Biometric and Ligaments Analysis of the Scaphotrapeziotrapezoid Joint: Implications for Arthroplasty

Abstract

Background

The periarticular ligament anatomy of the scaphotrapeziotrapezoid (STT) joint varies in the literature, complicating standardization. Preservation of this ligamentous array is critical in preventing intracarpal malalignment.

Purpose

This study aims to map ligament insertion sites on the bony components of the STT joint and define resection margins for the scaphoid, trapezium, and trapezoid during arthroplasty.

Materials and Methods

We examined 26 cadaveric wrists. Needles marked the STT joint before arthrotomy, allowing precise observation of ligament positioning intact. Ligament insertion sites on the scaphoid, trapezium, and trapezoid were measured with micrometric calipers. We recorded STT arthritis presence and distribution on the scaphoid, trapezium, and trapezoid articular surfaces. Each surface was divided into four quadrants voloulnar (VU), voloradial (VR), dorsoulnar (DU), and dorsoradial (DR).

Results

The dorsal intercarpal ligament (DIC) was the only extrinsic dorsal ligament of the STT joint. The average insertion distance from the articular surface was 3.033 mm (standard deviation [SD] = 0.693) on the trapezium and trapezoid, compared to 1.918 mm (SD = 0.329) on the scaphoid. This difference was statistically significant ( p  < 0.001). The palmar ligament organization resembled a rigid tripod anchored by the RS (radioscaphoid), ST (scaphotrapezial), and SC (scaphacapitate) ligaments around the scaphoid tubercle. Palmar ligament insertion points averaged 0.58 mm (SD = 0.32) from the articular surface, with no significant difference between the scaphoid and the trapezoid–trapezium complex ( p  = 0.558). STT arthritis was present in 80.8% of wrists. The VU sides of the STT were most affected, particularly the volar side of the trapezoid.

Conclusion

The DIC ligament and palmar ligamentous tripod, formed by the RS, SC, and ST ligaments, could acts as a mechanical lock preventing dorsal scaphoid translation. While distal scaphoid pole resection is standard, our findings suggest prioritizing proximal trapezium and trapezoid resections in arthroplasty to avoid instability.

The scaphotrapeziotrapezoid (STT) joint is the second most common site of wrist arthritis after the trapeziometacarpal (TMC) joint. ¹ Despite its prevalence, the anatomical and biomechanical understanding of the STT joint remains incomplete. The description of periarticular ligament anatomy varies in the literature, complicating standardization. ^{2 3 4 5 6} Primary ligaments include the dorsal intercarpal ligament (DIC), radioscaphoid ligament (RS) (also described as the radial collateral ligament), radioscaphocapitate ligament (RSC), scaphocapitate ligament (SC), and scapho-trapezial-trapezoidal ligament complex, including scaphotrapezial ligament (ST). ⁷ Preservation of this ligamentous array is critical in preventing intracarpal malalignment. ⁸

Pathomechanics of STT arthritis are still unclear. However, in advanced stages, imaging studies of the STT arthritic wrist show the malalignment of the scaphoid and the first carpal row in extension, as a pattern of carpal instability nondissociative. Recently, it has been hypothesized that this malalignment occurs in association to scapholunate dissociation. ^{9 10} However, clear understanding of the evolutive patter is still lacking. A better understanding of ligament anatomy is therefore essential for understanding STT mechanics. Currently, the development of STT arthritis is considered strongly correlated with ligament damage in a multifactorial etiology pattern. ¹¹

Various surgical treatments, such as arthrodesis, resection arthroplasty (with or without implants), and both open and arthroscopic techniques, aim to mitigate symptoms. ^{12 13 14} Surgeries that preserve periarticular ligaments may offer functional benefits, especially in the early symptomatic stages resistant to medical therapy.

This study aims to map ligament insertion sites on the bony components of the STT joint, clarify their role in wrist mechanics and define resection margins for the scaphoid, trapezium, and trapezoid during arthroplasty.

Materials and Methods

We examined 26 cadaveric wrists (13 male and 13 female) with no preexisting wrist pathology or history of wrist surgery. All the bodies were fresh with good passive wrist joint mobility. The mean age of the donors was 75.5 years (range: 43–94 years). The arms were obtained from body donations, frozen at −20°C before testing and thawed at room temperature for 12 hours before the experiment. Each specimen's laterality was documented. After removing musculotendinous structures, osteoligamentous components were dissected. The orientation of the cadaveric parts was defined in relation to the plane of the STT articular surface. Needles marked the STT joint before arthrotomy, allowing precise observation of ligament positioning intact. Following arthrotomy, we identified and isolated the palmar and dorsal periarticular ligaments stabilizing the STT joint. Ligament insertion sites on the scaphoid, trapezium, and trapezoid were measured with micrometric calipers (Beslands) ( Fig. 1 ). If a difference in insertion level existed on a bone, the two extremes were averaged. Surgical loupes (×4.5 zoom) were used when ligament individualization was too difficult in macroscopic view.

Fig. 1.

Dorsal view of a cadaveric left wrist. Micrometric caliper measurement of ligament insertions on the trapezium, trapezoid and scaphoid. Abbreviations: DIC, dorsal intercarpal ligament; M1-2, 1st and 2nd metacarpals.

We recorded STT arthritis presence and distribution on the scaphoid, trapezium, and trapezoid articular surfaces. Each surface was divided into four quadrants voloulnar (VU), voloradial (VR), dorsoulnar (DU), and dorsoradial (DR) as in TMC joint mapping ¹⁵ ( Fig. 2 ). The description of the quadrants and anatomical dissection planes were defined in relation to the articular surface of the STT and not in relation to the radiocarpal surface. After each dissection, a TMC arthrotomy assessed coexisting arthritis. Presence of macroscopically visible calcium pyrophosphate crystals (white crystals) was recorded as a sign of chondrocalcinosis in the STT joint.

Fig. 2.

Left STT joint on cadaveric bone. The anatomical plane is defined in relation to the plane of the STT joint. ( A ) In volar view; ( B ) in posterior view; ( C ) trapezium and trapezoid quadrant joint surfaces in proximal view; ( D ) scaphoid quadrant joint surfaces in distal view. Abbreviations: DU, dorsoulnar; DR, dorsoradial; VU, voloulnar; VR, voloradial.

Data analysis used Microsoft Excel for descriptive statistics and Student's t -tests for comparative analyses.

Results

Of the 26 cadaveric subjects, 50% were male and 50% female, with an average age of 75.5 years (range: 43–94 years).

TMC arthritis coexisted with STT arthritis in 80.8% of cases. Chondrocalcinosis was observed in nine specimens (34.6%), and 82.4% of cases of macroscopic chondrocalcinosis occurred alongside STT arthritis. Subjects with chondrocalcinosis were female in 89% of cases.

The DIC was the only extrinsic dorsal ligament of the STT joint ( Fig. 3 ). It inserted on the scaphoid, trapezium, and trapezoid, although its distal insertions often merged with dorsal capsular structures. The average insertion distance from the articular surface was 3.033 mm (SD = 0.693) on the trapezium and trapezoid, compared with 1.918 mm (SD = 0.329) on the scaphoid ( Fig. 4 ). This difference was statistically significant ( p  < 0.001). The difference in ligament insertion levels between quadrants could not be demonstrated.

Fig. 3.

Dissection of the posterior aspect of a right wrist. The needles are located in the STT joint. The dotted line represents the level of insertion of the DIC and dorsal joint capsule on the STT joint. Abbreviations: DIC, dorsal intercarpal ligament; DRC, dorsal radiocarpal ligament; M1-5, 1st to 5th metacarpals.

Fig. 4.

Dissection of the anatomical elements of the STT in dorsal ( A ) and dorsoradial oblique ( B-C ) views on a right wrist. The dotted line represents the dorsal capsulo-ligament insertion on the STT. The star (*) represents chondrolysis on the ulnar side of the scaphoid. Figure C is a schematic view of the dissection in figure B before the DIC incision. Abbreviations: M1-2-3, 1st, 2nd and 3rd metacarpals; DIC, dorsal intercarpal ligament; DRC, dorsal radiocarpal ligament; RS, radioscaphoid ligament; SC, scahocapitate ligament; SL, scapholunar ligament; ST, scaphotrapezial ligament.

Palmar extrinsic ligaments, such as the RS and RSC, were sturdier than the DIC and inserted exclusively on the scaphoid. Intrinsic ligaments, including the ST and SC ligaments, formed a rigid sling on the anterior side. The palmar ligament organization resembled a rigid tripod anchored by the RS, ST, and SC ligaments around the scaphoid tubercle ( Fig. 5 ). Palmar ligament insertion points averaged 0.58 mm (SD = 0.32) from the articular surface, with no significant difference between the scaphoid and the trapezoid–trapezium complex ( p  = 0.558).

Fig. 5.

Tripod organization of the palmar ligaments of the STT joint on dissection of a right wrist in anterior view. ( A ) Highlighting the scaphoid tubercle. ( B ) Palmar ligaments and bony elements of the STT joint, with the elements of the tripod ligament in red. The tripod ligament is represented by the links of a chain. ( C ) Schematic representation of the STT palmar tripod ligament with other palmar wrist ligaments. Abbreviations: RS, radioscaphoid ligament; SC, scaphocapitate ligament; ST, scaphotrapezial ligament; Td, trapezoid; M1-2, 1st and 2nd matacarpals; 1, long radiolunar ligament; 2, short radiolunar ligament; 3, radioscaphocapitate ligament; 4, ulnocapitate ligament; 5, ulnolunar ligament; 6, palmar radioulnar ligament; 7, ulnotriquetral ligament; 8, triquetrocapitate ligament; 9, pisohamate ligament.

STT arthritis was present in 80.8% of wrists ( Fig. 6 ). The trapezoid was the most affected bone, with an average of 67.3% of its articular surface exhibiting chondrolysis. The VR quadrant was most frequently involved (80.8%), followed by VU (69.2%), DR (61.5%), and DU. The scaphoid was the second most affected bone (55.8%), with the VU quadrant most involved (77.0%), followed by VR (65.4%), DU (53.8%), and DR (26.9%). The trapezium was the least affected, with less than 50% of its surface involved (47.1%), showing a similar quadrant distribution to the scaphoid.

Fig. 6.

Left STT joint on cadaveric bone. The anatomical plane is defined in relation to the plane of the STT joint. Palmar ( A ) and dorsal ( B ) ligament insertions around the STT joint highlighted by dotted lines corresponding to the entheses. Note that the ligament insertion surface is further from the joint line on the trapezium and trapezoid than on the scaphoid in dorsal view ( B ). Percentages of osteoarthritis observed during dissections according to the joint quadrant concerned trapezium, trapezoid ( C ) and scaphoid ( D ). Surfaces most affected by osteoarthritis are shown in red, and those least affected in green.

Discussion

Dissecting the STT joint ligaments is technically challenging due to their intricate anatomical arrangement. We recommend the use of surgical loupe during dissection to facilitate ligament individualization and avoid dissection errors. Drewniany et al proposed the STT ligament complex, encompassing the ST, SC, dorsal capsule, and palmar capsule. ¹⁶ Differentiating these ligaments from the articular capsule is difficult. The dorsal capsule likely mirrors the mechanical role of the DIC, whereas the palmar capsule aligns with the RS and RSC ligaments extending toward the trapezium. Palmar extrinsic ligaments are notably thicker and more robust than their dorsal counterparts. ⁶ This disparity may explain posterior scaphoid translation in wrist instability. ¹⁷

The DIC ligament and palmar ligamentous tripod, formed by the RS, SC, and ST ligaments, could acts as a mechanical lock preventing dorsal scaphoid translation ( Fig. 7 ) . Similar tripod configuration appear in Berger's anatomical drawings. ³ However, the STT joint's biomechanics are difficult to interpret due to its position between the distal TMC joint and proximal radiocarpal joint, where it absorbs axial pressure from the TMC joint. ¹⁸

Fig. 7.

Theoretical role of dorsal ligaments and palmar tripod ligaments of the STT as a “lock” against dorsal translation of the scaphoid in wrist instability. ( A ) Arthro-CT image of a right wrist in sagittal view showing posterior translation of the scaphoid. The purple lines define the posterior radioscaphoid angle (PRSA) abnormally high. Posterior subluxation of the scaphoid is indicated by the double blue arrow. ( B ) Dorsoradial oblique view illustration of a right wrist of posterior subluxation of the scaphoid after instability due to lesions of the dorsal intercarpal and dorsal radiocarpal ligaments. Abbreviations: M1-2-3, 1st; 2nd and 3rd metacarpals; DIC, dorsal intercarpal ligament; DRC, dorsal radiocarpal ligament; RS, radioscaphoid ligament; SC, scaphocapitate ligament; ST, scaphotrapezial ligament.

Our findings align with studies identifying preferential arthritis localization in the palmar–ulnar scaphoid and trapezoid–trapezium regions. ¹⁹ Axial forces from the TMC joint likely contribute affecting the distal trapezium's palmar–ulnar aspect. ^{15 20}

Surgical options for isolated STT arthritis resistant to medical therapy include STT arthrodesis, distal scaphoid pole resection, trapeziectomy, and STT arthroplasty with implants. ²¹ STT arthrodesis is often recommended for advanced arthritis with midcarpal instability. ^{22 23} Distal scaphoid pole resection offers simplicity but risks intracarpal instability due to loss of ligament function. ²⁴ Total trapeziectomy, as described by Langenhan et al, poses stability challenges. ²⁴ Implants such as STPI and Pyrocardan preserve scaphoid length and periarticular ligament tension, reducing instability risks. ^{25 26} Pyrocardan implant, with their thin profile (1 mm of central thickness), respects the distal scaphoid pole and its ligament insertions identified in this study. Studies show good results for Pyrocardan in STT. ^{26 27}

Arthroscopy has emerged as a viable approach for STT arthritis. ^{28 29 30} Although technically demanding and less commonly performed, ¹⁴ arthroscopic resection may have the advantages of preserving periarticular ligaments, particularly the ST ligament, a key stabilizer. ^{16 19} While distal scaphoid pole resection is standard, ^{31 32 33} our findings suggest prioritizing proximal trapezium and trapezoid resections to avoid instability. This aligns with Paeffgen et al's recent results, which highlight better outcomes with proximal trapeziectomy compared to distal scaphoid resection or total trapeziectomy. ³⁴

Our study has some limitations. Indeed, we have a limited number of anatomical pieces including important biometric variations. Although the ligament structures are different in vivo, the exclusive use of fresh cadavers with good passive joint mobility brings us closer to reality.

Detailed knowledge of ligament insertions around the STT joint is essential for understanding its biomechanics. Our findings support trapezium and trapezoid resections without scaphoid involvement, although clinical validation remains necessary.