Introduction

Traumatic brain injuries and pressure ulcers are common causes of scalp defects and skull exposures. The scalp is located close to the skull, with less subcutaneous soft tissue and less mobility than skin in other parts of the body. Studies have found that when the diameter of a scalp defect exceeds 2.5 cm, it becomes challenging to suture and close the wound directly. Consequently, clinical treatment becomes notably difficult, particularly in cases involving exposed skull injuries [1]. Several treatment methods are currently available for scalp defects combined with skull exposure. Researches have shown that local flap transfer can be used to cover wounds when the scalp defect area is less than 20 cm2, and larger defects can be covered with a free anterolateral femoral flap [2, 3]. Clinical studies have also shown that skin-stretching devices [4] and tissue dilators [5] can effectively treat scalp defects. However, these surgical treatments require the induction of general anaesthesia, which poses challenges for older adult patients with compromised cardiopulmonary function and limited anaesthesia tolerance. Consequently, non-surgical treatments have become the sole viable option for this demographic.

Recently, platelet-rich plasma (PRP) has been widely used for wound healing and has shown excellent clinical efficacy [6, 7], thus becoming an important means of treating skin defects. Clinical methods for PRP preparation include blood cell apheresis technology, and density gradient centrifugation which is typically employed as a two-step method. However, their complexity and cost of use per application make them inaccessible to most patients and countries worldwide. Platelet-rich gel (PRG) was prepared via a straightforward and cost-effective one-step centrifugation process. In this study, we assessed the clinical effectiveness of PRG prepared using a one-step centrifugation method for treating 12 scalp defects characterised by exposed skull wounds.

Patients and Methods

Study Population

This study was approved by the Ethics Committee of the Chongqing Emergency Medical Centre. This study included 12 patients with scalp defects and skull exposure caused by craniocerebral trauma between September 2018 and March 2022. The PRG treatment plan was introduced to the patients and their families, and relevant medical documents were signed after obtaining their consent. The inclusion criteria were as follows: scalp defects with concurrent skull exposure resulting from trauma, a wound edge distance exceeding 2.5 cm, and inability to directly close the wound. The exclusion criteria were exposure to titanium mesh wounds following cranioplasty, cancerous wounds, low platelet counts, and pre-existing abnormal coagulation function. Prior to treatment, routine blood and coagulation function assessments were performed to exclude individuals with abnormal coagulation and thrombocytopenia.

Autologous PRG Preparation

Centrifuge tubes containing coagulant were used to prepare PRG. Each tube contained five milliliters of blood that were drawn. The size and depth of the wound were used to determine the required volume of blood. Blood-filled tubes were centrifuged at 1450 G for 5 min using a low-speed centrifuge (BIORIDGE, Ltd., Shanghai, China). Centrifugation separated the blood into three distinct layers: the upper layer, a translucent light-yellow liquid consisting of acellular plasma; the middle layer, a light-yellow gel, constituted PRG; and the bottom layer, comprised red blood cells. PRG and red blood cells can be effortlessly separated using tweezers. Both the length of PRG and its platelet concentration were assessed after preparation.

Treatment Methods and Procedures

First, the scalp defect and skull-exposed wounds were debrided to remove the necrotic and inflammatory granulation tissues. A portion of the removed tissue was used for bacterial cultures. PRG was filled inside the wound, and the surface was covered with Vaseline gauze (ZHENDE, Ltd, Shaoxing, China) to prevent plasma containing growth factors from seeping out of the wound. The outermost layer was covered with a hydrogel dressing to close the wound, and the PRG was replaced every three days until the wound healed. The number of dressing changes required and wound healing time were recorded. Visual analogue scale (VAS), white blood cell (WBC) count, C-reactive protein (CRP), procalcitonin (PCT), and topical skin temperature were measured before and three days after treatment. Local scar formation and hair growth were determined during the follow-up.

Statistical Analysis

IBM SPSS Statistics (version 22.0; IBM Corp., Armonk, NY, USA) was used for the statistical analysis. Quantitative data are presented as the mean SD standard deviation, and the differences before and after treatment were compared using a paired t-test. Statistical significance was set at P < 0.05.

Results

In this study, twelve patients including 10 men and two women, with an average age of 62.8 years (43–86 years), and scalp defects combined with skull exposure, were included. Injuries resulting from vehicular accidents occurred in 66.67% of cases, falls from a height in 25% of cases, and being struck by heavy falling objects in 8.33% of cases. All wounds were situated on the head and forehead, with wound dimensions ranging from 3.0 cm × 3.0 cm to 5.0 cm × 6.0 cm, averaging at 17.08 SD5.49 cm2. The length of the PRG prepared using one-step centrifugation was 3.09 SD0.09 cm, and the platelet concentration increased by 2.43 SD0.07 times. The number of PRG replacements required for complete healing of skull defects in 12 patients ranged from 5 to 11, with an average of 8.3 SD2.0. The wound healing time was 15–33 days, with an average of 25.0 SD5.8 days. Except for one patient who died after wound healing due to other severe injuries, all other patients could be effectively followed up for 4–10 months, with an average follow-up duration of 5.8 SD1.9 months. None of the patients experienced local redness, swelling, or wound exudation. Most patients had small local scars, normal skin colour, sparse hair, and no obvious new hair growth. None of the patients complained of local skin pain, numbness, or other discomforts. Table 1 shows the patients' VAS score, WBC count, CRP level, PCT level, and local skin temperature before and after treatment. Statistical analysis revealed no significant differences before and after treatment, indicating that PRG treatment did not increase wound infection or local pain. Representative cases were presented in Figs. 1 and 2.

Table 1 Visual Analogue Scale scores, inflammatory indicators, and topical skin temperature before and after platelet-rich gel treatment
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Fig. 1
figure 1

Case 1: A 75-year-old man patient sustained a forehead contusion and laceration due to a vehicular accident. After debridement and suturing, the patient developed skin necrosis and skull exposure. Reconstruction of scalp defects and skull-exposed wounds in the frontal region using platelet-rich gel was performed as follows: (A) Preparation of platelet-rich gel by one-step centrifugation. (B) Skull exposed following frontal wound debridement. (C) The wound was filled with platelet-rich gel and covered with Vaseline gauze. (D) After five rounds of treatment with platelet-rich gel. (E) After seven rounds of treatment with platelet-rich gel. (F) Complete wound healing

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Fig. 2
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Case 2: A 57-year-old man patient experienced scalp contusion and laceration at the parietal site due to a vehicular accident. After debridement and suturing, the patient developed skin necrosis and skull exposure. Reconstruction of scalp defects and skull-exposed wounds in the parietal region using platelet-rich gel proceeded as follows: (A) Prior to debridement, the scalp wound exhibited signs of non-freshness and significant purulent exudation. (B) Skull exposed following parietal wound debridement. (C) The wound was filled with platelet-rich gel and covered with Vaseline gauze. (D) After four rounds of treatment with platelet-rich gel. (E) After nine rounds of treatment with platelet-rich gel. (F) Complete wound healing

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Discussion

Scalp defects can be caused by several etiologies, such as trauma, burns, pressure ulcers, infections, tumour resection, and radiotherapy necrosis [8]. In contrast to the repair of wounds in other regions, reconstruction of scalp defects requires careful consideration of both wound tissue coverage and aesthetic outcomes following surgery. Reconstruction of scalp defects is a complicated and challenging procedure for reconstructive surgeons because of limited movement of the scalp and hypovascularity of the calvaria. The correct choice of reconstruction method is often influenced by the size, depth, and location of the defect; periosteal injury; quality of the surrounding scalp tissue; hair damage; and patient comorbidities [8]. While smaller scalp defects can be closed directly through suturing, larger defects may require advanced reconstruction methods because of the limited elasticity of the surrounding tissue. The literature documented multiple options, including healing by secondary intention, full-thickness skin graft or split-thickness skin graft, tissue expanders or skin-stretching devices, local flaps, vascularised pedicled flaps, and free flap reconstructions, for the reconstruction of scalp defects [9]. In general, most scalp defects require surgical intervention, which carries inherent risks related to anaesthesia and the surgical procedure itself. Moreover, it presents challenges in patients with a compromised cardiopulmonary function who are unable to tolerate general anaesthesia. Non-surgical treatment was the only option for these patients. PRP and PRG, which are new and effective non-surgical treatments for wounds, have been widely used in various wound repairs. Researchers [10] first reported the successful reconstruction of a large scalp defect with skull exposure by trephination combined with PRP. Nevertheless, prior investigations have indicated that moderate (5–20 cm2) to large (> 20 cm2) scalp defects cannot be closed using direct sutures and often require surgical reconstruction [1]. In this study, we used PRG as a non-surgical method to repair moderate-to-large scalp defects and achieved excellent clinical efficacy.

PRP was first used in the early 1970s and gained popularity in the 1980s. It has been widely used in wound repair, sports injuries, osteoarthritis, fracture healing, and other fields. PRP is primarily utilised in clinical settings in two forms: local injection of a PRP solution and local application of PRP gel [11, 12]. The methods used to prepare PRP include blood cell apheresis technology and density-gradient centrifugation. In the blood cell apheresis technology, PRP is generated by isolating platelets using multifunctional automatic separation equipment designed for medical blood components. While this method facilitates the extraction of a large number of platelets with a high concentration, the required equipment is expensive and requires professionally trained blood transfusion personnel. The cost of a single platelet collection is high. Additionally, the remaining blood components must be transfused back into body after platelet extraction is completed, making this method less patient-friendly. A PRP preparation set employs the principle of density gradient, which allows for simple operation and extraction of platelets at relatively high concentrations. However, it is expensive and can benefit only a limited number of patients. The two-step centrifugation method can also use centrifuge tubes to prepare PRP under sterile operating conditions [13], which is a simple and inexpensive operation process. As it is difficult to meet the sterile conditions required for PRP preparation clinically, its clinical application is restricted. Regardless of the method used to prepare PRP, a platelet activator, such as calcium chloride or thrombin, must be added to the PRP solution to form a PRP gel suitable for local wound application. Consequently, the PRP gel preparation process is intricate and increases the risk of infection with the incorporation of an activator.

PRG is a platelet-rich gel directly prepared using a one-step centrifugation method. This method is simple to operate and convenient for clinical application. For PRG preparation in this study, only a centrifugal tube and centrifuge were required, eliminating the need for additional instruments in both the preparation and clinical application of PRG. The simplicity and low cost of PRG preparation make it accessible to most patients and can be performed at all levels of medical institutions. In contrast to platelet-rich fibrin (PRF) and PRP gel preparation, PRG can be prepared by centrifugation for only 5 min using centrifuge tubes containing coagulants. The time required for PRF and PRP gel preparation is 12 min [14] and 30 min, [12] respectively. Notably, the PRG preparation time in this study was much shorter than that required for PRF and PRP gel, which helps shorten the treatment time and improve clinical efficiency.

PRP and PRG promote wound healing by supplying various growth factors and their bacteriostatic and antibacterial properties. The mechanisms through which they exert these effects are complex and multifaceted. A previous study demonstrated that PRP could inhibit Staphylococcus aureus and Staphylococcus epidermidis, and activated PRP had a significantly stronger inhibitory activity than inactive PRP [15]. Researchers [16] found that PRP could significantly reduce the number of bacteria around wounds in animal experiments, indicating that PRP could be applied to wounds complicated with infection. In this study, we observed no significant differences in inflammatory indicators or local skin temperatures before and after PRG treatment, indicating that PRG treatment did not increase local wound infection.

Concentrated platelet products primarily use various growth factors released by platelet-activated α particles for wound treatment. Research has demonstrated a correlation between the temporal and spatial distributions of growth factors and wound healing. Specifically, the maintenance of higher concentrations of long-term growth factors is more supportive of the healing process [17]. After platelet activation in PRP, 95% of growth factors were released within 1 h. Because many growth factors are released in a short period, they cannot be used by all wound cells, and some growth factors are lost in the fluid. It is challenging to promote wound healing for a long time because natural growth factors have a short half-life and poor stability [18]. In most studies, the treatment cycle of PRP for wounds is 7–10 days [19, 20]. In this study, since the platelet concentration in PRG was only approximately 2.4 times the concentration in blood, it is far lower than the standard that the platelet concentration in PRP was 6–8 times higher than the concentration in blood [21], we adjusted the wound treatment cycle to 3 days to ensure that the local platelet concentration in the wound remained relatively high over an extended period. Their excellent efficacy has been confirmed in clinical practice.

Nevertheless, this study had several limitations. The primary limitation was that the number of patients included in this study was small and more cases need to be studied. Another limitation of this study was that it had no appropriately matched control groups. Given the absence of a standardised protocol for PRG preparation, further research is needed to determine the optimal centrifugal force and duration for PRG preparation. The efficacy of PRG and PRP in wound treatment needs to be compared in future studies.

Conclusion

In this study, platelet-rich gel prepared using a one-step centrifugation method was applied to treat scalp defects combined with skull exposure. We demonstrated that the one-step preparation of platelet-rich gel in reconstructing scalp defects is a simple, safe, and effective non-surgical treatment. The advantages of this method include speedy preparation, painless treatment, and small local scars after wound healing. We believe that this method can provide an alternative choice for clinicians to treat scalp defects with skull exposure and can be widely used in various medical institutions at all levels.