Immunohistochemical Investigation of Mechanoreceptors Within the Injured Scapholunate Ligament.

PURPOSE: Scapholunate ligaments (SLLs) play a well-established role in maintaining carpal alignment and kinematics, and are innervated with sensory mechanoreceptors located within the ligaments. They are involved in the afferent arc of dynamic wrist stability. The aim of this study was to describe the changes in these mechanoreceptor populations in injured SLLs. METHODS: Injured SLLs were collected from human wrists at the time of SLL reconstruction or limited wrist fusion, where the ligament remnants would otherwise be discarded. These specimens were formalin-fixed and paraffin-embedded for immunohistochemical analysis to identify mechanoreceptors, which were then classified by type and location within the ligament. RESULTS: A total of 15 ligaments were collected, with the interval from injury ranging from 39 days-20 years. Eleven ligaments were collected less than one year after injury, and four ligaments were collected two years or more after injury. A total of 66 mechanoreceptors were identified, with 50 mechanoreceptors identified in nine of the 11 specimens collected less than one year after injury. In this group, 54% of the mechanoreceptors resided in the volar subunit, 20% in the dorsal subunit, and 26% in the proximal subunit. Two of the four specimens collected two years or later after injury contained mechanoreceptors, all of which were located in the dorsal subunit. Increasing time from injury demonstrated a decline in mechanoreceptor numbers within the volar subunit. CONCLUSIONS: Mechanoreceptors were consistently located in the SLL, particularly in the volar subunit of specimens collected less than one year after injury. CLINICAL RELEVANCE: Ligament reconstruction techniques aim to primarily reconstitute the biomechanical function of the disrupted SLL; however, re-establishing the afferent proprioceptive capacity of the SLL may be a secondary objective. This suggests the need to consider the reconstruction of its volar subunit particularly in those managed within one year of injury.

Medial Femoral Condyle Corticoperiosteal Flap for Failed Total Wrist Fusions.

Background Recalcitrant nonunion following total wrist arthrodesis is a rare but challenging problem. Most commonly, in the setting of failed fusion after multiple attempts of refixation and cancellous bone grafting, the underlying cause for the failure is invariably multifactorial and is often associated with a range of host issues in addition to poor local soft-tissue and bony vascularity. The vascularized medial femoral condyle corticoperiosteal (MFC-CP) flap has been shown to be a viable option in a variety of similar settings, which provides vascularity and rich osteogenic progenitor cells to a nonunion site, with relatively low morbidity. While its utility has been described for many other anatomical locations throughout the body, its use for the treatment of failed total wrist fusions has not been previously described in detail in the literature. Methods In this article, we outline in detail the surgical technique for MFC-CP flap for the management of recalcitrant aseptic nonunions following failed total wrist arthrodesis. We discuss indications and contraindications, pearls and pitfalls, and potential complications of this technique. Results Two illustrative cases are presented of patients with recalcitrant nonunions following multiple failed total wrist fusions. Conclusion When all avenues have been exhausted, a free vascularized corticoperiosteal flap from the MFC is a sound alternative solution to achieve union, especially when biological healing has been compromised. We have been able to achieve good clinical outcomes and reliable fusion in this difficult patient population.

Determining the optimal radiologic wrist and forearm position to visualize screw protrusion in scaphoid fixation.

BACKGROUND: Surgical fixation of scaphoid fractures may result in unrecognized screw protrusion and subsequent cartilage damage to the adjacent joints. The purpose of this study was to use a three-dimensional (3D) scaphoid model to determine the wrist and forearm positioning that will allow intra-operative fluoroscopic visualization of screw protrusions. METHODS: Two 3D scaphoid models, with the wrist in neutral and 20° ulnar deviated, were reconstructed from a cadaveric wrist using the Mimics software. The scaphoid models were divided into three segments and further divided into four quadrants in each of the three segments along the scaphoid axes. Two virtual screws, with a 2 and 1 mm groove from the distal border, were placed so that the screws protrude from each quadrant. The wrist models were rotated along the long axis of the forearm and the angles at which the screw protrusions were visualized were recorded. RESULTS: One-millimetre screw protrusions were visualized at a narrower range of forearm rotation angles compared to 2 mm screw protrusions. One-millimetre screw protrusions in the middle dorsal ulnar quadrant could not be detected. Visualization of the screw protrusion in each quadrant varied with forearm and wrist positioning. CONCLUSION: In this model, all screw protrusions, except 1 mm protrusions in the middle dorsal ulnar quadrant, were visualized with the forearm in pronation, supination or in the mid-pronation position and with the wrist in neutral or 20° ulnar deviated.

Trapeziometarpal joint arthritis in the young patient.

Initial management of symptomatic trapeziometacarpal joint arthritis is generally non-operative. Though the aetiology of trapeziometacarpal arthritis remains controversial, unrecognized joint incongruity in early-stage arthritis (Eaton stage 1 or 2) is likely to lead to progression of joint degeneration. In established arthritis, salvage procedures can successfully alleviate symptoms and return of function; however the long-term outcome of these procedures has not been determined, and this is of particular concern in the younger patient. Recognition of the joint incongruity in these patients with early-stage disease can lead to measures which may prevent or delay the progression of joint degeneration.Level of evidence: V.

Biomechanical comparison of intramedullary screw fixation, dorsal plating and K-wire fixation for stable metacarpal shaft fractures.

We compared four methods of metacarpal shaft fixation: 2.2 mm intramedullary headless compression screw; 3.0 mm intramedullary headless compression screw; intramedullary K-wire fixation; and dorsal plate fixation. Transverse mid-diaphyseal fractures were created in 64 metacarpal sawbones and were assigned into four groups. Peak load to failure and stiffness were measured in cantilever bending and torsion. We found that dorsal plating had the highest peak load to failure. However, initial bending stiffness of the 3.0 mm intramedullary headless compression screw was higher than that of the dorsal plates. In torsion testing, dorsal plating had the highest peak torque, but there was no significant difference in torsional stiffness between the plate and intramedullary headless compression screw constructs. We concluded that intramedullary headless compression screw fixation is biomechanically superior to K-wires in cantilever bending and torsion; however, it is less stable than dorsal plating. In our study, the initial stability provided by K-wire fixation was sufficient to cope with expected loads in the early rehabilitation period, whereas dorsal plates and IHCS constructs provided stability far in excess of what is required.

Double-Screw Osteosynthesis in an Unstable Scaphoid Fracture Model: A Biomechanical Comparison of Two Screw Configurations.

PURPOSE: Although there is evidence that a single headless compression screw is sufficient for fixation of most scaphoid fractures, double-screw osteosynthesis has been shown to result in higher failure strength and stiffness than a single screw. However, the biomechanical effect of different screw configurations has not been determined. METHODS: A standardized unstable fracture model was produced in 28 cadaveric scaphoids. Specimens were randomly allocated to 1 of 2 fixation groups using 2 internal compression screws positioned in either the sagittal or coronal plane. A specimen-specific 3-dimensionally-printed customized screw placement and osteotomy device was developed using computer-aided design-generated models derived from computed tomography scan data of each individual scaphoid. Load to failure and stiffness of the repair constructs were evaluated using a mechanical testing system. RESULTS: There were no significant differences in size, weight, and density between the scaphoid specimens. The average distance between screws was significantly greater in the sagittal group than in the coronal group. There were no significant differences between the coronal and sagittal aligned double screws in load to 2 mm displacement (mean coronal 180.9 ± 109.7 N; mean sagittal 156.0 ± 85.8 N), load to failure (mean coronal 275.9 ± 150.6 N; mean sagittal 248.0 ± 109.5 N), stiffness (mean coronal 111.7 ± 67.3 N/mm; mean sagittal 101.2 ± 45.1 N/mm), and energy absorption (mean coronal 472.6 ± 261.4 mJ; mean sagittal 443.5 ± 272.7 mJ). CONCLUSIONS: There are no significant biomechanical differences between the sagittal or coronal aligned double headless compression screws in a scaphoid fracture model with bone loss. CLINICAL RELEVANCE: In cases where double-screw fixation of the scaphoid is being considered, the placement of double screws can be at the discretion of the surgeon, and can be dictated by ease of access, surgical preference, and fracture orientation.

Histomorphology of the Subregions of the Scapholunate Interosseous Ligament and Its Enthesis.

Background The scapholunate interosseous ligament (SLIL) has three subregions: dorsal, proximal, and volar. The SLIL enthesis has not previously been studied despite its important mechanical function in wrist joint biomechanics. Questions/Purposes This study aims to compare the histomorphological differences between the SLIL subregions, including at their entheses. Three questions are explored: Do the gross dimensions differ between SLIL subregions? Does the enthesis qualitatively, and its calcified fibrocartilage (CF) quantitatively, differ between (a) SLIL subregions and (b) scaphoid and lunate attachments? Methods Twelve fresh-frozen human cadaveric wrists were dissected and the gross dimensions of the SLIL subregions measured. Subregions were histologically processed for morphological and compositional analyses, including quantification of enthesis CF area. Results The dorsal subregion was the thickest. The dorsal and volar subregions had fibrocartilaginous entheses, while the proximal subregion was attached to articular cartilage. The dorsal subregion had significantly more CF than the volar subregion. There was no significant difference in the enthesis CF between scaphoid and lunate attachments in the three subregions. Conclusions There are significant morphological differences between the SLIL subregions. The dorsal subregion has the largest amount of CF, which is consistent with the greater biomechanical force subjected to this subregion. The similar histomorphology of the ligament at the scaphoid and lunate entheses suggests that similar biomechanical forces are applied to both attachments. Clinical Relevance The histomorphological results confirm that the dorsal subregion is the strongest of the three subregions. The results from the entheseal region may have important implications in the study of graft incorporation during SLIL reconstruction.

Ligamentization and Remnant Integration: Review and Analysis of Current Evidence and Implications for Scapholunate Reconstruction.

Background Scapholunate interosseous ligament injuries are common but remain a therapeutic challenge. Current treatment modalities prioritize restoration of normal anatomy with reconstruction where appropriate. To date no reconstructive technique has been described that discusses the potential benefit of preservation of the scapholunate ligament remnant. Little is known about the "ligamentization" of grafts within the wrist. However, a growing body of knee literature suggests that remnant sparing may confer some benefit. In the absence of wrist specific studies, this literature must guide areas for potential augmentation of current surgical practices. Objective The purpose of this study was to perform a review of the process of ligamentization and a systematic review of the current literature on the possible role of ligament sparring and its effect on ligamentization. Methods A systematic search of the literature was performed to identify all the studies related to remnant sparing and the ligamentization of reconstructed tendons, regardless of graft type or joint involved from MEDLINE, EMBASE, and PubMed until February 1, 2016 using the following keywords: ligamentization, graft, remodelling, reconstruction, biomechan*, histolo∗, scapholunate ligament. Each selected study was evaluated for methodological quality and risk of bias according to a modified Systematic Review Center for Laboratory Animal Experimentation criteria. Conclusions The available literature suggests that ligament sparring demonstrated a trend toward improvements in vascularity, mechanoreceptors, and biomechanics that lessens in significance over time. Clinical Relevance This review suggests that remnant sparing may be one way to improve outcomes of scapholunate ligament reconstructive surgery. Level of Evidence This is a level I/II, review study.

Ulnar-sided wrist pain: a prospective analysis of diagnostic clinical tests.

BACKGROUND: Identifying the cause of pain on the ulnar side of the wrist can be challenging. The outcome and recovery following surgery can be unpredictable. The aim of this study was to document and analyse the clinical tests used to evaluate the cause of ulnar-sided wrist pain and determine their diagnostic relevance. METHODS: This is a prospective evaluation of 110 patients who presented with pain on the ulnar side of the wrist. The clinical evaluation and results from radiological investigations were documented and analysed. RESULTS: There were 17 different diagnoses. Eighty-five percent of the diagnoses were triangular fibrocartilage complex (TFCC) injuries, ulnocarpal abutment syndrome (UCAS), pisotriquetral arthritis (PTA), triquetral fracture or non-union, distal radioulnar joint arthritis (DRUJ OA) and extensor carpi ulnaris (ECU) pathology. The ulnocarpal stress test and ulnar foveal sign were positive in several diagnoses. The ulnar foveal sign had a sensitivity and specificity of 89% and 48% for TFCC injuries, and 85% and 37% for UCAS, respectively. The sensitivity and specificity of pisotriquetral shear test for PTA was 100% and 92%, respectively. Patients with PTA or ECU pathology localised their pain better on the patient's pain localisation chart. CONCLUSION: Diagnosis of TFCC injuries, UCAS, DRUJ OA and ECU injuries are challenging as the clinical symptoms and signs for the four diagnoses were similar and required either magnetic resonance imaging or computed tomography for diagnostic confirmation after clinical examination. The ulnocarpal stress test and the ulnar foveal sign were not sufficiently specific.

Functional Recovery Following Trapeziectomy and Ligament Reconstruction and Tendon Interposition: A Prospective Longitudinal Study.

PURPOSE: Patients undergoing surgery for trapeziometacarpal (TMC) joint arthritis require preoperative counseling on the expectations of surgery. This study aims to document the objective and functional recovery over the initial 12 months following trapeziectomy and ligament reconstruction with tendon interposition (LRTI). METHODS: We prospectively followed 55 patients with symptomatic TMC joint osteoarthritis after trapeziectomy and LRTI. Patients were assessed on functional outcome measures, pain, and objective outcomes of grip, tip and key pinch strength, and range of motion. Outcomes were recorded preoperatively and at 3, 6, 9, and 12 months after surgery. RESULTS: Outcome measures of Disabilities of the Arm, Shoulder, and Hand (DASH), Patient-Rated Wrist Evaluation (PRWE), and pain, improved significantly after surgery at each 3-month interval up to 9 months. Palmar and radial abduction were significantly improved compared to their preoperative ranges, but opposition was unchanged. Power grip significantly exceeded the preoperative strength at 6 months and further increased at 9 months. Tip pinch significantly exceeded the preoperative strength at 12 months. There was no difference in the key pinch strength compared to the preoperative strength. CONCLUSIONS: Over a follow-up period of 12 months, trapeziectomy and LRTI is an effective treatment in significantly reducing pain in 80% of patients. Although normal patient-reported outcome measures of DASH and PRWE are not regained, when compared to normative values, these measures are significantly improved; the improvement plateaus at 9 months. Patients can expect to attain 37% and 46% of their eventual measured DASH and PRWE scores, respectively, at 3 months, and 82% and 79% of their eventual measured DASH and PRWE scores, respectively, at 6 months. Grip strength exceeded the preoperative strength by 15% at 6 months and by 30% at 9 months. Tip pinch strength significantly exceeded the preoperative strength by 20% at 9 months. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic II.

Surgical Repair of Triangular Fibrocartilage Complex Tears: A Systematic Review.

Objective This study systematically reviews the outcomes of surgical repair of triangular fibrocartilage complex (TFCC) tears. Existing surgical techniques include capsular sutures, suture anchors, and transosseous sutures. However, there is still no consensus as to which is the most reliable method for ulnar-sided peripheral and foveal TFCC tears. Methods A systematic review of MEDLINE and EMBASE was performed according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The focus was on traumatic Palmer 1B ulna-sided tears. Twenty-seven studies were included, including three comparative cohort studies. Results There was improvement in all functional outcome measures after repair of TFCC tears. The outcomes following peripheral and foveal repairs were good overall: Mayo Modified Wrist Evaluation (MMWE) score of 80.1 and 85.1, Disabilities of the Arm, Shoulder and Hand (DASH) score of 15.7 and 15.8, grip strength of 80.3 and 92.7% (of the nonoperated hand), and pain intensity score of 2.1 and 1.7, respectively. For peripheral tears, transosseous suture technique achieved better outcomes compared with capsular sutures in terms of grip strength, pain, Patient-Rated Wrist Evaluation (PRWE), and DASH scores (grip 85.8 vs. 77.7%; pain 1.5 vs. 2.2; PRWE 11.6 vs. 15.8; DASH 14.4 vs. 16.1). For foveal tears, transosseous sutures achieved overall better functional outcomes compared with suture anchors (MMWE 85.4 vs. 84.9, DASH 10.9 vs. 20.6, pain score 1.3 vs. 2.1), but did report slightly lower grip strength than the group with suture anchors (90.2 vs. 96.2%). Arthroscopic techniques achieved overall better outcomes compared with open repair technique. Conclusion Current evidence demonstrates that TFCC repair achieves good clinical outcomes, with low complication rates. Level of Evidence This is a Level IV, therapeutic study.

Reconstruction of the Proximal Scaphoid With a Medial Femoral Trochlea Osteochondral Graft: Minimum 2-Year Results.

PURPOSE: To report the clinical and radiological outcomes after medial femoral trochlear (MFT) osteochondral graft for the salvage of proximal scaphoid fractures with a minimum 2-year follow-up. METHODS: A retrospective review was performed of patients with comminuted fractures of the proximal scaphoid treated by excision of the proximal pole and replacement with free vascularized MFT osteochondral graft. Demographic data, objective and radiographic measurements, and patient-reported outcome measures of the upper limb and knee were collected. Pain was assessed by completion of a visual analog scale (VAS). RESULTS: Between February 2014 and May 2015, 12 MFT osteochondral grafts were performed. Eight patients were available for follow-up at a mean of 34 months (range, 28-39 months). The mean range of wrist flexion was 31° (range, 15°-60°), extension was 34° (range, 5°-60°), radial deviation was 9° (range, 0°-20°), ulnar deviation was 28° (range, 10°-45°) and grip strength was 42 kg (range, 25-53 kg). The median wrist pain, as measured by VAS, was 0.7 (mean, 1.3; range, 0-6). The average follow-up scapholunate, radiolunate, and radioscaphoid angles were 58.9° (range, 44°-93°), 12.9° (range, 0°-30°), and 46.0° (range, 35°-63°), respectively. The mean Disabilities of the Arm, Shoulder, and Hand (DASH) score was 13.9 (range, 3-43) and Patient Rated Wrist Evaluation (PRWE) score was 22.4 (range, 2-68). The mean postoperative Oxford Knee Score was 42 (range, 14-48). One patient suffered notable knee pain at 37-month follow-up. One patient suffered notable pain on the radial side of the wrist and underwent scaphoid excision and 4-corner arthrodesis. CONCLUSIONS: Replacement of the fragmented proximal scaphoid by MFT graft is an alternative to other salvage options and most patients can expect pain relief and acceptable wrist motion. These results need to be balanced against the potential for donor-site morbidity. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic V.

Three-and-a-half to 18 year outcome data for costal osteochondral grafts for salvage of the proximal pole of the scaphoid.

Twelve patients who had undergone costal osteochondral graft reconstruction of the proximal pole of scaphoid were evaluated with clinical examination, patient-reported outcome scores and radiographs with an average follow-up of 10 years (range 3.5-18). The range of wrist motion was not significantly changed compared with the preoperative range of motion and functional outcomes scores were acceptable. The patients reported low pain scores despite the universal presence of radiographic changes of reduced carpal height and arthritis of the midcarpal and radiocarpal joints. Costal osteochondral graft reconstruction of the proximal pole of scaphoid offers good long-term pain relief and function.Level of evidence: IV.

Measurement of Scaphoid Bone Microarchitecture: A Computed Tomography Imaging Study and Implications for Screw Placement.

PURPOSE: High bone density and quality is associated with improved screw fixation in fracture fixation. The objective of this study was to assess bone density and quality in the proximal and distal scaphoid to determine optimum sites for placement of 2 screws in scaphoid fracture fixation. METHODS: Twenty-nine cadaveric human scaphoid specimens were harvested and scanned using micro-computed tomography. Bone density (bone volume fraction) and bone quality (relative bone surface area, trabecular number, and trabecular thickness) were evaluated in 4 quadrants within each of the proximal and distal scaphoid. RESULTS: The proximal radial quadrant of the scaphoid had significantly greater bone volume than the distal ulnar (mean difference, 33.2%) and distal volar quadrants (mean difference, 32.3%). There was a significantly greater trabecular number in the proximal radial quadrant than in the distal ulnar (mean difference, 16.7%) and in the distal volar quadrants (mean difference, 15.9%) and between the proximal ulnar and the distal ulnar quadrants (mean difference, 12%). There was a significantly greater bone surface area in the proximal radial and distal radial quadrants than in the distal ulnar and distal volar quadrants. There were no significant differences in trabecular thickness between the 8 analyzed quadrants CONCLUSIONS: Although there are differences in bone volume, trabecular number, and bone surface area between the proximal pole of the scaphoid and that of the distal pole, there were no significant differences in the bone quality (trabecular thickness, trabecular number, and relative bone surface area) and density (bone volume fraction) between the 4 quadrants of the proximal or distal pole of the cadaveric scaphoids studied. CLINICAL RELEVANCE: Insertion of 2 headless compression screws can be determined by ease of surgical access and ease of screw positioning and not by differences in bone quality or density of the proximal or distal scaphoid.

Medial Femoral Trochlea Graft for Scaphoid Waist Nonunion: A Case Report and Review of the Literature.

The medial femoral trochlea (MFT) of the knee is a donor site for convex osteochondral vascularized bone that has been used for the salvage of fractures of the proximal pole of the scaphoid. Chronic nonunited fractures of the scaphoid may lead to a sequence of degenerative change often referred to as scaphoid nonunion advance collapse. The vascularized MFT osteochondral graft has been reported as a salvage procedure for fractures of the proximal pole of the scaphoid, in situations where fixation is not an option. In this "Special review," we describe the technique of free vascularized MFT graft in a case in which the nonunited scaphoid fracture was associated with segmental loss of the articular surface of the scaphoid waist. Given the likely progression of arthritis, if left untreated, we elected to treat this by replacing the lost articular surface using a vascularized intercalary osteochondral MFT graft between the nonunited scaphoid segments.

The Twist X-Ray: A Novel Test for Dynamic Scapholunate Instability.

Background Scapholunate instability (SLI) is the most common form of carpal instability. Early detection of SLI is imperative as early reconstructive procedures can potentially prevent the natural history of progressive degenerative arthritis. After wrist arthroscopy, magnetic resonance imaging (MRI) remains the next best noninvasive diagnostic option; however, access still remains costly and is often limited in many health care systems worldwide. In this article, we describe a novel device that allows for dynamic X-rays to be taken, accentuating the scapholunate (SL) widening. Description of Technique Twist X-ray views are generated by the patient clenching a device that combines the standard clenched fist views with ulnar deviation and supination. The test is easy to perform and functions by combining a higher grip force with the ulnar deviation and pronation effects of the extensor carpi ulnaris tendon, thus accentuating the SL gap in dynamic instability. Patients and Methods We present a series of four patients with dynamic SLI and compare the findings of the Twist X-rays with conventional wrist X-rays series, including standard anteroposterior, lateral, radial, and ulna deviation, clenched fist, and pencil grip views. Results In all the four patients, there was substantial dynamic SL widening. The SL interval increased from a mean of 1.8 mm (range: 1.5-2.8) on posteroanterior X-rays to 6.3 mm (range: 4.6-8.2) with the Twist views. Interestingly, on the pencil grip view, the mean widening was only 1.5 mm (range: 1-2.8 mm). Conclusion The authors describe a novel device that allows for improved detection of dynamic SL ligament instability when performing stress X-ray views of the wrist. Level of Evidence This is a Level IV study.

Fixation of the Fractured Lunate in Kienböck Disease.

PURPOSE: To describe an uncommon subset of fractured lunates in Kienböck disease that is salvageable by internal fixation. METHODS: We performed a retrospective review for patients with Kienböck disease treated by internal fixation. Demographic data, objective and radiographic measurements, patient-reported outcome measures (Disabilities of the Arm, Shoulder, and Hand and Patient-Rated Wrist Evaluation) and pain (visual analog scale) scores were collected. RESULTS: Of the 7 patients treated, 5 were available for review. At an average follow-up of 7.1 years (range, 1.5-15 years), all patients had activity-related wrist pain but were pain-free at rest. Radiographic assessment showed union in all lunates and a normal radioscaphoid angle and Stahl index. The modified carpal height ratio was reduced in 4 patients and normal in one. There was no observed narrowing or irregularity of the radiocarpal or midcarpal joints. Patient-reported outcome measures in 2 patients were unsatisfactory. CONCLUSIONS: Computed tomography of the lunate in Kienböck disease is an important investigative tool. A coronal split fracture of these lunates can be salvageable by internal fixation. Revascularization of the lunate can be performed when the fragment is of sufficient size. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic V.

Quantitative analysis of in-vivo thumb carpometacarpal joint kinematics using four-dimensional computed tomography.

The purpose of this study was to define the normal thumb carpometacarpal joint kinematics in-vivo during opposition and abduction using four-dimensional computed-tomography in four volunteers. Movement of the metacarpal relative to the trapezium was quantified using both Euler and helical axis representations. Articular surface contact patterns were also analysed. The overall axis of rotation for the movement of opposition and abduction passes through the trapezium and the base of the proximal phalanx, respectively. An abrupt change in instantaneous axis of rotation at terminal opposition was found. Ligament modelling shows dorsoradial ligament becomes tauter towards terminal opposition, whereas anterior oblique ligament becomes more slack. These results support the existence of the 'screw-home' pivot at terminal opposition and the importance of the dorsoradial ligament for stability in this position. The normal reference set in this study can help establish a diagnostic tool for subtle carpometacarpal instability, or for evaluating efficacy of surgery.