Postoperative Radiographic Outcomes Following Abduction–Extension Metacarpal Osteotomy: A Comparison between Early and Advanced Carpometacarpal Arthritis

Introduction

The thumb carpometacarpal (CMC) joint is a bicondylar joint consisting of two vertically articulating saddle-shaped bones. The width of the thumb metacarpal base is 34% greater than that of the trapezium. This structure produces a wider range of joint motion, allowing for pinching and grasping motions.¹ However, this excellent range of motion is associated with limited stability and there are frequent heavy loads on this joint. A 1-kg pinch at the thumb tip translates into a 13-kg load at the base of the thumb, which is transmitted dorsoradially and proximally.^2,3 These biomechanical factors result in ligamentous laxity, leading to incongruent contact of the CMC joint and initiating the progression of degeneration.^4,5

Wilson initially described metacarpal osteotomy as a therapeutic approach for thumb CMC osteoarthritis (OA), and suggested performing an abduction osteotomy to correct adduction deformities.⁶ Subsequently, various iterations of metacarpal osteotomy were documented, involving extension osteotomy, abduction-opposition osteotomy and abduction–extension osteotomy.^5,7,8 Many reports have corroborated the clinical efficacy of metacarpal osteotomy, not only in early-stage, but also advanced-stage CMC OA.^8,9–14 Additionally, this procedure has the advantage of preserving the integrity of the joint; thus, facilitating potential future salvage procedures. However, this surgical option has not received significant attention yet. One reason for this is that radiographic improvements following metacarpal osteotomy have not been demonstrated, despite successful clinical outcomes.^5,9,13,15

This study aimed to elucidate the effect of metacarpal osteotomy on the congruity of the CMC joint. We investigated pre- and postoperative radiographic findings, focussing on dorsal subluxation, and compared the effects of metacarpal osteotomy on early- and advanced-stage CMC OA.

Methods

Our institutional review board approved this study. We obtained informed consent from each study subject. Of the 40 patients who underwent abduction–extension osteotomy for CMC OA performed by a single highly experienced hand surgeon at our institution between January 2018 and October 2021, we retrospectively reviewed 42 thumbs from 37 patients. Patients who were followed up for >2 years after surgery were eligible for this study. Two patients (two thumbs) who were lost to follow-up and one patient (one thumb) with stage III CMC OA who required arthrodesis as salvage 6 months after metacarpal osteotomy due to residual pain were excluded.

The indication for this procedure was persistent pain despite conservative treatment involving nonsteroidal anti-inflammatory drugs, steroid injection and orthosis. A fixed web space or ankylosis of the CMC joint was contraindicated. All patients were diagnosed with primary nontraumatic CMC OA. Thumbs with posttraumatic arthritis, rheumatoid arthritis or scaphotrapezial joint arthritis were excluded from this study. Our surgical strategy for CMC OA is that primary OA whose subluxation can be manually reduced is indicated for osteotomy, whereas irreducible OA is indicated for arthrodesis (Fig. 1).

The patients were evaluated using the modified Eaton classification¹⁶ and divided into two groups according to the severity of OA: stage I, normal or slight widening of the joint; stage II, slight narrowing of the joint with minimal sclerotic changes of the subchondral bone; stage III, marked narrowing of the joint with cystic changes and sclerotic bone and stage IV, stage III CMC arthritis with scaphotrapezial joint arthritis. Stages I and II CMC OA were classified as early OA, and stage III OA was identified as advanced OA.

Surgical Technique: Under general or axillary block anaesthesia, and using an above-elbow tourniquet, a 4-cm longitudinal incision was made over the dorsal aspect of the first metacarpal. After preserving the sensory branches of the radial nerve, the extensor pollicis brevis tendon was retracted ulnarly, and the first metacarpal was exposed subperiosteally without incising the CMC joint capsule. A transverse cut was made using a micro sagittal saw at approximately 1 cm from the base of the first metacarpal. A second cut was made 5 mm distal to the first cut to perform a 30° closing-wedge osteotomy. The highest part of the wedge was designed to be 2–3 mm radial from the centre of the dorsal cortex, which was shaped to combine extension and abduction. The contralateral side of the cortex was incompletely sawed to maintain stability. Following removal of the wedge bone, the osteotomy site was manually compressed and temporally fixed with Kirschner wires. Subsequently, the extension angle was checked by fluoroscopy, and additional osteotomy was made if the angle was <90°. The extension angle was defined as the angle between the line tangential to the dorsal cortex of the thumb metacarpal and the line connecting the two edges of the metacarpal facet of the CMC joint in the lateral view radiograph (Fig. 2A). Our objective was to achieve an extension angle of 90° or more. Thereafter, the osteotomy site was fixated with a pre-bent Variable Angle Locking Hand System^® (VAL Hand; DePuy Synthes, West Chester, PA, USA). Postoperatively, a thumb spica splint was applied for 2 weeks, allowing the patient to perform daily tasks, including deskwork. Grip and pinch exercises, as tolerated, were started 4 weeks postoperatively. The plate was removed 6 months to 1 year after surgery, depending on the patient’s preference.

Radiographic Evaluation: To evaluate the congruity of the CMC joint after metacarpal osteotomy, the % subluxation was measured using the lateral view of the joint before surgery, 3 months and 1 year postoperatively and at the latest follow-up visit. The % subluxation was defined as the ratio of the joint width between the dorsal overhang of the first metacarpal proximal base on the trapezium and the first metacarpal proximal base (Fig. 2B).¹⁷ The reliability of radiographical measurements was confirmed using CT scans taken preoperatively and 1 year postoperatively. Intra-class correlation coefficients (ICCs) were used to statistically show the high concordance between the value from the X-ray and that from the CT scan at the corresponding time point.

For comparison between the two groups, we also used the reduction ratio as an indicator of improvement of the subluxation, which was defined as the value of % subluxation at each time point minus that before surgery. A lateral view of the joint was obtained using the Kapandji method¹⁸ with the forearm pronated at 20°.

Subjective and Objective Evaluation: Subjective and objective data were obtained for all thumbs before surgery, 3 months and 1 year postoperatively and at the latest follow-up. The subjective assessment included the visual analogue scale (VAS) to evaluate pain, and the objective assessment included the measurement of grip strength using a Jamar hydraulic dynamometer (SAKAI Medical, Tokyo, Japan) and lateral pinch strength using a pinch gauge (B&L Engineering, Santa Fe Springs, California, USA). Grip and lateral pinch strengths were compared with their respective preoperative values.

Statistical Analysis: Parameters were compared between the early and advanced OA groups using Welch’s t-test or an unpaired t-test according to the F-test, evaluating the assumption of equal variance as a pretest. Subsequently, we performed inter-time point comparisons of % subluxation, VAS, % grip strength and % pinch strength using a paired t-test or Wilcoxon signed-rank test for each group. We also compared the reduction ratio between the two groups at each time point using the Mann–Whitney U test because of the non-normal distribution of the reduction ratio at 3 months after surgery in the advanced OA group. Furthermore, to determine the factors influencing the postoperative improvement of dorsal subluxation in advanced-stage OA, the Spearman rank correlation coefficient test was used to assess the correlation between the reduction ratio at each time point and various parameters, including preoperative % subluxation and pre- and postoperative extension angles. Additionally, the correlation between the reduction ratio and clinical outcomes, including the VAS score, % grip strength and % pinch strength at each time point, was examined in the advanced OA group using the Spearman rank correlation coefficient test. Data are expressed as mean ± standard deviation. Statistical significance was set at p < 0.05.

Results

Table 1 presents the characteristics and clinical outcomes of the patients included in this study. The early OA group included 10 thumbs in 9 patients, while the advanced OA group included 32 thumbs in 29 patients. Five patients underwent bilateral thumb metacarpal osteotomies: one patient with bilateral stage I OA, another patient with stage II and stage III OA and the remaining three patients with bilateral stage III OA. In the early OA group, % subluxation was recorded preoperatively (34.5 ± 7.7), 3 months (19.1 ± 7.6) and 1 year postoperatively (18.9 ± 7.3), and at the latest follow-up (18.6 ± 7.2). There was a significant decrease from the preoperative period to 3 months postoperatively (p < 0.001), whereas no significant difference was found between the 3-month and 1-year postoperative time points, and between the 1-year postoperative point and the latest follow-up. In the advanced OA group, % subluxation was also recorded preoperatively (43.1 ± 7.6), 3 months (36.9 ± 9.9) and 1 year postoperatively (32.3 ± 10.5), and at the latest follow-up (30.4 ± 10.5). There was a significant decrease from the preoperative period to 3 months postoperatively (p < 0.001), between 3-month and 1-year postoperative time points (p < 0.001), and between 1-year postoperative point and the latest follow-up (p = 0.024). Table 1 also presents the inter-time point comparisons of VAS, % grip strength and % pinch strength.

Table 2 shows the results of the comparison of the reduction ratios between the two groups at each time point. The reduction ratio was significantly higher in the early OA group than in the advanced OA group at 3 months after surgery, whereas no significant difference was found between the two groups at 1 year after surgery or at the latest follow-up.

Table 3 shows the correlation between the reduction ratio and each parameter in the advanced OA group. Postoperative extension angle was significantly correlated with the reduction ratio 3 months postoperatively, 1 year postoperatively and at the latest follow-up, whereas the preoperative % subluxation and preoperative extension angle were not correlated with the reduction ratio at any time point. In terms of clinical outcomes, VAS score, % grip strength and % pinch strength were not significantly associated with the reduction ratio in the advanced OA group at any time point.

Discussion

In thumb CMC OA, dorsal displacement of the metacarpal provides compression force focussed on the volar side of the metacarpal facet, resulting in cartilage degeneration.^19–23 Various studies have demonstrated the biomechanical effect of metacarpal osteotomy in CMC OA. Pellegrini et al.⁵ examined the contact pressure patterns on the articular surface of the CMC joint following 30° extension osteotomy using a cadaver model simulating the lateral pinch. In joints without arthritis or with moderate arthritic changes, there was a redistribution of load from the diseased palmar to the intact dorsal surfaces, whereas such redistribution was not observed in end-stage CMC OA. Furthermore, Koff et al.⁴ demonstrated that 15° extension osteotomy in cadaveric specimens with stage I or II CMC OA significantly reduced joint laxity in the lateral pinch position, to a degree like that of standard ligament reconstruction. Therefore, metacarpal osteotomy is best suited for stage I or II CMC OA, where eburnation is confined to less than one-third of the palmar articular surface.

Despite these biomechanical advantages, previous studies rarely demonstrated postoperative radiographic improvement of joint congruity, even in early-stage CMC OA, unlike the response to osteotomy in the hip joint,^5,9,13,15 except that Futami et al.⁷ found a gradual widening of the CMC joint space after 30° abduction-opposition osteotomy. In this study, we made abduction–extension osteotomy with an extension angle of 90° or more for early- and advanced-stage CMC OA. Radiographic findings revealed a marked reduction in dorsal subluxation immediately after surgery in the early OA group (Fig. 3). We speculate that the excessive extension angle postoperatively strongly altered the load vector at the metacarpal facet volarly, thereby leading to an immediate improvement in CMC joint congruity.^21,22 In the advanced OA group, the reduction was mediocre early in the postoperative period but eventually progressed to a level of congruity comparable to that of the early OA group (Fig. 4). Furthermore, a statistically significant correlation was found between the postoperative extension angle and the reduction ratio in the advanced OA group. We speculate that eburnation of the joint facet initially disturbed smooth reduction, but the action of the abductor pollicis longus, flexor pollicis longus and extensor pollicis longus, in addition to the postoperative load vector, caused a gradual reduction in advanced-stage OA.¹²

Several reports have shown that metacarpal osteotomy provides sufficient pain relief and patient satisfaction in early-stage OA.^10,11,24 Hobby et al.⁸ and Parker et al.¹³ reported favourable pain relief following this procedure, even in patients with advanced-stage OA. Their findings suggested that positive subjective outcomes were not correlated with preoperative Eaton stage. Concerning objective outcomes, the effects of metacarpal osteotomy on grip and pinch strength remain conflicting. While Tomaino¹⁴ revealed an average increase in grip and pinch strength of 8.5 and 3.0 kg, respectively, in 12 thumbs with stage I CMC OA at the 2.1-year follow-up, longer follow-up studies for stage I, II and III CMC OA have not found a substantial increase in grip and pinch strength following this procedure.^9,13

In this study, metacarpal osteotomy provided sufficient pain relief in patients with both early- and advanced-stage OA. This procedure also yielded a marked increase in grip and lateral pinch strength in early-stage OA, whereas mediocre strength increased in advanced-stage OA. Furthermore, statistical analysis revealed that the VAS score, grip strength and lateral pinch strength were not correlated with the extent of CMC joint reduction at any postoperative time point. This suggests that even a slight improvement in the dorsal subluxation of the CMC joint following metacarpal osteotomy has the potential to improve both subjective and objective outcomes. However, longer follow-up is required, as acquired improvement in grip and pinch strength might deteriorate due to the progression of OA after the procedure.

Progression of the Eaton stage at longer follow-up after metacarpal osteotomy has been reported, although most patients did not require further operative intervention.²⁵ Parker et al.,¹³ Bachoura et al.⁹ and Chou et al.¹⁰ found postoperative radiographic deterioration in 3 out of 8 thumbs at 9 years of follow-up, in 4 out of 6 thumbs at more than 10 years of follow-up and in 3 out of 13 thumbs at 9.9 years of follow-up, respectively. Conversely, a few biomechanical studies have suggested that an excessive extension angle would prevent or slow the postoperative progression of the disease because it strongly increases the volar vector at the metacarpal base.^21,22 Therefore, we recommend a postoperative extension angle of 90° or more and the use of a mini plate to prevent postoperative loss of correction, especially in patients with advanced CMC OA.

This study has some limitations. First, this study had a retrospective design. Second, the follow-up period was relatively short. A longer follow-up period would reveal the effects of metacarpal osteotomies on disease progression. Third, the sample size of early-stage OA was small. A larger group of patients would allow a more precise comparison between early- and advanced-stage OA. Finally, the radiographic findings were evaluated only in the lateral view. Additional evaluations using the posteroanterior view would provide a better understanding of postoperative joint congruity after metacarpal osteotomy. However, previous studies have not focussed on postoperative radiographic findings following metacarpal osteotomy or compared these findings between early- and advanced-stage OA. Therefore, this study may help surgeons select appropriate surgical procedures for patients with thumb CMC OA.

Declarations

Conflict of Interest:

The author do NOT have any potential conflicts of interest with respect to this manuscript.

Funding:

The author received NO financial support for the preparation, research, authorship and/or publication of this manuscript.

Ethical Approval:

This study was approved by our institutional review board (Saitama Red Cross Hospital). Approval number: 23-BQ, date of approval: 31 March 2024.

Informed Consent:

There is NO information (names, initials, hospital identification numbers or photographs) in the submitted manuscript that can be used to identify patients.

Acknowledgements:

We would like to thank Editage (www.editage.com) for English language editing.