Patient with approximately five months of elbow and proximal dorsal forearm pain that developed after playing padel. Symptoms have gradually improved but remain persistent. Pain is localised to the proximal third of the dorsal forearm, along the anatomical course of the posterior interosseous nerve.
Ultrasound examination demonstrates no relevant structural abnormality of the common extensor tendon, distal biceps tendon, extensor musculature, posterior interosseous nerve, humeroradial joint, or proximal radioulnar joint.
At the lateral ulnar collateral ligament (LUCL), there is a small focal interruption of the normal fibrillar pattern, compatible with a partial tear measuring approximately 2 × 2 × 3 mm. No complete ligament rupture is identified.
The posterior interosseous nerve demonstrates normal sonographic morphology without focal enlargement, definite compression, or other structural abnormality. The nerve was assessed in short axis and during forearm pronation and supination.
1. Final diagnosis
Small partial tear of the lateral ulnar collateral ligament measuring approximately 2 × 2 × 3 mm. This lesion may be clinically relevant, although correlation with local pain and examination for functional lateral elbow instability is required to determine whether it fully explains the symptoms. No sonographic structural abnormality of the posterior interosseous nerve or other examined structures is demonstrated.
2. Differential diagnosis
The principal differential consideration is a symptomatic partial LUCL lesion, potentially associated with mild functional irritation or instability of the lateral ligament complex. A functional or dynamic radial tunnel/posterior interosseous nerve irritation remains another consideration despite the normal structural appearance of the nerve on static ultrasound. Pain related to radial tunnel or posterior interosseous nerve irritation may occur without demonstrable focal nerve enlargement, making clinical localisation and provocative testing important.
3. Teaching points
Small partial LUCL tears may be subtle on ultrasound and should be interpreted in combination with the site of tenderness and clinical assessment for varus or posterolateral instability. Ultrasound evaluation of the posterior interosseous nerve should include careful assessment around the proximal supinator tunnel and may benefit from dynamic examination during pronation and supination. A normal-appearing nerve does not exclude a clinically relevant dynamic or functional radial tunnel syndrome. Conversely, pain in the anatomical course of the nerve should not automatically be attributed to neuropathy when no neurological deficit or structural nerve abnormality is present.
4. Injury/disease information
The LUCL is an important stabilising component of the lateral collateral ligament complex of the elbow and contributes to resistance against posterolateral rotatory instability. Small partial injuries without clinical instability are commonly approached conservatively with activity modification and progressive rehabilitation.
In this case, targeted clinical examination of the lateral ligament complex is useful to assess pain provocation and possible varus or posterolateral instability. Clinical neurological examination of the posterior interosseous nerve and radial tunnel should include motor testing of the extensor musculature and relevant provocative manoeuvres.
Given the gradual improvement of symptoms, conservative management is reasonable in the absence of objective instability or neurological deficit. Persistent symptoms despite appropriate rehabilitation may warrant reassessment with dynamic ultrasound and/or additional imaging. Development of objective weakness or other neurological abnormalities would support further neurological evaluation.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
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