Osteoporotic vertebral fracture misdiagnosed as “normal postoperative phenomenon” in post decompression surgery: a case report

Currently, percutaneous transforaminal endoscopic decompression (PTED) is being widely used to treat degenerative lumbar disorders due to less iatrogenic trauma and quick recovery [1, 2]. However, “quick recovery” does not immediately lead to the resolution of symptoms after PTED. On the basis of classic literature, experts’ opinions and surgeons’ experience, occasionally, in postoperative stage, some patients still endure discomfort, such as pain, stiffness, and motion limitation, usually recognized as residual symptoms or normal postoperative phenomena (NPF) [3, 4]. Generally, NPF occurs within 3 to 8 weeks postoperatively or later and is mostly treated with conservative treatment including non-steroidal anti-inflammatory drugs (NSAIDs) and physical factor treatments, such as in the forms of heat therapy and massage.

Parkinson’s disease (PD) is a neurodegenerative disorder that commonly occurs in the elderly, has a tendency to reduce bone mass, and is closely associated with osteoporotic vertebral fracture (OVF), which might be missed during clinical check-up or neglected as soft tissue impairment if in the absence of a clear trauma history [5]. This circumstance might be very common clinically but is frequently missed.

Here, we present a rare case of a patient with PD post-PTED for degenerative lumbar disc herniation (LDH) who developed OVF during the early recovery stages, which seldom occurs and is rarely reported in literature. Initially, the OVF was misdiagnosed as NPF following PTED. Once diagnosed correctly, a percutaneous vertebroplasty (PVP) alleviated the symptoms dramatically.

PTED for spinal disorders firstly was introduced in 1992 [7], the advantages of which include small incision, quick recovery, and equivalent or superior clinical outcomes compared with open surgery. With new emerging technologies, PTED variants have been widely developed [8], and are well accepted currently by surgeons and patients for their ease of use and simplicity [6 above]. Usually, a foramen approach is selected for L1-L5 LDH, and an interlaminar approach for L5/S1 LDH. However, fracture following PTED rarely happens and has been seldom been reported in the literature. The novelty and complexity of this rare case should attract attention.

Although PTED is advantageous in terms of its shorter recovery time and lower invasiveness in spinal surgery, it does not completely eliminate all symptoms once and for all. Some patients require a certain period of time for recovery. There are two hypotheses for the mechanism of recovery and its duration [4]: (1) pathoanatomy: for example, pain sensation (mainly conducted via C fibers lacking myelin sheaths) recovers sooner than numbness and paresthesia (both mainly from myelinated A-delta fibers), so a patient following PTED still feels pain in the recovery stage; (2) pathophysiology: due to mechanical compression or chemical irritation/inflammation, sensory discomfort might last long and be neither quick nor easy to eradicate. It takes time, on one hand, for demyelinated and/or dead nerve cells and fibers to regenerate and grow, and, on the other hand, for inflammatory irritation to cease. Therefore, this is a usual phenomenon, and a common consideration for the surgeons performing PTED is that the lower back pain and leg radiating pain sometimes would last or recur in this period of the recovery stage, for approximately 3 to 8 weeks. Symptoms such as pain, stiffness, swelling and other discomfort mostly would be NPF, and NSAIDs and physical factor therapy are of great help. However, 2 months later, the back pain persisted or even worsened, which may be persistent radicular pain due to incomplete decompression or OVF rather than NPF and post-operative dysesthesia. As a result, it has always confused us whether the pain reported by the patient in the recovery stage was NPF or a new extra injury. We consider the time period as the reason associated with this, for our experience more than trial evidence, within 2 months or so. In this case, an osteoporotic fracture was beyond our expectations, which explained the recurrent pain.

The disappearance of radiating pain to the leg [9] supported our preoperative assessment and PTED surgery plan in this case. However, we misunderstood the recurrence of her lower back pain as being caused by a lesion in the surgical site, or due to the regeneration of nerve fibers, neglecting it as NPF, finally delaying a correct diagnosis. If we carry on thinking of the recurring pain as NPF, the fracture would not heal and the patient would not be able to stand up or walk in the future. Moreover, conducting a telephone follow-up rather than performing a physical examination was another error on our part. This underscores the importance of conducting physical and imaging examinations in case traditional conservative treatment fails to improve symptoms following PTED.

The day after PTED, the patient reported decreased low back pain and improving strength, which probably encouraged the patient to do some daily activity, namely putting her at risk of idiopathic fracture. Cough or idiopathic osteoporosis may be another cause of fracture.

The main symptoms of PD are resting tremor, progressive rigidity, slow bradykinesia, and unstable posture. Unstable posture, clumsy movement, and poor coordination might predispose multiple falls. In our case, OVF at T11 after a fall accident 5 years ago might be an indication of the deterioration of PD. DBEI was another hint indicating PD severity. Patients in the progressive stage have reduced mobility, poor appetite, aging, which lead to bone mass reduction and osteoporosis.

Osteoporosis, along with the abovementioned factors, might increase risk of OVFs, compared to that in the general population [5]. Lee et al. [10] pointed out that age over 65, female gender and low income may be significant factors for PD, as well as Osteoporosis and OVF, which could have happened without any radicular symptoms or trauma history. Furthermore, PD patients are more likely to develop OVFs, especially at the advanced stage of the disease, without necessarily having a clear trauma history. Even a normal daily activity could be a cause of OVF.

Perhaps in the past, the patient had adapted to frequent multiple falls and various other kinds of small trauma happened constantly as normal daily incidents, such as cough or lifting a slight object. She could not recall what caused the L2-OVF, explaining the poor osteoporosis condition on BMD. Besides the multiple fractures and DXA results, L1-OVF after a severe cough indicated that the patient had developed severe osteoporosis. So these clues should have been given more attention. Aggressive medical treatment using teriparatide (Forteo), Calcitriol, or a combination with denosumab (Prolia), and Vitamine-D3-calcium supplements, trunk protection, and various types of anti-osteoporosis treatments was recommended when discharged. We also suggested the patient to not overdo activities after both PTED and PVP, and to protect herself with a brace to ensure soft tissue injury restoration, reduce inflammation and facilitate fracture union.

For complex cases with multiple OVFs, the computed tomography Hounsfield unit (CT HU) is of great value in evaluating the BMD [11]. MRI lipid suppressed and diffusion weighted imaging are gold standards in an OVF diagnosis; however, this patient underwent DBEI for PD. We consulted the engineer involved when the DBEI was first placed and were informed that the magnetic solenoid field would severely impair DBEI, potentially leading to a destructive thermal burn. Hence, MRI was not suitable for her. Therefore, bone scintigraphy and CT HU might be a supplementary plan of MRI in checking spinal fracture.

To conclude after all, we firstly report an unusual case of recurring pain following PTED misdiagnosed as NPF. In elderly patients with existing osteoporosis and especially PD, it would be best to first check for any fractures. Besides, a relapse of back pain of PD patients following PTED, with no improvement after conservative treatment, may indicate that OVF and should not been taken for granted as NPF. In such instances, a further physical examination and imaging check-up are warranted. Furthermore, bone scintigraphy is an alternative to examine fractures in these extremely complicated cases.