|Home | About | Journals | Submit | Contact Us | Français|
Twenty eight patients with simple bone cyst that were treated by aspiration and percutaneous autogenous bone marrow injection were reviewed to evaluate the treatment outcome. There were 18 boys and ten girls. Their mean age was 10.9±2.75 years. Single injection was performed for 16 patients; the rest had double or triple injections. There were no operative complications. The mean follow-up was 34.7±6.87 months. The procedure succeeded in obtaining healing in 23 cysts (82%). Cysts with index of more than five and cortical thickness of less than 1 mm were significantly prone to pathological fractures and had significant poor results after treatment. Our results suggested that autogenous bone marrow injection is a safe and effective treatment method for simple bone cysts, but sometimes repeated injections are necessary. Cyst index and cortical thickness are good indicators for cyst aggressiveness and good predictors for treatment outcome.
Vingt huit patients avec un kyste osseux solitaire furent traités par aspiration suivie de l’injection per cutanée de moelle osseuse autologue. Il y avait 18 garçons et 10 filles d’age moyen 10,9 +−2,75 ans. Seize patients ont euune simple injection, les autres 2 ou 3 injections. Il n’y a pas eu de complication. Le suivi moyen était de 34,7 +− 6,87 mois. La cicatrisation fut obtenue pour 23 kystes. Les kystes avec un index de plus de 5 et une épaisseur corticale de moins de 1 mm était plus sujet aux fractures et avaient un moins bon résultat. Ces résultats suggèrent que l’injection de moelle osseuse autologue est une bonne méthode de traitement des kystes osseux, demandant quelquefois des injections répétées. L’index kystique et l’épaisseur corticale sont prédictifs de l’efficacité du traitement.
The simple bone cyst (SBC) is the most common benign lytic bone lesion in childhood, mainly affecting the proximal femur and proximal humerus. It is usually discovered because of pathological fracture, but sometimes it is incidentally detected [5, 7, 11, 12]. Though SBC is often asymptomatic and tends to disappear after skeletal maturity, repeated pathological fractures and growth arrest may occur before spontaneous resolution. The aim of treating SBC is to prevent all possible complications and to avoid prolonged restriction of physical activity [1, 3, 8, 10, 12]. The appropriate treatment, however, remains uncertain and a wide spectrum of treatment modalities have been proposed ranging from observation to subtotal resection [10, 11, 17, 18].
Bone grafting has been disappointing because of the high recurrence rate and considerable morbidity [7, 8, 14]. Percutaneous injection of steroids was introduced first by Scaglietti et al. who reported a success rate of up to 90% . The low morbidity and simplicity of this treatment method explain its popularity [3, 12, 18]. More recently, bone marrow has been proposed as an alternative to steroids because of its osteoinductive potential [1, 6, 15, 18]. The purpose of this study was to evaluate the clinical outcome of treating SBCs by aspiration and percutaneous autogenous bone marrow injection (ABMI). The effectiveness of this method was studied according to different factors that might affect the outcome including the aggressiveness of the cysts.
From January 2002 through December 2004, twenty eight consecutive patients with diagnosis of SBC were treated in the authors’ institute by aspiration and percutaneous ABMI. Confirmation of the diagnosis was based on characteristic radiographic appearance and histological study of the specimens taken by aspiration. Patients who received any kind of treatment other than immobilisation of the affected limb due to pathological fractures were excluded as well as patients lost during follow-up.
There were 18 boys and ten girls. The mean age at the outset of treatment was 10.9±2.75 years (range, 6–17). The cyst locations were proximal humerus in 16 cases (57%), proximal femur in nine cases (32%), distal humerus in two cases (7%), and proximal fibula in one case (4%). Fifteen cysts (54%) were uniloculated and 13 (46%) were multiloculated. Cyst size is defined as the ratio of the length of the cyst to the width of the adjacent physis, which allows direct comparison of the sizes without requiring correction factors for different ages . The mean size of all cysts in this study was 1.846±0.525 (range, 0.9–3). The fracture risk was evaluated by measuring the cyst index of Kaelin and MacEwen  and the cortical thickness. The cyst index is the cyst area divided by the diaphyseal diameter squared. One or more trapezoids are drawn around the cyst to measure the cyst area. Mechanically, a cyst is considered not prone to fracture when the index is <3 and cortical width >2 mm . The mean cyst index for all cysts in our study was 5.207±1.819 (range, 2.2–8.2), and the mean cortical thickness was 1.254±0.467 (range, 0.7–2.2).
Twelve patients (43%) presented for the first time in the authors’ institute with pathological fracture in the proximal humerus, and seven of those patients had sustained at least one previous pathological fracture. All had been treated conservatively to full union before any intervention. Seven cases (25%) with femoral cyst were diagnosed after radiographic work-up for pain and limp which were related to sports or daily activities. The other nine cases (32%) were discovered incidentally. At the time of surgery 20 cysts (71%) were active and eight cysts (29%) were latent according to the Rougraff and Kling  and Neer et al.  classifications.
All patients received the same treatment protocol. The procedures were carried out in the operating room under complete aseptic conditions and under general anaesthesia. A cyst was initially approached by percutaneously inserted 14-gauge needle under fluoroscopic guidance, through the thinnest part of the wall of the cyst if possible. The cyst cavity was evacuated without force, and the fluid was sent for histopathological examination. A second needle was inserted and the cavity was thoroughly flushed with normal saline. Cystogram with diluted Renografin contrast was performed to determine if the cyst was uniloculated or multiloculated. No attempt was made to disrupt the lining membrane of the cyst.
The bone marrow was harvested from the iliac crest using a 12-gauge bone-marrow aspiration needle. Aspiration was performed slowly to ensure that not only blood but also bone marrow was received. In all cases the required volume of bone marrow was obtained without difficulty. The marrow was injected after removal of the second needle until the cyst was completely filled. The mean volume of marrow injected was 20 ml. For multiloculated cysts, additional needles were used to ensure that all sections of the cyst were exposed to bone marrow. After injection, the patient was discharged on the same day. Normal activities were allowed immediately without restriction. Persistent cyst cavity with fracture risk three months after ABMI was an indication for repeating the procedure; this occurred once in seven of the patients (25%) and twice in five patients (18%) at three-month intervals.
All patients were reviewed clinically and radiologically every three months in the first year, every six months in the second year, and then annually. Mean follow-up was 34.7±6.87 months (range, 26–48). Assessment of radiological results was performed using the classification system described by Chang et al. . The final outcome was considered a failure if pathological fracture occurred during or after treatment or there was persistence, enlargement, or recurrence of the cyst after three ABMI. It was considered successful if the cyst was radiologically healed or healed with a defect and requiring no subsequent treatment.
All personal, clinical, and radiological data for each patient including gender, age, site of the cyst, presence of symptoms, occurrence of pathological fractures, cyst loculation, cyst size, cyst index, cortical thickness, activity of the cyst, number of injections received, time of healing, and the final outcome were collected. To study the relations between different variables and identify the significant factors that can affect the final result, the data collected were processed for statistical analysis using SPSS statistical software package, version 12 (SPSS Inc., Chicago, Illinois). For crude analysis of independent groups of data, chi-square test and Fisher’s exact test were used. P<0.05 was assumed to be significant and P<0.001 as highly significant. The significant variables in crude analysis were entered into a model of binary logistic regression analysis for multivariate statistical study, but they proved invalid.
The colour of the aspirated fluid and the result of histopathological examination confirmed the diagnosis of simple bone cyst in all cases of this study. No operative or postoperative complications related to the procedure occurred. All patients were fully active and pain free at the time of final follow-up.
Healing was achieved in 23 cysts (82%). The average time to healing was 6.13±1.576 months (range, 4–9). Complete disappearance of the cyst (Fig. 1) occurred in ten cases (36%). Healing with a remnant or a defect (Fig. 2) occurred in 13 cases (46%).
There were five failures according to our criteria. In three cases (two proximal humeri and one proximal fibula) the cysts persisted without further enlargement or pathological fracture (Fig. 3), and no active measure was carried out since there was no imminent risk of fracture. In the other two cases (one proximal humerus and one proximal femur), pathological fractures occurred during follow-up. The proximal humerus cyst showed signs of healing and became latent, but suddenly reactivated, enlarged, and pathological fracture followed at the distal end of the cyst (Fig. 4). The fracture was treated conservatively and the cyst became latent again. The proximal femoral cyst did not show any sign of healing and pathological fracture occurred causing coxa vara that was fixed internally with adolescent dynamic hip screws, curettage, and allograft (Fig. 5). The cyst healed with persistent coxa vara.
The gender of the patients had no significant relation with all clinical and radiological data or the final outcome. Patients older than ten years had significant predominance of SBC in the upper limb (P=0.043), and they had significant requirement for only single ABMI (P=0.019). Patients’ age, however, had no significant influence on treatment results (P=0.211).
Presence of SBCs in the upper limb (non weight-bearing bones) were significantly associated with cortical thinning <1 mm (P=0.011) and were more prone to pathological fractures (P=0.001). On the other hand, lower limb SBCs had a significant requirement of more than one ABMI (P=0.039). Uniloculated cysts were significantly symptomatic (P=0.029) and active (P=0.009). Both the site and loculation of the cysts did not affect the final results significantly (P=0.601 and 0.113, respectively).
There was highly significant correlation between cyst index and cortical thickening (P=0.0007). Furthermore, cyst index >5 and cortical thickness <1 mm were significantly prone to pathological fractures (P=0.002 and <0.001, respectively), and they had significant poor results after treatment with ABMI (P=0.031). In addition, cysts with cortical thickness <1 mm were significantly symptomatic (P=0.003) and active (P<0.001). Cyst size had no significant relation with any clinical or radiological data and it did not affect the final results (P=0.089).
Active cysts are significantly prone to pathological fractures (P=0.004) and to being symptomatic (P<0.001). Cyst activity, occurrence of fractures before treatment, and presence of symptoms had no significant effects on the number of injections needed (P=0.528, 0.783, and 0.612, respectively) or the final outcome (P=0.158, 0.357, and 0.473, respectively). Finally, there was no significant correlation between the number of ABMI needed and the final result (P=0.089).
Although it is accepted that the more radical the excision of the cysts, the lower is the rate of recurrence; SBC as a benign self-limiting lesion does not seem to justify radical surgery with high rate of associated complications including injury to the growth plate, donor site morbidity, and infection. Yet, simple curettage and grafting was not acceptable because of its high recurrence rate and requirement of long periods of immobilisation and hospitalisation [8, 12, 14, 16]. Moreover, SBCs are seen in children in whom it is difficult to obtain an adequate autograft [7, 17]. The technique of aspiration and injection of SBC has replaced aggressive bone grafting to limit surgical morbidity and improve rate of healing [3, 6, 11]. Scaglietti et al.  introduced methylprednisolone acetate in treatment of the simple bone cyst with initial excellent results. Later studies showed that steroid injection had a recurrence rate of 15–88% after three injections. A limb length discrepancy had also been reported in 5–15% of patients treated by steroid injection [2, 3, 17].
The percutaneous method is attractive and can be used with material such as bone marrow or bone substitutes to optimise results. Many conflicting results have been obtained in different studies regarding injection of osteoinductive material for treatment of SBC. This could be explained by the method and number of injections, the osteogenic potential of injected materials, or the multiple perforations done through the wall of the cyst before injection. The use of a single injection has been recommended by some authors [7, 11], while multiple injections was recommended by others [1, 13, 18]. Some authors injected bone marrow only [1, 6, 7, 12], others used bone substitutes, mainly demineralised bone matrix [8, 11], and others combined both [10, 15]. Multiple perforations of the cyst wall, breaking intralesional septa, and/or curetting the cyst membrane were performed by some authors [1, 8, 10, 12], while others never disturb the cyst wall nor its membrane [3, 6, 7, 18]. Although it was not our intention in this study to compare these different techniques, the authors feel that aspiration is sufficient to relieve pressure in the cyst and to evacuate cyst fluid, which has high bone resorbing activity. In addition, bone marrow in particular has osteogenic capacity that could promote cyst healing better than any other material . They also believe that there is no harm in multiple injections, which could be beneficial in many cases.
The first detailed study of ABMI in treating SBC was reported by Lokiec et al. . They reported that all patients with SBC were pain free within three weeks with consolidation on radiographs three months after single ABMI. In a subsequent study Lokiec and Wientroub reported that four of 25 patients (16%) required repeated injections of bone marrow . The results of our study suggest that percutaneous aspiration and ABMI is an effective treatment method of SBC and can satisfy our goal of relieving pain and preventing pathological fracture. Cyst healing was achieved in 82% of the cases. Prevention of pathological fractures was achieved in 93% of all cases and in 92% of patients that had previous fractures before treatment. Simply, the procedure places the appropriate cells in the right area and triggers early bone formation. Our study also showed that ABMI is almost atraumatic and obviates the need for operations to obtain autograft in most cases. It is safe with no operative or postoperative complications and could be performed on a single day case basis. Moreover, patients are allowed to undergo unrestricted activity immediately after the procedure.
Our results did not support the view that SBCs are more active in younger children and ABMI is more effective in older children  but agree with Lokiec et al.  that neither age nor the activity or site of the cyst affected the outcome. According to our results, younger children and cyst location in the lower extremities have tendency to require more than a single injection, which contradicts Delloye et al.  who claim that single ABMI is always able to achieve quiescence in an expanding cyst.
The only two variables in our study which had significant effect on the final outcome were cyst index and cortical thickening. The authors believe that these two indicators could be beneficial in deciding the level of activity of the patients after ABMI. Unfortunately, the number of patients did not allow multivariate statistical analysis that would be more appropriate to determine the effect of different variables on the outcome.
In conclusion, percutaneous aspiration and ABMI proved to be a reliable method of treating SBC that can produce complete healing in active and rather aggressive cysts. It appears safe, cheap, effective in most instances, and offers the merits of low morbidity making the technique preferable to other extensive interventions. Up to three injections may be necessary for some patients. Cyst index and cortical thickness are good indicators for cyst aggressiveness and good predictors for the treatment outcome. A study of more cases treated by this technique may provide reliable identification of the cysts that need special care during treatment.
Study conducted in King Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia.