Single vs double headless compression screw fixation for scaphoid nonunion

Abstract

BACKGROUND

Scaphoid nonunion remains a challenging problem, and the optimal fixation construct for surgical treatment is still debated. Although dual headless compression screw fixation may provide greater mechanical stability than single-screw fixation, clinical evidence comparing the two techniques with respect to patient-reported functional outcomes remains limited.

AIM

To compare the clinical, radiographic, and functional outcomes of single-screw vs dual-screw fixation for scaphoid nonunion, using the Disabilities of the Arm, Shoulder and Hand (DASH) score as the primary outcome measure and employing one-way analysis of covariance (ANCOVA) to control for baseline differences between groups. We hypothesized that dual-screw fixation would provide comparable or superior deformity correction and functional outcomes compared to single-screw fixation.

METHODS

This retrospective cohort study included patients with scaphoid waist nonunion treated surgically through a volar approach using a non-vascularized distal radius bone graft at King Abdullah University Hospital, Jordan, from August 2024 to August 2025. Patients with avascular necrosis, previous wrist surgery, vascularized grafts, grafts from sources other than the distal radius, or incomplete documentation were excluded. Twenty-three patients met the inclusion criteria: 15 treated with single-screw fixation and eight with double-screw fixation. Final outcome assessment was performed at six months and included DASH score, grip strength, wrist range of motion (ROM), time to union, and radiographic correction parameters. ANCOVA was performed to evaluate the independent effect of fixation method on DASH scores while controlling for age.

RESULTS

Baseline characteristics were comparable between the groups except for age, with the double-screw group being younger than the single-screw group (23.88 ± 7.30 years vs 32.80 ± 9.41 years; P = 0.030). Time to union was similar between the single- and double-screw groups (11.47 ± 3.38 weeks vs 11.13 ± 5.11 weeks; P = 0.849). Radiographic correction was also comparable, with no significant difference in change in height-to-length ratio or scapholunate angle between groups. Final grip strength did not differ significantly, although ROM showed a trend favoring double-screw fixation. The double-screw group demonstrated significantly better final DASH scores than the single-screw group (23.13 ± 11.40 vs 44.53 ± 21.39; P = 0.016). ANCOVA confirmed that the surgical group remained a significant independent predictor of final DASH scores after adjusting for age (F = 5.428, P = 0.030), while age did not exert a significant effect (F = 0.012, P = 0.915).

CONCLUSION

In this retrospective series of patients with scaphoid waist nonunion, double headless compression screw fixation was associated with superior patient-reported functional outcome compared with single-screw fixation, despite similar union time and radiographic correction. ANCOVA confirmed that this functional advantage was independent of the age difference between groups. These findings suggest that dual-screw fixation may offer a functional advantage in selected patients with scaphoid nonunion, although prospective randomized studies with larger sample sizes are needed to confirm these results.

Key Words: Scaphoid; Nonunion; Fixation; Screw; Outcome; Disabilities of the Arm; Shoulder and Hand

Core Tip: This retrospective cohort study of 23 patients with scaphoid waist nonunion found that double headless compression screw fixation yielded significantly better Disabilities of the Arm, Shoulder and Hand scores than single-screw fixation, despite comparable time to union and radiographic correction. These findings suggest dual-screw constructs may offer a functional advantage during rehabilitation, independent of anatomical restoration.

INTRODUCTION

Scaphoid fractures are the most common carpal bone fractures, accounting for approximately 60%-70% of all carpal injuries, and predominantly affect young, active individuals[1]. Despite advances in diagnosis and acute management, nonunion remains a well-recognized complication, occurring in an estimated 5%-15% of scaphoid fractures[2]. Left untreated, scaphoid nonunion leads to a predictable pattern of carpal collapse and degenerative arthritis known as scaphoid nonunion advanced collapse, which can result in significant long-term wrist disability[3].

The current standard of care for scaphoid nonunion involves surgical intervention, typically consisting of open reduction, bone grafting, and internal fixation with headless compression screws[4]. The goals of surgery are to achieve osseous union, restore scaphoid anatomy - including the height-to-length (H/L) ratio and scapholunate (SL) angle - and correct any associated carpal malalignment such as dorsal intercalated segment instability (DISI). Headless compression screws have become the preferred method of internal fixation due to their ability to provide interfragmentary compression while remaining entirely intraosseous, thereby minimizing soft tissue irritation and allowing early rehabilitation[5].

Although single-screw fixation has been the traditional approach, the use of dual-screw constructs has gained interest as a means of potentially enhancing rotational stability and rigidity at the nonunion site[6]. The rationale for dual-screw fixation is supported by biomechanical evidence. Mandaleson et al[7] demonstrated in a cadaveric nonunion model that double screw constructs provide significantly greater load to failure (mean difference 187.2 N), stiffness (mean difference 85.4 N/mm), and energy absorption (mean difference 386.5 mJ) compared to single screw fixation. More recently, Surke et al[8] showed that double screw fixation yields greater maximum torque and bending resistance than single screw constructs combined with either strut or wedge grafts, suggesting that rotational stability provided by a second screw may be a critical factor in optimizing the mechanical environment for healing. Rothenfluh et al[9] further corroborated these findings using finite element analysis, demonstrating enhanced stability with dual screw configurations.

Despite this biomechanical rationale, the clinical evidence comparing single- and dual-screw fixation remains limited and has not consistently demonstrated superiority of one construct over the other. Quadlbauer et al[6] reported union rates of 60% with single hollow compression screws (HCS), 83% with double HCS, and 85% with plate fixation in patients with scaphoid waist nonunion treated with a non-vascularized iliac crest bone graft, suggesting a potential union rate advantage for dual-screw fixation; however, no significant differences in functional outcome scores were observed between fixation methods. In a separate study comparing double HCS to angular stable plate fixation with intraoperative extracorporeal shockwave therapy, the same group found comparable high union rates (100% for double HCS vs 84% for plate) and no significant differences in range of motion (ROM), pain, grip strength, or patient-reported outcome measures[10]. Garcia et al[11] reported 100% union in 19 scaphoid nonunions treated with two headless compression screws and bone grafting, but this was a single-arm case series without a comparison group and did not report patient-reported outcome measures such as the Disabilities of the Arm, Shoulder and Hand (DASH) score. Yildirim et al[12] described the two-screw fixation technique for scaphoid waist fractures and proposed that the biomechanical advantages of dual-screw fixation may allow earlier ROM and strengthening exercises with greater confidence in construct stability, but did not provide comparative clinical outcome data. Most recently, Jing et al[13] performed a propensity score-matched comparison of one- vs two-screw fixation for scaphoid fractures and found no significant differences in union rates, time to union, or hardware complications, with the one-screw cohort actually demonstrating greater wrist extension at six months.

Several important gaps emerge from the existing literature. First, no study has directly compared single- vs dual-screw fixation for scaphoid nonunion with patient-reported functional outcomes (such as the DASH score) as a primary endpoint. The studies by Quadlbauer et al[6] and Garcia et al[11] used iliac crest bone graft rather than distal radius graft, and the study by Jing et al[13] included acute fractures rather than established nonunions. Second, the relationship between radiographic correction parameters and specific functional domains (such as grip strength) in the context of different fixation constructs has not been explored. Third, no prior study has employed inferential statistical methods to control for potential confounders when comparing functional outcomes between single- and dual-screw fixation groups.

The purpose of this study was to compare the clinical, radiographic, and functional outcomes of single-screw vs dual-screw fixation for scaphoid nonunion, using the DASH score as the primary outcome measure and employing one-way analysis of covariance (ANCOVA) to control for baseline differences between groups. We hypothesized that dual-screw fixation would provide comparable or superior deformity correction and functional outcomes compared to single-screw fixation.

MATERIALS AND METHODS

Study design and setting

This retrospective cohort study was conducted at King Abdullah University Hospital, Jordan, and included patients who underwent surgical treatment for scaphoid waist nonunion from August 2024 to August 2025. Medical records, operative notes, imaging studies, and follow-up assessments were reviewed retrospectively. The study population consisted of patients with scaphoid waist nonunion following failed conservative treatment or a missed diagnosis who subsequently underwent surgery and had complete documentation available for analysis. Functional assessment was performed at six months postoperatively, at which time DASH score, grip strength, and wrist ROM were recorded.

Patient selection

Patients were included if they had a scaphoid waist nonunion treated surgically through a volar approach and had complete clinical, radiographic, and functional documentation at six months after surgery. Only patients with sufficient follow-up data to allow complete outcome assessment were analyzed. Patients were excluded if they had avascular necrosis of the scaphoid, had undergone any previous surgery on the affected wrist, received a vascularized bone graft, or received a graft source other than the distal radius. Patients with incomplete medical records or missing 6-month outcome data were also excluded.

Participant flow

A total of 41 consecutive patients with scaphoid waist nonunion were assessed for eligibility. Eighteen were excluded due to avascular necrosis (n = 5), previous wrist surgery (n = 4), vascularized bone graft (n = 3), graft from source other than distal radius (n = 2), and incomplete medical records (n = 4). The remaining 23 patients were included and completed the 6-month follow-up. No patients were lost to follow-up.

Surgical technique and cohorts

All procedures were performed through a volar surgical approach. Eligible patients were divided into two groups according to the fixation method used: Single headless compression screw fixation (1-screw group, n = 15) and double headless compression screw fixation (2-screw group, n = 8). In all cases, bone grafting was performed using a non-vascularized graft harvested from the distal radius. The choice between single- and double-screw fixation was based on intraoperative judgment by the treating surgeon. All included patients were managed under the same institutional surgical pathway for scaphoid waist nonunion.

Data collection

Demographic, clinical, operative, radiographic, and functional data were extracted from the medical records. Collected variables included age, sex, body mass index (BMI), hand dominance, comorbidities, pre-operative deformity characteristics (including the presence of DISI), fixation method, time to union, and final functional outcomes. Radiographic parameters were reviewed from available imaging studies before and after surgery, and the degree of deformity correction was calculated. Union was assessed using serial wrist radiographs during follow-up. Final functional outcomes included DASH score, grip strength, and ROM at six months.

Outcome measures

The primary outcome of interest was the final DASH score at six months postoperatively. Secondary outcomes included grip strength, wrist ROM, time to union, and radiographic correction parameters [change in H/L ratio (∆H/L), change in SL angle (∆SL), and rate of DISI correction]. Final functional status was assessed at the routine 6-month follow-up visit, which served as the endpoint for analysis in this study.

Statistical analysis

Continuous variables are summarized as mean ± SD or median with range, depending on distribution. Categorical variables are expressed as n (%). Comparisons between the single-screw and double-screw groups were performed using independent-samples t-tests for normally distributed continuous variables, Mann-Whitney U tests for non-normally distributed or ordinal variables, and Fisher’s exact tests for categorical variables, as appropriate. Correlation analysis was performed using Spearman’s rank-order correlation.

To address the potential confounding effect of age on the primary outcome, ANCOVA was conducted in the surgical group (1-screw vs 2-screw) as the independent variable, final DASH score as the dependent variable, and patient age as the covariate. This approach was selected as ANCOVA is specifically designed to evaluate the effect of a categorical independent variable on a continuous outcome while statistically controlling for the influence of continuous covariates, thereby providing a more robust assessment of the independent effect of the fixation method than simple bivariate correlation analysis[14,15]. A P < 0.05 was considered statistically significant.

Ethical approval

The study was approved by the Institutional Review Board of King Abdullah University Hospital. Given the retrospective nature of the study, the requirement for informed consent was waived in accordance with institutional policy.

RESULTS

Baseline demographics and clinical characteristics

A total of 23 patients were included in the analysis, categorized into two surgical cohorts: 1-screw fixation (n = 15) and 2-screw fixation (n = 8) (Table 1). Baseline characteristics were predominantly comparable between the two groups. There were no statistically significant differences regarding hand dominance (Fisher’s exact test, P = 1.000) or the presence of baseline comorbidities (Fisher’s exact test, P = 0.558). The mean BMI was higher in the 1-screw group (28.84 ± 4.15) compared to the 2-screw group (25.84 ± 2.18); however, this difference did not reach statistical significance (independent samples t-test; t = 1.90, P = 0.072). Additionally, the pre-operative presence of DISI was statistically comparable between the 1-screw (46.7%) and 2-screw (87.5%) cohorts (Fisher’s exact test, P = 0.086).

Table 1 Baseline demographics and clinical characteristics, n (%)/mean ± SD.

Variable	1-screw group (n = 15)	2-screw group (n = 8)	Test statistic	P value
Age (years)	32.80 ± 9.41	23.88 ± 7.30	t = 2.326	0.030a
BMI (kg/m2)	28.84 ± 4.15	25.84 ± 2.18	t = 1.894	0.072
Dominant hand			N/A	1.000
Right	14 (93.3)	7 (87.5)
Left	1 (6.7)	1 (12.5)
Comorbidities			N/A	0.558
None (free)	13 (86.7)	8 (100.0)
DM + UC	1 (6.7)	0 (0.0)
Hyperlipidemia	1 (6.7)	0 (0.0)
Pre-operative DISI	7 (46.7)	7 (87.5)	N/A	0.086

^aP < 0.05.

Continuous variables (age, body mass index) were analyzed using an independent samples t-test. Categorical variables (Dominant Hand, Comorbidities, Pre-Operative dorsal intercalated segment instability) were analyzed using Fisher’s exact test. N/A indicates Fisher’s exact test was used, which computes exact probability directly without generating a standardized test statistic. BMI: Body mass index; DM: Diabetes mellitus; UC: Ulcerative colitis; DISI: Dorsal intercalated segment instability; N/A: Not applicable.

Notably, there was a statistically significant difference in age between the cohorts. Patients treated with 2-screw fixation were significantly younger (mean age 23.88 ± 7.30 years) compared to those treated with 1-screw fixation (mean age 32.80 ± 9.41 years) (independent samples t-test; t = 2.326, P = 0.030).

Radiographic outcomes and deformity correction

Across the entire patient cohort, surgical intervention resulted in measurable anatomical corrections (Table 2). The median ∆H/L from pre-operative to final follow-up was 0.02 (range: -0.09 to 0.34). Similarly, the mean ∆SL across all patients was -8.83 ± 21.11 degrees. When comparing the two surgical techniques, there was no statistically significant difference in the magnitude of radiographic correction. The ∆H/L did not significantly differ between the 1-screw and 2-screw groups (Mann-Whitney U = 49.00, P = 0.476), nor did the ∆SL (independent samples t-test; t = 0.477, P = 0.639).

Table 2 Post-operative radiographic changes and deformity correction.

Variable	1-screw group (n = 15)	2-screw group (n = 8)	Test statistic	P value
∆H/L, median (range)	0.01 (-0.07 to 0.13)	0.02 (-0.09 to 0.34)	U = 49.00	0.476
∆SL (degrees), mean ± SD	-7.27 ± 20.31	-11.75 ± 23.66	t = 0.477	0.639
DISI successfully corrected, n (%)	5 (71.4)	2 (28.6)	N/A	0.286

Change in height-to-length ratio was analyzed using the Mann-Whitney U test. Change in scapholunate angle was analyzed using an independent samples t-test. Dorsal intercalated segment instability correction rates were analyzed using Fisher’s exact test. N/A indicates Fisher’s exact test was used, which computes exact probability directly without generating a standardized test statistic. ∆H/L: Change in height-to-length ratio; ∆SL: Change in scapholunate angle; DISI: Dorsal intercalated segment instability; N/A: Not applicable.

Furthermore, pre-operative DISI was present in seven patients (five in the 1-screw group and two in the 2-screw group). The rate of successful DISI correction at final follow-up was not significantly influenced by the number of screws used for fixation (Fisher’s exact test, P = 0.286).

Clinical and functional outcomes

Post-operative clinical and functional outcomes were compared between the two fixation methods (Table 3). There was no statistically significant difference in the time to clinical union between the 1-screw group (11.47 ± 3.38 weeks) and the 2-screw group (11.13 ± 5.11 weeks) (independent samples t-test; t = 0.193, P = 0.849). Non-parametric analysis of ordinal outcomes revealed no significant difference in final grip strength between the 1-screw and 2-screw groups (Mann-Whitney U test; U = 48.00, mean rank 11.20 vs 13.50, respectively; P = 0.186). Final ROM demonstrated a trend favoring the 2-screw group (mean rank 14.50) over the 1-screw group (mean rank 10.67), although this did not achieve statistical significance (Mann-Whitney U = 40.00, P = 0.074).

Table 3 Post-operative clinical and functional outcomes, mean ± SD.

Outcome measure	1-screw group (n = 15)	2-screw group (n = 8)	Test statistic	P value
Time to union (weeks)	11.47 ± 3.38	11.13 ± 5.11	t = 0.193	0.849
Final DASH score	44.53 ± 21.39	23.13 ± 11.40	t = 2.620	0.016a
Final grip strength, mean rank	11.20	13.50	U = 48.0	0.186
Final ROM, mean rank	10.67	14.50	U = 40.0	0.074

^aP < 0.05.

Continuous parametric variables (time to union, final Disabilities of the Arm, Shoulder, and Hand) were analyzed using an independent samples t-test. Ordinal variables (final grip strength, final range of motion) were analyzed using the Mann-Whitney U test and are reported as mean ranks. DASH: Disabilities of the Arm, Shoulder, and Hand; ROM: Range of motion.

Regarding overall functional recovery, the 2-screw cohort demonstrated a statistically significant improvement in final DASH scores compared to the 1-screw cohort (23.13 ± 11.40 vs 44.53 ± 21.39, respectively; independent samples t-test; t = 2.620, P = 0.016), indicating reduced upper extremity disability.

Controlling for confounding: ANCOVA

Given the significant age difference between the groups, a one-way ANCOVA was conducted to determine whether the surgical technique remained an independent predictor of final DASH scores when controlling for patient age. The independent variable was the surgical group (1-screw vs 2-screw), the dependent variable was the final DASH score, and patient age was entered as a covariate. The analysis revealed that age did not exert a significant effect on the final DASH score (F = 0.012, P = 0.915). Most importantly, after adjusting for the effect of age, there remained a statistically significant main effect of the surgical group on the final DASH scores (F = 5.428, P = 0.030). This inferential analysis confirms that the superior functional outcomes observed in the 2-screw cohort are attributable to the surgical technique rather than the baseline age discrepancy between the groups.

Correlation analysis

Spearman’s rank-order correlations were performed to evaluate the relationship between anatomical restoration and functional recovery. A statistically significant positive correlation was identified between the degree of H/L ratio correction (∆H/L) and final grip strength (r = 0.454, P = 0.029). However, ∆H/L was not significantly correlated with final ROM (P = 0.142), and ∆SL showed no significant correlation with either grip strength or ROM. Finally, a strong, highly significant positive correlation was observed between final ROM and final grip strength (r = 0.747, P < 0.001).

DISCUSSION

This retrospective study of 23 patients with scaphoid nonunion compared single-screw (n = 15) and double-screw (n = 8) headless compression screw fixation across radiographic, clinical, and functional outcomes. The principal finding was that the 2-screw cohort demonstrated significantly better final DASH scores compared to the 1-screw cohort (23.13 ± 11.40 vs 44.53 ± 21.39; P = 0.016), while radiographic correction and time to union were comparable between the groups. Importantly, ANCOVA confirmed that this functional advantage was independent of the significant age difference between the groups (F = 5.428, P = 0.030 for surgical group effect after adjusting for age).

The two cohorts were well-matched in most baseline characteristics, including hand dominance, comorbidities, and BMI. However, patients in the 2-screw group were significantly younger (mean 23.88 years vs 32.80 years; P = 0.030), raising the possibility that age could confound the observed functional advantage. To address this, a one-way ANCOVA was performed - an inferential statistical technique specifically designed to evaluate the effect of a categorical independent variable on a continuous outcome while statistically controlling for the influence of continuous covariates[14,15]. The ANCOVA demonstrated that age did not exert a significant effect on final DASH scores (F = 0.012, P = 0.915), while the surgical group remained a significant independent predictor (F = 5.428, P = 0.030). This finding is consistent with the broader scaphoid literature, in which age has not been consistently identified as an independent predictor of functional recovery after scaphoid surgery[16]. Nonetheless, the possibility of residual confounding from unmeasured variables such as activity level, healing biology, or rehabilitation compliance cannot be entirely excluded in a non-randomized study of this size.

The DASH score difference of approximately 21 points between the groups exceeds the established minimal clinically important difference (MCID) for the DASH score, which has been reported as approximately 10 points to 15 points in upper extremity populations[17,18]. This suggests that the functional advantage observed with 2-screw fixation is not only statistically significant but also clinically meaningful. The mechanism underlying this functional benefit likely relates to the enhanced biomechanical stability conferred by dual screw fixation. Mandaleson et al[7] demonstrated that double screw constructs provide significantly greater load to failure (mean difference 187.2 N), stiffness (mean difference 85.4 N/mm), and energy absorption (mean difference 386.5 mJ) compared to single screw fixation in a cadaveric nonunion model. Surke et al[8] further showed that double screw fixation yields greater maximum torque and bending resistance than single screw constructs combined with either strut or wedge grafts, suggesting that the rotational stability provided by a second screw may be a critical factor in optimizing the mechanical environment for healing and functional recovery.

Despite the functional advantage, time to clinical union was remarkably similar between the 1-screw (11.47 ± 3.38 weeks) and 2-screw (11.13 ± 5.11 weeks) groups (P = 0.849). This finding suggests that both constructs provide sufficient stability to achieve union within a comparable timeframe, and that the functional benefits of dual screw fixation may relate more to the quality of the mechanical environment during rehabilitation - permitting earlier and more confident mobilization - rather than to accelerated bone healing per se. This interpretation aligns with the rationale proposed by Yildirim et al[12], who suggested that the biomechanical advantages of two-screw fixation may allow earlier ROM and strengthening exercises with greater confidence in construct stability.

Both fixation methods achieved comparable radiographic correction of scaphoid deformity. The ∆H/L did not differ significantly between the 1-screw and 2-screw cohorts (P = 0.476), nor did the ∆SL (P = 0.639) or the rate of DISI correction (P = 0.286). These equivalent radiographic results are notable as they indicate that the superior functional outcomes observed in the 2-screw group cannot be explained by differences in anatomical restoration. Instead, the functional advantage likely stems from other factors related to the dual screw construct, such as greater mechanical stability during the rehabilitation period.

Although radiographic correction was equivalent between the groups, the degree of anatomical restoration did have functional relevance when analyzed across the entire cohort. A significant positive correlation was identified between ∆H/L and final grip strength (r = 0.454, P = 0.029), indicating that patients who achieved greater correction of the scaphoid H/L ratio recovered more grip strength, regardless of which fixation method was used. This finding is noteworthy as it diverges from much of the existing literature. Megerle et al[19], in a study of 65 patients after scaphoid reconstruction, found that the H/L ratio did not significantly correlate with grip strength, ROM, or pain levels, although the radiolunate angle did correlate with all three outcomes. Similarly, Barbarin et al[3] reported no significant correlation between scaphoid shape (including the H/L ratio) and clinical or functional outcomes at a mean follow-up of 7.7 years after nonunion treatment. Kim et al[20] also found that radiological parameters of scaphoid and carpal alignment did not correlate with clinical wrist function after arthroscopic management of scaphoid nonunion. Oh et al[21] further demonstrated that even when open surgery achieved significantly better H/L ratio correction than arthroscopic surgery in patients with carpal collapse deformities, this superior radiographic restoration did not translate into differences in grip strength, ROM, or DASH scores.

The discrepancy between the present study and these prior reports may reflect differences in the specific functional outcomes assessed and the analytical approach used. The studies by Barbarin et al[3], Megerle et al[19], and Kim et al[20] evaluated the correlation between absolute postoperative radiographic values and composite functional measures, whereas the present study specifically examined the ∆H/L ratio and its relationship to an isolated functional variable - grip strength. It is possible that the magnitude of correction, rather than the final absolute value, is the more functionally relevant parameter. From a biomechanical standpoint, there is a plausible mechanism for this relationship. Tang et al[22] demonstrated in a cadaveric study that loss of scaphoid integrity significantly alters the moment arms of the principal wrist flexor and extensor tendons: The moment arm of the flexor carpi radialis increased while those of the extensor carpi radialis longus and brevis decreased following scaphoid fracture. These changes in tendon biomechanics would be expected to impair the efficiency of force generation during power grip. Restoration of scaphoid height through surgical correction of the humpback deformity may therefore normalize these moment arm relationships, improving the mechanical efficiency of the wrist motors for grip. This targeted biomechanical effect on grip strength may not be captured by broader composite outcome measures such as the DASH or by ROM assessments, which could explain why prior studies using those endpoints failed to detect a correlation. Consistent with this interpretation, ∆H/L did not correlate with final ROM (P = 0.142) in the present study, and change in SL showed no significant correlation with either grip strength or ROM, suggesting that the relationship between anatomical correction and functional recovery is selective rather than global. However, given the small sample size, this finding should be interpreted with caution and requires validation in larger cohorts before firm conclusions can be drawn.

The strong positive correlation between final ROM and final grip strength (r = 0.747, P < 0.001) underscores the interdependence of these functional parameters and suggests that interventions optimizing one are likely to benefit the other. This relationship is well established in the hand surgery and biomechanics literature. O'Driscoll et al[23] demonstrated that grip strength is significantly reduced when wrist position deviates from the optimal self-selected position of approximately 35 degrees of extension, with a minimum of 25 degrees of wrist extension required for optimum grip strength. LaStayo and Hartzel[24] described the synergistic relationship between wrist and forearm ROM and grip strength as one of the most important aspects of hand function, noting that maximal dynamic grip strength is directly dependent on the available arc of wrist motion.

The trend toward better final ROM in the 2-screw group (mean rank 14.50 vs 10.67; P = 0.074), while not reaching statistical significance, is noteworthy. Given the strong correlation between ROM and grip strength, and the significant DASH score advantage, this trend may reflect a true but underpowered effect. A larger sample size may have detected a statistically significant difference in ROM, which could further explain the functional superiority of the 2-screw construct.

The clinical findings of this study are consistent with the broader literature supporting dual screw fixation for scaphoid nonunion, but the present study makes several distinct contributions. Quadlbauer et al[6] reported higher union rates with double HCS (83%) compared to single HCS (60%) in scaphoid waist nonunion treated with a non-vascularized iliac crest bone graft, but found no significant differences in functional outcome scores between fixation methods. In a subsequent study, the same group compared double HCS to angular stable plate fixation with intraoperative extracorporeal shockwave therapy and again found no significant differences in patient-reported outcomes[10]. Garcia et al[11] reported 100% union in 19 scaphoid nonunions treated with two headless compression screws and bone grafting, but this was a single-arm case series without a comparison group and did not report DASH scores. In a separate study of unstable B2-type scaphoid fractures, Quadlbauer et al[25] demonstrated a 100% union rate with two HCS compared to 86% with a single HCS.

The present study differs from these prior investigations in several important respects. First, it is among the first to use the DASH score as a primary outcome measure for directly comparing single- vs dual-screw fixation in scaphoid nonunion, and it demonstrates a statistically significant and clinically meaningful difference (exceeding the MCID) favoring dual-screw fixation - a finding not previously reported. Second, unlike the studies by Garcia et al[11] and Quadlbauer et al[25] which used an iliac crest bone graft, the present study exclusively used a non-vascularized distal radius bone graft, reflecting a different and increasingly common grafting approach. Third, the present study employed ANCOVA to control for the confounding effect of age - an inferential statistical technique not used in prior comparative studies of scaphoid fixation constructs - thereby providing a more robust assessment of the independent effect of the fixation method on functional outcomes. Fourth, the identification of a significant correlation between ∆H/L and grip strength, which contrasts with prior literature, represents a novel finding that may reflect a domain-specific biomechanical effect of scaphoid height restoration on wrist motor tendon efficiency.

Several limitations of this study must be acknowledged. The retrospective design and small sample size (n = 23) limit the statistical power and increase the risk of type II error, particularly for secondary outcomes such as ROM. Although ANCOVA was employed to control for the significant age difference between the groups, this technique can only adjust for measured covariates; the possibility of residual confounding from unmeasured variables (such as activity level, occupation, smoking status, or rehabilitation compliance) cannot be excluded in a non-randomized study[14,15]. The absence of pre-operative DASH scores precludes assessment of change from baseline, and the cross-sectional nature of the functional assessment at a single time point limits the ability to attribute causality. Additionally, the heterogeneity in bone grafting techniques and adjunctive therapies across patients was not controlled for, which may influence outcomes independently of the fixation construct. The small size of the scaphoid also presents technical challenges with dual screw placement, including the risk of screw convergence and cortical breach - factors that may influence construct performance in vivo but were not specifically assessed. The higher prevalence of pre-operative DISI in the 2-screw group (87.5% vs 46.7%), while not statistically significant (P = 0.086), suggests that the 2-screw cohort may have had more severe initial deformity, which could bias against the 2-screw group and make the observed functional advantage even more notable. Finally, the non-randomized allocation of patients to fixation groups introduces selection bias, as the choice of fixation was based on intraoperative surgeon judgment. The conclusions of this study should therefore be interpreted as hypothesis-generating and applicable primarily to the study population; generalizability to broader populations requires confirmation through prospective, randomized, multicenter trials with larger sample sizes.

CONCLUSION

This study demonstrates that double headless compression screw fixation for scaphoid nonunion is associated with significantly better patient-reported functional outcomes compared to single screw fixation, as measured by the DASH score, with a difference exceeding the MCID. ANCOVA confirmed that this functional advantage was independent of the age difference between the groups. Radiographic correction and time to union were comparable between constructs, suggesting that the functional advantage of dual screw fixation may relate to enhanced construct stability during rehabilitation rather than superior anatomical restoration. The significant correlation between H/L ratio correction and grip strength - a finding that contrasts with prior literature reporting no relationship between radiographic parameters and function - may reflect a domain-specific biomechanical effect of scaphoid height restoration on wrist motor tendon efficiency, as supported by cadaveric evidence[22]. Prospective randomized trials with larger sample sizes are needed to confirm these findings and to better delineate the indications for single vs double screw fixation in scaphoid nonunion.