Does Midcarpal Joint Structure Affect Development of Arthritis in the Wrist

Abstract

Background  Degenerative wrist arthritis develops in specific patterns because of forces acting on existing structural configurations. The most common pattern of wrist osteoarthritis is scapholunate advanced collapse (SLAC). Other patterns include isolated scaphotrapezial trapezoid (STT) joint and isolated midcarpal or radiolunate joint arthritis. One predictor of degeneration pattern is the structure of the wrist.

Questions/Purposes  Our purpose was to evaluate the relationship between midcarpal joint structure and the pattern of degenerative arthritis. We hypothesized that a wrist type 2 will preferentially develop SLAC degeneration.

Patients and Methods  We retrospectively evaluated 195 degenerative wrist radiographs. Radiographs were reviewed for lunate/wrist type, degeneration pattern, ulnar variance, radial and volar tilt, inclination, carpal height, scapholunate angle, gap, and presence of thumb carpometacarpal (CMC) joint, STT joint, and midcarpal joint arthritis.

Results  We had 158 radiographs with SLAC degeneration and 37 with atypical patterns, 154 type 2 and 41 type 1 wrists. There was a significant correlation between wrist type and the pattern of wrist degeneration ( p  = 0.02). SLAC degeneration developed in wrists with type 2 lunate while isolated midcarpal arthritis was associated with type 1 wrist. Isolated midcarpal joint arthritis was associated with STT arthritis, p  < 0.01. Radial height, inclination, volar tilt, and ulnar variance, and scapholunate gap and angle were not associated with wrist type. Ulnar variance was associated with thumb CMC and STT joint arthritis while radial height was associated with isolated midcarpal joint arthritis.

Conclusion  This study found significant relationships between midcarpal joint structure and pattern of degeneration. This contributes to understanding the development of degeneration and can aid in future prevention of arthritis.

Level of Evidence  This is a Level IV, diagnostic study.

Osteoarthritis (OA) is one of the most common challenges we face as orthopaedic surgeons. ^{1 2 3} It is the most prevalent joint disease and affects more than 250 million people worldwide. ⁴ Since the general population continues to age and becomes more functionally demanding, the occurrence of OA continues to increase as does the morbidity and loss of function associated with it. ⁵ Although the pathogenesis of this disease is largely known and mechanical in nature, our interventions are limited to symptomatic treatment or joint replacements as there are no current effective interventions to restore cartilage loss or mitigate disease progression.

Hand and wrist OA are prevalent locations for arthritis and lead to debilitation comparable to their large joint counterparts. ⁵ However, they are often underrepresented in the literature when compared with these large joints. The wrist especially, results in considerable disability and loss of function. ⁵

Due to the structural complexity of the wrist joint, the mechanics of the wrist remain incompletely understood. ⁶ This restricts our ability to understand the pathology of wrist OA and to understand the development of the different patterns of degeneration. Ultimately, this limits effective treatment for wrist OA. The most common pattern of wrist OA is the scapholunate (SL) advanced collapse (SLAC) wrist. This pattern produces degenerative changes beginning at the radial styloid (stage I), which progresses to the proximal scaphoid (stage II), and finally ends at the capitolunate joint (stage III). ⁷ Some other less frequent patterns of wear exist such as isolated scaphotrapezial trapezoid (STT) joint OA and isolated midcarpal or radiolunate joint OA. ⁶ Previous studies have attempted to associate between morphological subtypes and the various patterns of arthritis. ^{6 8 9 10}

The purpose of this study is to evaluate the relationship between midcarpal joint structure and the pattern of degenerative arthritis in the wrist. We hypothesize that a wrist type 2 will preferentially develop SLAC degeneration.

Methods

A database of wrist radiographs performed in our institution and read by the radiologist as degenerative wrist arthritis was used. The radiographs were performed according to Hardy et al: the posteroanterior (PA) radiograph is performed with the shoulder abducted 90 degrees from the trunk and the elbow flexed at 90 degrees with the ulna perpendicular to the humerus and forearm in a fully pronated position. The wrist is in neutral position. The hand should be palm down on the cassette with the fingers extended. The lateral view is obtained with the elbow flexed to 90 degrees and adducted against the trunk. The forearm is mid-prone and the wrist should be in the neutral position such that, in the resulting radiograph, a straight line can be drawn through the axes of radius, lunate, capitate, and third metacarpal or they should be coaxial within 10 degrees. ¹¹

Exclusion criteria included wrists with other confounding pathology such as synovitis or inflammatory arthritis, and radiographs of insufficient quality. After further review by the authors, 221 wrist radiographs out of 300 were available for inclusion in the study. After evaluating for quality, 195 radiographs were used in the analysis.

The radiographs were retrospectively reviewed for:

(1) Lunate type and wrist type: Lunate type was defined according to Viegas et al. ¹⁰ Type 1 wrists were defined as lunate type 1 and a spherical distal capitate, while type 2 wrists were defined as lunate type 2 and a flat distal capitate. ⁹

(2) Pattern of degeneration: SLAC wrist, thumb carpometacarpal (CMC) joint OA, STT joint OA, midcarpal joint OA, and radiolunate OA.

(3) Radiographs were also evaluated for: ulnar variance, radial tilt, radial inclination, carpal height, volar tilt, lunate type, capitate type, SL angle, and SL gap. Presence or absence of other OA: thumb CMC joint OA, STT joint OA, and midcarpal joint OA.

OA was defined as narrowing of the joint space, subchondral sclerosis, subchondral cysts, and osteophytes; classified using the Kellgren–Lawrence classification. ^{12 13} We did not stratify by degree of involvement.

SL gap was measured on PA radiographs, and is considered enlarged if measured greater than 2 mm. The distance between the scaphoid and lunate was measured at midjoint of the SL joint from the ulnar cortex of the scaphoid to the radial cortex of the lunate. ^{13 14 15}

Radial inclination is the angle between the long axis of the radial shaft and a line connecting the tip of the radial styloid with the ulnar corner

Ulnar variance is the difference in axial length between the ulnar corner of the distal radius and the most distal extent of the ulnar head.

Volar tilt is the angle formed between a perpendicular to the longitudinal axis of the radial shaft and a line formed by connecting the apex of the volar and dorsal rim.

Statistical Analysis

The significance of association between SLAC type and wrist type versus each type of OA was assessed by chi-square test or Fisher's exact test, whichever appropriate. Continuous radiographic measurements were compared between cohorts of different SLAC type, different lunate type, and having certain type of OA or not, using the Wilcoxon rank-sum test due to the nonparametric characteristics. A p -value of < 0.05 was considered significant. All analysis was conducted in the R statistical software environment (The R Foundation, Vienna, Austria).

Results

One hundred and ninety-five radiographs were included in the study. Sixty-five percent were males and the average age was 71.6 years (standard deviation = 19.1). There were 158 radiographs with the typical SLAC pattern of degeneration and 37 radiographs with atypical patterns such as isolated midcarpal joint OA. We had 154 wrists type 2 and 41 wrists type 1. Three wrists could not be categorized according to both lunate and capitate type (1%).

There was a significant correlation between midcarpal joint wrist type ( p  = 0.02) and lunate type ( p  = 0.03) and the pattern of wrist degeneration. SLAC degeneration developed in wrists with a type 2 lunate while atypical patterns (specifically midcarpal arthritis) were associated with a type 1 lunate and wrist ( Table 1 ).

Table 1. Arthritis patterns and their association with a wrist type 2.

	N	%	Wrist type 2, N (%)	p -Value
SLAC wrist pattern	158	81.0	130 (82.3)	< 0.001
Thumb CMC joint arthritis	179	91.8	142 (79.3)	0.06
STT joint arthritis	167	85.6	133 (79.6)	0.12
Radiolunate joint arthritis	33	16.9	24 (72.7)	0.63
Isolated midcarpal joint arthritis	10	5.1	3 (30)	< 0.001

Abbreviations: CMC, carpometacarpal; SLAC, scapholunate advanced collapse; STT, scaphotrapezial trapezoid.

Note: While a SLAC wrist pattern is associated with a wrist type 2, isolated midcarpal joint arthritis is associated with a wrist type 1.

When evaluating the relationship between the different joints involved in the arthritic process, we found that thumb CMC joint OA and STT joint OA occurred commonly with both the SLAC pattern and the “atypical” patterns of degeneration (radiolunate arthritis and isolated midcarpal joint arthritis); however, the isolated midcarpal joint arthritis pattern was associated independently with STT joint OA, p  < 0.01.

Radiographic Measurements

Radial height, radial inclination, volar tilt, and ulnar variance as well as SL gap and SL angle were not associated with wrist/lunate type. Ulnar variance was associated with thumb CMC and STT joint arthritis while radial height was significantly associated with isolated midcarpal joint arthritis. Volar tilt and SL angle were associated with the “non-SLAC” degeneration pattern ( Table 2 ).

Table 2. Wrist measurements and degenerative pattern.

	Overall ( N  = 195)	SLAC ( N  = 158)	Other ( N  = 37)	p -Value
Ulnar variance	4.61 (2.54)	4.68 (2.60)	4.32 (2.28)	0.36
Radial height	12.5 (3.26)	12.7 (3.44)	11.7 (2.33)	0.34
Radial inclination	19.3 (4.70)	19.3 (4.69)	19.6 (4.80)	0.34
Volar tilt	10.1 (5.13)	9.75 (5.21)	11.8 (4.46)	0.04
Scapholunate angle	88.4 (24.70)	90.5 (25.10)	79.7 (21.3)	0.01
SL gap	4.14 (2.40)	4.24 (2.52)	3.69 (1.77)	0.14

Abbreviations: SL, scapholunate; SLAC, scapholunate advanced collapse.

Note: All values are continuous and therefore are described as mean (standard deviation). The boldfaced values represent statistically significant values/relationships

Discussion

This study supports the premise that the structure of the wrist will predict the pattern in which pathology develops. The distribution of the lunate types in our population is in tandem with most studies, demonstrating a higher occurrence of a wrist type 2. ^{16 17} This study found a significant association between a SLAC pattern degeneration and lunate/wrist type 2, ^{16 18} this explains why the SLAC pattern of degeneration is the common pattern.

A cadaver study examining the difference in distribution of forces to the radiocarpal joint demonstrated that a wrist type 2 transfers forces radially to the SL joint and radius while a wrist type 1 transfers the forces differentially in a more ulnar direction. ¹⁹ This differential transfer radially in type 2 wrists can explain failure of the SL ligament with repeated trauma or significant one-time injury and the development of the typical SLAC pattern with initial wear at the radial styloid-scaphoid joint followed by involvement of the whole radial-scaphoid joint. This disparate transfer of forces may also explain why in a type 1 wrist the radial-scaphoid joint remains relatively spared and the wrist tends to develop wear in just the midcarpal joint. Since in a type 1 wrist the forces are transferred preferentially from the capitate through the lunate and radiolunate joint rather than through the SL joint and radioscaphoid joint, the forces transfer through the capitolunate joint, lunate, and radiolunate joint without loading the SL ligament.

The STT joint was found to be involved in most of the degenerative wrists we evaluated. A radiographic study found an association between STT arthritis and isolated midcarpal joint arthritis. ¹³ This association is supported by the findings of this study ( p  < 0.01). Another observational study found STT arthritis to be inversely related to radioscaphoid arthritis. ⁶

Modeling and analysis of the arthritic STT joint has demonstrated two types of degenerative STT joints, one type in which there is more motion than a normal STT joint and another in which there is less motion than in a normal STT joint. ²⁰ In both of these mechanical options (of STT joint arthritis) it is likely less forces are transferred to the SL ligament since the scaphoid either slides from under the TT joint and the forces are then transferred through the capitate to the lunate (in the case of more motion in an arthritic joint than in a normal STT joint) or the scaphoid is stabilized by a stiff arthritic joint (the second mechanical option) which again will transfer the forces through a stable scaphoid to the capitate or radiocarpal joint rather than through the ligament. This would result in the observed inverse relationship between the degenerative joints and may explain forces traveling preferentially through the midcarpal joint in a type 1 wrist resulting in isolated midcarpal joint arthritis. However, since this is an observed association, it remains unclear which structure is affected first, and which is secondary (the STT joint arthritis or the midcarpal joint arthritis). Biomechanical testing would have to be done to understand the transfer of forces through a wrist with arthritis in the STT joint.

Radiolunate arthritis without a history of inflammatory disease is rare; however, a recent study by Miller et al found that radiolunate or scaphocapitate arthritis occurred in over a one-third of cases and that less than half of the degenerative wrists had a SLAC pattern of degeneration. ¹⁸ We found significant associations between non-SLAC arthritis pattern and volar tilt and (inverse) SL angle. These measurements may be a result of the arthritis rather than a precipitating factor in the development of this pattern of degeneration. Likewise, we found a significant association between radial height and isolated midcarpal joint arthritis. Further mechanical study is necessary to better understand these relationships.

This study was a retrospective review of radiographs that represent degenerative wrist arthritis as a final result of forces (over a lifetime of use and injury) working on a specific bony structure. We assume bony structure does not in itself cause arthritis but rather can predict the pattern in which degeneration occurs with wear.

Beyond injury and use, other factors will affect the development of arthritis such as specific activity, occupation, hand dominance, and age. Evaluation of the effect of these parameters was outside of the scope of this study.

In summary, there is significant variation in wrist structure. It is difficult to “prove” that this structure will affect the way pathology, specifically wear and tear/OA of the joint, will develop. This is especially true since forces and injuries need to occur and affect any specific structure for arthritis to develop, and these we do not control or know how to adequately record. This study looking at established osteoarthritic wrists has found some significant relationships that constitute another step in our understanding and may be used to prevent arthritis from developing.