Ulnar Impaction Syndrome is a degenerative wrist condition caused by the ulnar head impacting upon the ulnar-sided carpus and triangular fibrocartilage complex resulting in degeneration of these structures and a spectrum of symptoms.
It is also called ulnocarpal abutment, ulnocarpal loading, and impingement syndrome.
Ulnar impaction syndrome is a common cause of ulnar sided wrist pain.
It is a degenerative condition that occurs secondary to excessive load across the ulnocarpal joint, but the demographics and the natural history of ulnar impaction syndrome.
Relevant Biomechanics of Wrist Joint
Abutment of the distal ulna with the carpus often results in pain and progressive deterioration of the triangular fibrocartilage complex (TFCC) and other pathologic changes. These changes are can be noted in following structures-
- Dome of the ulnar head
- Ulnar corner of the lunate
- T triquetrum
- Lunotriquetral interosseous ligament [LTIL]
In the ulnar neutral wrist [ulnar neutral wrist is where the ulnar variance is less than 1mm], about 18% load is borne by the ulnocarpal joint bears. Triangular fibrocartilage is an important structure in the wrist that transfers the load from carpal bones to the ulna. Thicker triangular cartilage increases the load transfer whereas thinner cartilage transfers the lesser load.
Those with negative congenital negative ulnar variance have thicker TFCC and thus allows the load transfer effectively.
Thus ulnar variance or length of the ulna is an important factor. Increasing or decreasing the relative length of the ulna has been shown to cause significant changes in ulnocarpal load.
This rationale is used for the ulnar-shortening osteotomy in the treatment of ulnar impaction syndrome.
Thus, the ulnar impaction syndrome is less common in people with negative to neutral ulnar variance.
During forearm movements, pronation and grip both result in a relative increase in ulnar length which creates a dynamic positive ulnar variance resulting in the ulnocarpal load.
It has been suggested that the dynamic increase in relative ulnar length during pronation and grip leads to dorsal subluxation of the ulnar head in ulnar positive wrists.
Causes of Ulnar Impaction Syndrome
Ulnar impaction syndrome is more commonly seen in patients who have got an increased ulnar variance. Common conditions where this is seen are
- Distal radius fractures with radial shortening
- Radial head excision
- Essex Lopresti fracture
- Galeazzi fracture
- Dynamic positive ulnar variance [Due to excessive repeated loading of the ulnar-carpus in daily activities, refer to the explanation above]
- Madelung deformity
Most of the patients of ulnar impaction syndrome have the pain of insidious onset. However, there are some patients who in spite of abutment would have minimal or no symptoms.
The patients are generally middle-aged. Those with idiopathic ulnar impaction syndrome could be of younger age
The pain is often progressive. There may be complaints of swelling and stiffness of wrist and forearm rotation.
The activities of forceful grip, pronation, and ulnar deviation worsen the symptoms.
[These movements cause an increase in ulnar variance.]
A complete wrist examination should be carried to rule out other causes and establish a diagnosis. There are some special tests for the ulnocarpal abutment. These are
Nakamura’s Ulnocarpal Stress Test
This test involves placing the wrist in maximum ulnar deviation, axially loading the wrist, and passively rotating the forearm through supination to pronation.
Reproduction of the typical pain pattern is considered as positive and is suggestive of ulnar impaction syndrome.
The test is very sensitive for ulnar impaction syndrome. But a number of other processes like
- Lunotriquteral injury [LTIL injury]
- TFCC injury (without impaction)
Regan Shuck Test
With the wrist positioned in ulnar deviation, dorsal and palmar displacement of the ulna is attempted. The test is considered positive if the pain is produced. This test is done to know LTIL injury.
This test is done to evaluate for TFCC tear or ulnotriquetral ligament tear. The test is performed by palpation of the ulnar wrist between the styloid and flexor carpi ulnaris tendon. Tenderness suggest positive test.
Conditions that cause ulnar sided wrist pain should be considered as differential diagnoses. These commonly include
- Pisotriquetral arthritis
- Distal radioulnar joint or DRUJ arthrosis
- Extensor carpi ulnaris subluxation or tendonitis
- Dorsal cutaneous branch [of the ulnar nerve] neuritis
X-rays are normal in early disease. A positive ulnar variance may be noted. Degenerative changes in the ulnar side of the carpal bones may be noted when the condition advances.
X-rays should also be evaluated for any probable pathology that could lead to acquired positive ulnar variance. Comparison radiographs of the other side are often helpful.
Neutral rotation posterior-anterior wrist x-ray is done for determining the ulnar variance. The image is taken with the elbow flexed at 90 degrees and the forearm in neutral rotation.
Lateral x-rays should be evaluated for evidence of dorsal ulnar subluxation
Following changes may be noted in the x-ray.
- Subchondral sclerosis
- Cystic changes at the dome of the ulna
- Cystic changes in the proximal ulnar corner of the lunate
- Cystic changes in the proximal radial corner of the triquetrum
- Frank arthritis in severe cases
- Ulnar subluxation
MRI is not required for diagnosis. But in cases where the diagnosis is not clear, MRI may provide detailed images of the structures involved. it also shows occult pathologies.
The earliest detectable changes are noted in the articular cartilage and are fibrillation and chondromalacia,.
The other lesions are bone hyperemia or edema, localized to the involved regions, may also be evident
MRI is also able to rule out other possible sources of ulnar-sided wrist pain.
MR arthrography may be useful in select cases to ascertain the exact stage of ulnar impaction in pre-operative evaluation.
Treatment of Ulnar Impaction Syndrome
Treatment of ulnar impaction syndrome varies depending on the amount of ulnar variance, and the severity of pathological changes, the contour of the distal ulnar and the presence of lunotriquetral instability.
Initial treatment should be nonoperative in most cases. It incldeus
- Rest or immobilization for 6 to 12 weeks
- Modification of activities
- Local steroid injections
Surgery can be considered if the above modalities fail to work.
The goal of surgery for ulnar impaction syndrome is to decrease the length of the ulna relative to the radius. This leads to a decrease in the amount of load that crosses the ulnocarpal joint.
Ulnar-shortening osteotomy and the wafer procedure are two main surgeries for this.
Ulnar head excisional osteotomies have been described. These effectively shorten the ulnar head while preserving the domal cartilage.
In presence of distal radioulnar joint arthritis [DRUJA], the procedure should address both, DRUJA and the ulnar impaction syndrome.
These procedures include endoprosthetic ulnar head arthroplasty, Bowers’ hemiresection arthroplasty, matched distal ulna resection arthroplasty, the Darrach procedure, and the Sauve-Kapandji procedure.
Briefs of some common procedures is given below.
Ulnar Shortening Osteotomy
First described by Milch in 1941, this osteotomy is still considered the gold standard
It should be preferred over wafer procedure in-
- A wrist with positive ulnar variance and a prominent ulnar styloid
- Ulnocarpal abutment with dorsal subluxation of the ulna.
The osteotomy is performed at the junction of the distal and middle third of the ulna.
Ulnar shortening should be avoided in patients with DRUJ arthritis, and in patients with a reverse oblique DRUJ slope.
Delayed union or nonunion, and hardware-related complications may occur after this procedure.
The wafer procedure refers to resection of distal 2–3 mm of the dome of the ulnar head.
This can be done as an open procedure or arthroscopy. It allows rapid return to normal activities.
It is effective for decreasing the ulnocarpal load.
It avoids the complications of ulnar shortening osteotomy and can be done in DRUJ with reverse slope. But the resection is limited to 2-3 mm.
Unlike osteotomy, It does not improve dorsal subluxation of the ulna, and it does not tighten the ulnocarpal ligamentous complex.
Complete or partial ulnar head resection. Done in advanced lesions.
Arthrodesis of the distal radioulnar joint with distal ulnar pseudoarthrosis
When ulnocarpal impaction occurs following fractures of radius, the procedure can restore normal joint anatomy. This approach fixes the culprit bone rather than doing a compensation procedure on the other bone.
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