Minimally invasive placement of pedicle screws may lower incidence of proximal junctional kyphosis

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A recent study found that using a minimally invasive technique (MIS) for the placement of pedicle screws at the upper instrumented vertebra lowered the incidence of proximal junctional kyphosis (PJK) and revision surgery for PJK at two years. The results were presented by Floreana Kebaish (John Hopkins University, Baltimore, USA) at the 53rd annual meeting of the Scoliosis Research Society (SRS; 10–13 October, 2018, Bologna, Italy).

The investigators found that while the rate of PJK at two years was low overall, at 17% across all patients (6/35), it was found to be higher for patients who had undergone open surgery than for a group which had been treated using a minimally invasive technique. The rate for the open group was 20% (4/20), compared to 13% (2/15) among the MIS patients. Kebaish and colleagues noticed the same trend in the rate of revision surgery for PJK, which at two years was 11.4% across all patients (4/35). For the open group this figure was 15% (3/20) and for the MIS group it was 6.7% (1/15).

According to the authors, the study was carried out in response to a 30% rate of PJK in posterior spinal fusions. They note that intact soft tissue structures are “equally important” to bone structure in supporting the alignment of the spinal column and that the disruption of the posterior tension band is currently considered to be one of the main contributors to PJK incidence. They hypothesised that using the MIS technique at the upper instrumented vertebra to preserve the posterior tension band may decrease the incidence of PJK.

Kebaish concluded that there was a two times higher rate of PJK and a three times higher rate of revision for PJK in the open surgery group when compared to the MIS group, results which were “not statistically significant”. Kebaish suggested that the relatively small sample size “may have contributed to this” and announced that the investigators are continuing to add more patients to the study and follow them up for a longer period of time.

Kebaish and colleagues included adult spinal deformity (ASD) patients undergoing posterior instrumented fusion from the lower thoracic-spine to the sacrum in the study. They excluded osteoporotic patients requiring additional vertebral augmentation, among others. The average age of the MIS group was 66.5 years and for the open group, 65.2 years. There were five male and 10 female patients in the MIS group, compared with eight and 12, respectively, in the open group.

According to the investigators, the prospective randomised study included 42 patients who were randomly placed into MIS and open surgery groups. Six patients were lost to follow up and one patient died. Thirty-five patients completed the two year follow up, comprising 15 from the MIS group and 20 from the open group. Patient data were collected pre-operatively, and at four points postoperatively: immediately after surgery, after six weeks, six months, and at two years. Kebaish and colleagues were looking at radiographic data, including DEXA scans, surgical data, demographic data, complications, and HRQoL data.

Kebaish noted that during the open technique, the spine was exposed posteriorly from the upper instrumented vertebra to the sacrum and pedicle screws were then placed using an open free-hand technique at all levels. During the MIS procedure, the upper instrumented vertebra was not exposed. The instrumentation was placed subcutaneously under fluoroscopy and soft tissues at the upper level were preserved.

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