Introduction

The ulnar impaction syndrome refers to a painful overload of the ulnocarpal joint^1,2 and has been classified by Palmar based on pathoanatomy (Table 7.1).³ Palmer and Werner have shown that positive ulnar variance results in an increase in ulnocarpal load,⁴ and this has been implicated in the etiology of degenerative triangular fibrocartilage complex (TFCC) tears.^4,25 Ulnar impaction also develops in the wrists with neutral or negative ulnar variance, however.^5,6

Table 7.1 Classification of Traumatic and Degenerative Conditions of the TFCC

Dynamic increases in ulnar variance may occur with forearm pronation and grip,^7,8,9 and an inverse relationship may exist between TFCC thickness and ulnar variance.¹⁰ Further, it is known that TFCC wear and undersurface fibrillation occur clinically prior to perforation¹¹ and that innervation of the TFCC may in part explain pain early in the pathologic spectrum of this condition.¹² Palmer’s classification of ulnar impaction accounts for the existence of TFCC wear without central disc perforation class IIA and B lesions.³ This chapter addresses the feasibility of arthroscopic TFCC disc excision and wafer distal ulna resection as treatment of ulnar impaction when TFCC perforation has not yet occurred. This procedure is a viable alternative to ulnar shortening osteotomy.

Biomechanics

Palmer and Werner have shown that in the ulnar neutral wrist 80% of the load is transferred across the radiocarpal joint compared to 20% across the ulnocarpal joint.⁴ When variance increases from neutral to 2.5 cm positive, however, ulnocarpal load increases by approximately 20%. Decreasing variance by 2.5 cm lowers force transmission from 20 to 5% in the neutral variant.

This data provides a basis for treating ulnar impaction syndrome with a shortening osteotomy of the ulna.^1,2 Feldon advocated a wafer resection as an alternative in 1992,¹³ and in that same year Wnorowski et al. showed that an arthroscopic wafer procedure successfully diminished load across the ulnocarpal joint.¹⁴ Most recently, Markolf et al. have shown that wafer resection decreases distal ulna forces under all conditions of ulnar variance—although less effectively when variance exceeds 4 mm positive.¹⁵

Although Palmer and Werner have shown that increasing ulnar length results in an increase in force transmission across the distal ulna, and it is known that forearm pronation and forceful grip increase ulnar variance,^5,16,17 few studies have investigated loads across the distal ulna when the forearm is pronated.^10,18 In nine cadaver specimens in different wrist and forearm positions, Glisson et al. showed that loads across the distal ulna increased in pronation, wrist flexion, and ulnar deviation.¹⁸

Pfaeffle et al. evaluated the effect of axial load and forearm pronation on ulnar variance and distal ulna load in seven cadaver forearms.¹⁰ They found that ulnar variance increased an average of 2 mm in four ulnar positive and three ulnar neutral specimens. Distal ulna load increased in the ulnar neutral wrists and decreased in the ulnar positive wrists, in which greater dorsal subluxation of the distal radioulnar joint occurred. Accurate measurement of variance is important, therefore, when addressing ulnar wrist pain because the radioulnar length relationship has profound impact on load transfer across the wrist.¹⁹

Diagnosis

Our current diagnostic work-up for ulnar impaction syndrome revolves around the physical examination and plain radiographs. Patients typically complain of ulnar wrist pain. Thus, an evaluation of the ulnocarpal and distal radioulnar joint is required. One must evaluate the TFCC, LT ligament, extensor carpi ulnaris (ECU), flexor carpi ulnaris (FCU) tendons, and pisotriquetral joint and assess for the presence of a midcarpal clunk.

Nakamura’s ulnar stress test is routinely performed by ulnarly deviating the pronated wrist while axially loading, flexing, and extending.²⁰ The “fovea test” is performed by asking the patient to flex the wrist. This allows palpation of the FCU, which facilitates locating the fovea of the TFCC between the FCU and ulnar styloid process. Positive ulnar stress and fovea tests, in combination, are roughly 98% sensitive in terms of correlation with an objective problem with the TFCC and/or LT ligament. Exclusion of other sources of discomfort—such as pisotriquetral arthritis, distal radioulnar joint (DRUJ) instability or arthritis, and ECU tendonitis or hypermobility—increases the suspicion for pathology. An X-ray series is then obtained to evaluate ulnar variance and to assess for the presence of cystic changes in the ulnar corner of the lunate.

Imaging

Various methods of measuring ulnar variance have been described, but each uses neutral rotation posteroanterior (PA) radiographs of the wrist^5,19,21 because pronation will slightly increase the length of the ulna. We routinely check a zero-rotation PA and a lateral view. In addition, a “pronated grip” radiograph is typically taken with the patient making a fist of maximum intensity while the forearm is in pronation.¹⁶