the operated segment demonstrated opening of the superior aspect of the facet joint and compression of the inferior aspect [15]. In studies on lumbar TDR failures, Pettine [17] reported that 50% of failures were attributed to facet pathology while Rosen et al. [16] reported 100% of failures involved a facet aetiology [27]. In the cervical spine, Gautschi et al. [11] reported a case of failed disc arthroplasty due to segmental hypermobility which resulted in persisting axial neck pain worsening under motion. These studies describe sagittal imbalance and subsequent concentration of stresses to the posterior elements, especially the facet joints, as mechanisms of clinically significant facet degeneration.

Given the above complications, it is clear current techniques of disc arthroplasty are still inadequate in replicating the normal kinematics of the operated spinal segment, which include normal facet joint movement and loading [15]. In order to address the current limitations outlined above, emphasis should be directed towards restoring important components of the ligamentous network [28]. The senior author of the current study describes a novel technique of ALL reconstruction following cervical and lumbar disc replacement. It is speculated reconstruction of the ALL may mitigate the issues associated with current prosthesis designs including hypermobility especially in extension, non-physiological kinematics and potential secondary complications. This may provide spinal surgeons greater confidence in performing disc arthroplasty. 041b061a72


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