Clinical Assessment: 55M with Implanted Femoral Rod + New Neurological Symptoms

1. Bilateral feet numbness and burning (peripheral/systemic cause more likely)
2. Left leg pain and knee pain (could be local/mechanical or radicular)

Most Likely Diagnoses (Differential)

1. Peripheral Polyneuropathy (MOST LIKELY for the bilateral burning/numbness in feet)

• Diabetic peripheral neuropathy - by far the most common cause. Presents exactly as described: burning dysesthesias and pain beginning in the feet, spreading proximally, in a stocking distribution. A 55-year-old male is in the peak incidence group. Check fasting glucose and HbA1c.
• Alcoholic neuropathy - axonal sensorimotor neuropathy causing burning and paresthesias of the feet with distal numbness.
• Cryptogenic (idiopathic) sensory peripheral neuropathy (CSPN) - onset predominantly in the 6th-7th decade; patients complain of distal numbness, tingling, and burning pain beginning in the feet. Diagnosis of exclusion.
• Nutritional/Vitamin B12 deficiency neuropathy
• Hypothyroid neuropathy

Harrison's Principles of Internal Medicine 22E: "The onset of CSPN is predominantly in the sixth and seventh decades. Patients complain of distal numbness, tingling, and often burning pain that invariably begins in the feet."

2. Lumbar Spinal Stenosis / Radiculopathy (for the left leg pain)

• Lumbar stenosis causes pseudoclaudication - numbness, weakness, or pain in one or both lower limbs when standing or walking, relieved by sitting or bending forward.
• It can affect a single limb (left leg), mimicking a vascular or orthopedic complaint.
• A concomitant peripheral neuropathy (as above) can coexist and worsen symptoms.
• MRI lumbar spine is the diagnostic test of choice.

Goldman-Cecil Medicine: "Lumbar spinal stenosis causes a syndrome of pseudoclaudication...Patients report lower limb numbness, weakness, or pain, with or without back pain, when standing or walking."

3. Hardware/Implant-Related Causes (directly tied to the rod)

• Implant failure or loosening - after 8 years, screws (interlocking bolts) can break or the nail can migrate, causing mechanical pain at the fracture site or knee.
• Distal nail irritation at the knee - a femoral IM nail tip that sits near the distal femur can cause knee pain from bursitis, synovitis, or mechanical irritation, especially if the nail end is prominent. This is a recognized late complication.
• Malunion/malalignment - even subtle varus or valgus malalignment from the original femur fracture can cause abnormal loading of the knee, leading to secondary knee osteoarthritis and pain over years.
• Implant-site infection (late periprosthetic infection) - can present with pain, warmth, and swelling; less likely without fever/constitutional symptoms, but should be on the radar.
• Stress fracture around the nail (rare) - can occur with nail loosening.

S Das Manual on Clinical Surgery: Late nerve injury is a recognized late complication of fracture - a nerve can be involved in callus formation and sustain gradual injury by bony irregularity.

4. Knee Osteoarthritis (for the knee pain)

• Post-traumatic osteoarthritis of the knee is common after femur fractures due to altered limb mechanics, muscle weakness, and prolonged immobility during recovery.
• Primary OA is also very common at this age in males.
• A prominent distal nail tip at the supracondylar/intercondylar region can contribute to distal femoral or knee joint irritation.

5. Vascular Claudication (must exclude)

• Peripheral arterial disease (PAD) can cause left leg pain on exertion with some sensory symptoms.
• A 55-year-old male is at risk; ankle-brachial index (ABI) should be checked.
• Unlike spinal stenosis, PAD pain does not improve with trunk flexion.

6. Sciatic or Common Peroneal Nerve Entrapment

• The sciatic nerve runs in proximity to the subtrochanteric femur.
• After a fracture + IM nailing, late nerve entrapment in scar/callus is possible, though uncommon.
• The common peroneal nerve is the most commonly injured nerve around the knee and can cause foot drop and sensory loss in the dorsum of the foot.

Summary Table

Recommended Workup

1. Plain X-rays - left femur (full length) and left knee (weight-bearing) to assess hardware integrity, alignment, and OA changes
2. MRI lumbar spine - to evaluate for stenosis, disc prolapse, radiculopathy
3. NCS/EMG - nerve conduction studies to characterize any neuropathy (length-dependent vs. focal)
4. Metabolic screen - fasting glucose, HbA1c, B12, folate, TSH, LFTs, renal function
5. Ankle-brachial index - to exclude PAD
6. If infection suspected - ESR, CRP, WBC, and possibly bone scan or labeled WBC scan

Gabapentin and Pregabalin in This Patient

Mechanism of Action

Bradley and Daroff's Neurology in Clinical Practice: "Gabapentin modulates the function of the α2-δ subunit of voltage-dependent calcium channels in the dorsal horn of the spinal cord to decrease the release of excitatory neurotransmitters."

Why They Are Indicated Here

Kaplan & Sadock's Comprehensive Textbook of Psychiatry: "Pregabalin was more effective than a placebo in double-blind, randomized placebo-controlled trials in adults with diabetic peripheral neuropathy. Pain, mood, sleep, and quality of life measures improved."

Which Is Preferred?

1. Greater efficacy - NNT (number needed to treat) for diabetic neuropathy is 2.2 for pregabalin, meaning roughly 1 in 2 patients gets significant (≥50%) pain relief. Pregabalin is considered more effective than gabapentin for neuropathic pain overall.
2. Linear pharmacokinetics - Pregabalin has predictable absorption unlike gabapentin, whose bioavailability decreases as dose increases (non-linear kinetics), making dosing more consistent.

Goldman-Cecil Medicine: "Gabapentin and pregabalin may be better than antidepressants for prototypical 'lancinating-type' neuropathic pain... Gabapentin and pregabalin also act additively with antidepressants and opioids."

Dosing

Gabapentin

• Start: 100-300 mg at bedtime, titrate slowly
• Target: up to 1800-3600 mg/day in 3 divided doses
• Nonlinear absorption - higher doses absorb less efficiently per dose

Pregabalin

• Start: 75 mg twice daily (150 mg/day)
• Increase within 1 week to 300 mg/day in 2-3 divided doses based on response
• Can go up to 450-600 mg/day if needed

Important Cautions in THIS Patient (55M)

1. Renal Function - CRITICAL

2. Fall Risk

• Dizziness, somnolence, and unsteadiness are the most common side effects of both drugs.
• This patient has a history of femur fracture and may already have impaired gait or knee instability.
• Start low, titrate slowly - dizziness-related falls in this patient could be catastrophic (re-fracture around the implant).

3. Peripheral Edema

• Both drugs can cause ankle/peripheral edema, especially pregabalin. If the patient has any cardiac or venous insufficiency, monitor closely.

4. Dependence and Withdrawal

• Pregabalin is a Schedule V controlled substance (in many countries a controlled drug) due to misuse potential and euphoric effects at higher doses.
• Do not stop abruptly - both have a withdrawal syndrome similar to benzodiazepine withdrawal (anxiety, insomnia, sweating, seizures in high-dose users). Taper when discontinuing.

5. CNS Depression Additive Effects

• If the patient is on any opioids, benzodiazepines, or other CNS depressants for his pain, combining with gabapentinoids increases risk of respiratory depression and sedation.

6. Suicidality Warning (FDA Black Box)

• Like all anticonvulsants, both carry an FDA warning for increased risk of suicidal ideation - screen for mood before starting.

Summary - Can They Be Given?