In the literature, the majority of clinical studies have focused on platelet gel and important results have already been obtained in terms of osteo-induction [8
]. The efficacy of platelet concentrate for stimulating bone growth has also been demonstrated by many maxillo-facial studies [18
] as well as in vitro studies [3
], and in vivo in animals [13
]. In the neurosurgical field, the use of platelet gel has been employed in spinal fusion procedures. Lowery et al. [17
] described a series of 19 patients in a retrospective review of autologous growth factors (AGF) combined with autograft and hydroxyapatite as an extender in posterior and anterior lumbar fusion. The authors reported a 100% fusion rate based on surgical exploration in 5 patients and on plain X-ray films in 14. In their retrospective study, Bose and Balzarini [1
] described 60 cases of spinal fusion using AGF with autograft and reported a 96% fusion rate based on plain radiographic evidence.
Weiner and Wolker [26
] reported on a retrospective study comprising two groups of patients who had undergone single- level inter-transverse fusion. A 62% fusion rate was observed in 32 patients in whom autogenous iliac crest graft augmented with AGF was used, compared to a 91% fusion rate in a group with bone graft alone. Their evaluation was based on flexion/extension radiographs. Hee et al. [12
] in 2003 evaluated the effects of AGF combined with autograft in trans-foraminal lumbar interbody fusion performed in 23 patients: they compared these results with those obtained in a group of 111 patients treated by autograft alone, with a minimum follow-up of 2 years. Radiographic evaluation was performed at 4, 6 and 24 months, with more rapid incorporation of fusion at 4 and 6 months in AGF patients. At 24-month evaluation, no significant differences in fusion rate were detected. The authors concluded that AGF was capable of promoting graft incorporation, thus stimulating faster fusion.
In 2005, Jenis et al. [14
] described a study in which 37 consecutive patients were submitted to anterior–posterior lumbar interbody fusion (ALIF-PLIF) with bone graft harvested from the iliac crest (22 patients) or allograft combined with AGF (15 patients). Patients were evaluated at 6 and 12 months by CT scan and at 24 months by plain X-rays. The results at 12 and 24 months demonstrated an 85% fusion rate in patients with autograft in comparison to an 89% rate with allograft and AGF. The authors concluded that allograft with AGF could represent a valid alternative to homologous fusion.
In the study published by Carreon et al. [5
] in 2006, a series of 76 patients were treated with non-instrumental postero-lateral arthrodesis using autologous bone with AGF and the results were compared to those obtained in a group of patients treated with non-instrumental postero-lateral arthrodesis using autologous bone alone. A 25% non-fusion rate was observed in the AGF group compared to 17% in the control group. The authors concluded by recommending the use of autologous bone graft because it guarantees a higher rate of fusion.
In the present study, we decided to focus our attention to several aspects not taken into consideration in the studies previously published in the literature:
- In previous studies the comparison was made between groups of patients who had undergone postero-lateral fusion on both sides of the operative field with autograft and allograft + AGF, subsequently evaluating the fusion rate and comparing it with a control group treated with autograft alone. In the patients of our study, a traditional postero-lateral fusion was performed in the left half of the operative field and a postero-lateral fusion with autograft/allograft + platelet gel in the right half. This technique made it possible to directly compare the two systems in each single patient, eliminating variability due to individual clinical conditions favouring non-fusion, such as smoking and diabetes [2, 10].
- Critical analysis of previous published studies attracted our interest to comparative evaluation of the fusion rate. On the basis of CT images, a map of bone densities can be obtained using a variety of methods, so that a comparative assessment of the fusion rate at the instrumented level with and without platelet preparation is possible. The most simple and widely used method, that we use too, is a system of electronic targeting which delimitates the region of interest (ROI), a surface varying in size and shape (generally a square-shaped area 0.4 cm2 in size), that the operator can trace directly on the CT images. The computer is then able to perform an immediate calculation of the mean pixel content (bi-dimensional unit of measurement) in the perimeter traced by the operator over the diagnostic region of interest. In order to express the densitometric value of pixels, a scale of numbers has been introduced in which the value 0 corresponds to water, −1,000 to air and +1,000 to cortical bone. The unit of measurement employed is the Hounsfield Unit (HU) scale. It is important to emphasize that the numerical value obtained from such measurements is the average of the densitometric values of the pixels contained in the area studied. Together with the ROI measurement, the computer also gives us the standard deviation (SD) of the pixel concentration in the measured area, whose numerical value is inversely proportionate to tissue homogeneity. It is clear that in an area as large as 0.4 cm2 the SD will be extremely variable. A retrospective analysis of the SD values measured and recorded at the same time as ROI showed that all the SD values remained below 450.3, with a median value on the right side of 238.5 at 3-month follow-up and 239.96 at 6 months, and in the left side of 238.88 at 3 months and 240.1 at 6 months. In order to obtain a control value of bone tissue homogeneity, a series of ROI measurements were made in an area of homogenous cortical bone measuring 0.4 cm2 in another site: results showed that the value of SD remained within a range of 40–150. If we consider that PLF is performed on a composite of fragmented autologous–heterologous bone, which is far more dishomogenous than cortical bone, satisfactory values of bone fusion have been suggested as SD <500. A comparison between the SD values measured on the two opposite sides at 3 and 6 months showed a good homogeneity of bone fusion, with values always below 450.03 (median 239), and confirmed that the use of platelet gel does not influence the homogeneity of the newly formed bone callus.
In this context, it is important to point out that in previous studies it was the radiologist who evaluated fusion by direct visual appraisal of follow-up CT or plain X-ray images whereas in the present study evaluation of axial CT images, ROI and SD provided concrete numeric values regarding bone density and homogeneity.
- In our study the fusion rate at 6 months was 100%. Bone density in the right half of the operative field was higher by 125.95 HU (760.09 vs. 634.14 HU) in comparison to the left one in which AGF was not used. Moreover, a higher velocity of bone apposition was observed during the first 3 months after surgery in the half-field where the gel was employed: this subsequently normalized in the following 6 months, so that only slight differences existed between the two halves at 6-month follow-up. This feature has also been observed in diabetic patients and smokers, in which it was observed, similar to healthy subjects, an increase in the rate of bone growth during the first 3 months, with subsequent levelling of the rate of bone deposition at 6 months, while maintaining a level of fusion lower than in healthy subjects. This is a very important aspect because it suggests that the gel could be used to speed up post-operative recovery, in terms of mobility, thus reducing the duration of rehabilitation and the need for orthopaedic devices, especially in diabetic and smoker patients. Consequently, patients are able to make an early return to normal working activities.
- Another aspect which must not be underestimated is the low cost of gel preparation owing to the fact that the gel is prepared in the Institute of Haematology of our university structure, using the patient’s own blood. It should be pointed out that the entire cost of this method does not exceed 140,00 Euros The cost of each antiseptic “pastette” is 0,026 Euro each plus VAT. The capsules of Petri cost 0.151 each plus VAT, whereas the vials of calcium glutamate cost 0.25 cents each. The vials of ethyl alcohol cost 2.5 Euros each. These are the real costs and as far as the cost of centrifuge is concerned it can be quantified in 50 cents/1 Euro per procedure.