Postoperative Course
The patient’s final pathology confirmed a chordoma with negative margins. Postoperatively, the rectus flap became ischemic and a wound infection developed. It was irrigated, débrided, and treated with vacuum-assisted closure (VAC), in addition to perioperative antibiotic administration. An abdominal computed tomography (CT) scan did not show any fistula, and her wound remained healthy, pink, and viable as her VAC was changed every 3 days. Because the patient’s nutritional status was compromised, she started nutritional supplements in addition to a regular diet. Physical therapy was prescribed and the patient began bladder training with self-catheterization after a failed voiding trial attempt. After 2 months of convalescence, the patient had mobilized well and had progressed to walking without an ambulatory aide.
At her third postoperative month, the patient noted new onset of extreme pain in the groin and left thigh regions. The patient was examined and appeared to have a stable neurological exam. She had reproducible pain with a FABER (Flexion, Abduction, External Rotation, and Extension) test. MRI showed increased signal on short tau inversion recovery (STIR) sequences and T2-weighted images that was consistent with a left sacral ala stress fracture with a vertically oriented fracture line (Figures 2A, 2B). The patient was asked to begin utilizing a walker for ambulatory assistance, but her weight-bearing status was not changed. Over the course of 3 months, the patient noted a resolution of her pain. All postoperative MRI images confirmed the patient to be disease-free; and in addition, all of her follow-up radiographs showed a stable pelvic ring (Figures 3A, 3B). At her 2-year follow-up, the patient remained disease- and pain-free.
Discussion
Full discussions of the mechanical considerations of a partial sacrectomy have been described previously5-8; however, surgeons typically consider the need for lumbar-pelvic stabilization when the surgical resection requires a violation of the S1 body. Approximately two-thirds of sacral tumors occur at or below the level of the S2 body.8 These lesions of the caudal sacrum can sometimes be effectively resected with transverse partial sacrectomy. Great care is taken to resect only the portion of the sacrum necessary for local disease control, sparing as much of the sacroiliac joint and as many of the lumbosacral nerve roots as possible.
Under normal conditions, the sacroiliac articulation is stabilized by both its geometric interface and its extraordinarily strong ligaments. This spatial arrangement conveys stability primarily against caudal migration of the sacrum. The sacroiliac, sacrotuberous, sacrospinous, and lumbosacral ligaments, which are among the strongest ligaments in the body, primarily act to provide stability to the pelvic ring by preventing diastasis. The combination of these factors renders the spinopelvic segment especially stable. Previously, 2 biomechanical studies that specifically looked at extreme loading patterns to better understand the need for lumbar-pelvic instrumentation predicted a fracture pattern when there was an inability of the base of the sacral ala to resist shear.8,9 This is precisely where our patient’s insufficiency fracture occurred.
To our knowledge, this is the first reported in vivo evidence of this fracture pattern. While this patient’s potential history of osteoporosis may have elevated or contributed to her risk for fracture, her preoperative bone densitometry, with T scores of -1.0 on the left and right femur necks and 0.8 on her L1-L4 anteroposterior spine, would argue against this risk factor. None of these values represent a truly osteoporotic patient. It would appear that our patient sustained the fracture pattern predicted by Hugate and colleagues.8
The edema seen on the MRI most likely represents a fracture; however, sacroiliitis and infection are also potential diagnoses. Because there was no tumor in this region on the preoperative scans, we thought that a residual tumor was unlikely. The signal changes seen on T2 MRI sequences represent edema. The use of a bone scan that detects healing bone may have been a useful additional study to confirm this fracture as opposed to sacroiliitis. A CT scan would have been a potentially useful study to provide detail of fracture displacement and the overall fracture pattern. Standing plain radiographs are best for viewing fracture displacement with weight-bearing.
Surgeons contemplating performing partial sacrectomies should bear in mind that, even with preservation of the S1 body, a potential for fracture exists as evidenced by our patient. In our opinion, this patient did not require instrumentation but a more gradual rehabilitation program.