Six sigma analysis of minimally invasive acetabular arthroplasty: a preliminary investigation

Lewinnek Safe Zone References are Frequently Misquoted

BACKGROUND

Optimal acetabular component orientation in total hip arthroplasty (THA) is a necessity in achieving a stable implant. Although there has been considerable debate in the literature concerning the safe zone, to date, there has not been any review to determine if these references are consistent with the definition applied by Lewinnek et al. in 1978. Therefore, this article aims to examine the available literature in the PubMed database to determine how often a correct reference to the safe zone as defined by Lewinnek was applied to discussions regarding THA.

METHODS

A search for literature in the PubMed database was performed for articles from 1978 to 2019. Search criteria included terms 'Lewinnek,' 'safe zone,' and 'total hip arthroplasty.' Exclusions included abstract-only articles, non-English articles, articles unrelated to THA, and those lacking full content.

RESULTS

A review of literature yielded 147 articles for inclusion. Overall, only 11% (17) cited the Lewinnek article correctly. Forty-five percent (66) of articles referenced measurements in the supine position, 18% (26) referenced other positions, and 37% (55) did not specify. Nineteen percent (28) reported measurements of the acetabular cup orthogonal to the anterior pelvic plane, while 73% (108) did not, and 7% (11) did not specify. Twenty-three percent (34) measured from computed tomography scans instead of other methods.

CONCLUSIONS

In the discussion of the safe zone regarding THA, only 11% of articles listed are consistent with the definition established by Lewinnek. This warrants further investigation into a consistent application of the term and its implications for THA implant stability and dislocation rates.

Implementation and Analysis of a Lean Six Sigma Program in Microsurgery to Improve Operative Throughput in Perforator Flap Breast Reconstruction

PURPOSE

Perforator flaps have become a preferred method of breast reconstruction but can consume considerable resources. We examined the impact of a Six Sigma program on microsurgical breast reconstruction at an academic medical center.

METHODS

Using methods developed by Motorola and General Electric, we applied critical pathway planning, workflow analysis, lean manufacturing, continuous quality improvement, and defect reduction to microsurgical breast reconstruction. Primary goals were to decrease preoperative-to-cut time and total operative time, through reduced variability and improved efficiency. Secondary goals were to reduce length of stay, complications, and reoperation. The project was divided into 3 phases: (1) Pre-Six Sigma (24 months), (2) Six Sigma (10 months), (3) and Post-Six Sigma (24 months). These periods (baseline, intervention, control) were compared by Student t test and χ analysis.

RESULTS

Over a 5-year period, 112 patients underwent 168 perforator flaps for breast reconstructions, by experienced microsurgeons. Total operative time decreased from 714 to 607 minutes (P < 0.01), across the study period, with the greatest drop occurring in unilateral cases, from 672 to 498 minutes (P < 0.01). Length of stay decreased from 6.3 to 5.2 days (P = 0.01). Overall complication rates (35.9% vs 30%, not significant) and take-back rates (20.5% vs 23.9%, not significant) remained similar over the 5-year period. Physician revenue/minute increased from US $6.28 to US $7.59, whereas hospital revenue/minute increased from US $21.84 to US $25.11.

CONCLUSIONS

A Six Sigma program in microsurgical breast reconstruction was associated with better operational and financial outcomes. These incremental gains were maintained over the course of the study, suggesting that these benefits were due, in part, to process improvements. However, continued reductions in total operative time and length of stay, well after the intervention period, support the possibility that "learning curve" phenomenon may have contributed to the improvement in these outcomes.