Osteopetrosis is a group of rare sclerosing bone dysplasias that share the common pathogenesis of diminished osteoclast-mediated skeletal résorption.1·2 First described as a distinct entity by Albers-Schoenberg in 1904,1' approximately 300 cases of osteopetrosis have since been reported in the medical literature.
Osteopetrosis traditionally has been classified into three broad types. The first is an autosomal-recessive type that is malignant in progression and frequently fatal during infancy or early childhood.2·4 Patients with this type of Osteopetrosis have numerous neurological symptoms (eg, blindness, facial palsy, and deafness) and hématologie abnormalities (eg, anemia and thrornbocytopenia). Patients most often die from complications secondary to either bleeding or infection in the first few decades of life. A gene for the autosomalrecessive type of Osteopetrosis has been localized to chromosome 1 Iql3.5
The second category encompasses an intermediate form of Osteopetrosis with an autosomal -recessi ve pattern of inheritance; it is characterized by a milder course.6-7 A subtype of this form is associated with renal tubular acidosis and cerebral calcification secondary to a deficiency of carbonic anhydrase.8
The third category is autosomal-dominant Osteopetrosis. Patients with autosomal-dominant Osteopetrosis typically demonstrate a normal life expectancy but may develop cranial nerve compression (with subsequent deafness, vision loss, or facial nerve palsy), mandibular osteomyelitis, and multiple orthopedic problems.1™4,9
Orthopedic concerns in osteopetrosis include periodic back pain, bone pain, and recurrent fractures, which may be easily induced by relatively low-energy mechanisms.10 Although a gene for autosomaldominant osteopetrosis has been localized to chromosome Ip21, targeted therapies are not yet available."
There are two subtypes of autosomaldominant osteopetrosis that can be differentiated by radiographie characteristics. In autosomal -dominant osteopetrosis type I1 radiographie sclerosis is most notable in the cranial vault, while autosomal -dominant osteopetrosis type II is characterized by skull base sclerosis, vertebral end-plate thickening (Rugger-jersey spine), and pelvic endobones.1,12,13
Fractures in autosomal-dominant osteopetrosis are common, and because the healing response is variable, fracture management must be tempered to address the technical challenges unique to this patient population. Although the process involves all osseous tissues, the authors' experience supports reports that the anatomic regions most prone to fracture in osteopetrotic patients include the inferior border of the femoral neck as well as the proximal femoral shaft.1,14
Figure 1: Case 1. Radiograph shows a subtrochanteric femoral fracture with pullout of the revision compression hip screw.
This article presents a case series of nine osteopetrotic femoral fractures in three patients with autosomal -dominant osteopetrosis. In addition, the literature is reviewed with a comparative discussion of the difficulties associated with osteopetrotic femoral fracture management. Finally, a technique for safe intramedullary fixation with ultimate healing of these fractures is described.
The following cases illustrate the difficulties commonly encountered in applying conventional techniques of internal fixation to treat osteopetrotic patients with fractures of the proximal femur. Management of these cases prompted the authors to develop an intramedullary approach best suited to address the aberrant biology, biomechanics, and material properties specific to osteopetrotic bone.
SM was diagnosed with osteopetrosis at a young age. Her mother had an established history of osteopetrosis, and her maternal grandfather and maternal uncle also were affected.
Other than a fracture of her right index finger as a child, she was without orthopedic difficulty until January 1985 when, at age I8, she sustained a left subtrochanteric femoral fracture secondary to a fall onto her left hip. She was treated with a Jewett nail, which required revision in 1 986 secondary to a broken side plate.
Six months later, she fell a pop in her left hip, and radiographs demonstrated pullout of all the implant screws. She underwent re-revision to a compression hip screw and was simultaneously implanted with an internal electrical stimulator.
In August 1 987, she was diagnosed with a deep infection of her left hip (culture positive for Pseudomonas and Staphylococcus epidermis). She was treated with antibiotics, debridemem with removal of the electrical stimulator, and delayed primary closure. She did well until January 1 989 when she developed fever and new fluctuance over her left hip. At this time, she was referred Io lhe authors for definitive evaluation and management of her chronically infected subtrochanteric nonunion (Figure 1 ).
Surgical management in January 1989 included removal of the compression hip screw and side plate, irrigation and aggressive debridement of all devitalized tissue, and implantation of a wound irrigation system. Antibiotics were withheld until multiple deep-tissue samples had been obtained for culture. The broken tips of several screws were encased in osteopetrotic bone and could not be retrieved without substantially increasing the risk of iatrogenic fracture.
Postoperatively, she remained afebrile and without local evidence of wound infection throughout her hospital stay. Her antibiotic regimen was tailored in response to the intraoperalive culture results.
On postoperative day four, the wound irrigation system was removed without difficulty. By postoperative day seven, she was ambulating with crutches, remaining nonweight bearing on her left lower extremity. She was discharged with a plan to complete a 6week course of intravenous antibiotics as an outpatient.
Two weeks after being discharged, she fell and sustained a midshaft right humérus fracture as well as a subtrochanteric fracture to her previously unaffected right femur. She underwent open reduction and internal fixation of the right subtrochanteric femoral fracture with a compression hip screw, and closed reduction and splinting of the right humérus fracture.
Her immediate postoperative course was uncomplicated, and she was discharged to complete her course of intravenous antibiotics, Her left hip wound continued to heal without evidence of residual infection.
Despite the presence of early, abundant callus at the right femoral fracture site, she developed pulloul and disruption of the screws securing the side plate. The implant ultimately was removed, and she has persistent nonunion of both sublrochanteric femoral fractures. She has refused further operative intervention. Her humérus fracture healed uneventfully.
CM. who is the mother of SM. was first evaluated and diagnosed with osteopetrosis in 1961 at age 13 when she presented with a left tibia fracture that was successfully managed with closed reduction and casting. She has a brother who has been diagnosed with osteopetrosis, and she was able to recall her father having had a history of multiple rib fractures as well as a humérus fracture.
Although she sustained multiple rib fractures and stress fractures in her feet over the ensuing years, she avoided significant injury until age 41 when she presented in August 1989 with a left subtrochanteric femoral fracture and a right femoral shaft fracture after falling while climbing steps. She underwent open reduction and bilateral femoral intramedullary rodding.
Figure 2; Case 2. Radiograph obtained after elective intramedullary rod removal demonstrates the absence of the intramedullary canal below the rod site on the left.
Al surgery, no intramedullary canal could be identified, and considerable effort was directed to reforming the canal prior to placement of the intramedullary rod. The bone was hard and had a chalk-like consistency. After several drill bits were broken during the procedure, it was determined that by advancing the drill a small distance and then cleaning and cooling the drill flutes, the canal could gradually be lengthened and enlarged to accommodate a standard intramedullary nail.
On pastoperative day eight, she reported a popping sensation in her left thigh. Subsequent radiographs demonstrated proximal migration of the left intramedullary rod. She underwent exchange rodding of the left femoral fracture with wiring of the proximal end of the rod to the greater trochanter. She progressed well with physical therapy and was discharged I O days after her second procedure. Weight bearing was restricted to walker-assisted transfers to a wheelchair.
She developed abundant fracture callus at the fracture sites, and weight bearing was advanced accordingly. In 2 months, she was ambulating with a walker. In October 1989 her progress was interrupted when she fell while climbing stairs and sustained a periprosthetic right femoral fracture at the distal tip of her right intrameduliary rod.
Initially, the patient refused surgery, and an attempt was made to achieve fracture union with bracing and strict nonweight bearing. Despite failing to progress to osseous union, she began ambulating with a walker 6 weeks after her injury. Six months following her right femur periprosthetic fracture, she developed pain at the nonunion site and agreed to exchange nailing of her right femur to address the unhealed fracture.
In April 1990, she underwent further distal reaming and exchange of the right intramedullary Kuntscher nail in an effort to address her right femoral nonunion. The left Kuntscher nail was concomitantly removed to minimize the risk of similar periprosthetic fracture.
Her postoperative course was uncomplicated, and she developed satisfactory union at the fracture site. One year later, she was ambulating, and the fracture had healed completely.
In November 1 990, the right intramedullary rod was removed (Figure 2). The decision to remove the intramedullary rods was based on the patient's history of previous periprosthetic fractures and the difficulty of fixing a fracture through a nail. The options were discussed at length with the patient, and she ultimately decided nail removal was in her best interest.
In January 1991, at age 42. she fell onto her left hip with subsequent left hip pain and inability to ambulate. A left subtrochanleric fracture near the site of her 1989 injury was identified. She underwent open reduction and internal fixation of her refracture. This was accomplished via placement of an intramedullary rod.
Her postoperative course was uneventful. By postoperative day seven, she was able to toe-touch weight bear with walker assistance and was discharged to home. She gradually progressed to full weight bearing and stable osseous union.
In June 1992, she lost her balance and fell again, with subsequent complaints of right leg pain. Radiographs demonstrated a subtrochanteric fracture of her right femur. She again underwent open reduction with subsequent placement of a Kuntscher nail. A 16ga Luque wire was passed through the loop in the proximal nail and configured as a tension band about the proximal fracture fragment. Her postoperative course was uncomplicated, and the fracture healed without event.
She was lost to follow-up until 1996 when she became bed-bound by an unrelated illness. Prior to the illness, she had been ambulating without pain or difficulty. She had a total of five separate femoral fractures, each of which healed with intramedullary fixation.
SH was first diagnosed with osteopetrosis in 1964 after sustaining a right olecranon fracture at age 1 6. He has no family members with osteopetrosis, nor can he recall a history of multiple fractures among any relative. He also has undergone close follow-up for chronic anemia related to his disease.
In 1978, he sustained a left clavicle fracture that healed without event. He was next seen in 1988 with a nondisplaced stress fracture of his left femoral neck. The fracture was managed nonoperatively with modified weight bearing and crutch ambulation. Healing was gradual but progressed to complete union.
In 1990, at age 42, the patient fell and sustained a left proximal femoral shaft fracture. He was referred to the authors for definitive evaluation and management. At that time, he underwent open reduction and internal fixation of the fracture with intramedullary placement of a Kunlscher nail across the left femoral fracture site. The technique was similar to that described in the second case.
Figure 3: Case 3. MRI demonstrates a right subtrochanteric fracture with areas of soft-tissue swelling (arrows) and bony irregularities suggestive of a new fracture (A). Radiograph obtained after intramedullary nailing shows bridging callus formation (B).
The fracture site was exposed laterally, and attention was directed to the ends of the fracture fragments. No i ntramedullary canal could be identified. Drill bits of serially increasing diameter then were used to recreate an intramedullary canal in both the proximal and distal fragments, The femur was resistant to drilling, and the drill bits required frequent cleaning of the chalk-like bone.
After the drilling was completed, serial reaming of the canal was undertaken with similar difficulty. Standard intramedullary cutting reamers were used for this part of the procedure.
A guide wire was passed proximally through the newly formed canal, then driven further proximally until it could be palpated beneath the skin. An incision was made over the wire and the wire was drawn within the proximal fragment. The femur was reduced, and the guide wire was advanced across the fracture site.
The position of the wire was confirmed fluoroscopically, and a Kuntscher nail was inserted into the newly formed canal and across the fracture site without difficulty. Biplanar image intensification was used throughout the procedure to ensure central placement of the implant.
The patient's postoperative hospital course was uncomplicated, and he progressed well following surgery. On postoperative day eight, he was ambulating with crutches and was toetouch weight bearing on his left leg and he was discharged. Progression to union was uneventful, and he was advanced to full weight bearing 10 weeks postoperatively.
In 1993, he developed dull, persistent pain over his right hip, and an insufficiency fracture of his right subtrochanteric region was identified. He was treated with a course of protected weight bearing with crutch ambulation. His pain improved markedly within the first weeks, and he showed progressive evidence of radiographic healing over the next several months.
In August 1997, he presented with posterior right hip pain. Plain radiographs showed nearly complete resolution of the insufficiency fracture, and he underwent steroid injection for suspected trochunteric bursitis.
He returned 2 months later with persistence of the right hip pain. Plain radiographs remained without changes to suggest an etiology for the pain. Magnetic resonance imaging of his right hip demonstrated edema and soft-tissue swelling indicative of a new fracture at the site of the prior insufficiency fracture (Figure 3A).
Elective internal fixation of the impending pathologic right femoral fracture was scheduled. Using a lateral approach to expose the proximal femur, the proximal femoral intramedullary canal was recreated by drilling with two sets of bits of serially increasing diameter. The bits required frequent cleaning of the pathologic bone, as well as frequent cooling secondary to the heat generated in the laborious drilling process.
A similar technique was used with two sets of serial reamers, which greatly facilitated progress. A proximally locked intramedullary nail was then placed across the fracture site under fluoroscopic guidance.
His postoperative course was uncomplicated, and the fracture gradually healed (Figure 3B). He was advanced from toe-touch ambulation to full weight bearing in December 1997.
Autosomal-dominant osteopetrosis is a rare condition, which is reflected by the relatively limited literature pertaining to fracture management in patients with osteopetrosis. The skeletal area most subject to fracture in patients with osteopetrosis is around the proximal femur.1·1'1 This is supported by the authors' experience, although other references suggest other areas of the skeleton are affected just as commonly.12-'5A search of the medical literature yielded only four cases of femoral fracture management in patients with autosomal-dominant osteopetrosis.
Breck et al14 reported an 11-year-old girl who underwent intramedullary fixation of a proximal right femoral fracture with a Hansen-Street nail, followed 2 years later by similar treatment of a left proximal femoral fracture. The authors noted the hard, dense quality of the bone made drilling difficult. They used an elongated electrician's drill and a broach, and exercised extreme care to avoid fracturing the brittle bone. No further technical detail was provided regarding how the intramedullary canal was reconstituted. Satisfactory union was achieved in both fractures.
In the present case series, two graduated sets of drills were used to accomplish intramedullary fixation. One drill was used to reconstitute the canal while the second drill was allowed to cool and the bit was cleared of bone that adhered to the flutes. After the canal was sufficiently enlarged, a similar technique of alternating intramedullary reamers was used for serial reaming of the canal. Reconstitution and centralization of the newly formed canal was guided by image intensification and guide wires during drilling.
In another case report published in 1980, Yang et al16 described successful rehabilitation of a left femoral subtrochanteric fracture in a 21 year-old woman with osteopetrosis. The fracture initially was treated with a Jewett nail, which failed secondary to the patient's "marble-like fragile bone." Three interfragmentary screws were placed, and the patient remained immobilized in a hip spica cast for 3 months, yet callus formation remained poor. Nine months postoperatively, satisfactory callus formation was noted; however, the prolonged immobilization resulted in contractures of the left hip, knee, and ankle.
The most common observation during rehabilitation in this case series also was a generally increased time to union. This becomes particularly important when managing osteopetrotic fractures with load-bearing implants.
In the case reported by Yang et al,16 the load-bearing device failure was attributed to the poor quality of the patient's osteopetrotic bone. In the present case series, both subtrochanteric fractures in the first case were managed with load-bearing implants (conventional nail-plate devices), and both went on to failure.
Ashby17 also reported treatment of two subtrochanteric fractures in a patient with osteopetrosis. One of the two fractures eventually required total hip arthroplasty after initial device failure.
If the results reported in the literature are broadly combined with the present case series, of the five subtrochanteric fractures treated with load-bearing implants, four went on to failure. Of the four subtrochanteric fractures treated with load-sharing intramedullary fixation, one went on to failure but eventually healed with exchange intramedullary nailing.
Although this represents a survey of a heterogeneous population managed by multiple surgeons using different implants, a compelling observation can be made. The failures, regardless of treatment approach, can best be attributed to two primary factors. The first is the increased mechanical demands placed on implants in a setting of prolonged time to union. While the mechanical demands are increased in managing all osteopetrotic femoral fractures, the demands are much greater on load-bearing implants.
The second factor regards the pathologic nature of the osteopetrotic bone itself. The hardness and fragility of the bone combined with a biomechanical inability to securely hold screws serves to further confound successful treatment.
In 1992, Ashby17 reported two cases of total hip arlhroplasty in osteopetrosis. In the first case, he described management of a left subtrochanteric femoral fracture that was incurred prior to the patient's left total hip procedure. He related numerous difficulties associated with management of the fracture with a Zickel nail. No intramedullary canal could be identified and the bone was described as extremely hard, which compounded difficulty with drilling and reaming.
In addition, the procedure was complicated by iatrogenic comminution of the distal fragment, which occurred while driving the intramedullary nail into the newly formed canal. This difficulty emphasizes the overall fragility of the bone in patients with osteopetrosis despite the bone's hardness and resistance to drilling and reaming. It also underscores the importance of a cautious approach to implant placement in this fracture-susceptible group.
Ashby's first patient was managed postoperatively in balanced suspension and later fitted with a hip orthosis. Postoperatively, transcutaneous direct electrical stimulation was delivered to the fracture site for 4 months. The patient's compliance with weight bearing restrictions was at issue, but the fracture proceeded to union before the patient refractured her proximal femur and required total arthroplasty.
Ashby's second case was a patient with osteopetrosis who sustained a left hip fracture that was successfully managed with a nail-plate device placed by another surgeon. Ashby described the patient's healing from this fracture as prolonged, but uneventful, a finding consistent with the trend noted on the present case series of fractures.
Similar management of a contralateral right hip fracture in Ashby's second case was complicated by a deep infection postoperatively. The patient was treated with delayed total hip arthroplasty following removal of the infected implant and management of the infected tissues.
In patients with osteopetrosis, the incidence of osteomyelitis is increased and has been attributed to the lack of marrow vascularity. A common focus of osteomyelitis is the mandible, although long bone infections may occur as well.4 Although there are no reports of an increased incidence of postoperative infection in patients with osteopetrosis, the technical and biologic demands of secondary orthopedic procedures, combined with the established propensity for osteomyelitis among these patients, warrants a concerted effort to minimize the risk of postoperative infection in this difficult group.
A final report addressing surgical management of femoral shaft fracture in osteopetrosis was published by BeIz et al18 in 1988. They used a uniplanar external fixation construct applied via six lateral femoral pins. The patient demonstrated complete osseous union of the fracture with removal of the external fixator at 13 weeks. Their case represents the only report of external fixation of an osteopetrotic fracture in the literature.
In the present case series, several potential pitfalls were encountered during the management of femoral fractures in osteopetrotic bone. The first difficulty encountered was opening the marrow canal, which often could not be identified intraoperatively. To overcome this difficulty, the canal was opened using a series of progressively larger drill bits.
Using considerable effort and great care, the drill was advanced a centimeter or less at a time, followed by cleaning and cooling of the drill flutes. Despite this caution, several drill bits broke during the procedure but were easily removed. A high-speed burr offers an alternative technique for creating the canal.
After the canal was opened, standard intramedullary cutting reamers were used to expand the canal to accommodate the intramedullary nail. This procedure presumably could be used in any patient without a patent marrow canal who requires intramedullary nailing. In the patients in the present case series, this procedure took an average of 2 to 4 hours longer than a standard intramedullary nailing, although no significant increase in blood loss was noted.
Osteopetrosis introduces technical limitations to the traditional treatment of femoral fracture management that may be minimized with specific preoperative planning. Patience and caution are required when drilling, reaming, or inserting implants in patients with osteopetrosis. This same caution must be exercised throughout the postoperative course when these patients are at greatest risk for device failure or further injury.
Further molecular work, such as the mapping of the recently localized AlbersSchoenberg gene." will result in new insights into the regulation of osteoclast function and the development of a genebased therapy for osteopetrosis. Meanwhile, recognizing and addressing the demands inherent in treating osteopetrotic femoral fractures will facilitate fracture union with a hopeful return to preinjury function.
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