Orthopedics - Oleksa A.P. 2006

Metabolic Bone Diseases
Bone Cysts

Since Jaffei and Lichtenstein first described bone cysts in 1942, extensive literature has emerged regarding their Etiology, Diagnosis, and Treatment (Głowacki M., 1996). Unicameral bone cysts are most commonly diagnosed in children and adolescents (aged 2 to 16 years), predominantly (82%) in boys (Dimeter A. et al., 1974; Gakku L.N., 1997; Bilinski P.J. et al., 1998). Both uni- and multilocular cysts typically occur in the metaphysis of long tubular bones, most frequently in the humerus and Femur. Aneurysmal bone cysts generally localize to the metaphysis, abutting the physis (growth plate), but never extend into the epiphysis. Solitary unicameral cysts are more often situated in the diaphysis of tubular bones (Fig. 104). Pathogenetically, bone cysts belong to the group of dystrophic skeletal disorders (Berezhny A.P., Burkova L.M., 1990) and are typically caused by local circulatory disturbances in the Bone tissue (Sivak M.F., 1990). The Location of a cyst near the growth Cartilage—particularly in the proximal humerus, where longitudinal bone growth is most active—contributes to an aggressive clinical course (expansive growth, according to Ekkernkamp et al., 1990). Consequently, postoperative recurrences in this region are three times more frequent than in the diaphyseal area (Capanna R. et al., 1982). Elevated METABOLISM in the metaphysis may account for this phenomenon, leading to the clinical distinction between "active" and "passive" cysts.

The metabolic profile of cystic fluid is key to understanding the mechanisms behind the origin and development of these cavities (Toporova S.M. et al., 1990). The COMPOSITION OF THE cystic fluid reflects the metabolic processes occurring within the cyst wall and influences both cavity formation and vascular bed function. Using the same authors, the presence of B-galactosidase, B-N-acetylgalactosaminidase, B-N-acetylglucosaminidase, B-glucuronidase, acid phosphatase, Collagen peptidases, and cathepsin D has been established in the fluid of solitary bone cysts. In some cases, lysosomal enzyme levels in the cystic fluid were found to be higher than those in Blood serum.

The accumulation of fluid content is primarily driven by the activation of lysosomal Hydrolases within the cyst wall. This results in the degradation of the bone matrix, collagen, and other Proteins, which clinically manifests as a significant increase in the levels of hydroxyproline and hydroxyproline-containing Peptides, alongside a decrease in collagen content and enhanced Fibrinolysis.

A marked increase in the level of acid phosphatase—an established marker of tissue destruction—has been clearly demonstrated (Berezhny A.P., Burkova L.M., 1990). Because peptides and the breakdown products of certain colloids are more osmotically active than their parent compounds, theoretical calculations indicate the generation of a significant osmotic gradient directed toward the interior of the cyst cavity.

The rigidity of the bone cavity and its functional autonomy from the body drive the accumulation of cystic fluid and elevate intra-cystic hydrostatic pressure, which either maintains the cyst's volume or promotes its progression.

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Fig. 104. Unicameral cyst of the humeral diaphysis.

Clinical Features. Clinically, a bone cyst may remain entirely asymptomatic and is sometimes discovered only following a pathological fracture. Occasionally, elevated intra-cystic pressure causes patients to experience mild, dull, localized aching or a sensation of fullness.

In all cases, the diagnosis of a bone cyst is based on radiographic evaluation. Depending on the duration and activity of the pathological process, radiographs reveal a centrally located zone of bone destruction presenting as a well-defined radiolucency. In large cysts, the cortical layer is thinned without evidence of periosteal reaction.

Aspiration of a solitary cyst yields a straw-colored fluid, whereas an aneurysmal cyst yields a brownish-red fluid. Cytological examination in such cases reveals blood cellular elements and occasionally isolated fibroblasts.

Treatment. We strongly oppose a watchful waiting approach for "passive" cysts. Any diagnosed cyst, regardless of its location and size, must be treated immediately, as cysts invariably tend to progress over time, increasing in size and occasionally destroying extensive segments of bone. Lysosomal bone destruction should be regarded as a critical pathogenetic factor in the formation and clinical course of bone cysts, guiding the choice between conservative and surgical management.

Due to the variable clinical course of the pathological process, selecting the optimal treatment method has sparked controversy regarding the required degree of radical intervention (Cohen J., 1977; Harms J., Groh P., 1978). In recent years, the medical literature has advocated moving away from radical bone resection in favor of less traumatic Procedures, supported by a better understanding of disease Pathogenesis. Consequently, treatment is primarily based on puncture techniques aimed at: 1) decompression; 2) radical debridement/sanation; 3) protease inactivation; 4) fibrinolysis inhibition; 5) anti-collagenase activity; and 6) immobilization when necessary.

Needle aspiration of the cyst contents followed by irrigation of the cavity with saline dramatically reduces intra-cystic pressure and eliminates a high concentration of fibrinolytic Enzymes. Punctures are performed under anesthesia every 1.5 to 3 months, depending on The activity of the pathological process.

To drill through the cortical bone layer, trephine needles of various diameters featuring cutting Teeth at the tip are utilized. By manually rotating the needle with a stylet via a threaded handle, the surgeon drills through the bone and enters the cyst cavity. The stylet is then removed, and the needle is attached to a specialized syringe. The cyst contents must be submitted for cytological analysis. Following evacuation and irrigation of the cyst until the fluid runs clear, various targeted therapeutic agents are injected into the cavity. At the Kiev Research Institute of Orthopedics, synthetic fibrinolysis inhibitors were administered—namely, epsilon-aminocaproic acid and amben in amounts equal to 20–50% of the volume of the evacuated fluid (Sivak M.F., 1990). At the Moscow Central Institute of Traumatology and Orthopedics (CITO), contrykal was also added, while Kenalog-40 (a steroid anti-collagenase agent) was used during the recovery phase (Berezhny A.P., Burkova A.M., 1990). The administration of methylprednisolone (in doses appropriate for the child's age) has also proven effective, as confirmed by our clinical data following The Use of Medrol. To improve the efficacy of cyst irrigation, Ivchenko V., Fadeyev G., and Shvets O. (1993) perform similar drilling and dual-needle flushing, followed by the administration of a 2.5–10% solution of epsilon-aminocaproic acid and subsequent Filling of the cavity with a mixture of decalcified bone matrix and KL-3 polyurethane glue.

Following aspiration, some orthopedic surgeons also inject autogenous Bone Marrow into the cyst cavity (Companacci M., 1996; Faflic J. et al., 1986; Harms J., Groh R.P., 1978; Kaclin A., 1996). As a rule, successful outcomes with the puncture method are achieved after three to four procedures.

Berezhny A.P. and Burkova L.M. evaluated the efficacy of this method using Neer's Classification (Neer et al., 1998). Recovery was achieved in 90% of patients: complete recovery (disappearance of the cyst with cavity filling by bone tissue and restoration of bone trabeculae) in 73.4%, and incomplete recovery (disappearance of the cyst with residual cavities but fully remodeled Bone Structure) in 16.6%. Treatment was ineffective in 10% of patients.

When the puncture method fails, or in cases of large bone cysts (exceeding 10 cm) and recurrent cysts, surgical intervention is indicated, as championed by Ivchenko V. Curettage of the cyst using a Volkmann spoon combined with bone grafting (Dega W., 1931; Głowacki M. et al., 1998)—and nowadays porous ceramic grafts (Dubok V.A., Ulyanich N.V., Krysyuk A.P., 1998)—remains a standard and relevant Procedure. The surgery is performed under anesthesia, sometimes using a tourniquet. An optimally planned anatomical approach to the cyst is executed. The cortical bone is trephined subperiosteally, ensuring that the bone window is large enough to allow radical debridement of the cyst walls down to healthy bone tissue. Afterward, the cavity is vigorously irrigated and packed with a bone graft of appropriate size. The wound is closed, and a plaster cast is applied to the extremity if necessary.

Tissues removed during surgery are routinely subjected to histological examination to confirm the clinical and Radiological Diagnosis. The choice of graft depends on the surgeon's capabilities and clinical conditions. Small bone defects can be filled with autogenous bone grafts, which remain the gold standard due to their tissue histocompatibility and the presence of viable Cells, yielding the best surgical outcomes.

When a bone defect is too large to be filled with an autograft—particularly in children—preserved (e.g., paraffin-treated), frozen, or even lyophilized allografts must be used, ideally combined with an autograft.

The use of allografts, especially lyophilized bone, requires prolonged treatment periods because their remodeling process is slow and protracted, occasionally accompanied by foci of resorption and an increased risk of cyst recurrence, as noted by Głowacki and Neer (Głowacki M., 1996; Neer Ch., Francis C.K., Marcove O.R., 1996).

Allograft resorption is clinically silent and detectable only radiographically; however, it must be differentiated from a cyst recurrence. If resorptive changes occur, secondary surgical interventions are unnecessary and, as Neer et al. (1996) point out, ultimately still lead to the patient's complete recovery. Over the past 15 years, due to suboptimal results of bone alloplasty and xenoplasty—stemming from antigenic activity, resorption, and biomechanical insufficiency—the Kharkov Research Institute of Orthopedics (Korzh O.O.) has introduced porous ceramic grafts for bone defect filling.

In global surgical practice, as noted by Dubok V.A., Ulyanych N.V., Krysyuk A.P., and colleagues (1998), hydroxyapatite implants are employed because they "stimulate osteogenesis, restoring healthy bone tissue within the bone cavity." Hydroxyapatite is immunocompatible, capable of stimulating osteogenesis and "bonding" with bone, thereby serving as a structural scaffold for Bone Formation and integrating into native bone tissue. It is utilized in the form of powder, porous and dense granules, and porous or dense ceramics, and is sterilized in a dry-heat oven.

Hydroxyapatite and its composites are manufactured worldwide and produced in various forms in Ukraine under the trade name "Kergap," which meets international standards and is approved for use by the Ministry of Health of Ukraine (Order No. 269 dated August 28, 1996). It is now widely used in both children and adults whenever bone defect reconstruction is required. According to Krysyuk A.P., successful grafting was achieved in all cases (56 children), with zero instances of implant rejection or allergic reactions; however, The rate of remodeling varies depending on the location and size of the defect being filled. Replacement of the implant with native bone tissue occurs within 3 to 12 months. Clinical observations confirm that Kergap holds great promise for bone defect reconstruction. The dynamics of the reparative process are monitored radiographically at 3, 6, 12, and 18 months postoperatively.

According to Neer and Campanacci, the factors contributing to complete recovery—namely, the eradication of the cyst—depend on the following conditions during curettage: 1) a small cyst size; 2) packing with a minimal volume of graft material; and 3) the use of a cancellous bone graft, which facilitates superior vascular ingrowth and remodeling (Neer Ch. et al., 1966).

Głowacki (Głowacki M. et al., 1998) emphasizes that the absence of internal septa within the cyst cavity is crucial for graft incorporation and remodeling. Due to complete graft consolidation, the best recovery outcomes are observed in patients with small, unicameral cysts located in the metaepiphyseal region of long tubular bones, as well as in the talus and calcaneus, where intra-cystic septa are absent and the graft sits in tight contact with the cavity walls.

The patient's AGE AND SEX do not significantly affect graft remodeling. However, a slowdown in reparative processes is observed after the ecochleation of cysts adjacent to the epiphyseal cartilage, which can occasionally lead to incomplete recovery.

Today, the risk of cyst recurrence is widely acknowledged by most orthopedists. Recurrences occur most frequently following the use of lyophilized grafts and in children operated on under the age of 10.

Among surgical interventions, the best outcomes in bone cyst treatment are achieved through radical bone resection within healthy tissue margins. This procedure is indicated for large cysts (exceeding 10 cm in length) with severely thinned cortical layers, or when neurological and vascular complications are present. Due to the traumatic nature of such surgeries, they are typically performed in adolescents using internal metal osteosynthesis and auto-allografting. Postoperative immobilization with a plaster cast is applied until the grafts incorporate. The main drawback of this approach is the necessity for prolonged limb immobilization, which can cause joint contractures and Muscle atrophy.

It should be emphasized that early detection and treatment of a cyst prevent pathological bone fractures. If a patient presents with an established pathological fracture, treatment strategy must be determined on a case-by-case basis, depending on the patient's age, as well as the location and extent of bone destruction.

For small cysts and uncomplicated fractures (absent neurological and vascular disorders), conservative management is preferred, particularly in young children. Bone fragments are reduced and managed according to standard traumatological principles. Two to three weeks later, following The formation of a primary periosteal callus, the cyst is punctured under fluoroscopic guidance (image intensifier), although aspirating its contents with a syringe is rarely successful, and one of the aforementioned medications is injected. The progression of tissue repair and fracture healing is monitored radiographically. In some instances, bone fragments have been observed to unite following a pathological fracture even without the injection of medication into the cyst cavity.

According to Springfield and Brower (1984), Radiation therapy following conservative treatment and intramedullary osteosynthesis reduces recurrence rates and promotes the healing of pathological fractures.

In cases of significant diaphyseal bone destruction (most commonly in the humerus), surgical management of the pathological fracture is the method of choice. Bone resection is performed within healthy tissue limits, the fragments are stabilized with an intramedullary driven rod, and the bone defect around the rod is packed with auto-allografts using Volkov's technique, often referred to as the "bundle of brushwood" principle. The limb is immobilized in a plaster cast for 10–12 days. Following suture removal and wound healing, the subsequent method of limb segment immobilization is determined based on the location and size of the grafted bone defect, as well as the patient's age. Because reparative processes occur more vigorously in the metaphyseal region, cast immobilization is prolonged accordingly.

Following diaphyseal resections, external fixation devices are utilized whenever possible to prevent persistent joint contractures. When external fixation is unfeasible, treatment is continued with a plaster cast until the grafts become fully incorporated and remodeled.