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© 1997 The Journal of Bone and Joint Surgery, Inc. Stress Fracture of the Tibia after Arthrodesis of the Ankle or the Hindfoot*  , DURHAM , AKRON, OHIO, DURHAM, NORTH CAROLINAInvestigation performed at Crystal Clinic, Akron, and Duke University Medical Center, Durham
We studied twelve patients who had a stress fracture of the tibia and one patient who had a stress fracture of the fibula after arthrodesis of the ankle or the foot. A second stress fracture subsequently developed in two patients. All but two patients were managed non-operatively, and the fractures healed uneventfully. One patient who was managed operatively had a below-the-knee amputation to treat a painful non-union of a tibial fracture, and the other had interlocking intramedullary nailing for a displaced fracture. All but one of the arthrodesis sites had fused before the stress fracture occurred. All of the stress fractures that occurred after arthrodesis of the ankle were in the middle and distal aspects or the distal aspect of the tibia, while those that occurred after triple arthrodesis were in the distal aspect of the fibula or the medial malleolus. Although six of the thirteen patients still had uncorrected alignment and deformity after the arthrodesis, optimum alignment after the arthrodesis did not preclude the occurrence of a stress fracture. We conclude that stress fracture must be considered in the differential diagnosis of pain months or even years after solid fusion at the site of an ankle or triple arthrodesis.
The goal of arthrodesis around the ankle or of triple (hindfoot) arthrodesis is a painless, plantigrade, and stable foot26. These procedures are most commonly indicated for disabling pain caused by post-traumatic osteoarthrosis, degenerative osteoarthrosis, rheumatoid arthritis, or avascular necrosis of the talus that has not responded to non-operative therapy7,15,20. Other indications include deformities due to tendon dysfunction16, poliomyelitis2,13, cerebral palsy10,11, Charcot-Marie-Tooth disease23, diabetic neuropathic osteoarthropathy3,19,25, infection, and failed total ankle arthroplasty27. These arthrodeses have been reported to restore a normal or nearly normal level of activity15,26. However, complications, such as infection, skin slough, nerve disruption or entrapment, non-union7, malalignment, degenerative changes in nearby joints, avascular necrosis of the talus, and limb-length discrepancy, have been reported1,14,20,26. Some of these complications may be asymptomatic, and some can be treated or alleviated with a subsequent pantalar, tibiotalocalcaneal, or tibiocalcaneal arthrodesis21. The purpose of this study was to describe what we believe to be a previously unreported, important complication: stress fracture of the tibia or the fibula after either ankle or triple arthrodesis.
One hundred and five arthrodeses of the ankle (including tibiocalcaneal and pantalar arthrodeses performed concurrently or as a staged procedure) and sixty-two triple arthrodeses were performed in 165 patients by the senior ones of us (R. H., I. J. A., and J. A. N.) between July 1980 and February 1994 at Duke University Medical Center, Durham, North Carolina, and Crystal Clinic, Akron, Ohio. All patients were followed by the operating surgeon postoperatively in a routine manner, which consisted of an examination and radiographic assessment at three, six, and twelve months. Once radiographic union of the arthrodesis site was confirmed, and after a minimum of twelve months, the patients were followed on an as-needed basis. A stress fracture was identified in thirteen patients at a mean of sixteen months (range, three to thirty-two months) after the arthrodesis (Table I). In two patients (Cases 3 and 6), the fracture was identified on routine follow-up radiographs at three and four months postoperatively. In the remaining eleven patients, the fracture was identified on the basis of symptoms—that is, pain with areas of tenderness in a previously asymptomatic extremity. A subsequent stress fracture occurred in two patients (Cases 1 and 6). Thus, fifteen stress fractures were identified in thirteen patients through a review of the charts and radiographs. There were six women and seven men who were a mean of fifty-two years old (range, thirty-four to seventy years old). The diagnosis before the arthrodesis included post-traumatic osteoarthrosis (four patients), degenerative osteoarthrosis (four patients), rheumatoid arthritis (four patients), and diabetic Charcot arthropathy (one patient) (Table I).
Operative Technique The desired position for arthrodesis of the ankle was 0 degrees of equinus, 0 to 5 degrees of valgus, and 5 to 10 degrees of external rotation. We planned subtalar arthrodeses so that the ankle would fuse in 5 degrees of valgus, although as much as 10 degrees of valgus has been reported to be well tolerated by most patients3. A below-the-knee cast was worn for six weeks postoperatively. The patient was allowed to walk with crutches either without bearing weight or with touch-down. This was followed by six weeks of weight-bearing in a below-the-knee walking cast or a removable below-the-knee brace with a rigid ankle joint. When necessary, the protective brace was worn for more than three months postoperatively, until radiographic union was complete.
Radiographic Follow-up Any patient who had pain and localized tenderness after radiographic evidence of osseous union at the site of the arthrodesis had radiographs made of the painful leg. If a stress fracture was identified, the patient was instructed to reduce his or her level of activity and to resume using crutches until the stress fracture was radiographically healed. If the cause of the pain and tenderness was not identified on the plain radiographs, a technetium bone scan was performed.
All but one of the treated joints were determined to be fused radiographically (eleven joints) or histologically (one joint) before the stress fracture occurred. The remaining joint was in a patient (Case 7) who had a hypertrophic non-union (determined radiographically and histologically) after arthrodesis of the ankle; the non-union was treated successfully after the stress fracture healed. A stress fracture developed in the tibia of twelve patients and in the fibula of one (Table I). The stress fractures that occurred after arthrodesis of the ankle were located in the middle and distal aspects or the distal aspect of the tibia, whereas those that occurred after triple arthrodesis were in the distal aspect of the fibula or the medial malleolus. Two patients had a subsequent stress fracture two years (Case 6) and twelve years (Case 1) after the first one. Three of the stress fractures were diagnosed on a bone scan, and twelve were detected on plain radiographs. Seven of the twelve fractures that were detected radiographically had only a localized area of cortical thickening involving both periosteal and endosteal reaction (Figs. 1-A and 1-B), and five had visible fracture lines.
Four of the thirteen patients had had subtalar arthrodesis before the arthrodesis of the ankle and one had subtalar arthrodesis after the arthrodesis of the ankle. One patient (Case 9) had had a series of operations that resulted in a tibiocalcaneal fusion (Figs. 2-A and 2-B), but lengthening of the proximal aspect of the tibia was performed with the Ilizarov technique because of one and one-half inches (3.8 centimeters) of shortening. Eleven months after the tibial lengthening, the patient had a stress fracture of the distal end of the tibia, unrelated to the area of lengthening or to the pin sites. A painful non-union developed, leading to a below-the-knee amputation. At the time of the amputation, the tibiocalcaneal fusion was determined to be solid. Histological examination of the amputation specimen showed non-union of the stress fracture without evidence of infection, and bacteriological examination revealed negative findings.
One patient (Case 10) began a rigorous self-initiated exercise program nineteen months after the arthrodesis of the ankle. By two years postoperatively, the patient walked four miles (approximately six and one-half kilometers) a day but began to have pain in the distal aspect of the tibia. He discontinued his walking program, but the pain became worse and was present even with normal walking. There was no pain at rest so the patient did not seek medical attention, and he did not use assistive devices to walk. Four weeks after the onset of the pain, the patient had severe pain in the tibia while working in his garden. A displaced fracture of the middle and distal thirds of the tibia was diagnosed one week later and was fixed with an intramedullary locking nail (Titanium Unreamed Nailing System, Synthes USA). The fracture healed uneventfully. A severe valgus deformity developed in one patient (Case 12), who had rheumatoid arthritis, because of osteonecrosis of the lateral side of the talar body after triple arthrodesis. As the lateral wall of the talus collapsed, the deltoid ligament elongated and the ankle joint shifted into valgus angulation (Fig. 3-A and 3-B). The osteonecrosis was confirmed histologically during a subsequent arthrodesis of the ankle, five months after the diagnosis of the stress fracture of the distal third of the fibula.
Six patients had a malposition of the site of the arthrodesis (Table I). The joint fused in excessive equinus in two patients, in undesirable valgus angulation in two, and in varus malalignment and excessive equinus in two. The remaining seven patients had what was considered to be optimum alignment of the site of the arthrodesis.
A stress fracture results from the mechanical fatigue of bone when it is subjected to repetitive loading, such as can occur in healthy athletes24 and in military recruits12,17,18. Osteoporosis, the chronic administration of steroids6,8,22, and changes in the mechanical axis of an extremity caused by a malaligned joint4 (such as may occur after arthrodesis) can also result in a stress fracture. Factors related to ankle arthrodesis or triple arthrodesis, or both, that may contribute to stress fractures in the lower extremity include increased bending forces transmitted to the distal aspect of the tibia by the longer lever arm of a more rigid foot in association with a concomitant decrease in the mechanical strength of the bone, which occurs as a result of the operation and immobilization14; loss of the normal shock-absorption mechanism provided by the joints of the ankle and the hindfoot with each heel-strike; osteopenia related to disuse or to an underlying disease process, such as rheumatoid arthritis; magnified forces and changes in the gait pattern related to malposition of the foot5; and over-all diminished bone density and strength in the distal aspect of the tibia as compared with those in the talus15. In the present series of fifteen stress fractures, only two were identified within the perioperative period, and these were detected only as radiographic changes. The remaining thirteen stress fractures were discovered because of pain in a previously asymptomatic extremity. Occasionally, the orthopaedic surgeon sees a patient who has new pain despite having had what appeared to be a successful arthrodesis. Although the more common complications after arthrodesis, such as non-union, infection, and malposition, can cause pain, such pain is usually well localized. Pain from a non-union is usually manifest at the site of the non-union and is generally associated with swelling and tenderness in this region. Pain associated with malposition is frequently along the lateral border of the foot, if the arthrodesis resulted in excessive varus, or along the medial arch of the foot, if the arthrodesis resulted in excessive valgus. Callosities may also develop on the foot in response to malposition. Pain associated with a stress fracture is in the area of the fracture, which in most of our patients was the distal aspect of the tibia at a site proximal to the arthrodesis. The physical findings of mild tenderness or swelling may be subtle, and, although a bone scan reliably identifies stress fractures, such a scan was necessary for only three of our patients. Radiographs should include an area that extends proximal to the region of the tenderness. As the stress fracture may not be identified radiographically because of the obliquity of the fracture line to the radiograph, a bone scan should be made for patients who have persistent pain. In general, a stress fracture is treated with reduction of the amount of repetitive trauma to the bone; operative treatment is rarely necessary. If, however, patients do not reduce their level of activity, a minor stress fracture can progress to a complete, displaced fracture, as was seen in one of our patients (Case 10). Although we have identified several causes of stress fracture, it might seem obvious that malunion at the site of an ankle or subtalar arthrodesis would lead to a stress fracture because of altered biomechanics. We do not believe that this simple hypothesis explains our data since only six of our thirteen patients had a malunion at the arthrodesis site; the remaining seven fractures were in patients who were thought to have optimum positioning after the arthrodesis. It could also be speculated that a patient who has had an arthrodesis of both the tibiotalar and the subtalar joints (pantalar arthrodesis) might also be at a higher risk for stress fracture because of a diminished shock-absorbing capacity. As only six patients in our series had either a staged or a simultaneous pantalar arthrodesis, it does not seem that incorporation of additional joints in the arthrodesis necessarily predisposes to stress fracture. Rather, it seems that diminished bone in the anterior aspect of the tibia, which occurs with aging14, and osteopenia related to disuse or to an underlying disease process such as rheumatoid arthritis, in combination with the increased forces that occur during gait after arthrodesis5, substantially contribute to the development of stress fractures. The site of the stress fracture seems to be associated with malposition or rheumatoid arthritis. Severe postoperative valgus deformities developed in two patients (Cases 11 and 12), both of whom had rheumatoid arthritis, and the stress fracture occurred in the medial malleolus and the distal aspect of the fibula, respectively. These were the only patients in our series in whom the stress fracture did not occur in the distal aspect of the tibia, and we believe that malpositioning and osteopenia led to the development of these stress fractures. Stress fractures must be considered in the differential diagnosis of pain in the leg subsequent to a successful arthrodesis of the ankle or the hindfoot. Most patients who have such pain can be managed non-operatively, with eventual healing. However, there is a potential for recurrent stress fractures years later as the underlying etiology is not fully understood.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
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