Although spine surgery has become much more reliable in the last 20 years or so, some patients will still have leg pain after a lumbar decompression surgery for spinal stenosis or a disc herniation.
Sometimes this is a temporary condition as the nerve root or roots take time to heal. This can take days to weeks. If the pain is still there after 3 months, it is unlikely to improve on its own.
Below are a few reason why leg pain may persist after surgery.
The #1 cause of postoperative leg pain is that the preoperative diagnosis was incorrect. This has become less likely as our preoperative imaging methods (e.g. MRI scans) have improved. But that being said, diagnosing the source of a patient's pain remains and inexact science.
Dual problems causing pain
It is also possible that two different lesions are causing pain. For example, someone may have a herniated disc at the L4-L5 level with an L5 radiculopathy causing piriformis syndrome.
Decompressing the nerve may help resolve some of the patient’s pain, but the piriformis muscle also needs rehabilitation (which is often difficult).
Foraminal and central stenosis
Another common scenario is a patient who has both foraminal stenosis (narrowing of the disc space) and central stenosis. The central stenosis can be relieved with a decompression, but the decompression may not suffice for the foraminal stenosis. In these cases, a lumbar fusion may be necessary to address the foraminal stenosis.
Secondary disc herniation
After a microdiscectomy for a disc herniation, another disc may rupture and impinge again on the nerve root. This can happen anywhere from days to years after the surgery. The hallmark of this is pain that is gone initially after surgery, but then spontaneously returns. Postoperative inflammation of the nerve root can mimic a recurrent disc--with a return of pain 2-7 days after surgery--but will usually subside with time and rehabilitation.
Nerve damage during surgery
A much less common cause of leg pain after surgery is nerve damage at the time of surgery. Nerve roots are generally tough and difficult to damage with a common surgical procedure.
A really rare cause of postoperative leg pain, if it ever happens, is scar tissue. Scar tissue forms after all surgeries and it does not damage surrounding tissues. It can limit the mobility of a nerve root, but physical therapy can usually help in the early postoperative period.
Scar tissue only grows for 6-12 weeks and then gets softer with time. It is more commonly diagnosed as a cause of pain when there is no other obvious cause of postoperative pain, but the reality is that the patient’s pain is unlikely to be coming from scar tissue.
For patients who have continued leg pain after spinal decompression surgery, alternative causes of the pain should be sought. It is often a frustrating situation, but patience and continued effort will often help alleviate the pain.