Ulnar Impaction Syndrome

Ulnar impaction syndrome, or ulnocarpal abutment, is a degenerative condition caused by excessive load transmission between the distal ulna and the ulnar carpus, the lunate and triquetrum. It is a common cause of ulnar-sided wrist pain, and understanding the relationship between ulnar variance, degenerative TFCC tears and the treatment options is essential for hand surgery practice.

Who. Patients are aged 40-60, reflecting a degenerative process in which chronic overload leads to progressive degeneration. The sexes are equally affected, manual labourers and overhead workers are typical, and repetitive pronation-supination activities add to the risk. Bilateral variance is common, present in 50%.

Why. Any process that increases ulnar variance predisposes to ulnar impaction. The variance may be constitutional or acquired, and which it is divides the condition in two.

Ulnar impaction is either idiopathic, a constitutional or dynamic positive variance with no history of fracture or physeal arrest, or secondary, a positive variance manufactured by shortening or malposition of the radius. The distinction changes the operation: when the radius is the primary problem, correcting the radius may be preferable to simply shortening the ulna.

Idiopathic impaction is the classic degenerative picture, and the group in which ulnar shortening osteotomy has been most robustly validated. Baek et al reduced a mean variance of +4.6 mm to -0.7 mm with excellent scores.

Secondary impaction. These mechanisms create relative ulnar overlength:

• Distal radius fracture malunion, with radial shortening with or without dorsal tilt: the commonest acquired cause
• Premature distal radial physeal arrest in the skeletally immature, whether post-traumatic, infective, or Madelung deformity
• Radial head excision or Essex-Lopresti injury, where proximal migration of the radius unloads the elbow onto the wrist (see the dedicated Essex-Lopresti topic)
• Galeazzi or forearm malunion shortening the radius

Correct the radius when the radius is the problem. With a significant distal radius malunion, meaning large radial shortening, marked dorsal tilt or DRUJ incongruity, a radial corrective osteotomy restores anatomy and DRUJ congruity. An isolated ulnar shortening only neutralises the variance and leaves the radial deformity uncorrected, so assess the magnitude of the deformity and DRUJ articular congruity before choosing.

Isolated shortening after malunion still works. A systematic review of isolated USO performed for distal radius malunion (Laane et al) reported a 33% overall complication rate dominated by implant irritation, with removal in about 13% and nonunion only about 3%, and improved functional and patient-rated scores in most patients. It is a simpler, reliable option for lesser deformity; prefer a buried or low-profile implant to limit hardware irritation.

Load sharing. In a neutral wrist with neutral ulnar variance, approximately 60% of axial load passes through the radius and 40% through the ulna and TFCC. Every millimetre of positive variance increases ulnocarpal load: with 2.5mm of positive variance, ulnocarpal load rises to over 60%, and studies show TFCC load increases by over 40%.

Why it matters. This excess load causes TFCC degeneration and chondromalacia. It also explains why shortening the ulna by 2-4mm dramatically relieves symptoms, and why biomechanical correction is the goal of surgery.

The cascade. Positive variance sets off a biomechanical cascade:

1. Positive ulnar variance, constitutional or acquired
2. Increased ulnocarpal loading, especially at the lunate and triquetrum
3. TFCC central wear and perforation (Palmer 2C)
4. Lunate and ulnar head chondromalacia (Palmer 2B-2C)
5. Lunotriquetral ligament tear (Palmer 2D)
6. Ulnocarpal arthritis (Palmer 2E, end-stage)

Not only the lunate. The impaction can centre on the triquetrum rather than only on the lunate. Positive variance then accompanies opposing subcortical cystic degeneration in the distal ulna and proximal triquetrum.

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Palmer's class 2 describes the degenerative TFCC tears of chronic ulnar impaction, distinct from the class 1 traumatic tears. The stage guides the treatment algorithm, and Palmer 2C is the commonest presentation requiring surgical intervention. Variance is the second axis, and ulnar impaction usually requires over 2mm of positive variance.

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Ulnocarpal abutment sits within a spectrum of ulnar-sided impaction and impingement disorders. Examiners expect you to separate them, because each has a different key measurement and a different operation.

History. The pain is dorsal-ulnar, worse with ulnar deviation, grip and pronation, and better with rest and avoiding provocative activities. Insidious onset over months to years is typical, and there may be occasional clicking with forearm rotation.

Examination. Swelling is usually minimal and the range of motion normal or slightly reduced. The hallmark is ulnar-sided tenderness over the ulnocarpal joint, just distal to the ulnar styloid, and grip is weak because it hurts. Assess DRUJ stability with the piano key sign, then run the provocative tests.

Differential diagnosis. Ulnar-sided wrist pain has several mimics.

Plain radiographs. PA and lateral wrist radiographs come first. Measure the ulnar variance on the PA view and look for lunate sclerosis (increased density on the PA view), subchondral cysts in the ulnar head, and ulnocarpal joint narrowing, which marks end-stage Palmer 2E. A clenched-fist view may increase the variance and demonstrate pathology.

Measuring variance. Take the PA view with the forearm in neutral rotation, the shoulder abducted 90 degrees and the elbow flexed 90 degrees. Draw a perpendicular line from the ulnar articular surface to the radial articular surface. The variance is positive when the ulna extends distal to the radius and negative when it lies proximal to it.

Dynamic variance. Forearm rotation changes the reading. Pronation increases positive variance by 1-2mm and supination decreases it, which is why neutral rotation is critical; grip force also increases dynamic loading. Because rotation and grip both change the measurement, pre- and postoperative films must be taken in identical positions to be compared.

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MRI. T1, T2 and proton density sequences show the TFCC central tear, lunate chondromalacia, bone marrow oedema and the state of the LT ligament. An MR arthrogram increases sensitivity for TFCC tears but is usually not necessary. The findings:

• TFCC central perforation: high signal on T2
• Lunate bone marrow oedema: low T1, high T2 signal
• Chondromalacia: cartilage thinning or defects
• LT ligament tear: discontinuity or high signal

Reading the MRI against the film. Lunate marrow oedema in the ulnocarpal loading zone is a supportive sign when correlated with positive or dynamic variance and TFCC degeneration. Neutral films can look normal while MRI shows a central triangular-disc perforation, so dynamic variance and tissue injury must be considered when the PA film appears normal.

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Arthroscopy. Wrist arthroscopy is the diagnostic and therapeutic gold standard. It directly visualises the TFCC tear and the extent of chondromalacia and allows treatment (debridement, wafer), and radiocarpal and midcarpal portals assess all the pathology.

Conservative treatment. A trial of 3-6 months is the reasonable initial approach for early disease: Palmer 2A, mild symptoms, or a patient who prefers a non-operative trial. It has three parts:

• Activity modification: avoid provocative activities, reduce repetitive pronation, grip and ulnar deviation, and modify the workplace ergonomically
• Splinting: a forearm-based splint immobilising the wrist in neutral, worn during activities and at night, may decrease symptoms 30-50%
• NSAIDs and injection: NSAIDs for inflammation; a corticosteroid injection into the ulnocarpal joint may provide temporary relief (weeks to months), with a limit of 2-3 injections

Of these patients, 30-40% improve. Palmer 2C and beyond usually require surgery, and for Palmer 2A, arthroscopic TFCC debridement alone is an option.

Unloading: shortening or wafer. Both operations aim to unload the ulnocarpal joint, and DRUJ stability must be preserved with either. Ulnar shortening osteotomy is the gold standard: indicated for Palmer 2C-2D with positive variance over 2-3mm after failed conservative management, it shortens the ulna by 2-4mm to neutral or 1mm negative variance. It is more powerful, but it needs 3-4 months of healing and therapy and carries the hardware burden.

The limit of the wafer. The arthroscopic wafer procedure suits Palmer 2B-2C with mild positive variance (under 2-3mm) in a patient who wants a faster recovery. The wafer resects only the distal 2-4mm of the ulnar head, so Feldon's original contraindication is positive variance over 4mm, and because the resection must also leave the styloid and its ligaments intact, most surgeons confine it to 2-3mm. Every comparative trial of wafer against USO capped entry at 4mm, so nothing is known about the wafer above that.

Weighing the wafer. Its advantages are a faster recovery, no hardware, no nonunion risk and an outpatient procedure. Against it, the shortening possible is limited (a maximum of 2-3mm), it is less powerful than USO, and it cannot address LT tears or severe pathology. It is effective for mild disease, while USO is preferred for significant variance.

Salvage for Palmer 2E. Ulnocarpal arthritis, a failed USO or wafer, and end-stage disease call for salvage. Severe DRUJ degeneration, with cartilage thinning, joint-space loss and subchondral cysts, likewise moves treatment from isolated unloading toward DRUJ salvage. The choice depends on age, activity and DRUJ status; distal ulna hemiresection (the Bowers procedure) is a rare alternative.

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The decision in one table.

Planning the shortening. Measure the exact variance before surgery and plan the amount to remove. Too little fails to relieve symptoms; too much, over 4mm, risks DRUJ instability.

The osteotomy. A mid-diaphyseal or metaphyseal cut may take one of three configurations:

• Transverse: a perpendicular cut, easier but with delayed union
• Oblique: an angled cut, with a larger surface area for faster healing
• Step-cut: the most stable, but technically harder

Ulnar shortening osteotomy, step by step.

1. Positioning and approach. Supine on an arm table with a tourniquet. A direct lateral or dorsal approach to the mid-distal ulna through an 8-10cm incision; identify and protect the dorsal sensory branch of the ulnar nerve.
2. Exposure. Elevate ECU and FCU from the ulna by subperiosteal dissection, exposing 6-8cm of the shaft and protecting the interosseous membrane.
3. Osteotomy. Mark the osteotomy site, then measure and mark the bone to remove (2-4mm, from the preoperative plan) before cutting, to ensure accuracy. Make the transverse or oblique cut with a saw, remove the segment and compress the osteotomy.
4. Plate fixation. Apply a 6-8 hole compression plate with 3-4 screws each side of the osteotomy. Achieve rigid fixation with maximum interfragmentary compression, which decreases nonunion; a locking or non-locking plate is acceptable, and a low-profile plate minimises prominence.
5. DRUJ check and closure. Release the tourniquet and check DRUJ stability with forearm rotation, which should be smooth and stable. If the DRUJ is unstable, the shortening is excessive and should be revised. Close in layers and splint in neutral.

Guides and parallel cuts. A patient-specific guide translates the planned shortening and obliquity to the ulna, controls the saw cuts and plate holes, and permits compression to the intended postoperative variance. Parallel guided cuts create a minimal gap that accepts lag-screw compression; nonparallel freehand cuts leave a long reduction gap that the lag screw cannot compress, and union then comes slowly.

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Arthroscopic wafer, step by step. The wafer is a technically demanding arthroscopic procedure, and adequate visualisation is critical.

1. Set-up. Wrist arthroscopy tower with 10-15 lbs of traction; radiocarpal 3-4 and 6R portals. Inspect systematically: radiocarpal joint, TFCC, lunate, scaphoid.
2. TFCC assessment. Probe the central TFCC, identify the degenerative perforation and unstable flaps, and grade the Palmer class arthroscopically.
3. TFCC debridement. Debride the degenerative flap with a shaver to a stable rim, using the radiofrequency probe for haemostasis. Preserve the peripheral 1-2mm of the TFCC, which is vascular and stabilising.
4. Ulnar dome resection. Pass the arthroscopic burr through the radiocarpal joint and burr 2-3mm from the distal ulnar dome (articular surface); more causes instability. Smooth the contour to prevent catching, and use the probe to verify adequate decompression and the space created.
5. Final check. Visualise the decompression and a smooth ulnar surface, secure haemostasis, close the portals and apply a soft dressing.

Hardware irritation. Hardware prominence or irritation (10-15%) is the most common complication of USO and dominates pooled series, where the plate needs removal in roughly 1 in 8. Low-profile or buried implants help prevent it. Remove the plate only once union is confirmed and remodelled: a persistent osteotomy trace can precede refracture after removal, so hardware should not be removed solely for irritation until cortical remodelling and consolidation are convincing.

Nonunion. Nonunion is uncommon, about 3-6%, and smoking, diabetes and inadequate fixation are the risk factors. Prevent it with rigid fixation, interfragmentary compression and smoking cessation; treat it with ORIF, bone graft and compression plating.

Other complications of USO. DRUJ stiffness occurs in 5%, and the dorsal sensory branch of the ulnar nerve can be injured. DRUJ instability follows excessive shortening (over 4mm) and is worse in supination, with dorsal subluxation; splint it if mild and perform a Sauvé-Kapandji procedure if severe.

Persistent pain after USO. Persistent pain requires direct assessment of the osteotomy rather than an assumption that the symptoms are TFCC in origin. The causes:

• Hardware prominence, the most common: remove the plate after union
• Inadequate shortening: consider revision
• Unrecognised pathology (LT tear, arthritis): MRI and arthroscopy

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After shortening. The osteotomy is protected until it consolidates; a fall before union can loosen the plate. Full activities follow by 3-4 months if healed:

• Weeks 0-2: sugar-tong splint or cast; finger and shoulder range of motion; no forearm rotation; wound check at 10-14 days
• Weeks 2-6: removable splint; gentle wrist range of motion from week 3-4; no strengthening; radiograph at 6 weeks to assess union
• Weeks 6-12: progressive strengthening if union is progressing, with therapy for range of motion and grip

After a wafer. With no osteotomy to heal, rehabilitation is much faster:

• Weeks 0-2: soft dressing and removable splint; finger range of motion immediately; wrist range of motion from 1-2 weeks
• Weeks 2-6: progressive strengthening, with return to normal activities by 6-8 weeks

The USO figure is good-to-excellent pain relief with functional improvement; the wafer figure applies to appropriate indications.

Prognostic factors.

Natural history. Untreated, the disease progresses from Palmer 2A to 2E over 5-15 years. Most symptomatic patients eventually require surgery, and conservative management only temporises.

Global epidemiology: Ulnar impaction syndrome is one of the commonest causes of chronic ulnar-sided wrist pain worldwide. Positive ulnar variance is present in roughly 10-15% of the general population, but only a subset becomes symptomatic. Manual workers (construction, agriculture, mining), gymnasts and athletes loading the wrist in pronation are over-represented. There is no dedicated international registry; high-quality evidence comes from cohort series and a small number of randomised trials and meta-analyses.

Guideline and society positions (side by side):

There is broad international agreement on the principle (unload the ulnocarpal joint by correcting positive variance) and the staged algorithm; the main variation is the threshold and enthusiasm for arthroscopic wafer versus formal USO.

Related pages: Ulnar-Sided Wrist Pain is the parent presentation and the differential this diagnosis must be extracted from - impaction is one cause among many and the others are excluded before an osteotomy is contemplated; TFCC Injuries carries the Palmer classification in full and, more importantly, the foveal attachment that this page's Nishiwaki card shows must be intact for shortening to stabilise the DRUJ - a complete foveal avulsion needs repair and cannot be shortened into stability; Lunotriquetral Instability is the Palmer 2D lesion and coexists often enough that it must be assessed arthroscopically at the same sitting; DRUJ Arthritis is both a contraindication to the wafer and the endpoint (Palmer 2E) that pushes management to salvage - Darrach, Sauvé-Kapandji or ulnar head replacement; Distal Radius Fractures are the commonest cause of SECONDARY impaction through radial shortening and malunion, and the population in which the 33% complication figure was measured; Kienbock's Disease is the key differential for lunate signal change - note that it associates with NEGATIVE ulnar variance, the opposite of this condition, which is the discriminator examiners use; Madelung Deformity produces positive variance by a growth mechanism and presents younger; and Scapholunate Dissociation and Hamate Fractures complete the differential for mechanical wrist pain with a normal initial radiograph.

The wafer-versus-shortening threshold. The variance cut-off for choosing the wafer over USO is not firmly evidence-based. Trials and meta-analysis pooling subtle-variance patients (under 4mm) show equivalent patient-rated outcomes, with the wafer offering faster recovery and fewer complications, and most surgeons reserve it for stable-DRUJ, low-variance disease.

Osteotomy configuration. Oblique and step-cut osteotomies increase the union surface and allow interfragmentary compression, but high-quality comparative data are limited. The dominant complication is implant irritation requiring removal, not nonunion, and that has reframed the debate toward low-profile fixation.

Does shortening help an unstable DRUJ? Shortening re-tensions the TFCC and can stabilise the DRUJ, but cadaveric data show this works only if the radioulnar ligament remains attached to the fovea. A complete foveal avulsion is not corrected by shortening and requires separate foveal repair.

Salvage choice in Palmer 2E. For end-stage ulnocarpal or DRUJ arthritis there is no consensus winner. Selection is driven by age, demand and resources rather than by robust comparative trials.