Two-year efficacy after first transscleral controlled cyclophotocoagulation in patients with and without pseudoexfoliation

Purpose

Transscleral controlled cyclophotocoagulation (COCO) is a transscleral 810-nm diode laser cyclophotocoagulation that automatically adjusts the applied laser energy utilizing an optical feedback loop. The present study investigates the influence of pseudoexfoliation (PEX) on the efficacy of COCO in a Caucasian study population.

Methods

Retrospective data from 130 consecutive eyes were analyzed during a 2-year follow-up. Baseline characteristics, intraocular pressure (IOP), number of IOP-lowering medications, visual field, best-corrected visual acuity (BCVA), and secondary surgical interventions (SSI) were analyzed. The primary endpoint was IOP reduction at M24 compared to baseline, and the secondary endpoints were IOP course, reduction of IOP-lowering medications, surgical success, and IOP-lowering SSIs stratified by PEX and baseline IOP.

Results

IOP reductions of −35, −39, −25, −25, −23, −34, and −36% could be achieved from baseline to D1, W1, M1, M3, M6, M12, and M24 (all p < 0.001), respectively, while there was a significant overall reduction over time (p < 0.001) in the number of topical IOP-lowering medications postoperatively. The proportion of eyes requiring additional systemic IOP-lowering medication reduced from 31 to 0% at M24 (p = 0.025). Eyes without PEX and IOP < 30 mmHg at baseline had the lowest risk for IOP-lowering SSIs (p < 0.03). BCVA dropped at M12 (0.25 [95% CI: 0.12–0.38]), and the drop persisted during the following 12 months.

Conclusion

The present study demonstrates a midterm IOP-lowering effect after COCO while reducing the burden for topical and systemic IOP-lowering medications. Patients without PEX and IOP < 30 mmHg have a lower risk of SSI. The procedure per se cannot be excluded as causative for the decreased postoperative BCVA. Further prospective investigations are suggested.

     

Comparison of revision strategies for failed C2-posterior cervical pedicle screws: a biomechanical study

Study purpose

With increasing usage within challenging biomechanical constructs, failures of C2 posterior cervical pedicle screws (C2-pCPSs) will occur. The purpose of the study was therefore to investigate the biomechanical characteristics of two revision techniques after the failure of C2-pCPSs.

Materials and methods

Twelve human C2 vertebrae were tested in vitro in a biomechanical study to compare two strategies for revision screws after failure of C2-pCPSs. C2 pedicles were instrumented using unicortical 3.5-mm CPS bilaterally (Synapse/Synthes, Switzerland). Insertion accuracy was verified by fluoroscopy. C2 vertebrae were potted and fixed in an electromechanical testing machine with the screw axis coaxial to the pullout direction. Pullout testing was conducted with load and displacement data taken continuously. The peak load to failure was measured in newtons (N) and is reported as the pullout resistance (POR). After pullout, two revision strategies were tested in each vertebra. In Group-1, revision was performed with 4.0-mm C2-pCPSs. In Group-2, revision was performed with C2-pedicle bone-plastic combined with the use of a 4-mm C2-pCPSs. For the statistical analysis, the POR between screws was compared using absolute values (N) and the POR of the revision techniques normalized to that of the primary procedures (%).

Results

The POR of primary 3.5-mm CPSs was 1,140.5 ± 539.6 N for Group-1 and 1,007.7 ± 362.5 N for Group-2; the difference was not significant. In the revision setting, the POR in Group-1 was 705.8 ± 449.1 N, representing a reduction of 38.1 ± 32.9 % compared with that of primary screw fixation. For Group-2, the POR was 875.3 ± 367.9 N, representing a reduction of 13.1 ± 23.4 %. A statistical analysis showed a significantly higher POR for Group-2 compared with Group-1 (p = 0.02). Although the statistics showed a significantly reduced POR for both revision strategies compared with primary fixation (p < 0.001/p = 0.001), the loss of POR (in %) in Group-1 was significantly higher compared with the loss in Group-2 (p = 0.04).

Conclusions

Using a larger-diameter screw combined with the application of a pedicle bone-plastic, the POR can be significantly increased compared with the use of only an increased screw diameter.     

In vivo analysis of cervical kinematics after implantation of a minimally constrained cervical artificial disc replacement

Introduction

To better understand cervical kinematics following cervical disc replacement (CDR), the in vivo behavior of a minimally constrained CDR was assessed.

Methods

Radiographic analysis of 19 patients undergoing a 1-level CDR from C4–5 to C6–7 (DISCOVER, Depuy-Spine, USA) was performed. Neutral–lateral and flexion–extension radiographs obtained at preop, postop and late follow-up were analyzed for segmental angle and global angle (GA C2–7). Flexion–extension range of motion was analyzed using validated quantitative motion analysis software (QMA®, Medical Metrics, USA). The FSU motion parameters measured at the index and adjacent levels were angular range of motion (ROM), translation and center of rotation (COR). Translation and COR were normalized to the AP dimension of the inferior endplate of the caudal vertebra. All motion parameters, including COR, were compared with normative reference data.

Results

The average patient age was 43.5 ± 7.3 years. The mean follow-up was 15.3 ± 7.2 months. C2–7 ROM was 35.9° ± 15.7° at preop and 45.4° ± 13.6° at follow-up (?p < .01). Based on the QMA at follow-up, angular ROM at the CDR level measured 9.8° ± 5.9° and translation was 10.1 ± 7.8 %. Individuals with higher ROM at the CDR level had increased translation at that level (p < .001, r = 0.97), increased translation and ROM at the supra-adjacent level (p < .001, r = .8; p = .005, r = .6). There was a strong interrelation between angular ROM and translation at the supra-adjacent level (p < .001, r = .9) and caudal-adjacent level (p < .001, r = .9). The location of the COR at the CDR- and supra-adjacent levels was significantly different for the COR-X (p < .001). Notably, the COR-Y at the CDR level was significantly correlated with the extent of CDR-level translation (p = .02, r = .6). Shell angle, which may be influenced by implant size and positioning had no impact on angular ROM but was correlated with COR-X (p = .05, r = ?.6) and COR-Y (p = .04, r = ?.5).

Conclusion

The COR is an important parameter for assessing the ability of non-constrained CDRs to replicate the normal kinematics of a FSU. CDR size and location, both of which can impact shell angle, may influence the amount of translation by affecting the location of the COR. Future research is needed to show how much translation is beneficial concerning clinical outcomes and facet loading.     

Criteria for successful correction of thoracolumbar/lumbar curves in AIS patients: results of risk model calculations using target outcomes and failure analysis

Introduction

Failure to select the appropriate lowest instrumented vertebra (LIV) in selective lumbar fusion (SLF) for thoracolumbar/lumbar curves (LC) can result in adding-on in the lumbar curve (LC) or the need for fusion extension due to a decompensating thoracic curve (TC). The selection criteria that predict optimal outcomes still need to be refined. The objectives of the current study were to identify risk factors for failure of anterior scoliosis correction and fusion (ASF) as well as predictors of optimal outcomes and ASF efficacy for SLF.

Materials and methods

A retrospective review of all patients (n = 245) with AIS who had anterior SLF at one institution was conducted. Optimal outcomes were defined as a target LC ≤20° and a target TC ≤30°. The distance from the LIV to the SV was recorded. An increase in the LIV adjacent level disc angulation (LIVDA) ≥5° was defined as adding-on. An increase in the TC at follow-up was defined as TC-progression. Stepwise univariate and multivariate linear and logistic regression analyses were performed to identify criteria predicting the target LC and TC. A total of 68 % of the patients had the LIV at SV-2 (=2 levels above stable vertebra).

Results

The patients’ average age was 17 years, the average fusion length was 4.6 levels, and the average follow-up time was 32 months. The preoperative LC was 49 ± 14°, the LC-bending was 22 ± 13° (57 ± 18 %), and the follow-up LC was 25 ± 10°. LC correction was 59 ± 17 % (p < 0.01). The preoperative TC was 39 ± 13°, the TC-bending was 21 ± 12°, and the follow-up TC was 29 ± 13°. The TC-correction was 32 ± 19 % (p < 0.01). At follow-up, 85 patients (35 %) had an LC ≤20°, 110 patients (45 %) had a TC ≤30°. The follow-up LC and an LC ≤20° were predicted by LC-bending (p < 0.01, r = 0.6), preoperative LC (p < 0.01, r = 0.6). The logistic regression models could define patients at risk for failing the target LC ≤20° or TC ≤30°. At follow-up, TC ≤30° was best predicted by the preoperative TC (p < 0.01, r = 0.8; OR 1.2) and TC-bending (p < 0.01, r = 0.8; OR 1.06), with the logistic regression model revealing a correct prediction in 84 % of all cases. Among the patients, 8 % required late posterior surgery. Patients achieving the target LC ≤20° had a significantly reduced risk for failure (p = 0.01). Selecting an LIV at SV-1 vs. SV-2 significantly increased the chance of achieving a target LC ≤20° (p = 0.01) and reduced the risk of adding-on (p < 0.01). Predictors for failure also included a high preoperative LC (p = 0.02; OR 0.97), TC-bending (p < 0.01), and preoperative TC (p = 0.01). A cut-off in the failure risk analysis was established at a TC of 38°. Additionally, a significant cut-off for risk of adding-on was established at LIVDA <3.5°.

Conclusion

A high chance of achieving a target LC ≤20° and a low risk of revision was dependent on LC-bending, preoperative LC and TC, and a LIV at SV-1 with non-parallel LIVDA. Our risk model analysis may support the selection of a safe LIV to achieve the target LC.