Ulnar impaction syndrome (UIS), also known as ulnar abutment or ulnocarpal impaction or loading, is a condition in which the ulna of the forearm is too long relative to the radius, resulting in excessive loading on the ulnar side of the wrist. In most cases, this condition is congenital and present from birth, but sometimes ulnar impaction syndrome can be secondary to shortening of the radius after a fracture. Differentiation from ulnar impingement syndrome is critical, which is due to a shortened ulna that abuts and causes radial remodeling.
Regardless of the origin, however, most patients only become symptomatic in later life, when accumulated and degenerative wear and tear takes its toll on the ligaments and cartilage, causing ulnar-sided wrist pain. For athletes whose sports involve loading of the upper limbs, this can be a particular problem.
To fully appreciate how ulnar impaction can result in ulnar-sided wrist pain, it helps to understand the structure and role of the triangular fibrocartilage complex (TFCC) and loading across the ulnocarpal joint. Ulnar-sided wrist stability is enhanced via the TFCC, an arrangement of ligaments and fibrocartilage originating from the sigmoid notch on ulnar border of the radius and inserting into the base of the ulnar styloid and fovea of the ulnar head.
Studies have shown that there is a direct relationship between increasing ulnar length (relative to radius length) and increased force transmission across the TFCC. In a neutral wrist, the ulnacarpal joint takes around 18% of the total load applied to the wrist (with the radiocarpal joint taking the other 82% or so. However, a positive variance of 2mm will increase the ulnocarpal load to approximately 40%, while an increased dorsal tilt due to previous injury of the radius can further increase the ulnar load to 65% of total load transferred. In addition, thinning of the articular disc (which is common with increased ulnar length) also increases the risk of TFCC wear and perforation.
While it’s most commonly associated with congenital or acquired positive ulnar variance, UIS can also occur in ulnar neutral or even negative ulnar variance wrists. Athletes performing power and/or gripping tasks associated with axial loading and rotation are particularly at risk of ulnar impaction syndrome because of the ‘dynamic ulnar variance’ that occurs during tasks requiring maximal grip and pronation. More generally, athletic events that place repetitive compression and rotation demands on the upper limbs increase the risk of ulnar impaction via traumatic development.
The development of UIS leads to the progressive degeneration and increased abutment of the distal ulna or TFCC against the ulnar carpus. Although any athlete can suffer from this condition, gymnasts, boxers, racquet and stick sport athletes are particularly at risk, with symptoms of pain particularly occurring during wrist rotation. It’s important to understand, however, that the development of this condition is not always linear; the load-bearing demand placed on the TFCC means that there’s an increased susceptibility towards an acute traumatic injury, as well as the secondary degenerative concerns implicated with ulnar impaction.
Symptoms of ulnar impaction syndrome include:
What tends to distinguish chronic ulnar impaction syndrome from an acute TFCC injury (which may itself be made more likely by ulnar impaction) is the insidious, progressive nature of the pain, which gradually limits range of motion, grip strength, and performance.
When attempting to make a diagnosis of UIS, a comprehensive wrist examination is needed, together with a detailed patient history (for example, has the patient suffered a radius fracture in the past?). Unfortunately, however, there’s no single clinical test that can fully diagnose UIS, not least because many tests performed in the clinic are inconclusive as to whether TFCC-related pain is acute or degenerative in nature. For this reason, diagnostic imaging (eg MRI) should be performed to support the findings from the clinical exam. Having said this, the clinician can gain valuable supporting evidence from a thorough examination that includes the following:
On palpation, is there?
Do range of motion tests show?
Does a strength measurement reveal?
When treating athletes with UIS, earlier is better; studies show that early diagnosis and intervention may significantly reduce the risk of long-term disability and injury progression. Conservative treatment should be attempted before surgery and can include immobilization or limiting aggravating movements such as pronation, gripping and ulnar deviation for 6-12 weeks. Following immobilization/ restriction, other conservative treatment options include non-steroidal anti-inflammatories (NSAIDs) and corticosteroid injections.
However, while conservative treatments such as anti-inflammatories combined with immobilization or restricting range of movement may be reasonably effective for the general population, they are often insufficient for athletes because they don’t address the fundamental biomechanical factors that predispose the athlete to UIS. Therefore, when conservative management fails to produce a significant improvement, evidence suggests that surgery is indicated.
When surgery is required, many athletes opt to postpone surgery until the close of the season, allowing recovery from surgery to take place during the off-season. In terms of surgical options, this is best determined by the surgeon after thorough radiologic screening. These options may include:
Following surgery, athletes can expect to undergo at least 3-4 months or recovery/ rehabilitation, depending on the surgical procedure and individual response. Athletes should expect a return to full activity around 3-4 months after an arthroscopic wafer procedure, and around six months after an ulnar shortening osteotomy.
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