Neuropathic pain in the S2 dermatome occurred in our patient 2 days after bone marrow harvesting. T1 and T2 weighted images of the pelvis magnetic resonance image (MRI) revealed patchy edematous change with enhancement in the sacrum, retrosacral muscles, subcutaneous layer, and around the S2 neural foramen, which appeared to be signs of inflammation [5, 6] (Fig. 2a, b). Nerve conduction study (NCS) was within normal limits performed 4 weeks after onset. However, in the electromyography (EMG), foot intrinsic muscles, gastrocnemius, soleus and lumbar paraspinalis muscle that were innervated by the S1-S2 nerve root showed muscle membrane instability indicating neural injury (Table 1). Based on the patient’s clinical presentation, image studies, and electrodiagnostic studies, we diagnosed the patient with S2 radiculopathy.
Considering the clinical progress and work up results, we suggest mechanical sacral root damage that occurred during puncture needle insertion as the cause of nerve irritation and inflammation. In addition, the possibility of nerve root inflammation by bone marrow leaking into the neural foramen when aspirating the bone marrow should also be considered [12, 13]. There was no suspicious evidence of hematoma around the peripheral nerve, especially the sciatic nerve, located in the pelvic area and the needle’s trajectory appeared too medial and deep on the MRI image. In physical examination, all dermatome sensory were intact. Sensory nerve action potentials showed normal findings, and electromyography (EMG) revealed abnormal spontaneous activity in S2 innervated muscles (foot intrinsic muscle). Therefore, pre-nerve root ganglionic injury is suspected. S2 radiculopathy, which is the damage of the nerve root level, is valid [14].
Our patient took pregabalin for pain control [11]. The patient was followed up for 1 year, and the visual analogue scale (VAS) score that was initially 7 points improved to 1 point. However, because nerve root injury can present with various prognoses depending on the severity, long term follow-up is required for comparison if a same case develops.
We conducted nerve conduction studies (NCS) and electromyography (EMG) for specific neurologic diagnosis. Electromyography (EMG) is especially a useful tests to measure the progression and prognosis of nerve injuries. It is important to measure spontaneous activity and motor unit action potential (MUAP) to characterize nerve injury lesions. Spontaneous activity is the electrical activity recorded by a needle electrode placed in a relaxed muscle. Motor unit action potential (MUAP) is the electrical activity typically recorded by a needle electrode placed in a voluntarily contracting muscle. According to neurophysiologic changes, lesions that are less than one week old are likely to be normal in electromyography (EMG). Therefore, it is recommended to perform the study 3 to 4 weeks after the nerve injury [10]. Abnormal spontaneous activity was presented after more than 3 weeks and may persist up to 3 months. If the lesion is no longer worsening, abnormal spontaneous activity would show low amplitude of less than 100 μV, or abnormal spontaneous activity will not be present after 3 months, Motor unit action potential of the polyphasic pattern would be observed [14]. It is valuable to consider additional neurophysiologic evaluation as a useful study when nerve injury is suspected.
In our case, electromyography (EMG) results performed at 1 month and 3 months after neurological symptoms showed the amplitude of abnormal spontaneous activities of about 100 μV, 300 μV each (Fig. 3). After 6 months, abnormal spontaneous activity was not observed and polyphasic motor unit action potentials (MUAP) were observed (Fig. 4). These findings indicate that the nerve injury is in a recovery state that is no longer worsening and that the patient’s symptoms have improved.
A few studies present sacral nerve root injury. Common causes of sacral root injury are Tarlov cyst [7] and disc rupture [8]. One study reported as iatrogenic injury described a case of sacral nerve root injury after trans-sacral epiduroscopic laser decompression [9]. Our case is a unique sacral nerve root injury case after bone marrow harvesting which has not been previously reported.
Bone marrow harvesting was performed on the patient in the prone position using posterior superior iliac spine (PSIS) puncture [2]. Bone marrow harvesting is generally considered a relatively safe procedure with rare complications, but complications such as aspiration site pain, anemia, vasovagal reaction, and infection have been reported [1, 3]. This case reveals sacral nerve root injury (S2 radiculopathy) after bone marrow harvesting, which to our knowledge, has not yet been reported.
The donor’s safety is most important when conducting bone marrow harvesting. Puncture site positioning and needle manipulation are crucial to prevent side effects such as our case report. The posterior superior iliac spine (PSIS) is the most common collection area because of its prominence, easy access, and thick bone wall. Palpate the posterior superior iliac spine (PSIS) and the prominence of the posterior iliac crest. Mark the locations by drawing an outline using a surgical marking pen. Outline the lateral edge of the lumbar sacral spine as well. This landmark identification procedure is generally effective.
To avoid nerve and vessel injury, aim the needle at about 30° lateral from the para-sagittal plane and 20–25° inferior from the transverse plane when inserting the puncture needle. The exact depth of optimal advancement varies somewhat, but generally, the needle should not be advanced more than 6 cm. If it is unstable, remove the needle and reinsert [15,16,17]. In our case, puncture needle was inserted too medial from the para-sagittal plane and advanced too much.
Ultrasonography and fluoroscopy imaging are widely used for safe and accurate procedures. Several studies reported that procedures using ultrasonography and fluoroscopy reduced the risk of procedure failure and trauma [18,19,20]. However, there was no report that bone marrow harvesting was performed using ultrasonography or fluoroscopy. Because bone marrow harvesting is conducted as a blind procedure, It is important to consider how to perform it more accurately and safely if there is a possibility of injury to the donor as in this case. Therefore, we thought it may be helpful to use real-time images with either ultrasonography or fluoroscopy during bone marrow harvesting for the safety of the donor.
Bone marrow harvesting is considered to be a safe procedure with rare complications. However, rare complications of nerve damage may occur as in this case. Clinicians should consider the possibility of sacral nerve root injury and perform bone marrow harvesting with accurate anatomy knowledge and carefulness. Using real-time imaging methods such as ultrasonography or fluoroscopy during the procedure is considered to be a good method for safety.
