Pain on Wrist Extension Near the FCU Tendon

Anatomy Context

Common Causes

1. FCU Tendinopathy / Tendinitis

• Most common cause of pain directly over the FCU tendon
• Wrist extension stretches the FCU tendon, reproducing pain
• Often due to overuse (racquet sports, golf, manual labor)
• Tenderness over the pisiform and ulnar volar wrist

2. Triangular Fibrocartilage Complex (TFCC) Injury

• The TFCC stabilizes the distal radioulnar joint (DRUJ) and sits on the ulnar side of the wrist
• Traumatic or degenerative tears present with ulnar-sided wrist pain, which can be exacerbated by wrist loading and rotation in extension
• Diagnosed with MRI arthrogram or wrist arthroscopy (Bailey & Love's, p. 563)

3. Pisotriquetral Arthritis / Pisiform Pathology

• The FCU inserts onto the pisiform; arthritic or instability changes in the pisotriquetral joint can mimic FCU tendinopathy
• Pain on gripping and wrist extension; tenderness directly over the pisiform

4. ECU (Extensor Carpi Ulnaris) Tendon Pathology

• The ECU runs dorso-ulnar, but can cause pain that is confused with the volar FCU region
• ECU subluxation or tendinitis is provoked during forearm supination + wrist extension

5. Ulnar Tunnel Syndrome (Guyon's Canal Compression)

• Compression of the ulnar nerve in Guyon's canal (just adjacent to the FCU/pisiform)
• Pain, numbness, and weakness on the ulnar side; may worsen with wrist positions that tension the nerve

6. Distal Radioulnar Joint (DRUJ) Instability

• Instability or arthritis at the DRUJ produces ulnar-sided wrist pain reproduced by extension and forearm rotation

7. Hook of Hamate Fracture

• The FCU indirectly transmits force to the hamate; a hook fracture causes pain at the hypothenar/ulnar base reproduced by gripping and wrist movements
• Common in golfers and racquet sport athletes

Distinguishing Features

Key Clinical Pearl

Treatment of Schwannoma in the Cubital/Elbow Region

Background

Preoperative Workup

Definitive Treatment: Surgical Excision (Enucleation)

Key Principles

1. Nerve-sparing dissection — since schwannomas are eccentric to nerve fascicles, they can be shelled out from the nerve without sacrificing it
2. Fascicular preservation — the tumor is peeled away from the native fascicles under loupe magnification or microsurgical technique
3. Intraoperative nerve monitoring — used in many centers to reduce risk of post-excision neurological deficit
4. Do NOT perform en bloc resection — unlike neurofibromas (which are intrafascicular), schwannomas do not require nerve sacrifice; en bloc would cause unnecessary denervation

Surgical Approach for Cubital Region

• Medial approach to the elbow along the ulnar nerve course
• Identify the cubital tunnel; release the Osborne ligament if concurrent cubital tunnel syndrome is present
• Careful dissection under magnification to identify the tumor capsule
• Longitudinal incision through the epineurium; blunt dissection to enucleate the tumor
• If nerve compression coexists: ulnar nerve decompression or anterior transposition at the same sitting

When Malignancy is Suspected (Malignant Peripheral Nerve Sheath Tumor — MPNST)

• MPNSTs can arise from schwannomas, especially in neurofibromatosis type 1 (NF1) (Harrison's, p. 2745)
• Red flags: rapid growth, pain, firmness, size >5 cm, invasion on MRI
• Treatment shifts to wide local excision with clear margins ± adjuvant radiotherapy
• Chemotherapy (ifosfamide-based) for metastatic disease

Outcomes

Summary

Red Discolouration of Skin on Leg After ACL Surgery — Causes

1. Complex Regional Pain Syndrome (CRPS) — Most Likely

• Reddish/red-brown skin discolouration — classic
• Skin color shifts: red → blue → purple → pale (over minutes to hours)
• Livedo reticularis — red, non-blanchable, net-like pattern (~60% of patients)
• Shiny, atrophic skin; hyperpigmentation; telangiectases; brownish-red patches
• Edema (may mimic cellulitis in early stages)
• Temperature asymmetry between affected and unaffected limb

"Autonomic dysfunction may manifest as changes of skin color and temperature... The affected area may be reddish at one time and then become blue, purple, or pale over a course of minutes to hours." — Bradley and Daroff's Neurology, p. 52

CRPS I: Right foot and ankle are mildly swollen and reddish compared to the left (Bradley & Daroff's Neurology)

CRPS: Red, textured skin on the lower leg (Andrews' Diseases of the Skin)

• CRPS I (Reflex Sympathetic Dystrophy) — no definable nerve lesion (most common post-ACL)
• CRPS II (Causalgia) — definable nerve lesion present

2. Stasis Dermatitis / Chronic Venous Insufficiency

• Can develop post-operatively if deep venous damage or DVT occurred after ACL surgery
• Reddish-brown discolouration from hemosiderin leaking out of red blood cells in overtaxed dermal capillaries
• Associated pedal edema, scaling, varicosities
• "In all stages, reddish brown discoloration is caused by staining from hemosiderin that has leaked out of red blood cells in the overtaxed dermal capillaries" — Textbook of Family Medicine, p. 3781

3. Post-Thrombotic Syndrome (after DVT)

• ACL surgery is a risk factor for deep vein thrombosis (DVT)
• Chronic venous hypertension after DVT → skin discolouration, lipodermatosclerosis, ulceration
• Must be excluded with Doppler ultrasound

4. Scar/Graft Site Hyperpigmentation

• Post-inflammatory hyperpigmentation or vascular prominence at the graft harvest site (patellar tendon, hamstring)
• Usually localised and fades with time

5. Infection / Cellulitis (urgent to exclude)

• Post-operative infection presenting late (though 1 year is very late for primary infection)
• Acute redness, warmth, swelling, fever, raised CRP/WBC

Diagnostic Approach

Key Takeaway

Cellulitis of the leg — extensive erythema, swelling, and blistering (Andrews' Diseases of the Skin)

Treatment of Cellulitis of the Leg

Pathogens

• ~75% Streptococci (Group A Strep — S. pyogenes)
• Majority of remainder: Staphylococci (S. aureus, including MRSA)
• Less common: Vibrio vulnificus, Pseudomonas (immunocompromised)

Stratified Treatment by Severity

"Mild cases may be treated with oral cephalosporin, dicloxacillin, or clindamycin. Moderate cases: IV penicillin, ceftriaxone, cefazolin, or clindamycin. Severe cases: IV vancomycin + piperacillin/tazobactam." — Rosen's Emergency Medicine, p. 1245

General Measures

• Elevation of the affected leg — reduces swelling, accelerates resolution
• Mark the erythema border with a pen to monitor spread or regression
• Ice bags / cold compresses — for local symptom relief
• Antibiotics for at least 10 days when leg is involved, especially with bullae

Indications for Hospitalisation

• Bullae or skin necrosis present
• Lymphangitis / lymphadenopathy
• Systemic toxicity (fever, hypotension, tachycardia)
• Elderly or immunocompromised patients
• Longer duration before presentation
• Underlying leg ulcers or comorbidities (cardiac, renal, hepatic failure)

"Leg involvement, especially when bullae are present, will more likely require hospitalisation with intravenous antibiotics." — Andrews' Diseases of the Skin, p. 308

Common Portal of Entry on the Leg

• Tinea pedis (athlete's foot) — most common in lower leg cellulitis; treat concurrently with antifungal to prevent recurrence
• Wounds, ulcers, abrasions, insect bites

MRSA Risk Factors (escalate to vancomycin)

• Prior MRSA infection
• Healthcare exposure
• IV drug use
• Failure to respond to beta-lactam after 48–72 hrs

Recurrent Cellulitis — Prevention

• Long-term low-dose antibiotic prophylaxis (e.g., penicillin V or erythromycin) in patients with frequent recurrences
• Treat underlying predisposing conditions: tinea pedis, lymphedema, venous stasis, obesity
• Compression stockings for venous insufficiency
• Predisposing factors include: diabetes, alcoholism, immunodeficiency, venous stasis, lymphedema, prior knee/saphenous vein surgery, irradiation

Differentials to Exclude