Quantitative and qualitative analysis of bone flap resorption in patients undergoing cranioplasty after decompressive craniectomy

Abstract

OBJECTIVE Autologous bone cranioplasty after decompressive craniectomy entails a notable burden of difficult postoperative complications, such as infection and bone flap resorption (BFR), leading to mechanical failure. The prevalence and significance of asymptomatic BFR is currently unclear. The aim of this study was to radiologically monitor the long-term bone flap survival and bone quality change in patients undergoing autologous cranioplasty. METHODS The authors identified all 45 patients who underwent autologous cranioplasty at Oulu University Hospital, Finland, between January 2004 and December 2014. Using perioperative and follow-up CT scans, the volumes and radiodensities of the intact bone flap prior to surgery and at follow-up were calculated. Relative changes in bone flap volume and radiodensity were then determined to assess cranioplasty survival. Sufficient CT scans were obtainable from 41 (91.1%) of the 45 patients. RESULTS The 41 patients were followed up for a median duration of 3.79 years (25th and 75th percentiles = 1.55 and 6.66). Thirty-seven (90.2%) of the 41 patients had some degree of BFR and 13 (31.7%) had a remaining bone flap volume of less than 80%. Patients younger than 30 years of age had a mean decrease of 15.8% in bone flap volume compared with the rest of the cohort. Bone flap volume was not found to decrease linearly with the passing of time, however. The effects of lifestyle factors and comorbidities on BFR were nonsignificant. CONCLUSIONS In this study BFR was a very common phenomenon, occurring at least to some degree in 90% of the patients. Decreases in bone volume were especially prominent in patients younger than 30 years of age. Because the progression of resorption during follow-up was nonlinear, routine follow-up CT scans appear unnecessary in monitoring the progression of BFR; instead, clinical follow-up with mechanical stability assessment is advised. Partial resorption is most likely a normal physiological phenomenon during the bone revitalization process.

Predictors of primary autograft cranioplasty survival and resorption after craniectomy

“…Aseptic BFR is a late complication, and it has been well demonstrated that younger age increases the risk of BFR. 7,12,18,26,33,36,37 Most skull growth takes place during the 1st year of life, but growth proceeds until the cranial vault is fully formed in adulthood. Cranial growth includes resorptive activity, and the preadolescent skull bone may be metabolically more active than the adult skull in this respect, which could play a part in the higher BFR prevalence observed in young patients.…”

“…The latter cutoff values were applied in order to facilitate interstudy comparison, as similar cutoffs have been used in previous publications. 18,26,37 A 2-tailed p value of < 0.05 was considered statistically significant. Follow-up times, calculated as the time between the CP and removal of the bone flap, death, or December 31, 2015, are reported as the mean with SD.…”

Consensus statement from the international consensus meeting on post-traumatic cranioplasty

“…In a recent systemic review and meta-analysis [62], an increased risk of reoperation for autologous implant mainly related to BFR was reported, with no increased infection rates compared with synthetic material. Younger age, shunt dependency, and bone flap fragmentation as independent risk factors for BFR were also reported [53,81]. A prospective multi-centre study showed the development of major complications mainly due to BFR [38].…”

An improved process for the fabrication and surface treatment of custom-made titanium cranioplasty implants informed by surface analysis

“…2 Despite their prevalence, bone flaps are prone to resorption, 3 which reportedly occurs to some extent in 90% of patients undergoing cranioplasty. 4 Alternative synthetic materials include poly-methyl methacrylate (PMMA), titanium and hydroxyapatite. 2,5 The choice of material depends on a number of factors but direct comparison of their performance is difficult owing to the lack of prospective controlled trials with long-term follow up.…”